Estimating Finger Joint Motions Based on the Relative Sliding of Layered Belts

Abstract

This article introduces a new method for measuring finger joints’ motion based on the relative sliding motions of belts placed on the finger. Conventional mechanical methods used in wearable devices for measuring hand motions, such as a method using resistive sensors, require calibration for the difference in the fingers’ shapes of individuals. In contrast, the proposed method measures the metacarpophalangeal (MP), proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints flex motion of a finger except for the thumb without the above individual calibration using the difference in the sliding amount of belts on the finger surface. The simple equations show that the relative sliding amount of belts is proportional to joint angles with a factor of the belt thickness. Therefore, the method only need to know the belts’ thickness beforehand to calculate the joint angles from the relative belt positions but not the fingers’ shapes. Experiments with a prototype showed that the proposed method estimated the joint motion of the finger model driven by servomotors with an accuracy of less than 1° in three kinds of motions. The device was in an early stage of development as a data glove, but the accuracies were comparable to other wearable devices. The layered belts mechanism proposed here can provide an option to design a device to realize simplified hand motion measurement by eliminating cumbersome calibration processing for each execution. Furthermore, the simple measurement principle also has an advantage in robustness to noise, such as the drift seen in the devices using inertial measurement units (IMUs).