VIBRATION CONTROL OF RELATIVE TOOL-SPINDLE DISPLACEMENT FOR CNC LATHE WITH PIPE FRAME STRUCTURE

摘要

A new CNC lathe with a pipe frame bed has been developed. One requested improvement for machine tools is their downsizing by minimizing the number of mechanical parts. Some researchers aim to construct a desktop factory. This trend has been attracting a lot of attention lately in the industrial field. When a machine tool bed is designed using castings and/or welded steel plate structures to comply with this request, it is difficult to ensure space for chip evacuation because of the space limitations of solid body components. This led us to develop another type of structure for machine tools. A pipe frame bed has the ability to solve this problem. As represented by bridge trusses and flexible space structures, truss structures are traditional and fundamental in their design. This structure is expected to have enough space between the truss bars to solve the space problem. However, rigidity is the most significant issue for machine tools. Therefore, the desired rigidity is ensured by the use of diagonal braces. Based on this design concept, a CNC lathe whose frame consists of pipes, joints, and diagonal braces has been developed with enough rigidity and space utility for chip evacuation. From the viewpoint of machine tool usage, the rigidity and stable dynamic characteristics of the structure must be obtained. Then, real-time vibration control theory is applied to the relative displacement between the tool post and the spindle. Active vibration control is used to suppress specific relative vibration modes. In this paper, the effects of vibration control are evaluated by comparing the relative vibratory motion between the tool post and the spindle. Over 50% suppression has been achieved by applying vibration control to the target vibration mode. Additionally, using this control, the machined profile has been improved, and the roundness and harmonic analysis of the workpiece showed over 30% improvement.