Implementation of a Tray Management System (TMS) at the United States Postal Service Seattle Processing & Distribution Center (P&DC) has eliminated most of the physical labor in handling the mail and offers significantly greater management insight into operations. The TMS distributes mail to various processing stages and captures data, such as address and point of origin, for each mail tray using barcode labels.
In operation, this system distributes mail trays to various processing stages throughout the P&DC. TMS informs managers where each mail tray is located, how long it has been there and when it will move. Without all this information, managers are forced to send workers to manually inspect the progress of millions of mailpieces for each shift.
Morgan Fry, an independent contractor for the USPS, discusses the new system. �TMS is designed around the mail trays in use at postal facilities throughout the US.� Trays � carrying either a few feather-light pieces of mail or heavyweight totes carrying an entire branch�s mail � have to be conveyed on the same conveyor at the same time. �It�s important that the trays never bunch together or touch as they move through the system. The system is designed to transport trays ranging from empty to 50 to 60 pounds. Automatic scales will reject trays that are too heavy.� Zero-pressure accumulation means that lightly loaded trays won�t get pushed off the conveyor if they�re sandwiched between two heavily loaded ones.
The system, designed and installed by Siemens ElectroCom L.P., Novi, Michigan, is the centerpiece of a fully automated mail-processing facility. It consists of a network of 30-foot-high staging towers and conveyors to sort letters, flats and envelopes.
The heart of the TMS is an elevated monorail sorting system called NovaSort. The system consists of 33 trains that run on approximately 1.1 miles of extruded aluminum monorail throughout the building. The computer identifies each train and relates precise location in the building. The trains automatically unload mail trays, delivering them to various mail processing machines, automatic storage and retrieval systems (ASRS) or final dispatch operations, based on the destination information provided by one of several barcode scanners located along the track.
A key component of the system is the Intelliveyor motorized roller conveyor modules, supplied by Interroll Corporation, Wilmington, North Carolina, that provide a safe means of establishing zero-pressure accumulation. Each conveyor module contains one Driveroll, a self-contained 24VDC electric conveyor roller, and eight �slave� rollers connected via urethane o-rings. The design eliminates the need for external drive components such as belts, chains, sprockets or line shafts.
�Safety is one of the benefits of the Intelliveyor system,� says Frye. �There are no shafts or chains to catch loose clothing and, if necessary, you can grab a roller with your hand and stop it before it causes injury.�
A typical Intelliveyor 10-foot conveyor module contains four 30-inch Driveroll zones and the DriveControl devices needed for logic control and communication with other zones. Each zone operates independently. Controllers communicate via the Siemens ASI serial device network. This system now provides P&DC management with constant diagnostics and status reports on conditions at each conveyor area. By communicating up- and downstream, each zone knows whether to convey the tote or to hold it until the next zone is empty.
�The Intelliveyor is capable of running in either direction and at variable speeds,� Frye explains. �This means that it can bring totes to a gradual stop so that lightly loaded totes don�t slide forward as they would if the conveyor simply stopped abruptly.� Frye explains another benefit of the Intelliveyor system. �Line shaft conveyors run even when empty. Intelliveyor zones only run when needed, which saves on wear as well as energy costs.�
The Intelliveyor TMS system also includes 90-degree curves, each having two zones; 30- and 45-degree curves with one zone; five-foot long modules with two zones; and a unique 30-inch module that can be cut to any desired length. Also, special merge and diverge units are installed to help orchestrate tray traffic at conveyor intersections. Intelliveyor modules are plug and play. Twenty-four volt DC power passes from module to module using quick connect terminals. Each module operates in stand-alone form and can be mixed and matched with other Intelliveyor modules in any sequence or configuration.
Siemens� distributed ASI control modules are also key components of the TMS conveyor system. The ASI network allows external system commands to override DriveControl zone logic. The network capacity provides processing station buffering, traffic re-routing and other integration functions.
Fry explains the old system: �Prior to the introduction of TMS, incoming trays � holding letters or magazines weighing up to 50 pounds when full � were moved in wheeled carts (called gym paks by postal employees) with a modified electric forklift called a tugger.
The TMS completely eliminates tuggers, gym pak-wheeled carts and drivers. The computer controlled system tracks the history of thousands of trays accurately, allowing the USPS to deliver with pinpoint accuracy any tray in the building to the appropriate automated mail processing machine, such as optical character readers (OCR), delivery barcode sorters (DBCS) and high-speed flat sorting machines (FSM).
Steve Vineis is vice president of Interroll Corporation. You may contact him at 800-362-9616 or visit