Analysis on the vibration reduction for a new rigid–flexible gear transmission system

In this study, a new rigid–flexible gear with metal rubber is proposed to reduce the vibration of the gear transmission system. A nonlinear dynamic model with nine degrees of freedom considering bearing clearance, gear backlash, surface friction, and time-varying meshing stiffness is established. The nondimensional dynamic model of the transmission system is obtained and the bifurcation characteristics of the new rigid–flexible gear pair and the rigid gear pair are analyzed when the damping coefficient is, respectively, 0.03 and 0.1. The result shows that the motion state of the rigid–flexible gear pair is more stable. The dynamic responses of the rigid gear pair and the rigid–flexible gear pair are compared as well through numerical analysis and experiment to illustrate the advantage of the rigid–flexible gear pair in vibration reduction. The results can provide reference for vibration reduction of the novel gear transmission.

Nonlinear Dynamic Analysis of a Rigid–Flexible Gear Transmission Considering Geometric Eccentricities

Nonlinear vibration, a main factor affecting the dynamic stability, widely exists in the transmission system. In addition, geometric eccentricities caused by the manufacturing errors are inevitable in the gear transmission system, which may lead to the excessive nonlinear vibration. In order to suppress the nonlinear vibration under the excitation of the geometric eccentricities, a rigid–flexible gear pair consisting of the ring gear, the composite material, and the hub is proposed in this study. A dynamic model with nine degrees-of-freedom which considers geometric eccentricities is proposed to analyze the nonlinear dynamic characteristics of the rigid–flexible gear pair. Furthermore, the dynamic characteristics of the rigid–flexible gear pair and the rigid gear pair are compared within a wide range of operating conditions. The comparative analysis demonstrates that the rigid–flexible gear pair has better vibration suppression effect on the system.

Kinematic error of a harmonic drive

The article deals with the causes for kinematic error of harmonic drives. The error was determined theoretically using a mathematical model of a drive accounting elastic interactions of the drive elements. The paper identifies the main cause for the inherent kinematic error of a harmonic drive featuring a cam wave generator: a variation in a flexible gear deformation at rolling of flexible bearing balls. It was established that the highest kinematic error of a drive is significantly lower than the first harmonic of a flexible gear generating error. There is obtained a cam displacement dependence of the highest kinematic error for VZP-80 drive.

Design and implementation of a variable stiffness actuator based on flexible gear rack mechanism

SUMMARYVariable stiffness can improve the capability of human–robot interacting. Based on the mechanism of a flexible rack and gear, a rotational joint actuator named vsaFGR is proposed to regulate the joint stiffness. The flexible gear rack can be regarded as a combination of a non-linear elastic element and a linear adjusting mechanism, providing benefits of compactness. The joint stiffness is in the range of 217–3527 N.m/rad, and it is inversely proportional to the 4th-order of the gear displacement, and nearly independent from the joint angular deflection, providing benefits of quick stiffness regulation in a short displacement of 20 mm. The gear displacement with respect to the flexible gear rack is perpendicular to the joint loading force, so the power required for stiffness regulating is as low as 14.4 W, providing benefits of energy saving. The working principles of vsaFGR are elaborated, followed by presentation on the mechanics model and the prototype. The high compactness, great stiffness range and low power cost of vsaFGR are proved by simulations and experiments.