slit scan motion control mechanism

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Slit scanning is a form of digital imaging that works much the same way as a flatbed scanner. The center pixel column or “scan line” is taken from each frame of a digital camera’s video stream. The scan line is then appended to the end of a large panoramic image that develops in real-time. By moving the camera in precise increments, an entire 360-degree panorama can be created.

I have previously experimented with a turntable design for precisely stepping a digital video camera 360-degrees. My experiment resulted in an optimal gear ratio for reducing the stepping angle of a stepper motor to accurately move the camera one scan line width per step of the motor. This current iteration will be a refinement of the previous design and address issues of vibration, sturdiness, and dependability.

I started with a 12-volt stepper motor with a 1.8-degree stepping angle. This means that the motor would have 200 steps per 360-degree rotation. My previous experiments showed that it would require 5000 steps to accurately scan a 360-degree panorama with a standard definition digital video camera. To reduce the 1.8-degree stepping angle of the motor I would have to create a gear ratio of 25:1.

I found the Vex Robotics kit to be a very versatile when experimenting with various gears, ratios, and configurations. The Vex gear kit had various gears, all with the same tooth pitch and designed to fit within the pre-milled Vex hardware kit. I used a 12-tooth coupled to the motor shaft and meshed that to a 60-tooth gear giving me a 5:1 gear reduction. By adding another 12-tooh gear to the shaft of the 60-tooh gear an meshing that to another 60-tooth gear I was able to add another 5:1 gear reduction giving me an overall reduction of 25:1.

After experimenting with various layouts I finally settled on a design. I transferred the Vex hardware layout to a piece of 1” thick acrylic. I drilled the holes for the 1/8” square axel rods. I then coupled the stepper motor to the first shaft using a coupler with a flexible rubber spider in between to account for any misalignment. Small nylon washers were used to reduce friction at every point where a spinning shaft comes in contact with the gearbox case.

The final step before connecting a camera to the gearbox mechanism will be to create a turntable that spins with the shaft at the end of the gear reducer. To do so I will investigate thrust bearings to support the weight of the turntable while allowing it to spin freely on the top of the gearbox.