HMI touchscreen usability is more than capacitive versus resistive sensors -

HMI touchscreen usability is more than capacitive versus resistive sensors


Touchscreens are replacing keypads because of their intuitiveoperation, software flexibility, and space and cost savings. While thischange offers many benefits and solves many human-machineinterface (HMI) problems, the loss of tactile feedback thatusers experience when pressing a mechanical button creates other HMIproblems. Moreover, users say they like to use systems that providetactile response.

The simple solution is to add tactilefeedback to the touchscreen interface to securethe best features of both touchscreens and keypads. You don't reallyneed statistics to see touchscreen proliferation. It's everywhere:automobiles, casinos, consumer electronics, industrial controls,medical equipment, cellphones, point-of-sale systems and self-servicekiosks for applications from banking to ticket buying.

Strategy Analytics believes that by 2012, as many as 40 percent ofcellphones could be using touch-sensitive technology, compared withonly 3 percent today.

Many of the latest phone offerings sport large touchscreens at theexpense of keypads. Many reviewers, including U.S. News & WorldReport, however, commented that a touchscreen can be cumbersomecompared with a keypad because of the lack of feedback.

Without a keypad, you can't feel it depress and know “you've madeyour mark.” In some applications, the lack of tactile feedback has beenenough of a problem to prevent the conversion from mechanical switchesto digital controls.

Figure1: The Samsung SCH-W559 includes a touchscreen with tactile feedback.

And now, with much incentive for using touch-sensitive devices,designers would do well to consider the value that tactile feedbackbrings to the HMI.

For example, Businessweek. com says that touch-sensitivetechnologies are revolutionizing consumer electronics, citing SamsungSCH-W559as an example (Figure 1, above ).

This phone is different from other big-screen models, though. Itincludes technology that makes virtual onscreen buttons feel real andphysical, thus providing built-in, intuitive confirmation of the user'saction.

Figure2: The tactile feedback system drives the actuator according to apreprogrammed tactile effect.

'Essential component'
As shown in Figure 2, above ,besides touchscreens' problem of lack of confirmation, tactile feedbackhelps address other HMI problems:

1) In direct sunlight,youcan't easily see graphical changes.
2) When your're touching thescreen, the target is often obscured.
3) Whenengaged in other primary tasks (such as driving or attending topatients), you can't always be looking at the screen. Moreover,you can't always rely on audio cues for confirmation or guidance.Sometimes the environment is too noisy or requires silence.

Published research also shows that tactile feedback in the HMIsupplies an essential component. It provides a quantifiable effect onefficiency, error rate and user satisfaction. Moreover, incorporatingtactile feedback along with sight and sound provides additive gains inthese areas.

Findings show that a significant quantity of information can beconveyed through touch, not just simple notifications. In fact, thetouch channel may be particularly well-suited for providing particulartypes of information: private, immediate, dynamic and confirming.

Touch has been found to provide a highly effective secondary channelthat supports peripheral or subconscious communications, leaving theother senses better able to focus on primary tasks.

Several studies have shown that users strongly prefer tactilefeedback in the HMI, because it helps improve their performance andmakes them feel more in control.

Tactile feedback technology can be used with touchscreens for eitherportable or stationary devices. Depending on product design, thecomponents can vary in form.

But the basic architecture is the same, allowing the technology toexert high-speed control over one or more actuators (motors). In smalldevices, the actuator may be similar to a small pager motor used in acellphone. For larger devices, actuators optimized for differenttouchscreen sizes and weights are available.

When the user presses a graphical button, the tactile feedbacksystem drives the actuator according to a pre-programmed tactile”effect” (vibration). The actuator movement supplies the perceptionthat the graphical button moves, seeming to press and release as ifmechanical.

The system can synchronize tactile effects with sound and displaychanges, creating a more engaging, multisensory experience.

By varying the frequency, waveform, amplitude and duration of theeffect, a variety of responses that support various HMI features ispossible, such as:

1) Graphical buttons cansimulate the familiar up and down clicks of physical buttons.

2) Menu items can beprogrammed to supply a light pulse sensation or a confirming push-backresponse.

3) Controls can exhibitincreasing or decreasing vibrations corresponding to motor or fanspeed, radio volume level, lighting levels or other parameters.

4) Scrolling displays canprovide a pulse as each item displays and a special vibration to signalwhen the first or last items have been reached.

The technology can work with touchscreens and digital-switch controlpanels of different sizes. Integration has been successfully achievedfor many product designs, and millions of devices with the technologyhave been shipped throughout Asia, Europe and the United States.

The tactile feedback system architecture includes an actuator(either a pager motor or larger custom-designed devices), controlsoftware (either installed on a control board or embedded in theproduct's main microprocessor), a tactile effects library and aprogramming interface for calling tactile effects from the hostapplication.

Figure3: If the embedded approach is used, a runtime executable is provided.

For medium and large screen systems, application-specific circuitboards have been developed for either RS-232 or USB communication. ForUSB communication, an optional USB hub provides convenient connectionsto subsystems. If the embedded approach is used, a runtime executableis provided (Figure 3, above ).

As for the choice of actuation, it should be thoughtfully selectedto meet performance and life requirements. Design guidelines foractuator mounting and control circuitry are also part of the tactilefeedback system.

To actuate larger touchscreens, two sizes of actuators areavailable, both optimized for generating high forces with smalldisplacements. The type and number of actuators depends on the size,weight, and implementation of the touchscreen or panel.

As shown in Figure 4, below, guidelines for positioning and mounting the actuators are flexible, andallow the tactile feedback technology to be integrated into a varietyof product designs. In addition, some touchscreen implementations mayrequire a carrier (frame) for mechanical integration.

Figure4: Guidelines for positioning and mounting the actuators are flexibleand allow the tactile feedback technology to be integrated into a widerange of product designs.

The tactile effects library includes various effects so that thefeel of various touchscreen controls can be clearly distinguished andfunctions differentiated. The tactile feedback system gives designers aconvenient method for choosing appropriate effects and including themwithin the HMI.

Software-integration guidelines explain the use of a streamlined APIto call the tactile effects from the host application.

For some implementations, a software development kit can be used,giving designers several programming options, including a WindowsActiveX control, a cross-platform API in source code form andcommunications support for custom interfaces.

Sample code and a full description of the process of adding tactilefeedback to the host application are also included in the system. Toevaluate the technology, touchscreen demonstration units with exampleapplications are available.

Giving cues
When using a device with tactile feedback, it shouldn't take long tounderstand that if you didn't feel a response, the system didn'tregister your selection.

Tactile feedback can be used to improve the HMI by providing adistinct tactile cue for each type of function (e.g. Enter, Start,End). The consistent cue helps inform the user of a correct selectionand alert them to one they didn't intend.

Moreover, applications may offer the option for the user to selectfrom among a variety of tactile effects that they want for particularfunctions, allowing a unique type of personalization. Possibleapplications for the technology include:

Large and smallhousehold appliances. Especially for devices used often, thefamiliar mechanical feel that tactile feedback provides could helpusers adapt to and appreciate a transition from traditional to sleekand modern electronic controls.

Globalpositioning/navigation Systems. With an immediate tactile cue,users don't have to wait for a visual response, which can reduce glancetime, helping them keep their eyes on the road.

Remote controls. A confirming tactile response can improve the usability of smallbuttons (especially in lowlight conditions) and replace an audio cuethat would detract from music or video soundtracks.

Medicaldiagnostic equipment. In medical facilities where audible cuescould be unsettling or disturbing to a patient, tactile feedbackprovides unmistakable confirmation that can let the caregiver focusmore on the patient and less on the device.

With touch being the most personal of the senses, tactile feedbackcould be used to help extend a sense of caring in self-diagnosticequipment.

Test andmeasurement equipment. Tactile cues may help increase accuracyand productivity, especially in noisy or distracting environments.

Portableterminals. The added confirmation that touch provides can helpusers multitask, more fully supporting the freedom of movement and thevarious activities that portability allows. It can also support fasterand potentially more accurate data input.

Self-serviceterminals and kiosks. Tactile feedback in the self-serviceprocess provides an intuitive acknowledgement to the user that theirselection has been received and that service is proceeding.

Giving users a matched response to their touch input supplies agreater sense of control, which can improve user satisfaction andincrease the use of the self-service option.

Game devices,media players and entertainment systems. Increased interactionthrough tactile feedback can supply more fun and engagement.

Touchscreens with tactile feedback are just beginning to come tomarket. However, they are already showing much promise for improvingthe HMI and promoting a more intuitive, engaging and satisfying userexperience.

Michael Levin is Vice Presidentand General Manager for touch interface products at Immersion Corp. To download a PDFversion of this story, go to “ Integratetactile feedback into touchscreen HMI.” 

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