STBS is a program for short-term scheduling of batch plants with multiple stages and it is based on the MILP model that is developed by Pinto and Grossmann (1994). The model considers a plant with L stages involving parallel units which are not necessarily identical. There are M units distributed among the L stages. Given N products with their respective demands and deadlines, the batch times for batch units and production rates of processing units, and machine clean-up times it is possible to obtain the optimal assignment of orders to machines, the timing of operations at each unit and the flow of material through the L stages of the plant. The following assumptions are considered:
- Demands, due dates, processing times and transition times are deterministic
- Transition times are only equipment dependent
- Each order is to be processed by only one unit of every stage it must go through
- Each order represents one batch; therefore it is possible that there might exist several orders of the same product
- No resource constraints are considered
- Unlimited intermediate storage between stages
STBS interface has been developed for Unix and Windows .
STBS interface gives two solution strategies : The first one Basic model w/o the use of preordering constraints. Second one, Alternate model, relies on a decomposition scheme for large systems which is based on the solution of an MILP model that minimizes total in process time in which assignments are determined and the subsequent solution of an LP is obtained to minimize earliness and to eliminate unnecessary set-ups.
This interface is written in language C and it is implemented on IBM RS6000, HP and SUN (SunOS and Solaris) workstations. The way this interface works is through the use of different menus; it is flexible and easy to use. Given the data of the problem, STBS creates a new GAMS file containing the model equations and optimizes the problem using the solvers OSL for solving the MILP, and plots the Gantt charts and Order paths at each stage.
STBS UNIX screen shots
STBS Unix has been developed by Arzu Türkay and Beatriz Bolio under the supervision of Ignacio E. Grossmann .
This interface was written using Visual Basic 4.0 and run on Windows 95 or Windows NT 3.51 or above. It was designed trying to emulate the Windows Explorer environment, avoiding the necessity of learning new command and procedures. The problem is defined using a hierarchical structure. The same data can be input simultaneously to elements of the same type. Similarly, it is possible to modify the problem statement at different levels with automatic updating. The results can be displayed or printed as Gantt charts, order paths and tables. In addition, the interface has a friendly hypertext help menu, which explains in detail its use.
STBS WINDOWS screen shots
STBS Windows has been developed by Fabian Valli under the supervision of Ignacio E. Grossmann .
References for STBS:
- Pinto J.M. , A. Türkay, B. Bolio and I. E. Grossmann, Continuous Time MILP models for short term scheduling of batch plants with pre-ordering constraints , Comput. Chem. Engng., accepted for publication (1997).
- Pinto J.M. and I. E. Grossmann, A Continuos time MILP model for short term scheduling of batch plants , I&EC RESEARCH,Vol. 34, 1995, pp.3037-305.
- Pinto J.M. and I. E. Grossmann, An Alternate MILP model for short term scheduling of batch plants with pre-ordering constraints , I&EC RESEARCH, Vol. 35, No. 1, 1996, pp.338-342.
- Türkay, Arzu and Beatriz Bolio Guidelines for STBS Interface , Carnegie Mellon University, Engineering Design Research Center, Pittsburgh, PA.