Long-Stroke Rolling Diaphragm Cylinder for Low-Friction Sealing

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Traditional rolling diaphragm cylinders are limited to a stroke-to-bore ratio of 1:1, restricting their work per cycle and suitability for applications requiring longer stroke lengths, while also facing issues with friction and leakage.

Innovation Solution

The development of long-stroke rolling diaphragm cylinders with a stroke-to-bore ratio greater than 1:1, manufactured using a process involving 3D printed molds and polyurethane or cotton fabric, achieving low friction and zero leakage, suitable for passive hydraulic systems.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of moving object

If traditional compression molding process is used for rolling diaphragm, then manufacturing is simple, but stroke length is limited to 1:1 bore ratio

Engineering Contradiction:

Improvestroke lengthVSAvoidmanufacturing process complexity

Core Design Contradiction:

Length of moving objectVSEase of manufacture

Solution Approach 1:

The manufacturing process is divided into multiple stages: creating a mandrel, applying fabric layers, coating with rubber compound, curing in stages, and finishing operations. This segmented approach enables production of long-stroke diaphragms that cannot be made with traditional single-step compression molding.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A mandrel is prepared in advance with specific geometric features (tapered sections, relief zones) before the rubber compound is applied. This preliminary structuring of the core form allows the subsequent rubber layers to be formed into the required long-stroke diaphragm shape with controlled thickness distribution.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If O-ring seal is used in hydraulic cylinder, then sealing is effective, but friction is high

Engineering Contradiction:

Improvesealing performanceVSAvoidfriction force

Core Design Contradiction:

ReliabilityVSForce

Solution Approach 1:

A flexible rubber diaphragm replaces traditional rigid O-ring seals. The diaphragm is constructed with multiple fabric reinforcement layers embedded in rubber compound, creating a thin-film flexible sealing element that conforms to the cylinder wall and provides effective sealing with significantly reduced friction compared to O-ring seals.

Inventive Principle:

Principle #30Flexible shells and thin films

3Force

If gap seal cylinder is used, then friction is reduced, but leakage increases

Engineering Contradiction:

Improvefriction forceVSAvoidsealing performance

Core Design Contradiction:

ForceVSReliability

Solution Approach 1:

The flexible rubber diaphragm with fabric reinforcement acts as an active sealing film that maintains continuous contact with the cylinder wall through pressure differential. This eliminates the gap between piston and cylinder, preventing leakage while maintaining low friction, unlike passive gap seal designs.

Inventive Principle:

Principle #30Flexible shells and thin films

4Productivity

If rolling diaphragm with stroke-to-bore ratio >1:1 is manufactured, then work per cycle increases, but manufacturing complexity increases

Engineering Contradiction:

Improvework per cycleVSAvoidmanufacturing process complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The diaphragm manufacturing is segmented into discrete operational phases with dedicated tooling for each stage. The process includes: mandrel preparation, fabric layer application, rubber compound coating, staged curing, and finishing. This segmentation makes the complex manufacturing of long-stroke diaphragms systematic and repeatable.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The manufacturing process controls critical parameters including rubber compound viscosity, curing temperature profiles, fabric layer tension, and mandrel rotation speed. By precisely controlling these parameters, the process produces consistent long-stroke diaphragms with the required stroke-to-bore ratio greater than 1:1.

Inventive Principle:

Principle #35Parameter changes

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 long-stroke rolling diaphragm cylinders offer improved work per cycle, reduced friction, and increased efficiency compared to traditional cylinders, making them suitable for applications like wearable robots with higher stroke lengths and lower weight.

Implementation Method 1

Rolling diaphragm actuators have a diaphragm between the cylinder and piston which rolls back and forth

Methodology Applied

Scientific EffectRolling friction: Friction

Implementation Method 2

The fluid carries away the heat generated in the device and acts as a lubricant for the components

Methodology Applied

Scientific EffectConvection: Convection

Implementation Method 3

The fluid carries away the heat generated in the device and acts as a lubricant for the components

Methodology Applied

Scientific EffectFluid lubrication: Lubrication

Data Source

PatentUS11300116B2Long-stroke rolling diaphragm cylinder and methods of making same

Publication Date: 2022.04.12 REGENTS OF THE UNIVERSITY OF MINNESOTA

AI summary

Hydraulic cylinders and methods of fabricating hydraulic cylinders, including long-stroke rolling diaphragm cylinders with any stroke length. In some embodiments, the cylinders are manufactured to have a stroke length to bore diameter (“stroke-to-bore”) ratio optionally greater than 1:1. Various embodiments are suitable for use in a passive hydraulic body-powered wearable robot, for example.