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. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS ------------------------------------------------------------------------------ "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
