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Author Topic: Buying DSPMC - Why would I need Analog Inputs?  (Read 1955 times)
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pofo
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« on: September 13, 2010, 12:30:58 AM »


I'm about to buy a DSPMC. I have a Bridgeport mill with 3 axis motors/amplifiers waiting for a controller. I plan to start with the 3 axis and may expand to 4 axis. The motors are driven by +/-10V amplifiers.

There are two DSPMC; the cheaper has no analog input and the more expensive one has 8 analog input. I don't see any reason I would need analog inputs for this application, but before I buy, I want to be sure there isn't some future feature I may want to add that would require the analog inputs.

Are there any comments on why I might want to consider getting the analog input option?

Thanks,
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hanglide
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« Reply #1 on: September 13, 2010, 05:34:20 AM »

Disclaimer:  I know only what I've read about the DSPMC motion controller on their website so I'll reply in general terms only. 

Full disclosure: While I represent a company that sells another control, I'm simply trying to help answer your original question and I'm not trying to convince you to buy anything.


That said, there are several reasons why you may need an analog input and many reasons why you may not.


Reasons you may need an analog input:

1. Some BOSS machines return a 0-10VDC value that can be used to determine a rough spindle speed.  (from a pot on the vari-speed)
    You could use this, combined with the speed/up down solenoids to control spindle speed, in a rudimentary way.

2. An analog input can be used to display spindle load on the screen -either via an output from a VFD or directly through the use of a shunt.

3. Feedrate/Spindle Override knobs

4. For specific applications-thousands of reasons: Torch height control, flow rate monitoring etc.. etc..

Reasons you may not need an analog input:

1.  Spindle speed is probably better controlled through the use of an Inverter/VFD.  Also, do you really need spindle speed control on a knee mill?  You have to manually change the tools anyway -How hard is it to adjust the spindle speed when doing the tool change?

2.  Feedrate/Spindle Override - Mach allows you to control both through onscreen controls.  Unless you really want to use knobs (and it's understandable if you do) you can just use the onscreen controls. 

3.  Specific applications -that's up to you to decide if you need (or may need) something out of the ordinary for you knee mill.

Regards

Scott


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pofo
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« Reply #2 on: September 13, 2010, 09:31:22 AM »


Thanks Scott,

That's just what I was looking for. Some examples of uses for the analog inputs.

Much appreciated.
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Chestermarine
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« Reply #3 on: September 13, 2010, 12:58:49 PM »

Regarding analog input, I think the more expensive control is worth the increased cost. In the final machine modification total cost, the analog I/O controller is relatively small.
All commercial machines use knobs for spindle speed, feedrate modification, and analog motor load meters etc.

I have two commercially built CNC mills. When running a new program, you are always watching the cutting tool, with one hand on the feedrate knob, in case the cutter feed, or spindle speed is too high. You can tell a lot just watching and listening. A tool can break in an instant, if a particular spot loads up the tool. It is easy to just crank down the feedrate, and edit the program later. Much less effort, than installing a new cutter, cleaning out the broken tool bits, resetting the tool offsets, and going back to the beginning, and possibly having to reset the machine home position. All this if you did not scrap the part!!

Looking up at the screen, and using the feedrate jogs is way too cumbersom, and takes longer. Look at all the posts asking how to add a spindle speed, or feedrate and what hardware to use.

I own a dspmc controller without analog, and wish I had opted for it. The controller is absolutely amazing.  Plus, it is a great company always working to improve the firmware, willing to answer any question you may have. 


Regards,
John









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pofo
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« Reply #4 on: September 13, 2010, 06:13:12 PM »


Thank you John. Good notes.
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