MES in vehicle manufacturing - Part Picking Error Proofing

In Assembly Shop of vehicle/engine/transmission plant, there’re lots of assembly operations, and the lineside area is crowded and flexible, which brings lots of challenges in management:

-          How to deal with situation that a worker missed one part?

-          How to deal with situation that a worker picked wrong part?

-          How does conveyor line know the manual operations are done, and is ready to release from current station?

To meet these challenges, we can design a Part Picking Error Proofing module, and integrate with automation devices via sensors and PLC.

Let’s take an example of engine plant.

Firstly we need to expand BOM.

Normally when Engineering team release a product, an Engineering BOM and a Manufacturing BOM will be attached to the product.

Engineering BOM defines relationship between product and its semi-product and components.

For example, product A consists of semi-product A11 and A12, which consist of component A21, A22:

Layer	Part Number	Part Name	Qty
0	FG20170001	Product A	1
1	SA20170011	Semi-product A11	1
2	PR20170021	Component A21	10
2	PR20170022	Component A22	20
1	SA20170012	Semi-product A12	1
2	PR20170021	Component A21	4
2	PR20170022	Component A22	6

 

From Engineering BOM we can see the assembly relationship and quantity of each part.

But from point view of manufacturing, Engineering BOM is not detailed enough, so normally we need to expand it to Manufacturing BOM.

Manufacturing BOM will mark assembly part as building part or buying part, and for component, it will also mark assembly station and quantity. As showed in below table, we can see that part A22 under A11 has been split into station 1002 and 1003 for assembly:

Layer	Part Number	Part Name	Station	Qty
0	FG20170001	Product A		1
1	SA20170011	Semi-product A11	1010	1
2	PR20170021	Component A21	1001	10
2	PR20170022	Component A22	1002	10
2	PR20170022	Component A22	1003	10
1	SA20170012	Semi-product A12	2010	1
2	PR20170021	Component A21	2001	4
2	PR20170022	Component A22	2002	6

 

Manufacturing BOM is detailed enough for purchasing and manual assembly, but it’s still not good enough for Part Picking Error Proofing: we also need to know the storage location of each part, so we need to further expand it to Process BOM:

Layer	Part Number	Part Name	Station	Qty	Rack Number
0	FG20170001	Product A		1
1	SA20170011	Semi-product A11	1010	1
2	PR20170021	Component A21	1001	10	1
2	PR20170022	Component A22	1002	10	2
2	PR20170022	Component A22	1003	10	1
1	SA20170012	Semi-product A12	2010	1
2	PR20170021	Component A21	2001	4	1
2	PR20170022	Component A22	2002	6	1

 

By analyzing Process BOM, MES gets the Part Picking Error Proofing request of each station(which Stack Number and Quantity), and then transfer the request to station PLC via OPC, so now PLC knows in this station, which part from which stack should be picked, and how many of them is required to pick.

Then PLC will execute the detailed Error Proofing process.

We need to install additional lamp and sensors, the sensors can detect whether it’s blocked by object in short distance, and thus send signal to PLC accordingly, as referring to diagram 2.10-1:

Diagram 2.10-1 Part Picking Error Proofing process

 

The detailed process:

1)       Engine comes to station, PLC reads engine number from RFID, and sends it to MES.

2)       MES analyzes Process BOM and gets Part Picking Error Proofing request of this engine in current station, and then sends the request to PLC via OPC; PLC analyzes the request and turns on stack lamp accordingly.

3)       When worker picks a part from stack, his arm blocks the sensor, so sensor sends a blocked signal to PLC, which will be regarded as a part picking operation by PLC; when the total picking time has reached to the number in request, PLC will regard the error proofing of this part is completed, so it will turn off its stack lamp; when all parts have completed Part Picking Error Proofing, PLC sends Error Proofing Completed signal to MES, and allow engine to leave current station.