Question:
i700 servo inverter: What quantisation, resolution, accuracy can be achieved during operation with Hiperface SinCos absolute value encoders or SinCos encoders?
Answer:
For Hiperface SinCos absolute value encoders, two different cases are to be distinguished with regard to quantisation and the achievable resolution:
- Initialisation:
The absolute value is read out from the encoder via Hiperface communication and accepted as starting value for the calculation of the actual position in the controller.
- Operation:
Then, the actual position is updated by evaluating the SinCos tracks.
Position changes are cyclically determined from the SinCos tracks and integrated to the actual position.
For the evaluation of the SinCos tracks at first, the zero crossings of the SinCos signals are detected (quadruple evaluation). A base quantisation is resulting, which is determined by the number of periods of the encoder.
In addition, the amplitudes of the SinCos signals are evaluated (fine interpolation), in order to get more points in between. In this way, quantisation can once again be increased by a factor of 128 (7 bits).
Depending on the encoder type, the following quantisation values (base quantisation + fine interpolation) can be achieved during operation on i700 servo inverters:
SRS 50 / SRM 50 (number of periods: 1024 periods):
Hiperface: Quantisation: ~ 0.66` (resolution that can be actually displayed: 32768 inc/rev (15 bits)
SinCos tracks: Quantisation: ~ 0.16` (resolution that can be actually displayed: 131072 inc/rev (17 bits)
SRS 36 / SRM 36 (number of periods: 128 periods):
Hiperface: Quantisation: ~ 5.3` (resolution that can be actually displayed: 4096 inc/rev (12 bits)
SinCos tracks: Quantisation: ~ 1.4` (resolution that can be actually displayed: 16384 inc/rev (14 bits)
SEK / SEL 37 (number of periods: 16 periods):
Hiperface: Quantisation: ~ 42` (resolution that can be actually displayed: 256 inc/rev (8 bits)
SinCos tracks: Quantisation: ~ 10.5` (resolution that can be actually displayed: 2048 inc/rev (11 bits)
Quantisation:
Measure of the gradation / the smallest distinguishable signal change.
Resolution:
Representation format of an increment value.
Theposition resolution is, e.g., the representation format for the actual position: Number of increments per revolution [inc/rev].
In the controller, the position resolution is default set to 65536 inc/rev (16 bits). If required, higher values can be selected.
To ensure that a higher position resolution can be used appropriately, the feedback system must enable a correspondingly fine quantisation (see above).
Positioning accuracy:
The positioning accuracy indicates how precisely a position can be approached. It depends on different factors.
For practical operation, quantisation can be used for an approximate estimation:
Positioning accuracy = 1.5 x quantisation
