Kinematical analysis of the linkage of the index finger on the basis of the posture measurement.

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The purpose of the present study is to investigate how the kinematic parameters of the index finger (i.e. the length of the link, and the cooperation between the DIP joint angle and the PIP joint angle) influence the manipulability of the tip of the index finger. The flexion and extension of the index fingers of twenty subjects who were 22-25 years old were measured using a three dimensional position measurement method. The kinematic model of the linkage of the index finger in the tip pinch posture of the thumb and index finger was developed using the measurement data. The cooperation between the DIP joint angle and PIP joint angle of the index finger in the flexion and extension was also obtained using the three dimensional measurement method. The transformation from the finger tip velocity to the joint angular velocities in the tip-pinch posture was obtained using the kinematic model of the index finger and the cooperation between the DIP joint angle and PIP joint angle. Using the Mo … More ore Penrose inverse matrix instead of the cooperation between the DIP joint angle and PIP joint angle enabled us to obtain the transformation from the finger tip velocity to the joint angular velocities. In three tip-pinch postures of the thumb and index finger, the transformation from the finger tip velocity to the joint angular velocities obtained from the cooperation between the DIP joint angle and PIP joint angle was compared with the one obtained from the Moore Penrose inverse matrix. The average ratio of the link lengths of twenty subjects measured in this study was as follows; (the distance between the tip of the finger and the DIP joint axis ):(the distance between the DIP joint axis and the PIP joint axis):(the distance between the PIP joint axis and the MP joint axis)=2.7:2.5:4.8. The cooperation between the DIP joint angle and the PIP joint angle was represented by a gentle sigmoid curve. The transformation from the velocity of the finger tip to the joint angular velocities with the cooperation between the DIP joint angle and the PIP joint angle was very similar to the one with the Moore-Penrose inverse matrix. In the conclusion, it was found that the kinematic parameters of the index finger were determined so that the motion of the finger tip could be controlled by the input of the angular velocities whose magnitude was the minimum in motion. Less