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issue: October 2008 APPLIANCE Magazine

Touch Controls
Improving Usability of No- and Low-Travel Touch Controls


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by Steve Kingsley-Jones, director of product management, Immersion Corp.

Tactile feedback systems improve the usability of no- and low-travel touch controls by providing confirmation in response to user interactions.

Over time, designers have moved away from mechanical switches, rotary dials, push buttons, and full-travel membrane switches toward new types of touch controls. Technologies like subsurface digital switches and no- or low-travel membrane switches are now common in automotive interiors, mobile phones, consumer electronics, white goods, home security systems, computer peripherals, and medical and industrial equipment. These newer touch controls enable industrial design flexibility and advancements in aesthetics, sealing, reliability, and ease of cleaning.

But the benefits of touch controls are offset by the elimination of tactile feedback, an inherent characteristic of mechanical controls. Tactile feedback provides confirmation to the user, and without it, a usability problem can result. Audible beeps have been commonly used as a substitute. But these sounds can be intrusive and aren’t always effective in noisy health clubs, hospitals, kitchens, and offices. Fortunately, there are now technologies that can solve this problem by intelligently adding tactile (also known as vibrotactile or haptic) feedback to no- and low-travel touch surfaces without compromising aesthetics, design flexibility, sealing, or reliability. Haptic technology is already at work in millions of mobile phones, providing tactile response to touchscreen presses. It enlivens mobile games with game-console-like “rumble action.” And it is in use for other applications as well.

How It Works


Tactile feedback system components can make graphical buttons feel real, seeming to press and release like mechanical buttons. Illustration courtesy of Immersion Corp.

Haptic technology makes graphical and low-travel buttons feel real: They seem to press and release like mechanical buttons. The technology outputs vibrations that vary in frequency, waveform, amplitude, and duration so that a wide range of possible responses can be used for a variety of user interface features. Tactile feedback systems can be used with touch controls for either portable or stationary devices. Depending on product design, the components vary in form, but the basic architecture is the same, allowing the system to exert high-speed control over an actuator.

When the user presses a touch-control button, the system drives the actuator according to a preprogrammed tactile effect. The actuator movement supplies the perception that the button moves, providing unmistakable feedback to the user. Tactile vibrations, or “effects,” can also be synchronized with a sound or visual cue to create a more engaging and multisensory experience. Unlike mechanical controls that arbitrarily generate feedback based on their construction, programmable touch effects can be designed to provide the desired response.

Like the touch-control systems it operates with, the tactile feedback system’s digital output does not degrade over time. Its components can be integrated into sealed, backlit, or contoured housings made of plastic, steel, wood, or virtually any material that might be used for a panel control. 

Eccentric rotating mass actuators. Photo courtesy of Sanyo DC Micro Motors.

Design Considerations

Initially, designers commonly assume they must replicate the full motion of a button or switch for haptic feedback to be effective. This is not actually true because the human finger is not that discriminating. Certain mechanoreceptors in the human finger can detect very small amounts of motion if combined with moderate acceleration. Just 0.1 mm of motion, combined with an acceleration (G-force) of at least 1.5 G, supplies sensation users perceive as a confirming response.

The low threshold of 1.5 G of acceleration, however, does not necessarily produce the best tactile feedback—that which allows suitable confirmation of user input while not interfering with primary focus. Arriving at the best tactile feedback is a matter of matching the product’s appropriately sealed, movable mass to actuator(s) in order to produce mechanical motion that feels right. In addition to good dynamic response, the chosen actuators need to meet specifications for power, efficiency, and reliability.

Misusing solenoids or motors in order to generate a haptic effect can lead to a poor implementation of a tactile feedback system. Common problems include latency, or slow actuator acceleration, plus excessive displacement or lack of precise control over displacement due to unsuitable actuator performance characteristics.

Poor actuator mounting can also be an issue with haptic systems. This may cause the entire system to resonate, rather than the touch interface alone. In handheld devices, this may be intentional, but in fixed devices, overly strong resonance produces an effect more like an earthquake than a friendly confirmation. On the other hand, a mounting configuration can compress the interface so much that the acceleration and displacement are damped beyond the point of detection. Correct mounting of the actuators enables displacement to be effectively transferred to the user’s fingertip.

Probably the best way to evaluate the technology for an intended market is to use a design kit. These allow designers to build a tactile feedback prototype of the target appliance using a system architecture that includes control software, actuators, and a tactile effects library. In addition, some systems may include a software development kit with an application programming interface for calling the haptic effects from the host application.

Lateral actuators are usually used in larger systems. Photo courtesy of Immersion Corp.

Design Principles and Applications

Two principles to keep in mind during investigation of the possible benefits of tactile feedback include (1) the concept of the emotional buy-in (user inclination) and its competitive importance and (2) the principle of metaphor.

Donald Norman discusses the concept of emotional buy-in in the book Emotional Design. Norman’s research has revealed, “…products and systems that make you feel good are easier to deal with and produce more harmonious results.” And because of this phenomenon, good emotional design “…may be more critical to a product’s success than its practical elements.” Repeated and pointless pressing is not a harmonious result. If no- or low-travel touch controls are creating user issues, tactile feedback may provide a fast and easy solution.

Even in the absence of usability issues, there still may be advantages to adding tactile feedback. High on a de facto list of qualities that make interfaces easier to use is the principle of metaphor—that is, borrowing behaviors from systems familiar to users. Because users are familiar with mechanical keyboards and other controls that inherently include confirming tactile feedback, emulating that quality may provide superior usability and a competitive advantage. Many research studies performed by companies and academic institutions show that user satisfaction improves when tactile feedback is included in the user interface.

Consider how tactile feedback could be applied in touch panels to improve these applications:

Kitchen appliances. Consumers want easy-to-use features that help them do more, with less effort, in less time. Fingers can easily obscure the small-icon selections on a control panel. With only sight and sound cues to confirm a string of key presses, users need more concentrated attention to ensure that all their selections registered.

Office machines. Touch controls can permit a simpler user interface to eliminate a cluttered and confusing array of buttons, making sleeker designs possible. Audio cues can be distracting during conversation and an annoyance in open-cubicle offices. Tactile feedback restores the certainty of response and the tactile qualities people like about mechanical buttons and switches.

Exercise equipment. Users are accustomed to using membrane panels on fitness equipment. But in the noisy gym setting, especially when earphones are in use, audible beeps don’t provide a reliable method of confirming system response. Even if the LED display responds quickly, the user may be distracted. If every button press is met with an unmistakable tactile response, the user can feel more confident that the system is keeping up with their settings. Further, if pressing an up arrow supplies a vibration of increasing frequency or intensity, and pressing the down arrow has the opposite effect, less “cognitive load” is required to understand system operation. Simple, intuitive cues like these can make systems easier to use, and safer.

Medical applications. The medical environment can also be noisy and distracting, so relying on sound cues for system confirmation may be only somewhat effective, and sound may be unwanted at times. However, with tactile feedback supplying guidance to the operator, less attention is needed to ensure that the system is responding. As a further aid, every button can feel different, which can help alert the user to errors or system state.

Summary

For many applications, no- and low-travel touch controls can create a usability problem. Even when usability problems are minimal, however, adding tactile feedback may provide a competitive advantage. Components that supply tactile feedback responses to user interactions can now be easily added without compromising the benefits of aesthetics, design flexibility, sealing, and reliability.

About the Author

Steve Kingsley-Jones is director of product management for Immersion’s Touch Interface Products group. He holds a BS of Applied Science in Electrical Engineering and a BA in Economics from the University of Waterloo. He is a member of the Software Development Forum and the Silicon Valley Association of Start-Up Engineers (SVASE). If you would like to contact Kingsley-Jones, please e-mail lisa.bonnema@cancom.com.

 

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