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Resolution of Endat 2.2 encoder data channel

An Endat 2.2 encoder is not necessarily high resolution when used as a data-only device.  We use two very different Endat 2.2 devices.  The ECN113 is Endat 2.2/01, which is Endat 2.1 equivalent and uses sine/cosine analog signals and a data channel.  The ECN125 is Endat 2.2/22, which only has a data channel (no analog signals).

Some applications require using only the data/clock and not the sine/cosine analog signals in order to minimize the number of conductors in the feedback cable. The AKD drive supports this type of feedback as Endat 2.2.  An Endat 2.2/01 encoder can be used as Endat 2.2 (data-only) feedback type by just ignoring the analog signals.  However, there is a problem with using only the data channel of an Endat 2.2/01 encoder when it comes to tuning.  The data channel of Endat 2.2/01 has a resolution of only 13bit.  This is because it is expected to have the drive interpolate the analog sine/cosine signals to get high resolution (24bit in the AKD).  A resolution of 13bit is 8192 counts per revolution, which is the same resolution as a 2048 line quadrature encoder.  There is a drastic difference in the tuning between 13bit resolution and 24bit resolution.  In terms of servo performance and smoothness, using only the data channel of the Endat 2.2/01 encoder defeats the purpose of using an Endat encoder.  An inexpensive 2048 line comcoder can provide the same performance.

The solution in this type of application is to use an Endat 2.2/22 encoder.  This has a resolution of 25 bits per revolution on the data channel.  There is no analog channel.  So the data channel will provide better resolution, and performance, than using the analog + data of Endat 2.1 or Endat 2.2/01.

When using Endat 2.2 feedback type in the AKD, the drive reads the number of bits from the encoder, but the user never sees this.  It is only internal information.  The user will only see the difference play out in tuning performance and smoothness.  The user must know which type of Endat 2.2 is being used in order to determine the level of performance that can be achieved.