For automation systems that use servo drives or variable frequency drives (VFDs), many customers do not understand the performance of their encoders. Some customers think that if they provide best-in-class encoders, the accuracy of the system will certainly be high.
Sounds plausible? Yes, but there are other factors to consider.
Encoder-based systems have three common terms – resolution, accuracy, and repeatability.
All three factors are important when deciding system-based encoder performance, and the actual performance of the entire system depends on the weakest link.
1, the resolution is the minimum incremental position the automation system can detect. The resolution of each encoder parameter is generally “ppr” (pulses per revolution) to represent.
Ideally, the encoder should achieve the maximum resolution possible.
2, Accuracy is the maximum expected difference between the actual and set (desired) position / speed for a given input.
Ideally, the system should be as accurate as possible, that is, the minimum difference between the set and actual values.
Repeatability is the ability of a motion system to achieve a “set / desired” position in a reliable manner over multiple operations.
Ideally, the system should maximize repeatability.
Therefore, even users with best-in-class, best-of-breed encoders and best-of-breed best-in-class drives may have “under-optimized system performance” due to two factors.
1, Noise: The connection between encoder and PLC or electronic driver does not conform to the standard EMC guidelines (for example, a more practical method is to provide proper shielding for both ends of encoder connection). This connection is susceptible to noise or problems associated with electromagnetic interference.
2, Installation: The encoder is not installed on the motor for proper mechanical installation (eg poor connection will result in “frequency hopping” of the encoder). This may result in poor output repeatability.
Kollmorgen encoder-based servomotors come with factory-assembled encoders so users do not have to worry about their performance at all.
However, when installing a machine encoder or an encoder with an induction motor system, care must be taken to ensure that the encoder is mounted on the machine by suitable mechanical means and the connection of the electric drive or PLC complies with the requirements of the Electromagnetic Compatibility Directive .
This is the best way to get the best performance for your encoder system.