A set-point-generator for indirect-force-controlled manipulators operating unknown constrained mechanisms

Abstract

Abstract-In this paper we propose a set-point-generator (SPG) for indirect-force-controlled (IFC) manipulators, interacting with mechanisms, which impose narrow bilateral kinematic constraints on their end effector, like doors, cabinets and drawers. These mechanisms could also have dynamic properties, due to their inertia, friction and gravity, which demands to consider applied forces when choosing a set-point for the IFC. Neither the type of the constraint (linear, circular), nor required manipulation forces are assumed to be known.The proposed SPG consists of two parts: i) estimating the single direction of possible motion based on filtering of the measured end effector velocities; and ii) choosing an appropriate set-point for the underlying IFC, resulting in an effective operation of the mechanism. A major aspect of our approach is to explore the kinematic constraints with the manipulators desired set-point, avoiding direct force control, as the required interaction force is unknown and hence there is no definite reference force.The presented approach is a generalization of our previous work on constrained manipulation of unknown mechanisms and extends the applicability to a wider class of manipulators by considering joint-level IFC and taking into account the applied forces in yielding a robust and effective controller.The approach is evaluated in various experiments on a manipulator, providing joint space compliance.

A Survey of Robot Manipulation in Contact

“…A big portion of the modern approaches in force-driven door opening follow the seminal work of Nimeyer and Slotine [81] that is based on: i) the implementation of an damped desired behaviour along the allowed direction of motion, and ii) the estimation of the direction of motion. The realization of the desired behaviour have been achieved through indirect compliant control [82]. A richer desired impedance has been used instead of simple damping term in [83] realised in an admittance control framework.…”

“…The estimation of the direction of motion while opening a door/drawer is a specific case of estimation of constrained motion [127,128]. Velocity-based (twist-based) estimation has been employed aiming at reducing chattering due to measurement noise and dealing with the ill-definedness of the normalization for slow end-effector motion such as spatial filtering [81], moving average filters [83] employing simple drop-out heuristics [82]. From a control perspective, decoupled estimation and control is considered to be indirect adaptive control as opposed to direct adaptive control approaches [86] that are more robust particularly for cases where the estimation dynamics suffer from lags.…”