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. From its inception, Valley's policy is to ship every order the same day it is received. This has necessitated continuous improvements in the way the materials are handled.
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. Though this system is quite capable, a need for increased capacity led Valley to install a second sorting line. The goals for the new system were Modularity, High speed sortation, Ease of use, Low maintenance and built-in flexibility for future growth
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 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. Thousands of dollars were eliminated by not having to hard wire the I/O devices back to the main computers All of the original goals have been met or exceeded