We have to interact with a virtual environment using a plurality of portable devices that affect our visual and aural perception. But in the near future, there will be no need to carry a laptop around or a mobile phone with us. We already have so many electronic wearables, such as watches, wristbands, smart clothing… Implementation of haptic feedback technology within wearables will lead us into a new era, where we will be able to carry virtual world and feel it. It has already become possible with haptic suits.
What is a haptic feedback technology (haptics)?
Put it simply, haptics is a technology, which allows one to receive tactile information through one’s sensations.
Mobile phone vibration is very often described as an example of haptic feedback technology. But it is only one and simple illustration of how haptics can function.
Haptics allows a user to interact with computer based devices by receiving tactile and force feedback. The former may let us know what is the texture of the object. The latter simulates some physical properties of the object, such as its weight or pressure.
Haptic feedback typology
Five main types of haptic feedback technologies (haptics) are force, vibrotactile, electrotactile, ultrasound and thermal feedback.
It is the kind of haptic technology that appeared first. Therefore it is the most studied.
Force feedback affects the ligaments and muscles through our skin into the musculoskeletal system, whereas all other types of haptic feedback effect only on our skin receptors. Generally, other types’ haptic devices that affect the top layers of the skin are called cutaneous devices. They are quite compact and acupressure on small areas of the body.
By contrast, force devices are large, as a rule. They move together with a human and have an impact on large areas of the body such as an arm or a leg. These devices are more complex as they have to provide a person with sufficient freedom of movement.
Two kinds of force feedback devices exist, biomimetic and non-biomimetic. Biomimetic devices move as human limbs and resemble them by their forms. Such devices are difficult to develop because ideally they should have a functionality of human body and be suitable for different people. Non-biomimetic devices may be very different from the human body.
All force feedback appliances may be divided into resistive and active ones. Resistive devices limit the movement of the user with the help of the brakes. Active devices restrict movements of the user or move the body in space by means of motors.
Active devices can simulate a wider range of interactions, but they generally need to be more powerful than passive devices, and they are more difficult to control.
Vibrotactile feedback is the most common type of haptics. Vibrotactile stimulators apply pressure to definite human skin receptors. These receptors look layered like onions and can pick up vibrations of up to 1000 hertz. Ordinary human speech frequency varies from 80 to 250 hertz, so our skin is able to feel sounds.
Vibrotactile feedback has its advantages and disadvantages.
On one hand, it is relatively simple, cheap technology, easily powered and controlled. It has long been used in many devices like mobile phones, joysticks, steering wheels. Vibrotactile feedback requires fewer tracking parameters and quite small power consumption.
On the other hand, vibrating motors can not provide depth and diversity of sensations. Vibration may sometimes be irritating in comparison with other stimulators. Vibrating motors are hard to miniaturize efficiently. In addition, if used long enough vibrotactile feedback cause deep penetration, negatively affecting ligaments and joints. Furthermore, ghosting effect may appear with prolonged or strong impact.
Electrotactile stimulators affect not only receptors but also the nerve endings with electrical impulses. As a result, a person wearing the haptic suit based on electrotactile feedback technology can feel the texture of an object or feel a breeze, for example. In fact, almost any sensation may be simulated with electrical impulses.
This type of feedback has many forms depending on the intensity and frequency of the stimulus delivered to the wearer’s skin. Sensations can also vary depending on the current, voltage, material, form of a wave, electrode size, contact force, hydration and skin type.
Electrotactile feedback has great potential because with its help haptic effects can get a diversity of forms.
The principal advantage of the electrotactile haptic feedback system, compared to vibrotactile or force feedback, is the absence of mechanical or moving parts. By means of electrical impulses, a user is able to receive a wide range of sensations which can not be reproduced with any other feedback systems that currently exist.
One more benefit of electro-neural stimulation is that the electrodes can be customized into compact arrays and used to implement electrotactile displays.
Electrical muscle stimulation (EMS) is used in medicine for more than 30 years and has proven its safety. Moreover, electrical signals are the basis of the nervous system, so we can say сonfidently that this type of feedback is better suitable for generating and simulating sensations.
Ultrasound tactile feedback
Ultrasound is a sound wave of high frequency. One emitter or some of them are used to create ultrasound feedback.
One emitter located on one part of the body may send a signal to another part. This principle of transmission is called “acoustic time reversal”.
To ensure the impact on larger areas it’s necessary to form a haptic feedback field. Each emitter itself is not powerful enough to do it, so, several emitters are used. Together they create invisible tangible interfaces in the air. Ultrasound waves generate turbulence which one can feel through the skin.
The main advantage of ultrasound technology is the user do not need to wear any accessories. But this kind of haptic feedback technology is quite expensive and usually less perceptible than vibrotactile or electrotactile feedback.
For thermal feedback formation actuators’ grid is used. It is in direct contact with the skin.
People don’t define well the place of the thermal stimulus in contradiction to tactile communication. Therefore, there is no need in a large number actuators to create a heat feedback, and they can be positioned not so close to each other. Thus, in some way thermal feedback devices are easier to design.
However, due to the law of energy conservation heat can not be taken from nowhere. It can only be moved from one place to another. Furthermore, it should be done quickly to provide a realistic feel. So, haptic suits using thermal feedback require quite a lot of energy.
Thus, here we have described the main types of haptics. If you have any questions, feel free to contact us.
The next article will be devoted to the history of haptic technology in video gaming industry. Earlier we have also published posts “The History of Virtual Reality: Ultimate Guide.Part 1″ and “The History of Virtual Reality: Ultimate Guide. Part 2″.
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