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Encoder

An encoder (bliss.common.encoder.Encoder object) can be defined on its own and used standalone, or can be associated to an axis to perform some extra actions before or after a movement.

Encoder associated to an Axis

Configuration

An encoder associated to an Axis is defined in controller section and referenced in axes section.

controller:
  class: icepap
  host: iceid42
  axes:
      - name: m4mot
        address: 1
        steps_per_unit: 817
        velocity: 0.3
        acceleration: 3
        tolerance: 0.001
        encoder: $m4enc
        check_encoder: True
        read_position: encoder
  encoders:
      - name: m4enc
        address: 25
        steps_per_unit: 1e5
        tolerance: 0.02

Configuration parameters:

  • name
    • Encoder object’s name.
  • steps_per_unit
    • This value is used to define the conversion factor between encoder steps value and real position in user unit. It must be accurate to allow comparison between position required by user and real position.
  • tolerance
    • Value in user_units.
    • At end of a movement, the encoder value is read and compared to the target position of the movement. If the difference is outside the limit fixed by the encoder tolerance (beware to not confuse with Axis tolerance), an exception is raised with message: "didn't reach final position"
  • address

Note

For specific details about icepap encoders, see Icepap Encoder Configuration

Usage

  • the method .measured_position() uses encoder.read() to calculate the value returned in user units.

  • if Axis parameter check_encoder is set to True, then after a movement, the encoder position is read and compared to the target position. In case of difference outside the limit fixed by Encoder tolerance, an exception is raised with message: "didn't reach final position"

The Axis must then be re-synchronized with: mot1.sync_hard()

  • if Axis parameter read_position is set to encoder, then the hardware position returned by the axis is the position read by the encoder like .measured_position(). This option disables the discrepancy check at the beginning of a movement unless check_encoder is also set to True.

Note

This configuration (read_position is set to encoder) corresponds to the MAXE_E MAXEE mode in SPEC.

Note

This measured_position() method is used in particular by TangoDS and can be easily compared to the target position with atk-moni for tuning purposes.

  • dial_measured_position() returns the dial encoder position in user units.

Note

There are 2 tolerance parameters in configuration: one for Axis and the other one for Encoder.

An encoder can be used to define events to trig on special positions. See: Writing a motor controller - position-triggers

Standalone encoder

controller:
  class: icepap
  host: iceid42
  encoders:
      - name: m4enc
        address: 25
        steps_per_unit: 1e5

Encoder as a counter

It is possible to use an encoder alone to read it or to scan/count it.

DEMO [9]: samy.encoder
 Out [9]: ENCODER:
               encoder steps per unit: 52.0
               tolerance (to check pos at end of move): 0.001
               dial_measured_position:    7.39992

DEMO [13]:
DEMO [13]: ct(1, samy.encoder)
Fri Feb 07 11:53:15 2020

position = 7.399929 ( 7.399929 /s)
  Out [13]: Scan(number=4, name=ct, path=)

development

For details on how to implement an encoder in a new motor controller, see Writing a motor controller / Encoder methods