For a 5-axis milling machine, all things being equal, which controller would provide the best machined surface-finish quality for injection mold cavity work, and why exactly would that be?
1) Hickory controller running Sigma-7 drives via EtherCat, with external/secondary encoders on all 5 axis.
2) Acorn Six controller running Sigma-7 drives via pulse/step, with external/secondary encoders on all 5 axis.
I'm pretty certain the answer is Hickory... Would this be mostly because of:
1) Acorn Six's MPU 12 processing power vs. Hickory's MPU 13?
2) Acorn Six's maximum pulse frequency (per axis? total?) vs. Hickory's resolution/frequency?
3) Acorn Six's maximum encoder input frequency (per axis? total?)... vs. Hickory?
4) Any kinds of latency/ synchronization/ etc, issues that start showing up in surface finishes as speeds get higher with complex tool paths?
5) Any other factors I don't know enough about to even ask a question about?
Hickory or Acorn Six, for mold cavity surface finish?
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Hickory or Acorn Six, for mold cavity surface finish?
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Re: Hickory or Acorn Six, for mold cavity surface finish?
HICKORY can use higher resolution encoder data because of the way data is communicated with the drives. Acorn Six will need resolution divided down in the drives to lower the edge rate of quadrature or step command signals to the drives (a speed vs resolution tradeoff). For a high performance machine, I would use differential quadrature protocol at minimum, which requires an add on card for Acorn Six. Step pulses quickly get too short to be reliable as the maximum step rate is increased. HICKORY is the better choice for this application because it can communicate higher resolution position data without limiting maximum speed.
I would not expect improved surface finish from scales (external/secondary encoders). Accuracy improvements are what I would expect from scales.
Other Q/A:
1) No difference
2) Yes, winner: HICKORY
3)This is effectively the same as 2. Encoder pulses/rev and position request pulses/rev have to be the same on Centroid controls. Usually, the position request pulse rate will be the limiting factor. For example, if the position request is driven by open collector step and direction (200 kpps on Sigma 7), it will have much lower rate than the encoder repeat from the drive (quadrature over differential line drivers) (1.6 Mpps on Sigma 7).
4)Not that I know of. Latency is matched between axes with Centroid's delay tuning procedures. Both Acorn Six and HICKORY remain synchronous to a 250us cycle. If there is an advantage here, it would go to HICKORY. The EtherCAT distributed clock lets the drives know the system cycle time with sub microsecond accuracy. Step and direction could be sampled by a drive at any time in the cycle, so that protocol is only synchronous within whatever the drive's sampling period is.
5) Not that I know of for surface finish. HICKORY will have an advantage with robust communication to drives. If pulses are lost with step and direction or quadrature, there is no way to know that communication is compromised and correct for it. If encoder feedback is available (via ENCEXP12 on Acorn 6) parameters 261 and 262 can make a correction, but not immediately. HICKORY's communication has CRCs to detect bad communication, and 32 bits of position data available every cycle. If data is lost, the missing pulses can be recovered in 250us when the next data packet arrives.
I would not expect improved surface finish from scales (external/secondary encoders). Accuracy improvements are what I would expect from scales.
Other Q/A:
1) No difference
2) Yes, winner: HICKORY
3)This is effectively the same as 2. Encoder pulses/rev and position request pulses/rev have to be the same on Centroid controls. Usually, the position request pulse rate will be the limiting factor. For example, if the position request is driven by open collector step and direction (200 kpps on Sigma 7), it will have much lower rate than the encoder repeat from the drive (quadrature over differential line drivers) (1.6 Mpps on Sigma 7).
4)Not that I know of. Latency is matched between axes with Centroid's delay tuning procedures. Both Acorn Six and HICKORY remain synchronous to a 250us cycle. If there is an advantage here, it would go to HICKORY. The EtherCAT distributed clock lets the drives know the system cycle time with sub microsecond accuracy. Step and direction could be sampled by a drive at any time in the cycle, so that protocol is only synchronous within whatever the drive's sampling period is.
5) Not that I know of for surface finish. HICKORY will have an advantage with robust communication to drives. If pulses are lost with step and direction or quadrature, there is no way to know that communication is compromised and correct for it. If encoder feedback is available (via ENCEXP12 on Acorn 6) parameters 261 and 262 can make a correction, but not immediately. HICKORY's communication has CRCs to detect bad communication, and 32 bits of position data available every cycle. If data is lost, the missing pulses can be recovered in 250us when the next data packet arrives.
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Re: Hickory or Acorn Six, for mold cavity surface finish?
Thanks very descriptive and comprehensive answer eng199
I will go to Hickory no choice for a big size mold some time material cost is higher
For example
This is my customer made multiple cavity mold .high precision required .for such application Hickory the best .
This one I used oak with Yaskawa motor in torque closes loop.Drive I forgot as it's few years back
Next time will offer hickory.
I will go to Hickory no choice for a big size mold some time material cost is higher
For example
This is my customer made multiple cavity mold .high precision required .for such application Hickory the best .
This one I used oak with Yaskawa motor in torque closes loop.Drive I forgot as it's few years back
Next time will offer hickory.
1 user liked this post
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