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Bus bar vs cable based/serial Pick to light – Pros & Cons

Lately light directed picking technology has emerged as the most popular picking methodology & it has become an integral part of order fulfilment especially for ecommerce, retail, FMCG & auto components..etc industries. In case of smaller warehouses, to achieve the required throughputs, and to reduce manual errors; in case of larger warehouses, Pick to light are used for various applications like zone picking, cluster picking, batch picking etc. Whatever be the application, the goal is to amplify the picking with the speed, accuracy, and the ease of working offered by PTLs.

Every pick to light device will be assigned with a location code of the bin/shelf/rack/workstation/position on which this device is mounted and the software of the pick to light device communicates constantly with the warehouse management system or ERP solution or any warehouse control system. Whenever a picking operation needs to be performed, picker scans the barcode of the crate/tote in which the ordered items need to be kept after picking, correspondingly the pick to light device of the location which contains those ordered items gets illuminated along with indicating the no. of items to be picked on the LED display. After picking the items, the picker must acknowledge the pick by pressing the light, this information will be duly communicated in real time with the WMS/WCS/ERP software of the warehouse.

Despite the very light hardware of the product, it is very critical to properly implement it in terms of mounting the device and properly program & integrate in terms of software. Since the early days of pick to light invention, pick to lights have been installed using the serial cable system, where in the devices will be mounted on the racks and get power connection using these serial wired cables. However, the distribution challenges of the serial cables for the electronic power transmission prompted the way for the busbar trunking system. So, the same transformation has been passed on to the implementation of PTLs, so bus-bar enabled PTL mountings are a common sight of the warehouse today.

At Addverb, we offer Rapido, our pick to light solution in both cable based and bus-bar methods; similarly, many players also do offer both these solutions. So, through this blog, let us understand the differences between busbar vs cable based PTL implementations.

  1. Design friendliness – Bus bar based PTLs are compact in design, hence occupy less space, whereas cable based PTL systems require more space because of bending radiuses and the spacing required between parallel cables. Hence busbar based PTL will be beneficial when there are many PTL implementations. In terms of aesthetics and maintaining the entire system, busbar based PTLs look clean and easy to do maintenance activities instead of the clumsy cable based PTL system.
  2. Implementation ease– Cable based pick to light systems are resource intensive both efforts & cost, whereas with modular structure, the busbar trunking PTL installation is quite faster and installation error are practically zero due to the safe and user-guided connection technology.
  3. Flexibility — In the busbar trunking system, PTL units will be mounted on the tap off points of the trunking system, this creates a variable distribution system for linear and / or area-wide, distributed power supply for the entire PTL system. This provides flexibility and unlike the fixed cable-based units, it doesn’t require intensive planning and implementation. The easy retrofit nature of the busbar based PTLs plays a critical role in scaling up or down the entire PTL system.
  4. Voltage fluctuations – Busbars have better resistance than cables, especially to short circuits due to their strong design architecture vis-à-vis to the traditional cable based PTL system. The minimum distance between the conductors inside the busbars induces less resistance and the optimal distribution current density reduces the resistance. This in turn reduces the voltage loss when compared with the traditional cable system.
  5. Reduced Loss of Energy:Busbars have lower resistance than cables. Hence the loss of energy due to transmission and distribution is lower in Busbars. Busbars also have a limited growth of reactive power to operate compared to cable systems.
  6. Highly durable – Since the design is compact and has a metal casing with well-defined surface, busbars can absorb heat generated while transmissions and distribution of electricity in the walls of the enclosure. The system of cooling is much better than traditional cabling system.
  7. Increased safety – Busbars are fitted with a steel casing and the chances of getting damaged by human actions/rodents/any other such accident is lesser as compared to cables, on the other hand cables are more exposed and are susceptible to the environmental changes. Also, busbar trunking system will have standardized products across its implementation, as against the cable system.

The above is a short comparison of busbar vs cable-based pick to light systems. Despite being superior in its functionality and safety aspects, still cable based pick to light system is preferable to some majorly due to the implementation challenges, familiarity with cable based PTLs or the structural systems present inside the warehouse/a facility.

Batch Picking Vs Wave Picking – What is what?

In the previous blog on ‘Different Types of order picking in warehouse, we discussed briefly various types of order picking in a warehouse; in continuation to that, let’s delve in depth into the most common types of order picking, i.e., batch picking and wave picking, the differences between the two methods and when to use what.

Batch Picking: This is an order picking protocol that calls for the picker to compile a batch of the orders by picking from a single SKU or one SKU at a time. It helps to fulfill the order very fast by picking multiple orders at the same time. Single picker picks a batch of orders, which helps reduce repeated trips to the same location, essentially one location is visited only once by a picker. Let us illustrate this with an example;

Order1: 3 soaps, 5 shampoos, 3 Gels

Order2: 8 Shampoos, 5 Soaps

In case of batch picking, both the orders are combined for picking & when the picker goes to the soaps section, he picks all 8 soaps; and when he visits the shampoo section, he picks all 13 shampoos and then the 3 gels once. After that at the packing station, they will be packed into individual orders. In case of batch picking, many orders will include same SKUs, hence it is apt when your orders have minimal SKUs.

Batch picking is preferred when there is fewer no. of SKUs, typically 4-5 SKUs and each item is small, because this allows the picker to pick many items in his picking cart and bring them to the packing station. As it enables the picker to travel to a pick location only once while fulfilling many orders, it results in reduction of travel time as well as less congestion in the warehouse due to less traffic.

Batch picking is preferable when the warehouse size is smaller, as it helps in fast picking and less travel. In case of large warehouses, it is preferable when the SKU concentration at a location is high. Mostly, in case of batch picking, pickers use picking carts to pick and deliver the picked items to the packing stations unlike wave picking which utilizes conveyors, tilt-tray sorters etc.

Depending on the order volume, picking locations & manpower, warehouses can create one size batches, like all the batches have 50 orders per batch with an average no. of 3 SKUs per order.  Or warehouses can also create multi-size batches, where in the first batch can be of 50 orders with an average of 3 SKUs per order, and the next batch is of 25 orders with an average of 4 SKUs per batch.

Further optimized paths for these SKUs picking can be suggested by WMS or WCS if it is in place, thereby ensuring highest levels of picking efficiency, reduced travel time and labour requirement.

Wave Picking: Grouping of orders into waves is the first step in wave picking, it can be done on a small number of orders like 4 or 5 or on a large number of orders, like hundreds. In wave picking, picker picks one order and one SKU at a time & orders are grouped depending on the inventory characteristics, shipping routes, delivery schedules, shipping carrier, or even the type of packaging. After the picking, all the products will be brought to a staging area where sortation of them into individual orders will happen.

It can be illustrated with an example below;

Let us assume the warehouse got 50 orders to be fulfilled within a shift, out of this 50, let’s say 20 orders consist items from cold storage area, 10 orders are to be shipped to a specific location, and another 20 orders are to be packed in a glass packaging. So, there will be 3 waves to fulfill these 50 orders, and these 3 waves can be scheduled at different times, for different zones. Once the items in a wave are filled, they will be brought down to sorting area & then packed.

Orders for which all the items are picked during the wave can be sent for packing or wait till all the items for the orders get filled and then sent for packing, accordingly, it is called fixed wave picking and dynamic wave picking, respectively.

Batch Vs Wave: Which is the best?

One important distinction between batch picking and wave picking is that batch picking requires just one order picking window per shift. In contrast, wave picking may include multiple waves per shift.

In batch picking, average cubic size of the orders plays an important role in achieving the best picking rate, for some small businesses and warehouses, the pick rate can go as high as 200+ order lines per hour from 60-70 order lines per hour for single order picking. In case of wave picking, logical order flows make it more effective than straight forward or discrete order picking process and for businesses with large SKUs, batch picking creates heavy traffic and damages the picking efficiency, hence waves are recommended.

In batch picking, a picker makes only one trip to a location, greatly reducing the travel time, congestion and accidents in the warehouse. Whereas in wave picking, picking is always under control as waves can be allotted as per the requirement, like different zones, different timings which gives flexibility in terms of planning or coordinating other warehouse activities such as replenishment, packing, dispatch..etc.

So, both the methods are better in their own way and increases the picking productivity & efficiency and choosing which method to go with depends on the nature of the inventory, order profile characteristics, and the KPIs..etc. As wave picking deals with multiple SKUs, and several waves would be performed in a shift, it calls for some kind of automation to yield the best results in terms of sorter, conveyors, WMS..etc.