[Popular Science] Mechanism and rules of "precise position reset" after integrated motor power failure
In the fields of industrial automation, robotics and precision control, motors are core actuators, and their stable operation and precise control are crucial to the performance of the entire system.
However, the motor may encounter a sudden power outage during operation, which will cause the motor to lose driving force and stop at the current position, or even cause position offset in some cases.
Therefore, the position recovery mechanism after the motor loses power has become a key technical issue. This article will explore the principle mechanism of motor position recovery after power failure based on the absolute encoder built into the integrated motor, in order to provide a reference for research and application in related fields.
1. Position offset after the motor loses power
When the motor loses power suddenly, due to factors such as inertia, load influence and mechanical structure gap, the motor's rotor may continue to rotate for a distance and then stop, or move in the opposite direction due to the reverse action of the load, resulting in position offset.
This position offset is unacceptable for systems that require precise position control, so measures must be taken to recover.
2. Basic principles of position recovery after motor power failure
The basic principle of position recovery after motor power failure is to determine the current position of the motor in some way after the motor is powered on again, and drive the motor back to the preset starting position or safe position. This process involves the coordinated work of multiple aspects such as position detection, control algorithm, and mechanical structure.
3. Mechanism of position recovery after motor power failure
1. Position detection mechanism
Position detection is the first step in recovering the motor position after power failure. During a motor power failure, traditional position detection components (such as incremental encoders) may not work properly, so other methods are needed to determine the motor position.
Absolute encoder
Absolute encoders can save current position information when power is off. When power is restored, the controller reads the position data in the encoder and directly determines the position of the motor.
Mechanical limit switches
When a limit switch is installed on a mechanical structure, a signal is triggered when the motor touches the switch, indicating that the motor has reached a certain position. By reading these signals, the current position of the motor can be indirectly inferred.
Magnetic encoder or magnetic sensor
Use the change of magnetic field to detect the position of the motor. When the motor is powered off, the magnetic encoder or magnetic sensor can keep a memory of the change of magnetic field, so as to provide position information after the power is restored.
2. Control algorithm mechanism
After determining the current position of the motor, a control algorithm is needed to drive the motor back to the preset position. The choice of control algorithm depends on the type of motor, load characteristics and system requirements.
Open-loop control
For open-loop control motors such as stepper motors, pulse signals can be sent to drive the motor to perform single-step motion. After the motor loses power, pulse signals need to be resent to make the motor move step by step to the preset position.
Closed-loop control
For closed-loop control motors such as servo motors, the position of the motor can be detected in real time through an encoder or sensor, and the detected position can be compared with the preset position. The motor movement can be adjusted through the control algorithm to make the motor reach the preset position accurately.
Note: All our integrated motors have built-in absolute encoders.
IV. Description of position recovery after motor power failure
Here we only discuss the principle mechanism of absolute encoder motor position recovery after power failure
1. The position change can be accurately recorded during the motor power-on process
2. After the motor is powered off, the position at the time of power failure is 0°, and the rotation range of the motor shaft does not exceed plus or minus 180°. After powering on again, the motor can be updated to the accurate position value
3. If the rotation range of the motor shaft exceeds 180° after the motor is powered off, the position after powering on will be lost as a full circle (10000)
例如：
As shown in the figure, assume that the position is 0 and the angle is 0° when the power is off
1. After the power is off, the motor shaft rotates to 90° (counterclockwise or clockwise, or many turns), and the position after power is 2500
2. After the power is off, the motor shaft rotates to 270° (counterclockwise or clockwise or many turns), and the position after power is -2500
3. The position count after the motor is powered off is always within -5000 and 5000
