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The ABCs of Warehouse Technology

Dec. 1, 2008
What are RF, RFID, VDP, PTL and WMS? This article spells out the basics of some of the computerized systems distributors are starting to use in their warehouses.

For those readers who think that radio frequency (RF) and radio frequency identification (RFID) mean the same, welcome to a group of similarly confused people. If voice-directed packing (VDP) and pick-to-light (PTL) are unfamiliar terms, welcome to an even larger group. These acronyms refer to the warehouse technologies explained below.

RF. Radio frequency has come to mean the wireless reading of bar codes during picking and sometimes for counting inventory. Bar codes are read by devices that transmit (via RF) the data to the main system, where it's validated against data for the items on an order. If a wrong item or quantity is picked, the device alerts the picker.

Many electrical wholesalers use RF in two ways: where pickers use a printed ticket to find the items and then read the bar codes; and where data for items to be picked is shown on an LCD display on the device, which is then used to read the bar codes. RF devices are expensive, as is the equipment that communicates with the devices and the enterprise resource planning (ERP) system. RF is widely used because it increases picking accuracy, and can sometimes can increase productivity. Its limitations are described next.

RFID. Radio Frequency Identification does not involve bar codes. It refers to the wireless reading of data stored in a memory chip embedded in or attached to a box, piece of equipment, etc. In addition to an item's code number, a chip (often called a “smart label”) can store unit- or carton-specific data such as date of manufacture, manufacturer's spec number and serial number. A “read/write” chip allows data to be added or updated by each user (often the date of receipt), which allows tracking at every stage of a supply chain.

An RFID device sends a signal toward a chip, which then transmits its data to the device. The device then transmits the data to the ERP system, where it's verified against data for the order being picked. Reading and transmitting is done via radio frequency, which accounts for the confusion some distributors have in differentiating RFID from RF. To their advantage, RFID devices don't need a direct line of sight to read, items do not have to be standing still, and several chips can be read simultaneously. RFID dramatically reduces the time needed for all warehouse tasks that involve data capture. Chips can withstand high temperature and humidity, and are unaffected by dust, dirt, glaring light, lack of light, etc. — conditions that make many bar codes unreadable.

Wal-Mart has mandated that all of its suppliers place RFID chips on pallets and some cases, and the U.S. military has started to use them. But the cost of the reading devices and especially the chips is still so high that most manufacturers aren't using them. Few if any electrical wholesalers now use RFID or are likely to use it in the near term.

VDP. Voice-directed picking refers to a “voice recognition and synthesized-voice-response” system. Users wear devices they have “taught” to recognize their speech patterns and accents. Earphones and a microphone are attached to each device. The ERP system transmits data to the VDP server about each order ready to pick, and the server stores it. The VDP software determines which person is available at any time, and the VDP server transmits data to a specific device.

The device transforms the data into that user's voice, “telling” him or her the location to go to, the SKU number involved and the quantity. As users pick, they tell the device which SKU number is involved and its quantity. The speech is transformed into data, which is transmitted by the VDP server back to the main system for verification (and any error alert).

VDP is more expensive than RF, because it requires a second computer mentioned earlier and an interface between it and the main system. Despite its cost, VDP is used in many sizeable warehouses because users do not have to read anything or hold any devices, which clearly saves time. It also overcomes language challenges for workers whose primary language is not English. However, due to its comparatively higher cost, only a few electrical wholesalers might be interested in VDP.

PTL. Pick-to-light uses a system where one LCD display device is located next to the pick slot/bin for each item. Sometimes there will be one device for two items. Each LCD display unit is snapped onto a special cable that runs along the front edge of the shelving. The main ERP system transmits data to the PTL server about each order ready to pick, and the server stores this data. When pickers press a button to indicate they are available, the PTL server illuminates a light on the LCD device for each item involved and in that picker's zone; the quantity to pick is displayed on each device. Each device also contains buttons pickers use to confirm picks, and buttons they can use to enter the actual quantity picked if it differed from the quantity displayed. A glowing red light signifies an error. With PTL, several pickers are usually involved in picking any given order, but work independent of each other.

PTL is the fastest method of picking and can sometimes reduce the number of pickers needed by 50 percent. It can also allow the use of people without product knowledge (who get paid less). But the cost of hardware and installation make this by far the most expensive of the technologies. It's unlikely that any electrical wholesalers use PTL.

WMS. Warehouse Management System (WMS) refers to special software that can be installed without reading devices, but is almost always installed with RF. A WMS does things that RF, VDP and the other systems discussed in this article can't do. In real-time, it tracks the location(s) of every item in the warehouse, and the quantity stored in each location. It can also track two items that share a location. During put-away, if slot locations are “floating,” it determines which slot to use (based on item dimensions and weight, and slot availability); when to pull down overflow/bulk; how much to pull; and where to put it (especially if pick slots float). For picking, for each order it determines which picker(s) to use and how much to pick from pick slots versus bulk/overflow slots. Pick and put-away locations are selected in real-time to minimize travel time, subject to constraints such as ensuring wire is always in the wire room, chemicals are always in the hazardous storage area, etc. A WMS can also generate a manifest for each truck. For fixed-location slots, a WMS can be used regularly to determine how to re-slot a warehouse or area to reduce labor effort. Users can define activity standards (such as for picking), and the system captures labor data and prints productivity reports.

A WMS produces saving because users spend less time putting away or picking items. Costs include the software, training, (usually) a separate computer and interfacing with the main system. But another “cost” can be warehouse re-arrangements needed to ensure a WMS would not make things worse. Many electrical wholesalers use some form of WMS, but the cost is still prohibitive for small and even mid-size companies.

Dick Friedman is a recognized expert on warehouse operations, management and technology for electrical wholesalers, but he does not sell computer systems or warehouse technology or equipment. Based on more than 30 years of warehouse experience, he helps wholesalers reduce warehouse errors and increase productivity; often through inexpensive changes to operations, management or technology. He is a contributing author to Electrical Wholesaling, and consults with readers. Call (847) 256-3260 for a free consultation about improving warehouse accuracy and productivity or visit for more information or to send e-mail.

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