Vicent's blog
1.What is a closed-loop stepper motor
A closed-loop stepper motor is a motor that combines the characteristics of a stepper motor and a servo motor, and achieves high precision and high efficiency through closed-loop control. A closed-loop stepper motor can remain absolutely still when stationary, and will not have slight fluctuations when stopped like a servo motor. Its debugging and use are relatively simple, and only a few potentiometer positions of the driver need to be adjusted, which is suitable for users with low technical requirements.
2.Working principle of closed-loop stepper motors
The working principle of closed-loop stepper motors is to control the rotation of the motor by controlling the change of current, thereby converting electrical energy into mechanical energy. A closed-loop stepper motor is mainly composed of a stator, a rotor, a bearing seat and an encoder. The stator is the fixed part, and the rotor is the rotating part. The encoder is used to detect the position of the rotor and feed the position information back to the controller to form a closed-loop control.
3.Performance advantages of closed-loop stepper motors
1.Improve torque and speed: Closed-loop stepper motors achieve higher accuracy and more stable operation than open-loop control by adding position feedback devices (such as photoelectric encoders or magnetic encoders). It can maintain a large torque when running at high speed, suitable for 0-1500rpm occasions, and can even run to 3000-4000RPM without losing steps.
2.Improve motion accuracy: Closed-loop stepper motors can automatically adjust the winding current through encoder feedback, reduce heat and vibration, and improve motion accuracy. The higher the accuracy of the encoder, the higher the positioning accuracy of the motor. For example, the resolution of a 5000-line encoder can reach 0.018°, which is much higher than the accuracy of an open-loop stepper motor.
3.Reduce vibration and noise: Due to the existence of closed-loop control, the stepper motor can maintain the torque characteristics when stopped, and will not produce micro-vibrations like the servo system, thereby improving the repeated positioning accuracy of the motion system. This makes closed-loop stepper motors perform better in situations where high-precision positioning is required.
4.Adapt to frequent start and stop: Closed-loop stepper motors are suitable for occasions that require frequent start/stop. They can maintain stable positioning under load changes, without gain adjustment, and simplify the debugging process.
5.High response speed: Closed-loop stepper motors run synchronously with control instructions, can complete precise positioning in a short stroke and short time, have fast response speed, and are suitable for precise positioning needs of short strokes.
6.Adapt to large inertia loads: Closed-loop stepper motors can drive larger inertia loads than servo motors of the same installation size, and are suitable for occasions that need to drive large inertia loads.
7.Efficient acceleration and deceleration: Closed-loop stepper motors can be accelerated and decelerated automatically and effectively, reducing the need for manual adjustment and improving the overall efficiency of the system.
4.Operating instructions for closed-loop stepper motors
1.Hardware connection
The hardware connection of the closed-loop stepper motor requires the installation of an encoder. According to the subdivision requirements, encoders with different levels of resolution are used for real-time feedback. The circuit uses ultra-large-scale circuit FPGA, and the input and output can reach the corresponding frequency of mega-level. The power supply is 3.3V. The 2596 switching power supply is used to convert 24V to 3.3V, which is convenient and practical.
2.Origin control
According to the Z signal of the encoder, the coordinate origin is identified and calculated, and the accuracy can reach 2/encoder resolution × 4. In the origin mode, the pulse is output at a frequency synchronized with the input pulse. When the origin switch is touched, the output pulse frequency is reduced. According to the Z signal of the encoder, the coordinate origin is identified and calculated. After returning to the origin, the signal is output. This signal and its data are always maintained without power failure.
3.Out-of-step control
According to the feedback data of the encoder, the output pulse is adjusted in real time, and corresponding measures are taken according to the degree of out-of-step adjustment. In the running mode, the pulse is output at a frequency synchronized with the input pulse, and the feedback data is calculated at the same time. If an error occurs, it is corrected in time.
4.Circuit principle description
The circuit principle description includes the calculation of the input pulse and the feedback pulse after 4 times the frequency orthogonal decoding, and the output pulse quantity and frequency are corrected in time. The circuit has two modes: return to origin mode and running mode. In the origin mode, the pulse is output at a frequency synchronized with the input pulse. When the origin switch is touched, the output pulse frequency is reduced. In the operation mode, the pulse is output at a frequency synchronized with the input pulse, and the feedback data is calculated at the same time. If an error occurs, it is corrected in time.
5.Application description
The closed-loop stepper motor is suitable for various encoder interfaces and servo pulse control. Once the motion control solves the above problems, full closed-loop control can be achieved with an additional cost of several hundred yuan, which is no less than the servo motor.
Source:https://hahastepper.hatenablog.com/entry/2024/11/04/180205
