05-11-2012, 04:04 PM
Space Robotics
SPACE_ROBOTICS.doc (Size: 433 KB / Downloads: 21)
INTRODUCTION
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.
TESSELLATOR
Tessellator is a mobile manipulator system to service the space shuttle.The method of rewaterproofing for space shuttle orbiters involves repetitively injecting the extremely hazardous dimethyloxysilane (DMES) into approximately 15000 bottom tile after each space flight. The field robotic center at Carneige Mellon University has developed a mobile manipulating robot, Tessellator for autonomous tile rewaterproofing. Its automatic process yields tremendous benefit through increased productivity and safety.
In this project, a 2D-vehicle workspace covering and vehicle routing problem has been formulated as the Travelling Workstation Problem (TWP). In the TWP, a workstation is defined as a vehicle which occupies or serves a certain area and it can travel; a workspace is referred to as a 2D actuation envelop of manipulator systems or sensory systems which are carried on the workstation; a work area refers to a whole 2D working zone for a workstation.
ROBOTS TO REFUEL SATELLITES
The US department of defense is developing an orbital-refueling robot that could expand the life span of American spy satellites many times over, new scientists reported. The robotic refueler called an Autonomous Space Transporter and Robotic Orbiter (ASTRO) could shuttle between orbiting fuel dumps and satellites according to the Defense Advance Research Projects Agency. Therefore, life of a satellite would no longer be limited to the amount of fuel with which it is launched. Spy satellites carry a small amount of fuel, called hydrazine, which enable them to change position to scan different parts of the globe or to go into a higher orbit. Such maneuvering makes a satellites position difficult for an enemy to predict. But, under the current system, when the fuel runs out, the satellite gradually falls out of orbit and goes crashing to the earth. In the future the refueler could also carry out repair works on faulty satellites, provided the have modular electronic systems that can be fixed by slot in replacements.
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 degree of remoteness of the operator may vary from a few meters to millions of kilometers. 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
ZERO ‘g’ EFFECT ON DESIGN
The gravity free environment in which the space robot operates possesses both advantages and disadvantages. The mass to be handled by the manipulator arm is not a constraint in the zero ‘g’ environment. Hence, the arm and the joints of the space robot need not withstand the forces and the moment loads due to gravity. This will result in an arm which will be light in mass. The design of the manipulator arm will be stiffness based and the joint actuators will be selected based on dynamic torque (i.e.; based on the acceleration of the arm). The main disadvantage of this type of environment is the lack of inertial frame. Any motion of the manipulator arm will induce reaction forces and moment at the base which inturn will disturb the position and the altitude. The problem of dynamics, control and motion planning for the space robot is considering the dynamic interactions between the robot and the base (space shuttle, space station and satellite). Due to the dynamic interaction, the motion of the space robot can alter the base trajectory and the robot end effector can miss the desired target due to the motion of the base. The mutual dependence severely affects the performance of both the robot and the base, especially, when the mass and moment of inertia of the robot and the payload are not negligible in comparison to the base. Moreover, inefficiency in planning and control can considerably risk the success of space missions. The components in space do not stay in position. They freely float and are a problem to be picked up. Hence, the components will have to be properly secured. Also the joints in space do not sag as on earth. Unlike on earth the position of the arm can be within the band of the backlash at each joint.
VACUUM EFFECT AND THERMAL EFFECT
The vacuum in space can create heat transfer problems and mass loss of the material through evaporation or sublimation. This is to be taken care by proper selection of materials, lubricants etc., so as to meet the total mass loss (TML) of <1% and collected volatile condensable matter (CVCM) of <0.1%. The use of conventional lubricants in bearings is not possible in this environment. The preferred lubricants are dry lubricants like bonded/sputtered/ion plated molybdenum disulphide, lead, gold etc. Cold welding of molecularly similar metal in contact with each other is a possibility, which is to be avoided by proper selection of materials and dry lubricants. Some of the subsystem that cannot be exposed to vacuum will need hermetical sealing. The thermal cycles and large thermal variations will have to be taken care in design of robot elements. Low temperature can lead to embrittlement of the material, weaken adhesive bonding and increase friction in bearings.
SPACE_ROBOTICS.doc (Size: 433 KB / Downloads: 21)
INTRODUCTION
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.
TESSELLATOR
Tessellator is a mobile manipulator system to service the space shuttle.The method of rewaterproofing for space shuttle orbiters involves repetitively injecting the extremely hazardous dimethyloxysilane (DMES) into approximately 15000 bottom tile after each space flight. The field robotic center at Carneige Mellon University has developed a mobile manipulating robot, Tessellator for autonomous tile rewaterproofing. Its automatic process yields tremendous benefit through increased productivity and safety.
In this project, a 2D-vehicle workspace covering and vehicle routing problem has been formulated as the Travelling Workstation Problem (TWP). In the TWP, a workstation is defined as a vehicle which occupies or serves a certain area and it can travel; a workspace is referred to as a 2D actuation envelop of manipulator systems or sensory systems which are carried on the workstation; a work area refers to a whole 2D working zone for a workstation.
ROBOTS TO REFUEL SATELLITES
The US department of defense is developing an orbital-refueling robot that could expand the life span of American spy satellites many times over, new scientists reported. The robotic refueler called an Autonomous Space Transporter and Robotic Orbiter (ASTRO) could shuttle between orbiting fuel dumps and satellites according to the Defense Advance Research Projects Agency. Therefore, life of a satellite would no longer be limited to the amount of fuel with which it is launched. Spy satellites carry a small amount of fuel, called hydrazine, which enable them to change position to scan different parts of the globe or to go into a higher orbit. Such maneuvering makes a satellites position difficult for an enemy to predict. But, under the current system, when the fuel runs out, the satellite gradually falls out of orbit and goes crashing to the earth. In the future the refueler could also carry out repair works on faulty satellites, provided the have modular electronic systems that can be fixed by slot in replacements.
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 degree of remoteness of the operator may vary from a few meters to millions of kilometers. 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
ZERO ‘g’ EFFECT ON DESIGN
The gravity free environment in which the space robot operates possesses both advantages and disadvantages. The mass to be handled by the manipulator arm is not a constraint in the zero ‘g’ environment. Hence, the arm and the joints of the space robot need not withstand the forces and the moment loads due to gravity. This will result in an arm which will be light in mass. The design of the manipulator arm will be stiffness based and the joint actuators will be selected based on dynamic torque (i.e.; based on the acceleration of the arm). The main disadvantage of this type of environment is the lack of inertial frame. Any motion of the manipulator arm will induce reaction forces and moment at the base which inturn will disturb the position and the altitude. The problem of dynamics, control and motion planning for the space robot is considering the dynamic interactions between the robot and the base (space shuttle, space station and satellite). Due to the dynamic interaction, the motion of the space robot can alter the base trajectory and the robot end effector can miss the desired target due to the motion of the base. The mutual dependence severely affects the performance of both the robot and the base, especially, when the mass and moment of inertia of the robot and the payload are not negligible in comparison to the base. Moreover, inefficiency in planning and control can considerably risk the success of space missions. The components in space do not stay in position. They freely float and are a problem to be picked up. Hence, the components will have to be properly secured. Also the joints in space do not sag as on earth. Unlike on earth the position of the arm can be within the band of the backlash at each joint.
VACUUM EFFECT AND THERMAL EFFECT
The vacuum in space can create heat transfer problems and mass loss of the material through evaporation or sublimation. This is to be taken care by proper selection of materials, lubricants etc., so as to meet the total mass loss (TML) of <1% and collected volatile condensable matter (CVCM) of <0.1%. The use of conventional lubricants in bearings is not possible in this environment. The preferred lubricants are dry lubricants like bonded/sputtered/ion plated molybdenum disulphide, lead, gold etc. Cold welding of molecularly similar metal in contact with each other is a possibility, which is to be avoided by proper selection of materials and dry lubricants. Some of the subsystem that cannot be exposed to vacuum will need hermetical sealing. The thermal cycles and large thermal variations will have to be taken care in design of robot elements. Low temperature can lead to embrittlement of the material, weaken adhesive bonding and increase friction in bearings.