The role of wireless in modern production
Modern industrial wireless systems overcome the traditional problems with wireless and mark a revolutionary step forward over trailing cables.
It has been roughly a decade since the phrase Industry 4.0 was first introduced with much fanfare at Germany’s Hannover Fair in 2011; however, the concept is now entering a phase of maturity. Digital technologies are becoming increasingly common in industrial environments, and wireless serial communication is an integral part of that.
For many industrial businesses, the rise of smart factories has brought with it a renewed focus on industrial networking possibilities. This has meant a wealth of newer communications protocols and technologies, such as EtherNet/IP, RFID and Bluetooth, making their presence felt on the factory floor. However, the fundamental drivers behind field-level communication remain the same as they always have been: to reduce the need for extensive cabling of production applications, to improve the effectiveness of maintenance and to simplify the control and monitoring of devices on the factory floor.
Wireless is invaluable in any industry or application that makes regular use of motion with communication cables. Among these, and one area where this is particularly valuable, is parts assembly, whether that is in automotive, electronics production or any industry where rotary tables and robotic systems are commonly used. These systems make trailing communications cables problematic for two core reasons: first, the motion of the systems means the cables are often damaged or disconnected during operation, leading to frequent maintenance or replacement and higher operating expenditure (OPEX). Second, the design of many systems means communications cables run in close proximity to high-voltage power cables, which can cause interference with communications signals.
It’s in these areas that wireless communications devices offer a viable, cost-effective solution.
Modern wireless communication technology can be traced back to one man: German physicist Heinrich Hertz. In 1888, Hertz proved the existence of radio waves — something that until that point had been merely theorised by James Clerk Maxwell’s theory of electromagnetism.
A century later, in the 1990s, the world witnessed a wireless boom. This rise came from increasing cellular communication developments, extensive commercialisation of vital electronic components like MOSFETs and legal rulings that made industrial, scientific and medical (ISM) radiofrequency bands available for unlicensed use. The Institute of Electrical and Electronics Engineers (IEEE) promptly set about developing a new standard for wireless technology, called IEEE 802.11. The initial framework was established in 1997, specifying throughput bit rates of 1–2 Mb/s by either using frequency hopping spread spectrum (FHSS) or direct-sequence spread spectrum (DSSS) in the 2.4 GHz ISM radiofrequency band.
FHSS, as the name suggests, involves the transmitted signals rapidly hopping between different frequencies in a spectral band. The order and structure of the frequency changes is known by both the transmitter and receiver device, and this is done to make interception of signals and interference of communication more difficult. On the other hand, DSSS modulates the transmitted signal with a pseudorandom bit sequence to make it wider in bandwidth, which is descrambled by receivers.
Industrial networking technology also has its own illustrious past. In the 1960s, telemetry systems began being applied to industrial processes to provide monitoring functionality, which led the way to supervisory control and data acquisition (SCADA) systems and distributed control systems (DCSs) coming to the fore. These systems involve a base device, which collects and processes data from a series of field devices connected with serial communication cabling. The main difference between the two, initially, was mostly that of user interface and device spread; today, however, there are many more similarities between the two system types.
Similarly, the latter half of the 20th century brought automated systems to the factory floor, ranging from pneumatic rotary tables in automotive manufacturing and conveying systems to Cartesian manipulators and industrial robots. These systems remain staples of modern industrial settings, particularly in applications such as automotive sub-assembly, electronics manufacturing and welding.
All these systems — the control systems and the physical automated systems — have two things in common: they are tools for enhancing productivity and they must communicate data to operate effectively.
Cables and their challenges
Generally speaking, there are two main types of cabling used in modern industrial settings: copper and fibre optic (FO).
Traditionally, copper cabling has been dominant in industry. It is typically able to run to lengths of 100 m and, depending on the category of cabling used, allows for data transmission of up to 1 Gb/s. This type of wiring has found popularity predominately due to its low cost, ease of installation and general reliability with the right sheathing and protection, which makes it initially an attractive proposition for industrial manufacturers.
However, it has numerous disadvantages. First, it is limited in the volume of data flow that it can allow — something that will become increasingly troublesome as Industry 4.0 technologies continue to develop and enter the factory floor. Second, it can present a spark risk if damaged, which makes it generally unsafe for certain industries such as oil and gas. Finally, it is inherently susceptible to electromagnetic interference (EMI) from other industrial applications unless it is properly shielded and protected.
FO cabling overcomes many of these problems. It boasts a data transmission speed of up to 10 Gb/s and can be used for much longer runs of up to around 2 km. Of course, the maximum transmission speed varies depending on the length of the cable run — a 2 km run might only achieve speeds of approximately 100 Mbps, whereas a 500 m run may allow speeds of closer to 10 Gbps. In addition, FO cables overcome the disadvantages of copper cabling in that they do not pose spark risks and are immune to EMI. However, this all comes at a higher price point and typically requires specialist installation, both of which deter manufacturers with a lot of cabling to install.
EMI is a growing problem in the modern industrial environment for several reasons. Most pieces of equipment that are electrically powered will generate electromagnetic emissions under normal use — a by-product of the electrical conversion process for mains AC power and an increasing problem due to the advent of high-frequency power supplies and inverter drives. This is why proper care should be taken with the design of systems to mitigate the impact of these emissions interfering with one another.
Electric motors, which are understandably common in industrial environments, are prime culprits for causing harmful EM emissions that can radiate and interfere with nearby electrical and communications networks. For communications, this interference can mean data degradation and signal loss, which can make affected equipment become unreliable — not ideal for high-value or precision manufacturing.
Of course, this problem hasn’t been left unmitigated. EMI filters are commonly used in electrical networks to attenuate EM radiation, and copper cables are shielded to prevent interference. However, the threat remains for cabled applications.
Similarly, high-voltage electrical cables can affect communications cables. Engineers should typically avoid running communication cables parallel to high-voltage power cables, as the noise induced can cause communication loss or component damage. Yet this is the case for some industrial applications such as some industrial robotics, where wiring is confined to a set space.
All cabling is limiting in its application. It hinders the movement of motion applications, and rotary tables and industrial robotics commonly experience faults because of this. Rotary applications are considered to be heavy loads for most cables, especially FOs, because the twisting motion causes significant signal attenuation and can cause connection faults. Maintenance engineers are undoubtedly familiar with the frequent need to maintain or replace cabling in these cases, and the cost of the planned downtime that comes with it.
In these cases, businesses are forced to spend ongoing amounts of money maintaining and replacing cabling. The alternative is investing in expensive rotary connectors and joints, or extra flexible cabling that will, in reality, still face the same challenges over time.
Cabling requires careful assessment of integration possibilities and security. It can also be difficult to modify plant layouts as needed. Doing so often requires a great deal of reinstallation time, adding to further downtime. Cabling also limits the geographical distance that base and remote units can effectively operate at.
Wireless communications are not an entirely new concept in industrial environments and have risen in popularity in recent years. But for every benefit, there are some concerns about the security and robustness of wireless communications systems.
Security can be addressed through effective transmitter-receiver data encryption, by using FHSS and ensuring a modest range to minimise the ability of external agents to ‘listen in’ on the frequency.
Concerns about interference can be more difficult to manage in industrial environments, which are generally rich in electrical and electromagnetic noise. In a perfect world, the solution would be to use only systems that are designed and installed following good electromagnetic compatibility (EMC) design and installation practices. Luckily, we can tackle this with a combination of using a base frequency band that is outside the normal noise frequency of industrial settings and employing FHSS to hop around that frequency range to reduce the chance of interfering with other devices.
Traditionally, another major shortcoming of wireless standards used in industrial environments has been response times. Latency is somewhat acceptable for slow-moving processes, but fast response times are critical for real-time networks such as a bottling plant where the bottle, dispenser and cap need to align at very high speed. This is one reason why manufacturers have been reluctant to adopt wireless technologies and have opted to remain cabled in. The necessary low-latency wireless networks have, until now, not been available, but that is changing.
Now there are industrial wireless systems that utilise the 2.4 GHz ISM frequency band and use FHSS across up to 79 channels in the frequency range, changing channel every 5 ms to avoid interference with other technologies and electrical noise. Using this frequency band makes them ideal for use in industrial environments, such as in automotive manufacturing, where polluting frequencies vary from 5 MHz for motor driver and electric heaters up to 1 GHz for welding applications.
Such wireless gateways also integrate with a standard industrial Ethernet connection such as EtherNet/IP or Profinet. The base-station is typically able to wirelessly communicate and control up to 127 remote units in a range of up to 10 m.
Remote wireless units can come in the form of modules that can be fitted onto analog, digital and pneumatic equipment to provide control functionality for I/O and valves via one IP address, offering decentralised point-to-multipoint communication.
A good example of an application commonly found in the automotive industry is the use of rotary tables to produce cross beams. These tables are notorious in industry for being troublesome with fibre-optic communication cables.
Utilising a Wi-Fi solution the standard fibre-optic unit can be replaced with a Wi-Fi base station that controls the remote units directly within the working cell area. The remote wireless units can be mounted directly at the rotary tables, allowing operations to proceed with a significantly reduced need for maintenance.
Another influencing factor that drives some plants to consider wireless is the company’s measure of overall equipment effectiveness (OEE). OEE is a good practice manufacturing metric that is a simple way of evaluating the performance of production processes, by focusing on the losses in production and dividing them into three categories: availability, performance and quality.
An OEE analysis may show that machine availability is affecting a plant’s operations. In addition to the time lost in stops for maintenance, the level of communication failure can be very high, which can happen in high-motion applications such as robotic cells.
Installing wireless equipment on each of the robots in a cell — eliminating costly power packages and cabling and associated problems — means that communication between the base and the wireless robot remotes remains stable and robust, improving availability and therefore OEE.
Wireless systems can also have a significant impact on reducing costs in industrial environments. For example, implementing a rotary table the integrator has to solve the problem of signal transmission from auto-switches to a control unit.
Compared with the cost of using a multifunctional rotary connector and a valve manifold, wireless can offer a more cost-effective investment.
As Industry 4.0 enters a period of maturity, the need for wireless technology will only increase. The growing adoption of automated systems means that flexibility, availability and durability are vital in modern communications networks.
Modern industrial wireless systems overcome the traditional problems with wireless and mark a revolutionary step forward over the trailing cables that have limited industry to date. By making use of these systems, industry can finally begin to realise the true possibilities of Industry 4.0 technologies.
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