Ryozo Katoh

Robust adaptive motion/force tracking control of uncertain nonholonomic mechanical systems

The position/force tracking control of Lagrangian mechanical systems with classical nonholonomic constraints is addressed in this paper. The main feature of this paper is that 1) control strategy is developed at the dynamic level and can deal with model uncertainties in the mechanical systems; 2) the proposed control law ensures the desired trajectory tracking of the configuration state of the closed-loop system; 3) the tracking error of constraint force is bounded with a controllable bound; and 4) a global asymptotic stability result is obtained in the Lyapunov sense. A detailed numerical example is presented to illustrate the developed method.

Stability analysis of control system having PD type of fuzzy controller

Stability of a control system having PD type of fuzzy controller (a two-input and single-output controller) is analyzed in this paper using Yakubovichs method. In this analysis, the controller is treated as a two-input and two-output controller, and the nonlinearity of the controller is characterized as the sector condition. Absolute stability conditions are derived for the control system as three conditions; two are conditions for either one of control modes, P or D, is independently operating; the third is the condition for two modes are simultaneously active. The former two conditions are nothing but Popovs conditions for two SISO systems. A new graphical method is proposed to solve the latter condition. This method is explained illustratively using an example, and the results obtained are compared numerically with those by other graphical methods as well as simulation results.

Graphical stability analysis of a fuzzy control system

Stability of fuzzy control system is analyzed wherein control system with two inputs and single output is transformed to two inputs and two outputs control system which in turn is transformed to Lure system having a linear plant and nonlinear controller by checking the stability of the linear part of the control system. A new graphical method, which consists of three procedures, has been proposed to analyze the absolute stability of the fuzzy control system. The method is shown correctly using an example, and effect of plant parameters on the stability have also been studied.<<ETX>>

Peg-and-hole task by robot with force sensor: Simulation and experiment

A simple peg-and-hole task using a robot with a force-torque sensor mounted in a wrist was studied. The goal of the research was to test if the insertion can be successfully performed by using only a robot with force feedback and no other special tools. There was no chamfer provided either on the holes edge or on the pegs edge, to preserve geometrical independence of the insertion procedure. Simulations and experiments showed that the insertion is possible if an appropriate insertion procedure with a hybrid position/force controller is used. Conditions for a peg to be jammed in a hole were studied and it was found out that jamming can be avoided when a force control loop reference point is placed at the pegs tip.<<ETX>>

Digital adaptive control of space robot manipulators using transpose of generalized Jacobian matrix

We have proposed a digital control method of space robot manipulators using the transpose of a generalized Jacobian matrix. The trajectory of the end-effector, however, is generally curved, because a desired trajectory is not defined in the control method. Furthermore, the method is based on the supposition that all physical parameters of the robot manipulator are known; therefore, if the end-effector captures an unknown mass object, the physical parameters are changed, and the control performance gets worse. In the paper, setting a desired trajectory and parameter identification are applied to the control method so as to overcome the drawbacks. Computer simulation, where a 3 DOF planar manipulator mounted on a free-floating robot base is selected, is performed. The simulation result demonstrates the effectiveness of the combination of setting the desired trajectory and parameter identification.

Manipulation of a floating object by two space manipulators

This paper deals with manipulation of a floating object by two space robots with manipulators. It is shown in this paper that a total system consisting of two robots and a floating object could be treated as a distributed system, and then a new generalized Jacobian matrix (GJM) is defined. Moreover, it is confirmed that this type of GJM is effective for using adaptive control for decreasing the amount of calculation for the control algorithm.

Adaptive RMRC for cooperative manipulation of a floating object by two free-based space robots

This paper deals with an adaptive resolved motion rate control (RMRC) method for a cooperative manipulation of a floating object by two free-based space robots with manipulators. Discussions as for the adaptive estimation are done on the divided generalized Jacobi matrices, which can be derived by system partition of the whole robot system. The method proposed here has an advantage that control algorithm of each robot is same even if a number of robots increases. The validity of the method was successfully confirmed by computer simulation.

Stability analysis of fuzzy control system applying conventional methods

The authors discuss the stability of a fuzzy control system by applying conventional stability analysis methods. A nonlinear fuzzy controller is characterized by using a sector condition and the resultant system is transformed into a Lure system. A condition of absolute stability is derived for the system and the tracking property is checked for uncertain cases through simulation, by applying conventional stability criteria. Both continuous and discrete systems are considered.<<ETX>>

Experiments on a floating underwater robot with a two-link manipulator

This article concerns experiments with a free-floating underwater robot with a two-dimensional, horizontal planar, two-link manipulator. Some dynamic models of underwater manipulators have been proposed, but only a few experiments have been carried out. Here, we derive a dynamic model for a free-floating underwater robot with a two-link manipulator, including the hydrodynamic forces, and validate the effectiveness of the model by simulation and experiment. We also show an experimental result using a resolved acceleration control method. These experimental results show the effectiveness the model and the control method.

Digital adaptive control of space robot manipulator having input constraints

This paper deals with a digital adaptive control for a manipulator mounted on a space robot. Most control methods are based on the supposition that all physical parameters of the space robot are known. However, if the end-effector catches an unknown object, the physical parameters of the robot are changed. Furthermore, joint actuators of a manipulator generally have input constraints. Even though the end-effector does not catch any objects, if the inputs of the actuators become saturated, the control performance gets worse. In this paper, we propose a digital adaptive control method for a manipulator having input constraints. Experimental results from a Space Manipulator Robot Testbed demonstrate the effectiveness of the proposed method.