Robonaut The Future Of Space Exploration

I.          INTRODUCTION :

The future of robots in space is not a question of human versus machine, but rather a combination of the best capabilities of human and machine to achieve something which surpasses the capabilities of either alone.

Hitherto mechanical devices sent into outer space operated either by teleoperation (continuous remote control of a manipulator) or through robotics (involving preprogrammed control of a manipulator). Humans control both. The distinction is that in the former case the tele-operators are controlled by humans remote in distance while in the latter, robots are controlled by humans in time (through computer programs).

Robonaut is the first step towards achieving a synergy between tele-operation and robotics and when it is launched into space in the year 2004-05 by NASA, it will usher in a new era in Space Exploration.

An Industrial Robot Defined…

The Robotics Industries Association (RIA) defines an industrial robot as:

“A reprogrammable, multifunctional manipulator designed to move materials, parts, tools or special devices through variable programmed motions for the performance of a variety of tasks.”

The term robotics was coined by Isaac Asimov in his science fiction story “Runaround” where he had portrayed robots built with safety features in mind to assist human beings. In his story, he established the three ‘Fundamental Laws of Robotics’..:

·         A robot may not injure a human being or, through inaction, allow a human being to come to come to harm.

·         A robot must obey the orders given to it by human beings, except where such orders would conflict with the first law.

·         A robot must protect its own existence as long as such protection does not conflict with the first & second laws.

             

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II.        ROBONAUT`S HISTORY [6]:

Robonaut has no precedence. However, there are two other types of devices, which can be considered as space robots. The first is the Remotely Operated Vehicle (ROV) which can be an unmanned spacecraft that remains in flight, a lander that makes contact with an extraterrestrial body and operates from a stationary position, or a rover that can move over terrain once it has landed. The second one is the most common type of existing robotic device and is the. Remote Manipulator System (RMS), or robot arm, most often used in the Manufacturing Industry and in the field of material handling..

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IV.       THE ANATOMY OF ROBONAUT

1) Hands [5] [9]

The Robonaut has two flexible, five-fingered hands. Each Robonaut Hand is similar in size & capability to that of a suited Astronaut’s Hand. The hand components are toleranced to perform acceptably under extreme temperature variations (+120°C to –100°C) as normally experienced in Extra-Vehicular Activity (EVA) conditions. Brushless motors are used to ensure long life in vacuum. All parts are designed to use proven Space Lubricants.

Each hand possesses Fourteen Degrees of Freedom. The forearm houses the motors & drive electronics, a two degree of freedom wrist and a five finger - twelve degree of freedom hand. The forearm measures four inches in diameter at its base & is approximately eight inches long. It houses all of its fourteen motors, 12 separate circuit boards, & the wiring for the hand.

To enhance its tool using ability the hand (Fig.1) is broken down into two sections: a Dexterous work set which is used for manipulation, & a Grasping set which allows the hand to maintain a stable hold while manipulating or actuating a given object. The Dexterous Set consists of two 3 degree of freedom fingers (pointer & index) & a 3 degree of freedom opposable thumb. The Grasping Set consists of two 1 degree of freedom fingers (ring & pinkie) & a palm degree of freedom. All fingers are mounted into the palm.

                                                The hands are Gloved (Fig.2) with Kevlar skins, which are soft fabric coverings, that provide the hands with an improved texture, grip, & clean anatomy that avoids snagging. Each Glove is equipped with 19 moderate resolution force sensors. Three sensors are located in each finger of the Glove, four for the thumb, & three for the palm. The effectiveness of the grasp can be verified using data from this Glove.

 2) Arms [5] [9]

Robonaut’s arms (Fig.3) are human scale manipulators designed to fit within the exterior volume of an Astronaut’s suit. Each arm is a dense packaging of joints & avionics. The endoskeletal design of the arm, houses thermal vacuum rated motors, harmonic drives, fail safe brakes & 16 sensors in each joint. Custom lubricants, strain gauges, encoders & absolute angular position sensors make the dense packaging possible.

The arm is covered by a skin made of a series of synthetic fabric layers structured to provide protection from contact & extreme thermal variations in the environment of outer space. The arms are mounted through 5” pitch joints. The joints (Fig.4) are equipped with a full complement of sensors which allows Robonaut to perform a variety of tasks in a larger workspace around & especially above the body.

 
The two arms are mounted to a central junction, with a third limb, called the ‘Tail’, & a fourth called the neck. The Tail is similar to the arm design, but on a larger scale. Robonaut can be configured for many lower body arrangements, with the Tail ideally suited to operate in zero gravity.

          

3) Head [5] [9]

Robonaut’s Head  consists of two eyes, a nose, & a neck with two degrees of freedom (the ability to nod up & down & shake left & right) that allows the teleoperator to point Robonaut’s camera as eyes.

The eyes  consist of 4 cameras, designed as eye pods. Each pod has a primary camera with zoom, focus, & iris control, & a secondary camera with wide angle view for peripheral vision, all mounted on an independent verge mechanism.

Robonaut’s nose has an infrared thermometer mounted in the nose slot to enable it to measure and identify dangerously hot or cold objects in space before touching them. The built in red laser point places the resulting ‘red dot’ on an object & the object’s temperature can be read.

The neck drives are activated and controlled through a 6 axis Polhemus sensor mounted on the teleoperator’s helmet. The neck’s endoskeleton is covered in fabric skin, which is fitted into & under the helmet. The neck joint is similar to the arm joint & is controlled with the same real time control system.

Robonaut’s head is provided with a Helmet made of Epoxy Resin, ‘grown’ using a stereo lithography machine, & gives Robonaut the rugged design required for protection from collisions.

4) Body [5] [9]

Robonaut’s body is designed to house a Computer brain & a rechargeable power source, enabling tetherless operation. Its torso consists of a structural aluminum endoskeleton  covered by a protective shell. The endoskeleton terminates in a mounting flange for each robot limb, providing convenient locations for 3 six-axis load cells used to measure external forces affecting the robot. When the distal end of the Tail is held fixed, it becomes a leg capable of repositioning the body. In this configuration the Tail sensor measures the external forces acting on the arms, the head & the outer shell. When contact does occur, all the three load cells may be used together to classify the collision as either internal or external & to estimate the contact force & location.

For added protection, the body is covered with a custom-fitted fabric skin designed to contain electrical wire harnesses while keeping foreign material out of the joints. The torso section also contains a subcutaneous layer of foam padding designed to absorb impact energy while permitting contact forces to build up gradually.

The outer shell is dual purpose:-

Ø  It conceals the fragile electronic components & wire bundles, which would otherwise present a serious entanglement hazard.

Ø  It softens collision impact through a combination of a padded jacket & a floating suspension.

Arrays of tactile sensors are installed on the outer walls of the torso shells, below the skin. These sensors sense the contact that occurs between the arm (or objects) & the torso, & manage that contact for best effect. This gives Robonaut the versatility needed to work in unstructured environments.

            Robonaut’s carbon fiber shells are completed with a Backpack that covers & protects the avionics mounted on the robot’s back.

 Both, the torso & the backpack are split into front & back halves to permit easy access to internal electronics (Fig.8).

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V.        ROBONAUT’S CONTROL SYSTEM & OPERATION

1) Control System Architecture [3] [5]

The overall control architecture is based on the concept of sub-autonomies, which are used to build the main system. Each sub-autonomy is a self-contained peer system, which interacts with other peers. These autonomies combine controllers, safety systems, low-level intelligence & sequencing.

Consider the Force Controller sub-autonomy (Fig.9). The force safety system is an integral part of the sub-autonomy. Its limits are controlled by the force sequencer, which configures the sub-autonomy for the selected force mode. When the safety system detects a problem, an input prompts a design criteria. Similarly, when a mode change occurs the force sequencer handles an orderly configuration change of the force control sub-autonomy. The mode of the joint control system required to implement the force mode is decided by the force sequencer & is sent to the joint control sub-autonomy.

`System sub-autonomies include task sequences, Cartesian control, vision, teleoperator interface, joint control & grasping. Higher level sub-autonomies make decisions as to what services the lower level sub-autonomies need to provide to implement the required tasks. Each sub-autonomy handles its own internal safety & decision making. If a failure occurs, a lower sub-autonomy can request a shutdown or reconfiguration from a higher level sub-autonomy without a contagion effect. This is advantageous as each sub-autonomy can be developed & tested individually, enhancing the object oriented aspect of the system.

                                         

2) Computing Environment [5]

The real-time computing platform for Robonaut is the PowerPC processor. The computers & their required I/O devices are connected via a VME backplane. The processors run the VxWorks real-time operating system.

The software for Robonaut is written in C & C++. ControlShell provides a graphical development environment, which enhances the understanding of the system & code reusability.

3) Software Development / Rapid Software Prototyping [5]

System models and controller designs developed in Matlab are converted to C code directly by using the Matlab Real-Time workshop. This capability to rapidly produce code directly from verified system results allows many different techniques to be tried on hardware.

The Robonaut program also uses the Cooperative Manipulation Testbed (CMT) facility (Fig 10} which is a similar/dissimilar arrangement that allows testing of homogenous and heterogenous tasks.. The CMT is made up of three manipulators and their tooling. The three manipulators are seven degree of freedom devices. Two manipulators are identical while the third is a larger, scaled version of the others. The smaller manipulators have three fingered hands for tooling. This flexible tooling allows the manipulators to handle a wide variety of tasks. The larger manipulator has a quick-change mechanism allowing it to autonomously change special purpose end-effectors. All manipulators have six axis end-effector force/torque sensors and joint torque sensors for high bandwidth force control. The computing and development environment for CMT is identical to the Robonaut system for rapid software transfer, develop and test software and controls.

4) Telepresence [5] [8]

This is a technique that establishes remote control of Robonaut’s subsystems & enables the human operator to maintain situation awareness. The goal of telepresence is to provide an intuitive, unobtrusive, accurate & low-cost method for tracking operator motions & communicating them to the robotic system. The components used in Robonaut’s telepresence system (Fig.11) include Helmet Mounted Displays (HMD), force & tactile feedback gloves & posture trackers.

Telepresence uses virtual reality display technology to visually involve the operator in the robot's workspace. The teleoperator virtually takes the place of the robot. Visual feedback is provided by a stereo display helmet and includes live video from Robonaut's head cameras. The HMD provides a view into the robot's environment, facilitating intuitive operation and natural interaction with the work site.

Controlling Robonaut's highly dexterous fingers and hands is made possible by mapping the motions of the teleoperator's fingers onto the hand and finger motions of Robonaut. Finger tracking is accomplished through glove based finger pose sensors. Bend sensitive materials are used to track the orientation of each of the fingers. The information is used to command the action of Robonaut's fingers.

Force sensors are built into Robonaut's hands. The forces imparted on Robonaut's fingers can be displayed to the teleoperator by means of a mechanical exoskeleton worn by the teleoperator.

Arm, torso and head tracking is accomplished with the use of magnetic based position and orientation trackers. Mapping the motions of the human appendages to the motions of Robonaut's arms and head is accomplished similarly to the way the finger tracking is performed.

5) Control Electronics (Avionics) [5]

Robonaut Avionics has been so developed as to create tightly integrated electronics and mechanisms to reduce the volume of external electronics boxes, as well as the size and number of the cable harnesses needed to transmit signals throughout the system. The avionics consists of the following four main subsystems:

(a) Embedded Motor Control:

3-axis FPGA motor controllers coupled with hybrid 3-axis motor drivers have been used to efficiently package the motor control for 14 degrees of freedom in each dexterous hand & wrist module. This limits the number of wires for the motor control of Robonaut to just over 75. The hand motors are clustered in four triple-motor packs and each motor pack is interfaced to a 3-axis hybrid power driver and FPGA using flexible printed circuit boards (PCBs) and nano- connectors. The two wrist motors, which control pitch and yaw, are integrated with two single axis motor drivers. The FPGA motor control PCB has surface mount device (SMD) components on both sides. The hybrid motor driver is rated to deliver 2A continuously at 28 VDC. The flexible PCB serves as the interconnect between the three motor pack, the hybrid motor driver and the FPGA controller. Nano-connectors provide the 28VDC power and FPGA data interface, the hybrid motor driver is connected to the outside of the flex circuit for good thermal conductivity to the forearm structure.

(b)Data Acquisition & Sensory Input:

The two Robonaut hand/wrist modules contain 84 sensors for feedback and control, 60 of which are analog. Each degree of freedom has a motor position sensor, a joint force sensor, and a joint absolute position sensor. The two arm modules contain 90 sensors, 80 of which are analog. Each actuator contains a motor incremental position sensor, redundant joint torque sensors, redundant joint absolute position sensors, and four temperature sensors distributed throughout the joint. Robonaut’s data acquisition system (DAS) has been integrated with the analog sensors and the brainstem computers. The DAS has the capability to accept 48 channels of strain gage input, 32 channels of programmable 0-5V analog input, 96 channels of fixed 0-5V analog input, and 16 channels of thermocouple input.

Besides, Robonaut has 5 six-axis force/moment sensors (FMS) to enable endpoint and localized contact force sensing. The FMS are located in the forearms, shoulders, and upper torso. The FMS interface directly to the brainstem computer, having internal signal processing separate from the DAS.

 (c) Power Distribution & Control:

Power to the arm & waist brakes is implemented with computer & manual override shutdown controls. A manual enable switch is also included for each brake to facilitate partial element testing & reconfiguration. One or more humans are required to be involved in console & work area monitoring, & provide the safety backup to the main computers, or teleoperator error.

(d) Brainstem Data Processing:

The Robonaut computer chassis is 6U VME based & contains three 604 PowerPC computer boards, & several I/O boards to perform external data communication. This will improve system performance by reducing the CPU overhead for bus communications & performing local I/O stream data processing.

6) Mobility [5]

The choice of Robonaut’s mobility platform heavily depends upon the physical conditions into which the robot will be deployed. For extra-vehicular activity (EVA) it will be tethered to the space shuttle/station. Hence, its ‘Tail’ will provide adequate support. Besides this, Robonaut also has a two-piece cart interface . The interface attaches the body-interconnecting node to a welded steel pedestal suspended on top of a four-wheeled cart

. Manually propelled, a mobile Robonaut can easily be moved between rooms for different assembly, diagnostic & servicing operations within the space station or for future use on the surface of another planet.

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VI.       TESTS PERFORMED ON ROBONAUT [5]

The following tests were performed on Robonaut in NASA’s Dexterous Robotics Lab (DRL):

Task: Zero Gravity Climbing

·         To emulate zero gravity a mockup was built of the exterior of a spacecraft and mounted on a boom that is balanced with counterweights to allow it frictionless movement. If Robonaut pushes it, it falls away. This is dynamically equivalent to Robonaut pushing off from a spacecraft and falling away into space, allowing Robonaut to demonstrate climbing even though it is fixed at the hips to a test stand. Robonaut was shown to be able to climb across the surface of the mockup, using EVA handrails for grasp points. Climbing techniques were demonstrated for improving pace, and the impedance control modes for the arms were shown to improve performance when Robonaut held the mockup with a dual arm stance.

Task: Tool Exchange

• Robonaut was operated in an autonomous mode. The task was initiated with subsequent voice commands, asking the robot for a tool, and Robonaut finding that tool, grasping it, and handing it to the human commander. The interactions between the adjacent person and the robot were primarily in the form of communication (voice commands, voice syntheses back from the robot), but also involved a simple form of physical contact, at the points of tool exchange.

Task: Soldering Wires

• For Soldering it takes one hand to hold each of the wires, a third to hold the soldering iron, and a fourth to hold a piece of solder. Instead of using two adjacent humans, Robonaut was used through teleoperation to assist the human. In this task, the human steps up to the robot, and tells the teleoperator what they are going to accomplish. The human hands the robot each wire, then directs (through voice and gesture) the robot to put the wires together, while the human gets the solder and soldering iron. Both agents complete their parallel tasks, then the human solders the wires together, with  all six hands (two human, two robot, two remote human) working together.

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VII.     ALTERNATIVE APPLICATIONS FOR ROBONAUT:-

Robonaut has been primarily developed for assisting astronauts in repair of satellites & space stations by virtue of it`s capabilities in unstructured and hazardous environments. These capabilities will make it the obvious choice in the following fields :-

♠   exploration of other planets

♠   operations in hazardous locations such as mines, volcanoes, petroleum refineries and nuclear power plants

♠   health industry

♠   mining industry

♠   underwater surveying  and maintenance activities

♠   surveillance and guard duty

♠   construction industry

♠   firefighting

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   VIII.    ADVANTAGES OF ROBONAUT [9] [11]:

1)      Robonaut will help cut down on human spacewalk, hence reducing risk to an astronaut’s life.

2)      Robonaut`s is replaceable whereas loss of human life cannot be compensated.

3)      Robonaut can go into active mode almost without notice whereas a human is required to become acclimatized before being sent into hazardous situation.

4)      Robonaut is tireless whereas humans are easily prone to fatigue.

5)      The costs involved in training and equipping a human astronaut are enormous, almost around US$ 12 million per astronaut. Robonaut`s development cost is less than half of this – US$ 4 million. The benefit is obvious.

6)      Robonaut is programmed to be dispassionate whereas one has to contend with the “human factor” amongst human astronauts.

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IX.       CONCLUSION:

The architecture of Robonaut’s Anatomy & Control System appears to comply with advanced concepts and procedures that are designed to replace complex robots by simpler ones to achieve the desired goal. Notwithstanding the various components used to maintain its compactness, Robonaut has managed to retain simplicity & and an effective user-interface. Its use for Extra-Vehicular Activity can greatly reduce the risk to which Astronauts are presently exposed. Not only will it be able to lighten the work schedule of a manned space mission, a time will come when it will be able to travel to environs too hostile or too distant for human explorers.

Robonaut’s features make it a milestone in the future of Space Exploration.  

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