Pilot Valve Offset Compensation for Accurate Proportional Positioning
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Solution Overview
Problem
Pilot-operated position-controlled proportional valves experience offset errors due to deviations between electronically detected actual valve positions and hydraulic zero points, leading to potential system failures at high pressures.
Innovation Solution
An offset compensation system using a switched integrator with a large time constant, logic circuit, and non-volatile memory to detect and correct pilot position errors by integrating control errors when the valve is stationary, storing compensation values for rapid restarts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a pilot valve is used to control the proportional valve, then energy consumption is reduced and actuation is easier, but position offset errors occur between the electronically detected valve position and the hydraulic zero point
Solution Approach 1:
The patent implements a feedback mechanism where the actual valve position is continuously detected and compared with the desired position. The position offset error is integrated over time and fed back to the control system, which automatically adjusts the pilot valve actuation to compensate for the offset. This closed-loop feedback ensures that the valve maintains accurate positioning despite the inherent offset between electronic detection and hydraulic zero points.
Solution Approach 2:
The patent changes the control parameter by introducing an integrated position offset value that is added to the desired position signal. This parameter transformation converts the position offset error into a compensating control signal, allowing the system to maintain accuracy while using the energy-efficient pilot valve architecture.
2Measurement precision
If the integrator time constant is increased to improve offset compensation, then position accuracy improves, but the system responds more slowly to actual position changes
Solution Approach 1:
The patent applies dynamics by making the integrator active only under specific conditions detected by a logic circuit. The integrator is enabled when the valve is stationary (no actual position changes) and disabled when the valve is moving. This dynamic switching allows the system to achieve both high position accuracy during stationary periods and fast response during movement, resolving the contradiction between accuracy and speed.
Solution Approach 2:
The patent uses periodic sampling of valve position and conditional integration, where the integrator operates in discrete periods when the valve is stationary rather than continuously. This periodic action allows accumulation of offset compensation data during idle periods without interfering with dynamic response during operation.
3Measurement precision
If the integrator is always active to compensate for offset errors, then position accuracy is maintained, but control errors accumulate during valve movement causing instability
Solution Approach 1:
The patent dynamically controls the integrator activation through a logic circuit that monitors valve movement. The integrator is activated only when the valve is stationary and deactivated when movement is detected. This dynamic control prevents accumulation of control errors during valve movement while maintaining offset compensation during stationary periods, thus preserving both accuracy and stability.
Solution Approach 2:
The patent extracts the integrator function from continuous operation and isolates it to specific operational phases (stationary periods only). By separating the offset compensation function from the dynamic control function, the system avoids the instability that would result from continuous integration during movement while maintaining accuracy during idle periods.
4Loss of time
If compensation values are stored in memory for rapid restart, then system recovery time is reduced, but device complexity increases
Solution Approach 1:
The patent applies preliminary action by storing the integrated compensation value in non-volatile memory before system shutdown occurs. When the system restarts, this pre-stored value is immediately retrieved and used to initialize the offset compensation, eliminating the need for time-consuming re-calibration. This advance preparation reduces restart time while keeping the memory component simple and integrated into the existing control architecture.
Data Source
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AI summary
The present invention relates to an offset compensation for a position offset of a pilot valve 10 for a position-controlled proportional valve 20, comprising a switched integrator 3 with a delay element 2 with a predefined time constant, an offset compensation logic 5 that ensures that the integrator is only active when neither the target nor the actual position of the proportional valve changes, so that the proportional valve is stationary, and an integrator that adds up any control errors leading to an offset until an offset error is completely compensated.