Study On The Technologies Of Controlling Precision And Supperssing Chatter Vibration For "Zero-transmission" Hobber

"Zero-transmission"is also called"Direct-Drive", namely all the mechanical transmission parts between motor and final executive component are canceled. In machine tool, the typical function components with Direct-Drive include"motorized spindle", linear motor and internal torque motor. Zero-transmission technology provides many advantages for enhancing the machine tool performance, for example, maximally reducing the transmission error, offering the possibility of high-speed cutting, improving the movement sensitivity of the executive components, etc. Currently, this technology has been widely adopted in advanced hobber overseas, and has achieved good effect. However, all the interrelated design principles and technologies are kept as secret severely. In order to break this technology monopoly, cooperating with a Chinese machine tool company, the research group including the author has developed the No.1 CNC hobber prototype based on zero transmission function components in China, and many correlative theories and the technologies have been studied systematically in this process. These study results build a solid foundation for advancing the design and manufacture level of gear cutting machine of China.Applying the zero transmission technology in hobber is neither an onefold research on the zero transmission function components, nor a simple engineering process of replacing this type of function components into machine tool, but needs to solve a series of essential theory and the technical questions in design from whole to part. These problems include not only the particular one in hobber but also the general one in common machine tool. This article mainly discusses the strategies and methods of controlling the precision on a zero transmission hobber, and does some beneficial explorations on the anti-chatter structure optimization.(1) The main influential factors for generating motion precision and their action law are analyzed detailedly on a general CNC hobber, and the results show that the generating motion error also mainly comes from the mechanical transmission parts. Therefore, there's not enough room to improve the generating motion precision under the existing machine frame. Based on it, the action mechanism that zero transmission improves the generating motion accuracy is studied. The study results show that zero transmission has natural dominance in solving this difficult problem. So the key points of the precision-control problem on the zero-transmission hobber should be to control the position-pose precision between the two spindles and improve the ability of anti-disturbance.(2) To realize the precision-control of a machine tool effectively, it is necessary to establish a valid error model of the object machine tool. According to the structure and the motion characteristics of the hobber, a theoretical model is built by combining the multi-body system theory with the gear meshing principle. This model describes the position-pose and motion relations quantitatively between the components in this hobber, and especially, contains the action rule of machine error sources and the relations between the error sources. It is the theory foundation for the precision-control work.(3) Combining the sensitive direction of processing error and the transmission law of source error, a new concept called"the sensitive error in machine tool"is put forward, which is a more influential source errors to final processing precision in the machine tool. According to the idea of fastening main factor, a new machine precision-control strategy to control the sensitive errors is proposed. To realize the sensitivity analysis of machine errors, the theoretical error model of the hobber is simplified to an engineering error model with two sub-models by reconstructing, which separates reasonably the numerous position-pose error parameters, the movement error parameters in middle components from the complex space meshing relation of gear hobbing. This model has the better operability, operational versatility and pertinence. In this paper, the details of how to build and use the two sub-models are introduced, and their feasibility and effect are demonstrated.(4) Based on analyzing and integrating the relative information coming from the domestic and oversea research and taking the anti-chatter structure improvement of machine tool as goal, the regenerative chatter model has been studied systematically. According to the study results, the machine processing system is simplified as a single-degree of freedom (SDOF) chatter model, which only has two elasticity bodies. The new model can make the anti-chatter structure improvement more effective. Based on this model, a new scheme is proposed, in which only the structure of weak component among a machine tool needs to be improved. Then, the optimizing target function, mathematical model and optimizing algorithm are discussed respectively. The experimental research results demonstrate the process and the characteristic during the cutting chatter occurring and expanding, and also the accuracy of relative theories are confirmed basically. Taking the hob spindle system of YK3610 hobber as an example, a simulation test has been done, and the result is satisfactory. (5) In the final part of this paper, some evaluation experiments of the YK3610 prototype at primary stage is introduced. The experiment data has reflected the main performance of this prototype, exposed some extant questions, and provided firsthand information to improve and adjust the machine tool.