Implementation of an Hexapod for Optical Aberrations correction
Simulation of optical systems with the objective of understanding the correlation between optical aberrations, structural deflections and correcting mechanisms. Telescopes are built of heavy and rigid steel structures that can align optical instruments including mirrors for either refraction or reflection, along with optical systems and cooling systems. Thus, studying structural deflections and their impact on alignment is a highly critical point when designing astronomical instrumentation.
Background
Project completed as an Undergraduate Researcher in Observational Astronomy - Astronomical Instrumentation on-site at the Universidad Nacional Autónoma de México (UNAM), National Institute of Astronomy (2018). The Institute of Astronomy in Baja California, Mexico of the UNAM (National Autonomous University of Mexico) has among its objectives: research in the astrophysics field, developing astronomical instrumentation, as well as having high quality staff at undergraduate, master’s degree, and doctorate levels. The IA also works on the spreading and divulgation of astronomy and science in general.
As a research intern, part of my objectives and accomplishments include:
– Conducted literature review of advanced optomechanical instrumentation systems at the graduate level
– Design of critical opto-mechanical assemblies for astronomical instrumentation systems after receiving technical training in optics, optoelectronics, and ZEMAX
– 3D Modelled the 2.1m national telescope and ran over 5 FEA simulations to calculate displacements induced by structural weight of telescope when in different positions for observation
– Prototyping and testing of a mechanical and electronics Hexapod with 6 Degrees of Freedom for optic aberration correction
– Research published during the 2018 LXI National Physics Congress held by the Mexican Physical Society
As a research intern, part of my objectives and accomplishments include:
– Conducted literature review of advanced optomechanical instrumentation systems at the graduate level
– Design of critical opto-mechanical assemblies for astronomical instrumentation systems after receiving technical training in optics, optoelectronics, and ZEMAX
– 3D Modelled the 2.1m national telescope and ran over 5 FEA simulations to calculate displacements induced by structural weight of telescope when in different positions for observation
– Prototyping and testing of a mechanical and electronics Hexapod with 6 Degrees of Freedom for optic aberration correction
– Research published during the 2018 LXI National Physics Congress held by the Mexican Physical Society
Scope
1. Modeling optical system in ZEMAX to create benchmark and twin to real telescope optical arrangement
2. 3D Modeling (scaled) of 2.1m Optical Telescope
3. Detection of optical aberrations at structural inclination of 45 degrees
4. Simulation of an hexapod platform in Python to simulate correction of aberrations measured
5. Quick prototyping of hexapod platform
Optical systems simulation
Optical layout for the 2.1m Telescope (Ritchey – Chrétien reflector telescope)
Optical layout for primary and secondary lenses
3D Layout and Spot Diagram (0 degrees)
3D Layout and Spot Diagram at 0, 0.06 degree and 0.09 degree simulated aberrations
Solidworks Assembly of 2.1m Telescope
Primary mirror diameter: 2.118m
Secondary mirror diameter: 60cm, thickness of 6cm
Distance between mirrors:
Diameter of the declination axis: 25.7cm
The telescope was modeled using structural steel (AISI 1080) and glass for the lenses
Inclination at 45 degrees
The assembly was rotated on its declination axis from 0 to 45 degrees, simulating a general position commonly used during observation. This 45 degree inclination will affect the structure's integrity by the steel's weight and the force of gravity, and this deflection in turn displaces the lenses in 3 axis (in millimeters). These displacements create optical aberrations as they shift with the original lens alignment. Such mechanical displacement will be measured and quantified via FEA, after which the displacements can then be fed into a platform (hexapod) to mechanically counter the displacements and correct the aberrations.
45 degree inclination axis
FEA Simulation (45 degree inclination)
Static displacement [mm], entire structure.
Mirror displacement broken into corresponding axes: X, Y and Z. Force (gravity) was applied on Y axis
Optic aberrations (45 degree inclination)
The effect of gravity can be observed as the mechanical displacements were proyected into the optical system simulation, shown below. Compare to original system (no displacement) above.
Optical layout at 45 degree inclination
Wavefront of optical system (45 degree inclination) at 0, 90, 180 and 270 degrees
Hexapod platform control
In order to control the displacement of the lenses, a counter displacement can be applied using a mechanism with 6 degrees of freedom such as an Hexapod. Using both translational and rotational matrix formulas, a python script was developed to control rotation on axes x, y and z to allow for complete control and correction of 3 dimensional aberrations. Examples of rotations on z axis and axes y and x are shown below, respectively.
Prototype hexapod platform
A quick prototype (from scrap materials) was created to demonstrate control of rotation and translation of the correcting hexapod.
