Optimized passive dynamics improve transparency of haptic devices

Duschau-Wicke, Alexander; Riener, Robert

doi:10.1109/robot.2009.5152619

Cited by 27 publications

(22 citation statements)

References 28 publications

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“…The common strategy in robot control would be to tolerate this remaining inertia and to compensate "at least" the other force components, especially robot gravity. However, we have shown that gravity compensation of the robot is not always an effective means to reduce interaction forces [16]. On the contrary, gravity compensation of leg exoskeletons during gait is even counterproductive, and it increases interaction forces.…”

Section: Introductionmentioning

confidence: 96%

“…Without gravity acting on the exoskeleton leg, accelerating and decelerating forces have to be exerted on the robot by the human to overcome the exoskeleton's inertia, which severely increases interaction forces between human and robot. Inspired by this observation that the earth's gravitational field partially compensates robot inertia during gait, we have recently proposed the concept of Generalized Elasticities as a generic tool to hide robot dynamics using potential fields [16]. Given a particular robot and an estimate of the type of motion a human operator will perform (like walking in a gait rehabilitation robot), the optimal potential field manipulates robot dynamics in such a way that the resulting interaction forces between robot and operator are minimized.…”

Section: Introductionmentioning

confidence: 99%

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Hiding robot inertia using resonance

Duschau-Wicke¹,

Riener²

2010

2010 Annual International Conference of the IEEE Engineering in Medicine and Biology

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To enable compliant training modes with a rehabilitation robot, an important prerequisite is that any undesired human-robot interaction forces caused by robot dynamics must be avoided, either by an appropriate mechanical design or by compensating control strategies. Our recently proposed control scheme of "Generalized Elasticities" employs potential fields to compensate for robot dynamics, including inertia, beyond what can be done using closed-loop force control. In this paper, we give a simple mechanical equivalent using the example of the gait rehabilitation robot Lokomat. The robot consists of an exoskeleton that is attached to a frame around the patient's pelvis. This frame is suspended by a springloaded parallelogram structure. The mechanism allows vertical displacement while providing almost constant robot gravity compensation. However, inertia of the device when the patient's pelvis moves up and down remains a source of large interaction forces, which are reflected in increased ground reaction forces. Here, we investigate an alternative suspension: To hide not only gravity, but also robot inertia during vertical pelvis motion, we suspend the robot frame by a stiff linear spring that allows the robot to oscillate vertically at an eigenfrequency close to the natural gait frequency. This mechanism reduces human-robot interaction forces, which is demonstrated in pilot experimental results. Abstract-To enable compliant training modes with a rehabilitation robot, an important prerequisite is that any undesired human-robot interaction forces caused by robot dynamics must be avoided, either by an appropriate mechanical design or by compensating control strategies. Our recently proposed control scheme of "Generalized Elasticities" employs potential fields to compensate for robot dynamics, including inertia, beyond what can be done using closed-loop force control. In this paper, we give a simple mechanical equivalent using the example of the gait rehabilitation robot Lokomat. The robot consists of an exoskeleton that is attached to a frame around the patient's pelvis. This frame is suspended by a springloaded parallelogram structure. The mechanism allows vertical displacement while providing almost constant robot gravity compensation. However, inertia of the device when the patient's pelvis moves up and down remains a source of large interaction forces, which are reflected in increased ground reaction forces. Here, we investigate an alternative suspension: To hide not only gravity, but also robot inertia during vertical pelvis motion, we suspend the robot frame by a stiff linear spring that allows the robot to oscillate vertically at an eigenfrequency close to the natural gait frequency. This mechanism reduces human-robot interaction forces, which is demonstrated in pilot experimental results.

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Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Hiding robot inertia using resonance

Duschau-Wicke¹,

Riener²

2010

2010 Annual International Conference of the IEEE Engineering in Medicine and Biology

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“…To end the swing phase, the human has to decelerate the exoskeleton legs without the help of gravity, which actually increases the undesired interaction forces between the robot and user. Similar counterproductive results of gravity compensation, in terms of interaction forces, have also been reported for the LOKOMAT [166]. For position-controlled gait trainers that cannot employ the passive dynamics of the robot, the transparency can also be increased by adapting the predefined gait patterns in real time, such that interaction between the robot and the patient is minimized.…”

Section: Chaptersupporting

confidence: 66%

Robot aided gait training and assessment : development of support strategies and assessment methods for LOPES

Koopman¹

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“…Lateral translation was actuated, so that the device was able to apply balance-assisting forces to the pelvis in lateral direction. A force sensor between the lateral actuator and the pelvis orthosis enabled force control with a RMS force tracking error of 13 N. The sagittal-plane actuators of the robot were in zero-force control mode, minimally interfering with the subject's movement [29].…”

Section: Methodsmentioning

confidence: 99%

Cooperative Control Design for Robot-Assisted Balance During Gait

Bögel¹,

́Brien²,

Riener³

2012

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Summary Avoiding falls is a challenge for many persons in aging societies, and balance dysfunction is a major risk factor. Robotic solutions to assist human gait, however, focus on average kinematics, and less on instantaneous balance reactions. We propose a controller that only intervenes when needed, and that avoids stability issues when interacting with humans: Assistance is triggered only when balance is lost, and this action is purely feed-forward. Experiments show that subjects who start falling during gait can be uprighted by such feed-forward assistive forces. Zusammenfassung Sturzvermeidung ist eine ständige Herausforderung für viele Menschen in alternden Gesellschaften, und Gleichgewichtsprobleme stellen ein bedeutendes Risiko für einen Sturz dar. Heutige robotische Lösungen zur Unterstützung des menschlichen Gangs sind allerdings hauptsächlich auf das gemittelte Gangbild ausgerichtet und weniger auf instantane Gleichgewichtsreaktionen. Wir schlagen hier einen Regler vor, der nur dann interveniert, wenn nötig, und der keine Stabilitätsprobleme verursacht, wenn er mit dem Menschen interagiert: Stellgrößen werden erst dann generiert, wenn der Mensch das Gleichgewicht verliert, und diese Unterstützung fungiert als reine Vorsteuerung. Experimentelle Ergebnisse zeigen, dass menschliche Probanden, die während des Gehens zu fallen beginnen, durch solche unterstützenden, vorgesteuerten Kräfte in eine aufrechte Haltung gebracht werden können.

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Optimized passive dynamics improve transparency of haptic devices

Cited by 27 publications

References 28 publications

Hiding robot inertia using resonance

Hiding robot inertia using resonance

Robot aided gait training and assessment : development of support strategies and assessment methods for LOPES

Cooperative Control Design for Robot-Assisted Balance During Gait

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