Put-to-Light with IO-Link: faster packing at Ploonk

Cell phone cases, charging cables, smartwatch straps: Anyone who orders from Ploonk in the evening can often expect their package as early as the next day. The online retailer of smartphone and electronics accessories operates many online stores across Europe. Dutch customers order from Smartphonehoesjes.nl, while Handyhuellen.de is fairly well known in Germany. Ploonk also operates its own platforms in Austria, France, and Belgium. In addition, the company sells its products through online marketplaces in nearly every European country. About 200 employees handle the entire business from the company’s Dutch headquarters in Leusden.

The volume of orders is impressive: on a typical day, 8,000 to 12,000 orders leave the warehouse. Because the online stores continue to operate on weekends while the warehouse is closed, the number can sometimes reach 20,000 on Mondays. During peak periods, such as Black Friday week, Ploonk packs up to 35,000 orders per day. A large portion of these are single-item orders. Multi-item orders are more challenging: items picked for several orders arrive together in one basket and must first be sorted per order before they are placed together in the shipping box. For exactly this step, Ploonk has set up a put-to-light system in collaboration with TURCK and the warehouse management system (WMS) provider Diract IT. Put-to-light is a light-directed sorting method, also known as a put wall: after an item is scanned, a light signals the compartment where it belongs, so items from the same order end up together.

Source of error: movable dividers

In the previous system, consolidation was barcode-driven via the WMS packing app. Employees worked at two packing stations with movable dividers; each compartment had its own barcode. When an employee scanned an item, they were assigned an empty compartment, scanned its barcode, placed the item in the compartment, and slid the divider along. When the next item from the same order arrived, the app directed the employee to the already occupied compartment. Once the order was complete, the contents were transferred to the shipping box.

The weak point was the hardware itself. “It allowed items to be left behind in the compartments. And when scanning, it was very easy to select the wrong compartment. You think you’re scanning this one, but you’ve actually scanned the one behind it,” explains Michiel van Bendegem, Functional Application Manager responsible for the WMS as well as ERP and logistics systems at Ploonk. Added to this were jammed dividers behind which items could slip. If an item was left behind unnoticed, it would later be shipped out with the next order. Wrong items, too many, or too few: According to van Bendegem’s estimate, around 60 percent of these shipping errors stemmed from the consolidation process. Furthermore, the process was more time-consuming than necessary.

Customers who order with premium shipping should receive their items the next day—and Ploonk wants to achieve that with lean teams. Ploonk sets fixed performance metrics for packing. “Our employees shouldn’t have to choose between working carefully and working quickly. They should be able to do both. TURCK’s put-to-light solution made that possible,” says van Bendegem.

LED strips instead of 360 individual lights

The idea of using lights to guide employees to the right compartments came from Ploonk itself. While searching online for a suitable lighting solution, van Bendegem came across TURCK and submitted an inquiry via the contact form. Initially, the team considered individual lights with acknowledgment buttons for each compartment. With 120 compartments per packing station and three packing stations, that would have amounted to 360 lights—too expensive for the planned application.

TURCK instead proposed flexible WLF12 Pro LED strips from Banner Engineering. Each strip is driven by a compact LC25C-WLF12-KQ LED controller with IO-Link. The controllers are connected to a TURCK TBEN-S2-4IOL IO-Link master, which controls the put-to-light stations.

The team had previously considered lower-cost off-the-shelf LED strips as an alternative. “Considering the investment, we decided: Perhaps it’s better to work with a partner we can truly rely on,” says van Bendegem. In addition to what he considered a fair price, the key factors were support with software integration and industrial communication. Standard LED strips typically do not support IO-Link, whereas the Banner solution communicates via IO-Link, which simplifies integration with the WMS.

A short payback period was another important consideration. “We can’t buy a system that won’t pay for itself for ten years,” says van Bendegem. According to the project team, the put-to-light solution pays for itself in about a year, including the necessary modifications to the WMS.

Process at the packing station 

In operation, the process is simple: An order picker brings a basket of picked items to the packing station. They scan an item, and the compartment where it is to be placed lights up blue. They place the item in the compartment, confirm with a large button, and the light turns off. When an order is complete, the light below that compartment turns green. 

From JSON message to light signal

At each of the three packing stations, three LED strips are connected to a compact TBEN-S2-4IOL multiprotocol I/O module with four IO-Link master channels. IO-Link is a standardized communication interface for connecting sensors and actuators such as these LED strips to a control system. For the employees, the familiar packing app from the WMS looks unchanged. Diract extended it so that it generates JSON messages at the right points—such as “place,” “remove,” “error,” or “order complete.” The WMS interface is based on a REST API and cannot be connected directly to the I/O modules. A small Node-RED program (a low-code, flow-based programming tool) running on a server acts as a translator, communicating with the TBEN-S2-4IOL modules via Modbus TCP. On the modules themselves, logic based on TURCK’s ARGEE field logic controller processes the data accordingly. 

About 25 percent faster through the peak season

Ploonk wanted to have all three packing stations up and running before the 2025 holiday season—and they succeeded. “That really helped us during the peak season,” says van Bendegem. His assessment: At the put-to-light stations, employees pack about 25 percent faster than before. According to him, the feedback from the team has been very positive. “The hardware does exactly what it’s supposed to do,” he emphasizes. Ploonk is currently testing whether a tabletop scanner, handheld scanner, or glove scanner is the best fit for the workstation.

Outlook: light for the right flyer

Van Bendegem already has the next application in mind. Ploonk currently does not include promotional flyers at the manual packing stations because too many errors occurred there, and the information about which store an order is intended for is not available until late in the process. This is particularly tricky for marketplace orders: If a flyer for the retailer’s own store is included in the package, the retailer risks being excluded from the platform. The plan is to install a rack with eight compartments for different flyers, with a light indicating the correct compartment.

For van Bendegem, the project is more than just a process improvement: “For me, it’s been the best project I’ve worked on at this company so far. It had the IT component with software, but it also had a tangible element. And with the lights, it’s a real eye-catcher in our warehouse.”

Customer | www.ploonk.nl