Locking Rotary Actuator with Segmented Radial Keys
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Solution Overview
Problem
Rotary hydraulic actuators face challenges in maintaining positional accuracy and locking capability due to internal leakage, which can lead to complete loss of locking function upon seal failure, especially in applications requiring continuous inertial loading without external fluid power supply.
Innovation Solution
A locking mechanism for rotary actuators featuring a rotor with radially extending keys that become reversibly trapped in axial grooves of the outer housing, utilizing a piston with varying thickness and bevels to selectively lock or unlock the actuator, and an axial spring to bias the piston's movement, allowing for fluid pressure control to maintain position holding capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sealed hydraulic fluid is used to maintain angular position, then positional accuracy is improved, but reliability deteriorates because any single seal failure results in complete loss of locking capability
Solution Approach 1:
The locking function is segmented into multiple independent mechanical locking elements (keys) distributed around the rotor perimeter. Each key can independently engage with the housing to provide locking capability. This segmentation ensures that failure of one seal or locking element does not result in complete loss of locking capability, as other keys remain functional.
Solution Approach 2:
Different regions of the piston have different thicknesses (first portion with first thickness, second portion with second thickness). This local variation in geometry creates different functional zones: one for driving key extension and another for key retraction. This local quality differentiation enables the piston to control multiple keys with different operational characteristics.
2Reliability
If mechanical locking elements are added to provide fail-safe locking, then reliability is improved, but device complexity increases
Solution Approach 1:
The locking mechanism merges multiple functions into a single integrated system. The piston simultaneously performs: (1) driving keys radially outward for locking, (2) being driven radially inward for unlocking, (3) providing the driving force through fluid pressure, and (4) being biased by springs. This merging reduces the need for separate actuating mechanisms and simplifies the overall structure.
Solution Approach 2:
The piston serves multiple functions within the locking mechanism: it acts as a driver for key extension, a driven element for key retraction, a seal for fluid containment, and a spring-loaded return mechanism. This multi-functionality reduces the total number of components needed and simplifies the device architecture.
3Reliability
If multiple keys are used to prevent complete locking loss, then reliability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The piston features asymmetric geometry with a first portion having a first thickness and a second portion having a second thickness greater than the first thickness. This asymmetry creates corresponding asymmetric clearance zones that guide key positioning. The varying thickness profile ensures proper key alignment and engagement tolerance during manufacturing, as the geometry itself provides alignment guidance rather than requiring high-precision machining of all surfaces.
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 solution provides improved position-holding capability, a fail-safe mechanism against fluid pressure loss or leakage failures, and high external load-carrying capacity, with the option to incorporate visual or electrical indication for safety-critical applications.
Implementation Method 1
an axial spring in biasing contact with the piston. The axial spring can be configured to urge the piston into the first position or the second position
Implementation Method 2
a pressure chamber defined by the axial interior cavity, the piston, and the seal, the pressure chamber being configured to selectably apply fluid pressure to the piston to urge reciprocal axial movement of the piston within the axial interior cavity
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
The subject matter of this specification can be embodied in, among other things, a locking apparatus for a rotary actuator includes an outer housing comprising a cylindrical interior surface having a recess. A rotor is disposed within the outer housing. The rotor has an interior cavity and a port extending radially from the interior cavity to the cylindrical exterior surface. A piston is disposed for reciprocal movement within the interior cavity between a first position and a second position and includes a first portion having a first thickness, a second portion having a second thickness larger than the first thickness. A key is disposed for radially reciprocal movement within the port and includes a radially proximal end and a radially distal end. The radially proximal end contacts the first portion and the radially distal end does not extend into the recess when the piston is in the first position.