- Thank you chairperson.
I am Hiroyuki Manabe from NTT DOCOMO
and I will talk about capacitive touch sensing
technique with series-connected sensing electrodes.
Currently touch is measured input modalities,
for example PCs and smartphones accept touch input
via a touch part or touch panels.
The user can input wide variety of meaning through
touch input, for example simply on and off,
multi touches and gestures.
There are also several advantages to use touch input
from mechanical aspects, for example
touch sensors can be implemented in small and thin
form factors and they have no move operated elements,
and work with low power consumption.
Considering these merits of touch input, they would
be used much more, especially with personal
fabricated devices.
When prototyping the touch based devices
trial and error iterations are needed.
In such phases, touch sensors have to be attached
on any surfaces and the sensor congregation has
to be easily changed.
In other words, adaptability and flexibility are important.
It is also desired to implement easily and simply.
This is an example.
A maker wants to invent touch sensing capability
on eye glasses, like Google Glass.
There are many candidates, for example,
electrode position, shape, size and the number of
electrodes are different.
So optimal electrode configuration depends on
what the maker wants to detect and he will perform
trial and error to change the sensor configuration.
There are many techniques to detect touch by
electric based techniques.
For example, a technique based on Time Domain Reflectometry
can detect the touch point on wire.
Touche is a single touch sensor that
recognizes hand postures.
Makey Makey can change various objects into touch sensors,
Cuttable large touch sensors can easily change its
out of cone shape.
SensorTape is tape shaped sensor arrays.
Electrick can implement touch capability on various objects
by attaching many electrodes.
Unlike these smart techniques, there are basic
and traditional configurations to support multiple sensors.
Example one shows that the electrode has different wires
to connect to the sensing socket.
Paired press technique and the matrix technique
can reduce the number of wires.
Example four shows the touch based slider.
It compares two capacitors to form with the finger.
Example five shows resistive touch sensors.
Half of the electrodes are series connected via resistors
and three wires are needed to connect to the sensing socket.
For the switching technique, allows to exactly determine
which electrode is touched.
The electrodes have to be designed as the user,
the finger always touches the pair of electrodes.
Example six is RootCap.
The electrodes are pairs connected via capacitors
and only a single wire is needed.
It detects the touch electrode by
the absolute value of capacitors.
Unfortunately it is easily affected by the environment.
Our technique is inspired by example four and five.
It's features include two wires to connect to the
sensing socket, comparing a pair of capacitances.
So it is connected electrodes,
and polarity switching techniques.
This is our proposed technique.
The electrodes are connected in series via capacitors,
and electrodes are connected to the
sensing circuit by two wires.
The sensing circuit is almost the same as regular one,
but except the switch.
The switch controls the polarity and two capacitors
are measured.
There are many unknown parameters such as CE and the Cs
so from the measured capacitances it is impossible
to determine exactly the touched electrode.
So the measured capacitances are compared with
reference one, in calibration phase.
There are several assumptions to work properly.
For example, Ci and Ch is larger than CE,
and Cg is large enough.
Our technique brings adaptability and flexibility.
Shape, size, placement of electrodes and touch position
within an electrode have little limitation.
The touch sensor can be put on any surfaces
such as narrow and curved surfaces.
It is easy to change the number of electrodes
by rewiring and recalibration.
Thanks to polarity switching technique, our technique
has multi touch capability by two fingers.
It is easy to implement because of simple wiring
and simple socket and we can create capacitances
but sandwiching dielectric material with
two conductive materials.
We call it, capacitor-free design.
These are electrode examples that emphasize our technique.
The left figure shows wire and slim electrodes.
For example, wire electrode prototype one simply
connects actual lead capacitors with metal pipes.
The leads and pipes work as touch sensors.
Wire to the prototype two is made by single core cable
and conductive mesh hoses.
The mesh hoses work touch sensors.
The slim electrode prototype was made on a PCB.
It has 10 electrodes on the narrow PCB
with a width of three millimeters.
The right figure shows a flexible electrode.
We applied capacitor-free design to
paper electrode prototype.
It was made by just paper and conductive tape.
It is interesting that only touch sensors
are put on the surface and connecting elements
are on the back side.
Where a thin iterating film is used, more electrodes are
possible like flexible electrode prototype two.
When much smaller electrodes are needed, FPC and capacitors
can be used like flexible electrode prototype one.
I explain how our technique works.
This figure illustrates a situation when no finger touches.
The red line represents the current flow.
The total capacitance measured from the socket is small.
In case that Ci and Cg are 300 picofarad,
CE is five picofarad, the total capacitance is
calculated as 28 picofarad.
Even when the switch changes polarity,
the total capacitance does not change.
This figure illustrates the situation when the finger
touches electrode two.
The left pass is selected, that means that the
touched electrode is near the socket.
Assuming Ch is 300 picofarad, the total capacitance
is 78 picofaratd
After a while, the switch changes polarity.
These figure illustrates the situation
after polarity is changed.
The total capacitance is calculated as 43 picofarad
which is larger than no touches and smaller than
other polarity.
So when the finger touches the electrode, the total
capacitance increases but the pair of capacitances
differs according to the touched electrode.
We had a simulation.
This graph shows the result when 10 electrodes
are used with three different capacitors.
The capacitance is measured as duty cycle in the socket,
so x axis and y axis represents the duty cycle.
The pair of capacitances differs according
to the touched electrode.
The value of Ci affects the trace, but wide range
of Ci is acceptable, so the fraction of Ci is not severe.
The prototypes were developed.
The circuit is assumed to connect to the AC powered laptop
or AC adapter to establish the coupling to ground.
This is the measured result.
The left graph shows an actually measured result
and the right graph shows the
corresponding simulation result.
The measured result is almost the same as simulation result
and it is confirmed that the pair of capacitances
differ according to the touched electrode.
This graph shows the impact of the number of electrodes.
The trend of measured result is almost the same as
simulation result.
As you see, it becomes difficult to recognize
the touched electrode properly when the number
of electrodes is becoming larger.
So practical range seems up to 10 electrodes.
This graph shows a multi touch capability.
Black is single touch, and the red is multi touch
by two fingers.
These touches yield different forms,
that means our technique has multi touch capability.
Unfortunately, the simulation result indicates
that multi touch with three fingers over acted
on the other approach, so multi touch capability
is limited up to two fingers.
User test was conducted with 10 people.
10, 15, 20 electrodes were used in test one, two, three.
Test four used four electrodes and
10 touch crosses were recognized, including
single touch and multi touch by two fingers.
Test five used paper based electrodes, and test six
used flexible electrodes on smartphone.
The user with lower or higher accuracy in test one
also shows lower or higher accuracy in other tests.
From test one to test six, the calibration was
conducted by one particular person who did not
participate in these tests.
The test zero is the same as test one
except the calibration.
In test zero the calibration was conducted by
the test user himself, so comparing test zero and test one,
the user calibration is quite effective to
improve the accuracy.
This means that there are some differences among users
in terms of capacitance.
Test five indicates that capacitor-free design
actually works.
And test six indicates that connected to AC power
is not always necessary when it is applied to
handheld devices.
We think our technique is effective in prototyping phase
and to explore the design space we developed
several application examples.
This is demo movie.
This is a simple 10 electrodes.
This is multi touch capability.
Single touch.
And multi touch by two fingers.
We applied capacitor-free design on this interactive book.
This block building example encouraged rewiring
and the recalibration processes,
and this is calibration process.
This example is smartphone based.
And finally this is a wire based example.
Our technique has several limitations such as
calibration is needed in advance,
however we believe that our technique is effective
in prototyping phase because adaptability and flexibility
is much more important rather than these limitations.
It is possible to apply more robust technique after
tuning the sensor configurations.
Thank you very much.
(clapping)
- So if you have questions I invite you to come up,
in the meantime I have one relating to the calibration.
So you had quite a big difference whether it was
calibrated individually versus one for all the users.
Is there a way to improve that calibration so that you
can still do it once but it would work for all of the users
if you improve the way you're calibrating at the moment?
- You mean our technique to not use calibration
by individual users?
I think there is a possibility to estimate the
pair of capacitances according to the actual
attached electrodes.
When the different user touches the electrode,
some pair of capacitance can be measured,
so using this information the system
can (timer ringing)
update the calibration.
- Sorry, that's the end of your talk.