Grinding Force Control of Polishing Cubic Zirconia Gem by an Automatic Faceting Machine

Abstract

This research work is to develop a controller that combines the position and indirect force control for the gemstone polishing process. The polished gemstones are attached to the end of drop-stick of the Chula Automatic Faceting Machine. The Chula Automatic Faceting Machine has 4-axis high precision motion control and the other 2-axis for spindle and crank motion. Many gemstones (number of gemstones will depends on the size of the gemstone) can be grinded and polished simultaneously with the result of uniform size and quality. In this research work, the controller is developed based on PID motion control. The reference position of the controller for the grinding process is obtained based on the compliance force control technique with known compliance model. This reference position will specified the pressing force for the grinding process indirectly. The controller developed in-house is used for testing with Cubic Zirconia gemstone which the hardness is 8.5 Mohs. The compliance model and appropriate parameters including the minimum and maximum boundary of polishing process can be obtained experimentally. Then all parameters obtained from the experiment can be used in the controller. The uniform size and quality of the multi-stone grinding and polishing process can be obtained with this controller.