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In this paper, a finite time control strategy is investigated to realize motion control for a multi-DOF pneumatic manipulator (MDPM) with vertical downward equilibrium state. Angle deflection is existed for the MDPM at work when gravity compensation has to take into account. To estimate the disturbances on gravity from angle deflection, a nonlinear extended state observer (ESO) is designed for the MDPM. Backstepping super-twisting terminal integral sliding mode control (SMC) is proposed to improve control accuracy and convergence speed. Finite time convergence is shown for the nonlinear ESO and the backstepping super-twisting terminal integral SMC under angle deflection gravity compensation. Experiment results are given to show effectiveness of the finite time control strategy for the MDPM. [ABSTRACT FROM AUTHOR]

A gravity compensation (GC) device compensates for the torque originating from a constant mass or payload, which occupies a large part of the capacity and energy consumption of an actuator on the joint. Adapting a GC device can reduce energy consumption and capacity of the actuator. A GC device comprises an energy-storage component and a motion-converting mechanism. The energy storage component stores and releases energy according to the change in gravitational energy as the mass of the joint rotates. The motion-converting mechanism matches the energy from the energy storage component to the gravitational energy of the rotating mass. The majority of GC devices use springs as the energy storage component, and they are connected to the body by motion-converting mechanisms, such as gears and slide cranks. A GC device that uses magnetic energy as an energy storage component was proposed in this study. It uses noncontact permanent magnets (PMs) as energy storage components. It is designed to have a simple structure and compact size, and can be easily connected to the actuator module, similar to commercial gear reducers. It comprises two identical structures, consisting of one yoke and two PMs. The two structures are assembled as the PMs face each other and generate attractive and repulsive forces depending on the relative angle between the two facing PMs. The shapes of the PMs were determined to generate a sinusoidal torque profile to compensate for the gravitational torque by a mass. The designed mechanism is verified through simulations and experiments. [ABSTRACT FROM AUTHOR]

A novel cable-driven parallel robot (CDPR), featured with a simple structure and energy-efficient driving mechanism, for 3D printing building construction is proposed, and details of the design methodology are presented. To overcome the limitation of the previous approaches, the CDPR is designed to operate with only five cables; hence, its structure is simplified. To avoid the interference with the building being printed, lower cables are placed on a plane parallel to the ground and they are controlled to move synchronously up and down according to the height of the building being printed. Tension distribution of the cables required for the operation is analyzed using the constrained optimization problem. Workspace determination is presented in consideration of the cable strength as well using the tension distribution analysis. A gravity compensation mechanism is proposed and applied to reduce the energy consumption. The validity of the proposed CDPR and design methodology is verified through the simulation. [ABSTRACT FROM AUTHOR]

In this paper, an electrodynamic levitation gravity compensation system based on a new type of annular Halbach array permanent magnet is proposed. The magnetic levitation force model is established using the equivalent expansion method, and the reliability of the model is verified by comparing the results of numerical calculation and simulation analysis. Through magnetic field simulation experiments, the effects of rotating speed and air gap on magnetic levitation force and eddy current loss are analyzed. The control model of the electric magnetic levitation system considering the vertical speed is investigated, and the hybrid control method of force and position is used to realize the stable magnetic levitation control. Finally, an experimental platform is built to verify the feasibility of the electric magnetic levitation system. The results show that the magnetic levitation force can be improved and the eddy current loss can be reduced by setting the rotating speed and air gap reasonably. [ABSTRACT FROM AUTHOR]

Gravity compensation refers to the creation of a constant supporting force to fully or partly counteract the gravitational force for ground verification to simulate the spacecraft dynamics in outer space with zero- or micro-gravity. Gravity compensation is usually implemented via a very low stiffness suspension/supporting unit, and a servo system in series is adopted to extend the simulation range to hundreds of millimeters. The error of suspension force can be up to tens of Newton due to the contact/friction in the suspension/supporting unit and the error of the force/pressure sensor. It has become a bottleneck for the ground verification of spacecraft guidance, navigation, and control systems with extreme requirements, such as tons of payload and fine thrust in sub-Newtons. In this article, a novel gravity compensation method characterized by quasi-zero stiffness plus quasi-zero deformation (QZS-QZD) is proposed. A magnetic negative stiffness spring in parallel with positive springs and aerostatic bearing is adopted to form a QZS supporting unit, and disturbance forces, such as contact or friction, can be eliminated. The deformation of the QZS supporting unit is measured via a displacement sensor, and the QZD control strategy is applied to guarantee the force error of gravity compensation to be less than sub-newtons and irrelevant to the payload. The principle of gravity compensation with QZS-QZD is analyzed, and performance tests on a prototype are carried out. The results show that when the spacecraft moves smoothly, the absolute force error is less than 0.5 N, the relative error of gravity compensation is less than 0.1%, and when collisions with other objects occur, the relative errors are 0.32% and 0.65%. The proposed method can significantly improve the gravity compensation accuracy in comparison with conventional approaches. [ABSTRACT FROM AUTHOR]

This paper presents a new robust model free terminal sliding mode (MFTSM) with gravity compensation approach used to control an exoskeleton-upper limb system. The considered system is a 2 DoF robot in interaction with an upper limb. It is used for rehabilitation to control the flexion/extension movement of the shoulder and the elbow joints in the presence of disturbances. In the first part, we present the exoskeleton-upper limb system modeling. Then, we controlled the considered system by the model free terminal sliding mode with and without gravity compensation. A stability study is realized. To prove the controllers performance, a robustness analysis was needed. The simulation results demonstrate that the MFTSMC over performs the terminal sliding mode and the model free controllers in terms of performance, robustness and disturbance rejection and that the gravity compensation improved the efficiency of the system when tracking the desired trajectories. [ABSTRACT FROM AUTHOR]

The hybrid force/position control base on fuzzy proportional-integral-derivative (PID) is proposed to improve the quality of robotic automatic grinding aviation blades. First, the perception for the contact force/torque is discussed. A multi-source parameters gravity compensation matrix is established to identify the parameters through matrix reorganization. The contact force/torque is perceived according to the gravity compensation result. Then, the hybrid force/position control base on fuzzy PID is designed to realize active force control. Nevertheless, the sharp edge phenomenon occurs although the force control algorithm, which seriously affects the grinding quality of blades. Finally, the fusion control of force and torque is proposed to weaken the sharp edge phenomenon. The experiment proves that the introduction of torque control avoids effectively the sharp edge phenomenon. Meanwhile, comparing the proposed control algorithm with the traditional PID control, the results show that the proposed hybrid force/position control based on fuzzy PID can ensure the stability of the contact force and improve the quality of the aviation blades. [ABSTRACT FROM AUTHOR]

In our research, we proposed a system using multi-robot as a gravity compensation system for a ground test of a spacecraft with a deployable structure. The advantage of the system is its low cost and versatility. When the robots support the beam at the nodes, we can expect to simulate the free vibration of the space structure using the proposed system under gravity. In this study, supporting a uniform, flexible beam with vibration was first implemented to verify the performance of the proposed system. Then we investigated the performance of the system applying to the mock-up model of a spacecraft with a deployable structure as a demonstration. [ABSTRACT FROM AUTHOR]

Our research team combined humanoid robots with intelligent lower limb prostheses to study the dynamic characteristics of intelligent lower extremity prostheses for disabled people in the walking process, and proposed a biped robot with heterogeneous legs (BRHL). This paper proposes a new virtual-real inverted pendulum system model to unify the models for both single support phase and double support phase in walking process and builds a special simulation platform which can acquire the real-time center of mass (COM) trajectory. Initially, a gravity-compensated inverted pendulum model was built and improved the stability of gait, a natural ZMP trajectory improved the anthropomorphism of the gait. Furthermore, in double support phase, a virtual inverted pendulum model was established and a virtual-real inverted pendulum model was proposed and used to plan the gait of both single support phase and double support phase in the walking process. Additionally, the joint angles were obtained by inverse kinematics; the stability of the system was analyzed to be feasible and effective by phase trajectories. A special ADAMS simulation platform was built to simulate the walking process and acquire real-time COM trajectory. The feasibility of the gait planning was also verified. Finally, the trajectory of COM was optimized based on the minimum energy criterion according to the geodesic equation. [ABSTRACT FROM AUTHOR]

Tele-rehabilitation provides remote physiotherapy services for patients who have limited access to hospitals. This paper proposes a sensorless tele-rehabilitation system for the upper-limb using two robots in master–slave configuration. The system provides a transparent haptic feeling between the therapist and the patient by simultaneous tracking of both position and torque. The torque is measured using the reaction torque observer. Furthermore, an online recursive numerical parameter estimation method is proposed to identify the gravity disturbance in bilateral teleoperation. The system automatically estimates the parameters using the reaction torque observer output's data while the therapist is delivering remote physiotherapy services. The estimated gravity torque is compensated in the system as an improvement of the transparency of the teleoperated system. Therefore the therapist would feel only the abnormalities of the patient's arm. Estimated parameters automatically update the system and enhance the performance. The proposed method was practically verified with a master slave tele-rehabilitation system. Results suggest the applicability of the proposed method. [ABSTRACT FROM AUTHOR]

This paper proposes a Gravity compensator (GC) for a humanlike four Degrees-of-freedom (4-DOF) manipulator in that three 2-DOF and two 3-DOF unit GCs are used. The equivalent mapping analyses show that various types of multi-DOF GCs can be classified into their own type of DOF regardless of the order of successive rotations and selection of reference frames. Therefore, the selection of multi-DOF GCs has become simple. A method for the placement of unit GCs is proposed. For the 4-DOF manipulator sixteen combinations of unit GCs are obtained and various designs (mapping matrices) can be further developed for an each combination considering locations of unit GCs. The 5-GC combination is chosen among various designs. The placement of the unit GCs is conducted for the 5-GC combination, and its performance is evaluated with a numerical simulation. The case study showed that most of the unit GCs are applicable to the 4-DOF manipulator and the same placement of unit GCs is achieved for all applicable unit GCs. [ABSTRACT FROM AUTHOR]

This paper presents development and evaluation of a passive shoulder joint tracking device for allowing natural three-dimensional movement of the shoulder joint (Glenohumeral joint) during upper limb rehabilitation. The shoulder joint is one of the most sophisticated joint in human body as it involves not only three-dimensional rotation but also three-dimensional translation simultaneously. Existing upper limb rehabilitation devices account for three-dimensional rotation of the shoulder joint but lack in three-dimensional translation. This paper presents design and analysis of a three-degrees of freedom (DOF) passive shoulder joint tracker that allows natural translation of the joint in three-dimensional space. One-DOF vertical tracker compensates for the weight of arm and device by using simple spring mechanism and two-DOF horizontal tracker consists of two-link mechanism allowing twodimensional translation in horizontal plane. Performance of the passive tracker was evaluated through an experimental analysis with eight human subjects. An upper limb rehabilitation device (J-WREX) combined with the tracker allowed greater range of motion (ROM) of the shoulder joint in all three directions and followed the shoulder joint with acceptable tracking error. The passive tracker can be attached to existing upper limb devices to improve the performance by allowing natural shoulder joint movement. [ABSTRACT FROM AUTHOR]

This paper presents a transformation method by which a static balancer of a truss is transformed into static balancers of various mechanisms. For conventional design methods the kinematics and potential energy of every mechanism should be computed to design a static balancer. For the proposed design method, however, no computation of kinematics and potential energy is necessary to obtain static balancers of various mechanisms, once a static balancer of a truss has been designed. The concepts of the Baranov truss and associated linkage are adopted to determine transformation relations. Conversion rules are developed in the viewpoint of gravitational torques and deletion rules are determined to apply conversion rules to the design equation. Static balancers of various mechanisms (four-bar linkage, slider crank mechanism, Watt mechanism and sliding mechanism derived from the watt mechanism) are derived from those of the five-link and seven-link Baranov trusses in this paper. Simulations results showed that complete gravity compensation is achieved for all derived mechanisms from Baranov trusses. [ABSTRACT FROM AUTHOR]

This paper proposes gravity compensators for a 4-degree-of-freedom (4-DOF) humanlike manipulator. Eighteen springs (or 1-DOF gravity compensators) are required to achieve complete static balancing of a 4-DOF manipulator. Because locating 18 springs is impractical, incomplete gravity compensators are designed for practical implementation in this paper. Springs are selected using an objective function of the gravity compensation and design cost. The design cost indicates the complexity of the mechanisms. As a result, four- and two-spring designs are obtained. Optimizations of spring constants of the four- and two-spring designs are conducted for the objective function of gravity compensation. The torque ratios for the four-spring design are computed as [18.64%, 11.92%, 77.68%, 81.14%]. The torque ratios for the two-spring design are computed as [16.03%, 20.22%, 100.00%, 100.00%] and indicate that gravity compensation is made only at proximal joints to the base. Dynamic simulations are conducted, and simulation results show that the ratios of gravity compensation are achievable. [ABSTRACT FROM AUTHOR]

This paper presents a 2-dof gravity compensator used for roll-pitch rotations, which are often applied to the shoulder joint of a service or humanoid robot. The 2-dof gravity compensator is comprised of two 1-dof gravity compensators and a bevel differential. The rollpitch rotations are decoupled into two rotations on the moving link by the bevel differential; the two 1-dof gravity compensators are applied to the two rotations. The spring coefficients are determined through energy and torque analyses in order to achieve complete static balancing. The experiment results indicate that the proposed gravity compensator effectively counterbalances the gravitational torques and can also be operated in the hemispherical work space. [ABSTRACT FROM AUTHOR]

We present a design for a manipulator that is intrinsically mechanically safe, i.e. it can not cause pain (let alone damage) to a human being even if the control system has a failure. Based on the pressure pain thresholds for human skin, we derive a pinching safety constraint that limits the actuator torque, and an impact safety constraint that results in a trade-off between mass and velocity. To fulfill all constraints, the manipulator requires a spring balancing system that counteracts gravity in all configurations of the manipulator. This allows the use of extremely low-power DC motors (only 4.5 W). Thanks to the torque and speed limitations of these motors the manipulator is indeed intrinsically safe, yet still capable of moving a useful payload of 1.2 kg over a distance of 0.8 m in 1.5 s. [ABSTRACT FROM AUTHOR]

The present magnetic levitation facility offers an alternative to space means for studying fluids and especially liquid oxygen that exhibits important safety requirements. The station has great use flexibility. Thus it enables us to study hydrodynamic instabilities (acceleration and deceleration phase) and also to focus on thermal exchanges (nuclear and film boiling) and transition phase of fluids under reduced gravity such as Lunar, Martian or micro-gravity. The volume of liquid oxygen levitated is about two litres with a resulting acceleration less than 0.1 m/s2. Besides the aspect ratio of the working cell can be changed. [ABSTRACT FROM AUTHOR]

This paper considers the estimation and compensation of the unknown gravity force and static friction for robot motion control. Utilizing the stability feature of PD set-point control, the estimates of gravity-related parameters and static friction can be solved from two steady state equations obtained by stopping robots at two nonsingular positions. The estimates obtained can then be used to eliminate the position error. Under a mild assumption that the mass center of each robot link is distributed on a straight line connecting two adjacent joints, the gravity force regression matrix becomes upper-triangle which can significantly simplify the algorithm. The positive experimental result obtained for practical verification is also presented. [ABSTRACT FROM AUTHOR]

The phototropic dose-response relationship has been determined for Triticum aestivum cv. Broom coleoptiles growing on a purpose-built clinostat apparatus providing gravity compensation by rotation about a horizontal axis at 2 rev·min. These data are compared with data sets obtained with the clinostat axis vertical and stationary, as a 1· g control, and rotating vertically to examine clinostat effects other than gravity compensation. Triticum at 1· g follows the wellestablished pattern of other cereal coleoptiles with a first positive curvature at low doses, followed by an indifferent response region, and a second positive response at progressively increasing doses. However, these response regions lie at higher dose levels than reported for Avena. There is no significant difference between the responses observed with the clinostat axis vertical in the rotating and stationary modes, but gravity compensation by horizontal rotation increases the magnitude of first and second positive curvatures some threefold at 100 min after stimulation. The indifferent response is replaced by a significant curvature towards the light source, but remains apparent as a reduced curvature response at these dose levels. [ABSTRACT FROM AUTHOR]

Retinal surgery continues to be one of the most technical demanding surgeries for its high manipulation accuracy requirement, small and constrained workspace, and delicate retinal tissue. Robotic systems have the potential to enhance and expand the capabilities of surgeons during retinal surgery. Thus, focusing on retinal vessel bypass surgery, a master-slave robot system is developed in this paper. This robotic system is designed based on characteristics of retinal vascular bypass surgery and analysis of the surgical workspace in eyeball. A novel end-effector of two degrees of freedom is designed and a novel remote center of motion mechanism is adopted in the robot structure. The kinematics and the mapping relationship are then established, the gravity compensation control strategy and the hand tremor elimination algorithm are applied to achieve the high motion accuracy. The experiments on an artificial eyeball and an in vitro porcine eye are conducted, verifying the feasibility of this system. [ABSTRACT FROM AUTHOR]