Detailed Scheduling (DS) EGN 5623 Enterprise Systems Optimization (Professional MSEM) Fall, 2011 Detailed Scheduling (DS) Theories & Concepts EGN 5623 Enterprise Systems Optimization (Professional MSEM) Fall, 2011 Topics • DS concepts 1. Finite and infinite loading 2. Scheduling directions 3. Sequencing rules 4. Criteria for evaluation of sequencing rules 5. Example for comparison of sequencing rules 6. Controlling changeover costs 7. Minimize total production time 8. Assignment problems • DS in SAP APO Process-Focused Operations Process-focused factories are often called job shops. A job shop’s work centers are organized around similar types of equipment or operations. Workers and machines are flexible and can be assigned to and reassigned to many different orders. Job shops are complex to schedule. Scheduling and Shop-Floor Decisions Master Production Schedule (MPS) Product Design and Process Plans Material Requirements Plan (MRP) Capacity Requirements Plan (CRP) OrderProcessing or Routing Plans Planned Order Releases Report Work Center Loading and Overtime Plan Assignment of Orders to Work Centers Day-to-Day Scheduling and Shop-Floor Decisions Pre-production Planning Design the product in customer order Plan the operations the product must pass through ..... this is the routing plan Work moves between operations on a move ticket Common Shop Floor Control Activities The production control department controls and monitors order progress through the shop. ◦ ◦ ◦ ◦ ◦ Assigns priority to orders Issues dispatching lists Tracks WIP and keeps systems updated Controls input-output between work centers Measures efficiency, utilization, and productivity of shop Shop Floor Planning and Control Input-Output Control Gantt Chart Finite and Infinite Loading Forward and Backward Scheduling Input-Output Control Input-output control identifies problems such as insufficient or excessive capacity or any issues that prevents the order from being completed on time. Input-output control report compares planned and actual input, planned and actual output, and planned and actual WIP in each time period Gantt Charts Gantt charts are useful tools to coordinate jobs through shop; graphical summary of job status and loading of operations Work Centers Mon. Tue. Wed. Thu. Fri. Sat. E Machining Fabrication Assembly C D H Test Scheduled Gantt Charts F G E C F D H C Progress E D Setup, Maint. Assigning Jobs to Work Centers: How Many Jobs/Day/Work Center Infinite loading ◦ Assigns jobs to work centers without regard to capacity ◦ Unless excessive capacity exists, long queues occur Finite loading ◦ Uses work center capacity to schedule orders ◦ Popular scheduling approach ◦ Integral part of CRP Assigning Jobs to Work Centers: Which Job Gets Built First? Forward scheduling ◦ Jobs are given earliest available time slot in operation ◦ excessive WIP usually results Backward scheduling ◦ Start with promise date and work backward through operations reviewing lead times to determine when a job has to pass through each operation ◦ Less WIP but must have accurate lead times Order-Sequencing Problems Sequencing Rules Criteria for Evaluating Sequencing Rules Comparison of Sequencing Rules Controlling Changeover Costs Minimizing Total Production Time Order-Sequencing Problems We want to determine the sequence in which we will process a group of waiting orders at a work center. Many different sequencing rules can be followed in setting the priorities among orders. There are numerous criteria for evaluating the effectiveness of the sequencing rules. Order-Sequencing Rules First-Come First-Served (FCFS) Next job to process is the one that arrived first among the waiting jobs Shortest Processing Time (SPT) Next job to process is the one with the shortest processing time among the waiting jobs Earliest Due Date (EDD) Next job to process is the one with the earliest due (promised finished) date among the waiting jobs Order-Sequencing Rules Least Slack (LS) Next job to process is the one with the least [time to due date minus total remaining processing time] among the waiting jobs Critical Ratio (CR) Next job to process is the one with the least [time to due date divided by total remaining processing time] among the waiting jobs Least Changeover Cost (LCC) Sequence the waiting jobs such that total machine changeover cost is minimized Evaluating the Effectiveness of Sequencing Rules Average flow time - average amount of time jobs spend in shop Average number of jobs in system Average job lateness - average amount of time job’s completion date exceeds its promised delivery date Changeover cost - total cost of making machine changeovers for group of jobs Experience Says: First-come-first-served Shortest processing time Critical ratio ◦ Performs poorly on most evaluation criteria ◦ Does give customers a sense of fair play ◦ Performs well on most evaluation criteria ◦ But have to watch out for long-processing-time orders getting continuously pushed back ◦ Works well on average job lateness criterion ◦ May focus too much on jobs that cannot be completed on time, causing others to be late too. Example: Sequencing Rules Use the FCFS, SPT, and Critical Ratio rules to sequence the five jobs below. Evaluate the rules on the bases of average flow time, average number of jobs in the system, and average job lateness. Job A B C D E Processing Time 6 hours 12 9 14 8 Time to Promised Completion 10 hours 16 8 14 7 Example: Sequencing Rules FCFS Rule A>B>C>D>E Processing Promised Flow Job Time Completion Time Lateness A 6 10 6 0 B 12 16 18 2 C 9 8 27 19 D 14 14 41 27 E 8 7 49 42 49 141 90 Example: Sequencing Rules FCFS Rule Performance ◦ Average flow time: 141/5 = 28.2 hours ◦ Average number of jobs in the system: 141/49 = 2.88 jobs ◦ Average job lateness: 90/5 = 18.0 hours Example: Sequencing Rules SPT Rule Job A B C D E A>E>C>B>D Processing Promised Flow Time Completion Time Lateness 6 10 6 8 7 14 9 8 23 12 16 35 14 14 49 49 127 0 7 15 19 35 76 Example: Sequencing Rules SPT Rule Performance ◦ Average flow time: 127/5 = 25.4 hours ◦ Average number of jobs in the system: 127/49 = 2.59 jobs ◦ Average job lateness: 76/5 = 15.2 hours Example: Sequencing Rules Critical Ratio Rule Job E (.875) C (.889) D (1.00) B (1.33) A (1.67) Processing Time 8 9 14 12 6 49 E>C>D>B>A Promised Completion 7 8 14 16 10 Flow Time Lateness 8 1 17 9 31 17 43 27 49 39 148 93 Example: Sequencing Rules Critical Ratio Rule Performance ◦ Average flow time: 148/5 = 29.6 hours ◦ Average number of jobs in the system: 148/49 = 3.02 jobs ◦ Average job lateness: 93/5 = 18.6 hours Example: Sequencing Rules Comparison of Rule Performance Rule FCFS SPT CR Average Flow Time 28.2 25.4 29.6 Average Average Number of Jobs Job in System Lateness 2.88 2.59 3.02 18.0 15.2 18.6 SPT rule was superior for all 3 performance criteria. Controlling Changeover Costs Changeover costs - costs of changing a processing step in a production system over from one job to another ◦ ◦ ◦ ◦ Changing machine settings Getting job instructions Changing material Changing tools Usually, jobs should be processed in a sequence that minimizes changeover costs Controlling Changeover Costs Job Sequencing Heuristic ◦ First, select the lowest changeover cost among all changeovers (this establishes the first two jobs in the sequence) ◦ The next job to be selected will have the lowest changeover cost among the remaining jobs that follow the previously selected job Example: Minimizing Changeover Costs Hardtimes Heat Treating Service has 5 jobs waiting to be processed at work center #11. The job-to-job changeover costs are listed below. What should the job sequence be? Jobs That Precede A B C D E A -- 65 80 50 62 95 -- 69 67 65 Jobs B C 92 71 -- 67 75 That D 85 105 65 -- 95 Follow E 125 75 95 105 -- Example: Minimizing Changeover Costs Develop a job sequence: A follows D ($50 is the least c.o. cost) C follows A ($92 is the least following c.o. cost) B follows C ($69 is the least following c.o. cost) E follows B (E is the only remaining job) Job sequence is D–A–C–B–E Total changeover cost = $50 + 92 + 69 + 75 = $286 Minimizing Total Production Time Sequencing n Jobs through Two Work Centers ◦ When several jobs must be sequenced through two work centers, we may want to select a sequence that must hold for both work centers ◦ Johnson’s rule can be used to find the sequence that minimizes the total production time through both work centers Johnson’s Rule 1. Select the shortest processing time in either work center 2. If the shortest time is at the first work center, put the job in the first unassigned slot in the schedule. If the shortest time is at the second work center, put the job in the last unassigned slot in the schedule. 3. Eliminate the job assigned in step 2. 4. Repeat steps 1-3, filling the schedule from the front and back, until all jobs have been assigned a slot. Example: Minimizing Total Production Time It is early Saturday morning and The Finest Detail has five automobiles waiting for detailing service. Each vehicle goes through a thorough exterior wash/wax process and then an interior vacuum/shampoo/polish process. The entire detailing crew must stay until the last vehicle is completed. If the five vehicles are sequenced so that the total processing time is minimized, when can the crew go home. They will start the first vehicle at 7:30 a.m. Time estimates are shown on the next slide. Example: Minimizing Total Production Time Job Cadillac Bentley Lexus Porsche Infiniti Exterior Interior Time (hrs.) Time (hrs.) 2.0 2.1 1.9 1.8 1.5 2.5 2.4 2.2 1.6 1.4 Example: Minimizing Total Production Time Johnson’s Rule Least Time 1.4 1.6 1.9 2.0 2.1 Job Work Center Schedule Slot Infiniti Porsche Lexus Cadillac Bentley Interior Interior Exterior Exterior Exterior 5th 4th 1st 2nd 3rd Example: Minimizing Total Production Time 0 1.9 3.9 Exterior L C Interior Idle L 0 1.9 6.0 B 7.8 P C 4.1 9.3 I B 6.6 Idle P 9.0 12.0 I 10.6 12.0 It will take from 7:30 a.m. until 7:30 p.m. (not allowing for breaks) to complete the five vehicles. Minimize Total Production Time Minimize Total Production Time Minimize Total Production Time Minimize Total Production Time DS in SAP APO • Tasks and activities of detailed scheduling • • • • • • • • • • • • • Controlling Detailed Scheduling Dates/Times and Planning Directions Resource Availability Selection of Resources Time Relationships Pegging Relationships Automatic Propagation of Changes Determining the Setup Time for Sequence-Dependent Setup Activities Synchronizing Activities on Multi-resources Block planning Scheduling Log Terminating Scheduling Detailed Scheduling Heuristics Tasks of Detailed Scheduling Detailed scheduling is used to: 1. Determine the resources and dates/times for carrying out operations, taking resource and product availability into consideration. 2. Support the scheduler in scheduling resources when creating an optimal processing sequence for operations Activities of Detailed Scheduling Basic DS Activities: • Scheduling • dispatching operations to resources at a specific date/time • Rescheduling • dispatching already scheduled operations to a different date/time or to different resources • De-allocating • removing scheduled operations from the resource schedule • Adjusting • a new date/time or new resources are assigned to a de-allocated operation. • Fixing • the resource and date/time for the operation is fixed. Activities of DS: Schedule Schedule: For an operation of a newly created order or for a deallocated operation 1. The resources are determined on which the operation should be processed 2. The date/time is determined when the operation should be processed on the resources With scheduling, the operation is dispatched to the resources. Scheduling an order means scheduling all the operations of the order. Activities of DS: Reschedule Reschedule: 1. A new date/time or new resources are specified for a scheduled operation. 2. With rescheduling, the operation remains loaded on resources. 3. After rescheduling, it loads either the previous resources or the new resources. 4. Rescheduling an order means rescheduling all the operations of the order. Activities of DS: De-allocate • Remove an operation from the resource schedule. • With de-allocation, an operation is given the status de-allocated. The operation no longer loads any resources. • De-allocating an order means de-allocating all the operations of the order. • An operation in the SAP APO system is either scheduled with no separate status or de-allocated (in this case it has the status de-allocated). Activities of DS: Adjust • A new date/time or new resource is assigned to a deallocated operation. • In the case of an adjustment, the operation retains the status de-allocated. The operation does not load the resources to which it is assigned. Adjusting does not change any resources schedules. • Adjusting is a detailed scheduling activity that is carried out automatically by the system for dependent objects (for example, if relationships or pegging relationships have to be adhered to). You cannot adjust de-allocated operations manually. Activities of DS: Fix 1. The resource and date/time for the operation is fixed. 2. Through the fixing process, a scheduled or de-allocated operation is assigned the status fixed. 3. A fixed scheduled operation cannot be rescheduled or de-allocated, and a fixed de-allocated operation cannot be scheduled or adjusted. Integrated Distribution & Production Planning SAP Implementation EGN 5623 Enterprise Systems Optimization (Professional MSEM) Fall, 2011 Prerequisites of DS The system can trigger detailed scheduling activities automatically. For example, it automatically schedules the order operations when an order is created. Three ways to start detailed scheduling activities: •production planning run, •detailed scheduling planning board, or •resource planning table specifically for selected operations or orders. Production Planning Run To execute planning online or in the background for selected objects. •online planning is only suitable for small data quantities (for example, for test purposes), •background planning for mass planning. Detailed Scheduling Planning Board Purpose: •Graphical representation of the planning situation Graphically represent different aspects of scheduling in the charts of the detailed scheduling planning board. For example, you can show the situation of operations on resources over time and the development of the resource utilization or pegging relationships between orders over time. •Interactive solution of planning problems You can perform interactive scheduling on the detailed scheduling planning board to solve scheduling problems such as sequence or date/time problems on resources. Various scheduling functions and heuristics are available in addition to manual scheduling with Drag&Drop. Detailed Scheduling Planning Board •Integration The detailed scheduling planning board is integrated in different Production Planning applications. You can call up the detailed scheduling planning board: • Directly in the area menu for production planning • In order processing • In the product planning table SAP provides the detailed scheduling planning boards with standard settings (for example, for setup or layout). If you want to configure a detailed scheduling planning board for your specific scheduling requirements, you must make the appropriate settings. Detailed Scheduling Planning Board Layout of the Detailed Scheduling Planning Board When you invoke the detailed scheduling planning board for the first time, the selection area is shown in the left-hand part of the screen. You can control the display of the selection area via Settings -> User Settings and save the setting on a user-specific basis. The setting you make on the detailed scheduling planning board is independent of the setting in the resource planning table (see Configuring the Resource Planning Table). The selection area serves to provide an overview of the loaded products and resources and to show and hide objects (see Hiding and Showing Objects). SAP APO Planning Board (Interface) SAP APO – Production Planning – Interactive Production Planning – Detailed Scheduling – Detailed Scheduling Planning Board/Variable view (APO/CDPS0) SAP APO Planning Board SAP APO – Production Planning – Interactive Production Planning – Detailed Scheduling – Detailed Scheduling Planning Board/Variable view (APO/CDPS0) SAP APO Planning Board (Legend) SAP APO – Production Planning – Interactive Production Planning – Detailed Scheduling – Detailed Scheduling Planning Board/Variable view (APO/CDPS0) Detailed Scheduling Heuristics DS Heuristics Features: • Strategy settings Depending on the heuristic, you can change the selected strategy settings that the heuristic uses to schedule or reschedule operations. Certain strategy settings are permanently set by SAP and cannot be changed. •Planning period The system uses heuristics to reschedule operations that start in the planning period. Detailed Scheduling Heuristics DS Heuristic Activities • If you want to start a heuristic on the DS planning board, select the desired objects and call up the heuristic by choosing Functions Heuristics. You can change the settings for the heuristics on the DS planning board by choosing Settings Heuristics. •· If you want to use a heuristic in the production planning run, enter the heuristic and the objects for which you want to execute the heuristic in the corresponding processing step in the production planning run.
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