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Of Horntails, Hip Rasps, and Grinding Machines

German translation here

Modeled on the horntail: Fraunhofer IPA develops innovative drill for surgeons

Modeled on the horntail: Fraunhofer IPA develops innovative drill for surgeons


Insects Help the Science World
With the exception of entomologists like the great Frenchman Henri Fabre, most people place insects somewhere on the scale of annoying to unnecessary. And yet insects make up more than 60 percent of all living things on earth, and without these tiny, yet extremely industrious creatures‘ pollination work, we would have a dire food situation.

In the world of science, working with insects serves as a means of conducting fundamental research. It probably isn’t an exaggeration to say that Christine Nüsslein-Volhard, a German Nobel Prize winner, had a similarly close relationship with the fruit fly as you and I might have with our dog or cat.

Dr. Oliver Schwarz

Dr. Oliver Schwarz

Modeled on the Horntail
The biotechnologist Dr. Oliver Schwarz and his team from the Fraunhofer Institute for Manufacturing Engineering and Automation in Stuttgart has impressively demonstrated that there is a lot that we can learn from insects – like, for example, how to make holes with square cross-sections. The scientist and his coworkers were recently awarded second prize at the International Bionic Award 2014 for this achievement, and we would like to congratulate them on receiving this honor. Dr. Schwarz was inspired by the oscillating stroke technique of the horntail, otherwise known as a wood wasp (Siricidae), when developing this innovative hip rasp.

200,000 Hip Joints per Year
Hip rasps are used by surgeons to drill a large hole with a square cross-section into the femur. The hip implant is then inserted into this hole and needs to fit as tightly as possible to prevent the formation of hollow spaces. Each year around 200,000 prosthetic hip joints are implanted in Germany alone. And every time, the surgeons conduct their work primarily by hand with a selection of different rasps.

Bone Drill with Oscillating Stroke Technology
The innovative new drill can create holes with square cross-sections, since it works based on an unusual principle. In this context, Dr. Schwarz was inspired by the wasps and together with his team, transferred the principle to the new technology. Many types of wood and parasitic wasps drill holes into wood up to six centimeters deep, in which they lay their eggs. Since it isn’t possible for them to rotate, they use a neat trick to rasp the hollow spaces into the tree trunk. Their ovipositor is comprised of three separate rasps which can move independent of each other. A kind of guide rail ensures that they all stay close together. When drilling, the trio of rasps moves back and forth in a clever manner, eating into the wood all by themselves. Engineers refer to this as the oscillating stroke principle. While one of the rasps is moving, the other latches onto the wood and provides the necessary resistance. Using this method, the insect does not need to apply pressure with its delicate ovipostor as is usually necessary, like with a drill.

Can Even Be Used in Space or Underwater
This drilling technique offers significant advantages over conventional methods, and not just for surgeons. Above all else, it isn’t limited to round holes. Since nothing rotates, this technique can even be used to create holes with triangular or polygonal cross-sections. A dowel in such a hole would provide a much better hold, since it wouldn’t be able to slip. In addition, an oscillating stroke drill requires almost no pressure. It could even be used in space or underwater, where it is difficult to apply a significant amount of force.

Strong in Porous Materials
Initial testing has shown that it is particularly suited for use with porous materials such as bone. The bone drill used for hip replacement surgery should weigh about 1.5 kilograms and feel comfortable to hold. The designers spoke with physicians to find the ideal design. It is extremely easy to exchange the multi-part rasp head with a different one. The device can also be taken apart easily to sterilize it. As soon as they find an interested company, the Stuttgart-based team wants to build a prototype. Advancements are already being made to the device for non-medical drilling applications by a renowned company.
(Source: Fraunhofer IPA, Klaus Jacob)

Grinding of a Hip Rasp on a Multigrind® Grinding Machine from Haas.

Grinding of a Hip Rasp on a Multigrind® Grinding Machine from Haas.

Accurately Grinding Hip Rasps
You can imagine that our colleagues that primarily work at Haas on grinding applications for medical technology were extremely interested when they heard of the Fraunhofer hip rasp from Dr. Schwarz. After all, the Multgrind® CB and CA grinding machines are known the world over in the field of medical technology. As such, over two-thirds of all prosthetic knee joints used in the world are produced with grinding machines from Haas. And grinding hip rasps is not something we got into yesterday, as you can see from the photo. Thanks to the well-thought-out kinematics of our grinding machines and our high-performance Multigrind® Horizon grinding software, we have the ability to precision-grind the front and backside of the rasp’s teeth to the nearest micrometer. This is known as relief-grinding.

If you want to find out more about this topic, check out our website here or shoot me an e-mail.

Until next time, keep grinding with attitude!

Dirk Wember

P.S.
Jens Schneider from the software department just sent me a screenshot of our Multigrind® Horizon grinding software, which fits the topic nicely. It shows the calculation of the grinding path for a hip rasp:

Calculation of the grinding path for a hip rasp. Screenshot: Haas Schleifmaschinen GmbH

Calculation of the grinding path for a hip rasp Screenshot: Haas Schleifmaschinen GmbH

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