A study on the dynamics and control of a CMM for high-speed operations.

摘要

Coordinate Measuring Machines (CMMs) are frequently used for inspections in production lines. Because of the degree of accuracy required for the inspection, machine vibration during measurement is very undesirable and has to be minimized. Vibration in the structure of a CMM comes from several sources such as the machine's own motion, vibration transmitted through the shop floor, and so on. The scope of this study covers the vibration caused by the CMM's own motion. This type of vibration is generally reduced by using low acceleration/deceleration motion profile to minimize the excitation of the machine as much as possible. The problem with this method is the low operating speed, which may cause a bottleneck in the production line.; This research aims to develop control schemes that help minimize the residual vibration of the CMM. The motivation is that, for a given acceptable vibration limit, the acceleration and deceleration of the machine can be increased if the residual vibration can be reduced. This can help increase productivity.; The research was divided into two stages. The first stage was the study of the machine's dynamics. Theoretical models were constructed including a simple mathematical model, a 3D model and finite element models. The theoretical study concluded that the dynamics of the machine were highly dependent on its configuration. Therefore, the study focused on both single-axis operation where the dynamics did not change much during the motion, and multi-axis operation where the dynamics during the motion changed dramatically in response to the change in machine's configurations. Input shaping method was implemented for the vibration suppression of the machine in both cases. The evaluations were made by experiment. In single-axis operation, the proposed controller could reduce the residual vibration magnitude by 67--82%. In multi-axis operation, as much as 62--85% vibration reduction was achieved.