Hello. I am Artem. I will talk about haptics with input.
using LRAs as sensors.
This work was done at Google Research.
With Alex Olwal and Richard Lyon.
Linear resonant actuaors are used in almost every mobile device for haptics right now
They have largely replaced ecentric rotating motors.
because they are smaller, they provide crisper feeedback as well
And, for example a lot of mobile phones are using LRAs
Almost all of them
and you can see inside the pixel mobile phone
that LRA is the rectangular piece, next to the circuit board.
A lot of other devices such as smart watches use LRAs to provide feedback.
LRAs come in many different forms and sizes
they can be easily purchased on the market,
and they are very innexpensive as well.
In all of those cases LRA is used as output
In this paper we show thay they can be used as sensor as well.
as you can see in the applications on the right
We can use it for
Touch
Pressure
Tap detection
As well as detect surroundings of the LRA.
We hope this improves the usability of our haptics and our devices and provides richer feeddback
So how LRA is working, it is basically a linear electric motor, which is similar to a voice coil, a speaker.
The only difference is that mass that vibrates is attached to a spring, and that creates resonant frequency, which is determined by the spring constant
As you can see on the graph on the right, the LRA has a very narrow frequency response.
This is to increase vibration amplitude as well as to decrease the power consumption.
The other idea here is using back EMF for sensing.
Back EMF is generated in every electric motor, and it is a self induced voltage from the changes in the magnetic field
Actually, commercial LRA drivers use back EMF to tune their resonance
In our case, we designed our own circuit, because the commerical ones dont give you the raw output
The main parts are: the audio amplifier which creates the drive signals for the LRA
A set of analog switches, so we can disconnect the audio amplifier, So we can take undistrurbed measurements of the back EMF.
We have instrumentation amplifier to reduce the noise and to improve the signal quality, because back EMF signal is quite small.
This is how we do active sensing. We actuate LRA for very short period of time using custom PWM signal - pulse width modulation.
and you can see here , if we do it for short time and turn it off. We can see when we are not touching the LRA there is big peaks
In the light touch condition there are smaller peaks,
When you touch LRA applying a lot of pressure on LRA, there are no peaks
We figured, the finger dampens the oscillations of the LRA and this can be picked up very well
We also do technical evalutions, so we looked
how we can reduce active sensing acceleration, so we don't feel the LRA when we touch it . It is not noticable
We also looked at how we can get estimation of force of touching. We found it fits pretty well with quadratic fit
We also do power consumption, vibration noise and we compare different LRAs. Please look at the paper to see more detailed results.
We make some applications.
We put the LRA on the bracelet, so we can see how well the bracelet fits and if someone needs to adjust it using back EMF sensing.
We also attach side buttons on the phone that are sensitive to pressure, as you can see on the video.
And we use the LRA which was actually inside a mobile phone already, connecting it to our circuit we can sense if the phone is on the table, picked up with a hand or on a foam using our active sensing technique.
Thank you for listening