The term "linear actuator" covers a broad range of products. A linear actuator is a mechanical device that converts energy (power from air, electricity or liquid) to create motion in a straight line; contrasted with circular motion of a conventional electric motor. It can also be used to apply a force. Types of motion include: blocking, clamping, ejecting, lifting, descending, pushing or pulling.
Basic Designs of a Linear Actuator
As mentioned earlier, the term "linear actuator" covers a broad range of products; each sub-category looks and operates differently. In the majority of linear actuator designs, the basic principle of operation is that of an inclined plane. Simply stated, the threads of a lead screw act as a continuous ramp that allows a small rotational force to be used over a long distance to accomplish movement of a large load over a short distance.
How a Linear Actuator Works
Simply stated, all linear actuators depend on an external, non-linear force to drive some kind of a piston back and forth, yet, different types of linear actuator work in different ways. A ‘piston" is defined as sliding piece which is moved by or against fluid, air pressure, or electricity. It usually consists of a short cylinder fitting within a cylindrical vessel along which it moves back and forth. For example: in steam engines, motion is created by steam, and pumps transmit motion to a fluid.
Hydraulic pump actuators for example, depend on a hydraulic pump to compress and decompress the two sides of a piston in order to push it back and forth. The piston is attached to an external shaft, so the shaft moves with it. On the other hand, a wax motor linear actuator uses an electric current to melt a block of wax, causing it to expand. As the wax expands and contracts with varying electrical currents, a plunger that is pressed against it moves back and forth in a linear motion.
Linear Actuator Power and Operational Options:
There are many options regarding the linear actuator driving force: Manual mechanical methods include the lead screw systems of vises and clamps, and levers found in manual juicers or can crushers. Cylinders with pistons powered by compressed air are used to move parts of machines. Hydraulic cylinders with pistons provide large forces and strokes for construction equipment such as shovels, lifts and jacks, and short throw cylinders for braking systems. Solenoid coils, which are short throw electromagnetic linear actuators, turn switches and valves on and off in addition to locking and unlocking doors. Linear progressions of electromagnetic motor poles are used for trams, people movers, and material conveyors. Self-contained linear actuator motors are also available.
Linear Actuator Applications Are Endless!
Linear actuators are used in industrial automation and machinery, machine tools, computer peripherals such as disk drives and printers, home automation, packaging, assembly, electronic manufacturing, data storage, laser processing, and test and inspection. Linear actuators are typically used in applications along with motors, valves, pumps, switches, dampers, and in many other places where linear motion is required. Linear actuators are also used for medical imaging and diagnostics, solar, farming, construction, automotive, and robotics applications.
Linear actuators are used in nearly every type of electrical device that requires linear motion. Power drills, pumps, and other industrial appliances often rely on linear actuators to move other objects. Linear actuators are also used in some types of motors, and are often used in the robotics industry to provide robots with motor skills. In fact, a simple piston inside of an electric motor or fuel-injection engine uses linear motion, and therefore acts as a linear actuator.
Basic Variations of Linear Actuators
Many variations on the basic linear actuator design have been created throughout time. Most focus on providing general improvements such as a higher mechanical efficiency, speed, or load capacity. There is also a large engineering movement towards linear actuator miniaturization. It is seen by some manufacturers that the smaller the linear actuator, the better. This does not necessary equate to a cost-savings, rather, it is desirable for reducing the overall size and weight of a linear actuator motion control system.
- Rotary to Linear Motion - Some linear actuators use straight sections of a cogged belt or roller drive chain in a lengthwise circuit between two pulleys or sprockets. This type of linear actuator system is widely used in garage door openers. Other linear actuators also use standard rotational electric motors (such as Stepper, DC Brush, DC Brushless and AC motors) with mechanical conversion for steering systems, or crankshafts in sewing machines, and many other uses.
- Specialized Linear Actuators - Highly specialized linear actuators are used in critical applications, such as hydraulically actuated flight control surfaces on large aircraft, in ultra-fine machining equipment requiring precise positioning to tenths of thousandths, as well as tiny servo motors and cog belts, and for minute movements in medical procedures such as eye surgery. Even inexpensive stepper motor-driven linear actuator used in home computer printers have resolution down to single pixel size.
- Motion, Position, Velocity, and Force Combinations - Designers integrating linear actuators into equipment must examine their application carefully to determine whether motion, force, position, or velocity is the primary operational requirement, or whether the application requires some combination of all of them. For example: printer head skewing systems must be able to position the heads precisely across a long stroke, while braking cylinders must provide very large forces through relatively short strokes against the brake discs that limit their motion. The hydraulic cylinders on large excavators used in construction must be able to provide tens of thousands of pounds of force over many feet of stroke, with a degree of precision of an inch or two being considered adequate. Electronically controlled linear actuators used in circuit board assembly move at blinding speed as microchips are inserted into precise positions. Therefore, complex linear actuator applications will often incorporate position, force and velocity feedback sensors connected into programmable machine control systems to assure that all linear actuator performance is achieved consistently.
- Electromechanical Linear Actuator Designs: Most electromechanical designs incorporate a lead screw and lead nut, while some use a ball screw and ball nut. In either case, the screw may be connected to a motor or manual control knob either directly or through a series of gears. Gears are typically used to allow a smaller, weaker motor, rotating at a higher RPM to be geared down to provide the torque necessary to rotate the screw under a heavier load than the motor would otherwise be capable of driving directly. Generally speaking, this approach effectively sacrifices linear actuator speed in favor of increased actuator thrust. In some applications the use of a worm gear is common, as this approach allows a smaller built-in dimension, while allowing for greater travel length.
A traveling-nut linear actuator has a motor that stays attached to one end of the lead screw (perhaps indirectly through a gearbox). The motor rotates the lead screw, and the lead nut is restrained from rotating, therefore the nut "travels" up and down the lead screw.
A traveling-screw linear actuator has a lead screw that passes entirely through the motor. In a traveling-screw linear actuator, the motor "crawls" up and down a lead screw that is restrained from rotating. The only rotating parts are inside the motor. In some designs, the rotating parts may not even be visible from the outside of the linear actuator.
Some lead screws have multiple "starts". This means that they have multiple threads alternating on the same shaft. One simple way to visualize the multiple starts lead screw is the multiple color stripes on a candy cane. Multiple starts lead screws provide for more adjustment capability between thread pitch and the nut/screw thread contact area, which will determine the extension speed and load carrying capacity (of the threads), respectively.
Static Load Capacity of Linear Actuators
Screw-type linear actuators can have a static loading capacity, meaning that when the motor stops, the actuator is essentially locked in place and can support the load that is either pulling or pushing on the actuator. The braking force of the linear actuator varies with the angular pitch of the screw threads and the specific design of the threads.
Acme screws have a very high static load capacity, while ball screws have an extremely low load capacity and are nearly free-floating. Generally speaking, it is not possible to vary the static load capacity of screw-type linear actuators without additional technology. The screw thread pitch and drive nut design of the screw-type linear actuator defines the specific load capacity that cannot be dynamically adjusted.
Dynamic Load Capacity of Linear Actuators
A dynamic load capacity is in some designs added to a screw-type linear actuator using an electromagnetic brake system, which applies friction to the rotating drive nut. For example: A spring may be used to apply brake pads to the drive nut, holding it in position when power is turned off. When the actuator needs to be moved, an electromagnet counteracts the spring and releases the braking force on the drive nut. Similarly, an electromagnetic ratchet mechanism can be used with a screw-type linear actuator, so that the drive system lifting a load will lock in position when power to the actuator is turned off. To lower the actuator, an electromagnet is used to counteract the spring force and unlock the ratchet.
Specific Types of Linear Actuators
Mechanical Linear Actuators
Mechanical linear actuators typically operate by the conversion of rotary motion into linear motion (motion in a straight line). Mechanical linear actuators convert rotary motion of a control knob or handle into linear displacement using screws and/or gears to which the knob or handle is attached. A jackscrew or car jack is a familiar mechanical linear actuator.
Another type of linear actuator is based on the segmented spindle. Rotation of the jack handle is converted mechanically into the linear motion of the jack head. Mechanical linear actuators are also frequently used in the field of lasers and optics to manipulate the position of linear stages, rotary stages, mirror mounts, goniometers and other positioning instruments. For accurate and repeatable positioning, index marks may be used on control knobs. Some linear actuator designs include an encoder and digital position readout. These are similar to the adjustment knobs used on micrometers, except that their purpose is position adjustment rather than position measurement. Conversion is typically made using a few simple mechanisms:
- Screws: lead screw, screw jack, ball screw and roller screw linear actuators all operate on the principles and functions of a simple screw. By rotating the actuator's nut, the screw shaft moves in a straight line.
- Wheel and axle: Hoist, winch, rack and pinion, chain drive, belt drive, rigid chain and rigid belt linear actuators operate on the principles and functions of the wheel and axle, wherein a rotating wheel moves a cable, rack, chain or belt to produce linear motion.
- Cam: Cam linear actuators function on a principle similar to that of the wedge, but provide relatively limited travel. As a wheel-like cam rotates, its eccentric shape provides thrust at the base of a shaft.
Some mechanical linear actuators only pull (such as hoists, chain drive and belt drives), while other types only push (such as a cam actuator). Pneumatic and hydraulic cylinders, or lead screw linear actuators can be designed to provide force in both directions. The selection of the linear actuator is dependent upon the application and budget.
Hydraulic Linear Actuators
Hydraulic linear actuators, sometimes referred to as or hydraulic cylinders, typically involve a hollow cylinder with a piston inserted into it. An unbalanced pressure applied to the piston provides the necessary force that moves an external object. Since liquids are nearly incompressible, a hydraulic cylinder can provide controlled precise linear displacement of the piston. The displacement is only along the axis of the piston. Although the term "hydraulic actuator" refers to a device controlled by a hydraulic pump, an example of a manually operated hydraulic linear actuator is a simple hydraulic car jack.
Pneumatic Linear Actuators
Pneumatic linear actuators, sometimes referred to as pneumatic cylinders, are similar to hydraulic linear actuators except they use compressed gas to provide pressure, rather than of a liquid force.
Piezoelectric Linear Actuators
The piezoelectric effect is a property of certain materials in which the application of a voltage to the material causes it to expand. Very high voltages correspond to only tiny expansions. As a result, piezoelectric linear actuators can achieve extremely fine positioning resolution. The downside to the Piezoelectric linear actuator is that it has a very short range of motion. In addition, piezoelectric materials exhibit hysteresis, which makes it difficult to control its expansion in a repeatable manner.
Electromechanical Linear Actuators
A miniature electromechanical linear actuator is a design wherein the lead nut is part of the motor. The lead screw does not rotate; the lead nut is rotated by the motor and the lead screw is extended or retracted. Electromechanical linear actuators are similar to mechanical actuators, the only difference being the control knob or handle is replaced with an electric motor. Rotary motion of the motor is converted into linear displacement of the actuator. There are many designs of modern linear actuators. Every linear actuator manufacturer has their own proprietary methods and designs, making it difficult to cross parts from one manufacturer to another, for a given application. The following is a generalized description of a very simple electromechanical linear actuator.
Typically, an electric motor is mechanically connected to rotate a lead screw. A lead screw has a continuous helical thread machined on its circumference running along the length (similar to the thread on a bolt). Threaded onto the lead screw is a lead nut or ball nut with corresponding helical threads. The nut is prevented from rotating with the lead screw (typically the nut interlocks with a non-rotating part of the actuator body). Therefore, when the lead screw is rotated, the nut is driven along the threads. The direction of motion of the nut will depend on the direction of rotation of the lead screw. By connecting to the nut, the motion can be converted to usable linear displacement.
Standard Construction or Compact Construction?
A linear actuator using standard motors will typically use the motor as a separate cylinder attached to the side of the actuator, either parallel with the actuator or stuck out to the side, positioned perpendicular to the actuator. Sometimes the motor is attached to the back end of the actuator. The drive motor is of typical construction with a solid drive shaft that is geared to the drive nut or drive screw of the linear actuator.
Compact linear actuators use specially designed motors that fit the motor and actuator components into the smallest possible footprint. In such cases, the inner diameter of the motor shaft can be enlarged, so that the drive shaft can be hollow. The drive screw and nut can therefore occupy the center of the motor, with no need for additional gearing between the motor and the drive screw. Similarly, the motor can be made to have a small outer diameter, with the pole faces stretched out lengthwise so that the motor will provide high torque while fitting in a small diameter design.
Motor-Type Linear Actuators
A motor-type linear actuator basically functions the same as a rotary electric motor with the rotor and stator circular magnetic field components designed so that they are laid out in a straight line. Where a rotary motor rotates and re-uses the same magnetic pole faces again and again, instead the magnetic field structures of a motor-type linear actuator are physically repeated across the length of the actuator. Since the motor moves in a linear fashion to begin with, no lead screw is needed to convert rotary motion to linear. While high capacity is possible, the material and/or motor limitations on most designs are surpassed relatively quickly due to a reliance solely on magnetic attraction and repulsion forces. Most linear actuator motors have a low load capacity compared to other types of linear actuators. However, linear actuator motors have an advantage in outdoor or dirty environments, in that the two halves do not need to contact each other, and so the electromagnetic drive coils can be waterproofed and sealed against moisture and corrosion. The linear actuator motor design provides for a very long service life, so it can be an economical choice for some applications.
Special Design: Telescoping Linear Actuator
Telescoping linear actuators are specialized linear actuators that are typically used where space restrictions or other requirements dictate the best fit. The telescoping linear actuator's range of motion is many times greater than the unextended length of the actuating member. A common form is made of concentric tubes of approximately equal length that extend and retract like sleeves, one inside the other, such as the telescopic cylinder. Other more specialized telescoping linear actuators use actuating members that act as rigid linear shafts when extended, but break that line by folding, separating into pieces and/or uncoiling when retracted.
Examples of telescoping linear actuators include:
- Helical Band Linear Actuators
- Rigid Belt Linear Actuators
- Rigid Chain Linear Actuators
- Segmented Spindle Linear Actuators
Advantages and Disadvantages of Specific Linear Actuator Designs
Advantages of Linear Actuators
Each type of linear actuator is made differently and has its own advantages. Mechanical linear actuators, for example, are relatively inexpensive, reusable, and self-contained. Piezoelectric linear actuators can create extremely small linear motions and can consequently be used for microcomputer and micro-mechanical applications. Hydraulic linear actuators can produce a large amount of pressure, therefore they can be used for heavy duty applications. Pneumatic linear actuators are powerful, compact, lightweight, very simply designed, and provide repeatable motion. See chart for comparisons of linear actuator types.
Disadvantages of Linear Actuators
While each linear actuator has its own advantages, each also has its disadvantages. For example, mechanical linear actuators are strictly manual and cannot be automated. Piezoelectric linear actuators are slow, can only move across small areas, are very expensive, require a high voltage to be effective, and require a secondary force to push the shaft back into its initial position. See chart for comparisons of linear actuator types.
How to Select a Linear Actuator for a Specific Application:
"Linear actuator" is a broad term covering many different types of devices. The process of selecting the best device for a specific application is dependent upon the user's diligent research and development practices. It is not easy when comparing the specifications between linear actuator manufacturers, as there is very little standardization within the industry. Each type of each linear actuator fulfills a different set of design requirements.
There are many different types of motors that can be used in a linear actuator system as well. These include DC Brush, DC Brushless, Servo, Stepper, and in some cases, even AC induction motors. The application requirements and the loads the actuator is designed to move will dictate the best motor option. For example, a linear actuator using an integral horsepower AC induction motor driving a lead screw can be used to actuate a large valve in a refinery. In this case, accuracy and move resolution down to a thousandth isn't needed, but high force and speed is critical to the application. For electromechanical linear actuators used in laboratory instrumentation, robotics, optical and laser equipment, or X-Y tables, fine resolution (measured in microns) and high accuracy may require the use of a fractional horsepower stepper motor linear actuator with a fine pitch lead screw. Because there are many variations in the electromechanical linear actuator system, it is critical to understand all design requirements and application constraints for the proper selection.
The following is a guideline to the selection of the linear actuator, and will assist you through the process step by step. Carefully consider each step and you will be able to narrow down your choice.
BEFORE YOU START
IMPORTANT NOTES: Linear actuators are used in a variety of applications across numerous industries, including medical equipment, agriculture machinery, high-voltage switch gears, train and bus doors, and factory processes and assembly machinery. Typical end uses include medical beds, patient lifters, wheelchairs, adjustable tables and workstations, diagnostics, to name a few. Each linear actuator application has unique requirements.
Manufacturers throughout the world that offer innumerable models of linear actuators in a wide variety of stroke sizes, speeds, voltage and types. With the availability of so many manufacturers, models and options, selecting the right linear actuator for your application can be a daunting task. When contacting a manufacturer for application assistance for a linear actuator, please be able to provide as much of the application requirements as possible, including the environment in which you plan to use the linear actuator. Most linear actuators are built either for high speed, high force, or a compromise between the two.
Starting the Process
Step One: The Basics
Describe and discuss the application in as much detail as possible with a knowledgeable and experienced supplier. At this stage, focus on basic specifications for load, actuator, and power and control) in the selection process. When considering a linear actuator for a specific application, the most important specifications are: travel distance, speed, force, accuracy and lifetime requirements. Other aspects of the linear actuator application will help determine which products to choose. The following questions must be answered before the selection process can start:
- What type of energy source will you use? Air, fluid, electricity? Answering this question will eliminate many manufacturers and linear actuator types.
- Determine the amount of force required. This may be the weight of an object you are lifting or friction that needs to be overcome. How much force (in newtons or pounds-force) and in what directions (push, pull, vertical, and/or horizontal) will the actuator need to move? (Force is a function of maximum and average dynamic loads.) Rule out any linear actuators that are not capable of producing enough force.
- Speed: How fast (millimeters/second or inches/second) will the actuator need to move?
Decide how fast you need to move; you can rule out any linear actuators that are too fast or too slow. Determining the speed combined with the force from step one will give you the mechanical power required and how powerful the motor must be.
- Distance: Define how far your actuator needs to travel, also known as the stroke length. Whenever possible select the standard catalog options. How far will the actuator need to move? This will factor in both the stroke and retracted lengths and is usually expressed in millimeters. Special requirements are generally more costly. IMPORTANT: Keep in mind that the longer the stroke, the longer the linear actuator will be when fully retracted. This is especially important if you need to fit into an existing space.
- Duty Cycle: How often will the actuator operate, and how much time will elapse between operations? (This refers to the "duty cycle," which will be based on the number of expected repetitions per unit of time in hours/day, minutes/hour, and/or strokes/minute.) Check the duty cycle rating of your remaining choices. Except for high-end servo units, most linear actuators may not operate continuously without overheating.
- Options to consider: What are the power supply options (motor vs. battery)?
A battery-powered application will probably require a DC motor rated the same as the battery voltage. However, an AC powered application does not necessarily need an AC motor because AC is fairly easily converted to any DC voltage. Be flexible when choosing options such as built-in limit switches and position feedback devices such as potentiometers and encoders. Consider that limit switches, for example, can often be incorporated into part of your mechanism rather that being part of the actuator itself.
- Environmental Considerations: Will environmental factors (temperature variations, moisture, vibration, or end-product shock) pose a challenge to operation? Most linear actuators can operate well in an indoor environment, but harsh outdoor conditions, extreme temperatures or submersion will drastically limit your product choices. Sometimes it is easier to provide some external protection to the unit rather than find one with the proper ingress protection rating that meets all your other requirements.
Narrowing Down the Selection of the Linear Actuator
Careful review of your linear actuator application can help to eliminate costly mistakes and provide for optimal system performance.
Step Two: Beyond the Basics – Options to Consider
When a system is tailored for an application, the specific requirements will influence both the design and the manufacturing processes. Regardless of end use, an actuation system is designed by first identifying basic needs, and then evaluating certain key parameters that ultimately affect the overall system operation.
Electromechanical linear actuators are designed to provide precision, efficiency, accuracy, and repeatability in effecting and controlling linear movement. These devices serve as practical, efficient, and relatively maintenance-free alternatives to their hydraulic or pneumatic actuator counterparts. Depending on type and manufacturer, today's electromechanical linear actuators can handle loads up to 3,000 pounds (13 kilonewtons) and deliver speeds up to 6 inches/second (150 millimeters/second), with strokes ranging from 2 inches (50 millimeters) to 60 inches (1,500 millimeters). Actuators can be self-contained in aluminum, zinc, or polymer housings and ready to mount for easy plug-in operation (using either AC or DC power supplies).
What's more, actuators featuring both modular design and open architecture enable interchangeable internal and external components, according to specifications. Please note that standard components, including the types of drive screws, motors, front and rear attachments, controls, and limit switches used, will allow for desired customization without the costs typically associated with special modifications.
Note: The specific parameters that play a crucial role in every electromechanical actuator application is the: electrical power in, duty cycle, and actuator efficiency. Answering the following questions will help you to define the linear actuator further:
- What is the desired lifetime for the end product? (Those answers will impact virtually every component within a linear actuator system.)
- How will the actuator be mounted? Will front and/or back mounts require special configurations?
- Does the application suggest particular safety mechanisms (e.g., "manual operators" for use in case of emergency)?
- Is space limited? (If so, the actuator will have to be designed to fit in a specific footprint.
- If a motor is utilized, what are its type (AC, DC, or special) and voltage?
- Is feedback required for speed and/or position? (This will indicate a need for add-on components, such as encoders.)
Step Three: The Power Factor
A linear actuator is a device that produces linear motion by utilizing some external energy source. As far as the source of energy used is concerned, it can be piezoelectric, pneumatic, hydraulic, mechanical, electro-mechanical, etc. A linear actuator system draws principles from both electrical and mechanical engineering disciplines. Consequently, power (defined in watts) is usually the first requirement to be calculated. In order to get mechanical power out of an electric linear actuator, it's necessary to put electrical power into the system. Mechanical power out is usually the easier of the two to define because all that's needed for its calculation is the force, or the load that will be moved, and the speed required.
If the parameters are in metric (SI) units, multiply the force (in newtons) by the speed (in millimeters/second) to obtain watts. (To convert pounds to newtons, multiply by 4.448; to convert inches to millimeters, multiply by 25.4.)
Mechanical power out (Po):
Po = F x v
F = Force (N)
v = Velocity (meters/sec)
Information regarding electrical power can be ascertained through performance graphs and charts from suppliers' specification sheets. Suppliers chart this information differently, but more often than not, there are graphs for force vs. speed and force vs. current draw at a specified voltage. This data is often presented in two graphs or combined in one. The current draw may also be presented in tabular form. In addition, factors will be given based on a duty-cycle curve. The relevant formula is as follows:
Electrical power in (Pi):
Pi = E x I
E = Voltage (V)
I = Current (A)
Step Four: Calculating Duty Cycle
Users will want to establish the duty-cycle factor (sometimes called the "derating factor"). Duty cycle is important. Sometimes the preliminary actuator selection may not meet all of an application's operating requirements. The duty cycle indicates both how often an actuator will operate and how much time there is between operations. Because the power lost to inefficiency dissipates as heat, the actuator component with the lowest allowable temperature (usually this is the motor) establishes the duty-cycle limit for the complete linear actuator system. Please note: There are some heat losses from friction in a gearbox, and via ball-screw and acme-screw drive systems.
To demonstrate how the duty cycle is calculated, assume an actuator runs for 10 seconds cumulative, up and down, and then doesn't run for another 40 seconds. The duty cycle is 10/(40+10), or 20%. If duty cycle is increased, either load or speed must be reduced. Conversely, if either load or speed decreases, duty cycle can increase. The duty cycle is relatively easy to determine if a linear actuator is used on a machine or production device. In other, less predictable applications or those where the linear actuator will be used infrequently, it's advisable to estimate the worst-case scenario in order to assign a meaningful duty-cycle calculation. It is not advisable to operate on the edge of the manufacturer's power curves because this might cause the linear actuator and other components to run too hot. However, in some applications where the duty cycle is 10% or less, the actuator can run to the limit of its power curves.
Step Five: Ascertaining 'Efficiency' and Expected Life
A system's "efficiency" is usually missing from most manufacturers' literature, but it can tell the user how hot the actuator may get during operation; whether holding brakes should be specified in the system if the actuator uses a ball screw; and how long batteries may last in battery-powered systems, among other pertinent data. Calculating efficiency from performance curves is simple: Divide mechanical power out by electrical power in. This yields the efficiency percentage.
While these factors are being calculated and decision making is moving toward final selection, one additional parameter should be addressed:: the application's expected lifetime. Although linear actuator components (e.g., the motor or screw) can be replaced, most actuators can't be easily repaired. In addition, it's important to cover application life expectancy because suppliers will sometimes indicate acme or ball screw life at a certain load, or include mathematical formulae to calculate life based on application parameters. A good design practice is to strive to have the screw and motor life expectancies match as closely as possible.
In those cases where an existing linear actuator must be replaced, ensure that the application engineer has all the necessary information to ensure a good fit. Whenever a linear actuator is subject to replacement, it is recommended to review the application as if it were new.
Other Selection Considerations: Budget and Experience
Having a clear picture of a linear actuator system budget in your mind will help in selecting the best product at an affordable price. Advance budget planning can definitely save the user a lot of time in the selection process by eliminating some types that are too expensive for the application. As mentioned earlier, there are many companies providing linear actuators to the customers based on their requirements. It is important to choose a reliable company for the best results in terms of the actuator features and price.
Common products associated with motion control systems using linear actuators:
AC Motor: An AC Motor is an electric motor that is driven by alternating current. The AC Motor is used in the conversion of electrical energy into mechanical energy. This mechanical energy is made from utilizing the force that is exerted by the rotating magnetic fields produced by the alternating current that flows through its coils. The AC Motor is made up of two major components: the stationary stator that is on the outside and has coils supplied with AC current, and the inside rotor that is attached to the output shaft. Anaheim Automation has a full line of AC motors, with many options for budget considerations. To select the best fit for your application, refer to Anaheim Automation's AC Motors.
Brake: A brake is a device that resists and reduces the motion of a mechanism. When the brake is engaged, it "slips" until the driving mechanism stops. When the brake is disengaged, the mechanism can rotate freely. Brakes are similar in principle to clutches. A clutch couples two mechanisms in order to transmit motion and power, while a brake "couples" a mechanism to a fixed frame in order to reduce motion and power. Anaheim Automation offers a line of friction brakes in four series, in NEMA sizes 23, 34 and 42. Perfect for stopping and holding applications, these compact brakes can handle high torque requirements, from 80 to 1,152 oz-in. Their low-voltage design provides for applications that are susceptible to weak battery, brown out, or long wiring runs. To select the best fit for your application, refer to the Anaheim Automation's Accessories/Brakes.
Brush DC Motor: A brush DC motor is a direct current (DC) motor that is a relatively simple design. The brush motor is an electric motor that uses electricity and a magnetic field to produce torque, which rotates the motor. At its most simple design, a brush motor requires two magnets of opposite polarity and an electric coil, which acts as an electromagnet. The repellent and attractive electromagnetic forces of the magnets provide the torque that causes the brush motor to rotate. Anaheim Automation has a full line of brush DC motors, with many options for budget considerations. To select the best fit for your application, refer to Anaheim Automation's Brush Motors.
Brushless DC Motor (BLDC): A brushless DC motor is an electric motor powered by direct current (DC). Though typically more expensive than the standard electric or brushed motor, the brushless DC has considerable advantages over its predecessor. Most notably, a brushless DC motor boasts better performance and suffers less wear than brushed motors of similar size. Anaheim Automation has a full line of brushless DC motors, with many options for budget considerations. To select the best fit for your application, refer to Anaheim Automation's Brushless Motors.
Clutch: A clutch is a device that transmits power between two mechanisms (usually rotating) selectively. When the clutch is engaged, it "slips" until the two mechanisms rotate at the same speed and power is transmitted. When the clutch is disengaged, the two mechanisms are de-coupled and allowed to rotate at different speeds. Power is not transmitted. Clutches are similar in principle to brakes. In a brake, the driven mechanism would be connected to a fixed frame.
Coupling: A coupling is a device that connects two generally coaxial (inline) shafts at their ends in order to transmit power between them. A coupling can be incorporated with a clutch to serve as a clutch-coupling or a torque limiter. Anaheim Automation offers flexible and jaw couplings that are designed to handle demanding applications. At high speeds, the couplings are capable of transmitting high torque at a constant velocity. Anaheim Automation's couplings can compensate for lateral, axial, and angular misalignments. Flexible couplings are offered in two types, Bellows or Beam. These couplings have no backlash and require zero maintenance. Anaheim Automation offers a wide variety of sizes. To select the best fit for your application, refer to their website under Couplings.
Gearbox: A gearbox is a mechanical device for the purpose of transferring energy from one device to another. A gearbox is used to increase torque, while reducing speed. Torque is the power generated through the bending or twisting of a solid material. This term is often used interchangeably with transmission. Anaheim Automation has a full line of gearboxes, with many options for budget consideration. To select the best fit for your application, refer to Anaheim Automation's Gearboxes.
Linear Actuator Motors: Linear actuator motors are motors that provide push and pull motive force in a straight line. There are many uses for many different types of linear actuator motors: some will be used to move work tables on industrial machines, while others are better suited to modulate control valves, drive material handling equipment, bottling and packaging and robotics, and move printer and scanner heads back and forth on equipment. Large linear actuator motors can drive shovels and lifts on construction equipment. They can be used for home automation projects, such as providing the oscillatory motion of audio loudspeakers, lowering or raising televisions, and in some solar energy systems.
Linear Guide: A linear guide is a mechanical linear motion bearing system or linear slide that is designed to provide free motion. Linear guides are sometimes referred to as a linear actuator. Anaheim Automation has a full line of linear guides that are precision rails and matched bearing blocks, in many sizes (including miniature) with options for all budgets. To select the best fit for your application, refer to the Anaheim Automation's Linear Guides.
Rotary Union: A rotary union, or rotating union, is a device used to conduct fluids and gases from one point to another, often under high pressure. Additionally, a rotating union is designed to lock onto an input valve while rotating or swiveling to meet an outlet. Many rotary unions incorporate multiple ports, some of which are designed to handle different types of material simultaneously.
Slip Ring: A slip ring (in electrical engineering terms) is a method of making an electrical connection through a rotating assembly. Slip rings, also called rotary electrical interfaces, rotating electrical connectors, collectors, swivels, or electrical rotary joints, are commonly found in electrical generators for AC systems and alternators and in packaging machinery, cable reels, and wind turbines. One of the two rings is connected to one end of the armature winding and other one to the other end of the armature winding.
Servo Motor: A servo motor is defined as an automatic device that uses an error-correction routine to correct its motion. The term servo can be applied to systems other than a servo motor; systems that use a feedback mechanism such as an encoder or other feedback device to control the motion parameters. Typically when the term servo is used it applies to a 'servo motor' but is also used as a general control term, meaning that a feedback loop is used to position an item. Anaheim Automation has a full line of servo motors, including linear actuator servo motors, with many options for budget considerations. To select the best fit for your application, refer to Anaheim Automation's Linear Servo Actuators sections of its web site.
Stepper Motor: A stepper motor is an electrical device, which divides the full rotation of the motor into individual parts, called steps. Generally, stepper motors are brushless in order to facilitate a synchronous rotation and operate without the input of an external source on the gear itself. Simply stated, stepper motors are designed with electromagnets, which are arranged in specific locations around the shaft, each engraved with teeth. These teeth match the teeth that are placed on the gear itself. As the gear rotates, one section matches with the teeth of the first electromagnet; offsetting the teeth from the other electromagnets, repeating the action as it rotates. Anaheim Automation has a full line of stepper motors, including linear actuator stepper motors, with many options for budget considerations. To select the best fit for your application, refer to the Anaheim Automation's Stepper Motors or Linear Actuators.
Table/Slide/Stage: The terms table, slide, stage and linear actuator are often used inter-changeably, even though there are significant differences among them. Anaheim Automation carries two types of screw-driven tables: standard screw-driven and precision screw-driven tables. Some tables are designed with unsupported rails and others with supported rails that utilize the stainless steel 400 series precision rolled lead screw, accurate up to 0.003"ft, with a burnished finish and a zero backlash nut. These screw-driven tables (acme and ball screw) are available as open-loop or closed-loop systems (wherein stepper motors are assembled with encoders). Options available: light or heavy-duty configurations, travel lengths, homing and limit switches, and lead screw pitch. Ideal for pick-and-place operations, circular and linear interpolation, point-to-point motion, pin-insertion, inspection and test equipment, engraving, part positioning and assembly, these tables yield a great cost/performance ratio. To select the best fit for your application, refer to Anaheim Automation's Tables.
Glossary of Terms for Linear Actuator Motion Systems
A – Ampere – Amp - The basic unit measure of electric current. Related term: current
(Absolute) Accuracy - Difference between ideal position and real position.
Absolute Positioning – Refers to a motion control system employing position feedback devices to maintain a given mechanical location.
ACME Screw – The most common type of lead screw found in machine applications. The ACME thread is a particular type of thread. Compared to a ball screw, ACME lead screws have a very high friction and backlash, both of which are undesirable for high-performance applications.
AC Motor - A type of electric motor that runs on alternating current. AC motors are more commonly used in industry than DC motors, but do not operate well at low speeds.
AC Servo Motor - A servomotor based on the design of conventional AC motors, with the addition of an amplifier and a feedback device.
AC Synchronous Servo Motor - A servomotor based on the design of conventional AC synchronous motors, with the addition of an amplifier and a feedback device.
Acceleration - The rate at which something increases its velocity. Acceleration is usually measured in units of velocity change for each unit of time (inches/second (velocity)/second(time), and in this example would be written as in./sec/sec or in./sec2
Accuracy - The relative status of something compared to its absolute or perfect value. In motion control this will most often be a position description. A command may be set to 4.0 inches. The accuracy of the system will be defined on how close to the absolute value of 4.0 inches the system can affect the move. Accuracy may be defined as a one-time incident or the average over a number of cycles or motions. Positioning accuracy will normally be defined in terms of deviation (+/- from the theoretical) or limits (acceptable variation from the theoretical: i.e. 3.8 – 4.3 inches define acceptable limits of variation around a theoretical point.
Active front end – A front end processor which interacts with both upstream and downstream equipment and makes required changes based on the incoming and outgoing parameters and data, without external control.
Actual Position – The position of an axis relative to the commanded position. This may be the position at the end of the command move, or the lag between command position at any point during the move and the actual position of the axis at that point. The latter is commonly referred to as following error.
Alarm – An indication that a monitored parameter is not within the prescribed acceptable range. Usually this is in the form of an output than can be used to initiate an operator warning or advisory, to generate a corrective action, or to cause a cessation of the operation entirely.
Algorithm - A mathematical process designed to systematically solve a problem. A complex algorithm is used to control and stabilize the outputs in a closed-loop control system.
Amplifier – In motion control, the amplifier (sometimes referred to as a drive or driver) is the component that follows the command from a controller and provides power to the motor. A device that increases the size or strength of a signal. Servomotors use amplifiers as part of the motor control system.
Analog Servo – A servo system that utilizes analog control and feedback systems, such as voltage variation, pressure changes, etc.. Analog servos are most commonly found in hydraulic and similar systems.
Analog Signal – A communication within the system that is accomplished by means of a signal that varies in direct relation to the intensity or magnitude of the external quality being measured. Typical examples are a 0 – 10 volt motor control signal, a hydraulic pilot pressure, a pneumatic control pressure.
ARC Minute – An angular measurement equal to 1/60th of a degree.
Armature – An Armature is one of the components of a brushless DC motor. The armature is part of the permanent magnet or electromagnet, or the moving iron part of a solenoid or relay. The other component is the field winding or field magnet. The role of the "field" component is simply to create a magnetic field (magnetic flux) for the armature to interact with, so this component can comprise either permanent magnets, or electromagnets formed by a conducting coil.
ASCII (American Standard Code for Information Interchange) – This code assigns a number of electrical signals to each number and letter of the alphabet. In this manner, alphanumeric information can be transmitted between machines in a series of binary numbers.
Automatic Feedback - Feedback that is controlled by an electronic or electromechanical mechanism rather than a person. Automatic feedback is used in closed-loop control systems.
Axes of Motion: The specific major directions along which controlled movement occurs. Usually referred to as the number of these major directions employed in a specific machine. Generally defined as follows:
- X: Linear motion in a positioning direction
- Y: Linear motion perpendicular to the positioning direction
- Z: Vertical linear movement
- A: Angular motion around X (roll)
- B: Angular motion around Y (pitch)
- C: Angular motion around Z (yaw)
Axial Play - The axial displacement of the shaft due to a reversal of an axial force.
Axis: A principal direction along which movement of a tool, component, or workpiece occurs. The components that control each degree of freedom in a machine can be considered an axis. An X-Y-Z machine is a three axis machine where the X and Y axes control movement in the horizontal plane and the Z axis controls up and down motion. Each axis can consist of a controller, drive, motor, and transmission components necessary to couple to the load.
Axes - Plural of axis.
Back Driving - A condition that occurs in stepper motors in which there is an unwanted reversal of the motor shaft, resulting in step loss.
Back EMF (Back Electromotive Force) - The voltage, or electromotive force, that pushes against the current which induces it. Back EMF is one of two ways of locating the position of the rotor in speed control. The type of controller that utilizes this method is known as sensorless control.
Backlash - The play caused by loose connections between mechanical components. Backlash becomes a problem when an axis changes direction. When a motor turns, it pushes all the gears together in one direction. When the motor reverses direction the gear teeth separate from one side and meet on the other side. The distance between the separation is the backlash.
Ballscrew – Ballscrews are highly efficient low friction and low backlash lead screw devices that use ball bearings rolling in a channel cut into the screw. The low friction and backlash attributes are extremely valuable for precision applications where they are used to driver the axes of the machine.
Base Speed - The highest speed rating of a motor.
Baud Rate - The number of times per second a signal in a communications channel could changes states.
Bifilar Winding – refers to the winding configuration of a stepper motor where each stator pole has a pair of windings; the stepper motor will have either 6 or 8 lead wires, depending on termination. This wiring configuration can be driven from a unipolar or bipolar driver.
Bipolar Motors - These motors are composed of two windings and have four wires with no center taps. Current flow is bidirectional and runs through an entire winding at a time instead of just half of the winding. As a result, bipolar motors produce more torque than unipolar motors of the same size.
Brushless Motors - Brushless Motors are a class of motors that operate using electronic commutation of phase currents, rather than electromechanical (brush-type) commutation. Brushless motors typically have a permanent magnet rotor and a wound stator.
Brushless Servo – A servo drive in which commutation of the current is accomplished electronically, rather than through the use of mechanical brushes and a commutator. In a brushless motor, the windings are on the stator, and the magnetic field is provided by permanent magnets in the armature. This results in lower inertial loadings and increased heat dissipation capability over a standard brush type motor.
Brushless Servo Motor - A servomotor based on the design of a conventional brushless DC motor, with the addition of an amplifier and a feedback device.
Bus – One or more conductors used as a path over which information is sent from one of many sources to one of many destinations.
CAN - (CAN) Control Area Network - Is a serial bus system, which was originally developed for automotive applications in the early 1980's. The CAN protocol was internationally standardized in 1993 as ISO 11898-1 and comprise the data link layer of the seven layer ISO/OSI reference model.
CANopen - CANopen is a CAN-based higher layer protocol. It was developed as a standardized embedded network with highly flexible configuration capabilities. CANopen was designed motion oriented machine control networks, such as handling systems. It is used in many various fields, such as medical equipment, off-road vehicles, maritime electronics, public transportation, building automation, etc.
Centralized Control – A control system in which all of the primary processing is done at a single location rather than at multiple points throughout the system.
Circular Interpolation - The generation of an apparently circular motion through the coordinated movements of two axes. The actual path is a series of straight line approximations generated by software algorithms.
Clock – A pulse generator, which controls the timing of switching circuits that control the speed of the stepper motor.
Closed-loop – Closed-loop controls use feedback to correct for errors in the system. Central heating in a building is a common example. The thermostat measures the temperature and turns the heat on or off as necessary. If the temperature is too low the heat turns on, if the temperature is too high the heat turns off. The result is the temperature will hover around the set-point throughout the day regardless external fluctuations like time of day or the weather.
Closed loop control in motion control takes the form of a motor, drive, encoder and controller. The encoder is the feedback and senses if the motor is out of position. If out of position the system corrects itself until it is in the correct location.
Cogging - Torque ripple that is centered around specific locations of the motor revolution. When felt by hand the motor feels like it is easier to turn in some positions and more difficult to turn in others. A motor with no cogging would feel very smooth as it is spun by hand.
Collision Detection – The use of sensors to detect the imminent impact of two or more parts in a motion control system. The signals from the detection sensors can be used to stop motion or to provide a ramped slow down for a "soft" mating of the approaching components.
Commutation – A term which refers to the action of steering currents or voltages to the proper motor phases so as to produce optimum motor torque. In brush-type motors, commutation is done electromechanically with brushes and a commutator. In brushless motors, commutation is done by the switching electronics using rotor position information obtained by Hall sensors, a tachometer, or resolver.
Commutator - A rotary electrical switch that periodically reverses the current direction between the rotor and the external circuit.
Constant Current Driver - A control or device for adjusting the voltage to force or maintain design current in the winding when switching from one winding to another.
Continuous Current - The maximum amount of current that can be applied without overheating the motor. Continuous current is one of the specifications used for sizing AC servomotors.
Continuous Power Output - The ability of a motor to output its full power for a sustained period of time. Continuous power output is one of the specifications used for sizing AC servomotors.
Continuous Torque - The amount of torque that can be provided by the motor under normal running conditions. Typically, continuous torque is one of the specifications used for sizing AC servomotors.
Controller (Stepper Motor) is a regulating mechanism; essentially a DC power supply plus power switching with associated circuits for controlling the switching in the proper sequence.
Controller: (BLDC Speed Controller) takes a signal representing the demanded speed, and drives a motor at that speed. A controller is sometimes referred to as a driver or electronic speed controller), which is an electrical circuit or other electronic component used to control another circuit. A brushless DC motor controller acts to control the direction and speed of the motor, or perhaps act as a brake. The brushless DC motor controller is crucial to the operation of a brushless DC motor.
Control System - A manual or automatic mechanism used to manage dynamic processes by adjusting or maintaining physical variables such as temperature, speed, or flow rate.
Converter – The process of changing AC to DC and back to AC again. This is accomplished through the use of a diode rectifier or thyristor rectifier circuit. The term "converter" may also refer to the process in an adjustable frequency drive, consisting of a rectifier, a DC intermediate circuit, an inverter and a control unit.
Coordination – The integration of the movements of two or more axes of motion, so that the resultant motion is the path which none of the axes are capable of independently. Coordination may also involve the use of sensors and other internal or external commands in the integration effort which assist in effecting the movement or work desired.
Coupling (Couple, Coupler) - The transfer of energy from one circuit to another by means of the mutual capacitance between them. In feedback and control systems this is considered to be electrical noise and is a common problem.
Critically damped - A system tuned to achieve the fastest response without overshoot/oscillation is considered to be critically damped. In control theory this occurs when the damping ratio ζ = 1.
Current Controller – A system that utilizes an electronic method of limiting the maximum current available to a motor. This current is adjustable, so that the motor's maximum current can be controlled. It normally includes functions that serve as a protective measure to prevent extended overload conditions from damaging the motor or the controller.
Cut-to-Length – A sub-routine within a motion control processor or standalone processor that is designed to feed material being processed, at a preset distance. The distance is set prior to the performance of the task, and/or a secondary task such as a cut-off of the feed material. Feedback systems are employed to insure repeatability of the preset feed length.
Daisy Chain - This term is used to describe the linking of several devices in sequence, such that a single signal stream flows through one device and on to another.
Data Communications Equipment (DCE) - A device that establishes, maintains and terminates a session on a network. It may also convert signals for transmission. It is typically a modem. Contrast with DTE.
Data Terminating Equipment (DTE) - A communications device that is the source or destination of signals on a network. It is typically a computer or terminal. Contrast with DCE.
DC Bus – A type of circuit that serves as a common communications pathway shared by several components and which uses a direct current voltage level as a reference. It may also be used to describe a power distribution system shared by multiple components within a machine or power distribution system.
Dead Band - A range of input signals for which there is no system response.
Deceleration – The rate at which something decreases its velocity. Deceleration is usually measured in units of velocity change for each unit of time (inches/second(velocity)/second (time), and in this example would be written as in./sec/sec or in./sec2
Decentralized Control – A control system in which all of the primary processing, logic functioning, are located in individual pieces of equipment or sub-systems, and function essentially independently throughout the system. Normally these independent systems will have some form of communication, sharing vital information with each other for the overall desired result(s).
Delta Configuration (or Pi) - The Delta Configuration gives low torque at low RPM. The resistance between any two points is a series-parallel combination of all three resistors. Therefore, the effective resistance of the circuit will be less than the values of the individual resistors involved. This can be very useful in situations where it is desirable to use larger resistance values than the circuit would normally require.
Detent Torque – Detent torque is the holding torque when no current is flowing in the motor. The maximum torque which can be applied to the shaft of an un-energized step motor without causing continuous rotation. The minimal torque present in an un-energized motor. The detent torque of a step motor is typically about 1% of its static energized torque.
Digital Servo - A servo that outputs a series of pulses or signals that represent "on" or "off," often resulting in binary strings of 0s and 1s.
Driver (Stepper Motor) – often referred to as a translator, it drives a step motor based on pulses from a clock, pulse generator, or computer. It translates the train of pulses and applies power to the appropriate step motor windings.
Drive - In motion control this component follows the command from a controller and provides power to the motor. A drive can operate in current mode, velocity mode, or position mode. It can be commanded by many means such as analog signals, step and direction, encoder following and through network commands among others.
Dynamic Torque – the torque developed by a motor while stepping at low rates. Efficiency - In physics, the efficient energy use, useful work per quantity of energy, mechanical advantage over ideal mechanical advantage, often denoted by the Greek lowercase letter η (Eta). In thermodynamics: efficiency is energy conversion efficiency, a measure of second law thermodynamic loss. Thermal efficiency: useful work per the higher heating value of the fuel. In computing: Algorithmic efficiency is optimizing the speed and memory requirements of a computer program, while storage efficiency as the effectiveness of computer data storage.
Electromagnetic Interference (EMI) - An electromagnetic disturbance, phenomenon, signal or emission that causes or can cause undesired response of electrical or electronic equipment.
Electric Motor - An electric motor is a type of engine which uses electrical energy to produce mechanical energy.
Electronic Clutch – The process of generating a slave profile based on master position or time periods by enabling and disabling electronic cam or gearing functions.
Electronic Gearing – A method that stimulates mechanical gears by electrically synchronizing one closed-loop axis to a second axis (open- or closed-loop) through a variable ratio.
Electronic Line Shaft – A virtual axis that is used as the master axis on a machine to which other axes are synchronized by electronic gearing or camming profiles.
Encoder – An encoder is a feedback device. It consists of a disc, vane, or reflector, typically attached to a motor shaft to provide digital pulses, which are provided to a translator and /or counters. This provides positional information if fed into a counter. Speed information may be derived if the time between successive pulses is measured and decoded.
Encoder Resolution – The number of electrically identified positions occurring in 360 degrees of input shaft rotation.
Event – A change-of-state of an input parameter, such as the triggering of a limit switch or proximity sensor.
Fault – The error received when a drive or control has attempted an illegal process and becomes disabled.
Feedback - Feedback is the measurement of the parameter that is being controlled. For a positioning system to accurately compensate for an error, the actual position must be known relative to the commanded position. In this case, position feedback would be used to provide the actual position.
Feedback Signal - The actual value detected by a sensor as a process is taking place. The feedback signal is part of a closed-loop control system.
Feedforward – A method that "precompensates" a control loop for known errors due to motor, drive, or load characteristics to improve response. It depends only on the command, not the measured error.
FieldBus – A process control local area network used for interconnecting sensors, actuators, and control devices to one another, as defined by ISA standard S50.02.
Flying Restart - The ability of a drive to restart a spinning motor. This is normally done by sampling the motor speed, encoder input, or back EMF to restart the motor from the sped at which it is coasting.
Frequency – Frequency is the number of occurrences of a repeating event per unit time.
the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency. The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example, if a newborn baby's heart beats at a frequency of 120 times a minute, its period (the interval between beats) is half a second. For cyclical processes, such as rotation, oscillations, or waves, frequency is defined as a number of cycles per unit time. In physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by a Greek letter ν (nu).
In SI units, the unit of frequency is the hertz (Hz), named after the German physicist Heinrich Hertz: 1 Hz means that an event repeats once per second. A previous name for this unit was cycles per second.
A traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated RPM. 60 RPM equals one hertz.
The period, usually denoted by T, is the length of time taken by one cycle, and is the reciprocal of the frequency f:
T = 1/f
The SI unit for period is the second.
Full Step - This means that the shaft will rotate 1.8 degree mechanically for each digital pulse received by the driver. In full step mode, the motor requires 200 digital pulses to move one shaft revolution divide 360 degree by 1.8 degree.
Gantry – An overhead framework that is designed to linearly in the X, Y, and/or Z axes. Tooling or other devices are generally designed into the framework to perform various functions as it moves from one location to another.
Gearbox - A system of gears that transmits mechanical power from a prime mover such as an electric motor to a typically rotary output device at a lower momentum but at a higher torque.
Graphical User Interface (GUI) - A type of user interface that allows people to interact with a computer and computer-controlled devices which employs graphical icons, visual indicators or special graphical elements, along with text labels or text navigation to represent the information available to the user.
Ground Loop - A ground loop is any part of the DC return path (ground) that has more than one possible path between any two points.
Half Duplex - The transmission of data in just one direction at a time. For example, a walkie-talkie is a half-duplex device because only one party can talk at a time.
Half Step - This term means that the motor shaft will move a distance of 0.9 degree (400 steps per shaft revolution) instead of moving 1.8 degree per digital pulse.
Hall (effect) sensor(s): A Hall-effect sensor is a transducer that varies its output voltage in response to a magnetic field.
Heat Sink: A heat sink is a term for a component used to dissipate heat; keep electronic and optoelectronic devices cool.
Holding Torque – Holding torque is the maximum torque that can be externally applied to the motor shaft without causing continuous rotation when one or more phases of the motor are energized.
Home Position – A reference position for all absolute positioning movements. Usually defined by a home limit switch and/or encoder marker. Normally set at power-up
Homing – Locating a unique reference position at power-up for axis calibration.
Hybrid Motors - Hybrid stepper motors feature the best characteristics of PM and VR motors. Hybrid steppers are best suited for industrial applications because of high static and run torque, a standard low step angle of 1.8°, and the ability to Microstep. Hybrid stepper motors offer the ability to precisely position a load without using a closed-loop feedback device such as an encoder.
Human-Machine Interface (HMI) – The console at which an operator or mechanic interacts with the controller of a packaging machine or line. An HMI, or MMI (man-machine interface) or OI (operator interface), often is a computer display with a PC or industrial computer built into or connected to run specialized HMI software.
Indexer - In the context of stepper motor-based systems, the indexer is a device that provides step and direction control signals to a stepper motor driver. More sophisticated dedicated stepper motor controllers will also have I/O points and various other higher level functions and programmability similar to a PLC. In many cases a PLC may be used as an Indexer.
Indexing – An axis or axes in the process of moving to a pre-programmed position, at a defined velocity and acceleration/deceleration rate.
Inductance – The property that exists between two-current carrying conductors or coils when magnetic lines of force from one coil or conductor are linked with those of the other.
Induction Motor - A type of AC motor that uses electrical current to induce rotation in the coils.
Inertia - Inertia is a measure of an object's resistance to a change in velocity. A measure of an object's resistance to a change in velocity. The larger an object's inertia, the greater the torque required to accelerate or decelerate it. Inertia is a function of an object's mass and shape. For the most efficient operation, the system-coupling ratio should be selected so that the reflected inertia of the load is equal to or no greater than 10 times the rotor inertia of the stepper motor.
Inertia (Reflected) - Inertia as seen by the stepper motor when driving through a speed change, reducer or gear train.
Interpolation – A coordinated move of two or more axes in a linear and/or circular motion.
Jog – An axis running at a fixed velocity and acceleration/deceleration rate, in a selected direction, with no specific destination.
Lead - The linear distance a nut on a leadscrew travels during one revolution of the lead screw, e.g. in./rev.
Lead Screw - A device that converts rotary motion into linear motion.
LED - Light Emitting Diode. A semiconductor device that emits a narrow spectrum of light in a forward direction.
Limits - A stepper motor system with sensors that alert the control electronics that a physical end of travel has approached and that the motion is not allowed in a specific direction.
Linear Actuator - A linear actuator is an actuator that creates motion in a straight line, as contrasted with circular motion of a conventional electric motor. Linear actuators are used in machine tools and industrial machinery, in computer peripherals such as disk drives and printers, in valves and dampers, and in many other places where linear motion is required. Hydraulic or pneumatic cylinders inherently produce linear motion; many other mechanisms are used to provide a linear motion from a rotating motor. Linear Servo Motor - A linear servo motor is a flattened out servo motor where the rotor is on the inside, and the coils are on the outside of a moveable u-channel. Both servo motor types are becoming more popular as costs continue to lower.
Linear Slide - Linear slides are precision products designed to turn motion or torque into straight-line movements. Linear slides are designed to move mounted mechanisms across a given axis. Complete slides normally consist of at least a base, a saddle, adjusting screw and a straight gib.
Load - Any external resistance (static or dynamic) to motion that is applied to the motor.
Logic Ground - The reference "zero" voltage that a group of control signals in a particular system are referenced.
Maximum Running Torque – With respect to stepper motors, maximum running torque is the maximum torque load that the motor can drive without missing a step. This typically occurs when the windings are sequentially energized at approximately 5 PPS.
Microprocessor - A tiny central processing unit. Digital servos use a microprocessor to process input signals.
Microstepping - A control electronic technique that proportions the current in a stepper motor's windings to provide additional intermediate positions between poles. Produces smooth rotation over a wide range and high positional resolution. Typically, step resolutions range from 400 to 51,200 steps per shaft revolution.
Minimum Incremental Motion (Sensitivity) - The smallest increment of motion a device is capable of delivering consistently and reliably
Multidrop - A communications configuration in which several devices share the same transmission line, although generally only one may transmit at a time. This configuration usually uses some kind of polling mechanism to address each connected device with a unique address code.
National Electrical Manufacturer's Association (NEMA) - The acronym for the organization that sets standards for motors and other industrial electrical equipment.
Noise – An unwanted electrical signal. Typically from RFI or EMI induced onto the drive's components, speed reference or feedback wiring, and can cause the axis to react unexpectedly. Sources of noise are AC power lines, motors, generators, transformers, fluorescent lights, CRT displays, and radio transmitters.
Offset – A preset distance between the actual zero reference point and a programmed zero reference point.
On-Axis Accuracy - Difference between ideal position and real position after the compensation of linear errors. Linear errors include: cosine errors, inaccuracy of screw or linear scale pitch, angular deviation at the measuring point (Abbe error) and thermal expansion effects. The relation between absolute accuracy and on-axis accuracy is as follows:
Absolute Accuracy = On-Axis Accuracy + Correction Factor x Travel
Open-Loop - A type of control system that uses only an input signal to actuate an output. There is no automatic feedback to adjust the process, so adjustments must be made manually by the operator.
Opto-Isolated - A method of sending a signal from one piece of equipment to another without the usual requirement of common ground potentials. The signal is transmitted optically with a light source (usually a Light Emitting Diode) and a light sensor (usually a photo-sensitive transistor). These optical components provide electrical isolation.
Output Shaft - The part of a motor that transmits torque.
Overcurrent - Any current in excess of the rated current of the drive to maintain or move to a new position at a given velocity and acceleration of deceleration rate.
Override – To force an axis to move during a faulted condition. Often required to get an axis to move off of an overtravel limit switch.
Overshoot - To exceed a set value.
Over-Temperature – A warning or alarm generated by a motor or drive that indicates the device is too hot. This is generally caused by the demand for too much current through the device. There may be binding at the motor, calling for more torque, or the motor or drive may be undersized.
Permanent Magnet Motors - Permanent Magnet Motors are typically not used in industrial applications. PM motors generally have a high step angle, are low torque, low cost and used in high volume consumer applications such as printers, fax machines and toys.
Phasing – Asjusting the position of one axis with respect to others during synchronization or electronic line shafting. This is usually done while the axes are moving, and done to correct for small registration problems.
Pick and Place - An application in which objects are transferred from one place to another.
Pitch - The distance from any point on one thread of the screw to a corresponding point on the next successive thread, e.g. rev/in.
Prime Ratio Stepper - A "Prime Ratio Stepper" is a hybrid stepper motor that has an increased stator to rotor tooth ratio. Where a standard stepper motor has 40 stator teeth to 50 rotor teeth, a ratio of 4:5, a prime ratio motor has 48 stator teeth to 50 rotor teeth, a ratio of 4.8:5. This difference means 16% more area of the face of the stator.
PLC – A Programmable Logic Controller is a type of computer that provides hard, real-time control of packaging and other equipment thanks to fast, repeatable deterministic scan times.
Position Error – Error caused when the difference between the actual position and the command position is greater than a set amount.
Positioning – Specifying a move by giving a target position, a velocity and an acceleration. The target position can be an absolute position, or a relative position from the current position.
Position Control - A type of control system designed for moving objects or machines to a known position. For example: stepper motors are used for position control.
Program Mode - This mode is used to input user program into the motion controller.
Programmable Logic Controller (PLC) - A specialized device used to provide high speed, low-level control of a process.
Pull-In Torque (also called Starting Torque) - This is the maximum torque the stepper motor can develop when instantaneously started at that speed.
Pull-Out Torque (also called Slewing Torque) - This is the maximum torque that the stepper can develop once an acceleration profile has been used to "ramp" it to the target speed.
Pulse – A pulse is an electrical signal or voltage of short duration, used in conveying intelligence.
Pulse-Width Modulation - PWM or PDM (Pulse-Duration Modulation), is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches.
Rated Torque – The rated torque is the torque-producing capacity of a motor at a given speed. This is the maximum torque the motor can deliver to a load and is usually specified with a torque/speed curve.
Recommended Standard 232 (RS-232) - The standard for serial transmission between a DTE (computer) and a DCE (modem, mouse, etc.). This is a single-ended (unbalanced) hardware configuration that employs a method of communicating digital information in which the data bits are transmitted sequentially over one line. The typical transmission speed of an RS-232 connection is 9600 bps over a maximum distance of 50ft (15m).
Recommended Standard 422 (RS-422) - The standard for serial data communication protocol which specifies 4 wire, full duplex, differential line, multi-drop communications. It provides for balanced data transmission with unidirectional/non-reversible, terminated or non-terminated transmission lines. With a transmission rate of 9600 bps, RS-422 can be used at distances up to 4,000 feet (1,275 meters).
Recommended Standard 485 (RS-485) - This standard is an enhanced version of RS-422 with the added capability to allow up to 32 devices (transmitters and receivers) that share the same serial data communication lines. It uses a 2 wire, half duplex, multipoint serial connection.
Repeatability - Ability of a system to achieve a commanded position over many attempts.
Resolution - The smallest increment that a motion device can be commanded to move and/or detect. Resolution is the smallest positioning increment that can be achieved. With respect to stepper motors, it is frequently defined as the number of steps required for a motor's shaft to rotate one complete revolution. The reciprocal of the number of steps per revolution of the motor.
Resolver - A high-resolution feedback device that is an alternative to encoders. Resolvers are suited to harsh environments such as high temperatures and severe vibration since they do not rely on optical sensors or glass disks which can fail in these conditions. Resolvers use inductive couplings to determine rotor position. Since resolver signals are not discrete, resolution is determined by the amount of interpolation used in the interface circuitry in the drive or controller. Typical resolutions range from 1000 to 65000 counts / revolution.
Resonance - The frequency that a stepper motor system may begin to oscillate. Primary resonance frequency occurs at about one revolution per second. This oscillation will cause a loss of effective torque and may result in loss of synchronism. The designer should consider reducing or shifting the resonance frequency by utilizing half step or micro-step techniques or work outside the primary resonance frequency.
Reversal Value (Hysteresis) - Difference between actual position values obtained for a given target position when approached from opposite directions.
Rotor – The rotor is the rotating part of the motor (the shaft may be included). The moving part of the motor, consisting of the shaft and the magnets. These magnets are similar to the field winding of a brush type DC motor.
Rotor Inertia - The rotational inertia of the rotor and shaft.
Serial Peripheral Interface Bus (SPI) - Is a synchronous serial data link that operates in full duplex mode. Devices communicate in master/slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select lines.
Servo Drive - A motor control device that outputs electrical signals to a servomotor to induce motion. The servo drive can be built in as part of the motor or it can be a separate device.
Servo Mechanism - A servomechanism may or may not use a servo motor. For example, a household furnace is a servomechanism that is controlled by a thermostat. Once a set temperature is reached, there is feedback signaling it to shut off; making it a "servo" in nature. The term "servo" describes more of a function or task, than it does a specific product line.
Servo Motor – A servo motor is a motor which is part of a servomechanism. It is typically paired with some type of encoder to provide positioning and speed feedback. A servo motor is an an automatic device that uses an error-correction routine to correct its motion. The term servo can be applied to systems other than a servo motor; systems that use a feedback mechanism such as an encoder or other feedback device to control the motion parameters. Typically when the term servo is used it applies to a 'Servo Motor' but is also used as a general control term, meaning that a feedback loop is used to position an item. A servo motor can be a DC, AC, or brushless DC motor, combined with a position sensor; in most cases, a digital encoder. A servo motor is typically the motor selected when it is essential that there is a high degree of confidence that the servo motor and drive system will closely track what is asked of it. There is typically a higher cost to a servo motor system than a stepper motor system, due to the servo motor's feedback sensor and processing electronics.
Shaft - The portion of the rotor that lies on the spin axis of the rotor and is the rotor interface to the stator portion of the magnetic bearings and motor generators.
Shaft Speed - The rate at which the motor shaft turns. Shaft speed is measured in feet per minute (fpm) or in meters per minute (mpm).
Sine Wave - The most common type of AC waveform. A sine wave consists of 360 electrical degrees and is produced by rotating machines.
Single Phase - AC voltage that has only one sine wave.
Sinking Current - Refers to the current flowing into the output of the chip. This means that a device connected between the positive supply and the chip output will be switched on when the output is low.
Slew - The position of a move profile where the motor is operating at a constant velocity.
Sourcing Current - Refers to the current flowing out of the output of the chip. This means that a device connected between the chip output and the negative supply will be switched on when the output is high.
Start-Stop Test - A troubleshooting method in which the stepper motor is connected to a load and a fixed frequency is applied to the driver. Stop-start tests are used to diagnose the causes of step loss.
Stator – The stator is the stationary magnetic parts of the motor including the windings.
Step Loss - A phenomenon in which the stepper motor does not take a step after receiving an input pulse.
Stepper Motor - A type of motor that rotates in small, precise increments in response to an electronic pulse. Stepper motors can rotate forward or reverse, but they cannot move large loads. A stepper motor (also referred to as step or stepping motor) is an electromechanical device achieving mechanical movements through conversion of electrical pulses. Stepper motors are driven by digital pulses rather than by a continuous applied voltage. Unlike conventional electric motors which rotate continuously, stepper motors rotate or step in fixed angular increments. A stepper motor is most commonly used for position control. With a stepper motor/driver/controller system design, it is assumed the stepper motor will follow digital instructions. One important aspect of stepper motors is the lack of feedback to maintain control of position, which classifies stepper motors as open-loop systems.
Step – A step is the movement of the rotor of a stepper motor from one energized position to the next.
Step Angle – The step angle is the nominal angle through which the shaft of a stepper motor turns between adjacent step positions. It depends upon the motor and driving sequence (mode of drive).
Step Increment – Step increment is an indication of step or motion size. Usually this is specified in degrees for a rotary motor and inches or millimeters for a linear motor.
Step (Stepping, Stepper) Motor – A Stepper is synonymous with Step and Stepping motor,:a digital actuator, which operates from discrete pulses (input signals) and produces motion in discrete increments. May be rotary or linear increment. See stepper motor definition above.
Step Position – the angular position that the shaft of an unloaded step motor assumes when energized. The step position is not necessarily the same as the detent position.
Synchronous Motor - A constant-speed AC motor that does not use induction to operate. A synchronous motor needs DC excitation to operate.
Target Value - A preset value such as a specific temperature, speed, or flow rate that the control system is supposed to reach. For example: the type of preset value for servomotors is position.
Teeth – The teeth are projections on both the rotor and stator such that when aligned they produce a low reluctance magnetic path.
Torque - A rotational force. Torque is measured in N*m, lb*in, lb*ft, etc. 1 N*m is the torque produced by 1N of force applied to a lever arm that is 1m long.
Train Pulse – A train pulse is a series of spaced pulses.
Tuning - A system of adjusting the servomotor's outputs by adjusting values in the algorithm controlling the closed-loop system.
Undershoot - To fall short of or below a set value.
Unifilar Winding – Unifilar winding refers to the winding configuration of the stepper motor where each stator pole has one set of windings; the stepper motor will have only 4 lead wires. This winding configuration can only be driven from a bipolar driver.
Unipolar Motors – These motors are composed of two windings, each with a center tap. The center taps are either brought outside the motor as two separate wires or connected to each other internally and brought outside the motor as one wire, resulting in 5 or 6 wires.
Variable Reluctance Stepper Motor - Variable Reluctance Motors have no permanent magnet, thus the rotor spins freely as there is no detent torque. The step angle of a VR motor is in the medium range, generally 5 to 15 degrees. This type of motor is also used in non-industrial applications where a high degree of torque is not required.
Windings - The conducting wire connected to the armature that energize the pole pieces of a motor.
Wye (Y or Star) Configuration - The Wye Configuration provides high torque at low RPM, but not as high top RPM. The resistance between any two of the three external connections will be the series combination of two of the three resistors.
Yaw, Pitch: Rotation of carriage around the Z axis (Yaw) or Y axis (Pitch), when it moves. The testing of on-axis accuracy, repeatability, and reversal error are made systematically with test equipment in an air-conditioned room (20 °C±1 °C). A linear cycle with 21 data points on the travel and 4 cycles in each direction gives a total of 164 points.