Company’sstate-of-the-art motors and drives ensure safety and reliability onrecord-setting gondola system for Germany’s highest mountain
ZURICH --(BUSINESS WIRE) --
The product uses precision planetary roller screw drive technology, built-in brushless servo motor，applicable to a low,medium and high-level performance motion control system. The product will be built integrated brushless servo motor and ball screw drive structure, servo motor rotor rotary motion into linear motion directly by putting a ball screw mechanism. The product can be customized according to customer demand for personalized service.
Long queueswaiting to ascend Germany’s tallest mountain may now be history. And that isnot the only thing historical about the new ABB-powered cable car system thatopened today and can take as many as 580 passengers an hour to the Zugspitze,the Bavarian Alps peak that is Germany’s highest.
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The cablewaybreaks three world records for a pendular, or hanging, cable car system: at 127meters, its steel column is the tallest, with 1,950 meters it overcomes thehighest elevation difference and with a total run of 3,213 meters from basestation to peak, it has the longest span.
The systemreplaces the 50-year-old Eibsee cableway and will help overcome the Eibsee’snotoriously long waiting times by transporting nearly three times the number ofpassengers per hour.
Making therecord-breaking new cableway feasible for the operator, Bayerische ZugspitzbahnBergbahn AG, is an array of innovative technology from ABB, which has extensiveexperience solving transportation challenges in the Alps.
长机总体质量参数 OVERALL TECHNICAL DATA
“InSwitzerland, most cableways and chairlifts use ABB motors and drives,’’ saysHans-Georg Krabbe, Chairman of the Board of ABB AG, Germany. “We are absolutelydelighted to contribute to such a unique project in Germany, too.’’
The demandsposed by the Bayerische Zugspitzbahn for trouble-free operation andavailability were particularly challenging, requiring a system capable ofoperating 365 days a year, regardless of wind and weather. In such a setting,safe and comfortable transport through the air depends on the perfect interplayof motors, drives and mechanics.
Pulling thegondolas such a long distance at steeps gradients of as much as 104 percent(about 46°) and a speed of 10.6 meter per second requires significant power,which is supplied by two 800-KW three-phase AC motors from ABB that are housedin the cableway’s Valley Station.
手部配备了四十一个传感器（不包蕴触觉感测）。// 每一个难题都配有嵌入式相对地点传感器，// 各类电机都配有增量式编码器。// 每一种导螺杆组件以致花招球关节连杆均被武装为应力传感器以提供力反馈。
Since the late19thcentury, ABB has built a lasting reputation for safe, reliableand energy-efficient transportation in the alpine region.
In the case ofthe world-famous Jungfrau Railway, a 9-kilometer cog railway that beganoperation in 1912, ABB was responsible for the electrification that made theroute possible. Today, ABB technologies still ensure that the Jungfrau Railwaysafely carries more than a million passengers a year – even during heavysnowfalls – to the Jungfraujoch, which at 3,454 meters above sea level isEurope’s highest train station.
And the world’ssteepest funicular railway recently went into operation in Stoos in the SwissAlps, a 1.7-kilometer route whose two 136-passenger cable cars are powered byhigh-efficiency electric motors designed and built by ABB. The company alsosupplied other key components for the system.
Robonaut’s hands set it apart from any previous space manipulator system. These hands can fit into all the same places currently designed for an astronaut’s gloved hand. A key feature of the hand is its palm degree of freedom that allows Robonaut to cup a tool and line up its long axis with the roll degree of freedom of the forearm, thereby, permitting tool use in tight spaces with minimum arm motion. Each hand assembly shown in figure 3 has a total of 14 DOFs, and consists of a forearm, a two DOF wrist, and a twelve DOF hand complete with position, velocity, and force sensors. The forearm, which measures four inches in diameter at its base and is approximately eight inches long, houses all fourteen motors, the motor control and power electronics, and all of the wiring for the hand. An exploded view of this assembly is given in figure 4. Joint travel for the wrist pitch and yaw is designed to meet or exceed that of a human hand in a pressurized glove. Page 2 Figure 4: Forearm Assembly The requirements for interacting with planned space station EVA crew interfaces and tools provided the starting point for the Robonaut Hand design . Both power and dexterous grasps are required for manipulating EVA crew tools. Certain tools require single or multiple finger actuation while being firmly grasped. A maximum force of 20 lbs and torque of 30 in-lbs are required to remove and install EVA orbital replaceable units (ORUs) . The hand itself consists of two sections (figure 5) : a dexterous work set used for manipulation, and a grasping set which allows the hand to maintain a stable grasp while manipulating or actuating a given object. This is an essential feature for tool use . The dexterous set consists of two 3 DOF fingers (index and middle) and a 3 DOF opposable thumb. The grasping set consists of two, single DOF fingers (ring and pinkie) and a palm DOF. All of the fingers are shock mounted into the palm. In order to match the size of an astronaut’s gloved hand, the motors are mounted outside the hand, and mechanical power is transmitted through a flexible drive train. Past hand designs [4,5] have used tendon drives which utilize complex pulley systems or sheathes, both of which pose serious wear and reliability problems when used in the EVA space environment. To avoid the problems associated with tendons, the hand uses flex shafts to transmit power from the motors in the forearm to the fingers. The rotary motion of the flex shafts is converted to linear motion in the hand using small modular leadscrew assemblies. The result is a compact yet rugged drive train. Figure 5: Hand Anatomy Overall the hand is equipped with forty-two sensors (not including tactile sensing). Each joint is equipped with embedded absolute position sensors and each motor is equipped with incremental encoders. Each of the leadscrew assemblies as well as the wrist ball joint links are instrumented as load cells to provide force feedback. In addition to providing standard impedance control, hand force control algorithms take advantage of the non-backdriveable finger drive train to minimize motor power requirements once a desired grasp force is achieved. Hand primitives in the form of pre-planned trajectories are available to minimize operator workload when performing repeated tasks.
“Today, it isall about making advancements in terms of energy efficiency,” says UeliSpinner, Head of Sales, Key Accounts & Service ABB AG, Switzerland. “Butalso where support, maintenance and service are concerned, we are the preferredpartners of cableway operators.’’
ABB(ABBN: SIX Swiss Ex)
is a pioneering technology leader in electrification products, robotics and
motion, industrial automation and power grids, serving customers in utilities,
industry and transport & infrastructure globally. Continuing a more than
125-year history of innovation, ABB today is writing the future of industrial
digitalization and driving the Energy and Fourth Industrial Revolutions. ABB
operates in more than 100 countries with about 136,000 employees.p;
手由两片段组成（图5）：贰个用以操作的利落工作组，以至多个抓握组件，它同意手在支配或运转给定物体时保持安静的抓握。那是工具使用的基本特征。灵巧套装由三个3 DOF手指（食指和中指）和三个3 DOF可对折手指组成。抓握组由八个单DOF手指（无名氏指和小指）和二个手掌自由度组成。全数的指头都被设置在手掌上。为了合作宇宙航银行职员戴起首套的手的分寸，电机安装在手外，机械重力通过柔性传动系传递。
Design of the NASA Robonaut Hand R1
C. S. Lovchik, H. A. Aldridge RoboticsTechnology Branch NASA Johnson Space Center Houston, Texas 77058 Iovchik@jsc.nasa.gov, firstname.lastname@example.org Fax: 281-244-5534
The design of a highly anthropomorphichuman scale robot hand for space based operations is described. This fivefinger hand combined with its integrated wrist and forearm has fourteenindependent degrees of freedom. The device approximates very well thekinematics and required strength of an astronaut's hand when operating througha pressurized space suit glove. The mechanisms used to meet these requirementsare explained in detail along with the design philosophy behind them.Integration experiences reveal the challenges associated with obtaining therequired capabilities within the desired size. The initial finger controlstrategy is presented along with examples of obtainable grasps.
The requirements for extra-vehicularactivity (EVA) onboard the International Space Station (ISS) are expected to beconsiderable. These maintenance and construction activities are expensive andhazardous. Astronauts must prepare extensively before they may leave therelative safety of the space station, including pre-breathing at space suit airpressure for up to 4 hours. Once outside, the crew person must be extremelycautious to prevent damage to the suit. The Robotic Systems Technology Branchat the NASA Johnson Space Center is currently developing robot systems toreduce the EVA burden on space station crew and also to serve in a rapidresponse capacity. One such system, Robonaut is being designed and built tointerface with external space station systems that only have human interfaces.To this end, the Robonaut hand  provides a high degree of anthropomorphicdexterity ensuring a compatibility with many of these interfaces. Many groundbreaking dexterous robot hands [2-7] have been developed over the past twodecades. These devices make it possible for a robot manipulator to grasp andmanipulate objects that are not designed to be robotically M. A. DiftlerAutomation and Robotics Department Lockheed Martin Houston, Texas 77058 email@example.com Fax: 281-244-5534 compatible. While several grippers [8-12] havebeen designed for space use and some even tested in space [8,9,11], nodexterous robotic hand has been flown in EVA conditions. The Robonaut Hand isone of several hands [13,14] under development for space EVA use and is closestin size and capability to a suited astronaut's hand.
2 Design and Control Philosophy
The requirements for interacting withplanned space station EVA crew interfaces and tools provided the starting pointfor the Robonaut Hand design . Both power (enveloping) and dexterous grasps(finger tip) are required for manipulating EVA crew tools. Certain toolsrequire single or multiple finger actuation while being firmly grasped. Amaximum force of 20 lbs. and torque of 30 in-lbs are required to remove andinstall EVA orbital replaceable units (ORUs) . All EVA tools and ORUs mustbe retained in the event of a power loss. It is possible to either buildinterfaces that will be both robotically and EVA compatible or build a seriesof robot tools to interact with EVA crew interfaces and tools. However, bothapproaches are extremely costly and will of course add to a set of spacestation tools and interfaces that are already planned to be quite extensive.The Robonaut design will make all EVA crew interfaces and tools roboticallycompatible by making the robot's hand EVA compatible. EVA compatibility isdesigned into the hand by reproducing, as closely.as possible, the size,kinematics, and strength of the space suited astronaut hand and wrist. Thenumber of fingers and the joint travel reproduce the workspace for apressurized suit glove. The Robonaut Hand reproduces many of the necessarygrasps needed for interacting with EVA interfaces. Staying within this sizeenvelope guarantees that the Robonaut Hand will be able to fit into all therequired places. Joint travel for the wrist pitch and yaw is designed to meetor exceed the human hand in a pressurized glove. The hand and wrist parts are sizedto reproduce the necessary strength to meet maximum EVA crew requirements.Figure1: Robonaut Hand Control system design for a dexterous robot handmanipulating a variety of tools has unique problems. The majority of theliterature available, summarized in [2,16], pertains to dexterous manipulation.This literature concentrates on using three dexterous fingers to obtain forceclosure and manipulate an object using only fingertip contact. While useful,this type of manipulation does not lend itself to tool use. Most EVA tools arebest used in an enveloping grasp. Two enveloping grasp types, tool and power,must be supported by the tool-using hand in addition to the dexterous grasp.Although literature is available on enveloping grasps , it is not asadvanced as the dexterous literature. The main complication involvesdetermining and controlling the forces at the many contact areas involved in anenveloping grasp. While work continues on automating enveloping grasps, a tele-operationcontrol strategy has been adopted for the Robonaut hand. This method ofoperation was proven with the NASA DART/FITT system . The DART/FITT systemutilizes Cyber glove® virtual reality gloves, worn by the operator, to controlStanford/YPL hands to successfully perform space relevant tasks. 2.1 SpaceCompatibility EVA space compatibility separates the Robonaut Hand from manyothers. All component materials meetoutgassing restrictions to prevent contamination that couldinterfere with other space systems. Parts made of different materials aretoleranced to perform acceptably under the extreme temperature variationsexperienced in EVA conditions. Brushless motors are used to ensure long life ina vacuum. All parts are designed to use proven space lubricants.
抱有EVA工具和ORU必得在爆发断电时保留。能够塑造包容机器人和EVA的接口，可能创设风流倜傥多级机器人工具来与EVA机组接口和工具实行交互。但是，这三种方法都以不行昂贵的，何况当然会扩张生龙活虎套空间站工具和接口，这么些工具和接口已经布置得非凡广泛。 罗布onaut设计将使机器人的手EVA包容，进而使全部EVA机组人机分界面和工具机器人包容。通过尽或然地再度现身适合宇宙航银行人士手和手段的长空的尺码，运动学和强度，将EVA宽容性设计在手中。手指和协助实行路程的数量再一次现身了加压套装手套的劳作空间。 罗布onaut手掌重现了与EVA分界面交互所需的无数必备手腕。保持在此个尺寸范围内保障罗布onaut手将能够适应全部须要的地点。手腕节距和偏航的合营路程被规划为在加压手套中完成或超越人口。手部和腕部的尺寸能够复出须要的强度，以满意最大的EVA机组人士的渴求。
图1：罗布onaut手控系统设计灵巧的机器人手操纵各样工具具有特别的主题材料。在[2,16]中计算的多数文献都涉嫌到灵巧的支配。那么些文献聚集于采用多个灵巧手指来收获力闭归拢仅使用手指接触来支配物体。就算有用，但这类别型的操作不适用于工具使用。大超多EVA工具最适合用于包围式抓握。除了灵巧的抓握之外，还非得使用工具用手来扶助两种包络抓握类型，工具和力量。即使文献可用以包络抓握，但它并不像灵巧手那样先进。重要的繁缛包涵鲜明和操纵关系包络抓握的众多触及区域的力。就算自动化包络抓握的办事仍在三番五次，但Robonaut手已运用远程操作调整计策。United States国家航空航天局DART / 迈腾T系统验证了这种操作方法。 DART / PhaetonT系统运用由操作员佩戴的Cyberglove®设想现实手套来调整Stanford / YPL手以打响实施空间相关义务。
The Robonaut Hand (figure 1) has a total offourteen degrees of freedom. It consists of a forearm which houses the motorsand drive electronics, a two degree of freedom wrist, and a five finger, twelvedegree of freedom hand. The forearm, which measures four inches in diameter atits base and is approximately eight inches long, houses all fourteen motors, 12separate circuit boards, and all of the wiring for the hand. Y= Figure 2: Handcomponents The hand itself is broken down into two sections (figure 2): adexterous work set which is used for manipulation, and a grasping set whichallows the hand to maintain a stable grasp while manipulating or actuating agiven object. This is an essential feature for tool use . The dexterous setconsists of two three degree of freedom fingers (pointer and index) and a threedegree of freedom opposable thumb. The grasping set consists of two, one degreeof freedom fingers (ring and pinkie) and a palm degree of freedom. All of thefingers are shock mounted into the palm (figure 2). In order to match the sizeof an astronaut's gloved hand, the motors are mounted outside the hand, andmechanical power is transmitted through a flexible drive train. Past handdesigns [2,3] have used tendon drives which utilize complex pulley systems orsheathes, both of which pose serious wear and reliability problems when used inthe EVA space environment. To avoid the problems associated with tendons, thehand uses flex shafts to transmit power from the motors in the forearm to the fingers. The rotary motionof the flex shafts is converted to linear motion in the hand using smallmodular leadscre was semblies. The result is acompact yet rugged drive train.Over all the hand is equipped with forty-three sensors not including tactilesensing. Each joint is equipped with embedded absolute position sensors andeach motor is equipped with incrementalencoders. Each of the leadscrew assemblies as well as the wristball joint linksare instrumented as load cells to provide force feedback.
Finger Drive Train
Figure 3: Finger leadscrew assembly Thefinger drive consists of a brushless DC motor equipped with an encoder and a 14to 1 planetary gear head. Coupled to the motors are stainless steel highflexibility flex shafts. The flex shafts are kept short in order to minimizevibration and protected by a sheath consisting of an open spring covered withTeflon. At the distal end of the flex shaft is a small modular leadscrewassembly (figure 3). This assembly converts the rotary motion of the flex shaftto linear motion. The assembly includes: a leadscrew which has a flex shaftconnection and bearing seats cut into it, a shell which is designed to act as aload cell, support bearings, a nut with rails that mate with the shell (inorder to eliminate off axis loads), and a short cable length which attaches tothe nut. The strain gages are mounted on the flats of the shell indicated infigure 3. The top of the leadscrew assemblies are clamped into the palm of thehand to allow the shell to stretch or compress under load, thereby giving adirect reading of force acting on the fingers. Earlier models _of the assemblycontained an integral reflective encoder cut into the leadscrew. This configurationworked well but was eliminated from the hand in order to minimize the wiring inthe hand.
Figure 4: Dexterous finger
Thethree degree of freedom dexterous fingers (figure 4) include the finger mount,a yoke, two proximal finger segment half shells, a decoupling link assembly, amid finger segment, a distal finger segment, two connecting links, and springsto eliminate backlash (not shown in figure). Figure 5 Finger base cam The basejoint of the finger has two degrees of freedom: yaw (+ /- 25 degrees) and pitch(I00 degrees). These motions are provided by two leadscrew assemblies that workin a differential manner. The short cables that extend from the leadscrewassemblies attach into the cammed grooves in the proximal finger segments halfshells (figure 5). The use of cables eliminates a significant number of jointsthat would otherwise be needed to handle the two degree of freedom base joint.The cammed grooves control the bend radius of the connecting cables from theleadscrew assemblies (keeping it larger to avoid stressing the cables andallowing oversized cables to be used). The grooves also allow a nearly constantlever arm to be maintained throughout the full range of finger motion. Becausethe connecting cables are kept short (approximately I inch) and their bendradius is controlled (allowing the cables to be relatively large in diameter(.07 inches)), the cables act like stiff rods in the working direction (closingtoward the palm) and like springs in the opposite direction. In other words,the ratio of the cable length to its
diameter is such that the cables are stiff enough to push the finger openbut if the finger contacts or impacts anobject the cables will buckle, allowing the finger to collapse out of the way.
Figure 6: Decoupling link The second and thirdjoints of the dexterous fingers are directly linked so that they close withequal angles. These joints are driven by a separate leadscrew assembly througha decoupling linkage (figure 6). The short cable on the leadscrew assembly isattached to the pivoting cable termination in the decoupling link. The flex inthe cable allows the actuation to pass across the two degree of freedom basejoint, without the need for complex mechanisms. The linkage is designed so thatthe arc length of the cable is nearly constant regardless of the position ofthe base joint (compare arc A to arc B in figure 6). This makes the motion ofdistal joints approximately independent of the base joint. figure 2 has aproximal and distal segment and is similar in design to the dexterous fingersbut has significantly more yaw travel and a hyper extended pitch. The thumb isalso mounted to the palm at such an angle that the increase in range of motionresults in a reasonable emulation of human thumb motion. This type of mountingenables the hand to perform grasps that are not possible with the common practiceof mounting the thumb directly opposed to the fingers [2,3,14]. The thumb basejoint has 70 degrees of yaw and 110 degrees of pitch. The distal joint has 80degrees of pitch. Linkages Finger Mount Figure 7:Grasping Finger The actuationof the base joint is the same as the dexterous fingers with the exception thatcammed detents have been added to keep the bend radius of the cable large atthe extreme yaw angles. The distal segment of the thumb is driven through adecoupling linkage in a manner similar to that of the manipulating fingers. Theextended yaw travel of the thumb base makes complete distal mechanicaldecoupling difficult. Instead the joints are decoupled in software.
手指的底盘接头具备七个自由度：偏航（+ / -
The grasping fingers have three pitchjoints each with 90 degrees of travel. The fingers are actuated by oneleadscrew assembly and use the same cam groove (figure 5) in the proximalfinger segment half shell as with the manipulating fingers. The 7-bar fingerlinkage is similar to that of the dexterous fingers except that the decouplinglink is removed and the linkage ties to the finger mount (figure 7). In thisconfiguration each joint of the finger closes down with approximately equalangles. An alternative configuration of the finger that is currently beingevaluated replaces the distal link with a stiff limited travel spring to allowthe finger to better conform while grasping an object.
The thumb is key to obtaining many of thegrasps required for interfacing with EVA tools. The thumb shown in The palmmechanism (figure 8) provides a mount for the two grasping fingers and acupping motion that enhances stability for tool grasps. This allows the hand tograsp an object in a manner that aligns the tool's axis with the forearm rollaxis. This is essential for the use of many common tools, like screwdrivers.The mechanism includes two pivoting metacarpals, a common shaft, and twotorsion springs. The grasping fingers and their leadscrew assemblies mount intothe metacarpals. The metacarpals are attached to the palm on a common shaft.The first torsion spring is placed between the two metacarpals providing a pivotingforce between the two. The second torsion spring is placed between the secondmetacarpal and the palm, forcing both of the metacarpals back against the palm.The actuating leadscrew assembly mounts into the palm and the short cableattaches to the cable termination on the first metacarpal. The torsion springsare sized such that as the leadscrew assembly pulls down the first metacarpal, thesecond metacarpal folows a troughly half the angle of the first. In this waythe palm is able to cup in a way similar to that of the human hand without thefingers colliding.
Figure 9 Wrist mechanism
COMMON SHAFT PALM CASTING The wrist isactuated in a differential manner through two linear actuators (figure 9). Thelinear actuators consist of a slider riding in recirculating ball tracks and acustom, hollow shaft brushless DC motor with an integral ballscrew. Theactuators attach to the palm through ball joint links, which are mounted in thepre-loaded ball sockets. Figure 8: Palm mechanism The fingers are mounted tothe palm at slight angles to each other as opposed to the common practice ofmounting them parallel to each other• This mounting allows the fingers to closetogether similar to a human hand. To further improve the reliability andruggedness of the hand, all of the fingers are mounted on shock loaders. Thisallows them to take very high impacts without incurring damage.
Design The wrist (figure 9) provides anunconstrained pass through to maximize the bend radii for the finger flexshafts while approximating the wrist pitch and yaw travel of a pressurizedastronaut glove. Total travel is +/- 70 degrees of pitch and +/- 30 degrees ofyaw. The two axes intersect with each other and the centerline of the forearmroll axis. When connected with the Robonaut Arm , these three axes combineat the center of the wrist cuff yielding an efficient kinematic solution. Thecuff is mounted to the forearm through shock loaders for added safety. Figure10: Forearm The forearm is configured as a ribbed shell with six cover plates.Packaging all the required equipment in an EVA forearm size volume is achallenging task. The six cover plates are skewed at a variety of angles andkeyed mounting tabs are used to minimize forearm surface area. Mounted on twoof the cover plates are the wrist linear actuators, which fit into the forearmsymmetrically to maintain efficient kinematics. The other four cover plateprovides mounts for clusters of three finger motors (Figure 10). Symmetry isnot required here since the flex shafts easily bend to accommodate odd angles.The cover plates are also designed to act as heat sinks. Along with the motors,custom hybrid motor driver chips are mounted to the cover plates.
设计手腕（图9）提供了无约束的经过，以最大化手指柔性轴的波折半径，同一时候肖似加压宇宙航银行人士手套的手腕节距和偏航行路线程。总行程为+/- 70度的俯仰和+/- 30度的偏航。这两条轴线相互交叉，并与前臂滚动轴的宗旨线相交。当与Robonaut Arm 连天时，那四个轴线结合在花招袖口的中坚，发生神速的运动学解决方案。袖套通过减震器安装在前臂上，以追加安全性。
As might be expected, many integrationchallenges arose during hand prototyping, assembly and initial testing. Some ofthe issues and current resolutions follow. Many of the parts in the hand useextremely complex geometry to minimize the part count and reduce the size ofthe hand. Fabrication of these parts was made possible by casting them inaluminum directly from stereo lithography models. This process yieldsrelatively high accuracy parts at a minimal cost. The best example of this isthe palm, which has a complex shape, and over 50 holes in it, few of which areorthogonal to each other. Finger joint control is achieved through antagonisticcable pairs for the yaw joints and pre-load springs for the pitch joints.Initially, single compression springs connected through ball links to the frontof the dexterous fingers applied insufficient moment to the base joints at thefull open position. Double tension springs connected to the backs of thefingers improved pre-loading over more of the joint range. However, desiredpre-loading in the fully open position resulted in high forces during closing.Work on establishing the optimal pre-load and making the preload forces linearover the full range is under way. The finger cables have presented bothmechanical mounting and mathematical challenges. The dexterous fingers usesingle mounting screws to hold the cables in place while avoiding cable pinch.This configuration allows the cables to flex during finger motion and yields areasonably constant lever arm. However assembly with a single screw isdifficult especially when evaluating different cable diameters. The thumb usesa more secure lock that includes a plate with a protrusion that securely pressesdown on the cable in its channel. The trade between these two techniques iscontinuing. Similar cable attachment devices are also evolving for the otherfinger joints. The cable flexibility makes closed form kinematics difficult.The bend of the cable at the mounting points as the finger moves is not easy tomodel accurately. Any closed form model requires simplifying assumptionsregarding cable bending and moving contact with the finger cams. A simplersolution that captures all the relevant data employs multi-dimensional datamaps that are empirically obtained off-line. With a sufficiently highresolution these maps provide accurate forward and inverse kinematics data. Thewrist design (figure 9) evolved from a complex multibar mechanism to a simplertwo-dimensional slider crank hook joint. Initially curved ball links connectedthe sliders to the palm with cams that rotated the links to avoid the wristcuff during pitch motion. After wrist cuff and palm redesign, the presentstraight ball links were achieved. The finger leadscrews are non-back drivableand in an enveloping grasp ensure positive capture in the event of a powerfailure. If power can not be restored in a timely fashion, it may be necessaryfor the other Robonaut hand  or for an EVA crew person to manually open thehand. An early hand design incorporated a simple back out ring that throughfriction wheels engaged each finger drive train and slowly opened each fingerjoint. While this works well in the event of a power failure, experiments withthe coreless brushless DC motors revealed a problem when a motor fails due tooverheating. The motor winding insulation heats up, expands and seizes themotor, preventing back-driving. A new contingency technique for opening thehand that will accommodate both motor seizing and power loss is beinginvestigated.
Initial Finger Control Design and Test
Before any operation can occur, basicposition control of the Robonaut hand joints must be developed. Depending onthe joint, finger joints are controlled either by a single motor or anantagonistic pair of motors. Each of these motors is attached to the fingerdrive train assembly shown in figure 3. A simple PD controller is used toperform motor position control tests. When the finger joint is unloaded,position control of the motor drive system is simple. When the finger isloaded, two mechanical effects influence the drive system dynamics. The flexshaft, which connects the motor to the lead screw, winds up and acts as atorsional spring. Although adding an extra system dynamic, the high ratio ofthe lead screw sufficiently masks the position error caused by the state of theflex shaft for teleoperated control. The second effect during loading is theincreased frictional force in the lead screw. The non-backdrivable nature ofthe motor drive system effectively decouples the motor from the applied force.Therefore, during joint loading, the motor sees the increasing torque requiredto turn the lead screw. The motor is capable of supplying the torque requiredto turn the lead screw during normal loading. However, thermal constraintslimit the motor's endurance at high torque. To accommodate this constraint, thecontroller incorporates force feedback from the strain gauges installed on thelead screw shell. The controller utilizes the non-back drivability of the motordrive system and properly turns down motor output torque once a desired forceis attained. During a grasp, a command to move in a direction that willincrease the force beyond the desired level is ignored. If the forced rops offor a command in a direction that will relieve the force is issued, the motor revertsto normal position control operation. This control strategy successfully lowersmotor heating to acceptable levels and reduces power consumption. To perform jointcontrol, the kinematics, which relates motor output joint output, must be determined. As statedearlier, due to varying cable interactions a closed form kinematics algorithm isnot tractable. Once the finger joint hall-effect based position sensors arecalibrated using are solver, a semi-autonomous kinematic calibration procedure forboth forward and inverse kinematics is used to build look-up tables. Variationsbetween kinematics and hall-effect sensor outputs during operation are seen inregions where the pre-loading springs are not effective. Designs using differentspring strategies are underdevelopment to resolve this problem. To enhance positioningaccuracy, a closed loop finger joint position controller employing hall-effect sensorposition feedback is used as part of this kinematic calibration procedure. ableto successfully manipulate many EVA tool.
SeveralexampletoolmanipulationsusingtheRobonauthand underteleoperatedcontrolareshowninfigures11and12. Figure11:ExamplesoftheRobonaut Handusingenvelopingpowergraspstoholdtools An importantsafetyfeatureof thehand,itsabilityto passivelycloseinresponsetoacontactonthebackof thefingers,causesproblemsfor closedloopjoint controlduringnormaloperation.Furtherrefinementof the kinematiccalibrationandthestraingaugeforcesensorsirequiredtoreliablydeterminewhenthefingersarebeing uncontrollablycosed.Oncethisinformation, alongwithabettermodelforthedrivetraindynamicsisavailable,thejointcontrollercanbemodifiedtodistinguishteloaded fromthenormaloperatingmode.Althoughconsiderableworkstillneedstobedone,joint controlsatisfactoryforteleoperatedcontrolof thehand hasbeenattained. For initial tests,the handwascontrolledin joint modefrominputsderivedfromtheCyberglove®wornbytheoperator.TheCybergloveuses bendsensors,whichareinterpretedbytheCyberglove electronicstodeterminethepositionof 18actionsof theoperator'shand. Someof theseactionsareabsolute positionsoffingerjointswhileotherarerelativemotions betweenjoints.Thechallengeisdevelopingamapping betweenthe 18 absoluteandrelativejointpositions determinedby theCybergloveandthe12jointsof the Robonaut hand. Thismapping must result in the Robonaut hand tracking the operator's hand as well aspossible. While some joints are directly mapped, others required heuristic algorithmsto fuse data from several glove sensors to produce a hand joint position command.In conjunction with an auto mated glove calibration program, a satisfactory mappingis experimentally obtainable.
Using these custom mappings, operators are
using dexterousgraspsforfinetoolmaipulationTofacilitatetestingofthehandbaselevelpadsasshown infigures11,12werefabricatedfromDow Cornings Silastic®E. Thepadsprovideanonslipcompliant surfacenecessary forpositivelygraspinganobject.Thesepadswillserveasthefoundationfortactilesensorsandbe coveredwithaprotectiveglove.Futureplansincludethedevelopment of agraspcriteriameasureforthestabilityofthehandgrasp.Thesecriteriawillbeusedtoassisttheoperatorindeterminingif agrasp isacceptable.Sincethebaselineoperationplandoesnot involveforcefeedbacktotheoperator,visualfeedback onlymaybeinsufficient toproperlydetermineif agraspisstable.Usingsomeknowledgeof theobjectwhichisbeinggraspedinconjunctionwiththeexistingleadscrew forcesensorsandasmallsetofadditional tactilesensors installedonthefingersandpalm,thecontrolsystemwilldeterminetheacceptabilityof thegraspandindicatethat measuretotheoperator.Theoperatorcanthendecide howbestousethisdatainreconfiguringthegrasptoa morestableconfiguration.Thisgraspcriteriameasurecouldevolveintoanimportantpartof anautonomous graspingsystem. 6 Conclusions TheRobonaut Hand is presented. This highly anthropomorphic human scale hand builtat the NASA Johnson Space Center is designed to interface with EVA crewinterfaces thereby increasing the number of robotically compatible operationsavailable to the International Space Station. Several novel mechanisms aredescribed that allow the Robonaut hand to achieve capabilities approaching thatof an astronaut wearing a pressurized space suited glove. The initial jointbased control strategy is discussed and example tool manipulations areillustrated. References 1. Lovchik, C. S., Difiler, M. A., Compact DexterousRobotic Hand. Patent Pending. 2. Salisbury, J. K., & Mason, M. T., RobotHands and the Mechanics of Manipulation. MIT Press, Cambridge, MA, 1985. 3.Jacobsen, S., et al., Design of the Utah/M.I.T. Dextrous Hand. Proceedings ofthe IEEE International Conference on Robotics and Automation, San Francisco, CA,1520-1532, 1986. 4. Bekey, G., Tomovic, R., Zeljkovic, I., Control Architecturefor the Belgrade/USC Hand. Dexterous Robot Hands, 136-149, Springer-Verlag, NewYork, 1990. 5. Maeda, Y., Susumu, T., Fujikawa, A., Development of anAnthropomorphic Hand (Mark-l). Proceedings of the 20 th International Symposiumon Industrial Robots, Tokyo, Japan, 53-544, 1989.
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