Fluid Power Screw Actuator for Precise Self-Locking Positioning
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Solution Overview
Problem
Conventional hydraulic, electric, and electro-hydraulic linear actuators suffer from issues such as poor position precision, susceptibility to leaking and drifting, high cost, difficulty in compact packaging, and failure to meet safety standards, particularly in applications like loading munitions onto aircraft.
Innovation Solution
A fluid power actuator utilizing a screw assembly with minimal friction, providing high precision positioning, simplified mechanical locking, and convenient manual backup operation, which includes a screw assembly with trapezoidal thread geometry or recirculating ball/roller screw geometry to enhance performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional hydraulic actuators are used, then high force can be generated, but position precision deteriorates and leaking/drifting occurs
Solution Approach 1:
A screw assembly is introduced as an intermediary mechanism between the hydraulic piston and the load. The piston drives the screw, which converts rotational motion to linear motion with high precision. The screw threads act as precision elements that eliminate the direct contact issues between hydraulic components and the load, providing accurate positioning while maintaining high force capability through mechanical advantage.
Solution Approach 2:
The patent replaces the direct hydraulic mechanical system with a hybrid system incorporating a screw mechanism. Instead of relying solely on hydraulic piston-seal contact for positioning, the system uses screw threads that provide inherent mechanical precision and self-locking characteristics, eliminating the need for complex sealing arrangements that cause drifting.
2Force
If conventional electric linear actuators are used for high force applications, then force capability is improved, but cost increases, lubrication is required, and manual movement during power loss becomes difficult
Solution Approach 1:
The screw assembly provides self-locking capability through its thread geometry, where the friction between screw and nut prevents backward motion under load without requiring external braking mechanisms. This self-service feature allows manual repositioning during power loss by simply applying torque to the screw, eliminating the need for complex motor-brake systems while maintaining high force capability.
3Force
If conventional electro-hydraulic linear actuators are used, then force and control are improved, but device complexity increases and compact packaging becomes difficult
Solution Approach 1:
The patent merges the hydraulic power transmission function with the mechanical motion control function into a single integrated actuator assembly. The hydraulic piston directly drives the screw mechanism, combining what would traditionally be separate motor and drive train components into one compact unit. This integration eliminates the need for separate electric motors, gearboxes, and coupling mechanisms, achieving compact packaging while maintaining high force capability.
4Reliability
If conventional actuators are used to meet safety standards, then reliability is improved, but device complexity and cost increase
Solution Approach 1:
The screw assembly's self-locking characteristic provides inherent safety by mechanically preventing load descent or position drift even during complete power failure. The friction in the screw threads creates a natural barrier against unintended motion, eliminating the need for complex redundant braking systems, multiple actuators, or sophisticated control algorithms required by conventional systems to achieve similar safety factors.
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
The fluid power actuator achieves high precision, stability, and reliability with reduced component demands, enabling safe and efficient operation even without power, suitable for critical applications like munitions loading.
Implementation Method 1
the screw assembly has a recirculating ball screw geometry or roller screw geometry for low friction operation
Implementation Method 2
the screw assembly includes a low efficiency screw (e.g., a screw/nut assembly having ACME threads or similar thread geometry) to provide self-locking
Data Source
AI summary
A fluid power actuator includes a fluid power actuator housing, a piston assembly, and a screw assembly. The piston assembly is constructed and arranged to move relative to the fluid power actuator housing in response to changes in fluid pressure within the fluid power actuator housing. The screw assembly couples with the fluid power actuator housing and the piston assembly. The screw assembly is constructed and arranged to control movement of the piston assembly relative to the fluid power actuator housing. Such a fluid power actuator is well-suited for various applications such as in loading equipment which is involved in high precision munitions loading, among others.