Resolver rule

Sergio155

Joined Jul 12, 2022
8
Hello everyone. Does anyone know, if there is any rule between the number of polar pairs of the motor and the number of polar pairs of the resolver? I have a pp=5 motor and a pp = 2 resolver and I'm in doubt how to control it.

panic mode

Joined Oct 10, 2011
2,524
They need to match... and be correctly aligned
4 pole motor is paired with 4 pole resolver.
3 pole motor is paired with 3 pole resolver

Sergio155

Joined Jul 12, 2022
8
They need to match
Thank you! But i think it is enough if, for example, we have pp=4 for motor and pp=2 for resolver. Another words the motor pp must be divided by 2(reso pp) entirely

panic mode

Joined Oct 10, 2011
2,524
How would they be aligned?

Sergio155

Joined Jul 12, 2022
8
How would they be aligned?
You can recalculate the measurements given by resolver into different pole pairs during runtime using your microcontroller . For example I multiply resolver data by 2 and then, if the result more than 360grd i substract 360grd. For given pp numbers

Joined Jul 18, 2013
28,026
What is the role of the resolver exactly?
, Commutation of a ECM or BLDC motor?
Or means of positioning?
Generally the means of commutation has to be aligned with the poles.

atferrari

Joined Jan 6, 2004
4,730
Resolver - learnt a new name today. Not that I know a lot about electric motors; they are, in fact; one of my major stumbling blocks.

Joined Jul 18, 2013
28,026
Resolver - learnt a new name today. Not that I know a lot about electric motors; they are, in fact; one of my major stumbling blocks.
They were often one early means of motor positioning, prior to incremental encoder.
I still have a few kicking around, gathering dust ! .

panic mode

Joined Oct 10, 2011
2,524
They are used as axis position feedback in many industrial robots.

panic mode

Joined Oct 10, 2011
2,524
And they have some serious advantages over optical encoder.

nsaspook

Joined Aug 27, 2009
12,273
We still use resolvers for direct drive motor commutation (absolute position) with an encoder(relative position) for accurate and precision motion control. The motor controller software calculates the revolver and motor pole parameters
https://www.mouser.com/applications/resolver-encoder-motor-control/

The 200mm wafer disk inside a vacuum chamber is driven at 1200 RPM (resolver commutation and speed control) once it's loaded but needs very precise positioning while loading using a high end encoder.

Joined Jul 18, 2013
28,026
And they have some serious advantages over optical encoder.
What do you see those as?

panic mode

Joined Oct 10, 2011
2,524
Much better suited for harsh environment, for example vibration. High accuracy, only limited by sampling circuit. All signals are continuous sine waves of fixed frequency rather than square pulses of random frequency making it far more suitable for transmission over significant length. Absolute position over single pole meaning no need for battery power.. this not only means much simpler working with when commissioning or transferring equipment and maintenance but also can be stored for years without risk of losing position due to battery failure.if axis is moved by external force while resolver was powered off, one can tell instantly if that was the case by comparing current value against one saved while powering down.

Sergio155

Joined Jul 12, 2022
8
They were often one early means of motor positioning, prior to incremental encoder.
I still have a few kicking around, gathering dust !
Much better suited for harsh environment, for example vibration. High accuracy, only limited by sampling circuit. All signals are continuous sine waves of fixed frequency rather than square pulses of random frequency making it far more suitable for transmission over significant length. Absolute position over single pole meaning no need for battery power.. this not only means much simpler working with when commissioning or transferring equipment and maintenance but also can be stored for years without risk of losing position due to battery failure.if axis is moved by external force while resolver was powered off, one can tell instantly if that was the case by comparing current value against one saved while powering down.
You are complitely right. And I want to make a remark that at the moment my motor works with motor pp=16 and resolver pp=2.

Joined Jul 18, 2013
28,026
All signals are continuous sine waves of fixed frequency rather than square pulses of random frequency making it far more suitable for transmission over significant length. Absolute position over single pole meaning no need for battery power.. this not only means much simpler working with when commissioning or transferring equipment and maintenance but also can be stored for years without risk of losing position due to battery failure.if axis is moved by external force while resolver was powered off, one can tell instantly if that was the case by comparing current value against one saved while powering down.
Not always obvious, but a quadrature optical encoder starts off as the same wave form, i.e. dual sine waves 90° apart, in fact manuf. such as Heidenhain use this feature without squaring up to produce arc-tangent output encoders that simulates the resolver, but higher resolution.
The older versions I am familiar with simply have three windings, the sine, cosine and the third for excitation.
Absolute optical encoders can also contain battery backup for such uses as Robots, which typically are not suited to zero'ing procedure at power up.

panic mode

Joined Oct 10, 2011
2,524
Yes there are many options with encoders.... Often people dont even know that something else also exists Versions like sin/cos produce analog signal like resolvers and for the most part act like resolvers relying on DSP for high resolution.
True absolute encoders are parallel and expensive. Cabling in that case is problem too as many conductors are not light or flexible. This means usually tradeoff to low resolution and that is a compromise nobody likes.
The need for battery is generally an issue even for products that are easily accessible for service.
For example simple and common task of re-dressing cables on a robot, or inspection requires disconnecting things. Not a problem on a robot using resolvers but this can be an issue for encoders since it would require recalibration. And even then points are likely no longer the same meaning one may beed to spend time touching up points.
Tolerable temperature range, vibrations and not to mention radiation immunity is hands down resolver domain since there us no onboard electronics. For hot environment (temperature and or radiation) electronics can be moved away and properly shielded. But for encoders that would mean adding suitable temperature control or heavy shielding on each axis. But adding weights to the robots is exactly one thing one tries to avoid, not to mention that may not be possible due to motor placement or travel required.
As for troubleshooting, most resolver related issues can be found using simplest and most readily available tool - a multimeter. And this can be done without loosing position or needing calibration.
It is great that there are plenty of feedback choices so designers can pick the best for application needs. I have worked in different industries (automotive, chemical, nuclear, aerospace) so knowing product characteristics is of great value.
Resolvers may be old and not seen as clear winner on every point but have plenty of characteristics that are attractive in many applications.

Joined Jul 18, 2013
28,026
I first got involved with robot technology back in the 1980's, the first was a hydraulically operated one.
Since then, I have been involved with a few makes, including Fanuc and Mitsubishi, et-al, And so far have never come across one with resolvers fitted.

panic mode

Joined Oct 10, 2011
2,524
Those are Japanese products. Take a look at European brands. Kuka, Abb etc.

Sergio155

Joined Jul 12, 2022
8
Those are Japanese products. Take a look at European brands. Kuka, Abb etc.
Has anybody met this type of resolvers? I mean it's really interesting.

panic mode

Joined Oct 10, 2011
2,524
Looks interesting, thanks..