The control system is built around a step-based CASE structure using SCL, with each step representing a specific state in the sorting process. The logic was carefully structured to ensure reliable detection, sorting, and handling of all workpiece conditions.

Steps 0–20: Initialisation and Detection

• All actuators are reset.

• The stopper is extended to block the incoming part.

• If a workpiece is detected by the workpiece sensor, both conveyor tracks (SORT_TS_1 and SORT_TS_2) are activated. (In future testing, if using the workpiece sensor to control the conveyor fails, it may be a better idea to use Lightgate at the end of the previous (Pick And Place) station. With that logic, when the workpiece leaves the Pick And Place station, it will activate the conveyors at the Sorting Station.) 

• If the workpiece detection sensor triggers, both conveyors (SORT_TS_1 and SORT_TS_2) are activated, and a delay is introduced to allow the part to reach the stopper. This delay helps synchronise the mechanical motion with logic flow and prevent premature sensor readings.

Step 30: Colour Assignment Logic

This is a crucial step. The colour of the incoming workpiece is identified using a combination of two sensors:

• A Red sensor detects the presence of any red-colored surface.

• An Inductive sensor detects metallic properties.

These sensors are configured with the Prevent Collision feature in NX MCD, which helps ensure accurate interaction without interfering with object motion.

The logic assigns an integer value to the #MyCurrentPuck variable:

• If only the Red sensor is active → RED (2)

• If both Red and Inductive sensors are active → SILVER (3)

• If neither sensor detects → BLACK (1)

This allows for a reliable classification of the workpiece before it’s sorted.

IF "SORT_SENSOR_Red" AND NOT "SORT_SENSOR_Inductive" THEN

    #MyCurrentPuck := 2;

ELSIF "SORT_SENSOR_Red" AND "SORT_SENSOR_Inductive" THEN

    #MyCurrentPuck := 3;

ELSE

    #MyCurrentPuck := 1;

END_IF;

Step 40: Order Evaluating and Routing

Once the colour is known, the system uses HMI-defined targets to decide which slide needs the part. These orders can be set manually by the operator for both Slide 1 and Slide 2 via the HMI.

If neither slide needs the current colour, the workpiece is passed forward to the conveyor belt for de-assembly. Each workpiece type has a separate evaluation sequence. For example:

IF #Slide1.Black < "HMIVars".Slide1_HMI_Selection.Black THEN

    #Slide1.Black := #Slide1.Black + 1;

    #Step := 100;

ELSIF #Slide2.Black < "HMIVars".Slide2_HMI_Selection.Black THEN

    #Slide2.Black := #Slide2.Black + 1;

    #Step := 200;

ELSE

    #Slide3.Total := #Slide3.Total + 1;

    #Step := 300;

END_IF;

Steps 100–210: Separator Engagement

Based on the assigned destination, the appropriate separator is engaged:

• Step 100 extends Separator 1 for Slide 1.

• Step 200 prepares and extends Separator 2 for Slide 2.

Additionally, to correctly route the workpiece to Slide 2 using Separator 2, it is essential to know the current position of Separator 1 to ensure it does not block the workpiece if extended. Each action is followed by sensor confirmation before releasing the part.

Step 300: Workpiece Release

Once the separator is ready, the stopper retracts, allowing the workpiece to roll into the correct slide or move further to the De-assemble Station.

Steps 310–320: Reflex Sensor Check

A reflex sensor checks whether the part has passed into a slide. A timer confirms its presence; if not detected, the system proceeds to Step 330.

Step 330: Reset State

All actuator states are cleared, and the system returns to the start of the sequence (Step := 0;).

Reset Function

The HMI Reset Button clears all order counters, system flags, and actuator states. This is useful during station reinitialization or after completing an order (to be moved to the HMI Function Block in future development).