Movie:

In this picture you see the very bottom of the extruder, where the icing tip pokes through the hole in the bottom piece of wood. The Frost Bot is squirting frosting onto a piece of wood covered with aluminum foil (for testing). You can see that we forgot to turn off the extruder after we moved up away from the foil (after the image was complete) and so there is a 'tendril' of frosting from the foil up to the icing tip that shouldn't be there. The kind of circle/arrow logo that you see in these images is my company's logo.

Now these are some great pictures. They both show the Frost Bot in its entirety. You can just barely see the icing bag inside the extruder. (The bag is clear plastic, and so looks blue because I had blue frosting in it.) You can see the extruder stepper motor on top of the extruder. It is supported by the red plastic tubes. The belt connects a pulley beneath the stepper motor to another pulley. Inside the second pulley is an aluminum shaft I machined on the lathe. There are two ball bearings (one above the pulley and one below). That top piece of MDF wood is bolted down, and squeezes the sandwich of bearing, pulley, bearing. The aluminum shaft is tapped for the 1/4 20 threaded rod that it rotates around. As the shaft is turned by the pulley, the threaded rod goes up or down. This in turn pushes on the metal tube (not visible in these pictures) that squeezes the frosting out of the bag.

Here are two pictures - both have the front guide of the extruder removed so you can see what it looks like on the inside. There is no frosting in the bag, which is why it looks clear/white. The first picture has the extruder up, where we put it to load the bag of frosting in. The second picture has the extruder down, where it would be pushing on the frosting and extruding it onto the cookie (if there was frosting in the bag).

Electronics: The electronic portion of this project consists of a UBW controller board, a single board holding four EasyDriver stepper motor drivers, and a normal computer power supply delivering 12V to the motor driver chips. There are four home switches (one for each axis) that the UBW reads with four of its digital inputs. The UBW sends step and direction data to the Easy Driver Quad board using a simple SPI like shift-register scheme. It has a Clock, Data and Latch signal (and ground) to send the data into the latch chips, and then latch the data to the four driver chips. The motor driver chips are rated at about 750mA/phase, and even with this fairly weak current the stepper motors turn quite rapidly and with considerable power. Using a higher voltage power supply, or stronger motor drivers would allow the robot to move faster, but this would compromise the quality of the frosting job.

Here is the UBW board and the Easy Driver Quad board without the fan so you can see how things sit on the breadboard.

Software: There are two pieces of software that the Frost Bot team wrote. One lives on the UBW board and interprets motor move commands from the PC (over USB) and generates the step and direction pulses for the four motors. It also reads the home switches and executes special instructions like 'home' and 'abort'. The other piece of software is a full Windows application written in Liberty Basic by Jemiah Aitch. It reads in HPGL files (graphics files) and interprets the files, breaking them into individual move commands which are sent to the UBW board. It also has logic for handling homing, offsets (i.e. zeroing), soft limits on all axes, pausing, and generating the correct among of extrude motor motion for each unit of distance traveled by the tip.

This screenshot shows what the LibertyBasic PC application looks like. You can see that it has loaded in a simple HPGL file and converted it to UBW step commands. The graphics start out as SVG files drawn in InkScape, then saved as PostScript files. Those *.ps files are read into GhostScript and saved as HPGL files, which are then read in by the LibertyBasic app and sent to the UBW.

The Frost Bot Team: I (Brian Schmalz) did much of the work on this first version. However, I had considerable help. Jemiah Aitch (a co-worker of mine at Logic and all-around awesome guy) wrote all of the software that runs on the PC to control the robot. He also helped out (in a string of very late-night hacking sessions) with the systems engineering and integration of the whole thing. John Hansford designed and built the 3-axis CNC mill kit that I assembled and modified into the final Frost Bot base. I built the frosting extruder assembly (4th axis), designed both the UBW controller board and Quad Easy Driver motor driver boards, and the step and direction software running on the UBW. Much of the UBW software and EDQ work was based upon work I've been doing to help out Elias Crespin and Bruce Shapiro.