Designing Cell phone Camera Lenses Part 2: Optomechanical Packaging

This article is part of a 3-series articles that will discuss the challenges of smartphone lens modules, from the conception and design to the manufacturing and analysis of structural deformation. This article is the second part of the three-part series, that introduces editing optics within the Ansys Speos environment and analyzing the system after incorporating mechanical components. The show-case example is a smart phone lens system from a worldwide operating manufacturer which consists of five lenses, a cover glass and an infrared filter. The main objective is to extend these lenses with complex edges, so they can be fitted into a mechanical mounting.

Designing Cell phone Camera Lenses Part 1: Optics
Designing Cell phone Camera Lenses Part 3: STOP analysis by using STAR module and ZOS-API

Authored By Akhil Dutt Vijayakumar, Flurin Herren

Introduction

After the optical system was optimized in Ansys Zemax OpticStudio (Zemax), the optical design can be further analyzed in Ansys Speos (Speos) and the mechanical modelling can be done at Creo Parametric 9 (Creo). Before doing the conversion make sure to set the image surface as global coordinate reference, which helps to align the final system easily in Speos.

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Figure 1. Lens assembly in Zemax

When an optical system is converted to a .ODX file with Export Optical System to Speos, the tool automatically converts the lens position and its characteristics from either sequential/non sequential format to an optical design exchange file suitable for opening Speos.

The lens assembly is housed within a mechanical barrel that requires a slight length adjustment. CAD software such as Creo is the preferred software for modifying the mechanical housing design, while Speos handles the intricate lens edge modifications. To initiate this process, the STEP file is exported from Zemax using the "Export CAD Files" tool found in the file menu.

Modifying Mechanical Barrel dimension 

A given mechanical barrel needing modification to its dimension can be opened in Creo. The STEP is initially imported to the Creo environment using the assemble tab, and it is followed by other mechanical parts.

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Figure 2. Optomechanical assembly in Creo

The Mechanical barrel is created by sketching and revolving the design around the beam axis. To modify the length, the sketch needs to be redesigned as shown in Figure 3. The highlighted green areas show the modified drawing.

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Figure 3. Mechanical Barrel modification

The remaining mechanical parts, such as the baffles, are added to the design and suitable colors are added to distinguish the components in the final design.

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Figure 4. Modified design

The CAD model is then saved as an assembly file and the complex lens design and further analysis can be completed in Speos.

Complex lens edge modelling using Speos

To begin, import the lens model into Speos using the .ODX import tool located in the Light Simulation tab of the Speos interface.

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Figure 5. Importing modified design to Speos

The camera lens assembly contains several lenses which are numbered as follows. Some of the lens edges need to be redesigned to a complex form using Speos. 

Part List:

  • Infrared Filter (A)
  • Lens (B)
  • Lens (C)
  • Lens (D)
  • Lens (E)
  • Lens (F)
  • Cover Glass (G)

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Figure 6. Camera lens assembly

The geometrical requirement for the extended lens edges is to retain the lenses between mechanical baffle rings and the main barrel.

  • Disclaimer: For display purposes the IR Filter (A) and the Cover Glass (G) are retained within the barrel assembly. In a real-life application, these two components would very likely not be in the same optomechanical sub-assembly as the lenses.

Add complex lens edges

The complex lens edge can be created by sketching a new design on top of the parent lens and revolving the sketch around the optical axis of the lens. In the Sketch Mode of the Speos interface, the ‘line’ tool can be used to create the complex design. While sketching the design, it is required to consider space for baffle rings.

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Figure 7. Sketching complex lens edges

When the sketch of all new lens edges is complete, the design is revolved around the optical axis to create a new solid surface. All the lens edges are formed as a separate solid surface as shown in the Figure 8.

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Figure 8. Redesigned lens assembly

The next step combines the parent and added lens edges into a single lens unit. The following procedure is recommended:

  1. To update the .ODX file, you can move the new solid surfaces (highlighted in figure 9) into the assembly using the cut, copy, and paste commands.
  2. Select the geometries that need to be combined and use the ‘Combine’ object tool in the Speos Design tab. Repeat for the remaining lenses. The design is shown in Figure 9.A shows how the .ODX file was modified.  In Figure 9.B, an error is displayed. 
  3. 9.pngFigure 9.A: Combining new lens parts with parent lens, B Combined design 
  4. The error likely occurred due to modifications made to the .ODX file. When we modify the lens edges, additional drawing elements create new faces corresponding to each edge segment. Clicking on a modified lens now displays a brush icon, and a dialog box shows the newly added lens faces (as illustrated in the Figure 10). To fix the error and complete the complex lens edge design, simply move these new lens parts to the original lens edge faces found in the Feature Tree. Repeat this process for all modified lenses.

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Figure 10. Arranging new lens edges to the feature tree

Conclusion

This article demonstrated the Optical Desgin Exchange workflow between Zemax and Speos and show cased the designing of complex smartphone lens edges using Speos. The next article in this series, will delve into the stop analysis using the Star Module and ZOS-API.

 

 

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