Hydraulic Clamp Force Equalization Across Free Lift Mast Stages
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Solution Overview
Problem
Hydraulic control systems for free lift masts in material handling equipment face challenges in automatically regulating gripping forces based on load weight due to the need for stepped hoist line pressures, leading to undesirable telescoping and increased complexity with electronic controllers.
Innovation Solution
A hydraulic valve circuitry system that includes load-clamping valve assemblies with pilot-operated check valves and pressure-differential regulating valves, allowing for weight-responsive control of load-clamping members independent of the lifting device's position, using a combination of fluid power actuators and hydraulic circuits to manage pressure and maintain consistent gripping forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If free lift masts use stepped hoist line pressures for extending beyond free lift range, then mast extension is achieved, but automatic weight-responsive gripping force control cannot be implemented
Solution Approach 1:
The hydraulic circuit is designed so that the same hoist line pressure serves dual purposes: both extending the mast stages and providing the sensing signal for automatic gripping force control. The pressure differential regulating valve enables the system to derive clamping pressure information from the hoist line pressure without requiring separate sensing systems, making the hydraulic system multi-functional.
Solution Approach 2:
A pressure differential regulating valve is introduced as an intermediary component between the hoist line pressure source and the clamping pressure control. This valve mediates the pressure signal, creating a derived pressure that is proportional to load weight while being independent of mast position. This intermediary enables automatic gripping force control without direct electronic intervention.
2Extent of automation
If electronic controllers are used for gripping force regulation, then automatic weight-responsive control is achieved, but unit cost and system complexity increase
Solution Approach 1:
The patent replaces electronic control systems with a purely hydraulic control mechanism. The pressure differential regulating valve uses hydraulic principles to automatically adjust clamping pressure based on hoist line pressure, eliminating the need for electronic sensors, controllers, and movable electrical conductors. This mechanical-hydraulic substitution reduces system complexity and unit cost while maintaining automatic control functionality.
Solution Approach 2:
The hydraulic system is designed to be self-regulating, where the hoist line pressure itself serves as the sensing signal for load weight. The pressure differential regulating valve automatically adjusts the clamping pressure without external intervention, allowing the system to self-regulate gripping forces based on the actual load being handled.
3Stress or pressure
If free lift masts require higher hoist pressures for main lift stage extension, then mast telescoping control is achieved, but load weight sensing for gripping force control becomes unavailable
Solution Approach 1:
The hydraulic control system is segmented into independent pressure zones. The pressure differential regulating valve creates a separate, regulated pressure circuit that is derived from but independent of the main hoist line pressure. This segmentation allows the main hoist pressure to perform mast extension while the regulated pressure circuit simultaneously provides load weight sensing for gripping force control.
Solution Approach 2:
The pressure differential regulating valve transforms the hoist line pressure parameter into a different pressure parameter that is suitable for load weight sensing. By regulating the pressure differential across the valve, the system converts high-pressure hoist signals into proportional clamping pressure signals that accurately reflect load weight regardless of mast extension stage.
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
Enables full-time automatic weight-responsive force control of load-clamping members, reducing telescoping and system complexity, while maintaining consistent gripping forces across different lift stages without the need for movable electrical conductors.
Implementation Method 1
pilot-operated check valves and pressure-differential regulating valves
Implementation Method 2
hydraulic valve circuits adapted for weight-responsive control of clamping members
Data Source
AI summary
Hydraulic valve circuitry adapted for automatic weight-responsive control of load-clamping members of a load-lifting system having a free lift mast. The load-lifting system generally includes one or more fluid power actuator for applying a gripping force to a load, at least one elongate, longitudinally-extensible fluid power lifting device having a free lift range of motion and at least one main lift range of motion, and manually operated load-clamping and load-lifting selector valves. The hydraulic valve circuitry provides, independently, weight-responsive control of the load-clamping members when lifting a load, full-time automatic weight-responsive force control of the load-clamping members without concurrent manual actuation of load-clamping or load-lifting selector valves, and equalization of sensed load weight so that the sensed load weight is substantially independent of the longitudinally-extensible position of the lifting device.