Transcript
Page 1: A Physically-Based Fault Detection and Isolation Method ... · A Physically-Based Fault Detection and Isolation Method ... on-line adaptation of both friction and gravity parameters

38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

A Physically-BasedFault Detection and Isolation Methodand Its Uses in Robot Manipulators

Alessandro De LucaDipartimento di Informatica e SistemisticaUniversità di Roma “La Sapienza”

currently on leave atInstitute of Robotics and Mechatronics

DLR Oberpfaffenhofen

38. VDI/VDE Sitzung des FA 4.13“Steuerung und Regelung von Robotern”

Page 2: A Physically-Based Fault Detection and Isolation Method ... · A Physically-Based Fault Detection and Isolation Method ... on-line adaptation of both friction and gravity parameters

38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Outline

FDI problems Robot dynamics and physical properties Detection and isolation of actuator faults Adaptive scheme for actuator FDI Collision detection and reaction Extension to robots with joint elasticity

collision detection/reaction + motor friction compensation

Conclusions

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

FDI problems

Fault Detection recognizing that a fault is affecting a dynamic system

Fault Isolation discriminating the occurrence of a fault f from that of all other

considered possible faults and disturbances

FDI solution approach (model-based) design a residual generator system whose output

is only affected by the fault f to be detected and isolated is not affected by any other fault or disturbance converges (asymptotically) to zero whenever f = 0

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Robot dynamic models

fully rigid case

presence of transmission/joint elasticity

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Relevant physical properties

kinetic and potential energy

relation between inertia and velocity terms

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Relevant physical properties (cont’d)

total energy and its variation

generalized momenta and their decoupled dynamics

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Robot actuators FDI

faulted model

fault types

total failure power loss saturation bias … possibly concurrent, intermittent, incipient, abrupt,…

commanded torque

fault torque

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Basic assumptions

full state measurements implementation with available sensors (typically, position only)

robot dynamic model accurately known adaptation might be included for uncertain parameters

use of detection thresholds to handle noise (false alarms)

only commanded torque available (no fault model is needed)

any control input law open or closed-loop, linear or nonlinear model-based feedback

no need of a specified reference motion

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Early solutions …

1. : compare computed model-based torque(from measures) with commanded one

2. : compare simulated acceleration(inverse robot dynamics) with those frommeasurements

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

… and their limitations

noisy acceleration (e.g., from double numericaldifferentiation of position measures)

inversion of inertia matrix intrinsic delay (one or more digital steps) dependence on commanded input dynamics poor or no fault isolation (only detection)

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Energy-based fault detection

scalar detector

… and its dynamics (needed only for analysis)

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Momentum-based FDI

vector of residuals

… and its decoupled dynamics (a stable first-orderlinear filter)

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Experimental setup

Quanser Pendubot2nd link

(passive)

1st link(actuated)

video swing-up Pendubot

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Actuator FDI on Pendubot

partially concurrent 10% power loss on actuator 1 and total failure on(missing) actuator 2

PID control on first joint to 30°

commanded torques joint positions

joint 1 joint 2

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Actuator FDI on Pendubot (cont’d)

thresholding and dynamic filtering of residuals

residuals filtered residuals

joint 1 joint 2

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

An adaptive FDI scheme

include friction (difficult to estimate) in the model

linear parametrization (may be extended togravity and inertia-related terms)

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Adapt and detect

using an estimate of friction parameters

residual dynamics

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Adapt and detect (cont’d)

stability analysis via standard Lyapunov and LaSalletechniques (in absence of faults)

parameter estimates converge to constant values (=correct ones for sufficient excitation)

by overparametrization and suitable gain scaling, one may stilladapt also during faults

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Adaptive actuator FDI on Pendubot

situation as before, with power loss increased to 50% on actuator 1 on-line adaptation of both friction and gravity parameters

commanded torques residuals

joint 1 joint 2

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Collision as a fault

rigid robot model

use only proprioceptive sensors possible contact at any point along the arm simplifying assumptions

single contact robot as open kinematic chain unfaulted actuators

transpose ofcontact point Jacobian

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Analysis of collisions

q1

d1d2

FK

FK

q2

x1

y1

x0

y0

x2y2

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Collision detection

as before, scalar detector

only contact forces (wrenches) that perform workon contact velocity (twists) can be detected

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Directional detection and isolation

as before, vector of residuals

ideal situation (no noise)

collision point is located up to link i

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Choice of residual gains

evaluation by simulation on 7-dof DLR-III arm(impact on last link)

joint 2@30°/s

joint 4@200°/s

10 ms

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Collision reaction strategies

normal operation in “zero-gravity”

once collision is detected ( above threshold) either stop the robot (braking) and then possibly

reverse commanded motion (backtracking) or apply a reflex strategy with torque control using

directional information of residual vector(move in the same direction of sensed force)

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Dissipating energy

when contact is lost, the residual decays until

dissipate kinetic energy at highest rate (usingmaximum available torque) until robot stops

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Operative robot states

normal operationin zero-gravity reflex reaction

energy dissipation

collision = 0

collision = 1

|| residual || > low

|| residual || ≤ low

velocity ≠ 0

velocity = 0

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Robots with elastic joints (EJ)

harmonic drives introduce joint elasticity effects motor friction and possible arm collisions

DLR-III arm: motor position and joint torque sensors

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Multiple detection for EJ robots

it is simultaneously possible to compensate friction (a fault) on motor side detect collision at link side

1. unmodeled motor friction detection and compensation(based on motor generalized momenta)

decentralized linear observer(includes acceleration estimation)

motor friction compensation

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Multiple detection for EJ robots (cont’d)

collision detection: several alternatives are possible forgeneralizing the rigid case analysis, the most simple is

2.

replace joint to motor torque

robot control laws should be modified (e.g., in DLR-III arm) reflex strategies to contact detection include

torque mode reaction admittance mode reaction

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

DLR-III robot controller

motor inertia reduction based on joint torque sensing

leads to with general position/torque control law (depending on reference

and gain values)

obtaining a full state feedback law

static gravity compensation (based on motor position)

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Reflex strategies

strategy 2: free-floating torque mode

strategy 3: torque control mode

strategy 4: admittance control mode

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Experiments on DLR-III arm (1)

Head Injury Criterion (HIC) tests on dummy head

3D accelerometeron dummy head

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Results on dummy head impact

approaching at 30°/s with each joint residual gains = diag{25}

joint 1

2 ms

joint torque

residual

0/1 detection

acceleration

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Experiments on DLR-III arm (2)

…one of“99 luftballons”

strategy 4@90°/s

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Results on balloon impact

residual & velocity on joint 4 for different reaction strategies

impact at 10°/s with coordinated joint motion

no reaction

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Results on balloon impact (cont’d)

residual & velocity on joint 4 for different reaction strategies

impact at 100°/s with coordinated joint motion

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Human-robot interaction (1)

strategy 4: admittance control based on residuals

first impact @60°/sec

video HRI - 1

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Human-robot interaction (2)

strategy 3: torque control based on residuals

first impact @60°/sec

video HRI - 2

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Human-robot interaction (3)

strategy 3: torque control based on residuals

first impact @90°/sec

video HRI - 3

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Conclusions

powerful FDI technique for mechanical systems based onphysical quantities (energy, momenta)

direct extensions to joint elasticity, actuator dynamics, frictioncompensation, adaptation to uncertain parameters

special case of a more general “geometric” theory valid forsensor/actuator faults of nonlinear (affine) plants

under possible concurrency, exact FDI for a maximum numberof faults = N (# of generalized coordinates)

principle feasible also for industrial robots, for advanced safetyrequirements in human-robot physical interaction

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

Acknowledgments

scientific contributions by Raffaella Mattone (DIS, Roma)

Giulio Milighetti (ex DIS, Roma; now Fraunhofer IITB, Karlsruhe)

Alin Albu-Schäffer (DLR, Oberpfaffenhofen)

Sami Haddadin (DLR, Oberpfaffenhofen)

work supported by Humboldt-Helmholtz Association

(2005 Research Award for foreign scientists)

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38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006

References

De Luca, Mattone: Actuator FDI using generalized momenta, ICRA’03

De Luca, Mattone: Adapt-and-detect robot actuator faults, ICRA’04

De Luca, Mattone: Identification of robot actuator faults, IROS’05

De Luca, Mattone: Sensorless robot collision detection and hybridforce/motion control, ICRA’05

Mattone, De Luca: FDI in Euler-Lagrange mechanical systems, ASME JDSMC(submitted), May 2005

Mattone, De Luca: Relaxed FDI for nonlinear systems, Automatica, 2006

Albu-Schäffer, De Luca, Haddadin, Hirzinger: Collision detection and reactionstrategies with DLR-III arm, IROS’06 (to be submitted)


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