Does it all come down to wearing a glove?

The tasks confronting HMIs are becoming more and more complex as time goes on. Machines and plant are now being networked on a larger scale and integration is pushing ahead both horizontally and vertically. The demand for data and information is constantly growing. This is partly due to modern trends like ‘shop floor analytics’ and ‘smart manufacturing’. More transparency and more efficiency are wanted, from the feeder through production lines to the entire factory.

Multitouch panel PCs have many advantages, of course, both for monitoring such complex plant in process industries and also in increasingly networked discrete manufacturing. Just think of the greater user-friendliness and reliability due to intuitive operation in the form of gestures to rotate or zoom a complex visualisation with two fingers. Or swiping to scroll through a list.

So, many users get precisely the kind of support they are used to from their own tablets or smartphones. Multitouch even enables you to write with 10 fingers. Overall, then, HMI interaction is much more effective than single-finger operation. That means more usability and thus greater productivity.

The likes of this is not always possible, though. You have to remember that some operators need to wear thick gloves for their work, so they do not really benefit from multitouch because gloves increase the distance between the interface and your finger, dampening its sensitivity and spoiling the ‘feel’ of the panel. Consequently, there are applications where the potential of multitouch technology is not going to be exploited to the full - that is, when you think of the efficiency of the work process overall - for if you need to wear gloves for an assembly job, you can’t keep taking them off to move through a parts list displayed on a panel.

Applications where price is a sensitive factor are not suitable for multitouch either - not yet anyway - because a capacitive touch solution is more expensive than a resistive one. But the potential is there. Applications where pricing is a sensitive issue tend to be the smaller machines and plant. If the producer of this kind of solution is able to combine control and visualisation in a panel PC, they can save enough to opt for a better-value multitouch panel, upgrade the application and still cut their costs. So is it gloves that determine whether or not multitouch technology goes into an application? Well, not gloves alone, because there is also the subject of software. And this is where the focus turns to the producers of the tools.

Time for software tool producers to make a move

The German study ‘Usability and human machine interfaces in production’ presented by the Fraunhofer Institute for Human Factors and Organization in 2011 attests to optimisation potential overall on the part of tool producers in both touch and multitouch technology. It mentions that most HMI tools for zooming objects support the presentation of intermediate states, making it easier for the application programmer to implement such functionality, but if you want to scroll in PDFs, for example, or fast-forward through audio instructions or video tutorials, it often takes some programming of your own to do so. Nor do operating systems with multitouch capability exonerate the tool producer from qualifying their mouse and keypad controls as well as (multi)touch configuration, or from creating templates with (multi)touch capability to structure tables.

The Fraunhofer study also found comparatively few functions to improve usability, such as ‘iceberg buttons’ where the area that can be touched is larger than shown. So there is still a way to go when it comes to tools for the development of user interfaces. The same applies, of course, to integrated systems combining a SoftPLC and a HMI.

Users who have programmed their GUI without the constraints of a specific platform, for example with open web technologies or Java, are less dependent on progress in HMI software tools. There is already a Touch Events version 2 specification by W3C for web-based HMI and the MT4j multitouch platform for Java has been around since 2009. But here, too, it is bound to take some time before all the desirable multitouch functionality is comfortably implemented in the various development platforms.

This is no time to sit back and wait, however, because innovations in smart multitouch applications for the consumer market have come on tremendously fast. Industrial users therefore expect to be able to find or implement the comfort and convenience of their personal devices in the industrial devices, machines and plant that are newly purchased.

Multitouch becomes mainstream

In any case, the industry-compatible hardware is already with us, and in the long term, we can expect multitouch technology to become mainstream in panel PCs. The machine or plant builder who can come up with the new state-of-the-art in their sector will be at a competitive advantage. By the way, designing a multitouch HMI for installation on machines or in plant is just the beginning of a larger-scale process of change. Think of how the user would benefit if, in addition to an HMI, they were presented with an integrated portable control unit. Multitouch implemented on panel PCs thus marks the start of our way into some completely new operating concepts.

How many wires does it take for an industrial touch panel?

When touch panels are called ‘resistive’, this has nothing to do with robustness or toughness, as the attribute might lead you to suppose. What is meant here is electrical resistance, measured every time the surface of a screen is touched. How resistance enables to determine exactly where a screen is touched depends on the panel’s design. There are resistive touch panels with four, five, or eight measuring wires. What is the difference between them? To find out, you have to take a closer look at their structure.

Basically, all resistive touch panels consist of two substrates on which the measuring wires are configured. In 4-wire technology, there are two wires on each substrate. These are at opposite edges and offset between the upper and lower substrates. So if the wires are placed right and left on the upper substrate, on the lower one they will be at the top and bottom edges. This way, both x and y coordinates can be measured. Touching the upper flexible layer of the screen produces a coordinate axis with four different resistances from which it is possible to precisely define where a screen is touched - that is, provided no fluctuating environmental effects get in the way, such as humidity or temperature, for these can alter the voltage relationships of the upper substrate and result in incorrect calculations. Consequently, 4-wire technology should only be used where temperature and humidity conditions are largely stable.

8-wire technology was developed to compensate for the drawbacks of its 4-wire counterpart. 8-wire panels are basically structured like 4-wire panels except that they feature an extra measuring wire at each edge. These wires produce a reference voltage to which the measured results of the touch coordinates can be referred. Temperature and humidity can then fluctuate without the system having to be calibrated anew.

The structure of 5-wire technology is very different. In this case, the measuring wires are not attached at the edges but in the corners. On the lower substrate there are four measuring wires, all used to determine the x and y coordinates, while the fifth wire on the upper substrate only serves to conduct voltage from the lower substrate. In this way, 5-wire technology generally means better long-term accuracy compared to both 4- and 8-wire technologies because both coordinates are measured on the firm glass substrate below, which is not directly exposed to any environmental contamination and is thus virtually free of wear. 5-wire technology is also better because its price is lower compared to the 8-wire equivalent. Both arguments naturally add up when it comes to total cost of ownership, making five-wire designs currently the most attractive resistive touch technology for industrial users.

Gloves or not?

On a final note, let’s return to the matter of gloves again. These days, there are projected capacitive panels that you can actually operate properly wearing thin gloves. But it is hardly efficient to work this way - after all, it is difficult to do your buttons up with your gloves on, isn’t it? Well-made multitouch functionality will still be of a kind that calls for all the dexterity your fingers can muster. So ultimately it is gloves that determine if and how multitouch technology can be implemented. In other words, there will continue to be applications for resistive touch panels, too.