[Titaniumboy]

I have a 110SM04030 servo motor (maybe made by Changzhou Changhua Electric Motor?) that drives my spindle through a 1 to 1.5 pulley ratio. The servo is rated at 1.2kW, 3000 rpm, and 5.0 Amps with a rated zero-speed torque of 4 Nm. The pulley ratio turns the 3000 rpm of the servo motor into 4500 rpm at the spindle.

The servo motor is driven by a Maxsine EP1 220V servo driver.

The 4500 max rpm at the spindle is slower than I would like. Is it possible to run the servo motor at higher than its rated speed?


Attachment 502664

[cncmakers001]

I have a 110SM04030 servo motor (maybe made by Changzhou Changhua Electric Motor?) that drives my spindle through a 1 to 1.5 pulley ratio. The servo is rated at 1.2kW, 3000 rpm, and 5.0 Amps with a rated zero-speed torque of 4 Nm. The pulley ratio turns the 3000 rpm of the servo motor into 4500 rpm at the spindle.

The servo motor is driven by a Maxsine EP1 220V servo driver.

The 4500 max rpm at the spindle is slower than I would like. Is it possible to run the servo motor at higher than its rated speed?


Attachment 502664

It is not suggested to run the servo motor at higher than its rated speed
The motor or even the driver could be over heat and burnt.

[joeavaerage]

Hi,
I disagree.

I use Delta B2 servos and the 750W version is rated at 3000 rpm, but its maximum is 5000rpm. It does this by 'field weakening'. Its rated torque
is 2.4Nm at its rated speed 3000rpm. Beyond its rated speed its torque decreases, but it power output reamains the same. Thus at 5000rpm the torque is:

T= 2.4 x 3000/5000
=1.44Nm

It does not overheat or do anything weird.

Whether your particular servo can go faster than its rated speed depends on the drive, in particular has the manufacturer included a field weakening mode.

All AC servos use a 'Field Oriented Control' algorithm first published in the late 60's, and another important paper in 1972. The basic idea is that and encoder (or some other angular sensor)
reports accurately and faithfully the angular position of the rotor and therefore the magnetic direction of the rotor at any given instant. The algorithm calculates the required stator currents (three phase)
such that the net magnetic field of the stator is exactly 90 degrees to that of the rotor, and thus produce maximum torque for the minimum of current. Very VERY clever indeed.

This has another feature, that you can apply a current to the stator that opposes the magnetic field of the rotor. Lets imagine the rotor field is 0.8Tesla, but the stator applies an opposing field of
0.2Tesla. The effective net magnetic field would then be 0.6Tesla. This is very convenient because the limiting speed of an electric motor is determined by its back EMF. When the back EMF matches
the applied input voltage the motor can go no faster. With field weakening you can artificially reduce the magnetic field and therefor reduce the back EMF. This in turn means that you can persuade the motor
to run faster than it supposed maximum.....but with slightly reduced torque.

In the example I've given if the field is weakened to 0.6Tesla form its normal 0.8Tesla then the back EMF will reduce by 0.6/0.8 or 75%, so you can increase the speed by 25% but with a 25% reduction in torque.

In the case of my Delta servo all I do is program my max speed. It is normally by default set at 3000rpm, but I can set it to 4000rpm and the servo just goes faster, albeit with a little less torque right at the top end.
In fact I can tell it to go up to 5000rpm and the servo just does it. I don't have to program any of the internal field weakening stuff, it just does as its told. Very convenient.

I would suggest you look very closely at your servo parameters that would allow you to do the same.

I have a 1.8 kW Allen Bradley servo as a spindle motor, and I cannot find anyway to make it go faster than its rated speed. I guess Allen Bradley declined to build that feature in. I could be mistaken
of course, just that I have not found a way to have the servo exploit a field weakened mode.

Craig

[joeavaerage]

Hi,
I've just had a look at the Maxsine EP1 driver manual, and it looks like there may be a way.

See P075...that sets the max speed. I presume there is a max current setting somewhere as well. If you set the max speed to 5000rpm but set the max current to rated current, whatever that is,
then the max power to the servo never exceeds its rated 1.2kW and yet it can go faster....is that not field weakening mode?

Craig

[Titaniumboy]

In the case of my Delta servo all I do is program my max speed. It is normally by default set at 3000rpm, but I can set it to 4000rpm and the servo just goes faster, albeit with a little less torque right at the top end.
In fact I can tell it to go up to 5000rpm and the servo just does it. I don't have to program any of the internal field weakening stuff, it just does as its told. Very convenient.

So you don’t have to enter both a rated speed and a max speed? Does the Delta control already know that the servo rated speed is 3000 rpm. Does your Delta servo motor show somewhere that is has both a rated speed and a max speed?

How does the Delta control “know” at what rpm to start the field weakening regime?

Any thoughts on whether field weakening or a higher pulley ratio would be more appropriate to increase my spindle speeds? Thanks again for your help.

[joeavaerage]

Hi,
that is a good question, and the short answer is I don't know.

I have looked and looked again at all the programming parameters of the B2 servos, there is something like 270 of them and I cannot find any parameters which set 'Rated Speed or Rated Torque'
There is however a parameter that is 'Set by model', that is to say the drive reads the servo. The parameter is not user programmable, and presumably it identifies the the servo motor to the drive.
The numeric value of the parameter does not really give any indication.

Any thoughts on whether field weakening or a higher pulley ratio would be more appropriate to increase my spindle speeds? Thanks again for your help.

Not a lot in it I would have thought.

You may have seen quite a range of servo style motors made for spindle drives. The Chinese seem to specialise in them. Often they have a rated speed of only 1500rpm, and because of that low rpm
have very good torque, but also have a max rpm of 8000rpm or so. They are using field weakening to a very great extent, and that in turn means great flexibility of use and application.
More typical servos do not make such extensive use of field weakening.

The way field weakening works is that a portion of the applied stator current (actually three currents being three phase) opposes the permanent magnetic field of the rotor. You have to ask yourself how much can you oppose
that permanent field without degrading it? I mean we presume that when the opposing currents are stopped the permanent magnetic field returns to normal, but surely if you opposed the permanent field strongly enough
you would de-magnetize the rotor? There is a parameter of magnetic materials called 'Coercivity' which describes the level of magnetic field required to overcome the internal magnetic domains. There is another
parameter called 'Remanence' which describes the magnetic field that remains after a material has been magnetized beyond its Coercivity.

I would presume that these servo like spindle motors have had materials selected to prevent the permanent degradation of the rotor magnets under severe field weakening whereas regular servos are less
amenable to such severe demagnetization events.

Craig

[Titaniumboy]

There is however a parameter that is 'Set by model', that is to say the drive reads the servo. The parameter is not user programmable, and presumably it identifies the the servo motor to the drive.
The numeric value of the parameter does not really give any indication.

Interesting. My Maxsine EP1 servo driver has a Parameter P002 “Identity Code of Servomotor”. There is a table of servomotor codes later in the manual as shown below.

A code of “A102” is shown for a 110ST-M04030L servomotor. I still need to verify what the actual setting is in the Maxsine.

I have an electrical background, but I had never heard of Coercivity or Remanence before. Goes to show that often I don’t know what I don’t know.

[joeavaerage]

Hi,

I have an electrical background, but I had never heard of Coercivity or Remanence before. Goes to show that often I don’t know what I don’t know.

I am an Electrical Engineer also and until a few years ago I'd never heard of them either.

They are important parameters of permanent magnetic materials. You'll find them mentioned in any technical document relating to rare-earth magnets. It is common for instance to have to apply
1.5Telsa to overcome a materials Coercivity and then find when you remove the magnetizing field, that the material retains 0.8Tesla of field, ie its Remanence.

Craig