CUBE: a Cable-driven Device for Limb Rehabilitation

This tech spec was submitted by Giuseppe Carbone as part of the University Technology Exposure Program.

Problem / Solution

Physical rehabilitation is the process of helping patients in gaining control over parts of their body after a prolonged illness or a traumatic event. The most common exercises are based on slow, repetitive movements. These exercises require one-on-one interaction between the patient and a trained professional therapist. Factors such as the availability of trained professionals, the duration of therapeutic sessions, and program cost affect both therapist and patient. Interactive rehabilitation is time-consuming and labor-intensive for both the therapist and the patient. Years of research in engineering and robotics have considered the possibility of substituting the therapist or clinician with a robot to assist patients in rehabilitating.

The vision of aiding in patient rehabilitation with upper and lower limb difficulty and 3D printing allows the manufacturing of a cable-driven robot assistant. The device paves safe human-robot interaction, given its lightweight structure and easy operability. This programmable device can instruct exercises so clinicians and therapists can use it without complex training. Its user-friendly interface allows easy control and can benefit physicians in overseeing more patients in the future.

Design

The device is usable in clinic and home setups with pre-determined exercising activities. Its safe design uses the cable-driven design that provides low inertia. The novel end-effector design makes it wearable without disassembling any of its structures. The design is kinematically analyzed with motion tests done along simple trajectories and spatial exercises.

The CUBE design is a 5 DOF parallel manipulator with a cable-driven architecture based on six cables. The end-effector shaped as a ring is worn as a wristband by the user. Its position is controlled by the six cables giving the end-effector 3 DOF, while its orientation is assumed to be constrained by fixed support for the elbow. Three cables are attached and converge in the upper part of the structure, while the three remaining cables connect to the lower part. The prototype is prism-shaped, with an equilateral triangle base of the same height as the side of the triangle. This configuration helps building tension in the six cables and moving the center of mass to the geometrical center of the prism.

 To actuate the prototype and to manipulate cables, the end-effector uses an algorithm with position feedback. Six motors with an encoder act as actuators, each receiving a speed input that depends on the difference between the current position and the desired one. These motors move in sync to maintain the cables in tension and allow the entire system to work efficiently. A PID controller ensure that movements made by the cable are in minimum adjustments allowing a comfortable motion.

 The CUBE GUI is divided into two sections: the manual calibration section and the exercise performance section. The manual calibration section helps the user to move each motor to the desired position at the desired speed. The exercise performance section moves the end-effector along a given trajectory. It is possible to perform a previously-programmed exercise that returns to the central starting position at the end or a customized exercise activity given through the point-to-point command.