AT A GLANCE

Client

www.henkesasswolf.de

IndustryLeading medical-technology company producing sophisticated medical and veterinary instruments sold worldwide, most under private label. Products include endoscopes, reusable and disposable syringes, needles, and flow switches.

Zemax products used• OpticStudio 20.1.3

Key capabilities for Henke-Sass, Wolf• Zemax OpticStudio Application

Programming Interface (ZOS-API), which enables connections to, and customization of the application, using the latest software technology

• Using ZOS-API, ability to tolerance rotational symmetric irregularity (RSI) to incorporate RSI limits into design constraints

• Contrast optimization to significantly speed up Modulation Transfer Function (MTF) optimization

Results• Substantial improvement in

image quality for endoscopes with high-numerical apertures

• Streamlined workflow, which saves considerable time and effort during tolerancing

Advanced tolerancing techniques for endoscope optical design

CUSTOMER SUCCESS STORY

2 | CUSTOMER SUCCESS STORY Henke-Sass, Wolf

“Customizing OpticStudio through the use of the built-in API was a huge step forward in being able to specify RSI in a sensible way.”

Oliver Rehe, Group Manager, Advanced Technology Development, Henke-Sass, Wolf

Endoscopes are extremely sophisticated medical instruments that are increasing in sophistication and usage. Typically consisting of a long, thin tube that is attached to a light and video camera, endoscopes make use of fiber optics and powerful lens systems to enable medical professionals to peer inside a body for diagnostics, biopsy, and surgery. To be effective, endoscopes need to capture images of the highest quality, be capable of a wide range of motion, and be impervious to biological fluids, disinfectants, and sterilization at high temperatures.

As an international leader in the design and production of endoscopes and other medical and veterinary instruments, Henke-Sass, Wolf markets their products primarily as an OEM to prominent medical technology businesses Based in Germany with offices also in the U.S., China, and Poland, Henke-Sass, Wolf has a long track record of meeting the highest standards for quality, durability, and reliability.

Although the products delivered to customers continued to meet their exceptionally high standards, Henke-Sass, Wolf recently encountered challenges in development of High-precision/performance endoscopes. They struggled with an inefficient workflow that wasted time and material to meet their strict product specifications. They discovered that the problem had to do with errors in rotational symmetric irregularity (RSI) tolerancing. And the solution they deployed involved customizing OpticStudio using the Zemax OpticStudio Application Programming Interface (ZOS-API).

According to Oliver Rehe, group manager of advanced technology development, “Customizing OpticStudio through the use of the built-in API was a huge step forward in being able to specify RSI in a sensible way.”

Customizing OpticStudio through a built-in, easy-to-use API reduces rotational symmetric irregularity (RSI) tolerancing errors and improves manufacturability

3 | CUSTOMER SUCCESS STORY Henke-Sass, Wolf

High-precision endoscopes require unusually complex optical design solutions.

Rehe leads a team of three optical engineers in designing advanced optical systems for endoscopes, including flexible, rigid, and chip-on-tip solutions. To capitalize on emerging technologies such as high-resolution systems in 4K cameras, the company is committed to developing innovative new techniques and solutions on an ongoing basis.

Every day, the team contends with intriguing design challenges. Their high-precision imaging systems require extremely precise tolerances in order to achieve diffraction-limited performance. This is difficult to achieve because the endoscopes can include as many as 50 optical surfaces. Further, because the optic diameters are extremely small—from 1.1mm to 7mm—the surfaces are hard to manufacture and handle. Depending on the length and numerical aperture a specific number of relay stages is required which introduce additional aberrations and tolerances.

Correcting RSI errors through new code developed in MATLAB, which was then imported into OpticStudio via ZOS-API.

Henke-Sass, Wolf uses the ISO 10110-5 standard—indicated as 3/A(B/C) RMSs < D (all Ø…)—to specify surface shape tolerances. After performing Monte Carlo analysis on some new designs, they discovered an unacceptable level of degradation. Although the

surfaces carried tight tolerances on surface shape, a particular form of surface error was causing the degradation. The error was one of RSI tolerancing.

According to the ISO standard, the RSI of a surface shape needs to be toleranced to a maximum PV of “C” in fringes or nm. The RSI term is part of the total surface irregularity, “B,” so the two specifications are coupled. Therein lies the challenge for optical software, which is that tolerancing of B (surface irregularity) and C (RSI) terms must be done together.

OpticStudio can easily be adapted to meet the unique needs of any design team through the highly flexible ZOS-API that enables connections to, and customization of, the application. Code was developed in MATLAB that solved this problem by tolerancing the B (total irregularity) and C (RSI) terms together in a coupled fashion. The code converted the surface to a Zernike Standard Sag surface, added RSI terms, and scaled to the correct value of C. And then it added random Zernikes and scaled to achieve the correct value of B, without perturbing the terms used to specify C (RSI).

The challenges with the RSI tolerancing affected the workflow not only for the designers but also in the manufacturing process. As Rehe notes, “Our customers expect the best endoscopes and in general we deliver perfect products. But if we produce 100 endoscopes and maybe five or ten endoscopes are rejected during quality control, that’s a serious issue with the workflow”—one that affects both efficiency and costs through wastage.

Sophisticated diffraction-limited endoscopes pose special challenges for optical designers, including the need to place as many as 50 lenses in an assembly. Henke-Sass, Wolf rose to the challenge with a custom RSI tolerancing solution in OpticStudio that significantly improved final image quality.

4 | CUSTOMER SUCCESS STORY Henke-Sass, WolfZemax.comCopyright © 2020. Zemax LLC. All rights reserved.

Contrast Optimization significantly streamlines the design phase

Henke-Sass, Wolf strives for exceptional

image quality using Modular Transfer

Function (MTF) specifications. They have

made great use of the Contrast Optimization

capability in OpticStudio to speed up

design processes, as well as to achieve their

high standards. Previously, optimizing on

the MTF was exceedingly slow because

of the complexity of the calculation and

the need to repeat it so many times. Using

Contrast Optimization, they can now target

the best MTF response up to a specific

spatial frequency, without requiring a slow

autocorrelation calculation.

Benefits of using OpticStudio

Henke-Sass, Wolf has applied the new RSI code to their manufacturing process. As a result, they can readily determine the maximum RSI that is acceptable for each surface, and they can measure each surface for RSI as it is manufactured. This fulfills their overall goal of building higher-precision endoscopes with improved final image quality.

In addition, Rehe reports that use of the RSI solution is speeding up their process considerably. “We used to need to have hundreds of discussions about a lens . . . Is it in specification? Or is it not in specification?” The solution has eliminated the need for many back-and-forth conversations.

Once the team had tackled the RSI problem, a secondary issue emerged, which was that the lens surfaces also contained trefoil errors. These errors appeared after the switch from a traditional manufacturing process to an automated computer numerical control (CNC) machining process. By identifying the problem early, they were able to correct the problem and deliver the required image quality without significant delays or burdens.

Looking ahead, Henke-Sass, Wolf has encouraged their lens manufacturer to begin using Zemax OpticsViewer, a new application which gives manufacturing engineers the ability to load sequential OpticStudio design files and view them without loss of precision or information. Rehe envisions that using OpticStudio and OpticsViewer together will greatly improve the engineer-to-manufacturing workflow. As he puts it, “There would be great benefit to enabling our manufacturers to get involved and check things like bench drawings prior to service production.”

Whatever new advancements that Rehe and his staff come up with for optical design, he is confident that OpticStudio will continue to evolve to provide the expert capabilities and flexibility they need to fulfill their vision.

About ZemaxZemax’s industry-leading optical software, OpticStudio®, OpticsBuilder™, and OpticsViewer™, helps optical, mechanical, and manufacturing engineering teams turn their ideas into reality. Standardizing on Zemax software reduces design iterations and repeated prototypes, speeding time to market and reducing development costs. Zemax touches nearly every optical system manufactured today, including virtual reality systems, cell phone cameras, autonomous-vehicle sensor systems, and intraocular lenses—even imaging systems for the Mars Rover. By listening to customers, Zemax delivers unmatched value and have the largest, most passionate user base in the industry.

Designing for Manufacturability Whitepaper www.zemax.com/resources/eguides

Learn more about how you can improve manufacturability with the help of Zemax.

Expert training options www.zemax.com/training/opticstudio-training

Learn more about OpticStudio www.zemax.com/products/opticstudio