It Just Can’t Work Without It!

The Problem: Shangai GM needed state-of-the-art air compressors for their new plant, but they also needed central control.
The Answer: Atlas Copco+Modbus+ProSoft Technology

Shanghai General Motors

When the white, 1999 Buick Xin Shi Ji (New Century), the first made by Shanghai General Motors (SGM), rolled off the assembly line, it broke new records in auto production.
 “Not only did we build this plant in 18 months,” said John Smith, CEO of General Motors in the U.S., “we also put into place all of the quality, safety, environmental and manufacturing processes necessary to build an outstanding product. We have transferred state-of-the-art technology to this plant, including third generation robotic technology not even used in North America.”
 What is this state-of-the-art technology? Let’s ask another question. What would you say is one of the most important pieces of equipment in an automobile assembly line plant--something that is tied to nearly every function in the production of a new car?
 Give up? It’s easy: the air compressors. When a worker puts on a tire or attaches the new seats, they use a pneumatic tool. These tools are run by...you guessed it...air pressure. So, it goes without saying that the air compressors in an auto assembly line plant would be of primary importance.
 Central Control for the Compressors
 

There are a total of 8 Atlas Copco compressors in the Shanghai plant. Six of these compressors are the ZH model, which is a centrifugal type, having an Allen-Bradley SLC 5/03 embedded in their control systems. The impeller design of the ZH model is state-of-the-art, with capacities starting at 3,000 cfm, in both single and multi-stage, these compressors can provide discharge pressures ranging from 25 to 400 psig.
 The remaining two compressors are the Z-pack model, equipped with built-in Modbus communications. This created a problem in networking the compressors together, since the Allen-Bradley SLCs are not Modbus compatible. The System Integrator, Shanghai Yuandong Science & Technology contacted Rockwell Automation Shanghai and ProSoft Technology in California, a company specializing in protocol communication devices. They installed ProSoft’s 3150 Modbus interface module into the SLCs onboard the ZH compressors, which then allowed all of the compressors to link to the HMI Host Station via DH485 network.
 “Normally every Atlas Copco compressor would be controlled individually,” said Chen Zong Liang, General Manager of Shanghai Yuandong. “With individual control, we found that some compressors would load, unload, and even stop running simultaneously. This made compressor output very inconsistent and therefore unstable. By using ProSoft’s 3150-MCM module, we were able to directly connect Allen-Bradley’s SLC with Atlas Copco’s compressors using the Modbus protocol. With central control, it was possible to stagger the actions (start, load, unload or stop) of every compressor according to the charge situation.”
 “Enabling the compressors with central control was easy to implement and created a smooth running operation,” said Lenus Hong, Asian Regional Sales Manager for ProSoft Technology. “Not only did it help increase production, it created a cost savings in terms of electricity and maintenance costs. All of this translates into higher profits.”
 When asked how the ProSoft module improved the plant processes, i.e. functionality, speed, convenience, or financial benefits, Liang simply replied, “It just can’t work without it!”
 Modbus Interface
 “With these Modbus communication interfaces, manufacturers are making a great deal of data available to the processor which can enhance the system control,” said Doug Sharratt, lead developer for ProSoft Technology. “The 3150-MCM product, when configured as a Master, is able to read and write to these devices, allowing the SLC ladder program direct access to the devices’s data.”
 In the past, many communication systems were closed. Since the Modbus protocol is open it has become an industry standard for many industrial devices available today.
 State-of-the-art Auto Manufacturing
 The opening of the Shanghai GM Plant was met with a considerable amount of fanfare. More than 2,000 Chinese and U.S. government officials, including Shanghai GM president Chen Xianglin, CEO of General Motors in the U.S. John Smith and Shanghai Communist Party Chief Huang Ju, along with journalists from around the world attended the opening ceremony at the new SGM plant in the Pudong New Area, Shanghai’s industrial development zone.
 The first year of production at the new plant was so successful that, according to “Automotive Intelligence News,” one year after the first Buick came off the assembly line, SGM began producing a second vehicle, the first Buick GL8 wagon, becoming the first automaker in China to make two distinct vehicles on the same production line.
 Denis Dougherty, Executive Director of Manufacturing for SGM, said the plant’s highly automated equipment was designed so it could be re-tooled within minutes to make different products. The facility is capable of making “the gamut of single-body cars,” said Dougherty. “You’re crazy if you can’t do that in today’s auto industry.”
 

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