Adrian Bonchis Peter I. Corke David C. Rye A Pressure-Based, Velocity Independent, Friction Model for Asymmetric Hydraulic Cylinders. 1746-1751 1999 conf/icra/1999 ICRA db/conf/icra/icra1999-3.html#BonchisCR99 http://dx.doi.org/10.1109/ROBOT.1999.770361