Optical Feedback Control (OFC) Developer Guide

Important classes:

• BaseOFCData a python data class that contains the static data for the ofc operation.

• OFCData a data container class that inherits BaseOFCData and handles the dynamic data for ofc operations. This includes reading and storing data from files and higher level data manipulation.

• SensitivityMatrix calculates the sensitivity matrix at the given sensors and camera rotation angle.

• StateEstimator contains facilities to estimate the state of the system.

• OICController Optimal Integral Controller that calculates the degrees of freedom (DoF) offset by minimizing the cost function.

• PIDController Proportional-Integral-Derivative Controller that calculates the degrees of freedom (DoF) offset with gains.

• OFC is the main class of the system, responsible for managing the conversion of wavefront errors into corrections.

classDiagram namespace ofc_data { class OFCData class BaseOFCData } class OFC StateEstimator *-- OFCData BaseController *-- OFCData OICController "1" *-- "2" BendModeToForce BendModeToForce *-- OFCData OFC *-- OFCData OFC *-- SensitivityMatrix OFC *-- StateEstimator OFC *-- OICController OFC *-- PIDController OFC ..> Correction BaseOFCData <|-- OFCData BaseController <|-- OICController BaseController <|-- PIDController

Figure 1 OFC Class diagram.

Control Algorithm

• Control Algorithm in Optical Feedback Control
  • Optimal Integral Controller (OIC)
  • Proportional-Integral-Derivative Controller (PID)
• Camera Rotation with Double Zernikes
  • Rotation of the sensor
  • Rotation of the field angle
• Camera Rotation and Degree of Freedom
  • Mirror Bending Mode
  • Hexapod Position

For more additional details about the algorithm see [Angeli2014], [Angeli2016a], [Angeli2016b], [MegiasHomar2024] and [Xin2021].

Python API reference

lsst.ts.ofc Package

Classes

BaseController(ofc_data[, log])	Base Controller.
BendModeToForce(component, ofc_data)	Transform Bend mode to forces.
Correction(*args)	Container for corrections.
OFC(ofc_data[, log])	Optical Feedback Control.
OFCData([name, config_dir, log])	Optical Feedback Control Data.
OICController(ofc_data[, log])	Optimal Integral Controller (OIC)
PIDController(ofc_data[, log])	PID controller.
SensitivityMatrix(ofc_data)	Class to handle the sensitivity matrix.
StateEstimator(ofc_data[, rcond, log])	(Optical) State Estimator.

lsst.ts.ofc.ofc_data Package

Functions

default_eff_wavelenght()

Default effective wavelenght.

Classes

BaseOFCData(y2_filename_root, ...)	Base Optical Feedback Control Data.
OFCData([name, config_dir, log])	Optical Feedback Control Data.

lsst.ts.ofc.utils Package

Functions

get_config_dir()	Return the path to the policy dir within this package.
get_filter_name(filter_name)	Return the filter name in the format used by the OFC.
get_pkg_root()	Return the root directory of this package.
rot_1d_array(array, rot_mat)	Rotate 1D array from one basis to another.

Classes

CorrectionType(value[, names, module, ...])

Contributing

lsst.ts.ofc is developed at https://github.com/lsst-ts/ts_ofc.

References

[Angeli2014]

Angeli, George Z. et al., Real time wavefront control system for the Large Synoptic Survey Telescope (LSST). Proc. SPIE 9150, Modeling, Systems Engineering, and Project Management for Astronomy VI, 91500H (2014).

[Angeli2016a]

Angeli, George Z. et al., An integrated modeling framework for the Large Synoptic Survey Telescope (LSST). Proc. SPIE 9911, Modeling, Systems Engineering, and Project Management for Astronomy VI, 991118 (2016).

[Angeli2016b]

Angeli, George Z. and Xin, Bo, Normalized Point Source Sensitivity for LSST. document-17242.

[MegiasHomar2024]

Megias Homar, G., et al., The Active Optics System on the Vera C. Rubin Observatory: Optimal Control of Degeneracy Among the Large Number of Degrees of Freedom arXiv (2024)

[Xin2021]

Xin, Bo, SITCOMTN-003: Coordinate Transformations within the Rubin Active Optics System. sticomtn-003