maxon Controllers with Resolver?

Topic

• Can a motor combination with a resolver operated with maxon controllers?
• What controller has to be used in case of a resolver?

Solution

The general answer is that maxon does not offer controllers with a direct resolver interface. Nevertheless there are solutions present based on 3rd party add-on components to connect a motor combination with a resolver to a maxon controller. There is a so-called RDC - "Resolver to Digital Converter" required to do so. The RDC processes the resolver signal and provides "digital incremental encoder" signals to the maxon controller.

Resolver versus encoder?

Resolvers had been mainly in use for powerful drives operating in harsh environments in the past. Nowadays there are different types of encoders available which can be in use by all types of motors and environments and which can fulfill almost any system requirement like resolvers.

Encoders have a lot of advantages compared to resolvers:

• Incremental and absolute encoders are often more compact in size than resolvers.
• The digital (differential) signals of encoders are less sensitive concerning electrical noise than analog resolver signals.
• The total system cost of encoders and controllers are typically lower than a solution based on a resolver.

Due to all these advantages the request for encoder based solutions is much higher than for resolvers. maxon offers resolvers as part of a motor combination for specific applications but no controllers with a direct resolver interface. There was almost no demand for controllers with a resolver interface during the last years. The integration of such a resolver interface as a standard feature of the controller would increase the cost remarkably although most applications do not need it all.

Resolver = Analog incremental encoder? -> No!

The EPOS4 has an "Analog incremental encoder" interface. There is sometimes the misunderstanding that a resolver is like an analog incremental encoder. It is not!

A resolver is no(!) "Analog incremental encoder".

• An analog incremental encoder has an A and B channel (plus quite often differential signals) which output an analog sinus and cosine waveform. (Digital incremental encoders output a square-wave pulse signal.)
• A resolver is like a small transformer and demands for an input frequency ("Prim +", "Prim -") fro its functionality. The output voltage ("sin+", sin-", "cos+", "cos-") of a resolver is a function of the rotor angle then, see also here:
  https://en.wikipedia.org/wiki/Resolver_(electrical) 
  Finally this means that there is some specific hardware interface (and firmware) required to process resolver signals directly by a controller. The interface has to provide the analog input frequency signal required by the resolver and it has to processes the sinus and cosine output signal of the resolver.

Solution: RDC - Resolver to Digital Converter

A resolver can be operated by a so-called RDC (= Resolver to Digital Converter). Please google for "Resolver to Digital Converter" to find suppliers of such a 3rd party add-on components. Such RDCs can be added externally in between the motor's resolver and controller. The RDC generates digital incremental signals of the resolver signal.  This digital incremental output signal can be connected and processed by the controller then. 

There are chip sets (e.g. by TI, Analog Devices) which are intended for integration into an electronics design (e.g. by a customized EPOS4 or ESCON motherboard). There are also ready to run modules which have a resolver interface and output digital incremental 5V signals (A, A\, B, B\). Such 5V digital incremental encoder signals can be processed by almost any kind of controller (like maxon's ESCON, EPOS, or MAXPOS). 

Remark:
maxon does not recommend a specific RDC and cannot provide support for the RDC's configuration or functionality. We highly recommend to check the information and specification of the RDC supplier firmly if such a solution is chosen.

Additional notes:

• All maxon controllers demand for Hall sensor signals for commutation of brushless motors if there are incremental encoder signals present (independent if these are provided by an encoder directly or processed by an RDC).
  => Even if there is a resolver and RDC in use, there are still Hall sensor signals required in case of an EC motor (= brushless DC motor).
• In case of virtual Hall sensor signals generated by a RDC in addition, these virtual Hall sensor signals have to match with the pole pair number of the motor and comply with maxon's Hall sensor switching logic and timing.
  
  

Conclusion: Resolvers?

If there is a motor combination with a resolver in use, you have to ...

• ...  add a RDC (= Resolver to Digital Converter) externally.

or

• ... look for a controller by a 3rd party which has an integrated resolver interface and can process resolver signals directly. 
  Remark:
  It is recommended to choose a controller with a high PWM frequency (typ. 50 kHz), fast control rates (current control at least 10 kHz, position control at least 1 kHz), plus possibly internal or external motor chokes due to the typically low inductance and high dynamics of maxon motors.

Another typically more compact solution with even less cost is to select a motor combination with an encoder instead of the resolver. 

If you have any further questions or need some assistance concerning an optimized system design, please contact your local maxon site or use the Support Center to "Submit a request" and let us know more about your application, system requirements and intended components in use.