Force-free Control Research Articles

Force-Free Control for Direct Teaching of a Surgical Assistant Robot End Effector with Wire-Driven Bidirectional Telescopic Mechanism.

This paper shows the design and modeling of an end effector with a bidirectional telescopic mechanism to allow a surgical assistant robot to hold and handle surgical instruments. It also presents a force-free control algorithm for the direct teaching of end effectors. The bidirectional telescopic mechanism can actively transmit force both upwards and downwards by staggering the wires on both sides. In order to estimate and control torque via motor current without a force/torque sensor, the gravity model and friction model of the device are derived through repeated experiments. The LuGre model is applied to the friction model, and the static and dynamic parameters are obtained using a curve fitting function and a genetic algorithm. Direct teaching control is designed using a force-free control algorithm that compensates for the estimated torque from the motor current for gravity and friction, and then converts it into a position control input. Direct teaching operation sensitivity is verified through hand-guiding experiments.

Force-free control of low drag resistance for humanoid robot joint

A method for the force-free control of humanoid robot joints is presented that meets human–machine cooperation functions of a humanoid robot. To ensure accurate torque control, the current loop of the permanent magnet synchronous motor was initially optimised and its dynamic response improved with a compensating back electromotive force. The motor speed is then estimated by sampling the voltage and current, the values of which are used in the calculation of the joint angle and the gravitational-force compensation. Finally, a method to evaluate the dynamic force compensation is applied that then yields the motor output offset, the total gravitational load, the partial inertia force, and the partial friction moment. Experimental results show that this method reduces the drag torque to less than 1 Nm. This method can be widely applied to a variety of robotic joints.

Research on the forcefree control of cooperative robots based on dynamic parameters identification

PurposeThis paper aims to propose a forcefree control algorithm that is based on a dynamic model with full torque compensation is proposed to improve the compliance and flexibility of the direct teaching of cooperative robots.Design/methodology/approachDynamic parameters identification is performed first to obtain an accurate dynamic model. The identification process is divided into two steps to reduce the complexity of trajectory simplification, and each step contains two excitation trajectories for higher identification precision. A nonlinear friction model that considers the angular displacement and angular velocity of joints is proposed as a secondary compensation for identification. A torque compensation algorithm that is based on the Hogan impedance model is proposed, and the torque obtained by an impedance equation is regarded as the command torque, which can be adjusted. The compensatory torque, including gravity torque, inertia torque, friction torque and Coriolis torque, is added to the compensation to improve the effect of forcefree control.FindingsThe model improves the total accuracy of the dynamic model by approximately 20% after compensation. Compared with the traditional method, the results prove that the forcefree control algorithm can effectively reduce the drag force approximately 50% for direct teaching and realize a flexible and smooth drag.Practical implicationsThe entire algorithm is verified by the laboratory-developed six degrees-of-freedom cooperative robot, and it can be applied to other robots as well.Originality/valueA full torque compensation is performed after parameters identification, and a more accurate forcefree control is guaranteed. This allows the cooperative robot to be dragged more smoothly without external sensors.

Demonstration-based Programming of Multi-Point Trajectories for Collaborative Continuum Robots

Soft robots can sense deformations caused by small external forces such that the robot itself is a suitable interface for teaching motions. We present an operational concept for collaborative continuum robots, consisting of an adapted force-free control as haptic interface for recording points and a replay algorithm to execute point-to-point motions with an extension to multi-point trajectories. The proposed method is general with the exception of an estimate of transition times between arbitrary static configurations which depends on the dynamic constraints of the considered robot. In-spite of it’s simplicity the provided setup illustrates the potential of interactive continuum robots for individualized assistance.

Design and Implementation of Admittance Control for a Dual-Arm Robot under Space Limitation

Aimed at the situation lack of suitable industrial robots with speed requirement and space limitation, a novel simple structured and high speed dual-arm robot is designed. The robot control system has been achieved by using high speed controller, real-time bus EtherCAT and integrating the sensor system via Ethernet interface. Kinematic and dynamic analysis are the basis of its kinematic control and trajectory planning. This paper presents a force-free control method for direct teaching of the robot and adopts a Cartesian admittance control algorithm to realize human-machine interaction. The admittance control is conducted by utilizing six-dimensional force/torque sensor fixed to the end-effector of manipulator. To evaluate the performance of the proposed controller and control algorithm, a point-to-point teaching task is conducted.

Force-free control for the flexible-joint robot in human-robot interaction

The force-free control means that the robot arm does not seem to be affected by gravity, frictions, and inertial force during the interaction with human. An advanced force-free control method can greatly improve work efficiency. In this paper, a novel force-free control method of the flexible-joint robot is proposed. First, the mathematical models of flexible joint and flexible-joint robot are established, and the force-free controller which can realize the gravity-free situation and reduce the frictions and inertial torques is designed based on the models. Then, the dynamic parameters of the robot arm are obtained by means of a self-measuring way. Finally, a flexible-joint robot experimental system is assembled, and the verification of force-free control method is carried out. Moreover, the method converts external force into joint velocities in the joint servo controllers to improve the stability of the movement.

Force-free Control for the Direct Teaching of Robots

Force-free Control for the Direct Teaching of Robots

Experimental evaluation of teleoperation system with force-free control and visual servo control by human operator perception

This research considers the teleoperation of an articulated robot arm by means of force-free control and visual servo control (VSC) over communication channels using the Internet technology. A semi-autonomous type teleoperation system contains a human supervisory control and VSC schemes and switches one scheme to another for accomplishing the required task accurately. The main investigation is carried out to find how it effectively improves the accuracy and the effectiveness of the teleoperation after provision of a visual feedback channel to the system. The system accuracy, effectiveness, repeatability and handleability based on the human operator's skills and operator's cognitive aspects are evaluated using experimental results and statistical data analysis. Effectiveness of the statistical analysis is assured by increasing the number of experiment data and assuming environmental factors, and implicit variables maintain to be unchanged. Correlation coefficients are calculated to find out how controlled input parameters are related to the successful output given by the system.

Investigation of Lighting Conditions for Teleoperation of Robot Arms by Image Processing and Force-free Control

Investigation of Lighting Conditions for Teleoperation of Robot Arms by Image Processing and Force-free Control

フォースフリー制御を用いた産業用多関節ロボットアームの遠隔操作システム

A lot of robots are operated in industry. In this paper, teleoperation system of industrial articulated robot arms is proposed. Both of the operation side and the work side, the industrial robot arms are used. In the operation side, the forcefree control technique is adopted for realization of the passive motion due to the influence of external force, and in the work side, the contour control is adopted for realization of the same motion of the robot arm in the operation side. The information of the motion of the robot in the operation side is sent to the work side through network. The method can realize replacement of the roles in the operation side and the work side only by changing the control techniques. The effectiveness of the proposed teleoperation system is confirmed by the experimental results using actual robot arms.

Development of meal assistance orthosis for disabled persons using EOG signal and dish image

A meal assistance orthosis is developed for elderly and/or disabled persons who have partly or completely lost the ability of moving their upper limbs by themselves independently. The meal assistance orthosis supports the disabled persons and brings foods from dishes to their mouth by their own forearms. Target positions of the meal assistance orthosis, i.e., the scooping points on dishes can be determined by using image processing of the dish image taken by a video camera. Human intention of food selection can be extracted from electrooculogram (EOG) signals which are measured by electrodes on the face. Position control is adopted for control strategy of the meal assistance orthosis and force-free control which can realise flexible motion of the meal assistance orthosis is adopted in order to avoid injuring the users. The effectiveness of the developed meal assistance orthosis is assured by experimental works on normal persons.

Forcefree control with independent compensation for industrial articulated robot arms

Forcefree control of robot manipulators so far has been the passive motion of the arm due to the influence of external force under ideal conditions of zero gravity and zero friction, whereas this paper demonstrates forcefree control under assigned friction, gravity and inertia. The effectiveness of the proposed forcefree control with independent compensation is confirmed by comparing the experimental results with simulation results. Comparisons of the forcefree control with independent compensation to the other force control methods are also presented.

Neural network-based hybrid human-in-the-loop control for meal assistance orthosis

In order to assist some elderly and disabled people, who have partly or completely lost the ability of moving their upper limbs due to neurological disabilities or spinal cord disease, to take meals by themselves independently, a new type of meal assistance orthosis was recently developed. This paper presents a neural network-based hybrid human-in-the-loop control for this meal assistance orthosis with functional and safety purposes. In this approach, the position control and the force-free control are integrated into a single controller based on the model of meal assistance orthosis. By means of the position control, the meal assistance orthosis is controlled to generate appropriate compensation forces for assisting the movement of upper limb. In order to reduce the risk of hurting the bodies of human end-users and of damaging the device due to the impact from large external forces, with the force-free control, the meal assistance orthosis can flexibly move with the driven of large external forces. In addition, the controller of the meal assistance orthosis can be smoothly switched between the position control and the force-free control through a designed process to avoid instantaneously generating large external force owing to hard switching. In order to improve the adaptability of the proposed approach to different subjects, neural networks are adopted in the controller. Moreover, the proposed approach fully takes into account the influence of external forces induced by upper limb in the control process to form a kind of human-in-the-loop control. With the simulation and experiment of the meal assistance orthosis, the effectiveness of the proposed method was verified.

FORCEFREE CONTROL WITH INDEPENDENT COMPENSATION FOR INDUSTRIAL ARTICULATED ROBOT ARM

In this paper, the concept of forcefree control is extended to realize flexible motion of industrial articulated robot arms under the virtual operational circumstances such as free of inertia, friction and gravity through independent compensation of inertia, friction and gravity. The forcefree control with independent compensation was verified with an experimental study of an actual industrial robot arm.

Forcefree Control with Independent Compensation of Inertia, Friction and Gravity for Industrial Articulated Robot Arms

Forcefree control is a kind of robot arm control method as if it existed under non-gravity and non-friction conditions. In this paper, the forcefree control with independent compensation was proposed, in which inertia, friction and gravity torque were compensated independently. The proposed forcefree control with independent compensation was assured by simulation and experimental results. Furthermore, experimental results of pull-out-work and direct teaching of an industrial articulated robot arm were shown as applications of the proposed method.

Orthogonal Type Forcefree Control by Considering Following Locus for Industrial Articulated Robot Arm

Orthogonal Type Forcefree Control by Considering Following Locus for Industrial Articulated Robot Arm

Forcefree Control with Assigned Locus for Position Input Type Articulated Robot Arm

Forcefree Control with Assigned Locus for Position Input Type Articulated Robot Arm

Human direct teaching of industrial articulated robot arms based on force-free control

Force-free control produces motion in a robot arm as if it were under conditions with no gravity and no friction. In this study, a method of force-free control is proposed for industrial articulated robot arms. The force-free control proposed was applied to the direct teaching of industrial articulated robot arms in that the robot arm was moved by direct human force. Generally, the teaching of industrial articulated robot arms is carried out using operational equipment called a teach-pendant. Smooth teaching can be achieved if direct teaching is applicable. The force-free control proposed enables humans to teach industrial articulated robot arms directly. The effectiveness of force-free control was confirmed by experimental work on an articulated robot arm with two degrees of freedom.

産業用多関節ロボットアームに対するカセンサレスのフォースフリー制御

This paper realized forcefree control of industrial articulated robot arm without external addition of force sensors. The forcefree control enables a motion of the industrial articulated robot arm as if it were in circumstance of non-gravity and non-friction condition. External force is detected by a torque monitor which is usually used in the servo controller of the industrial robot arm. The effectiveness of the proposed force sensor-less forcefree control was assured by simulation and experimental results of an actual industrial robot arm.