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Zero-backlash high precision roller enveloping reducers (ZHPRER) possess a wide array of potential applications in the field of industrial robot because of their high precision and efficiency. This paper presents a pilot study to verify the applicability of this type of reducers in industrial robots. An industrial robot was designed, whose joint reducers were the roller enveloping reducers. A dynamic model for this robot which accounts for the dynamic responses of the reducers was also established using multibody dynamics. This dynamic model was then used for analyzing the dynamic behavior of the joint reducers and the body of the robot under different operating conditions. Simulation results yielded from the developed model were verified by comparing them with the data obtained from experiments. The present study for the first time confirms the evident advantages of ZHPRER for industrial robotic applications. Meanwhile, the proposed dynamic model for the industrial robot provides theoretical support for the subsequent design of error compensation control.

This paper presents an investigation to find out how lubrication parameters affect lubrication characteristics of gear transmission systems for the purpose to acquire enhanced lubrication performance for such systems through design optimization. A novel high precision roller enveloping reducer is selected, and effects of key parameters on its lubrication performance were thoroughly studied. The key parameters include oil viscosity, immersion depth, rotation speed of the worm gear, worm arrangement, and volume of oil recess. Taguchi method was then applied to optimize those parameters to achieve an enhanced lubrication performance in the roller enveloping reducer. The research approach employed for this study can be described as follows: at first, a numerical simulation study was performed and simulation results were validated using experimental data; next, design domains for the key parameters were created over a wide range of values, and the design of experiments (DOE) method was applied to determine how the parametric values affect the lubrication characteristics via numerical calculations; afterwards, analysis of variance (ANOVA) was performed to determine the parametric values that would lead to the optimal lubrication performance. Our results showed that the novel roller enveloping reducer can provide desirable lubrication and meshing performance by applying the optimal parametric values. In our study, the lubrication performance is indicated in terms of churning losses and number of lubrication particles. Effects of the key parameter on them are discussed in this paper. This study presents a design method for screening the optimal parameters for best lubrication performance of gear systems. The employed research approach can be applied for lubrication design of other transmission systems.

Anti-backlash roller enveloping hourglass worm gear drives, as a new precision transmission system, has been extensively applied in robot joint design, and CNC (computer numerical control) machine tools. However, tooth profiles of the roller enveloping hourglass worms are spatial complex surfaces and very difficult to machine. The meshing and transmission properties such type of worm gear drive are especially sensitive to the errors in machining the tooth profiles of such worms. Thus, in order to improve the accuracy in machining their tooth profile surfaces and reduce the surface roughness, barriers to achieve precision machining of these complex surfaces have to be overcome. In the present study, an equation of grinding contact line for the roller enveloping hourglass worm gear drives with seven critical error parameters was for the first time established based on modern theory of gear meshing. Influence of each error parameter on the grinding contact line was decided through numerical analysis. Also, in order to find the best relationship between the grinding speed and the grinding feed rage, real contact patterns between the grinding rod and the machined worm tooth surface at different grinding speeds were observed using a metallurgical microscope and compared with the theoretical contact pattern calculated from the developed line of contact equation. Based on the obtained results, an innovative grinding method that can offset the loss of radius of the grinding rod was developed and a grinding process under the optimal rotational speed was presented. The proposed grinding process was then applied to generate the complex helical surface of a high precision roller enveloping hourglass worm. Outcomes of this study formed a profound theoretical and practical background for manufacturing and machining of the roller enveloping hourglass worm gear drives.

This paper presents a study to investigate the effects of the shape of rollers in high precision enveloping speed reducer on the reducer’s lubrication performance. Theoretical models for the precision speed reducer with cylindrical and conical rollers as its transmission components were constructed at first based on the meshing theory. Next, numerical analysis was conducted investigate the lubrication status of the speed reducers with different types of rollers at four rotation speeds using ParticleWorks. The moving particle semi-implicit method embedded in that software was used to model the reducers and the inside lubricant flow. A sequence of tests was performed to inspect the transmission efficiency of the reducers at four different rotation speeds. Experimental data were compared to the simulation predictions. Comparisons showed that the data measured from the experiments matched the simulation results very well. Both experimental and computational results confirmed that the lubrication performance of the enveloping speed reducer with conical rollers is better than that of the speed reducer with cylindrical rollers. It has also been proven that the method of using the churning power losses to assess the effects of the shape of the rollers on the roller enveloping speed reducer’s lubrication behavior is highly reliable.

In gear transmission, temperature rise has a non-negligible impact on the accuracy, noise and transmission efficiency. However, there is no relevant research on the temperature rise of the anti-backlash single-roller enveloping hourglass worm (ASEHW) gear. To solve this problem, based on tribology principle and Hertz contact theory, the thermal power calculation method of the ASEHW gear was proposed for the first time and thermal analysis was carried out by Ansys software. The bulk temperature of the ASEHW gear under four different rotating speed (300 r/min, 600 r/min, 900 r/min, 1200 r/min) is calculated. The main factors causing temperature rise of the ASEHW gear are analyzed theoretically. Meanwhile, an experimental study is performed to verify the simulation results and validate the theory methods. The theory presented in this paper provides a solution for the thermal power calculation of ASEHW gear. This research provides a theoretical basis for further optimization of ASEHW gear.

ZC1 worm drives are traditionally machined by grinding with grinding wheels. However, the process efficiency and machining precision of the grinding method are low and cannot meet the design requirements of worm/worm gear transmissions. In order to overcome those shortcomings, we propose a methodology of using five-axis machining to machine the ZC1 worm drives to attain higher efficiency and precision. A ZC1 worm gear drive model with was first created using MATLAB based on the gear meshing theory. Meshing analysis of the ZC1 worm drive was then performed using ANSYS to obtain equivalent stress and contact patterns under different operation conditions. Finally, ZC1 worm drives were machined via five-axis machining and grinding separately. The prototyped ZC1 worm drives were compared through experiments. Experimental data indicated that the distributions of surface wear and contact patterns of the five-axis machined worm drive are more uniform. Moreover, the application of the five-axis machining dramatically enhanced the machining efficiency and precision by significantly reducing the manufacturing time from 30 days to two days and minimizing the influence of human factor on the product properties.

Anti-backlash roller enveloping hourglass worm gears, as a new precision transmission system, has been extensively applied in robot joint design, packaging production line, and CNC (computer numerical control) machine tools. However, their corresponding transmission principles are seldom reported in the literature. Based on the theories of differential geometry and gear meshing, this paper carefully analyzes and compares meshing characteristics of anti-backlash single- and double-roller enveloping hourglass worm gears in terms of their transmission principle, engagement equation, induced normal curvature, lubrication angle, autorotation angle, entrainment velocity, helix angle, and distribution of contact curves. Major differences between these two roller enveloping hourglass worms are theoretically demonstrated through this study. Our results show that the anti-backlash single-roller enveloping hourglass worm (ASEHW) gears provide better performance with respect to gear meshing and transmission than the anti-backlash double-roller enveloping hour glass worm (ADEHW) gears. Also, compared with the ADEHW gears, the ASEHW gears are easier to fabricate, install, and calibrate. However, the ADEHW gears are more auto-adjustable in eliminating gear backlash. The outcomes of this study will form a theoretical background for futuristic design, application, and promotion of the anti-backlash roller enveloping hourglass worm gears.

Analysis of friction and lubrication between meshing gear teeth with complicated tooth surfaces has been a difficult problem in analysis of meshing contact of gear real tooth surfaces. Traditional computational fluid dynamics (CFD) methods cannot precisely create a structured mesh for complicated space surface and thus have limited applicability for solving problems. In this study, the moving particle semi-implicit (MPS) method is proposed to find out impacts of ration speed, immersion depth, worm arrangement, viscosity of lubricant on the churning power losses and oil pressure distribution in a roller enveloping worm gear drive. The application of MPS method for the simulation of gear meshing and lubrication overcomes the difficulty of meshing gear tooth surfaces that maintain all complex structural details. Meanwhile, an experimental study is performed to verify the simulation results and validate the applied computational methods. The combined experimental and computational approach presented in this paper thus represents a solution for numerically analyzing the friction and lubrication between two moving curved surfaces and can be applied for solving a broad range of transmission problems.

This paper proposes a single-roller enveloping hourglass worm gear design and verifies its advantages compared to the existing double-roller worm gear system and the conventional worm gear set. Our hypothesis is that the single-roller worm gear with appropriate configurations and parametric values can eliminate the backlash in mating gear transmission while maintaining advantages of the double-roller worm gears. Also, the self-rotation of the rollers when they are in the worm tooth space (TS) will help the gear system to avoid jamming and gear tooth scuffing/seizing problems caused by zero backlash and thermal expansion. In order to test that hypothesis, a mathematical model for the single-roller enveloping hourglass worm gear is developed, which includes a gear engagement equation and a tooth profile equation. Using that model, a parametric study is conducted to inspect the influences of center distance, roller radius, transmission ratio, and the radius of base circle on the worm gear meshing characteristics. It is found that the most effective way in eliminating the backlash is to adjust the roller radius and the radius of base circle. Finally, a single-roller enveloping hourglass worm gear set is manufactured and scanned to generate a 3D computer model. That model is compared with a theoretical model calculated from the developed mathematical model. Comparison results show that both models match very well, which verifies the accuracy of the developed mathematical model and our initial hypothesis that it is possible to achieve transmissions with zero backlash by adjusting the design parameters.