Supporting Maintenance Scheduling: a case Study

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• Identification of the scheduling period and equipment availability for preventive maintenance in this period
(step 1of the algorithm)
• Tasks ordering (steps 2 and 3);
• Allocation of tasks to each technician based on the defined order and equipment availability (steps 5 – 6). The tasks ordering is made in two steps. In the first step, all the maintenance tasks are ordered by a criticality index for equipment, designated by Business Impact Rating (BIR), in descending order. Then, in the second step, for each maintenance tasks with the same BIR, a second sorting is done by due dates. The tasks will be assigned following this last order. Both ordering have the aim to minimize delays on the execution of maintenance tasks, especially in the most critical equipment. Maintenance tasks with the same BIR and due date will be sorted by their processing times in descending order. These orderings, besides being used to prioritize the assignment of tasks, will also allow the visualization of all the maintenance tasks that should be executed in a short–term horizon and to be a support in the negotiation between manufacturing and maintenance departments to provide time for preventive maintenance performing. The visualization is possible through Maintenance Tasks Table, a table in the company’s
CMMS that contains all tasks ordered to be scheduled. The main objective of BIR is the impact evaluation of equipment breakdown on productivity. BIR is obtained through two criteria CA – Equipment utilization and CB – Availability of alternative equipment. The equipment utilization criterion shows the production line’s criticality. Aline that is being used more than other lines is more critical because it has less time available to perform maintenance tasks and less capacity slack to be able to recover from downtimes and meet deadlines when there are delays. The criterion availability of alternative equipment intends to show if there are equipment in the production line that can do the same operations as the equipment that is being assessed. The existence of alternative equipment can decrease the impact of a breakdown since production can continue, using the other equipment. Each criterion can be classified in three levels, where the higher level is the most critical. Each combination of two criteria was analyzed and for each one, a classification with four levels was assigned as presented in Table 1. Table 1 - Business impact rating Equipment utilization Availability of alternative equipment BIR
3 2 4
3 1 3
2 2 3
2 1 2
1 2 2
1 1 1 The planner defines and introduces in the scheduling tool a scheduling period. Consequently, it will be possible to identify the equipment with available intervals during this period. Consecutively, the equipment should be ordered by BIR and the maintenance tasks associated to the available equipment should be imported from the Maintenance Tasks Table. The allocation of maintenance tasks as previously mentioned, should consider the availability of spare parts, equipment and technicians. So, the algorithm starts the allocation process with the equipment with higher BIR. This way, the allocation is done in parallel among equipment with the same the BIR taking into account due date of maintenance tasks, and in serial among the equipment with different BIR value. The ordering by processing times prioritizes the tasks with higher durations. While the equipment is available and there are also available technicians, the PMS will check if the task requires spare parts, and if they are available. In case of unavailability of the spare parts, spare part acquisition is requested and the maintenance task will not be scheduled. In contrast, if the spare part is available the PMS will search an available and competent technician. The same process happens when the maintenance task does not require spare part. The allocation of maintenance task to technician starts selecting the technician with, at least, the lowest level competence required. If there is an available and competent technician, the maintenance task is scheduled. When a maintenance task is scheduled, its data information is updated. At the end, after checking if all the maintenance tasks imported can be scheduled during the availability time window of equipment, the PMS will return a schedule solution. The PMS structure is the following
Step 1. Identify the time windows availability of equipment and technicians
Step 2. Sort the maintenance tasks by BIR in descending order

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Step 3. For each BIR value
3.1 Sort the maintenance tasks by due date.
3.2 When the maintenance tasks have the same BIR and due date, order by processing time in descending order.
3.3 Return a Maintenance Tasks Table.
Step 4. (Scheduling period)
Define the scheduling period.
4.2 Filter the available equipment for the pre-selected scheduling period
4.2.1 Order the equipment by BIR in descending order
4.2.2 Import the maintenance tasks previously ordered associated to each available equipment in the scheduling period.
Step 5. (Allocation for each equipment following the order defined in 4.21.)
5.1 While the equipment is available and there is competent technician For each imported maintenance tasks ordered by BIR and due date
5.1.1.1 If the maintenance task requires spare-parts:
5.1.1.1.1 The spare part is available Go to step 5.1.1.3.
5.1.1.1.2 The spare part is not available Request the spare part acquisition and the maintenance task returns to Maintenance Tasks Table to be scheduled later.
5.1.1.2 Else Go to step 5.1.1.3.
5.1.1.3 Filter the technician with a level of competence equal or higher than it is required.
5.1.1.3.1 For each technician
5.1.1.3.1.1 If the technician is available Schedule the maintenance task and go back to 5.1.
5.1.1.3.1.2 Else Maintenance task returns to Maintenance Tasks Table to be schedule later and go back to 5.1.
Step 6. Return the solution.

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