Read an encoder at the end of travel

[jeff_scharpf]

I am using an encoder to read a one time rotation of approximately 270 degrees. This is testing a hammer attached to a rotating cylinder. I am measuring the speed of the hammer head as it hits by using the encoder.

I have no problem calculating the speed once I know the frequency of the pulses.

I am trying to figure out how to read a specific set of pulses (maybe at the end, maybe near the end) so I can use a few of these to calculate the angular speed.

I want to fire the cylinder, capture the pulses, find some pulses near the end of travel, then find the period at that point. Maybe it's an average of several  periods.

Any ideas how to get this out of the waveform?

[srikrishnaNF]

Hi Jeff_scharpf,

  Which kind of data acquisition device you are using?COuld you please explain a little bit more abt your problrm?

Thanks and regards,

srikrishnaNF

[jeff_scharpf]

Thanks for the response. I will most likely use a cRIo module in either a USB carrier, or in a compactDAQ.  I have several cRIO modules, I just need one with a relatively high speed digital input.

My application is to test a hammer by rotating it 270 degrees until it hits a metal surface. I will have an encoder (lets say 1000 pulses per revolution) mounted on the shaft that the hammer will rotate around. I will ask the user for the length between the center of the shaft to the hammer head. The goal is to measure the rotating speed right when the hammer hits the metal (end of travel) and I will then calculate the linear head speed of the hammer.

Currently I use an oscilloscope and capture the pulses. I use a quadature encoder only so that I can see where the hammer "reverses" so I don't count the pulses after it hits (while it might bounce).

I would also like to do this in Labview but I'm not sure if I can.

Summary:

1) Fire a relay to cause the hammer to rotate quickly until it hits a stop, all the while measuring the pulses from an encoder.

2) Determine when the encoder "reverses" by looking at the quadature output.

3) Go back a few (still to be determined) pulses and average maybe 10 periods to get an average angular velocity just before the hammer hits.

4) Calculate the linear speed of the hammer head. I will have a user input arm length.

I have no problems finding a relay output to fire the cylinder, I can capture the quadature encoder pulses, I am stuck on trying to search through the entire set of pulses, find here the hammer reversed, pick out a select number of pulses, then average those periods.

[aeastet]

You can do this in LabVIEW. I have a few applications where I am doing something similar. I am using an encoder with over 5000 pulses per revolution as well. Make sure that you get a DAQ card witht he ability to do Quad encoder inputs. This will make you life easy. All you will have to do to set it up is tell it how many pulses the encoder has and what you want out (i.e. linear, anglular etc...)