Force Tracking Impedance Control with Variable Target Stiffness

Force and trajectory control of industrial robots in stiff contact

“…when moving or teaching the robot by holding an end-effector fixed handle which is connected to the robot by a force-/ torque-sensor. But there are also applications which require an explicit force control scheme since otherwise intolerable forces would occur [4], [5]. This is typically the case when the robot is in contact with a stiff environment, e.g.…”

Force tracking control for motion synchronization in human-robot collaboration

“…Therefore, the equilibrium position is deemed as the desired trajectory/motion intention of the human partner, which is planned in the central nervous system (CNS) of the human partner and unknown to the robot. Since this desired trajectory is generally timevarying and uncertain due to the modeling error and external disturbance, it is different from the constant rest position studied in [14,15,16,17]. Three typical cases will be discussed under the same framework: adaptive control will be developed to deal with the point-topoint movement, and learning control and neural networks (NN) control to generate periodic and arbitrary continuous trajectories, respectively.…”

“…In this regard, the robot under impedance control will act as a load to the human partner when he/she changes his/her intended motion [3]. To cope with this issue, much effort has been made to realize force tracking under the framework of impedance control [14,15,16,17]. In [14], two adaptive schemes are proposed to achieve force tracking by adjusting the rest position in the impedance model.…”

“…In [15], an impedance model with zero stiffness is adopted, and the force error is eliminated by an adaptive scheme subject to uncertainties in robot dynamics and little knowledge of environment dynamics. Instead of adjusting the rest position in the impedance model, the stiffness parameter is updated to achieve force tracking with a small tracking error in [16].…”

On autonomous and teleoperated aerial service robots

“…On the other hand, as force control is not often the goal of classical impedance controllers, it is difficult, if not impossible, to regulate interaction force when the position of the environment is not known a priori. Methods suggested in the literature to mend this limitation of impedance controllers mainly involve varying the position command [105], [95], or the stiffness of the impedance controller [55], [19]. The aforementioned works, use force sensors and regard one dimensional system.…”