Can You Feel the Force? Advanced Haptics Makes Touch More Realistic

Article By : Shahram Tadayon

As a new generation of haptic ICs emerges, designers are pushing the technology into new roles, with the potential to provide a much richer human-machine interface experience...

Haptic technology augments standard user interfaces by bringing the sense of touch into the mix, conveying information to the user via a vibration or motion. Designers are using haptic interfaces in a broadening range of end products to add functionality and enhance the user experience beyond simple visual and audible indicators, text, or screen displays (Figure 1).

Figure 1: By adding tangible feedback to the user’s actions, haptics enhances the user experience beyond the obvious basic visual and audible indicators in consumer products such as smartphones.

The technology is already embedded and accepted as a part of the user experience in many mass-market, consumer products, even though consumers aren’t always aware of it. The smartphone that buzzes in your pocket is the most high-profile example. Automobile consoles and standalone kiosks use haptics to provide meaningful feedback to users.

But as a new generation of haptic ICs emerges, designers are pushing the technology into new roles, with the potential to provide a much richer human-machine interface (HMI) experience for PC trackpads, watches and wearables, smartphone-based gaming, virtual/augmented reality (VR/AR), and automotive touchscreens and buttons (Figure 2).

Figure 2: Haptics interactions are not limited to a single set of stimuli or responses and can be implemented in different ways for diverse user devices and situations. (Image: Cirrus Logic)

Enhancing and differentiating the look and feel of a product — the user experience — gets more important as the consumer market grows increasingly competitive and becomes saturated with “me too” products. Flagship smartphones have incorporated advanced haptics, as have some laptop PC trackpads, and in doing so have pushed consumer expectations higher via their additional and richer functionality — accompanied by a crisp, consistent haptics feel and sleek, clean, buttonless look.

Market growth tells the story

Growth and opportunities are often driven by requirements from end-product and OEM designers who, in turn, are enabled by technical advances from component suppliers; it’s the familiar complementary “resonating” relationship as each side repeatedly drives and enables the other. The demand for haptics in gaming consoles and the rising implementation of haptics in consumer electronic devices help fuel market growth. By engaging sound, light, and touch, haptics allows the user to feel and influence the overall experience.

Figure 3: According to market-research firm IDTechEx, key haptics-related numbers — total revenues, haptics spend per device, and percentage of devices with haptics — have increased substantially from 2010 to 2019, even as total device sales are relatively flat.

According to IDTechEx, both the haptics “spend” per device and the percentage of devices with haptics have grown significantly in the past decade (Figure 3). Looking ahead, according to Markets and Markets, the global haptics-technology market is expected to be valued at US$19.55 billion by 2022, at a compound annual growth rate 16.2% between 2016 and 2022. Other sources, such as Market Research Future, forecast similar numbers. And the consensus is that the key growth driver is the increasing adoption of haptics in consumer devices beyond the smartphone.

Delivering a total haptics solution

It is one thing to talk about enhancing the user experience with richer functionality and a sleeker design, but it is another thing to make it happen, especially for a mass-produced consumer or even industrial product. Effective haptics design requires attention to multiple details across three primary areas: understanding the dimensions of the user experience, developing the associated haptic waveforms, and assuring a quality, consistent end product.

Understanding the user experience

Building for the user experience can involve a carefully considered design effort to achieve three goals: ensuring low latency; delivering strong, sharp haptics; and employing DSP-based algorithms.
• Low latency between a user’s action and the observed response, with a negligible time lag from action to effect, minimizes user frustration with the interface. Excessive latency isn’t just irritating; the user may assume the first tap was not recognized and thus might repeat the action one or more times, potentially queuing up a series of pushes at the device that only serves to delay the system response.
• Strong, sharp haptics simulates the feeling of pressing an actual button. In contrast, poor haptics rumble or buzz, which can annoy or jolt customers. The reality is that users have an expectation of what a “real” button feels like from their lifelong experience with hardwired keypads on ATMs, kiosks, older phones, and countless other products.

Figure 4: By monitoring key signals, Cirrus Logic’s Closed Loop Active Braking enables closed-loop control, resulting in an accurate, consistent haptics experience for the user.

• DSP-based algorithms provide a consistent drive to the linear resonant actuator (LRA), protecting against over-excursion and thereby ensuring the LRA’s long-term reliability. Among its other capabilities, the unique Closed Loop Active Braking (CLAB) algorithm from Cirrus Logic creates a crisper, less “buzzy” haptics effect, reducing the ringing duration by a factor of 4× to 8× in lab tests compared with open-loop performance (Figure 4). It does so by acquiring signals from voltage and current actuator monitors in real time to effectively and accurately close the loop for enhanced performance.

Creating the haptic waveforms

For designers of haptic products, the haptic waveforms that users encounter can be critical. Developing these waveforms requires vendor tools such as effective graphical user interfaces (GUIs) and the ability to deliver fully programmable effects.

• Advanced haptics GUI with tools that enable easy creation of the “right feeling” for each product’s unique shape, weight, and mechanical structure can be key for developing and ensuring the expected user experience. Because that right feel is a matter of personal preference, creating a user experience that will satisfy a large population often requires user studies along with multiple iterations. Therefore, it’s important for system and product developers to have tools that provide the ability to quickly change the strength and feel of a haptics click or waveform in order to get just the right feel.

This situation is complicated by the fact that different devices and even applications within a single device often require a different feel. For example, a non-critical function such as changing a screen color during initial setup may be invoked with a light touch, but initiating a critical step such as “start test sequence” or “change operating modes” may require a longer, more definitive user assertion along with amplified feedback.

Figure 5: Haptics buttons can do much more than create simple “fixed” effects; they can dynamically link the haptics “expression” to the specifics of the application at a specific moment.

• Programmable effects for the user experience go beyond a few standard buttons (Figure 5). Creating sensor-based effects such as heartbeats, camera shutter clicks, zoom, bumps, scroll, and multiple ringtones can greatly improve the HMI experience by tying the haptic expression to the specifics of the application dynamics. These are extended via gestures that enhance the user interface and augment apps (Figure 6).

Figure 6: The user experience is enhanced when the user “actuation” gestures can take many comfortable forms, each evoking a different haptics response.

Delivering a quality end product

The definition and implications of “quality” can vary widely depending on the context and the product specifics. For systems with haptics-enabled functions, the user is usually not immediately aware of factors such as standby power consumption, the benefits of built-in diagnostics, or calibration for manufacturing consistency, despite their importance.
• Ultra-low standby power consumption can be critical when a device must always “listen” for a haptic trigger because maximizing battery life minimizes user frustration. This power-saving operation can be complemented by high-voltage, high-efficiency Class H drivers to provide sharp, crisp actuator performance, even as battery life is preserved.
• Diagnostics and compensation help to maintain a consistent haptics experience by dynamically compensating for changes in the operating environment (temperature, humidity) or for system and component aging. Although environmental shifts can have a significant impact on the strength and feel of the haptics operation, users still expect the same response intensity as they go from the ski slopes to a warm lodge or from an air-conditioned office to their car on a hot summer day.
• Calibration for unit-to-unit consistency is an important function that is sometimes given short shrift, most likely because it creates challenges, raises doubts, and presents uncertainty. But the fact remains that building a system with an actuator and different moving parts and tolerances can lead to unacceptable levels of unit-to-unit variations and inconsistencies in performance in a production environment.

There are several ways to approach this potential problem. One is to simply ignore it and perform no calibration, which leads to an inconsistent feel. Another is to have OEM customers measure individual components and discard components that do not fit within very tight tolerances, which leads to yield loss. A third option is to have them design their own programs and create their own calibration algorithms, which is time-consuming and often not as reliable. In contrast, a top-tier vendor offers a more comprehensive solution via a DSP-based algorithm that addresses and simplifies these calibration challenges.

Importance of the vendor relationship

In principle, haptics offers the potential of a richer, differentiated user experience for the human-machine interface of consumer products. However, achieving a genuinely superior haptics-based user experience requires more than just a leading-edge driver IC. It also requires a vendor that understands the multiple dimensions and subtleties of the user interaction with the end product and then delivers the design, support, and diagnostic tools to enrich the user-haptics interaction with meaningful and consistent performance.

The next generation of haptic ICs and tools, along with their combined capabilities, is enabling OEMs of laptop PCs, VR/AR systems, and even automobile consoles to leverage the attributes of buttonless touch and feel. In turn, this allows them to introduce a new range of more exciting, user-satisfying haptics-enabled devices beyond the smartphone.

— Shahram Tadayon is a product marketing manager within the Haptics group at Cirrus Logic.

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