# Axiomatic Design for Waveplate Mechanism I.E-655, Advanced CAD/CAM -Krishnan V Kumar -Rohan P Gavande.

## Presentation on theme: "Axiomatic Design for Waveplate Mechanism I.E-655, Advanced CAD/CAM -Krishnan V Kumar -Rohan P Gavande."— Presentation transcript:

Axiomatic Design for Waveplate Mechanism I.E-655, Advanced CAD/CAM -Krishnan V Kumar -Rohan P Gavande

Motivation  The mechanism is an important constituent of the South Africa Large Telescope (SALT)  Interesting system dynamics to address: - relative linear motions and rotations  Simple functionality and complex in terms of accuracy, repeatability, and control

Problem Statement  Analysis of the existing design of the Waveplate mechanism in the PFIS structure using Acclaro software, to determine the scope of improvement and  Implementation of principles of Axiomatic Design to generate a new design plan.

Terminology  Waveplate – An optical surface used to polarize light  Blank – Another optical surface, does not polarize the light  The Waveplate mechanism consists of combinations of waveplates and blanks, used to study the light beam

Current Design ½ WP ¼ WP Full Blank Half Blank Supporting top frame Supporting bottom frame Light beam

Operational Mode 1 No Polarimetry: Full Blank only

Operational Mode 2 Linear: ½ waveplate + ¼ waveplate Blank

Operational Mode 3&4 Circular: ½ waveplate + ¼ waveplate All Stokes: ½ waveplate + ¼ waveplate

Specs  The maximum insertion mode changeover time is 6 sec  The ½ and ¼ waveplates should be able to rotate about their own axes through 45  in 1 – 1.2 secs  Motion of waveplates should be possible in both directions.  Rotational positioning of both the waveplates must be repeatable to the same angular position in steps of 360/32  to 3 arc minutes.

Constraints The maximum heat and power generated should not exceed 50W The z envelope of the mechanism should not exceed 55 mm The gap width between the top and bottom frame is 5 mm

Approach & Methodology phase I Understand the functionality of every component in the current design (system dynamics) Formulate the parent level FRs from the given specs Assign DPs present in the design satisfy the FRs

Approach & Methodology phase I Decompose the parent level FRs to maintain independence Map the decomposed FRs to respective decomposed DPs in physical domain Construct the design matrix

Acclaro software Useful tool for applying Axiomatic Design Database contains theorems and corollaries of Axiomatic Design Built in examples to illustrate the design process Most useful - Allows documentation of comments

Working with Acclaro

Functional Requirements FR 1: Align the central axis of top waveplate (1/2 WP) with the beam of light FR 11: Guide way for motion of top frame FR 12: Positioning of the waveplate in the frame in less than 6 sec FR 13: Provide support for guiding and positioning mechanism FR 3: Rotate ½ WP to observe polarization at different angles FR 31: Provide drive for the driving gear such that ½ WP be able to rotate through 45  in 1 to 1.2 sec FR 32: Rotate ½ WP in steps of 360/32  FR 33: Provide accuracy of 3 arcminutes

Design Parameters (phase I) DP1: Linear motion of the top frame mounted with the ½ WP DP 11: Rail mechanism DP 12: Pneumatic cylinder DP 13: A supporting frame (box) structure in which the rail system is mounted on the outer side DP 3: Gear mechanism of suitable gear ratio DP 31: Motor DP 32: Indexing mechanism. Slots are provided on the waveplate holder at 360/32  and an indexing detent (rod) is provided that drives in and out of these slots DP 33: Anti-backlash mechanism

Design Matrix (phase I)

Conclusion (phase I) The Design Matrix displays a decoupled design  The rail mechanism affects both FR11(Align) and FR12(Guide)  The Motor DP31 affects FR31(Rotation) FR32(Indexing) and FR33(Accuracy) Solution:  Change DPs or reduce coefficient of X

Phase II  Customer Attributes: CA1 :Polarize light with waveplates CA11: Compactness of structure  Functional Requirements FR1 :Waveplate Mechanism FR11:Suitable configuration of waveplates FR12:Minimum travel of the mechanism FR13:FR13: The central axes of the waveplates should be along the same line

Possible Configurations

New Schematic ½ WP Full Blank Half Blank Supporting top frame Supporting bottom frame Light beam ¼ WP Advantages:- -Reduced travel of the waveplates resulting in better positioning accuracy. -Reduction in total space occupied by the mechanism.

New FRs  FR 1: Align the central axis of top waveplate (1/2 WP) with the beam of light FR 11: Positioning of the waveplate in the frame in less than 6 sec. FR 12: Provide support for positioning mechanism  FR 3: Rotate ½ WP to observe polarization at different angles. o FR 31: Provide drive for the driving gear such that ½ WP be able to rotate through 45  in 1 to 1.2 sec. FR 32: Rotate ½ WP in steps of 360/32 . o FR 33: Provide accuracy of 3 arcminutes.

DPs  DP1: Linear motion of the top frame mounted with the ½ WP -DP 11: Lead Screw Actuator. -DP 12: End Supports  DP 3: Gear mechanism of suitable gear ratio  -DP 31: Motor -DP 32: Indexing mechanism. Slots are provided on the waveplate holder at 360/32  and an indexing detent (rod) is provided that drives in and out of these slots. o -DP 33: Anti-backlash mechanism

New FR-DP Matrix

Further Analysis  Determine the coefficient of X to reduce the impact of DPs  The coefficient of X can be reduced based on the configuration of anti-backlash mechanism and the indexing mechanism

Salient Features of New Design  Uncoupled design for two FRs  Reduction in overall weight of the mechanism  Only one set of rails is needed  DP12 and DP to be integrated since functional independence can be maintained and same material can be used