Benefits of Clearpath servos?

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Reedfirst
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Re: Benefits of Clearpath servos?

Post by Reedfirst »

I just wanted to add to my statement above.

I'm getting 330ipm with a 2:1 reduction and 5 tpi ballscrews.

Running on 120vac
frijoli
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Re: Benefits of Clearpath servos?

Post by frijoli »

Reedfirst wrote: Wed Nov 22, 2017 8:12 am I just wanted to add to my statement above.

I'm getting 330ipm with a 2:1 reduction and 5 tpi ballscrews.

Running on 120vac
What drive and motor?
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Re: Benefits of Clearpath servos?

Post by Reedfirst »

The drives are DMM Dyn4' and the servo motors are their 86M-DHT .75kw (750w)
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Re: Benefits of Clearpath servos?

Post by DocsMachine »

Okay, let me ask you (the collective "you" :) ) this: In the video on setting up an Acorn (the single-axis demo) we see a stepper skipping or stuttering if the controller tries to drive it too fast. And this is adapted for by limiting the maximum speed of the stepper (presumably by limiting the rate of or number of steps sent to the driver.)

Do the closed-loop steppers have to be similarly "tuned"? Can they be driven faster thanks to the closed loop, since the driver can adapt/adjust for any skips or missed steps? (Which is, after all, the reason for a closed-loop system.)

If we try to drastically overdrive the stepper (in closed loop mode) and the stepper driver has to do a lot of extra work (adding or restricting pulses in order to smooth out the chatter) would it potentially get out of place, since doing that would almost certainly take longer than running the signal straight? (Basically, could that axis "lag" compared to the other, or to the spindle?)

As I understand it there's no feedback to the Acorn board, the stepper encoder is only feeding back to the stepper driver. It seems it'd still be possible to send more signals to the driver than the stepper could handle. (I'm also presuming that limit would be pretty high, but at the moment, this is all just spitballing anyway. :) )

Doc.
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Re: Benefits of Clearpath servos?

Post by frijoli »

DocsMachine wrote: Fri Nov 24, 2017 3:44 am Okay, let me ask you (the collective "you" :) ) this: In the video on setting up an Acorn (the single-axis demo) we see a stepper skipping or stuttering if the controller tries to drive it too fast. And this is adapted for by limiting the maximum speed of the stepper (presumably by limiting the rate of or number of steps sent to the driver.)

Do the closed-loop steppers have to be similarly "tuned"? Can they be driven faster thanks to the closed loop, since the driver can adapt/adjust for any skips or missed steps? (Which is, after all, the reason for a closed-loop system.)

If we try to drastically overdrive the stepper (in closed loop mode) and the stepper driver has to do a lot of extra work (adding or restricting pulses in order to smooth out the chatter) would it potentially get out of place, since doing that would almost certainly take longer than running the signal straight? (Basically, could that axis "lag" compared to the other, or to the spindle?)

As I understand it there's no feedback to the Acorn board, the stepper encoder is only feeding back to the stepper driver. It seems it'd still be possible to send more signals to the driver than the stepper could handle. (I'm also presuming that limit would be pretty high, but at the moment, this is all just spitballing anyway. :) )

Doc.
Short answer is any motor can be put in that position.
In the case of overloading a stepper with closed loop, the drive "knows" when it failed to reach the intended point based on the feedback from the encoder.
There are several things that can happen after the overload, but I have always seen a fault signal sent out and the drive stops sending pulses. That is dependent on how the drive is configured to handle the following error, and there is usually a tolerance built in to how many pulses it can miss before the fault. If it's within tolerance and the overload goes away, the drive will attempt to catch up.

That is the simplified explanation, and I don't have a lot of experience with closed loop steppers, but that is how most servos that I have dealt with react.

There should be current and voltage monitoring(limiting) in the drive as well, so even if the motor is following but the power has reached it's limit it may fault as well. Again, this is based on servo drives, but they use the same philosophy.

Clay

PS
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Re: Benefits of Clearpath servos?

Post by martyscncgarage »

DocsMachine wrote: Fri Nov 24, 2017 3:44 am Okay, let me ask you (the collective "you" :) ) this: In the video on setting up an Acorn (the single-axis demo) we see a stepper skipping or stuttering if the controller tries to drive it too fast. And this is adapted for by limiting the maximum speed of the stepper (presumably by limiting the rate of or number of steps sent to the driver.)

Do the closed-loop steppers have to be similarly "tuned"? Can they be driven faster thanks to the closed loop, since the driver can adapt/adjust for any skips or missed steps? (Which is, after all, the reason for a closed-loop system.)

If we try to drastically overdrive the stepper (in closed loop mode) and the stepper driver has to do a lot of extra work (adding or restricting pulses in order to smooth out the chatter) would it potentially get out of place, since doing that would almost certainly take longer than running the signal straight? (Basically, could that axis "lag" compared to the other, or to the spindle?)

As I understand it there's no feedback to the Acorn board, the stepper encoder is only feeding back to the stepper driver. It seems it'd still be possible to send more signals to the driver than the stepper could handle. (I'm also presuming that limit would be pretty high, but at the moment, this is all just spitballing anyway. :) )

Doc.
Short answer is if you push a closed loop device, eventually the excessive following error will cause the drive to fault and stop. The fault should be wired as an alarm to the Acorn input. (Drive Fault)

A following error is a threshold value set in the software. Simply, if a pulse stream to a drive/motor from the motion controller, the motor driver attempts to turn that motor and receives feedback from the motor's encoder to ensure that the motor turned the commanded position. If it fails to do so, or can't keep up, after the following error threshold is exceeded, the drive will fault because it can't keep the motor in position. So you still have to size the motor appropriately.

An open loop stepper design is sized to usually be 20-30% greater than necessary for the application. This allows for a performance "cushion" so that the motor operates the machine within its designed torque requirements. A closed loop system will monitor motor position and try to maintain position. As long as the "advertised" torque rating is accurate, you should be able to use a closed loop motor derated from the original open loop stepper by about 20% (I belileve that Teknic Clearpath SDSK mentions this in their literature)

Did I explain it well enough? Lots of info out there on "Following Error"


Marty
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Re: Benefits of Clearpath servos?

Post by frijoli »

Lots of short answers out there. lol
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Re: Benefits of Clearpath servos?

Post by Gary Campbell »

Doc...
I have used a number (each) steppers, closed loop steppers,Clearpath and the DMM products in various sytems and hopefully can answer your questions.

Do the closed-loop steppers have to be similarly "tuned"? No they do not.

Can they be driven faster thanks to the closed loop, since the driver can adapt/adjust for any skips or missed steps? (Which is, after all, the reason for a closed-loop system.) The encoder and internal circuitry does not add speed

If we try to drastically overdrive the stepper (in closed loop mode) and the stepper driver has to do a lot of extra work (adding or restricting pulses in order to smooth out the chatter) would it potentially get out of place, since doing that would almost certainly take longer than running the signal straight? (Basically, could that axis "lag" compared to the other, or to the spindle?)
Once the error threshold has been exceeded, the drive will alarm and shut down. It will also activate the alarm signal and in a properly configured system should work similar to an ESTOP.

As I understand it there's no feedback to the Acorn board, the stepper encoder is only feeding back to the stepper driver. It seems it'd still be possible to send more signals to the driver than the stepper could handle. (I'm also presuming that limit would be pretty high, but at the moment, this is all just spitballing anyway.
There is no encoder feedback to the acorn, but I am assuming that appropriate alarm actions can be or are included as part of the Acorn canned actions. At the very least the drive alarm circuits can be connected via a relay to the estop circuit stopping the machine if a drive alarms out.

Hope this helps
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Re: Benefits of Clearpath servos?

Post by martyscncgarage »

Great explanations Gary!
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