Developing a 3-Dimensional Kinematic Model of the Hand for Ergonomic Analyses of Hand Posture, Hand Space Envelope, and Tendon Excursion.

Abstract

Ergonomic analyses of hand function remain a challenge for engineers and designers. The hand strength is closely related to hand posture, which is one of the major determinants of the required space for the hand during manual tasks. The hand posture is also imperative to estimate tendon excursion, because tendon displacement is determined by the joint angles of the fingers. This dissertation reports the development of a 3-D kinematic model that predicts hand posture during gripping cylindrical objects using power and pinch grips, and its application to estimating hand space envelope and tendon excursions. The following objectives were attained: • A 3-dimensional kinematic model of the hand was developed to predict hand posture using a contact algorithm. The model gave a reasonable prediction of hand posture for both power grip (R2 = 0.76) and pulp pinch grip (R2 = 0.88) • Hand space envelopes during a hose placement task were estimated using the kinematic model of the hand. The simulation results show good agreement with measured data with an average 17% underestimation of sectional areas. The simulated space envelopes were affected by grip type (pinch grip requires 72% more sectional areas than power grip), method (rotation method requires 26% more sectional areas than straight method), and hand size (95% male hand requires 44% more sectional areas than 5% female hand). • Finger movements during grasping differently sized objects were characterized quantitatively using spatial and temporal variables, which can be applied to the model that predicts hand posture using a contact algorithm. • Normalized cumulative tendon excursion of both FDP and FDS tendons significantly differentiated the risk levels of MSDs.

The outcomes of this study can be useful to engineers and designers in the design and analysis of manual tasks.