Sensorless Force Control Research Articles

Improvement of force-sensorless grinding accuracy with resistance compensation

This research aims to achieve a new grinding robot system that can grind an object into desired shape with force-sensorless control. In order to grind the target object into desired shape with sufficient accuracy, the hand of the robot arm has to generate desired constrained force immediately after the grindstone being contacted with the metal object to be ground. Based on the algebraic equation, we have proposed constraint-combined force controller, which has the ability to achieve the force control without time delay if the motors should ideally generate required torques without time delay. In this paper, the relation between contacting force and grinding resistance force have been derived analytically and the relation is used for grinding force control, having brought improved grinding force accuracy.

Sensorless force feedback joystick control for teleoperation of construction equipment

This paper aims to develop an innovative approach named sensorless force feedback joystick control for teleoperation of construction equipment. First, a force sensorless supervisory controller is designed with two advanced modules: a neural network-based environment classifier to estimate environment characteristics without requiring a force sensor and, a fuzzy-based force feedback tuner to generate properly a force reflection to the joystick. Second, two local robust adaptive controllers are simply built using neural network and Lyapunov stability condition to ensure desired task performances at both master and slave sites. A teleoperation system is setup to demonstrate the applicability of the proposed approach.

Force Sensorless Multi-functional Impedance Control for Rehabilitation Robot

As more robotic technology has been developed and implemented for rehabilitation training, the conventional rehabilitation methodology is expected to change and to have various functional modes other than Continuous Passive Movement (CPM). In this paper, the multifunctional training that are expected for the rehabilitation robot to provide is introduced, and the control algorithm to achieve these functional training is proposed.As the multi-functions of rehabilitation training are categorized based on the type of reaction force of the robot, force control of robot is required in the realization of the functions, and force sensorless methodology is employed in this paper taking into consideration of the expense of sensors and mechanical design. A upper limb rehabilitation robot is utilized in the experiments, and the performance of the proposed force sensorless control for multi-functional rehabilitation is verified through the experiments.

Control of Low-Cost Customizable Robot Arm Actuated by Elastic Tendons

[abstFig src='/00280004/09.jpg' width='300' text='Elastic tendon driven robot arm' ] This paper presents a low-cost, lightweight robot arm with very low stiffness actuated by elastic tendons. To simplify the string tension control, a new winding device was developed. Small pulleys were incorporated into the winding drum to reduce friction between the tendon and the drum. A marionette-style two-link robot arm with compliant joints was prototyped. Because the arm and winding devices were separate from each other, the cost and weight of the robot were reduced. The links are made with lightweight wood connected by simple shaft joints. The robot design can be easily modified by the user because the mechanical parts do not require high machining accuracy. This robot is intended for implementation in tasks that do not require high positioning accuracy using a simple force control under environmental constraints. Because of its low stiffness, simple and sensor-less force control can be easily implemented based on the relationship between forces under static conditions. The proposed simple control method was evaluated experimentally by conducting position, static force, and hybrid position/force control tasks and was shown to perform well. The results also demonstrate that employing additional sensors, such as a camera, improves the accuracy of the controller.

High‐Precision Sensorless Force Control by Mode Switching Controller for Positioning Devices with Contact Operation

SUMMARYThis paper presents an approach to high‐precision sensorless force control for positioning devices that engage in a contact operation. The sensorless force control is designed with a sliding mode controller and contact model that provide the required control specifications to compensate for the nonlinear spring characteristics of the contact mechanism. The effectiveness of the proposed control approach was verified through numerical simulations and experiments using a prototype.

Constraint-Based and Sensorless Force Control With an Application to a Lightweight Dual-Arm Robot

The increasing demand for flexible robotized solutions in SMEs motivates the research on innovative and general control algorithms suitable for a large variety of applications. Particularly suited for this are constraint-based trajectory generation and control methods, which have been deeply investigated in the last decade. In this letter, we present an application of such a control framework for sensorless execution of a force control task as applied to a dual-arm redundant manipulator. Experiments and simulations confirm the effectiveness of the approach, even in the case of parametric uncertainties.

Micro-Macro Bilateral Control in Delta Robot

This paper presents new method to perform micro-macro bilateral control system in robot with non-linear kinematic property between task space and controllable space. An example is the parallel Delta Robot which is selected due to better interaction with human, light weight, fast movement and 3-dimension movement. The conventional micro-macro bilateral control using Hadamard matrix cannot achieve micro-macro bilateral properties of Delta Robot due to dimension shifting which leads to differences in both position and force space and loss of sensibility in haptic interface properties. The actual robot is built with design properties of low friction that reduce the complexity of dynamic model of Delta Robot. The controllable space or joint space is converted to task space using mathematic model. Moreover, the force applied on task space is estimated using sensorless force control system or disturbance observer and converted to task space by Andre Olsson’s dynamic model of Delta Robot.

Variable Dynamic Threshold of Jerk Signal for Contact Detection in Industrial Robots without Force Sensor

SUMMARYThis study proposes a variable dynamic threshold for a jerk signal for achieving contact detection in industrial robots. Sensorless force control is useful in applications in advanced industrial robots. The external torque of each joint is estimated accurately by using a disturbance observer and by inverse dynamics calculations. However, the phase lag of the disturbance observer and the dynamic parameter error create force estimation errors. These errors hamper quick and reliable contact detection in industrial robots. Therefore, this study proposes a useful approach to contact detection that uses a variable dynamic threshold for a jerk signal. The proposed variable dynamic threshold reduces contact detection failures caused by force estimation errors during the free motion of a robot. The proposed threshold is suitable for robot motion and improves the speed of contact detection. Numerical simulation results show that the proposed method is valid for the parameter variations in an actual industrial robot. In addition, experimental results show that the dynamic threshold is a useful technique for application to general robot systems as well. The dynamic threshold is useful in applications for any industrial sensorless force control system.

High-Precision Sensorless Force Control by Mode Switching Controller for Positioning Devices with Contact Operation

This paper presents a high-precision sensorless force control for positioning devices with contact operation. The sensorless force control is designed with a sliding mode controller and contact model that provide the required control specifications to compensate for the non-linear spring characteristics of the contact mechanism. The effectiveness of the proposed control approach was verified through numerical simulations and experiments using a prototype.

G-P-2 確率共鳴を用いたサーボモータの力センサレス化

In this paper, force sensor-less servo control technique for haptic interfaces using stochastic resonance is proposed. The haptic interface developed in this research consists of an AC servo motor with a ball screw. For estimation of applied force, Reaction Force Observer is employed. Since the ball screw structure has high viscosity, response of the force estimation is not suitable for practical industrial application. In this paper, to improve the system responsiveness, servo control system with stochastic resonance is proposed. Finally, several experiments show the effectiveness of the stochastic resonance.

センサレス力覚制御のための周波数領域における摩擦補償フィルタの設計

センサレス力覚制御のための周波数領域における摩擦補償フィルタの設計

Active chatter suppression in turning by band-limited force control

The suppression of chatter vibration is required to enhance the machined surface quality and to increase tool life. In this study, a new, conceptually active approach for chatter suppression in machining is proposed. The hybrid control method developed by applying sensorless force control with a disturbance observer enables the simultaneous and independent control of the position trajectory and band-limited forces. The proposed method is introduced to the carriage of a prototype desktop-sized turning machine, and the ability to suppress chatter is evaluated by end-face cutting tests. The results demonstrate that actively controlling a band-limited force leads to the avoidance of chatter.

706 磁気センサを用いた空気圧駆動ロボットハンドの角度・力センサレス化(OS12-1 北陸信越のロボティクス・メカトロニクス,オーガナイズドセッション12:「北陸信越のロボティクス・メカトロニクス」)

706 磁気センサを用いた空気圧駆動ロボットハンドの角度・力センサレス化(OS12-1 北陸信越のロボティクス・メカトロニクス,オーガナイズドセッション12:「北陸信越のロボティクス・メカトロニクス」)

Force sensorless control of power-assisted wheelchair based on motion coordinate transformation

Wheelchairs used by disabled people or caregivers are typical human-in-the-loop systems, of which the power-assisted control in accordance to a human’s perception is essential. This paper presents a force sensorless control based on a force/torque observer with a motion coordinate transformation for power-assisted wheelchairs. The output linear movement and angular velocity motions of a power wheelchair can be controlled independently by inherent coupling dual-driving-wheels with this transformation. A force observer design without numerical differentiation, which is utilized to indirectly measure the human’s pushing force, is proposed for realizing the force sensorless power-assisted control. An assistant performance index is adopted to evaluate the validity of the power-assisted control according to a specified power-assisted gain. Experimental results show that the proposed method can effectively estimate the human force exerted on the wheelchair for achieving power-assisted control.

Development of 5-axis polishing machine capable of simultaneous trajectory, posture, and force control

The buffing process for finishing an automobile's body is still done manually, and the final surface quality of the body depends on the skill and technique of the worker. To automate buffing, not only tool path control but also precise and fast force control is required. In this study, a novel methodology based on the sensor-less force control technique and the quarry matrix capable of the mode decoupling is proposed for a parallel mechanism polishing machine to control x–y trajectory, tool posture, and polishing force in z-direction, and its validity for automated buffing is verified.

Design for Sensorless Force Control of Flexible Robot by Using Resonance Ratio Control Based on Coefficient Diagram Method

Generally, the flexible robot system can be modeled as the two-mass system which consists of a motor and load connected by a spring. Thus, its elasticity causes resonance in the system. By using the conventional PID controller, this method cannot perform well in this situation. Much research has proceeded with the aim of reducing vibration. A new effective control method, the resonance ratio control, has been introduced as a new way to guarantee the robustness and suppress the oscillation during task executions for a position and force control. In this paper, three techniques are proposed for improving the performance of resonance ratio control. Firstly, a new multi encoder based disturbance observer (MEDOB) is shown to estimate the disturbance force on the load side. The proposed observer is not necessary to identify the nominal spring coefficient. Secondly, coefficient diagram method (CDM) has been applied to calculate a new gain of the force controller. A new resonance ratio gain has been presented as 2.0. Finally, the MEDOB and load side disturbance observer (LDOB) are employed to identify a spring coefficient of flexible robot system. By using the proposed identification method, it is simple to identify the spring coefficient and easy to implement in the real flexible robot system. The effectiveness of the proposed identification method is verified by simulation and experimental results.

A Basic Study on Biological Signal of Operator During Master-Slave System Control

In a master-slave system, operators control the master device based on visual information and sensory feedback. This suggests that the position sensors on the slave side are not always necessary. However, position signals are required to estimate the acting force conveyed to the slave using an observer which realize the force sensorless control. In this paper, we focused on the biological signals of the operator to estimate the slave side’s condition which can be used to estimate the external force. In the early stage of the research, we investigate biological signals just with 1-DOF masterslave system. First, we measured electromyographic (EMG) and gripping force of operators when pushing objects. We verified that predictive signals can be used for estimation of touching the objects. Second, we propose a method, which uses wrist joint torque and Total Contraction Level (TCL) calculated by the EMG when pushing the virtual elastic films, of estimating the acting force conveyed to the slave. We verify that the proposed method can estimate external force under specific conditions with a trained subject.

Actuators for Motion Control: Fine Actuator Force Control for Electric Injection Molding Machines

Currently, most plastic products are manufactured using injection molding machines, where the product quality largely depends on the injection force. In a typical injection molding machines force control system, force information from the machine environment is obtained by a force sensor. However, these sensors have a few disadvantages in terms of signal noise, sensor cost, and narrow bandwidth, and thus a sensorless force detection method is desirable. The use of a reaction force observer, based on the two-inertia resonant model, has been proposed, but this method suffers from some estimation errors due to the influence of nonlinear characteristics in the holding process and the screw back-pressure process. This article proposes a new injection force estimation method based on a high-order reaction force observer (HORFO) with Coulomb friction compensation, which is not significantly influenced by the nonlinear friction phenomenon. Moreover, this article evaluates the possibility and versatility of a sensorless force control system using the proposed HORFO with Coulomb friction compensation.

Fine-Motion-Control Method for Realizing High-Accuracy and High-Speed Contact Motion of Industrial Robots by Employing Sensorless Force Control

This paper proposes a new fine-motion-control method for realizing high-accuracy and high-speed contact motion of industrial robots by employing sensorless force control. Today, although industrial robots have become considerably important in the modern industrial society, their functions are limited. A typical limited function is the positioning motion control of robots used in the manufacturing industry. Contact motion is necessary for almost all new applications. In this study, by employing the proposed motion control, smooth and quick contact motion of industrial robots is realized by using a sensorless I-P (Integral-Proportional) force feedback controller. The proposed method is simple and effective, takes into account both the inertia of a robot and the behavior of the I-P force controller. In the experiments, a three-degree-of-freedom robot is brought into contact with an object (a concrete block or a rubber board) by the I-P force control using the proposed method. Further, in the experiment, the motion of the robot's end-effector was considered. The validity of the proposed method is confirmed by using a six-axis force sensor and an acceleration sensor in the contact motion experiments.

Nonlinear black-box models and force-sensorless damping control for damping systems using magneto-rheological fluid dampers

In vibration control field, magneto-rheological (MR) fluid dampers are semi-active control devices that have recently begun to receive more attention. This paper presents a nonlinear black-box model (BBM) and an inverse black-box model (IBBM) for the identification of a MR fluid damper and their application to design a novel force-sensorless control method for any damping system using that damper. The nonlinear model named ‘black-box’ is a simple direct modeling method which was designed based on fuzzy-neural technique. Characteristics of the damper in study are directly estimated through a fuzzy mapping system. In order to improve the model accuracy, neural network technique including back-propagation and gradient descent method were used to train the fuzzy parameters to minimize the modeling error function. The inverse model, IBBM with self-learning ability, was then derived based on the BBM with optimized parameters and neural network technique. Consequently, the designed BBM and IBBM models can be used as a ‘virtual’ force sensor and an adaptive force controller, respectively, to perform a closed-loop feedback force-sensorless control for any damping system which uses the corresponding MR fluid damper. Effectiveness of the proposed models for modeling as well as force-sensorless damping control technique has been investigated through a series of simulations and real-time experiments on two vibrating systems employing the same MR fluid damper. The simulation and experimental results show that the suggested BBM could describe well the MR fluid damper behavior and could be combined with the IBBM for the force-sensorless damping control system.