Motor Shaft Position Control With Switching-Point Deceleration
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Solution Overview
Problem
Existing motor position control systems face challenges in achieving precise angular positioning without overshooting, particularly in applications like top drive operations, where operational efficiency and smoothness are affected by system-specified limits on acceleration, deceleration, and velocity.
Innovation Solution
A motor control method utilizing a proportional controller and a time-optimal controller, with a switching point determined to minimize overshooting by ensuring smooth transitions between these controllers, accounting for system delays and velocity limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a proportional controller is used to control rotational speed near the target position, then positioning accuracy is improved, but the time to reach the target position increases
Solution Approach 1:
The control process is divided into two segments: a time-optimal control segment for most of the travel distance, and a proportional control segment near the target position. This segmentation allows the system to use aggressive time-optimal control for the majority of the journey while switching to precise proportional control only when needed for accurate positioning, thereby resolving the contradiction between speed and accuracy.
Solution Approach 2:
The control strategy dynamically switches between two different control modes based on the current position relative to the target. The switching point is determined by system parameters including communication delays, allowing the system to adapt its control approach in real-time to optimize both response time and positioning accuracy.
2Productivity
If the motor operates at maximum speed to improve productivity, then the time to reach target position is reduced, but overshooting the target position occurs
Solution Approach 1:
The system performs preliminary deceleration planning by determining a switching point before reaching the target position. At this switching point, the control mode changes from time-optimal to proportional control, allowing the motor to be slowed down in advance to prevent overshooting while maintaining maximum speed for as long as possible to preserve productivity.
Solution Approach 2:
The proportional controller provides continuous feedback-based speed adjustment near the target position, using the position error to modulate the motor speed and ensure the motor stops precisely at the target without overshooting, even after operating at maximum speed.
3Measurement precision
If system communication delays are accounted for in the control strategy, then positioning accuracy is improved, but the control system complexity increases
Solution Approach 1:
The switching point is predetermined based on system parameters including communication delays, rather than being calculated in real-time during operation. This preliminary determination simplifies the control system by avoiding complex real-time calculations while still compensating for known delay characteristics.
Solution Approach 2:
The control strategy incorporates communication delay as a fixed parameter in the switching point calculation. By treating the delay as a known constant that shifts the effective switching point, the system compensates for delays without requiring complex adaptive algorithms, thus maintaining relatively simple control logic while improving accuracy.
Data Source
AI summary
A motor controller to control rotational speed of an output shaft of an electric motor. The motor controller includes a proportional controller and a time-optimal controller. The proportional controller controls the rotational speed when a present rotational position of the shaft is between a target rotational position and a switching point, inclusively. The time-optimal controller controls the rotational speed when the present rotational position is not between the target rotational position and the switching point. Also introduced herein are aspects pertaining to determining the switching point in a manner that minimizes overshooting the target rotational position while maximizing expediency at which the target rotational position is reached.