Question about Encoder Scale

Hello.

I have modified an old manuell MIll to CNC with Mesa Cards and Linux CNC.
On the axis I have for closed loop linear glass scales with 1000 units / mm.

To get the actuall travel distanz correct, I have to set the "Encoder Scale" to 1600.
But doesn´t this to be 1000?
I have measure it with an dial gage, so 5mm travel on the display are with the 1600 scale 5mm ravel on the dial gage.

The linear scales are feed direct to the Mesa 7i33.
The encoders on the Motors are only connected to the Servo driver. The Servo driver is also conected to the 7i33 (Enable, +-10V).

The Spindel pitch is 5mm, and the ratio from Motor to Spindel is 1.636.
The Machine is in set up in velocity mode.

Best regards
Marcel

Can you share a datasheet or details on the glass scale? 1600 seems odd. Normally glass scales come in 5 um, 1 um , 0.5um resolution.

Hello Henk,

the scale has a resolution of 1µm.
Here are the details:

Technische Daten GP 10:

Teilungsperiode 20 µm
Lesekopf Kugelgelagert
Auflösung programmierbar: Standard 5 µm, 1µm oder 0,5 µm
Wiederholgenauigkeit +/- 1 Inkrement
Ausgangssignal RS422
Volt DC 5 V
Temperatur -10°C bis 45°C
Relative Feuchtigkeit < 90%

You can select betwen 1µm and 5µm resolution, I have selected the 1µm ones.


One thing I have find out: Its only on the Y axis. The X axis is set to 1000 and is OK with the scaling.
I will check the wireing again and swap out X and Y to see if I can narrow down the error...

Thanks, best regards
Marcel

Best regards
Marcel

Also check if it is consistent at a scale of 1600. It could be electrical noise as well. Is the encoder cable screen properly grounded? Normally the screen is connected to the reader head frame. If this is the case, make sure there is a proper connection between the reader head and the machine frame and that the other end is left unconnected. Also if the cable goes through a connector, check that the screen is also connected to one of the pins on both sides.

Right I don't see how you could get that count, Also make sure that the 7I33 is jumpered for differential encoder inputs and that the A,/A B,/B pairs are wired correctly.

You can verify that differential pairs are wired correctly by measuring the voltage from A to / A
( and B to / B ) and making sure that the _absolute_ voltage is always >2V between the pairs
and any of the 4 quadrature states (you will have to jog/wiggle the axis to see all states)

Hi,

I´ve cheked the connections, rewired the cables and plugs and switched the scales on the different axis.

The error doesn´t be a error in LinuxCNC, because when I unplug an replug it, sometimes it works and sometimes I got the scale of 1600.
It is always the same scale of 1600. So I don´t think it is electrical noise, or the error would more differently?

I have now wired 5V to the 7i33 instead of using the power from the 50pin header connector.
I have played a little bit and till now no error.
Can this be the solution? The 50 pin header cable are not very long, around 30cm.

PCW, I will mesaure this now with the external 5V on the 7i33...

Best regards
Marcel

30cm can be OK but it depends on the 5V draw of the encoders
Older encoders may have significant current consumption
(the oldest Heidenhain scales use incandescent lamps!)

I have a question it's in the same context.

I build a spindle driven by a HF chinesium Rattm motor. I gear it down to apprx. 1:2. I also have an encoder from IFM with 4096 ppr. I will attach it to the spindle by a belt. I'll try to make booth pulleys at the same diameter. But we dont live in a perfect world. So when i turn the motor twice, the spindle turns 1 times. The encoder turns 1,1 times because the pulley is a little larger in diameter as the spindle pulley. So what is the right scale i need to set on the encoder scale?

The motor and spindle difference i handle in the VFD controller. that is not difficult.

How i fix the 1.1:1 from the spindle and the attached encoder. The encoder have a+ b+ and z+ (index) so i need an exact revolution of the spindle at the encoder.

Is the formula:

Encoder Scale=PPR*revoution when spindle turns 1 ?
Encoder Scale=4096 * 1.1?
encoder Scale 4505.6?

Thanks in advance!

Best,
Udo

Hi PCW,

the Voltage between A /A B /A and GND is 300mV or 3.2V.
Between A and A/ or B and B/ is between -2.8 and 2.8V.
Is this correct?! Also, if A /A is 2.8V, b /b is also 2.8V. Didnt B /B need to be -2.8V?

Best regards
Marcel

No one any ideas?