A team of international researchers has utilized 3D printing and low-cost parts to create an inexpensive hyperspectral imager that is light enough to use onboard drones. The prototype construction visible-wavelength hyperspectral imager weighs less than half a pound and could cost as little as $700.

The new research could provide insight into how to make the high-priced and bulky analytical technique more widely accessible.

“The instruments we made can be used very effectively on a drone or unmanned vehicle to acquire spectral images,” research team leader Fred Sigernes of University Centre in Svalbard (UNIS), Norway, said in a statement. “This means that hyperspectral imaging could be used to map large areas of terrain, for example, without the need to hire a plane or helicopter to carry an expensive and large instrument.”

Hyperspectral imagers produce images like a traditional color camera, but detect several hundred colors instead of the three detected by normal cameras. Each pixel of a hyperspectral image contains information covering the entire visible spectrum, providing data that can be used to automatically detect and sort objects.

To create the instrument, the dispersive element housings were printed with a thermoplastic 3D printer that is combined with S-mount optical components and commercial off-the-shelf camera heads. The grating is collimated using the mix and match S-Mount components of the company Edmund Optics (EO) Ltd. The basic optical parts comprise one high precision slit, a collimator lens and a front lens. This requires three thin lens holders, one focus tube and one lock ring. 

According to the study, the holder can be split into two halves that encompass the optical element in order to avoid both gluing and threading.

Because thermoplastic materials tend to shrink during 3D printing, the researchers scaled up the parts one to two percent of their original designed size to make the embedded components frictional snap-fit fixed.

“Making items in metal is time consuming and can be very expensive,” Sigernes said. “However, 3D printing with plastic is inexpensive and very effective for making even complex parts, such as the piece needed to hold the grating that disperses the light. “I was able to print several versions and try them out.”

The researchers conducted three test experiments with motorized gimbals to stabilize attitude and found that the instruments are capable of push broom spectral imaging from various platforms, including airborne drone to handheld operations.

According to the study, the push broom method records a perpendicular cross-section of any target along the track direction.

“Push-broom hyperspectral imagers typically require expensive orientation stabilization,” Sigernes said. “However, you can now buy very inexpensive gyroscope-based, electronically stabilizing systems.

“The advent of these new systems made is possible for us to make inexpensive hyperspectral imagers.”

The push broom technique requires line scanning of the target with high precision. For example, on an airborne or satellite platform, the instrument needs to be stabilized in attitude by a 3-axis gyro in order to sweep the target without spatial distortions along the direction of flight.

The team tested one of the instruments onboard an octocopter drone equipped with a two-axis electronic stabilizing system. They also performed handheld tests with the hyperspectral imagers and three-axis electronic stabilizing system.

For one experiment, they swept the imager across a computer screen displaying a fruit collection, acquiring 571 spectrograms in 22 seconds. The testing showed that 3D printing could produce prototype parts for optical systems that were strong enough to keep the overall system light and small.

After testing, metal versions of 3D printed parts could be ordered if desired to create imagers that would be more durable.

The study was published in Optical Express.