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Intricacies of interface design

The design of the HMI, or human-machine interface, can be as vital to the success of today’s products as the design of the product itself. The effectively designed HMI has made a vital contribution to the success of countless products across the spectrum of industries ranging from the most sought-after consumer products to the most advanced military and aerospace equipment.


May 6, 2015
By Special to Wings
Integrating all components of an HMI during the design phase ensures for smoother performance later on. The design of the HMI

Aerospace applications range from cockpit controls and displays, cabin environment controls, to in-flight entertainment systems. HMIs are used throughout the defense industries, whether shipboard, airborne or ground mobile applications, such as hand-held computers, high-resolution monitors and secure voice/data communications devices. Because of their exposure to harsh environments and rough treatment, these products often require a ruggedized HMI.

While it may be viewed that the HMI is an integral part of the product itself (which it ultimately becomes), the design and manufacture of the interface is often a separate, specialized process that involves the highest levels of complexity, both human and technological. At the same time, build-to-print HMI designs created without the collaboration of an interface specialist is almost always fraught with problems.

Developing a successful machine interface involves design subtleties such as ergonomics, psychology and other “user-centric” considerations. Plus, there is a host of available materials and interface technologies to choose from, the need to perform in harsh environments and, increasingly, the need to fit the most effective HMI within extremely limited space on smaller products.

Whether the interface is displaying information, collecting data or controlling operations, it may require special design consideration such as ruggedized features or the integration of multiple elements into one. These are indicative of the many design challenges at the higher levels of complexity shared by HMIs.

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Avoiding design pitfalls
The past shows us that the improper design of an HMI can render a product astonishingly ineffective. The VCR stands out in the consumer electronics arena as a product that was designed to revolutionize television viewing habits, yet the product interface was daunting enough to discourage users from even setting the time.

Other newly developed consumer, scientific and industrial products have also been compromised by user-unfriendly interfaces. One example is requiring the use of touchscreen typing, which is considerably more difficult to perform than keyboard typing, particularly in turbulent or bumping conditions.

Today, particularly when developing professional equipment for critical applications, designing the most appropriate HMI has become in many respects even more challenging.

With such a dizzying array of solutions available, it is extremely difficult for most product designers to determine which switch and display technologies are appropriate, which control modalities should be used, which functions require direct user access, which materials and construction techniques are optimum, and what engineering constraints influence both design and costs.

Seasoned engineers well versed with HMI solutions often provide complete documentation for their designs. While these are often excellent, they may be losing opportunities for cost reduction or other benefits if they do not consult with expert HMI manufacturers before completing their designs.

“There are serious challenges involved when customers build-to-print their own interface designs,” Keith Heinzig, VP engineering at Secure Communication Systems, Inc. in Santa Ana, Calif says. “Those include possible errors requiring redesign and additional time and money. Also, depending on the application, reliability is always a key constraint.”

Heinzig adds that Secure Communications Systems engineers are not open to compromises that may impact reliability. The company provides custom rugged computer solutions and custom contract manufacturing solutions for defense, aerospace and industrial applications that involve cold weather and other extreme conditions. Secure Communications Systems specializes in the integration of commercial off-the-shelf equipment (COTS) into rugged solutions that are reliable and cost-effective.

Also, from an interface developer/manufacturer’s perspective, the built-to-print approach carries with it certain avoidable risks.

“In most cases, a build-to-print HMI requires re-design, re-thinking that can be unnecessarily expensive and delay product releases,” Jayco’s Mistry says. Founded in 1980, his firm designs, engineers and manufactures a wide variety of interface products, specializing in extreme applications for defense, aerospace and other sectors.

Jayco designs and builds parts to meet or exceed MIL-STDS and other rigorous specifications for environmental conditions, shielding, and lighting conditions. Mistry views the HMI as a system, not just a component, starting with what the user sees and touches all the way through to communication with the host computer.

Early involvement during the design phase and integrating all the various components of an HMI into a complete subassembly including enclosures, displays, switches, and electronics, ensures that all the parts work in harmony to meet the required performance levels. The end result is a higher performing HMI that is easier for the end user to manage and integrate into their system.

Mistry says that the most efficient and effective approach to HMI design usually involves a team approach that includes the product engineering staff as well as the interface supplier. The latter would provide consulting and design expertise based on the experience and diversity of interface hardware and software engineers, human factor experts, product designers and manufacturing expertise. This consultative process can reduce product development time and costs while solving complex problems with superior solutions and packaging.

“I think the best HMIs are actually simple and intuitive,” he adds. “But to make them simple and intuitive is not easy.”

Ensuring that interface devices are ruggedized for environmental conditions are a major concern in military and aerospace applications. This includes protection against corrosive environments, providing for ultra-rugged applications that require military-grade shielding, protection against shock or vibration, contaminate sealing, sunlight readability, night vision lighting and extended-life grade products.

To complement the consultative approach, Mistry’s firm goes a step further by providing a digital or virtual prototype so that the customer can see precisely the proposed solution as well as how it will fit and operate in the end-user’s environment.

Heinzig adds that finding room for the HMI controls on the product often requires creativity and a bit of finesse: “It is often necessary to place the controls on the periphery of the product, and that requires advanced planning.” Virtual prototyping aids in the process and shows exactly what is possible.