: operations scheduling with applications in manufacturing and services
Erwin Hans (T&M-OMST)
BB-235, tel. 3523, e.w.hans@sms.utwente.nl
Johann Hurink (TW-STOR)
J.L.Hurink@math.utwente.nl
Faculty of Technology and Management
University of Twente
Enschede, The Netherlands

Literature
Book: Operations Scheduling with applications in manufacturing and services
Authors: M. Pinedo, X. Chao
Handouts, also downloadable from website

Exam
These methods must be learned entirely
(one or two questions about these will be in the exam):
• adaptive search
• branch-and-bound, beam-search
• shifting bottleneck
The idea (approach) and application of all other discussed methods must be learned (i.e., no formulas)
One question will be asked about the software demonstration
Aside from the discussed chapters from the book, the handouts must be learned

Scheduling: definition
Allocation of jobs to scarce resources the types of jobs and resources depend on the specific situation
Combinatorial optimization problem maximize/minimize objective subject to constraints

Application areas
 Manufacturing, e.g.:
 job shop / flow shop scheduling
 workforce scheduling
 tool scheduling
 Services, e.g.:
 Hotel / airline reservation systems
 Hospitals (operating rooms)
 Transportation and distribution, e.g.:
 vehicle scheduling, and routing
 railways

Application areas (cont.)
 Information processing and communications:
 CPU’s, series and parallel computing
 call centers
 Time-tabling, e.g.:
 lecture planning at a University
 soccer competition
 flight scheduling
 Warehousing, e.g.:
 AGV scheduling, and routing
 Maintenance, e.g.:
 scheduling maintenance of a fleet of ships

Scheduling in manufacturing
Due to increasing market competition, companies strive to:
 shorten delivery times
 increase variety in end-products
 shorten production lead times
 increase resource utilization
 improve quality, reduce WIP
 prevent production disturbances (machine breakdowns)
--> more products in less time!

Different types of manufacturing control
 Make and assemble to stock
 Make to stock, assemble to order
 Make to order
 Engineer to order

Scheduling in a manufacturing planning and control framework
 Long range forecasting and sales planning
 Facility and resources planning
 Demand management, aggregate and workforce planning
 Order acceptance and resource group loading
 Shop floor scheduling, workforce scheduling

Relations with other management areas
 Product and process design
 Process planning
 Inventory management and materials planning
 Purchasing and procurement management
 Warehousing and physical distribution

Scheduling in services
 Workforce Scheduling in
 Call Centers
 Hospitals
 Employment agencies
 Schools, universities
 Reservation Systems in
 Airlines
 Hotels
 Car Rentals
 Travel Agencies
 Postal services

Our approach
Scheduling problem
Problem formulation
Model
Solve with algorithms
Conclusions

Scheduling models
 Job shop scheduling
 Project scheduling
 Flexible Assembly Systems
 Lot sizing and scheduling
 Workforce scheduling, staffing
 Interval scheduling, reservation systems, timetabling

Scheduling algorithms
General solution Techniques:
 Mathematical programming
 linear, non-linear, (mixed) integer programming
 Exact methods (enumeration)
 branch-and-bound
 dynamic programming
 cutting plane / column generation methods
 Local search methods, heuristics
 simulated annealing
 tabu search
 adaptive search
 k-opt methods
 genetic algorithms
 neural networks

Scheduling algorithms (cont.)
 Heuristics
 dispatching rules
 composite dispatching rules
 beam-search
 Decomposition Techniques
 Temporal decomposition (rolling horizon approach)
 Machine decomposition (Shifting Bottleneck)
 Hybrid Methods
 combined usage of scheduling methods

Important characteristics of optimization techniques
 Quality of Solutions Obtained
(How Close to Optimal?)
 Amount of CPU-Time Needed
(Real-Time on a PC?)
 Ease of Development and Implementation
(How much time needed to code, test, adjust and modify)
 Implementation costs
(Are expensive LP-solvers required?)

Value
Objective
Function
Dispatching
Rules
Beam
Search
Local
Search
Branch and Bound
CPU - Time

Consideration of software companies w.r.t. optimization techniques
Implementation costs
(Are expensive LP-solvers required? Easy to implement?) vs.
What solution quality does the customer require?
online scheduling offline scheduling
(Is an immediate answer required, or are long calculations allowed? Does customer accept complex solutions?)

Commercial Packages
 ERP-SYSTEMS
 SAP, Baan, JD Edwards, People Soft, Navision, MFG Pro
 GENERAL OPTIMIZATION
 Ilog, Dash, MINTO, OSL (IBM), XPRESS-MP, OML, XA
 GENERAL SCHEDULING
 I2, Cybertec, AutoSimulation, IDS Professor Scheer,
ORTEC
 SCHEDULING OIL AND PROCESS INDUSTRIES
 Haverly Systems, Chesapeake, Finity, ORTEC
 SCHEDULING CONSUMER PRODUCTS
 Manugistics, Numetrix
 SCHEDULING WORKFORCE IN CALL CENTERS
 AIX, TCS, Siebel

Decision Support Systems
Important issues in design of DSS:
 Database design and management
 Data collection (e.g. barcoding system)
 Module Design and Interfacing
 GUI Design (Gantt-charts, etc.)
 Design of link between GUI and algorithm library
(data organization before transfer)
 Internal Re-optimization
 External Re-optimization

GUI’S should allow:
 Interactive Optimization
 Freezing Jobs and Re-optimizing
 Creating New Schedules by Combining Different
Parts from Different Schedules
 Cascading and Propagation Effects
After a Change or Mutation by the User, the system:
 does Feasibility Analysis
 takes care of Cascading and Propagation Effects,
 does Internal Re-optimization

Graphics user interfaces for scheduling production processes
 Gantt Chart Interface
 Dispatch List Interface
 Time Buckets (resource capacity loading)
 Throughput Diagrams
 Time tables

Important objectives to be displayed
 Due Date Related
 Number of late jobs
 Maximum lateness
 Average lateness, tardiness
 Productivity and Inventory Related
 Total Setup Time
 Total Machine Idle Time
 Average Time Jobs Remain in System, WIP
 Resource usage
 resource shortage