dynamic modeling and control of variable stiffness actuators
TRANSCRIPT
Dynamic Modeling and Control of Variable Stiffness Actuators
A. Albu-Schäffer, O. Eiberger, M. Grebenstein, S. Haddadin, M. Nickl, F. Petit and S. Wolf
DLR – German Aeorospace CenterCenter of Robotics and Mechatronics
Skilful Manipulation with Variable Impedance Robots
Design and control of VIA hand/arm Safety and performance analysis of VIA devices
Size, force and dynamics of a human arm/handVariable stiffness 54 motors,108 position sensors
DLR - Anthropomorphic Hand-Arm-System
A Hand-Arm System for Space Assistance
Extension of the passivity based control approaches to the VIA robots:
Variable, nonlinear stiffnessStrongly coupled joints
Challenges for the Hand: DLR Hand IIb to the integrated hand arm system
Robot hand with size and force similar to the human one
Relocation of motors via tendons.Variable stiffness elements.
Critical tendon routingNonlinearity vs. Workspace/Friction.Joint coupling.
Challenges:Modeling and optimization of the mechanismElectronics integrationA controller to set joint position and stiffness independently.Stiffness trajectories for manipulation
Electronics Integration
Finger Prototype I
Tendon controlled finger with novel jointsHyperboloid joints.Hinge joints hold together by tendon force.
4 Joints.8 Tendons.Nonlinear tendon routing.
Finger Prototype II (STL)
Problem Formulation
Given the desired joint position and the desired mechanical joint stiffnessSolve for the desired motor position.Insert desired motor positions and desired tendon forces into a low-level motor controller → Active motor compliance in series with
mechanical (passive) compliance
Inverse
Simulation & Experimental Results
Step in desired joint positionof 0.2 rad joint positions Motor positions
Challenges for the VIA Arm and Leg Actuation
• Maximal peak power/weight ratio at reasonable stiffness adjusting rate
• Maximal efficiency in energy storage and release• High storable energy density
DLR Arm Joint PrototypesVS-Joint (Wolf & Hirzinger ICRA2008, TuF2.6) QA-Joint (Eiberger & al. ICRA2010) TuF2.6
New armjoint design
Testbed for Evaluation of the First Joint Prototypes
Motor
Encoder
TorqueSensor
VIA - Unit
QA- Prototype
Load
VS-Prototype
Joint Data Sheet: DLR VS-Joint
217°/sMax. Equilibrium Velocity
Variable StiffnessActuator Type
270 + 50 = 320 WNominal Power(not max./peak!)
16.8 JMax. Storable Energy
± 14° / ± 14°Max. Deflection Range (min./max Stiff.)
Ø97x106 / ~ Ø97x166 mmSize (w/wo Motors)
1.4 / ~ 2.0 kgWeight (w/wo Motors)
7.3%Torque Hysteresis at Max. Torque
0.2 sMin. Stiffness Adjusting Time(from 3% to 97% stiffness)
0 / 315 Nm/radMin./Max. Stiffness (no external load)
± 180 NmMaximum Joint Torque(repeatable, evaluated by measurement)
c : Radius of Cam DiskJoint Deflection cφφ
Common descriptionunder developmentby VIACTORS partners
Joint Data Sheet: DLR QA-Joint
217°/sMax. Equilibrium Velocity
Quasi AntagonisticActuator Type
270 + 50 = 320 WNominal Power(not max./peak!)
2.7 JMax. Storable Energy
± 15° / ± 3°Max. Deflection Range (min./max Stiff.)
Ø90x100 / ~ Ø90x160 mmSize (w/wo Motors)
1.4 / ~ 2.0 kgWeight (w/wo Motors)
+/-12.5%Torque Hysteresis at Max. Torque
0.15 sMin. Stiffness Adjusting Time(from 3% to 97% stiffness)
20 / 550 Nm/radMin./Max. Stiffness (no external load)
± 40 NmMaximum Joint Torque(repeatable, evaluated by measurement)
Control of VIA Joints
useful for cyclic movementsinvolving energy storage
(running or throwing)
damping of the arm for fast,fine positioning tasks has to be
realized by control.
The joints have very low intrinsic damping
Ensuring the achievement of the desired link position with motor position based control.Providing the desired stiffness property.
(Albu-Schäffer & al. ICRA 2010, WeA1.5 )
Active Vibration Damping for VIA Joints
No damping Active damping
External disturbance torque
Generic VS joint model – underactuated systemwith p.d.
Validation on 2dof Prototype
Performance Validation
VIA jointRigid joint
Optimal Control for Maximal Performance
Optimized stiffness and motion trajectory
Kicking Performance: Motivation
Kicking Experiments
Experimental Results
Impact joint torque
Kicking range
Speed
10 Nm85 Nm
4.05 m1.6 m
6.35 m/s3.06 m/s
VS-JointStiff Joint