On 2014-05-12 19:13, Gene Heskett wrote: > On Monday 12 May 2014 10:48:52 Marius Liebenberg did opine > And Gene did reply: >> Will it be possible for me to read an encoder signal on my lathe >> spindle with a normal parport input. I will fit a Hall effect Sensor >> or an Interrupted light source signal. The max RMP will be 2000 and I >> might have 10 slots or more. > It is not a problem at those rpms Marius, my encoder is led interrupter > based and has 50 slots with the interruptors spaced for quadrature output. > By my calcs, I can probably track it to nearly 6000 rpm. So I quite > worrying about it 2 or 3 years ago. > > Here is how to get a rough idea, assuming the read encoder function is in > the base thread. My base thread runs at 27500 ns, converted to a > frequency by the usual math, is 36,363 times a second that the port and > encoder data will be updated. Now, and this assumes a nearly 50% duty > cycle from the A/B slots of the encoder wheel get at least one sample per > state of the quadrature signal generated. Overtaking that will raise the > apparent noise in the velocity signal by quite a bit. Most of the time > you are under it but and several identical samples per state. > > Since in my case an edge occurs 200 times per rev, and the base thread is > 27500 ns in this example, then calc how much time it takes edge to edge by > taking the rpms/60 to get the scale in seconds, so > 2000/60=33.333333333333333333 rps. > > Now, 200 edges per turn is 33.333333333333333333 *200 = > 6,666.6666666666666667, the resultant frequency of the edges. > So in my case, 2000 rpm is about 1/6th of the speed I can track it at, or > around 12,000 rpms. I hope my math is correct. ;-) > > The more slots you have, the smoother the Z drive will be when cutting > threads or some such. 10 would be pretty coarse.
I realized that I could have a lot more slots. 50 sound good to me as well. I will have a disc laser cut to be very precise. Ans also one does not cut thread at break neck speed so I could afford a higher number of slots. On the lathe I normally cut at a spindle speed of about 45 RPM but I guess that could become a lot faster once the cnc conversion is completed. > Cheers, Gene -- Regards /Groete Marius D. Liebenberg +27 82 698 3251 +27 12 743 6064 QQ 1767394877 ------------------------------------------------------------------------------ "Accelerate Dev Cycles with Automated Cross-Browser Testing - For FREE Instantly run your Selenium tests across 300+ browser/OS combos. Get unparalleled scalability from the best Selenium testing platform available Simple to use. Nothing to install. Get started now for free." http://p.sf.net/sfu/SauceLabs _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
