BY MOSES DHILIP KUMAR
Robot is a system with a
mechanical body, using computer as its brain. Integrating the sensors and
actuators built into the mechanical body, the motions are realised with the
computer software to execute the desired task. Robots are more flexible in
terms of ability to perform new tasks or to carry out complex sequence of
motion than other categories of automated manufacturing equipment. Today there
is lot of interest in this field and a separate branch of technology ‘robotics’
has emerged. It is concerned with all problems of robot design, development and
applications. The technology to substitute or subsidise the manned activities
in space is called space robotics. Various applications of space robots are the
inspection of a defective satellite, its repair, or the construction of a space
station and supply goods to this station and its retrieval etc. With the over lap of knowledge of
kinematics, dynamics and control and progress in fundamental technologies it is
about to become possible to design and develop the advanced robotics systems.
And this will throw open the doors to explore and experience the universe and
bring countless changes for the better in the ways we live.
Robot is a mechanical body with the brain of a computer. Integrating the sensors and the actuators and with the help of the computers, we can use it to perform the desired tasks. Robot can do hazardous jobs and can reach places where it’s difficult for human beings to reach. Robots, which substitute the manned activities in space, are known as space robots. The interest in this field led to the development of new branch of technology called space robotics. Through this paper, I intend to discuss about the applications, environmental condition, testing and structure of space robots.
SPACE ROBOT—CHALLENGES IN DESIGN AND TESTING
Robots developed for space applications will be significantly different from their counter part in ground. Space robots have to satisfy unique requirements to operate in zero ‘g’ conditions (lack of gravity), in vacuum and in high thermal gradients, and far away from earth. The phenomenon of zero gravity effects physical action and mechanism performance. The vacuum and thermal conditions of space influence material and sensor performance. The principle effect of distance is the time delay in command communication and its repercussions on the action of the arms. The details are discussed below
SYSTEM VERIFICATION AND TESTING
The reliability is to be demonstrated by a number of tests enveloping all the environmental conditions (thermal and vacuum) that the system will be subjected to. Verification of functions and tests will be conducted on subsystems, subassemblies and final qualification and acceptance tests will be done on complete system. The most difficult and the nearly impossible simulation during testing will be zero ‘g’ simulation.
1 Flat floor test facility: It simulates zero ‘g’ environments in the horizontal plane. In this system flat floor concept is based on air bearing sliding over a large slab of polished granite.
2 Water immersion: Reduced gravity is simulated by totally submerging the robot under water and testing. This system provides multi degree of freedom for testing. This method is used by astronauts for extra vehicular activities with robot.
3 Compensation system: Gravitational force is compensated by a passive and vertical counter system and actively controlled horizontal system.. However, the counter mechanism increases the inertia and the friction of joints of rotating mechanism.
Calibration is performed in five steps:
· Identification, which uses the parametric model and the measured data to determine the optimal set of error parameters.
· Model implementation, which may be done either by updating the root controller data or by correcting the robot pose with expected standard deviation of the error.
· Verification, that the improvement in the positioning accuracy of the robot in all three axes have been achieved.
STRUCTURE OF SPACE ROBOTS
SPACE SHUTTLE ROBOT ARM (SHUTTLE REMOTE MANIPULATOR SYSTEM)
1. USE OF SHUTTLE ROBOT ARM
Satellite deployment and retrieval
· Construction of International Space Station
· Transport an EVA crew member at the end of the arm and provide a scaffold to him or her. (An EVA crew member moves inside the cargo bay in co-operation with the support crew inside the Shuttle.)
· Survey the outside of the Space Shuttle with a TV camera attached to the elbow or the wrist of the robot arm.
Shuttle robot arm observed from the deck
2 ROBOT ARM OPERATION MODE
SRMS is operated inside the Space Shuttle cabin. The operation is performed from the aft flight deck (AFD), right behind the cockpit; either through the window or by watching two TV monitors. To control the SRMS, the operator uses the translational hand controller (THC) with his or her left hand and manipulates the rotational hand controller (RHC) with his or her right hand.
3. FREE FLYING SPACE ROBOTS
The figure below shows an example of a free flying space robot. It is called ETS VII (engineering test satellite VII). It was designed by NASDA and launched in November 1997. When the robot arm moves, it disturbs the altitude of the satellite base. This is not desirable because,
· The satellite may start rotating in an uncontrollable way.
· The antenna communication link may be interrupted.
Free flying space robots
4. SPACE STATION MOUNTED ROBOTS
The international space station (ISS) is a sophisticated structural assembly. There will be several robot arms which will help astronauts in performing a variety of tasks.
The figure shows a part of ISS including the Japanese Experimental Module (JEM). A long manipulator arm can be seen. The arm is called JEMRMS (JEM Remote Manipulating System). A small manipulator arm called SPDM (Special purpose dexterous Manipulator) can be attached to JEMRMS to improve the accuracy of operation.
5. SPACE ROBOT TELEOPERATION
Space robotics is one of the important technologies in space developments. Especially, it is highly desired to develop a completely autonomous robot, which can work without any aid of the astronauts. However, with the present state of technologies, it is not possible to develop a complete autonomous space robot. For this reason, it has become highly desired to develop the technologies for the teleoperation of space robots from the ground in the future space missions.
In the future, robotics will make it possible for billions of people to have lives of leisure instead of the current preoccupation with material needs. There are hundreds of millions who are now fascinated by space but do not have the means to explore it. For them space robotics will throw open the door to explore and experience the universe.