Satoru Sakai

Robust Control Systems of a Heavy Material Handling Agricultural Robot: A Case Study for Initial Cost Problem

As a case study for initial cost problem, we realize new manipulation and perception for a heavy material handling agricultural robot with high-cost components reductions, which requires more robust controllers. More precisely, first, we give a new manipulator with a passive joint and a new camera configuration with only one camera. Second, we design robust controllers using gain-scheduling and -synthesis based on some structural properties such as the friction in the presence of uncertainty, nonlinearity, and constraint, while avoiding conservative results by an analytical approach. Finally, we evaluate the validity by experiments in an actual open field, which is the most important part of this paper. The robust controllers reduce the initial cost.

Passivity based control of a class of Hamiltonian systems with nonholonomic constraints

This paper is concerned with state and output feedback stabilization of a class of port-Hamiltonian systems with nonholonomic constraints. First we study canonical forms for port-Hamiltonian systems with nonholonomic constraints. Second, we give a new state feedback stabilization method by using non-smooth Hamiltonian functions via generalized canonical transformations. Third, we propose a dynamic output feedback stabilization method without measuring the velocity based on the corresponding state feedback result. Numerical examples demonstrate the effectiveness of the proposed method.

Design and control of a heavy material handling manipulator for agricultural robots

In this paper, we propose a manipulation system for agricultural robots that handle heavy materials. The structural systems of a mobile platform and a manipulator are selected and designed after proposing new knowledge about agricultural robots. Also, the control systems for these structural systems are designed in the presence of parametric perturbation and uncertainty while avoiding conservative results. The validity of both the structural and control systems is confirmed by conducting watermelon harvesting experiments in an open field. Furthermore, an explicit design procedure is confirmed for both the structural and control systems and three key design tools are clarified.

DYNAMIC OUTPUT FEEDBACK STABILIZATION OF A CLASS OF NONHOLONOMIC HAMILTONIAN SYSTEMS

Abstract This paper is concerned with discontinuous output feedback stabilization of a class of nonholonomic systems in a port-controlled Hamiltonian form. First, in order to obtain a dynamic feedback, an integrator is added to the system via a generalized canonical transformation. Second, we clarify an equivalence between asymptotic stability of a state feedback system and that of the corresponding output feedback system. An output feedback stabilization method is derived based on this equivalence. Furthermore, some numerical examples show the effectiveness of our technique.

Active vision of a heavy material handling agricultural robot using robust control: a case study for initial cost problem

We propose a new active vision of a heavy material handling agricultural robot emphasizing the initial cost. A key point is a new combination of a structure system and a control system, not only one of the two. First, a camera configuration with only one camera is proposed to achieve lower initial cost. This configuration requires more robustness. Second, in order to realize the vision, a robust control system is designed in the presence of uncertainty and constraint. Finally, the validity is confirmed by experiments in an actual open field. The camera configuration can not work well without the designed controllers. That is, the robust controllers reduce the initial cost.

Passivity based control of hydraulic robot arms using natural Casimir functions: Theory and experiments

This paper gives a new passivity based control of hydraulic arms based on a new model using ldquonaturalrdquo Casimir functions. Not only passivity but also Casimir functions are used in the modeling and control as a new structural property. First, we refer port-Hamiltonian systems and their properties. Second, we propose two stabilization methods, a new dynamic asymptotic stabilization method and a new partial stabilization method. Third, we give a new model of hydraulic arms using Casimir functions. Furthermore, the proposed two stabilization methods are applied to this model and finally, the validity of our methods are confirmed by not only numerical simulations but also experiments even thought the bulk modulus is not identified at all.

Port-Hamiltonian approaches to motion generation for mechanical systems

This paper gives new motion generation methods for mechanical port-Hamiltonian systems. First, we propose a generation method based on an asymptotic stabilization method without damping assignment. This asymptotic stabilization method preserves the Hamiltonian structure in the closed-loop system although the controller itself is not a port-Hamiltonian system. Second, we propose another method based on an adaptive asymptotic stabilization method for unknown damping. This adaptive asymptotic stabilizer does not use the value and the sign of the damping at all. Finally, we confirm the effectiveness of our techniques in some numerical simulation.

Global performance of agricultural robots

Global performance of agricultural robots is discussed to design the structure system reasonably. First, problems of the theoretical field capacity are summarized. Then a new macroscopic working environmental model is proposed. Third, the theoretical field capacity is extended to solve the problems based on two fundamental equations of working space and working time. Finally the validity of the extended theoretical field capacity is confirmed by deriving two design guidelines for structure systems of agricultural robots.

Heavy material handling manipulator for agricultural robot

This paper presents a manipulator which is able to handle heavy materials for agricultural applications. The characteristics of agricultural operation are discussed and extracted. As the manipulator for handling heavy materials is analyzed using kinematic indices, the parallel type manipulator is shown to be superior to the other manipulators (i.e. the polar coordinate type, articulated type and cylindrical coordinate type manipulators). A parallel type manipulator has therefore been designed and developed. The robotic harvesting experiment was carried out using the parallel type manipulator in a watermelon field.

A new method for parameter identification for N-DOF hydraulic robots

Parameter identification for N-DOF hydraulic robots (e.g., BigDog, PETMAN and developing automated excavators) is not an old problem at all. Indeed, recent papers still identify difficult parameters (the bulk modulus and the flow gain coefficients) by trial and error. This paper is the first report to solve this problem. First, new structural properties of hydraulic robots are found in comparison with electric robots and then the drawbacks of the conventional methods are discussed. Second, by modifying one of the conventional methods, a scientific method is proposed and applied to an actual hydraulic manipulator. Third, the validity of the proposed method is confirmed by model validation. Remarkably, the difficult parameters are identified very well without any trial and error. The proposed method is applicable to electric robots even on the unknown inclination.