Algorithm?

[unterhaus]

Originally Posted by HuFlungDung Question on the application of this algorithm to machine motion: it would seem that none of the axis can move less than a pulse, so how do you prevent the loss of steps due to rounding off errors? Or how does the computer create what appears to be a smooth output over this bumpy road of digital bits? Is there some kind of averaging thing that is having all these "go, don't go" signals fed in?

Bresenham's algorithm has advantages over the brute force method: it can be done with integer only math, errors don't acummulate, and it uses a very nice method to decide if you should move on the minor axis. If you think about how this works, one of the axis is going to move one step every time because it has more distance to cover. The other one - the minor axis - may or may not move. So if the error between where you are and where the line exceeds half a step (not how they calculate it, but it's equivalent) you move the minor axis. This minimizes the error. On a machine, cutting forces and inertia may be your friend. On your screen, they also blend colors to make the jaggies look less stark, can't really do this with a stepper motor.

I just used it for an image processing algorithm, and it worked great. Of course, I didn't care about jaggies at all, just speed and accumulated error. I did have to modify it a little from the normal computer video implementation, because I wanted to start in one place and end in the other. I looked it up on Wikipedia.

[hobby.club]

Hello,
I use an very simple algoritme .
i write a program for AT90S2313,it communicate to Pc via RS232
on the PC runs a program in VB6
maybe its usefull for you?
I am new on the internet i dont now how to attach the code,maybe i can
mail it to you?
Sorry for my english
my email adres:ludo.van.ginderen@telenet.be

[mwalach]

I am working on a CNC driver program and am trying to wrap my head around the G2 and G3 codes. It looks like the Bresenham Algorithm is the answer, but I'm having trouble getting my head wrapped around this. How do I use the algarithm to generate my steps from a centerpoint and a radius as I would have in a G2 or G3 gcode?

[BartW]

Any one done a 3d version?

[Larken]

I've used this algoithm in both my controllers (Lcam and StarCam), The Starcam runs it in a 40 mhz PIC with 64K ram buffer. It can run 35000 steps/sec running a 16 bit 3d vector. My older DOS (Lcam) could run 90K /sec

Bresenham's Algorithm is a 'on the fly' integer divide. There are arc routines out there for drawing on screens, but I couldn't find a arc routine that would allow starting in the middle of a quadrant, but i developed a fast sqrt routine that can run in integer and decide whether an axis should step or not dependine on a pre-calculated radius.

Mach 3 works differently, it 'steers' 6 free running timers by correcting the trajectory at a periodic rate. This is great but the faster you go the more error and slop there is. A Bresenham loop is perfectly accurate at any speed, the draw back is pulse timing is not evenly spaced, ( but this doesn't matter on a servo or microstepping drive.)

Larry K


Larry K