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Re: Any word on the I/O expansion acorn board.
Posted: Fri Jan 04, 2019 11:04 am
by cnckeith
Re: Any word on the I/O expansion acorn board.
Posted: Fri Jan 04, 2019 2:25 pm
by Wolfenstien
cnckeith wrote: ↑Fri Jan 04, 2019 11:04 am
shooting for $225 ish...
Thanks for the response Keith.
Since this board wasn't out when I did my SL1H conversion I went with the Oak board. (Retrofit status: in progress) I also have a Mori SL2-B (Chucker lathe) That is a bit heavier that will be retrofitted if I get to it. Once this board comes out my understanding is this will make retrofitting these simple 2 axis lathes with turrets within the scope of the Acorn board.
Can you list any specifics reasons that would still make Oak (or ALLINONE) the preferable choice on these more industrial grade machines?
Re: Any word on the I/O expansion acorn board.
Posted: Fri Jan 04, 2019 2:36 pm
by cnckeith
yeah..number one reason is that both OAK and ALLin1DC are both real closed loop cnc controllers.
Re: Any word on the I/O expansion acorn board.
Posted: Fri Jan 04, 2019 10:00 pm
by Wolfenstien
cnckeith wrote: ↑Fri Jan 04, 2019 2:36 pm
yeah..number one reason is that both OAK and ALLin1DC are both real closed loop cnc controllers.
In my case despite using an oak board I used dmm servos. So an acorn probably would work fairly equivalently would you agree. Of course if I ever needed it I can drop in yaskawa replacements and go full featured on the oak.
Re: Any word on the I/O expansion acorn board.
Posted: Fri Jan 18, 2019 11:22 am
by cbb1962
cnckeith wrote: ↑Fri Jan 04, 2019 2:36 pm
yeah..number one reason is that both OAK and ALLin1DC are both real closed loop cnc controllers.
What exactly does that mean?
If I am using the same servo motor and controllers on two different systems:
- The first is configured for step & direction commands and connected to an Acorn.
- The second is configured for either velocity or position mode and connected to an Oak.
What are the net differences? I know the Acorn doesn't actually get feedback that the requested moves were completed, and I'm guessing that the Oak receives feedback directly from the encoder.
Re: Any word on the I/O expansion acorn board.
Posted: Fri Jan 18, 2019 11:38 am
by martyscncgarage
cbb1962 wrote: ↑Fri Jan 18, 2019 11:22 am
cnckeith wrote: ↑Fri Jan 04, 2019 2:36 pm
yeah..number one reason is that both OAK and ALLin1DC are both real closed loop cnc controllers.
What exactly does that mean?
If I am using the same servo motor and controllers on two different systems:
- The first is configured for step & direction commands and connected to an Acorn.
- The second is configured for either velocity or position mode and connected to an Oak.
What are the net differences? I know the Acorn doesn't actually get feedback that the requested moves were completed, and I'm guessing that the Oak receives feedback directly from the encoder.
You got it right
Open loop (usually step and direction), motion controller sees no feedback. Commands signals to the motor drive. Has no idea if the motor turned what it was told to. You could "miss steps" and keep cutting the part, then you see the artifacts of a missed step, ruining the part.
Closed loop (OAK and All in One DC fall into this category), motion controller sees feedback via encoders. Commands signals to the motor drive, watches encoders to see if the motor moved as director or needs a "PUSH" to get there and does so. If motor stops and does not complete the move, drive or motion controller faults and stops motion.
Hybrid (usually step and direction control), motion controller does not get feedback. However there is an encoder on the motor, which provides feedback to the axis motor driver. Acorn sends step and direction pulses to the motor drive, drive commands the motor to move, watches the motor to see if it turns the commanded number of turns, if the motor is lagging a bit, drive will push harder to get it there. If motor can't drive faults and lets Acorn know there is a fault, halting motion.
That's the short answer?
Re: Any word on the I/O expansion acorn board.
Posted: Fri Jan 18, 2019 11:45 am
by cbb1962
So, would a hybrid step/direction servo system be equivalent to a full-blown closed loop system?
Would there be any noticeable performance/accuracy differences?
Re: Any word on the I/O expansion acorn board.
Posted: Fri Jan 18, 2019 4:21 pm
by Gary Campbell
cbb1962 wrote: ↑Fri Jan 18, 2019 11:45 am
So, would a hybrid step/direction servo system be equivalent to a full-blown closed loop system?
Of Course. Its the "steppers vs. Servos" conversation. Servos have continuous torque, steppers only put out 10-35% of their advertised holding torque
Would there be any noticeable performance/accuracy differences?
Yes. Most servos have 2-5 times the available power of steppers (same size range) Servos usually have higher encoder capabilities, steppers have reduced torque with each level of increased microstepping
Re: Any word on the I/O expansion acorn board.
Posted: Fri Jan 18, 2019 6:01 pm
by cbb1962
Gary thanks for the explanation.
Let me clarify, I wasn't asking about the performance/accuracy differences of a servo vs. stepper. I was trying to compare apples to apples, or more accurately Acorns to Oaks.
For Example:
Yaskawa Sigma5's configured for step/direction on an Acorn.
VS.
Yaskawa Sigma5's in a fully closed-loop configuration on an Oak.
Will there be any performance or accuracy differences between the Acorn and Oak setups?
On a 3-axis machine that has a Sigma5's and an Acorn (if the I/O stays the same) is there ever a use-case to upgrade to an OAK? I'm trying to understand when an Oak is the correct choice. From what I gather; it's the correct choice if you need more than 4-axis, more I/O, need to attach additional encoders, what am I missing?
Re: Any word on the I/O expansion acorn board.
Posted: Sat Jan 19, 2019 7:24 am
by martyscncgarage
cbb1962 wrote: ↑Fri Jan 18, 2019 11:45 am
So, would a hybrid step/direction servo system be equivalent to a full-blown closed loop system?
Would there be any noticeable performance/accuracy differences?
No. It would not be "full blown closed loop" Why? Because the motion controller does not receive the encoder feedback.
Is it just as accurate? Yes, in my opinion it could be, provided the signals are clean and accurately delivered to the Axis motor drive. That would require you to use proper shielding and wiring practices.
The other differences are how much IO you need. Do you need dual handwheels(MPGs or manual pulse generators which are basically encoders) for a CNC lathe? Do you need a different signal to drive a spindle motor? Do you need more than 4 axis of motion control? Do you need more I/O? Is it a complex machine? Those sorts of applications would drive me to OAK or All in One DC(if it had good DC brush servos)
I hope this helped answer your question.
Marty