Analytical modelling for overall torsional stiffness of rotate vector (RV) reducer has been a meaningful research priority owing to its over-constrained and multi-crank actuation structural characteristics. This paper presents an analytical modelling approach for overall torsional stiffness of RV reducer. The approach starts from analysing stiffness topological relations among all components, in order to convert the stiffness modelling of entire machine into the stiffness calculation of several subsystems. Then, time-varying meshing information including contact points, contact pins, contact deformation, and multi-tooth mesh stiffness, are precisely identified with consideration of profile modification and loads. Subsequently, the nonlinear stiffness of turning-arm bearings and support bearings is calculated through the force analysis of crankshafts. On this basis, the overall torsional stiffness model of RV reducer is developed, which concerns various stiffness parameters of high-speed stage and low-speed stage. Furthermore, the sensitivities and influences of stiffness parameters on the overall torsional stiffness of RV reducer are systematically analysed. Finally, the effectiveness and accuracy of the proposed model are validated by the physical prototype test. The outcomes of this paper are beneficial to the stiffness prediction and design of RV reducer according to its performance requirement.

This paper focuses on a novel harmonic movable tooth drive as an alternative of currently used harmonic gear drives. Different from the harmonic gear drives, the novel drive removes small module teeth from thin-walled flexible rim, instead, adopts several rigid movable teeth with logarithmic spiral tooth profile. Such tooth geometry makes almost surface contact possible under load condition, in comparison with the conventional involute tooth profile creating a linear contact. Aiming at the issue of cusp meshing between movable tooth and ring gear during the meshing process, this paper proposes a modification design method for the conjugate tooth profiles. First, the radial motion law of movable tooth is modified, in order to avoid rigid impacts at the exchange point of the rise travel and return travel. Then, the tooth profile of ring gear is generated by the envelope of the modified profile of movable tooth. Based on the formulated modification scheme, the equations of the conjugate tooth profiles are derived, and the influences of spiral angle and modification parameters on the meshing characteristics are systematically investigated. Finally, the wave generator cam profile and pivoted segment profile are established considering the strength consistency. The outcomes can provide significance guidance for the parametric design and optimization of this novel drive.

提出了一种新型活动柱销式精密摆线减速器.首先,阐述了活动柱销式摆线减速器的传动原理与结构特点,该新型摆线减速器设有活动柱销输出机构,将输出柱销与柱销孔之间的滑动摩擦转变为滚动摩擦,可显著提高减速器传动效率;其次,对关键传动零部件的静力学特性进行了计算,分析了摆线齿廓修形和柱销孔配合间隙分别对摆线传动啮合力和活动柱销接触力的影响;然后,基于有限元技术对减速器整机的模态特性进行分析,获得了减速器各阶固有频率和振型特征;最后,完成了活动柱销式摆线减速器物理样机制造并进行了传动效率测试,为工业机器人精密减速器产品创新提供了一种有效的技术方案.

A new type of one-stage precision cycloidal-pin reducer is designed and explored in this study. The design innovatively replaces the fixed output-pin mechanism of conventional cycloidal-pin reducers with a rotatable output-pin mechanism, thereby transforming the sliding contact be-tween the output-pin and the output-hole into a rolling contact. This new structural design is found to significantly improve the transmission efficiency of the reducer. To evaluate the dynamic transmission error (DTE) characteristics of the proposed reducer, a general dynamic model of the cycloidal-pin transmission system considering the influences of multi-source error factors on the geometry of the main components is established. The geometric error of the component is determined by taking random values within a given design-tolerance zone. The geometric error distribution introduced using this method can well match the actual machining situation. Finally, the DTEs of the new reducers with three different tolerance designs are analyzed numerically and tested experimentally. The results show that the new reducer with a reasonable tolerance design can achieve high transmission accuracy and has the potential for application in the joints of in-dustrial robots.

Delicate manipulation for continuum robots remains challenging. The key is to establish a motion controller with real-time perception, fast response, and high precision. Integrating visual sensors into the system can enhance the precision of end position control while minimizing uncertainties in the robot model. In this paper, a depth camera is used to identify the Aruco code to provide pose information to the continuum robot. Then the end-effector is controlled to achieve horizontal linear displacement and plug into a socket based on the pose information. Based on experimental findings, it has been demonstrated that the control accuracy can achieve a level of precision in the centimeter range. The presented methods expand the potential scenarios of the continuum robot.

Continuum manipulators (CMs) have redundancy and flexibility and show good adaptability in unstructured environments. Traditional CMs mostly utilize a backbone to provide structural support and produce bending, which limits the internal space. In this paper, an internally hollow CM is designed. The orthogonal segment ensures two bending degrees of freedom in a single module. In this design, each module contains four cables that can be divided into two pairs driven by two motors respectively, forming a closed-loop cable drive mechanism. For each pair of cables, they have different length change when the module bends. Thus, the actuation space of the manipulator is further mapped to the “motor space” to form the complete kinematic model. As the multi-moduled body has motion coupling, kinematic decoupling is achieved through using Bowden tube. Simulated and experimental results show that the CM designed in our work has high structural load capacity and flexible motion ability.

The ankle joint is the most important weight-bearing joint in the human body and is easily injured. Therefore, a lot of research has been carried out on the robotic mechanism of ankle rehabilitation. However, most rehabilitation mechanisms are difficult to apply due to the lack of compliance and adaptability. According to the anatomic structure of an ankle joint, a bio-inspired ankle rehabilitation mechanism driven by cables was designed by simulating antagonistic muscles. The kinematics of the rehabilitation mechanism is then analyzed. Finally, the ankle joint trajectories of five participants were compared in the case of normal movement and using the rehabilitation mechanism, demonstrating the compliance and adaptability of the presented rehabilitation mechanism.

The rotate vector (RV) reducer's needle roller bearings (NRBs) are vulnerable to wear and flaws such as fatigue spalling of the raceway material. Studying the vibration mechanism and the excitation laws of NRB failures is essential to enhancing the RV reducer's performance and comprehending its operating state. This paper presents a dynamic model of the RV reducer based on the theory of contact multibody dynamics. It integrates internal and external raceway defects and takes into account the synchronous contact interaction between NRB groups and the crankshaft and cycloidal gears, as well as the time-varying mesh stiffness in the planetary gear transmission and cycloidal pin transmission. The study demonstrates that the rolling of bearings and the meshing of internal transmission components are the primary causes of vibration in a healthy RV reducer through experimental verification and dynamic simulation analysis of the system with and without NRB failures. Both the crankshaft rotation frequency and the cycloidal gear rotation frequency affect the vibration excitation source's characteristic frequency. The vibration amplitude of the RV reducer is influenced by bearing flaws on a periodic basis. The impact of internal raceway defects is greater than that of external raceway faults, resulting in a notable rise in vibration amplitude.

The precision rotary vector reducer with involute variable tooth thickness (PRVT) is a high-performance precision transmission device, which is very suitable for aerospace, medical machinery, industrial robots, automation equipment, and other fields, and its torsional stiffness is an important performance index. This paper establishes a dynamics model of the whole machine based on the Lagrangian method by considering gear meshing stiffness, damping, and machining errors, and the influence of different machining errors on dynamic torsional stiffness is studied. The results show that increasing the distribution circle radius error of the crankshaft, the crank angle error and the distribution circle radius error of the crankshaft bearing hole on the carrier will cause the peak-to-peak torsional stiffness to increase. Therefore, the machining errors should be controlled within a reasonable range to improve the whole machine’s stability. An increase in the crankshaft bearing hole rotation error on the No. 1 beveloid gear has no notable impact on the peak-to-peak value and the average value of the torsional stiffness. Similarly, the rotation angle error of the crankshaft bearing hole on the No. 1 carrier has no significant effect on the torsional stiffness. The research results provide a useful reference for the torsional stiffness analysis of PRVT.

This paper presents a method for the analytical error modelling of RV reducer concerning its over-constrained structure, which explicitly establishes the relations between the original errors and the transmission precision. According to the structural characteristic, i.e., the rotation and revolution of the cycloidal gear share three crankshafts, an equivalent multi loop mechanism of the reducer is achieved through replacing higher pairs by lower pairs, which decouples the over-constrained relations among the multi-crank actuation. And the error model of the reducer is thus developed by the loop incremental method, in which the manufacturing and assembly errors are represented by the linkage length errors in the equivalent mechanism. Finally, the proposed model is validated by the test results of prototypes, and the influence of original errors is respectively investigated. The outcomes provide a new idea for error modelling and components accuracy design of RV reducer and other precision gear systems. (c) 2021 Elsevier Ltd. All rights reserved.