Views: 0 Author: July Publish Time: 2026-10-07 Origin: Site
Stepper motors are widely used in automation equipment, robotics, CNC machines, medical devices, printers, inspection systems, and precision positioning applications. Unlike conventional motors, a stepper motor converts electrical pulse signals into controlled angular movement, allowing engineers to control position, speed, and direction with a relatively simple control system.
However, selecting and operating a stepper motor correctly requires an understanding of its control modes, motor types, drive technology, acceleration characteristics, microstepping, and load requirements.
This guide explains the fundamentals of stepper motor control, stepper motor selection, open-loop and closed-loop operation, microstepping, heating, acceleration and deceleration, and bipolar versus unipolar stepper motors.
Pulse-and-direction control, also known as single-pulse mode, means that the STEP input continuously receives pulse signals, while the DIR input uses a high or low logic level to control the motor's direction.
This mode is also known as clock-direction mode, or pulse-and-direction control.
Dual-pulse control means that both the pulse input and direction input use pulse signals. One input is used for forward pulses, while the other is used for reverse pulses.
In dual-pulse mode:
· Pulses sent to the STEP input make the motor rotate forward.
· Pulses sent to the DIR input make the motor rotate in reverse.
In this configuration, the Direction input becomes the reverse-pulse input.
Stepper motors are generally used in low-speed applications. The rotational speed should not exceed 1,000 rpm. For a 0.9° step angle motor, 6,666 PPS corresponds to approximately 1,000 rpm.
It is recommended to operate the motor within approximately 1,000–3,000 PPS for a 0.9° step angle motor.
A reduction mechanism can be used to allow the motor to operate within this range. Under these conditions, the motor can achieve higher efficiency and lower noise.
Stepper motors are generally not recommended to operate in full-step mode because full-step operation produces relatively high vibration.
For historical reasons, only motors with a nominal voltage of 12 V should be operated with 12 V.
For other stepper motors, the voltage value marked on the motor is not necessarily the required driver supply voltage.
The driver supply voltage can be selected according to the driver requirements.
Recommended examples:
· 57BYJ: 24–36 VDC
· 86BYJ: 50 VDC
· 110BYJ: Above 80 VDC
A 12 V motor can also be operated with a different drive supply under appropriate conditions, but the resulting temperature rise must be considered.
When the load has a large moment of inertia, a stepper motor with a larger frame size should be selected.
When operating at relatively high speed or driving a load with high inertia, the motor should generally not start directly at the operating speed.
Instead, the pulse frequency should gradually increase.
This can:
· Reduce the possibility of lost steps
· Reduce noise
· Improve stopping and positioning accuracy
For high-precision applications, accuracy can be improved through:
· Mechanical reduction
· Increasing the motor speed
· Using a driver with a higher microstepping resolution
· Using a five-phase motor
Five-phase motors have a relatively higher overall system cost, and fewer manufacturers produce them. The statement that five-phase motors have been eliminated is incorrect.
Stepper motors should not operate within resonance regions.
If operation within a resonance region is unavoidable, the problem can be addressed by:
· Changing the voltage
· Adjusting the current
· Adding damping
For operation below 600 PPS with a 0.9° step angle motor, a lower current, higher inductance, and lower voltage should be used for driving.
The recommended selection principle is:
Select the motor first, then select the driver.
Open-loop control can control the motor's movement, but it does not provide feedback on the result.
Closed-loop control can analyze the result of the motor's movement and provide feedback for adjustment.
Based on their structural design, stepper motors can be divided into several types, including:
· Variable Reluctance (VR) Stepper Motors
· Permanent Magnet (PM) Stepper Motors
· Hybrid Stepper Motors (HS)
· Single-Phase Stepper Motors
· Planar Stepper Motors
Among the stepper motors used in China, variable-reluctance stepper motors have historically been widely used.
The operating performance of a stepper motor is closely related to its control method.
Based on the control method, stepper motor control systems can generally be divided into:
1. Open-loop control systems
2. Closed-loop control systems
3. Semi-closed-loop control systems
In practical applications, semi-closed-loop control systems are generally classified as either open-loop or closed-loop systems.
A variable-reluctance stepper motor has windings on the stator and a rotor made of soft magnetic material.
Its characteristics include:
· Simple structure
· Low cost
· Small step angle, which can reach 1.2°
· Poor dynamic performance
· Low efficiency
· High heat generation
· Reliability that can be difficult to guarantee
The rotor of a permanent magnet stepper motor is made of permanent magnetic material.
The number of rotor poles is the same as the number of stator poles.
Its characteristics include:
· Good dynamic performance
· High output torque
· Lower positioning accuracy
· Relatively large step angle
The typical step angle is 7.5° or 15°.
Hybrid stepper motors combine the advantages of variable-reluctance and permanent-magnet stepper motors.
The stator contains multiple-phase windings, while the rotor uses permanent magnetic material. Both the rotor and stator contain multiple small teeth to improve step positioning accuracy.
Its characteristics include:
· High output torque
· Good dynamic performance
· Small step angle
· More complex structure
· Relatively higher cost
Based on the stator winding configuration, hybrid stepper motors can be divided into:
· Two-phase
· Three-phase
· Five-phase
Two-phase hybrid stepper motors are widely used because of their cost-performance ratio. When combined with a microstepping driver, they provide good overall performance.
A typical two-phase hybrid stepper motor has a basic step angle of 1.8° per step.
With half-step driving, the step angle is reduced to 0.9°.
With a microstepping driver, the step angle can theoretically be divided into as many as 256 microsteps:
1.8° ÷ 256 ≈ 0.007° per microstep
Because of friction, manufacturing accuracy, and other factors, the actual control accuracy is slightly lower.
The same stepper motor can be used with drivers providing different microstepping levels to change the positioning resolution and operating characteristics.
The three main factors for selecting a stepper motor are:
· Step angle
· Holding torque
· Current
Once these three factors have been determined, the appropriate stepper motor model can be selected.
The required motor step angle depends on the positioning accuracy required by the load.
The minimum required resolution of the load should be converted into the corresponding angular movement at the motor shaft.
The motor step angle should be equal to or smaller than this angular value.
Common step angles available on the market include:
· 0.36° / 0.72° for five-phase motors
· 0.9° / 1.8° for two- and four-phase motors
· 1.5° / 3° for three-phase motors
Dynamic torque is relatively difficult to determine directly, so holding torque is often used as the starting point for motor selection.
The holding torque should be selected according to the motor load.
The load can be divided into:
· Inertial load
· Friction load
In practice, purely inertial or purely frictional loads do not normally exist.
When starting directly, usually from a low speed, both types of load should be considered.
During acceleration and starting, inertial load is particularly important.
During constant-speed operation, friction load becomes the primary consideration.
Under general conditions, the holding torque should be approximately 2–3 times the friction load.
Once the required holding torque is determined, the motor frame size and length can be selected.
Two motors with the same holding torque can have different operating characteristics because their current parameters are different.
The appropriate motor current should be selected by referring to the motor's torque-speed characteristic curve.
Unipolar and bipolar are two of the most commonly used stepper motor drive configurations.
A unipolar drive circuit uses four transistors to drive the two phases of a stepper motor.
The motor structure contains two coils with center taps, and the motor typically has six wires connected externally.
This type of motor is sometimes referred to as a four-phase motor. However, this terminology can be confusing and is not technically accurate.
A more accurate description is a two-phase, six-wire stepper motor.
Although a six-wire stepper motor is commonly referred to as a unipolar stepper motor, it can actually be used with either a unipolar or bipolar drive circuit.
A bipolar drive circuit uses eight transistors to drive the two phases.
A bipolar drive circuit can drive both four-wire and six-wire stepper motors.
A four-wire motor can only be used with a bipolar drive circuit.
However, the four-wire motor can significantly reduce the cost of mass-produced applications.
The number of transistors in a bipolar stepper motor drive circuit is twice that of a unipolar drive circuit.
Among them, the four lower transistors are usually driven directly by the microcontroller, while the upper transistors require relatively expensive high-side driver circuits.
The transistors in a bipolar drive circuit only need to withstand the motor voltage, so unlike a unipolar drive circuit, a clamp circuit is not required.
The rotor of a typical stepper motor is a permanent magnet.
When current flows through the stator windings, the stator windings generate a vector magnetic field.
This magnetic field causes the rotor to rotate through a certain angle, bringing one pair of rotor magnetic poles into alignment with the direction of the stator magnetic field.
When the stator's vector magnetic field rotates through a certain angle, the rotor follows and rotates through the corresponding angle.
Each electrical pulse causes the motor to rotate through a specific angle and advance by one step.
The angular displacement of the motor is proportional to the number of input pulses, while the rotational speed is proportional to the pulse frequency.
Changing the energizing sequence of the windings reverses the motor's direction.
Therefore, the rotation of a stepper motor can be controlled by controlling:
· The number of pulses
· The pulse frequency
· The energizing sequence of each motor phase
Most motors contain iron cores and winding coils.
The windings have electrical resistance. When current flows through the windings, power is dissipated.
The amount of power loss is proportional to the resistance and the square of the current.
This is commonly referred to as copper loss.
If the current is not standard DC or sinusoidal current, harmonic losses can also occur.
The iron core is also affected by hysteresis and eddy-current effects when exposed to an alternating magnetic field.
These losses are related to factors such as:
· Material
· Current
· Frequency
· Voltage
These losses are referred to as iron losses.
Both copper loss and iron loss appear as heat and affect motor efficiency.
Stepper motors generally prioritize positioning accuracy and torque output. Their operating current is often relatively high, and the current waveform may contain significant harmonic components.
The frequency of the alternating current also changes with motor speed.
Therefore, stepper motors commonly experience noticeable heat generation, which can be more significant than that of some conventional AC motors.
Because stepper motors are widely used, considerable research has been conducted on their control.
During starting or acceleration, if the stepper pulse frequency changes too quickly, the rotor may fail to follow the changing electrical signal because of inertia.
This can result in:
· Stall
· Lost steps
During stopping or deceleration, the same type of effect can result in overshoot.
To prevent stalling, lost steps, and overshoot, and to increase the operating frequency, the stepper motor needs appropriate acceleration and deceleration control.
The rotational speed of a stepper motor depends on:
· Pulse frequency
· Number of rotor teeth
· Number of phases or drive steps
The angular velocity is proportional to pulse frequency and remains synchronized with the pulses.
Therefore, when the number of rotor teeth and the operating sequence are fixed, the required motor speed can be obtained by controlling the pulse frequency.
A stepper motor starts through its synchronizing torque. To prevent lost steps, the starting frequency cannot be too high.
As motor power increases, the rotor diameter and inertia also increase. Therefore, the starting frequency and maximum operating frequency can differ significantly, sometimes by an order of magnitude.
The starting frequency characteristics of a stepper motor mean that the motor cannot normally start directly at its operating frequency.
Instead, it needs a starting process in which the speed gradually increases from a low speed to the required operating speed.
Similarly, during stopping, the operating frequency should not immediately drop to zero. The motor should gradually decelerate from a high speed to zero.
The output torque of a stepper motor decreases as pulse frequency increases.
The higher the starting frequency, the lower the starting torque and the weaker the motor's ability to drive the load.
Starting at an excessively high frequency may cause lost steps.
During stopping, excessive deceleration may cause overshoot.
To enable the motor to reach the required speed quickly without losing steps or overshooting, the key is to ensure that the torque required during acceleration remains within the torque available from the stepper motor at each operating frequency.
Therefore, stepper motor operation generally consists of three stages:
1. Acceleration
2. Constant-speed operation
3. Deceleration
The acceleration and deceleration periods should be as short as possible, while the constant-speed period should be as long as possible.
For applications requiring fast response, the total travel time from the starting point to the final position should be minimized.
This requires:
· Short acceleration time
· Short deceleration time
· High constant operating speed
Because of manufacturing limitations, the basic step angle of a stepper motor is determined by factors such as rotor tooth count and the operating sequence.
The number of rotor teeth and operating sequences is limited, so the basic step angle of a stepper motor is generally relatively large and fixed.
This results in:
· Lower resolution
· Limited flexibility
· Vibration at low frequencies
· Higher noise than some other types of miniature motors
These characteristics can cause fatigue or damage to mechanical equipment.
Because of these limitations, stepper motors may be suitable for applications with relatively modest requirements. For more demanding applications, closed-loop control can be introduced, but this increases system complexity.
These limitations can restrict the effective use of stepper motors as open-loop positioning components.
Microstepping drive technology can overcome these limitations to a certain extent.
Stepper motor microstepping technology was developed in the mid-20th century as a drive technology capable of significantly improving the overall performance of stepper motors.
In the following decades, microstepping technology continued to develop and became mature during the 1990s.
Research into microstepping technology in China began at approximately the same time as research overseas.
By the mid-1990s, microstepping technology had developed significantly.
It was mainly applied in:
· Industrial equipment
· Aerospace
· Robotics
· Precision measurement
Applications included photoelectric theodolites for satellite tracking, military instruments, communications equipment, and radar systems.
The widespread use of microstepping technology reduced the dependence of motor design on step angle and provided greater flexibility for product design.
Modern stepper motor microstepping technology commonly uses:
· Chopper constant-current control
· Pulse-width modulation control
· Constant-amplitude current-vector control
These technologies significantly improve stepper motor operating accuracy and enable stepper motors to move toward higher-speed and higher-precision applications in low- and medium-power systems.
Initially, phase-current control for stepper motors was implemented using hardware.
Two common methods were used.
The first method used multiple power-switching circuits to supply current and superimpose current in the windings.
This method reduced power transistor losses, but required many circuits and therefore resulted in more components and a larger system size.
The second method first superimposed the pulse signals and then used power transistors for linear amplification to produce a stepped current waveform.
Its advantages included a smaller number of components.
However, power transistor losses were high and system efficiency was low.
If the transistors operated in a nonlinear region, waveform distortion could also occur.
Because of these inherent limitations, these two methods are now rarely used.
The typical accuracy of a stepper motor is approximately 3–5% of the step angle, and this error does not accumulate from one step to the next.
The maximum allowable surface temperature of a stepper motor depends on the motor's magnetic material.
Excessive motor temperature can first cause demagnetization of the magnetic material, resulting in reduced torque and potentially lost steps.
Therefore, the maximum allowable motor surface temperature depends on the demagnetization temperature of the magnetic material.
Generally, the demagnetization temperature of magnetic materials is above 130°C, and some materials can withstand temperatures above 200°C.
Therefore, a stepper motor surface temperature of 80–90°C can be normal.
The torque of a stepper motor decreases as rotational speed increases.
When the stepper motor rotates, the inductance of the motor windings generates back EMF.
The higher the frequency, the greater the back EMF.
Under the influence of back EMF, the phase current decreases as frequency, or motor speed, increases.
As a result, motor torque decreases.
A stepper motor can operate normally at low speed but may fail to start when the speed exceeds a certain level.
The motor may produce abnormal noise or stall.
A stepper motor has a technical parameter called the starting frequency, which refers to the maximum pulse frequency at which the motor can start normally under no-load conditions.
If the pulse frequency exceeds this value, the motor may fail to start properly and may experience lost steps or stall.
Under load, the starting frequency should be lower.
If the motor needs to reach a high rotational speed, the pulse frequency should be increased gradually.
In other words, the motor should start at a relatively low frequency and then accelerate at a certain rate until the required high frequency is reached.
Stepper motors have played an important role in the era of digital manufacturing because of these characteristics.
With the development of various digital technologies and improvements in stepper motor technology, stepper motors will continue to be used in more applications.
A stepper motor must be used with a driver in order to operate.
The drive signal must be a pulse signal.
Without pulses, the stepper motor remains stationary.
When an appropriate pulse signal is applied, the motor rotates through a certain angle, known as the step angle.
The motor's rotational speed is proportional to the pulse frequency.
A three-phase stepper motor has a step angle of 7.5°.
One complete revolution is 360°, so 48 pulses are required to complete one revolution.
Stepper motors provide good starting and stopping characteristics.
The motor's rotation direction can be changed conveniently by changing the pulse sequence.
For this reason, stepper motors are widely used as motion-control components in:
· Printers
· Plotters
· Robots
· Other equipment
1. The rotation angle of the motor is proportional to the number of input pulses.
2. When the motor is stopped and the windings are energized, the motor has its maximum holding torque.
3. Because the accuracy of each step is approximately 3–5% and the error does not accumulate from one step to the next, stepper motors provide good positioning accuracy and motion repeatability.
4. Stepper motors have excellent starting, stopping, and reversing response.
5. Because there are no brushes, reliability is relatively high. Motor life mainly depends on bearing life.
6. Motor response is determined by digital input pulses, allowing open-loop control. This makes the motor structure relatively simple and keeps control costs low.
7. The motor can rotate synchronously at extremely low speeds even when the load is directly connected to the motor shaft.
8. Because speed is proportional to pulse frequency, stepper motors provide a relatively wide speed range.
1. Improper control can cause resonance.
2. It is difficult to operate at very high speeds.
3. It is difficult to obtain high torque at high speed.
4. Stepper motors do not have advantages in terms of size and weight in some applications, and energy utilization can be relatively low.
5. When the load exceeds the motor's capability, synchronism can be lost. High-speed operation may also produce vibration and noise.
Stepper motors are mainly selected according to three key parameters:
· Step angle
· Holding torque
· Current
The motor step angle depends on the accuracy requirement of the load.
The minimum resolution required by the load should be converted into the corresponding angular movement at the motor shaft.
The step angle of the motor should be equal to or smaller than this angular requirement.
Common stepper motor step angles include:
· 0.36° / 0.72° for five-phase motors
· 0.9° / 1.8° for two- and four-phase motors
· 1.5° / 3° for three-phase motors
The dynamic torque of a stepper motor is difficult to determine directly, so holding torque is often used first when selecting a motor.
The required holding torque depends on the motor load.
The load can be divided into:
· Inertial load
· Friction load
When starting directly, usually from low speed, both types of load should be considered.
During acceleration and starting, inertial load is particularly important.
During constant-speed operation, friction load is the main consideration.
Under general conditions, the holding torque should be approximately 2–3 times the friction load.
Once the holding torque has been selected, the motor frame size and motor length can be determined.
Motors with the same holding torque can have different operating characteristics because their current parameters differ.
The motor current should be selected by referring to the motor's torque-speed characteristic curve.
Unipolar and bipolar are the two most commonly used stepper motor drive architectures.
A unipolar drive circuit uses four transistors to drive the two phases of a stepper motor.
The motor contains two center-tapped coils and normally has six external wires.
This type of motor is sometimes called a four-phase motor, but this terminology can cause confusion and is not technically correct.
The more accurate description is a two-phase, six-wire stepper motor.
Although a six-wire stepper motor is commonly called a unipolar stepper motor, it can actually be used with either a unipolar or bipolar drive circuit.
A bipolar drive circuit uses eight transistors to drive the two phases.
A bipolar drive circuit can drive both four-wire and six-wire stepper motors.
A four-wire motor can only be operated using a bipolar drive circuit.
However, four-wire motors can significantly reduce costs in mass-production applications.
The number of transistors used in a bipolar stepper motor driver is twice that of a unipolar driver.
The four lower transistors are normally driven directly by the microcontroller, while the upper transistors require relatively expensive high-side driver circuits.
The transistors in a bipolar drive circuit only need to withstand the motor voltage.
Therefore, unlike a unipolar drive circuit, a bipolar drive circuit does not require a clamp circuit.
