Dynomotion

Group: DynoMotion Message: 9018 From: andy.brman Date: 1/27/2014
Subject: Encoder use with Kanalog
I came across some very affordable stepper motors that had encoders included. I am still designing my machine and I am wondering if these Encoders will be useable or if they are too low in the number of pulses per revolution.

The encoders are Optical,Quadrature(incremental),5VDC...
which I can tell I am in the right range from reading the FAQs at dynomotion
... but these are listed as 500 pulses per revolution.
They are attached to nema 23 steppers with a 1.8 degree step... so 200 steps per revolution.
Am I right to assume that If I do not employ microstepping that this encoder will work for my needs with the Kanalog board.  I am pretty sure I will have to get a converter to make the single ended signal into a differential signal for use with the Kanalog.
Thanks for any advice.
Group: DynoMotion Message: 9019 From: Tom Kerekes Date: 1/27/2014
Subject: Re: Encoder use with Kanalog
I think that is correct.  Post quadrature that would probably be 2000 counts/rev.  I don't understand why you would say "If I do not employ microstepping"?  The encoders should work with or without microstepping, better to have microstepping. 

You would of course need stepper motor drivers somewhere.

Regards
TK

Group: DynoMotion Message: 9032 From: andy.brman Date: 1/27/2014
Subject: Re: Encoder use with Kanalog
Tom,
Thanks for the response.
 I clearly didn't understand how the encoder resolution is determined and I was thinking that it would be a problem to use microstepping that may allow more microsteps per revolution than available encoder counts per revolution.

But if I understand correctly, The encoders that are attached to my 1.8 degree steppers are 500 pulses per revolution. And if there are two channels: A and B, that means I am at 1000 count... and if I employ a single to differential converter (for use with the Kanalog) then that means A, -A,B,-B will mean 2000 count.

Did I get the logic right?
I am also reading about the use of microstepping and what it causes in lost torque.... it seems as though there are some strong conflicting opinions out there about the benefits of microstepping. I am leaning towards using some to achieve smoother motion at slow speeds and increased accuracy when coupled with Encoder feedback.

Thanks.
Group: DynoMotion Message: 9034 From: Tom Kerekes Date: 1/27/2014
Subject: Re: Encoder use with Kanalog
Hi,

Actually no.  Single ended or differential has the same resolution.  In both cases you have A and B cycles that are 90 degrees out of phase where for each complete cycle there are for quadrature edges.  The benefit of differential is that they are less susceptible to noise.

Regards
TK

Group: DynoMotion Message: 9035 From: andy.brman Date: 1/27/2014
Subject: Re: Encoder use with Kanalog

ok.

so when you said this earlier...in response to my description of 500 pulses per revolution.

"I think that is correct.  Post quadrature that would probably be 2000 counts/rev...."


Sorry if I am being slow here, I'm just trying to understand the logic so I can purchase wisely for my build.


In addition to understanding the math, I would like to understand what using an 3rd party adapter will do.

I now understand that converting single ended to differential does not increase resolution... Do the 3rd party converters that you reference in the FAQ page about going from single to differential signals simply allow the inputs on the Kanalog to be used... I suspect that the noise resistance of the differential signals is only there if the encoder is truly a differential encoder... not just a single ended that has been "converted" through a cheap adapter.

Thanks
Group: DynoMotion Message: 9036 From: Tom Kerekes Date: 1/27/2014
Subject: Re: Encoder use with Kanalog
No worries.  No I don't think that is true.  The internals of the encoder is likely to be exactly the same.  The only difference is the circuit that is used to drive the cable.  A good quality line driver chip is very inexpensive in either case.  Probably the main issue is the number of pins required in the encoder's connector.  But if you have the option then spend a few extra dollars and buy encoders with differential drivers.  You can still connect them to single ended inputs if you don't have differential inputs available by just not using the complementary signal.  But then you have them if you have noise problems and decide to go differential you will have them.  The opposite is not true.  You can not connect single ended outputs to differential inputs by just leaving one input open circuit.

HTH
Regards
TK

Group: DynoMotion Message: 9038 From: andy.brman Date: 1/27/2014
Subject: Re: Encoder use with Kanalog
TK,
So I already have three steppers with the encoder listed below...
<http://www.avagotech.com/pages/en/motion_control_encoder_products/incremental_encoders/transmissive_encoders/heds-5505a06/>
the version that I have is a 500 PPR.
If I get a 3rd party adapter for the Kanalog Board to go from single to differential what should I expect the resolution of the encoder to be?
Would it be 500? or does the Kanalog count both A and B channels which would be 500 per channel per revolution = 1000 counts per revolution?

I am just trying to determine if these are high enough resolution for a stepper driven machine that moves 75mm per revolution of the stepper shaft.  I am confident that I am not going to be in danger of driving these steppers so fast that the Kanalog couldn't keep up.

I understand your point about paying the extra for differential encoders if possible... as they can be used as single or differential easily.  I will keep this in mind when purchasing my remaining encoders.
Group: DynoMotion Message: 9045 From: Tom Kerekes Date: 1/28/2014
Subject: Re: Encoder use with Kanalog
No.  Each of the A and B signals each have 2 transitions per cycle so there is always 4 transitions per cycle.  Quadrature counts = 4 X PPR.

Think of a picket fence with 2 inch boards and 2 inch gaps between the boards.  The pitch of the boards is a board every 4 inches.  Now assume you have A and B sensors 1 inch apart.  As you move along the fence A or B will change state every 1 inch.

It doesn't matter whether you have an internal differential line driver, or external module line driver, or just run single ended sending the A B signals to the control, this is always true.

Regards
TK