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.

An interacting multiple-model (IMM) approach to sensor fault detection and identification (FDI) in the dead reckoning of mobile robots is proposed Changes of sensor normal/failure modes are explicitly modeled as switching from one mode to another in a probabilistic manner; mode probabilities and robot states are estimated via a bank of Kalman filters with mutual interaction. To provide better fault decision, mode probability averaging and heuristic decision-making rule are incorporated into the IMM based algorithm. The proposed FDI algorithm is implemented on our mobile robot. 16 system modes (one normal mode and 15 'hard' sensor-failure modes) of four internal sensors (two wheel-encoders, one steering potentiometer and one yaw-rate gyro) are handled. Experimental results validate that the proposed FDI algorithm allows robust navigation of the robot subject to sensor failures.

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.

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.

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 material's 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.>