A Human Machine Interface, or HMI, is a computer with a touchscreen interface. It communicates with a programmable controller(s) to operate a machine. The HMI can replace lights, buttons, and dials to simplify the interface and greatly expand functionality.
Machines typically need some sort of interface to control their operation. It could be as simple as a single on/off button or as complex as multiple consoles with flashing light, squawking buzzers, and myriad dials, buttons, and switches.
Lights and Switches Cost, Too
When designing a new machine or upgrading an existing one, many people struggle with the expense of an HMI and think the upfront cost cannot be justified. Especially if it is a simple system with only a few ways for the operator to interact with it. They reason a few lights and switches cost much less than a computer with a touchscreen interface. However, there are other costs that come with the lights and switches:
These input and output devices must be mounted and wired into the machine. This involves drilling or punching a hole for every device and mounting them, running wires from the controller and/or power source to the devices, and physically making the wiring connections. This all takes time.
The controller needs the inputs and outputs available to interface to these devices. As the I/O count of a controller goes up, so does the cost. And if any of these devices are analog, like gauges or potentiometers, the cost of additional analog inputs and outputs can add up fast. Remember, this is not I/O required for the controller to interface to the machine (sensors, thermocouples, valves, etc.); this is I/O just so the user can operate the machine.
An HMI, like the Parker CTC and its Xpress HMI software, can replace these devices by using one simple connection to the controller to allow communication. Once the HMI and controller are talking, the buttons, lights, switches, dials, gauges… can be represented graphically on the touchscreen. The user can push virtual buttons instead of physical ones. Need a blue button instead of green? No problem, a simple program change and you’re done; no need to order a new device and physically swap it out. Want to add some new status lights? Presto, just a few mouse clicks away.
Human Machine Interface Opens Possibilities
The HMI can also do things that were not possible before. What if the machine runs unattended most of the time? Would it be helpful if it could send alerts via text message or email if it had a problem? Getting it back up and running quickly eliminates downtime and keeps it making money. Would it be nice to know how many parts were made last week compared to this week? The Human Machine Interface can track, store, and present data easily to help pinpoint subtle trends that lead to lost productivity.
The upfront cost of the HMI is not the whole picture. When compared to the labor and I/O points associated with traditional user interface devices, the cost of the HMI might be justified even in simple machines. Adding in the increased flexibility and functionality an Human Machine Interface can provide makes it starts to look like a very easy decision.
Jack Marsh is a motion control specialist for Innovative-IDM, and a member of the IIDM President's Club. He can be reached at firstname.lastname@example.org