Robust Power, Communication, and Safety for Automation

­Industrial automation has transformed the modern factory. Communication is now just as important as the electricity used for the drives and servo motors of the large machines that manufacture goods, and safety is critical as humans and robots work close together. The challenge for the automation engineer is selecting and installing power, communication, and safety cabling that takes advantage of today’s technology while having one eye on the future in terms of scalability.

It’s a tough challenge because factories are a large investment and built to last. During their lifetime, manufacturing technology will evolve and wiring systems that were satisfactory only a few years earlier may no longer be adequate. Moreover, as production capacity increases, each additional system will require its own connectivity, and recabling a factory is not only expensive and time-consuming, it also means expensive machinery sits idle.

Engineers are increasingly turning to modular systems which accommodate wiring for power, communications, and safety in the same sheath while allowing for future growth in the form of spare wires. A key part of this approach is the M23 connector system, so-called because the diameter of the thread of the cable coupling is 23 millimeters (mm). The system is relatively easy to assemble and test, and makes for a robust and reliable power and communication infrastructure (Figure 1).

M23 connectors and cabling are designed for servicing the electric drives, servo motors and encoders common to industrial automation. The M23 system features a range of inserts and housings for data, communication, and combined power and data, making it equally suited for applications involving signal or power transmission. M23 cordsets can carry voltages of 250, 630, or 800 volts at currents of 9, 18, or 30 amperes (A).

M23 cabling is not governed by an international standard. However, manufacturers generally follow recommendations concerning the fabrication of the cordsets which allows for interoperability. As such, M23 can be considered a de facto standard.

A variant of the M23 system is the M12, which has a 12 mm coupling thread diameter. Because the M12 is not used for power, the cordsets are more compact, saving cost and space (Figure 2).

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Figure 2: The M12 cordset is used for communication and safety only; it features a more compact form factor than the M23 (Image source: Molex)

The key to the M23/M12’s success is their flexibility. First, designers can elect to make up their own customized systems by specifying cables, couplings, receptacles, inserts, connector housings, and even the diameter of the mating pins. The couplings are available in straight and angled designs, and the inserts can be procured with multiple pin counts and patterns. The result is a wide range of customizable variations for virtually any application.

Alternatively, the designer can choose from a range of factory-supplied cable/coupling or cable/receptacle assemblies. The advantage of choosing pre-built products is the assembly time savings and the reassurance that the integrity of the cable and connector has already been factory tested. The downside is a relatively limited range of solutions compared with building from scratch. However, the pre-built range is still wide and covers connector alternatives and cable lengths for most factory automation options, including rotating machines, welding robots, or automated assembly equipment.

Protection Against Contamination, Vibration, and EMC

With some exceptions, such as the manufacture of food, pharmaceuticals, and hi-tech electronics, the factory environment is typically full of moisture, dust, grease, and other contaminants that are the enemy of electrical systems. In other applications, the cable and connector solution might be required to be resistant to acid and alkaline solutions used during production and cleaning, making it vital that they resist the penetration of all liquids, particles, and other substances.

The specific resistance to contaminants required will change depending on the factory requirement. Manufacturers helpfully categorize their products according to the IP classification system. The IP rating indicates the degree of protection provided by the product and is defined by the international standard EN 60529.

The scheme comprises two digits, the first representing the level of protection from solid objects, ranging from tools or fingers that could be hazardous if they encountered electrical conductors, to airborne dirt and dust that could damage circuitry. The second digit defines the protection from various drips, sprays, or submersion. The range extends from IP00 (no protection against dust or water) to IP69 (total protection against dust and powerful, high-temperature jets of water).

It’s not just pollutants that can cause problems for poorly designed factory electrical systems. The cable assemblies are also potentially subject to thermal stress, vibration, and mechanical bending (particularly if used in a robotic application where the cables can be in constant motion). Moreover, factories are typically home to large electric motors that draw large starting currents, creating power and voltage surges and electromagnetic interference (EMI) that can upset delicate communication systems.

M23 and M12 cable assemblies are specifically designed to deal with factory environments, and their screw-together couplings resist vibration and mechanical load. For challenging EMI environments, cable set makers typically offer options with integrated shielding.

For example, Molex offers a range of particularly robust power cables with its Brad® 120480 M23 power overmolded cordsets. These cable assemblies are built for demanding environments with features such as plastic overmolded sheaths to protect the cable/connector joint and optional EMI shielding. They are available in discrete lengths from 1 meter (m) up to 20 m and colored orange for high visibility (Figure 3).

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Figure 3: The 120480 M23 cordsets feature overmolding for additional protection and a range of inserts; six and eight-pole variants are shown here (Image source: Molex)

The cables are available in either six or eight-pole (wire) versions. The maximum voltage and current are 800 volts and 18 A, with a contact resistance of 3 ohms (Ω) and an insulation resistance of 100 megaohms (MΩ). The cordsets can operate across a temperature range of 25°C to +85°C, and offer an IP67 dust and water protection rating, once mated.

The advantage of a modular system such as M23 is that factory wiring can be built-up and adapted quickly as the factory grows. The system allows the engineer to easily couple wiring networks together and mate the cable ends directly to machinery equipped with M23 sockets. The wiring not only offers the high voltage and current required for factory automation, but it is also capable of supporting factory communication systems such as Ethernet, EtherCAT, Modbus, and PROFINET (Figure 4).

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Figure 4: M23 cabling makes it easier to extend the factory wired network as new manufacturing cells are added (Image source: Molex)

Ensuring Factory Safety

Connectivity plays a key role in the modern factory. Controlling and updating equipment is a big part of the network’s job, but factory automation safety is also important, particularly where people and robots are in proximity. The robot typically features multiple sensors to stop movement if a worker encroaches on the work envelope, and the safety cell is completed by interlocked gates and access panels. All of these systems demand connectivity, and the wired network can quickly become complex and unwieldy if each sensor is served by a branch of the main factory network.

Instead, engineers are simplifying things by using multiport interconnection system (MPIS) distribution boxes attached to the main factory network. From there, M12 control cables are connected to the boxes’ outputs to wire-up the manufacturing cell’s safety systems. An example is Molex’s rugged, IP67 rated 1202480510 safety MPIS distribution box which aids the management of safety devices installed around machinery (Figure 5).

The 1202480510 features a 5 m length of integrated cable for connection to the main factory network, four M12 eight-pin ports, and four M12 four and five-pin ports in one housing. The distribution box permits the installation of standard I/O wiring systems in limited space while maximizing safety design flexibility. Each port can handle up to 30 volts DC with a maximum current of 4 A (12 A total current for the distribution box). The distribution box is designed for use with cordsets such as Molex’s 1 m, M12, eight-pole 1200652383 Micro-Change series, and the 1 m, M12, four-pole 1200652378 version.

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Figure 5: Safety MPIS distribution boxes simplify safety wiring while saving space and cost (Image source: Molex)

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