Kinematic and dynamic analysis of a serial-link robot for inspection process in EAST vacuum vessel

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Abstract

The present paper introduces a serial-link robot which is named flexible in-vessel inspection robot (FIVIR) and developed for Experimental Advanced Superconducting Tokamak (EAST). The task of the robot is to carry process tools, such as viewing camera and leakage detector, to inspect the components installed inside of EAST vacuum vessel. The FIVIR can help to understand the physical phenomena which could be happened in the vacuum vessel during plasma operation and could be one part of EAST remote handling system if needed. The FIVIR was designed with the consideration of having easy control and a good mechanics property which drives it resulted in function modular design. The workspace simulation and kinematic analysis are given in this paper. The dynamic behavior of the FIVIR is studied by multi-body system simulation using ADAMS software. The study result shows the FIVIR has ascendant kinematic and dynamic performance and can fulfill the design requirement for inspection process in EAST vacuum vessel.

Highlights

► A serial-link robot FIVIR is proposed for inspection of EAST PFCs between plasma shots. ► The FIVIR is a function modular design and has specially designed curvilinear mechanism for axes 4–6. ► The D-H coordinate systems, forward and inverse kinematic model can be easily established and solved for the FIVIR. ► The FIVIR can fulfill the required workspace and has a good dynamic performance in the inspection process.

Introduction

EAST is the first full superconducting tokamak in the world which is operated more than 5 years. With D shape vacuum vessel (VV), actively cooled plasma facing components (PFCs) and superconducting coils, it has the ability to study scientific and engineering issues of superconducting tokamak in steady state operation and high plasma parameters. During past experiment campaigns, EAST devices has already given a good performance for long pulse divertor plasma operation, fruitful physical results, such as 1MA plasma operation and 100 s divertor plasma operation, have been gotten. However, some local structures in the VV were damaged during experiments (like bolts loosing [1]), which had big influence to physical experiment or even stopped the experiment campaign, and then the VV had to be opened for the purpose of finding out what specific damage was happened. The task of designed robot is to carry viewing camera or other inspection tools into the VV between plasma shots for the purpose of: (1) letting physicist and operator know well exactly what happened to the in-vessel components and enhancing the operation efficiency, (2) even giving a more useful way for plasma surface interactions study by sampling deposition on or fragment and dust of first wall during experiment campaign.

The robot, named flexible in-vessel inspection robot (FIVIR), is assumed to be retreated in an extended equatorial port of the VV, and can be deployed into the VV for inspection process. The FIVIR must has not only large workspace but also flexible enough to move into/out of the VV through the narrow port. The large workspace has oriented the design of FIVIR into a serial-link robot. As a consequence, there some essential and important issues for the study of FIVIR: kinematic capability covering from the status of storage to inspection process in the whole VV, dynamic properties and controllable prospect of the robot. The investigation on these aspects is presented in this paper.

Section snippets

The FIVIR [2]

The FIVIR, shown in Fig. 1, is a long reach multi-articulated robot with 10 degrees of freedom (DOFs). It is a function modular design, consisting of a main robot and an end-effector. Different tools can be installed onto the end-effector for different inspection purpose. The main robot, which has six DOFs with combination of four sliding joints and two rotation joints, can manipulate the end-effector to the specific toroidal position. The first three joints make the FIVIR can move into/out of

Coordinate systems

As shown in Fig. 1, the joints 1–3 and 7–10 are common joints and easy for Cartesian coordinate system establishment, but not for joints 4–6. However, these three joints can be simplified and integrated into one rotary joint about the axis which normal to the plane of curvilinear sliding trajectory. The number of DOFs of FIVIR is reduced from 10 to 8 and all the joints are parallel or perpendicular to their former axis. According to D-H convention for robot, the coordinate systems of the FIVIR

Dynamic simulation

In addition to kinematics, dynamics is another very important prospect for a robot. It has a big influence on the development of control system and the design and sizing of links, bearings and actuators. Excellent dynamic performance can drive an easier and reliable control system and simple and light structure. In reality, the end-effector of the FIVIR has much higher frequency of motion than the main robot. So a multi-body system model of the end-effector is created using ADAMS software to

Conclusion

A serial-link robot FIVIR has been proposed and studied for the inspection of EAST PFCs between plasma shots. The FIVIR is a function modular design which matches the dividable required workspace well. This advantage also gives the FIVIR simple kinematics formulations. Kinematic analysis and workspace investigation show that the FIVIR is dexterous to reach the needed workspace and a pair of FIVIRs can fulfill the inspection requirement of the whole surface of PFCs. An elementary dynamic

Acknowledgements

The design work presented in both this paper and the paper Fusion Eng. Des. 85 (2010) 1362–1365 is the results of cooperation between Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) and Shanghai Jiao Tong University (SJTU) with a funded contract supported by ASIPP. The authors would like to thank all staffs in both two affiliations who were involved in the design of EAST FIVIR.

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