5 Common HMI Failures
As with any machine, an HMI is going to be subject to failure, and you need to be able to identify what the problem is before you can go about fixing it. Rowse fields a team of experts in automation and control, and with their help, we've identified 5 common HMI failures experienced by users.
What Is An HMI?
The array of complex machinery that comprises an automated system requires some accessible connection between the equipment and the person who controls it. HMI is simply the abbreviation of this go-between, and stands for Human Machine Interface. This interface is generally a screen or dashboard, by means of which a person can connect to any device, machine or system. Technically, this means that any screen you use to interact with some electronic device, even your smartphone, could be called an HMI, though the term is mostly used in an industrial context. HMIs are an increasingly common sight in today's automated factories, together with various types of visual control panels.
Other terms can be used to refer to this technology, including Operator Interface Terminal (OIT), Local Operator Interface (LOI), and Man-Machine Interface (MMI), but HMI is the most common. It is sometimes used to mean a Graphical User Interface (GUI), but the two things aren't the same. A GUI enables a user to navigate a screen via images or icons, rather than text or commands. It has some similar capabilities to an HMI, but will usually be used for enabling visualisation within the HMI. An HMI might take the form of a tablet, a computer monitor or a built-in screen on a piece of equipment, but they all function to give the human operator insight into the performance and progress of the machine.
HMIs in industry are commonly used for control purposes, including monitoring inputs and outputs, overseeing Key Performance Indicators, tracking production statistics, and providing a visual display of key data. In a factory, an HMI might be used to monitor pump functions, operate safety systems, control production lines, or maintain optimum working conditions for personnel. Most domestic HMI functions are basic versions of this, such as washing machine or air conditioning controls, and smart houses can be completely controlled using just a tablet.
An HMI is a source of constant feedback about its own health, providing a lot of information about potential future failures. This is important, because if an HMI fails while in operation, your equipment will also stop, incurring costly downtime and loss of productivity.
How can you interpret this information to make sure this doesn't happen? In our experience of working with HMIs at Rowse, these are the signs you should be looking out for to prevent 5 common HMI failures.
If it takes several tries to power up your HMI, or it needs frequent power-cycling (reset), this is a common sign of incipient failure. Difficulty in starting your HMI indicates the likely failure in the near future of an internal power supply.
The most frequently used keys on an HMI are those most likely to fail first. Keys like Start, Enter or passcode keys are likely to experience the heaviest use, and the identifying lettering may get worn away. Operators may find themselves pressing the key a bit harder each time, and eventually these keys will fail. This is an indicator that the switch itself is failing, and you'll need a new switch or even an entire new membrane.
Certain commonly used areas of a touchscreen might stop working or an operator might have to press a soft-button several times to get a response. This is a sure sign of failure of the touchscreen element. Touchscreens are very sensitive and will wear like any other part. You should never use anything other than fingers to operate them, or you may cause scratching and breakage. Shattering the LCD glass can lead to instant HMI failure, and the risk is greatly increased if you prod your screen with a pen or other implement.
You might just find this annoying as an operator, but it’s more important than that, as it indicates the imminent failure of the HMI backlights. It might take months until the backlights fail altogether, so you have plenty of time to fit a replacement unit or refurbish the HMI.
Vertical or horizontal lines across the screen are similarly annoying, but they indicate the incipient failure of the LCD. As with flickering, it will probably start with only a few lines and take a while to fail completely, but it's a sure sign that a failure will happen.
Many of these signs appear months before a complete failure occurs, so you should initiate a continual dialogue with the system operators to prevent this happening. They are the ones interacting daily with the HMI, and they are the ones who might be putting up with perceived minor problems, rather than getting them fixed. If operators learn to identify the advance indicators of these 5 common HMI failures, you can keep your system running more smoothly without sudden, unforeseen breakdowns.
This is where some predictive maintenance comes in, which can take the form of a few simple questions.
- Does your HMI power up straight away every time?
- Are you experiencing any diminished response of the touchscreen or membrane keys?
- Have you noticed the screen flickering or seeming dull?
- Have you noticed any lines on the screen?
The operator's answers to these questions should give you a heads-up on likely failures of your HMI, and whether it needs refurbishing or replacing. Don't wait for an operator to tell you after a failure that some of these symptoms had been happening for months. They won't go away on their own, and preventative maintenance will help you avoid downtime and loss of production.
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