Editorial Feature

How Haptic Sensors Work

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Haptic sensors have been around for a while now and come in various forms. Regardless of the type of haptic technology utilized, they all work around similar principles of using a combination of force, vibration and motion to recreate the sense of touch. In this article, we look haptic sensors a whole and how they work.

Haptic sensors recreate the sense of touch by creating a combination of force, vibration and motion sensations to the user. Haptic technologies are significantly growing and are used in everything from automobiles, to games console controllers and smart phones. It is thought that the production and implementation of haptic sensors will be a $12.8 billion industry by 2022.

There are three main types of haptic sensor – eccentric rotating mass vibration (ERMV) motors, linear resonant actuators (LRAs) and piezo haptics sensors.

How Haptic Sensors Work

Even though there is a general principle for haptic sensors, this article will highlight some of the operational differences between the different types of sensor. Aside from using a combination of force, vibration and motions, haptic technologies use a force feedback loop to manipulate the movement of the user and go beyond a simple vibration alert. The basic principle of a haptic sensor is the generation of an electric current that drives a response to create a vibration. How this happens, is where the different technologies differ.

However, not all haptic sensors require touch to work. These are known as non-contact haptics and uses technologies such as ultrasound and concentrated air pockets to create an interactive 3D space around the user. The user then interacts with the space around a device without the need to physically touch it.

Here we look a bit more in detail at the three most common types. Whilst they all work on the same basic principle, the way in which they work and operate does vary significantly.

ERMVs

ERMVs operates in a similar way to a DC motor. ERMVs work by generating a magnetic field from an electric current. The magnetic field drives an object in a circle, using an off-center bias from the point of rotation. The magnetic force applied to the rotating mass creates an uneven centripetal force that causes the motor to create a forward and backwards motions, as well as producing lateral vibrations. The intensity of the vibrations produced by ERMVs are often dependent on the current supplied to the device. ERMVs are often the haptic sensor of choice when the driving circuit is simple, a low-cost is required, and the haptic resolution is not the highest priority.

LRAs

LRAs use both magnetic fields and electrical currents to create an oscillating force along a single axis. In comparison to ERMVs, LRAs use an AC voltage instead of DC. This current drives a voice coil that is pressed against a moving mass. The moving mass is attached to a spring, and when the voice coil resonates at the same frequency of the spring, a magnetic field is generated. This magnetic field causes the actuator to vibrate with a force that can be felt by a human. LRAs can be easily adjusted by changing the AC input, but the actuator must always be driven at its resonant frequency. LRAs are best utilized when start/stop timing is critical, the circuit can implement a driver chip, or the vibrational amplitude needs to be adjusted independently.

Piezo Haptics

Piezo haptic sensors work on the principle of the piezo effect to generate a vibration. The piezo effect is a well-known phenomenon that generates an electrical current when a material is mechanically stressed. Under various stresses, such as bending and deformation, a piezo haptic sensor will generate a vibration. Piezo haptic sensors are more precise than inertia-based sensors because they vibrate at a wider range of frequencies and amplitude. Piezo haptic sensors also vibrate in multiple directions, unlike LRAs and ERMVs which are confined to a single direction. The operation of piezo haptic sensors requires a higher voltage, but the consumption of current is better than, or colloquial to, other haptic sensors. Piezo haptic sensors are often used when a larger space is available to integrate the actuator, the frequency and amplitude need to be adjusted independently, or the circuit can implement a driver chip and produce waveforms.

Applications

Because haptic technologies are used to recreate a touch sensation, the applications are widespread. Applications to date include the remote control of machines and devices (telerobotics), the touch screen of a smart phone, Sat Nav or other touchscreen technology, vibration packs in games console controllers, flight and medical simulators, virtual reality systems and in multi-functional touchscreen dashboards within automobiles.

Sources:

“Bringing haptic technology to automobiles”- McCann K., Autotechnology, 2002, DOI: 10.1007/BF03246722

Texas Instruments: http://www.ti.com/lit/ml/slyt539/slyt539.pdf

http://www.ti.com/lit/an/slyt483/slyt483.pdf

Precision Microdrives: https://www.precisionmicrodrives.com/vibration-motors/linear-resonant-actuators-lras

https://www.precisionmicrodrives.com/application-notes/ab-020-understanding-linear-resonant-actuator-characteristics

https://www.precisionmicrodrives.com/vibration-motors/automotive-applications-vibration-motors

https://www.precisionmicrodrives.com/vibration-motors/eccentric-rotating-mass-vibration-motors-erms

Somatic Labs: https://blog.somaticlabs.io/how-it-works-linear-resonant-actuators/

https://blog.somaticlabs.io/how-devices-provide-haptic-feedback/

PR Newswire/Research and Markets: https://www.prnewswire.com/news-releases/haptic-technology-applications-and-global-markets-report-2017-300484007.html

DMEGC: https://www.dmegc.de/files/New_DMEGC_Haptic_Device_for_Automotive.pdf

Dialog Semiconductor: https://www.dialog-semiconductor.com/eccentric-rotating-mass-motor-control

TDK: https://en.tdk.eu/download/1911088/8b64d61a15a406fa74e9ea1dc14dc1ea/charts.pdf

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