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Arm under control

Researchers study how to correct failings in industrial robots and make them operate in an environment of microgravity

MIGUEL BOYAYAN Device simulates a robot floating, as if it were in spaceMIGUEL BOYAYAN

Over 1 million robots are nowadays to be found scattered over the planet, carrying out tasks in nuclear power stations, submarine platforms, automobile factories, and even in hospitals, helping doctors to carry out delicate heart surgeries and neurosurgeries, according to the International Federation of Robotics. Some specialists estimate that, around 2010, the number of robotic systems present in households will be in the region of 5 million units. This means that aspects related to reliability and safety of these machines have been receiving redoubled attention from specialists in robotics.

Over the last few years, the group of researchers from the São Carlos Engineering School (EESC/USP), under the command of electrical engineer Marco Henrique Terra, has dedicated itself to studying how to detect and correct defects in manipulative robots, the technical jargon for robotic arms. “Defects in manipulative robots may originate uncontrolled movements that can cause damage to equipment, the workplace environment and to the people present there”, says Marco Terra, one of the coordinators of the Intelligent Systems Laboratory (Lasi) of the EESC’s Electrical Engineering Department.

They have developed prototypes that succeed in simulating movements in space, thanks to a device, present in the robot itself, able to create a cushion of air, simulating an environment of zero gravity. The cushion is a fine layer of air, 2 millimeters thick, that is located between the robotic arm and the surface of the marble table where they operate. It is made up using a compressor and a system of hoses connected to the base of the robot that blow air on the table. This makes the robots float, without any friction at all with the surface, exactly as if it were in space. “This technology makes it possible to study aspects of controlling a robot in environments where gravity is absent. Our studies are important, because, when recoverable failings occur, correcting the problem should be doneby  the robot itself”, Marco Terra explains. “I believe that the research can be useful for space agencies and research institutes.”

Simultaneous work
The studies, which started five years ago, have enjoyed the support of FAPESP, under the regular research benefit line. Since 1998, Marco Terra has been working on the assembly and control of a robotic arm. The research is done with the participation of researchers from the Robotics Institute of the Carnegie Mellon University, in Pennsylvania, United States. It was they who assembled the two robots that there are at Lasi, called UArm II. The second project, in 1999, aimed at studying the problem of detecting and isolating defects in cooperative robots, and then resetting the control system. Cooperative robot is the name given to two robots that work simultaneously and complementing each other one the same task. They are generally applied to tasks that cannot be carried out satisfactorily by a single robot, such as handling very heavy cargo and assemblies that involve several parts.

Each one of Lasi’s two robotic arms measure about 1 meter in length, and they have the format of a human arm, with three powered joints and two segments – the joints correspond to the shoulder, elbow and wrist, and the segments, to the arm and forearm. In simulating defects, the power is usually taken away from one of the joints, which causes an alteration to the robot’s movement. From then on, the researchers are studying how they can correct the trajectory of the arm – for example, by increasing the power in the other joints – in order not avoid any problem to the task being carried out. The various methods developed by the researchers for detecting and isolating defects and post-defect control are based on theories of control and artificial intelligence.

The researches also involve the development of a simulator on which the most varied problems involving manipulative robots can be reproduced. Three different versions of the program have been developed, intended both for elementary and secondary schools and for doctorate programs, chiefly in the areas of electrical, mechanical and mechatronic engineering. The first version is oriented towards the study of kinematics and dynamics of individual robots. The second is intended for experiments with manipulative robots that show defects, and the third for cooperative manipulative robots. “The simulator, which is denominated an environment for simulating and controlling manipulators, can be used for more basic teaching, as well as for more advanced research topics”, the researcher explains.

The simplest version of the simulator has now been successfully tested by several specialists, and is distributed free of charge to researchers and students in the area of robotics. For the time being, the complete version is not available, since the legalization of copyright is still under way. The researchers’ intention is to have the simulator be incorporated, like a toolbox, in Matlab, one of the most used programs for simulation and mathematical calculations, developed by the American company Mathworks. “We are now in conversation with them”, Marco Terra explains. The next step will be the development of the control of manipulators via the Internet. The user will design the controller he wants, using the simulators, and will be able to remote test these techniques on Lasi’s robots.

International recognition
The researches carried out at Lasi have earned international recognition. Besides the publication of articles in Brazilian periodicals (Revista Automação e Controle [Automation and Control Magazine]) and in international ones (International Journal of Robotics), one of the members of the team was paid homage by the Institute of Electrical and Electronic Engineers (IEEE) of the United States, in December last year.

During the 41st Conference on Decision and Control, the main scientific event promoted by the entity, a work on non-linear control techniques for manipulative robots developed by Adriano Almeida Gonçalves Siqueira, studying under Professor Marco Terra for his doctorate, was chosen as one of the best five in a category for awarding prizes to articles whose first author is a student. The importance of the award becomes clear, when one finds out that some 1,400 works were submitted to the conference, roughly 850 of which were accepted.

According to Marco, the importance of the studies carried out by Lasi can be measured by the select club of countries that are active in this field of research. “Only the United States, Japan, Germany and France have shown significant results for problems of defects with manipulative robots”, says the researcher. Mastering this knowledge is fundamental for the good performance of the activities that increasingly need the assistance of these machines.

The project
Resetting the Control Action after a Defect in Cooperative Manipulative Robots (nº 99/10031-1); Modality Regular research benefit line; Coordinator Marco Henrique Terra – USP; Investment R$ 23,411.25 and US$ 17,000.00