Shigeru Okuma

Realization of skill controllers for manipulation of deformable objects based on hybrid automata

The requirement of handling deformable objects such as leather, paper and rubber is growing. Since it is very difficult to make a physical model of them, the design of a controller to manipulate them becomes one of the significant problems in the field of robotics. If we look at the operation of a human worker, the deformable objects seem to be handled naturally and smoothly. The paper presents a method to design a controller for assembly tasks which involves the manipulation of deformable objects. The proposed method extracts the dynamics that human workers used in executing the demonstrated task, and embeds that in an event driven hybrid controller. In our control system, an event observer estimates the change of task state based on force and visual information like human workers, and switches the dynamics appropriately according to the task state. The proposed method is applied to a hose insertion task by implementing it in an industrial robot controller.

FMS scheduling based on timed Petri net model and RTA* algorithm

Presents a scheduling method for a manufacturing system based on a timed Petri net model and a reactive fast search algorithm. The following two typical problems are addressed in the paper. (1) Minimize the maximum completion time. (2) Minimize the total deadline over-time. As for problem (1), a search algorithm which combines RTA* and a rule-based supervisor is proposed. Since both RTA* and the rule-based supervisor can be executed in a reactive manner, machines and AGVs allocations can be scheduled reactively, and simultaneously. As for problem (2), the original Petri net model is converted to its reverse model and the algorithm developed in problem (1) is applied with regard to the due time as a starting time in the reverse model.

Line following control of two wheeled vehicle by symbolic controller

Hybrid dynamical systems (HDS), which contain both discrete logical symbol and continuous signal, are attracting great attention in the field of system control. In this paper, a new symbol based control strategy for a line following control of a two wheeled vehicle is proposed. The vehicle is supposed to have a low-resolution sensor and actuator. The control requirement, however, is specified so as to keep the vehicle as close as possible to the center of the line. The controllability and observability issues are investigated, and a concrete control policy based on the continuous state estimation is proposed. Experimental result is shown to demonstrate the usefulness of our idea.

Indirect adaptive control of two wheeled vehicle by quantized input and output

Hybrid Dynamical Systems (HDS), which contain both discrete logical symbol and continuous signal, are attracting great attention in the field of system control. In this paper, we deal with the control problem in which the continuous plant is controlled by the discrete logic-based controller, while the control requirements are specified for continuous variables. A new indirect adaptive control strategy for a line following control of a two wheeled vehicle with quantized input and output is proposed. The vehicle is supposed to have a low-resolution sensor and actuator. The control requirement, however, is specified so as to keep the vehicle as close as possible to the center of the line. Firstly, the controllability and observability issues are investigated. Secondly, it is shown that some unknown parameters of the system can be estimated from quantized input and output by making use of partial information on the system. Thirdly, an indirect adaptive control policy based on simultaneous estimation of continuous state and parameters is proposed.

Realization of fault tolerant manufacturing system and its scheduling based on hierarchical Petri net modeling

This paper presents a new hierarchical scheduling method for a large-scale production system based on a hierarchical Petri net model, which consists of FOHPN and TPN. The automobile production system equipped with 2 stand-by lines is focused as one of a typical large-scale system and these stand-by lines are controlled by binary signal. In a high level, the FOHPN model is used to represent continuous flow in production of an entire system, and MLD description is used to control the net dynamics of FOHPN. Also in a low level, TPN is used to represent production environment of each sub-line in a decentralized manner, and MCT algorithm is applied to find a feasible semi-optimal process sequences for each sub-line.

Optimal motion planning of peg-in-hole task based on mixed logical dynamical system theory

The assembly skill can be regarded as one of the hybrid dynamical systems since the interactive dynamics between an end-effector and an environment varies according to the contact configurations (physical constraints). This paper, firstly, tries to make a model of the assembly skill based on the theory of a mixed logical dynamical system (MLDS), which includes both physical (continuous) dynamics and logical switching. The optimal control problem for standard MLDS can usually be formulated as a mixed integer quadratic programming (MIQP) problem, therefore an optimal sequence of both continuous and logical variables can be found simultaneously by solving MIQP. In case of assembly skill, however, the resulting MLDS includes nonlinear constraints unlike the standard MLDS. This implies that the MLDS based optimal control problem for assembly skill leads to mixed integer nonlinear programming (MINLP). It is also well-known that finding the solution for MINLP is much harder than that for MIQP. Therefore, secondly, this paper presents some ideas to find the optimal solution for assembly skill with less computation. Finally, some simulation results on peg-in-hole task are shown to verify the usefulness of our idea.

Indirect adaptive control of two wheeled vehicle by symbolic controller

Hybrid dynamical systems (HDS), which contain both discrete logical symbol and continuous signal, are attracting great attention in the field of system control. In this paper, we deal with the control problem in which the continuous plant is controlled by the discrete logic-based controller, while the control requirements are specified for continuous variables. A new symbol based indirect adaptive control strategy for a line following control of a two wheeled vehicle is proposed. The vehicle is supposed to have a low-resolution sensor and actuator. The control requirement, however, is specified so as to keep the vehicle as close as possible to the center of the line. Firstly, the controllability and observability issues are investigated. Secondly, it is shown that some unknown parameters of the system can be estimated from symbolized input and output by making use of partial information on the system. Thirdly, an indirect adaptive control policy based on simultaneous estimation of continuous state and parameters is proposed. Some experimental results are also shown to demonstrate the usefulness of our idea.

Hierarchical memory structure for the real-time search for action acquisition of an autonomous mobile robot

This paper proposes a new memory structure for the real-time search with the computational resource boundary. In the proposed memory, each memory is hierarchically stored based an the frequency recall. Moreover, the number of checked memories is varied based on the available computational resource for the action acquisition in order to treat the trade-off between the computational amount for the memory retrieval and the one of the search. When the search system utilises stored memories, the one with the highest frequency of recall is started checking from. This makes the efficient retrieval possible even if the available computational resource for the memory retrieval is not enough. In this paper, the proposed method is applied to the action acquisition for autonomous mobile robots in the moving obstacles avoidance problem. Its usefulness is shown through some experimental results and the verification.

FMS scheduling based on Petri net model

Presents a scheduling method for a manufacturing system based on a timed Petri net model and a reactive fast search algorithm. The following two typical problems are addressed in the paper. (1) Minimize the maximum completion time. (2) Minimize the total deadline over-time. As for problem (1), a search algorithm which combines RTA* and a rule-based supervisor is proposed. Since both RTA* and the rule-based supervisor can be executed in a reactive manner, machines and AGVs allocations can be scheduled reactively, and simultaneously. As for problem (2), the original Petri net model is converted to its reverse model and the algorithm developed in problem (1) is applied with regard to the due time as a starting time in the reverse model.

Design of controller switching scenario for reusable launch vehicle with elevon jamming failure

When Reusable Launch Vehicles (RLV) return to earth, it flies just by gliding without thrust. In this phase, one of the most likely and important faults to occur in the airframe is a jamming of the elevon. To tolerate this failure, the flight control system must keep stability and performance during such a failure. One of the effective ways to overcome this problem is to switch the controllers based on the information of the detected failure in the plant. Generally speaking, the controller must have integrators so as to yield the zero steady-state error for the controlled output even if there exist some perturbations in the plant dynamics. In this paper, the design of controller switching scenario is addressed especially focusing on the decision of the controller state at the instant of switching the controllers with integrator. Then, the proposed switching scenario is applied to the control of ALFLEX (Automatic Landing Flight EXperiment), which is the automatic landing experimental vehicle being developed for RLV, considering the occurrence of the jamming fault. Some simulations are shown to verify the usefulness of the proposed idea.