robust and smooth force sensor-less power assist control
DESCRIPTION
Robust and Smooth Force Sensor-less Power Assist ControlTRANSCRIPT
Robust and Smooth Force Sensor-less
Power Assist Control
V. Salvucci S. Oh H. Fujimoto Y. Hori
The University of Tokyo
Outline
1 Power Assist Robots without Force Sensor?
2 Proposed Force Sensor-Less Power Assist Control
3 ResultsHuman Input Based EvaluationRigorous Experimental Verification
4 Conclusions
Outline
1 Power Assist Robots without Force Sensor?
2 Proposed Force Sensor-Less Power Assist Control
3 ResultsHuman Input Based EvaluationRigorous Experimental Verification
4 Conclusions
Power Assist Robots without Force Sensor?
Can we control these robots by estimating the user force with cheap sensors?
Why without Force Sensors?
Control key point
Knowledge of user’s applied force
1 Force Sensor
2 Force Sensor-less Control(encoder based)
Why without force sensors?
Advantages
Low cost
Low weight
Compactness
Faster Response: No delay in forcemeasurement
Safety: the robot is a sensor
Difficulties
Robustness (ex: friction non-linearities)
Difficult to provide smooth assistance
Outline
1 Power Assist Robots without Force Sensor?
2 Proposed Force Sensor-Less Power Assist Control
3 ResultsHuman Input Based EvaluationRigorous Experimental Verification
4 Conclusions
Force Sensor-Less Power Assist Control (FSPAC)
Constant gain [Oh 2008]
Based on disturbance observer for:
Disturbance rejection
Force-to-assist estimation
Variable Gain [Salvucci 2010]
VD-TG = Velocity DependentTriangular Gain (i.e. variableimpedance)
VD-TG = Velocity Dependent Triangular Gain
|va| VD-TG why
|va| < |v1| 0 no assistance stability in unknown environment
|va| ≈ |v2| high high assistance at low speed to overcome inertia
|va| → |v3| decrease low assistance at high and dangerous speed
Outline
1 Power Assist Robots without Force Sensor?
2 Proposed Force Sensor-Less Power Assist Control
3 ResultsHuman Input Based EvaluationRigorous Experimental Verification
4 Conclusions
Human Input for a “Feeling” Evaluation
No assistance
Low backdrivability
Conventional FSPAC
Not smooth(oscillatorymovements)
Unstable
Not Robust
Proposed FSPAC
Smooth
Stable
Robust
Experimental Apparatus
High Back-drivable System
Actuators: 1 linear motor
Sensors: 1 linear encoder
Motion is transmitted to the doorthrough the linear motor→ low friction, and highback-drivable
Low Back-drivable System
Actuators: 1 AC motor
Sensors: 1 rotary encoder
Motion is transmitted to the doorthrough the ball screw system→ high friction, and lowback-drivable
Experiment Input
Constant-force (in absolute value) input
Applied on the doors’ end from position 1 (left) to 2 (right)
Outline
1 Power Assist Robots without Force Sensor?
2 Proposed Force Sensor-Less Power Assist Control
3 ResultsHuman Input Based EvaluationRigorous Experimental Verification
4 Conclusions
FSPAC with Variable Impedance Works
Proposal
A simple-to-implement Variable Impedance Controller for Power AssistRobots with low cost Position Sensors
Advantages
1 Higher robustness:Experimentally stable for different humidity and room temperatureconditions (i.e. friction modeling error)
2 Smoother assistance:Higher assistance to the user at low velocities (=assistance when needed!)Better input tracking
3 Higher safety:No oscillatory torque references and velocities that can cause instability
Thank you for your kind attention
Hori-Fujimoto Lab— Eco and Human-friendly Motion Control—
References
S. Oh and Y. Hori. Generalized discussion on design of force-sensor-less power assistcontrol. In Advanced Motion Control, 2008. AMC ’08. 10th IEEE InternationalWorkshop on, pages 492–497, 2008.
V. Salvucci, S. Oh, and Y. Hori. New approach to force Sensor-Less power assistcontrol for high friction and high inertia systems. In Industrial Electronics (ISIE),IEEE International Symposium on, pages 3559–3564, 2010.