E. CONCLUSION


The Stewart Platform-type manipulator has been described as a platform for a CABG surgery device on a beating heart. Manual surgery on a beating heart represents a major difficulty for surgeons if the heart is not restrained. A robotic device would hel p the surgeon perform this operation by maintaining a constant pose between the telerobotic instruments and a target on the heart surface. The Stewart Platform-type manipulator has better precision and stiffness, and smaller overall dimensions than equiva lent conventional serial-link manipulators. Its small workspace is large enough to carry out surgery. The simplicity of its inverse kinematics makes it well suited for real time trajectory calculation with a high update rate. A modified version of this ty pe of manipulator, called Stewart Platform with Fixed Actuators (SPFA), appears to be a more appropriate option for high-speed operation with small overall dimensions. This paper gives equations for the inverse kinematics and a procedure for obtaining for ward kinematics. The dimensions of the manipulator are determined by minimizing the overall size while keeping the structure away from the singular positions. The sensitivity of the platform pose is analyzed as a function of the actuator step size and the platform and base shape. Simulations have shown that the calculated dimensions are valid for the required workspace. Finally, practical aspects of building such a device are considered and it is shown that required motion can be achieved using readily av ailable actuators.