Encoder vs. Resolver for better tuning? 1

[NemosDogs]

I am a mech. engineer designing the "muscle" (motor/amp sizing) of a servo system where we will have to do some high speed moves (.050 sec) and where we want fast settling. I have plenty of torque but one of our E's has said that he thinks the resolver based motors I have spec'd will be less tuneable than encoder based motors due to the RDC (analog to digital ) conversion that requires time and therefore will lower bandwidth. Does anyone have experience with this or know how I can prove or disprove the idea?

 

[sreid]

What your EE is refering to to is the acceleration phase lag that R/D converters have. This is due to the conversion process almost always being a tracking sero itself.

Resolvers were originally used in brushless motors because they are extremelly rugged. Glass encoder technology has improved to the point that encoders are the usual choice for industrial applications.

For fast settling times the most important consideration is the stiffness of the motor-feedback device coupling. Resolvers used in motors are usually of the unhoused type (resolver rotor mounted directy on the motor shaft)and this is a stiffness advantage.

If an encoder is used it should be the "Kit" style where the encoder disk is also mounted on the motor shaft. If housed encoders are used they should be what's called "Servo class." Encoders coupled to the motor shaft with hellical couplers are horrible re mechanical stiffness.

There are other pluses/minuses with resolvers vs. encoders. However, settling times in servos are usually dominated by mechanical resonances in the load.

If you want a further discussion I can be reached at stevelreid-at-aol-dot-com.

 

[Barry1961]

Many of the people worried about quick settling are using steppers and hybrid steppers. The hybrid steppers are steppers with feedback. Circuit board stuffers will use steppers.

Barry1961

 

[blacksea]

Barry,
hybrid stepper motor is type of steppers, i.e. open loop sytem without any feedback.

 

[sreid]

When I responded to you last night it was late and I had my enginering hat on. This morning with my engineering manager's hat on I think this is what you might do.

Call up Kollmorgen and say you might be having problems with a Moog servo system and you'ed like to try out a Kollmorgen motor/servo amp. Could they send a tech rep down with the proper motor and amplifier, help set it up and give it a whril. And if it works loan it to you for, say, 30 days.