Many products use energy in some way – to alter heat, to provide light, some form of vibration or most commonly to move in one way or another. Any product that falls into this category needs some form of control, whether that is as simple as an on-off switch up to the latest touchscreens.
Traditionally such things were not strictly the domain of the mechanical design engineer, and as such, like the power supply, often came under the category of 'after thought'. However, the HMI (human machine interface) determines how effectively a human communicates with the machine, both on an emotional and practical level. While this is accepted with consumer products, it is equally true of industrial equipment, as we address here.
Dan Rossek, product marketing manager of automation, Omron, observed: "Traditionally, the HMI was selected almost as an afterthought, simply to replace pushbuttons and lamps. Quite often today, this is still the case! However, many forward-thinking machine builders will look at the ergonomics of the HMI in the early stages of development in order to ensure that it is intuitive and enables easy operation of the machine."
"On an upgrade program," said Stuart Greenwood, product marketing manager for industrial control and automation, Eaton UK, "where potentially additional features are being added to access data for example, it is often one of the first considerations. When the PLC is being integrated with the HMI, it affects the whole architecture of the machine, and of course that decision has to be made very early on."
HMI development
The earliest form of HMI was the simple switch, replaced by membrane switches and subsequently resistive touchscreens, usually alongside some membrane switches as back-up. Ian Smith, sales manager for Danielson, described the evolution: "As the resistive touch screens became much more reliable and prices came down, then people moved away from incorporating membrane switch panels with the touch screens, and they tended to be all resistive. They tended to be what we call 'closed front systems'.So you had a resistive touch screen with a graphic overlay on the front of it that was then built into a housing and could be sealed."
Greenwood added: "There are some harsh environments where a touchscreen just is not practical therefore we wouldn't recommend it. But lately we've found that the cost of touchscreens has come down to a point where they could almost be used in all applications."
There are two types of touchscreens – resistive and projective capacitive (PCAP). Resistive screens work by the mechanical pressing a top layer (typically a polyester film with a thin coating of indium tin oxide) onto a layer beneath, and the changes in voltage, and hence resistance, identify the spot that has been pressed. One problem with this is that there are durability issues with the front layer.
The other problem is that people are now used to their touchscreens operating like their smartphones or tablet computers. This necessitates the ability to slide a finger over the screen and 'multi-touch' to give a far greater degree of control.
Smith commented: "With the PCAP, if you've got a picture on there of something happening, a valve for example, then you can open up and expand it or contract it and move pages, scroll, and this sort of thing.So, it's much more versatile in terms of operation. Also it hasn't got a plastic front surface - it either has a glass or poly-carbonate front surface which is quite thick, so they are considerably more durable."
Resistive touchscreens are still widely used at the moment for applications that don't require the same depth of control, principally because they have become so much cheaper in recent years.
Integrating the HMI
Pulling an HMI into a design is not necessarily any more involved than a 'drag and drop' operation, requiring no further programming skills. Equally it could be that further integration, or to implement a higher level of functionality, could require a level of control re-engineering and software/code writing required which not all mechanical engineers are trained in.
And working with the HMI supplier can allow designers to enhance their products. "The HMI is often regarded as the window into a machine," claimed Rossek. "A poorly executed set of operator screens can give the impression of a poor quality machine, even if it is mechanically the best! Many machine builders add value to their machines via the HMI, in the form of production statistics, preventative maintenance, using video and other rich-media to assist fault recovery, etc."
Greenwood added: "Eaton offers a lean automation solution which uses an HMI/PLC with integrated smart cabling and intelligent remote components.Starting from the display, the SmartWire-DT (lean panel wiring system) connects pushbutton actuators, indicator lights, switchgear right up to the sensors. We can bring the world of hydraulics and the world of electric together."
"Perhaps more important is the HMIs ability to assist fault-finding/troubleshooting and speedy recovery of the machine in the event of a fault," observed Rossek. "A poorly designed and unintuitive set of operator screens can actually hinder production and increase downtime."
However, while the availability of the technology will inevitably 'push' the design of new equipment, there is also a considerable 'pull' factor emerging. Smith explained: "What we're seeing in the market is, from the companies that we supply resistive touch screens to who actually build the HMI, they are now being driven by their customers. It's really the end customers that are now wanting the new touch technology, and that again comes down, I think, to the fact that they have operators within these various plants who are of a younger age, who use their I-Phones and want to actually continue that touch screen experience across the range of products that we use in our factory."
But where will it all go? Some machine builders might prefer an industrial PC rather than a dedicated HMI, particularly if a PC is also required on the system for other things (What's the point of having a PC screen and an HMI next to one another?).Rossek said: "In these cases, just HMI software might be required, that can run in a standard PC environment. However, industrial PCs are typically much more expensive than HMIs, with standalone HMI software often costing as much as a physical HMI itself, so is generally an expensive option."
Or will the people's attachment to their smartphones and laptops go to the level of removing the need for an HMI on individual products and equipment altogether?Unlikely, according to Greenwood: "We've found that users are requesting the ability to use their everyday communication devices. However, the machine builder needs to use controls with multi-protocol capability to ensure they are future-proof. Smartphone and tablet operating systems change very quickly as technology progresses, and so using them could lead to issues with backwards compatibility."
www.industrial.omron.co.uk
www.eaton.com
www.danielsoneurope.com
