Blank-holding means and method of surveying same

The invention relates to holding means for a blank for the production of dental fitted shells, including connection geometry for the blank and a shaft for attachment thereof in a chuck of a processing machine. The holding means has, above the shaft, survey geometry, the orientation of the connection geometry relative to the survey geometry being known.

RELATED APPLICATIONS

This application claims benefit of priority of German Patent Application No. 103 22 762.8, filed May 19, 2003.

TECHNICAL FIELD

The invention relates to a holding means for a blank for the production of dental fitted shells and having connection geometry for the blank and a shaft to be clamped in a chuck of a processing machine and to a method of determining the position and orientation of (surveying) connection geometry provided on a holding means for a blank releasably attached to said holding means, particularly a blank for the production of dental fitted shells, which holding means is clamped by way of its shaft in a chuck in a processing machine and is at least roughly aligned in space with reference to the chuck axis, and various points of a survey geometry on said holding means are contacted by a processing instrument.

BACKGROUND OF THE INVENTION

When machining a ceramic block having preformed connection geometry, as disclosed, for example, in EP 1 023 876 A2, the position and orientation of said geometry relative to the geometry of the processing machine must be known. However, the connection geometry itself cannot always be directly surveyed, since an optical surveying device is not always present.

For this reason, ceramic blocks having preformed connection geometry have either not been processed mechanically, or the shape to be machined has not required, for reasons of symmetry, any precise knowledge of the position and shape of the preformed geometry.

In the field of fabricating dental fitted shells from blanks in the form of ceramic blocks, EP 0 160 797 A1 discloses a method of causing the processing tool to contact a specially calibrated area of a holding means for the blank and thus of utilizing the processing tool for locating the position of the center axis of the blank with reference to the processing tool. Preferably, the holding means itself should be shaped such that it is automatically accurately positioned in the processing machine by means of reference stops.

A drawback of this is that it is not possible to precisely locate the position of the abrasive tools relative to the blank, as is necessary for machining blanks having a preformed connection geometry.

The object of the invention consists in making it possible to machine ceramic blocks having a preformed connection geometry and to mechanically fabricate any desired symmetrical or asymmetrical shape from such a block.

SUMMARY OF THE INVENTION

According to the invention, the holding means has, above its shaft, a survey geometry, the orientation of the connection geometry relative to said survey geometry being known.

Thus it is possible to effect, by way of the holding means, precise measurement of the dimensions relevant for locating the position of the connection geometry, by which means the position and orientation of the block geometry can be indirectly measured where direct measurement is not possible.

Advantageously, the survey geometry comprises a surface normal to the longitudinal axis of the holding means and a plane lateral surface parallel to said longitudinal axis.

According to a further development, the survey geometry contains information on the type of connection geometry involved. This makes it possible to check whether the correct type is fixed in the processing machine.

Another object of the invention is a blank for the production of a dental fitted shell, which blank has preformed connection geometry and, in addition, survey geometry, the orientation of the connection geometry relative to the survey geometry being known. Here again, the survey geometry can contain information on the type of connection geometry involved.

Advantageously, the blank has a region for attachment to a processing machine and the connection geometry is oriented relative to said attachment region such that the connection geometry is accessible for surveying when the blank is secured in the processing machine. Thus surveying can be readily carried out and it is possible to detect, if necessary, whether the inserted block is suitable for processing.

The present method of determining the position and orientation of (surveying) the connection geometry located on holding means for a blank releasably attached to said holding means, in particular for the production of a dental fitted shell, consists in determining the position and orientation of said connection geometry by surveying survey geometry whose position and orientation relative to said connection geometry is known.

Advantageously, this purpose is achieved by surveying survey geometry provided on the blank.

Another object of the invention consists in a method of determining the position and orientation of implant-specific connection geometry of a blank for the production of a dental fitted shell, in which the blank is secured in a processing machine such that the connection geometry is accessible for surveying, and surveying of said connection geometry is carried out.

Advantageously, the blank is connected, for the purpose of attachment to a processing machine, to holding means, part of said holding means being connected to the processing machine. This has the advantage that the holding means can be of a different material and that one and the same holding means can be used for a plurality of blanks.

Another object of the invention consists in a method of determining the position and orientation of connection geometry located on holding means for a blank releasably attached to said holding means for the production of a dental fitted shell, wherein said holding means is clamped by way of its shaft in a chuck of a processing machine and an at least rough spatial alignment thereof relative to the chuck axis is given, and various points of a survey geometry of said holding means are contacted by a processing instrument.

The amount of longitudinal displacement of the connection geometry with respect to the longitudinal axis of the shaft is measured by at least one contacting operation with respect to a surface of said holding means normal to said longitudinal axis and the extent of rotation of said connection geometry about said longitudinal axis and also the degree of eccentricity of said connection geometry with reference to said longitudinal axis are determined by at least one contacting operation directed toward a plane lateral surface parallel to the longitudinal axis of said holding means, and the position and orientation of said connection geometry of said holding means relative to said blank are deduced from the readings obtained by said measurements.

A final object the invention consists in a method of determining the position and orientation of connection geometry located on holding means for a blank releasably attached to said holding means for the production of a dental fitted shell, wherein said holding means is clamped by way of its shaft in a chuck of a processing machine and an at least rough spatial alignment thereof relative to the chuck axis is given. By means of a measuring device various points of the survey geometry on the holding means are surveyed.

In order to determine the amount of longitudinal displacement of the connection geometry with respect to the longitudinal axis of the shaft, at least one surface of said holding means normal to said longitudinal is surveyed and the extent of rotation of said connection geometry about said longitudinal axis, and the degree of eccentricity of said connection geometry with reference to said longitudinal axis, a plane lateral surface parallel to the longitudinal axis of said holding means is surveyed, and the position and orientation of said connection geometry of said holding means relative to said blank are deduced from the readings obtained by said surveying measurements.

One procedure thus involves carrying out a contacting operation, for example, with a processing tool, whilst another procedure involves contactless surveying.

The basic method, as carried out in practice, may be described as follows:in a first step, the holding means is inserted with its shaft in the chuck of a processing machine, so that at least rough spatial alignment thereof with reference to the chuck axis is achieved,in the second step, the shaft is clamped in the chuck, andin a third step, various points of the survey geometry of the holding means are surveyed with a processing instrument or in some other way.

Exact determination of the position of the holding means in the chuck is thus made possible by measuring the amount of longitudinal displacement of the connection geometry with respect to the longitudinal axis of the shaft by means of at least one contacting or surveying operation directed toward a surface normal to the longitudinal axis of the holding means, and by determining the extent of rotation of the connection geometry about the longitudinal axis by means of at least one contacting or surveying operation directed toward a plane lateral surface parallel to the longitudinal axis of the holding means, and by deducing, in a fourth step, the position and orientation of the connection geometry of the holding means relative to the blank from the readings obtained by such surveying. This surveying operation can be carried out without contacting any surface, if desired.

The aforementioned device satisfies four requirements. Firstly, the holding means is adapted, by reason of its securing geometry, to be clamped in rough orientation in the chuck of a processing machine. In the present embodiment this requirement is satisfied by a shaft and a disk provided with a notch.

Secondly, the holding means is configured such that it can be positively connected, via the connection geometry, to the preformed geometry of the ceramic block. In the present embodiment this requirement is satisfied in that the preformed geometry of the blank is present in negative form. The holding means positively engages the preformed geometry of the blank via the connection geometry.

The symmetry of the blank including any preformed geometry can be represented by the shape of the holding means. Multidentate symmetry need not be unequivocally resolved. If the block is, say, axially symmetrical and the preformed symmetry is hexa- or octa-dentate, the connection between the holding means and the blank will likewise have a hexa- or octa-dentate symmetry, which need not be further resolved.

Theoretically, any type of connection geometry can be used for the attachment of the holding means to the blank, provided it permits neither translational nor rotational displacements of the blank relatively to the holding means. A multidentate symmetry is possible but should be designed such that accidental mounting of an asymmetrical blank in a direction not conforming to the proper securing direction will be immediately optically apparent to the user.

Thirdly, the holding means is adapted to allow for surveying of the survey geometry. In the present embodiment this requirement is satisfied in that mechanical surveying of the device is made possible by suitable geometry. This surveying takes into account and measures all tolerances permitted by the type of fixture, eg, translational, rotational, and eccentric tolerances.

Fourthly, the holding means is designed such that surveying of the survey geometry makes it possible to clearly deduce the position and orientation of the connection geometry.

Furthermore, the survey geometry can be designed such that the type of connection geometry is coded in the survey geometry as a feature of the implant to be supplied.

WO 99/13796 discloses a method of surveying a surface mounted on a holding means by means of a laser beam and interpreting the length and width or the axial length and the distance from the center axis as an identification of the type of blank used, but this is carried out prior to moving the holding means toward the processing machine.

EMBODIMENT ACCORDING TO THE INVENTION

The holding means1shown inFIG. 1comprises a shaft2, a disk3, and an extension4. The securing geometry of shaft2is free to vary in several ways.

By reason of a vaguely defined position of a stop member5disposed at the end of shaft2in a workholding device, the position of shaft2in the accommodating chuck6may vary in the longitudinal direction of the shaft.

Since only rough prepositioning is achieved by the engagement of an alignment pin8in a locking notch7in the disk3, rotational displacement about the longitudinal axis9of the accommodating chuck6is possible.

By reason of the fact that shaft2is secured in chuck6by means of a grub screw11acting on a securing region10on the periphery of the shaft, asymmetrical fixation of the securing geometry in the chuck6can cause eccentricity with reference to the longitudinal axis9of chuck6.

In order to be able to put shaft2into chuck6, the radius of shaft2must necessarily be smaller than the internal radius of chuck6. These radii are usually subject to batch variations. Fixing by means of grub screw11from the side thus leads to an undefined degree of eccentricity between the longitudinal axis9′ of shaft2and the longitudinal axis9of chuck6. Since shaft2is itself a precision turned part and connection geometry12is also in precise concentric alignment with shaft2, the connection geometry will be eccentrically mounted with respect to longitudinal axis9of the chuck.

The aforementioned tolerances all contribute to the fact that the position of connection geometry12for a blank13is not reliably reproducible. If an implant or skeletal framework is to be machined out of blank13, however, all of said geometrical interrelations will be significant.

FIG. 2shows, besides the features already described, some other features of holding means1. In its center there is situated connection geometry12for the blank (not shown). The dimensions of said connection geometry12conform to the prior art. Also visible is disk3with locking notch7on its perimeter.

A beam14having lateral surfaces15,16is shown as being part of the survey geometry. Lateral surfaces15,16are oriented in parallelism. As may be seen fromFIG. 1, lateral surfaces15,16also extend parallel to, and at a distance from, longitudinal axis9′ of holding means1.

The top surface17of disk3is part of the survey geometry and is disposed normal to the longitudinal axis of holding means1.

The surveying device used for locating the position of holding means1fixed in chuck6is a processing tool20of a processing machine illustrated inFIG. 3. This tool20is moved toward the various reference surfaces16,17of the survey geometry at a slow feed rate and a very slow rotatory speed until mechanical contact between tool20and reference surface16,17retards the speed of rotation. This contacting method is known per se from the prior art and makes it possible to deduce the position of the reference surface by computation based on the knowledge of the position of the tool.

The survey geometry in this case consists of top surface17of the disk and a lateral surface16of beam14, said lateral surface being parallel to longitudinal axis9.

The amount of longitudinal displacement along shaft2is surveyed by at least one contacting operation on the top surface17of disk3, suitable surveying points being indicated inFIGS. 1,2by filled circles. In this case contact is achieved by the lateral surface21of processing tool20. If top surface17of disk3is a plane surface which is also normal to longitudinal axis9of chuck6, the point at which the top surface is contacted is theoretically insignificant.

Rotation of the holding means about longitudinal axis9and the degree of eccentricity of the holding means with reference to this axis can be determined by a number of contacting operations directed toward lateral surfaces15,16of beam14. The quality of the surveying operation is improved the further away the points of contact are from the beam. Suitable surveying points are indicated inFIG. 1,2by circles.

Basically, optical surveying of the survey geometry is alternatively possible.

Due to the fact that holding means1is adapted to allow for surveying of the survey geometry to provide precise information on the position and orientation of the connection geometry, the position and orientation of said connection geometry12can be calculated from such surveying measurements. The extension4between connection geometry12and beam14allows for free movement of the processing tool while surveying the survey geometry and during subsequent processing.

Once the holding means has been surveyed, the position of blank13secured therein is known and an asymmetrical shape can be machined out of the blank. Knowledge of the exact position of the rotation axis of the ceramic block in the coordinate system of the processing machine can be utilized to resolve the shape into profiles radial to this axis. These can then be machined out while rotating the blank about longitudinal axis9of the workholding device.

In particular, fabrication of the holding means and connection geometry as a single unit and the resulting precise knowledge of the position and alignment of the connection geometry with reference to the holding means makes it possible to deduce the position and alignment of the blank by surveying the holding means. Theoretically, the holding means may alternatively be composed of a number of parts, provided the appropriate geometrical relationships are maintained.

This procedure guarantees that the finished fitted shell has the desired position and orientation relative to the connection geometry.

A split holding means is illustrated inFIG. 4. Holding means40comprises a shaft41adapted to be clamped in a processing machine (not shown) and furthermore a disk42having centering means43for connection to an attachment44. Only attachment44is provided with survey geometry45, which is exchangeable and attachable to the centering means. In the present embodiment, attachment44is open at its center and is mounted on a neck46extending away from disk42. At the end of neck46there is provided connection geometry47for a blank48.

FIG. 5shows a blank51that has a shaft52for securing in a workholding device. The shaft is of metal and extends into at least a portion of blank51. Shaft52thus represents a metal core that projects from the blank and can be directly clamped. Following processing, shaft52is cut off. The connection geometry53is disposed at the end of the blank remote from shaft52.

FIG. 6demonstrates that a blank60may be provided not only with connection geometry61but also with survey geometry62. The survey geometry is discernible in the view shown inFIG. 6band has surfaces63to67which are comparable to beam14and surface17ofFIG. 1. Surveying these surfaces, or some of them, makes it possible to determine the position of connection geometry61with a sufficiently degree of accuracy.

A blank70having connection geometry capable of being surveyed is illustrated inFIG. 7. For this purpose the connection geometry71is disposed on the side of blank70. A shaft72extends away from blank70. When blank70is clamped by way of shaft72in a workholding device, the connection geometry71disposed on the blank itself remains available for surveying. Additional survey geometry is then no longer necessary.