APPARATUS FOR VARYING A FOCAL POINT OF AN OPTICAL SYSTEM IN A DENTAL 3D-SCANNER AND DENTAL 3D-SCANNER

Abstract

The present invention relates to an apparatus (28) for varying a focal point (24) of an optical system in a dental 3D-scanner (10), comprising: a lens unit (30) with a lens (20) being movable between a front reversal position and a rear reversal position to vary a position of a focal point with respect to a scan object (22): a guide unit (34) for guiding a movement of the lens unit between the front reversal position and the rear reversal position along a guide axis (48) being parallel to an optical axis (46) of the lens; and a drive unit (36) for driving the movement of the lens unit, said drive unit including a linear motor (38) with an anchor (40) and a stator (42), said anchor being movable along a drive axis (44) of the drive unit that is parallel to the guide axis, said stator being affixed to the guide unit. The present invention further relates to a dental 3D-scanner (10) for scanning a three-dimensional scan object.

Claims

1. Apparatus for varying a focal point of an optical system in a dental 3D-scanner, comprising: a lens unit with a lens being movable between a front reversal position and a rear reversal position to vary a position of a focal point with respect to a scan object; a guide unit for guiding a movement of the lens unit between the front reversal position and the rear reversal position along a guide axis being parallel to an optical axis of the lens; and a drive unit for driving the movement of the lens unit, said drive unit including a linear motor with an anchor and a stator, said anchor being movable along a drive axis of the drive unit that is parallel to the guide axis, said stator being affixed to the guide unit.

2. Apparatus as claimed in claim 1, wherein the drive unit includes a coupling arrangement for coupling a movement of the anchor and the lens unit so that a movement of the anchor in a first direction is transferred to a movement of the lens in a second direction opposite to the first direction.

3. Apparatus as claimed in claim 2, wherein the coupling arrangement includes a flexible connection element for connecting the anchor and the lens unit to transfer a force from the anchor to the lens unit.

4. Apparatus as claimed in claim 3, wherein the coupling arrangement includes a tension element for tensioning the flexible connection element.

5. Apparatus of claim 2, wherein the coupling arrangement includes an inverting element for inverting the movement of the anchor.

6. Apparatus as claimed in claim 1, wherein the guide unit includes a position sensor for determining a position of the lens unit between the front reversal position and the rear reversal position.

7. Apparatus as claimed in claim 6, wherein the drive unit is configured to control the movement of the lens unit based on a sensor signal of the position sensor.

8. Apparatus as claimed in claim 1, wherein the guide unit includes a linear recirculating ball bearing guide; and the lens unit includes an engaging element for engaging into said linear recirculating ball bearing guide.

9. Apparatus as claimed in claim 1, wherein a mass of the lens unit is equal to a mass of the anchor to compensate reaction forces resulting from accelerations of the lens and the anchor.

10. Apparatus as claimed in claim 1, wherein a centerline of mass of the lens unit parallel to the guide axis corresponds to a centerline of mass of the anchor parallel to the guide axis.

11. Apparatus as claimed in claim 1, wherein the linear motor is a brushless 3-phase linear servomotor; and the linear motor preferably includes a hall sensor for measuring a position of the anchor with respect to the stator.

12. Apparatus as claimed in claim 1, wherein a maximum displacement of the anchor is equal to a distance between the front reversal position and the rear reversal position.

13. Apparatus as claimed in claim 1, wherein the drive unit is configured to drive the movement of the lens unit to oscillate between a selectable front oscillation position and a selectable rear oscillation position at an oscillation frequency of 2 to 20 Hz.

14. Dental 3D-scanner for scanning a three-dimensional scan object, comprising: an apparatus as claimed in claim 1; a detector for detecting a light signal from the scan object passing through the lens, and a handheld housing for manually guiding the 3D-scanner around the scan object.

15. Dental 3D-scanner as claimed in claim 14, comprising a control unit for controlling the drive unit.

16. Apparatus of claim 3, wherein said connection element includes a steel strip.

17. Apparatus of claim 4, wherein said tension element includes a spring.

18. Apparatus of claim 5, wherein said inverting element includes a ball bearing.

19. Apparatus of claim 6, wherein the position sensor includes an optical distance measurement sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. In the following drawings

[0029] FIG. 1 shows a schematic illustration of a dental 3D-scanner according to an aspect of the present invention;

[0030] FIG. 2 shows a schematic illustration of a measurement principle based on a moving lens in a 3D-scanner:

[0031] FIG. 3 shows a schematic perspective illustration of an apparatus according to the present invention with a lens unit in the rear reversal position:

[0032] FIG. 4 shows a schematic perspective illustration of the apparatus with a lens unit in the front reversal position;

[0033] FIG. 5 shows a schematic side view of the apparatus;

[0034] FIG. 6 shows a schematic top view of the apparatus;

[0035] FIG. 7 shows a schematic illustration of the positions of the centerlines of mass in a side view; and

[0036] FIG. 8 shows a schematic illustration of the positions of the centerlines of mass in a bottom view.

[0037] In FIG. 1, a dental 3D-scanner 10 for scanning a 3-dimensional scan object according to the present invention is schematically illustrated. The dental 3D-scanner 10 includes a handheld housing 12. In the illustrated example, the handheld housing 12 has a widening rear section 12a to be held in the hand of an operator and a tapered front section 12b to be inserted into the mouth of a patient. Attached to the rear section 12a is a cable via which the handheld housing 12 is connected to a control device 14 that can, e.g., correspond to a personal computer. The dental 3D-scanner 10 has a window in its tapered front section 12b through which a light signal can pass and can reach a detector 16 inside the handheld housing 12. The dental 3D-scanner 10 is controlled by a control unit 18 that, in the illustrated example, is included in the control device 14.

[0038] The dental 3D-scanner 10 of the present invention can particularly be put to use in a dentist's surgery or also in a dental laboratory to obtain an in-situ scan of a situation in the mouth of a patient. Usually, the situation in the mouth of a patient is scanned intraorally. It is, however, also possible that a scan object outside the mouth of a patient is scanned. The handheld housing 12 is hand-guided by a dentist or dental technician that moves the 3D-scanner around the scan object. This allows to obtain an in-situ scan to obtain a 3D representation. It is advantageous if a live visualization of the scan object, in particular the teeth or the jaw of the patient, is displayed on a screen during the data collection as schematically illustrated.

[0039] It is to be understood that the illustrated embodiment is an example and that it is also possible that the different components are arranged in a different way. For instance, it is possible that the handheld housing 12 includes the control unit 18 and/or that the handheld housing 12 is connected via a wireless connection with the control device 14. Also, it is possible that the handheld housing 12 includes all components of the dental 3D-scanner and that only an image of the scan object is transferred to a separate external screen.

[0040] In FIG. 2, the measurement principle of the dental 3D-scanner 10 is schematically illustrated. The dental 3D-scanner 10 has a lens 20 through which a light signal from a scan object 22 passes prior to reaching the detector 16. The scan process thereby is based on a variable focal point 24. The focal point 24 corresponds to a focal plane. The focal point 24 is varied so that the entire spatial dimension of the scan object 22 is sampled. In other words, the image obtained by means of the detector 16 is focused at variable distances from the 3D-scanner 10 or its detector 16, respectively. The measurement principle thereby corresponds to a confocal microscope. Usually, the lens oscillates to periodically vary the focal point.

[0041] In the illustrated embodiment, the lens 20 is moved between a front oscillation position 20a and a rear oscillation position 20b. By moving the lens 20, the focal point 24 is moved from a first position 24a above the scan object 22 to a second position 24b below the scan object 22 or the area of interest of the scan object 22. Usually, the lens 20 oscillates between the two positions at a constant oscillation frequency so that a constant sampling of the scan object 22 is obtained. Since the dental 3D-scanner 10 is not fixed in its position versus the scan object 22 but manually moved around the scan object 22 to allow for manual intraoral application, the oscillation frequency is thereby in the order of 10 Hz. By making use of such a comparatively high oscillation frequency, a blurring of the obtained scan due to movements of the scanner versus the scan object 22 is avoided. In the illustrated embodiment, a mirror 26 is arranged between the lens 20 and the scan object 22. The movement of the lens 20 is thereby obtained by means of an apparatus 28 for varying a focal point of an optical system according to the present invention.

[0042] In FIGS. 3 and 4, the apparatus 28 for varying a focal point of an optical system in the dental 3D-scanner of the present invention is schematically illustrated in a perspective view. The apparatus 28 includes a lens unit 30 with a lens 20 and a corresponding holding arrangement 32 for holding the lens 20, a guide unit 34 for guiding the movement of the lens unit 30 and a drive unit 36 for driving the movement.

[0043] The lens unit 30 thereby includes all movable parts. The lens unit 30 is movable between a front reversal position as illustrated in FIG. 4 and a rear reversal position as illustrated in FIG. 3. In the front reversal position, the distance to a detector (not illustrated in the Figs.) is increased so that the focal point of the optical system formed by the lens 20 and the detector is moved further away from the lens.

[0044] The drive unit 36 includes a linear motor 38 with an anchor 40 and a stator 42. The anchor 40 is moved versus the stator 42 along a drive axis 44. Usually a 3-phase linear servomotor is used as the linear motor 38. The linear motor 38 may include a hall sensor 39 (not illustrated) that is integrated with the linear motor housing and that provides a sensor signal to be used for controlling the power supply of the linear motor 38. The movement induced by the drive unit 36 is parallel to the drive axis 44. Thereby, the drive axis 44 is parallel to an optical axis 46 of the lens 20 and a guide axis 48 along which the movement of the lens unit 30 is guided by the guide unit 34. The optical axis 46 of the lens 20 runs through the center of the lens 20.

[0045] As illustrated in FIGS. 3 and 4, the linear movement of the lens unit 30 between the front reversal position and the rear reversal position is in the opposite direction of the movement of the anchor 40. When the lens unit 30 is moved forward, the anchor 40 is moved backward as illustrated in FIG. 4. By making use of this counter movement, it becomes possible to compensate for vibrations caused by the mass of the lens unit 30 when it oscillates. Preferably, a mass of the lens unit 30 is thereby equivalent to a mass of the anchor 40 so that optimal vibration cancellation is obtained. It is possible to add weight to one of the anchor 40 and the lens unit 30.

[0046] On the one hand, it is possible that the lens unit 30 is moved between the front reversal position and the rear reversal position. Thereby, the distance between the front and rear reversal positions represents a maximum displacement. It is, however, also possible that the linear motor 38 is controlled so that the movement of the lens unit 30 is subject to a smaller displacement. The use of a linear motor 38 has the advantage that the movement of the lens unit 30 can be inverted at any desired position between the front and rear reversal positions. In this respect, a front and rear oscillation position correspond to positions in which the movement of the lens unit 30 is inverted. The distance between the front and rear oscillation positions is smaller than the distance between the front and rear reversal positions.

[0047] In FIG. 5, the apparatus 28 is illustrated in a schematic side view to further describe the motion of the lens unit 30 and drive unit 36. In order to transform the movement of the anchor 40 in a rear direction (right in the illustration in FIG. 5) into a movement of the lens unit 30 in a front direction (left), it is required to invert the movement. For this, a coupling arrangement 50 of the drive unit 36 is arranged between the linear motor 38 and the lens unit 30.

[0048] The coupling arrangement 50 may particularly include a flexible connection element 52 which transfers the force from the anchor 40 to the lens unit 30. In the illustrated embodiment, the flexible connection element 52 is a steel strip which is sufficiently strong to transport the recurrent forces at higher oscillation frequencies and which allows transferring both tractive and compressive forces. The coupling arrangement 50 preferably includes a tension element 54 which comprises a spring in the illustrated embodiment. The tension element 54 is used to exert a force on the flexible connection element 52 so that this flexible connection element 52 is under tension and can transfer forces without shaking. This is particularly important when the movement of the lens unit 30 is inverted in the front or rear reversal positions or in the front or rear oscillation positions.

[0049] The coupling arrangement 50 further includes an inverting element 56 which comprises a ball bearing in the illustrated embodiment. This inverting element 56 inverts the movement of the anchor 40 by guiding the flexible connection element 52 through a 180° direction change. In the illustrated embodiment, two ball bearings are used.

[0050] In FIG. 6, the functionality of the guide unit 34 is illustrated based on a top view of the apparatus 28. The guide unit 34 connects the lens unit 30 and the drive unit 36. The guide unit 34 is affixed to the stator 42 of the linear motor 38. The lens unit 30 and the anchor 40 of the linear motor 38 are moved with respect to the guide unit 34 and the stator 42.

[0051] In the illustrated embodiment, the guide unit 34 includes a recirculating ball bearing guide 58 in which an engaging element 60 of the lens unit 30 is guided. The linear recirculating ball bearing guide 58 thereby functions comparable to a railing. By making use of a ball bearing, friction is minimized so that high oscillation frequencies are possible.

[0052] Furthermore, the guide unit 34 includes a position sensor 62 which allows obtaining information on a position, in particular a lateral position, of the lens unit 30 with respect to the guide unit 34. In the illustrated embodiment, the position sensor 62 is an optical sensor that measures a distance. This position of the lens unit 30 is direct measure of the current position of the lens and the focal point as well as the current position of the anchor 40 of the linear motor 38. The sensor signal of the position sensor 62 can be used to control the drive unit 36 so that a direct feedback and control loop becomes possible. In particular, it is possible to specify specific front and rear oscillation positions and control the current position to decide whether to move in the other direction based on the sensor signal of the position sensor. Thereby, the corresponding control can be exercised in a control unit that can also be included in a dental 3D-scanner or that can be externally arranged in a separate processing device.

[0053] In FIGS. 7 and 8, the apparatus 28 is schematically illustrated in a side view (FIG. 7) and in base view (FIG. 8). In order to minimize torque moments and rotational forces that could also result in vibrations of the dental 3D-scanner, it is advantageous that a centerline of mass 64 of the anchor 40 is equal to a centerline of mass 66 of the lens unit 30. The centerlines of mass 64, 66 are thereby parallel to the guide axis. As illustrated in the two different views in FIGS. 7 and 8, the centerline of mass 64 of the anchor and the centerline of mass 66 of the lens unit are equal both in the side view and in the bottom view. This construction allows preventing torque forces from occurring.

[0054] The foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. As will be understood by those skilled in the art, the present disclosure may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the description is intended to be illustrative, but not limiting the scope of the disclosure, as well as other claims. The disclosure, including any readily discernible variants of the teachings herein, defines, in part, the scope of the foregoing claim terminology such that no inventive subject matter is dedicated to the public.

[0055] In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.