Replacing an Outdated Sorter-Conveyor Control System

Eastman Kodak Co. recently asked Optimation Technology Inc. (OTI, Rush, N.Y.) to help replace the warehouse control system at its distribution facility in Rochester, N.Y. Virtually all shipments from the facility are funneled through one sorting conveyor on the way to trailer trucks. Any downtime in this conveyor can cause catastrophic results, upstream and downstream.

12/15/2001


Eastman Kodak Co. recently asked Optimation Technology Inc. (OTI, Rush, N.Y.) to help replace the warehouse control system at its distribution facility in Rochester, N.Y. Virtually all shipments from the facility are funneled through one sorting conveyor on the way to trailer trucks. Any downtime in this conveyor can cause catastrophic results, upstream and downstream.

For 10 years, this conveyor was handled by a control system based around STD Bus technology. Three Intel processors, sharing memory and programmed in a combination of Ladder Logic and "C," controlled the sorting operation. All I/O points were based around Opto 22's Pamux Brain Boards and solid-state relay racks.

Though fast and efficient, the existing control system as configured required rebooting to escape communication problems and database corruption. Also, the new system needed a state-of-the-art database to reduce downtime by eliminating the need for daily data initialization. OTI, working with Eastman Kodak's engineers, was asked to find and implement a replacement sorter control system.

The solution required the control system to perform the following functions every second:

  • Induct a variable-sized carton;

  • Read, track and continuously confirm proper carton length;

  • Read the serial bar-code scanner;

  • Send the bar code to the Oracle-based ERP system, and retrieve lane assignment information in return;

  • Read and verify the weight from a scale;

  • Read tracking pulses every 10 milliseconds;

  • Track the carton to the appropriate lane;

  • Divert the carton to the appropriate lane;

  • Perform all tracking position updates, error checking, and divert confirmation logic; and

  • Insert a tracking history record into the Oracle database;

Another important requirement of the new conveyor control system would be its ability to allow Kodak to switch back to its former control system if debug and startup of the new system did not proceed well. Meeting this requirement would almost certainly require using existing I/O signal or coming up with some means of switching all the I/O signals.

Alternative solutions

During initial investigations, possible solutions were narrowed to two scenarios. The first was PLC-based control using new I/O points. The second was PC- based control using existing I/Os. PC-based control technology was chosen to fully simulate the conveyor to pursue this option further. Using the PLC as a conveyor simulator, and using an Oracle database on a development system, control code was put through its paces. After some debugging, it was found that the PC-based technology could do the job. Even though the Oracle database was located remotely on a large corporate network, reads and writes to the database were happening in milliseconds, along with all the tracking code running.

The conveyor system's most critical performance requirement was to scan its I/O points at least every 10 milliseconds to capture every pulse from the conveyor tracking encoder. This was necessary because missing a pulse would mean crushed boxes at the conveyor diverters. Even after scanning all the tracking code and performing database reads/writes, total program execution times were routinely about 1 millisecond. PC-based control worked well and performed all of the tasks.

Ability of I/O points to be switched from the old to the new system in seconds also turned out to be an advantage. During downtime on the conveyor, the startup team moved one PC into the warehouse, and performed debug operations by switching a cable. As bugs in the code were found, they were fixed. Earlier simulation was so realistic that the actual on-site debug was virtually identical. This saved numerous off-hours of testing, which brought the project in on time and under budget.

For more information about OTI, www.optimationtech.com or visit www.controleng.com/freeinfo

To find integrators, go to www.controleng.com/integrators





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