ROBINSPEC ROBot for INSPECtion

ROBINSPEC is a new mobile service robot that has been designed and built at the DEES System and Control Laboratory of the University of Catania and is actually at the test phase. Recently the term Service robot has been defined in order to classify all that kind of robots that are designed for the execution of useful work for humans and equipment different from the classical applications of industrial robots [1],[2],[5]. The production of Service robots is at the beginning and most of the robots are actually built as research prototypes. Nowadays the low cost of high-power computing systems and of complex sensors, like vision based systems, allow robotic technologies to be applied also in applications different from the traditional ones. Among them several service robots have been realized for solving inspection problems [3],[4]. The robot ROBINSPEC has been designed in order to solve inspection problems in dangerous or hard- to-reach environments such has storage tanks, long or high pipe-lines, factory chimneys, distillation columns etc. Actually such inspection problems are usually solved by using human operators, but very often they have to operate in hazardous environment with high health risks. Moreover in most cases such inspections have to be done in environment that are not easy to reach by an human operator. The availability of an autonomous system which could be used for inspection in all these situation is then needed. Another possible application of ROBINSPEC consists in the remote positioning of sensors for non-destructive materials testing. In the following a brief description of the mechanical structure, the electronic system and the control strategies is discussed.

MECHANICAL STRUCTURE

A picture of the robot structure is reported in this figure. The robot is moved by means of three legs each connected to the surface with two electro-magnets that allows the robot to operate also on vertical surfaces or upside-down. The main actuators for the three legs are three independent DC motors connected to a gear speed reducer and to a potentiometer for position measurement. The skeleton of the robot is made of aluminium. The motion of ROBINSPEC consists of seven different steps. The adoption of legs allows also to avoid small obstacles like bolts, flanges etc. The central legs will be equipped with an auxiliar motor that permits the rotation of the system. A video camera is positioned on the robot by using a stepper motor which allows to change the view angle.

CONTROL

ROBINSPEC has been designed to work in a semi-autonomous way. This means that even if all the operations and movements of the robot can be tele-controlled from a base station , for several simple tasks ROBINSPEC can operate autonomously. For example, during the inspection of the wall of a storage tank the robot can inspect automatically the whole surface of the tank requiring the help of the operator only for not scheduled operations. The measurements obtained from the sensors and the images captured from the camera are radio-transmitted to the base station in order to be elaborated or monitored from the operator.

Base-station

• The base station is based on a 486 Personal computer with an image acquisition board. The station is connected via a serial interface to a radio transceiver in order to establish a data link with the robot. The image acquisition board is linked with a video radio receiver which allows the remote images from ROBINSPEC to be acquired and processed. At present the image processing algorithm allows to detect the presence of rust in the surface. An extra audio channel is available to give to the operator an audio feedback of the remote operations by using a microphone on the robot.

Robinspec

• The heart of ROBINSPEC is the motion planner module which is linked to most of the function of the system. This module, implemented using an ST9 microcontroller, on the basis of the commands received from the base station and on the measurements of the ultrasonic radar, communicates to the trajectory planner the references for the three legs. The module is also responsible for the orientation of the support of the camera. The ultrasonic radar is implemented by using three POLAROID sensors placed in the front part of the system and allows to detect unplanned obstacles that could be present along the trajectory. The three legs are controlled by using an ST6 microcontroller interfaced with a WARP 2.0 SGS/Thompson Fuzzy processor. The microcontroller is used to acquire the position of the legs by using three A/D channels connected to the potentiometer. Once the signals have been acquired, the error and the rate of the error with respect to a reference trajectory are computed and given as inputs to the Fuzzy rule processor. The WARP 2.0 (Weight Associative Rule Processor) is a digital Fuzzy processor with 8bit I/O able to elaborate up to 256 fuzzy rules, 8 inputs, 4 outputs with a clock frequency of 40 MHz. The fuzzy processor compute the fuzzy rules and gives the outputs to three PWM modulators connected to the three DC motors. A fourth input channel given to WARP allows to change the reference of the three legs to modify the inclination of the system. The ST6 microcontroller gives also the outputs to the three blocks of electromagnets.

CONCLUSIONS

The design of ROBINSPEC was an engineering problem that involved several different disciplines. Among these particular attention has been devoted to the mechanics of the system (optimization of weights, kinematic) , the electronics , the control (Fuzzy control of the legs and of the electro-magnets), telecommunication (radio-link with the base station), image processing and software engineering. The robot ROBINSPEC is actually at the end of the first phase of the design which includes the following main steps :

• Optimization of the walking sequence with tuning of the parameters of the leg Fuzzy controller;

• Optimization of the current of the electro-magnets in order to minimize energy consumption while guaranteeing surface adhesion;

• Optimization of the interface on the base station;

At the present the trajectory of the robot is telecontrolled from the base-station. The second phase of the design will consist in making ROBINSPEC able to automatically generate motion planning, minimizing the intervention of the operator.