While 3D printing is essential for rapid prototyping mechanical parts, it doesn't usually offer much assistance when it comes to electronic systems. Most designers add electronic functionality to a prototype after printing the mechanical parts. What if 3D printing could allow some of that functionality to be included? This would allow for faster development, lower costs, and more design flexibility. A team of engineers at MIT devised a new way of 3D printing sensors that can detect the direction, speed, rotation, and direction of mechanical joints.
These sensors are based on capacitance, which refers to a material composite's ability store an electric charge. A standard capacitor is an example of a component that has two pieces of conductive material separated from an insulator. Capacitive sensing can be used to detect touch. A person's finger can alter the capacitance of a circuit. Capacitive sensing is a common feature of touchscreens and touch sensors. You may have noticed that touch sensors with high sensitivities can sometimes trigger even before you touch them. Because capacitance is not affected by physical contact, it doesn't need to be touched. This fact is what 3D-printed sensors rely upon.
A 3D printer that can extrude multiple materials is required to print one of these sensors. The first material must be an insulator such as ABS, PLA, or other common filament types. The second material must be conductive. Although they are not common, there are some conductive filament materials on the market today.
Although there is a lot of flexibility, the basic sensor design includes a base plate and three capacitive sensing pad printed with the conductive filament. The rotating part attaches directly to the base plate and contains one patch of conductive material. The circuit is not connected to the latter part. The base plate pads connect to a capacitive sensor board or to the analog input pins on a microcontroller. The conductive patch on a rotating plate does not need to be in direct contact with the base plates pads. It will affect the capacitance of those pads by simply being close.
It's all software from there. The software can determine the position and capacitance of the rotating parts by monitoring their relative capacitances. The software can also monitor speed and direction by adding a time variable.
These 3D-printed rotational sensors could be used to control knobs or determine the angle of joints like those in a robot arms. Engineers can simplify their designs by integrating them into 3D-printed mechanical components. This will reduce the number of parts.
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