The PrintBot

Step 3 The Print Head

As much of the original print head assembly that could be was removed. We were left with a plastic box which made it easy to attach our print head. A small 5V DC motor was attached with a drill bit. The bit was chosen to have as close to the same diameter as a funnel as possible. This will allow the drill to fill the entire outlet of the funnel. When the bit spins, powder enters the grooves and rotates down the bit towards the exit. By rotating the bit one rotation we could create a constantly sized pixel. Careful tuning will be required to make everything fit just right. Initially we had problems with the powder simply spraying all over the place, but by adding a second funnel and raising the drill bit, the longer fall while constrained to the funnel made a clean pixel.

Since this motor must only be controlled on or off, a H-bridge was not necessary here. Instead we used a simple transistor in series with the ground connection of the motor. The gate of the transistor was controlled by a digital output from our micro controller the same as the digital inputs the H-bridge.

The small PCB next to the DC motor is a infrared black and white sensor. This board simply outputs a digital high or low signal when the sensor sees black or white respectively. Combined with the black and white encoder strip allows us to know the position of the print head at all times by counting black to white transitions.