Hydraulic Drive Control with Pump Speed and Valve Stiffness
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Solution Overview
Problem
Existing hydraulic drive systems, particularly electro-hydraulic axes, face issues with insufficient rigidity, inaccurate positioning dynamics, varying resonance frequency, and performance losses due to pressure drops and non-linear characteristics in valve-based control systems.
Innovation Solution
A procedure for operating a hydraulic drive that utilizes a proportional valve connected to a tank, with a model-based control approach that employs an inverse system model to regulate the position of the piston by adjusting the speed of the pump and the position of the proportional valve, thereby achieving precise control and energy efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If speed of the pump is used as manipulated variable for position control, then the control simplicity is improved, but the rigidity of the hydraulic drive deteriorates
Solution Approach 1:
The hydraulic drive control is segmented into two independent control loops: an outer position control loop that manages pump speed for overall position accuracy, and an inner force control loop that manages valve position for stiffness and resonance stability. This segmentation allows each loop to optimize for its specific function without compromising the other.
Solution Approach 2:
The proportional valve acts as an intermediary element between the position control command and the actual piston position. By controlling the valve position based on the difference between actual and desired piston positions, it provides the necessary force control to maintain rigidity while the pump speed control handles the overall positioning.
2Measurement precision
If proportional valve is used to change volume flow, then the positioning precision is improved, but energy losses increase due to pressure drop
Solution Approach 1:
The control system dynamically adjusts the pump speed to match the actual demand for hydraulic fluid. By using model-based prediction of required flow rates and integrating this with feedback from actual piston position and pressures, the system minimizes unnecessary valve opening and associated pressure drops, thereby reducing energy losses while maintaining positioning precision.
Solution Approach 2:
A closed feedback control loop continuously monitors the actual piston position and compares it with the desired position. The control unit adjusts the proportional valve position based on this error signal, enabling precise positioning while minimizing energy losses through optimized valve operation. The feedback mechanism ensures the valve is only open when necessary and to the minimum degree required.
3Measurement precision
If valve position is controlled to adjust flow, then the flow control accuracy is improved, but the resonance frequency varies causing stability issues
Solution Approach 1:
The control system uses an inverse model of the hydraulic drive to predict the required valve position and pump speed in advance. By calculating the anticipated flow requirements based on the desired piston trajectory and current system state, the controller can proactively adjust control parameters to maintain stable resonance characteristics throughout the motion cycle.
4Measurement precision
If variable-displacement pump is used with constant speed, then the delivery flow control is improved, but the response time to pressure changes deteriorates
Solution Approach 1:
The system transitions from constant pump speed to dynamic speed control. The control unit continuously adjusts the pump speed based on real-time feedback from pressure sensors and piston position, enabling the hydraulic drive to respond rapidly to pressure changes while maintaining precise delivery flow control. This dynamic adaptation allows the system to optimize both flow precision and response time.
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 enhances the rigidity and energy efficiency of the hydraulic drive, allows for quick and precise reaction to different operational phases, and reduces response time of the valve to approximately 7 ms, compared to traditional methods.
Implementation Method 1
a variable-speed pump (110) which is connected to a hydraulic consumer (130)... The pump (110) is connected to a hydraulic consumer (130), which in this case is a cylinder (132) with a positionable piston (134)
Implementation Method 2
at another port (e.g. on the B side) via a proportional valve... a valve can be used to change the volume flow of hydraulic fluid into or out of the cylinder
Implementation Method 3
pressure control can also be provided, which are equivalent due to the relationship between force and pressure across the pressure application area, for example, in a hydraulic cylinder
Data Source
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AI summary
The invention relates to a method for operating a hydraulic drive (100) comprising a hydraulic consumer (130) with a positionable piston in a cylinder, which is connected to a tank at one port via a variable speed pump (110) and at another port (B) via a proportional valve (140), wherein a position (x) of the piston is controlled using a model-based control in which a speed (n) of the pump (110) is used as a control variable, and in which a position (y) of the proportional valve (140) is specified.