usb 6008 angle mesurement?

[svijay]

hello friends

i need to measure angle of shaft rotation with accuracy of 1 degree....is there any simple device i can connect with usb 6008 to measure angle...

thank u

[johnsold]

Unless your shaft is rotating fairly slowly, probably not.

I can think of two methods which might work.

1. Use an absolute encoder with parallel digital outputs.  A 9-bit encoder has a resolution of 1 part in 512 which is better than 1 degree. At the software timed maximum rate of 150 S/s, you could get to about 100 rpm.

2. Use a continuous rotation potentiometer with sine/cosine outputs and read them with analog inputs. DO some trigonometry in software to calculate the angle.  You could theoretically reach ~800 rpm.

Neither absolute encoders nor sine/cosine pots are cheap.

Lynn

[svijay]

Thanks johnsold

in my application it is only limited to 30 rpm .....

 if possible see this video in link below... Is it possible to use this kind of voltage regulator

http://www.youtube.com/watch?feature=endscreen&NR=1&v=IjJWWGPjc-w

once again thank you......

[johnsold]

I have used LM317 regulators to control the speed of small motors in several projects.  What does this have to do with your angular postion measurement?

At 30 rpm you have 0.5 revolution per second or 180 degrees per second.  To read the position with 1 degree resolution you need to be able to read at least 180 times per second.  This exceeds the rate at which the 6008 can read digital inputs.  So the only possibility with the 6008 is through some kind of analog sensor.  Continuous rotation potentiometers with sine and cosine outputs can provide this kind of signal. A continuous rotation linear potentiometer might work but it is more sensitive to noise and voltage variations. There are a variety of optical and capacitive devices which can probably work also, but they will either be quite expensive or will need to be made by you.

Do you need an absolute encoder or can you use an incremental encoder with a reference mark?  Does your direction ever reverse?

Lynn

[svijay]

Thank u for your reply

johnsold,

I am actually final year mechanical engineering student..I don’t know much about electronics...

Can u please elaborate little bit more.....

I thought, if we can find some voltage variation  while we rotate something, we could couple the same with the shaft to which the angle to be measured.

And I thought that the output comes from that voltage regulator is analog and the sample rate for the same in  USB 6008 is 10ks/s so, we can use this kind of voltage regulator as angle measurement sensors.

but I really don’t know the sensitivity and responds time for the voltage regulator if we use it as a sensor.

Even if it is digital input to usb6008 we can reduce the speed up to 15 rpm by mating proper gear with that...

Thank u

[johnsold]

To get a voltage from the regulator which varied with shaft angle you would need to connect the shaft to a continuous rotation potentiometer.  But the voltage on the potentiometer itself would be related to the angle, so you do not need the regulator.  Keep it simple.

For about $14 (US dollars) you can buy a continuous rotation potentiometer (Bourns 6539/6639) but the electrical angle is only about 340 degrees.  That means that about 20 degrees of the rotation will produce no variation in output voltage or an undefined output.  You could use two of these mounted so that the dead zones do not overlap.  In your software you could detect when one potentiometer output was in the dead zone and use only the other output during that time.

Lynn

[svijay]

Thank u johnsold

I need to measure the angle with in 180 degree of rotation only.... Thank for your idea....

Even we can use lm317 voltage regulator also ..Right?

Can we able to acquire the voltage variation while the shaft rotates in labview front panel with the numerical indicator..

If it can able to show in terms of voltage I can calibrate the angle of rotation...

[johnsold · Accepted solution]

180 degrees is much different from continuous rotation. Just wire a potentiometer to one of the analog inputs and try to calibrate it.

You do not need the LM317.  It will not help you with anything you have described so far.

Lynn

[svijay]

Thank you Johnsold

I am expecting the answer for following question also

http://forums.ni.com/t5/Multifunction-DAQ/USB-6008-for-stepper-motor/m-p/1814010

once again thank you