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André Carvalho BittencourtStatic Friction
ABB CRCVästerås, SE
Static FrictionLoad torques andTemperaturedependency
André Carvalho BittencourtStatic Friction
ABB CRCVästerås, SE
Motivation What is the most common researched phenomenon in robotics?
0200400600
80010001200140016001800
Control
Observer
Learning
T. planing
Diagnosis
FrictionFlexibilityBacklashRipple
Why?
André Carvalho BittencourtStatic Friction
ABB CRCVästerås, SE
Motivation - Diagnosis
Robots eventually break down Increase of wear debris Increase of friction
However! Many other things affect friction- Temperature- Load- Position- Velocity/acceleration- Lubricant, etc
André Carvalho BittencourtStatic Friction
ABB CRCVästerås, SE
Objectives
How does friction changes with Position Load torques
•Manipulated•Perpendicular
Temperature
Scope IRB 6620 Joint 2
André Carvalho BittencourtStatic Friction
ABB CRCVästerås, SE
Friction Curve Estimation In steady-state one joint at a
time
Average fwd and bwd movements
and use it as an estimate of the direction independent friction
André Carvalho BittencourtStatic Friction
ABB CRCVästerås, SE
Joint angles 50 static curves Angles range
8.5 to 60º
Effects Not significant
M0 should do it
André Carvalho BittencourtStatic Friction
ABB CRCVästerås, SE
Perpendicular load torque Tp range
[0.04, 0,10] Small variations possible
Effects Not significant At joint 1, small increase in
Fs
For joint 2, M0 is enough
André Carvalho BittencourtStatic Friction
ABB CRCVästerås, SE
Manipulated Load Torque 50 static curves Tm range
[-0.7, 0,4]
Effects (linear) Fc increase (linear) Fs increase cte vs
Proposed model, M0 +2 terms
André Carvalho BittencourtStatic Friction
ABB CRCVästerås, SE
Temperature 50 static curves (min/max) T range
34-80ºC
Effects (linear) Fs increase (linear) vs increase (exp-like) Fv increase
Load torque co-effects Subtract surfaces Subtract identified gravity
terms from surfaces Independent!
André Carvalho BittencourtStatic Friction
ABB CRCVästerås, SE
Proposed Model
M0 + 4 terms 7 terms (5 vel-weak, 2 vel-str)
Total of 11 parameters
Tm (3): (linear) increase of Fc and Fs
T (4): (linear) increase of Fs and vs (exp) increase of Fv
André Carvalho BittencourtStatic Friction
ABB CRCVästerås, SE
Validation
Parameters identified with previous data
Error reduced by a factor of 6
M0:mean=0.027,max=0.071M*:mean=0.004,max=0.018
André Carvalho BittencourtStatic Friction
ABB CRCVästerås, SE
Summary & Conclusions Empirically motivated model to describe T and Tm
So far, 1 joint! Tp might also affect
Tm affects vel-weak only (inc) T affects vel-weak (dec) and vel-str (nonlinear inc) 11 parameters (4nlin: 3 vs,TVo)
Id requires excitation over large range of T and Tm Can T-params be directly related to lubricant props?
No T meas and Tm estimated* Right now, more useful for design/evaluation
Can the model simply be plugged into a dynamic model (LuGre)?
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