Akio Inaba

On algebraic and graph structural properties of assembly Petri net

Assembly planning is a significant problem for automatic assembling using robotic manipulators. An assembly planning method using a Petri net is presented. The assembly network is modeled by using the Petri net with reference to the conventional and/or net. The state shift equation of the Petri net, which is a mathematical model of the net, is analyzed. From this analysis, it is clarified that the set of a basis solution of a state shift matrix is an actual assembly sequence. When considering an optimization problem which minimizes a summation of a weight value of all tasks included in the assembly sequence, a linear programming (LP) technique can be used. Some numerical examples to certify the validity of the proposed analysis are shown.<<ETX>>

On algebraic and graph structural properties of assembly Petri net - Searching by linear programming

An assembly planning method using Petri nets is presented. First, the assembly network is modeled using the conventional AND/OR net. Second, the state shift equation of the Petri net, which is its mathematical model, is analyzed. This analysis shows that the basis solution the of a state shift matrix is identical to the set of a solution which corresponds to an actual assembly sequence. This means that in considering an optimization problem which minimizes a summation of a weight value of all tasks included in the assembly sequence, a linear programming technique can be used. Some numerical examples are given to certify the validity of the analysis.

Development of a transformational mobile robot to search victims under debris and rubble. 2nd report: improvement of mechanism and interface

Mobile robots are expected to support relief activities, after a great scale disaster. These robots need ability to move on/in rubble in order to collect information related to victims and the conditions. In order to attain this purpose, we proposed a transformational mobile robot (CUBIC-R), which can traverse rubble omni-directional. The robots shape is regular hexahedron and each surface has a crawler unit with a couple of crawlers. As each surface is united by transformational mechanism which has IDOF, it can overcome rough terrains (step, stairs, gap and so on) using transformation. Additionally, it can traverse terrains in the direction of the front, back, left or right without rotating the platform, because its shape is cross-shape. As the robot can traverse terrains in the left or right direction if it can not overcome obstacles in the front or back directions, stuck possibility of the robot may be small. Therefore we consider that CUBIC-R can be operated widely in the stricken-area. However, we found that there were several problems in CUBIC-R, such as the heavy weight, the complexity of the mechanism, the stability of the robot and the difficult robot operation. In this paper, we improve the robot mechanism focused on the operability and develop a fundamental robot/human interface in order to solve the above-mentioned problems.

Learning control of disassembly Petri net-an approach with discrete event system theory

This paper studies the learning control problem of disassembly task sequence. The proposed learning control system has two sub systems. One of them is a supervisory control system which can realize the implicit specifications such as equipment-related or task-independent specifications. The other one is a learning automata system which can realize the explicit specifications such as task-dependent specifications. This approach allows the flexible design to accommodate frequently changing manufacturing requirements. Some simulation results to verify the effectiveness of the proposed system are shown.

Development of a transformational mobile robot to search victims under debris and rubbles

Mobile robots are expected to support relief activities, after a great scale disaster. These robots need ability to move on/in rubble in order to gather information related to victims and conditions. However, there is no mobile robot which has enough movement ability. Mobile robots need big bodies in order to traverse on unstructured terrain composed of big rubbles, but they need small bodies in order to enter in narrow space. In this paper, we proposed novel concept of a transformational mobile robot in order to solve this inconsistency, and manufactured the proposed mechanism and evaluated its fundamental movement ability.

A transformation algorithm from ladder diagram to SFC using temporal logic

Summary form only given. A ladder diagram (LD) has been widely used in industries as a language for sequential controls. However, LD can not represent sequential flows of control logics explicitly. This leads to difficulties in understanding the control logics for other engineering. To overcome this problem, a sequential function chart (SFC) has been proposed. As the SFC can represent the sequential flow explicitly, it is expected to be used more widely. As many know-hows have been required in the LD, it is necessary to develop transformation algorithm from the LD to the SFC. In this paper, a technique to transform the LD to the corresponding SFC by using temporal logic is proposed. In the closed-loop system which consists of the LD and the controlled plant, informations in the sequence including parallel path divergences are extracted to develop the transformation algorithm. An example is shown verify feasibility of the proposed algorithm.

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.

Feasibility of disassembly tasks considering a posture of a subassembly using genetic algorithm

Summary form only given. An automatic generation of assembly or disassembly sequences is a significant problem for assemblies using robot manipulators. We need to judge the feasibility of assembly/disassembly tasks based on geometric information of products. In previous research, only translational motion of a subassembly has been considered. However, there are many cases in which a subassembly can be separated from another subassembly using rotational motion. In this paper, we propose a new algorithm with which we can search a posture of a subassembly to avoid collision with another subassembly. The algorithm is based on the genetic algorithm. The proposed method makes it possible to search a posture of a subassembly to realize assembly/disassembly tasks with small computational amount.

Design recovery for ladder diagram with information of controlled plant

SFC (sequential function chart), which is a graphical tool for control logic and can also represent the order for events to be controlled explicitly, has been presented as a programming language of sequential control. Since even a nonspecialist can understand SFC, it will be the main tool of sequential control. In spite of this excellent characteristic of SFC, ladder diagrams (LD) are still used in various industrial applications. In this paper, we regard LD and controlled plant as one closed loop, and propose the algorithm for picking up order of events based on the closed-loop system. We try to model the plant by means of temporal logic.

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.