Considerations when specifying enclosures for Industry 4.0 applications
Industry 4.0, the deployment of distributed automation and data exchange in manufacturing technologies, is based around the Internet of Things (IoT) and cloud computing to create the ‘smart factory’, where physical machines are monitored and controlled in pseudo real time and autonomous decentralised decision-making manages the process.
The move to complex distributed computing brings with it some high-level technical issues: IT security, greatly aggravated by the inherent need to open up previously closed production systems; the need for high levels of IT system reliability; the repeatable low system latency requirements and stability needed for critical machine-to-machine communication; and the need to maintain the integrity of production processes. The distributed mini-systems will often have embedded IP capability, Wi-Fi and Bluetooth connectivity, processing and communicating information from their attached sensors and controls throughout the IoT rather than raw signals going back to a central control room.
In addition to these macro level concerns, at the micro level the widespread distribution of electronic modules and subsystems in the factory environment requires considerable thought to be given to the selection of the housing for the electronics. Given that the selected enclosure must provide a secure and physically robust environment for the electronics, there are several criteria to consider when choosing the optimum product design.
A standard or application-specific design?
Selecting a standard enclosure from one of the many suppliers has some obvious benefits: there are no upfront non-recurrent design, engineering and tooling charges; products are on the shelf ready for immediate delivery, so time to market is low; the unit costs are attractive; and the design will have been field proven in many different applications. Compared with an application-specific custom enclosure, designed specifically for the project, standard products are immediately available and, certainly in volumes up to the low thousands, are extremely cost-effective.
However, any standard enclosure will need modifying to meet the requirements of a specific application, requiring machining with suitable apertures to accept switches, displays, I/O connectors and other components. They will also need to be printed with legends and logos. The best option is for the original manufacturer to provide a modified enclosure configured to the specific requirements of the equipment. It is certainly of great benefit to involve the standard enclosure manufacturer as early as possible in the development cycle. There is no need to over-order to allow for set-up and wastage quantities if the standard enclosure is purchased and the modifications outsourced to one or more suppliers.
Small enclosures are usually made from die-cast or extruded aluminium or are moulded from flame-retardant or standard ABS or polycarbonate. As all materials have specific properties in terms of impact resistance, resistance to chemicals, resistance to abrasion and so on, the choice of material will to a certain extent be controlled by the location and expected environment.
By definition, Industry 4.0 requires electronic modules and systems to be installed on the factory floor, close to the equipment that is being monitored and controlled. The question of the level of protection against the ingress of dust and water therefore becomes significant in the specification criteria, defined in EN 60529 as IPxx, where the first digit defines the protection against solid objects and the second the protection against water ingress. An enclosure for general-purpose use would typically be rated IP54, whereas one for use in hostile environments would need to perform to a minimum level of IP65, but nowadays IP67 is becoming the de facto minimum requirement.
In general, enclosure manufacturers use two main techniques to achieve the designed protection level. Satisfactory IP54 sealing is readily achieved by using a tongue and groove construction to the joint between the body of the enclosure and a removable panel or lid. No gaskets are used; the seal is achieved through the combination of a recess in the base section that mates to the corresponding mirror profile in the lid when the lid is screwed down. To achieve higher levels of sealing in metal, plastic and extruded small enclosures will require a gasket between the two mating halves. Normally a separate, preformed moulded gasket is sandwiched between the two mating surfaces. A metal enclosure can be painted if required without having to mask the gasket area; the gasket can be easily replaced if it is damaged.
In many applications EMC capability is of no interest, but in the potentially electrically noisy factory floor environment, it can be a consideration. Moulded enclosures have one specific weakness: by virtue of the intrinsic properties of the material itself, plastic, unlike metal, offers no inherent attenuation to the passage of electric or magnetic fields. If EM radiation emitted by the housed electronics or their susceptibility to external fields is a potential problem, the lack of screening could be an issue.
Internal coatings in a variety of materials can be applied to the inner surfaces of a plastic enclosure to give different degrees of attenuation dependent on the project requirements. By offering different materials in a range of thicknesses, the most cost-effective and technically competent solution can be provided. Metal enclosures, providing they are manufactured in such a way that electrical continuity is present between the top, base and removable panels and that any painted or anodised finish is purely for external decorative purposes, will provide a level of EMC likely to be more than sufficient for the majority of applications.
With small low-power systems, heat dissipation is not usually an issue, but if systems are generating sufficient waste heat it can become a problem. As with EMC, metal and plastic enclosures have significantly different properties. Metal enclosures have greater ability to provide conduction and convection cooling because of their greater conductivity; indeed, some extruded enclosures are designed with increased surface area to improve cooling performance. All types of enclosure can be modified with arrays of holes to improve convection cooling if required.
In order to make a standard enclosure suitable for a specific use, it will need to be modified. The purchaser has three main options.
1. Purchase standard products, either directly from the manufacturer or through distribution, and then modify them as required in-house. However, many electronic OEMs may not have the plant, equipment, expertise or interest in undertaking machining and painting procedures in their own premises. If there is in-house capability, to modify the housing as a part of the overall assembly process could be the best way to proceed. However, more standard units than are actually required will have to be purchased to allow for set-up procedures and wastage.
2. Buy standard products and outsource the modification processes to external contractors. This will incur additional costs, time penalties and logistics complications associated with managing the process of subcontracting, often to multiple suppliers, potentially further increasing the costs as each process will require extra units to allow for first-offs and set-up wastage.
3. By far the best option is for the original manufacturer to provide a modified enclosure configured to the specific requirements of the project. With this option, there is no need to over-order to allow for set-up and wastage quantities. Hammond Electronics has a long-established network of international and national broadline catalogue and specialist distributors throughout Europe. The close working relationship between Hammond and the distribution partners means that factory modified enclosures can be sourced from the distributor or from Hammond direct.
Enclosure manufacturers will typically be able to provide milling, drilling, punching, engraving, screen printing, painting and EMC coatings for their range of standard products. Manufacturers of moulded enclosures can normally also offer enclosures moulded in custom colours to meet any applicable identifying requirements or corporate branding needs.
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