Scientific prototyping with 3D RepRap printer.

One of the reasons for building the 3D RepRap printer was to use it for what I would call "Rapid Scientific Prototyping":  In my research I spend fair amount of time desingning scientific instrumentation and for that very often we need custom mechanical components. While our institute has fairly decent machine shop that makes such custom components for us, however it is fairly SLOW process: I have to make reasonably detailed and accurate drawing and description of what I need, talk to the shop staff and then submit a request. Then it takes couple of weeks (or longer) before the parts come back.

The problem is that often I do not quite know at the begining exactly how the part should look. I come with the best design I can think off, but often only after the pieces come back and I test the device I find out that some modifications will be needed. So it is back to the drawing.... With two or three itterations needed to make the design really work, it can take months before the job is done.

Therefore, at least for the early stages of the development we absolutely need a fast prototyping method, that would allow us to build work-shift first version of the device that that would allow us to figure out what exactly is needed in the final version. We need to test it, rebuild it, abuse it, until we are sure we know what we need. And exactly for this purpose the plastic 3D printing is a great help.  It is NOT by any means an universal solution, as the capabilities are rather limited at this point (the parts can not be too big nor too small, the mechanical properties of the plastic are not perfect...).  But many things can be designed and built very quickly by this method and furthermore subsequent modifications of the design are very rapid. Thus several modifications of the design can be achieved in a short time.

   Following example shows a design of a holder for small geared DC motor that we want to use to automatically adjust a precision screw that moves an optical grating in a diode laser.  The mount has to allow for small adjustments of the motor position in all three directions to position the motor exactly with respect to the grating mount. The design philosophy we use is based on the same ideas as the RepRap printer itself: we use combination of threaded rods, nuts, washers and custom printed pieces.  All the plastic pieces were designed using the OpenSCAD package, sliced with Slic3r and printed using Proterface software on standard RepRap Prusa (built mid 2012). We print using PLA.

Figure 1: set of basic pieces needed for the motor mount.  Nuts and bolts are M6, the base is 40mm x 40mm. 

 Figure 2: The base with mounting threded rods

 Figure 3: adding the optical gate holder. 

 Figures 4:  mounting the little DC motor between two plastic retaining plates. Motor height can be adjusted by moving the mounting nuts up and down the threaded rods.

Figure 5: The complete mount including the encoder wheel.  The wheel interrupts the optical gate (the black part) when the motor rotates thus the angle of rotation and/or angular velocity can be measured.  The encoder wheel is printed on a laser printer usning a laser printer transparency, it privides 4° resolution.

The function of the whole unit is demonstrated ofn following short video:

Encoder output signal