Evaluation of Commercial Ropes Applied as Artificial Tendons in Robotic Rehabilitation Orthoses

Abstract

This study aims to present the design, selection and testing of commercial ropes (artificial tendons) used on robotic orthosis to perform the hand movements for stroke individuals over upper limb rehabilitation. It was determined the load applied in the rope would through direct measurements performed on four individuals after stroke using a bulb dynamometer. A tensile strength test was performed using eight commercial ropes in order to evaluate the maximum breaking force and select the most suitable to be used in this application. Finally, a pilot test was performed with a user of the device to ratify the effectiveness of the rope. The load on the cable was 12.38 kgf (121.4 N) in the stroke-affected hand, which is the maximum tensile force that the rope must to supports. Paragliding rope (DuPont™ Kevlar ® ) supporting a load of 250 N at a strain of 37 mm was selected. The clinical test proved the effectiveness of the rope, supporting the requested efforts, without presenting permanent deformation, effectively performing the participant’s finger opening.

Robotic Orthosis for Upper Limb Rehabilitation

“…For the artificial tendons, Kevlar multi-wire cables were used, because it is light, durable, flexible, has a low friction coefficient, tensile strength, low cost, and low percentage elongation. These advantages were evidenced in a previous work, developed by these authors [21], using the EMIC 23-5D machine for the tensile test, was being possible to generate the rope deformation graph using the Tesc Software version 3.04 and the test method is called rectangular tie pull. The artificial phalanges consist of rigid lactic polyacid (PLA) rods, it has a function of limiting the movement of the user's phalanges, preventing hyperextension of the metacarpophalangeal joints and flexion of the interphalangeal joints during a finger extension.…”

Development of portable robotic orthosis and biomechanical validation in people with limited upper limb function after stroke

“…The transmission system of the elbow module also consists of a power screw [28]. It acts as a physical limiter that prevents elbow movement from reaching undesirable angles.…”

“…The AM is also made by PLA and covers the user's metacarpal fixing the module transmission system and blocking the proximal AP rotating movement. Finally, the AT is Kevlar ropes, which were selected as previously shown [28].…”

Development of a Passive Prosthetic Hand That Restores Finger Movements Made by Additive Manufacturing

“…For a better understanding of the methodology for performing the tensile test, Figure 5 shows a brief flowchart aiming to illustrate in general the methodological steps of analysis through the tensile test. Thus, the material properties estimated in this experiment are (1) maximum stress (tensile strength), i.e., the maximum stress that the material can withstand when stretched or pulled without showing any trace of internal or external fracture in the body proof; (2) flow limit or stress (0.2%), point where the flow phenomenon begins, plastic strain starts, i.e., start of permanent TB strain; (3) elasticity modulus or Young's modulus, mechanical property that measures the stiffness of a solid material, in the higher the modulus of elasticity, the less elastic deformation resulting from the application of a given stress; and (4) elongation at break [31].…”

“…For the development of the simulation finite element model to evaluate the stress concentration on the surface [31,[37][38][39][40], forces of 7.5 N were used in the distal region of the phalanges individually, according to the bibliographic orientation [19,20,23,25,35,36]. Responses to the proposed loads showed maximum stress of 13.45 MPa on the braided line near the proximal phalanges, as shown in Figure 20.…”