Force Control of Flexible Integrated Joint Based on Model-free Adaptive Control

The flexible integrated joint (FIJ) is a key part of the collaborative robots, which has the characteristics of lightweight and highly integration. The force control is pivotal for achieving compliant interactions with environments and humans, such as impendence control and force tracking control. However, the controller design for force control of the flexible joint is a challenging issue with unmodeled uncertainties, nonlinear friction, time-varying load and other disturbances forced by environments in general. In this paper, a control scheme based on model-free adaptive control (MFAC) was developed for the force control of the FIJ. First, the model of the FIJ was transformed into a virtual dynamic linearization data model by a dynamic linearization approach. Second, a MFAC algorithm was designed for force control of the FIJ, including its corresponding pseudo gradient estimating algorithm and pseudo gradient resetting algorithm. To evaluate the performance of the proposed method, the experiments including zero force tracking and step force tracking were carried out in this research. The experimental results show that the developed control approach can get a high performance as the dynamical parameters of the FIJ are time-varying and uncertain.