Automated construction of orthopedic aids
In orthopedic technology, aids are predominantly manufactured via process chains that make use of classic plaster casting and molding technology. CNC milling or 3D printing are used sparingly because they require digital geometry models of the objects to be manufactured. Current 3D measurement technology can pave the way for the generation of such models, but for this it must be possible to integrate it into the tried and tested workflows of orthopedic technology. This requires the development of a specially adapted acquisition methodology and new process chains to achieve a link between craftsmanship and digital processing.
A first sensible integration step is the digitization of body models, which originate from impressions of body parts and thus define the body geometry in the interior. For a measuring system, however, this means also being able to measure inside plaster models in order to generate 3D models of the body parts, which are the central basis for the subsequent design process. A direct measurement of such impression geometries increases the quality of the manufactured product on the one hand and achieves a higher degree of automation compared to the current state of the art on the other hand.
The aim of the research project is to develop a new digitization tool in orthopedic technology that allows efficient, complete and precise recording of body models or aids and can completely replace the conventional manual impression technique.
The goal was achieved by developing a system that ensures precise three-dimensional detection and measurement of body models from the inside and outside. For this purpose, an image-based approach was pursued and prototypically implemented for both external and internal detection. Furthermore, the measurement system allows the manually defined features by the prosthetist, together with the scanned body model, to be transferred to a design program. In order to generate a final orthopedic device from these digital body models, an evaluation unit was developed for the automation of sub-processes as well as for automated construction.
In the course of the project, an image-based approach was pursued and prototypically implemented for the acquisition of the exterior of body models and also for the acquisition of interior areas. The outdoor scanner has a 3D measurement volume (1m³) consisting of 32 distributed 5 mega pixel CMOS cameras with 4.14mm lenses. After determining the inner as well as outer orientations, an RMS error of 0.3mm is achieved in the object space of the outdoor scan. This error is significantly below the accuracy of a plaster and impression technique. A physically oriented simulation serves as a plausibility test. The results achieved in real life correspond to the simulation calculations. The inner area is scanned with an elongated suspension consisting of a handle and several vortex-like elements. Its end is formed by a movable 5 MP camera head with a 4.14mm lens. The deflection can be controlled with the grip piece and thus also allows a complete capture in the area of the toes. Inside the hollow body, geometric support is provided by calibrated reference marks. In the object space, the RMS error is less than 1mm. It can be stated that the planned concept completely fulfills the specified accuracy requirements.
As a result of the successful work in the project, a patent was filed together with the project partner F. Gottinger Orthopädietechnik GmbH “Method for creating a model of an aid from an existing aid or negative impression, devices for digitizing an aid and unit for carrying out the method”.