MAXPOS: Replacing a MAXPOS by an EPOS4

Topic:

• What has to be taken into account or checked in advance if a MAXPOS has to be replaced by an EPOS4?

Solution:

1.) Availability of "MAXPOS 50/5"

• The "MAXPOS 50/5" is still available but in "NRND - Not recommended for new designs" state. This means that we do not recommend to use the "MAXPOS 50/5" in case of new projects or updated system designs. There will be no software or firmware updates available for the MAXPOS in future anymore due to the fact that there are no more development activities planned for this product. Technical support and repair service is still ensured as long as possible (even after the product will be finally canceled sometimes and cannot be ordered anymore).
  Please find more information what NRND means about the availability of maxon controllers by the following linked Support Center document:
  -> maxon controllers in NRND state? 
• Recommendation:
  We recommend to think about replacing the MAXPOS by an EPOS4 if there is some new design or upcoming redesign required by your system anyway. A trigger of such a replacement might be if there is some replacement or upgrade of other components required or some update or upgrade of the master's application program features is planned anyway.

2.) Power rating & design: MAXPOS vs. EPOS4

• The MAXPOS was just available as a single product type with up to 50V and just 5A continuous motor output current. 
• The EPOS4 product line offers a wider variety of power ratings and different designs (e.g. "Micro", "Module", "Compact" and cased versions):
  -> http://epos.maxongroup.com
  • Please note that some EPOS4 product types (e.g. "Module" and cased versions) demand for the additional "EPOS4 EtherCAT Card" (P/N: 581245) if the term "EtherCAT" is not already present by the EPOS4's product name. 
• Recommendation:
  Select the EPOS4 product type which fits best to your application based on the required supply voltage, motor current, and preferred design.
  • Due to the fact that the "MAXPOS 50/5" was a cased product type, the "EPOS4 50/5" (P/N: 546047) plus the "EPOS4 EtherCAT card" (P/N: 581245) might be the first choice.
  • If a much more compact size is required, the "EPOS4 Compact 50/5 EtherCAT" (P/N: 628094) is a great choice.
  • Less and more powerful EPOS4 product types are also available and offer a chance to select a product type which fits best to the motor data and application.
• Additional note:
  Please have an eye for the supply voltage required based on maximum motor speed demands by your application. The EPOS4 product line offers controllers with a maximum supply voltage of 24V, 50V, or even 70V. 
  Please find some information concerning the required supply voltage depending on motor speed and motor data by the following linked Support Center document:
  -> What supply voltage is required by a controller?

3.) Compatibility MAXPOS vs. EPOS4

3.a.) I/Os and pin assignment

• Restrictions:
  • The number of I/Os, connector types, and pin assignment is not the same by the MAXPOS and EPOS4.
    Finally this will mean some adaptation of your wiring and cables with connectors has to be taken into account and must be acceptable by your redesign.
  • The EPOS4 does not(!) support "BISS-C" encoders.
    Please think about using a SSI (or incremental) encoder instead if possible. The EPOS4 supports SSI encoder even in a much more flexible way than the MAXPOS and can adapt to almost any manufacturer specific SSI protocol types.
    Please find some more information about the EPOS4's SSI configuration features by the following linked Support Center document:
    -> EPOS4: SSI configuration features 
• Recommendation:
  Please check if the EPOS4 I/Os fit to your system's actuators and sensors (incl. encoder) before you decide to replace the MAXPOS. Please be aware of required cable modifications (due to differing connector types and pin assignments). maxon's support teams are pleased to discuss details with you based on your information about sensors and actuators in use by your current system as well as your concrete MAXPOS project file.

3.b.) Commanding

• The "MAXPOS 50/5" as well as the "EPOS4" comply with the CiA 402 "CANopen device profile for drives and motion control" standard.
• Both controllers support the same "Operating modes" of the CiA 402:
  ​

3.c.) Specific features and objects

• Restrictions:
  • There might be some not very often used specific MAXPOS features present which do not exist in an identical way by the EPOS4 anymore.
  • There might be some specific MAXPOS objects which do not exist anymore by the EPOS4 or have updated object numbers or scaling.
• Recommendation:
  • Please check the MAXPOS features actually in use by your application. Please provide a list about the operating modes, object numbers, features, and I/O configuration in use as well as the MAXPOS project file (-> MAXPOS: Export / upload the configuration into a *.mxpj project file) to us by a support ticket.
  • This information will be the base of maxon's support team to check your probably required code adaptations and critical points in case of using the EPOS4 in future.

3.d.) Bus performance & bus cycle times

• The MAXPOS offers a faster bus performance than the EPOS4.
  • The MAXPOS can cope with bus cycle rates (= SYNC period) down to 200 us depending on the operating mode. 
• Restrictions:
  • The fastest EPOS4 EtherCAT bus cycle rate is 1 ms (resp. 1 kHz update rate).
  • If it is mandatory to have EtherCAT bus cycle rates less than 1 ms, the EPOS4 cannot(!) be used as a replacement.
• Recommendation:
  • Please check what fastest bus cycle rate (resp. SYNC period) is currently in use by your master and actually required by your application?
    If the required EtherCAT bus cycle rate is 1 ms or slower (i.e. 1, 2, 3, 4, ... ms), the EPOS4 can cope with it too.

3.e.) Control performance

• The MAXPOS offers extreme fast motor control rates:
  • Current/torque control: 100 kHz (= 0.01 ms)
  • Velocity and position control: 10 kHz (= 0.1 ms).
• The EPOS4 offers a fast control rates too but these are slower than by the MAXPOS:
  • Current/torque control: 25 kHz (= 0.04 ms)
  • Velocity and position control: 2.5 kHz (= 0.4 ms).
• The EPOS4 has strongly improved and enhanced control and tuning algorithms compared to the MAXPOS.
  • The slower EPOS4 control rates (compared to the MAXPOS) mean no drawback or restrictions by most applications and mechanical systems. The improved control algorithms and automatic control tuning result often in an even better overall control performance of the EPOS4 in practice finally.
• Recommendation:
  Please let us know more details about your application and mechanical system. This helps us to provide some estimation if some restrictions of your application have to be expected based on the EPOS4 control rates.

Conclusion

Required adaptation:

If a MAXPOS has to be replaced by an EPOS4, there will be ...

• ... some wiring modification required due to partly more compact connectors in use by the EPOS4.
• ... an update of the master's application code required to match again with EPOS4's updated object numbers or specific features.

Main restrictions:

• If an EtherCAT bus cycle rate (resp. SYNC period) faster than 1 ms is required, the EPOS4 cannot(!) be used. 
• The EPOS4 has no "BISS-C" encoder interface.
  If your system has a "BISS-C" encoder in use, it is required to use a SSI encoder instead.  

Advantages of the EPOS4:

• Broad variety of different product types concerning design, power ratings and integration (based on "Micro" and "Module" versions).
• Most compact size
• High power density without additional cooling.
• Lower price.
• Improved control algorithms.
• Improved automatic control tuning.
• Enhanced configuration features.
• Enhanced functions (e.g. "Dual Loop" control).