Injection Molding Controller Lag Compensation
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Solution Overview
Problem
Existing injection molding machine controllers experience delays in changing over from injection velocity control to pressure control, leading to inaccurate and unstable injection processes due to time lags in detecting changeover points, resulting in motion deficiencies and peak pressure variations.
Innovation Solution
A controller that sets and determines changeover conditions for injection molding machines, calculates compensation amounts for time lags, and adjusts motion commands to compensate for delays, ensuring accurate and stable transitions between injection velocity and pressure control by distributing compensation across subsequent sampling periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If changeover from injection velocity control to pressure control is performed by detecting set changeover points in every sampling period, then the control system can implement switching between control modes, but the detection is delayed by one sampling period causing inaccurate changeover timing
Solution Approach 1:
The system performs preliminary action by calculating a compensation amount based on the difference between the commanded screw position and actual position before the changeover occurs. This compensation amount is then applied to adjust the changeover point detection timing, effectively predicting and correcting the detection delay before it affects the control switching accuracy.
Solution Approach 2:
The system uses feedback by continuously monitoring the screw position and comparing it with the commanded position. The position deviation detected in each sampling period is fed back to calculate the compensation amount, which is then used to adjust the changeover detection timing in subsequent periods, creating a closed-loop correction mechanism.
2Productivity
If the screw position is detected in every sampling period to determine changeover points, then the system can monitor the injection process continuously, but the changeover is always detected after a delay of one sampling period
Solution Approach 1:
The system performs preliminary calculation of the compensation amount using the position deviation data available before the changeover point is reached. This allows the system to proactively adjust the changeover detection timing rather than passively accepting the sampling delay, effectively compensating for the time loss in advance.
Solution Approach 2:
The system creates a compensated changeover point timing by applying the calculated compensation amount to the detected changeover point. This compensated timing serves as a corrected copy of the actual changeover moment, eliminating the sampling period delay effect while maintaining continuous monitoring capability.
3Extent of automation
If injection velocity control is switched to pressure control at the detected changeover point, then the system can transition between control modes, but motion deficiency occurs due to the detection delay
Solution Approach 1:
The system uses feedback from the screw position deviation to calculate a compensation amount that is applied to the changeover detection timing. This feedback-based compensation ensures that the control mode switching occurs at the correct moment, eliminating motion deficiency and maintaining injection process accuracy.
Solution Approach 2:
The system changes the parameter of changeover detection timing by applying a compensation amount calculated from position deviation data. This parameter adjustment transforms the delayed detected changeover point into an accurate compensated changeover point, ensuring precise control mode switching without motion deficiency.
Data Source
AI summary
A controller of an injection molding machine which compensates a delay in an injection velocity changeover and a delay at the time of changeover to the pressure-holding process, and is capable of more accurate and stable injection velocity control and changing control from the injection velocity control to pressure control. In the injection process, a motion command is outputted in every sampling period τ according to the command injection velocity. When a screw position overshoots the set velocity changeover positions Psw(2) and Psw(1), a motion command based on a velocity command of the next interval is outputted from the next period. However, there is time lag between the point when the set changeover position is reached and the point when the motion command is changed after detection thereof. There generates a motion deficiency in a motion amount shown by mark A and overshoot shown by B. Motion commands of the next period or the next and subsequent several periods are compensated with errors in the motion amount caused by the time lag used as compensation amounts A′ and B′. The generated error motion amount is immediately compensated, which enables accurate velocity changing control. By performing the compensation in the same manner when the injection velocity control is switched to the holding pressure control, it is possible to suppress the peak pressure and the dispersion.