Estimation of contact forces in an inverted pendulum robot

In this paper a method for force estimation on inverted pendulum type balancing platforms is presented and examined. Inverted pendulum systems are sensitive to small external forces because they are being balanced about an unstable position of zero force. The perturbations that result from external forces cause noticeable changes to the system state variables and it is these changes that are used to estimate the force. We present a dynamic model for the inverted pendulum and then examine several methods for estimating an external force. Use of the open loop plant parameters offers the best method for estimating the net torques acting on the system. A significant outcome is that estimation can be performed using only the system mass properties along with the inertial and displacement sensors that are required for balancing and this estimate is more accurate than a comparable drive system in a statically stable robot. Thus improved one axis force estimation may be accomplished using the same sensors that are used to stabilize the platform.