Planning coordinated motions for tethered planar mobile robots

Abstract

This paper considers the motion planning problem for multiple tethered planar mobile robots. Each robot is attached to a fixed base by a flexible cable. Since the robots share a common workspace, the interactions amongst the robots, cables, and obstacles pose significant difficulties for planning. Previous works have studied the problem of detecting whether a target cable configuration is intersecting (or entangled). Here, we are interested in the motion planning problem: how to plan and coordinate the robot motions to realize a given non-intersecting target cable configuration. We identify four possible modes of motion, depending on whether (i) the robots move in straight lines or following their cable lines; (ii) the robots move sequentially or concurrently. We present an in-depth analysis of Straight & Concurrent, which is the most practically-interesting mode of motion. In particular, we propose algorithms that (a) detect whether a given target cable configuration is realizable by a Straight & Concurrent motion, and (b) return a valid coordinated motion plan. The algorithms are analyzed in detail and validated in simulations and in a hardware experiment.

Non-Crossing Anonymous MAPF for Tethered Robots

“…The procedure that we use for detecting path crossings (described in Section 2.2) is adapted from this work. (Zhang & Pham, 2019) consider the same problem as (Hert & Lumelsky, 1994), but the workspace may contain obstacles and there is no objective function to optimize: they simply search for a valid schedule such that robots do not cross cables. To avoid crossings, precedence constraints and waiting times are introduced, and a precedence graph is used to detect deadlocks.…”

“…2(a), the blue path is closer to the triangle than the red path whereas the red path is closer to the rectangle than the blue path. Given two paths that share a same obstacle vertex, we can decide in constant time which one is the closer to the obstacle, as described in (Zhang & Pham, 2019). This may be extended to the case of two paths that share some sub-path, by ensuring that paths never cross.…”

Projector-Guided Non-Holonomic Mobile 3D Printing

“…This algorithm could obtain localized feedback and adjust the motion error from the AprilTags [6] on the ground. Since concrete needs to be pumped through a pipe, Zhang and Pham [7] designed an algorithm that included four different modes to solve the motion planning problem for multiple tethered planar mobile robots. Similar to [4], Lv et al [8] proposed a holonomic mobile printing method by switching the workspace and used the contour of the printed object to estimate the pose of the mobile platform and update the mobile platform control.…”

Four-Arm Collaboration: Two Dual-Arm Robots Work Together to Maneuver Tethered Tools

“…For example, a hydrodynamics and control model to simulate a tethered underwater robot system is presented in [21]. A motion planning algorithm for multiple tethered planar mobile robots, emphasizing entanglement avoidance, is proposed in [22]. An approach for cooperative manipulation of a cablesuspended load with two aerial robots is presented in [23].…”