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Z speed limiting xy speed
« on: February 13, 2018, 08:25:53 AM »
Hi there,

I am using the Z pulses to drive a laser TTL trough a micro. So I really do not mind about how fast the Z speed is because there is no motor connected to it and I need it fast..
I have set x and y at 15000mm/min  (that's my max speed on these axis) and Z at 50000 mm/min. When I run the gcode with a feed rate of 1800 mm/min I expect z to be so fast that should not slow down xy.
I do not know why but z is slowing xy and it is running at merely 500-800 mm/min.
The situation does not change if I increase the feedrate. Mach3 is running at 75 kHz so this shlould not be the issue either. The Z acceleration is also very high (10000) so neither this is the issue.

I have tried different gcodess produced with different cam software but still, despite the settings, Z is slowing down XY which I can hear stepping all the time. I have set constant speed but the machine sounds like the gcode is running in exact stop.
I have attached the gcode I am using for the above test. As you will see the Z movement are from 0 to -1 mm so at the speet I have set the Z, I am not expecting xy to slow dons or to step..

Is there a setting to detach Z speed from xy? Any hint?

Thanks for helping,
Felice


Re: Z speed limiting xy speed
« Reply #1 on: February 13, 2018, 12:06:12 PM »
Hi,
the X,Y and Z axes are coordinated and cant be detached from one another.

You could use the spindle, the spindle is an out-of-band axis. You can use step/dir pulses for a servo type spindle, you only need the step signal.
Also allows you to separately adjust the pulserate without affecting coordinated moves of the other axes.

Craig
My wife left with my best friend...
     and I miss him!
Re: Z speed limiting xy speed
« Reply #2 on: February 13, 2018, 01:16:59 PM »
Hi Craig,
thanks for your answer. I suspected that. I did try using the S vaules but was even worst. The machine was stepping all the time waiting for the S value to change.
I tought that using Z should have been much faster.
What I do not understand at present is why Z is so slow despite the very high performance I mentioned in my original post above.
Do you think is a problem generated by the gcode?
Re: Z speed limiting xy speed
« Reply #3 on: February 13, 2018, 06:44:32 PM »
Hi,
if I understand what you're trying to do is use the Z axis step pulses in some sort of frequency to voltage
conversion to control a laser?

Seems like a difficult way of doing it. The Z axis pulse rate will change at each move determined by the other
coordinated axes.

Using S commands wont work either as they are read per line, thus a move has to complete BEFORE the next
line and therefore the next S command can be read.

What you have to do is start the laser with an S command but the S (speed DRO or pound variable) will need to be updated
either by a brain or a macro at the macro pump rate.  At the macro pump rate the laser pulse stream can be
modified  ten times a second even during a coordinated move. Would that suffice?

My VB coding has never been strong, I converted to Mach4 and Lua, if I'm going to learn something new I wanted it to
be up to date, ie Lua. While I can see how I would go about coding this I'm not going to offer help to do it in VB.
If you wish to download Mach4 I could and would be keen to help you code it in Lua.

Craig
My wife left with my best friend...
     and I miss him!
Re: Z speed limiting xy speed
« Reply #4 on: February 13, 2018, 06:46:27 PM »
When moving 3 axis simultaneously the actual feed rate is along the vector between the 3 axis. So if Mach 3 sees the Z distance as a long move then motion along XY will be slowed a lot. Your Z move needs to be seen as very short by Mach 3. Maybe setting the step pulses per unit move to a very high number would do the job.
Re: Z speed limiting xy speed
« Reply #5 on: February 19, 2018, 11:40:36 AM »
When moving 3 axis simultaneously the actual feed rate is along the vector between the 3 axis. So if Mach 3 sees the Z distance as a long move then motion along XY will be slowed a lot. Your Z move needs to be seen as very short by Mach 3. Maybe setting the step pulses per unit move to a very high number would do the job.

Thanks for your explanation. Actually the move in Z is maximum 0.5 mm and I did set the Z speed 20 times faster than the other two axis. I have 250 steps per mm on Z and 500 steps per mm on XY. But still the machine is slowing down and running in steps with a feed rate of 2000 mm/min rather than in a smooth linear motion. I am not sure if there is anything else I can set in Mach3 or in the Gcode to avoid this issue. I did also set G64 constant velocity but no changes.

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Re: Z speed limiting xy speed
« Reply #6 on: February 19, 2018, 01:05:48 PM »
Hi,
steps per mm and Speed is one thing,
acceleration is an other Point.

i don't know the dimensions of your machine, but i would start with some test's
by entering command into mdi.

for example:

F500
G1 X500 -> measure the needed time

 F500
G1 Y500 -> measure the needed time

F500
G1 X500 Y500 -> measure the needed time

just to make sure not one of the 'major' axis are making the Limit.

then

F500
G1 X500 Y500 Z5 -> measure the needed time

to get a 'feeling' what is 'pushing' the brake.

Thomas
 
anything is possible, just try to do it.
if you find some mistakes, in my bad bavarian english,they are yours.
Re: Z speed limiting xy speed
« Reply #7 on: February 19, 2018, 01:38:08 PM »
@TPS

Hi, thanks for your suggestion. Since the Z motor is disconnected because I am using such output to feed the laser board trough a microprocessor, I have set huge acceleration (100000),  but still Z is slowing down XY. Looks like doesn't matter how fast and reactive I make Z , when there is a change in Z, the other axis slow down for a fraction of second but slow down causing the machine to sound really hugly.  This does not happen with with X and Y if I make Z constand and change a value  in X or Y.


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Re: Z speed limiting xy speed
« Reply #8 on: February 19, 2018, 01:41:19 PM »
have you tryed "real" (x3) instead of "huge" values?
anything is possible, just try to do it.
if you find some mistakes, in my bad bavarian english,they are yours.

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Re: Z speed limiting xy speed
« Reply #9 on: February 19, 2018, 01:42:59 PM »
@TPS
  This does not happen with with X and Y if I make Z constand and change a value  in X or Y.

can you please explain a Little bit, sorry my english is not good enough.
anything is possible, just try to do it.
if you find some mistakes, in my bad bavarian english,they are yours.