Yes, there is a sync pin, but if you add ramp up/down profiles and the X motor must move 200 steps and the Y motor must move 10 steps then the motion profiles are going to make a mess of things…
I assume that a laser micrometer has a full scale range of -+1mm? That will make it useless for CNC, but can have other interesting applications. I also assume that it isn’t cheap…
@ kertnell, you can look at Optical Linear encoder, or rulers, they are designed for what you need, and they are expensive, new anyway… I have looked at adding an encoder to my lathe for a digital readout, but was quoted, if I remember correctly, $700 for a 500mm encoder…
See Linear encoder - Wikipedia
I have not read the datasheet fully but I would assume that the sync would trigger any slave drives to a master drive, the master emits the sync and then all start moving at the same time. In the case of a CNC machine you would have to plan the moves sent ot each drive to that they could be cooridinated. For example break a path into n chucnks and in each chunk you know where each axis needs to move and at what velocity. Each axis will be done executing each chunk at the same time. You may have to control the IC in velcoity mode to keep it from wantign to accel/deccel with each small move though.
I just ordered a couple of Eval boards to play with, nobody has them yet but Mouser shows they should have a few about 7/7/2011.
EDIT: Also, using a shared external clock should provide better syncing I would think.
I was thinking to use the the divergence factor of a laser pointer to measure the the current position of the axis. (See image attached)
Lasers spread out over distance; this amount is knowable. This means that if you are further away, the beam spreads out. If then passed through a small hole, and diffused with a colour filter, then you can measure distance with a light sensor. Since I have 24bit ADC’s I can connect it to the photosensor with almost no system noise (since the sensor will be soldered directly to the board, very close to the IC).
@ kurtnelle, sorry I copied your name from Jeff’s post… :). Digikey lists the price at ±$13 per chip…
Generally laser micrometers mix the transmitted laser with the received laser. This gives you destructive and constructive interferance, but at the wavelenth of the laser, ie 808nm. Thus you can’t destinguish between 808nm distance and 1616nm as both will give you the same distance.
You can frequency modulate the laser at 100MHz, then do the same mixing. This will give you a full range of 6 meters. But it isnt easy woking at these frequencies…
Yea, I have no idea how it works. I’m assuming that the color (i.e. frequency) changes based on the mixing of the 2 frequencies of light that you are receiving, and that based on the resultant frequency that would be the point at which the light beams are forming constructive and destructive interference.
Since I don’t have a method for determining the frequency of the light; what about my previous suggestion?
No, the frequency won’t change. Two streams of light that are out of phase will interfere with each other and produce specific patterns. Think of splashing both of your hands in the water 1M apart at the same time but one hand hits 1/2 second before the other. When the waves hit they will interfere with each other, the resultant pattern will be be determined by the difference in their phase (time arriving at a given point.)
@ Jeff So the beams are fired one side the other, and the image of them interfering at the point of contact where they disperse (like splashing water) is what determines the distance?
There are other types too that use rotating mirror and optics to create a sheet of light which which broken by an object allows the size to be measured. If the object is rotated you can measure its profile.
Nice CNC project kurtnelle… I was wondering, have you looked into some “ACME” threads or similar threads; they can move your cnc faster, with more power, and they wouldn’t over heat like the regular threads your using.
keep up the good work.
I have encountred extreme difficulty and expense in obtaining acme lead screws, which is why I’m forgoing them for the time being. This CNC’s purpose is to create a pretty cnc that will be used long term.
The most exciting feature this chip has is it’s stall detection. That could prove useful. I’ve read on the overflow forums that if a stepper stalls and you keep driving it, you will demagnetize the magnets eventually.
