Cable-Actuated Differential for Zero-Backlash 2-DOF Joints
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Solution Overview
Problem
Current mechanical differentials for robotics and teleoperation struggle with bi-directional control of degrees of freedom, often requiring multiple uni-sense actuators and transmissions, which can lead to issues like stiction, hysteresis, and backlash, limiting the dynamic force range and stability.
Innovation Solution
A cable-actuated differential system with N+1 tensioning cables and pulleys, where each pulley has multiple cables independently attached and co-activated to minimize co-activation, using bevel gears and smooth surfaced rotating members to achieve bi-directional motion without slack, thereby reducing friction and increasing dynamic force range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple uni-sense actuators and transmissions are used to achieve bi-directional control of degrees of freedom, then complete freedom of control is achieved, but stiction, hysteresis, and backlash occur which limit dynamic force range and stability
Solution Approach 1:
The patent replaces traditional mechanical actuators (motors, gears, shafts) with a cable-based tensioning system. Cables are used to apply controlled tension forces to pulleys, which then rotate to control the degrees of freedom. This substitution eliminates gear meshing (removing backlash and hysteresis) while maintaining bi-directional control capability through differential cable tensioning.
Solution Approach 2:
The patent employs flexible cables instead of rigid mechanical linkages. These cables wrap around pulleys and can be tensioned independently to control rotation in both directions. The flexibility of the cables allows them to conform to the pulley surfaces without creating stiction, while the tensioning mechanism provides precise control over the applied forces.
2Adaptability or versatility
If traditional mechanical transmissions (gears, shafts, belts) are used to conduct motions and forces, then bi-directional transmission is achieved, but friction and mechanical complexity increase
Solution Approach 1:
The patent extracts and removes the complex intermediate mechanical components (gears, shafts, timing belts) from the transmission system. Instead of using these multiple components to transmit motion and force, the invention directly uses tensioned cables wrapped around pulleys to achieve the same bi-directional transmission function with significantly reduced mechanical complexity.
Solution Approach 2:
The patent substitutes traditional rigid mechanical transmission elements with a flexible cable-pulley system. The cables replace gears and belts, and the pulleys replace shafts and gear assemblies. This substitution maintains the bi-directional transmission capability while eliminating the friction and complexity associated with meshing gears and multiple mechanical joints.
3Device complexity
If uni-sense actuators are used to generate force in one direction, then actuator simplicity is maintained, but multiple actuators (N+1) are required for N degrees of freedom
Solution Approach 1:
The patent merges the functionality of multiple uni-sense actuators into a coordinated cable tensioning system. Instead of using N+1 separate actuators, the invention uses a set of cables that can be tensioned in combination to achieve bi-directional control of N degrees of freedom. The cables work together through the pulley mechanism to provide the equivalent control freedom with reduced actuator count.
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 effectively increases the dynamic force range by minimizing co-activation and friction, allowing precise control of mechanical characteristics like joint friction and stiffness, and achieving zero backlash, enhancing the fidelity and stability of mechanical transmissions.
Implementation Method 1
Tension cables conduct motion and force through tension
Implementation Method 2
a cable-actuated differential having N degrees of freedom is provided that includes a plurality of actuation elements, a plurality of pulleys, each pulley having one or more tensioning cables independently attached along the perimeter of the respective pulley
Implementation Method 3
a plurality of gears in association with each of the pulleys, where two or more of the gears are circular and have faces that oppose each other and which are mounted to a respective shaft
Data Source
AI summary
Cable-actuated differential enabling N degrees of freedom provided by a plurality of pulleys and at least N+1 tensioning cables. The cable-actuated differential increases a dynamic force range by minimizing co-activation of the tensioning cables at any operating point. A cable-actuated differential having three cables provides motor based control of a 2 DOF joint that can be applied to robots or teleoperation. A cable-actuated mechanical differential having opposing bevel gears and a middle bevel gear meshed with the opposing gear allows an output connector to controllably and independently rotate about the x axis or y axis via three operational modes without backlash.