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Author Topic: Stepper Servo Hybrids with Mach 3  (Read 3269 times)

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Offline Storm

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Stepper Servo Hybrids with Mach 3
« on: October 19, 2015, 12:04:35 PM »
I was wondering if anyone has incorporated using stepper servo hybrid motors on their CNC.  The stepper servo hybrids have the encoders which would prevent your CNC from losing or missing steps.  I have seen some machines with these and give a encoder fault which in turn stops the machine.  It's an expensive upgrade but maybe well worth it.  I would want to tie that into the mach 3 software, through the BOB to accomplish this.  Would love some feed back from anyone who has done this already.  Thanks
Re: Stepper Servo Hybrids with Mach 3
« Reply #1 on: October 20, 2015, 04:27:38 AM »
The concept of encoder feedback into mach is incompatible with the basic design of Mach.
Can't be done.

Cheers
Roger

Offline RICH

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Re: Stepper Servo Hybrids with Mach 3
« Reply #2 on: October 20, 2015, 07:12:16 AM »
Proper tuning of the stepper motors will provide for accurate and  repeatable results without missing or  losing steps.
So in my mind  find the fault situation of no value.

FWIW,

RICH

Offline Storm

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Re: Stepper Servo Hybrids with Mach 3
« Reply #3 on: October 20, 2015, 08:17:23 AM »
2 great replies so far.  

I understand that Mach doesn't have the ability for encoder feedback. That is done in the servo controller.  The whole reasons for the stepper servo question are this.  1. A servo motor runs much cooler than a stepper.  2. A servo motor creates less noise than stepper. 3. You can use a smaller servo motor than a stepper because of the torque ratio.  I have been researching these hybrids and see more and more of them available and being used.  Another reason is that when you run 2 steppers in parallel this should prevent racking and possible damage to your machine.  It would also give you an early indication that there is a problem with you machine on any axis that needs to be addressed before it does any major damage.   These are all just questions in my mind and wanted to see if anyone out there had done this and what the results were.   It is a spendy option to do but in my opinion may be worth it in the long run.   Feedback is always welcome and wanted.  Thanks

Offline ger21

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Re: Stepper Servo Hybrids with Mach 3
« Reply #4 on: October 20, 2015, 08:50:35 AM »
1) Steppers are designed to run hot. There's no harm in them in them being hot. Not sure if these "hybrid" motors actually run cooler, because they are still steppers.

2) True, but I can't hear my steppers when the machine is cutting.

3) Your machine will require a certain amount of torque to achieve a certain performance goal. That torque doesn't change with a stepper or servo. To utilize a smaller servo, it must run at much higher rpm, and you need to add appropriate gear reduction.

4) My stepper driven gantry machine has never racked in the 7 years it's been running.

In my opinion, steppers with encoders is a fix to a problem with the user, not the machine.
A properly setup and maintained stepper driven machine should not lose steps, ever.

People lose steps mainly for one of two reasons.

1) They want the machine to go faster than their steppers are capable of. Adding "servo steppers" to this situation will result in drives that fault, rather than lose steps. Your losing steps from a lack of power. Adding the same size motors will still leave you with an underpowered machine.

2) There's a problem somewhere with the electronics. THis could be anything from the PC or mach3 not outputting signals properly, all the way to drives that are prone to resonance.


THese "hybrid" systems are not exactly cheap. For not much more money, you can get a real servo system which should provide much better performance, if the servos are sized properly.





Gerry

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Offline Storm

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Re: Stepper Servo Hybrids with Mach 3
« Reply #5 on: October 20, 2015, 12:59:14 PM »
Thanks again for the reply.  I'm always eager to learn and get info from others.  It's not that my machine is acting up but more my thought process in building my machine.  I have had these questions from the beginning and just never asked them.  

The one thing that would be helpful though to make sure my machine is operating at it's best is motor tuning.  I believe I have done it properly but ALWAYS open to suggestions.  Is there a guide to the proper tuning for MACH 3?   I am also still a novice, finished my machine just last fall and still learning.  Would absolutely love to make sure that it is at it's best and not what I think it should be.  My machine is based on the design from PDJ Pilot Pro with some changes.  
Re: Stepper Servo Hybrids with Mach 3
« Reply #6 on: October 20, 2015, 05:11:03 PM »
Quote
1. A servo motor runs much cooler than a stepper.
Mostly irrelevant. And a good stepper controller includes a 'power-down' feature to reduce the static power consumption.

Quote
2. A servo motor creates less noise than stepper.
Completely false today. Both use MOSFET switching controls, and BOTH generate a lot of RFI.

Quote
I have been researching these hybrids and see more and more of them available and being used.
That may be because a lot of machine mfrs still use encoder feedback into their main control board. That's an old (and cumbersome and expensive) design, but there are a lot of them around still.

Tuning:
This is done in the motor driver, not in Mach. Mach does not have the performance to run several axes of PID while doing everything else.
What you must check is whether you have told Mach to assume it can use too much acceleration. Telling Mach to exceed what your hardware can do and you WILL have problems.

Cheers
Roger


Quote
Another reason is that when you run 2 steppers in parallel this should prevent racking and possible damage to your machine.  It would also give you an early indication that there is a problem with you machine on any axis that needs to be addressed before it does any major damage.
Better to fix your machine first. But it rarely happens anyhow with a well-designed machine.

Offline BR549

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Re: Stepper Servo Hybrids with Mach 3
« Reply #7 on: October 20, 2015, 05:55:07 PM »
IF you are just interested in being alerted to a missed step you can the Rogers machine board to read encoders and report back any missed steps and stop Mach3. It may even offer a reset and restart function to correct for missed steps.

Just a thought, (;-) TP

Offline Mc2

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Stepper Servo Hybrids with Mach 3
« Reply #8 on: October 30, 2015, 08:02:32 PM »
Just wanted to let you know that I have started using clearpath motors from Teknic. These would fall under the hybrid you are talking about. The SDSK motors work great.  I will never buy another stepper motor.  The enhanced ver. has 6,400 steps per rotation of the motor. The motor is a self contained unit with two connectors. One for signal and one for power. You will need to send an enable signal, step, and direction. If there is a fault a feeback signal can put mach into a reset state.  I used an ESS smoothstepper as a printer port is too slow to provide the pulse stream. They are worth looking into.

Jim.