Research on Meshing Characteristics of Strain Wave Gearing with Three Different Types of Tooth Profiles

Congbin Yang,Honglie Ma,Tao Zhang,Zhifeng Liu,Yongsheng Zhao,Qiushi Hu 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.22 No.10

Harmonic drive (HD) is one of the core components of the robot joint. Studies show that tooth shape design and meshing characteristics of the HD directly affect the motion control accuracy and vibration characteristics of the robot. In the present study, common coordinate systems are established for three tooth profiles to analyze the differences between them. To this end, expressions for the double circular arc common-tangent tooth profile (DCTP), cycloid common tangent tooth profile (CCTP), and the involute tooth profile (ITP) are established in the same coordinate system. By applying the envelope conjugate theory, the conjugate existent domain (CED) and conjugate tooth profile (CTP) of the HD transmission are solved independently for each profile. Furthermore, the influences of tooth profile parameters on both the CTP and CED are analyzed. Obtained results show that both the DCTP and CCTP have more robust envelope processes when compared with the ITP. Moreover, it is found that both profiles can achieve the second conjugate and two-point conjugate engagement through applying variations in the tooth shape design parameters. It is concluded that meshing performances of the DCTP and CCTP are better than that of the ITP, providing guidelines for the future development of the harmonic reducer tooth shape design.

Analysis of the Partial Axial Load of a Very Thin-Walled Spur-Gear (Flexspline) of a Harmonic Drive

Congbin Yang,Qiushi Hu,Zhifeng Liu,Yongsheng Zhao,Qiang Cheng,Caixia Zhang 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.21 No.7

Harmonic drives are the core components to enable movement in industrial robots. Unfortunately, the deformation of flexspline causes obvious partial axial load on gear engagement. This synthetic error leads to a series of additional problems, such as the deterioration of transmission quality, and the reduction of both precision and fatigue life. This study focuses on a harmonic drive with a double circular-arc tooth profile. A coordinate transformation is carried out based on the kinematics of harmonic drives. On this basis, the conjugate tooth profile of a circular spline is derived. A simulation model is developed based on the motion relationship for harmonic transmission. The effect of inhomogeneity of the load distribution on the surface of the gear teeth was investigated using the partial axial-load index. The effect of different factors on the partial axial load is analyzed. To reduce the effect of partial axial load of flexspline, we select a suitable material and wall thickness. For a certain practical range, both tooth width and chamfering of the flexspline teeth help reduce the partial axial load and increase the flexspline length. These conclusions enable improvements of future designs of reliable flexspline.

Calculation of Tooth Thickness Errors and Its Adjustment on Meshing Backlash of Harmonic Drive

Congbin Yang,Honglie Ma,Tao Zhang,Jigui Zheng,Zhifeng Liu,Qiang Cheng 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.24 No.2

Meshing backlash mainly determines the transmission accuracy of harmonic drive, which is an important index in design. In this paper, a design method for short tooth involute profile is proposed. By intercepting part of the tooth profile, meshing interference of the addendum can be effectively avoided. Based on the dimensions of over pins of circular spline and flexspline, a calculation method of tooth thickness deviation is proposed, and the positive and negative tooth thickness deviation are defined. Involute functions need not be calculated by this method, which simplifies the solution process. By discretizing the teeth profile points of circular spline and flexspline, a calculation method of time-varying backlash is proposed, the variation of backlash in meshing in and out is analyzed, and the influence law of tooth thickness deviation on backlash is studied. On this basis, an algorithm for adjusting the radial deformation to compensate for the backlash is proposed. The results show that the excessive backlash in the meshing area can be reduced by increasing the radial deformation. When meshing interference occurs, the interference-free meshing can be realized by decreasing the radial deformation.

Analysis and Optimization of an Internal Feedback Hydrostatic Turntable Oil Pad Power Consumption Based on Finite Difference Method

Congbin Yang,Shuaihua Shao,Yanhong Cheng,Zhifeng Liu,Yongsheng Zhao 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.24 No.12

The hydrostatic turntable is a critical component of numerous CNC machine tools, as it performs a supporting function and enables precise rotary motion. To ensure that high-precision CNC machines can operate under heavy loads, it is imperative to minimize power consumption. The power consumption of a hydrostatic turntable is affected by various factors, such as oil viscosity, initial oil film thickness, and oil pad structure. This study focuses on investigating a hydrostatic turntable with internal feedback. The Reynolds equation of the sector oil pad is solved using the finite difference method to establish the pressure distribution model. Subsequently, the study examines the power consumed by the axial oil pad at different initial oil film thickness, lubricating oil viscosity, and sealing edge width. To minimize power consumption caused by the axial oil pad, this paper employs the genetic algorithm to identify optimal design parameters within specified constraints. Additionally, the load-bearing performance of the optimized axial oil pad is checked to ensure that the load-bearing capacity and stiffness meet the requirements. Finally, the use of simulation software for oil pads in finite element simulation can preliminarily demonstrate the reliability of the proposed method.

Tangential Damping Model of Bolted Joint with the Physics-Based Friction Coefficient

Yongsheng Zhao,Hongchao Wu,Congbin Yang,Zhifeng Liu,Qiang Cheng 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.22 No.5

The stiff ness and damping modeling of joint surfaces are important for analyzing the dynamic characteristics of bolted joints, which has a great influence on the working precision of the machine tool. In this paper, a damping model is presented to predict the tangential damping of the joint accurately. The fractal theory is introduced to characterize the rough contact surface by using fractal dimension D and fractal roughness parameter G. For each micro-contact, the contact region can be divided into stick section and slip one. The energy dissipation of the micro-contact, which can be described as the tangential damping of bolted joint, emerges in the slip section. The physics-based friction coefficient is introduced to define the energy dissipation function based on the relationship between the deformation of micro-contact and the normal pressure. The energy dissipation factor and the proportional damping of the micro-contact can be obtained. The total tangential damping of bolted joint can be obtained by integrating the whole contact surfaces. Experimental set-up is designed to verify the proposed model. Compared with the constant friction coefficient damping model, the results show that the proposed model can more accurately describe the tangential damping of bolted joint.

Experimental studies on torsional stiffness of cycloid gear based on machining parameters of tooth surfaces

Zhifeng Liu,Tao Zhang,Yida Wang,Congbin Yang,Yongsheng Zhao 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.6

Estimating the torsional stiffness has always been the primary issue in analyzing the dynamic characteristics of cycloid gears. The traditional method of obtaining torsional rigidity involves calculating the ratio of the input torque and rotation angle, treating the deformation of cycloid gear as a black box. In order to thoroughly understand the rotation angle caused by the local contact deformation of each cycloid pin gear, a Majumdar–Bhushan contact model and the finite element method are combined to express the normal contact stiffness. By multiplying the normal contact stiffness of each pin gear and the arm of normal contact force, the torsional stiffness of the cycloidal pin wheel system can be calculated. Experiments are conducted to establish the relationship between the torsional stiffness and roughness parameters of the machined tooth surface. The effect of input torque on the torsional stiffness has also been analyzed. This study formulates a relationship between the torsional stiffness and surface characteristics of cycloid gears, which can help improve their design and manufacture in the future.

Establishment and analysis of thermo-fluid-solid coupling model of ink roller-ink under dynamic pressing contact

Hongyan Chu,Yingjie Hong,Caixia Zhang,Qi Chen,Ruilong Ding,Congbin Yang 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.7

In order to improve the printing quality, this study focused on the thermo-fluidsolid coupling process of ink roller-ink. One of the highlights of this study is to consider the influence of temperature on the rubber hyperelastic parameters, viscoelastic parameters, and ink viscosity. The other highlight is to improve the elastohydrodynamic lubrication theory and Hertz contact theory through the rubber elastic modulus, which is determined by the relaxation curve considering the temperature and working conditions. Furthermore, based on the improved theory, the thermo-fluid-solid coupling model of ink roller-ink was established. Finally, the effect of temperature on the coupling process was analyzed. The results show that under the working conditions, with increasing temperature from 20 °C to 40 °C, the contact half-width increases from 4.2335 mm to 4.4701 mm, and the minimum ink film thickness decreases from 0.5097 mm to 0.1410 mm, and the maximum ink pressure decreases from 0.6802 MPa to 0.6618 MPa.

Trajectory Planning with Minimum Synthesis Error for Industrial Robots Using Screw Theory

Zhifeng Liu,Jingjing Xu,Qiang Cheng,Yongsheng Zhao,Yanhu Pei,Congbin Yang 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.19 No.2

This work aims to propose a trajectory planning technique to minimize the end-effector synthesis error for industrial robots, while obtaining a stable movement. With ER3A-C60 robot as a research subject, the kinematic and dynamic models are established by using screw theory and Kane equations, and based on that, the end-effector synthesis error is modeled by considering the effects of interpolation algorithm and flexibilities of all joints. The septic polynomial is used to interpolate the via points in each joint space to obtain a stable movement. Finally, the PSO algorithm with suitable parameters is applied to find the minimum synthesis error under kinematic and dynamic constraints. The results show that the optimal synthesis error decreases by 88.94% compared with the initial one, the angular parameters are all far less than the limitations of joints and the optimal movement has a high stability, and this optimal trajectory has better overall performance than that based on the previous technique (with the minimum total motion time). The main contribution is that the proposed trajectory planning technique can significantly improve the tracking precision of the end effector while controlling the motion time within a given span under the requirements of continuous path control.