We have worked with several South African companies that have progressed through the stages of pick technology evolution from paper to RF and seen huge productivity and accuracy improvements. One of the hottest topics in these discussions is around "Which is better, Pick To Light or Pick To Voice?"
One of the hottest topics in these discussions is around “Which is better: Pick To Light or Pick To Voice?” To be honest It depends on many factors including the number of pick faces, number of pickers, amount of travel between picks, etc. But there are also some other considerations, such as the amount of re-slotting done, the client's tolerance for errors, desire for common technologies, internal IT capability, cost of ownership and ROI, just to name a few.
There are some general guidelines that help to point us in one direction or another when evaluating whether PTL or PTV (or something else) is the best alternative for a picking operation.
The Obvious Ones
Generally, voice picking technology wins over PTL when there is a very large number of SKUs spread over a large amount of real estate. Because PTL modules are placed physically at the pick location, the cost to place many of these over a large area is usually cost prohibitive. Also, if the pick locations are constantly being re-configured, voice technology will probably be a better fit given its flexibility.
On the other hand, PTL is chosen for high speed picking for a lower SKU count or if the picking environment is very dense. It is often a better choice in a zoned picking operation. As the number of pickers increases, the cost per light module decreases, compared to the cost of every voice unit that must be worn by every picker.
Accuracy Comparisons
Most studies show that pickers using PTV technology make fewer errors over those using PTL. These studies show that a voice picking operation can expect an error rate of 0.2 to 2 errors per 1000 picks (99.8 - 99.98% accuracy). On the other hand, PTL operations make about 3 to 5 errors per 1000 picks (99.5 - 99.7% accuracy). When I first saw this information it did not make sense to me. Initially I thought that if a picker could see a light and the quantity to pick in a PTL operation, they would make fewer errors than an operator who is simply told where to go and how many to pick.
However, a few factors come into play here. First, in order to save capital costs, some PTL installations use simply a light at the pick location, but display the quantity to pick on a bay display that is not directly at the pick location. Since the lights that do not have the integrated displays are less expensive, the DCs that have installed these have made a trade-off between initial capital cost and long term accuracy.
A second factor that may cause PTL to be less accurate is focus. Because the picker must change their focus from the pick to the light (to extinguish it), it has been argued that this may introduce an error factor that is not present in a voice directed picking environment.
Also, in a voice directed picking environment the picker can ask the system to repeat the last instruction. In a Pick to Light environment, once the light is extinguished, the picking information is usually wiped from the display (although there are techniques for leaving this information on until the next pick). These factors may point to why voice picking is generally more accurate than PTL.
Productivity Comparisons
This is an interesting one as the same studies that show that Pick to Light is less accurate show that it is also more productive. Again, depending on the application, PTL operations can have rates of 350 lines per man-hour or more, while voice picking in the same applications run 300 lines per man-hour or less. Why such a difference? In a PTL environment, the picker can “look ahead” and pre-plan their pick movements. Although this may be a subtle advantage, the benefits of these planned movements can add up over time. There are several key issues/ considerations that can affect the productivity of either system. These include the balancing of work across a pick zone, the number of cartons worked concurrently by the operator, the ergonomics and slotting of the pick module, and the picking density of the operation. The key to getting the most out of a Pick To Light system (or any picking equipment) is a proper understanding of the technology and the operation.
Maturing Technologies & the African Factor
Although voice picking is a newer technology, both PTV and PTL are considered mature technologies. There are more choices of hardware and software for both types of systems than were available just a few years ago. Also, because of this, integrators and consultants are finding more uses for the technologies and thus increasing the value to the operations who adopt either. So neither technology is considered state-of-the-art anymore. Another interesting point that potential evaluators of PTV raise is the different dialects, accents and intonations of the South African population. Interestingly PTV is “trained” to be receptive to each individual's specific nuances so this isn't really a problem for South Africa.
Flexibility & Cost
Although the base cost of PTL and PTV is around the same there are quite a few cost and flexibility considerations that one should investigate before locking in a specific technology. PTL typically is costed based on the number of lights that are used, it then typically requires a warehouse control system to manage the specific picking zones, this is not always necessary as a best of breed WMS can manage the pick area but it will require some hefty integration time and cost. As a PTL is designed to improve a certain type of picking process, generally a company will need to have a WMS to manage the other activities within its facility.
Which is the Right Weapon?
Most distribution facilities only start to consider PTL or PTV when they have reached “best in class” pick rate metrics and are trying to improve productivity and accuracy to a new optimal level. Both are great technologies but the key to success if setting the baseline and then evaluating the pro's and con's of each option as more than likely you will have to live with your choice for 5+ years.
Contributed by: Michael Badwi, Managing Director, Supply Chain Junction
