Patent Application
20090063107
The present invention is directed to a method for manufacturing hearing aid shells in order to reduce surface distortions and to provide an adaptive shell surface modification to improve fit.
The issue of fit, i.e., whether a given hearing instrument designed from a mold of a patient's ear can fit the wearer comfortably after it has been produced, has been a great challenge to the hearing instruments industry. This challenge is the result of the interdependence of fit on many prevailing and competing parameters.
In modern hearing aid design, a rapid shell modelling (RSM) process is often utilized in which a three-dimensional model of the patient's ear canal is computed from a scanned ear canal impression. Such a model can be further manipulated by using sophisticated geometrical algorithms to obtain the finished hearing aid shell that can be produced in a matter of minutes. The production of a shell from a computer model can be achieved, e.g., by laser sintering in which a laser fuses liquid material into a solid in layers based on the shell model. However, this process (and other 3D manufacturing technologies) can create artifacts on the shell that must be removed.
One of the steps in the manufacturing of such a hearing aid shell is a tumbling and buffing procedure (involving subjecting the shell to a barrage of fine pebbles) to smooth the shell surface which thereby makes the hearing aid fit more precise and improves comfort for the wearer. Both tumbling and buffing remove a thin layer of material from shells—however, this removal can also compromise the surface integrity of the shell.
In known custom hearing aids with RSM shells, the shell surface is constructed with a constant offset in order to compensate for the erosion of the shell material during the tumbling process. However, tumbling and buffing cause more material to be removed from the shell areas with high curvatures, because the tumbling media creates more impact to such areas. The result is that the shell geometry gets distorted, and therefore the shell does not fit well into the customer's ear.
The invention is directed to a method for manufacturing a hearing aid shell, comprising: dividing a surface of the shell into a number of predefined patches; calculating a Gaussian curvature value for each predefined patch; determining a variable offset value for each of a respective patch for a new surface, the offset value of an isosurface function being dependent on the calculated curvature value; calculating the new surface for the shell at the determined offset values; and physically creating the hearing aid shell with the new calculated surface prior to a tumbling or buffing operation.
The invention is also directed to a computer system having a processor, user interface (input and output), a memory, and algorithms that are stored in the memory and executed on the processor for implementing the method. The computer algorithms for producing the shell model can be stored on a computer readable media, such as a COD-ROM, tape, or server storage.
According to various embodiments of the invention, the method for manufacturing the shell surface is pre-distorted by offsetting it by an isosurface function. The isosurface function is directly related to the principle curvatures of the surface in order to compensate for the more aggressive tumbling of zones with high curvature. In a preferred embodiment of this system, the modifications are performed mathematically on a virtual 3-D data representation on the shell prior to the shell actually being produced. An appertaining system for implementing the method is further provided.
As noted above, and as provided according to embodiments of the invention, in the method for manufacturing, the shell surface is pre-distorted by offsetting it by an isosurface function which is directly related to the principle curvatures of the surface in order to compensate for the more aggressive tumbling of zones with high curvature. Although the drawings and descriptions rely on 2D illustrations, it should be clear that these can easily be extended to a real-world 3D model using the relevant mathematics, such as where principle eigenvectors are derived from the principal curvatures of shell surface, and a surface normal vector direction are used as an offset direction for each patch defining a zone of curvature.
As is illustrated in
Q
i
=C+f(Kj)
This formula describes the necessary amount of the surface offset, depending on the surface curvature. It includes the concave (K is negative) and convex (K is positive) areas. The function of K reflects the erosion of the shell material form areas with various K values during tumbling. The formula includes the constant offset C and curvature-dependant offset f(K). The definition of curvature as used herein is well known in the art (see, e.g., Barrett O'Nell Elementary Differential Geometry. Academic Press NY and London 1966. Page 310-317, on Gaussian curvature).
The principal directions k are the eigenvectors of the principal Gaussian curvatures. They refer to the local orientation of the principal Gaussian curvatures, and the normal vector n can be used to identify the direction for compensation. Additionally, the shape index may be used to determined the generalized concavity and convexity and what manufacturing corrective measures are implemented. When the software, based on the curvature computation, identifies a region that is concave, then no additional material is added to this region. In the convex areas however, compensatory material is added to address the susceptibility of these localized patched regions to surface modification during tumbling.
This accomplished after the software system has determined the degree of curvature of the shell surface. In
In
A system for implementing the above method is further provided, in which a computer system has a processor, user interface (input and output), a memory, and algorithms that are stored in the memory and executed on the processor. The algorithms are used to transform the initial shell model into the final shell model that is to be produced based on the above algorithms. The computer system has an input for entering the initial shell model, and an output for sending the final shell model to a device that can actually produce the shell model. The computer algorithms for producing the shell model can be stored on a computer readable media, such as a CD-ROM, tape, or server storage.
Although the present invention is optimally suited for virtual shells and mathematical manipulation thereon, it could theoretically be applied in any context of hearing aid shells.
For the purposes of promoting an understanding of the principles of the invention, reference has been made to the preferred embodiments illustrated in the drawings, and specific language has been used to describe these embodiments. However, no limitation of the scope of the invention is intended by this specific language, and the invention should be construed to encompass all embodiments that would normally occur to one of ordinary skill in the art.
The present invention may be described in terms of functional block components and various processing steps. Such functional blocks may be realized by any number of hardware and/or software components configured to perform the specified functions. For example, the present invention may employ various integrated circuit components, e.g., memory elements, processing elements, logic elements, look-up tables, and the like, which may carry out a variety of functions under the control of one or more microprocessors or other control devices. Similarly, where the elements of the present invention are implemented using software programming or software elements the invention may be implemented with any programming or scripting language such as C, C++, Java, assembler, or the like, with the various algorithms being implemented with any combination of data structures, objects, processes, routines or other programming elements. Furthermore, the present invention could employ any number of conventional techniques for electronics configuration, signal processing and/or control, data processing and the like. The word mechanism is used broadly and is not limited to mechanical or physical embodiments, but can include software routines in conjunction with processors, etc.
The particular implementations shown and described herein are illustrative examples of the invention and are not intended to otherwise limit the scope of the invention in any way. For the sake of brevity, conventional electronics, control systems, software development and other functional aspects of the systems (and components of the individual operating components of the systems) may not be described in detail. Furthermore, the connecting lines, or connectors shown in the various figures presented are intended to represent exemplary functional relationships and/or physical or logical couplings between the various elements. It should be noted that many alternative or additional functional relationships, physical connections or logical connections may be present in a practical device. Moreover, no item or component is essential to the practice of the invention unless the element is specifically described as “essential” or “critical”. Numerous modifications and adaptations will be readily apparent to those skilled in this art without departing from the spirit and scope of the present invention.
