Controller Confusion

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Controller Confusion

Postby Patrick34 » Mon Feb 06, 2012 1:58 am

In the near future I intend to build my first laser cutter. I am very familiar with running cnc machines, but not so much into what is in the cabinet. My understanding of the electronics its this: computer>breakout board>stepper driver>motor. This represents the basic structure for the electronics on a standard cnc setup.

My confusion is when it comes to using a DSP. At first I though this replaced everything and could directly control the motors, but I have read a few things and now I am confused. Does the DSP only actually replace the computer, and you still need something like the Gecko G540 to control your motors?

Also, I am now reading that the new DSP does not work well with the G540. It now requires extra circuitry to avoid offsetting that many are getting (and some are not aware of). Something to do with opto-isolators instead of using ground like the old DSP.

Any clarification here would be appreciated.
-Patrick-

"Measure twice, cut once."
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Re: Controller Confusion

Postby twehr » Mon Feb 06, 2012 2:26 am

Think of it this way:

Traditional CNC: Design -> Conversion to GCode -> Mach3 -> Breakout board -> Drivers -> Motors
DSP uses proprietary software to replace step 2 and a controller board to replace the 3rd and 4th steps - so it is: Design -> LaserCAD Software -> Controller -> Drives -> Motors

PHCad is somewhat capable of replacing the Design step as well, but not adequate for most professional use.

I believe it is true that the DSP does not directly support the Geckos. Most other tradition drives are fine, as well as the BuildLog 4 axis drive board that works exceptionally well on the 2x.
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Re: Controller Confusion

Postby Greolt » Mon Feb 06, 2012 3:12 am

twehr wrote:
I believe it is true that the DSP does not directly support the Geckos.


This is not actually correct.

Gecko stepper drives come in two different flavours as far as signal connection.

One is Step - Direction - 5v

The other is Step - Direction - Ground (0v)

Despite what may be commonly said, both of these signal types are very common in step and direction motion control.

I have recently had it confirmed by the DSP engineer that either connection type is supported by the DSP. (as you would expect)

However the G540 is a case on its own. It is a LPT interface with four stepper drives integrated into one unit.

I have not looked into it, to see how you could drive it with something like the DSP

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Re: Controller Confusion

Postby Patrick34 » Mon Feb 06, 2012 3:18 am

So just so I am clear on this, the DSP gets the stepper drivers directly connected and functions as the PC and breakout (with laser power control as well)...

That seems to lead into why it is not a good idea to use the G540 because you are sort of piggybacking two controllers...

Thanks
-Patrick-

"Measure twice, cut once."
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Re: Controller Confusion

Postby Patrick34 » Mon Feb 06, 2012 3:52 am

Are there things you can do using traditional g&m code/CAM software setup that you cannot do so well with the DSP?

My impression of the DSP is that it is great for quickly get up and running, and an insane time saver when engraving. How is the DSP at precisely placing your work to a given coordinate? Does it still work based on the xy coordinate system with origins and work offsets? Or is it more of an "Ah, that seems like its where I want it." approach? Are you forever set to run test cuts to see if the cut is "scaled" correctly before running your parts?

I guess another way to ask is, if I wanted to cut a bunch of 1" squares, and accounting for the kerf width of the cut, will the DSP always cut 1" squares, or will I have to scale the size up or down every time I turn the machine on to run it?

I ask this because I worked at a place that had a commercially built laser cutter that we had to vary the DWG scale from 85 - 110% to get our parts to come out to the correct size, and it placed the part arbitrarily in the stock (drag and drop style). While many times this did not matter, sometimes it did and resulted in lots of wasted material and time.

It may be that it was so long ago that this is no longer any sort of issue with small laser cutter.

Has anyone done a dual controller setup where you can switch the DSP off and run a G540 with Mach3 as well?

Steer me in the right direction if I'm way off base with these thoughts.
-Patrick-

"Measure twice, cut once."
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Re: Controller Confusion

Postby Greolt » Mon Feb 06, 2012 3:57 am

Patrick34 wrote:
That seems to lead into why it is not a good idea to use the G540 because you are sort of piggybacking two controllers...


I wouldn't say it is not a good idea.

Just that I have not personally looked into how you would do it.

The G540 is not a controller, it is just a bank of stepper drives with an integrated BoB.

A BoB, as referred to here, is just an interface for a LPT connection, with some handy connection for IO. Usually buffered and sometimes isolated.

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Re: Controller Confusion

Postby twehr » Mon Feb 06, 2012 1:29 pm

DSP does not have any tooling offset. It cuts center-line on what ever line you design. Therefore, it is necessary to do your compensation in the design software. In CorelDraw, for example, you can apply a Contour set to half the width of your kerf (beam) and that works well. When I need accuracy, I design -> compensate -> send the job.

As for the positioning ... I find the DSP to be extremely good. You have machine zero (0,0) and your job origin set as needed. In the previous version of the DSP (which I have), you have to move the head to the specific spot you want and then set the origin at that location. Every reset and after each job run, the head automatically returns to the origin. To get there in the first place, I go to 0,0 and then enter the distance I want to move (to get to my desired origin), move the head x, reset the distance if necessary and move head to y, set origin and run the job. Its precision is very good.

I believe the newer version of the DSP allows you to have multiple origins and MAY (I am not sure) allow you to more easily and directly enter the position you want to move the head to - I requested that functionality several times.

Regardless of what controller you end up with, you will have to learn how to make it do what you need. Once you do that, it will work great for you, I believe.
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Re: Controller Confusion

Postby Patrick34 » Mon Feb 06, 2012 8:05 pm

Thank you. That is most helpful. It sounds as though these things have come a long way since I last dealt with one. I am now further reassured that starting with the DSP is indeed the best way to go.
-Patrick-

"Measure twice, cut once."
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Re: Controller Confusion

Postby Speedythinker » Mon Feb 06, 2012 8:47 pm

twehr wrote:DSP does not have any tooling offset. It cuts center-line on what ever line you design. Therefore, it is necessary to do your compensation in the design software. In CorelDraw, for example, you can apply a Contour set to half the width of your kerf (beam) and that works well. When I need accuracy, I design -> compensate -> send the job.


Tim:

There is a new feature on the new software V5.85. It allow you to set "offset" in either direction: Expanding or shrinkage. By doing so, you can offset as much you want by enter a number on a input box. Assuming that the diameter of light beam burning is 0.1mm, so you will end up lost 0.05mm after cutting. In that case, you set +0.05 and the whole object that being cut will be stratch out(expand) by 0.05mm to offset the lost of 0.05mm materials by the laser.

My post: http://www.lightobject.info/viewtopic.php?f=8&t=964

Is it something you're talking about?

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Re: Controller Confusion

Postby twehr » Mon Feb 06, 2012 11:17 pm

Speedythinker wrote:
twehr wrote:DSP does not have any tooling offset. It cuts center-line on what ever line you design. Therefore, it is necessary to do your compensation in the design software. In CorelDraw, for example, you can apply a Contour set to half the width of your kerf (beam) and that works well. When I need accuracy, I design -> compensate -> send the job.


Tim:

There is a new feature on the new software V5.85. It allow you to set "offset" in either direction: Expanding or shrinkage. By doing so, you can offset as much you want by enter a number on a input box. Assuming that the diameter of light beam burning is 0.1mm, so you will end up lost 0.05mm after cutting. In that case, you set +0.05 and the whole object that being cut will be stratch out(expand) by 0.05mm to offset the lost of 0.05mm materials by the laser.

My post: http://www.lightobject.info/viewtopic.php?f=8&t=964

Is it something you're talking about?

Marco


Excellent. I have been trying to keep up with the info on the latest version. Maybe you should GIVE me one so I don't misspeak! :mrgreen:
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