Linear vs Rotary A Tech Authority（线性和旋转技术权威）.pdfVIP

Linear vs. Rotary Is thermal expansion relevant? Rewritten By Craig D’Ambrosio A Tech Authority, Inc. (909) 972-7520 (Based on “Accuracy of Feed Axes by Dr. Jan Braasch, Dr. Johannes HEIDENHAIN GmbH) The discussion as to whether linear encoders or rotary encoders are the best solution for measurement on NC machine tools is experiencing quite a comeback. This is due, in part, to the post recession idea that machine tool manufacturer’s need to cut costs to maintain machine sales. Could it be that too much attention has been put on cost, and too much reliance on new technology? Under the pressure of such opinion, one can easily come upon the idea of cutting costs by leaving linear encoders off the lowest- priced models, and then offer them as an accuracy-enhancing optional feature. This line of thought is reinforced by the drive industry where a large portion of the new servo motors now feature built-in rotary encoders. With this trend, there is now a decision of choosing between a ballscrew/rotary encoder system, or a linear encoder solution for position control. In the heat of such decisions, one should not forget to consider the problems known to be involved with position measurement using a rotary encoder/ballscrew system. In order to make an educated decision, you must first have a general understanding of mechanical feed drive systems. Although machine tool designs vary, their feed drive systems remain largely standardized (Fig. 1). In almost all cases, the recirculating ballscrew has established itself as the solution for converting the rotary motion of the servo motor into linear slide motion. The ballscrew is normally fixed at only one end with preloaded ball bearings, which take up the axial forces of the slide. Fig. 1. Feed axis drive on milling