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

Abstract

SUMMARYThis paper establishes a novel approach of robotic hand posture and grasping control. For this purpose, the control uses the operational space approach. This permits the consideration of the shape of the object to be grasped. Thus, the control is split into a task control and a particular optimizing posture control. The task controller employs Cylindrical and Spherical coordinate systems due to their simplicity and geometric suitability. This is achieved by using an integral sliding mode controller (ISMC) as task controller. The ISMC allows us to introduce a model reference approach where a virtual mass-spring-damper system can be used to design a compliant trajectory tracking controller. The optimizing posture controller together with the task controller creates a simple approach to obtain pre-grasping/object approach hand postures. The experimental results show that target trajectories can be easily followed by the task control despite the presence of friction and stiction. When the object is grasped, the compliant control will automatically adjust to a specific compliance level due to an augmented compliance parameter adjustment algorithm. Once a specific compliance model has been achieved, the fixed compliance controller can be tested for a specific object grasp scenario. The experimental results prove that the Bristol Elumotion robot hand (BERUL) can automatically and successfully attain different compliance levels for a particular object via the ISMC.

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

“…Choosing suitable value for α > 0 large enough to reduce the effect of uncertainty and achieve robustness. The scalar ζ , is selected to minimize the chattering effect (Jalani et al, 2010a;Herrmann et al, 2014).…”

“…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):…”

“…The idea is that multiple configurations were avoided by introducing and minimizing cost which resolves the redundancy issues. Other applications by using decoupling technique can be found in Herrmann et al (2014) and Spiers et al (2009a, b).…”

“…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.…”

Hydraulic systems control based on the characteristics of major-motion mechanism for an open-die forging manipulator

“…J Wang et al 19 attempted to use adaptive compliance control for a hydraulic manipulator in free forging. Herrmann et al 20 designed a compliant trajectory tracking controller for a manipulator using operational space and integral sliding mode control. The manipulator may work in active mode to comply with the motions of the forging die while cooperating with the forging press to deform a workpiece.…”