The FreeForm 3D modeling system allows technicians to sculpt custom body parts by touch
The FreeForm 3D modeling system allows technicians to sculpt custom body parts by touch

Fundamentally, haptics is any form of non-verbal communication involving touch. Shaking hands when you greet someone is a haptic custom originated from western countries. What we are going to discuss here is the technological aspect of using haptics. When you receive a call on your mobile phone while it is in silent mode, and feel that gentle buzzing in your pocket, that is haptic technology at work.

How does it work?
Haptic technology utilises haptic perception, which is the ability to recognise objects by touch. While tra-ditionally the object that was referred to was a physical object, modern-day implementations include the ability to recognise virtual objects such as those that exist in a world connected by the Internet of Things.

Haptics uses tactile feedback, executed by applying force or motion on the body of a person, in the form of vibrations or other similarly identifable effects. The human somatosensory system is an impressively complex sensory system which comprises sensors that allow our body to feel touch, temperature, pain and movement. These sensors detect the force applied by the actuators in a haptics system and allow the user to have an additional level of interaction with the device that he is working with.

Overall, it could be said that haptics allows a person to feel input from the device, other than the conventional methods of either seeing or hearing it. Thus, it adds further depth to the level of interaction between humans and machines.

Why integrate haptics in your project?
Haptic technology works by using different kinds of actuators to create vibrations and movements that are perceived as tactile feedback by the user. These haptic effects are enabled by the actuators that apply force on the skin so that the user can feel the force. A variety of actuators are available these days for use by a designer.

“Many technology companies such as Immersion, Texas Instruments (TI), Senseg and AAC Technologies have come up with a set of development tools to work with haptics—to design, develop and test haptics-based applications. As the technology is in a fairly nascent stage, not many players have resources available for learning in the field,”explains Anand Tamboli, managing director, Knewron.

Eccentric rotating mass motors
The most commonly used (and the least expensive) form of actuators use electromagnetic technologies to form eccentric rotating mass (ERM) motors, which are off-centre weighted motors that apply very strong force. While the force that we can leverage from this device is impressive, you will not be able to use it for applying subtler effects. This actuator would be suitable when the device only needs to alert a user urgently when a certain event occurs. ERM motor also suffers from lower response times as it takes a little extra time for the vibration to begin or end.

Linear resonant actuators
The latest smartphones use linear resonant actuators (LRAs) that are capable of providing a more precise and softer vibration that does not feel jarring in your pants. In an LRA, you will finda magnet attached to a spring which is surrounded by a coil. As the magnet is controlled, it oscillates linearly until the frequency reaches the resonant frequency of that component. Frequencies on either side of the resonant frequencies can also be used at the loss of performance. On the brighter side, the LRA is more power-efficientthan the ERM motor. However, it also has a weakness—linear vibrators are much larger than rotational vibrators.

Fig. 1: ERM and LRA components
Fig. 1: ERM and LRA components
Fig. 2: Drive waveforms
Fig. 2: Drive waveforms

Piezoelectric actuators
Piezoelectric actuators, or piezos as they are lovingly called, are yet another technology that allows very power-efficien vibrations. Most of you must be familiar with the piezoelectric buzzer used in electronics projects. Well, this is almost the same thing. While piezoelectric actuators allow a far wider range of frequencies to be put on the device, these also require a far higher voltage than an ERM or LRA.

The DRV8662 is a single-chip piezo haptic driver from TI that solves the high voltage requirements of piezos by including an integrated on-chip boost converter which can boost up to 105 V.

Components of haptic devices
PicoVibe 304-002. A small eccentric rotating mass motor from Precision Microdrives based on neodymium (an exotic metal) magnets for improved performance. Its size is mere 4 mm.
Fairchild Semiconductor’s FAH4830. A haptic driver that supports both ERM motors and LRA and features very low wake-up time of 30 μs.
Texas Instruments’ DRV8601. A haptic driver that supports both ERM motors and LRA. It is a low-power-consumption model that consumes just 10 nA of shutdown current.
Texas Instruments’ DRV8662. A haptic driver that supports piezo actuators and has an integrated voltage boost converter to account for the high voltages required of piezoelectric actuators.
PrecisionVibe C10-100. An LRA-based actuator with 1.4G amplitude. It is based on a brushless design that gives it an enhanced working life due to the reduction of mechanical components compared to the ERM-based motors.

Although piezos require far higher voltage than ERMs and LRAs, their extremely quick response rate results in a more power-effcient performance than the others.

Haptic drivers
Another component that is needed for implementing haptics is the haptic driver. The driver is instrumental in providing a touch sensation when the user interacts with a device. It is also capable of creating a more local effect and assures the user of a correct ‘point-of-touch’ on the screen.

Some of the newer drivers, like the FAH4830 haptic driver from Fairchild Semiconductor, are capable of driving both ERM and LRA motors while also performing at a very low wake-up time of less than 30 µs. Quick wake-up time is important if the user experience holds value in the system designer’s plans, as it provides low latency and thus creates a faster and more realistic haptic response.

New haptic drivers also fall in line with the general consensus of design engineers that power efficiencyis vital to the success of a product. Hence the latest drivers feature very low current consumption—the FAH4830 uses less than 500 nA of current on standby. TI also has an interesting haptic driver known as the DRV8601, which works on a quiescent current of 1.7 mA and a shutdown current of 10 nA while featuring a turn-on time of 100 µs.

Implementing a different haptic technique
Next-generation actuator technologies focus more on being able to deliver a wider range of effects by manipulating the response times and frequency of the vibration. One of the most interesting techniques for effecting haptics is ‘reverse-electrovibration.’

Fig. 3: Primary haptic design criteria
Fig. 3: Primary haptic design criteria

You may have experienced a very basic version of this technique if you use a unibody aluminium Macbook Pro notebook computer. Dragging a dry fingerover the laptop creates a characteristic rubbery feeling, although you are actually touching aluminium. This is caused due to the capacitive set-up created by the finge and the metal surface that attracts the finger.

You can create this effect on a system by giving weak current to the device being used or, more specifically to the area of the device that is being used for interaction. If the material is conducting, a capacitive set-up will be created when a dry fingertouches it. The capacitive set-up will generate an oscillating electric feld around the skin and the fingertips, which then go on to create a variable sensation of friction depending on the frequency and amplitude of the applied signal. The ability to control friction by varying the frequency and amplitude will allow to create different ‘virtual’ surfaces as you desire. These surfaces are called virtual because they are only felt to be different—the actual surface remains the same (aluminium in the example above).

Design tips you need to keep in mind
The main challenge in designing a haptic device is to make the control interface feel exactly like the tool being used originally by the operator.

“Take the case of a haptic device that mimics the tools of an endoscopic surgeon. The haptic device has to feel like the tools of a endoscopic surgeon. The actuators and sensors have to be implemented to look almost like that. The major issue would be balancing the weight of different actuators along different axes so that the surgeon feels like he is using his original equipment,” explains Biju R. Varkey, CEO, Designs and Projects Development.

“Another design aspect would be to provide kinetic motion and freedom exactly like he would feel while conducting the said operation on an actual patient. It is also very important to make the software and control mechanism fast and accurate,” he adds.

Fig. 4: 4-axis haptic concept by Designs & Projects Development
Fig. 4: 4-axis haptic concept by Designs & Projects Development

Haptics applications can be extremely complex as they are expected to produce response to human touch. Therefore integrating haptics into any device requires a confluence of system-level design expertise.

“Appropriate actuators and their respective locations must be selected carefully as these are crucial from an end-user experience point of view. Additionally, software written for the device should not only control but also optimise the actuators to ensure that the quality of the haptics’ sensations is near to reality. Giving consistent experience to the user could be a success factor for such a device. It is important to recognise that designing haptics into any device requires a system-level approach,” advises Tamboli.

“The value of a well-designed multimodal interface can provide great differentiation and an enhanced user experience to consumers. In short, haptics is all about giving feedback to the user in touch-sensation form, and hence it may have cultural influenc too. For instance, softer touch-sense might mean one thing to one type of users while it would mean different (or lesser) to others. Therefore user study and adaptation of the device should be taken critically as it would defin success or failure of the device with haptics,” he said.

Satwinder Singh, senior design engineer, Designs and Projects Development, explains, “Recent advances in haptics have added more degrees of freedom of motion to the haptic device with more and very precise control of force being exerted. These devices have very precise motion and force sensors to determine the actions being taken by the user.”

“Fig. 4 shows the design of a three degrees of freedom haptic device that we have developed. This device is capable of withstanding two rotary axes and one linear axis. The design is made so that the whole mechanical structure is balanced at the centre of the whole device. This is important because unbalanced weight can cause the user to feel the weight as force. If this was not balanced by design, we would have had to pre-force it in the other direction to compensate for the weight imbalance, thus causing more delay and more computation,” he adds.

What’s next?
One of the most welcomed applications of haptics technology is in medicine. Utilising haptics in medical simulation allows training of future doctors in surgical procedures without the need of an actual human body. Improvements in the technology could also lead to more robust systems for performing remote surgeries.

Haptics is also used in electronic prosthetics to give patients a better sense of touch, pressure and position to imitate the complexity of a human grip.

A tight-fitting shirt with haptic actuators linked to sensors would provide pulses in different forms like pixels on a display, giving sensory impression of the surroundings or of any event to which they are linked. It would function like a whole new sense for a human, just like how we are able to currently sense light and sound in our surroundings. Interfacing this with motion-detecting cameras would allow a person to identify his surroundings without actually seeing them.

A more ambitious implementation would be the merger of new concepts of wearable consumer electronics, such as Google Glass, with haptic technology, thus allowing people to interact ‘physically’ with virtual objects as if they were real-world objects.

Haptics could also be extremely useful for visually or hearing impaired people. These people have superb touch-sense ability and haptics-based devices could be a boon for them.

“Imagine a computer with Braille keypad available today getting replaced with a computer with a normal keypad that is not only usable by the non-impaired people but also has haptics for each key, thus providing usability to the visually impaired users. Such advances would prove to be useful for communication and commercial devices, benefittingthe physically impaired in addition to typical regular users. I don’t see any application or device in WIP phase which could cater to this idea or needs but it would be interesting to see this in the near future,” suggests Tamboli.

“As of now, in the gaming sector, haptic technology seems to be restricted to tactile feedback in consoles and in providing risk-free environments for medical research. However, a truly open source haptic hardware with an IDE could totally change the scenario in the same way as Arduino, Raspberry Pi and Lego NXT have changed microcontroller programming and robotics. It could totally revolutionise each and every aspect of our life in the same way as computer graphics did two decades ago. Haptics may take time to enter our daily life, but it defnitely has a place in the entertainment industry and in research in life sciences and robotics,” adds George Thomas, Foss evangelist and Arduino hobbyist.

The other concurrent research is being done by Anupam Varkey, head, computer department, Thapar Polytechnic, Thapar University, Patiala. It includes developing predictive kinematic positioning algorithms for haptic device control.

“There is always a delay in sensing and its inherent haptic control, howsoever small. This is because it takes time for an actuator to work at the desired force. Once these predictive algorithms are developed, it will be possible to feel the actions much more realistically. Another benefitof this research is in developing visualisation software for use of haptics in simulation. Use of haptics in ‘what-if’ scenarios becomes more realistic and less computation power has to be used. If developed fully, it will be very easy to use haptics-based devices in numerous applications, especially teaching technology. An engineering student can practice maybe taking apart and putting together a whole turbine in a power generation house.”

There is a limit to the range of senses that we can employ to interact with the virtual world. Audio-visual interaction has peaked and there is very little that can be added to the three-dimensional visuals and multiple-channel surround sound.

The author is a tech corespondent at EFY Bengaluru


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