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Active compensation using a PZT based table during surface grinding

Authors Yu, Chi Wai
Issue Date 1999
Summary Surface grinding is a fundamental material removal process that involves forces during machining. The forces would cause deformation in the machine tool system and the workpiece. Because of the deformation, the required volume of workpiece material cannot be removed completely, causing an error in the workpiece surface profile. A typical solution to solve this type of problem is to use a method called spark-out. However, the efficiency of the spark-out method is low and the error in the surface profile cannot be eliminated completely within a limited number of grinding passes. In order to improve the accuracy and efficiency, a new method based on an active compensator is proposed and investigated. The compensator is essentially utilizes a method of increasing the depth of cut in order to remove the required volume of workpiece material. In this method, the relationship between the nominal depth of cut and the deformation is established and the effect of deformation during grinding is controlled. In order to realize the proposed method, a workpiece micro positioning table has been designed and manufactured to generate a compensation action. In the workpiece table, a piezoelectric actuator is used. Its fine resolution and no backlash help the workpiece table to achieve very high performance. The design of the workpiece micro positioning table was assisted by using a FEA software called ANSYS and a high stiffness in the workpiece table has been achieved. Because of the stiffness of piezoelectric actuator is only 17N/μm, a capacitive sensor has been used to detect the position of the workpiece table and the position is used as the feedback for closed-loop control of the workpiece table. PID control is applied and good performance has been achieved. The developed workpiece table has a natural frequency of 223Hz and a static stiffness of 43-65N/μm at the comers and a static stiffness greater than 400N/μm at the center under the condition of closed loop control. Experimental testing has been carried out to test the proposed method. The initial workpiece shape prepared was an inclined straight surface with an error of 10μm. The experimental testing shows that the error could be reduced to approximately 2μm after two grinding passes, representing an improvement of nearly 50% in the resulting workpiece surface profile accuracy.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 1999
Language English
Format Thesis
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