Jozef Suchy

Multisensor Contour Following With Vision, Force, and Acceleration Sensors for an Industrial Robot

In robotic contour-following tasks, such as sewing or cutting, an industrial robot guides a tool along the contour of a workpiece. Manually teaching the robot is time consuming and results in a system that is unable to react to uncertainties or changes in the environment. Because the cost effectiveness of a robotic solution depends on the amount of human intervention, particularly small series production benefits from greater system autonomy through the integration of sensor systems. In this paper, we present an integrated approach for multisensor contour following. A look-ahead vision sensor steers the robot along the workpiece while force-feedback control maintains the desired contact force. Acceleration sensors are used to compensate the force measurements for inertial forces, so the arrangement of the acceleration sensors is investigated. Couplings that arise between force and vision control systems are estimated, and online measurements of contact forces between the robot and the environment are used to adjust measurement results from the vision sensor to compensate for environmental deformations. Parameters of a second-order linear model of the environment are estimated by online identification. The identification combines force and acceleration sensors in an observer-based control scheme. The system is validated by experiments that involve contour following on compliant objects.

Dynamic force/torque measurement using a 12DOF sensor

This article presents an algorithm for dynamic force/torque measurement and robot load identification using the so called 12DOF sensor to measure forces/torques and linear/angular accelerations. The basic equations of dynamic forces and torques arising during robot motion and acting on the end-effector were worked out. To be able to perform the experiments suitable robot system based on a six axes articulated manipulator was constituted. For this system also the appropriate software was developed. The load parameters of the tool were determined during particular motion sequence of the robot and the values were compared with values from CAD software. The compensation of dynamic forces and torques is verified using the experimental robot system and the results are presented.

Force-guided motions of a 6-d.o.f. industrial robot with a joint space approach

This article deals with the interaction between humans and industrial robots, more specifically with the new design and implementation of an algorithm for force-guided motions of a 6-d.o.f. robot. It may be used to comfortably teach positions without using any teaching pendant or for some assistance tasks. For this purpose, from readings of the force/torque sensor mounted in the robot wrist, the gravity forces and torques first have to be eliminated. To control the robot in joint space, it is then convenient to transform the external force and torque values from Cartesian space into joint space using the manipulator transposed Jacobian. This is why with the present approach the Jacobian matrix of the robot used was calculated. Now, from the computed joint torques, suitable position commands of the robot arm can be generated to obtain the desired behavior. A suggestion for this desired behavior is also included in this article. It is based on the impedance control approach in joint space. The proposed algorithm was implemented with the standard Stäubli RX90B industrial robot.

Position feedback in force control of industrial manipulators - An experimental comparison with basic algorithms

This paper investigates simple position based force control algorithms for an industrial robot. A lot of approaches to robot force control published in the previous three decades are difficult to implement in commercial robot controllers. This fact is one reason why force controlled robots rarely appear in industrial applications. On the other side force control may improve some robot tasks like automated assembling or material processing. Therefore, is seems to be necessary to concentrate on simple controller structures on the field of robot force control which are easily realizable and adjustable. For this purpose in this paper linear standard control algorithms have been selected and implemented with a real robot. One proposed structure is the proportional controller with positive position feedback which dealt probably here for the first time and shows very good control behavior. Some proposals to parameterization of different controllers are given and their performance with respect to contact detection, impact and response to setpoint changes is shown and compared by practical experiments.

Library automation using different structures of vision-force robot control and automatic decision system

Most of robot applications require robots to interact with environment, objects or even with human, which need to integrate vision and force information. 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 successive tasks and to choose the optimal structure of vision/force control without human intervention. This research will focus on the operations of library automation as real application for the proposed control system such as shelving, storage and sorting of inaccurately placed objects.

Force, acceleration and vision sensor fusion for contour following tasks with an industrial robot

In robotic contour following tasks such as sewing or cutting an industrial robot guides a tool along a contour of a workpiece. Teaching the task manually is very time consuming and the process would be unable to react to uncertainties or changes of the environment. Thus sensor systems are applied to reduce human intervention, making the robot more autonomous. In this paper we present an integrated approach for multisensor contour following. A look-ahead vision sensor guides the tool along a contour of a workpiece while force feedback control maintains a desired contact force. Couplings that arise between these two controllers are estimated and compensated through online measurements of contact forces between robot and environment. The identification of the environment combines force and acceleration sensors in an observer-based control scheme. The system is validated by experiments that involve contour following on compliant objects

Traded and shared vision-force robot control for improved impact control

Many automated manufacturing processes require robots to interact with environment and to perform force/torque interaction such as mechanical assembly. Importantly, impact forces occur while robot and environment are in contact. Robot manipulators and control systems can experience instability or poor control performance after impacting with an environment. In this paper we combine vision and force feedback in shared/traded vision-force control to reduce the impact forces and to increase the performance of robot, by calculating the distance between robots end-effector and the environment and reducing the speed according to it. Experimental results are presented to illustrate the performance of robot in two cases with and without vision feedback and to compare these results with simulation.

Tunnel-shaped potential force fields for improved hand-guiding of robotic arms

In this paper we introduce a new approach for improving hand-guiding of robotic arms. We present the tunnel-shaped potential force field (TSPFF) which guides the user along a reference trajectory in order to improve the user comfort of handling robots. The reference trajectory is computed using the learning data of experienced users. The TSPFF is realized by an impedance control of the robot. The main focus of this paper is to find a robust parametrization of the TSPFF. For this purpose the stability of user-robot interaction is analyzed by means of the Lyapunov stability theory. The results are complemented by simulation studies in which the influence of the parametrization on control performance and user comfort is analyzed. The resulting rules for parametrization are validated by experimental studies with a robot with six degrees of freedom.

Robot visual servoing using the example of the inverted pendulum

In this paper the control of the well known inverted pendulum will be performed by using visual servoing algorithms. The pendulum will be mounted on the flange of an articulated robot arm and it will be observed by 2D-camera. The inclination angle of the pendulum will be computed in the real time with the help of image processing algorithms. In order to swing-up the pendulum, a special algorithm will be designed to generate the coordinated robot motions. Whereas, the balancing of the pendulum will be performed by a state space controller. Both algorithms will be implemented in the standard robot controller with a relatively high cycle time. Furthermore, the calculation of the inclination angle of the pendulum by the camera, which is integrated in the closed loop controller, instead of an angular transmitter will make the successful achievement of the task more difficult. All the proposed algorithms are verified successfully in the practical experiments.

Handing-over model-free objects to human hand with the help of vision/force robot control

Handing-over objects from robot to humans is essential step to perform different tasks especially those requiring physical interaction between the robot and the human, e.g. service robots can help elderly, blind and disabled people or human-robot teamwork could work together in factories. This work will propose a new robot system which combines visual servoing and force control in order to hand over model-free objects from undefined place to human hand. This work will present: 1. vision algorithms which help the robot system to detect and to segment the objects without any information about their model. 2. The possibility for visual tracking of human hand with the help of Kinect camera. 3. The importance of fusion vision and force control in order to ensure the safety during the human-robot interaction. 4. How the robot will deliver the objects to the human hand with the help of vision and force control. This work will be supported with experimental results.