The screen test: displays for industrial applications

4 min read

How a supplier of displays for industrial applications is responding to tougher requirements.

The displays used in industrial applications have traditionally not been selected from the high tech end of the market. And for good reason; industrial applications are tough on displays, so it makes sense to select devices which will do the job, rather than look good. But the last few years has seen an explosion in the number of displays developed with the industrial market in mind. While some would see this as a good thing, the number of choices available can cause confusion, leading designers to specify a device that isn't suitable. Mark Stephenson, product marketing manager for Hitachi Display Products Group Europe, said: "The industry has changed dramatically in the last 10 years, moving away from character modules and STN displays. A decade ago, the display of choice was a 5.7in quarter vga and Hitachi still has about 14 variants in its catalogue. Our challenge then was to provide mechanical compatibility; today, it's different. While demand for 4:3 format displays is still strong, we are now starting to see true industrial applications adopting the 16:9 widescreen format." One attractive feature of the industrial market, said Stephenson, is that most applications now support the use of some form of display. "LCDs bring designers more scope to introduce a GUI." Hitachi is but one of many companies vying for industrial business. According to Stephenson: "Where there were few competitors 10 years ago, we now have around 25 competitors for 3.5, 5.7 and 7in TFT displays, which have become something of a de facto standard." Hitachi competes in this market as a 'premium supplier'. "We have to differentiate our products, but that's hard when there is a focus on cost." And it's this range of choice that Stephenson believes is confusing, 'particularly for beginners'. He says that selecting an lcd panel on cost alone could be a mistake. "The prices of 3.5in displays do not reflect the cost of building them," he asserted. "Those who do play in this market do so with their focus elsewhere to cater for the lack of margins." Stephenson claimed Hitachi competes on the basis of product quality. "If you look at other products, you begin to understand where cost savings are being made. Examples include thinner cables and a smaller module. The result is less reliability and lower quality." It's not a problem that's obvious at the sample stage, he contended. "Everyone can do a 400candela sample. It's when you take it apart, that you can see potential reliability problems." Industrial customers have more stringent reliability requirements than those designing displays into consumer products. "One of the important things for them is to see a guaranteed product availability of five years," Stephenson claimed. But there are also increasing technical requirements. "Transmittance is much higher; it was 150cd, now it's 600cd. Alongside this, customers want a contrast ratio of 600:1 and extended temperature ranges." And the industrial application range is broadening. More recent markets that are being addressed include marine and in vehicle applications, the latter being separate from automotive applications. "Where industrial applications require a -20 to 70°C temperature range, these newer applications need -30 to 80°C, as well as 600cd and a 600:1 contrast ratio. We can meet these needs by bringing in panels developed for the automotive sector, which have to meet TS16949 standards." LVDS is no longer a challenge, said Stephenson. The reason? "Single board computers. These feature LVDS and will only drive displays with a resolution in excess of vga. Because some sbcs only have an LVDS interface, we've responded with LVDS only displays." Hitachi makes its own lcd glass, so has an advantage over competitors who buy glass in. "We've made a number of developments," Stephenson noted, "including silicon on glass, where the drive electronics are embedded on the glass. This brings mechanical and response time benefits for low temperature polysilicon. But Hitachi has also developed a patented technology called in plane switching (IPS). This is a fundamentally different way of switching liquid crystals." What Hitachi has done with IPS is to change the way the liquid crystals are aligned. Instead of being aligned vertically, IPS displays feature horizontally aligned crystals and this brings a much wider viewing angle – up to 176° – and better colour reproduction. Initially, IPS transmittance was low. But IPS-Pro – the latest version of the technology – has improved this by using a transparent common/storage electrode over the pixel aperture (see fig 1). This replaces a metal storage line in the previous AS-IPS design. By removing this, a higher aperture ratio is achieved and transmittance is increased. Despite the fact that IPS was originally targeted at tvs, Stephenson said the approach is being adopted as an industrial format. "It was 150cd," Stephenson pointed out, "but it's now 600cd and the technology is more stable in industrial applications." The influence of consumer devices such as the iPhone is reaching the industrial market, Stephenson believes. "Designers are wanting to include the same kind of functionality in their products, having seen what touch can offer in terms of user activity." Not all industrial applications are suited to touch interaction. "But some applications are suited and designers want to add another dimension to the user interface," Stephenson continued. Glass bonding technology is helping to enable these applications. The touch panel is bonded to the display using optical adhesives and three main options are available. With in frame bonding, the touch panel is attached within the lcd's area. On frame bonding joins the touch panel to all or part of the front bezel and to the lcd's surface, while over frame bonding joins the touch panel to all of the front bezel and overlaps the bezel's dimensions. According to Hitachi, glass bonding offers a number of advantages in harsh environments, including: scratch resistance; impact resistance; parallax issues; and poor readability. Module size has been a continuing discussion point between display suppliers and their customers. In early models, the housing would often be much larger than the screen, creating problems in space constrained applications. Manufacturers have been working on this and some 'slim' modules are now available, particularly 5.7in units. "It's a reaction to demand for slimmer products," said Stephenson. "But some companies are trying to produce slimmer modules using thinner glass; in some cases, 0.5mm thick." The problem here, of course, is thinner glass is less robust. "Industrial products can't be too thin," Stephenson contended. "Some companies are selling modules featuring glass intended for use in laptops and these are not designed to resist shock and vibration." As with all markets, cost is a major issue and only the potential high volumes will justify the development of new products – the mask costs for a new tft display now run to some €700,000. "We've seen this with wide panels, originally developed for consumer, then automotive and now industrial. While it brings economies of scale and better yield, it does mean new formats are more difficult to find," Stephenson concluded.