Static Friction 26032010 Load torques and Temperature dependency

Static Friction 26/03/2010 Load torques and Temperature dependency André Carvalho Bittencourt Static Friction ABB CRC Västerås, SE

Motivation § What is the most common researched phenomenon in robotics? § Why? André Carvalho Bittencourt Static Friction ABB CRC Västerås, SE

Motivation - Diagnosis § Robots eventually break down Increase of wear debris à Increase of friction § However! - Many other things affect friction Temperature Load Position Velocity/acceleration Lubricant, etc André Carvalho Bittencourt Static Friction ABB CRC Västerås, SE

Objectives § How does friction changes with § Position Load torques • Manipulated • Perpendicular Temperature Scope IRB 6620 Joint 2 André Carvalho Bittencourt Static Friction ABB CRC Västerås, 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 Bittencourt Static Friction ABB CRC Västerås, SE

Joint angles § § 50 static curves Angles range 8. 5 to 60º Effects § Not significant § M 0 should do it André Carvalho Bittencourt Static Friction ABB CRC Västerås, 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, M 0 is enough André Carvalho Bittencourt Static Friction ABB CRC Västerås, SE

Manipulated Load Torque § § 50 static curves Tm range [-0. 7, 0, 4] Effects § (linear) Fc increase § (linear) Fs increase § cte vs § Proposed model, M 0 +2 terms André Carvalho Bittencourt Static Friction ABB CRC Västerås, 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 Bittencourt Static Friction ABB CRC Västerås, SE

Proposed Model § § § M 0 + 4 terms 7 terms (5 vel-weak, 2 vel-str) Total of 11 parameters § § Tm (3): (linear) increase of Fc and Fs T (4): André Carvalho Bittencourt Static Friction (linear) increase of Fs and vs (exp) increase of Fv ABB CRC Västerås, SE

Validation § Parameters identified with previous data § Error reduced by a factor of 6 M 0: mean=0. 027, max=0. 071 M*: mean=0. 004, max=0. 018 André Carvalho Bittencourt Static Friction ABB CRC Västerås, 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 (4 nlin: 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 (Lu. Gre)? André Carvalho Bittencourt Static Friction ABB CRC Västerås, SE