Wireless networks provide more with less

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April 16, 2010

Gary Marrs

802.11 networks are becoming nearly ubiquitous in many enterprise settings and can often be tapped to solve embedded problems in the same location. In this example, a logistics cart used for warehouse operations becomes 802.11 enabled, improving the efficiency of a critical process.

In a tough economy with increased competition from global markets, companies are forced to do more with less. Supply chain management is one area where companies realize this challenge. Organizations are continually struggling to ship more orders, decrease processing time, and increase order accuracy, all the while reducing costs. The nature of order processing has changed as well. With just-in-time and lean manufacturing techniques becoming common practices, distribution warehouses often need to process a high volume of small orders, which often involve a large mix of products, adding further complexity to the process.

The end result is that the order picking process is increasingly challenging. In a typical warehouse or distribution center, studies have shown that order picking can consume as much as two-thirds of the facility’s operating cost and time. As a result, companies are continually looking for new technologies and innovations to automate the order picking process.

Pick-to-light goes paperless …

In the first days of order picking, an order list was created, and a fast-footed person would chase down all of the parts, collect the correct quantities of each part, and transport them to the shipping area. This batch process saw many improvements, including techniques to optimize the ideal locations for each part and algorithms to minimize the travel distance of the person picking the order.

Computer and networking technologies facilitated the development of an innovative system known as pick-to-light that significantly improved this process. The pick-to-light system provides an automated, paperless, order picking solution. With this system, the order list is sequenced to LED displays that direct the order picker to a location and indicate the quantity of parts to pick. This system significantly increased order accuracy and reduced order picking times by providing the shortest pick path through the warehouse.

The next step was extending this system to leverage a mobile vehicle or cart for pickers to gather more parts in a highly effective manner. In the mid-1990s, Innovative Picking Technologies (IPTI) developed the first pick-to-light cart called the RF Batch PicKart (Figure 1), a patented paperless order fulfillment system that utilizes PICK-MAX pick-to-light displays mounted to a mobile cart.

Figure 1: The RF Batch PicKart was the first pick-to-light cart that enabled a paperless order fulfillment system.

(Click graphic to zoom)

The first versions of the RF PicKart used proprietary RF radios to communicate. The radios were mostly 900 MHz point-to-point. Although these radios could provide a wireless data link to the cart, they were expensive to deploy, and the data throughput was generally slow.

… then moves to 802.11

With the growing popularity of IEEE 802.11 wireless networking, IPTI found that customers usually had a secure and reliable 802.11 Wireless Local Area Network (WLAN) infrastructure that could be leveraged. IPTI migrated the design of the RF PicKart to 802.11b/g, providing customers with high-speed data transfers, seamless data connections to back-end server processing, and much lower price points.

IPTI performed extensive system testing to make sure that the wireless network could:

Allow robust communications to multiple mobile carts in a warehouse environment
Extend to provide complete coverage in large warehouse environments
Handle the normal shock/vibration issues with robust client radios used on carts

To support the pick-to-light functions and WLAN communications, the RF PicKarts have an onboard 16-bit microprocessor that communicates to the WLAN through a UART connection. The microprocessor also supports two serial channels for bar-code scanners and a serial printer. The displays and push buttons interface to the microprocessor through the address/data bus. The carts’ pick-to-light displays and push buttons are mounted on a faceplate for easy visibility. All of the electronics are powered by a built-in 12 V lead-acid battery that can provide power for up to 12 hours between charges.

Device servers make design straightforward

For the RF wireless link, IPTI initially chose the Lantronix WiBox, a wireless device server module that creates a transparent data tunnel between an RS-232 serial connection on the RF PicKart microprocessor and the 802.11b/g WLAN. The WiBox was interfaced to the RF PicKart in a couple of days, and a working wireless demonstration was completed in less than one week.

To provide tighter integration of the WLAN interface in the PicKart at a lower price point, IPTI upgraded the RF PicKart design to use the Lantronix MatchPort b/g (Figure 2), an embedded radio module that easily integrates an 802.11b/g link directly onto the main CPU board. The module interfaces to the host processor’s UART and transparently tunnels data from the host to the server without requiring any special software driver development.

Figure 2: The MatchPort b/g provides an easy way to integrate an 802.11b/g link onto the main CPU board.

(Click graphic to zoom by 1.9x)

On power-up, the MatchPort b/g is configured to make a TCP connection directly to the back-end server, which runs four turnkey software programs for a complete solution. The software modules include the Host Interface program, Real-Time Pick-to-Light program, IPTI Statistics program, and the Order Reconciliation program. The Host Interface program is the middleware that processes order information to be used in the pick-to-light system. The Real-Time Pick-to-Light program shows the orders that are active in the system and sends order picking details across the WLAN network to the displays. Communication is event-driven, so when the push buttons are pressed, the system acknowledges those events in real time.

For WLAN security, IPTI uses IEEE 802.11 Wi-Fi Protected Access (WPA) Temporal Key Integrity Protocol Pre-Shared Key security. To set up the security, a few simple configuration settings are established through the serial or network interface. A Web-based configuration manager is also available. For data security from the pick-to-light displays all the way through to the server, the system offers support for optional 256-bit Advanced Encryption Standard, enabling secure end-to-end data transfer. For applications that require enterprise-grade WLAN security, the MatchPort b/g Pro offers enhanced features, including WPA2 Transport Layer Security (TLS), Tunneled TLS, or Protected Extensible Authentication Protocol.

The MatchPort b/g is pretested for European telecommunications regulations and FCC certified, which allowed IPTI to leverage the FCC license grant and bypass 802.11 regulatory testing, speeding time to market and minimizing development and testing costs.

Fitting in the network

One problem identified during application testing was roaming. Larger deployments with more than one Access Point (AP) experienced some delays or dropped TCP connections between the RF PicKart and the enterprise server when the carts traveled between APs in the warehouse. Evidently, roaming is not handled the same by all AP vendors. The MatchPort b/g thus could not maintain a seamless association between the different APs as the carts moved around the warehouse.

To solve this problem, Lantronix implemented SmartRoam technology, which enables the MatchPort b/g to continuously track the signal strength of all APs within range that meet the network and security profile. If a stronger AP is available, the module will make a seamless transition to the better AP. This greatly enhanced the mobility of the RF PicKart within a large warehouse and resolved all of the roaming issues.

For the WLAN infrastructure, IPTI chose the Cisco AP1231 APs, which set the enterprise standard for high-performance, secure, manageable, and reliable WLAN networks. These APs provide robust communications in noisy environments, a particularly important feature in warehouse environments where multiple vehicles and excessive RF traffic make it difficult to obtain good link margins. The Cisco APs also offer extensive debugging facilities and the ability to log debug messages with time stamps. These debug features were helpful when troubleshooting the roaming issues.

WLANs solve embedded challenges

Continuous process improvement is demanding cost-effective ways to solve tough supply chain management issues. Secure and robust WLAN networks are providing solutions to these challenges. The order picking process is just one area where WLAN-enabled carts are allowing companies to remain competitive by doing more with less. On a wider scale, many more creative applications can utilize embedded WLAN technology to solve problems with similar ease.

Figure 3: ECD in 2D: For more on connecting devices, Lantronix overviews device networking – use your smartphone, scan this code, watch a video: http://bit.ly/drrcin, or visit http://bit.ly/ecdin2d_apr10

Gary Marrs is a senior field application engineer with Lantronix, where he is responsible for helping customers design-in Lantronix device servers for applications that require network connectivity and security. Prior to working at Lantronix, Gary spent 17 years at Grayhill, where he worked in design engineering, marketing, and sales capacities. He holds a BS in Electrical Engineering from Illinois Institute of Technology and an MBA from DePaul University’s Kellstadt Graduate School of Business.

Lantronix 949-453-3990 www.lantronix.com