As we’ve mentioned previously on this blog, we have begun testing an early prototype of the eForge version 1.0 printer that we will be launching to the public in the future. We have been conducting a variety of tests, and in this post we’re going to walk through the 3D printing of a two-material pressure sensor.
The eForge Prototype
The eForge prototype printer that we are working with for current testing is capable of printing up to three materials at once. The full production model of the eForge version 1.0 will be capable of printing up to eight different materials at once. The filaments are approximately 4mm in diameter and consist of the various proprietary mixtures for the printing of electronic devices.
We use Autodesk Tinkercad to lay out the design for devices that will be printed with the eForge.
We associated a set of Tinkercad’s colors to the six primary materials required to print electronics.
- Red - conducting
- Green - insulating
- Grey - resistive
- Yellow - capacitive
- Blue - n-type semiconducting
- Purple - p-type semiconducting
Test Print Setup
In this demo, our goal is to design a simple capacitive driven pressure sensor and to print it with eForge, then run a simple experiment to show its performance.
This pressure sensor is a two-material device, which is an ideal device to demonstrate the capabilities of the printer. For this device we'll use gray and yellow on our layout. After the layout is completed the resulting OBJ file is exported to a slicer program where each portion is associated to an appropriate extruder on the printer. G-code is produced by the slicer program.
Printing the Sensor
A USB drive holds the g-code files that can be selected from the touch-screen interface.
Our pressure-sensor file is selected and we’re ready to start printing.
The first layer of resistive material is printed into our desired shape. This is followed by the middle section of the capacitive material and finally the top layer of resistive material is added.
At last, the complete device is cooled and extracted from the eForge. It has a roughly 20x25mm surface area, and is about 5mm thick. The entire print took about 9 minutes to complete.
Testing the Sensor
With the pressure sensor completed, we’re ready to begin the testing of the sensor.
For testing, we apply a +/- 5 volt 10khz square wave signal across the device as the input while measuring the output voltage across the larger pad, which essentially makes up the capacitor.
The formulas that we use for testing are:
C= Ae/d and T=1/RC
Capacitance = Area of the planar surface times dielectric constant of the inner material divided by the distance between the two surfaces.
Time-constant = inverse of the resistance times the capacitance.
When we depress the sensor, we are decreasing the distance d, thereby increasing the capacitance. Thus, if the capacitance increases the time constant decreases.
Without depressing the sensor, it takes about 12 microseconds for the voltage to charge up to its maximum value. After depression, it only takes 5 microseconds. This reduction can be associated with an amount of pressure, and thus you have a sensor.
This is demonstration shows just one of the many potential applications for devices that can be printed with the eForge. As we continue testing this and subsequent prototypes, we will continue sharing additional printing demonstrations.