In this paper, a force servo for hydraulic robot joints is designed and applied to an inverted pendulum demo. First, the nonlinear nominal model of the hydraulic cylinder is reviewed, and the nominal integrator is introduced. Second, through a partial fusion of our modeling and control techniques, a force servo is designed based on a modification of the nominal integrator as an intermediate stage. Finally, against the non-short hydraulic pipes (1.9 m), the response is improved by the designed force servo in the presence of rotational motion effects.

This paper proposes a non-dimensional representation for hydraulic arms whose original representation is complex in terms of the nonlinear dynamics and many physical parameters. Unlike the usual nondimensional representations, the proposed nondimensional representation preserves a parametric structure in the original representation. Without loss of generality, only by changing the damping constant, the rod area, the source pressure, and the cylinder allocation, and also assuming that all the other parameters are unit, any numerical property such as the numerical existence is investigated efficiently.

For hydraulic robots, modeling of the control flows is a key issue. The conventional modeling methods are based on the Bernoulli equation (i.e., the control flow is a function of the form equation which needs assumption of steady flow. In robotics, since the actual control flow is not always a steady flow, this paper provides a new practical modeling method without the Bernoulli equation. In a word, the proposed modeling method is a systematic version of the industrial modeling in which table representations are accepted and the assumption of steady flow is not needed. First, based on the input-state equation of hydraulic robots, we propose a new matrix representation of control flows via off-line input-output calculations. Second, based on the projection theorem in the matrix space, the optimal table representation is uniquely determined to be implementable. Finally, in comparison with the conventional modeling method with the Bernoulli equation, the effectiveness of the proposed modeling method is confirmed experimentally. The proposed modeling method is applicable to electric robots with complex friction and so on.

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.

This paper presents a fast computation method of hydraulic robot dynamics and shows the effectiveness in design optimization that needs a lot of repetitive simulation. First, an exact simplification of the conventional representation of hydraulic robots with external forces is presented based on the Casimir functions. Second, a further exact simplification is given via an integration by parts of the Hamiltonian function as a structural property and a new representation of the hydraulic robots is proposed. The new representation allows us to define a back fluidmotive force (back-FMF) as a hydraulic version of the well-known back electromotive force (back-EMF). Third, the proposed representation and the conventional representation are compared with each other with respect to computational cost and the effectiveness of the proposed representation is confirmed.

This paper proposes a new impedance control principle for mechanical systems which have driving systems whose control input is not the torque any more. It is shown how to transform such mechanical systems with driving systems into another systems with the desired mechanical impedance. Also it is proved that the proposed principle achieves a robustness in the presence of parameter perturbations. First, we propose a new state space expression of mechanical systems with driving systems based on a natural Casimir function. Second, we propose an impedance control using an artificial Casimir function as well as the natural Casimir function. Third, we analyze a robustness not on the closed-loop stability but on the closed-loop structure. Finally, the validity of the proposed method is confirmed by numerical simulations. Remarkably, the closed-loop system keeps the mechanical impedance structure robustly and thus achieves a robust behavior.

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.

This paper gives a novel pick-and-place hand mechanism without any actuators and sensors. Any payload does not effect to the internal mechanism at all. First we discuss the design guideline and a working principle. Second, we realize and apply the mechanism by combining a mechanical finite four states system and our previously developed passive closure gripper. Third, we analyze and clarify some properties of the hand. Furthermore, we confirm the validity of the developed hand by manipulation experiments.

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.

This paper gives an exact and explicit expression of the structured singular value for robotic manipulators with a passivity based control in port-controlled Hamiltonian form, even though it is not possible to give the exact or explicit structured singular value for general systems. First, we focus on dynamics with endlink mass perturbation after the settling time. Second, we derive the exact and explicit structured singular value for manipulators by using structural properties of the dynamics. The derived structured singular value is nothing but the structured singular value of manipulators without control because the passivity based control preserves the Hamiltonian structure. Furthermore, based on the derived structured singular value, we quantitatively analyze the robust stability of robotic manipulators with the passivity based control

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.

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.

An experimental study is presented on control of a heavy material handling agricultural manipulator using robust control. The harvesting of heavy vegetables and organic compost fertilization requires hard manual labor. For heavy material handling, an agricultural robot was proposed in the first step. And then a control system using LQ control was designed and high-speed manipulation was realized in the second step. In this paper, we designed a control system to achieve robust performance in the presence of uncertainty. The robotic harvesting experiment was done in the watermelon field and the use of robust gain scheduling and /spl mu/-synthesis was confirmed.

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.

For heavy material handling, we first propose an agricultural robot which consists of a 4-DOF underactuated manipulator, a crawler vehicle, and a passive hand in the first step. Then, we discuss the use of LQ control for high speed manipulation. We design a control system based on the characteristics of agricultural operations and the manipulator. The robust stability is analyzed under the structured uncertainty. The robotic harvesting experiment was done in a watermelon field and the effectiveness of LQ control was confirmed.