Velocity Measurement from FPQuad-510 encoder pulse counter

[Caner]

Hi, I have a quad-510 quadrature encoder counter and a 1024pulse/1rotation encoder. How can I read or calculate angular velocity(accurately and without much delay) from encoder readings?

Is there a special vi or another algorithm (other than derivative.vi) that could help?

Thank you.

[SimonH]

Caner,

The FP-QUAD-510 can use a timebase counter to determine the rate of change of position (velocity) for each axis.  See pages 9-11 of the manual for more details.

I don't know of a better VI for calculating angular velocity based on the current encoder count than derivative.vi.  Perhaps you could use lower-level LabVIEW VIs to implement an algorithm that approximates the derivative of your count?

Regards,

Simon H
Applications Engineer
National Instruments
http://www.ni.com/support/

[Caner]

Hi,

I have read the manual and in MAX I tried to read the velocity values for channels 8 9 10 11 but its all zero always. When I move my hardware I have to see some velocity values but its all zero. I can see the LSB values for count input tab for channels 0 1 2 3 but I dont see any velocity value for the other channels as I said.(the channels 8 9 10 11 are type : analog input)

I have connected the encoders correctly because I can read the position values but how will I manage to read the velocity values at the same time?

[SimonH]

Caner,

What do you see listed for the status of the velocity channels in MAX?



Also check your channel configuration to make sure you have an appropriate range set.



Regards,

Simon

Message Edited by Simon H on 02-02-2007 06:50 PM

[Caner]

Simon;

I have chekced it and its all successful. Also I have tried all the ranges while moving the hardware and it all shows zero just like the MAX picture you've send me.  Might this be happening because the type changes while measuring the velocity? It says analog input for velocity channel type and count input  for the position measurement type? I have just connected encoders to the module so I think there is no analog input to the fieldpoint but only pulses from the encoders.

Also I couldnt figure out which range is the best suitable one for me? I have 1024 pulse encoders for 1 rotation.

What do you think?

Thank you.

[SimonH]

Caner,

Velocity should show up as an analog input in MAX.  As the calculation for velocity is counts over time the resultant value is analog in nature.  Position is a count input because the position is always an integer number of counts.

The range is measured in terms of counts/µsec so the appropriate range would depend on how fast your encoder is rotating.  The screenshots I attached were of my configuration which worked as expected for a quadrature encoder hooked up to a motor I turned by hand (consequently the returned velocity was very low).

~Simon

[Caner]

Simon,

I see your point and thank you for the explanation but there is still one thing  I dont understand. The encoder I use is attached to a link of a manipulator. When I move the link by hand manually, I see the encoder pulse counts increasing but why I dont see any velocity value at the same time?

Its always zero on my part and thats the thing I couldnt solve? While the encoder pulses are increasing (while the encoder is rotating) the speed value must be something else other than zero isnt it?

[SimonH]

Caner,

What kind of quadrature encoder do you have?  Do you have all 8 wires hooked up or just 5?

~Simon