July/August 2020

| 24 | July/August 2020 | SOLUTIONS | S mart factories incorporate various cyber-physical systems that require faster and more reliable wireless solutions to handle ever increasing amounts of data in the toughest industrial settings. The main drivers facilitating new developments of these solutions to be deployed in highly demanding Industry 4.0 scenarios include the implementation of mobile SCADA, replacement of legacy systems, and realisation of data transmission from moving equipment where it was not possible or was limited before. This article focuses on the wireless technologies driven by this latter aspect. Industrial requirements A rotary joint, also often interchanged with the term slip ring, is an assembly for transmitting data and power across a rotating connection. The growing need for faster and more reliable data transmission between rotating components in modern industrial scenarios imposes strict requirements on bandwidth, crosstalk, and EMI performance of the data interfaces used in rotary joints. Meeting these requirements is essential to guarantee real-time operation, continuous uptime, and maximum efficiency of the corresponding industrial equipment. Industrial rotary data interface assemblies must ensure constant transmission quality at very fast rotational speeds of 5000 rpm to 6000 rpm at rates of typically 100 Mbps. In most cases these data rates are sufficient, but some specialised applications require faster transmission at 1 Gbps and higher, which is becoming a fairly standard benchmark nowadays. Industrial applications also call for support of IEEE802.3-based (Ethernet) and other industrial bus protocols, as well as deterministic real-time communication, to permit time sensitive applications and IIoT functionality. Data interface solutions designed for these applications must be immune to physical misalignments, electromagnetic interferences, and crosstalk to enable error- free data transmission with bit error rates (BER) of 1 ? 10?12 or better. Contaminants present in the industrial environment should not affect the operation of a rotary joint that ideally must be maintenance-free and not suffer from wear. Finally, the data interface technology must be compatible with power transmission subsystem of a rotary joint assembly to meet all functional requirements of a target application. Data interface technologies There are different types of rotary joints that vary in terms of their functional features, form factor, rotational speeds (rpm), maximum data rate, power ranges, type of supported interfaces, channel count, and many other design aspects shaped by application requirements. Among these design considerations, the data interface has some of the most critical requirements and it is therefore crucial to make the right choice of technology for its implementation in a slip ring assembly. Data communication technologies used to realise this function can generally be classified into contacting and contactless. They abound with many variations depending on the type of coupling they utilise in order to realize a communication channel for data transmission. Contact-type interfaces Contact-type solutions typically rely on composite, monofilament, or polyfilament brushes on a stator that slide against conducting rings on a rotor, thereby creating an uninterrupted passage of electrical signals between moving and stationary components. The selection of brush type with regard to data communication depends on the signal bandwidth, data transfer rate, required transmission quality, operational currents, and rpm. Although this is a well-established technology that has been employed in slip rings since their invention, it has certain limitations. Reliability of contact-type slip rings suffers in harsh operating environments due to the presence of mechanical contacts requiring regular maintenance. Contactless interfaces Contactless rotary joints overcome those limitations by using radiating or non-radiating electromagnetic fields to transfer the data across rotating parts. This technology offers several performance advantages over electrical signal transmission. The lack of mechanical contacts avoids contact wear requiring less maintenance and does not suffer from data loss arising from resistance at high rotational speeds. Fiber optic rotary joints: The most common example of a contactless solution is a fiber optic slip ring known as a fiber Data interconnection The Fourth Industrial Revolution drives digital manufacturing forward by implementing new scenarios into the production process. These scenarios rely on fundamental design principles that include device interconnection, information transparency, technical assistance, and decentralised decisions. The realisation of all these principles in modern smart factories would not be possible without advanced wireless communication technologies. They enable multifaceted applications for a broad range of areas including process automation, asset tracking, machinery control, intralogistics, and infrastructure networking. Smart Machines & Factories reports.