Shared Tendon Actuator for Grasp Assist Device
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Solution Overview
Problem
Existing grasp assist devices require oversized actuators to achieve sufficient tension for grasping, leading to increased size and weight, and are not optimal for improving grasp strength or accommodating irregularly shaped objects.
Innovation Solution
A grasp assist device featuring a shared tendon actuator assembly with a flexible tendon and a drive assembly that includes a servo motor, ball screw mechanism, and gear set, which applies balanced tension to the tendon portions, reducing the number of required linear actuators and enabling grasp of a wider variety of objects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If oversized actuators are used to provide sufficient actuator travel for applying necessary tension to the tendon, then the grasp strength is improved, but the size and weight of the device increase substantially
Solution Approach 1:
The tendon is divided into two separate tendon portions that can be independently routed and tensioned. This segmentation allows each portion to be optimized for specific finger movements, reducing the total travel distance required and enabling the use of more compact actuators while maintaining sufficient tension force.
Solution Approach 2:
The patent introduces a shared tendon actuator assembly that uses a pulley system to redirect forces in multiple dimensions. By routing tendons through pulleys and using a shared actuator positioned centrally, the system achieves efficient force transmission with reduced actuator travel requirements, thereby reducing actuator size and weight.
2Manufacturing precision
If multiple separate actuators are used for each finger, then the grasp precision is improved, but the device complexity and number of components increase
Solution Approach 1:
The patent merges the actuation function for multiple fingers into a single shared tendon actuator assembly. This assembly uses a common motor and pulley system to control multiple tendon portions simultaneously, reducing the total number of actuators while maintaining independent control capability for each finger through separate tendon routing.
Solution Approach 2:
The shared tendon actuator assembly is designed to perform multiple functions: it can tension different tendon portions independently, accommodate various grasp configurations, and provide both active tensioning and passive return functions. This multi-functionality reduces the need for separate specialized actuators for each finger.
3Adaptability or versatility
If the tendon is routed to accommodate irregularly shaped objects, then the adaptability is improved, but the device complexity increases
Solution Approach 1:
The patent employs dynamic tendon routing where the tendon portions can be repositioned and reconfigured based on the object being grasped. The shared actuator assembly allows for adjustable tension distribution across different tendon portions, enabling adaptation to various object shapes and sizes without requiring a completely different mechanical structure.
Solution Approach 2:
The system changes operational parameters such as tendon tension distribution, actuator travel distance, and pulley positioning to accommodate different object geometries. By adjusting these parameters rather than changing the physical structure, the system achieves high adaptability while maintaining relatively simple device architecture.
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 solution enhances grasp strength, reduces device weight, and allows for a wider range of object grasping, including irregularly shaped ones, while minimizing the number of linear actuators needed, thus addressing the limitations of prior art designs.
Implementation Method 1
The ball-screw assembly includes a tendon hook which is connected to an internally-threaded ball nut, which in turn is engaged with an externally-threaded length of ball screw. The servo motor applies torque to the ball screw to linearly translate the tendon hook and ball nut with respect to the primary axis/length of the ball screw.
Implementation Method 2
The tendon is connected at its approximate midpoint to a drive assembly of the shared tendon actuator assembly, such that the tendon portions are selectively tensioned in a balanced manner via application by the shared actuator assembly of a calculated tensile force.
Data Source
AI summary
A grasp assist device includes a glove with first and second tendon-driven fingers, a tendon, and a sleeve with a shared tendon actuator assembly. Tendon ends are connected to the respective first and second fingers. The actuator assembly includes a drive assembly having a drive axis and a tendon hook. The tendon hook, which defines an arcuate surface slot, is linearly translatable along the drive axis via the drive assembly, e.g., a servo motor thereof. The flexible tendon is routed through the surface slot such that the surface slot divides the flexible tendon into two portions each terminating in a respective one of the first and second ends. The drive assembly may include a ball screw and nut. An end cap of the actuator assembly may define two channels through which the respective tendon portions pass. The servo motor may be positioned off-axis with respect to the drive axis.