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Author Topic: Servio motor Delta adas b2 Software and electronic gear ratio  (Read 10265 times)

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Re: Servio motor Delta adas b2 Software and electronic gear ratio
« Reply #80 on: October 29, 2019, 09:50:51 AM »
Thank you for answer. I will study it a bit later however why only 5000cpr are required (seems low) ? Does delta encoder have any some special encoding (X4?). What is the calculation behind? Lastly if max pulse rate from ECC is 4Mhz then are you are limited by servo drive counting capabilities? Did you considered eg. Yaskawa or Argon drive which claims to support up to 4 MHz count rate for step/pulse

[Argon] https://granitedevices.com/wiki/Argon_specifications
[Yaskawa] http://www.e-mechatronics.com/download/datas/catalog/cheps80000061/cheps80000061d_3_0.pdf

Regards
Re: Servio motor Delta adas b2 Software and electronic gear ratio
« Reply #81 on: October 29, 2019, 02:36:03 PM »
Hi,

Quote
I will study it a bit later however why only 5000cpr are required (seems low) ?

If the effective cpr is 5000 and the distance traveled is 5mm ( the pitch of the screw) in one revolution:

resolution=5/5000
              =0.001 mm
              =1um

As I posted earlier 1um resolution is entirely adequate. I could have much more resolution but why?

Quote
Does delta encoder have any some special encoding (X4?).

Yes, in fact the B2 series encoder has 40,000 lines which (x4) means 160,000cpr. The numerator and denominator
of the electronic gear ratio are based on 160,000. No need to confuse yourself with lines vs counts per rev.

You can program the drive to output a simulated encoder of anywhere from 4 lines to 40,000 lines should you require an
encoder output stream, that does not affect the basic encoder built into the servo nor the numerator/denominator
of the gear ratio.

Lets imagine that you wanted the max resolution that the servo can achieve, in this case 160,000 cpr or
8.1 arc sec (31nm if direct coupled to a 5mm pitch screw) then at 3000 rpm the required step rate would be:

step rate=160,000 x 3000
             =480 MHz
That is well in excess of the step rate of the ESS and you could never signal a servo drive down a cable at that
frequency anyway.

Note that the B2 series  Delta servos can be signaled at 4Mhz in its highspeed differential mode. But still the question
is why bother? I have used my existing mini-mill for years with a 1um resolution and never had need for finer resolution
so why do I require more with this new mill......I don't. That decision has made the design of the signaling that much simpler.

I am not familiar with Argon but Yaskawa is of course justifiably famous.......and about twice to three times the price and quite
frankly, they are not anything like two to three times as good.

There is only one instance that I would consider Yaskawa an that is if I required Ethercat, Yaskawa has a market leading position
in Ethercat capable servos. Mach4 at this time is natively step/direction. There is a current development by Kingstar/Interval Zero
that has made Mach4 Ethercat capable but it is not yet mainstream. I have, at this time, no need to step up to Ethercat so
why bother with (expensive) Yaskawa servos?

Craig
My wife left with my best friend...
     and I miss him!
Re: Servio motor Delta adas b2 Software and electronic gear ratio
« Reply #82 on: October 30, 2019, 07:25:02 AM »
Thank you for your time and answer. Learned a lot from it. I assume that your ball screw lead = pitch means they are one start type (not double or four start) that's why you need only 5000 cpr for 1um.  Can you tell where did you bought them?

I thought that to calculate needed pulse rate we take into account not ppr but quadrature counts/rev (cpr, unless some encoding is in place)
so 3000rpm (50 RPS) with 1000 ppr encoder (4000 quadrature counts/rev) I need 12 Mhz step rate

Anyway I also do not see a point to buy expensive servo set if we can't use their all capabilities. However we can also see that Delta price comparing to Chinese servo's is bigger.
eg. price for 750W from delta is 364$
https://pl.aliexpress.com/item/32326080829.html?spm=a2g0o.productlist.0.0.52923c68IKfP6Q&algo_pvid=f62e7d55-b9fd-488b-8fc1-f67669d79a71&algo_expid=f62e7d55-b9fd-488b-8fc1-f67669d79a71-13&btsid=558db7fd-b9b1-4379-8b06-8365530e1541&ws_ab_test=searchweb0_0,searchweb201602_5,searchweb201603_52

while Lichuan 750W servo set price is 264 $
https://pl.aliexpress.com/item/32521880849.html?spm=a2g0o.productlist.0.0.50734680wdtcuv&algo_pvid=c0121e19-2367-4a38-b1ce-dc17b729bb2a&algo_expid=c0121e19-2367-4a38-b1ce-dc17b729bb2a-1&btsid=746ce6a0-008f-421e-82bd-1e958a8bbaee&ws_ab_test=searchweb0_0,searchweb201602_5,searchweb201603_52

Last servo is capable of 2500 ppr so with 5mm pitch we can get 2um accuracy. Isn't so bad so why bother for Delta?. What else did you consider to select them (eg. documentation, support) or some other params (motor inertia, maximum peak current (A), encoder frequency response or maybe how fast it can stop/change direction  etc
Re: Servio motor Delta adas b2 Software and electronic gear ratio
« Reply #83 on: October 30, 2019, 01:04:09 PM »
Hi,
Delta is not the cheapest servo out there but it is the cheapest 'quality' servo.

I considered DMM (Canadian brand manufactured in China) and Delta (Taiwanese brand manufactured in China) and
ruled out the even cheaper Chinese brands.

I have good results with Delta VFDs.....and they have been in business for a long time whereas the cheapest Chinese brands are
newcomers to the market.

Quote
There is always a manufacturer somewhere who will make an item cheaper but of lesser quality. People who buy
on price alone are that manufacturers legitimate prey.

I tend to buy the best I can afford....often the cheapest IS the best I can afford but in the case of servos I wanted
better than the cheapest Chinese servos....there are quite a few posts on the forum about them, by no means all bad but often
there are shortcomings with them. One of the worst complaints is the atrocious 'Chinglish' used in the scanty user manuals.
Secondly many of the cheapest servos can only be programmed by button pushing on the drive whereas Delta (and DMM)
have software that resides on a PC and can be used to program the drive. You will see that in my previous post I now regard
that feature as essential. Modern servos have that many parameters, tuning options an modeling parameters that button
pushing is increasingly unrealistic.

I bought the ballscrews off Ebay from DYGlobal in Korea. He has become a favoured supplier having provided linear guides
and ballscrews for this new build and linear guides and various Vexta stepper motors/drives for my previous build mini-mill.

https://www.ebay.com/itm/THK-Double-nut-ground-Ball-Scr-BNFN3205-5-638mm-FK25-Precision-Z-axis-CNC-Router/201960959809?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160727114228%26meid%3Dd16a24a45f9b46f5a5d6059dc4911ec3%26pid%3D100290%26rk%3D1%26rkt%3D4%26sd%3D201960959809%26itm%3D201960959809%26pmt%3D1%26noa%3D1%26pg%3D2060778&_trksid=p2060778.c100290.m3507

Craig
My wife left with my best friend...
     and I miss him!
Re: Servio motor Delta adas b2 Software and electronic gear ratio
« Reply #84 on: October 30, 2019, 01:34:23 PM »
Hi,

Quote
Last servo is capable of 2500 ppr so with 5mm pitch we can get 2um accuracy

Re-reading this and I don't think you are correct.

The 2500ppr (lines) encoders used on cheap Chinese servos are all Tamagawa encoders or a Chinese made copy of a
Tamagawa. They are pretty damn good, especially for the money, such encoders ten to twenty years ago would have been
considered 'state of the art' and very expensive.

2500 ppr with quadrature becomes 10000 cpr. Thus a servo equipped with such an encoder has an angular resolution of:

angular resolution= 360 / 10000
                          =0.036 degrees
                          =2.16 minutes of arc

If such a servo is direct coupled to a single start 5mm pitch ballscrew like mine then its linear resolution is:

linear resolution= 5 / 10000
                       =0.0005mm
                       =0.5um

So.....yes, the current entry level 2500 ppr (10,000 cpr) encoders offer very good resolution at affordable prices. It is not
really necessary in my opinion to have even greater resolution in an encoder but ALL the leading servo makers are going that
way.

For instance the latest Delta A3 series servos are equipped with 24 bit absolute multiturn encoders with battery backup.
This means for example that you could use 16 bits (65536 cpr) of resolution for the angle within any given turn and 8 bits
(+128,-128 turns) to keep track of the number of complete turns from the nominal 'home' of the servo. Additionally the encoder
is absolute reading, that is as soon as it is powered up it knows where it is whereas the cheaper previous generation incremental
encoders (like mine.....sigh) require an initialization procedure before that are effective in determining servo angular position.
With a battery backup when you turn your machine off and the servo does not lose home reference, when you turn your machine
back on you don't need to home it as is common practice. Pretty 'groovy'.....but as nice as those features are I don't really
need them and don't want to pay the extra to get them. Maybe you do....if you do be sure to tell us all about how they work.

Craig
My wife left with my best friend...
     and I miss him!