The two-inertia system with variable-length flexible load (TSVFL) is a typical dynamic model uncertain system. It is affected by transmission flexibility, flexible load length variation, and inaccurate friction torque, in which the flexible load will vibrate during rotation. In this study, a neural network compensation sliding mode control (SMC) strategy mixed with the angle-independent method (AIM) is proposed to suppress the vibration of the TSVFL. Among them, the AIM is proposed to design the fluctuating desired input of the motor. The vibration of the flexible load is offset by the speed fluctuation of the motor. The RBF neural networks are proposed to recognize the uncertain term in the TSVFL's dynamic model. First, the nonlinear mathematical model of the TSVFL is deduced based on the assumed mode method. Then, the Lyapunov stability theorem is proposed to design the weight coefficients’ adaptive law in neural networks and the robust term in the control law. Finally, simulation and physical experiments on output speed control are implemented. The results show that the proposed strategy is able to effectively decrease the error and weaken the vibration.

A typical serial manipulator consists of a servo motor, a serial mechanism and an independent joint placed between the motor and the serial mechanism. Both the time-varying characteristics of the inertia of the serial mechanism and the flexibility characteristics of the independent joint are widely found in serial manipulator servo drive systems. These two characteristics not only increase the resonance magnitude of serial manipulators, but also affect the dynamic characteristics of the system. In order to obtain a stable output speed of serial manipulators, the variable parameters of a PI control strategy is applied to a serial manipulator servo drive system. Firstly, dynamic model of a serial manipulator servo drive system is established based on a two-inertia system. Then the transfer function from motor speed to motor electromagnetic torque is derived by the state-space equation. Furthermore, the parameters of the PI controller are designed and optimized utilizing three different pole assignment strategies with the identical radius, the identical damping coefficients, and the identical real parts. The results indicate that a serial manipulator servo drive system can obtain good dynamic characteristics by selecting parameters of the PI controller appropriately.

Lateral resistance walk exercise (LRWE) is a popular method for fitness and rehabilitation training. However, current methods such as lateral band walks (LBW) cannot actively control the resistance training intensity. In this article, we proposed a novel hip exoskeleton, which can strengthen hip adductors by applying active resistance torque during lateral walking. The spatial linkage mechanism of the hip exoskeleton was designed and a prototype was fabricated. The dynamic model of transmission system coupling exoskeleton and human body was established. The proportional-integral-differential (PID) control strategy based on fuzzy tuning was presented to control the resistance torque. Physical prototype experiments showed that the fuzzy tuning PID control strategy could significantly improve the torque tracking accuracy compared to the traditional PID control strategy. The muscle activities of No-exo, Exo-off, LBW, and Exo-on (10 Nm, 15 Nm, 20 Nm) conditions were evaluated on ten healthy male subjects walking laterally at a speed of one step per second. The muscle activities of gluteus medius increased by 51.4%, 413.5%, 591.9%, 721.6%, and 918.9% under Exo-off, LBW, and Exo-on (10 Nm, 15 Nm, 20 Nm) conditions, respectively. The corresponding increments for tensor fasciae latae were 52.6%, 1136.8%, 1626.3%, 1994.7%, and 2331.6%, respectively. The results demonstrate that the proposed hip exoskeleton can apply to LRWE and improve muscle activities of hip adductors. It will upgrade the exercise method of LRWE and has good potential in strengthening hip abductors.

Harmonic gear reducer is widely used in industrial robots, aerospace, optics, and other high‐end fields. The failure of harmonic gear reducer is mainly caused by the damage of flexible bearing and flexspline of thin‐walled vulnerable components. To study the contact mechanical characteristics of flexible components such as flexible bearing and flexspline in harmonic gear reducer, the contact mechanical model of flexible bearing, vibration differential equation of flexspline, and finite element model of each component in harmonic gear reducer were established. Based on the established model of harmonic gear reducer, the influence of the length of flexspline cylinder and the thickness of cylinder bottom on the stress of flexspline is discussed, respectively, and the motion characteristics of flexible bearing are studied. At the same time, the spatial distribution of the displacement of the flexspline and the axial vibration response of the flexspline are studied. The correctness of the model established in this paper is verified by experiments. The results show that the increase of cylinder length can improve the stress of flexspline in harmonic gear reducer; the wall thickness of cylinder bottom mainly affects the stress at the bottom of flexspline but has little effect on the stress of gear ring and smooth cylinder. Along the axis direction of the flexspline, the radial displacement, circumferential displacement, and angular displacement increase linearly with the increase of the axial distance between the cylinder and the bottom. When the excitation frequency is high, the vibration mode of flexspline shell is mainly axial vibration. The research results will provide a theoretical reference for the optimal design of harmonic gear reducer and improving the service life of flexible parts.