Torgny Brogårdh

Present and future robot control development—An industrial perspective

Abstract Robot control is a key competence for robot manufacturers and a lot of development is made to increase robot performance, reduce robot cost and introduce new functionalities. Examples of development areas that get big attention today are multi robot control, safe control, force control, 3D vision, remote robot supervision and wireless communication. The application benefits from these developments are discussed as well as the technical challenges that the robot manufacturers meet. Model-based control is now a key technology for the control of industrial robots and models and control schemes are continuously refined to meet the requirements on higher performance even when the cost pressure leads to the design of robot mechanics that is more difficult to control. Driving forces for the future development of robots can be found in, for example, new robot applications in the automotive industry, especially for the final assembly, in small and medium size enterprises, in foundries, in food industry and in the processing and assembly of large structures. Some scenarios on future robot control development are proposed. One scenario is that light-weight robot concepts could have an impact on future car manufacturing and on future automation of small and medium size enterprises (SMEs). Such a development could result in modular robots and in control schemes using sensors in the robot arm structure, sensors that could also be used for the implementation of redundant safe control. Introducing highly modular robots will increase the need of robot installation support, making Plug and Play functionality even more important. One possibility to obtain a highly modular robot program could be to use a recently developed new type of parallel kinematic robot structure with large work space in relation to the robot foot print. For further efficient use of robots, the scenario of adaptive robot performance is introduced. This means that the robot control is optimised with respect to the thermal and fatigue load on the robot for the specific program that the robot performs. The main conclusion of the presentation is that industrial robot development is far away from its limits and that a lot of research and development is needed to obtain a more widely use of robot automation in industry.

Extending an industrial robot controller: implementation and applications of a fast open sensor interface

This paper describes the design and implementation of a platform for fast external sensor integration in an industrial robot control system. As an application and motivating example, the implementation of force controlled grinding and deburring within the AUTOFETT-project (EU Growth Programme) is reported.

Sensor Integration in Task-level Programming and Industrial Robotic Task Execution Control

Presents an approach to improved performance and flexibility in industrial robotics by means of sensor integration and feedback control in task‐level programming and task execution. Also presents feasibility studies in support of the ideas. Discusses some solutions to the problem using six degrees of freedom force control together with the ABB S4CPlus system as an illustrative example. Consider various problems in the design of an open sensor interface for industrial robotics and discusses possible solutions. Finally, presents experimental results from industrial force controlled grinding.

Kinematic error calibration of the Gantry-Tau parallel manipulator

This paper presents a new error kinematic model containing twelve parameters for the three linear actuators of the Gantry-Tau parallel kinematic manipulator. Three different types of measurement equipment, laser interferometers, linear encoders and double-ball bars, can successfully be used to calibrate the linear actuators. A method for selecting an optimal set of Cartesian coordinates is presented and a small set of fifty coordinates have been found to be sufficient. The methods presented in this paper allow for a fast and easy set up calibration procedure of the Gantry-Tau after assembly and installation, which is a pre-requisite for flexible automation with parallel kinematic manipulators

An extended friction model to capture load and temperature effects in robot joints

Friction is the result of complex interactions between contacting surfaces in a nanoscale perspective. Depending on the application, the different models available are more or less suitable. Available static friction models are typically considered to be dependent only on relative speed of interacting surfaces. However, it is known that friction can be affected by other factors than speed. In this paper, static friction in robot joints is studied with respect to changes in joint angle, load torque and temperature. The effects of these variables are analyzed by means of experiments on a standard industrial robot. Justified by their significance, load torque and temperature are included in an extended static friction model. The proposed model is validated in a wide operating range, reducing the average error a factor of 6 when compared to a standard static friction model.

Collision-Free Workspace Design of the 5-Axis Gantry-Tau Parallel Kinematic Machine

This paper describes the workspace of the 5-axis variant of the Gantry-Tau parallel manipulator. The 5-axis movements are achieved by extending the 3-axis Gantry-Tau with two linear telescope link actuators. A new analytic inverse kinematic solution for the 5-axis machine and an analysis of the collision-free zones of the machine are presented. The results show that by careful design of the manipulated platform, a collision-free 5-axis workspace can be achieved. The achievable re-orientation of 30 degrees in the entire workspace is large for a parallel kinematic machine

Improving the kinematic performance of the SCARA-Tau PKM

One well acknowledged drawback of traditional parallel kinematic machines (PKMs) is that the ratio of accessible workspace to robot footprint is small for these structures. This is most likely a contributing reason why relatively few PKMs are used in industry today. The SCARA-Tau structure is a parallel robot concept designed with the explicit goal of overcoming this limitation and developing a PKM with a workspace similar to that of a serial type robot of the same size. This paper shows for the first time how a proposed variant of the SCARA-Tau PKM can improve the usability of this robot concept further by significantly reducing the dependence between tool platform position and orientation of the original concept. The inverse kinematics of the proposed variant is derived and a comparison is made between this structure and the original SCARA-Tau concept, both with respect to platform orientation changes and workspace.

Modeling and Parameter Estimation of Robot Manipulators Using Extended Flexible Joint Models

This paper considers the problem of dynamic modeling and identification of robot manipulators with respect to their elasticities. The so-called flexible joint model, modeling only the torsional gea ...

Parallel Manipulators With a Rotation-Symmetric Arm System

Parallel manipulators with a rotation-symmetric arm system possess all the typical advantages of parallel robots, such as high acceleration and high-accuracy positioning. Contrary to the majority of proposed parallel manipulators, the rotation-symmetric arm system leads to a large workspace in relation to the footprint of the manipulator. This paper focuses on a subclass of these manipulators with additional favorable qualities, including low inertia and high eigenfrequencies. These qualities are achieved using only 5-DOF lower arm links and by mounting all actuators on the nonmoving base column of the manipulator. The common feature of all previously proposed manipulators in this subclass is identified and several novel 3-DOF and 4-DOF members are introduced.

The Tau PKM Structures

In this chapter, a new family of PKM structures based on the Tau concept is described. It is shown that the non-symmetrical Tau link structures solve the problem of obtaining a large accessible workspace in relation to the footprint of a PKM and examples of large workspace of Tau PKMs are given both for rotating and linear actuators. Some results are presented from an investigation of the SCARA Tau manipulator with respect to its workspace and elastodynamical properties, showing its potential for applications with high performance requirements. The main part of the chapter is about the Gantry Tau manipulator, which is based on the same non-symmetrical link structure as the SCARA Tau manipulator. It is shown that this manipulator will get a large accessible workspace, that it can be reconfigured to increase the workspace further, that it can be calibrated to non-parallel linear guide-ways and that it can be designed for very high stiffness and bandwidth. The nominal kinematics as well as the kinematics with non parallel linear guide ways are derived and the stiffness is calculated using the duality between the statics and the link Jacobian for a PKM. The mechanical bandwidth calculations are based on a new method with mass-spring-damper link models. With the promising performance results obtained with the Tau family of manipulators, the potential for the use of these in industry is discussed.