A study of The Parameter Calibration And Servo-Control Accuracy of Cartesian-Guided Tripod Machine Tool

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The Cartesian-Guided Tripod Machine Tool (CGT) is a new kind of parallel kinematic machine tool. The CGT has two kinds of functional independent legs, the driving functional leg and the integrated Cartesian guiding/metrology functional leg and ball-joints and universal-joints. Therefore we can separate the metrology loop and the driving mechanisms loop. First to be aimed at the Acc/Dec planning relation with Jacobian matrix of the Global coordinate and Local coordinate, and to analyze the velocity/acceleration/jerk values, and to discover global coordinate and local coordinate maximum ratio is 1.73. The compliant components such as ball- and universal- joints and driving system (including axial and torsional of the ballscrew shaft, ballscrew supporting bearing and nut) are all considered in the dynamic model. The servo-controlled contouring errors caused by the nonlinear dynamics, gravity effect and nonlinear compliance are evaluated. The space can be divided into four quadrants, and the Z axis vibration error and contouring error in the first and second quadrants is bigger than that in the third and fourth quadrants. The auto calibration model is formulated base on the volumetric error model and the gravity term weighs in calibration model, in order to expect fast and correct to calibration eleven parameters, and finally the estimated error will be smaller than 0.04µm.