Karguth, A.

Kunz, Jürgen

Lens, Thomas

Schweitzer, M.

Stryk, Oskar von

Trommer, Christian

TUbiblio

Safe Human Interaction with the Compliant Robot Arm BioRob

Schweitzer, Markus

Karguth, Andreas

Digitale Bibliothek Thüringen

PROCEEDINGS            13 - 17 September 2010   Crossing Borders within the ABC  Automation, Biomedical Engineering and Computer Science    Faculty of  Computer Science and Automation    www.tu-ilmenau.de     Home / Index: http://www.db-thueringen.de/servlets/DocumentServlet?id=16739 55. IWKInternationales Wissenschaftliches KolloquiumInternational Scientific ColloquiumImpressum Published by  Publisher: Rector of the Ilmenau University of Technology Univ.-Prof. Dr. rer. nat. habil. Dr. h. c. Prof. h. c. Peter Scharff  Editor: Marketing Department (Phone: +49 3677 69-2520) Andrea Schneider (conferences@tu-ilmenau.de)   Faculty of Computer Science and Automation (Phone: +49 3677 69-2860) Univ.-Prof. Dr.-Ing. habil. Jens Haueisen  Editorial Deadline:  20. August 2010  Implementation:  Ilmenau University of Technology Felix Böckelmann Philipp Schmidt   USB-Flash-Version.  Publishing House: Verlag ISLE, Betriebsstätte des ISLE e.V. Werner-von-Siemens-Str. 16 98693 llmenau  Production:  CDA Datenträger Albrechts GmbH, 98529 Suhl/Albrechts  Order trough:  Marketing Department (+49 3677 69-2520) Andrea Schneider (conferences@tu-ilmenau.de)  ISBN: 978-3-938843-53-6 (USB-Flash Version)   Online-Version:  Publisher: Universitätsbibliothek Ilmenau   Postfach 10 05 65  98684 Ilmenau   © Ilmenau University of Technology (Thür.) 2010  The content of the USB-Flash and online-documents are copyright protected by law. Der Inhalt des USB-Flash und die Online-Dokumente sind urheberrechtlich geschützt.   Home / Index: http://www.db-thueringen.de/servlets/DocumentServlet?id=16739 SAFE HUMAN INTERACTIONWITH THE COMPLIANT ROBOT ARM BIOROBM. Schweitzer, C. Trommer, A. KarguthTetra GmbH Ilmenau, Germanywww.tetra-ilmenau.de[ms|ct|aku]@tetra-ilmenau.comwww.biorob.deJ. Kunz, T. Lens, O. von StrykTechnische Universita¨t Darmstadt,Department of Computer Science,Simulation, Systems Optimizationand Robotics Group, Germany[jkunz|lens|stryk]@sim.tu-darmstadt.deABSTRACTTo open up a highly expanded functionality in directcooperation with humans regarding mobile service andassistance robotics applications, as well as new appli-cations in the field of automation in industries, the newbiologically inspired, lightweight and elastic robot arm“BioRob” offers a new kind of human machine interac-tion. The functional principle of the robot arm permitsthe system to apply forces, to estimate the weight ofpayload and to detect collision and touch in a similarway as the human arm. Further this technology allowsfor a direct teach-in or a hand guided robot movement.In this paper, strategies for this novel, more flexible,easily reconfigurable and highly safe human robot in-terface are shown and discussed.Index Terms— human-robot interaction, compli-ant robot, collision detection, service robotics1. INTRODUCTIONFor many assembly lines industrial robots are indis-pensable. They are construed to execute routine pro-cesses with high speeds, endurance and precision. Theseconventional industrial robots are machine tools andentirely inapplicable to work in co-operation with hu-mans. Only at the cost of additional safety measuressuch as mechanical security fences, electronic super-vision systems or limitation of performance parame-ters, industrial robots can be deployed for service taskstogether with humans. Still, these systems are onlysafe to a limited extent because of possible hardwareand software failures. Flexible and fast programming,which is essential for efficient service robotics solu-tions, is also restricted by the hardware, as can be seenin the standard defining the safety requirements andregulating the use of industrial robots for service ap-plications [1].For safe and reliable human-machine interaction anew generation of robot arms is required. These robotsneed characteristics comparable to the human arm, asthey are intended for safe interaction with humans inworkspace designed for humans. The robot arm shouldhave human-like capabilities such as handling, posi-tioning, assembling, estimating weights, detecting col-lisions and guided movements. Ideally, the effort forprogramming these capabilities would be as small aspossible, to achieve a “plug and play” behavior. Thecommunication between robot and human should be asdirect as possible, using the mechanical structure of thearm, especially in service and assistance applications.Fig. 1. BioRob X4 Version 3Compliant actuator design is widely seen as a keyto increase safety and flexibility [2]. The BioRob robotarm aims at satisfying these requirements by combin-ing passive and active joint compliance with an ex-tremely light-weight construction, resulting in very lowenergy consumption and high fail-safe safety proper-ties. In the following sections, we will describe thehardware design of the BioRob robot arm and discussits passive and active (controlled) characteristics.2. FUNCTIONAL CHARACTERISTICS OF AHUMAN ARMThe human arm is a manipulator, which is able to covera huge range of tasks and applications. It consists pri-marily of a endoskeleton and a muscle-tendon appara-tus with variable stiffness. The intrinsic accuracy of thehuman arm is rather low, but is increased by using the624Fig. 2. Principle of movement of the human arm [3]eyes as a visual feedback system. In addition, the bi-ological compliance of the human arm supports grasp-ing and contact situations, allowing for more inaccuratemovements. Objects of various weights can be handledby varying the stiffness of the muscle-tendon appara-tus. Collisions can be detected by the arm itself witha high level of safety. But most important for safety isthe lightweight structure which results from the antag-onistic arrangement of muscles and tendons as serieselastic actuators which relieves the bones from bendingstress when carrying a load (cf. Fig. 2). The lightweightstructure also ensures a low energy consumption.3. FUNCTIONAL PRINCIPLE AND DESIGN OFTHE BIOROB X4 ROBOT ARMThe BioRob robot arm is a biologically inspired robotarm. The aluminum skeleton is the basic structure. Ac-tuator and joint are connected by several compliant el-ements such as wires, linear and radial springs. Theseelements are coupled antagonistically. The effect of thesprings in combination with DC motors is compara-ble to the human muscles. Springs in the transmissionof robot joints provide a passive compliance, which isable to protect the motors and gearboxes from externalshocks, and the users from the reflected inertia of themotors in case of a collision. Cables can transmit mo-tions and forces similar to tendons and are much lighterthan gears or chains. They allow placing the actuatorsaway from the driven joints. In the BioRob robot arm,the actuators are located in the first and second link, re-ducing the system inertia and the energy consumption.To be able to position the end effector exactly, anabsolute measurement system fixed to the joints of thestiff skeleton is used (q in Figure 3). For this mea-surement system the elasticity is irrelevant. A secondmeasurement system is located inside the motors of therobot (θ in Figure 3). By combining these two encodersystems, it is possible to calculate the deflection of theelastic coupled elements and estimate the joint torques.The electronics including power amplifiers are com-pletely integrated into the shoulder of the BioRob robotarm and can drive up to six joints. The robot is con-trolled by an ultra compact PC, which operates with arealtime Linux. The controller communicates with therobot via EtherCAT, a hard realtime capable bus systeml clJc1τmkθqy0z0 x0Fig. 3. Principle of a BioRob joint [4]BioRob X4Compliant joints 4Total weight (including controller 4 kgPC and power electronics)Arm length (shoulder to flange) 666 mmLength of first link (base to shoulder) 276 mmPayload (maximum) 2 kgPayload (nominal) 0.5 kgEnergy consumption (w/o load) nominal 15 WMounting position arbitraryPower supply 12 V, max. 40 WController compact PCTable 1. BioRob X4 parameters [8]which allows very high control frequencies.The load can have a weight of up to 2 kg, which is aremarkable high weight regarding to the robots weightof 4 kg (including the controller PC). The average en-ergy consumption of the arm is about 15–20 Watts (alsoincluding the controller PC) and allows for using therobot arm on mobile platforms. Actual states of therobot system are shown by the full color column lightsand presented by sounds which are played back by theintegrated sound system.Several patents were filed for the BioRob robot armtechnology by Bernhard Mo¨hl [5] and TETRA GmbH,Ilmenau [6],[7].4. PASSIVE CHARACTERISTICS OF THEBIOROB ROBOT ARMThe reactions of the BioRob system to its environmentare passive characteristics. A part of the belongingproperties results from the robots mechanical structure,another part is implemented in the robots software and625Fig. 4. Manually guided teach-in [9]control. Primarily passive characteristics are used forthe human machine interaction between the user andthe robot system.Application based it can be complex to teach a robota complete workflow trajectory. Using active proper-ties, the possibility to move single or multiple axes viacoordinate transformation is offered. Otherwise a mucheasier way is to take the robot passively “by the hand”to show it the desired trajectory. With conventionalrobots, this is not possible because of their weight andhigh gearbox ratios. The BioRob robot arm is verylight-weight and in addition the motors, the heaviestpart of the arm, are located at the opposite side of thejoint to the next joints. Combined with a low, non self-locking motor gear ratio, a manual passive arm move-ment and positioning is easily possible for each user.This property can be used for a direct hand guidedteach in. The user takes the robots end effector at hishand, and moves the robot arm as needed for the par-ticular application (Figure 4). To record the movementof the robot, several methods are feasible. For the firstone, the user teaches a series of position setups step bystep. Between these steps the BioRob trajectory gener-ator plans the final trajectory. For the second one thecomplete movement will be scanned, saved and finallyoptimized. Using a special editor the trajectory can bechanged, adjusted and optimized in a table of positionsets in dependency of time. For another method if somekind of application profile exists the hand guided teachcan be used for fast and easy calibration of this pro-file for trajectory generation, as described in [4] for apick-and-place application as example. With this newprocess of trajectory teaching the robot is ready for anapplication between minutes and not days when usingconventional robot systems.The position difference between motor and jointcan be used for gesture detection. As the robot struc-ture can be moved easily because of the elasticity, itis very easy for a human to input gestures like pullingthe end effector, pushing the robot or stressing it with aload to start trajectory playback or to reset the currentcollision state. So the robot itself plays the role of ahuman machine interface.Fig. 5. Playback of the trajectory with unknown load[10]5. ACTIVE CHARACTERISTICS OF THEBIOROB ROBOT ARMActive characteristics refer to properties of the robot,which can be realized by controlling the robot. Collid-ing on an object the mechanical compliance is a passivecharacteristic while the reaction of the controller is anactive one.Without a proper control the robot would not be us-able because of the elasticity in the system. Appropri-ate controlling strategies are necessary to obtain goodproperties as a non-oscillating movement, good perfor-mance, such as high speed for pick-and-place applica-tions, and adequate high positioning precision, depend-ing on the application requirements.The BioRob robot arm is a complex non-linear sys-tem. Single joint based PID-controllers, as they are of-ten used in conventional industrial robots, are not suffi-cient. Necessarily non-linear model based controllers,which contain models of the drives, the elasticity andthe robot structure, have to be used to obtain the desiredproperties. The controller considers the position sen-sor information from all motors and joints at the lowestlevel of control. Based in the models, a feed-forwardcontrol is possible, which allows to control the robotat a higher frequency and speed as the sensor informa-tion is coming for a closed control loop, increasing theperformance.Fig. 6. Execution of a pick-and-place application [11]626An additional active safety property is realized, basedon the dynamics robot model, by a collision detectionand handling. The motor and joint sensor informationcan be used to determine the elongation of the elastic-ity, which can be seen in Figure 3. With this informa-tion, an estimation for the respective joint torque canbe calculated. If the real joint torques differs too muchfrom the computed joint torque, which is necessary tomove the robot and the load, a collision is detected.This also allows limiting the joint torques on softwareside, which is realized by limiting the maximum differ-ence between motor and joint position. If a collision isdetected, the control switches to a special mode. Basedon the user defaults, different collision handling strate-gies are possible, from stopping the trajectory, a bounceback, an active backward moving, disabling outputs orswitching to a very soft mode, where the user can easilymove the robot [12].Fig. 7. Collision detection [13]Based on the joint torque control and a zero-gravitymode, unknown loads can be measured. With the modelbased computed torque, it is known which static torquesare necessary in every joint position and which dynamictorques are necessary to do specific movements. If aload is applied to the end effector, there is a differencebetween the model based computed torque and the realnecessary torque at the specific positions or for the spe-cific movements. This difference is measured as thereis a higher position difference between motor and jointposition sensor values. With this information an esti-mation can be made about the load the robot is carry-ing.Other possible active strategies based on joint torquecontrol and measurement of unknown load is a forceassisted movement for a hand guided teaching or an as-sisted handling of objects. If a load is applied to the endeffector, the robot can measure the load and take it intoaccount in control. So if a human is doing a teaching orwants to move the robot, he does not feel that the robothas a load applied to the end effector. Or the robot canactively follow the applied movement from the human,so the human does only need to apply very low forcesto move the robot arm. But if he releases the robot, therobot will stay in its position.6. SUMMARYFor safe, flexible and reliable human-robot interactionin service robotics applications, novel types of roboticarms are needed. A lightweight structure and joint com-pliance, two key properties of the human arm, are es-sential to meet these requirements. We presented theBioRob robot arm that was designed for these applica-tions. We discussed methods for fast reconfigurationand programming of service robotics applications.AcknowledgementsThe research presented in this paper was supported bythe German Federal Ministry of Education and ResearchBMBF under grants 01 RB 0908 A and 01 RI 0620 A.The authors would like to thank Bernhard Mo¨hl forthe original idea of the BioRob actuation principle [14]and for his continuous advice and support in the en-hancement of the concept.7. REFERENCES[1] “ISO 10218-1:2009, robots for industrial envi-ronments - safety requirements - part 1: Robot,”2009.[2] R. Van Ham, T. Sugar, B. Vanderborght, K. Hol-lander, and D. Lefeber, “Compliant actuator de-signs,” Robotics & Automation Magazine, IEEE,vol. 16, no. 3, pp. 81–94, sep 2009.[3] D. Pol, “La main a` la paˆte,”http://www.sonnentaler.net, 2002.[4] T. Lens, J. Kunz, C. Trommer, A. Karguth, andO. von Stryk, “Biorob-arm: A quickly deploy-able and intrinsically safe, light-weight robot armfor service robotics applications,” in 41st In-ternational Symposium on Robotics (ISR 2010) /6th German Conference on Robotics (ROBOTIK2010), Munich, Germany, 2010.[5] B. Mo¨hl, “Patent DE 197 19931 A 1,” 1998.[6] TETRA GmbH Ilmenau, “Patent DE 102009000261.8,” 2009.[7] TETRA GmbH Ilmenau, “PatentPCT/EP2010/050170,” 2010.[8] TETRA GmbH Ilmenau, “TETRA BioRobv3 product information,” http://www.tetra-ilmenau.com, 2010.[9] TU Darmstadt, FG Simulation, Systemop-timierung und Robotik, “BioRob: Pro-gramming of a Task by Human Guidance,”http://www.youtube.com/watch?v=jIRBW1Mgbiw,2009.627[10] TU Darmstadt, FG Simulation, Systemopti-mierung und Robotik, “BioRob: Playback ofa Task Programmed by Human Guidance (2),”http://www.youtube.com/watch?v=hrzfKQb12mE,2009.[11] TU Darmstadt, FG Simulation, Systemopti-mierung und Robotik, “BioRob: Pick And Place,”http://www.youtube.com/watch?v=MEgQ-6LoYuQ, 2010.[12] S. Haddadin, A. Albu-Scha¨ffer, A. De Luca, andG. Hirzinger, “Collision detection and reaction:A contribution to safe physical human-robot in-teraction,” in Proc. IEEE IROS, 2008, pp. 3356–3363.[13] TU Darmstadt, FG Simulation, Systemop-timierung und Robotik, “BioRob: De-tecting a Collision with a Human Finger,”http://www.youtube.com/watch?v=gHkgkGgTIvk,2009.[14] B. Mo¨hl, “A two jointed robot arm with elasticdrives and active oscillation damping,” in Proc. ofWorkshop Bio-Mechatronic Systems at the 1997IEEE/RSJ Int. Conf. on Intelligent Robots andSystems, Grenoble, France, 1997.628

Safe human interaction with the compliant robot arm BioRob

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Safe human interaction with the compliant robot arm BioRob

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