Valley Record Distributors of Woodland, California is one of the nation's largest, full-service wholesale distributors of pre-recorded music and video in the United States. Their customers consist of the thousands of retail music and video stores, ranging from small family firms to large chain operations. Founded out of the back of CEO Barney Cohen's garage in the early 1980's, Valley today distributes over 200,000 different selections from its 200,000 square foot warehouse outside of Sacramento with a state-of-the-art material handling system. From its inception, Valley's policy was to ship every order the same day it is received. But this policy has been tested over the years as business volume grew, with over 200,000 pieces currently being shipped each day. This has necessitated continuous improvements in the way the materials are handled.

Project

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In 1994, Valley added its first automated conveyor system that would apply pricing and bar code labels, as well as provide a means to sort the pieces using a bar code reading system. The system was installed by Dorner Manufacturing Corporation of Harland, Wisconsin. 100 sorting stations are split in two rows, 50 per side. Sensors are at every station. When an item arrives at its assigned station, a gate opens to allow the item to be stacked and accumulated at the sort location. All of the sorters and their respective readers are hard wired back to a central computer at the front of the line through a data terminal block. When the computer sees that an order has been completed at any of the stations, it automatically turns on a light beacon to indicate that the items can now be placed in a shipping box and removed from the sorting station.

Though this system is quite capable, a need for increased capacity led Valley to install a second sorting line. One big short coming is the fact that if any sorter station has to be shut down for any reason, the whole line must come to a halt. Fortunately, the reliability of the system makes this relatively infrequent. A second weakness is space. All of the sorting stations are in one long straight line covering almost 300 feet of floor space.
The goals for the new system were:

• Modularity
  
• High speed sortation
  
• Ease of use
  
• Low maintenance
  
• Built-in flexibility for future growth
  

Design Concept

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In 1997, Dorner was once again called upon to develop and install the second labeling and sorting system adjacent to the older system. Dorner awarded the control aspects of the system to Professional Controls Corporation (PCC) near Milwaukee, Wis. PCC incorporated Dorner's newer, more flexible electronics into the modular design that would allow each sorter station to be maintained individually. At any time a sorter station could be taken out of service without affecting the rest of the sorting operations, which can't be done on the previously installed system. Another innovation to the new design, would be a Y-spit at the front end that would allow 50 sorting stations on one side and 50 sorting stations on the other side, operating simultaneously. The advantage is that each side is independent.
Dorner provided special vertical dispensers for the front of the conveyor line for the purpose of loading the product. All dispensers are configurable to accommodate any type of product, be they CDs, audio, or video cassettes. These dispensers are hand loaded from the totes containing the picked items. The picking procedure remained the same. There are ten different dispensers in total. Dorner also supplied seven high speed labelers that are located between the bar-code readers and dispensing area.

The control system utilizes six computers for main control and monitoring, three PROFIBUS -DP networks that are controlled by Siemens PROFIBUS interface cards used in conjunction with 126 Siemens S7-215 micro programmable logic controllers (PLCs). Also being used are 12 Siemens ET200B distributed I/O nodes of PROFIBUS-DP.

Aside from the obvious advantage of eliminating straight wiring to all the I/O points in the system, the PROFIBUS-DP system has some tremendous advantages over non-networked systems. The biggest of these is modularity. Each sorting station has its own unique PLC and operates independently from the other sorting stations. The PLCs communicate with the main computers via the PROFIBUS network. Because PROFIBUS can communicate at almost 12 megabaud per second, it is extremely fast, being more than adequate to handle the speed requirements of the system described here.

The new sortation system provides the ability to off load some of the overhead of the main control system to individual stackers. This simplifies the overall control scheme, dramatically decreasing troubleshooting time. Dorner also developed a special maintenance tool that connects directly to the S7-215 PLCs that allows the stackers to be repaired and maintained individually. This means if there is a problem with one of the stackers, production does not need to stop for the repair.

Summary

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Thousands of dollars were eliminated by not having to hard wire the I/O devices back to the main computers. The PLCs and PROFIBUS made that benefit possible.
The line operates very efficiently, increasing production substantially. Less warehouse space is consumed by the machine layout. If the machinery has to be moved to another location, its modular design makes this much easier than previous designs. For example, four stackers can be broken down and shipped as one unit, making it easy to dismantle and reconstruct quickly.
All of the original goals have been met or exceeded. During the first few weeks of operation, the speed and efficiency of the new sortation line was exceeding that of the first-installed system. There has been little downtime for maintenance and repair, and there are fewer errors with the bar code reading and transfer process. The older system will not be retired, but the newer system is certainly a big boost to overall productivity. As Valley continues to grow its operations into the new millennium, the new capacity is ready to meet the challenges that lie ahead.