Masato Ishikawa

Simultaneous control of position and orientation for ball-plate manipulation problem based on time-State control form

This paper deals with the ball-plate manipulation problem considered as a typical but complicated model of a driftless nonholonomic system. Due to a strong nonlinearity of the ball-plate system, a state equation of the kinematic model cannot be transformed into a chained form, which is known to be effective in constructing a feedback control law for some driftless nonholonomic systems. To address this problem, we utilize a time-state control form, a kind of canonical form which covers a broader class of systems than the chained form. This form is first applied to two separate subproblems, position control, in which the planar position of the ball is controlled but not the orientation, and orientation control, in which the orientation is controlled without changing the positional relation between the ball and the plates. It turns out that there exists a linearly uncontrollable subspace in the transformed subsystem, which turns into controllable by a change of coordinates. This implies that the system has the structure of a system with two generators. We propose a control strategy using iterative changes of coordinates, ensuring convergence in the neighborhood of the origin. Finally, we unify the subproblems into simultaneous control of position and orientation, i.e., the whole configuration of the system. The important idea in the simultaneous control is the coordinate transformation, which enables us to avoid a singular point. Results of simulations show that the proposed method achieve robustness to a measurement noise and perturbation of radius of the ball.

Time-State Control Form and its Application to a Non-Holonomic Space Robot

Abstract Many non-holonomic systems, such as vehicles and space robots, are modeled in state equations which can not be stabilized with continuous static state feedback. Thus, we can not design stabilizing controllers for such systems using conventional methods. For vehicle control, feedback position controllers for multi-trailer systems were proposed by Sordalen and Canudas de Wit (1992a),(1992b). But their works are restricted to systems which can be represented in the chained form. For space robots, a motion planning method using bidirectional search was proposed by Nakamura and Mukherjee (1991), but the feedback stabilizing controller for space robots has not been discussed yet. On the other hand, the authors proposed the time-state control form and used it for the position control of multi-trailer systems(Sampei, 1994). It was also shown that the proposed strategy can also be used for the system which can not be transformed into the chained form. In this paper, we will show that this control strategy can be applied to a space robot. We will show, in simulation, that our control strategy allows us to control the position of a space robot. This is the first feedback control strategy for space robots.

Energy preserving control of a hopping robot based on hybrid port-controlled Hamiltonian modeling

In this paper, we propose an energy-based approach to feedback control problem for a hopping robot on an elastic ground. In order that the system behaves in a periodic hopping motion, we make an attempt to keep the systems total energy (Hamiltonian) to a certain specified value. Since our target is inherently a hybrid system that has discontinuous and discrete event dynamics, we suggest a suitable impact model and describe it as a hybrid version of port-controlled Hamiltonian system. Then a passivity based control called IDA (interconnection and damping assignment) is applied to this problem, which results in a good performance in the ideal situation. Moreover, we introduce a servo-like integrator into this controller to reject disturbances due to modeling uncertainty. Efficiency of the proposed method is validated both in simulations and experiments using our newly developed hopping robot system.In this paper, we propose an energy-based approach to feedback control problem for a hopping robot on an elastic ground. In order that the system behaves in a periodic hopping motion, we make an attempt to keep the systems total energy (Hamiltonian) to a certain specified value. Since our target is inherently a hybrid system, which has discontinuous, and discrete event dynamics, we suggest a suitable impact model and describe it as a hybrid version of port-controlled Hamiltonian system. Then a passivity based control called IDA (interconnection and damping assignment) is applied to this problem, which results in a good performance in the ideal situation. Moreover, we introduce a servo-like integrator into this controller to reject disturbances due to modeling uncertainty. Efficiency of the proposed method is validated both in simulations and experiments using our newly developed hopping robot system.

Control strategies for mechanical systems with various constraints-control of non-holonomic systems

Investigates control strategies for nonholonomic mechanical systems subject to various constraints. First, for driftless systems which are transformable to chained forms, we compare three existing strategies including a time-state based controller proposed by the authors. They are mainly examined through an application to a well-known wheeled vehicle system; numerical simulations help to see their practical advantages and drawbacks. Secondly, we describe a ball-and-plate problem which is not transformable to chained form and propose a feedback type strategy for it by modifying the time-state-control form based controller. Thirdly, we deal with a control problem of a flying object with non-zero initial angular momentum, which is modeled as state equation with drift term, no configurations of which are equilibria. We also propose a feedback controller via time-varying coordinate transformation by constructing an appropriate problem formulation.

Manipulation problem of a ball between two parallel plates based on time-state control form

This paper deals with the ball-plate problem being considered as an effective model for nonholonomic constraints, and gives simultaneous control method for both the position and orientation of the ball based on the time-state control form.

Optimal control strategy for high jump based on complementarity modeling

This paper proposes an optimal control strategy for a jumping robot system based on the complementarity modeling. We consider a variable constraint jumping system consisting of a robot part and an environment (catapult) part. Such a system can be efficiently modeled as a complementarity system, in the sense that the discontinuous phenomena such as collision or separation are handled in a unified framework. First, we give a simple criterion to judge the contact/taking-off condition based on the complementarity modeling. Next, we formulate an optimal control problem to maximize the peak height in a jump and give a numerical solution; due to the pre-specified input limitation, the resulting control is of bang-bang type. Finally, the optimal controller is analytically reconsidered and is implemented as a switching state feedback law.

Spin fluctuations and magnetic order in the heavy fermion compound CePt2Sn2

We present zero and longitudinal field μ SR measurements of single crystal and polycrystalline specimens of the heavy fermion compound CePt2Sn2. Above 1 K the behaviour of the two samples is indistinguishable; the muon 1/T_1 increases with decreasing temperature until 25 K when it plateaus. The 1/T_1 relaxation rate differs strongly for the two cases below sim,0.8 K. At 0.1 K a rate of about 20 μ s-1 is seen in the polycrystal while in the single crystal it is only about 5 μ s-1. Even more revealing is the fact that longitudinal field decoupling spectra at very low temperatures demonstrate an essentially static spin system to be present in the polycrystalline material while the single crystal shows definite dynamic spin properties. We conclude that, in the presence of the distortion, long range magnetic order occurs below 0.9 K while in tetragonal symmetry long range order is suppressed (probably due to frustration) and spin fluctuations remain for Trightarrow0.

Constrained vertebrate evolution by pleiotropic genes

Despite morphological diversification of chordates over 550 million years of evolution, their shared basic anatomical pattern (or ‘bodyplan’) remains conserved by unknown mechanisms. The developmental hourglass model attributes this to phylum-wide conserved, constrained organogenesis stages that pattern the bodyplan (the phylotype hypothesis); however, there has been no quantitative testing of this idea with a phylum-wide comparison of species. Here, based on data from early-to-late embryonic transcriptomes collected from eight chordates, we suggest that the phylotype hypothesis would be better applied to vertebrates than chordates. Furthermore, we found that vertebrates’ conserved mid-embryonic developmental programmes are intensively recruited to other developmental processes, and the degree of the recruitment positively correlates with their evolutionary conservation and essentiality for normal development. Thus, we propose that the intensively recruited genetic system during vertebrates’ organogenesis period imposed constraints on its diversification through pleiotropic constraints, which ultimately led to the common anatomical pattern observed in vertebrates.Basic anatomical patterns are conserved in chordates. Here, the authors show mid-embryonic conservation during vertebrates’ development and evolutionary constraints introduced by recruitment of mid-embryonic programmes to later stages of development.

Ferromagnetic interaction and superconductivity of CeCu2Si2

We have carefully reinvestigated the superconducting heavy-electron system CeCu2Si2 by preparing very homogeneous polycrystalline samples at many different compositions in the homogeneity range by levitation melting and discovered in the Cu-deficient region a weakly ferromagnetic phase, presumably due to heavy quasiparticles of the Kondo compound. We, in addition, confirmed that the superconducting phase emerges at the fading end of the novel ferromagnetic phase in a very limited region of the phase diagram, which has revealed some salient superconducting properties.

Symmetric Affine Systems with Two-Generators: Topology and Discontinuous Feedback Control

Abstract In this paper, we investigate a discontinuous state feedback control law for a symmetric affine system with two-generators, whose controllability Lie algebra is essentially different from conventional chained(single-generator) structures. At first, we provide a topological principle to design a discontinuous surface to get rid of the nonexistence of continuous stabilizing feedback, with a pair of illustrative examples of single-generator case. Based on this concept and nonlinear controllability analysis, we propose a discontinuous control strategy for a 2-input 5-state two-generator system.