Dan Hebert is a former senior technical editor for Control, Control Design and Industrial Networking.
Machine and robot builder OEMs have been using embedded control for decades, and many now use embedded HMIs. These embedded platforms typically are purchased from a vendor in a package that includes the display with the embedded operating system, usually Windows, pre-installed. Also included is the HMI programming software, often free, and the right to run the software in run-time mode on the display.
This is in contrast to PC-based HMI platforms that require OEMs to buy the software and the hardware separately. The other HMI option is a low-end graphics terminal with very basic functionality and limited flexibility.
Should you consider an embedded HMI instead of a PC-based HMI or a graphics terminal to provide an operator interface for your machine or robot? Here are some reasons and some cautions.
A simple graphics terminal is cost-effective and is usually adequate for basic machines with few inputs and outputs, but on more advanced and automated equipment, it could be insufficient in terms of operator interface, connectivity and data handling.
At the other end of the scale are PC-based HMI platforms—top of the line in terms of price and performance. Within this option are two approaches, each of which requires the user to buy a PC. The first is to buy off-the-shelf HMI software and configure it for the application, and the second is to write software using standard programming languages such as Visual Basic. Either option will provide a full-featured HMI, but with a few caveats.
Compatibility and Reliability Issues
The PC will have a short lifecycle of just a few years, so if it fails in part or whole, it might not be possible to make replacements using the same technology. Upgrading the PC or its operating system can cause compatibility issues with the HMI software and sometimes with connected components.
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Rick Lamb, president of Midwest Technology Ventures, a distributor and system integration firm, concurs. "PC-based Windows systems get difficult to change/upgrade/support after about five years because of obsolescence of the operating system, drivers, utilities or hardware. One piece breaks, and you can't get a replacement, and nothing is compatible with newer hardware or operating systems."
Because the HMI is a PC, probably with a Windows operating system, there can be software reliability issues, as well as the temptation to load additional software onto the PC to perform other activities, both work-related and personal.
In between a PC-based HMI and a simple graphics terminal with respect to price and performance is an embedded HMI, which can be the best solution in many machine and robotic applications.
Modern embedded HMIs provide a wide range of capabilities, flexibility and connectivity. "We provide an extremely easy-to-use software toolkit containing a very rich feature set that hardware manufacturers, OEMs and vertical industries use in their products," says Richard Clark, an engineer at InduSoft, a supplier of HMI and SCADA software.
"An embedded HMI configuration can be designed for many types of equipment, and can host a variety of external features such as thin-client server, web server, database access, a variety of I/O drivers and third-party reporting tools," Clark adds. "Such a configuration provides the flexibility required by machine and robot designers."
In many cases, a machine builder can get by with an embedded HMI instead of a PC-based HMI, resulting in substantial savings. For example, a vision-guided robotic system typically would have three controllers: a PLC, a robot controller and a camera controller. Most of the data exchange among the HMI and controllers would be discrete or floating point and typically limited to simple values such as setpoints, part numbers, lot numbers and measurement data. The HMI would have to display, collect and report machine status and alarms and configure functions. An embedded HMI fits well here, and if it fails, it's simpler to replace than a PC-based HMI.
When selecting an embedded HMI, you should consider the application, features, future expansion and customer requirements. You'll find a variety of available embedded HMIs in cost-effective packages from a wide range of suppliers, and these expandable, customizable HMI solutions quite often are the best option to meet your operator interface requirements.
