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This work presents a novel method for the estimation of stride length (SL) from inertial sensor-based wireless foot sensor module (WFSM). SL variability is a widely used and clinically relevant spa...

With the rapid development of mechatronics and robotics technology, the application of robots has been extended from the industrial field to daily life and has become an indispensable part of work and daily life. The accuracy and flexibility of the operator determine the operating efficiency of the robot. Although the level of development of the operator is constantly improving, the traditional operator has a simple structure and generally adopts parallel movement or tightening. The holding structure has poor flexibility and stability, making it difficult to achieve precise position capture and control and cannot meet the requirements of delicate tasks. In this paper, a basic force analysis of the manipulator is carried out, and the change trend of the force and driving force of each joint when the manipulator is grasping objects is obtained, so as to determine that the manipulator can grasp the object stably; then, in the strength analysis of the manipulator, it is determined that the material meets the strength requirements. This paper conducts an output voltage experiment on the static performance and coupling error of the mechanical arm wrist force sensor. Secondly, in order to study the influence of the temperature change in the space environment on the zero-point output of the mechanical arm sensor, a high and low temperature test box are used to simulate the temperature brought by the temperature change to the sensor. Experiments show that the maximum coupling error of the sensor is 1.81%, which is less than 2% of the design index. This indicates that the operator sensor is used to detect the force and torque that the space operator’s edge operator experiences when it interacts with the external environment and provides the necessary power sensing information for power control and compatible operator motion control, completing some complex; the Fine project is an important prerequisite for realizing the intelligence of space operators.

Because the human arm and leg have a similar skeletal structure, it may be possible to use the leg to operate a robot by the master-slave method. However, operation by the leg with six degrees of freedom has two problems. First, people move their ankle with a curved motion despite intending to move it linearly. Second, it is a burden for the operator to suspend their legs in the air during operation. This study dealt with these problems. For the first problem, we hypothesized that one of the reasons was that the muscle load of a curved motion was smaller than that of a linear motion, and we quantitatively compared them by musculoskeletal analysis. The muscle loads of curved motions were 20% smaller in the anteroposterior direction, 3.1% to 23.8% smaller in the lateral direction, and 10% smaller in the vertical direction than linear motions, which showed that the hypothesis was consistent. Further, comparison of the analysis results with the results of a previous study suggested that subjects unconsciously tried to reduce the muscle load and to move closer to a linear line when they moved their ankle while consciously intending to make a linear motion. For the second problem, we developed two different prototypes of a leg support device. An experiment to evaluate the effectiveness of these devices showed that subjective exercise intensity of the tasks in the experiment using the devices was 40% or more less than that without the device, which proved the effectiveness of the devices.

When using a force feedback device to interact with a virtual world, the effect of immersion is highly dependent on its performance of gravity compensation. In this work, an active and passive combined gravity compensation approach is presented for a horizontally mounted 6-DOF hybrid force feedback device (HFFD-6). Both active and passive methods are analyzed with simulation and corresponding parameters in the passive approach are then optimized. And to evaluate the performance of the gravity compensation approach, physical experiments are also conducted to measure the gravity compensation errors in the workspace. Moreover, comparison studies are conducted to illustrate the superiority of the proposed approach in terms of output force capability. These experiments have demonstrated that the proposed approach is feasible to achieve gravity compensation and improve the output force capability of the device.

In this letter, we show that soft robotic hands provide a robust means of performing basic primitives of in-hand manipulation in the presence of uncertainty. We first discuss the design of a prototype hand with dexterous soft fingers capable of moving objects within the hand using several basic motion primitives. We then empirically validate the ability of the hand to perform the desired object motion primitives while still maintaining strong grasping capabilities. Based on these primitives, we examine a simple, heuristic finger gait which enables continuous object rotation for a wide variety of object shapes and sizes. Finally, we demonstrate the utility of our dexterous soft robotic hand in three real-world cases: unscrewing the cap of a jar, orienting food items for packaging, and gravity compensation during grasping. Overall, we show that even for complex tasks such as in-hand manipulation, soft robots can perform robustly without the need for local sensing or complex control.

Robotic rehabilitation for poststroke therapies is an emerging new domain of application for robotics with proven success stories and clinical studies. New robotic devices and software applications are hitting the market, with the aim of assisting specialists carrying out physical therapies and even patients exercising at home. Rehabilitation robots are designed to assist patients performing repetitive movements with their hemiparetic limbs to regain motion. A successful robotic device for rehabilitation demands high workspace and force feedback capabilities similar to a human physiotherapist. These desired features are usually achieved at the expense of other important requirements, such as transparency and backdrivability, degrading the overall human-machine interaction experience.

A pneumatic gravity compensation system is typically nonlinear in behavior. It is difficult to establish an accurate mathematical model for it, and it is particularly difficult to realize high-precision pressure control. A pneumatic gravity compensation system driven by a frictionless cylinder is built. Considering that the traditional model-free adaptive control is slow for pseudo-gradient identification, an improved model-free adaptive control is proposed to predict the changes in the pseudo gradient and accelerate the process of pseudo gradient identification. The static and dynamic gravity compensation of the pneumatic gravity compensation system is realized. Finally, the experimental results show that the steady-error of step response of the improved model-free adaptive controller is less than 200 Pa, and the rise time is approximately 13 seconds. The sinusoidal tracking error (0.04 Hz) is approximately 1.94 KPa.

Adaptive nonlinear optimal control methods, as proposed in the literature, give rise to some questions around practical implementation in robotics, especially how to find a solution in a reasonable time and how to deal with gravity. This paper proposes a method to solve these problems by using a neural network with local basis-function domains, specifically the Cerebellar Model Articulation Controller (CMAC). The algorithm uses the local domains in order to keep track of the value of local cost-functionals. In this way, it can freeze the learning of the network’s weights in a feedforward-like component in the CMAC when the bias has been overcome identified by using an error-based cost-functional e.g. automatic gravity compensation in a robot. After the feedforward component has been established, the algorithm then starts to learn another set of weights which contribute to feedback-like terms in the CMAC and these weights get frozen when they no longer reduce a cost-functional that includes additional control effort e.g. in a robot the control effort beyond that needed to compensate for gravity is penalized. Lyapunov methods guarantee uniformly ultimately bounded signals and ensure weight drift and bursting do not occur. One advantage is that the training time for finding a near-optimal control does not increase over previous neural-adaptive methods. Another advantage is that penalizing the control effort in a search for optimization does result in any steady-state error due to gravity. Simulations show that the proposed method significantly outperforms a standard adaptive-CMAC control using e-modification, without increasing control effort or training time. An experimental flexible-joint robot verifies that the adaptive method significantly outperforms a linear quadratic regulator.

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.

During overhead work, workers need to keep raising weights of approximately 2 to 4 kg with the muscular strength of their upper limbs, and the burden of this work is high. Therefore, we developed an assistive device, named TasKi, using a self-weighted compensation mechanism to reduce the burden on upper limbs during overhead work. It can compensate for upper limb weight using the force of a spring in various postures of the upper limbs, without a battery. In this study, to provide effective assistance to many users, we clarified the crucial assistance and parameter adjustment range of settings corresponding to physical differences. First, the assistive force value of TasKi to reduce the work burden of each user was confirmed via a subjective evaluation experiment and myoelectric potential measurements. Next, we conducted a test survey of TasKi users and investigated the relationship between physique and the wearing feeling. According to the survey, 80% of the subjects provided favorable opinions on the assistive method used by TasKi. Finally, we had subjects of various physiques wear the device and investigated the relationship between physique and the wearing feeling with respect to shoulder joint movements. It was observed that the subjects with greater shoulder widths experienced difficulties when moving in the direction of internal-external rotation because of the small size of TasKi. The influence on the ease of motion and perception of size was less in the direction of flexion-extension and adduction-abduction motions.

Proportional-Derivative (PD) control is one of the most widely used controllers, especially for robot manipulators. When the robot presents gravitational terms, PD control cannot guarantee position convergence, therefore compensation is required such as PD with gravity compensation, PD+G. PD+G control requires knowledge of the gravitational term and there exist several results that prove global asymptotic stability. However, there is no method to tune the PD gains. In this work, a novel method to tune the PD+G controller is proposed. The tuning method is obtained using the global asymptotic stability result of the La Salle's theorem and robot dynamics properties. A comparison between previous works is realized via simulations and experiments to verify our approach. The results show fast and smooth convergence to the desired reference without overshoots.

This paper describes a semi-active assistive exoskeleton for upper-body motion assistance. The exoskeleton combines a passive shoulder exoskeleton and an active elbow joint unit, which can achieve both passive gravity compensation and also active assistance to carrying and sit-to-stand motion. The design, sensing and control are introduced, with preliminary test results performed.

This work investigates the gravity compensation topic, from a control perspective. Thegravity could be levelled by a compensating mechanical system or in the control law, suchas proportional derivative (PD) plus gravity, sliding mode control, or computed torquemethod. The gravity compensation term is missing in linear and nonlinear optimal con-trol, in both continuous- and discrete-time domains. The equilibrium point of the controlsystem is usually zero and this makes it impossible to perform regulation when the desiredcondition is not set at origin or in other cases, where the gravity vector is not zero at theequilibrium point. The system needs a steady-state input signal to compensate for the grav-ity in those conditions. The stability proof of the gravity compensated control law basedon nonlinear optimal control and the corresponding deviation from optimality, with proof,are introduced in this work. The same concept exists in discrete-time control since it usesanalog to digital conversion of the system and that includes the gravity vector of the sys-tem. The simulation results highlight two important cases, a robotic manipulator and atilted-rotor hexacopter, as an application to the claimed theoretical statements. GRIFFIN ERC-2017-Advanced Grant, Action: 788247 EU H2020 AERIAL-CORE project contract 871479 EU H2020 HYFLIERS project 779411

Our sensorimotor control is well adapted to normogravity environment encountered on Earth and any change in gravity significantly disturbs our movement. In order to produce appropriate motor commands for aimed arm movements such as pointing or reaching, environmental changes have to be taken into account. This adaptation is crucial when performing successful movements during microgravity and hypergravity conditions. To mitigate the effects of changing gravitational levels, such as the changed movement duration and decreased accuracy, we explored the possible beneficial effects of gravity compensation on movement. Local gravity compensation was achieved using a motorized robotic device capable of applying precise forces to the subject’s wrist that generated a normogravity equivalent torque at the shoulder joint during periods of microgravity and hypergravity. The efficiency of the local gravity compensation was assessed with an experiment in which participants performed a series of pointing movements toward the target on a screen during a parabolic flight. We compared movement duration, accuracy, movement trajectory, and muscle activations of movements during periods of microgravity and hypergravity with conditions when local gravity compensation was provided. By using local gravity compensation at the arm, we were able to mitigate the changes in movement duration, accuracy, and muscle activity. Our results suggest that the use of such an assistive device would help with movements during unfamiliar environmental gravity.

This paper presents a new concept of supplementary arms for the collaborative task with a worker during a thin panel installation on the wall. Foldable robot arms for holding and installation (FRAHI) using scissor structure have been proposed as a new concept of the human-robot collaboration. The foldable and wearable FRAHI arm has been designed to influence cooperativeness and worker safety. FRAHI arms are developed and integrated with a worker's safety suit, and a soft and flexible waist belt is introduced for the arms and worker interface, comfortable to the user while working. The design principle of FRAHI is based on folding capability, gravity compensation for the cooperative thin-panel installation with workers. The experimental demonstration of a thin panel installation on the wall has been performed for the feasibility of the supplementary arm for worker assistance and cooperativeness in construction works.

Dynamics of a two degree-of-freedom suspension mechanism is incorporated into nonlinear control design to facilitate its potential use as a rehabilitation device to aid people with lower-limb injuries. The proposed mechanism is a variation of the standard four-bar linkage with an extra link and two springs. The system dynamic model is first extracted based on the Lagrange’s equations in conservative form. The performance deviations due to the link inertia is demonstrated in open-loop numerical simulations under an impulsive force scenario. Finally, the dynamic model of the suspension mechanism is incorporated into feedback control design based on nonlinear, sliding mode control strategy that can add robustness against modeling uncertainties and external disturbances. The tracking performance of the proposed nonlinear controller is validated in closed-loop numerical simulations to demonstrate possible performance improvements under feedback control.

In a fine mold manufacturing process, the polishing process plays an important role in enhancing the surface quality and is performed manually by skilled workers. However, there are many problems such as decrease in skilled workers, health hazards due to scattering of abrasives, and difference in surface quality due to difference in the proficiency. Hence, there is a strong demand for automation of the polishing process at present. In this research, a robot polishing system that applies macro-micro mechanism is proposed. The functional polishing module of the end effector is developed and attached to the hand of the serial link robot. Tool path and posture are controlled in a serial link robot as a macro mechanism, and polishing force and tool rotation speed are controlled in the developed polishing module as micro mechanism. This mechanism ideally controls position, force, and rotation speed at the same time. An interlocking control system for position and force has already been constructed. In this paper, we constructed gravity compensation and evaluated the force control performance of the constructed system. Through the evaluation, the followability of the estimated reaction force to the command force and the validity of the actual force behavior measured by the force sensor were evaluated.

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.

If a robot system can take various shapes, then it can play various roles, such as humanoid, dog robot, and robot arm. A modular robot is a robot system in which robots are configured using multiple modules, and it is possible to configure robots of other shapes by varying the combinations of the modules. In conventional modular robots, the shape is restricted by gravity, and configurable shapes are limited. In this study, we propose a gravity compensation modular robot to solve this problem. This paper describes the design and prototyping of the gravity compensation modular robot, and provides examples of robot shapes configured using the gravity compensation modules and motion experiments of the robots. In the experiments, there were motions that the robots could perform and could not perform. We considered the lack in the gravity compensation level and module rigidity as the main factor of the failures. This paper also discusses the solutions to these problems.

External disturbance forces caused by nonlinear springy electrical cables in the Master Tool Manipulator (MTM) of the da Vinci Research Kit (dVRK) limits the usage of the existing gravity compensation methods. Significant motion drifts at the MTM tip are often observed when the MTM is located far from its identification trajectory, preventing the usage of these methods for the entire workspace reliably. In this paper, we propose a general and systematic framework to address the problems of the gravity compensation for the MTM of the dVRK. Particularly, high order polynomial models were used to capture the highly nonlinear disturbance forces and integrated with the Multi-step Least Square Estimation (MLSE) framework. This method allows us to identify the parameters of both the gravitational and disturbance forces for each link sequentially, preventing residual error passing among the links of the MTM with uneven mass distribution. A corresponding gravity compensation controller was developed to compensate the gravitational and disturbance forces. The method was validated with extensive experiments in the majority of the manipulator's workspace, showing significant performance enhancements over existing methods. Finally, a deliverable software package in MATLAB and C++ was integrated with dVRK and published in the dVRK community for open-source research and development.

Static balancing through passive devices is a suitable strategy to reduce motor loads for numerous applications in the automation and robotics fields. Many known methods require initially defining which balancing elements to install, thus possibly limiting the compensation effectiveness, since potentially optimal solutions may be neglected. This work presents an approach to statically balance linkages characterized by open and/or closed kinematic chains. The proposed algorithm searches for possible balanced variants of the mechanism that can be arranged by installing combinations of counterweights and springs, without auxiliary linkages. If solutions are found, the corresponding balancing parameters are tuned for optimizing the mechanism energy consumption, by considering the mechanism dynamics when performing its operational tasks. Actual benefits and drawbacks of the variants are assessed through quantitative criteria. The corresponding performance indicators are proposed as a guideline for designers to identify the most convenient balancing solutions. The implemented procedure is general and suitable to study any mechanism admitting closed-form solutions for its forward kinematics. A case study concerning an industrial palletizing robot is reported as an example of application. Overload issues affecting the robot actuators are solved through gravity compensation. The results achieved for the industrial problem prove the procedure effectiveness.

In the present contribution, a methodology to solve the tracking control problem of robot manipulators through the use of a Proportional Retarded plus Gravity (PR+G) compensation scheme is presented. The main advantage of the proposal is to avoid the necessity of velocity measurements or their estimation, which is commonly used in most control schemes, such as the proportional derivative-type controllers or the computed torque control. The design of the PR+G controller is addressed via σ-stability analysis and its performance is tested in an experimental platform that consists of 2 degrees of the freedom robot manipulator. The proposed controller is compared with a classic proportional derivative plus gravity compensation scheme. The results are analyzed from a frequency perspective and measured by a quadratic error index.

The decommissioning of the Fukushima Daiichi Nuclear Power Plants is a national urgent problem in Japan. The distribution and characteristics of the fuel debris inside the nuclear reactor must be investigated to safely retrieve them. This letter describes a 10-m-long articulated manipulator for investigation inside the primary container vessel. We employed a coupled tendon-driven mechanism and a gravity compensation mechanism using synthetic fiber ropes to design a lightweight and slender articulated manipulator. After discussing the basic principle and control algorithm, we focus on the detailed mechanical design of a prototype model. We confirmed its feasibility through basic motion experiments.

Door-opening is a critical problem for robots used for rescue purposes in nuclear power plants (NPPs). A force and torque (F/T) sensor is not used in the rescue task for door-opening in the NPPs environment. It is, therefore, necessary to study the dynamic model of door-opening. The NPPs door and a door handle dynamic model are significant to the mechanical design, simulation, and dynamic feed-forward control of an NPP robot. To obtain the accurate force data of door-opening, a method based on a gravity compensation algorithm combined with a transformation of the contact force of the end effector is proposed. This paper analyzes the structural features and dynamics model of a fire door and a door handle. Methods for identifying the model parameters are also developed by combining a Nelder-Mead simplex search with the least-squares algorithm. The extensive door-opening experiments were carried out in this paper, and the results validate the fidelity of the derived dynamic models of the door and the door handle.

This paper presents a novel two degrees of freedom (DOFs) contact force control method for robotic blisk grinding. The grinding tool is controlled to automatically adapt to the curvity change of the blisk blade and maintain a constant contact force as expected. A smart end effector is used as the actuating device for contact force control. The proposed force controller includes a gravity compensation module, a force prediction module, and a force-position controller. The direction and amplitude of the contact force are predicted with the force prediction module and are controlled with the force-position controller. The tool path of the robotic blisk grinding process is generated and optimized so that the contact points between the tool tip and the workpiece are evenly distributed along the grinding path. Both simulations and experiments are carried out to validate the effectiveness of the proposed method. The results show that the proposed method provides a good contact force control performance, with less than 1 N force fluctuation. The surface finish and roughness are significantly improved compared to the case without force control. The grinding efficiency is raised by about sixfold compared to the case with one DOF force control.

The paper studies the angle tracking control of the elbow joint and the end-point of the human musculoskeletal arm model. It uses a Hill-type planar model with six muscles and two links. During the motion, the gravity compensation is emphasized since it has significant influence on actual anthropomorphic arm system. An adaptive fuzzy sliding mode control method is proposed and applied to make the elbow joint and the end point of the human musculoskeletal arm model track certain angles. Through the adaptive fuzzy system, it may realize the adaptive approximation of switching scales of sliding mode controller so as to avoid chattering. Numerical simulations are performed in order to verify the proposed control method. Results show that accurate angle tracking control may well be accomplished by proposed sliding mode controller.

This paper presents the static balancing design of a special reconfigurable linkage that can switch between two one-degree-of-freedom (DoF) working configurations. We will show that the studied dual-mode linkage only requires one mechanical spring or one counterweight for completely balancing its gravitational effect in theory at both modes. First, the theoretical models of the spring-based and the counterweight-based designs are derived. The proposed design concepts were then demonstrated by a numerical example and validated by software simulation. Experimental tests on both designs were also performed. The result of this study shows that a reconfigurable mechanism with N working configurations can be completely statically balanced by using less than N passive energy elements.

In order to improve the control efficiency of the guidance law of mortar shells, this paper uses Python tools to perform gravity compensation on the traditional proportional guidance method, and designs a PID controller to simulate the control of mortar shells. Monte carlo uncontrolled mortar shells and mortar shells are subjected to simulated target shooting tests, and the circle probability error of the stationary target is calculated, and the control ability is analyzed.

Advances in machine learning technologies in recent years have facilitated developments in autonomous robotic systems. Designing these autonomous systems typically requires manually specified models of the robotic system and world when using classical control-based strategies, or time consuming and computationally expensive data-driven training when using learning-based strategies. Combination of classical control and learning-based strategies may mitigate both requirements. However, the performance of the combined control system is not obvious given that there are two separate controllers. This paper focuses on one such combination, which uses gravity-compensation together with reinforcement learning (RL). We present a study of the effects of gravity compensation on the performance of two reinforcement learning algorithms when solving reaching tasks using a simulated seven-degree-of-freedom robotic arm. The results of our study demonstrate that gravity compensation coupled with RL can reduce the training required in reaching tasks involving elevated target locations, but not all target locations.

Nowadays, robotic research focuses more and more on attaining energy-efficient and safe solutions. They are key-aspects of industrial robots, such as inspection and maintenance robots. The introduction of a mechanism that passively compensates the joint torque caused by the weight of the robot may offer a valid solution. Avoiding the need for actuators to balance gravity torques helps decrease the power consumption and the size of the actuators. Furthermore, a passive gravity compensation mechanism allows the robot to hold a static position without the need for an external power source, hence avoiding the risk of collapsing in case of failure of the actuators. This work focuses on designing a torque generator composed of a non-circular pulley and a spring, which, by solving a convex optimisation problem, offers a new methodology for creating any generic torque and thereby also succeeds in solving gravity compensation problems. This methodology guarantees the outcome of feasible non-circular pulleys which minimise the torque required to perform any specific task.

Surgical robots are safety-critical devices that require multiple domains of safety features. This article focuses on the passive gravity compensation design optimization of a surgical robot. The limits of this optimization are related with the safety features including minimization of the total moving mass/inertia and compactness of the design. The particle swarm optimization method is used as a novel approach for the optimization of a parallel remote-center-of-motion mechanism. A compact design is achieved by partially balancing the mechanism, which also decreases the torque requirements from the actuators.

The chapter approaches the issues of modeling the process of load lifting by a person while wearing an exoskeleton. The classification of existing gravitational compensation systems for industrial exoskeletons is shown, as well as examples of its use. A mathematical model of lifting a person's load in the exoskeleton is presented, as well as numerical parameters are calculated. It is shown that the introduction of an elastic element reduces the level of energy consumption during work, and can also facilitate the level of the worker. Industrial exoskeleton prototype design is presented. A particular focus is given to studying the influence of the gravity compensator on the magnitude of the moments generated by the electric drives of the hip and knee joints. It is shown that the use of gravity compensators enables to reduce significantly the load on electric drives.

Serial robot manipulators have their servo motors with reduction gears on the link joints. When it comes to hyper-redundant robots, this kind of joint actuation mechanism cannot be implemented since this makes hyper-redundant robots too heavy. Instead, cable driven mechanisms are preferred. However, the positioning accuracy is negatively affected by the cables. This paper addresses the positioning accuracy problem of cable driven hyper-redundant robots by employing a 2-DOF robotic arm whose modules are counter-balanced. While the actuators connected to the base actively do most of the work using cables and springs, light and compact actuators connected to the links produce precise motion. The method will result in compact, light and precise hyper-redundant robotic arms. The above-mentioned procedure governed by a control software including a 2D simulator developed is experimentally proved to be a feasible method to compensate the gravitational torque successfully.

Good trajectory tracking and fast convergence are critical characteristics on medical and industrial applications. This behavior must be ensured despite the presence of disturbances to successfully complete the task. This work presents the design and robustness comparison of two control approaches computationally implemented on UR5 robot for trajectory tracking. The control methods that will be compared are proportional-derivative control with gravity compensation and sliding mode control. Both control methods will be designed to ensure stability and good tracking of circular helicoidal trajectory on the operational space. In order to evaluate the robustness of both control methods, a controlled white-noise signal will be added to robot model. The obtained results indicate that sliding mode control deals better with external disturbances than proportional-derivative control with gravity compensation.

This paper presents a design concept for the gravity compensation of the renowned Delta parallel robot. The design is constructed by using three gear-spring modules, each being installed on the proximal link of each leg of the robot. This implementation can allow the balancing design to merely request a relatively small assembly space on the robot, thereby avoiding mechanical interference between the supplemental structures and robot links during operation. The spring design is realized by an analytical approximation to perfect balancing. A design example for an industrial Delta robot, namely FANUC M-3iA/12H, is also given. It is shown that the studied robot can theoretically demonstrate a 41.4% total motor torque reduction during a pick-and-place operation under a 10-kg load of the moving platform.

This paper addresses the problem of balancing as applied to robotic manipulators. After briefly outlining the existing balancing techniques, this paper proposes to achieve the balancing by adding non-linear springs to compensate gravity. Numerical simulations are carried out to demonstrate the feasibility and effectiveness of the proposed approach by referring to a pick-and-place task.

Busy agricultural seasons involve long-term continuous work and heavy labor. Particularly during overhead work, such as harvesting, gibberellin treatment, and bagging, workers need to consistently raise upper limb weights of approximately 2 to 4 kg with their own muscular strength, resulting in a high work burden. For long-duration work in the field, a passive and robust assist system is advantageous. Therefore, we propose an assistance device named TasKi that uses self-weight compensation mechanisms and horizontal link mechanisms to reduce the burden on a worker’s upper limbs during overhead work. TasKi can compensate for upper limb weight by using the force of a spring in various postures of the upper limbs without battery support. In this report, we describe the design of the TasKi mechanisms that achieve the upward work assist in actual agriculture with a simple structure. The mechanism of self-weight compensation and the degree of freedom and parameters of the link mechanism are studied.

A multi-DoF (Degrees of Freedom) haptic device is a crucial module in a teleoperation-based surgical robotic system. Numerous haptic devices have been developed for a surgeon to teleoperate slave surgical manipulators. However, these research prototypes can be arduous to reproduce outside the original lab, while the commercially available products are often quite expensive. To fulfill the need of affordable haptic devices for a teleoperated laparoscopic surgical system, a new master haptic device, the ParaMaster, with a parallelogram structure, is proposed in this study. The ParaMaster design is based on affordable direct drive motors and with 6-DoF inputs and 6-DoF outputs. The design concept, kinematics, dimension optimization, gravity compensation, design description and preliminary experimental verifications are elaborated. The ParaMaster is expected to be integrated into a laparoscopic surgical system after receiving full calibrations of its motion sensing and wrench outputs capabilities in the near future.

As the traditional teaching technology can not meet the requirements of complex teaching tasks, this paper studies the direct teaching technology of robots based on the force sensor's gravity compensation and admittance control. Through the gravity compensation of the force sensor, the influence of the gravity of the robot end tool, the installation tilt angle of the robot base and the zero point of the force sensor on the force sensor is reduced, and the teaching accuracy is improved. Using the admittance control principle, the robot can move according to the traction of the teaching staff, and regularly record the teaching points in the process to form the teaching trajectory. Finally, a direct teaching system was established, and the proposed gravity compensation algorithm and direct teaching algorithm were experimentally verified. The experimental results show that the proposed gravity compensation algorithm can achieve better compensation effect. The direct teaching algorithm based on admittance control can simplify the teaching process and complete complex teaching tasks.

In the field of intelligent assembly, it is often necessary to assemble workpieces without precise position relationship. For some workpieces with special position relationship, it is difficult to achieve accurate relative position measurement by machine vision. A good solution is provided by the way of force sensing guidance. According to the direction of the workpiece in the assembly process, the position deviation can be judged and the guidance can be corrected in real time, so the intelligent assembly can be realized. In this paper, an intelligent assembly method based on six dimensional force sensing guidance is designed, and the gravity compensation and solution method are designed.

During the Industry 4.0 era, the open source-based robotic arms control applications have been developed, in which the control algorithms apply for movement precision in the trajectory tracking paths based on direct or reverse kinematics. Therefore, small errors in the joint positions can summarize in large position errors of the end-effector in the industrial activities. Besides the change of the end-effector position for a given variation of the set-point in manipulator joint positions depends on the manipulator configuration. This research proposes a control based on Proportional Derivative (PD) Control with gravity compensation to show the robustness of this control scheme in the robotic arm&rsquo, s industrial applications. The control algorithm is developed using a low-cost board like Raspberry Pi (RPI) where the Robot Operating System (ROS) is installed. The novelty of this approach is the development of new functions in ROS to make the PD control with gravity compensation in low-cost systems. This platform brings a fast exchange of information between the Kuka&trade, youBot robotic arm and a graphical user&rsquo, s interface that allows a transparent interaction between them.

Wheelchair upper-limb exoskeletons can offer a new paradigm to assist people with neuromuscular dysfunction in their activities of daily living such as eating and drinking. A key challenge in their control is to ensure safe and comfortable interaction between the human upper limb and exoskeleton. Compared with industrial manipulators, exoskeletons suffer severe kinematic and dynamic uncertainties and external disturbances. Therefore, the selection of optimal control methods that can address the aforementioned challenge is required. In this article, a method combining proportional-derivative (PD) control, sliding mode control, and fuzzy logic control, i.e., PD-based fuzzy sliding mode control, is developed to deal with unmodeled dynamics and external disturbances in the human-exoskeleton system. The sliding mode control can be generally divided by the equivalent control law and the switching control law. For the basic equivalent control part, it adopts the PD controller due to its simplicity in controller design and parameter tuning. For the switching control part, it is replaced by fuzzy logic control to eliminate the chattering of control input such that the smooth motion of the system is achieved. Simulation and experiment results are provided to show the effectiveness of the proposed control method.

This paper presents a design concept for gravity compensation of planar articulated robotic arms using a series of gear-slider mechanisms with springs. The spring-attached gear-slider mechanism has one degree-of-freedom (DOF) of motion, which can serve as a gear-spring module (GSM) to be installed onto the robot joints for leveraging the gravitational energy of the robot arm. The proposing GSM-based design is featured by its structure compactness, less assemblage effort, ease of modularization, and high performance for gravity compensation of articulated robotic manipulators. As a key part of the design, the stiffness of the spring in the GSM can be determined through either a design optimization or an analytical approximation to perfect balancing. The analyses on several 1-, 2-, and 3-DOF GSM-based robot arms illustrate that the analytical approximation to perfect balancing can reach nearly the same performance as provided through the design optimization. The power loss due to the gear contact is considered when evaluating the gravity compensation performance. A formula for spring stiffness correction is suggested for taking the power loss into account. An experimental study on a one-DOF GSM-based robot arm was performed, which shows that a power reduction rate of 86.5% is attained by the actuation motor when the GSM is installed on the robot arm.

This paper presents a novel portable passive lower limb exoskeleton for walking assistance. The exoskeleton is designed with built-in spring mechanisms at the hip and knee joints to realize gravity balancing of the human leg. A pair of mating gears is used to convert the tension force from the built-in springs into balancing torques at hip and knee joints for overcoming the influence of gravity. Such a design makes the exoskeleton has a compact layout with small protrusion, which improves its safety and user acceptance. In this paper, the design principle of gravity balancing is described. Simulation results show a significant reduction of driving torques at the limb joints. A prototype of single leg exoskeleton has been constructed and preliminary test results show the effectiveness of the exoskeleton. This paper presents a novel portable passive lower limb exoskeleton for walking assistance. The exoskeleton is designed with built-in spring mechanisms at the hip and knee joints to realize gravity balancing of the human leg. A pair of mating gears is used to convert the tension force from the built-in springs into balancing torques at hip and knee joints for overcoming the influence of gravity. Such a design makes the exoskeleton has a compact layout with small protrusion, which improves its safety and user acceptance. In this paper, the design principle of gravity balancing is described. Simulation results show a significant reduction of driving torques at the limb joints. A prototype of single leg exoskeleton has been constructed and preliminary test results show the effectiveness of the exoskeleton.

The paper deals with technical solutions for human walking and sitting balanced portable exoskeletons, in which the gravity compensation is carried out via cylindrical compression springs mounted on a slider mechanism. The proposed devices provide easy switching operation modes and can be used in both assisting of the human musculoskeletal system and in the physiotherapy. The performed analysis of developed devices has revealed their advantages: compactness, adjustability, balance, universality and also some drawbacks: the device compactness entails limitations on balancing capabilities, allowing exact static balancing of the human legs during walking, but only partial balancing of the body during sitting. Features of the design or the adjusting mechanism require considerable effort by the user to switch balancing modes, elimination of which requires an increase of spring’s stiffness coefficients. Compared with the previous ones, the proposed solution does not require a high spring stiffness to balance the system. The achieved main advantages of the device are universality and adjustability, the ability to provide dosing loads and ranges of angular displacements, and, consequently, improved efficiency in human physiotherapy.

Advances in legged robotics are strongly rooted in animal observations. A clear illustration of this claim is the generalization of Central Pattern Generators (CPG), first identified in the cat spinal cord, to generate cyclic motion in robotic locomotion. Despite a global endorsement of this model, physiological and functional experiments in mammals have also indicated the presence of descending signals from the cerebellum, and reflex feedback from the lower limb sensory cells, that closely interact with CPGs. To this day, these interactions are not fully understood. In some studies, it was demonstrated that pure reflex-based locomotion in the absence of oscillatory signals could be achieved in realistic musculoskeletal simulation models or small compliant quadruped robots. At the same time, biological evidence has attested the functional role of the cerebellum for predictive control of balance and stance within mammals. In this paper, we promote both approaches and successfully apply reflex-based dynamic locomotion, coupled with a balance and gravity compensation mechanism, on the state-of-art HyQ robot. We discuss the importance of this stability module to ensure a correct foot lift-off and maintain a reliable gait. The robotic platform is further used to test two different architectural hypotheses inspired by the cerebellum. An analysis of experimental results demonstrates that the most biologically plausible alternative also leads to better results for robust locomotion.

In this paper, a new asinh-type control scheme with gravity compensation for the position control problem of robot manipulators in joint space is presented. The properties and characteristics of the asinh control structure make the position error and the motion velocity asymptotically converge to the equilibrium point. A strict Lyapunov function to formally prove global asymptotic stability is developed. The tuning of the control gains is obtained by PSO (Particle Swarm Optimization) technique without saturating the servomotors. To illustrate the effectiveness and performance of the proposed scheme, an experimental comparative analysis between the proportional-derivative (PD) and atanh controls against the proposed algorithm on a three degrees of freedom direct-drive robot manipulator is carried out., The authors would like to thank the Benemérita Universidad Autonoma de Puebla, for its financial support with the project VIEP-100048866-2019 (Control de posición con ganancias variables de robots manipuladores), which partially supported this work.

Tethered satellite systems (TSSs) have shown great application potential in space missions, such as debris capture, active debris removal, and tether assisted observation. When the tether is deployed on-orbit, it may undergo a taut-slack process. This makes controlling a tether deployment more difficult than controlling a suspended tether. This paper examines a tether deployment subjected to an analytical control law in a ground-based experimental testbed. A dynamics similarity is proposed for the ground-based experiment to reproduce the dynamic environment of the tether deployment of the on-orbit TSS. Gravity compensation is used in the experiment to balance the friction forces and gravitation components that arise from the slight inclination of the testbed. The controlled stability is evaluated by the convergence of the pitch motion of the tether. The experimental results show that the controlled tether is successfully deployed along an assigned direction under a taut state during the deployment phase.

The vibration of the robot during the movement brings various irregular motion disturbances to the robot’s head, these vibration results into unstable images captures by the head-mounted vision system and therefor the vision system cannot accurately perceive the environment. This paper presents a mechanical stabilization method based on gravity and disturbance compensations, which considers and compensates the gravity influences of the mechanical structure and external disturbances. Finally, the current command of the joint motor is generated based on the compensations, which can quickly stabilize the image. We performed simulation and physical experiments to verify the performance of our proposed method.