3D-printed rotating devices can sense them moving – Zoo House News
- March 19, 2023
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Integrating sensors into rotating mechanisms could allow engineers to build smart hinges that know when a door has been opened, or gears in a motor that tell a mechanic how fast they are turning. MIT engineers have now devised a way to easily integrate sensors into these types of mechanisms using 3D printing.
Although advances in 3D printing allow rotary mechanisms to be manufactured quickly, integrating sensors into designs is still notoriously difficult. Due to the complexity of the rotating parts, sensors are usually embedded manually after the device has already been manufactured.
However, the manual integration of sensors is not an easy task. Embedding them in a device could result in wires tangling in the rotating parts or impeding their rotation, but mounting external sensors would increase a mechanism’s size and potentially limit its movement.
Instead, the new system the MIT researchers have developed allows a manufacturer to 3D print sensors directly into the moving parts of a mechanism using conductive filament. This gives devices the ability to sense their angular position, rotational speed, and direction of rotation.
With their system, called MechSense, a manufacturer can create rotary mechanisms with integrated sensors in just one pass using a multi-material 3D printer. These types of printers use multiple materials at once to create a device.
To streamline the manufacturing process, researchers built a plugin for SolidWorks computer-aided design software that automatically integrates sensors into a model of the mechanism, which could then be sent directly to the 3D printer for manufacture.
MechSense could allow engineers to quickly prototype devices with rotating parts, such as turbines or motors, while integrating the sensing directly into the designs. It could be particularly useful for creating concrete user interfaces for augmented reality environments, where perception is crucial for tracking a user’s movements and interactions with objects.
“A lot of the research we do in our lab is taking manufacturing methods that factories or specialized institutions develop and then making them available to humans. 3D printing is a tool that many people can afford in their homes. So how can we provide the average manufacturer with the tools needed to develop these types of interactive mechanisms? Ultimately, it’s all about that goal,” says Marwa AlAlawi, a mechanical engineering student and lead author of an article on MechSense.
AlAlawi’s co-authors include Michael Wessely, a former postdoc at MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) who is now an assistant professor at Aarhus University; and senior author Stefanie Mueller, Associate Professor at MIT’s Departments of Electrical and Computer Engineering and Mechanical Engineering and a member of CSAIL; as well as others at MIT and Accenture Labs collaborators. Research results will be presented at the ACM CHI Conference on Human Factors in Computing Systems.
The researchers used capacitive sensors to integrate sensors into a rotation mechanism in such a way that the movement of the device would not be disturbed.
A capacitor consists of two plates of conductive material with an insulating material between them. If the area of overlap or distance between the conductive plates is changed, perhaps by turning the mechanism, a capacitive sensor can detect the resulting changes in the electric field between the plates. This information could then be used to calculate speed, for example.
“With capacitive sensing, contact between the two opposing conductive plates is not necessarily required to monitor changes in this particular sensor. We took advantage of this for our sensor design,” says AlAlawi.
Rotary mechanisms typically consist of a rotary element located above, below, or adjacent to a stationary element, such as a gear wheel, rotating on a static shaft across a flat surface. The spinning gear is the rotating element and the flat surface underneath is the stationary element.
The MechSense sensor includes three patches of conductive material printed into the stationary plate, with each patch separated from its neighbors by non-conductive material. A fourth patch of conductive material that has the same area as the other three patches is printed into the rotating platen.
As the device rotates, the patch on the rotating platter, called the floating capacitor, in turn overlaps each of the patches on the stationary platter. As the overlap between the rotating patch and each stationary patch changes (from fully covered to half covered to not covered at all), each patch individually sees the resulting change in capacitance.
The floating capacitor is not connected to any circuitry, so the wires don’t get tangled with rotating components.
Rather, the stationary patches are wired to electronics that use software the researchers developed to convert raw sensor data into estimates of angular position, direction of rotation, and rate of rotation.
Enable rapid prototyping
To simplify the sensor integration process for one user, researchers built a SolidWorks extension. A manufacturer specifies the rotating and stationary parts of its mechanism, as well as the center of rotation, and then the system automatically adds sensor patches to the model.
“The design doesn’t change at all. It just replaces part of the device with a different material, in this case conductive material,” says AlAlawi.
The researchers used their system to prototype several devices, including a smart desk lamp that changes the color and brightness of its light depending on how the user rotates the bottom or center of the lamp. They also produced a planetary gear like those used in robotic arms and a wheel that measures distance as it rolls across a surface.
During prototyping, the team also conducted engineering experiments to optimize the sensor design. They found that reducing the size of the patches increased the error rate in the sensor data.
“In an effort to produce electronic devices with very little e-waste, we want devices that have a smaller footprint but still perform well. If we take the same approach and maybe use a different material or manufacturing process, I think we can go smaller for a while and accumulate less errors with the same geometry,” she says.
In addition to testing different materials, AlAlawi and her collaborators plan to investigate how to increase the robustness of their sensor design to external noise and also develop printable sensors for other types of motion mechanisms.
This research was funded in part by Accenture Labs.