Hydraulic Actuator Deceleration Control via Variable Filter
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Solution Overview
Problem
Hydraulically driven equipment, such as backhoes, experience oscillation or 'wag' due to inertia when decelerating or reversing, leading to reduced productivity and operator discomfort, as existing solutions require additional valves and components.
Innovation Solution
A control method that uses a variable filter function to regulate the deceleration of the hydraulic actuator, adjusting the filter frequency based on the load force to ensure the valve responds at a rate compatible with the actuator's capabilities, implemented through a digital filter and software programming without adding hardware components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the control valve closes quickly to stop the boom swing, then the stopping time is reduced, but the load force causes the boom velocity to respond too slowly, resulting in oscillation or 'wag'
Solution Approach 1:
The control system anticipates the stop command and begins reducing fluid flow to the hydraulic actuator before the valve fully closes. By preliminarily reducing the fluid flow rate in response to the stop command, the system prepares the actuator for deceleration, allowing the valve to close quickly while the actuator velocity responds smoothly, preventing oscillation.
Solution Approach 2:
The control system monitors the actual velocity of the boom assembly and compares it to the commanded velocity. Based on this feedback, the controller dynamically adjusts the fluid flow rate to the hydraulic actuator, ensuring the deceleration rate matches the actuator's response capability and prevents overshoot or oscillation during stopping.
2Reliability
If additional relief valves and makeup valves are added to vent fluid and counteract cavitation, then cavitation is prevented, but the device complexity increases
Solution Approach 1:
The patent replaces the mechanical valve-based solution (relief valves and makeup valves) with an electronic control system that uses sensors, a controller, and electronic control of the hydraulic actuator. The controller electronically regulates fluid flow to prevent cavitation and manage pressure, eliminating the need for additional mechanical valves while maintaining reliability.
Solution Approach 2:
The hydraulic actuator is equipped with integrated sensors and control mechanisms that allow it to self-regulate fluid flow and pressure in response to operational conditions. The actuator monitors its own state and automatically adjusts to prevent cavitation without requiring external relief or makeup valves.
3Loss of time
If the valve position changes rapidly to reverse boom direction, then the direction change time is reduced, but the actuator cannot respond fast enough, causing oscillation
Solution Approach 1:
When a direction change is commanded, the control system preliminarily adjusts the fluid flow rate to the hydraulic actuator at a rate compatible with the actuator's response capability. This preliminary action ensures the actuator is prepared for the direction change without being overwhelmed by rapid valve movement, reducing oscillation while maintaining quick response time.
Solution Approach 2:
The control system dynamically adjusts the fluid flow rate based on the actuator's current state and the commanded direction change. By making the control adaptive and dynamic rather than fixed, the system can optimize the response rate for each specific situation, achieving fast direction changes without causing oscillation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces oscillation by controlling the deceleration rate of the hydraulic actuator, improving responsiveness and reducing 'wag' without requiring additional components, thus enhancing equipment productivity and operator comfort.
Implementation Method 1
a hydraulic actuator is connected to the machine member to move the machine member in response to a command
Implementation Method 2
The filter function controls the rate at which the motion command goes to zero to stop the machine member so that the command does not close the related valve faster than a rate the actuator and machine member are able to operate
Implementation Method 3
When the operator suddenly stops the boom swing, inertia causes the motion of the backhoe boom assembly 3 to continue in the previously commanded direction
Implementation Method 4
This continued movement due to inertia compresses the hydraulic fluid in the previous exhausting chamber of the boom swing cylinder 9
Implementation Method 5
may produce cavitation in the previous driving cylinder chamber
Data Source
AI summary
A machine member driven by a hydraulic actuator may oscillate, or wag, when the hydraulic actuator decelerates or stops. The degree of oscillation is a function of the machine member's ability to track a deceleration command, which ability varies with changes in the position of the machine member and the load force acting thereon. To reduce the oscillation, a command that controls operation of the hydraulic actuator is filtered using a filter function that changes with the machine member's load. The load force exerted on the hydraulic actuator which in turn can be designated by fluid pressure that results from the hydraulic actuator. Preferably, the frequency of the filter function is varied inversely with the magnitude of the actuator load force.