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Workspace of Human Limbs

Forearm Workspace

Consider the forearm modeled as a 4-DOF system, where the spherical joint at the shoulder is modeled as three intersecting revolute joints and the elbow as a revolute joint. This is consistent with published results except that we have not considered the wrist joint (which is an additional 3 revolute joints) as fixed and we have limited the motion of the shoulder to rotational. It should be noted that the most difficult and the least successful modeling of a major articulating joint has been the shoulder complex because of the lack of appropriate biomechanical data as well as the anatomical complexity of the region. Fig. 1a depicts the joint motions to be modeled where each joint is given an independent coordinate and Fig. 1b depicts the equivalent kinematic skeleton of the system where z-axes have been located per the D-H representation method.

Fig. 1 (a) A schematic of the forearm (b) Kinematic modeling of the forearm as a spherical joint and a revolute joint

For an adult male, typical joint ranges are measured as follows: , , , and .

Fig. 2 Two cross-sectional views of the workspace of the forearm

Fig. 3 Depicting the workspace and barriers with respect to the torso

Finger Workspace

Consider the workspace of a point located at the tip of the index finger as shown in Fig. 5a. The kinematic motion of the finger is modeled as four revolute joints, two of which intersect and shown in Fig. 5b. Limits for the finger joints are as follows: , , , and . The complete workspace (every point touched by P) is shown in Fig. 6.

Fig. 4 (a) A schematic of a finger (b) Kinematic modeling of the finger as four revolute joints

Fig. 5 Workspace of the finger