Die Cushion Control Stabilizing Switching via Deviation Signals
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Solution Overview
Problem
Conventional die cushion controllers experience unstable switching between position control and pressure control due to incorrect detection of electric current changes caused by impacts and vibrations, leading to inaccurate control of the die cushion pad operation, which affects the precision of the molding process.
Innovation Solution
A die cushion controller that includes a pressure command signal output unit, pressure detecting means, pressure comparing unit, position command signal output unit, position detecting means, position comparing unit, and a position/pressure control switching unit, which constantly monitors and compares pressure and position deviation signals to stabilize the switching between position control and pressure control, ensuring accurate and timely transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If switching between position control and pressure control is effected through detection of a predetermined change in the electric current of the servomotor, then switching is possible, but the electric current is not constantly monitored for any change, making the operation of switching unstable
Solution Approach 1:
The patent implements constant monitoring of both electric current and position deviation through feedback mechanisms. The position detecting means continuously provides position feedback, and the control system compares actual position with target position to generate deviation signals. This feedback approach ensures stable switching by constantly monitoring system state rather than relying on intermittent current detection alone.
Solution Approach 2:
The patent introduces a position deviation signal as an intermediary parameter to facilitate stable switching between control modes. By using position deviation as a mediator that combines information from both current monitoring and position detection, the system achieves more reliable switching decisions than direct current detection alone.
2Measurement precision
If switching is effected solely through the output of a detection signal indicating a change in the electric current of the servomotor, then the structure is simpler, but the change in pressure and position cannot be more accurately recognized, making switching less stable
Solution Approach 1:
The patent merges multiple detection approaches by combining electric current monitoring with position detection. The position detecting means (such as encoders or sensors) work together with current sensors to provide comprehensive system state information. This merging of detection methods enables accurate recognition of both pressure changes and position changes simultaneously.
Solution Approach 2:
The control system is designed with multi-functionality to handle both position control and pressure control modes using a unified detection framework. The same position detecting means and control structure serve both control modes, eliminating the need for separate detection systems while achieving accurate measurement in both modes.
3Manufacturing precision
If the upper die comes into contact with the die cushion pad with impact and vibration, then the molding process can proceed, but the electric current change cannot be correctly detected, affecting control accuracy
Solution Approach 1:
The patent converts the harmful effects of impact and vibration into useful information by using position deviation as a robust switching criterion. Instead of relying on electric current detection that is susceptible to vibration noise, the system uses position feedback which remains accurate during impact. The position deviation signal effectively filters out the harmful vibration effects while capturing the essential contact information.
Solution Approach 2:
The patent changes the detection parameter from electric current to position deviation for switching control modes. This parameter change makes the detection process insensitive to vibration and impact effects, as position measurement remains accurate during mechanical contact. The switching decision is based on position feedback rather than current magnitude, effectively eliminating the harmful effects of vibration on detection accuracy.
Data Source
AI summary
A die cushion controller controls an ascending/descending speed of a die cushion pad based on a preset pressure pattern and positional pattern. A position/pressure control switching unit constantly monitors and compares a first speed command signal υpc corresponding to a pressure deviation signal ep and a second speed command signal υhc corresponding to a position deviation signal eh, and selects a smaller one of the speed command signals to be sent to a speed control unit.