Hello Guest it is March 08, 2021, 04:58:50 AM

Author Topic: Pulse Frequency  (Read 15786 times)

0 Members and 1 Guest are viewing this topic.

Pulse Frequency
« on: May 31, 2009, 06:58:46 PM »
I've just completed the video tutloriials, so I'm really new here.

I'm curious about the Pulse Frequency setting in Mach 3.  All the tutorial said was that you should set it at 25,000.  Why are there higher values?  When would you want to increase this setting?

I'm one of those people that just can't settle for "just do this" without knowing the why.

Thanks!
Bill (the Cat) Shubert

Offline Chip

*
  • *
  •  2,055 2,055
  • Gainesville Florida USA
    • View Profile
Re: Pulse Frequency
« Reply #1 on: May 31, 2009, 07:43:13 PM »
Hi, Bill

In short you don't need to increase the pulse frequency unless you max out your motor tuning velocity values.

If your steps per values are below 10,000 per unit, 25 K should be fine for now, It will all make sense in a while.

Chip
Re: Pulse Frequency
« Reply #2 on: June 01, 2009, 09:19:30 AM »
Thanks for the quick response Chip!

However, your answer still leaves me with questions. 

My steps/unit is (are?) 40,000, if I calculated it correctly. (200 motor steps/rev X 10 driver micro-steps/step X 20 TPI Lead Screw).

Your could just tell me if 25,000 is still a good setting for Pulse Frequency, or what setting I should use.

However,  instead of just telling me what value to use, I'd rather get more insight into exactly how the Pulse Frequency setting relates to the overall configuration of Mach 3. That way I can understand the implications of this setting and answer my own question.

"Give a man a fish and he eats for a day.  Teach a man to fish and he eats for a lifetime."
Bill (the Cat) Shubert
Re: Pulse Frequency
« Reply #3 on: June 01, 2009, 11:05:01 AM »
Bill,

The pulse frequency is the maximum step rate Mach can generate.  If your machine has 2000 steps/inch, and you want to run 100 IPM rapids, you need a step rate of 2000 * 100 / 60 = 3333Hz.  So, 25kHz is more than plenty.  However, if you have a machine like mine, which has 20000 steps/inch, and want to run 100 IPM rapids, you'd need 20000 * 100 / 60 = 33,333 steps/inch, so you'd need to increase the pulse rate.  Most modern PCs will handle 45kHz pulse rate, some will go higher.  If you need higher still, the SmoothStepper will go up to 4MHz.  In general, you want to run the lowest pulse rate that meets your needs, to keep from just wasting a lot of CPU power on the PC.  There is no advantage to running faster than required.

Regards,
Ray L.
Regards,
Ray L.
Re: Pulse Frequency
« Reply #4 on: June 01, 2009, 03:29:28 PM »
Thanks Ray! That's the answer I was looking for  ;D

One more question.  You say "most modern PC's will handle 45kHz pulse rate". How do I know what MY PC will handle?  Will I just get bad results from the driver test if I try to go too high?
Bill (the Cat) Shubert
Re: Pulse Frequency
« Reply #5 on: June 01, 2009, 03:43:39 PM »
Thanks Ray! That's the answer I was looking for  ;D

One more question.  You say "most modern PC's will handle 45kHz pulse rate". How do I know what MY PC will handle?  Will I just get bad results from the driver test if I try to go too high?

Bill,

Yup, driver test is the only way to know, and even that may not be 100%.  If driver test says it's OK, try it.  If you have wierd problems, back off and see if they go away.

Regards,
Ray L.
Regards,
Ray L.

Offline Chris.Botha

*
  •  489 489
  • wine me.. dine me.. tram my mill for me...
    • View Profile
    • Digital-Jeweller
Re: Pulse Frequency
« Reply #6 on: June 01, 2009, 05:29:02 PM »
I have 0.9 degree stepper so 400(steps) x 10(tpi) x 10(Microsteps) = 40000 Steps per inch or 1574.8031496 steps per mm.

I want to run at 1200mm/min or in your funky American talk 47.244 IPM

As I calculate it I need to have

40000 * 47.244 / 60 = 31496hz...

so I set at 36000hz? no point in going to 45000hz?

Offline Chris.Botha

*
  •  489 489
  • wine me.. dine me.. tram my mill for me...
    • View Profile
    • Digital-Jeweller
Re: Pulse Frequency
« Reply #7 on: June 01, 2009, 05:38:40 PM »
PS. my little dell optiplex 3.2 HT box with 1gb of ram runs driver test fine all the way thru to 100 000HZ.. at 100 000 i go from "system excellent" to "stable" intermittently.

BUT..

at 24000hz cutting at 600mm/min (23.622IPM) my mach freaks out or my mill does and throws away moves when my fourth axis rotates to cut the opposite side of a flip cut. The rotation will be incomplete or of Y by up to 20mm and then continue cutting.

I can cancel out this problem by killing the toolpath display window.. to some extent (thanks ken for tip) but it occurs to me that mach should have ample grunt to update the toolpath display and still be sending out a simple A rotation sequence?

possible my motor tuning is wrong for A axis?? if so why would turning off  toolpath display help?


[edit]  this only happens with larger paths. 15mb or more


« Last Edit: June 01, 2009, 06:25:06 PM by Chris.Botha »

Offline Chip

*
  • *
  •  2,055 2,055
  • Gainesville Florida USA
    • View Profile
Re: Pulse Frequency
« Reply #8 on: June 01, 2009, 05:53:23 PM »
Hi, Bill

Try referring to the manual, It's under Support above.

Her's a Link, http://www.machsupport.com/docs/Mach3Mill_1.84.pdf

" **** 5.2.2 Defining engine frequency

The Mach3 driver can work at a frequency of 25,000 Hz (pulses per second), 35,000 Hz or
45,000 Hz depending on the speed of your processor and other loads placed on it when
running Mach3.
The frequency you need depends on the maximum pulse rate you need to drive any axis at
its top speed. 25,000 Hz will probably be suitable for stepper motor systems. With a 10
micro-step driver like a Gecko 201, you will get around 750 RPM from a standard 1.8o
stepper motor. High pulse rates are needed for servo drives that have high resolution shaft
encoders on the motor. Further details are given in the section on motor tuning.
Computers with a 1 GHz clock speed will almost certainly run at 35,000 Hz so you can
choose this if you need a higher step rate (e.g. if you have very fine pitch lead screws).

******************************************************************************************

The demonstration version will only run at 25,000 Hz. In addition if Mach3 is forcibly

closed then on re-start it will automatically revert to 25,000 Hz operation.

******************************************************************************************

The actual
frequency in the running system is displayed on the standard Diagnostics screen.
Don't forget to click the Apply button before proceeding. ***** "

Hard to read your mind, Way to go, Your Cat, Tell's it All.

Good Luck, Chip
Re: Pulse Frequency
« Reply #9 on: June 01, 2009, 06:18:40 PM »
Thanks for the manual reference Chip!  I read through that llong before I actually got the software up and running.  I guess it didn't mean anything to me at the time and I didn't remember it when I needed it.

I honestly try to answer my own questions before I come on here and ask.  Guess I just had a senior moment on this one ;)
Bill (the Cat) Shubert