Hydraulic Actuator Force Control Using Stroke Feedforward Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing hydraulic actuator systems exhibit non-linear behaviors such as non-linear flow, spool lap cross-over, variating pressures, and seal friction, leading to inaccurate force control during multi-actuator fatigue tests, which affect test cycle speed and controllability.
Innovation Solution
A control system utilizing combined stroke feedforward and stroke feedback compensation methods to manage actuator non-linearities, incorporating a feedforward path to differentiate stroke command signals and a feedback path to adjust for errors, with proportional and integral compensators to stabilize actuator control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If classical PID force control loops are used to control hydraulic actuators, then the control system is simple to implement, but force control accuracy deteriorates due to non-linear actuator behaviors
Solution Approach 1:
The patent implements a stroke feedback mechanism that continuously monitors the actual stroke position of the actuator and feeds it back to the control system. This feedback signal is used to generate a compensation signal that corrects for non-linear behaviors including spool lap cross-over, seal friction, and pin slop, thereby improving force control accuracy without overcomplicating the control architecture
Solution Approach 2:
The patent modifies the control parameters by introducing a stroke-dependent compensation signal that dynamically adjusts the control output based on the actuator's position. This parameter change approach accounts for varying non-linear effects at different stroke positions, improving force control accuracy across the full range of motion
2Device complexity
If proportional-integral-differential (PID) force control loops are used, then the control structure remains conventional, but the ability to address actuator non-linear behaviors deteriorates
Solution Approach 1:
The patent introduces a stroke feedback compensation signal as an intermediary element between the force command and the actuator. This compensation signal acts as a mediator that counteracts the non-linear effects of spool lap cross-over, seal friction, and pin slop, improving the reliability of force control without fundamentally changing the conventional PID control structure
3Device complexity
If non-linear actuator behaviors are not compensated, then the control system operates simply, but test cycle speed and force controllability deteriorate
Solution Approach 1:
The patent implements preliminary action by pre-characterizing the actuator's non-linear behaviors through stroke feedback measurements and using this information to generate compensatory control signals before executing the test cycle. This preliminary characterization enables faster test cycles by eliminating the need for slow, iterative force adjustments during testing
Data Source
AI summary
Control compensation methods and configurations for controlling actuators that are applying forces to a test article. The control compensation methods and configurations reduce force control tracking errors by the use of combined stroke feedforward and stroke feedback signals. These counteract errors caused by multi-actuator cross coupling and other challenging behaviors caused by various issues with the actuators.