Motor Control Device Suppressing Pressure Overshoot via Gradient Limits
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Solution Overview
Problem
Conventional motor control devices for molding and forming machines experience overshoot issues due to the lack of a specific index for determining the rate of pressure command value increase, leading to inefficiencies in machine operation and quality of products.
Innovation Solution
A motor control device that calculates a physical quantity command value with a derivative equal to or less than the product of the elastic constant of the subject and the maximum motor speed, ensuring the gradient of the change in the command value corresponds to the motor's maximum speed, thereby suppressing overshoot and improving the capability to follow the command value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a stepwise pressure command signal is used, then the target pressure value is clearly defined, but an overshoot is generated causing excessive actual pressure value
Solution Approach 1:
The pressure command signal is changed from a static stepwise function to a dynamic time-varying function with a gradient that adapts to the system's response characteristics. The gradient is determined based on the relationship between motor speed and pressure change rate, allowing the command signal to evolve optimally over time rather than abruptly changing.
Solution Approach 2:
The invention changes the parameter of the pressure command signal from a fixed stepwise value to a variable gradient determined by system parameters (motor maximum speed and elastic constant). This parameter transformation allows the command signal to account for the physical characteristics of the motor-subject system, preventing overshoot while maintaining clear target definition.
2Manufacturing precision
If a linear pressure command signal with small gradient is used, then overshoot is suppressed, but the time to reach target pressure increases
Solution Approach 1:
The gradient of the pressure command signal is optimized by changing it from an arbitrary small value to a specific value determined by the product of motor maximum speed and elastic constant. This parameter optimization allows the system to achieve the fastest possible pressure increase without exceeding the motor's physical capabilities, thus preventing overshoot while minimizing operation time.
3Productivity
If a linear pressure command signal with large gradient is used, then the time to reach target pressure is reduced, but an overshoot is generated
Solution Approach 1:
The invention performs preliminary calculation of the maximum safe gradient before generating the pressure command signal. By pre-determining the gradient based on motor maximum speed and elastic constant, the system prepares an optimized command profile that prevents overshoot from the outset, allowing aggressive pressure increase without sacrificing control accuracy.
Data Source
AI summary
A motor control device main unit includes a pressure command signal generation module, a pressure control module, a speed control module, and a current control module. The pressure command signal generation module of the motor control device main unit generates a pressure command value so that a derivative of the pressure command value is equal to or less than a product of an elastic constant of the pressurized target and a maximum motor speed. The pressure control module carries out pressure control calculation to calculate a motor speed command value based on a deviation between the pressure command value and an actual pressure value, and generates a motor speed command signal, which is a signal of the motor speed command value.