Backlash In Cycloidal Gearbox

Tentative title Design and development of a backlash-free cycloidal gear reducer

Introduction Cycloid speed reducers have found wide applications in the automation field such as industry robots, machine tools and automatic machinery. Compared to planetary gear reducers, cycloid gear reducers possess better characteristics. They are high transmission accuracy, large reduction ratio, great load capacity, high efficiency, low backlash, long service life and high shock load capacity. The state of technology and research topics on cycloid gearbox The research and development study conducted by various researchers on the cycloid speed reducers have covered the following topics 1. Operating principle 2. Conditions for non-undercutting manufacturing 3. Force analysis and efficiency 4. Development of new mechanisms The research problem in this study All the gear drives have certain amount of backlash which is undesirable in applications requiring high positional accuracy. Examples of such applications are in the automation field such as industry robots, machine tools and automatic machinery. So there is a need to develop a cycloid gearbox with zero backlash. The tentative title is fixed based on the various research papers on different aspects of cycloid gearboxes and backlash of planetary gearboxes. The main objective of this study is to design, analyse and develop a high efficient cycloid gear reducer with minimum backlash. The literature survey In the design of the cycloid speed reducer, designers always consider certain objectives such as efficiency, weight, load capacity, contact strength depending on the requirements. Also, there are interactions and constraints between these objectives. Jian Wang [1] carried out an optimization methodology based on genetic algorithm. The goal of the study was to simultaneously minimize volume and maximize efficiency. The research results can help designers to employ for minimum material and cost by fulfilling high efficiency and other performance requirements. Cycloid gear drives have some inherent drawbacks namely, backlash and torque ripple which lower the performance of a drive in high precision and high speed applications. Backlash and torque ripple are caused directly by the existence of machining tolerances. They are usually inevitable due to many practical considerations such as precision of machine tools, prevention of jamming conditions, and application of lubricants, etc. Very slight machining tolerance will cause a significant amount of backlash in the joint. If this

mechanism is used as a joint transmission in a robot arm, the resulting positional error would be unacceptable [2]. The work done by Wan-Sung Lin [3] presents the new design of a two-stage cycloidal speed reducer. Two new structures of two-stage cycloidal speed reducers were enumerated after topological analysis. A new configuration with the least number of links and joints was chosen to establish the design procedure and a mock-up was fabricated to validate the feasibility of this type of two-stage cycloidal drive. Modifications of the cycloidal gear profile and transmission errors were analyzed quantitatively. It was shown that a smaller quantity of modification in a single type of modification yields smaller kinematic errors. Based on the results obtained, this new cycloidal drive is realizable as a compact, high speed reduction ratio, and high accuracy speed reduction device. In the work done by Bingkui Chen [4], a new cycloid drive with double contact lines between one tooth pair was generated by applying double-enveloping theory in cycloid drives. The meshing equation, tooth profile equation, meshing line equation, and the induced normal curvature formula for this new cycloid drive are established and derived. The author made the physical prototype and the transmission error of the prototype was also tested. A nonlinear manipulator joint model with planetary gear train transmission was developed in the research conducted by Tianfu Yang [5]. In this model, the time-variant stiffness of planetary gear train and the backlash were taken into consideration. The stiffness of the equivalent model was built based on the gear parameters and meshing phase relationship. The backlash effect was modeled as an alternate engagement mechanism. The backlash was the main source of positioning error and impact. The backlash could not be avoided. Hence, precision modeling and manufacturing technology in controlling backlash is critical in precision manipulator systems. The study by Chiu-Fan Hsieh [6] constructed an analytic model of system dynamics in a cycloid reducer with a small tooth difference. Specifically, taking a transmission ratio of 17 as an example, it analyzed both free-pin and fixed-pin designs to show the shortcomings of traditional designs. It then proposed a non pin design that improved on these shortcomings, one in which the pinwheel is replaced by a cycloid internal gear. It determined the parameter design range of non undercutting. The results indicated that appropriate design parameters could indeed improve on the shortcomings of the traditional design.

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References Jian Wang, Shanming Luo, Deyu Su, “Multi-objective optimal design of cycloid speed reducer based on genetic algorithm”, Mechanism and Machine Theory 102 (2016) 135–148 Yang D. C. H., Blanche J. G., “Design and application guidelines for cycloid drives with machining tolerances”, Mech. Mach. Theory, Vol. 25, No. 5, pp 487-501, 1990 Wan-Sung Lin, Yi-Pei Shih, Jyh-Jone Lee, “Design of a two-stage cycloidal gear reducer with tooth modifications”, Mechanism and Machine Theory 79 (2014) 184– 197 Bingkui Chen, Hui Zhong, Jingya Liu, Chaoyang Li, Tingting Fang, “Generation and investigation of a new cycloid drive with double contact”, Mechanism and Machine Theory 49 (2012) 270–283

5. Tianfu Yang, ShaozeYan, ZengyaoHan, “Nonlinear model of space manipulator joint considering time-variant stiffness and backlash”, Journal of Sound and Vibration 341 (2015) 246–259 6. Chiu-Fan Hsieh, “Traditional versus improved designs for cycloidal speed reducers with a small tooth difference: The effect on dynamics”, Mechanism and Machine Theory 86 (2015) 15–35