Start with something familiar
If you paint two blue shelves and then one red shelf, you clean the brush once between colors. If you alternate blue, red, and blue, you clean twice. The cleaning is real work even though no shelf gets painted during it. Grouping colors saves time, but a red shelf promised early may wait too long. A bottle line has the same tradeoff when label or color changes consume a shared machine.
Words to know: Setup family, No overlap, Makespan.
A setup is an interval
Northstar needs thirty minutes to move its label line between blue and red settings. The machine begins in blue, so a first blue job has no initial change. A first red job needs a change before it runs. Put setup blocks on the same timeline as production blocks. They cannot be hidden in spare time while the same machine is running.
This case treats same-family transitions as zero and cross-family transitions as thirty in either direction. That symmetry is an assumption. A real cleaning matrix could differ by direction or require a setup after idle time. Start with the supplied matrix and explicitly list the initial family; otherwise two correct-looking schedules may use different starting conditions.
Group families without losing promises
Grouping blue jobs can reduce changes, leaving more time for runs or recovery. Yet the grouped plan may push a red job past its due time. Compare saved setup minutes with changed job tardiness instead of calling the grouped plan automatically better. Time savings are useful only within the service policy the business accepts.
The number of family changes depends on sequence, not merely the count of jobs. Three jobs in two families can require one or two changes after the initial state is considered. Count each actual transition and reconcile total occupied time with run time plus setup time. That reconciliation is a strong check against missing work.
Draw setup ownership clearly
Record setup start, setup finish, and the following job. In the simplified case the machine itself is the only constrained setup resource. If a technician were also needed, that person would need a second calendar check. Do not assume a saved machine minute means a saved paid labor minute; the case has not specified that cost relationship.
Explore both a family-first and due-first sequence. Keep job quantities and run durations unchanged. A fair comparison should not quietly shrink a batch to help one policy. The lab asks you to write where each minute went and which customer would be affected. That turns a visual schedule into a decision that can be reviewed.
- Validate inputs
- Place legal work
- Check every resource
- Compare outcomes
- Release with conditions
Northstar worked schedule
All data are fictional. Time is elapsed minutes from the stated shift origin; unlisted transfer times are zero. Use the explicit resource and setup assumptions below.
| Job | Family | Run minutes | Due |
|---|---|---|---|
| A | Blue | 60 | 100 |
| B | Red | 40 | 150 |
| C | Blue | 50 | 220 |
- 1. Initial state Blue. A-B-C needs Blue→Red and Red→Blue, each 30 minutes.
- 2. A 0-60, change 60-90, B 90-130, change 130-160, C 160-210.
- 3. A-C-B runs A 0-60, C 60-110, change 110-140, B 140-180.
A-B-C finishes at210 with no tardiness. A-C-B finishes at180 but B is30 minutes late.
Assumptions
- All times and quantities are deterministic inputs unless explicitly labeled expected or scenario-dependent.
- Operations cannot be split; touching interval boundaries are allowed. Additional constraints are only those stated in the lesson.
Where this can fail: These small cases teach traceable decisions, not a promise of performance in an unmodeled plant.
Build, test and explain a plan
Use the example jobs, release all at0, machine open0-300, initial Blue, same-family setup0 and cross-family setup30. Enumerate six orders with setup blocks. Compare total setup, final finish, and total tardiness. Then halve cross-family setup to15. In a separate scenario retain30 but change initial family toRed. No job splitting is permitted. The eight hours are self-paced estimates for modeling, scenario work, checks, and explanation; they have not been experimentally validated.
Use paper or a spreadsheet. The estimates below include the study and worked example already on this page.
| Estimated hours | Activity |
|---|---|
| 0.5 | Study the lesson and make a one-page input dictionary. Define the clock, units, resource names, release rule, and all assumptions. Mark which inputs are fixed and which will change in the scenarios. |
| 0.5 | Reproduce the worked example without looking at its result, then compare every intermediate start and finish. Explain any difference in a short error log before building the larger table. |
| 3 | Build a complete operation-by-operation planning table for every requested sequence or scenario in the lab brief. Include starts, finishes, blocked intervals, due comparisons, and a resource timeline. Cross-check each row against its input and reconcile resource totals. Use paper or a spreadsheet; no special software is required. |
| 2 | Run the specified stress cases independently, restore the base between cases, and compare each changed result with the original. Create a small sensitivity table and identify which assumption caused each difference. Audit feasibility before ranking the outcomes. |
| 1 | Write a decision memo with the selected feasible option, numeric evidence, the losing option’s advantage, and any unmet promise. State the condition that would cause you to reconsider. Do not invent additional capacity or missing data. |
| 1 | Teach the result aloud or in writing to an imagined operator. Rebuild one key check from a blank page, answer the recap questions, and revise the memo if your explanation reveals an unsupported assumption. |
Your deliverables
- Input dictionary and checked schedule table.
- Scenario comparison with job-level or quantity-level evidence.
- Decision memo and teach-back record.
Check your practice work
- A-B-C baseline: run150 + setup60 = finish210; total tardiness0.
- A-C-B baseline: run150 + setup30 = finish180; total tardiness30.
- With setup15, A-B-C finishes180 with no tardiness; A-C-B finishes165 and B is15 late.
- With initial Red, B-A-C finishes180; A completes130 and is30 late, B completes40, C180.
Keep these three ideas
- Charge sequence-dependent setup time to the actual resource timeline.
- Which constraint or metric changes the choice in this case?
- What assumption must be confirmed before this plan can be released?
Common mistakes
- Comparing plans before checking every stated constraint.
- Changing several assumptions at once and losing the explanation for the result.
Optional video study
Charge sequence-dependent setup time to the actual resource timeline.
- Introduce the specific Northstar inputs
- 1. Initial state Blue. A-B-C needs Blue→Red and Red→Blue, each 30 minutes.
- A-B-C finishes at210 with no tardiness. A-C-B finishes at180 but B is30 minutes late.
First half of module narration
Open the module media & quizPut this idea to use
Carry your assumptions into a practical tool, then compare your result with a short guide.
Open a related planning toolRead the related planning guidePractice with the planning gameThis saves a completion marker in this browser only. It does not verify time spent.