Automated production dispatch system with feedback control

A conceptual decision analysis tool for production dispatch process is used to evaluate alternatives during a production process and generate an optimum path to follow after a process disruption at a given production center in order to maintain the promised due date. The objective is not only to decide on a dispatch rule to be followed for an order under progress at a given work center in the event of a disruption, but also to re-analyze dispatch rules for existing orders waiting in line to be processed at that work center. In the event of production stoppage or disruption, this system analyzes the revised sequence for orders in progress as well as passes the recommended results to a planning system so that this information can be used to re-plan the release sequence of orders waiting for release. This provides a feedback control mechanism and an element of artificial intelligence.

CROSS REFERENCE TO RELATED APPLICATION 
The subject matter of this application is related to that of my copending 
application Ser. No. 07/127,334 filed Dec. 1, 1987, for "Automated 
Production Release System", which is assigned to a common assignee 
herewith. The disclosure of application Ser. No. 07/127,334 is 
incorporated herein by reference. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to a computer based production 
dispatch system on the manufacturing shop floor and, more particularly, to 
a system which automatically interfaces a production dispatch tool to a 
production planning system to provide an integrated approach to a 
manufacturing softward design. The invention provides an easy to use, user 
friendly interface for the shop foreman to dispatch orders in the most 
efficient way in the event of production stoppage at any point in the 
manufacturing process. This invention deals with released orders that have 
to be dispatched, whereas the invention of application Ser. No. 07/127,334 
deals with the issue of planning and releasing orders prior to actual 
release. 
2. Description of the Prior Art 
The process of designing, developing and manufacturing a new product, or 
making major changes to existing products, presents many challenges to 
product managers and manufacturing managers to bring a product to market 
for the least cost, within schedule while maintaining product quality. In 
today's highly competitive industries, product managers and manufacturing 
managers require information to address many problems that arise because 
of the complexity of new products and the complexity of world-wide 
production and the changing nature of competition. The requirement that 
products be manufactured in as short a period as possible while 
maintaining a low level of inventory on the shop floor to meet customer 
needs presents conflicting criteria to be analyzed in order to make timely 
decisions. 
Many authors have written books in the field of production management. For 
example, Joseph Orlicky wrote Material Requirements Planning, published by 
McGraw-Hill, which has become the industry standard reference for almost 
all job shop planning requirements. This concept of planning and releasing 
work to the manufacturing shop floor is well accepted and, even today, 
many vendors are selling software based on the concept. From a dispatching 
point of view, this system takes into account only the general concept of 
a first in, first out (FIFO) basis of dispatching. As mentioned in my 
copending application Ser. No. 07/127,334, D. T. Phillips and G. L. Hogg 
published a paper entitled "A State-of-the-Art Survey of Dispatching Rules 
for Manufacturing Job Shop Operation", International Journal of Production 
Research, vol. 20, no. 1, (1982) pp. 27-45, which provides varying 
dispatching rules that can be used in a planning process. IBM Corp. has a 
product called "Capacity Planning and Operation Sequencing System 
(CAPOSS)", described in Education Guide No. SR19-5004-0, that provides 
static dispatching functions in the form of deciding the next operation to 
be performed for an order after completion of a prior operation. This 
product provides the capability to change a dispatching process that is 
pre-assigned to another process. The limitation with this approach is that 
the system does not analyze the impact of a change to another operation. 
The system just provides the capability to change the operation and does 
not analyze the operational dynamics of one order affecting another in the 
downstream process. What is needed is an expert system that is simple to 
use and is user friendly to anaylze the dispatch decisions to be made and 
recommends the alternatives based on a given criteria; e.g., reduce the 
number of late orders or maximize throughput. 
Expert systems are a branch of computer science, generally referred to as 
artificial intelligence, which exhibits characteristics normally 
associated with human behavior including learning, reasoning, solving 
problems and so forth. More specifically, an expert system or "knowledge 
based" system uses certain rules and a database to provide a user 
interactive environment in the form of a "consultation dialog", just as 
the user would interact with a human expert. 
SUMMARY OF THE INVENTION 
It is therefore an object of this invention to provide an easy to use 
system that takes a planned release of shop floor orders and, in the event 
of a production disruption, re-analyzes the planned release and recommends 
alternative dispatch rules based on current conditions. 
It is another object of the invention to provide a system that prompts the 
production planner to alternate decision capabilities through graphic 
displays. 
The automated production release system disclosed in my copending 
application Ser. No. 07/127,334 uses a set of order release and dispatch 
rules to meet certain management criteria of increased throughout, reduced 
cycle time and reduced work-in-process inventory and recommends a set of 
order release sequences to the manufacturing floor prior to actual 
release. The system according to the present invention is used after 
orders are released and production disruption is encountered on the shop 
floor. The key management criteria at such time would be to make sure 
orders are not late or, in the alternative, to minimize the tardiness of 
orders and reduce the manufacturing cycle time. Most of the material 
bought for the manufacturing process would already be on the shop floor. 
The system based on this invention analyzes current dispatch rules, using 
a simulation process, to determine if those rules will satisfy the 
management criteria of reducing cycle time and minimizing tardiness of 
shop orders. Based on the priority settings of orders, the system 
recommends the rule to be used. When such decisions have to be made and 
action taken, the information needs to be passed to the planning system so 
that the current status of the floor is used for future release of orders 
to the manufacturing floor. 
The subject invention builds on the foundation of the automated production 
release system of my copending patent application Ser. No. 07/127,334, 
although the invention can be implemented and practiced independently. As 
mentioned above, this invention aims primarily at developing revised 
dispatch rules to be followed and the associated sequence of operations to 
be followed after a production disruption on the shop floor which causes 
re-analysis of the dispatching system. The approach taken by the invention 
is repeated interactively and forms what may be characterized as a 
"bottoms up" approach to feed information to the original planning 
process. More specifically, the system automatically creates a list of 
alternative processes that any production order can follow and establishes 
the optimum process flows in the event of a disruption on the 
manufacturing shop floor. The system automatically passes the information 
to the planning system which then recalculates the revised order release 
sequence for the remaining orders in the release process.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
Referring now to the drawings, and more particularly to FIG. 1, there is 
shown in functional block diagram form the normal set of processes that 
take place in a typical manufacturing environment from the time of 
planning through production and shipment. The key parts of this system 
includes the master schedule planning 10, where items are planned at the 
completed item level, the material requirement planning (MRP) system 20, 
where completed item requirements are exploded into sub-components and 
planned, and the production release system 30, where shop orders planned 
at the material requirement planning level are set for releasing to the 
shop floor. The production release system 30 is the subject of my 
copending patent application Ser. No. 07/127,334. The next part of the 
system, the manufacturing control system 40, is the process affected 
according to the present invention. This system monitors and analyzes the 
performance at the shop floor and provides signals to move items from one 
work center to another. The last block in the system is the shipping 
system 50 and is standard to any manufacturing enterprise. 
FIG. 2 illustrates the production dispatch system, which constitutes that 
part of the manufacturing control system 40 according to the present 
invention, and its relationship to the simulation and production release 
planning system 30. Here the list of orders and due dates 41 as received 
from the production release system 30 are monitored by the production 
dispatch system 42 to ensure that all dispatching is done as planned. In 
the event of a production disruption, the dispatch system 42 takes charge 
and decides the revised dispatch rule to be followed and the location for 
the item in the process to be sent. The system does this function by 
invoking the common function simulation system of the shop manufacturing 
floor 43. Using planned priority rules, as set out in List 1 below, and 
completed operations, an analysis is made to determine the effect of the 
production disruption. Based on the modified capacity and/or usage 
availability, the system performs calculations to determine if the 
original planned quantities and dates can be met. If not, the system 
prompts the user to input the priorities from among order tardiness, 
work-in-process inventory and cycle time. This is done by displaying the 
original management criteria priority as developed by the production 
planning system 30, and the user responds and provides input at block 44. 
Based on the revised priority input by the user, the production dispatch 
system 42 then re-calculates the dispatch rule to be followed together 
with the sequence to complete the work units and generates a recommended 
revised sequence and priorities in block 45 based on the results of the 
analysis. This information is then fed back to the production release 
system 30, providing the "bottoms up" approach to generating the planned 
list of orders 41. The system also automatically sets up management 
reports in block 46 which can be printed upon request. 
LIST 1 
Dispatching Rules: 
(i) Shortest Imminent Operation Time (SI) is the rule that dispatches jobs 
that have a short processing time as opposed to long jobs. In order to 
have a limit on the maximum allowable time that a job can be waiting, this 
rule is often modified such that jobs with short processing times are 
released provided no other job in the queue is made to wait more than a 
given specified amount of time. This revised rule is often describes as 
SI/T (truncated) rule. 
(ii) Earliest Due Date is the rule that dispatches jobs that have the 
earliest due dates. 
(iii) First-in, First-out (FIFO) is the rule that dispatches jobs based on 
the order they arrive for processing. 
(iv) Critical Ratio is the rule that dispatches jobs based on the ratio 
Time Remaining/Time Needed. The lesser the ratio, the more critical the 
job is and consequently gets a higher priority for dispatching. 
While FIG. 2 illustrates that part of the manufacturing control system 40 
according to the invention as self-contained, in the preferred embodiment 
of the invention, the system illustrated is actually integrated with the 
production planning system 30. More specifically, the common function 
simulation system 43 is shared with the production planning system 30. As 
described in more detail in my copending application Ser. No. 07/127,334, 
the simulation function 43 can be accomplished with a commercially 
available computer program marketed under the name of "GEMS II", a 
Generalized Manufacturing Simulator published by Loadestone-II, Inc. of 
Bryan, Texas. This software package has the natural orientation to 
modeling manufacturing environments. GEMS II is a network based technique 
such that its model is largely represented in a graphical format which 
resembles both manufacturing process flow diagrams and a PERT (Program 
Evaluation and Review Technique) chart. The model consists of boxes or 
nodes which, in general, represent various manufacturing and decision 
activities of the system, and arcs which show the procedural relationships 
among the activities. The logic of GEMS II recognizes queues (in-process 
inventories, production backlogs, etc.) and assembly processes. Further, 
it recognizes competition among activities for limited resources, such as 
tools, fixtures, space and manpower. 
A more detailed description of the GEMS II simulation program is provided 
in my copending application Ser. No. 07/127,334. Those skilled in the art 
will, however, recognize that the simulation of the manufacturing system 
can be accomplished in a number of ways. The practice of the invention is 
not limited to any specific simulation program, and other programs may be 
used. 
To illustrate the point that the system according to the invention can 
interface with any production release system, consider the COPICS 
(Communications Oriented Production Information Control System) product 
marketed by IBM Corp. Order release is a critical application in COPICS 
because it provides an interface between two main planning systems, 
inventory management and manufacturing activity planning, and between 
planning systems and execution systems. The COPICS product is described in 
publication G320-1978 by IBM Corp. In Chapter 7, volume V of that 
publication, order release is described as having two major conceptual 
parts: The functions to release shop orders for manufactured items, and 
the functions required to communicate the need for purchased items to the 
purchasing systems. The shop order release system as described in the 
COPICS publication addresses the functions required to release shop orders 
and establish the database records needed to maintain the information by 
which other systems will monitor and control the detailed feedback 
throughout the order. The system provides shop order reports with a list 
of open orders. Assuming this list or a similar list is sent to the 
manufacturing floor and the manufacturing process begins, the sequence of 
orders started would be displayed under the shop order generated by 
COPICS. In the event of a production disruption, the production dispatch 
system according to the invention, as stated earlier, would re-analyze the 
sequence and priority and re-set the sequence in order to meet the due 
dates or best reduce tardiness. The results would then be provided to the 
COPICS product as the production release system 30. Other similar systems 
marketed by MSA Corp. and Cullinet, for example, could also be used as the 
production release system 30. Nevertheless, the preferred embodiment of my 
invention contemplates an integration with the production release system 
of my copending application Ser. No. 07/127,334. 
The logic of the process illustrated in FIG. 2 is shown by the flow chart 
of FIG. 3. With reference to FIG. 3, the process begins in function block 
60 where the original management priority on work-in-process, cycle time 
and tardiness is extracted. The process is then simulated in function 
block 62 to determine how the process is affected through the end of the 
process. Based on the simulation, an estimate is made in function block 64 
to order tardiness, work-in-process and cycle time with varied dispatching 
rules. This estimate is then tested in decision block 66 to determine if 
it is acceptable. The estimate would be considered acceptable, for 
example, if the original release schedule is not significantly affected by 
the production disruption. What is significant in each case could be a 
default value or a user input value. Thus, if only a slight slippage in 
scheduling work at the various work stations on the production floor is 
experienced, this might be considered acceptable. 
If the estimate is not acceptable, the system prompts the user to re-state 
the priority sequence between work-in-process, tardiness and cycle time in 
operation block 68, and then control passes back to function block 62 to 
simulate the process again with the re-ordered priorities input by the 
user. 
When the test made in decision block 66 is positive, that is the estimated 
value based on the simulation of the process is acceptable, then in 
function block 70 the dispatch orders and work centers are ordered in a 
list, and the dispatch list is printed at 72. 
FIG. 4 illustrates the key parts of the system from the user point of view. 
The key parts are the database 81 and the query system 82. The database 
can be any of several products currently available, but for purposes of 
the preferred embodiments, IBM's DataBase 2 (DB2) is used. DB2 is a 
relational database system, but it will be understood by those skilled in 
the art that other databases, including hierarchical databases, could be 
used. General information on IBM's DB2 can be has with reference to 
publication GC26-4073-2 published by IBM Corp. The query system can be an 
expert system, but for purposes of the preferred embodiment of this 
invention, IBM's Restructured EXtended eXecutor (REXX) language is used. A 
description of the REXX language is provided in "Virtual Machine/Systems 
Product, System Product Interpreter User's Guide", Release 4, publication 
SC24-5238-2 published by IBM Corp. 
The user 83 can query the current status, completion date and the priority 
sequence of any job in question using the query system 82. The query 
system 82 interfaces with the production dispatch system 42 which accesses 
database 81 and provides the revised dispatch sequence to be followed. The 
database 81 as defined has the capability to capture the decision 
variables tested and the results obtained for each test. The user can 
access the results using the query facility at a later date, if needed, 
and obtain an output in the form of a revised order sequence for dispatch 
in block 84. This enhances the analysis capability of future test data. 
This also provides an additional enhancement to the system. 
When a disruption occurs in the production process, the operations manager 
is very concerned about the expected completion time of the order that has 
been affected as well as the impact on other orders on the shop floor. He 
or she would also be concerned with the excessive work-in-process 
inventory and the cycle time needed to complete all orders on the shop 
floor. This dispatch system gives the manager the needed capability to 
recover from the situation, if possible, or the best alternative. Having 
taken a course of action as analyzed by the production dispatch system, 
the planning system and production release system need to be informed of 
the revised plan and status of the operation centers in order to 
effectively plan future orders. This is an added enhancement to this 
system. 
This decision making capability of the dispatch system based on user 
defined rules and objectives provides the artificial intelligence of the 
system. 
While the invention has been described in terms of a single preferred 
embodiment, those skilled in the art will recognize that the invention can 
be practiced with modification within the spirit and scope of the appended 
claims.