PLC system transformation saves hardware investment

Abstract: In order not to increase the cost of transformation, we conducted an in-depth study on the PLC control software of different parts of the equipment. We found that the MOBY-i program of CC09-RB056 stored the reading and writing results in a data block DB580, while the other parts of the program obtained the vehicle model information from the data block, so we focused our research on this data block. At the CC09-RB056 station, if the current actual vehicle model is B12, the reading and writing results of MOBY-i are modified, and the problem is finally solved.

Our company plans to launch a new B-class car B12. Due to the particularity of the process line, this model needs to be sprayed in the paint shop of the fourth plant, and then enter the general assembly workshop of the second plant through the wax spraying line of the paint shop of the second plant. The specific process layout is shown in Figure 1: B12 passes through RB003~RB001 (the red part in the figure) to CC09-TC/RB048 (the black part in the figure), and then passes through CC09-RB050, CC09-RB052/054 to CC09-RB056. The MOBY-i read-write head here reads the information in the mobile data carrier on the sled and sends the model information to the general assembly workshop. Other models come from CC09-RD026 or CC09-RD06 and enter the wax spraying line through CC09-TC/RB048. However, the sled used for the B12 model is randomly drawn from the sled return line, and the sled data carrier still records the relevant information of the previous body, which does not match the current model B12. In order to ensure that the vehicle model information read here is consistent with the actual vehicle model, the most direct way is to add a new read-write station before this read-write station and write the vehicle model information into the sled data carrier manually.

Figure 1 On-site process flow layout

Since the equipment of the second plant's paint shop is provided by Dürr of Germany, the conveying system adopts the conveying method of roller bed and skid. The control of the equipment adopts the modular standard program developed by Dürr based on Siemens S7-PLC. In order to realize the transmission of vehicle model and spray color information between the conveying equipment and the automatic spraying system, and to judge the direction of vehicle body logistics based on quality information, the conveying equipment adopts RFID radio frequency identification system.
The second plant's paint shop adopts Siemens MOBY-i identification system, whose hardware system includes data carrier MDS430 installed on the skid, read-write head SLG43 installed in a specific position, and ASM451 interface module installed on the PLC main frame. The interface module has a built-in CM422 communication card to communicate with the read-write head.
In addition, the software system of MOBY-i is also relatively complex. Dürr has carried out a lot of packaging processing inside its software, which brings great difficulties for users to adjust and modify its software.
At the same time, adding the MOBY-i system also requires adding related hardware equipment, and requires the read/write head to be installed on the red device in Figure 1. The red part and the black part belong to two different PLC control groups, and a large number of interlocking signals need to be designed between the two, which also brings us great technical difficulties.
Solution
In order not to increase the cost of transformation, we looked for other ways and conducted in-depth research on the PLC control software of these two parts of the equipment. We found that the MOBY-i program of CC09-RB056 stores the read and write results in a data block DB580, and the other parts of the program obtain the vehicle model information from the data block, so we put the research direction on this data block. At the CC09-RB056 station, if the current actual vehicle model is B12, the read and write results of MOBY-i are modified, and finally the problem is solved.
First, define 4 Boolean type variables to record whether the vehicle model entering CC09-RB048, RB050, RB052 and RB056 is B12. The specific variable definitions are shown in the table.

Variable Definition

Since the models from RB001 (red part) are all new models B12, and the models from CC09-RD026 and CC09-RD046 (black part) are not B12, this rule can be used to determine the model entering CC09-TC/RB048, and the judgment result is stored in RB048-TYPE-B12. When the sled enters CC09-RB050 from CC09-RB048, the information of variable RB048-TYPE-B12 is copied to variable RB050-TYPE-B12, and then passed on in sequence. At the CC09-RB056 rolling bed position, the MOBY-i read/write head reads all the information inside the sled MDS and stores it inside the data block DB580. At this time, we can decide whether to modify the vehicle model information data in the data block DB580 according to the state of the variable RB056-TYPE-B12:
if RB056-TYPE-B12 = "TRUE", then modify;
if RB056-TYPE-B12 = "FALSE", then the data remains unchanged.
Other programs will send information to the assembly equipment based on the vehicle model information stored in DB580, notifying it to send the corresponding hanger to receive the painted body.
The above method involves three key technical links, namely information acquisition, transmission and modification.

1. Acquisition of RB048-TYPE-B12 initial information
The key is to detect the triggering sequence of the three proximity switches on CC09-RB048 when the roller bed is in motion: if the occupant switch of RB001 and the front occupant switch of CC09-RB048 are triggered at the same time, it indicates that the vehicle model is B12, and RB048-TYPE-B12 = "TRUE"; if the occupant switch of CC09-RD026 or CC09-RD026 and the rear occupant switch of CC09-RB048 are triggered at the same time, it indicates that the vehicle model is not B12, and RB048-TYPE-B12 = "FALSE". The specific procedure is shown in Figure 2.

Figure 2 Initial vehicle model information acquisition

2. Vehicle type information transmission
The vehicle type information needs to be transmitted from RB048-TYPE-B12 to RB050-TYPE-B12, and from RB052-TYPE-B12 to RB056-TYPE-B12. Taking the vehicle body sled moving from CC09-RB048 to CC09-RB050 as an example, the key step is to determine that during the process of the vehicle body moving from CC09-RB048 to CC09-RB050, if RB048-TYPE-B12 = "TRUE", then RB050-TYPE-B12 is set, otherwise RB050-TYPE-B12 is reset. The detailed procedure is shown in Figure 3.

Figure 3 Vehicle type information transmission

3. Modification of vehicle model information
According to the workshop vehicle model definition table, the B12 vehicle model code is defined as "0940". At CC09-RB056, the MOBY-i read/write station reads the skid MDS information and stores it in the data block DB580. All subsequent operations are based on this data. If RB056-TYPE-B12 = "TRUE", the data block DB580 is modified with the new vehicle model information "0940". The subsequent program will notify the assembly workshop to send the corresponding hoist according to the vehicle model information in the data block. The specific procedure is shown in Figure 4.

Figure 4 Model information modification

Conclusion
So far, we have completed the relevant technical transformation. Without any additional hardware investment, we have achieved the same functions as adding MOBY-i stations by exploring the existing software and adding some PLC programs. This has greatly simplified the technical solution for project transformation, saved equipment investment costs and the labor costs of hiring Dürr experts, and also greatly encouraged employees to learn, research and improve their business skills.