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Gears
Published in Asok Kumar Mallik, Amitabha Ghosh, Günter Dittrich, Kinematic Analysis and Synthesis of Mechanisms, 1994
Asok Kumar Mallik, Amitabha Ghosh, Günter Dittrich
Backlash can be qualitatively defined as the amount of play between a mating pair of gear teeth in assembled condition. Because of manufacturing errors the teeth profiles do not conform exactly to the theoretical involute shapes; the gear dimensions and the center distance are also never exactly equal to the specified values. Besides these, any change in temperature also results in variations in the gear dimensions. Because of all these, the tooth thickness of each gear is so chosen that contact takes place on one face only. Otherwise, there is a possibility of jamming, overheating, damage and objectionable noise. The small gap between the noncontacting surfaces of the teeth of the gears is the backlash. If the directions of rotation of the gears do not change, backlash does not create any problem. However, excessive backlash may lead to not only inaccuracy in the system, but also noise and impact loading. Choice of proper amount of backlash is, therefore, extremely important.
Design and Kinematic Analysis of Gears
Published in Kevin Russell, Qiong Shen, Raj S. Sodhi, Kinematics and Dynamics of Mechanical Systems Implementation in MATLAB® and Simmechanics®, 2018
Kevin Russell, Qiong Shen, Raj S. Sodhi
Backlash is the clearance measured along the pitch circle between the nondriving surfaces of mating gear teeth (in general, it is the amount of play between mating teeth). Figure 8.13 illustrates mating gear teeth with corresponding backlash labeled. A limited amount of backlash is necessary to prevent the mating gear teeth from binding with each other. Backlash also helps to enable gear-tooth lubrication because it provides clearance for lubricant flow. Although it is important to include clearance between mating gear teeth for proper gear operation, excessive backlash can produce inaccurate gear motion as well as large dynamic loads. AGMA provides tables of recommended backlash ranges [4].
Power Transmission and Gearing Systems
Published in Wei Tong, Mechanical Design and Manufacturing of Electric Motors, 2022
Backlash is defined as the clearance between mating gear teeth, which compromises positioning accuracy and repeatability in precision systems (Figure 9.6). This implies that the output shaft in a gearing system can freely rotate bi-directional at a small angle without the input shaft moving. In fact, backlash is resulted from a number of factors, for instance, operation inability of machine tool, manufacturing imperfects, mounting tolerances, bearing play, and deflected workpiece under loads. For a gearing system that repeatedly changes the direction of rotation, backlash can lead to the loss in contact between the gear teeth and thus make the driven system difficult to achieve accurate positioning.
Experimental assessment and feedforward control of backlash and stiction in industrial serial robots for low-speed operations
Published in International Journal of Computer Integrated Manufacturing, 2023
Runan Zhang, Zheng Wang, Nicola Bailey, Patrick Keogh
It is worth considering stiction and backlash altogether for high-precision robotic manufacturing because both are closely associated with joint reversal. At low robot movement speeds, viscous friction is insignificant, and the static friction and the Stribeck effect become the main error sources of friction. For backlash, even though the induced errors persist throughout an operation, the error propagation at joint reversal is more problematic, creating unsatisfactory surface finish at corners on machined workpieces (Wang, Zhang, and Keogh 2020). Both stiction and backlash may have already been considered during the design and manufacturing of modern industrial robots to achieve moderate accuracy, but residual errors from the control action of the robot controller remain significant for high-precision robotic manufacturing. Therefore, addressing these challenges using feedforward control in conventional industrial serial robots, without using extra sensors, would be especially attractive to attain higher robot accuracy for large volume manufacturing, where joint reversals are inevitable.
Assessment of contact forces and stresses, torque ripple and efficiency of a cycloidal gear drive and its involute kinematical equivalent
Published in Mechanics Based Design of Structures and Machines, 2022
Hamza Tariq, Zhaksylyk Galym, Andas Amrin, Christos Spitas
Besides, the cycloidal teeth profile can lead to the primary limitations due to dimensional tolerances such as torque ripple and backlash (Yang and Blanche 1990). The backlash is defined as an angular deviation between the actual rotational angle of the planetary gear and the rotational angle of a cycloidal tooth of pin-holes (Li et al. 2017b). A study by Blagojevic (2014) examined the impact of deformations and clearances of cycloid disk teeth on the efficiency of the drive. Moreover, another study by Blagojevic et al. (2012) investigated the impact of frictional torque on the performance of the gear. It should be noted that the study ignored frictional interfaces in bearings or the HSS. Han and Guo (2016) investigated the transmission accuracy of the cycloidal drive with assembly and manufacturing errors, along with bearing clearances. Tran, Pham, and Ahn (2016) utilized the finite element method and kinematic analysis to study the loss of motion in cycloidal drive and showed that tolerance and torsional stiffness has a significant impact on the gear loss of motion. Lin, Chan, and Lee (2018) propose a technique for analysis of kinematic error and tolerance design in the cycloidal gear. Theory of gearing was used for investigating the relationship between the following parameters: geometry, manufacturing, and precision performance. These studies have shown that the the primary consequence of the phenomenon is the reduction of mechanical efficiency of the drive, which is significantly magnified in high-precision high-speed applications.
Modelling and identification of nonlinear cascade systems with backlash input and static output nonlinearities
Published in Mathematical and Computer Modelling of Dynamical Systems, 2018
Backlash is one of the most important nonlinearities that strongly affect the chosen control strategies in industrial processes and its presence gives rise to inaccuracies in the position and velocity. This nonlinearity, which can be classified as a dynamic (i.e. with memory) and hard (i.e. non-differentiable) one, commonly occurs in mechanical, hydraulic and other components, e.g. bearings, gears. The backlash can arise from unavoidable manufacturing tolerances or sometimes can be deliberately incorporated in the system in order to cope with thermal expansion.