Hello Everyone, I am Narges Pourjafarian, and I am presenting Print-A-Sketch.
This is work done with Marion Koelle, Fjolla Mjaku, Paul Strohmeier and Jürgen Steimle
at Saarland university.
Imagine you could create customized interfaces anytime and anywhere, just like sketching
creatively on a freely chosen surface.
Such an approach might even allow you to improvise during fabrication.
Now, If you think of a complex circuit that requires high precision,
sketching might not be ideal.
For example, it is not easy to draw such a complex design without receiving support
to prevent short circuits or to connect the elements to each other.
Here, printing is the better alternative.
Printing allows to rapidly create complex and high-resolution prototypes.
But, It separates design and fabrication steps; and doesn’t support ad-hoc design
and on-the-fly customization of circuits.
There are also a variety of large and immobile objects that don’t fit inside a printer.
Commercially available handheld printers have already tried to address some of these issues
and brought the design process closer to the object.
However, these devices don’t track the speed and direction of movement.
This means the user requires a lot of practice to learn how to control the device
and how to print undistorted images.
And most importantly, current hand-held printers are limited to non-conductive ink.
For Print-A-Sketch, we combined the benefits of sketching, such as the ability to improvise on the fly
while printing functional electronics and high resolution, fine-grained control of details
by actively sensing context plus device movement,
and by dynamically supporting the user.
At CHI, we present Print-A-Sketch, the first computer-supported approach for rapid free-hand
sketching of high-resolution electrical interfaces.
Print-A-Sketch tightly integrates the ease and expressiveness of free sketching
with high-resolution printing, that dynamically adapts to the device movement,
prior sketched elements, and the surface material.
This novel in-situ design and fabrication technique allows augmenting existing objects
with customized circuits and sensors.
Now, let’s see what Print-A-Sketch is made of.
Print-A-Sketch includes a handheld printer, functional ink, an Arduino, and Protoshield.
The handheld printer consists of a piezo printhead and a pair of visual sensors
for tracking the device movement and sensing the print context,
To better understand how the handheld tool works,
I’ll briefly introduce some basics of piezo technology.
In our current implementation, we use a piezoelectric inkjet printhead,
consisting of an array of nozzles.
Piezoelectric printheads create patterns of expansion and contraction
to jet the ink out of each nozzle, in response to firing pulses.
I will return to it as I explain the challenges Print-A-Sketch addresses.
Sketching with a handheld printer creates a number of challenges:
First, Freehand sketching comes with hand movement.
This means, our hands move at different speeds and might shake or shiver.
This is a problem not only for creating constant and continuous patterns
but also for printing straight lines.
Second, Sketching is an incremental and iterative process and requires spontaneous decision-making.
Iterative printing, however, can result in misaligned patterns or short circuits
without real-time support.
And finally, Sketching with a handheld printer allows you to print on everyday objects.
However, objects and surfaces come in many materials with different absorption power;
Without adjusting the amount of ink, it is not possible to create conductive traces.
In the following, I will explain how we addressed these three challenges.
Imagine you are holding the handheld tool and drawing a curved line.
This seems really easy to do, but actually, it is not.
If the print speed doesn’t adjust to the speed of movement,
the result will be visually inconsistent and non-conductive,
as we can see here.
Based on the principles that I told you, the reason is that
when we eject droplets at constant firing frequency, the space between droplets on the substrate
becomes dependent on the speed of movement, which is not desirable.
To be able to print a consistent trace, we used an optical motion sensor
to detect the speed, and then adjusted the firing frequency accordingly.
To print straight lines and compensate for unsteady motion or shaky hands,
we used optical sensor data and shifted the print data accordingly.
For more technical details, please look at the paper.
By addressing this challenge, now, we can move the device freely
without worrying about the speed or unsteady motion.
Now, let’s see how Print-A-Sketch facilitates computer-supported sketching.
Consider the following situation: you want to connect a new trace
to a previously printed pad.
Without computer support, it is difficult to precisely align old and new prints.
To overcome this issue, Print-A-Sketch detects the pre-printed traces,
using the integrated camera,
and then the new data are shifted to align with the previous pattern.
Using the camera also allows us to scan and print the desired shape,
or scan an existing component and print the footprints.
To see the rest of the sketching techniques, Please look at our Video Figure.
Using Print-A-Sketch, you might want to print on any type of surface.
But, objects come in many materials with different absorption power;
If we eject the same amount of ink on material with different absorption power,
the result might not be conductive.
As we can see on the right.
To solve this problem, the size of droplets should be adjusted
to the absorption power of the substrate.
Using the built-in optical sensor, Print-A-Sketch continuously monitors the material
and dynamically adjusts the size of droplets.
Finally, to evaluate Print-A-Sketch, we conducted various technical studies
on conductivity, the accuracy of adaptive printing, and a case study with naive participants.
To see the results, we invite you to have a look at our paper.
To summarise, Print-A-Sketch combines desirable properties from manual sketching
and computer-supported functional electronic printing,
that dynamically adapts to the user movement,
prior sketched elements, and the surface material.
Thanks for listening!
I’m looking forward to the discussion.