Robot force control

Robot Force Control

VII Scuola Nazionale di Dottorato CIRA Bertinoro (FC)Controllo di Sistemi Robotici per la Manipolazione e la Cooperazione 14–16 Luglio 2003

IntroductionLorenzo SciaviccoMotion control

Bruno SicilianoIndirect force control

Luigi VillaniDirect force control

Stefano ChiaveriniExperimentsBruno Siciliano

Hybrid force control and contact estimationin the task frame formalism

Herman Bruyninckx


Research @ PRISMA Lab

Dual-robot system Redundancy resolution Singularity robustness Cooperative tasks Fault tolerance Model identification Inverse dynamics

control Force control Visual tracking

Interaction control


Robot Force Control

IntroductionLorenzo SCIAVICCO

Dipartimento di Informatica e Automazione

Università degli Studi di Roma [email protected]


Outline

Force control Motion control vs. interaction control Indirect vs. direct force control

Modelling Kinematics Dynamics

Control Strategy Joint space control vs. task space control


Force control

Motion control vs. interaction control Object manipulation or surface operation requires control of

interaction between robot manipulator and environment Use of purely motion control strategy is candidate to fail

(task planning accuracy) Control of contact force (compliant behaviour) Use of force/torque sensor (interfaced with robot control

unit) Indirect vs. direct force control

Indirect force control: force control via motion control (w/out explicit closure of force feedback loop)

Direct force control: force controlled to desired value (w/ closure of force feedback loop)


Modelling

Kinematics Kinematic model


Modelling (cont’d)

Differential kinematics

task variables

: kinematic redundancy

: matrix geometric Jacobian

kinematic singularities (!)



Dynamics Lagrange formulation

Dynamic model



Skew-symmetry of

Hamilton principle

Linearity in the dynamic parameters


Control strategy

Joint space control Task references transformed into joint references Redundancy resolution at kinematic level


Control strategy (cont’d)

Task space control Control directly in task (operational) space Redundancy resolution at dynamic level


Motion controlBruno SICILIANO

Dipartimento di Ingegneria dell’Informazionee Ingegneria Elettrica

Università degli Studi di [email protected]

Robot Force Control


Outline

Tracking control Dynamic model-based compensation Euler angles error Angle/axis error Quaternion error Computational issues Redundancy resolution

Regulation Static model-based compensation Orientation errors


Tracking Control

Dynamic model-based compensation

Position control

Orientation controlEuler anglesAngle/axisQuaternion


Tracking Control (cont’d)

Euler angles error: Resolved angular acceleration

Error dynamics

representation singularities (!)



Alternative Euler angles error: Resolved angular acceleration

Error dynamics

choose so that is nonsingular (!)



Angle/axis error:

Representation

Classical angle/axisQuaternionRodrigues parametersSimple rotation



Angle/axis error: Resolved angular acceleration

Error dynamics



Simpler choice:

Error dynamics

… stability via Lyapunov argument ( )



Quaternion error: Resolved angular acceleration

Error dynamics

… stability via Lyapunov argument



Computational issues

Resolved acceleration

Trajectory generation

Orientation error Flops Funcs Flops FuncsClassical Euler angles

68 8 52 8

Alternative Euler angles

136 8 0 0

Angle/axis 55 0 0 0Quaternion 60 1 21 1



Comparison

Orientation error Pros ConsClassical Euler angles

Similar to position Computational loadRepres. singularities


Repres. singularities

Computational loadLarge errors

Angle/axis Computational load

Sing.-free trajectory

Quaternion Large errors Nonlinear error dyn.



Redundancy resolution

dynamically consistentpseudo-inverse

… stability via Lyapunov argument



Inverse dynamics control with redundancy resolution


Regulation

Static model-based compensation

Position control

Orientation control

Euler

anglesAngle/axisQuaternion


Regulation (cont’d)

Orientation errors Euler angles


Angle/axis

Quaternion

for all… stability via Lyapunov argument


A.D. MCCXXIV

Indirect force controlLuigi VILLANI

Dipartimento di Informatica e Sistemistica

Università degli Studi di Napoli Federico II

[email protected]

Robot Force Control


Outline

Compliance control Active compliance

Impedance control Active impedance Inner motion control Three-DOF impedance control Six-DOF impedance control

A.D. MCCXXIV


Compliance control

Active compliance

… at steady state (position/force)

A.D. MCCXXIV


Impedance control

Active impedance force/torque sensor

A.D. MCCXXIV


Impedance control (cont’d)

Impedance control (w/ force/torque measurements)

A.D. MCCXXIV



Inner motion control Enhanced disturbance rejection

compliant frame

A.D. MCCXXIV



Three-DOF impedance control Translational impedance

Linear acceleration (inner motion loop)

A.D. MCCXXIV



Six-DOF impedance control Rotational impedance (Euler angles)

Infinitesimal orientation displacement

Angular acceleration (inner motion loop)

task geometric inconsistency

A.D. MCCXXIV



Rotational impedance (alternative Euler angles)


Angular acceleration (inner motion loop)task geometric consistency

(XYZ Euler angles + diagonal stiffness)

A.D. MCCXXIV



Rotational impedance (angle/axis)



task geometric consistency

A.D. MCCXXIV



Rotational impedance (quaternion)



task geometric consistency

A.D. MCCXXIV


Direct force controlStefano CHIAVERINI

Dipartimento di Automazione, Elettromagnetismo,Ingegneria dell’Informazione e Matematica Industriale

Università degli Studi di [email protected]

Robot Force Control


Outline

Force regulation Static model-based compensation Dynamic model-based compensation

Force/motion control Force and position regulation Force and position control Moment and orientation control Force tracking


Force regulation

Static model-based compensation

PI control

… at steady state


Force regulation (cont’d)

Dynamic model-based compensation

Force and moment control with inner motion control loop


Force/motion control

Force and motion control Regulation of force but loss of motion control Recover motion control along unconstrained directions while

ensuring force control along constrained directions

parallel control strategy


Force/motion control (cont’d)

Force and position regulation

At steady state



Force and position control



Force and position control with full parallel composition



Moment and orientation control



Force tracking Full parallel composition

Time-varying force

tracking if exactly known



Contact stiffness adaptation ( )


Experiments

Set-up COMAU Smart 3-S

robot Open control

architecture ATI force/torque sensor

Force-motion control Compliance control Impedance control Force control Parallel control Hybrid control


Experiments (cont’d)

Impedance control Contact with

unknown surface Accommodation of

both force and moment

Geometric consistency


Experiments (cont’d)

Extension to dual-robot system

typical peg-in-hole assembly task

robot holding the hole controlled as 6-DOF impedance

robot holding the peg programmed in PDL-2

accommodation of misalignment and overshoot


Further experiments

Set-up @ ARTS Lab, SSSA Pisa

DEXTER cable-actuated robot arm

Compliance control tasks of assisting disabled

people


Further experiments (cont’d)

Set-up @ DLR, Germany

KUKA robot with force sensor and camera embedded in the gripper

Integration of vision and force

visual feedback in gross motion

force feedback in fine motion


References F. Caccavale, C. Natale, B. Siciliano, L. Villani, "Resolved-

acceleration control of robot manipulators: A critical review with experiments", Robotica, 16, 565–573, 1998

F. Caccavale, C. Natale, B. Siciliano, L. Villani, "Six-DOF impedance control based on angle/axis representations", IEEE Transactions on Robotics and Automation, 15, 289–300, 1999

F. Caccavale, C. Natale, B. Siciliano, L. Villani, "Achieving a cooperative behaviour in a dual-arm robot system via a modular control structure", Journal of Robotic Systems, 18, 691–700, 2001

F. Caccavale, B. Siciliano, L. Villani, "Robot impedance control with nondiagonal stiffness", IEEE Transactions on Automatic Control, 44, 1943–1946, 1999


References (cont’d) S. Chiaverini, L. Sciavicco, "The parallel approach to

force/position control of robotic manipulators", IEEE Transactions on Robotics and Automation, 9, 361–373, 1993

S. Chiaverini, B. Siciliano, L. Villani, "Force/position regulation of compliant robot manipulators", IEEE Transactions on Automatic Control, 39, 647–652, 1994

S. Chiaverini, B. Siciliano, L. Villani, "A survey of robot interaction control schemes with experimental comparison", IEEE/ASME Transactions on Mechatronics, 4, 273–285, 1999

C. Natale, Interaction Control of Robot Manipulators: Six-degrees-of-freedom Tasks, Springer, Heidelberg, Germany, 2003

B. Siciliano, L. Villani, Robot Force Control, Kluwer, Boston, MA, 1999

Education

Robot force control