Jozef Suchý

An approach to compliant motion of an industrial manipulator

Abstract This article presents an approach to robot force control for a compliant motion task with a commercial robot system. It consists of two parts: First is the algorithm for fast and sure environment contact detection. Second is the hybrid position/force control algorithm for contour following of an unknown surface. It contains the estimation of gradient of environment surface at contact point and the adaptation of working velocity. The approach is implemented in the robot controller and its functionality is shown on the drawing example task. The results of new algorithm are compared with results of the standard force control functions.

NOVEL JOINT SPACE FORCE GUIDANCE ALGORITHM WITH LABORATORY ROBOT SYSTEM

Abstract This article presents the implementation of a new algorithm of force guided motions with a six axis articulated robot frequently used in research laboratories. This new approach is based on the idea of impedance control in joint space and it is implemented on a digital signal processor-based robot controller. It allows an intuitive force guidance of the robot by taking the gripper by the hand. Robot may be also guided over the singularities in this way. Behaviour of the robot is thus freely programmable in the wide range.

Possibilities of force based interaction with robot manipulators

One way of interaction between a human and a robot manipulator is the interaction via forces and torques. We will call it also force guidance. For this purpose the human acts on the robot arm or on the robot end-effector. From the interaction forces and torques than a suitable motion of the robot is generated. This kind of human robot interaction may be useful e.g. for the comfortable teach-in process. Commonly, positions and orientations of the robot tool are taught by the operator using the manual control pendant. With the keys on this device he or she moves the robot in joint or in task space. To improve the usability of the robot, some manual control pendants are additionally equipped with a more intuitive teach in device. It is called 6D mouse or space mouse (Hirzinger & Heindl, 1986). For further optimization of the teach-in process another way to move the robot would be force guidance. It will be shown that it is possible, with some differences, both in joint or in task space. Force based human robot interaction can be seen as a special kind of active robot force control (Zeng & Hemami, 1997). To perform this, the robot has to be equipped with a force/torque sensor (Gorinevsky et al., 1997). Usually this sensor is mounted in the robot wrist and it measures forces and torques in all Cartesian directions. The cost of such a 6D F/T sensor can exceed 10% of the price of a low payload six axes articulated robot. For that reason it should be searched for an alternative possibility of force/torque measurement. One idea is to estimate the interaction forces and torques from the joint motor currents. For this purpose an algorithm is presented and verified with experiments. Besides the kinematics of the robot motion during human robot interaction also its dynamics is important. For its representation the so called target or desired impedance behaviour will be defined as the relationship between interaction forces/torques and the velocity components of the robot motion. The simplest desired impedance behaviour is the behaviour of the mass damper system. Moreover, there are some more variants and additional features, e.g. the intuitive collision avoidance which will be described in this article. Apart from the desired impedance behaviour selected and parameterized by the operator the dynamics of the robot system has been respected. It depends on the access level of motion generation. Commonly, the robot motion is controlled by the trajectory generator. However, some robot systems permit the direct access to the position or velocity control loops which is favourable in all kinds of robot force control.

Intuitive Collision Avoidance of Robots Using Charge Generated Virtual Force Fields

This article presents an approach to intuitive collision avoidance of handoperated robots. Hand-operations are realized by means of zero-force impedance control using force/torque sensor. Impedance control is then combined with the method of artificial potential fields exerting force on the end-effector. This force can be felt by human, who acts on the manipulator and cooperates with the robot. The way to generate potential fields in this work is based on virtual electrical charges placed on the obstacle surfaces. In comparison with other approaches this method is quite universal and can be flexibly used for all forms of obstacles. It may be favourable to implement an additional artificial damping field to prevent hurting obstacles in the case of higher end-effector velocities. It is also possible to use this approach with moving obstacles. In this situation the charges would be placed dependent on sensor information provided e.g. by camera.

Vision Based Collision Avoidance of Industrial Robots

Abstract This article presents an approach to collision avoidance of industrial robots. It is based on the method of artificial potential or force fields. The field is generated by virtual charges which are placed on obstacles. The virtual force acts on the robot which results in the modification of the manipulator path to avoid collisions. Robot path modification is performed by means of impedance control. The positions of the obstacles are determined continuously by image processing using a simple USB camera, therefore collision avoidance is also able to deal with moving obstacles, e.g. other manipulators. All algorithms are implemented with a real robot system and experimental results are presented.

Automated Assistance Robot System for Transferring Model-Free Objects From/To Human Hand Using Vision/Force Control

This paper will propose an assistance robot system which is able to transfer model-free objects from/to human hand with the help of visual servoing and force control. The proposed robot system is fully automated, i.e. the handing-over task is performed exclusively by the robot and the human will be considered as the weakest party, e.g. elderly, disabled, blind, etc. The proposed system is supported with different real time vision algorithms to detect, to recognize and to track: 1. Any object located on flat surface or conveyor. 2. Any object carried by human hand. 3. The loadfree human hand. Furthermore, the proposed robot system has integrated vision and force feedback in order to: 1. Perform the handing-over task successfully starting from the free space motion until the full physical human-robot integration. 2. Guarantee the safety of the human and react to the motion of the human hand during the handing-over task. The proposed system has shown a great efficiency during the experiments.

Robot Force/Torque Control in Assembly Tasks

Abstract Force/ torque control of robot manipulators has been quite intensively investigated during the last decades and it becomes more and more important in manufacturing tasks. However, most of industrial robots are predominantly position-controlled. In this article we will show examples to perform challenging assembling or disassembling tasks by manipulators using standard commercial robot controllers. This fact reduces the possibilities of force/torque control with respect to controller structures and parameters. Two experiments were chosen to demonstrate force controlled robot assembly. First task is to mount a nut on a thread bolt by a single robot using hybrid position/force control. In the second task two cooperating robots assemble the screw fitting using force/torque control. In this work the tasks are divided into some subtasks. For every scenario the convenient controller structure and the controller parameters have to be found out. The example tasks are successfully verified by practical experiments and the corresponding results are presented.

Development of the Fragmented-Motion-Segment Concept for Flexible Joint Robots to Raise Energy Efficiency in Handling Tasks

Abstract To maximize the use of flexible joints in robotic applications it is helpful to consider energy efficiency as a practical criterion. For position control in context with joints having inherent compliance many contributions do not attend to their energy storage capability, while they exclusively concentrate on its control aspects. Energy balance can already improve sparsely without special treatment of the stiffness from control point of view. However, stronger legitimation is needed considering the effort to integrate a complex assembly like a joint with (variable) compliance into the robot. This contribution presents a motion control strategy utilizing the principle of reduced energy difference. An arrangement of switchable clutches enables unleashing of absorbed energy on demand. Therefore a simulation is provided that models a single flexible joint following a planned trajectory for comparison with a traditional robot joint.

Dynamic Collision Avoidance of Industrial Cooperating Robots Using Virtual Force Fields

Abstract This article presents an approach to dynamic collision avoidance of industrial robots working in a shared workspace. It is based on artificial potential or force fields generated by virtual charges which are placed on the moving obstacles e.g. on other manipulators. The positions of the charges will be calculated in real time using CAD data of the obstacles and measured values of its positions. Between different groups of virtual charges artificial forces act on manipulators and hinder their collision by shifting robot motions. This is performed by means of impedance control. The artificial forces acting on the robot generate position offsets in the manipulator path defined by target impedance. All algorithms are implemented with a real robot system and experimental results are presented.

Automatic Decision System for the Structure of Vision-Force Robotic Control

Abstract Robotic applications are gradually taking a huge role in our everyday lives and even in the tasks which are previously thought that only human can do them. Most of these applications require robots to interact with environment, objects or even with human, which is performed by combining vision and force feedback. Generally there are five types of vision-force control: pure position control, pure force control, traded control, shared control and hybrid control. The important questions here are: How to define the most appropriate control mode for every part of different tasks and when the control system should switch from one control mode to the other. In this work an automatic decision system is suggested to define the most appropriate control mode for uncertain tasks and to choose the optimal structure of vision/force control depending on the surrounding environments and the conditions of the tasks. This research will focus on the operations of library automation as real application for the proposed control system such as sorting, storage and retrieval of imprecisely placed objects.