Choosing servo encoders for Mesa 5i20 and D510MO

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20 Jun 2011 20:09 #10681 by machete
Hello!

My configuration (plan) for retrofitting small horizontal milling center VM501 (made in USSR 1987 ;-)

Motherboard D510MO (latency < 8000) with Mesa 5i20

2xMesa 7i29 (4axis - XYZA)
Mesa 7i37TA (for toolchanger)
Mesa 7i47S (for spindle and adittional automatic IO)

I am planning to connect 7i29 directly to my servo motors (110V 6.5A 1000rpm 5.2N\m ) but they do not have encoders. So I have to buy it.

But I'm not sure - how many impulses per rotation is posible for this combination and latency?
Is Mesa5i20 fast enough for 4axis about 2000-2500 impulses per rotation each?
I dion't want to loose axis speed (maximum is 5x1000=5000mm\min) if Mesa will not be able to handle too much impulses per second for all axis.

Best Regards
Maksim

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20 Jun 2011 21:16 #10684 by BigJohnT
Latency is not as critical when using hardware like Mesa as you only need the servo-period and not the high speed base-period. The 7i29's can share one cable so make sure you get the split cable for that. I'm sure the encoder inputs on the 7i29's are plenty fast, I just can't find the number... maybe Peter will pop in.

John

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21 Jun 2011 01:15 #10689 by PCW
With differential encoders and filtering enabled, the 5I20 will be the limiting factor. Maximum count rate of the normal encoder counters in the 5I20 is about 4.4 MHz with filtering on, this is about 30K RPM with a 2000 line (8000 count/turn) encoder. TTL encoder inputs on the 7I29 are limited to about 1MHz or about 7.5K RPM with the same encoder. If you are buying encoders, I would use differential interfaced models as they have much better noise immunity than TTL interfaced encoders

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21 Jun 2011 08:47 #10693 by machete
Thanks for answers!

PCW wrote:

With differential encoders and filtering enabled, the 5I20 will be the limiting factor. Maximum count rate of the normal encoder counters in the 5I20 is about 4.4 MHz with filtering on, this is about 30K RPM with a 2000 line (8000 count/turn) encoder. TTL encoder inputs on the 7I29 are limited to about 1MHz or about 7.5K RPM with the same encoder. If you are buying encoders, I would use differential interfaced models as they have much better noise immunity than TTL interfaced encoders


We try to save budget (we are very small company), so we have to choose not expensive encoders. And as i understand cheapest encoders usually have only TTL output.

Our servo motors is only 1000rpm, and cables from encoders will be screened.

Please check my calculation way: 2000line encoder have 2 signals changing 2 times per encoder line 2000*2*2=8000changes per turn. 1Mhz is 1000.000 changes per second. 1000.000/8000=125 turns per second. 125*60=7500rpm.

And back: if i have maximum 1000rpm it equal 1000/60=~17 turns per second. 1Mhz maximum frequency for 7i29, so it can handle 1000.000/17=58823 signal changes per turn maximum. 58823/(2*2)=14750 line is theoretic maximum number of encoder lines for 7i29?

So if i choose 3000line TTL encoder with screened cable (max 2-2.5m) it will be completely OK?

..The 7i29's can share one cable so make sure you get the split cable for that. ...


About cables: as i am understand i can make this cable myself - i already bought 50pin cable and 7 IDC 50pin connectors:
www.brownbear.ru/components/idc-50.html
www.brownbear.ru/goods/1538.html

And just press it with vise:
kevtris.org/Projects/copynes/idc.html

Cable for 2x7i29 should have 3 connectors, and i can choose 1st or 2nd line with jumper on 7i29.

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21 Jun 2011 12:10 #10699 by andypugh
machete wrote:

So if i choose 3000line TTL encoder with screened cable (max 2-2.5m) it will be completely OK?

Sounds right to me.

About cables: as i am understand i can make this cable myself

I always have.
In fact, with the machine I am currently building I am using discrete wires into the 5i23 headers, using these:
uk.rs-online.com/web/search/searchBrowse...etProduct&R=681-2865
The following user(s) said Thank You: KobeYang

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21 Jun 2011 14:32 #10702 by PCW
Your calculations look correct (for TTL) but I would again strongly suggest that you use differential encoders, they are usually only a little more expensive than TTl models and much better at rejecting noise. You don't want to start out chasing noise problems...

The theoretical maximum 7I29/5I20 count rate is actually much higher, ~ 10MHz with the encoder filter off and differential inputs, but I don't know that encoders with such high count rates actually exist

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21 Jun 2011 15:32 #10704 by machete
PCW wrote:

Your calculations look correct (for TTL) but I would again strongly suggest that you use differential encoders...


ÎÊ!

What you can say about this encoder: MH4-25LN65CA8

www.delta.com.tw/product/em/motion/motio...ROE_catalouge_en.pdf

Features
ROE-M Series is a commutation encoder which is designed for servo motor. It can not only output the signals of A,B, Z phase but also can detect the U, V, W signals of servo motor for commutation. There are 4, 6, 8, and 10 pairs of magnetic poles for user’s selection.
MH&#65288;Hollow Shaft&#65289;MT&#65288;Through Hole Shaft&#65289;
Specifications
&#8231;MH Series: Outer Diameter of Hollow Shaft: 38.7mm
&#8231;MT Series: Outer Diameter of Through Hole Shaft: 38.7mm
&#8231;Resolution: 2500ppr
&#8231;Output Form: Line Driver
&#8231;Power Voltage Range: 5-12V
&#8231;Responsiveness: 300kHz max



"Output Form: Line Driver" - means differential encoder?

And what is "U, V, W signals" - do i need it?

Attachments:

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21 Jun 2011 15:39 #10705 by andypugh
machete wrote:

And what is "U, V, W signals" - do i need it?


They would be the three signals, normally from Hall sensors, that allow you to commutate brushless motors.

For some applications I can see that being extremely useful.

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21 Jun 2011 15:45 #10706 by machete
andypugh wrote:

machete wrote:

And what is "U, V, W signals" - do i need it?


They would be the three signals, normally from Hall sensors, that allow you to commutate brushless motors.

For some applications I can see that being extremely useful.


But i have brush motors - so, can i just ignore this wires?

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21 Jun 2011 16:21 #10710 by andypugh
machete wrote:
[quoteBut i have brush motors - so, can i just ignore this wires?[/quote]

Yes, or get an encoder without them.

I think that this encoder might have differential outputs, and is cheap:
www.slidesandballscrews.com/hkt300635301...-p-494.html?cPath=88
The data sheet uses an "E" as the last code letter to identify voltage output, so perhaps "L" is line driver?
Note that in that encoder model the 1000 and 1024 line versions do not have an index (Z) line.

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