Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
Evaluation of the use of parallel kinematic mechanisms for robotic human wrist
Submission Author:
Thales Travaglini Galanti , SP
Co-Authors:
Thales Travaglini Galanti, Chi Nan Pai
Presenter: Thales Travaglini Galanti
doi://10.26678/ABCM.COBEM2021.COB2021-0553
Abstract
Robotic upper limbs have been researched for several applications, such as biomechanical prosthesis, parts of an android, robotic cookers, etc. Among all the joints of human upper limb, the wrist joint stands out as an extremely difficult one to be replicated by using conventional motors. This is because it presents two rotational movements with the same rotational center, which is almost impossible to be replicated by using rotary motors. In the present work we evaluated the use of parallel kinematic mechanisms to replicate the movements of the human wrist, which are: flexion/extension and adduction/abduction of the hand, and the combination of both, called circumduction. Three designs were evaluated. Two of them use three linear actuators, and the third one uses four linear actuators. The fundamental difference between the first two designs is the position of the rotational center, which is also the center of movement of the hand. In the first one the center is located at the barycenter of the equilateral triangle formed by the linear actuators, while in the second one it is located at the intersection between two orthogonal planes, where one plane contains one actuator and is equidistant to others two, and one plane is located equidistant to all three actuators. A computer-aided design (CAD) software was used to simulate the movements of all mechanisms, and mechanical equations were delivered from the CAD model to calculate the rotational angles and the output torques. As a result, the first two mechanisms present a total angular variation of 43.6 degrees and a torque of 1 Nm for adduction/abduction, 49.6 degrees and a torque of 1.15 Nm for flexion/extension. The first one presented a little displacement of the rotational center in axial direction, while there is no variation in the position of the rotational center in the second mechanism. The third mechanism, with four linear actuators, achieved 52 degrees of total angular rotation in both adduction/abduction and flexion/extension, with a torque of 1.64 Nm. Therefore, for the movement of adduction/abduction, our designs achieved, respectively, 67.1 % and 80 % of the angular movement of human wrist, and for the movement of flexion/extension, 33.1 % and 34.7 % of the human wrist.
Keywords
Robotic upper limb, Artificial wrist, Parallel kinematic mechanism, Biomechanic, Linear actuator
