What is a Stepper Motor?
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.
Block Diagram for Stepper Motor System
Physical Properties of a Stepper Motor
The main components of a stepper motor are the shaft, rotor and stator laminations, magnets, bearings, copper wires and lead wires, washers, and front and end covers. The shaft of a stepper motor is typically made of stainless steel metal, while the stator and the rotor laminations are comprised of silicon steel. The silicon steel allows for higher electrical resistivity which lowers core loss. The various magnets available in stepper motors allow for multiple construction considerations. These magnets are ferrite plastic, ferrite sintered and Nd-Fe-B bonded magnets. The bearings of a stepper motor vary with size of the motor. The housing materials are composed of various other metals like aluminum, which allow for high resistance to heat.
How Does a Stepper Motor Work?
The main use of stepper motors is to control motion, whether it is linear or rotational. In the case of rotational motion, receiving digital pulses in a correct sequence allows the shaft of a stepper motor to rotate in discrete step increments. A pulse (also referred to as a clock or step signal) used in a stepper motor system can be produced by microprocessors, timing logic, a toggle switch or relay closure. A train of digital pulses translates into shaft revolutions. Each revolution requires a given number of pulses and each pulse equals one rotary increment or step, which is only a portion of one complete rotation. There are numerous relationships between the motors shaft rotation and input pulses. One such relationship is the direction of rotation and the sequence of applied pulses. With proper sequential pulses being delivered to the device, the rotation of the shaft motor will undergo a clockwise or counterclockwise rotation. Another relation between the motor’s rotation and input pulses is the relationship between frequency and speed. Increasing the frequency of the input pulses allows for the speed of the motor shaft rotation to increase.
Basic Types of Stepper Motors
A stepper motor varies per application by construction and functionality. The three most common stepper motor types are Variable Reluctance, Permanent Magnet, and Hybrid Stepper Motors.
Variable Reluctance (VR) Stepper Motor
VR stepper motors are characterized as having multiple soft iron rotors and a wound stator. VR stepper motors generally operate on the basic principle of the magnetic flux finding the lowest reluctance pathway through a magnetic circuit. In general operation, VR stepper motors have relatively high step rates of 5 to 15 degrees and have no detent torque. The step angles taken in VR stepper motors are related to the number of teeth the stator and rotor have. The equation relating these two variables can be found in the formula section of this guide.
How Does a Variable Reluctance Stepper Motor Work?
Referring to Figure 1 on Page 2, the poles become magnetized when the stator windings are energized with DC current. With the poles becoming magnetized, the rotor teeth are now attracted to the energized stator poles and rotate to line up. With the windings around stator A becoming energized the rotor teeth become attracted allowing the poles to line up. When A’s windings become de-energized and B’s windings become energized, the rotor rotates to line its teeth with the stator teeth. This process continues in sequence with C, followed by D being energized allowing for the rotor to rotate.
Brief Summary of Variable Reluctance Stepper Motors:
|• The rotor has multiple soft iron rotors with a wound stator|
|• Least complex, therefore least expensive stepper motor|
|• Large step angles|
|• No detent torque detected in hand rotation of a de-energized motor shaft|
Permanent Magnet (PM) Stepper Motor
PM stepper motors are comprised of permanent magnet rotors with no teeth, which are magnetized perpendicular to the axis of rotation. By energizing the four phases in sequence, the rotor rotates due to the attraction of magnetic poles. The stepper motor shown in Figure 2 on page 3 will take 90 degree steps as the windings are energized in clockwise sequence: ABAB. PM stepper motors generally have step angles of 45 or 90 degrees and step at relatively low rates. However, they exhibit high torque and good damping characteristics. Anaheim Automation carries a wide selection of PM stepper motors, ranging from 15 to 57mm in diameter.
Brief Summary of Permanent Magnet (PM) Stepper Motors:
|• The rotor is a permanent magnet|
|• Large to moderate step angle|
|• Often utilized in computer printers as a paper feeder|
Hybrid Stepper Motors
Hybrid stepper motors incorporate the qualities of both the VR and PM stepper motor designs. With the Hybrid stepper motor’s multi-toothed rotor resemblance of the VR, and an axially magnetized concentric magnet around its shaft, the Hybrid stepper motor provides an increase in detent, holding and dynamic torque. In comparison to the PM stepper motor, the Hybrid stepper motor provides performance enhancement with respect to step resolution, torque, and speed. In addition, the Hybrid stepper motor is capable of operating at high stepping speeds. Typical Hybrid stepper motors are designed with step angles of 0.9°, 1.8°, 3.6° and 4.5°; 1.8° being the most commonly used step angle. Hybrid stepper motors are ideally suited for applications having stable loads with speeds under 1,000 rpm. There are key components which are influential with respect to the running torque of a Hybrid stepper motor; laminations, teeth and magnetic materials. Increasing the amount of laminations on the rotor, precision and sharpness of the rotor and stator teeth, and strength of magnetic material are all factors taken into consideration in designing for optimal torque output for Hybrid stepper motors.
Brief Summary of Hybrid Stepper Motors:
|• Smaller step angles in comparison to VR and PM stepper motors|
|• Rotor is made of a permanent magnet with fine teeth|
|• Increase in detent, holding and dynamic torque|
|• 1.8° is the most common step angle|
NOTE: At Anaheim Automation, the 1.8 degree Hybrid stepper motor is the most widely stocked stepper motor type, ranging in size from NEMA 08 to 42. The Hybrid stepper motor can also be driven two phases at a time to yield more torque, or alternately one then two then one phase, to produce half-steps or 0.9 degree increments.
The primary difference between individual Stepper Gearmotors is their performance characteristics. The main function of a Stepper Gearmotor is to convert the input of a Stepper Motor into an output, with high torque and low RPM. Anaheim Automation carries both Planetary and Spur Stepper Gearmotors offering various gear ratios, stack lengths and torque outputs.
Stepper Motors with Spur Gearboxes
Stepper motors integrated with spur gearboxes are readily available, compact and efficient. Anaheim Automation’s Stepper Gearmotors are available with gear ratios ranging from 3:1 to 150:1. Stepper Motors with Spur Gearboxes are widely used in applications requiring either an increase or reduction in speed, and high output torque. When considering Spur Gearboxes, it is important to take into consideration the bore and shaft diameter and the gear center, in order to meet specific application needs.
Stepper Motors with Planetary Gearboxes
Stepper Motors integrated with Planetary Gearboxes are compact in size, efficient, and are offered in various stack lengths. The word “planetary” derives from the gearbox’s resemblance to the solar system. This system consists of three main components: the sun gear, ring gear, and two or more planet gears. The sun gear is the located in the center, the ring gear is the outermost gear, and the planet gears surround the sun gear inside the ring gear. The Planetary Gearbox is utilized in applications for low backlash, compact size, high efficiency, resistance to shock, high torque to weight ratio, and improved lubrication.
How are Stepper Motors Controlled?
A stepper motor performs the conversion of logic pulses by sequencing power to the stepper motor windings; generally, one supplied pulse will yield one rotational step of the motor. This precise control is provided by a stepper driver which controls speed and positioning of the motor. The stepper motor increments a precise amount with each control pulse, converting digital information into exact incremental rotation without the need for feedback devices, such as tachometers or encoders. Since the stepper motor and driver is an open-loop system, the problems of feedback loop phase shift and resultant instability, common with servo motor systems are eliminated.
How to Select a Stepper Motor
There are several important criteria involved in selecting the proper stepper motor:
|1. Desired Mechanical Motion|
|2. Speed Required|
|4. Stepper Mode|
|5. Winding Configuration|
With appropriate logic pulses, stepper motors can be bi-directional, synchronous, provide rapid acceleration, run/stop, and can interface easily with other digital mechanisms. Characterized as having low-rotor moment of inertia, no drift, and a noncumulative positioning error, a stepper motor is a cost-effective solution for many motion control applications. Generally, stepper motors are operated without feedback in an open-loop fashion and sometimes match the performance of more expensive DC Servo Systems. As mentioned earlier, the only inaccuracy associated with a stepper motor is a noncumulative positioning error which is measured in % of step angle. Typically, stepper motors are manufactured within a 3-5% step accuracy.
Motion requirements, load characteristics, coupling techniques, and electrical requirements need to be understood before the system designer can select the best stepper motor/driver/controller combination for a specific application. While not a difficult task, several key factors need to be considered when determining an optimal stepper motor solution. The system designer should adjust the characteristics of the elements under his/her control, to meet the application requirements. Anaheim Automation offers many options in its broad line of stepper motor products, allowing for the maximum amount of design flexibility. Although it may appear overwhelming to choose, the result of having a large number of options is a high-performance system that is cost-effective. Elements needed to be considered include the stepper motor, driver, and power supply selections, as well as the mechanical transmission, such as gearing or load weight reduction through the use of alternative materials. Some of these relationships and system parameters are described in this guide.
Inertia is a measure of an object’s resistance to a change in velocity. The larger an object’s inertia, the greater the torque is required to accelerate or decelerate it. Inertia is a function of an object’s mass and shape. A system designer may wish to select an alternative shape or low-density material for optimal performance. If a limited amount of torque is available in a selected system, then the acceleration and deceleration times must increase. For most efficient stepper motor systems, the coupling ratio (gear ratio) should be selected so the reflected inertia of the load is equal to, or greater than, the rotor inertia of the stepper motor. It is recommended that this ratio not be less than 10 times the rotor inertia. The system design may require the inertia to be added or subtracted by selecting different materials or shapes of the loads.
NOTE: The reflected inertia is reduced by a square of the gear ratio, and the speed is increased by a multiple of the gear ratio.
All mechanical systems exhibit some frictional force. The designer of a stepper motor system must be able to predict elements causing friction within the system. These elements may be in the form of bearing drag, sliding friction, system wear, or the viscosity of an oil filled gear box (temperature dependent). A stepper motor must be selected that can overcome any system friction and still provide the necessary torque to accelerate the inertial load.
NOTE: Some friction is desired, since it can reduce settling time and improve performance.
The positioning resolution required by the application may have an effect on the type of transmission used, and/or selection of the stepper motor driver. For example: A lead screw with 5 threads per inch on a full-step drive provides 0.001 inch/step; half-step provides 0.0005 inch/step; a microstep resolution of 25,400 steps/rev provides 0.0000015 inch/step.
Stepper Motor Modes
Stepper motors are driven by waveforms which approximate to sinusoidal waveforms. There are three excitation modes commonly used with stepper motors: full-step, half-step and microstepping.
Stepper Motor - Full-Step (Two Phases are on)
In full-step operation, the stepper motor steps through the normal step angle, e.g. with a 200 step/revolution the motor rotates 1.8° per full step, while in half-step operation the motor rotates 0.9° per full step. There are two kinds of full-step modes which are single-phase full-step excitation and dual-phase full-step excitation. In single-phase full-step excitation, the stepper motor operates with only one phase energized at a time. This mode is typically used in applications where torque and speed performances are less important, wherein the motor operates at a fixed speed and load conditions are well defined. Typically, stepper motors are used in full-step mode as replacements in existing motion systems, and not used in new developments. Problems with resonance can prohibit operation at some speeds. This mode requires the least amount of power from the drive power supply of any of the excitation modes. In dual-phase full-step excitation, the stepper motor operates with two phases energized at a time. This mode provides excellent torque and speed performance with minimal resonance problems.
NOTE: Dual excitation provides about 30 to 40 percent more torque than single excitation, but does require twice the power from the drive power supply. Many of Anaheim Automation's microstepping drivers can be set to operate at full-step mode if necessary.
Stepper Motor - Half-Step
Stepper motor half-step excitation mode alternates between single and dual-phase operations resulting in steps that are half the normal step size. Therefore, this mode provides twice the resolution. While the motor torque output varies on alternate steps, this is more than offset by the need to step through only half the angle. This mode had become the predominately used mode by Anaheim Automation beginning in the 1970’s, because it offers almost complete freedom from resonance issues. The stepper motor can operate over a wide range of speeds and drive almost any load commonly encountered. Although half-step drivers are still a popular and affordable choice, many newer microstepping drivers are cost-effective alternatives. Anaheim Automation’s BLD75 series is a popular half-step driver and is suitable for a wide range of stepper motors. With this driver, the customer only needs a transformer, as the other power supply components are built into the driver itself.
Stepper Motor - Microstepping
In the stepper motor microstepping mode, a stepper motor's natural step angle can be partitioned into smaller angles. For example: a conventional 1.8 degree motor has 200 steps per revolution. If the motor is microstepped with a 'divide-by-10,' then each microstep moves the motor 0.18 degrees, which becomes 2,000 steps per revolution. The microsteps are produced by proportioning the current in the two windings according to sine and cosine functions. This mode is widely used in applications requiring smoother motion or higher resolution. Typical microstep modes range from 'divide-by-10' to 'divide-by-256' (51,200 steps per revolution for a 1.8 degree motor). Some microstep drivers have a fixed divisor, while the more expensive microstep drivers provide for selectable divisors. For cost-effective microstep drivers, see Anaheim Automation’s MBC and MLA Series.
NOTE: In general, the larger the microstep divisor provided, the more costly will be the stepper motor driver. Should you prefer, Anaheim Automation also manufactures a series of Integrated Stepper Motors/Drivers, meaning the stepper motor and driver are in one unit. This design approach takes the guesswork out of motor and driver compatibility. For more information, please see the 17MD, 23MD and 34MD Series.
Motor Windings Configuration
Stepper motors are wound on the stator poles in either a unifilar or bifilar configuration. The term 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. The term bifilar winding refers to the winding configuration of a stepper motor where each stator pole has a pair of identical windings; the stepper motor will have either 6 or 8 lead wires, depending on termination. This type of winding configuration simplifies operation in that transferring current from one coil to another, wound in the opposite direction, will reverse the rotation of the motor shaft. Unlike the unifilar winding which can only work with a bipolar driver, the bifilar winding configuration can be driven by a unipolar or bipolar driver.
Formulas for a Stepper Motor
Step angle calculation:
φ = Step Angle
Ns = Number of teeth on stator
Nr = Number of teeth on rotor
Steps per second = (rpm * steps per revolution )*60
Advantages of a Stepper Motor
• Simple designs
• High reliability
• Brushless construction
• If windings are energized at standstill, the motor has full torque
• No feedback mechanisms required
• High acceleration and power rate
• A wide range of rotational speeds can be attained as the speed is proportional to the frequency of the input pulses
• Known limit to the dynamic position error
*Stepper motor products vary in cost based on the criteria for each application. Some criteria include options of 0.9°, 1.8°, 3.6° and 4.5° step angles, torque ranging from 1 to 5,700 oz-in, and NEMA frame sizes of 08 to 42. Additional attachments such as cables and encoders can be purchased separately for an additional cost. With our friendly customer service and professional application assistance, Anaheim Automation often surpasses customer expectations for fulfilling specific stepper motor and driver requirements, as well as other motion control needs.
Disadvantages of a Stepper Motor
|• Low efficiency (Motor attracts a substantial amount of power regardless of the load)|
|• Torque drops rapidly with speed (torque is inversely proportional of speed)|
|• Prone to resonance* (Microstepping allows for smooth motion)|
|• No feedback to indicate missed steps|
|• Low torque-to-inertia ratio|
|• Cannot accelerate loads very rapidly|
|• Motor gets very hot in high performance configurations|
|• Motor will not “pick up” after momentary overload|
|• Motor is noisy at moderate to high speeds|
|• Low output power for size and weight|
*Resonance-is inherent in the design and operation of all stepping motors and occurs at specific step rates. It is the combination of slow stepping rates, high rotor inertia, and elevated torque which produce ringing as the rotor overshoots its desired angular displacement and is pulled back into position causing resonance to occur. Adjusting either one of the three parameters –inertial load, step rate, or torque- will reduce or eliminate resonance. In practical practice, the torque parameter is more controllable using microstepping. In microstepping mode, power is applied to the stator windings incrementally which causes torque to slowly build, reducing overshoot and therefore reducing resonance.
Where are Stepper Motors Used?
Although the stepper motor has been overshadowed in the past by servo systems for motion control, it has emerged as the preferred technology in more and more areas. The major factor in this trend towards the stepper motor is the prevalence of digital control, the emergence of the microprocessor, improved designed (i.e. high-torque models), and lower cost. Today, stepper motor applications are all around us: they are used in printers (paper feed, print wheel), disk drives, clocks and watches, as well as used in factory automation and machinery. A stepper motor is most often found in motion systems requiring position control.
Anaheim Automation’s cost-effective stepper motor product line is the wise choice for both OEM and user accounts. Anaheim Automation's customers for the stepper motor product line is diverse: industrial companies operating or designing automated machinery or processes involving food, cosmetics or medical packaging, labeling or tamper-evident requirements, cut-to-length applications, assembly, conveyor, material handling, robotics, special filming and projection effects, medical diagnostics, camera tracking, inspection and security devices, aircraft controls, pump flow control, metal fabrication (CNC machinery), and equipment upgrades.
Anaheim Automation, Inc. stepper motor product line integrates a matched stepper motor, driver and controller in one unit. This design concept makes selection easy, thus reducing errors and wiring time. With friendly customer service and professional application assistance, Anaheim Automation often surpasses the customer's expectations for fulfilling specific stepper motor and driver requirements, as well as other motion control needs.
Stepper Motors are Used in Many Industries
Stepper motors have become an essential component to applications in many different industries. The following is a list of industries making use of stepper motors:
• Aircraft – In the aircraft industry, stepper motors are used in aircraft instrumentations, antenna and sensing applications, and equipment scanning
• Automotive – The automotive industry implements stepper motors for applications concerning cruise control, sensing devices, and cameras. The military also utilizes stepper motors in their application of positioning antennas
• Chemical – The chemical industry makes use of stepper motors for mixing and sampling of materials. They also utilize stepper motor controllers with single and multi-axis stepper motors for equipment testing
• Consumer Electronics and Office Equipment – In the consumer electronics industry, stepper motors are widely used in digital cameras for focus and zoom functionality features. In office equipment, stepper motors are implemented in PC-based scanning equipment, data storage drives, optical disk drive driving mechanisms, printers, and scanners
• Gaming – In the gaming industry, stepper motors are widely used in applications like slot and lottery machines, wheel spinners, and even card shufflers
• Industrial – In the industrial industry, stepper motors are used in automotive gauges, machine tooling with single and multi-axis stepper motor controllers, and retrofit kits which make use of stepper motor controllers as well. Stepper motors can also be found in CNC machine control
• Medical – In the medical industry, stepper motors are utilized in medical scanners, microscopic or nanoscopic motion control of automated devices, dispensing pumps, and chromatograph auto-injectors. Stepper motors are also found inside digital dental photography (X-RAY), fluid pumps, respirators, and blood analysis machinery, centrifuge
• Scientific Instruments –Scientific equipment implement stepper motors in the positioning of an observatory telescope, spectrographs, and centrifuge
• Surveillance Systems – Stepper motors are used in camera surveillance
Environmental Considerations for a Stepper Motor
The following environmental and safety considerations must be observed during all phases of operation, service and repair of a stepper motor system. Failure to comply with these precautions violates safety standards of design, manufacture and intended use of the stepper motor, driver and controller. Please note that even with a well-built stepper motor, products operated and installed improperly can be hazardous. Precaution must be observed by the user with respect to the load and operating environment. The customer is ultimately responsible for the proper selection, installation, and operation of the stepper motor system.
The atmosphere in which a stepper motor is used must be conducive to good general practices of electrical/electronic equipment. Do not operate the stepper motor in the presence of flammable gases, dust, oil, vapor or moisture. For outdoor use, the stepper motor, driver and controller must be protected from the elements by an adequate cover, while still providing adequate air flow and cooling. Moisture may cause an electrical shock hazard and/or induce system breakdown. Due consideration should be given to the avoidance of liquids and vapors of any kind. Contact the factory should your application require specific IP ratings. It is wise to install the stepper motor, driver and controller in an environment which is free from condensation, dust, electrical noise, vibration and shock.
Additionally, it is preferable to work with the stepper motor/driver /controller system in a non-static, protective environment. Exposed circuitry should always be properly guarded and/or enclosed to prevent unauthorized human contact with live circuitry. No work should be performed while power is applied. Don’t plug in or unplug the connectors when power is ON. Wait for at least 5 minutes before doing inspection work on the stepper motor system after turning power OFF, because even after the power is turned off, there will still be some electrical energy remaining in the capacitors of the internal circuit of the stepper motor driver.
Plan the installation of the stepper motor, driver and/or controller in a system design that is free from debris, such as metal debris from cutting, drilling, tapping, and welding, or any other foreign material that could come in contact with circuitry. Failure to prevent debris from entering the stepper motor system can result in damage and/or shock.
Note: Anaheim Automation supplies IP65 Rated Sealed Motors, available for use in harsh environments.
Lifetime for a Stepper Motor
The typical lifetime for a stepper motor is 10,000 operating hours. This approximates to 4.8 years; given the stepper motor operates one eight-hour shift per day. The lifetime of a stepper motor may vary in regards to user application and how rigorous the stepper motor is run.
Required Maintenance for a Stepper Motor?
Since stepper motors are brushless, they require no maintenance for wear and tear on brushes and commutators.
Stepper Motor Glossary
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.
Clock – a pulse generator, which controls the timing of switching circuits that control the speed of the step motor.
Closed-Loop – a system with a feedback type of control, such that the output is used to modify the input.
Controller (Stepper Motor) – a regulating mechanism; essentially a DC power supply plus power switching with associated circuits for controlling the switching in the proper sequence.
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 unenergized step motor without causing continuous rotation. The minimal torque present in an unenergized motor. The detent torque of a step motor is typically about 1% of its static energized torque.
Driver (Stepper Motor) – often referred to as a translator, drives a step motor based on pulses from a clock, pulse generator, or computer. Translates the train of pulses and applied power to the appropriate step motor windings.
Dynamic Torque – the torque developed by a motor while stepping at low rates.
Encoder – often called a pulse generator, is a feedback device for step motors. It consists of a disc, vane, or reflector attached to a step 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.
Holding Torque – the maximum torque that can be externally applied to the step motor shaft without causing continuous rotation when one or more phases of the motor are energized.
Inertia – is a measure of an object’s resistance to a change in velocity.
Maximum Running Torque – 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.
Open-Loop – refers to a motion control system where no external sensors are used to provide position or velocity correction signals.
Permanent Magnet Stepper Motor – a step motor having permanent magnet poles.
Pole – the part of a magnetic circuit where a magnetic pole is generated either by a permanent magnet or by windings.
Pulse – an electrical signal or voltage of short duration, used in conveying intelligence.
Rated Torque – 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.
Resolution – the smallest positioning increment that can be achieved. 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.
Rotor – the rotating part of the motor (the shaft may be included).
Stator – the stationary magnetic parts of the motor including the windings.
Step – movement of the rotor from one energized position to the next.
Step Angle – the nominal angle through which the shaft of a step motor turns between adjacent step positions. It depends upon the motor and driving sequence (mode of drive).
Step Increment – 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 digital actuator, which operates from discrete pulses (input signals) and produces motion in discrete increments. May be rotary or linear increment.
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.
Teeth – projections on both rotor and stator such that when aligned they produce a low reluctance magnetic path.
Torque – a force or couple tending to, or producing, rotation. Common step motor torque units are oz-in, N-m, or mNm.
Train Pulse – a series of spaced pulses.
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.
Variable Reluctance Step Motor – a step motor having only soft iron poles.
Troubleshooting a Stepper Motor
Problem: Intermittent or erratic stepper motor or stepper driver function.
Solution: This is the most common cause of failure and one of the most difficult to detect. Start by checking to ensure all connections are tight between the stepper motor and the stepper driver and controllers. Evidence of discoloration at the terminals/connections, may indicate a loose connection. When replacing a stepper motor, stepper driver or driver pack, or controller in a motion control system, and be sure to inspect all terminal blocks and connectors. Check cabling/wiring for accuracy. Stress stepper motor wiring and connections for poor conditions and check with an ohmmeter. Whenever possible, use Anaheim Automation’s shielded cables for stepper motor wiring.
Problem: Poor system performance.
Solution: Check to see if the wire/cables are too long. Keep stepper motor wire/cables less than 25 feet in length. For applications where the wiring from the stepper motor to the stepper driver exceeds 25 feet, please contact the factory for instructions, as it is likely that transient voltage protection devices will be required. Another possibility is the stepper motor lead wires are of a gauge too small. Do not match your cable wires to the gauge size of the stepper motor lead wires, this is a common mistake. To avoid this mistake, Anaheim Automation suggests using its shielded cable for such wiring purposes (purchased separately). Additionally, check the age of your stepper motor, as with time and use, stepper motors lose a portion of their magnetism which affects performance. Typically one can expect 10,000 operating hours for stepper motors (approximately 4.8 years, running a one eight-hour shift per work day). Also, make certain your stepper motor and driver combination is a good match for your application. Contact the factory should you have any concerns.
Problem: The stepper motor is stalling.
Solution: In some cases, stalling of a stepper motor causes a large voltage spike that often damages the phase transistors on the driver. Some drivers are designed to protect themselves from such occurrences. If not, Transient Suppression Devices can be added externally. Consult the factory for further information.
Stepper Motor Wiring:
The following information is intended as a general guideline for wiring of the Anaheim Automation stepper motor product line. Be aware when you route power and signal wiring on a machine or system; radiated noise from the nearby relays, transformers, and other electronic devices can be introduced into the stepper motor and encoder signals, input/output communications, and other sensitive low-voltage signals. This can cause system faults and communication errors.
WARNING – Dangerous voltages capable of causing injury or death may be present in a stepper motor system. Use extreme caution when handling, wiring, testing, and adjusting during installation, set-up, tuning, and operation. Don’t make extreme adjustments or changes to the stepper motor system parameters, which can cause mechanical vibration and result in failure and/or loss. Once the stepper motor is wired, do not run the stepper driver by switching On/Off the power supply directly. Frequent power On/Off switching will cause fast aging of the internal components, which will reduce the lifetime of the stepper motor system.
Strictly comply with the following rules:
• Follow the wiring diagram for each stepper motor
• Route high-voltage power cables separately from low-voltage power cables
• Segregate input power wiring and stepper motor power cables from control wiring and motor feedback cables as they leave the stepper motor driver. Maintain this separation throughout the wire run
• Use shielded cable for power wiring and provide a grounded 360 degree clamp termination to the enclosure wall. Allow room on the sub-panel for wire bends
• Make all cable routes short as possible
NOTE: Factory-made cables are recommended for use in our stepper motor and driver systems. These cables are purchased separately, and are designed to minimize EMI. These cables are recommended over customer-built cables to optimize system performance and to provide additional safety for the stepper motor system and the user.
WARNING – To avoid the possibility of electrical shock, perform all mounting and wiring of the stepper motor and driver system prior to applying power. Once power is applied, connection terminals may have voltage present.
Common Causes for Stepper Motor Failure
NOTE: Always read the specification sheet/user's guide accompanying each product.
Problem: Stepper motor wires were disconnected while the driver was powered up.
Solution: Avoid performing any service to the stepper motor, driver or controller while the power is on, especially in regard to the motor connections. This precaution is imperative for both the driver and the technician/installer.
Problem: The stepper motor has a shorted winding or a short to the motor case.
Solution: It is likely you have a defective stepper motor. Do not attempt to repair motors. Opening the stepper motor may cause the motor to lose its magnetism, causing poor performance. Opening of the stepper motor case will also void your warranty. The motor windings can be tested with an ohmmeter. As a rule of thumb, if the stepper motor is a frame size of NEMA 08, 11, 14, 15, 17, 23, or 34 and the warranty period has expired, it is not cost-effective to return these stepper motors for repair. Contact the factory if you suspect a defective stepper motor that is still under warranty, or if the stepper motor is a NEMA frame size 42 or a K-series motor.
Problem: Environmental factors are less than ideal.
Solution: Environmental factors such as welding, chemical vapors, moisture, humidity, dust, metal debris, etc., can damage the electronic components and the stepper motor. Protect drivers, controllers and stepper motors from environments that are corrosive, contain voltage spikes, or prevent good ventilation. Anaheim Automation offers products in several line voltage ranges, as well as splash-proof, IP65 rated stepper motors. For wash-down or explosion-proof motors, contact the factory directly. For AC lines containing voltage spikes, a line regulator (filter) will likely be required.
NOTE: If your application requires welding, or if welding is done in the same work environment, contact the factory for advice on how to protect the stepper motor driver and controller.
Problem: The stepper motor is back-driving the stepper driver.
Solution: A stepper motor being turned by a load creates a back EMF voltage on the driver. Higher speeds will produce higher voltage levels. If the rotational speed gets excessively high, this voltage may cause damage to the driver. This is especially dangerous when the motor is back-driven while the driver is still on. Place a mechanical stop or brake in applications which may be subject to these phenomena.
PLEASE NOTE: Technical assistance regarding its Stepper Motor product line, as well as all the products manufactured or distributed by Anaheim Automation, is available at no charge. This assistance is offered to help the customer in choosing Anaheim Automation products for a specific application. However, any selection, quotation, or application suggestion for a Stepper Motor, or any other product, offered from Anaheim Automation’s staff, its' representatives or distributors, are only to assist the customer. In all cases, determination of fitness of the custom Stepper Motor in a specific system design is solely the customers' responsibility. While every effort is made to offer solid advice regarding the Stepper Motor product line, as well as other motion control products, and to produce technical data and illustrations accurately, such advice and documents are for reference only, and subject to change without notice.
Contact Us: Anaheim Automation has applications engineers readily available and happy to help with most troubleshooting issues. Contact us for detailed assistance.
Stepper Motor FAQs
Q: Why is the stepper motor size important? Is it possible to just choose a large motor size?
A: The stepper motor size is important because if the motor’s rotor inertia predominately consists of the load, resonance increases and poses issues. Also, larger rotors require more time to accelerate and decelerate and therefore it is important to choose a motor size dependent on the criteria for user applications.
Q: While increasing speed, why do stepper motors lose torque?
A: Inductance is the leading cause for motors losing torque at high speeds. The electrical time constant, τ, is the amount of time it takes a motor winding to charge up to 63% of its rated value given a resistance, R, and inductance, L. With τ = R/L, at low speeds, high inductance is not an issue since current can easily flow through the motor windings quickly. However, at high speeds, sufficient current cannot pass through the windings quick enough before the current is switched to the next phase, thereby reducing the torque provided by the motor. Therefore, it is the current and number of turns in the windings which determines the maximum output torque in a motor, while the applied voltage to the motor and the inductance value of the winding will affect on the speed at which a given amount of torque can be produced.
Q: Why does increasing the voltage increase the torque if stepper motors are not voltage driven?
A: Voltage can be viewed as forcing current through the coil windings. By increasing voltage, pressure to force current through the coil also increases. This in turn causes the current to build faster in the winding and is able to produce a larger magnetic field. This larger magnetic field is what produces more torque.
Q: What temperatures are stepper motors able to run at?
A: Most stepper motors include Class B insulation. This allows the motor to sustain temperatures of up to 130° C. Therefore, with an ambient temperature of 40° C, the stepper motor has a temperature rise allowance of 90° C allowing for stepper motors to run at high temperatures.
Q: Is it possible to get more torque by running the stepper motor at double its rated current?
A: It is possible to increase torque by increasing the current but by doing so, it weakens the motor’s ability to run smoother.
Q: What is the difference between four, six and eight leads in motors?
A: Stepper motors have the capability to run in either parallel or series modes. In a parallel mode, only a four lead motor can be run while in a series mode a six lead motor can be run. Eight lead motors can run in either parallel or series configurations. In applications where more torque is required at higher speeds, a lower inductance value given from a four lead motor is better choice.
Q: What is the difference between Unipolar and Bipolar motors?
A: A unipolar wound motor has six lead wires with each winding having a center tap. Most applications implementing unipolar wound motors require high speed and torque. On the other hand, a bipolar wound motor has four lead wires with having no center tap connections. Most applications implementing bipolar wound motors require high torque at low speeds.
Q: What is the difference between a closed-loop stepper motor controller and an open-loop stepper motor controller?
A: In an open-loop stepper motor controller, no feedback is going from the motor to the controller. This type of controller is effective when the motor is carrying a constant load at a steady speed. A closed-loop motor controller is more applicable in applications where load or speed varies. In comparison to the closed-loop controller, the open-loop controller lacks complexity and is more affordable.
Q: When should I use microstepping?
A: Microstepping is typically used in applications which require the motor to operate at less than 700 pulses per second.
Q: What do brakes do on a Stepper Motor?
A: Brakes do not slow the shaft of a motor, they only hold it in place. If 24V is supplied to the brake, the brake is "released" and the motor shaft is free to spin. If 24V is not supplied to the brake, it locks position, and holds the motor shaft in place.
Q: What is the difference between a round and square stepper motor?
A: A round (D and W series) motor is an older style design with a flatter T/S curve. They offer more torque at a higher RPM than the square (Y or L series) motors. The square motors offer more torque at lower RPM.
Q: What is the recommended cable distance between Anaheim Automation stepper motors and drivers?
A: We recommend that the wiring between stepper motors and drivers not exceed 25 feet. Although it is not required, we suggest using Anaheim Automation shielded motor cable. This cable is ideally suited to handle all driver and motor combinations that we offer. We can also add connectors to the cables. Please contact an Applications Engineer for more details.
Q: I have a motor with 4 leads plus a ground wire. Can I hook it up to Anaheim Automation products?
A: If the motor is a true 4 lead motor, you must look at specific models that accommodate 4-lead motors. If it is a 6 or 8 lead motor that was modified to be used as a 4 lead motor, the ground wire is not required if the motor is grounded to the machine.
Q: If I apply too much load to a stepper motor which causes the shaft to stop rotating, will I damage the motor?
A: No. The stepper motor will just stall. However, damage can be done to drivers if this stall condition lasts for long periods.
Q: Does Anaheim Automation sell encoders for stepper motors?
A: Yes. We supply encoders for any size orders for customers that require a complete motor/encoder assemble ready to mount. We can assemble the encoder to the motor for a nominal charge. Ask a Customer Service representative for more details.
Q: What is the life expectancy of Anaheim Automation Stepper Motors?
A: Anaheim Automation stepper motors have a 10,000 hour life expectancy under normal operating conditions. Anaheim Automation’s warranty is 12 months after the invoice date. See the “Environmental Conditions” sections of the stepper motor guide for more details.
Q: What gauge wire should be used for a NEMA 34 stepper motor @ 10 feet of distance?
A: Anaheim Automation motor cable is ideal. It is 16 gauge, 8 conductor with matching color code for the stepper motors carried by Anaheim Automation. We can also add connectors for you if you prefer. See the Accessories section of our web site for more details.
Q: How can I change the direction of my six-lead 23D309S standard round stepper motor without changing the logic?
A: Reverse the Phase 1 (red wire) with the Phase 3 (red/white wire) and the motor will run in the opposite direction.
Q: Is there any damage caused by a stepper motor that is disassembled?
A: Yes! Up to 60% magnetizing loss can be the result if the rotor is pulled apart. If all parts are replaced properly, the motor can be remagnetized at the factory, but the charge is substantial. If you have a motor failure, or are concerned about the performance, contact Anaheim Automation. Please note that the warranty period is 12 months from the date of invoice.
Q: Does Anaheim Automation have Permanent Magnet Stepper Motors?
A: Yes. In size ranging from 15 to 57 mm in diameter, with torque ranges of 1 to 23 oz.-in. (model dependent). See PM Stepper Motors under the Stepper Motor category on our web site for more details and product specifications.
Q: Can I order a stepper motor with 3% accuracy instead of 5%?
A: Because almost all of our 5% rated stepper motors fall into the 3% accuracy category, we usually recommend that you order our standard motors. If you require a “guarantee” for the 3% accuracy, contact the factory for assistance.
Q: Are stepper motors with optional conduit box, keyway, encoder-ready features considered "special"?
A: Yes, they are considered a "special", non-stock item and may require a NRE or SET-UP charge. There is an additional cost for some changes as well. Many stepper motor series already have shaft-flat and encoder-ready provisions. Check the specification sheet for more details. Some stepper motor series include a conduit (terminal) box. The shaft flat and encoder-ready motors do not incur an extra cost (if it’s already a feature of that series). Motors with conduit boxes will cost more than the standard motors. See individual dimension drawings for details.
Q: I need a stepper gearmotor. Does Anaheim Automation offer these motors?
A: Yes. Anaheim Automation offers stepper motors with Planetary Gearboxes in NEMA sizes 11, 17 and 23. We also have stepper motors with Spur Gearboxes in NEMA sizes 23 and 34, and PM stepper gearmotors in sized 24 to 42 mm diameters. Visit the Stepper Gearmotor section of our web site for more details. Please Note: We also offer gearboxes and motors separately, should you not find the size or gear ratio you require.
Q: Does Anaheim Automation make stepper motors with drivers attached?
A: Yes. Anaheim Automation offers a line of Integrated Stepper Motors with Drivers and/or Controllers, in NEMA sizes 17, 23 and 34.Check our 17MD, 23MD, and 34MD series for Integrated Motor/Drivers, and our 17MDSI and 23MDSI series for our Integrated Motor/Driver/Controller product lines.
Q: Does Anaheim Automation have stepper motor-based linear actuators?
A: Yes, in many different types. Anaheim Automation offers Hybrid Non-Captive Linear Actuator in NEMA sizes 11, 17, 23 and 34, Hybrid Threaded Shaft Linear Actuators in NEMA 17 size, PM Non-Captive Linear Actuators in sizes 20 – 57 mm diameters, and PM Captive Linear Actuators in sizes 20 – 42 mm diameters.
Q: Can I purchase an IP65 rated Stepper Motor?
A: Yes. Anaheim Automation offers a IP65 version for NEMA sizes 17, 23, 34 and 42 frame stepper motors, torque ranges from 35 to 5,700 oz.-in.(model specific). Visit our web site under Stepper Motors, and search IP65 motors.
Stepper Motor QUIZ
How does a stepper motor move?
|A. Electrical Pulse|
|B. Continuous Applied Voltage|
|C. Alternates from A and B|
A pulse can be produce by which means?
|B. Timing Logic|
|C. Toggle Switch|
|D. All of the above|
Which of the following is not a type of stepper motor?
|A. Variable Reluctance|
Which of the following is not a component of a stepper motor?
|B. Rotor and Stator|
|E. Both C and D|
What is the difference between full-step and half-step?
|A. In full-step two phases are on and in half-step only one phase is on.|
|B. More resonance is evident in half-step|
|C. More power required for full-step|
|D. Half-step offers better resolution|
What criteria’s are necessary to consider when selecting a stepper motor?
|A. Mechanical Motion|
|B. Inertial Load|
|C. Speed Requirements|
|D. All of the above|
Which of the following is NOT an advantage of stepper motors?
|C. No feedback|
|D. More complex circuitry|
With a stator having 8 teeth and a rotor having 6 teeth, what step angle will an application be able to achieve?
If an application using a stepper motor required feedback, which device would be needed to accomplish this?
|C. Linear Guide|
Along with stepper motors, Anaheim Automation carries a comprehensive line of drivers and controllers, power supplies, gear motors, gearboxes, stepper motor linear actuators and integrated stepper motor/driver packages. Additionally, Anaheim Automation offers encoders, brakes, HMI, couplings, cables and connectors, linear guides and X-Y tables. If stepper motors are not ideal for your application, you might consider brushless DC, brush DC, servo, or AC motors, and their compatible drivers/controllers.