Batch Schedules and Production Schedules Which Should You Use?

Transcription

1 Presented at the World Forum North American Conference Atlantic City, NJ April S. Southgate Drive Chandler, Arizona Fax Schedules and Schedules Which Should You Use? David Emerson Sr. System Architect Yokogawa Corporation of America 2155 Chenault Drive Suite 401 Carrollton, TX Tel: (972) Fax: (972) Dennis Brandl Director, Enterprise Initiative Sequencia Corporation 8000 Regency Parkway, #515 Cary, NC Tel: (919) Fax: (919) KEY WORDS Bradley Ward Director of Technology Bradley Ward Systems, Inc. 750 Hammond Drive, Building 10, Suite 200 Atlanta, GA Tel: (404) Fax: (404) SP88, S88.02, SP95, S9501, Schedule, Schedule, Schedule, XML ABSTRACT The integration of scheduling and control systems invariably involves custom programming or the use of proprietary formats to enable the transfer of production schedules. Currently there are two ISA standards committees developing standard schedule formats. The ISA SP88 committee's S88.02 draft 14 presents a batch schedule object model and a set of relational database tables for the exchange of schedule data. At the time this paper was written the ISA SP95 committee was finishing work on the S95.01 Enterprise/Control Integration standard 1. S95.01 defines a production schedule object model. The SP95 committee is continuing work on this model as part of the S95.02 development effort. The committee is expected to develop attributes for the objects. This paper analyzes the two committee's work and proposes a mapping between the different sets of work. The mapping shows how the S88.02 schedule object model and exchange tables can fit into the S95.01 production schedule model and the on-going S95.02 work. 1 The final 30-day period of the review process ends on March 31, As this is before the presentation date of this paper, the S95.01 reference is used throughout the paper rather than the ds95.01 reference indicating draft status World Forum. All rights reserved. Page 1

2 INTRODUCTION There are two ISA standards that define scheduling in production facilities; the S88.02 Control Standard, and the S95.01 Enterprise/Control System Integration standard. At first glance these two standards appear to be in conflict, since they both seem to deal with defining schedules for manufacturing production. The first glance also reveals that the S95.01 standard has a relatively complex structure compared to the S88.02 structure. However; upon further examination the two schedule formats can be seen to be complementary and designed with different scopes. The two standards deal with different levels of functions normally used to run a production facility. Figure 1 illustrates the functional hierarchy defined in the S95.01 standard and illustrates where each of the two different scheduling standards applies. S88.02 Standard Level 4 Business Planning & Logistics Plant Scheduling, Operational Management, etc Level 3 Manufacturing Operations & Control Dispatching, Detailed Scheduling, Reliability Assurance,... Control Continuous Control Discrete Control S95.01 Standard Levels 2, 1, 0 Figure 1- Functional Hierarchy The S88.02 schedule standard addresses what is primarily a dispatching function. Dispatching is a level 3 function, which sends batch control systems (represented by level 0-2) instructions regarding products to produce. These instructions typically include the batch ID, the master recipe to use, and the equipment to use. In some instances it may include other information such as the criteria for selecting the equipment the master recipe specifies, formulation, and key parameters. The S95.01 schedule standard addresses the level 4 and level 3 interface which typically involves bridging business systems and operational & control systems. Therefore the S95.01 schedule needs to address the information needs of business systems as well as the production information needs of operations & control systems. Also as Figure 1 shows, the S95.01 schedule must be capable of World Forum. All rights reserved. Page 2

3 handling continuous and discrete control applications as well as batch control applications. This requirement means that some of the batch focused terms in the S88.02 schedule cannot be used in the S95.01 schedule, although their capability must be supported in S95.01 otherwise the schedule may not work for batch control. S88.02 SCHEDULE The S88.02 draft standard provides two definitions of a batch schedule. In section 4 of S88.02, a batch schedule data model is presented. This uses a high level of abstraction and identifies the batch schedule entry as the central entity in a schedule. The data model defines the relationship of the batch schedule entry to parameters, master recipe entities, control recipe entities, equipment as well as the recursive nature of batch schedule entities. Section 5 of S88.02 provides a detailed implementation of the data model using relational tables specified using ANSI SQL and meeting the requirements of the data model. The relational tables also provide additional detail in the form of specific table fields that are customized to batch scheduling (e.g. Lot ID, Campaign ID, InitialMode). Figure 2 shows a simplified view of the structure of an S88.02 schedule. As mentioned in S88.02 section 4, the schedule entry is the key element in a schedule. The recursive capability permits unit recipes to be scheduled inside of batches and for items such as campaigns, which include schedules for multiple batches. The use of parameters and equipment information in a batch schedule is optional. Schedule Entry (campaign, batch, unit recipe) Schedule Entries may contain other Schedule Entries 0..N equipment requirements per schedule entry 0..N parameters per schedule entry Equipment Parameters Parameters may consist of other parameters Figure 2- S88.02 Schedule Simplified Structure As part of the relational table definition, the S88.02 draft standard provides a comprehensive set of attributes for each of the objects in a batch schedule. These attributes are customized for the batch industry and although many of them can apply to other industries, examination of the attribute list makes it clear that they are primarily applicable to batch scheduling. S95.01 SCHEDULE World Forum. All rights reserved. Page 3

4 The S95.01 draft standard defines a production schedule that has been designed to cover a broad range of industries. It also contains the information needed by business systems in order to request the manufacture of products and permit the tracking of manufacturing performance. Although the production schedule may be used at various levels in the equipment hierarchy, for the batch industry it is intended to serve as an interface between the area and process cell levels. S95.01 has a requirement for the production schedule to apply to different industries and to meet the needs of business systems. This results in the use of terms that avoid industry specific terminology. Therefore in comparison to the S88.02 batch schedule, the S95.01 production schedule introduces new terms. Figure 3 Figure 3 shows a simplified structure for an S95.01 production schedule. For example the term "segment requirement" defines a sub-section of a production request. However, since different industries are covered the name segment is used rather than the batch equivalent of campaign, batch or unit procedure. Therefore in the batch industries a "segment requirement" is the set of schedule requirements for scheduling a campaign, batch or unit procedure. A segment requirement is further broken down into parameters, personnel, equipment and material (produced, consumed & consumables) requirements. These are the resources scheduled by a planning system and managed by a control system. Schedule Request A Schedule is made up of 1..n Requests A Request is made up of 0..n Segment s Segment A Segment may contain 0..n of each Parameter Personnel Equipment Material Consumed Material Produced Consumable Expected Figure 3- S95.01 Schedule Simplified Structure The SP95 committee completed work on Part 1 of the standard, which contains the Schedule Object Model and is currently working on Part 2, which will provide more detailed attributes for the objects in the production schedule. The approach being used is to define a small number of core attributes for each object and then define a structure so an unlimited number of properties may be defined for each of the lower level requirements. This approach will result in a core set of attributes that World Forum. All rights reserved. Page 4

5 are applicable to a broad range of industries and meet the needs of business system and control systems while providing the ability to add industry, vendor, and end-user specific attributes as custom properties. WORKING WITH S88.02 AND S95.01 SCHEDULES Although the S88.02 batch schedule and the S95.01 production schedule appear to conflict and overlap on first appearance they should be viewed as complementary. Figure 44 shows the relative scopes of the two schedule standards. ENTERPRISE S88.02 Standard SITE S95.01 Standard AREA AREA AREA CONTINUOUS PRODUCTION UNIT BATCH PROCESS CELL DISCRETE PRODUCTION LINE Figure 44 - Relative S88 and S95 Scopes This example shows how the S95.01 schedule is designed to meet the needs of more than just the batch industry. Another example of how the S95.01 schedule can be used in a batch processing facility is shown in Figure 5 where a batch plant is shown to utilize operations that have both continuous and discrete characteristics. In this example a S95.01 production schedule may be used to coordinate manufacturing activities in a plant that have different characteristics, such as the continuous premix that may feed batch reactors and the discrete packaging operations that receive the output of the batch reactors and prepare the product for shipment. In this case a S95.01 production schedule could be used to transmit a comprehensive schedule from the local, or remote, planning system to the work dispatching system. The work dispatching system is then responsible for breaking up the schedule and transmitting the appropriate portions to individual systems, or manual operations. Each of these may be in a different World Forum. All rights reserved. Page 5

6 format depending upon the schedule s characteristics and the systems involved. The S88.02 batch schedule is the preferred method to transfer schedules from the work dispatching system to the batch control system. S95.01 Schedule Work Dispatching Setpoints & Flowpaths S88.02 Schedule Entry Setup Instructions Continuous Premix Process Discrete Packaging Figure 5 - Mixed Format Schedule Application The S88.02 batch schedule is designed for sending schedules to batch control systems. This is a very focused scope and permits the batch schedule to have standard attributes that are applicable to the batch processing industry. However, this does not always meet all the scheduling requirements in a processing facility. The S95.01 production schedule is designed to serve the business system and control system interface for the continuous, batch and discrete industries. Therefore the production schedule has a more general structure and list of attributes than the batch schedule. Each instance of the production schedule will require use of specific properties applicable for the instance scope, industry, company and systems involved. When it is used for batch applications it should be possible to standardize on the S88.02 terms and use them as properties. The actual mapping of S88.02 batch schedule attributes and S95.01 production schedule attributes are dependent upon the granularity of the schedule, that is the breadth and depth of the scheduling application s scope. Figure 6 shows three possible mappings World Forum. All rights reserved. Page 6

7 The top example of Figure 6 shows a schedule with low granularity, The production request object is mapped to a production item that encompasses not only the batch process area, but also processes that feed the batch process and handle the output of the batch process. From this perspective the batch schedule is only one segment of the production request since the production request s focus is on everything required to produce a product. In this example the segment requirement scheduling the batch process has a requirement for a specific amount of product and the batch control system is responsible for determining the number of batches required to accomplish this. In this case when the batch control system receives the segment requests in a production schedule it may perform an additional scheduling activity to optimize the use of the processing equipment under its control. The middle example in Figure 6 shows a sample of a production schedule with medium granularity. In this case each production request represents a campaign, or a group of batches with a common trait. Each segment requirement would map to a specific batch. However, the number of unit procedures in each batch is not specifically called out in the production schedule. As in the low granularity example a scheduling activity could be performed in the batch control system to optimize the use of the equipment when assigning units for the unit procedures. The last example in Figure 6 shows a high granularity production schedule. In this case the production request maps to a batch and each unit procedure is mapped to a segment requirement. This is considered highly granular since it schedules down to the unit procedure level. Low Granularity in Schedule Request Segment Unknown Number of es Medium Granularity in Schedule Request Specified Number of es Segment Segment Segment Unknown Number of Unit Procedures High Granularity in Schedule Specified Number of Unit Procedures Request Segment Segment Segment UP UP Unit Procedure Figure 6 - Scheduling Granularity World Forum. All rights reserved. Page 7

8 As the SP95 committee defines the attributes of the S95.01 objects, a more detailed mapping of batch and production schedules will be possible. It is anticipated that the S88.02 batch schedule attributes will become commonly used (e.g. de facto standard) property IDs in S95.02 production schedules. CONCLUSION One of the most valuable benefits of using the S88 and S95 schedule standards occur when they are used to interface software implementations from different organizational levels. The S88 batch schedule and the S95 production schedule will both find widespread application as the industry matures, and therefore represent complimentary additions to the best practice tools available to manufacturing system designers. The S95 production schedule will primarily be used to facilitate communications between enterprise level business systems (ERP and APS) and process execution and control systems (e.g. MES), whereas the S88 batch schedule will primarily be used between process execution and control systems and the batching elements of the manufacturing process. Advanced commercial batch control systems based on S88 will likely provide the ability to deal with both types of schedules and will be particularly useful when dealing with batch centric processes World Forum. All rights reserved. Page 8