Resolution of Endat 2.2 encoder data channel

It is not enough to define an encoder as Endat 2.2.  Endat 2.2 defines the communication protocol, but does not specify which channels are available.  For Kollmorgen drives, we must define the encoders as Endat 2.2/01 (order code Endat01) and Endat 2.2/22 (order code Endat22).

• Endat 2.2/01: analog sine/cosine + Data/Clock
• Endat 2.2/22: Data/Clock only

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).

There are two aspects of resolution (precision and accuracy) for an Endat Absolute encoder:

• Resolution of the incremental positioning
• Resolution of the absolute position (initial position upon bootup)

Incremental positioning resolution

Endat 2.2/01: The incremental resolution is determined by the drive interpolating the analog sine/cosine signals.

Endat 2.2/22: The incremental resolution is determined by the encoder's data channel resolution.

For Endat 2.2/01 encoders used in Kollmorgen motors, the data channel has a resolution of only 13bit but the overall resolution of the encoder is 27bit.  This is because the drive interpolates the analog sine/cosine (incremental) signals to get high resolution (27bit in the AKD).  Servo performance, precision, and smoothness are affected by the resulting resolution of the analog signals being interpolated in the drive.  Different drives may have different interpolation rates, resulting in different tuning.  In this case, the Endat 2.2/01 provides higher incremental resolution than a 25bit Endat 2.2/22 encoder.

Absolute Position Resolution

The absolute position resolution is determined by the encoder's data channel resolution for both Endat 2.2/01 and Endat 2.2/22.

While the analog signals provide high resolution after interpolation, the Endat 2.2/01 data channel is typically very low resolution.  In the case of the ECN113, the 13bit data channel provides only the same positional resolution of a 2048 line quadrature encoder for absolute positioning upon bootup of the drive.  The initial absolute position of the ECN125 is much higher resolution, at 25bit.