servo motors

[Flatbush]

Sorry if this sounds silly, but how does a servo motor actually work? I've seen them used in hundreds of applications but I don't know how they actually work. Again, sorry if it is a dumb question.

 

[buzzp]

I believe (no expert) they have multiple windings. The smaller increments they can resolve, the more windings.

 

[Barry1961]

Servo refers to a type of control "closed loop". There are also servo vavles and servo linear motors. The thing that makes a servo system is some type of positioning feedback device that will allow a servo controller to stop the motion at a set position or reverse and go back the a set position if it has over shot the set position. The cruise control in a car is a servo system which tries to maitain a set position (speed) while going up and down hills.

The feedback on a servo motor is usally a encoder or resolver which is attached to the back of the motor rotor and produces a number of pulses or sine waves per revolution of the motor. You then command the controller to rotate the motor x pulses, which it does then holds that position until told otherwise. The type of voltage waveform mostly used is a constant amplitude square wave that is modulated by the pulse width(PWM). The algorithm (formula) used by the contoller has 3 basic factors. Proportional Gain which causes increases power in proportion to the position error, Integral Gain which increases over time and Derivative Gain which acts as a damper.

Servo motors are very high preformance motors with a built in feedback device.

If you go to different servo mfg websites they will usally have more detailed info. Some of the mfgs are Baldor, Allen Bradley, Yaskawa, Sanyo-Denki, Baumuller, Kollmorgen and pacsi.

Hope this helps
Barry

 

[jbartos]

Suggestion: Visit

http://www.ctc-control.com/customer/elearning/servotut/bode.asp

for servo basics

 

[jbartos]

Suggestion: Visit

http://www.ctc-control.com/customer/elearning/servotut/pid.asp

for PID and Servo

 

[jbartos]

Suggestion: Actually, the servo is covered wery well on Web. Also, it is a popular area to study at various educational levels. Visit

http://www.packagingdigest.com/articles/200308/99.html

http://209.41.165.153/stepper/Tutorials/UniTutor.htm

(for servo systems)

http://www.uoguelph.ca/~antoon/hobby/servo1.htm

http://www.manufacturingcenter.com/dfx/archives/0499/499motut.asp

http://www.microcore.dk/index.php?page=walker3mtr

http://www-csl.cs.colorado.edu/LegoRobots/motors.html#5517

http://www.icspat.com/papers/460mfi.pdf

(for Robust Optimal Servo Controller)
etc. for more info

 

[jbartos]

Suggestion: Actually, the servo is covered wery well on Web. Also, it is a popular area to study at various educational levels. Visit

http://www.ctc-control.com/customer/elea...

for servo basics

http://www.ctc-control.com/customer/elea...

for PID and Servo

http://www.packagingdigest.com/articles/...

http://209.41.165.153/stepper/Tutorials/...

(for servo systems)

http://www.uoguelph.ca/~antoon/hobby/ser...

http://www.manufacturingcenter.com/dfx/a...

http://www.microcore.dk/index.php?page=w...

http://www-csl.cs.colorado.edu/LegoRobot...

http://www.icspat.com/papers/460mfi.pdf

(for Robust Optimal Servo Controller)
etc. for more info
Servo hardware is available over

http://www.thomasregister.com

and type Servo Systems under Product or Service, which will return 139 companies to approach to
Alternately,
type Motors: Servo that will return 232 companies to approach to
and
type Drives: Servo that will return 146 companies to approach to

 

[dazmac]

Plenty of useful stuff !! I have little experience with servo motors myself - I am currently trying to replace a 6-pole servo and having lots of fun, the motor insists on going in the wrong direction. I've re-programmed the controller to the best of my ability (it's in Italian!) with a simple direction command (MD=0 fwd MD=1 reverse) but it still goes the wrong way !!! AGggggghhhhh

 

[analogkid2digitalman]

Dazmac-

Is it a brushed servo, if so make sure power polarity is correct. Also check polarity of +/-10 position command signal if applicable.

 

[jbartos]

Suggestion: Call the controller tech support to verify that the controller is compatible with the servo motor you have.

 

[Barry1961]

On the servo going reverse, two things to check.

That the motor is compatable with the drive. Unless the feedback is clocked the way the drive expects it to be it won't work.
If this is an old DC servo with a tach it need to be the right polarity also.

Barry

 

[dazmac]

Thanks guys, spent 2 solid days on it (apart from stopping to talk to production managers who ask how it's going- why do they do that ?)

Furhter details, a brushless drive, resolver.

As I said, I found a command in the controller for direction (MD), then slept on it last night and went in this morning, looked again at the application code and jumping out at me was XR=0 -- Resolver direction ! changed this and hey presto!

Tried the drive and it ran 1/4 speed, spent all day messing with tweeks to the application before working out new resolver is 14-bit, the old one was 12-bit !

Changed resolver settings in initialisation routine and it runs like a dream!