It Just Can't Work Without It!

Danetta Bramhall

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."

Experts in Action

(Sidebar to the Shanghai General Motors Story)

by Danetta York

The building of Buicks by Shanghai General Motors was a joint venture between the Shanghai Industry Automotive Corporation and General Motors Corporation. John Smith, chairman and chief executive officer of General Motors, called the project an example of a successful Sino-American business partnership.

In a massive advertising campaign, Shanghai GM said they were "doing things that nobody has done in China before. Appropriate actions were taken in every aspect of our manufacturing. It takes the courage of pioneering to stay ahead of others."

Employing over 1,700 Chinese workers, the Shanghai Municipal Government designated the building of the plant as their number one project for 1998. "In a city where it's said to have 20,000 construction projects underway at any given time, that's quite a statement," said Rudolph A. Schlais, Chairman of the Board Shanghai GM,

Atlas Copco Compressor Technique

Headquartered in Belgium, Atlas Copco has made a name for themselves as a world leader in the field of compressors, generators and expansion turbines. So, when plans to build the new 160,000 square meter Shanghai General Motors plant were being drawn, it was only natural that a call was made to Simon Ding in Atlas Copco's Shanghai office. Atlas Copco's job was a vital one for the new plant. Quite simply, they needed to help SGM choose the correct type of compressor to ensure the quantity and quality of the compressed air the plant would need.

But this was no easy task. With a plant this size, capable of manufacturing 100,000 vehicles per year (that's an average of 273 cars per day, 7 days a week) the need for the proper compressors, with enough pressure and volume, delivered at precisely the right time, with minimal operating costs, was crucial.

With over 100 years of experience in the compressor business, Atlas Copco understood SGM's needs. Their engineers helped calculate the energy consumption needed, compared options and recommended the system currently in use at the plant.

Shanghai Yuandong Science & Technology

The air compressor station for the new plant was constructed by Shanghai-MG Gas Products Co., Ltd., and consisted of six ZH air compressors and two ZR air compressors. Shanghai Yuandong Science & Technology, Ltd. then built the central control system using Allen-Bradley SLC-500s for all eight compressors.

"Because the two ZR compressors were only equipped with built-in COM2 fixed communications via the Modbus protocol we needed an interface module to be able to link all of the compressors to the Host Station," said Chen Zongliang, General Manager for Shanghai Yuandong Science & Technology. "We chose ProSoft Technology's 3150-MCM module, which was designed to fit into Allen-Bradley's SLC rack. ProSoft's module allowed us to use central control on all of the air compressors, keeping the output steady and running normally. This was the first time this type of central control had been done in China."

ProSoft Technology, Inc.

ProSoft Technology, Inc. specializes in the development of inter-network communication solutions. The company was incorporated just over 10 years ago with three employees and a single product. It now boasts over 200 products and 150 distributors in 32 countries.

"The first module we manufactured allowed Allen-Bradley PLCs and SLCs to communicate with Modbus devices," said Lenus Hong, Asian Regional Sales Manager for ProSoft Technology. "We're still known in many circles as the 'Modbus communication company,' even though we also have modules for numerous other protocols including, Modbus Plus, PROFIBUS, Honeywell DE, DNP, Modbus TCP/IP, and HART. Our newest product line, the ProLinx Communication Gateways, are out-of-the-chassis connectivity options previously unavailable. With these applications, connectivity solutions can easily be added to new Allen-Bradley ControlNet, Ethernet and DF1 based implementations and to older Remote I/O legacy systems."

The ProSoft team has been optimized to quickly develop solutions based on market needs and customer requests. With this active product development program, customer recognition of their product quality has positioned ProSoft Technology as a world leader in the development of new industrial connectivity solutions.