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Application of the telbot robot in hazardous environments
Abstract
In recent years, the acceptable levels of worker exposure to environmental hazardous such as radiation, toxic fumes and asbestos has steadily decreased. As a result, the use of both tele-operated and computer-controlled robots has increased dramatically. This paper presents an overview of a new tele robot system, trade named Telbot, which is developed by Hans Wälischmiller GmbH and has been used for nuclear steam generator maintenance in Canada and for decommissioning glove boxes in Japan. The novel mechanical design of the Telbot robot enables that all the joints can be rotated over 360 degrees continuously. Joints and arms with different sizes are designed for meeting the requirements of different payloads. The manipulator can be easily protected from the dirty environment, and some of the parts can be quickly changed when a defect happens. The control system is designed as an open system, the hardware is the VME bus system and the software is based on the VxWorks real-time operating system. A 3-D simulation system is connected to the control system for real-time visualization and off-line simulation.
Some new results concerned with the design of POLYCRANK manipulators without joint limits are presented. Main features of such a solution are links in the form of light hollow cranks connected one to the other by cross-roller bearings. The first pre-prototype of POLYCRANK with six DOF’s has been completed and tested. Three first DOF’s, with parallel vertical axes are driven by electric Direct Drive units mounted coaxial in the base of the manipulator. Three last DOF’s are driven by light motors with gears mounted on the last link of the horizontal chain with using parallelograms. High speed of cyclic gross motion in the convex workspace and good isotropic properties are the main advantages of this manipulator. Proper choosing of such mechanical properties like high natural frequency with good damping of vibrations, high stiffness, relatively low Lost Motion, is the basic requirement and it was the main purpose of investigations. Main disadvantages of the previous version are high cost of DD motors and of big diameter cross-roller bearings. A new one version with much more less cost is consider. One of the basic features of it’s is a new serial-parallel modular arrangement of the arm and untypical spherical wrist.
Nuclear robots play a very important role in safe operation of nuclear power plants. In this paper, the operating principle of nuclear power plants is firstly introduced and the safety levels of key nuclear facilities are illustrated. Then the present research status of nuclear robots in the world is summarized from three main aspects: maintenance of key nuclear facilities, inspection and warning of nuclear radiation, accident management and rescuing. Finally, the key technologies of nuclear power plant robots are discussed, and the research prospects are presented.
A special robot is developed for in-service maintenance of steam generator (SG) in nuclear plant. It is of a two-end 6R serial chain structure. With the help of propulsion device, the robot with 7-axis can enter the limited quarter-sphere chamber through the manhole of the SG, and fix on the tube-sheet with the distensible mechanism at one end. By attaching different tools at the other end, the robot can provide services such as eddy current inspection, ultrasound inspection, plugging, and setting sleeves. In this paper, the new servicing scheme and robotic configuration are presented firstly. Then, by considering obstacle avoidance and two-end operation factors, the robot's workspace, kinematics solution and compound movement are discussed to confirm the feasibility of the structure scheme. Finally, the robot prototype is tested by field experiment, and the result shows that the robot can meet the requirements of SG maintenance.
A master-slave six degree of freedom (DOF) robot is developed for performing tasks such as eddy current inspection, ultrasound inspection, plugging, and sleeving inside water chamber of nuclear steam generator (SG). The virtual master robot is operated in a container of nonradiation area, while slave robot provides real service correspondingly inside of SG with high level of radiation. The software and hardware architecture of the robot is opening and blocking. This paper presents the system design, key technological components and comprehensive test in simulated field. When commercialized, it will extremely promote overhaul efficiency, and have the fundamental role in development of in-service technology for nuclear power plant in China.
Some new results concerned with design and dynamics analysis of the redundant POLYCRANK manipulator with eight DOFs are presented. The main links of an arm in the form of light skew hollow cranks are connected one to the other by cross-roller bearings. In the new concept of the POLYCRANK manipulator all drive units are mounted coaxially in the base. The three first DOFs with vertical axes and the three next DOFs with parallel horizontal axes are driven by electric direct drive units while the last two DOFs are driven by electric motors with gears. The first link is driven directly, the second and third are driven remotely by special skew parallelograms. The other DOFs are driven remotely in a similar way by using skew parallelograms and bevel gears mounted on the third link. The kinematics scheme of this redundant manipulator is very simple and it has some specific properties. Inside of its vertex workspace the POLYCRANK manipulator can realize various high-speed cyclic gross motions. However, a big problem is strong reaction forces occurring in the joints. This may be the case in emergency situations too, e.g. when the power supply breaks down. A method of solving these problems has been presented. The possibility of easy manipulation of large bodies using two redundant POLYCRANK manipulators is stressed. Finally, a method of virtual design, which was used for the development of the conception of the manipulator, has been presented.
An overview is given of the existing work on robot calibration, and some of the basic issues are identified in calibration and improvement of robot precision. Modeling, measurement, identification, and correction issues in robot calibration are discussed, and some of the unresolved questions are identified.
The cleaning of steam generator tubes has predominantly been carried out from the secondary side. The cleaning of the heat transfer tubes from the inside is not as common and has mainly been carried out by chemical methods. Chemical cleaning results in a large volume of waste that has to be handled and decontaminated. Recently, tests have been carried out using mechanical methods of cleaning tubes from the primary side. This method uses steel beads. The beads are blasted from the cold leg of the primary head and are collected at the hot leg. They are then recirculated back to the cold leg for the blasting of the next tube. The waste product is retrieved during the recirculation cycle. The only waste generated is from the tubes that are being cleaned and is always confined to the recirculation system and tank. This method of cleaning has been developed by Siemens and is called the Vacublast system.
The inverse kinematic problem of the general 6R robot manipulator is completely solved by means of a 16th degree polynomial equation in the tangent of the half-angle of a revolute joint. An algorithm is developed to compute the desired joint angles of all possible configurations of the kinematic chain for a given position of the end-effector. Examples for robots with maximal 16 different configurations show that the polynomial degree 16 is the lowest tossible for the general 6R robot manipulator. Further, a numerical method for the determination of the boundaries of the workspace and its subspaces with different numbers of configurations is developed. These boundaries indicate the singular positions of the end-effector.
COBRA -Design and Development of a Manipulator for Nuclear Steam Generator Maintenance
- P H Tidwell
- S W Glass
Tidwell, P. H., Glass, S. W. and et al, 1991, "COBRA -Design and Development of a Manipulator for Nuclear
Steam Generator Maintenance", Proceedings of the 2nd
National Applied Mechanisms and Robotics Conference,
USA, Vol. 1, pp. IVB1-1 to IVB1-10.
TELBOT® -A Modular Tele-Robot System for Hostile Environments with Unlimited Revolutionary Joints and Motors, Drive Sensors and Cables in the Base
- W Wälischmiller
- O Frager
Wälischmiller, W. and Frager, O., 1995, "TELBOT® -A Modular Tele-Robot System for Hostile Environments
with Unlimited Revolutionary Joints and Motors, Drive
Sensors and Cables in the Base", Proceedings of the ANS
6th Topical Meeting on Robotics and Remote Systems,
Monterey, California, USA, Vol. 1, pp.274-280.