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soildruper
06-01-2008, 06:24 PM
Hi all.

I have a Closed Loop Servo MicroMill DSLS 3000 running Mach3 and DeskProto.

I have seen some pretty nice home made automatic Z axis tool setters being used with Taig CNC mills/ Mach 3. The concept seems simple enough but what these videos never show is where do you plug in the wire so Mach 3 knows where to set the Z? Do you plug into your CNC control box or plug into your computer? Anyone have any links about this?
Here is a link that shows what I want to do-
YouTube - CNC Mill Auto Tool Zero Mach3


My second question is about the Taig machine limits. I assume when you max out any of your axis a switch is triggered. Say I accidentally max out my X axis and I get a Limit switch triggered, does Mach3 or the CNC controller sense the resistance and stop the operation or is there a switch being triggered? If there is not a switch should I consider installing some?

Third question is about the "hybrid" stepper motors with servo encoders. Are these in fact better than a straight servo motors?


Thanks in advance for your time!

Vince

Stepper Monkey
06-01-2008, 07:39 PM
"Hybrid" steppers are a type of motor design, the most commonly used type for CNC machines. They have nothing to do with servos, they are simply a standard type of stepper. Putting rotary encoders on a stepper motor is redundant, and gives no better accuracy than a standard stepper system. If the stepper system is properly designed and installed, adding shaft encoders actually serves no measurable purpose at all.
It would require linear, not rotary, encoders on a stepper system to have a feedback setup that increases accuracy or in any way tells you anything you don't already know. Those are much more expensive though. The rotary encoders are primarily for window dressing - it's just for marketing really.
Just treat it like a standard stepper system, which is in itself a perfectly adequate system for this machine.

fretsman
06-01-2008, 08:25 PM
wow, talk about feeling like a sucker for buying one of these myself....... :(

soildruper
06-01-2008, 08:37 PM
Thanks for the reply stepper monkey.

So the rotary encoder does not give you a closed loop system? It is my understanding that if I miss a step the servo rotary encoder on the stepper will notice missed step and the step/ tool path will be corrected.

Any input on my other two questions listed below would be greatly appreciated!

Vince

phomann
06-01-2008, 10:07 PM
wow, talk about feeling like a sucker for buying one of these myself....... :(


Don't feel too bad. Encoders on steppers do have a useful purpose unlike what Stepper Monkey is saying. Yes, if you set everything up correctly, use the correct speeds and feeds then you don't need encoders on steppers. In the same vain, you don't need seatbelts in cars, if every one and everthing does the right thing.

Yes you won't get any additional accuracy. And BTW, a servo is only as accurate as the encoder it uses.

Encoders on steppers such as in the Taig setup monitor the actual position vs the expected position, and if they vary by a certain amount, an estop is generated. This feature alone can save you a lot of time and money.

If you break a bit or it goes blunt, you have less chance of ruining your work.

As to the closed loop label, the stepper movement is monitored and controlled by what the encoder is doing, and so is closed loop

It's just that all closed loops are not the same. :-)

I hope you feel a bit better now.

Cheers,

Peter.

Stepper Monkey
06-02-2008, 03:13 AM
So the rotary encoder does not give you a closed loop system? It is my understanding that if I miss a step the servo rotary encoder on the stepper will notice missed step and the step/ tool path will be corrected.

I guess I should clarify; this type of system has some useful features, they just aren't useful as regards cutting accuracy.

The system will indeed notice missed steps, though will not usually be able to correct for them, only stop and warn you of the failure instead of continuing. It would only be possible for it to correct in mid-cut and continue on only if steps could just "miss" randomly in mid-cut. This is virtually impossible with properly functioning and well-maintained equipment. Steps don't just "miss" by themselves, ever. You first have to either a) have broken/malfunctioning equipment, or b) have crashed the machine. In this case, rotary encoders can be very useful to help recover from a hard crash without losing your starting place. There is no mid-cut correction, however, a system like this only can normally only come into play during a hard failure condition.

They don't help accuracy, however, as unless something is broken or you exceed force the motor is able to overcome, if you tell a stepper to step, it does. If it steps, it steps a fixed known amount, no more and no less. This is what they do. This is why a shaft encoder can be relatively redundant while the machine is running as you already know what the motor is doing. Just because the motor moved a known amount doesn't tell you the actual table has moved the right amount, however. Backlash and the like are not taken into account with a rotary encoder. It only tells you what the motor did, which like I said before you already know to a pretty exacting degree as steppers have zero repeating error by definition. The errors are induced elsewhere in the system not covered by a rotary encoder.

It is possible to cause a motor to lose steps by exceeding the force the motor can exert, but with the mechanical advantage of 20tpi screws and the small diameter tools on a Taig sized mill, the hundred+ pounds of required force to jump steps will inevitably snap or stall a bit and ruin the cut well before the motor gives way and loses position. In other words, if steps got missed and this sort of feedback system ever comes into play, something else was already causing a catastrophic failure.

The example of a seatbelt was appropriate in that the encoder system CAN indeed be useful for recovering from crashes and other equipment/tool failures, but will not prevent them. Also like a seatbelt, it does nothing during any normal operation state.

It isn't that they aren't quite useful, their purpose just isn't related to accuracy.

fretsman
06-02-2008, 10:38 AM
I hope you feel a bit better now.

Cheers,

Peter.

Yes, sir, a bit, as I guess to truly appreciate the whole idea of the system would be for me to have a taig setup that didn't have the encoders to help stop the program when a problem arose. This will indeed be the case because this is very addicting and I will be building my own in the future without any sort of encoder, as I've learned so much from all of you here.

Thanks again for your explanation-

soildruper
06-02-2008, 07:23 PM
Thanks to Phomann and Stepper Monkey for the information.

Does anyone have any input on my other two questions?-

I have seen some pretty nice home made automatic Z axis tool setters being used with Taig CNC mills/ Mach 3. The concept seems simple enough but what these videos never show is where do you plug in the wire so Mach 3 knows where to set the Z? Do you plug into your CNC control box or plug into your computer? Anyone have any links about this?


My second question is about the Taig machine limits. I assume when you max out any of your axis a switch is triggered. Say I accidentally max out my X axis and I get a Limit switch triggered, does Mach3 or the CNC controller sense the resistance and stop the operation or is there a switch being triggered? If there is not a switch should I consider installing some?


Thanks again for all of the help!

Vince

phomann
06-02-2008, 08:10 PM
Thanks to Phomann and Stepper Monkey for the information.

Does anyone have any input on my other two questions?-

I have seen some pretty nice home made automatic Z axis tool setters being used with Taig CNC mills/ Mach 3. The concept seems simple enough but what these videos never show is where do you plug in the wire so Mach 3 knows where to set the Z? Do you plug into your CNC control box or plug into your computer? Anyone have any links about this?


My second question is about the Taig machine limits. I assume when you max out any of your axis a switch is triggered. Say I accidentally max out my X axis and I get a Limit switch triggered, does Mach3 or the CNC controller sense the resistance and stop the operation or is there a switch being triggered? If there is not a switch should I consider installing some?


Thanks again for all of the help!

Vince

Hi Vince,

The toolsetter input goes into one of Machs inputs, then when the tool touches the sensor, the circuit is closed and Mach knows where it is.

As to limit switches there are a lot of options, some use opto switches, some use micro switches. Me, I use nothing as no harm is done by stalling a motor into a stop. Just harm to my pride. :-)

The best thing to do is look through the photos on the taigtools yahoo group.

Cheers,

Peter.

soildruper
06-02-2008, 09:45 PM
Thanks again Phomann,

Sorry I'm a newbie. Where exactly is the mach 3 input? Do I route the input through my controller or route through my computer? I have no idea about this.

When I hit a physical limit on any of the axis I am stalling my motor and doing no harm to my encoded steppers?

Thanks agian for the help and advice!

Does "Phomann" stand for Pho the vietnamese soup?

Vince

phomann
06-02-2008, 10:19 PM
Thanks again Phomann,

Sorry I'm a newbie. Where exactly is the mach 3 input? Do I route the input through my controller or route through my computer? I have no idea about this.

When I hit a physical limit on any of the axis I am stalling my motor and doing no harm to my encoded steppers?

Thanks agian for the help and advice!

Does "Phomann" stand for Pho the vietnamese soup?

Vince

Hi Vince,

In Mach3, go to config>ports&pins>inputs There you will see the list of possible inputs. You can assign them to certain pins on the parallel printer port. Some of them will already be used. I don't know how may Taig use for feeding an encoder detect error into Mach. Each parallel port only has 5 inputs.

There is also the diagnostic page in Mach. It shows you what the state of the inputs and outputs are.

If there is a spare input, it should be accessible through your Taig controller box. Does it have a connector on it for aux inputs and outputs? If so it wuld be connected through there.
There are guys on the taigtools Yahoo group who also have the same controller as you, it may be better to ask your questions there.

Also you really need to read the Mach3 manuals. They are at;
http://www.machsupport.com/documentation.php

You won't do any harm to the encoder or stepper by stalling a stepper. Also the encoders will shutdown the steppers soon after as it will detect a position loss.

phomann stands for Peter Homann.

Cheers,

Peter.

fretsman
06-03-2008, 12:34 PM
Vince, I also may be of help to you down the road as I'm working on connecting a touch off plate for this system. I'll be sneaking into the 8 pin connector on the back of the controller - ;)

I had some luck last night with a touch test so hopefully it's only a matter of time now. I'll post a thread here in the benchtop area when I get it down to how I want it.

awerby
06-11-2008, 06:56 PM
My second question is about the Taig machine limits. I assume when you max out any of your axis a switch is triggered. Say I accidentally max out my X axis and I get a Limit switch triggered, does Mach3 or the CNC controller sense the resistance and stop the operation or is there a switch being triggered? If there is not a switch should I consider installing some?



Vince[/QUOTE]

[Taigs don't come with limit switches, and the DSLS system uses the limit switch function in Mach to trigger an error shutdown if there is a discrepancy of a certain number of steps between commanded and recorded positions. So if you're getting "limit switch" errors, that's what's happening.

If you want a limit switch function, you can set the "soft limits" in Mach to trigger errors at the extremes of travel in any axis. But steppers, as was mentioned, don't have a big problem when they are commanded to go somewhere and hit an immovable obstacle partway there. Servos are different; they'll kill themselves or break something trying to get there; steppers are easier to work with in this regard.]

Andrew Werby
www.computersculpture.com