Fuminori Oba

Dynamic control approach for motion coordination of multiple wheeled mobile robots transporting a single object

This paper proposes a coordinate dynamic control method for the transfer of a common heavy object by several wheeled mobile robots. The coupler, which comprises an active prismatic link and a passive rotary joint, is installed on each robot so that even an ordinary nonholomonic mobile robot with inferior mobility can correctly manipulate the object. A hierarchical coordinative control system composed of a leader and other staff robots is designed to synchronously control the motions of the robots under severe dynamic interactions. The leader robot successively defines the desired motion of the object along its reference trajectory and broadcasts the information to the staff robots. Each staff robot controls the motions of its own body and the onboard prismatic link so as to achieve the desired object behavior without sideways slippages. When the prismatic link approaches the limit for its movement, the staff robot requests the leader to temporarily modify the desired behavior of the object. The control algorithm is formulated on the basis of the kinematics and the dynamics of the wheeled mobile robot. Simulation results illustrate the validity of the method.

A multi-model based fault detection and diagnosis of internal sensors for mobile robot

A multi-model based approach to fault detection and diagnosis (FDD) of internal sensor for mobile robot is proposed. Three failure modes (hard failure mode, noise failure mode, and scale failure mode) of the sensor are handled; on the hard failure the sensor output is stuck at a constant value. The noise failure causes the sensor output with large noise. On the scale failure the gain (scale) of the sensor output differs from the normal. The detection and diagnosis of the hard/noise failure (HNFDD) is based on the variable structure interacting multiple-model (VSIMM) estimator; changes of the failure modes are modeled as switching from one mode to another in a probabilistic manner. The mode probabilities, which are estimated based on a bank of Kalman filters, provide the fault decision. The detection and diagnosis of the scale failure (SFDD) is achieved via single-model based Kalman filters, each of which is based on a model matching to a failure mode of particular sensors; the fault decision is made by comparing the model conditional estimates in the sensor gain. The proposed FDD algorithm is implemented on our skid-steered mobile robot with five internal sensors (four wheel-encoders and one yaw-rate gyro). Experimental results show the property of the FDD algorithm.

Computer-aided redesign for improving recyclability

This paper presents a software tool assisting designers in redesigning products for improving recyclability. Taking a 3D-model of a mechanical product as input, this tool generates a disassembly sequence of the product automatically. Using the disassembly sequence, the tool generates some suggestions for improving the recyclability and gives them to the designer. The suggestions include: changing the materials of parts, integrating some parts into one part: changing some fixing methods, and reducing some parts used for fixing some other parts. The suggestions bring about the reduction of disassembly time as well as the improvement in the occupancy rate of recyclable materials. If the designer accepts the suggestions, the tool modifies the model according to the suggestions. An electric drill has been used to experiment with the tool.

Trajectory generation and tracking control methods for a multiple transfer robots system

This paper proposes trajectory generation and tracking control methods for the advanced transportation system METROS (Multiple Transfer Robots System). The methods enable several transfer robots to transfer materials cooperatively in an automated factory. The materials reference trajectory guaranteeing smooth motions of robots is represented by simple combinations of line trajectories with constant velocity profiles and transition ones with 8th order polynomials. In order to transfer the material stably along the reference trajectory, a cooperative control architecture which consists of a master robot and slave ones is introduced. The master robot determines a behavior of the material for the specified reference trajectory, and thereafter distributes the forces required to realize the desired behavior to the slaves. Each slave robot generates its own trajectory and controls the speed and steering so as to exert the force commanded by the master robot. An impedance model is defined to determine the behavior of the material so that the material can behave as a desired mass-spring-dashpot system. The simulation results justify both the proposed methods.<<ETX>>

Object-transportation control by multiple wheeled vehicle-planar Cartesian manipulator systems

This paper proposes a control scheme to transport a palletized load by several wheeled vehicles (automated guided vehicles in factory). The planar Cartesian manipulator with two-degrees-of-freedom prismatic joint and one-degree-of-freedom rotary joint is mounted on each vehicle so that the vehicle with nonholonomic constraint and slow dynamic response can dexterously manipulate the pallet. Each vehicle-manipulator system independently controls the acceleration of its own hand grasping the pallet based on the prescribed mechanical impedance model. The kinematical redundancy of the vehicle-manipulator system is exploited to keep the manipulator arm within its workspace while executing the hand desired acceleration faithfully. The simulation result for the object-transportation by four vehicle-manipulator systems illustrates the validity of the proposed control scheme.

Assembly partitioning by genetic algorithm for generating assembly sequences efficiently

This paper describes a method for identifying a subassembly or part to be removed from an assembly in order to generate an assembly sequence efficiently. In this method, the assembly is represented as a graph, and some cut sets of the graph are calculated by using heuristics and a genetic algorithm. Each of the calculated cut sets partitions the graph into two subgraphs, one of which expresses the subassembly or part to be removed.

Life cycle profitability analysis and LCA by simulating material and money flows

The authors propose a simulation-based approach to the evaluation of a products life cycle including recycling and reuse from the viewpoints of not only environmental impact but also the profitability of every companys business related to the life cycle. The flow of the material and money among the companies concerned with the life cycle are modeled and simulated. The simulation reveals whether each of the companies obtains a profit and how strong the environmental impact is. The simulation also shows the change in the environmental impact and profit with the passage of time. The modeling and simulation for a copier drum is presented as a validation example.

Path tracking control of a non-holonomic modular omnidirectional vehicle

This paper proposes a method for controlling a non-holonomic omnidirectional vehicle. We modularize wheel units assembled in the vehicle to easily tailor the vehicle to individual transfer applications. A controller consisting of deck-module and wheel-module controllers is designed to coordinate wheel modules and to ensure correct vehicle motion. The deck-module controller decides the desired vehicle motion based on the Ackerman geometry to track the reference path of the vehicle, while each wheel-module controller controlling the wheel motion to produce the desired vehicle motion defined by the deck-module controller. To reduce wheel slip caused by control errors in wheel modules, we design two types of wheel modules: active and passive. The active wheel module produces the desired vehicle motion, and the passive wheel module corrects its own velocity to mimic caster behavior. Simulation and experiments confirmed the effectiveness of the proposed path tracking control.

Mathematical model of reusability

Recently the reuse of products or their components has been recognized as an effective way to reduce solid waste and to conserve natural resources. To decide whether a product or its component should be reused or not, we need to evaluate its reusability adequately. In this paper, as a criterion for the evaluation, the authors define and model the reusabilities of a product and its component, based on reliability theory. The authors define the reusability of a component as a probability that a product having been used for a time period ends its life but a component included in it is reusable. Based on the definition, the authors develop a mathematical model of reusability, which is a function of use time. The authors made several graphs of the mathematical model, with changing values for parameters such as shape parameter of the Weibull distribution. As a result, it is found that the reusability of a component does not always decrease as the use time is lengthened. This is interesting because it goes against the general impression that the reusability decreases as the use time is lengthened. Next, the authors define and model the reusabilities of a product and a unit. The authors believe that the models of reusabilities are useful for deciding whether a product or its component should be reused or not and the models may be used for production management for reuse and remanufacturing.

Disassembly/assembly path search reusing solutions

It is important to generate and evaluate disassembly paths in product design stages for reducing the recycling and repairing costs of products. This paper proposes a method for generating the disassembly paths automatically by using CAD data. The method is efficient especially to generate the disassembly paths of the design objects got by modifying the original ones whose disassembly paths have been generated before. In the method, the disassembly paths of such modified design objects are generated efficiently by using those of the original ones. Based on the method, the authors developed a software tool integrated with a CAD system and performed an experiment using the tool.