Issue with MDI setting RPM using M3 and actual RPM in the mill

[LorenzoRR]

Hello,

I have a wabeco 1210 HS quite successfully working with Centroid Acorn.
I want to try riggid tapping, and have incorporated an encoder with 4096 lines.
Basic implemented setup:
- Encoder is a SICK incremental, wired according to schematics in Acorn documentation.
- Counts per revolucion = 16384 (4096 lines).
- Parameter 33, high spindle ratio = 0.6319 (spindle turns quicker than the motor)
- Wizard: Rigid tapping = yes
- Wizard: Encoder in spindle = yes
- Wizard: min spindle rpm = 0
- Wizard: max spindle rpm = 7500

Issue: making MDI of speeds (i.e. M3 S1000), there is a difference between the commanded RPM and the indicated rpm in the screen (that is SAME as the actual in the spindle -measured with a sensor-).
Below table shows the discrepancy at various rpms. Even the difference is not linear or just bias... you can see the bottom table with difference % (even moving from negative to positive across different RPM values).

I see that screen indicted RPM is very much same as the actual one, but totally different to the commanded one...

Can somebody help me to investigate what can be happening? Thanks very much!

[centroid467]

Please measure the voltage coming out of the terminals with VFD disconnected at various commanded spindle speeds including max and min. If the measurements aren't close to what you would expect from v = (10 * commanded speed) / 7500 then there may be a problem with the Acorn.

If that works out, then you may need to install a 0.1uF ceramic capacitor across the Acorn terminals as explained in the linked thread.

[LorenzoRR]

Thank you, I will see those posts.

[LorenzoRR]

Issue has been almost solved... !
Below there are several data about tests today.
I have measured voltage for different commanded Speeds, in a variaty of situations.

Basically these have been the learnings:
1) I had parameter #33 as the mechanical ratio between electric motor and spindle (0.62). By default it is 1.
I did not know that when P#33 is <0 (spindle rotates faster than the motor), the 0-10 voltage is cut when the rpms reach the Wizard HSP (High Speed) of the spindle!. This is seen in one of the cases.
2) Once P#33=1, linearity of 0-10V is almost perfect with the commanded RPMs (measured with NO LOAD -no motor).
3) When engaging the motor, in the very same conditions as 2), the RPMs were considerably greater than the commanded ones.
4) I have bought a polyester capacitor, 0.1 microF, and the error has been greatly reduced.
There is one chart showing this.
5) I thought that with a spindle encoder, the Motor RPMs were setup using its pulses and the mechanical ratio, but I was mistaken.

Now, my "electronic" question is: Would the error reduce (red curve) if I change the capacity ?

Thanks for the support and guiding me to the two other posts.

TABLE WITH TODAY´S TESTS:

CHART WITH VOLTAGE vs COMMANDED RPMs:

CHART WITH ACTUAL RPMs vs COMMANDED RPMs: (and error actual vs theoretical -deep blue line)

[tblough]

Now, my "electronic" question is: Would the error reduce (red curve) if I change the capacity ?

No. The capacitor only removes the high frequency AC component of the signal resulting in a cleaner DC voltage. To reduce the "error" between the measured RPM and the commanded RPM, you will need to adjust the span and slope of the remote input in your VFD using the VFD's configuration parameters.

[LorenzoRR]

Now, my "electronic" question is: Would the error reduce (red curve) if I change the capacity ?

No. The capacitor only removes the high frequency AC component of the signal resulting in a cleaner DC voltage. To reduce the "error" between the measured RPM and the commanded RPM, you will need to adjust the span and slope of the remote input in your VFD using the VFD's configuration parameters.

Thanks.
Then I will check if I can leave with this error... most likely yes I presume.
My main worry was the role of the encoder in rigid tapping cycle. As I think it just gives rotational feedback to the control, and it adjusts the Z feed according to the TPI, then a small error in actual RPMs vs commanded should not be critical.
I will make tests using really soft materials.