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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”
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
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
38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006
Robot dynamic models
fully rigid case
presence of transmission/joint elasticity
38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006
Relevant physical properties
kinetic and potential energy
relation between inertia and velocity terms
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
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
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
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
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)
38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006
Energy-based fault detection
scalar detector
… and its dynamics (needed only for analysis)
38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006
Momentum-based FDI
vector of residuals
… and its decoupled dynamics (a stable first-orderlinear filter)
38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006
Experimental setup
Quanser Pendubot2nd link
(passive)
1st link(actuated)
video swing-up Pendubot
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
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
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)
38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006
Adapt and detect
using an estimate of friction parameters
residual dynamics
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
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
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
38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006
Analysis of collisions
q1
d1d2
FK
FK
q2
x1
y1
x0
y0
x2y2
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
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
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
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)
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
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
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
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
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
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)
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
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
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
38. VDI/VDE SitzungABB, Ladenburg, Germany 25 January 2006
Experiments on DLR-III arm (2)
…one of“99 luftballons”
strategy 4@90°/s
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
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
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
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
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
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
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)
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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