Will these encoders work with my Geckos?

[ozzie34231]

I bought some servos on Ebay a while back ignoring the encoders that were attached, and intending to buy new US Digital units.
Now I'm about to put a servo to use and I opened the encoder housing and what's inside sure is beautiful.
I know how to hook up a regular four wire encoder, but I'm wondering if there is a way to use what is already there?
I'm attaching a picture of the nameplate in hope that someone can enlighten me. I'm pretty much electronically disadvantaged so speak in easy non tech language.

[Al_The_Man]

Thats a four wire encoder, if you ignore the C pulse which is a marker pulse.
I think there may be a maximum speed problem AFAIK Gecko's multiply the count x4, so you end up with 4000counts/rev.
If the current draw is above the max supplied by the drive you may need a separate 5v supply.
Some of the Sanyo-Denki encoders I have come across are open collector, if so you may need a pull up resistor.
Al.

[ozzie34231]

Hi Al,
Thank-you but I hardly understand a word you said.
I understand that there may be too many pulses per rev.
I understand the power supply may be inadequate.
Beyond that I'm lost.
What wires would I connect where; black and red to the power supply, then what?
And pull up resistor???????????

Make it simple for me if you can.
Thanks,
Ozzie

[Al_The_Man]

Black=common Red=+5v Blue=A pulse green=B pulse.
If you apply a 5v supply to the red/black and put a volt meter on either A or B and common and turn the shaft SUPER slow, see if the voltage goes from 0 to 5v, if it does NOT, the chances are you need ~1kohm pull up resistor on A & B to 5+.
Al.

[ozzie34231]

COOL!
You are, ,,,,"the man"

Ozzie

[ozzie34231]

Hi again Al and All,
I did as you suggested Al. I did need the pull-up resistor.
I don't know what the ~ notation means; I used a 1.5k ohm and that seemed to work.
So my remaining questions are:
You don't seem positive that the Gecko's will see this encoder as 4000 steps. How can I test that and how do I test if the Gecko will supply enough power.
I feed some things, like the spindle encoder, 5 V from the computer. Can I do that in this case?
What would be the effect of using only the A or B channel ? Is that possible? Would it change the count?

Thanks in advance,
Ozzie

[Al_The_Man]

I believe there is a current restriction for the 5v supply on Gecko, so you may have to supply a separate supply.
I believe they do not need the complementary encoder, if so single ended A&B should be OK.
Hopefully someone conversant with Gecko's will jump in to answer you questions.
Al.

[CoAMarcus]

The G320 and the G340 provide a +5V signal up to 50mA, and if it is more than that you will need an external power supply. With such a high count encoder, I would highly recommend the use of a step pulse multiplier, which will have the ability of bringing your encoder down to 400PPR. The drives will run the 1000 line encoder, but it will be very slow.

If you assume your step pulse frequency is going to be 40kHz, then you are looking at a maximum of 10RPS, or 600 RPM with no load, in theory. This is miserably slow for a servo motor, because you must gear it to develop any kind of torque. Have you calculated your optimal encoder line count? The formula is as follows:

(Step Pulse Frequency / RPS) / 4 = Encoder Line Count

Determine your RPS by taking 80% of the motor's maximum RPM and dividing by 60. Hope this helps.

-Marcus

[ozzie34231]

I'm not sure it is a 1000 line encoder. The nameplate says 1000 p/r. The US digital website differentiates between CPR and PPR. This may not be a US Digital but do I have 1000 lines or 1000 pulses?
I'd like to accomplish 20,000 steps per inch with a .2 pitch screw.
I agree that a 2-1 or 3-1 reduction would be wise maybe even 4-1.
There is also a possibility of mounting the encoders on the screw rather than the motor.
If this IS a 1000 line/4000 pulse encoder and I put it on the end of the screw that would give me 20,000 pulses per inch.
So then what happens to speed and what reduction would I use?
The presently intended motor is 3000 max RPM. 75v which I would run at 70v.,7.7A..
Is the step pulse frequency the speed at which Mach3 is running?

Ozzie

[CoAMarcus]

Ah, yes, I did not see the "P/R" by the 1000. I suppose my mind just got stuck on 1000 lines, and would not budge. That means you have a 250 line count encoder, which is much more manageable in regards to speed.

Think of your step pulse frequency as a fixed rate. The more pulses required per revolution, the slower the motor will turn, but the higher resolution it will have. The step pulse frequency is the rate at which Mach3 outputs the pulses, which it should say what frequency it is in the program.

It is not a smart idea to attach the encoder to the end of the screw due to backlash. Just keep the encoder on your motor, and you will be fine. Another thing to remember is that if the encoders do require their own power supply (i.e. Above 50mA), then you must have a separate PS for each encoder.

Let me know what your step pulse frequency is, and I can let you know what your optimal line count is.

[ozzie34231]

I don't quite get that part about backlash????????
It seems to me that mounting on the screw involves less backlash, more accuracy, no belt backlash. Let the motor do what's needed to get the screw in the right place!
Anyway Mach3 speed depends on your computer, anywhere from 25mhz to 100mhz. 45 should be little problem, maybe 60.
How do I know how many amps the encoder needs?

[CoAMarcus]

The backlash is only a problem on lead- and ball-screws, but not on tooth-belt and pulleys. The encoder current rating should be in the data sheet, or on the website of the manufacturer.

Judging by your 60kHz number, your ideal line count will be 375. Your 250 will still work just fine, but your resolution will not be what it can be.