Mechanism Design, Moiton Control And Kinematic Calibration Of A Serial-Parallel HIFU Prototype Machine For Cancer Treatment

This paper introduces robotic technology into the design of HIFU (HIFU –High Intensity Focused Ultrasound) treatment machine and puts forward a serial-parallel HIFU cancer treatment prototype based on 3PRS parallel mechanism. Both nominal and practical kinematic models have been set up with respect to the existance of kinematic errors. Analytical resolution has been obtained according to the 3PRS mechanism mobile platform normal vector in the form of elementary functions by the derivation of nominal inverse kinematic equations. Control system of this machine takes Pmac (Programmable Multi-Axis Card) as its hardware kernel. Motion control works in a 2-grade interpolations mode, in which exponential pre-acceleration/deceleration law is employed for rough interpolation. Precise interpolation is fulfilled by linear mode and PVT mode specificly. Rough interpolation sample time is about half of the time that each motor axis accelerates to its maximum speed by its maxium acceleration. Motion codes processing and communication workload could be lowered down while overall performance be ensured. Interpolation accuracy analysis has been carried out according to above two motion control modes by singularity value analysis under classical movement modes. Results show that selected interpolation parameters are reasonable and effective. With theoretical works above, this paper puts forward a constraint plane normal vector evaluation method which is based on the motion constraints of auxiliary cap. Together considering about self kinematic calibration method for robots, this paper carried out kinematic calibration for the 3PRS paralle mechanism in studied serial-parallel HIFU treatment machine. Numeric simulations show that kinematic parameters could be reasonably approximated by optimization calculation for two different calibration experiment configurations which tests or does not test constraint plane normal vectors. Practical calibration experiments were carried out without any measurement of constraint plane normal vectors. Kinematic parameters have been achieved for practical 3PRS paralle mechanism in the prototype machine without measured constraint plane normal vectors.