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Author Topic: Laser control on and off using Z  (Read 4300 times)

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Laser control on and off using Z
« on: September 22, 2016, 06:03:39 PM »
Been searching the internet for anything about controlling a relay (which controls a laser on/off) by using the Z axis.  There is a lot of talk about -Z turning the laser on and +Z turning the laser off.  That is exactly what I want to do.  But there is nothing mentioned for my hardware configuration, which I figured is quite common.

I use Solidworks and HSMxpress to produce my G-code.  I don't want to edit my G-code at all.  And I don't want to have to change to another suite of software. 

I am using a USB BOB http://www.automationtechnologiesinc.com/products-page/breakout-boards/3-axis-cnc-usb-card-mach3-200khz-breakout-board on my laser gantry. 

Anyway, I am not sure how to wire in a relay on the Z Axis outputs of this card.  Pulse+ and Direction+ are always 5V and so I am not exactly sure how to integrate the Pulse- and Direction- into the scheme of controlling a relay.  Even a circuit to latch the relay to itself may work.  Any ideas?

On a side note, will research setting up Mach3 as a plasma cutter, but even on this board there isn't much on that.  And I am not sure of its features and how it will operate the laser.   

Offline Tweakie.CNC

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Re: Laser control on and off using Z
« Reply #1 on: September 23, 2016, 04:27:38 AM »
For your Z axis if you measure the voltage between +5v (Dir+) and Dir- it will change between 0v and 5v depending on which direction the axis was last moved.
Connecting a relay directly may not be a good idea (the Dir- can only sink 50mA current and it is already driving the Z axis controller) so use an opto coupler (or similar device) to drive your relay from the +5v and Dir- terminals.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Laser control on and off using Z
« Reply #2 on: September 23, 2016, 09:20:53 AM »
Thanks Tweakie for the info, I've got a stash of 5V optically coupled solid state relays that may fit the bill. 

Offline boxin

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Re: Laser control on and off using Z
« Reply #3 on: March 01, 2017, 12:05:06 AM »
For your Z axis if you measure the voltage between +5v (Dir+) and Dir- it will change between 0v and 5v depending on which direction the axis was last moved.
Connecting a relay directly may not be a good idea (the Dir- can only sink 50mA current and it is already driving the Z axis controller) so use an opto coupler (or similar device) to drive your relay from the +5v and Dir- terminals.

Tweakie.


Hi Tweakie.
I just asked this a moment ago, but on a very old thread. I think it's more appropriate to do it here, I hope you can help me.
Could you tell me why when I use this method, the laser stays on only a flash? The laser does not stay on for the entire path, only turns on for an instant.

Offline Tweakie.CNC

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Re: Laser control on and off using Z
« Reply #4 on: March 01, 2017, 01:40:54 AM »
Quote
Could you tell me why when I use this method, the laser stays on only a flash? The laser does not stay on for the entire path, only turns on for an instant.

Hi Boxin,

I can't explain that. The Direction signals are persistent (they will remain at the set TTL level until changed). I have never used a relay because of the switching delay introduced but I have never had any trouble switching my laser on / off just using TTL level signals.

Could you perhaps explain in a bit more detail how you are controlling your laser ?

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline boxin

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Re: Laser control on and off using Z
« Reply #5 on: March 01, 2017, 02:04:56 AM »
I'll try...

But I think that if the signal must be persistent, there must be the problem ...
My BOB is this (due to my laptop, I can not use the parallel port for a traditional one):

https://www.aliexpress.com/item/Factory-outlets-100KHz-CNC-mach3-USB-4-Axis-Stepper-Motor-Driver-Breakout-Board-USBCNC-Smooth-Stepper/32334451366.html?spm=2114.13010608.0.0.cJRtzN

Mi laser:

https://www.aliexpress.com/item/Focusable-450nm-2W-Laser-Engraver-445nm-2000mW-Blue-Laser-Diode-Module-with-TTL-for-CNC-Engrave/32745647304.html?spm=2114.13010608.0.0.bcOG86

The laser takes 12V from an ATX power supply.
To excite the TTL input of the laser, I am connecting a relay between + 5V and DIR- on my BOB (DIR- of Z & A axis, I have tried both).
This relay connects 5V from the same ATX power supply and sends them to the TTL input.

But beyond this connection, now I understand that the DIR signal must be persistent as you say (If I do not want to use some kind of monostable or flip-flop).
I have not measured the DIR-voltage changes, but I assume it will be almost imperceptible in my digital tester.
What I'm wondering is: is it possible that this USB BOB works differently than a traditional BOB via parallel port?
Would it affect Mach3 at all if the DIR signal is not persistent?
From what I could see when setting high values on the Z axis when the laser is turned on, it stays on during the travel of this axis. That's why there is only a flash when I want to activate it quickly.

What do you think?

Offline boxin

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Re: Laser control on and off using Z
« Reply #6 on: March 01, 2017, 02:15:24 AM »
One more thing. The outputs work properly, I mean, their signals are persistent (M3) until I turn them off (M5), I have used them for the laser but there was an unwanted response time, so my interest in using one of the axes (as everyone, I think).

Offline Tweakie.CNC

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Re: Laser control on and off using Z
« Reply #7 on: March 01, 2017, 02:15:54 AM »
Hi Boxin,

Firstly, connect a multimeter to the 5 Volt supply from your ATX and confirm that the voltage remains constant

If that is OK then measure the direction signal TTL voltage from your BoB - it could be that it does not have persistent TTL levels for the direction signal output (as you suspect).

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline boxin

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Re: Laser control on and off using Z
« Reply #8 on: March 01, 2017, 02:20:19 AM »
I'm at work right now, but I will.
However, as I said above, using the same ATX power supply and the outputs activated with M3 and M5, I had no problems. So I do not think the problem are the 5V.

Offline boxin

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Re: Laser control on and off using Z
« Reply #9 on: March 01, 2017, 02:24:23 AM »
Wait, please completely rule out a power supply fault.
Now I remember that at the recommendation of the seller of the laser, the only thing I'm doing with the relay is to join TTL- with TTL +, there is no need to send any level of voltage if it is working at all-nothing.