Background Art When a tooth is missing because of a fracture or decay of the tooth, gums ailment, or an external wound, the missing tooth is repaired using artificial tooth to recover the reduced chewing function, appearance, and pronunciation capability, which process is referred to as dental prosthesis. In the following clauses, we briefly review deficiencies to be repaired by the dental prosthesis. One or more teeth may be totally missing for some patients while just some portion of a tooth is missing for another patient. One of several prosthetic alternatives is used depending on the missing style. For example, a whole. denture is used when the whole teeth are missing while a partial denture is used when a plurality of teeth are missing with a few teeth remained. If a few teeth are missing, the missing teeth are replaced by a bridgework, which means a teeth replacement joined to adjacent natural teeth. Meanwhile, in the case that a single tooth is missing, the missing tooth is repaired using a simple crown. On the other hand, implantation is attracting attention recently for the case that one or more teeth are missing because it does not result in damages of adjacent teeth contrary to the bridgework.

Even though a different prosthetic approach is chosen depending on the missing style as described above, the processes that a dental technician makes an artificial tooth are almost the same for all the cases. An exemplary repairing process is described below for the case that some dental crown portion of a single tooth is missing. First, the top of the tooth is removed by 1 or 1.5 millimeters and an impression is made using an impression material. Afterwards, a dental technician makes a gypsum model using the impression and produces an artificial tooth, i. e., an artificial dental crown based on the gypsum model.

Sometimes, when little natural dental crown remains because of the fracture or decay of the teeth, a post is installed into the dentin and a core is formed around the post, and then the artificial dental crown is formed on the post. In such a case, the artificial dental crown is produced by the same process described above also.

The artificial tooth production of the dental technician is a simple manual work, and it takes so long time to produce an artificial tooth (for example, a dental crown). Thus, it is desirable to automate the extraction of the characteristic feature of the tooth to be made and cutting of the artificial tooth in order to enhance the productivity and working efficiency. The inventors of the present invention address the use of a 3-dimensional input apparatus to extract of the characteristic feature of the tooth.

Conventional 3-dimensional input devices generally capture photograph images of objects using a charge coupled device (CCD) and extract the 3-dimensional shape data from the photographed images by respective software. Korean Laid-open Patent No.

1993-6430 filed on 6 September 1991 and published on 21 April 1993 and entitled METHOD FOR INPUTTING 3-DIMENSIONAL SHAPE USING CAMERA AND

AUTOMATIC INPUT SYSTEM USING THE SAME is an example of that. However, if the 3-dimensional shape is extracted using an image captured by a single camera, the precision of the shape data may be quite poor and cannot be used practically.

In order to overcome the drawback above, the use of a plurality of cameras has been proposed, for example, in Korean Laid-open Patent No. 2000-466 filed on 22 October 1999 and published on 15 January 2000 and entitled A 3-DIMENSIONAL DIGITAL INPUT APPARATUS. The apparatus described in the publication captures side view images and top view images using several CCDs and composes the captured images to obtain a 3-dimensional object image data. However, the complicated configuration of the apparatus increases the manufacturing cost of the apparatus.

Furthermore, the precision of the obtained image data is still not so high enough to be used in the production of the artificial tooth.

Disclosure of the Invention To solve the above problems, an object of the present invention is to provide a 3-dimensional shape scanner and shape scanning method for rapidly and accurately scanning a shape of an object, e. g., an artificial tooth model, which requires a precise processing.

The shape scanner and shape scanning method according to the present invention to achieve the above object scans a contour shape of an object having a conductive exterior surface or applied with conductive material on its exterior surface. Particularly, the present

invention scans the shape of the object by detecting the contact of a probe to the exterior surface of the object rather than impact detection.

In the 3-dimensional shape scanner of the present invention, a first probe is installed to be electrically connected to an exterior point of the object and a second probe is installed to be movable around the object. Position control means changes a relative position of the second probe with relative to the object in a 3-dimensional space. Contact detection means detects a contact of the second probe to the object by checking an electrical conduction state between the first and second probes. Preferably, the shape scanner further includes recording means for recording a spatial position of the second probe when the first probe is electrically connected to the second probe.

The position control means includes a first position controller for driving the second probe to a first direction directing to the exterior surface of the object or to an opposite direction, and a second position controller for changing a relative position of the second probe with respect to the object in a plane orthogonal to the first direction. The second position controller drives the second probe in the plane orthogonal to the first direction while the position of the object is fixed. Alternatively, the second position controller may drive the object in the plane orthogonal to the first direction while the vertical position of the second probe is fixed.

On the other hand, according to the shape scanning method according to the present invention, (a) contact detection means including a first and a second probes is provided along with recording means for recording the scanned data in a recording medium. Afterwards, (b) conductive material is applied to an exterior surface of the object

and the first probe is electrically connected to an exterior point of the object. (c) While the second probe is being moved along a first direction directing to the exterior surface of the object, an electrical conduction state between the first and second probes is determined.

(d) When it is determined that the first and second probes are electrically connected to each other, the position of the second probe is recorded and then the second probe is driven oppositely to the first direction. (e) After a relative position of the second probe with respect to the object is changed in a plane orthogonal to the first direction, the steps (c) and (d) are repeatedly carried out.

Brief Description of the Drawings The above objectives and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: FIG. 1 is a block diagram of a preferred embodiment of a 3-dimensional shape scanner according to the present invention; FIG. 2 is a flowchart showing the operation of the 3-dimensional shape scanner according to the present invention; FIG. 3 is a flowchart showing a process of producing an artificial tooth as an application of the present invention; and FIGS. 4A through 4E are graphical representations of examples of numerical tooth models generated by use of the shape scanner of the present invention.

Embodiments FIG. 1 shows a preferred embodiment of a 3-dimensional shape scanner according to the present invention. The shape scanner shown in the figure includes a first and a second probes 10 and 12, a probe position controller 30, a contact detector 40, and a position registration unit 50. The shape scanner is suitable for scanning the shape of an object which allows being applied with foreign substance on its exterior surface or has a conductive exterior surface. Hereinbelow, the shape scanner is described for the example of scanning the shape of a tooth gypsum model.

In the example of FIG. 1, the gypsum model 90 is installed on a work table 92 after water or another conductive liquid is sprayed or applied on its exterior surface. The first probe 10 is installed to be electrically connected to the bottom or one side of the gypsum model 90 or the work table 92. The second probe 12, being supported by a supporting member 14, is installed to be movable over gypsum model 90.

In the preferred embodiment, the work table 92 is fixed and the probe position controller 30 controls the movement of the second probe 12 in the x-, y-, and z-directions.

In such an embodiment, the probe position controller 30 includes a first controller 32 for driving the second probe 12 in the z-direction and a second controller 34 for driving the second probe 12 in the x-and y-directions. The first controller 32 drives a first stepping motor (not shown in the figure) in the supporting member 14 to move the second probe 12 vertically. Meanwhile, the second controller 34 drives a second and a third stepping motors (not shown in the figure) to move the supporting member 14 and the second probe 12 in the (X, Y) plane.

In an alternative embodiment, however, the second probe 12 may be fixed in the x-and y-directions but movable in the z-direction while the work table 92 is movable in the x-and y-directions. In such an embodiment, the first controller 32 of the probe position controller 30 drives the second probe 12 in the z-direction and the second controller 34 drives the second and the third stepping motors to move the work table 92 horizontally.

In FIG. 1, the contact detector 40 is electrically connected to the first and the second probes 10 and 12, and detects a contact of the second probe 12 to the gypsum model 90 by checking an electrical conduction state between the first and second probes 10 and 12. The first and the second probes 10 and 12 are electrically open when the second probe 12 is not in contact with the gypsum model 90, but connected to each other when the second probe 12 is in contact with the gypsum model 90. Detecting the contact, the contact detector 40 controls the position controller 30 to prevent the second probe from moving downward further and makes the position registration unit 50 to record the spatial coordinates of the second probe 12 in a database or a memory device.

FIG. 2 is a flowchart showing the operation of the 3-dimensional shape scanner according to the present invention. The operation of the shape scanner of FIG. 1 will now be described with reference to FIG. 2. Before the operation of the scanner, water or another conductive liquid is sprayed or applied on the exterior surface of the gypsum model 90 so that the exterior surface of the gypsum model 90 is electrically conductive.

Then, the first probe 10 is electrically connected to the gypsum model 90 (step 100).

Afterwards, the second probe 12 is arranged over the gypsum model 90 (step 102). The operation of the shape scanner is initiated under such arrangements.

In step 104, the (X, Y) coordinates of the second probe 12 is recorded in the recording device 60. Subsequently, the second probe 12 is moved downward, i. e., in the -z direction bit by bit (step 106). Whenever the second probe 12 proceeds downward by a step, the contact detector 40 determines whether the first and the second probes are electrically connected to each other (step 108). In the case that it is determined in the step 108 that the first and the second probes are not electrically connected to each other, the second probe 12 is moved downward by one step further and the determination is carried out repeatedly.

On the other hand, when it is determined in the step 108 that the first and the second probes are electrically connected to each other, the z-coordinate of the second probe 12 is recorded in the recording device 60 and then the second probe 12 is moved upward so that the second probe 12 is separated from the gypsum model (step 110).

Afterwards, it is determined whether a certain condition for scanning completion is reached (step 112). If the scanning completion condition is reached in the step 112, the scanning process ends. If, however, the scanning completion condition is not reached in the step 112, the second probe 12 is moved in the x-or y-direction by a certain distance and the steps 104 through 112 are carried out repeatedly. Such repetition is proceeded until the total shape of the gypsum model is completely scanned.

FIG. 3 is a flowchart showing a process of producing an artificial tooth as an application of the present invention. First, a tooth gypsum model is scanned and modeled into a numerical model using the shape scanner of the present invention (step 200). FIGS.

4A through 4E are graphical representations of examples of numerical tooth models

generated by use of the shape scanner of the present invention. The inventors have discovered, by an experimentation, that the error in the 3-dimensional modeling is 0.01 millimeters or less. Then, the geometrical characteristics of the tooth may be analyzed based on the numerical model to design an artificial tooth such as a cap, a conus, a crown, and a bridgework (step 202). Finally, the artificial tooth is produced by a material (for example, ceramic) using a 3-dimensional processing machine such as a numerically- controlled lathe (step 204). According to the process of the present invention, the Pin-and- die process in the manual production of the artificial tooth is replaced by the 3-dimensional shape scanning process, and the production using wax is replaced by the automatic cutting process.

Although the present invention has been described in detail above, it should be understood that the foregoing description is illustrative and not restrictive. Those of ordinary skill in the art will appreciate that many obvious modifications can be made to the invention without departing from its spirit or essential characteristics. Thus, it should be apparent that the invention can be modified in arrangement and detail without departing from such principles. We claim all modifications and variation coming within the spirit and scope of the following claims.

Industrial Applicability As describes above, the present invention enables precise scanning of the 3- dimensional shape an object having a conductive exterior surface or applied with conductive material on its exterior surface. In determining the contact of a probe to the

exterior surface of the object, it can be contemplated to detect the collision impact, which, however, is disadvantageous in that the probe may skid on the surface of the object and thus the precise scanning is difficult. On the contrary, the present invention can precisely scan the shape of the object regardless of the skid of the probe.

Due to the capability of the rapid and precise scanning of the object, the present invention may be applied to scanning process of an object which requires a precise processing (for example, an artificial tooth model) and can mechanize or automate the production of the artificial tooth. Since the artificial tooth production can be mechanized while maintaining preciseness, the productivity and efficiency of the artificial tooth production can be enhanced also. For example, while a skilled dental technician can produce 20 through 30 artificial teeth a day, one operator can produce about 400 artificial teeth a day using a single scanning and cutting system of the present invention.