Table of Contents ECNDT '98 Session: Ultrasonic Examination Copenhagen 26 - 29 May 1998

Robot System for Ultrasonic Examination of Complex Geometries Lars Vesth, Peder B. Hansen and Willy Damgaard Kristensen FORCE Institute, Park Allé 345, DK-2605 Brøndby, Denmark Corresponding Contact: E-mail: lv@force.dk, Internet: http://www.ultrasim.com This work received the NDT Innovation Prize for outstanding applications.

Abstract

Introduction

With the development and introduction of a new complete 3D ultrasonic inspection system FORCE Institute enlarges the inspection possibilities and increases the overall quality of UT inspection of complex geometry components.

Advanced 3D Inspection System

The complete advanced 3D inspection system contains three main components: the Advanced Inspection Robot - AIR-1, the new generation P-scan ultrasonic data acquisition system - PS-4 and the 3D ultrasonic simulation system - UltraSIM. AIR-1 and PS-4 are used on-site for recording of A-scan data during the on-site inspection. UltraSIM is used for initial ultrasonic simulation, scan path generation and robot simulation (together with the ROBCAD^(r) robot simulation software), online control and monitoring of the real AIR-1 robot and finally for 3D reconstruction of ultrasonic A-scan data.

Advanced Inspection Robot - AIR-1

Figure 1: 3D inspection system concept principle drawing

Figure 2: AIR-1 robot mounted on inclined inspection nozzle

Figure 3: PS-4 A-scan / composite A-scan view

Figure 4: UltraSIM 3D reconstruction of A-scan data

The Advanced Inspection Robot - AIR-1 is a portable (weight approx. 25 kg.) 6-axis articulated elbow type robot manipulator with 6 degrees of freedom. It is build from standard motor and control module components from FORCE Institutes Modular Scanner System and is controlled from within the UltraSIM/UlScan graphical generic robot control application. In addition to the controlling computer the system contains only a small control unit - PSP-4 (weight approx. 5 kg.) which among other system components includes a motor control system integrated closely with the PS-4 ultrasonic system. For communication between the PSP-4 control unit and the robot as well as robot power supply is used a single cable less than 10 mm. in diameter.

ROBCAD^(r) Robot Simulation System

Before any physical movement is done in the real inspection environment, the optimal robot configuration and motion are planned and simulated in a virtual inspection environment in the ROBCAD^(r) 3D robot simulation system. If any collisions or near-collisions are occurring or all the calculated inspection points can not be reached the robot configuration and/or robot inspection programs can be adjusted off-line accordingly without the need of the physical robot or inspection environment. This ensures that the time scheduled for the physical inspection is used actively for inspection instead of testing and configuration.

UltraSIM Simulation Module

Besides simulation of the robot motion, a full virtual inspection includes simulation of the ultrasonic sound propagation during the inspection. For this purpose the UltraSIM/UlSim simulation module is used. In UltraSIM/UlSim the ultrasonic sound propagation from a virtual ultrasonic transducer can be simulated in ray tracing mode in any isotropic and homogeneous 3D geometry, including possible mode conversions phenomenons, etc. The CAD geometry for the simulation is a 3D NURBS surface model of the test object. It can be created in ROBCAD^(r) or imported from another 3D CAD system. The virtual transducer can be placed in a specific location on the test object surface, it can be moved along a path (e.g. a robot scanning path generated off-line or a path resulting from a real inspection sequence) or it can be moved along the surface, dynamically updating the ultrasonic sound propagation in the material.

UltraSIM Path Planning Module

Based on the simulation of the ultrasonic sound propagation in the test object material, the UltraSIM/UlPath module calculates test object surface points from specifications of the 3D inspection volume, the "sound intensity" in the inspection volume and the desired transducer angle. These surface inspection points are then collected in scanner paths, which are collected in scanner programs. The principle of generating scanning paths from specification of the test object inspection volume ensures, that scanning sequences containing correct surface positions and orientations as well as a minimum of inspection points are obtained. A scanner program is the direct input to the UltraSIM/UlScan scanner control module.

UltraSIM Scanner Control Module

Online control of the AIR-1 robot is done from within the UltraSIM/UlScan generic scanner control module. With a scanning program as input, the control application is able to calculate and perform cartesian motion for any usual robot manipulator having an inverse solution. The planned robot motion can be simulated off-line before online execution regarding joint and robot position, speed and acceleration. During robot inspection the 3D virtual inspection environment is updated real-time according to the actual robot motion. In order to optimise the general on-site system performance, time and resource consuming motion calculations are done immediately after execution of the previous path in the current scanning program - simultaneously with the storing of digital A-scan data by the PS-4 system.

P-Scan System 4 Ultrasonic Data Acquisition System

The principal equipment for the ultrasonic examination is the P-scan system, PS-4, which is a computerised ultrasonic system, developed by FORCE Institute, for automatic, mechanical and manual ultrasonic examination of welds and materials. The system has documentation and storage facilities for all data related to each inspection operation, and includes visualisation of the inspection results in the form of images of the material volume examined. The PS-4 ultrasonic examination system provides many new features, which allows the operator to perform several inspections simultaneously. Both pulse-echo and time-of-flight-diffraction technique can be applied together with storage of digital A-scan data at the same time. When used in the 3D inspection system PS-4 is configured only for recording of A-scan data with attached unambiguous 3D transducer position and orientation information, since the reconstruction is done in the attached 3D UltraSIM/UlRecon reconstruction module.

UltraSIM Reconstruction Module

Conversion from digital A-scan samples to 3D defect images is done within the UltraSIM/UlRecon 3D reconstruction module. Using a customized echo-detection algorithm and the UltraSIM/UlSim ray tracing algorithms the reconstruction module can create real 3D images of defects with attached amplitude and halfskip information in the virtual 3D inspection environment. Data from several transducers can be applied at the same time and the data can be analysed by adjusting the amplitude level and turning on and off data from the individual tranducers.

UltraSIM Report and Utility Modules

The 3D inspection system has a number of measuring and report utilities that enables the user to easily find, analyse and report possible indications in the test object. As an example, a moveable 2D projection view plane can be moved along e.g. the welding geometry dynamically updating the content of the 2D projection view window. Indications can be measured using any reference co-ordinate system and the results and screen dumps can automatically be dumped in report files suited for later import into a word processing application.

3D System Application

The 3D-inspection system can be applied to many complex inspection tasks where ordinary XY scanners can not perform the job, e.g. nozzle welding inspections and nozzle inner radius inspection in nuclear and petrochemical environments. The system has recently been used with success for inspection of 11 inclined nozzle welds during the R1 SPRINT project at Vattenfall Ringhals, Sweden during the summer 1997. At the moment a full system and personal qualification is prepared for inspection of the pressurizer spray nozzle weld at Vattenfall Ringhals, block 2 at May, 1998.

Future Development

In order to assure that the 3D inspection system concept also in the future fulfills all the requirements for a 3D inspection system for complex geometry, the system is constantly developed and extended with new and powerful facilities. Some options assumed to be implemented in near future are:
• 3D anisotropic sound propagation in UltraSIM.
• Introduction of AIR-1e robot with adjustable links.
• Multi transducer fixture for inspection robots.
• Optimised robot motion calculations in order to reduce inspection time further.