HUMANOID ROBOTICS

Robonaut: NASA’s Space Humanoid

Robert O. Ambrose, Hal Aldridge, R. Scott Askew, Robert R. Burridge, William Bluethmann, Myron Diftler, Chris Lovchik, Darby Magruder, and Fredrik Rehnmark, NASA Johnson Space Center

OVER THE YEARS, NASA HAS TO MEET THE DEXTEROUS MANIPULATION NEEDS OF FUTURE experimented with humanoid robots, mainly to use with space hardware and tools MISSIONS, NASA IS DEVELOPING ROBONAUT, AN ASTRONAUT- designed for astronaut use. In 1973, the John- SIZED ROBOT WITH TWO ARMS TWO FIVE FINGERED HANDS A son Space Center built a robot with two arms, , - , grippers, and stereo head cameras mounted HEAD, AND A TORSO. ROBONAUT IS ADVANCING THE STATE OF on a movable base. More recently JSC’s Dex- terous Anthropomorphic Robotic Testbed has THE ART IN ANTHROPOMORPHIC ROBOTIC SYSTEMS, DEXTEROUS found that astronaut tasks once thought ROBOTIC HANDS, MODULAR ROBOTIC SYSTEMS COMPONENTS, impossible for robots can be performed with multifingered robotic hands. AND TELEPRESENCE CONTROL SYSTEMS. NASA’s latest effort in humanoid robotics is Robonaut, shown in Figure 1a. With a human form and scale, Robonaut can use many astronaut tools and can work in the torque control required for dexterous tasks ence instruments, work with soft materials same tight corridors as astronauts. This is an needed in space environments. For example, such as Velcro and thermal insulation, and important accomplishment in humanoid sys- Robonaut could help assemble and service perform other tasks that current robots can- tems, but it is even more significant consid- space science satellites in orbits beyond the not handle. Although now possessing only ering NASA’s need for a system that can oper- Space Shuttle’s reach, or it could handle one arm, Robonaut has passed a series of task ate in the extreme environments of space. To long-duration exposed payloads on board the trials, including those using extra-vehicular meet this challenge, the Robonaut team Shuttle or International Space Station. Robo- activity (EVA) tools, geologic tools, and focused on the upper body, designing an arm naut could complement the work of larger medical instruments. and hand offering greater dexterity, strength, robots or serve as an astronaut’s assistant dur- In its final form, shown in Figure 1b, sensing abilities, and thermal endurance than ing space walks. We are designing it to pro- Robonaut will look much like an astronaut. any other system packaged in human form. vide humanlike capabilities in a broad vari- During EVA,astronauts generally keep their ety of environments. legs together, with their feet inserted in a foot Unlike humanoid robots now being devel- restraint. Robonaut recreates this stabilized Robonaut’s mission oped for entertainment or as technological position with a single leg and uses a “stinger” curiosities, Robonaut will actually perform identical to the one on the foot restraint to Robonaut is the first anthropomorphic work. Starting with this practical goal, we interface with the space vehicle. robot possessing the fine motion and force– have built a robot that can use tools and sci- Through a combination of teleoperation and

JULY/AUGUST 2000 1094-7167/00/$10.00 © 2000 IEEE 57 Stereo vision Helmet 2 DOF neck RMS interface Arms Shoulder Elbow Wrist Hand Body Backpack Leg Hip Knee Ankle ISS load limiter WIFF “Stinger” (a) (b)

Figure 1. Robonaut’s (a) upper body and (b) full anatomy, showing its single leg. automation, Robonaut will be able to do a select set of astronaut tasks. It will act more as an assistant, handling lower-skilled work and saving human EVA time for more valuable Grasping fingers tasks. In higher orbits, however, or in ships Shock mounts bound for Mars or orbital locations beyond our current reach, Robonaut will be the preferred choice for dexterous manipulation. Dexterous fingers Robonaut is notable both for its collection Metacarpals of world-class subsystems and for the qual- ity of its system integration. We are making Palm casting technological achievements in each of the robot’s main subsystems—hands, manipula- tors, head, avionics, control software, and Thumb teleoperator’s interface. Leadscrew assemblies (a) (b)

Hand design Figure 2. Robonaut’s (a) hand, holding a space torque tool; (b) hand parts, showing the dexterous and grasping sets. In the past two decades, engineers have developed many dexterous robotic hands that pressurized glove, and we sized hand and long life in a vacuum, and all hand parts use can grasp and manipulate various objects.1,2 wrist parts to provide the strength needed for proven space lubricants. They have designed several grippers for EVA work. Robonaut’s hand is approaching the capa- space use and have tested them in space,3 but As Figure 2b shows, the hand is divided bilities of a gloved astronaut, and we have we have yet to use a dexterous robotic hand into a dexterous set used for manipulation and demonstrated its use with a large set of EVA for EVA. Robonaut’s hand is one of the first a grasping set used to maintain a stable grasp tools, conventional hand tools, and even med- developed explicitly for EVA use and is the while manipulating an object—both needed ical instruments. We are now working to add closest in size to a suited astronaut’s hand.4 for tool use.5 The dexterous set consists of two tactile sensing and other features for improved Its technology is based on 12 years of cut- three-DOF fingers—index and middle—and control. A second-generation hand under ting-edge work at JSC’s Automation, Robot- a three-DOF opposable thumb. The grasping development will employ a new linear drive ics, and Simulation Division. set consists of two one-DOF fingers—ring and system, reducing hand size and weight while Robonaut’s hand, shown in Figure 2a, will pinkie—and a one-DOF palm. All fingers are providing significantly higher performance. fit into all the same places as a gloved astro- shock-mounted in the palm, giving the hand naut’s hand. With a total of 14 degrees of rugged grasping options. freedom, the hand consists of a forearm, a Robonaut’s hand stands apart from others Arm design two-DOF wrist, and a 12-DOF hand with in its design for space work. All component five fingers. The forearm, which is four materials meet out-gassing restrictions, pre- The Robonaut arm is approximately the inches in diameter at its base and about eight venting contamination that could interfere size of a human arm, with similar strength inches long, houses all 14 motors, 12 sepa- with other space systems. Parts made of dif- and reach but with a greater range of motion. rate circuit boards, and all hand wiring. We ferent materials are toleranced to perform It is capable of fine motion, has a high-band- designed joint travel for wrist pitch and yaw acceptably under the extreme temperature width dynamic response, includes redun- to meet or exceed that of a human hand in a variations of EVA. Brushless motors ensure dancy and safety features, and can endure the

58 IEEE INTELLIGENT SYSTEMS Figure 3. Robonaut’s upper extremity. Figure 4. Robonaut head, neck, and camera subsystem. thermal conditions of an eight-hour EVA. mobility systems, such as rovers. We also Avionics design The five-DOF arm mates with the 14-DOF plan to investigate new manipulator tech- hand and forearm, producing the 19-DOF nologies, including linear actuators and sleek For avionics, our objective has been to upper extremity shown in Figure 3. All of inline packaging. Our new development develop motor control and sensor processing Robonaut’s other manipulators use the same objectives include reducing the forearm that are integrally packaged within the actu- technology as the arm, resulting in a modu- length to improve wrist and hand motor ators and local structure. The primary focus lar family of joints. packaging and reducing the overall weight. of first-generation avionics development has We developed the arm’s dense packaging been to integrate multiaxis hybrid power dri- of joints and avionics using the mechatronics vers, embedded-logic motor controllers, and philosophy—combining mechanicals, elec- Head and neck design packaging technology, producing compact tronics, and software to make intelligent integrated actuator modules needing only machines. Its endoskeleton houses a thermal- Robonaut’s current head and neck are power and data connections. vacuum-rated motor, a harmonic drive, a fail- early prototypes. The head, shown in Figure The motor controller, based on a field- safe brake, and 16 sensors for each of the five 4, holds two small color cameras that deliver programmable gate array, provides motor upper joints. The arm’s small size, one-to- stereo vision to the operator’s virtual reality commutation, pulse width modulation con- one strength-to-weight ratio, high density, display, providing depth perception. The trol, velocity and current control, and position, and thermal vacuum capabilities make it state cameras’spacing equals typical human inter- velocity, and current feedback. The hybrid of the art in space manipulators. ocular spacing, with a fixed verge at arm’s motor driver translates logic-level control sig- To make the dense packaging possible, we reach. We are now investigating new optics nals, serves as the gate drive of the high- and developed custom lubricants, strain gauges, for a wider field of view, ways to enhance low-side metal-oxide-semiconductor field- encoders, and absolute angular position sen- depth perception by giving the teleoperator effect transistors of the three-phase power sors. A series of synthetic fabric layers will better verge control, new cameras that are bridge, and provides motor-phase sourcing cover the manipulators, forming a skin that insensitive to solar light, and ways to inte- and sinking using the MOSFETs and ultra- protects against contact and thermal damage. grate a stereo computer vision system. fast recovery flyback diodes. The hybrid dri- We have tested two of these joints in JSC’s The articulated neck lets the teleoperator ver is rated to deliver 2 amps continuously thermal vacuum chamber, and they per- point Robonaut’s head. Like the arms, the at 28 Vdc from –55 C to +125 C, measures formed well in temperatures from –25 C to neck’s endoskeleton is covered with a fabric 2.88" × 0.8" × 0.175", and is housed in a con- 105 C. The new lubricants that make this pos- skin, which is fitted into and under the hel- formal flexible circuit board that wraps around sible are a major breakthrough in harmonic met. Using a helmet is unusual in robotics, a triple-motor pack, as Figure 5 shows. drive technology. where cameras are typically mounted on Next-generation avionics will incorporate In designing the arm, we used custom soft- exposed pan-tilt-verge units, but we felt we a recently developed radiation-tolerant appli- ware to size and select components,6 evalu- needed a rugged design to protect the cam- cation-specific integrated circuit, which can ate strength requirements, and simulate ther- eras in cluttered environments. be fabricated at commercial semiconductor mal endurance for specific task timelines.7 The design of the neck joints is similar to foundries. A radiation-hardened hybrid power We also used custom analysis techniques to that of the arm joints, using the same real-time stage will integrate with the ASIC to provide design the arm (and other Robonaut parts) control system. The neck joints’kinematics is a fully functional three-axis motor con- for zero-gravity applications, where load based on a pan-tilt serial chain, with the first troller/driver. The integration of these fun- sharing and compliance require an under- rotation about Robonaut’s spine, and then a damental components of motor control will standing of serial, parallel, and bifurcating pitch motion about a lateral axis. The pitch provide intelligent actuators that perform sig- chain kinetics.8 motion axis does not pass through the camera nal and power processing integral to their We are now exploring arm requirements lenses, but is instead three inches below them. electromechanical structure. This greatly for advanced applications, such as climbing This offset allows the cameras to translate for- reduces external components, reducing vol- in zero gravity and integration with surface ward, letting Robonaut see down over its chest. umetric requirements, and simplifies the

JULY/AUGUST 2000 59 Figure 5. Triple-motor pack. Figure 6. The data acquisition system. interface to the motors. The first-generation classical robot control methods. To fully real- sequencer, which configures the subauton- design has reduced the wire count from 400 ize Robonaut’s capabilities, we will need omy for the selected force mode. When the to 250, with the majority of these being advances in control theory in the areas of safety system detects a problem, an input motor power wires. grasping, force control, intelligent control, reaches a design criterion, or a mode change The Robonaut hand and wrist module con- and shared control. occurs, the force sequencer handles an tains 42 sensors for feedback and control, 28 For Robonaut’s development, we will orderly configuration change of the force of which are analog and require signal con- need both safe functionality under teleoper- control subautonomy. The force sequencer ditioning and digitization. The arm module ator control and high-level partial or fully decides the mode of the joint control system contains an even greater number of sensors autonomous control incorporating artificial required to implement the force mode and with similar requirements. Handling this large intelligence and machine vision. The result- sends it to the joint control subautonomy. data stream is made more difficult by the need ing system will be able to make safety deci- Robonaut’s computing environment in- for small packaging, which limits overall sions and provide reflexive actions—such as cludes several state-of-the-art technologies. electronics volume and geometry, both in the force control and basic grasping—at a low We chose the PowerPC processor for the limbs and in the body. level. This architecture makes the control real-time computing platform because of its The first-generation data acquisition sys- system inherently safe and enables the performance and continued development for tem shown in Figure 6 is compact, rugged, research and development of teleoperation space applications. A VME backplane con- and commercially available, and can sample and machine intelligence. nects the computers and their required I/O. the hundreds of sensors distributed through- To allow this safe interaction, we are The processors run the VxWorks real-time out the Robonaut system. To meet the chal- developing the overall control architecture operating system. We are using C and C++ lenge of embedding the DAS, we have been around subautonomies—each combining to write Robonaut’s software. prototyping mixed-signal ASICs, which pro- controllers, safety systems, low-level intel- For Robonaut’s development, we are using vide signal conditioning and A/D conversion ligence, and sequencing, and each acting as ControlShell, an object-oriented, real-time and can be both distributed throughout the a self-contained peer system that interacts software development environment. Con- system and embedded close to the sensors. with other peers. For example, Figure 7 trolShell provides a graphical development These prototypes have shown the potential shows the force controller subautonomy. One environment that enhances the understanding for a truly distributed DAS capable of pro- integral part of it is the force safety system, of the system and code reusability. We are cessing the numerous Robonaut sensors. whose limits are controlled by the force also using JSC’s Cooperative Manipulation

Control design Force sensor

The Robonaut control system must Force safety

• provide safe, reliable control for 43-plus Force command Torque command DOF using data from 150-plus sensors; • be controllable through direct teleopera- Force controller tion, shared control, and full autonomy; Force mode Joint control mode • maintain performance in a harsh thermal Force environment; and sequencer • execute at the required rate on available Joint position computing hardware.

We cannot meet these challenges using only Figure 7. Force controller subautonomy, showing the decision-making, safety, and control processes.

60 IEEE INTELLIGENT SYSTEMS improve robot safety and performance dur- ing space operations, such as the use of a torque tool (see Figure 9a). We’ve achieved this goal using

• an intuitive mapping of the human oper- ator to Robonaut’s anthropomorphic design; • unencumbering telepresence equipment; • text and graphical advising capabilities, including status, warning, and safety information, for robot operators; • an immersion environment for the opera- tor that maximizes situational awareness; • voice recognition for operator com- mands; and • feedback devices that give the operator natural cues for force and contact.

Figure 8. JSC’s Cooperative Manipulation Testbed is a three-manipulator system used to prototype and develop Wearing the virtual-reality-based tele- advanced control systems for use in space. Control techniques and software developed on CMT enhance the capabilities presence gloves and helmet shown in Fig- of systems such as Robonaut. ure 9b, an operator’s hand, arm, and neck map directly to the Robonaut system. Sen- sors in the gloves determine finger positions Testbed facility, shown in Figure 8, to develop We will be able to add higher-level autonomous and send commands to the Robonaut hand. and test software and control strategies. functions using an application programming Six-axis Polhemus sensors on the operator’s Robonaut’s control system currently sup- interface for Robonaut, with interfaces for helmet and wrist generate neck and arm ports teleoperative control of the right extrem- higher-level computing and reasoning systems. commands. ity and the head, with subautonomies for Our goal is to give Robonaut’s supervisor a Robonaut’s human scale and form make Cartesian control, motor control, and tele- combination of autonomous and telepresence it possible for teleoperators to apply their operation. We are now testing on CMT pro- control modes to accomplish complex tasks. own experience, training, and instincts. totypes of the force control and multiarm con- Using the system now in development at trol systems, which we will shift to Robonaut JSC, novice operators have become profi- as sensors and mechanisms become available. Teleoperator interface cient in less than five minutes. An orthope- While teleoperation is the initial mode, the dic surgeon, who had never operated the Robonaut control system is fully sensate and Robonaut’s teleoperator interface uses new robot before, was able to competently han- will execute commands regardless of origin. methods and algorithms to significantly dle medical instruments within minutes.

(a) (b)

Figure 9. (a) Robonaut under teleoperation and (b) VR gear used to control Robonaut.

JULY/AUGUST 2000 61 Figure 10. Robonaut unlatching a locking tether hook. Figure 11. The centaur concept, where the Robonaut attaches to a rover.

Much of Robonaut’s dexterous work will References involve force-controlled manipulation, OBONAUT IS A WORK IN PRO- R 1. J.K. Salisbury and M.T. Mason, Robot Hands where small motions produce significant gress, but the JSC team is committed to and the Mechanics of Manipulation, MIT force and torque. Humans can easily handle developing a series of Robonaut systems, Press, Cambridge, Mass., 1985. this work, but robot operators don’t receive with new generations outfitted for a spectrum the same feedback. The Robonaut project of missions. The zero-gravity servicing sys- 2. S. Jacobsen et al., “Design of the Utah/M.I.T. Dexterous Hand,” Proc. IEEE Int’l Conf. will integrate new force and tactile feed- tem, configured with a single leg, has been Robotics and Automation, IEEE Computer back devices to give the operator natural the team’s primary focus. This configuration Soc. Press, Los Alamitos, Calif., 1986, pp. cues to the system’s force amplitude and seems ideal for outside work on the Interna- 1520–1532. direction. These devices include tactile dis- tional Space Station, the Space Shuttle, high- plays and haptic force feedback, which will orbit science or military platforms, or a Mars- 3. G. Hirzinger et al., “Sensor-Based Space Robotics: ROTEX and Its Telerobotic Fea- provide intuitive and effective closed-loop bound spacecraft. tures,” IEEE Trans. Robotics and Automation, control. One intriguing configuration, shown in Vol. 9, No. 5, 1993, pp. 649–663. Figure 11, attaches Robonaut to a rover, resembling the centaur, a mythical creature 4. C. Lovchik, H. Aldridge, and M. Diftler, “Design of the NASA Robonaut Hand,” Proc. Task testing with the upper torso of a man and lower torso ASME Dynamics and Control Division, DSC- of a horse. This design would be well suited Vol. 67, Amer. Soc. of Mechanical Engineers, We have begun testing the Robonaut sys- for planetary operations, habitat building, New York, 1999, pp. 813–830. tem in representative tasks, including those work with humans in exploration, or rescue for applications in space, geology, and med- and recovery. 5. B. Jau, “Dexterous Telemanipulation with Four-Fingered Hand System,” Proc. IEEE icine. For example, Figure 10 shows Robo- Our work now, though, is to continue Int’l Conf. Robotics and Automation, IEEE naut unlatching a locking tether hook used developing Robonaut’s subsystems. In arm Computer Soc. Press, Los Alamitos, Calif., to secure objects in zero gravity—a task and hand designs, we are pushing the state 1995, pp. 338–343. requiring complex manipulation. Geologic of the art in packaging, strength, and sensor 6. R. Ambrose, “Interactive Robot Joint Design, operations, such as digging, require signifi- count. We are making avionics smaller and Analysis, and Prototyping,” Proc. IEEE Int’l cant strength and the ability to handle multi- better integrated, which will lead to a true Conf. Robotics and Automation, IEEE Com- ple tools, including scoops, drills, and picks. mechatronic design. We are moving the puter Soc. Press, Los Alamitos, Calif., 1995, Medical tasks require fine positioning and control system beyond teleoperation to pp. 2119–2124. dexterous movement to operate complex shared or fully autonomous control. We are 7. R. Ambrose and C. Ambrose, “Robot Mod- tools, such as the arthroscopic wand. These making the teleoperation interface even els for Space Environments,” Proc. IEEE Int’l diverse tasks show Robonaut’s flexibility. We more intuitive. The common denominator Conf. Robotics and Automation, IEEE Com- will continue working to quantify operator for these technologies is the dexterous puter Soc. Press, Los Alamitos, Calif., 1995, workload, build capabilities for complete upper-body system, our initial focus. We pp. 2113–2118. end-to-end tasks, and develop new opera- will continue to advance its dexterity while 8. R. Ambrose and M. Diftler, “The Serial Form tional methods to best utilize the Robonaut investigating lower-body options for new of Strength in Serial, Parallel, and Bifurcated system. missions. Manipulators,” Proc. IEEE Int’l Conf. Robot-

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ics and Automation, IEEE Computer Soc. avionics lead for the Robonaut project. His research mated assembly. He received a PhD in mechanical Press, Los Alamitos, Calif., 1998, pp. interests include power electronics, motion control, engineering from Rice University. Contact him at 1334–1339. and embedded electronics for control of electro- diftler@jsc.nasa.gov. mechanical devices. He received an MS in electri- cal engineering from Virginia Polytechnic Institute. Robert O. Ambrose is a senior engineer working Contact him at [email protected]. Chris Lovchik is a senior engineer in JSC’s for Metrica, Inc., at the Johnson Space Center. He Robotic Systems Technology Branch and is the is the Robonaut project leader for JSC’s Automa- designer of the Robonaut hand. His research inter- tion, Robotics, and Simulation Division. His Robert R. Burridge is a senior scientist working ests include robotic hands, miniaturized actuators, research interests include modular manipulators, for S&K Electronics at JSC. His research interests and mechanical design. He earned a BS in mechan- manipulator design optimization, and tribology. He include dynamical systems theory, hybrid control, ical engineering from Wichita State University. received a PhD in mechanical engineering from the controller composition, intelligent robot control Contact him at [email protected]. University of Texas at Austin. Contact him at the architectures, and adjustable autonomy. He earned NASA Johnson Space Center, Mail Code ER4, a PhD in computer science and engineering from Houston, TX 77058; [email protected]. the University of Michigan. Contact him at bur- Darby Magruder is a senior engineer in JSC’s [email protected]. Robotic Systems Technology Branch and is the telepresence systems lead for the Robonaut project. His research interests include unencumbering tele- Hal Aldridge is a senior engineer in JSC’s operation equipment, human–computer interfaces, Robotic Systems Technology Branch and cur- William Bluethmann is a senior engineer working and operator training. He earned an MS in electro- rently the software lead for the Robonaut project. for Hernandez Engineering at JSC. His research optics from the University of Houston–Clear Lake. His research interests include robot control, interests include manipulator control, force control, Contact him at [email protected]. embedded systems, and fault tolerance. He earned and redundancy resolution. He earned a PhD in a PhD in electrical and computer engineering from mechanicalengineering from the University of Carnegie Mellon University. Contact him at Kansas. Contact him at [email protected]. Fredrik Rehnmark is a robotics specialist working [email protected]. for Lockheed Martin at JSC. His research interests include human augmentation and anthropomorphic Myron Diftler is a senior systems engineer work- robots. He earned an MS in mechanical engineering R. Scott Askew is a senior engineer in JSC’s ing for Lockheed Martin at JSC. His research inter- from the University of California at Berkeley. Con- Robotic Systems Technology Branch and the ests include robotic hands, grasping, and auto- tact him at [email protected].

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