WMS Pros and Cons

Sept. 1, 2006
Modern warehouse management systems (WMSs) can produce fewer fill errors, greater productivity and better customer service.

Although the majority of electrical distributors have not yet implemented a traditional warehouse management system (WMS), which scans bar codes for receiving, stocking and picking, those that have taken this step enjoy increased productivity and accuracy. While many electrical distributors are still contemplating moving to bar-code scanning, there's a whole new generation of WMS technology that improves even more upon the positive results of bar-code scanning.

Before looking at newer hardware devices, let's review the major functions of a true WMS, which approximately one-third of the electrical distributors on Electrical Wholesaling's Top 200 list use. It employs bar-code readers, special software and doesn't print any tickets — it's almost paperless.

Traditional WMS


The process starts when a wireless bar-code reader — referred to as an RF (radio frequency) reader — is used to read bar codes on the shipping labels of pallets. This identifies the purchase order (PO) number involved. (Without a coded shipping label, someone literally reads the packing list and keys in the PO number.) Next, the bar code on each box, case or piece is read to capture the item's ID and quantity. For each scan, the WMS software compares the scanned item ID and quantity to the PO (or received EDI) data and alerts the user if an item is not on the PO or if the quantity scanned is not equal to the quantity ordered. If items lack a readable bar-code label, the receiver prints labels, often with a wireless, portable printer and affixes them to the items.

Put away

For put away, the user scans the shipping label on a pallet, and the RF device displays the location (or address), item code and description of a few items. An address is either the permanent primary home of the item, the permanent bulk-storage home of the item or a system-determined location for warehouses that do not use fixed locations. When determining location, the software's user-defined rules establish where an item is to be put away. The location information is displayed on the scanning device's liquid crystal display (LCD) in a software-determined sequence that minimizes travel time. When an item is placed in its slot, bin or rack, the user scans the bar code on each box or item and then scans a bar-code label on the shelf, which captures data about what, where and how much was stored. If incorrect data is scanned, an alert message displays immediately.


If items are stored in both a pick area and a bulk or overflow area, the WMS software determines when it's time to refill the pick area. The scanner's LCD shows the location, item code and description for a few items to be retrieved with the items sequenced in an order to minimize pulling time. The scanner also displays the item's final destination. When an item is pulled, the user scans the item's code and location bar code; when an item is placed in its new slot, the user scans the bar code on each box or item in addition to scanning a bar-code label on the shelf. Feedback on any mistake is immediate.

Picking and shipping

Remember, no pick tickets. When it's time to pick an order, the LCD on an RF device displays general data about the order, location, description and quantity of each item to pick. The location to pick from may or may not be the primary storage location for an item; it could be the bulk or overflow area. Again, the sequence in which the item data is displayed minimizes the picking time. The bar code for each picked item is scanned. As usual, feedback on any mistake is immediate. The last step is for the system to print a packing list containing data on what was actually picked — unless a separate ship-confirm step is used.


When used, this step takes place near a loading dock. The bar code for the order and for each item picked is scanned to determine if the order was filled properly.

Physical counting

Based on user-defined count rules, the WMS software determines when and what items and locations to count, and it displays this data on a user's RF device. Like picking, counting involves scanning the bar code of each item, box and location, or scanning a code and keying in a manually counted quantity.


Re-slotting doesn't involve any hardware. True WMS software uses data on the warehouse-slotting arrangement and data on transactions (for example, the number of trips to pick a particular item) to suggest a different slotting arrangement — one that would increase productivity and reduce space requirements.

Pros and Cons

A WMS can reduce operating costs by increasing warehouse productivity. With a WMS, warehouse personnel don't have to spend time reading or handling paper, keying in data or thinking about where they need to go. A true WMS can help avoid warehouse expansion by determining a slotting arrangement that needs less space. Furthermore, because the WMS software does the processing, fewer mistakes are made, and errors that do creep in are immediately identified. All this increases the level of customer service, which also can reduce costs.

The initial investment is the biggest negative for any form of WMS. RF devices have gotten less expensive, but they still aren't cheap. The cost of special WMS software and required training can easily exceed the cost of the devices. Another negative is the need to rearrange many warehouses for a WMS to work well. And don't forget to add the need to implement tight procedures and controls. This can all cost many thousands of dollars.

New Technologies

Voice-directed picking

With voice-directed picking (VDP), each picker wears a headset with an earpiece and a mouthpiece microphone. The headset attaches to a wireless computer worn on a work belt. Each person “teaches” their wireless computer their speech patterns. When an order is being picked, the main business system sends data to the VDP computer-server, which in turn transmits data to the wireless computer of the system-determined picker. The wireless computer then transforms the data into audible commands — the picker is told where to go, what to pick and how much to pick. As they pull orders, pickers talk into the microphone, identifying what was picked at what location. The portable computer transforms the speech into data and transmits it to the computer server, which in turn transmits it back to the main system for verification. The picker is immediately notified of any picking errors. VDP can also be used for put away.

It's no secret that VDP costs more than bar-code reading, and each picker must have his or her own device, which also adds to the cost. Unlike bar-code readers, a wireless belt computer cannot be used quickly by anyone other than the original teacher, and it can take several hours to program a device and teach someone how to use it. On the plus side, the cost of educating pickers is minimal, and VDP can increase productivity more than bar-code reading. VDP also reduces errors more than bar-code reading.

Pick to light

With pick-to-light (PTL) technology, a display device with light-bulb-like indicators and a numeric readout is mounted on the front of each shelf where items are stored. All display devices in the warehouse are wired together and connected to a PTL computer, which in turn is connected to the main business system.

When an order is to be picked, the main business system sends data to the PTL computer, which illuminates a green light on the shelf display device for each involved item. The device also displays the quantity to be picked. After an item is picked, the picker presses a button on the device to indicate the item has been picked. When the pick-confirm button on all of the display devices has been pressed, a master display device illuminates a green light to indicate that the picker is ready for the next order, or a red master light indicates there is an error to be corrected.

As buttons are pressed, data is transmitted to the PTL computer, which in turn transmits it back to the main system. PTL can also be used (as put to light) for put away and replenishment.

Productivity is very high because pickers do not spend time reading RF displays, pointing RF scanners or waiting for confirmation that a RF scan worked properly. Error rates are also very low because there is only one display device for each item.

PTL is the most expensive of the WMS technologies described because each item requires its own device, and the cost of installing the devices and connector cable is considerable. As with other technologies, the warehouse needs to be specifically arranged for VDP or PTL, and tight procedures and controls must be implemented.

Richard “Dick” Friedman's firm helps distributors select ERP and WMS systems, and negotiate specific performance contracts. Visit his Web site at www.GenBusCon.com. Reach at (847) 256-3260 or e-mail him at [email protected].