Critical connectivity elements for wireless AS/RS and AGV systems
October 2016, Industrial Wireless
Evolution of automated materials handling (AMH) - AMH refers to automation of loading, moving, and unloading of materials used by a production unit. The main objectives of AMH systems are reducing the cost of operation, minimising human errors by using automation, and meeting safety requirements in factories and warehouses.
The traditional approach, which is still followed in some small and medium scale industries, is for workers to walk from one shelf to another in a warehouse and retrieve items as and when they are required. This activity is not only time consuming but also error-prone. Some industries adopted a mechanised approach to handling materials in a warehouse around the 1950s, which involved humans and machines working together to move materials and finished goods. Although the mechanised approach sped up material handling tasks, there was clearly a need for solutions to monitor and control the process and to increase the efficiency of materials handling in warehouses and factories. In the early 2000s, manufacturers started to automate their materials-handling process, resulting in fully-automated solutions being available in the market. Systems such as automated guided vehicles (AGVs), pallets, automated conveyors, automated cranes, automated storage and retrieval systems (AS/RS), and clean room transport and storage systems were built and implemented during this period.
The AMH market has seen a boom in recent years because of the many benefits that AMH solutions provide, and the need for manufacturers to be part of the next level of industrial automation – the Industrial IoT.
Industrial IoT – the future of industrial automation
The Industrial IoT (Internet of Things) is set to revolutionise how machines on a network interact with each other. Although currently the adoption of the IoT by industry is limited to achieving operational efficiency, its full potential has yet to be tapped. As the standards for the Industrial IoT evolve and move towards open standards, more and more devices and equipment on a network will be able to communicate directly with each other. The Industrial IoT is also expected to drive the communication interfaces for conveyors, AS/RSs, forklifts, and other AMH-related systems. The centralisation of data collected from these types of equipment can provide useful information that can aid decision makers in the industry. The AMH industry is currently using Big Data applications to help with maintenance, service delivery, and managing and streamlining processes.
Automated guided vehicles
An AGV is a battery powered driverless vehicle that can be programmed with positioning and path selection capabilities. The AGVs can follow markers or wires on the floor, or use sensors, magnets, or lasers for navigation. They are often used in industrial applications to move materials around a manufacturing facility or warehouse. Benefits include reduced labour and operational costs in distribution and supply chain applications in warehouses.
Automatic storage and retrieval systems
An AS/RS consists of a variety of computer-controlled systems that automatically pick, transport and store materials based on pre-defined storage locations. AS/RS installations are typically used in applications where high volumes of material are moved in and out of storage. The storage density in such applications is a key factor in implementing AS/RS systems due to storage space constraints. The accuracy of the process is critical and any error in the process could lead to potential damage to the goods, which could be expensive. AS/RS systems can be used for applications with standard as well as non-standard loads. The benefits are faster and more accurate storage and retrieval of goods using less space.
Critical points when developing wireless communication for AS/RS and AGV systems
Wi-Fi-based technology is the most commonly used communication method in such systems as compared to other technologies like infrared, power line communication (PLC) or FSK radio communication, for the following reasons:
• Flexibility: Compared to linear technologies such as infrared, wireless technology lets you deploy multiple access points to support the roaming of clients that are installed on moving platforms.
• Easy implementation: Unlike devices using PLC technology, Wi-Fi-based devices on moving vehicles can communicate without a physical connection. Even though devices in some modern PLC-based implementations are able to power up and transmit digital data through metal rails, the underlying technology is relatively complex to deploy.
• Scalability: The standardisation of the 802.11 Wi-Fi-based technologies makes interoperability between wireless devices from different vendors much easier as compared to non-standard technologies. Expanding your system or network as well as finding replacements for the wireless devices deployed in the system also becomes much easier.
Although Wi-Fi-based technology has advantages, system integrators need to pay special attention to the following points when deploying wireless solutions in AS/RS and AGV systems.
Dealing with constantly moving platforms
Ensuring reliable communications while on the move is a key concern for AS/RS and AGV systems. Seamless roaming and anti-vibration protection of the client devices are the top two considerations when choosing a suitable solution.
Wi-Fi networks have limited signal coverage, which means multiple access points might be needed to achieve full signal coverage in a warehouse. It is critical to ensure that the clients can roam smoothly between these access points with minimal handover time. Wi-Fi devices that are based on older technology commonly experience a 3 to 5-second disconnection time as they move between access points, causing severe disruption to real-time operations. If this happens to a client device installed on an AGV, the vehicle might simply stop until it re-establishes its network connection, causing production delays that could lead to an increase in operational costs.
The basic requirement of a reliable wireless roaming technology is to seek out neighbouring access points with strong signals and prepare to connect to new access points as the client moves closer to them. The following advanced wireless roaming features can also increase the efficiency of the client devices:
• Reliable roaming performance with multiple channels: Due to the limited bandwidth available on each channel frequency, system integrators must use multiple frequency channels to avoid channel congestion. The wireless-roaming technology should be able to provide smooth roaming between different APs using different channels.
• Adjustable roaming parameters: System integrators usually have multiple customers with widely varying needs, so the roaming function must allow users to adjust the roaming parameters to adapt to different venues and site environments. The roaming parameters are configured to allow location-based load balancing to ensure that wireless clients are connected to the closest access point to avoid network traffic congestion.
• Best wireless encryption possible without affecting the roaming performance: Wireless signals are transmitted through the air and are therefore vulnerable to hacking. However, encryption protocols that provide high data security such as WPA/WPA2 are complex to implement and can sometimes affect roaming performance – particularly by causing a delay during the secure key exchange process when the client moves to a new access point. An advanced wireless roaming function that can provide the most secure data encryption possible and millisecond-level handoff times for clients is required to secure the network.
AS/RS and AGV systems are constantly on the move to supply materials to production processes or store finished goods. Wireless devices mounted on systems that are prone to vibration and shock can cause electrical shorts, broken solder joints, loose PCB components and cracked housings. Shock and vibration can also disable a wireless device by shaking loose wires for power, data, and redundancy. The IEC 60068-2-6 standard specifies the guidelines that wireless devices must abide by to ensure protection against high vibration and shock. Devices must be tested against these standards and pass the criteria set by the standards to be able to provide reliable performance in highly mobile environments.
Limited space for system integration
Mobile industrial equipment such as AGVs have very limited space and weight-carrying capacity. The main concern for most system integrators when choosing wireless devices for compact and reliable AGV systems is the ability of the wireless devices to withstand electrical interference.
Electrical disturbance usually interrupts wireless transmission by entering through the power inputs and antenna ports. To utilise the limited space on AGV systems, all the onboard devices usually share the same power source, including wireless devices and motors. When the motor is turned on, it could generate inrush current that can damage the wireless device through the power port and in extreme cases stop the wireless communications. The antenna extensions are usually mounted on the metal casing of the AGV or the shuttles used by the AS/RS to achieve better signal strength, which sometimes leads to airborne electrostatic charges damaging the wireless components through the antennas and antenna cables. System integrators typically use extra power and antenna-isolator accessories to strengthen their system, but this method could increase the system cost and also require extra installation space. Wireless devices should be provided with built-in isolation to protect them from electrical disturbance.
The intricacies of wireless installations
A brief interruption of a few seconds to wireless service is viewed as a mere nuisance for routine applications, but in an industrial setup, especially one that involves critical processes or functions, any disruption to wireless service – even one that lasts just a few seconds – can lead to catastrophic results. Therefore, it is extremely important to set up your wireless network correctly in the first place to avoid operational glitches.
Countering the effects of multipath propagation
In wireless communications, multipath is a propagation phenomenon that results in radio signals reaching the receiving antenna via two or more paths. In a typical warehouse environment, metal frames and shelves can easily cause reflection and refraction of the radiated signals resulting in multipath fading. The fact that reflected/refracted signals traverse a longer distance than direct line-of-sight transmissions could cause the signals to arrive out of phase, leading to signal degradation at the receiver’s end. However, you can utilise 802.11n MIMO technology to turn the effects of multipath propagation to your advantage by reconstructing a strong signal at the receiver by applying error-correction techniques on the weak reflected/refracted signals.
Complex configuration and maintenance
Wireless networks are known for their ease of deployment, but many industrial operators still need to deal with complex installation processes. The hundreds and sometimes thousands of wireless devices that need to be set up before enabling the entire wireless network in warehouses makes the task even more daunting. The wireless clients deployed in AS/RS or AGV systems have to be set up one-by-one to ensure proper connection with the APs. When device errors occur, the AS/RS or AGV systems need to be halted, or in a particularly bad situation, they have to be taken apart for troubleshooting. Restarting or rebooting these systems is extremely time-consuming and disruptive for operators. Although the demands on APs are far less than for wireless clients, making manual setup much easier, access points that are installed on the top of storage shelves to provide greater coverage make device maintenance difficult. Wireless devices that are easy to configure and maintain can make installation and troubleshooting easier in warehouse environments as well as increase efficiency and productivity.
To make wireless network deployments easier in warehouses, wireless devices require a smart setup function that can simplify the setup, configuration, and maintenance processes for operators. This function should be able to detect the role of each wireless device inside a warehouse and automatically choose suitable setup options to connect APs and clients, thereby reducing installation time.
Some warehouses are subject to less-than-ideal environments, such as very high or low humidity, or sub-zero storage temperatures. AS/RS and AGV system integrators need to build systems that can adapt to different customer needs and many different environments. For this reason, it is important to choose wireless devices that can handle sub-zero temperatures and have sufficient ingress protection to keep out dust and moisture.
Moxa’s AWK-A series devices provide all the basic building blocks for a reliable, high-performance mobile Wi-Fi network and a solution that is tailor-made for AS/RS and AGV markets. The AWK-A solution comes with the following features to ensure reliable Wi-Fi systems for your mobile applications:
• Turbo Roaming technology for seamless roaming with millisecond-level handover time.
• Adherence to IEC 60068-2-6 standards for protection against severe onboard vibration.
• Power and RF isolation for disturbance-free Wi-Fi connections.
• 2 x 2 MIMO technology to maximise Wi-Fi availability.
• Wide operating temperature range from -40 to 75°C.
For more information contact RJ Connect, +27 (0)11 781 0777, firstname.lastname@example.org, www.rjconnect.co.za