EPOS2 <-> EPOS4 <-> CiA402: Compatibility?

Topic:

• Is the EPOS2 and EPOS4 fully compatible?
• Can the EPOS4 be used as an replacement for an EPOS2 (or even EPOS) of an existing system design?
• What does fulfilling the CiA402 standard mean in practice?
  Is there still some risk of incompatibility or limitations in between different CiA402 devices? If yes, why?

Solution:

Basically, all EPOS product lines (i.e. EPOS, EPOS2, EPOS4) are based on the "CiA301 - CANopen application layer and communication profile" and "CiA402 - CANopen device profile for drives and motion control" standard (-> www.can-cia.org/can-knowledge/canopen/cia402/). These standards hold the detailed specification of a large number of operating modes, functions, and objects.

It must be taken into account that only a very limited number of the specified functions and objects must be implemented in order to comply with the standards. The majority of operating modes, functions and objects can be but do not have to be implemented by a CiA402 CANopen controller.

Some operating modes (e.g. the "Cyclic" modes) and associated objects have been added and specified successively in CiA402 over the years. The standard also allows supplementary functions, operating modes and objects to be made available on a manufacturer-specific basis.

The relatively large freedom of implementation can lead to incompatibility between CiA402-based motor controllers from different manufacturers. However, a certain incompatibility may also exist between the product lines of one manufacturer (such as in particular between the EPOS4 and EPOS2) due to the time of development and the respective valid (extended) CiA402 specification. 

EPOS2 aspects:

• The basics of EPOS (and EPOS2 based on it) were developed about 20 years ago based on the then valid (still very "young") CiA402 standard.

  • At that time CiA402 mainly specified only the "profile oriented" operation modes like "PPM -Profile Position Mode", "PVM -Profile Velocity Mode", "HM - Homing Mode" and "IPM - Interpolated Position Mode". These standardized modes like "PPM", "PVM", "HM" and "IPM" were also provided by EPOS and EPOS2 and extended by some manufacturer specific modes.

  • At that time, CiA402 did not(!) yet specify any of the "Cyclic" operating modes (such as "CSP - Cyclic Synchronous Position", "CSV - Cyclic Synchronous Velocity", "CST - Cyclic Synchronous Torque"), in which a CANopen master executes a higher-level control and specifies new set points in a fast cyclic cycle. 

  • Since the "Cyclic" operating modes were not yet standardized for EPOS at the time of development, most manufacturers defined additional customer-specific extensions, such as the maxon operating modes "PM - Position mode", "VM - Velocity mode" and "CM - Current mode" in the case of EPOS and EPOS2.

EPOS4 aspects:

• The EPOS4 has been developed based on the latest CiA402 standard:
  • The EPOS4 offers the operating modes "CSP", "CSV", and "CST", "PPM", "PVM", and "HM" operating modes which are all fully compliant with CiA402 specification nowadays. 
  • The former maxon specific operating modes like "Position mode", "Velocity mode", and "Current mode", which were available by the EPOS and EPOS2, are no(!) longer present by the EPOS4 anymore and have been replaced by the standardized "Cyclic" operating modes "CSP", "CSV", and "CST". However it must be taken into account that these "Cyclic" operating modes are functionally very similar to the earlier maxon operating but partly demand for different standardized object numbers for configuration and commanding.
  • The CiA402 operating mode "IPM - Interpolated position mode" and also some very application specific maxon operating modes (e.g. "Master encoder mode", Step/Direction mode") of the EPOS and EPOS2 are no(!) longer present by the EPOS4 due to missing or only very low demand for such features. 

Further details where the EPOS4 has some remarkable differences in comparison with an EPOS and EPOS2:

• The EPOS4 has greatly improved controller algorithms and the scaling of the control parameters has also been better adapted to physical values.
• The maxon-specific object numbers have also been adapted in the EPOS4 to meet the requirements of the current CiA402 standard and also EtherCAT systems.

Conclusion:

• The EPOS4 is no(!) 1:1 or plug-and-play replacement for the EPOS2 (or EPOS).
  • Some EPOS2 features, supported operating modes, and objects partly differ or might even not exist in case of an EPOS4.
    
    
• Before deciding to replace an EPOS or EPOS2 by an EPOS4 in an existing system design or as a replacement, it is necessary to clarify which operating modes and objects are actually in use. This can be done the most reliable way by some analysis of the master's application code which configures and commands the EPOS2.
  • If the EPOS2 operating modes "PPM - Profile Position Mode", "PVM - Profile Velocity Mode" or "HM - Homing Mode" are used, these are almost identically by the EPOS4. An adaptation of the application program might be not necessary at all or only in a limited way when specific EPOS2 objects and additional functions have been in use too.
  • If the EPOS2's "Position mode", "Velocity mode", or "Current mode" has been in use, the EPOS4 operating modes "CSP", "CSV" and "CST" are suitable as an alternative. It should be possible without much effort to adapt the master's application code to the EPOS4 and updated CiA402 standards then.
  • If the EPOS2 operating modes "PPM - Profile Position Mode", "PVM - Profile Velocity Mode" or "HM - Homing Mode" are used, these are identically also available at the EPOS4. An adaptation of the application program is mostly not necessary at all or only when using EPOS2 specific objects and additional functions.
    
    

• It is almost ever necessary to adapt the application program of the master when changing from EPOS2 to EPOS4!

  • Based on the knowledge about the master in use and some features of the application program, a first rough effort estimation and advice concerning necessary code adaptations is possible.

Cross reference:

There is another Support Center document present addressing the most importing distinguishing marks of the EPOS4 compared to the EPOS2 (resp. EPOS):
-> EPOS2 versus EPOS4: Connectors, Object Dictionary, Operating modes, Libraries