Flexible Collet Rectangular Shaft Coupling Eliminates Backlash

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Solution Overview

Problem

Existing shaft couplings in rotary valves, such as levers, often experience backlash due to improper sizing, leading to lost motion and reduced accuracy in fluid flow control, and existing collets with square bores may not provide sufficient clamping force to prevent this issue, especially when interfacing with differently sized actuators and valves from various manufacturers.

Innovation Solution

The use of a collet with flexible members featuring an involute outer surface and inner surfaces forming a rectangular bore, which engages a lever's involute inner surface to provide a tight coupling and effective clamping force to a rectangular or square valve shaft, minimizing lost motion by applying thicker material at the corners for enhanced torque transmission and engagement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a collet with a square bore is used to receive differently sized square valve shafts, then adaptability to various actuators and valves is improved, but lost motion occurs due to insufficient clamping force

Engineering Contradiction:

Improvecompatibility with various actuator and valve sizesVSAvoidaccuracy of fluid flow control

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The collet is divided into multiple flexible members (typically three or more) that can independently deflect and apply clamping force to the shaft. This segmentation allows each flexible member to conform to the shaft surface and provide sufficient clamping force while maintaining adaptability to different shaft sizes through the standardized square bore configuration.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The flexible members are designed with specific material properties and geometric parameters (thickness, length, cross-section) that enable them to deflect under load and provide the necessary clamping force. The involute outer surface geometry is specifically designed to engage with the involute inner surface of the lever, creating a self-centering mechanism that eliminates lost motion while accommodating various shaft sizes.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the collet provides sufficient clamping force to prevent lost motion, then accuracy of fluid flow control is improved, but the coupling becomes tighter and may reduce adaptability

Engineering Contradiction:

Improveaccuracy of fluid flow controlVSAvoidcompatibility with various actuator and valve sizes

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The flexible members transition from a rigid, fixed-geometry structure to a dynamic, deformable structure that adapts its shape and clamping force based on the shaft size and applied loads. This dynamic behavior allows the same collet design to provide optimal clamping force across a range of shaft sizes while maintaining adaptability through the standardized square bore interface.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The collet design with standardized square bore and involute outer surface serves multiple functions: it provides adaptability to various shaft sizes through the universal square interface, generates sufficient clamping force through flexible member deflection, and eliminates lost motion through the involute engagement geometry. This multi-functionality resolves the contradiction between adaptability and reliability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Ease of operation

If a lever is used to convert linear displacement to rotational movement, then ease of operation is improved, but backlash occurs due to clearance between contacting surfaces

Engineering Contradiction:

Improveconversion of linear to rotational movementVSAvoidaccuracy of positioning

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The involute outer surface of the flexible members engages with the involute inner surface of the lever, creating a curved, self-centering interface. This curved geometry eliminates clearance and backlash between the lever and shaft by providing continuous surface contact that self-adjusts to the exact shaft size, while still allowing the lever to effectively convert linear actuator displacement into rotational valve shaft movement.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Data Source

PatentUS8205633B2Collets for use with valves

Publication Date: 2012.06.26 FISHER CONTROLS INT LLC

AI summary

Collets for coupling rotary actuators to valves are disclosed. An example collet includes a plurality of flexible members configured to be coupled to an elongated member and each having an inner surface that forms at least a portion of a substantially rectangular bore configured to receive a rectangular shaft. The plurality of flexible members form an involute outer surface for engaging an involute inner surface of an opening of a lever. The opening of the lever is configured to cause the plurality of flexible members to be displaced toward an axis of the elongated member to cause the inner surface of each of the plurality of flexible members to engage one or more surfaces of the rectangular shaft.