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Modern APS (Advanced Planning and Scheduling) systems do more than simply sequence jobs; they generate feasible production plans by modeling real physical and operational constraints on the shop floor.
Accurately defining simultaneous operation limits for resources connected to the same production line is critical to ensure that production plans can be executed smoothly in real operations.

This article examines the simultaneous operation constraint defined for 20CNC01 and 20CNC02 machines on the CNC Machining Line.

Scenario: Line-Based Simultaneous Operation Constraint

In production lines connected through conveyors or transfer systems, some machines cannot operate at the same time. The reasons include:

• Unidirectional material flow on the line
• Shared transfer mechanisms
• Shared line capacity
• Physical limitations preventing simultaneous loading on the same segment

In this scenario, 20CNC01 and 20CNC02 are connected to the same CNC Machining Line, and due to the line structure, they cannot operate simultaneously.

If this constraint is not defined in the system, the planning engine may theoretically schedule both machines in the same time period. However, in reality, the conveyor flow or line capacity would not allow this, making the plan infeasible on the shop floor.

The CNC Machining Line contains two machines:

• 20CNC01 – CNC Machine 1
• 20CNC02 – CNC Machine 2

How Is This Constraint Defined in an APS System?

The simultaneous operation constraint is defined at the production line level rather than at the individual machine level.

The implementation steps are as follows:

1. First, a production line code is defined (e.g., 0000000007).
2. Then, the parameter “maximum number of resources that can operate simultaneously” is specified for this line.

Example:
Maximum number of simultaneously operating resources = 1

3. The machines connected to the line (20CNC01 and 20CNC02) are grouped under this production line.

With this structure, the system ensures that only the specified number of machines connected to the line can operate simultaneously.

APS System Implementation Logic

After the constraint is defined, the scheduling engine:

• Does not schedule machines connected to the same line simultaneously.
• Ensures that the simultaneously operating resource limit is not exceeded.
• Maintains the production flow by placing operations sequentially.

Example:

• 08:00 – 09:30 → 20CNC01 active
• 09:30 – 11:00 → 20CNC02 active

The system automatically enforces the rule “simultaneous capacity = 1” defined for the line.

Reflection on the Gantt Screen

This constraint can be observed on the Gantt screen as follows:

When the Gantt chart is examined, it can be seen that 20CNC01 and 20CNC02 do not overlap on the time axis. While one machine is active, the other remains in a waiting state.

This situation shows that the simultaneous operation constraint defined at the line level is correctly enforced by the system.

Concurrent Resource Record in the Scheduled Jobs Tab

After the APS scheduling process is completed, the constraints applied by the system for each operation can be viewed in detail in the “Scheduled Jobs” tab.

As shown in the screen below, Line Concurrent Resource records appear in the “Assignment Status Description” field.

These records show the time intervals during which the line-based simultaneous operation constraint becomes active.

Example:

• Line Concurrent Resource: T1:03.03.2026 09:00 >>> T2:03.03.2026 09:30
• Line Concurrent Resource: T1:04.03.2026 09:00 >>> T2:04.03.2026 13:00

Here:

• T1 → Time when the constraint starts
• T2 → Time when the constraint ends

These logs indicate that the scheduling engine monitors the simultaneous capacity limit on the line over time and prevents the defined limit from being exceeded.

Why Is This Screen Important?

This section demonstrates that the system manages the constraint not only theoretically but also actively at the execution level.

• The line capacity limit has not been violated
• Alternative resources have not been scheduled in a conflicting manner
• The constraint has been applied based on specific time intervals