Oblong Collet Design for Rotary Valve Actuator Positioning

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Solution Overview

Problem

Existing collets with cylindrically-shaped outer surfaces are prone to lost motion during torque reversal in throttling applications, leading to inaccurate positioning of flow control members in rotary valves, due to slippage between the collet and the lever.

Innovation Solution

The use of elongated members with oblong-shaped coupling portions and flexible members that engage a rectangular shaft, providing a tight fit and minimizing slippage by using tapered and curved surfaces to ensure precise alignment and clamping force, eliminating the need for wedges or shaft keys.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a cylindrically-shaped collet is used to engage the lever, then the structure is simple and easy to manufacture, but lost motion occurs between the collet and lever during torque reversal

Engineering Contradiction:

Improvecollet structure simplicityVSAvoidconnection stability during torque reversal

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The collet is designed with an oblong-shaped outer surface instead of a cylindrical shape, creating an asymmetric geometry that prevents rotation within the lever's opening. This asymmetric shape ensures that the collet cannot slip or experience lost motion during torque reversal, while still maintaining ease of manufacture through standard forming processes.

Inventive Principle:

Principle #4Asymmetry

2Measurement precision

If a tight fit between collet and lever is achieved to eliminate lost motion, then positioning accuracy improves, but the coupling and decoupling process becomes more difficult

Engineering Contradiction:

Improveflow control member positioning accuracyVSAvoidcoupling and decoupling ease

Core Design Contradiction:

Measurement precisionVSEase of operation

Solution Approach 1:

The collet incorporates flexible members that can dynamically change the internal bore size. During coupling, the flexible members are compressed to reduce the bore size for a tight fit around the rectangular shaft. During decoupling, the flexible members expand to increase the bore size, facilitating easy removal. This dynamic adaptation maintains positioning accuracy while enabling easy operation.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The internal bore dimensions of the collet are made variable through the use of flexible members that can expand and contract. This parameter change allows the collet to provide a tight fit for accurate positioning during operation, while also enabling easy coupling and decoupling when the flexible members are compressed or expanded, respectively.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If flexible members are used to provide clamping force on the rectangular shaft, then lost motion is eliminated, but the collet structure becomes more complex

Engineering Contradiction:

Improveconnection stability during torque reversalVSAvoidcollet internal structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The collet uses flexible members that act as thin-walled structures to provide clamping force on the rectangular shaft. These flexible members are integrated into the collet body and can be formed from elastic materials or metal springs, providing the necessary clamping force while maintaining a relatively simple overall structure. The flexibility allows the members to conform to the shaft and maintain tight engagement without complex adjustment mechanisms.

Inventive Principle:

Principle #30Flexible shells and thin films

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 configuration substantially reduces or eliminates lost motion between the actuator and the flow control member, ensuring accurate positioning and improved control of fluid flow through the valve, even during torque reversals, and facilitates easy coupling and decoupling for installation and repair processes.

Implementation Method 1

The first and the second plurality of flexible members are displaced toward an axis of the elongated member to cause the first and the second inner surfaces to engage one or more surfaces of a rectangular shaft

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Data Source

PatentUS8408837B2Collets for use with valves

Publication Date: 2013.04.02 FISHER CONTROLS INT LLC

AI summary

Collets for coupling rotary actuators to valves are disclosed. An example collet includes a first plurality of flexible members configured to be coupled to an elongated member and each having a first inner surface and a first outer surface. The first inner surface and the first outer surface define a first cross-sectional shape. The example collet further includes a second plurality of flexible members configured to be coupled to the elongated member and each having a second inner surface and a second outer surface. The second inner surface and the second outer surface define a second cross-sectional shape that is different from the first cross-sectional shape of the first plurality of flexible members. The first and the second outer surfaces are to engage a third inner surface of an opening of a lever that is configured to cause the first and the second plurality of flexible members to be displaced toward an axis of the elongated member to cause the first and the second inner surfaces to engage one or more surfaces of the rectangular shaft.