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HMI Design: The Key to Process Efficiency [Tech Tip]

Instant impressions are important. Visitors quickly flee from a poorly designed website to others with more visual appeal. It is the same with the Human Machine Interface (HMI). Some companies go to great lengths to ensure their product caters to every possible need – yet spoil them with a poorly conceived HMI.

According to recent surveys, 95.1% of companies believe design plays a major role in how a brand is perceived. It makes sense, then, to ensure that any HMI looks great and is perfectly aligned to the needs of the user. This is especially important when it comes to the management of complex processes and systems. An intuitively understandable design with clear information helps operators to rapidly make the right decisions. This has everything to do with enhanced productivity and efficiency.

HMI design, then, consists of five key steps:

  1. Strategy: In this step, gather customer requirements and isolate the precise needs for equipment operation. Too often, HMI’s are created with little input from their operators – big mistake.
  2. Focus: Zero in on how the HMI will be used. Will it be near-field or far-field? Indoor or outdoor usage? Will personnel be wearing gloves or not? Prioritize possible use cases based on how the HMI will be deployed in the real world.
  3. Structure: Develop the right information architecture. This includes how information should flow smoothly to the user and the hierarchy of individual screens.
  4. Composition: Consider icons, screen objects and overall composition. This can only be done successfully with the earlier steps thoroughly completed.
  5. Design: Now we come to actual HMI design. It is time to define colors, icons, objects and how best to graphically enhance information delivery. Avoid too busy a screen. Usability studies indicate that around seven items are the optimum number on any single screen. In some cases, it may be a few less, but rarely should it be any more. Exceed that number and the operator can no longer scan the HMI to act promptly with confidence.

The first few of the above steps concern themselves with the vital ingredient of successful HMI design: Know your customer. For example, find out what users call things. Too many developers burden users with unfamiliar terminology. HMI designers should always seek to speak the language of the user.

Designers, too, should operate with a firm purpose. Colorful images and sophisticated design for their own sake can lead to confusing HMIs. All creative elements should be aligned with usability. Therefore, simplicity should prevail over complexity. For the HMI, less is more.

Another HMI best practice is to follow previously learned patterns. Many users, these days, have grown accustomed to the interfaces they see everyday on their smartphones and tablets. Why baffle them with something foreign? It is best to take advantage of the familiar and harness it in design.

Therefore, maintain consistency from one screen or interface to another. The look and feel of the main screen should not be too dissimilar to sub-screens as operators drill down into the information. Further, avoid arranging screens that are completely different from others they utilize in their everyday operations.

If an operator makes a mistake or makes an incorrect action, provide an easy way to undo the error. In other words, be forgiving of errors that operators may occasionally make in the hurly burly of shop floor life.

Finally, understand that design work is not over once the product has been delivered. Just as users should be given feedback and allowed to express their view during the design process, they should be consulted afterwards. A few months of real-world operation are likely to bring areas of potential improvement sharply into view. Gather such feedback and fold it into HMI updates and future products.

Overall, the best way to look upon the HMI is via a glacier analogy. The user interface represents the part of the ice showing above the surface. The machine represents 90% of the iceberg hidden from view under water. A good HMI enables the operator to control the entire iceberg without becoming overwhelmed by its complexity.

Excerpted from the Siemens Totally Integrated Automation Newsletter:

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