Motor Control Device Asymmetric Integral Limit for Pressure Undershoot
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Solution Overview
Problem
Forging machines experience pressure undershoot during pressure control, leading to potential damage to hydraulic pumps and compromised product quality due to elastic properties between the slide and die cushion mechanism, especially when hydraulic pressure falls to negative values.
Innovation Solution
A motor control device that includes a pressure command unit, pressure detection unit, pressure control unit, and servo control unit, which performs integral operation with a median between upper and lower limits set larger than zero to prevent pressure undershoot, and sets the upper limit to the speed command for speed control to prevent overshoot, ensuring positive hydraulic pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pressure control including integral (I) control is used to asymptotically bring the final pressure error to zero, then pressure control precision is improved, but pressure may overshoot or undershoot during the control process
Solution Approach 1:
The patent changes the parameter of the integral operation by setting the lower limit to a value greater than zero (specifically, 0.01 times the upper limit). This parameter modification prevents the integral accumulation from reaching negative values that cause pressure undershoot, while still allowing sufficient integral action to eliminate steady-state error and achieve precise pressure control.
2Speed
If the lower limit in the integral operation is set to a negative value to allow pressure correction, then pressure control responsiveness is improved, but hydraulic pump damage may occur when pressure falls to negative values
Solution Approach 1:
The patent applies preliminary anti-action by preemptively setting the lower limit of the integral operation to a positive value before pressure undershoot can occur. This prevents the integral accumulation from reaching values that would cause negative pressure and potential pump damage, while still maintaining adequate control responsiveness through appropriate upper limit settings.
3Adaptability or versatility
If the median between upper and lower limits in the integral operation is set to zero to allow symmetric pressure control, then control flexibility is improved, but pressure undershoot cannot be suppressed
Solution Approach 1:
The patent introduces asymmetry into the integral operation by setting the lower limit to a positive value (0.01 times the upper limit), creating an asymmetric range where the median is greater than zero. This asymmetric configuration prevents the integral accumulation from reaching negative values that cause pressure undershoot, while maintaining sufficient control flexibility through appropriate upper limit settings.
Data Source
AI summary
A motor control device includes a pressure command unit calculating a pressure command for commanding pressure generated in a pressure control object, a pressure detection unit detecting the pressure generated in the pressure control object, a pressure control unit calculating a speed command for pressure control for the servo motor, based on the calculated pressure command and the detected pressure, and a servo control unit controlling speed of the servo motor, based on the calculated speed command. The pressure control unit performs an integral operation. When a direction of increasing pressure in the integral operation is defined as a positive direction in the integral operation, and a direction of decreasing the pressure is defined as a negative direction, a median between an upper limit in the positive direction and a lower limit in the negative direction in the integral operation is larger than zero.