Design of a variable damping mechanism for shoulder joint tracking device

Abstract

This paper proposes an improved design of the previously devised low-end robot system for comprehensive shoulder rehabilitation. It focuses on depicting the design of a variable damping mechanism. The low-end robot system consists of an actuation module and a passive shoulder joint tracking mechanism. Unlike conventional rehabilitation devices, this robot system tracks the gleno-humeral joint and allows more natural shoulder motion during rehabilitation exercises. The system provides five control modes. However, in active exercise modes, the system offers an inadequate shoulder joint tracking. This is due to an external force applied to the device by the user's arm. To solve this problem, a variable damping mechanism is designed. This mechanism is composed of a constant load spring, a micro electromagnetic clutch, and a rotary damper. During the passive stretching mode, the clutch is deactivated and only the constant load spring rotates. So the mechanism works in the same way as the previous robot system. For stretching modes in which the patient applies force to the device, the clutch is turned on. This allows the rotary damper and the constant load spring to rotate together at the same speed. In other words, damping is applied to the system, adding an extra weight supporting force to the mechanism. Due to an increased force, the external force applied to the device is compensated, and the mechanism regains its shoulder joint tracking ability. The extent of extra weight supporting force depends on the rotary damper's characteristics. The variable damping mechanism remodels the previous design and allows an enhanced shoulder joint tracking.