Continuous sliding mode control for the translational oscillator with a rotating actuator system

The stabilization and disturbance rejection of the translational oscillator with a rotating actuator (TORA) are considered in this paper. To deal with the control issues, a novel continuous sliding mode control method is designed for the TORA system. Compared with existing sliding mode control methods for the TORA system, the proposed method here is continuous. Specifically, first, a global diffeomorphism is introduced for the model of the TORA system. Then, an elaborate sliding manifold is constructed, and a continuous sliding mode control scheme is developed to ensure the convergence of the sliding manifold. Furthermore, rigorous theoretical analysis is given. Finally, simulation tests are carried out, and the obtained simulation results demonstrate that the proposed method exhibits superior stabilization control performance and strong robustness.

Validation of a coupled multibody and TEHL simulation by a piston/cylinder component test rig

A tribological highly stressed contact in the actuating system of axial piston machines is located between the control piston and the control chamber. This paper presents a new type of component test rig for measuring the frictional force and the gap heights between piston and cylinder. For this purpose, the original system is reduced to the actuator system, whereby the real kinematics and the loading forces are maintained. The axial movement of the control piston and the pressure in the control chamber can be configured individually. The measurement results of different parameter variations are compared with the results of the simulation. The simulation based on a coupled multibody and TEHL simulation with a transient, three-dimensional, thermal elastohydrodynamic contact calculation.

High-bandwidth controller design for dual-stage actuator system in hard disk drives

Large-capacity hard disk drives are important for the development of an information society. The capacities of hard disk drives depend on the positioning accuracy of magnetic heads, which read and write digital data, in disk-positioning control systems. Therefore, it is necessary to improve positioning accuracy to develop hard disk drives with large capacities. Hard disk drives employ dual-stage actuator systems to accurately control the magnetic heads. A dual-stage actuator system consists of a voice coil motor and micro-actuator. In micro-actuators, there is a trade-off between head-positioning accuracy and stroke limitation. In particular, in a conventional controller design, the micro-actuator is required to actuate such that it compensates for low-frequency vibration. To overcome this trade-off, this study proposes a high-bandwidth controller design for the micro-actuator in a dual-stage actuator system. The proposed method can reduce the required stroke of the micro-actuator by increasing the gain of the feedback controller of the voice coil motor at low frequencies. Although the voice coil motor control loop becomes unstable, the micro-actuator stabilizes the entire feedback loop at high frequencies. As a result, the control system improves the positioning accuracy compared to that achieved by conventional control methods, and the required micro-actuator stroke is reduced.

Modeling and Parameter Sensitivity Analysis of Valve-controlled Helical Hydraulic Rotary Actuator System

As a kind of hydraulic rotary actuator, helical hydraulic rotary actuator has the excellent characteristics of large angle, high torque and compact structure, which has been widely used in various fields. However, the core technology is in the hands of several companies and has not been disclosed, and the relevant reports are mostly limited to the component level. From the perspective of designing the driving system, the dynamic characteristics of the output when the helical rotary actuator is applied to the closed-loop system are explored. There are two main problems to be studied: one is to establish a reliable mathematical model, and the other is to consider the influence of system parameter perturbation on the output in practice. In this paper, firstly, the dynamic model of valve-controlled helical rotary actuator angle closed-loop system is derived in detail, which has never been reported in the existing literature. Then, the sensitivity analysis of 23 main parameters in the model with perturbation of 10% is carried out under nine working conditions. Finally, the system dynamics model and the sensitivity analysis results are verified by the prototype experiment and co-simulation, which shows the reliability of the theoretical results in this paper.

A new bionic hydraulic actuator system for legged robots with impact buffering, impact energy absorption, impact energy storage, and force burst

It is a big challenge for bionic legged robots to realize desired jumping heights and forward-running speeds, let alone achieve springbok-style jump-running. A key limitation is that there is no actuator system that can mimic the springbok’s muscle system to drive leg–foot system movements. In this paper, we analyze the movement process of springboks and summarize some key characteristics of actuator systems. Some key concepts are then identified based on these key characteristics. Next, we propose a new bionic hydraulic joint actuator system with impact buffering, impact energy absorption, impact energy storage, and force burst, which can be applied to various legged robots to achieve higher running speeds, higher jumping heights, longer endurance, heavier loads, and lighter mass.

Nonsmooth control based on finite-time disturbance estimator for the translational oscillator with a rotational actuator system with nonvanishing disturbances

In this article, the stabilization and disturbance estimation of the translational oscillator with a rotational actuator with nonvanishing disturbances are considered. Different from existing methods, a disturbance estimator is designed to eliminate the effects of unexpected external disturbances. As far as we know, this article presents the first finite-time disturbance-estimator-based nonsmooth control scheme for the translational oscillator with a rotational actuator system. Specifically, first, a series of changes of coordinates is made for the model of the translational oscillator with a rotational actuator system. Then, a disturbance estimator is presented to estimate uncertain disturbances and a nonsmooth control scheme is designed to ensure the convergence of all the states. Furthermore, rigorous theoretical analysis is given. Finally, simulation tests are carried out and the obtained results demonstrate that the designed approach exhibits better control performance and stronger robustness than the existing methods.

Investigation of the Dynamics of a 2-DoF Actuation Unit Cell for a Cooperative Electrostatic Actuation System

The mechanism of the inchworm motor, which overcomes the intrinsic displacement and force limitations of MEMS electrostatic actuators, has undergone constant development in the past few decades. In this work, the electrostatic actuation unit cell (AUC) that is designed to cooperate with many other counterparts in a novel concept of a modular-like cooperative actuator system is examined. First, the cooperative system is briefly discussed. A simplified analytical model of the AUC, which is a 2-Degree-of-Freedom (2-DoF) gap-closing actuator (GCA), is presented, taking into account the major source of dissipation in the system, the squeeze-film damping (SQFD). Then, the results of a series of coupled-field numerical simulation studies by the Finite Element Method (FEM) on parameterized models of the AUC are shown, whereby sensible comparisons with available analytical models from the literature are made. The numerical simulations that focused on the dynamic behavior of the AUC highlighted the substantial influence of the SQFD on the pull-in and pull-out times, and revealed how these performance characteristics are considerably determined by the structure’s height. It was found that the pull-out time is the critical parameter for the dynamic behavior of the AUC, and that a larger damping profile significantly shortens the actuator cycle time as a consequence.

Adaptive Control for Quadrotors with Uncertain and Faulty Actuators

Two adaptive control strategies are presented in this paper for two types of quadrotors to cope with potential uncertainties and faults in the actuator system. The four actuators of the considered quadrotors are distinct and suffered from loss of effectiveness (LOE) as well. To accomandate unknown actuator parameters, a filter-based immersion and invariance (I&I) adaptive controllers are designed for attitude and altitude subsystems, respectively, and an integral backstepping controller is developed for the horizontal subsystem to achieve null steady-state error. Both simulation and experiment results are carried out to illustrate the effectiveness of trajectory tracking performance and fault-tolerant accomondation ability of the proposed control schemes.