Soft Bladder Workholder for Low-Pressure Collet Actuation
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Solution Overview
Problem
Existing workholders require high fluid pressures to grip workpieces, leading to energy consumption issues, leakage, and potential damage due to high pressure conditions, and previous solutions either use complex configurations or many additional precision-manufactured parts.
Innovation Solution
A workholder design featuring a bladder with a 90 durometer Shore A scale hardness cast polyurethane and annular seals of 70 durometer Shore A scale hardness, providing a 15:1 diameter-to-wall-thickness ratio, which allows for low-pressure fluid actuation and effective gripping with a steel collet, reducing leakage and part complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If high fluid pressure (6000 PSI) is applied to achieve workpiece gripping, then gripping force is sufficient, but energy consumption increases and leakage occurs
Solution Approach 1:
The patent changes the material parameter of the bladder from hard plastic (85 durometer Shore D) to soft elastomeric material (70 durometer Shore A), which fundamentally alters the pressure-force relationship. This material parameter change enables achieving the same gripping force at much lower fluid pressures (200-2000 PSI vs. 6000 PSI), directly resolving the energy consumption issue while maintaining sufficient grip force
2Force
If high fluid pressure (6000 PSI) is applied to achieve workpiece gripping, then gripping force is sufficient, but leakage occurs
Solution Approach 1:
The patent changes the material hardness parameter from 85 durometer Shore D to 70 durometer Shore A, creating a softer, more compliant bladder that can deform to seal against the workpiece and holder surfaces. This parameter change improves reliability by preventing leakage at lower operating pressures, as the soft material conforms to surface irregularities and maintains sealing effectiveness
3Strength
If hard plastic bladder (85 durometer Shore D) is used to withstand high pressure, then structural strength is sufficient, but the bladder may extrude through collet slots causing permanent damage
Solution Approach 1:
The patent changes the bladder material hardness from 85 durometer Shore D to 70 durometer Shore A, transforming it from a rigid structure to a compliant element. This parameter change eliminates the extrusion problem because the soft material can deform and flow around collet slots rather than forcing its way through them, preventing permanent damage to the workholder
Solution Approach 2:
The patent converts what would traditionally be considered a weakness (soft material deformability) into a benefit. The soft bladder material's ability to deform under pressure prevents the harmful extrusion effect, turning potential damage into a protective mechanism that safeguards the workholder structure
4Ease of manufacture
If thin bladder wall is used to reduce material, then cost is reduced, but high pressure causes extrusion through collet slots
Solution Approach 1:
The patent changes the material hardness parameter to 70 durometer Shore A, creating a soft material that can be made thin without suffering from extrusion problems. The parameter change enables the thin-walled design to work effectively, as the soft material deforms rather than extrudes under pressure, combining manufacturing economy with damage prevention
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 design achieves equal or greater holding power under lower fluid pressures, with a greater expansion range, reduced leakage, and improved durability, allowing for reliable and economical workpiece holding with a simple design.
Implementation Method 1
hydraulic fluid in the chamber is pressurized to radially displace the sleeve into gripping engagement with a workpiece
Implementation Method 2
A bladder is carried by the main body with an interference fit of approximately 0.001 inch. The bladder further defines the fluid chamber, and is composed of approximately 90 durometer Shore A scale hardness cast polyurethane
Data Source
AI summary
A workholder to hold a workpiece, including a main body partially defining a fluid chamber, and a bladder carried by the main body with an interference fit, further defining the fluid chamber, and composed of an 80 to 100 durometer Shore A scale hardness polymer of a 12:1 to 18:1 diameter-to-wall-thickness ratio. Annular seals may further define the fluid chamber, and are disposed radially between the bladder and main body and axially adjacent the fluid chamber, and are composed of a 60 to 80 durometer Shore A scale hardness polymer. A collet is carried and driven by the bladder for gripping engagement with the workpiece.