Spherical Scissors Linkage Mechanism for Singularity-Free Joint Motion
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Solution Overview
Problem
Conventional industrial serial manipulators face issues with singularity and collision when approaching objects, and existing spherical mechanisms suffer from locking in inevitable singular configurations, which complicates their use in applications like exoskeletons, particularly at complex joints like the shoulder joint, where they need to mimic human movements without interfering with biological structures.
Innovation Solution
A curved spherical scissors linkage mechanism with four or more linkage elements, arranged to form rhombi or parallelograms, with revolute joints coinciding at a common remote center of motion, allowing for three degrees-of-freedom movements without singularity, and equipped with actuator means and control mechanisms for independent rotation control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional industrial serial manipulators are used to work around an object, then they can achieve three degrees-of-freedom movements, but they require reconfiguration when approaching singularity which may cause collision with objects
Solution Approach 1:
The mechanism divides the movement into three independent rotational degrees of freedom about concurrent axes, with each axis represented by a separate scissor linkage assembly. This segmentation allows independent control of each rotational movement without requiring reconfiguration of the entire mechanism
Solution Approach 2:
The patent uses curved linkage elements arranged in scissor linkages that operate on a spherical surface, allowing the mechanism to maintain constant distance from the singularity point while achieving full three-degree-of-freedom rotational movement around the object
2Adaptability or versatility
If 3R spherical mechanisms with three perpendicular rotational axes are used, then they can achieve spherical movement, but they lock in singular configurations when two axes are aligned
Solution Approach 1:
The mechanism uses non-perpendicular rotational axes with specific angle relationships that prevent alignment of any two axes. The asymmetric arrangement of the scissor linkages ensures that the mechanism can achieve full spherical movement without encountering singular configurations where axes become collinear
Solution Approach 2:
The scissor linkage mechanism dynamically adjusts the effective length of linkage elements during movement, allowing continuous adaptation of the mechanism configuration to maintain operational freedom and avoid static singular positions
3Ease of operation
If spherical linkage mechanisms are designed to surround the anatomical shoulder structure, then they can replicate human joint movements, but they increase the volume and protrusion of the device
Solution Approach 1:
The scissor linkage mechanism allows nested arrangement of linkage elements where the four-bar linkages are positioned concentrically around the shoulder joint center. This nesting enables the mechanism to surround the anatomical structure while minimizing the external volume and protrusion of the device
Solution Approach 2:
The mechanism transitions from a planar arrangement to a three-dimensional spherical configuration, allowing the linkage elements to be distributed in multiple dimensions around the shoulder joint. This dimensional arrangement enables compact packaging that minimizes protrusion while maintaining full range of motion
4Reliability
If redundant linkages are used to avoid singularity complications, then singularity-free operation can be achieved, but the device complexity and size increase
Solution Approach 1:
Each scissor linkage assembly serves multiple functions: it provides one degree of freedom rotation, maintains constant distance from the singularity point, and enables spherical movement. This multi-functionality achieves singularity-free operation without requiring additional redundant linkages that would increase complexity
Data Source
AI summary
The invention relates to a curved spherical scissors linkage mechanism (1) comprising at least four linkage elements (2) each having a first end (3) and a second end (4); the linkage elements are arranged to form sides of one rhombus or parallelogram, or a series, such as a network, of joined rhombi or parallelograms. Each of the linkage elements is rotationally connected to one of the other linkage elements via a revolute joint (5) at or near the first end and is rotationally connected to another one of the other linkage elements via another revolute joint at or near the second end. The linkage elements are shaped, dimensioned and arranged so that the axes of all the revolute joints coincide at one common remote centre of motion (RCM). Furthermore, the mechanism is grounded or connected or connectable to a first external member (7) at a proximal end and is rotationally connected or connectable to a second external member (9) at an opposite distal end. Hereby a spherical linkage mechanism with three DOFs is obtained. The spherical scissors linkage mechanism may further comprise a motion controlling mechanism at the proximal and/or at the distal end. It further comprises actuator means as control means.