Abstract
The kinematics of a two rotational degrees-of-freedom (DOF) spherical parallel manipulator (SPM) is developed based on the coordinate transformation approach and the cosine rule of a trihedral angle. The angular displacement, angular velocity, and angular acceleration between the actuators and end-effector are thus determined. Moreover, the dynamic model of the 2-DOF SPM is established by using the virtual work principle and the first-order influence coefficient matrix of the manipulator. Eventually, a typical motion plan and simulations are carried out, and the actuating torque needed for these motions are worked out by employing the derived inverse dynamic equations. In addition, an analysis of the mechanical characteristics of the parallel manipulator is made. This study lays a solid base for the control of the 2-DOF SPM, and also provides the possibility of using this kind of spherical manipulator as a 2-DOF orientation, angular velocity, or even torque sensor.
Highlights
Compared with traditional serial manipulators, the parallel manipulator is a more promising branch of robotic mechanism which has the distinct advantages of high stiffness, high precision, large load-weight ratio, high speed, and high acceleration
The kinematics of a 2-DOF spherical parallel manipulator (SPM) was elaborated based on the coordinate transformation approach and cosine rule of a trihedral angle
The dynamic model of the parallel manipulator were established by employing the virtual work principle
Summary
Compared with traditional serial manipulators, the parallel manipulator is a more promising branch of robotic mechanism which has the distinct advantages of high stiffness, high precision, large load-weight ratio, high speed, and high acceleration. Gosselin and Angeles proposed a spherical 3-DOF parallel manipulator with three coplanar actuators [9] wherein the revolute joint axes of the base and mobile platforms intersect at one point. This special structure results in its preferable symmetry in Sensors 2016, 16, 1485; doi:10.3390/s16091485 www.mdpi.com/journal/sensors. The miniaturization of this mechanism can be used as 2-DOF orientation and force/torque sensors by replacing the servo actuator with optical encoders and strain load cells, respectively The advantage of this type of sensor lies in its extra load capacity; for instance, it will be able to carry a heavy instrument and measure its pitch and yaw angles.
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