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One important feature of our manufacturing systems has been the capability to plan by exception. Items that have been planned and require no further changes need not be reviewed. Those that have possible availability changes are identified to the planners by exception mes­sages from the system for review.


In most systems, if a planner accepts a recommenda­tion by taking the recommended action, the message does not reappear in the next planning cycle. If a mes­sage is ignored or no action is taken, it reappears. The problem comes when a planner reviews an item and re­jects the message or intentionally decides to take a dif­ferent action than the system recommends. Many systems treat a rejected message as one that has been ignored. They repeat the message continually until an­other change occurs or the order closes.



This means the planners receive messages that they have already handled in addition to new messages. It becomes difficult to sort the new messages from the old ones, and the pile grows larger. This can result in switching off the exception messages and reviewing all the items instead of just the exceptions.


There are two common methods of dealing with this problem. You can run net change MRP instead of regen­eration. Most net change logic involves the creation of an activity file that determines which items are reviewed. Removing the item from the activity file eliminates the message from the next planning cycle. It will take a new change to put the same item in the activity file for review again. The problem with this is that net change does not work properly in many of the software packages. Al­though it is offered as a feature during the software se­lection process, many vendors recommend that you do not actually use it. They suggest that regeneration is safer and that it plans differently than net change.

The second method is to create a suspense file that stores the rejected messages. When MRP regenerates, the system reviews the new exception messages against those in the suspense file. If they are identical, the messages are suppressed.

To Be Continued

For balance of this article, click on the below link:

Lean Manufacturing Articles and click on Series 14

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