Is your HMI ergonomically correct?

Does your operator interface terminal give you a pain? No, not the frustrating kind of pain that comes from an application that just won't function properly, but real, physical pain. Like any other computer terminal, an HMI (human-machine interface) is subject to health and safety-related usage problems and concerns.

By Jeanine Katzel, Control Engineering April 1, 2004

Does your operator interface terminal give you a pain? No, not the frustrating kind of pain that comes from an application that just won’t function properly, but real, physical pain.

Like any other computer terminal, an HMI (human-machine interface) is subject to health and safety-related usage problems and concerns. When working with HMIs, ergonomically correct typically is not the first thing on an engineer’s mind. However, not paying attention to ergonomic principles can lead to expensive workplace consequences, not to mention eyestrain, carpal tunnel syndrome, tendonitis…

What is ergonomics? It is defined in many ways, but is essentially the science of work. Microsoft’s Encarta Online Encyclopedia defines ergonomics as “the science of designing machines, products, and systems to maximize the safety, comfort, and efficiency of the people who use them.” The Board of Certification in Professional Ergonomics (BCPE) calls it a “body of knowledge about human abilities, human limitations and human characteristics that are relevant to design.”

However you define it, ergonomics plays a role in every HMI application, affecting how effectively an operator can use the product. More importantly, ergonomic hazards may be governed by state and/or federal-government regulations, and OSHA may cite employers for violations under its general-duty clause. In addition, workplace-related ergonomic injuries may be the source of costly worker compensation claims and lost work time.

It makes a difference

HMI products can be ergonomically challenged in a variety of ways, including, but not limited to, muscular-skeletal problems and visual difficulties. Notes Bill Martin, PanelView Plus 700/1500 product manager at Rockwell Automation, about panel-mount products: “There are two main ergonomic considerations for HMI devices: anti-glare screens and easy-to-use buttons. Items such as anti-glare overlays reduce stress on the user’s eyes and are easily removed and replaced when they get too dirty. Operators use anti-glare overlays for visual safety, but also because of their convenience and maintenance benefits.

“Many operators use touchscreens because they are easier on the hand,” he continues, “but for those who prefer buttons, tactical feedback reduces stress on a user’s hands because they can hear and feel when a button has been pressed. They don’t have to repeatedly press the button and wonder if it made contact.”

Looking at handheld HMIs, Dave Kaley, MobileView product manager at Rockwell Automation, observes, “Since the terminal rests in the user’s hands, it is important to consider whether the terminal is easily held and operated.” For example, portable terminals should be comfortable and ergonomically friendly for left- and right-handed people. The hand that holds the terminal should rest in a neutral position, with no awkward bending or uncomfortable positions that can lead to long-term problems, such as carpal tunnel, Kaley suggests.

One ergonomic area often overlooked, points out Norma Dorst, National Instruments’ LabView platform manager, is sound. “Alarm conditions are part of the ergonomic design as well. They tell people to pay attention, but the same alarms can’t be used for everything. Sound needs to distract the operator, but not to the point of interfering with the ability to react. Many HMIs have way too many blinking and flashing lights. That’s not an ergonomic design.”

Tips to follow

Consider the following ergonomic factors when selecting and designing any HMI system:

  • Evaluate an HMI product’s ergonomic characteristics along with its functional features before making a selection. Is the screen glare resistant? Is it easy to operate? Is it ergonomically friendly?

  • Exercise the same cautions and restraints when using an HMI product as with any computer activity. Minimize repetitive motion. Be open to modifications to accommodate individual needs.

  • Take time to understand ergonomic concepts and principles when installing any new system. Working smart ergonomically increases workplace efficiency and reduces lost time injuries and worker compensation claims.