Fluid-Cable Transmission With Rolling Diaphragm Seals for Robotic Arms
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Solution Overview
Problem
Conventional hydraulic robots face issues with fluid leaks, friction, and accuracy due to the use of o-ring seals and unidirectional pistons, which limit their efficiency and compactness, and pneumatic robots are noisy and less accurate.
Innovation Solution
A fluid-cable transmission system utilizing rolling diaphragm seals and a tubing assembly with a cable connecting two hydraulic cylinders, allowing for flexible transmission of forces and motions while minimizing friction and leaks, and enabling the use of lightweight materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional hydraulic systems use o-ring seals, then fluid containment is achieved, but friction and leaks occur reducing efficiency
Solution Approach 1:
The patent extracts the sealing function from traditional o-ring seals and implements it through fluid pressure itself. The system uses positive fluid pressure to maintain seal engagement with the cavity wall, eliminating the need for separate sealing components that generate friction. This resolves the contradiction by removing the friction-generating sealing mechanism while maintaining fluid containment through pressure-based sealing.
Solution Approach 2:
The patent replaces the mechanical o-ring seal system with a pressure-based sealing mechanism. Instead of relying on mechanical contact between sealing rings and surfaces, the system uses fluid pressure to create and maintain the seal against the cavity wall, substituting a mechanical friction-based system with a pressure-based system that eliminates sliding friction.
2Reliability
If unidirectional hydraulic pistons are used, then leak-free operation is achieved, but system compactness and efficiency deteriorate due to spring requirements or antagonistic pairs
Solution Approach 1:
The patent creates a bidirectional piston system where a single piston can operate in both directions without requiring separate antagonistic pairs or spring mechanisms. The positive pressure sealing mechanism works equally well in both extension and retraction directions, allowing one piston to perform the work of multiple unidirectional pistons, thereby improving compactness while maintaining leak-free operation.
Solution Approach 2:
Instead of using unidirectional pistons that require springs or antagonistic pairs to return to center position, the patent inverts the approach by creating a bidirectional piston where fluid pressure actively seals in both directions. This eliminates the need for return springs or additional antagonistic pistons, reducing system complexity and improving compactness while maintaining reliable sealing.
3Reliability
If cable drives are used instead of hydraulics, then leaks and seal friction are eliminated, but positioning accuracy deteriorates due to cable elasticity
Solution Approach 1:
The patent introduces a fluid medium as an intermediary between the cable drive system and the piston. The incompressible fluid transmits force from the cable to the piston without the elasticity problems of direct cable attachment, combining the leak-free benefits of cable drives with the positioning accuracy of hydraulic systems. The fluid acts as a compliant intermediary that eliminates cable elasticity effects on positioning accuracy.
4Force
If hydraulic fluid is used, then incompressible force transmission is achieved, but system weight and complexity increase
Solution Approach 1:
The patent changes the physical parameters of the transmission medium by using air instead of hydraulic fluid. By operating with pressurized air and using the positive pressure sealing mechanism, the system achieves sufficient force transmission without the weight and complexity of hydraulic fluid systems, while maintaining the incompressible force transmission characteristic through pressure control.
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 system provides improved accuracy, reduced friction, and increased pulling forces, making it suitable for actuating joints in robotic arms with enhanced haptic transparency and safety, while allowing for the use of lightweight and agile robotic arms.
Implementation Method 1
Researchers have used rolling diaphragm seals instead of o-rings on master/slave hydraulic pistons to eliminate leaks and minimize friction
Implementation Method 2
Hydraulic fluid fills the cylinder on each side of the piston and can push it in either direction. The pressure drop across the piston and hence the piston force is regulated by electronically controlled valves
Implementation Method 3
a cable connecting the first and second pistons through the tubing assembly
Data Source
AI summary
A mechanical transmission system that transmits motions and forces from one location to another while allowing the relative position/orientation of the two locations to change continuously is disclosed. The system can be used to actuate the joints and tooling of a robotic arm using stationary motors in the robot's base. Since the motors do not contribute any weight or inertia to the arm, this yields a lightweight and agile arm that is more human safe. The transmission includes a controller hydraulic cylinder connected to a remote cylinder by a tubing assembly, which contains hydraulic fluid, and a wire cable. The fluid transmits pushing forces between pistons of the cylinders, while the cable transmits pulling forces. The tubing assembly allows the cylinders to move in space relative to one another.