WO2001004741A9

WO2001004741A9 - Automated work in process management system and method

Info

Publication number: WO2001004741A9
Application number: PCT/US2000/018781
Authority: WO
Inventors: Adrian L Pyke; Warren J Clement; George W Horn
Original assignee: Middlesex General Ind Inc
Priority date: 1999-07-09
Filing date: 2000-07-10
Publication date: 2002-05-02
Also published as: WO2001004741A1; AU6082700A

Abstract

A transport network control and method for a Work In Process (WIP) distribution system, such as a conveyer (52) or vehicle network(11). Carriers (50) are destined for logical process steps, rather than physical locations. Tools or tool operators broadcast active pulls or requests to the WIP distribution system, indicating which process steps each tool is currently able to process. Carriers (50) circulating in the transport network (25) are distributed to tools currently broadcasting the appropriate process step (6). An automated Work In Process distribution system is implemented through a distributed control architecture either physically distributed or distributed within a centralized computer (40, 24) such that each WIP object (26) in the system is autonomous and able to execute an independent software program. Each WIP object has the freedom to make decisions, based upon real time system status, contingent upon internal program conditions, buffer or tool status etc., will determine the travel path (54), storage, and delivery location. Inlcuded is a statistical distribution of independent decisions with recursive WIP flow.

Description

AUTOMATED WORK IN PROCESS MANAGEMENT SYSTEM AND METHOD

FIELD OF THE INVENTION

This invention relates generally to manuf cturing work in process management systems, such as a conveyor or vehicle network, and more particularly to work in process traffic handling and routing through a series of process steps in a transport and storage system for bringing workpieces to tools.

BACKGROUND OF THE INVENTION

In current state of the art Work in Process (WIP) management systems, if carriers are in transport, then they are typically destined for a particular location. The destination location may be, for example, a particular process tool or a storage location. In a WIP management system, a control system is required in order to control the flow of traffic and the routing and storage of carriers through the system. A central controller, or sometimes many distributed controllers are used to implement this type of system. Generally, in more complicated systems requiring WIP tracking and routing of carriers, an identifier (ID) exists for each carrier (sometimes this ID is also written on the carrier, in the form of a bar code, or RF tag, or through other means) . Based on this ID (which may also indicate the desired destination) the transport controller routes the carrier through the network in order to reach the desired destination.

It remains desirable to have a more flexible automated WIP system and method.

It is an object of the present invention to provide a method and apparatus to route carriers according to next process step rather than to a particular location.

SUMMARY OF THE INVENTION

The problems of managing Work in Process are solved by the present invention of an automated Work in Process system and method. In a transport network control system, a carrier is destined for a process step, not a particular physical location. The operators (or tools) distributed around the factory keep the WIP management system updated in a dynamic fashion as to which tools are available (by requesting carriers, also referred to as pulling) for particular process steps. In this way, a carrier may be in transport and the final destination is not known until it is delivered to a tool handling the next scheduled process step. According to system rules, the carrier may be delivered to any tool currently subscribing to its process step. Operators managing process tools must inform the WIP management system only as to which tool may currently perform each process step (as this may change rapidly or frequently in certain factories) and carriers of the correct type will automatically be delivered to these tools. Similarly, operators (or tools) sending carriers need not send (or push) the carrier to a particular location, but rather just return the carrier to the WIP management system. The WIP system determines the next process step, and the carrier becomes destined to any tool subscribing to that process step.

For many factories to run efficiently, it has become desirable that process tools be flexible enough to perform many types of process steps with only minor reconfiguration. This invention provides a control method which helps operators or tools determine when a process changeover should take place and manages the current WIP objects in the factory to be available at the correct process tools at the correct time . This improves the overall tool utilization and efficiency of the factory.

In the present invention, the carrier (or WIP object) is given the autonomy and intelligence to make these routing decisions on its own, and the transport hardware is responsible only for providing status to the carrier and executing the carrier's decisions. In this method, there is a potentially unique software program for each carrier in the system, which together with status information provided by the transport system, such as traffic conditions, buffer or tool status etc., will determine the travel path, potential storage, and ultimate delivery location of the carrier. This carrier program may include only enough information to direct the carrier to the next destination (such as a tool) , or it may include enough information to bring the carrier through many destinations as value is added to the work piece through the manufacturing process (such as a complete process step sequence for manufacturing) . Through the use of this invention the statistical distribution of independent decisions allows a higher efficiency to be achieved in equipment utilization, especially in the environment of recursive WIP flow. This methodology is an economic advantage in manufacturing. The present invention together with the above and other advantages may best be understood from the following detailed description of the embodiments of the invention illustrated in the drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a block diagram of a complex conveyor network;

Figure 2 is a block diagram of a first embodiment of the control system according to principles of the invention;

Figure 3 is an operator screen according to principles of the invention;

Figure 4 is a controller network according to principles of the invention; Figure 5 is a side view of a conveyor in a first embodiment of an autonomous WIP system according to principles of the present invention;

Figure. 6 is a side view of a conveyor in a second embodiment of an autonomous WIP system according to principles of the present invention;

Figure 7 is a side view of a conveyor in a third embodiment of an autonomous WIP system according to principles of the present invention; and, Figure 8 is a side view of a conveyor in a fourth embodiment of an autonomous WIP system according to principles of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 is a block diagram of an exemplary complex conveyor network. The conveyor network 11 has a plurality of conveyor loops 12, 13, 14, 15, 16, each having a plurality of tools, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. A cross conveyor loop 17 carries items between conveyor loops . The figure shows tools placed around only one loop for convenience. The network shown here is merely exemplary. The invention may be practiced on other conveyor networks . An item in the conveyor network can travel from any tool in the network to any other tool in the network.

The present invention has two major components. The first component is a system and method of defining process tool capability (pull requests) and the second is a method of delivering to such groups of tools that subscribe to a given process step.

In the first component, where tool pulls are defined, there are two possible implementations. First, pull information may be provided through an automatic communication between the tool controller, or some other controller, and the WIP management controller.

Alternatively, an operator using a computer screen that is dedicated to each tool may provide this information. The computer screen will not only allow the operator to select which process steps are currently requested by a particular tool, but the screen will also display status information to the operator, such as the number of carriers in the system destined for each process step, in order to help the operator decide when to change their tool to a new process step. The second component is best implemented through the use of the autonomous WIP system and method described below in conjunction with Figure 5 through 8. In this component, a software process exists for each carrier in the system, and this software process may be updated dynamically as tools change their active pull requests. The software process provides the rules and logic used to select from the many tools currently pulling, which particular tool to deliver to. Additionally, the software process may provide other logic such as where to buffer if there are no tools currently available, or how to resolve priorities among carriers competing for the tools etc.

Alternatively, the second component may be implemented with any number of standard control technologies, including distributed control without intelligent WIP, or centralized control .

Figure 2 is a block diagram of a first embodiment of the transport network control system of the present invention. Figure 2 shows a plurality of tools T. 20, T₂ 21, T₃ 22, T_n 23 connected to a conveyor control computer 24 over a factory network 25. Each of these tools contains a tool control computer 26 which is able to communicate via the factory network 25 to the conveyer control computer 24. In this embodiment, each tool control computer communicates to the conveyer control computer the types of processes that can be performed by that particular tool. The conveyer control computer accumulates this information into a tabular database as shown below:

Table 1

As carriers are entered into the conveyer system from any location, a "next process step" ID is assigned to the carrier. In order to direct the carrier to the correct location, the conveyer control computer reorders the above table in order of process steps as :

Table 2

From Table 2 , the conveyer control computer is able to determine that a carrier needing process_step_123 may be directed to Tl or T3. The carrier is sent in the direction of these tools, and when a decision must be made between Tl and T3 , a defined set of rules is applied (such as tool with the emptiest buffer, closest tool, load sharing percentages etc.) and the carrier becomes destined for a particular tool. In the meantime, during the travel of this carrier, if an additional tool is brought on line that is able to handle process_step_123 , then the definition of this group is extended to include the new tool . The carrier may then be routed to the newly added tool, according to the defined rules of the defined tool group. Likewise, if a particular tool is removed from the group because the tool is no longer able to perform the process step, then the carrier will be delivered to one of the other tools in the group.

In a second embodiment of the present invention, the tools are not able to communicate directly to the conveyer controller. In this embodiment, a terminal is located near the tool that is used by the tool operator to define to the conveyer system the process capabilities of the tool. Figure 3 shows a sample operator screen for this function. In this embodiment, not only is the operator able to inform the conveyer system of tool process capabilities, but also the conveyer system is able to provide information to the operator which helps the operator decide when to change over tools to a new process step. In a third embodiment of the present invention, autonomous WIP is used. Autonomous WIP is described below in conjunction with Figures 5 through 8. In this third embodiment, a software process is created for a each carrier at the start of the carrier's journey. This software process travels with the carrier in the distributed control network of the conveyer network. Alternatively, the software process travels with the virtual carrier in a centralized implementation of a distributed control network. In this embodiment, the logic in the software process has knowledge of the group definitions (which tools may perform which process steps) and applies potentially carrier specific rules for determining which particular tool to seek and by which conveyer path. This software process is updated as the tool groups are redefined.

A fourth embodiment of the present invention takes the third embodiment of the invention and adds the operator screen of the second embodiment to replace direct communications between the tools and the conveyer network. A fifth embodiment is shown in Figure 4. This embodiment of the invention may be the same as the first or the third embodiments with the additional element that the tools are all connected to a factory controller 40 and the factory controller is connected to the conveyer controller 42 in order to communicate tool status and process capability to the conveyor hardware 44 or to any other output including operator terminals .

The autonomous WIP portion of the present invention is now described. There are four embodiments of autonomous WIP.

Figure 5 is a side view of a conveyor in a first embodiment of the autonomous WIP system according to principles of the invention. A carrier 50 is moved along the conveyor 52 which is part of a conveyor network. A peer to peer conveyor communications network 54 connects to conveyor controllers 56 distributed through the conveyor network. The conveyor controllers control conveyor motors 58 that operate on the conveyor to move the carrier. Sensors 60 in the conveyor system detect the progression of the carrier. The communications network transmits status of buffers, tool status and other conveyor data throughout the system. In the first embodiment of autonomous WIP, the carrier 50 has a microcontroller 64 or other type of processor. The microcontroller communicates with the local conveyor controller in order to read system status and transmit commands for the required actions to the conveyor hardware . The microcontroller 64 has local battery power, and also an RF (radio frequency) or IR (Infrared) communications link to the conveyer controllers by way of an antenna 62 on the conveyor. The software in the carrier microcontroller, also referred to as the carrier microcontroller 64, is specific to that particular carrier and is placed in the carrier when the carrier started its journey in the transport system. This software includes the process requirements of the carrier, also referred to as the WIP object. The process requirements include which types of tools are needed to process this carrier and in which order. The software also includes the conveyer layout, and locations of tools able to perform the process steps required by the carrier. The carrier controller communicates with the conveyer controllers over the conveyer communications network in order to determine which tool is capable of performing the next process step and which tool is best to seek (based on rules programmed into the carrier microcontroller such as emptiest buffer, closest tool etc.) and so which direction the carrier should move at each conveyer intersection. This decision is communicated to the conveyer controller and is implemented by the conveyer controllers . The conveyer controllers are responsible then for accumulating and communicating conveyer status and for exercising the hardware (such as motors etc.) in order to execute the demands of the carrier microcontroller. The carrier microcontroller is responsible for requesting the appropriate status information from the conveyer controller network, and making routing and delivery decisions for the carrier.

Figure 6 is a side view of a conveyor in a second embodiment of the autonomous WIP system according to principles of the invention. In the second embodiment of autonomous WIP, the carrier has an electronic tag 80 which is not a microprocessor. A tag memory in the tag holds a program that has the process steps for the carrier. The conveyor has a wireless reader/writer 82 in the controller 56 which reads the program from the tag. The controller processes the program and decides which tool station to send the carrier. If the controller has to change the program, it writes the new program to the tag. The memory or tag stores the WIP software, but the software is loaded into a portion of the conveyer controller for execution on the conveyer controller's microcontroller. The logic is otherwise the same as that described in embodiment one .

Figure 7 is a side view of a conveyor in a third embodiment of the autonomous WIP system according to principles of the invention. In the third embodiment, the carrier has no microcontroller or tag. Instead, as the carrier moves through the conveyor network, the program for the carrier is transmitted from one microcontroller to the next microcontroller that are distributed throughout the conveyor system. Each microcontroller in the conveyor network is capable of determining system status, executing the received carrier program, and communicating the proper actions to the conveyor hardware.

In the third embodiment, only a unique ID 90 exists on the physical carrier. In this case, the WIP microcontroller software is stored in the local memory 92 of the conveyer controller holding that WIP object (i.e. the carrier) . The software is executed on the conveyer microcontroller independently of the conveyer control software just as in the second embodiment of autonomous WIP, and the logic remains the same. Once the carrier is moved to another zone (controlled by a different conveyer controller) the WIP software is moved via the conveyer communications network 54 along with the carrier to the next conveyer controller.

Figure 8 is a side view of a conveyor in a fourth embodiment of the autonomous WIP system according to principles of- the invention. As in the third embodiment, each carrier has a tag 90. In this embodiment, however, the controlling software 102 resides in a central controller 104 rather than as distributed processes in the controller network. An independent, asynchronous process 106 executes for each carrier in the system. The process receives the status information (e.g. buffer status, tool status, etc.) from the conveyor system, and sends commands to the conveyor system about where to send the carrier.

It is to be understood that the above-described embodiments are simply illustrative of the principles of the invention. Various and other modifications and changes may be made by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof .

Claims

What is claimed is :

1. A transport network control system, comprising: means for defining a carrier destination by a next process step for said carrier; and configurable means for mapping said next process step to a physical location in the transport network control system.

2. The system of Claim 1, wherein said means for mapping is reconfigured by communications from a tool connected to said transport network control system.

3. The system of Claim 1 wherein said means for mapping is reconfigured by communications from one of a plurality of microcontrollers distributed throughout said transport network control system.

4. The system of Claim 1 wherein said means for mapping is reconfigured by input from an operator terminal .

5. The system of Claim 1 wherein said next process step may be performed in one of a plurality of physical locations and said means for mapping maps said next process step to one of said plurality of physical locations.

6. The system of Claim 1 wherein said physical location may perform more than one process step.

7. A transport network control system, comprising: a plurality of controllers controlling a conveyor network; a communications network connecting said plurality of controllers, said communications network providing a status of the transport network to each said plurality of controllers; and means for a carrier to determine its next destination in response to a carrier process and said status of the transport network.