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What are the symptoms of a bad resolver/encoder connected to the motor ?

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phatcreators

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What are the symptoms of a bad resolver/encoder connected to the motor ?

If a resolver/encoder gone bad then what might be the possible symptoms ?


thanks a lot in advance
 

If we first look at what is the function of resolver and encoder in motor,
so its more easy to understand the consequences of faults.

Encoders produce pulses indicating movement over a short distance;
counting these pulses indicates distance (and speed over time) and
checking the order of pulses in channel A vs. channel B indicates direction (quadrature).

Encoder Applications:
AC Induction Motor Speed and Position Control
DC Motor Speed and Position Control
AC & DC Servo Motors (with commutation tracks added)

Resolvers produce a set of sine/cosine waves (analog voltage) indicating
absolute position within a single revolution; these signals are typically converted
with a resolver interface board to a digital signal.

Resolver Applications
Permanent Magnet (PM) Motor Commutation and Speed Control
AC & DC Servo Motor Commutation and Speed Control
Motor Speed and Position Control

Of these, we see that the activity relates to the speed or position control.

Thus, the most common disturbances be noticed as...
the motor is vibrating, rotating speed varies, strange engine noises

movement positioning accuracy varies, positioning system vibrates,
incorrect positioning, random stops in movement

Most modern motor drives and motion-/positioning controls perform run-time monitoring
of the operation in the measuring equipment
and they can indicate the most common faults and stop the motor.
 
phatcreators said:
What are the symptoms of a bad resolver/encoder connected to the motor ?
Click to expand...

I work repairing a lot of devices, including Encoders.
The most frequent behaviours noticed, in happening rate order :

--> Lost pulses ( merging someones )
--> Deformed pulses
--> No signal at a chanel ( at one, or both )

+++
 
andre_teprom said:
I work repairing a lot of devices, including Encoders.
The most frequent behaviours noticed, in happening rate order :

--> Lost pulses ( merging someones )
--> Deformed pulses
--> No signal at a chanel ( at one, or both )

+++
Click to expand...


thanks all of you guys for your replies & responses .....

How to figure out that the encoder is not able to send the signals at a channel (at one or both) ?
 

Kak111 , would you tell that how to measure with multimeter or any other device these disturbances that you explained above :

the motor is vibrating, rotating speed varies, strange engine noises

movement positioning accuracy varies, positioning system vibrates,
incorrect positioning, random stops in movement
 
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    munzir

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Here is some hints for you...........

motor is vibrating
position controller or motor drive gives continously variable motor position or(and) motor continously accelerate-decelerate
usually easier to find out when motor run in low rpm´s , some rpm`s can generate strong mechanical oscillation.
Check position controller output and motor drive input signal and motor voltage & current. (Oscilloscope)

rotating speed varies
Check motor drive input signal , check motor shaft rpm. ( Oscilloscope, rpm-meter)
Test should do with different speeds.

strange engine noises
listen in different rpm`s
(is sound from drive PWM frequency normal , vibrating sound in PWM is usually abnormal)

movement positioning accuracy varies
mark some exact position , do some moves to random positions and back to marked position
( measure error in position)
-check mechanical backlashes in system

positioning system vibrates
( look motor vibrating)
-something wrong in positioning system parameters

incorrect positioning
Check position controller output (Oscilloscope)
(look movement positioning accuracy varies)
-check mechanical backlashes in system

random stops in movement
Check position controller output and motor drive input signal and motor voltage & current. (Oscilloscope)
-check cable failures , bad contacts

Electrical measurements should be done with oscilloscope, because signals may include fast changes and
different frequencies. ( Impossible to detect with multimeter.)
 
kak111 said:
Here is some hints for you...........

motor is vibrating
position controller or motor drive gives continously variable motor position or(and) motor continously accelerate-decelerate
usually easier to find out when motor run in low rpm´s , some rpm`s can generate strong mechanical oscillation.
Check position controller output and motor drive input signal and motor voltage & current. (Oscilloscope)

rotating speed varies
Check motor drive input signal , check motor shaft rpm. ( Oscilloscope, rpm-meter)
Test should do with different speeds.

strange engine noises
listen in different rpm`s
(is sound from drive PWM frequency normal , vibrating sound in PWM is usually abnormal)

movement positioning accuracy varies
mark some exact position , do some moves to random positions and back to marked position
( measure error in position)
-check mechanical backlashes in system

positioning system vibrates
( look motor vibrating)
-something wrong in positioning system parameters

incorrect positioning
Check position controller output (Oscilloscope)
(look movement positioning accuracy varies)
-check mechanical backlashes in system

random stops in movement
Check position controller output and motor drive input signal and motor voltage & current. (Oscilloscope)
-check cable failures , bad contacts

Electrical measurements should be done with oscilloscope, because signals may include fast changes and
different frequencies. ( Impossible to detect with multimeter.)
Click to expand...


would i have to connect the oscilloscope to the motor (connected to the machine) ? take the oscilloscope to the place where its connected to the machine ?
 

would i have to connect the oscilloscope to the motor (connected to the machine) ? take the oscilloscope to the place where its connected to the machine ?
Click to expand...

When trying to find and locate problems and fails in machines and machine control systems,
measurements must be performed in the machine and when the machine and control system is
running in a situation where a fault occurs.


Check position controller output and motor drive input signal ....

These are control signals usually +/- 10Vdc.

And use differential probe for safety reasons and to prevent
ground loops and accidental groundings in control signals.

Vibrating frequencies can be so high that it cant be detected with DMM or even
with analog multimeters.

When measuring voltages in power grid 240Vac or 400Vac connected devices with oscilloscope,
you need high voltage differential probes ( 2000V minimum ).
and for current measurements use clamp type current probes ( 2kV).

Look here....
Oscilloscope probes :: Electronic Measurements
 
what does it mean by that : Check position controller output and motor drive input signal .... ?

How to check these out ?

thanks anyways
 

There are other assymptomatic problems :

For instance : If mechanical coupling is not properly concentric to the axis, unbalanced force will result in a wear of rollers.
Resulted gap will generate further grinding of optic wheel.

+++
 
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