Kinematic modeling and singularity treatment of steerable wheeled mobile robots with joint acceleration limits

Abstract

Non-holonomic omnidirectional mobile robots have higher load carrying capacity than their holonomic counterparts. Once the steer joint configuration is initialized, they can perform arbitrarily complex three-dimensional trajectories in the plane of motion and, as such, are more suitable for industrial contexts. However, their kinematic model presents representational and structural singularities, solutions to which must respect actuator performance limits. Recent research efforts have provided either simple restricting of the velocity space (among which few considered hardware limits) or complex non-restricting (no hardware limits considered) solutions. Most of these efforts are providing solutions at the kinematic control level. Instead, here we propose both a representational singularity free kinematic model, and a simple numeric treatment for the kinematic singularity. We further provide a method to tune the latter, to respect the actuator acceleration limits. Thanks to its steer rate damping behavior, the method can be further extended, to respect joint limits. Another benefit is the treatment of the singularity at the level of the kinematic model, which enhances real time capabilities. The developed method has been tested successfully on the Neobotix-MPO700 mobile robot and shown superior results as compared to the embedded controller.

A collaborative robot for the factory of the future: BAZAR

“…1. proper steering coordination [10,58,61,68], 2. avoidance of kinematic and representational singularities [19,20,21,24,30,60,64,68], 3. fulfillment of steer joint performance limits [11,18,22,50,51,52,53,60,63].…”

“…In a first work [63], we present a numeric treatment of SWMR kinematic singularities and a benchmark test trajectory for evaluating the performance of any SMWR controller with respect to these singularities. We also show that our approach outperforms the embedded controller of the BAZAR base (Neobotix-MPO700) in addressing the singularities.…”

Motion Control for Steerable Wheeled Mobile Manipulation

“…where d and r w denote the wheel offset and radius respectively. For more details about the framework and the kinematic model, the reader is referred to [23], [24], [29].…”

Motion Discontinuity-Robust Controller for Steerable Mobile Robots

“…The kinematic model presented in this section (detailed in previous work by the authors [10]) is inspired by the pioneer work of Muir [11], Campion [12], Betourne [13] and Low et al [14]. The schematic of a SWMR is shown in Fig.…”

“…at the ground contact point o ci (expressed in the wheel frame F wi ), with v ti and v ni respectively the i th tangential and normal velocities, it can be shown that [10]:…”