New 3D-Printable Sensors Detect Rotation

3D printing is indispensable for rapid prototyping of mechanical parts, but it doesn't typically provide much help when it comes to electronic systems. If a prototype requires electronic functionality, most designers add off-the-shelf components after printing the mechanical parts. But what if some of that functionality could be incorporated through 3D printing? That would speed up development, keep costs down, and introduce more design flexibility. That's why a team of engineers from MIT developed a new way to 3D print sensors that can detect the rotation angle, speed, and direction of mechanical joints.

These sensors rely on capacitance, which is a material composite's ability to store an electric charge. A standard capacitor, for instance, is a component with two pieces of conductive material separated by an insulator. Capacitive sensing is a common way to detect touch, as a person's finger can affect the capacitance of a circuit. Touchscreens and touch sensors commonly rely on capacitive sensing. If you've used a device with very sensitive touch sensors, you may have noticed that they sometimes trigger before you physically touch them. That's because physical contact isn't required to affect capacitance. These new 3D-printable sensors rely on that fact.

Printing one of these sensors requires a 3D printer capable of extruding two or more materials. The first material needs to be an insulator, such as PLA, ABS, and other common filament types. The second material needs to be something conductive. While they aren't common, there are a handful of conductive filament materials available on the consumer market today.

There is a lot of flexibility, but the basic sensor design consists of a base plate with three capacitive sensing pads printed with the conductive filament. The rotating part attaches to that base plate and contains a single patch of conductive material. The latter part isn't connected to the circuit at all. The pads on the base plate connect to a capacitive sensing board or the analog input pins of a microcontroller. The conductive patch on the rotating plate doesn't need to make physical contact with the base plate pads, because it will affect the capacitance of the base plate pads just by being in close proximity.

From there, it's all software. By monitoring the relative capacitance of each of the three pads, the software can determine the position of the rotating part. Add a time variable, and the software can monitor speed and rotation direction.

3D-printed rotational sensors like these would be very useful for control knobs and for determining the angle of joints, like those in a robot arm. By integrating them into the 3D-printed mechanical parts, engineers can simplify their designs and reduce part counts.