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Author Topic: Encoder vs resolver  (Read 3267 times)
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zero
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« on: January 27, 2009, 06:38:24 18:38 »

Hi everyone!! Grin

I had like to ask  if it is possible to change a resolver if necessary? I rephrase i know that the resolver works like e rotary transformer and give an analog signal <VS and VC> V sin, Vcos, and the question is if for some reason the resolver is damage its is possible to us change the resolver in way that don't compromisses the god working of the servo, this is if will be sincronysed with the servo windings.

Best regards ZERO. Huh
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insane4evr
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« Reply #1 on: January 27, 2009, 09:32:19 21:32 »

Hi,

This is what I know: Resolvers are used to translate angular position of its shaft to Sin and Cos voltages. These output voltages comes from the sin and cos windings in the resolver that have fixed transformation ratios with its reference winding. Resolution and accuracy are usually high with resolvers.

So, it depends on your application whether it is do-able or not. You might need complex circuits to be able to emulate resolvers with encoders and still not match the resolution and accuracy.
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gem1144aaa
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« Reply #2 on: January 27, 2009, 11:08:36 23:08 »

Hi everyone!! Grin

I had like to ask  if it is possible to change a resolver if necessary? I rephrase i know that the resolver works like e rotary transformer and give an analog signal <VS and VC> V sin, Vcos, and the question is if for some reason the resolver is damage its is possible to us change the resolver in way that don't compromisses the god working of the servo, this is if will be sincronysed with the servo windings.

Best regards ZERO. Huh

hi

nothing is impossible
but u got to know the following:
1-resolvers has their special power supply
2-they are mainly analog
3-its hard to get there digital converters (hard to find and hard prices)
4-encoders are mainly digital and work normally on 5v
5-so you have to change a lot or at least you will add extra interface circuits when you want to change

if you share your circuits both the original and the suggested then i can help
best regards
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zero
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« Reply #3 on: January 27, 2009, 11:41:01 23:41 »

Hi!
Well i asked because i had made mainetenance in some servo industrial servos, for change their bearing and i need act on the resolvers, so i must be carefull to mark the position on the shaft and on estator too. So i though if one day something happens on the resolver and we most change for a new one. How can i find the right position for the new resolver on the servo shaft and the estator??, because if will not be well mounted we will had sveral problems for the machine.
So have anyone the knowledge or idea if its possible for a field techician execute this job or most delivery the servo to the manufacture?
thanks for the replays!!

Best regards
Zero.
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gem1144aaa
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« Reply #4 on: January 29, 2009, 01:20:48 13:20 »

Hi!
Well i asked because i had made mainetenance in some servo industrial servos, for change their bearing and i need act on the resolvers, so i must be carefull to mark the position on the shaft and on estator too. So i though if one day something happens on the resolver and we most change for a new one. How can i find the right position for the new resolver on the servo shaft and the estator??, because if will not be well mounted we will had sveral problems for the machine.
So have anyone the knowledge or idea if its possible for a field techician execute this job or most delivery the servo to the manufacture?
thanks for the replays!!

Best regards
Zero.

hi

how to adjust the new resolver in place with no shifts ?
and you have no marking for shaft position.
this operation is named calibrating the system to the new resolver and this operation should be found on the maintenance manuals of the manufacturer of the machine that contains resolvers inside.

best regards
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insane4evr
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« Reply #5 on: January 31, 2009, 05:55:39 17:55 »

Hi!
Well i asked because i had made mainetenance in some servo industrial servos, for change their bearing and i need act on the resolvers, so i must be carefull to mark the position on the shaft and on estator too. So i though if one day something happens on the resolver and we most change for a new one. How can i find the right position for the new resolver on the servo shaft and the estator??, because if will not be well mounted we will had sveral problems for the machine.
So have anyone the knowledge or idea if its possible for a field techician execute this job or most delivery the servo to the manufacture?
thanks for the replays!!

Best regards
Zero.


There could be a way to prepare for this.
Can the existing working resolver be powered and its shaft manually turned safely?
Are you handy with a DVM?
Can you attached the DVM to the terminals of the resolver?
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zero
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« Reply #6 on: January 31, 2009, 11:07:45 23:07 »

Hi!
Well, about your question insane4evr, I think that it's a pretty dificult but maybe possible, perhaps in a preventive mainetenance on the machine. Undecided Grin
Now i ask, it´s possible do this job with a DVM? The signal are Vsen and Vcos, how can we calibrate the resolver with DVM? Huh

Thanks best rgards
Zero Grin
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insane4evr
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« Reply #7 on: February 01, 2009, 03:13:22 03:13 »

Hi!
Well, about your question insane4evr, I think that it's a pretty dificult but maybe possible, perhaps in a preventive mainetenance on the machine. Undecided Grin
Now i ask, it´s possible do this job with a DVM? The signal are Vsen and Vcos, how can we calibrate the resolver with DVM? Huh

Thanks best rgards
Zero Grin


Hi zero,

I am not sure this is called calibration.

I will probably call it characterizing a resolver.

To make sure we both don't get lost in the steps, I will need feedback of the readings from you.

Step 1: Measure input reference voltage and post it: ? Vrms. If you can get frequency post it also: ?Hz.
Step 2: Using a non-permanent marker, place a temporary mark on the resolver shaft.
Step 3: Attach DVM leads to the Vsin(or Vcos) leads of the resolver.
Step 4: Slowly rotate clockwise the resolver shaft until you read the maximum AC voltage. Post it: ? Vrms.
Step 5: Note the position of the shaft at the condition of step 4 by placing an opposite mark to the resolver end bell housing.
Step 6: Continue slowly rotating the shaft in the same direction as in step 4 until you get to the next position with the maximum AC voltage.
Step 7: Continue slowly rotating the shaft for one complete revolution and count how many times you get maximum AC voltage readings.

I will continue with the procedure after you have posted data for:

Step 1
Step 4
Step 7

Regards.
« Last Edit: February 01, 2009, 03:39:24 03:39 by insane4evr » Logged
zero
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« Reply #8 on: February 01, 2009, 11:57:29 23:57 »

Hi! Grin
At first i'm gratefull for your attention insane4evr;
At moment it is not possible to answer to your questions because i must wait for the momemt for an preventive programeted maintenance in one machine. But i will pay attention and as soon as possible i try post the measures.
I have resolvers that in the place of the shaft is a hall and so the rotational part is mounted directly on the motor shaft.
When you mean powered the resolver you meaning feed the resolver by the motor drive? I ask, because in his condition the motor is blocked on the position until he receives order to start, and if i try move the shaft he motor spins untill get is position again, this could be a dangerous task.Exist an alternatif way to take this task foward?
When i had to interview in one servo i use a temporary mark for dismount a resolver for change the servo bearings, and for now  i have been sucessed.
best regards
Zero Wink
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insane4evr
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« Reply #9 on: February 02, 2009, 02:44:24 02:44 »

Hi! Grin
At first i'm gratefull for your attention insane4evr;
At moment it is not possible to answer to your questions because i must wait for the momemt for an preventive programeted maintenance in one machine. But i will pay attention and as soon as possible i try post the measures.
I have resolvers that in the place of the shaft is a hall and so the rotational part is mounted directly on the motor shaft.
When you mean powered the resolver you meaning feed the resolver by the motor drive? I ask, because in his condition the motor is blocked on the position until he receives order to start, and if i try move the shaft he motor spins untill get is position again, this could be a dangerous task.Exist an alternatif way to take this task foward?
When i had to interview in one servo i use a temporary mark for dismount a resolver for change the servo bearings, and for now  i have been sucessed.
best regards
Zero Wink

Hi zero,

When I said powered, I mean the reference winding is being fed by the proper reference AC voltage and not being driven mechanically. Typical resolvers have three windings, the reference winding, the cos winding and the sine winding. So, they have 6 wires or terminals at a minimum. You can think of a resolver as a special type of transformer with two secondarys (1: sine, 2: cos) and the reference winding (3) as the primary.

Based on your above post, it seems that it is un-safe to do the measurements when the resolver is in the machine. My assumption is you can remove the resolver from the machine and take measurements while it is on a work bench.

****I strongly advice you not to proceed unless you can disconnect the resolver from the drive motor/shaft and do it on a work bench.****

Please be safe.
« Last Edit: February 02, 2009, 02:52:58 02:52 by insane4evr » Logged
zero
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« Reply #10 on: February 02, 2009, 05:09:59 17:09 »

Hi insane4evr,  Grin

About the resolver, I basicaly understand how they works, the question is first i need to know what is the proper AC power and frequency, unless I try measure on the electronic drive, because I can not find his information on the machine manual, because if I don´t have this information is useless to test on the bench.
Other way is looking on the net in the manufacture resolver site!!
Now, the informations that you post here put me very curioses about the subject, by what I understand the resolvers in one completly turn shaft can reach more than one time the maximum value signal. It is right ??
Forgive  my bad english but is not my native language.

Best regards
Zero Wink
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insane4evr
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« Reply #11 on: February 03, 2009, 08:31:06 08:31 »

Hi insane4evr,  Grin

About the resolver, I basicaly understand how they works, the question is first i need to know what is the proper AC power and frequency, unless I try measure on the electronic drive, because I can not find his information on the machine manual, because if I don´t have this information is useless to test on the bench.
Other way is looking on the net in the manufacture resolver site!!
Now, the informations that you post here put me very curioses about the subject, by what I understand the resolvers in one completly turn shaft can reach more than one time the maximum value signal. It is right ??
Forgive  my bad english but is not my native language.

Best regards
Zero Wink
Hi zero,

The reference winding for most resolvers (like size 11) usually has operating voltage that can be any value between 5 and 26 V rms. Frequency usually is between 1KHz to 10KHz. Some can be as low as 400 Hz, these low frequency units are usually used in aircraft application.

In a typical resolver, if you measure with a DVM the output of either the cos or sin winding while you rotate the shaft one complete revolution starting from a reading of close to zero Vrms, you will observe that the reading will increase then decrease close to zero, then increase and decrease again back to close to zero. If you plot, this voltage versus shaft angular rotation, the plot will be two half sines. One of the half sine should be opposite the other half about the zero volt axis in the plot giving you a complete cycle. Resolver manufacturers use various measuring equipment better than a DVM. see http://www.naii.com/products/viewProduct.aspx?productID=4

For the above example, one electrical cycle occurs in one mechanical rotation. This resolver is said to have a 'speed' of 1X. So, a 2X 'speed' resolver will have two electrical cycles in one mechanical rotation, etc.
« Last Edit: February 03, 2009, 08:47:31 08:47 by insane4evr » Logged
zero
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« Reply #12 on: February 03, 2009, 06:49:58 18:49 »

Hi, insane4evr! Grin

For what i understand, i need a wave generator to produce the reference voltage and frequency, it is a equipment that i dont have in my company, however i'm still interesting on your very clear explanation about resolvers, and so i have to ask, what is the relation between plot wave of the resolver and the correct position for mounting the resolver on the motor shaft?
Very thank's for your compreention.
Best regards

Zero. Wink
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insane4evr
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« Reply #13 on: February 05, 2009, 06:14:14 06:14 »

Hi zero,

If you have an oscilloscope with three or more channels and can scope the terminals of the resolver, you could see something similar to my sketch in:
http://img187.imageshack.us/img187/7195/resolverwaveformvsshafttj3.jpg
Voltages and frequency may be different as I made this sketch for somebody else.

The sketch shows the phase and amplitude relationship of the reference, sin and cos at six different shaft positions. Note that the amplitude of the sin and cos changes depending upon the rotational position of the shaft. The reference voltage (R1) is the thick line sinewave. Starting from left to right, top to bottom:

1. Using this condition as 0 degree shaft angle, cos ampltude is zero and sin amplitude is at maximum (33.3V peak to peak). Sin is also going positive.

2. At 45 degrees shaft angle, sin and cos wave are on top of each other (in-phase) and amplitude is lower (23.5V peak to peak). Both going positive.

3. At 90 degrees shaft angle, sin amplitude is zero and cos amplitude is at maximum (33.3V peak to peak). Cos is going positive.

You can figure out the rest.

Note that with only a DVM, you will not be able to determine phase relationship.

Special chips/circuits are used to calculate the shaft angle based on the above basic relationships. Of course there are also other factors.
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zero
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« Reply #14 on: February 05, 2009, 06:16:15 18:16 »

Hi Insane4evr, Grin

That was realy a good explanation, unhappily at moment i dont have a source supply for resolver applications, neither an oscilloscope with 3 channels, only an fluke scopemeter with 2 channels.
But I´m very happy because you give me a good lessons and so improve my knowledge. Cheesy
Best regards
Zero, Wink
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insane4evr
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« Reply #15 on: February 05, 2009, 09:05:05 21:05 »

Hi Insane4evr, Grin

That was realy a good explanation, unhappily at moment i dont have a source supply for resolver applications, neither an oscilloscope with 3 channels, only an fluke scopemeter with 2 channels.
But I´m very happy because you give me a good lessons and so improve my knowledge. Cheesy
Best regards
Zero, Wink

Hi zero,

If your fluke scopemeter has a separate external trigger input, then you can feed it with the reference voltage and just imagine how it looks on the screen. Then you can use the two channels for the sin and cos.
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