Servo Motor Position Control Hunting Suppression
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Solution Overview
Problem
Servo motor position control systems face instability and oscillation issues when the motor reaches a target position and stops, due to the minimum resolution of the pulse encoder, leading to hunting phenomena.
Innovation Solution
Implementing a servo motor position control device with a cascade configuration that switches from proportional-integral control to proportional control in the q-axis current controller when the servo motor reaches the target position, maintaining the current instruction signal value and stabilizing the q-axis voltage instruction signal to prevent unnecessary movement and oscillation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If proportional-integral control is used in the q-axis current controller, then the servo motor can reach the target position accurately, but the servo motor oscillates and hunts when it stops at the target position
Solution Approach 1:
The control method dynamically switches between proportional-integral control and proportional control based on the servo motor's operational state. When the motor is moving, proportional-integral control maintains high position accuracy. When the motor reaches the target position and stops, the system transitions to proportional control to eliminate oscillation and maintain stop stability, thus resolving the contradiction between position accuracy and stop stability.
Solution Approach 2:
The invention changes the control parameters by switching the control mode in the q-axis current controller. By disabling integral control when the servo motor is at the target position, the system prevents the accumulation of position deviation errors that cause hunting, while maintaining the ability to achieve accurate positioning through proportional control alone in the stopped state.
2Measurement precision
If the pulse encoder resolution is increased to reduce hunting range, then the position detection precision improves, but the device complexity and cost increase
Solution Approach 1:
Instead of increasing the hardware resolution of the pulse encoder, the invention changes the control parameters and control mode in the q-axis current controller. By switching from proportional-integral control to proportional control when the servo motor stops at the target position, the system effectively reduces hunting within the existing encoder resolution range, avoiding the need for higher-resolution (and more complex/expensive) encoders.
Data Source
AI summary
Provided is a technique to suppress hunting in a range of a minimum resolution of a pulse encoder when a servo motor has reached a target position and stopped, thereby maintaining a stable stop state. A servo motor position control device uses a cascade configuration having a position control loop as a main loop and a velocity and current control loop as a minor loop. A proportion control is performed for a position control while a proportion integration control is performed for a velocity control and a current control. When the servo motor position has reached the target position and stopped (S201), a current instruction value for the current control is maintained at a value upon stop (S202) and the current control is switched to the proportion control (S204).