Various different communication standards are used for transmitting human data input to the machine – or more precisely, to the machine control system. The right one depends on factors such as the industry, the data to be transmitted and the transmission path.
For a long time, the individual control elements of a Human Machine Interface were connected discretely, meaning each had its own cable: in complex control systems, this quickly led to cable bundles that had to be connected to the machine. This installation effort can be significantly reduced by bus systems – only one connector and one cable are required.
Each industry has its own bus systems
Currently, a significant number of bus systems can be found on the market. There are a number of reasons for this: every industry and application has different requirements when it comes to data transmission, different technical solutions are available, and several manufacturers have brought their own bus system to the market. In industrial applications, systems like Profibus, Modbus, CC-Link and DeviceNet have become established. Other industries use different solutions: for example, KNX, LON (Local Operating Network) or BACnet in building technology.
In the automotive sector, the CAN bus (Control Area Network) has the largest revenue share at 37.8 percent, according to Precedence Research. Other bus systems that are in use today include Local Interconnect Network (LIN), Media-Oriented Systems Transport (MOST), FlexRay and Ethernet. Each bus system focuses on specific requirements: LIN, for example, enables the cost-effective integration of sensors and actuators in vehicle networks, while FlexRay can be used in safety-relevant distributed controls.
Ethernet gains market share
Ethernet is also gaining importance across industries. This bus was developed in the first half of the 1970s and is currently the transmission standard in the IT world. For industrial applications, Ethernet has been adapted to be fast enough for the high demands of industrial automation. These “Industrial Ethernet” protocols include Profinet, EtherCAT and Ethernet IP. The factors driving growth in the area of Industrial Ethernet systems include higher performance, larger data volumes, better real-time properties, the integration of safety protocols and the continuity into office networks – and thus also easier connection to the Internet of Things and to the cloud. Ethernet has been further developed to be able to control safety-relevant tasks: with TNS (Time Sensitive Networking), a set of standards has been defined that supplements Ethernet with functions for the real-time transmission of data.
Manufacturer-independent communication
When integrating an HMI into complex machines, there is the problem that devices from different manufacturers must be connected. A potential solution here is the data exchange standard OPC Unified Architecture (OPC-UA). It was developed in close cooperation between manufacturers, users, research institutes and consortia. OPC-UA bridges the gap between the IP-based IT world and the production world.
Remote control of machines via radio
Operating machines, systems and devices via radio remote control has many advantages. A radio remote control enables the free choice of location during a process or action. Typical frequency bands for radio remote control are 433 MHz and 868 MHz. The 433 MHz frequency band offers greater range, but this band is more susceptible to interference than the 868 MHz band due to high utilisation. The use of the 2.4 GHz frequency band is also very widespread. It can be freely used around the world and is the only frequency band that can be used in all countries without additional permission. The uncomplicated access process makes the 2.4 GHz band very popular and particularly interesting for non-professional use. Model building, drones and WLAN routers often operate on this frequency.
Stable radio connections are a prerequisite for operating a machine via remote control. Various radio systems therefore use LBT/AFA technologies (“Listen Before Talk”/ “Adaptive Frequency Agility”). First, a channel is checked to determine whether it is free, and if it is, a connection is established on this channel. If not, the next channel is checked and used if possible. In this way, emergency stop functions can also be realised via radio.
From the consumer segment to professional use
Cutting-edge products in terms of ergonomic user interfaces were smartphones and tablets. Many people now use them on a daily basis, a fact that many companies are leveraging to enable professional applications to be increasingly controlled via mobile devices. Depending on the application, the connection is established via a WLAN modem or Bluetooth.
The USB interface is another well-known development from the consumer sector. Today, it is also used in professional applications to connect an HMI to a control device, or to connect auxiliary devices, such as a mouse, keyboard, signal lights or fingerprint scanner, to the operating terminal.
