Implicit force control for an industrial robot based on stiffness estimation and compensation during motion

Abstract

Although force control algorithms have been studied for three decades, this technology is not largely exploited in industry yet. The present paper proposes a position-based adaptive force control strategy, that relies on a novel method for the on line estimation of the environment stiffness. The control design is targeted to industrial controller structures and it is theoretically proven to be robust to time varying estimation errors of the environment stiffness and joint friction disturbances. The estimation algorithm succeeds in identifying the environment stiffness even in presence of geometrical irregularities of the contact surface during motion. The identification and control approaches are experimentally validated on an industrial robot equipped with a force sensor

Convex Controller Synthesis for Robot Contact

“…As mentioned, one approach to dealing with uncertainties in environment stiffness is to estimate the stiffness online and adapt the controller gains accordingly. In [1], [2], [3], [4], researchers used a Least-Square-based estimator to estimate the stiffness of the environment, which is then used to select the actual gains for the force control loop. More recently, [5] proposed to use Virtual Reference Feedback Tuning [10] to adapt the controller directly to stiffness measurements.…”

“…There has been substantial work on contact controllers that can deal with environment uncertainty, in particular, unknown environment stiffness. One approach consists in estimating the environment stiffness in real time and adapting controller gains accordingly [1], [2], [3], [4], [5]. One major limitation is the comparatively low sensitivity and speed of the stiffness estimator, which, in turn, severely restricts the reactivity of the controller.…”

Implicit Control

“…Applications of implicit force control have been presented in Kröger et al (2004), Osypiuk et al (2006), and Winkler and Suchy (2016). Rossi et al (2014Rossi et al ( , 2016 discussed the effects of joint and link elasticities in the performance of implicit force control, while Parigi Polverini et al (2017) applied advanced methods based on set invariance to design an implicit force controller.…”

High-Gain Observer-Based Sliding Mode Force Control for the Single-Rod Electrohydraulic Servo Actuator

“…Simulations and experiments indicate that the proposed approach can achieve smaller human-machine interaction force and good robust performance to model uncertainties. Rossi et al [4] presented an online estimation algorithm of environment stiffness in the force control for the industrial robot. The control approaches are experimentally validated on an industrial robot and proved to be robust to environment stiffness and joint friction disturbances.…”