This paper is organised as follows: section 2 summarises the remote handling issues in the design of control rooms for teleoperating dissimilar master-slave bilateral systems, section 3 covers the radiation tolerance of robotics systems with special attention to force sensors, in section 4 the sensorless virtual slave architecture is explained and the theory behind the sensorless force feedback is discussed.
Section 5 details the experimental equipment used in this research while in section 6 we present the results obtained in 1 degree of freedom.
Finally in 7 we present the conclusions and future applications of this technique in multiple degrees of freedom.
The use of telerobotic systems is essential for remote handling (RH) operations in radioactive areas of scientific facilities that generate high doses of radiation.
Recent developments in remote handling technology has seen a great deal of effort being directed towards the design of modular remote handling control rooms equipped with a standard master arm which will be used to separately control a range of different slave devices.
This application thus requires a kinematically dissimilar master-slave control scheme. In order to avoid drag and other effects such as friction or other non-linear and unmodelled slave arm effects of the common position-position architecture in nonbackdrivable slaves, this research has implemented a force position control scheme.
End-effector force is derived from motor torque values which, to avoid the use of radiation intolerant and costly sensing devices, are inferred from motor current measurement. This has been demonstrated on a 1-DOF test-rig with a permanent magnet synchronous motor teleoperated by a Sensable Phantom Omni® haptic master. This has been shown to allow accurate control while realistically conveying dynamic force information back to the operator.
Table of Contents
1. Introduction
2. Remote handling control rooms
3. Radiation tolerance of telerobotic systems
3.1.1 Force sensor for robots and radiation performance
4. Sensorless force feedback approach
4.1 Dissimilar master-slave algorithm
4.2 Master control and inertial forces
4.3 Sensorless torque measurement
4.4 Non-Backdrivable control scheme
5. Experimental equipment
6. Single degree of freedom results
6.1 Open loop results
6.2 Close loop with force feedback in the Phantom OMNI® haptic master
7. Conclusions and future work
8. Acknowledgment
9. References
Research Objectives and Key Topics
The primary research objective is to develop and validate a sensorless, kinematically dissimilar master-slave control scheme for teleoperation in hazardous environments, such as nuclear facilities, where traditional force sensors fail due to extreme radiation levels.
- Design of modular remote handling control rooms for diverse slave devices.
- Development of a "sensorless virtual slave" architecture to estimate forces via motor current measurement.
- Implementation of dissimilar master-slave algorithms to bridge the gap between human-interface devices and industrial robots.
- Performance testing of force feedback mechanisms in radioactive-tolerant robotics systems.
- Optimization of bilateral teleoperation control for non-backdrivable industrial manipulators.
Excerpt from the Book
4. Sensorless force feedback approach
The radioactive environments can be significantly different from each other depending on the dose rate emitted and with them the requirements of the manipulators or robots used within them. In order to cope with the less demanding doses it is likely enough to mount a hard-rad force/torque sensor in the robotic gripper increasing with this the total cost of the robot. When the radiation dose rate becomes very high the solution implemented by [27] consists in a hydraulic manipulator based in water with the consequent risk of water leaks. If that risk is wanted to be totally discarded as well as to maintain a solution with components off-the-shelf when the dose rate increases such as in ITER-like projects, a sensorless approach can be used. This term indicates the indirect end-effector’s force and actuator’s torques determination without using force and torque sensors. This sensorless approach would avoid replacing every industrial robot based on electrical actuators for a new and relatively high cost hydraulic solution with the disruptions that this change would cause.
With the objective of developing a bilateral control with dissimilar master and slave devices the approach called state convergence is implemented allowing each couple of joints (master and slave joints) to be controlled separately. This research also tries to convey force feedback to the operator by using a force-position based architecture where the force exerted by the master to the operator is based in the composition of the environment forces as well as other forces arising from the restriction of the master movements due the different kinematics. That external force over the robot end-effector will be determined in an indirect way by the sensorless algorithm based on measurements of the current waveform in each actuator. This method, termed sensorless virtual slave, permits the implementation of teleoperation systems based in force-position architecture where the master and slave have different kinematics producing a cost effective solution as well as a radiation hardened approach.
Summary of Chapters
1. Introduction: This chapter provides an overview of remote handling (RH) in hazardous environments and introduces the necessity for kinematically dissimilar master-slave teleoperation systems.
2. Remote handling control rooms: This section details the design of standard work cells for the ITER project, focusing on human factors and the requirement for modular control.
3. Radiation tolerance of telerobotic systems: This chapter discusses the impacts of radiation on electronic components and evaluates current force-sensing technologies used in radioactive environments.
4. Sensorless force feedback approach: This core section presents the proposed sensorless architecture that uses current waveforms to estimate torque, bypassing the need for radiation-vulnerable force sensors.
5. Experimental equipment: This chapter describes the laboratory setup, including the Phantom OMNI haptic device, AC motors, and data acquisition hardware.
6. Single degree of freedom results: This chapter presents the data from both open-loop and closed-loop trials, demonstrating the effectiveness of the current-based torque calculation.
7. Conclusions and future work: This concluding chapter summarizes the research findings and proposes future steps for scaling the system to 6-degree-of-freedom industrial manipulators.
Keywords
Telerobotics, Remote Handling, Force Feedback, Sensorless Control, Kinematically Dissimilar, ITER, Radiation Tolerance, Haptic Master, Bilateral Control, State Convergence, Industrial Robots, Motor Current Measurement, Torque Estimation, Teleoperation, Virtual Slave.
Frequently Asked Questions
What is the core problem addressed in this research?
The research addresses the failure of traditional force sensors in high-radiation environments like fusion reactors, which necessitates a more robust, sensorless method for force feedback in teleoperation.
Which primary scientific method is utilized?
The study implements a "sensorless virtual slave" architecture, which infers the torque exerted by a motor by measuring the electrical current waveform of its actuators, thereby avoiding radiation-sensitive external sensors.
What is the goal of the proposed control scheme?
The goal is to allow a human operator to control various kinematically dissimilar industrial robots (slave) using a standard haptic interface (master) while maintaining stability and transparency in force feedback.
How does the system maintain operator safety?
Safety is ensured through an algorithm that continuously checks if the master's position is within the slave's reachable workspace; if not, it provides resistive haptic feedback to prevent the operator from forcing the system beyond its limits.
What main components are discussed in the experimental setup?
The setup involves a Sensable Phantom OMNI haptic master, an Aerotech brushless AC motor, custom Hall Effect sensors, and National Instruments data acquisition hardware.
Which industrial projects are highlighted?
The research is heavily influenced by the requirements of the ITER fusion project and remote maintenance practices at JET and CERN.
Does the sensorless approach currently support 6 degrees of freedom?
The presented research focuses on a 1-degree-of-freedom test rig, but it provides the theoretical framework and future roadmap to extend this to 6-degree-of-freedom industrial manipulators.
What limitation was identified during the experimental testing?
A significant issue identified was the current offset in sensors, which, when translated into the control algorithm, can introduce inaccuracies in the estimated torque.
How is the accuracy of the torque estimation verified?
Accuracy was verified by inserting a commercial torque transducer directly between the motor and the load to compare calculated values against actual measured torque.
Why are industrial robots often unsuitable for traditional teleoperation?
Most industrial robots are non-backdrivable, meaning they resist external movement, which creates a lack of transparency for the operator unless a high-quality, stable force-feedback loop is implemented.
- Quote paper
- Enrique del Sol (Author), R. Scott (Author), R. King (Author), 2012, A Sensorless Virtual Slave Control Scheme for Kinematically Disslimilar Master-Slave Teleoperation, Munich, GRIN Verlag, https://www.grin.com/document/308190
