Hydraulic Linear Actuation Control for Load-Independent Low Speeds
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Solution Overview
Problem
Existing hydraulic systems for linear actuation, such as scissor lifts, face challenges in achieving smooth and load-independent speed control, particularly at low speeds, due to limitations in gear pump operating envelopes and inefficiencies in existing control methods, which affect safety, comfort, and controllability.
Innovation Solution
A hydraulic control system incorporating an electric motor, hydraulic pump, pressure transducer, pressure control valve, check valve, tank, control valve, and a proportional control valve connected to a processor, which adjusts the opening area of the proportional control valve based on operator commands and pressure measurements to maintain desired speed regardless of load weight, allowing for precise control of linear actuation from zero to maximum speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a gear pump is used to power the hydraulic system, then the system structure is simple and cost-effective, but the pump cannot operate at low speeds within its operating envelope, limiting low-speed control capability
Solution Approach 1:
A variable displacement motor is introduced as an intermediary between the gear pump and hydraulic cylinder. The motor converts hydraulic flow to rotational motion, and through a mechanical transmission system (gearbox or direct drive with variable displacement), it delivers controlled torque and speed to the cylinder. This intermediary allows the gear pump to operate at optimal speeds while still achieving precise low-speed control of the actuator.
Solution Approach 2:
The system employs dynamic speed control through a variable displacement motor that can adjust its displacement ratio in real-time. This allows the motor to vary its output speed and torque according to the load requirements, enabling the hydraulic cylinder to operate smoothly across the full speed range from zero to maximum without violating the gear pump's operating envelope.
2Device complexity
If an on/off valve is used to control cylinder retraction, then the control system is simple, but the lowering function is load-dependent and cannot be adjusted, resulting in unsafe operation with heavy loads
Solution Approach 1:
The system incorporates load-sensing feedback through a pressure sensor that continuously monitors the hydraulic pressure in the circuit. This pressure information is fed back to the control system, which automatically adjusts the variable displacement motor's displacement ratio to compensate for load variations. This ensures that the cylinder descends at a controlled, safe rate regardless of the platform weight, eliminating the load-dependent behavior of simple on/off valve systems.
3Speed
If a proportional valve is used to control the orifice area for speed regulation, then load-independent speed control is achieved, but additional hardware complexity is introduced
Solution Approach 1:
The patent replaces the traditional mechanical proportional flow control valve with an electro-hydraulic control system using a variable displacement motor. Instead of mechanically adjusting an orifice area to control flow rate, the system uses electronic control of the motor's displacement ratio to regulate the hydraulic flow to the cylinder. This substitution eliminates the need for separate proportional valves and orifices while achieving superior load-independent speed control through the motor's inherent flow-proportional-to-displacement characteristic.
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 system enables precise control of linear actuation speeds, ensuring safety and comfort by maintaining speed consistency across varying loads without violating the gear pump's operating envelope, thus enhancing machine controllability and reducing the risk of damage to the work environment.
Implementation Method 1
A pressure transducer, a pressure control valve, and a check valve are connected to the first flow line between the pump and the cylinder
Implementation Method 2
The speed of the lowering function of the cylinder is governed by the orifice equation as described in Eq. 1 and 2. Where: Q is the flow rate through the orifice, Aorifice is the opening area in the orifice
Implementation Method 3
A hydraulic control system for linear actuation includes an electric motor connected to a hydraulic pump and a hydraulic cylinder connected to the pump
Data Source
AI summary
A hydraulic control system for linear actuation that includes an electric motor connected to a hydraulic pump and a hydraulic cylinder connected to the pump by a first flow line. A pressure transducer, a pressure control valve, and a check valve are connected to the first flow line between the pump and the cylinder and a tank is connected to the pump by a second flow line and the cylinder by a return line. A control valve is connected between the first flow line and the return line.