Machine Design and Performance Analysis of the Cartesian-Guided Tripod Machine Tool
2003
Hochschulschrift
Zugriff:
91
A new kind parallel kinematic machine tool call Cartesian guided Tripod (CGT) machine tools is proposed in this dissertation. The CGT has two kinds of functional independent legs: the driving functional leg and the integrated Cartesian guiding/metrology functional leg. Because of the separation of metrology function from the driving mechanisms, the metrology loop of CGT is immunized to the geometric-, thermal-, and forced-induced-errors of the driving mechanism. Another feature of the CGT is the kinematic parameters can be auto-calibrated on line. Besides, the CGT has analytic solutions of forward and inverse kinematic models. The CGT can be divided into two basic types: the sliding leg CGT which has constant leg length and sliding joint between the leg and based-frame and the telescoping leg CGT which has variance leg length and fixed joints. The specifications, such as footprint/workspace ratio, velocity/acceleration ratio between the Cartesian coordinate and driving space, required driving strokes, and stiffness are all analyzed and compared of the two types CGT. The telescoping leg CGT has the higher edges in the kinematic categories than the sliding leg CGT. Conversely, the sliding leg CGT has better stiffness than the telescoping leg CGT. The volumetric error model and dynamic model of the telescoping leg CGT are formulated in this dissertation. The kinematic error sources are joint location errors and driving leg initial length errors. The auto-calibration model is formulated base on the volumetric error model and there are only 9 independent kinematic parameters due to well coordinate assignment. Gravity forced error effect and orientation error effect due to imperfect constraint of the guiding system are also considered in the auto-calibration model. 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 motion control is used of the cascaded P/PI controller. The servo-controlled contouring errors caused by the nonlinear dynamics, gravity effect and nonlinear compliance are evaluated. These effects result the slow rate variation errors depending on the platform position and velocity. Due to slow variation, the nonlinear/gravity/compliance effects can be corrected to an acceptable low level by using the high gain servo control.
Titel: |
Machine Design and Performance Analysis of the Cartesian-Guided Tripod Machine Tool
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Autor/in / Beteiligte Person: | Wei-Yao, Hsu ; 許巍耀 |
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Veröffentlichung: | 2003 |
Medientyp: | Hochschulschrift |
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