Hi Hood

I can go up to a 1kw motor as it won't make much difference on the price. If so should the drive be increased to the 1.5kw or is it ok to use the same size drive. I have attached a picture of the Sem motor plate.
Great to hear from you again.

Cheers
Mick

I would say that  if you can get 1Kw for not much more then it would be better.
Just looked at the specs of the drives/motors and the one you linked to earlier is actually 5000rpm max but only rated 3000 rpm so you probably wouldn't be able to gear it too much in comparison to the original.
It would depend however what the original was actually supplied, voltage wise, from the Norwin drives, it may have just been 90v which would mean approx 2000rpm would have been the normal max rpm of the motor on the lathe.

As said I just looked at the specs and that drive can handle 1KW motors so it would be fine, they show three that are compatible. Just different inertias, I would probably opt for the medium inertia myself.

Hi Mick,
the prices you quoted for Schneider units are considerably better than is obtainable in New Zealand.

I think the critical number in the pic of your existing servos is the continuous rated torque. Provided any servo that you choose can match
or exceed that then the machine will have all the grunt that the manufacturer intended. It may well be that you can find a servo of even greater
torque but at a lower speed. You could as Hood suggests gear it suit and make the match near perfect OR accept that your machine in hobby
service may be somewhat slower than it was.

If you do the calculation it may prove that the maximum axis speed of the by using the max servo speed is ridiculously high anyway. In production
machines where cycle time is critical acceleration (read torque) figures as highly as maximum speed (read rated motor rpm), if anything  slightly
more torque would prove more satisfying with respect to following accuracy than high speed.

That you are investigating AC servos and coming to the conclusion that they can be had if, not cheaply, at least affordably will allow you to advance
your project very considerably and in a very satisfying manner, AC servos will eat the SEM's for breakfast.

Craig

Hi,
the power calculation:

angular frequency (radians/sec) =4000 X PI X 2 / 60
                                              =410.9 rad/sec
Power= torque X angular frequency
         =2.1 X 410.9
         = 879.6 W


As a double check:
Power = Voltage X Current
          =130 X 6.8
          =884 W

My contention that a 750W servo would suffice seems correct, if you can get 1kW or greater servos for the same money then why not?
I think 1 horsepower axis motors should be ANY AMOUNT for a hobby machine as it is!

Craig

Hood Craig

Thank you for your time again. Definitely gonna go for the AC servos and drives.

Craig
Great explanation of how you got to the 900watts. This makes much more sense now!

Can't believe the resolution on the modern encoders.

I can see what you mean now when you said 10,000 line was entry level.

Cheers
Mick

 

Hi,
in some respects resolution beyond 10,000 count is beyond the mechanical accuracy of our machines
and is of academic interest.

However multiturn absolute encoders are increasingly common and with a little battery pack don't lose
position when depowered. With a 24 bit encoder such as the Delta A3 series you could have 8 bits for
complete revolutions, ie +127 and -128 revolutions and still have 16 bit resolution within any one revolution,
that is 1:65536 or 0.32 arc min. Enough for any purpose I would have thought!

Craig

Hi Hood

The Norwin Drives were putting 108v to the motors. The max speed according to the Denford Manual was 5M Minute and ball screws have a 5mm pitch. Where did you find the info from the screenshot? I can't find some of those part numbers.

Cheers
Mick

108V would be in the region of 2500rpm on the motor, 5m/min with 5mm pitch would be 1000rpm on the screw so sounds like the motor gearing is 2.5:1 at the moment.

Page 26 of the manual from Schneiders site.

http://download.schneider-electric.com/files?p_enDocType=User%20guide&p_File_Name=LXM28A_Manual_V2.1_EN.pdf&p_Doc_Ref=0198441114054-EN&_ga=2.219455582.630719219.1533230045-1043352968.1533230045

Hi Hood

Thanks for the link. We have no gearing on the motors. It's 1:1 ratio. I presume the OT control restricted the max rpm to limit the axis speed to 5m Min I have a slight problem with the BCH2MM102∙C∙6C motor as the flange size is too big for the X-axis. I could get it to fit on the Z axis but still a bit tight.

If I use the BCH2LF073∙C∙5C or the BCH2LF073∙C∙5C and gear down 2:1 I believe this will double the torque? Which would be above the Sem motors as you suggested in a previous post. That will give me an axis speed of 7.5 M min well above what I require. Does that sound about right or would you suggest something different? 

I have noticed there is only an option for the High and Low inertia on that motor. What would be the better option?

Cheers
Mick

Hi,
how do you intend on gearing it?

Low lash planetary gearboxes are worth as much as a servo.

If I read correctly the servo you are looking at (BCH2.F) has an 80mm frame and a bolt hole pitch circle of 90mm, is this correct?

The SEM you are replacing is an MT30, correct? If that's the case then the motor is 110mm in diameter and the pitch circle of the
bolts is 75mm. Is this correct?

The BCh2.H has a 100mm frame and a pitch circle of 115mm, would that not be a closer physical fit?
I would be trying to couple in directly, no gearing.

Craig