Servo Die Cushion Control Reducing Force Overshoot
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Solution Overview
Problem
Conventional die cushion mechanisms using servo-motors face challenges in accurately controlling force during press working due to excessive overshoot and slow response to sudden pressure fluctuations, especially during collisions, due to limitations in speed feedback and control mode transitions.
Innovation Solution
A control apparatus for a die cushion mechanism incorporating a servo-motor, which includes a force commanding section, a force detecting section, a motor-speed detecting section, and a slide-speed detecting section, allowing for precise force control by calculating and correcting speed commands and adjusting rise time constants based on detected values, and employing preliminary acceleration control to mitigate collision impacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a servo-motor with force control is used in the die cushion mechanism, then the response performance to pressure variations is improved, but excessive overshoot occurs during collision due to slow integrator response and large force deviation
Solution Approach 1:
The control apparatus performs preliminary acceleration control by detecting slide speed and calculating a preliminary speed command value before collision occurs. This preliminary action prepares the cushion pad for upcoming collision, reducing the impact of sudden force changes and preventing excessive overshoot while maintaining fast response capability
Solution Approach 2:
The control apparatus continuously detects slide speed and cushion pad position, using this feedback to calculate corrected speed command values. This closed-loop feedback mechanism adjusts the servo-motor response in real-time, maintaining force control stability while achieving fast response to pressure variations
2Force
If the control mode is changed from position control to force control at collision instant, then force control capability is improved, but the overshoot becomes excessively large due to step-like force command and large force deviation
Solution Approach 1:
The control apparatus dynamically adjusts the force command value based on detected slide speed and cushion pad position. Instead of using a fixed step-like force command, the system continuously modifies the force command to match actual collision conditions, eliminating excessive overshoot while maintaining accurate force control capability
Solution Approach 2:
The control apparatus changes the rise time constant of the force command based on detected collision conditions and slide speed. By dynamically adjusting this parameter, the system optimizes the force command transition smoothness, preventing large force deviations and excessive overshoot while maintaining responsive force control
3Stability of the object's composition
If an integrator is used to hold the speed command during force control, then the speed command stability is improved, but the response becomes too slow to follow rapid force fluctuations during collision
Solution Approach 1:
The control apparatus calculates a preliminary speed command value based on detected slide speed before collision occurs. This preliminary calculation provides a head start on speed adjustment, allowing the system to respond rapidly to force fluctuations without relying solely on the slow integrator response
Solution Approach 2:
The control apparatus introduces a corrected speed command value as an intermediary between the integrator output and the actual servo-motor command. This intermediary incorporates real-time slide speed detection and position feedback, enabling fast response to force fluctuations while the integrator maintains overall speed command stability
Data Source
AI summary
A control apparatus for controlling a die cushion mechanism including a servo-motor as a drive source and producing a force adapted to be applied to a slide in a press machine. The control apparatus includes a force commanding section for commanding a force to be produced by the die cushion mechanism; a force detecting section for detecting the force produced by the die cushion mechanism; a motor-speed detecting section for detecting an operating speed of the servo-motor; a slide-speed detecting section for detecting a moving speed of the slide; and a force controlling section for executing a force control on the servo-motor, based on a force command value commanded by the force commanding section, a force detected value detected by the force detecting section, a motor-speed detected value detected by the motor-speed detecting section and a slide-speed detected value detected by the slide-speed detecting section.