Trigonometric Function for Axis Values

[anthonyjules]

Not sure if this is the best place for this...

I am thinking of making a B axis for my PRS Alpha. This would simply be a table that my indexer sits on that is hinged at one end. The other end would be able to feed up or down on a lead screw (driven by a motor) to change the angle of the indexer. The range would only be 15-25 degrees.

As I understand it now the axis values are calculated by a simple linear formula like:

x (inches) = const*motor_pos + offset

For the geometry of the hinged table I want to build, the motor/lead screw will be changing the height of the table edge and not the angle directly, so the angle of the B axis will be something like:

b(degrees) = atan( motor_pos / const ) + offset

So is there a way to use a trigonometric formula to map the motor position to an axis value like this?

Thanks

[dana_swift]

Anthony, the SB3 program makes no attempt to correct for installation geometry. That is the job of the toolpathing software.

There are commercial toolpathing programs that can do that kind of computation automatically. I found the cost to be pretty high, so I designed my own parametric toolpathing program in C#. It can do that kind of operation and (of course) is correct for my bots configuration (only).

If you know anything about programming (it seems you do) write a toolpath generator that does what you are looking for. You will probably find that route will be most satisfying. (And also break the most bits!) Check the output carefully.. the voice of experience here.

Good luck, looks like you are on to some interesting stuff.

D

[Gary Campbell]

Anthony...
If you are looking to compute an appropriate position for the B axis based on another axes position (or a variable) using a trig function, then I think it is possible. For the funtions available look here: C:\Program Files (or x86 if 64 bit)\Shopbot\Shopbot3\Help\Calculated functions.pdf.

The PDF includes a comprehensive list of the funtions available along with some syntax help.

[anthonyjules]

Thank you so much for the reply. I appreciate the time and effort in giving me pointers.

I am likely going to write my own toolpath generation software and head in the direction Dana describes.

Gary, thank you for the link to the calculated functions PDF. That is really useful. I have used some of those based on seeing them used in examples, but the breadth of functions was more than I knew.

Thanks again for the help!

[dana_swift]

Anthony, I have found the rewards in creating computational toolpaths completely outweighs the difficulty of doing it.

When I want a "Z arch" - no problem. When I want a parabolic dish- no problem. When I want a true eliptical surface - no problem.

Part of my design for the SBP file generator, was to allow automatic DXF file generation. So now I automatically generate 2 dxf for each SBP file. One is the outline of the part, so I can import it into Aspire and add features graphically if that is needed. The other file shows the jogs, moves, and comments, each in a seperate layer. Line moves and arcs are in separate layers. Then I can preview the cut to be sure I am not doing something completely stupid. That saves me needing to write my own 3D visualization software.

Its the best of both worlds. The only hard part was getting the DXF generator to work correctly.

I still find doing things in Aspire is easier for a quick one-off part. But being able to have the option of parametric toolpath generation is "priceless".

Keep us posted-

D