Head Start: Account for Offline Intervals

Key Concepts

The 'Account for Offline Intervals' option is found under the Optimize Settings dialog in the Release Rules section. Release Rules determine how Manufacturing Orders are released for scheduling during an optimization. Each Manufacturing Order is prevented from scheduling until it is "released."

The JIT Release Rules sets the Manufacturing Order Release Date to the lead Activity's JIT Start Date minus the JIT Slack Days. The Head Start Span is the amount of time that a job can schedule before the JIT Start Date (specified by the JIT Slack Days).

This checkbox modifies how Head Start is normally calculated by accounting for offline intervals and resource capacity hours. When checked, the Head Start will account for offline capacity time (i.e., Head Start will be calculated based on available resource capacity).

This feature is available in PlanetTogether versions 11.48 and later.

Example:

The following example will show the effects of having the 'Account For Offline Intervals' option set to 'False' or 'True.'

Scenario 1:

  • Job Need Date: 2021-06-01 3:00PM
  • JIT Start Date: 2021-06-01 7:00AM
  • Release Rules: JIT With Global HeadStart
    • JIT Slack = 3
    • Account For Offline Intervals = 'False'

Outcome:

The Release Date (HeadStart) is 3 days before the activity's JIT Start, and it falls on an interval with no online capacity (on 2021-05-29 7:000AM). The job is scheduled at the next available online capacity interval (on 2021-05-31 7:00 AM).

While this may not be an issue for those with long lead times, it can cause problems for manufacturers with short lead times as not enough jobs would schedule on Friday, and there would be a bottleneck on Monday.

The next scenario will demonstrate the effects of setting the 'Account For Offline Intervals' set to 'True.

Scenario 2:

  • Job Need Date: 2021-06-01 3:00PM
  • JIT Start Date: 2021-06-01 7:00AM
  • Release Rules: JIT With Global HeadStart
    • JIT Slack = 3
    • Account For Offline Intervals = 'True'

Outcome:

The Release Date (HeadStart) accounts for offline capacity intervals and resource capacity hours. The job is released and scheduled for 2021-05-19 at 7:00 AM.

This feature looks at the available hours of online capacity intervals and may not reflect the number of JIT Slack Days specified. For example, specifying a JIT Slack Days of ‘3’ could cause the activity to be released too early (in this case, 9 workdays before its JIT Start Date.)

A facility that operates with a single 8-hour shift per day and would like to give a 3-day Head Start would specify a JIT Slack Day of ‘1’ (8 hrs x 3 = 24 hours = 1 day).

Scenario 3:

  • Job Need Date: 2021-06-01 3:00PM
  • JIT Start Date: 2021-06-01 7:00AM
  • Release Rules: JIT With Global HeadStart
    • JIT Slack = 1
    • Account For Offline Intervals = 'True'

Outcome:

The Release Date (HeadStart) accounts for offline capacity intervals and resource capacity hours. For example, the job is released and scheduled for 2021-05-27 at 7:00 AM, which constitutes a Head Start of 3 workdays from the JIT Start Date.