Distributed Torque Actuation for Exoskeleton Joints
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Solution Overview
Problem
Existing robotic systems, such as active orthoses and haptic interfaces, face challenges in reducing actuator torque requirements and increasing transmission stiffness without increasing overall dimensions or using cumbersome components, particularly in achieving kinematics isomorphic to human limbs for applications like VR and tele-operated systems.
Innovation Solution
The distributed torque actuation technique involves arranging multiple small diameter idle pulleys at revolute joints of a mechanism, allowing for a multiplied torque output through inextensible cables, reducing the torque needed from actuators and enhancing transmission stiffness without bulky components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If actuators are positioned on a fixed base or proximal link far from the mechanism, then the weight and encumbrance of movable parts is reduced, but the torque transmission efficiency decreases and larger actuators are required
Solution Approach 1:
The patent divides the torque transmission path into multiple segments by introducing intermediate pulleys at different locations along the mechanism. Instead of a direct cable connection from the actuator to the mechanism, the cable is routed through multiple pulleys (first pulley on proximal link, second pulley on medial link, third pulley on distal link), creating segmented transmission stages that distribute the torque requirement across the mechanism structure.
Solution Approach 2:
The patent introduces intermediate pulleys as mediator elements between the actuator and the mechanism. These pulleys (particularly the second pulley on the medial link and third pulley on the distal link) serve as intermediary components that redirect and transmit the cable force, enabling efficient torque transmission while maintaining the actuator's remote position on the proximal link.
2Area of stationary object
If remote centre of rotation mechanisms are used to limit physical encumbrance near the rotational axis, then interference with the human body is reduced, but the components required to actuate the mechanism increase encumbrance
Solution Approach 1:
The patent extracts the bulky actuator components from the vicinity of the mechanism's rotational axis. By positioning the actuator on the proximal link far from the distal mechanism, and using a long cable routed through multiple pulleys, the heavy actuator is taken out from the constrained space near the rotational axis, leaving only lightweight pulleys and cable in the immediate mechanism area.
Solution Approach 2:
The patent resolves the spatial conflict by utilizing the longitudinal dimension of the mechanism. Instead of trying to fit compact actuation components in the lateral space near the rotational axis, the solution extends the actuation path along the length of the mechanism, routing the cable from the proximal link through intermediate links to the distal mechanism, thereby using available space in a different dimensional direction.
3Device complexity
If cable transmission systems with low gear ratio are used, then the device is more compact, but the transmission stiffness is insufficient
Solution Approach 1:
The patent applies local quality enhancement at critical transmission points by introducing multiple pulleys at specific locations (particularly the second pulley on the medial link and third pulley on the distal link). These locally placed pulleys create additional friction and mechanical advantage at key points in the transmission path, increasing overall transmission stiffness without requiring a high global gear ratio that would compromise compactness.
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
This technique achieves higher torque output and improved stiffness with reduced actuator size and overall dimensions, enhancing the performance and comfort of robotic systems by minimizing cumbersome components near the human interface.
Implementation Method 1
arranging an inextensible cable according to a prefixed routing, the routing extending between a traction point on the cable upstream of a first idle pulley and a terminal point fixed on one of the links or on the mechanism; and the routing comprising respective contact arcs of the inextensible cable about the idle pulleys
Implementation Method 2
by pulling the inextensible cable at the traction point a multiplied torque is produced which is the sum of singular torques produced by the inextensible cable at each idle pulley
Data Source
Figure 1'~1''
Figure 2~3
Figure 4~5
AI summary
A method for actuating a mechanism adapted to impose a prefixed relative movement between said first rigid link (3) and said second rigid link (5). The mechanism comprises revolute joints and may be a parallelogram mechanism (10a, 10b), a pantograph remote centre of rotation mechanism (RCRM, 11 ), or a multiple-degrees-of-freedom mechanism (10c) thereof. The method allows reducing the torque requirements of the actuators and increasing the stiffness of the transmission, for a given required actuating torque/force, with no need of particularly cumbersome components proximate to moving parts. The method provides coaxially arranging at one or more selected revolute joint/s (37a-d, 47c-d) a number of idle pulleys (32a-d, 47a-f) which is greater than the number of degrees of freedom of the mechanism, the first of the selected revolute joint/s (37a, 47a) having preferably its rotation axis fixed with respect to the rigid link (3); the methods provides furthermore arranging an inextensible cable (33, 43) between a traction point (34, 44), e.g. a gripping point of an actuator, and a terminal point (36, 46) on the mechanism or on the second rigid link (5). By pulling the inextensible cable (33, 43) at the traction point (34, 44), a multiplied torque is produced which is the sum of singular torques produced by the inextensible cable (33, 43) at each idle pulley (32a-d, 47a-f), the multiplied torque causing a relative movement between the links (3, 5). The method provides arranging a further inextensible cable which forms contact arcs preferably symmetrically to said contact arcs about the same pulleys of the other cable, for bilaterally actuating the mechanism, i.e. causing opposite relative movements between the first and the second links (3, 5), which allows implementing such opposite limb movement as abduction/adduction of the phalanx of a finger. A hand exoskeleton that uses the method is preferably obtained by serially arranging two pantograph RCRM to implement proximal and medial phalanx and a crossed parallelogram mech. for implementing distal phalanx joints of at least a finger. In a mechanism like the one used for the cable used to actuate a more distal mechanism must cross more proximal mechanisms, which may occur in active, collaborating mode, or in a neutral mode.