Double-Leg Parallel Mechanism for Wider Rotation Without Singularities
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Solution Overview
Problem
Conventional parallel mechanisms, such as Gough-Stewart platforms, have limited rotational range of motion due to kinematic singularities, which restricts their application in flight simulation and robotics, especially when handling large payloads, as they often require link arrangements that lead to bending or complex guiding tracks, limiting payload capacity and increasing costs.
Innovation Solution
A novel parallel mechanism with kinematically redundant actuation is introduced, featuring double legs composed of two conventional six-degree-of-freedom legs connected at their tips with a passive revolute joint and an additional link attached to the platform via a spherical joint, allowing for increased rotational range of motion while maintaining tension/compression loads, and a redundancy resolution algorithm to optimize force transmission and avoid singularities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional Gough-Stewart platform structures are used, then the mechanism can support large payloads through tension/compression loads, but the rotational range of motion is limited by kinematic singularities
Solution Approach 1:
Each leg is segmented into two sub-legs connected by a passive revolute joint, allowing the leg to change its configuration and avoid singularities while maintaining load-bearing capability. The segmentation enables independent optimization of each sub-leg's orientation.
Solution Approach 2:
The passive revolute joints introduce dynamic adaptability to the leg structure, allowing automatic adjustment of leg configuration in response to platform orientation changes. This dynamic reconfiguration enables the mechanism to operate beyond static singularity boundaries.
2Ease of operation
If links subjected to bending are used to increase rotational range of motion, then the rotational workspace is expanded, but the payload capacity is significantly reduced
Solution Approach 1:
By segmenting each leg into two sub-legs with a passive revolute joint, the mechanism maintains straight link geometry (avoiding bending) while achieving enhanced rotational capability through configuration changes at the joint.
Solution Approach 2:
The mechanism changes the orientation parameter of the passive revolute joints dynamically, allowing the legs to reconfigure and avoid singularities without altering the fundamental tension/compression load regime, thus preserving payload capacity.
3Ease of operation
If hybrid architectures are used to increase rotational range of motion, then some rotational capability is improved, but the mechanism cannot support large payloads and still suffers from kinematic singularities
Solution Approach 1:
The parallel mechanism with redundant actuation serves multiple functions: it maintains the payload-bearing capability of conventional parallel mechanisms while simultaneously achieving enhanced rotational workspace, combining advantages previously available only in separate mechanism types.
Solution Approach 2:
The dynamic reconfiguration capability through passive revolute joints allows the mechanism to adapt its geometry to avoid singularities while maintaining parallel kinematics, enabling both large payloads and extended rotational workspace.
4Ease of operation
If constant length struts mounted on linear or circular rails are used, then rotational range of motion is increased, but the forces induced in the rails are too large for large payloads and the rails are costly and difficult to build with precision
Solution Approach 1:
The complex rail guiding structures are extracted and replaced by simple passive revolute joints integrated into the leg structure. This eliminates the need for external rails while achieving similar or superior rotational capability with much simpler mechanics.
Solution Approach 2:
The complex mechanical rail system is replaced by a simpler joint-based mechanism where passive revolute joints provide the necessary motion constraints without requiring external guiding infrastructure.
Data Source
AI summary
A parallel mechanism comprises legs with kinematically redundant actuation for a parallel mechanism. Each of these legs comprises a first sub-leg and a second sub-leg each with a proximal end and a distal end. A link has a proximal end and a distal end. A joint with a rotational degree of freedom (DOF) is between and common to the distal ends of the sub-legs, and the proximal end of the link. A joint provides two or more rotational DOFs at the distal end of the link and connects the distal end of the link to one end of the parallel mechanism. Joints in the sub-legs provide DOFs to the sub-legs and connect the proximal ends of the sub-legs to the other end of the parallel mechanism. A degree of actuation (DOA) is provided for each of the sub-legs to control movement of the link.