Human-machine interfaces (HMI) allow users to monitor relevant data and control the connected machines. Using programmable software, these devices can be configured to your specific needs.
While the term HMI can technically apply to any device that relays information to a human operator, most HMIs share several defining features including a screen, some form of input device, and programmable software. (Said software is usually a separate program from the software used to program PLCs).
Displaying Data and PLC Integration
HMIs can be programmed to display information such as a machine’s current operating state or statistics from its runtime. The way in which this information is displayed is highly customizable, granting HMIs flexibility for use in all sorts of automated systems. It is important to keep in mind that HMIs are an extension of a PLC system, and that any data being processed by the PLC can be sent in some form directly to the HMI.
For example, say you wanted to implement an HMI for a robot that takes packages from a conveyor belt and places them onto pallets. You could program the HMI to display an overlay of the pallets, indicating how many packages are on each one. You could also add a camera feed from the robot arm POV to see what is being taken off the conveyor belt.
Further statistics like arm runtime and packages moved could be added to assist with maintenance, or help troubleshoot issues with performance.
Control Capabilities of HMIs
Information output is only half of an HMI’s capabilities though. Operators can also use an HMI to control various components within an automated system. This makes on-the-fly adjustments to automated systems much easier, as control technicians can circumvent having to connect to the PLC using a computer to make changes to its associated output devices.
Like the information displays, the controls can be configured to meet the requirements for a wide range of machinery. Again, HMIs are an extension of the PLC system, meaning that an HMI can be programmed to interface with any devices also connected to the PLC system.
Furthermore, one can program the HMI to allow only certain adjustments to be made, with some settings being locked behind authorization codes or even just hidden (I once worked with an HMI that hid technician-level settings in a menu that could only be accessed by pressing the upper-right corner of the screen for 5 seconds!). While not always necessary, such design prevents random operators from making changes that could cause interruptions or damage to machine operation.
Going back to the previous robot arm example, the HMI could include digital buttons for stopping the robot or moving it to a preset location. The “fingers” of the robot could have manual controls be incorporated into the HMI.
Beyond just the robot arm, the conveyor and safety cage around the robot may have their controls tied to the robot HMI, or otherwise have their own dedicated panels for operator control.
However, not every piece of machinery needs to have an HMI — there are some systems where having a single point of access for control is desirable, and that there are advantages to physical controls over digital ones.
Why Invest in an HMI?
For one thing, HMI makes monitoring automated systems easier. Having a visual indicator for the status and/or operational state of a piece of machinery helps users identify troubleshoot errors or prevent problems prematurely.
With our robot arm example, say that the HMI is mistakenly reporting the robot arm holding nothing when an object is present. This could indicate a problem with the camera lens on the arm, or the fingers being calibrated incorrectly. If programmed for it, the HMI could let the operator stop the robot, manually drop the package being held, and move it to a better position for repair, all without having to connect to the PLC directly via a computer.
HMIs can be exceptionally useful for almost every automated system you could imagine. While not strictly necessary, their flexibility makes installation a breeze, and grants you greater control over any automated system connected to one.
Check out MISUMI’s selection of HMIs here.
