Order picking techniques compared

Published on: April 6, 2021 / Updated on: October 27, 2021 – Author: Konrad Wolfenstein

Pick-by-Light vs. Pick-by-Voice – Image: Monkey Business Images|Shutterstock.com

Order picking techniques compared

In times of increasingly fierce national and international competition for businesses, the pressure to increase productivity is steadily growing in logistics as well. This pressure doesn't stop at intralogistics, where order picking is a particular focus: More and more goods, components, or raw materials need to be stored and moved – ideally faster, more cost-effectively, and with greater resource efficiency. It's no wonder, then, that automation is becoming increasingly prevalent in many companies. Dynamic storage solutions, such as shuttle systems or horizontal carousel storage systems, offer one way to boost warehouse productivity.

However, even the widespread use of such equipment requires human workers to pick all the items, although their number decreases with increasing automation. To make the work easier for warehouse employees and increase throughput, there are a number of tools that guide people using visual or acoustic signals.

However, which system is better, when, and for whom is highly dependent on the situation. Depending on the warehouse structure, type of goods, and noise level, one picking system or another has advantages and disadvantages.

Pick-by-Light

With pick-by-light, warehouse workers are guided to the storage location or order container by visual signals. There, a signal light and display provide employees with all the information relevant to the picking process. This system enables the storage and retrieval of items: employees either remove items from the storage location or distribute the goods to different locations. The employee then confirms the completion of the picking process using a confirmation button, which is also located on the display. This information is then transmitted to the ERP system in real time.

Advantages

• Fast order picking
• Reduced error rate
• High picking frequency per storage location
• No long learning curve
• The employee has their hands free

Disadvantages

• Comparatively high costs for acquisition, maintenance and repair
• Inflexible, as adjustments to storage location, item or quantity have to be laboriously implemented in the displays
• Picking errors due to undetected system failure

Pick-by-light is particularly suitable when high picking speeds are required. The system is often used in combination with automated storage solutions where items are provided according to the goods-to-person principle . Examples include picking small parts, picking components for assembly, or splitting large quantities of goods into smaller shipping units.

Pick-by-Voice

Pick-by-voice is now one of the most established order picking methods. No wonder, since the system guarantees maximum freedom of movement and flexibility for the order picker, as they always have their hands and eyes free to process the order.

Instead of a handheld scanner, the warehouse worker wears a headset through which he receives orders via computer voice. The orders are transmitted wirelessly from the warehouse management system and later reported back to the system via the same method. Once an order is completed, the employee confirms this with a voice prompt.

Advantages

• Short search times
• Precise order picking
• Employee has hands and view free
• Freedom of movement and flexibility

Disadvantages

• High initial investments
• Limited use in noisy environments such as warehouses
• Multilingualism may be required
• More complicated onboarding

Comparison

The methods presented have specific advantages and disadvantages and are each suitable for certain types of articles and areas of application:

Size and weight:
For large and heavy goods, pick-by-voice systems offer greater flexibility and easier operation, whereas pick-by-light reaches its limits with such items. Pick-by-light's advantages are particularly evident in small warehouses or when used in conjunction with automated storage systems.

Inventory turnover:
For frequently picked, fast-moving items, pick-by-voice systems typically only achieve a medium picking rate. Pick-by-light, on the other hand, excels here with its high picking rate.

Especially compared to pick-by-light, the voice solution offers advantages in versatility, flexibility, and higher precision. However, this comes at the cost of reduced speed.

Another advantage is that order pickers have an unobstructed view, free from distractions like lamps or displays. This allows them to focus more effectively on their tasks. Furthermore, the error rate is reduced because information can not only be received by the control system but also sent back to it. This enables efficient monitoring and, if necessary, immediate error correction. If shortages are detected, reorders can be initiated.

Pick-by-voice technology is enjoying increasing popularity among intralogistics professionals. However, there are also counterexamples. For instance, the office supply retailer Soennecken switched its small parts picking processes in its logistics center from pick-by-voice to pick-by-light. According to the company, the conversion improved working conditions in order picking and increased picking performance by 10 percent. The switch was prompted by complaints from employees who found the visual signals of the pick-by-voice system increasingly stressful. The conversion took place while operations continued, after which, according to Soennecken, working conditions improved dramatically.

Pick-by-Vision: Combining the advantages

One of the newer methods for simplifying order picking is pick-by-vision, which combines the advantages of pick-by-voice and pick-by-light in a single system. In this approach, co-developed by the Technical University of Munich , the employee uses smart glasses whose display shows relevant data for the current order in real time. This data guides the picker step-by-step through the order. A navigation function leads them directly to the storage location of the item to be picked, where the corresponding storage location and the required number of picks are displayed visually. Optionally, the smart glasses can be equipped with a camera for scanning barcodes, eliminating the need for the otherwise standard handheld scanner.

The advantage of smart glasses (also called head-mounted displays, or HMDs) is that, in addition to viewing the data projected onto the display, the user can still perceive their surroundings without distractions and has both hands free to process the order. In this way, the employee is constantly informed about the type and condition of the items to be picked or their location. Furthermore, they receive immediate feedback if a picking error has occurred.

But the smart glasses aren't a one-way street where the warehouse worker is simply occupied with completing assigned tasks. Instead, the order picker can interact with the control system via voice commands and make changes. This innovative method is still in its infancy, but with the ongoing development of such communication systems, it's expected that these glasses will be found in more and more logistics facilities in the near future.