The International Journal of Robotics Research

We address an on-line version of the visibility-based pursuit-evasion problem. We take a minimalist approach in modeling the capabilities of a pursuer robot. A point pursuer moves in an unknown, simplyconnected, piecewise-smooth planar environment, and is given the task of locating any unpredictable, moving evaders that have unbounded speed. The evaders are assumed to be points that move continuously. To solve the problem, the pursuer must for each target have an unobstructed view of it at some time during execution. The pursuer is equipped with a range sensor that measures the direction of depth discontinuities, but cannot provide precise depth measurements. All pursuer control is specified either in terms of this sensor or wall-following movements. The pursuer does not have localization capability or perfect control. We present a complete algorithm that enables the limited pursuer to clear the same environments that a pursuer with a complete map, perfect localization, and perfect control can clear (under certain general position assumptions). Theoretical guarantees that the evaders will be found are provided. The resulting algorithm to compute this strategy has been implemented in simulation. Results are shown for several examples. The approach is efficient and simple enough to be useful towards the development of real robot systems that perform visual searching.

We propose a practical maneuvering control strategy for an aquatic vehicle (AV) that uses an oscillating foil as a propulsor. The challenge of this problem lies in the need to consider the hydrodynamic interaction as well as the underactuated and non-minimum phase natures of the AV system. The control task is decomposed into the off-line step of motion planning and the on-line step of feedback tracking. Optimal control techniques are used to compute a repertoire of time-scalable and concatenable motion primitives. The complete motion plan is obtained by concatenating time-scaled copies of the primitives. The computed optimal motion plans are regulated by a controller that consists of a cascade of linear quadratic regulator, input–output feedback linearization and sliding mode control. Time-varying linear quadratic controllers can also be time-scaled and concatenated. Therefore, they can be computed beforehand. The proposed strategy has been experimentally validated for both constrained longitudinal only maneuvers and unconstrained longitudinal/lateral maneuvers.

In this paper we present a theoretical and experimental study of the self-excited walking of a biped mechanism with knees and feet on level ground. This biped mechanism possesses a single motor at the hip joint and active lock mechanisms at both knee joints. We first show that the self-excitation control enables the three-degrees-of-freedom planar biped model with feet to walk on level ground, and that a stable walking locomotion is possible over a wide range of feedback gain and a foot radius of up to 0.3 m. Subsequently, we describe the manufactured biped Robot 2 which is similar to the analytical model and we show that the biped robot can perform natural dynamic walking on a level floor. It is also shown that the simulated results agree well with the experimental results. We further describe the wireless-controlled biped Robot 3, which can walk on a level floor carrying batteries and electronic circuits inside the thighs.

In this paper, a novel planning method is proposed to solve initial velocities of the free sliding object for given initial and final configurations. Finding the desired initial velocities for free sliding objects is a key step for implementing impulse manipulation and multi-agent dynamic cooperative manipulation. The motion of free sliding objects on a plane is governed by friction forces and the initial state of the object; this motion can be modeled by a set of six first-order differential equations. In this paper, the planning problem is formulated as a free boundary value problem (FBVP). In order to solve the problem, the FBVP is first reduced to a standard two-point boundary value problem, then quasi-Newton based optimization procedures are utilized to solve the planning problem. The proposed method does not require qualitative motion characteristics; thus, it can be used for objects with general shape and arbitrary pressure distribution. Numerical and experimental results on objects with different geometries and pressure distributions are used to demonstrate the performance of the proposed planner.

The DELTA robot and the manipulators derived from the DELTA robot are a relevant class of translational manipulators. In this paper, the mobility analysis of these parallel translational manipulators is developed in full. The manufacturing and mounting conditions that guarantee the pure translation of the platform are analytically derived. Moreover, it is demonstrated that these manipulators can assume singular configurations, called rotation singularities, in which they are no longer able to impose the platform translation. Finally, the geometric and analytic conditions that make it possible to find all the singular configurations of these manipulators are provided.