Encoder

Hi,

My stepper motor moves 1.8 degree per Full step. 360/1.8 = 200 full steps per revolution. I will further sub divided full step into 16 micro-steps to get 3200 steps /rev by using software.


My question is how to choose encoder for this stepper motor. My goal is very simple , move the motor and read the outputs of the encoder. What should be the "cycles per revolution" and "pulses per revolution"?

Jess

 

On Wed, 27 Jul 2016 18:47:46 -0700 (PDT), jsscshaw88@gmail.com wrote:

Hi,

My stepper motor moves 1.8 degree per Full step. 360/1.8 = 200 full steps per revolution. I will further sub divided full step into 16 micro-steps to get 3200 steps /rev by using software.


My question is how to choose encoder for this stepper motor. My goal is very simple , move the motor and read the outputs of the encoder. What should be the "cycles per revolution" and "pulses per revolution"?

Jess

Greetings Jess,
Cycles per revolution for a rotary optical encoder means how many
lines there are on the disc inside the encoder. Modern optical
encoders typically have two detectors for reading the lines on the
disc. They are placed physically so that as the disc rotates an
individual line will be detected first by one and then the other
detector. Since the encoders are digital this means that each line
returns two signals, off and on. Since there are two detectors there
are 4 signals per line. An encoder can be read in two ways, one count
per line or 4 counts per line. This means, for example, that an
encoder with 200 lines can be used to get 200 signals per rev. or, if
read in quadrature, 800 signals per rev. When reading the signals it
works like this: channel A goes high, then channel B goes high, then
channel A goes low, then channel B goes low.
Ideally, since you are microstepping the motor at 3200 steps per
rev you should use an encoder that will give exactly 3200 pulses per
rev. Good luck finding one though. See this link:
http://www.usdigital.com/products/encoders?gclid=CN3Oh_O-ls4CFYqIfgodhEYIYQ
There are lots of encoders to choose from at reasonable prices from
these folks. You will see that there are none that can be used to get
exactly 3200 pulses per rev.
However there is another way. If you use an encoder with 4000
lines, or cycles per revolution, and read it in quadrature, you will
get 16,000 pulses per revolution. Then you will get 5 counts per
revolution. You can massage the output with a computer so that it
divides the count by five which would then show 3200 pulses per
revolution.
Or you could buy the ED3 digital display from US Digital and let it
do the work. Not only can you scale the count with the display you can
also get RPM. And it powers the encoder as well.
I use encoders from US Digital on several of my machines. I also
use encoders from other makers, such as CUI.
One advantage with having 5 pulses per step from your motor is
being able to see the rotation error when microstepping. It is
intrinsic with the motor you are using that any rotational error will
be corrected after every 4 complete steps. This means that when you
command the motor to move one complete step it may not move exactly
1.8 degrees. When microstepping the situation is that there will be
errors in rotation. It is unavoidable. If there is a significant load
on the motor the errors will be larger. With 16,000 pulses per
revolution you will be able to better see these errors in positioning.
Eric

 

[Tim Wescott]

On Wed, 27 Jul 2016 18:47:46 -0700, jsscshaw88 wrote:

Hi,

My stepper motor moves 1.8 degree per Full step. 360/1.8 = 200 full
steps per revolution. I will further sub divided full step into 16
micro-steps to get 3200 steps /rev by using software.


My question is how to choose encoder for this stepper motor. My goal is
very simple , move the motor and read the outputs of the encoder. What
should be the "cycles per revolution" and "pulses per revolution"?

I'm used to encoders that are specified in "lines" and "counts". On a
quadrature encoder there's four counts per line. I suspect that a
"cycle" is a line, and a "pulse" is a count.

Do you need to have the encoder be in sync with the motor? Or can you
stand them being different?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!