Active robot hand compliance using operational space and Integral Sliding Mode Control

Abstract

This paper establishes a novel approach of robust active compliance control for a robot hand via an Integral Sliding Mode Controller (ISMC). The ISMC allows us to introduce a model reference approach where a virtual mass-spring damper system can be used to design a compliant control. In order to allow for practical grasping, we consider the shape of the object to be grasped. Hence, the work exploits a grasping technique via Cylindrical and Spherical coordinate systems due to their simplicity and geometric suitability. The control uses the operational space approach. Thus, the control is split into a task control and a particular optimizing posture control. The experimental results show that target trajectories can be easily followed by the task control despite the presence of friction and stiction while the posture controller maintains a desired finger posture. When the object is grasped, the compliant control will automatically adjust to a specific compliance level. Once a specific compliance model has been achieved, the fixed compliance controller can be tested for a specific scenario. The experimental results prove that the BERUL hand can automatically and successfully attain different compliancy levels for a particular object via the ISMC.

Robotic hand posture and compliant grasping control using operational space and integral sliding mode control

“…Hence, we also extend significantly over our own recent work on compliant grasping (Jalani et al (2013) 11 ; Jalani et al…”

“…The grasping task needs to guarantee that the fingers sufficiently surround the object, staying in good contact and creating a suitable ergonomicsinspired posture 10 . As a result of such analysis, the authors of this paper suggested for hand positioning for grasp and for grasping an object-based coordinate system (see early ideas in Jalani, Mahyuddin, Herrmann & Melhuish (2013) 11 and Jalani, Herrmann & Melhuish (2011) 12 ); hence, this choice of coordinate system focuses on the object shape. Thus, the control is carried out in relation to the object shape rather than in a global Cartesian coordinate frame.…”

Realisation of model reference compliance control of a humanoid robot arm via integral sliding mode control

“…The sliding mode element r given by Eq. (1) is modified to introduce the compliance effect based on the external sensed force via joint torque sensors (Jalani et al, 2013;Herrmann et al, 2014):…”

“…A Cartesian (X, Y and Z) model reference type of ISMC compliant scheme is simulated for 4 DOF of the humanoid BERT II robot arm 1 . Different compliance levels are produced by choosing spring constant and damping coefficients in the reference model (Jalani et al, 2013;Herrmann et al, 2014). The scheme will be used to address safety issues in human-robot interaction.…”

“…ISMC has been employed here to deal with uncertainties and unmodelled nonlinearities. In addition, external force (the interaction force between robot and its environment (including human) has been included in the ISMC which results into a model reference compliance controller (Jalani et al, 2013). The dynamic model of the BERT II robot arm for the FL is obtained via MapleSim (a package of Maple) (Maplesoft, 2015).…”