Due to the urgent need for high precision surgical equipment for minimally invasive spinal\nsurgery, a novel robot-assistant system was developed for the accurate placement of pedicle screws\nin lumbar spinal surgeries. The structure of the robot was based on a macro-micro mechanism,\nwhich includes a serial mechanism (macro part) and a bi-planar 5R parallel mechanism (micro part).\nThe macro part was used to achieve a large workspace, while the micro part was used to obtain\nhigh stiffness and accuracy. Based on the transfer function of dimension errors, the factors affecting\nthe accuracy of the end effectors were analyzed. Then the manufacturing errors and joint angle\nerror on the position-stance of the end effectors were investigated. Eventually, the mechanism of the\nstrain energy produced by the deformation of linkage via forced assembly and displacements of the\noutput point were calculated. The amount of the transfer errors was quantitatively analyzed by the\nsimulation. Experimental tests show that the error of the bi-planar 5R mechanism can be controlled\nno more than 1 mm for translation and 1ââ??¦ for rotation, which satisfies the required absolute position\naccuracy of the robot.
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