Method and reference model for checking a measuring system

• US 9,462,993 B2
• Filed: 01/28/2013
• Issued: 10/11/2016
• Est. Priority Date: 01/27/2012
• Status: Active Grant

• Current Assignee: Sirona Dental Systems GmbH (Sirona Dental Systems Incorporated)
• Original Assignee: Sirona Dental Systems GmbH (Sirona Dental Systems Incorporated)
• Inventors: Popilka, Bjrn, Wedler, Volker, Adamson, Anders, Thiel, Frank
• Primary Examiner(s): Parl, Chan
• Assistant Examiner(s): Summers, Geoffrey E
• Application Number:
  US14/372,255
• Publication Number:
  US 20140365140A1
• Time in Patent Office: 1,352 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: A61B 2560/0233 Optical standards
• CPC Class Codes: A61B 5/1077 Measuring of profiles
• CPC Class Codes: A61B 5/1079 using optical or photographic means
• CPC Class Codes: A61B 6/582 Calibration
• CPC Class Codes: A61C 13/34 Making or working of models, e.g. preliminary castings, trial dentures; Dowel pins [4]
• CPC Class Codes: A61C 19/04 Measuring instruments specially adapted for dentistry A61C5/44 takes precedence; testing vitality of teeth A61B5/0534; radiation diagnosis specially adapted for dentistry A61B6/51
• CPC Class Codes: A61C 9/006 projecting one or more stripes or patterns on the teeth
• CPC Class Codes: A61C 9/0066 Depth determination through adaptive focusing
• CPC Class Codes: G01B 21/042 Calibration or calibration artifacts G01B3/30, G01B9/02072 take precedence
• CPC Class Codes: G06T 19/20 Editing of 3D images, e.g. changing shapes or colours, aligning objects or positioning parts
• CPC Class Codes: G06T 2207/30036 Dental; Teeth
• CPC Class Codes: G06T 2207/30204 Marker
• CPC Class Codes: G06T 2219/2004 Aligning objects, relative positioning of parts
• CPC Class Codes: G06T 7/80 Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration
• CPC Class Codes: G06T 7/85 Stereo camera calibration
• CPC Class Codes: G09B 23/283 for dentistry or oral hygiene G09B23/286 takes precedence

Abstract

The invention relates to a reference object (3) and a method for checking a measuring system (1), wherein a plurality of three-dimensional recordings (4, 8) of a reference object are recorded from different recording directions (5) by means of the measuring system (1). The reference object (3) has a closed shape, wherein each of the three-dimensional recordings (4) is registered with at least the preceding recording (4). In the case of a faulty calibration and/or in the case of a faulty registration, the individual recordings (4, 8) are deformed compared to the actual shape of the reference object (3), so that the deformation continues when assembling the individual three-dimensional recordings (4) to form an overall recording (54) and the generated overall recording (54) deviates in its dimensions from the dimensions of the reference object (3) as a result thereof. At least one object region (10) of the reference object (3) is measured twice, at the beginning of a circuit and at the end of the circuit, wherein a distance (55) is determined in the overall recording (54) between a first position of the object region (10) in a first recording at the beginning of the circuit and a second position of the object region (10) in a second recording at the end of the circuit.

Claims

1. A method of determining a calibration error in a measuring system, the method comprising:

recording a plurality of three-dimensional images of a reference object from a plurality of different image directions in a circuit along the reference object using the measuring system, wherein an object region of the reference object is imaged twice, at a start of the circuit and at an end of the circuit;

registering each of the three-dimensional images with another of the three-dimensional images using a registration algorithm for the measuring system so that the three-dimensional images are combined into an overall image;

determining a distance in the overall image between a first position of the object region in a three-dimensional image from the start of the circuit and a second position of the object region in a three-dimensional image from the end of the circuit;

determining a total measuring error based on the distance in the overall image;

determining a registration error of the measuring system from a deviation between an ideal virtual three-dimensional model of the reference object and another virtual model of the reference object generated by applying the registration algorithm for the measuring system to a plurality of virtual sub-regions of the ideal virtual three-dimensional model of the reference object; and

determining a calibration error by subtracting the registration error from the total measuring error.

2. The method according to claim 1, wherein the reference object is ring-shaped and provides models of multiple teeth next to one another in a row.

3. The method according to claim 2, wherein the measuring system orbits around the ring-shaped reference object during the recording of the three-dimensional images.

4. The method according to claim 1, wherein the reference object is an articulator with a closed upper jaw and lower jaw.

5. The method according to claim 4, wherein a trajectory of the measuring system is along a shape of the articulator during the recording of the three-dimensional images.

6. The method according to claim 1, wherein an image direction of the three-dimensional image from the end of the circuit corresponds to an image direction of the three-dimensional image from the start of the circuit.

7. The method according to claim 1, wherein a first image region of the three-dimensional image from the start of the circuit corresponds, at least partially, to an image region of a following three-dimensional image in the circuit.

8. The method according to claim 1, wherein dimensions of the plurality of virtual sub-regions correspond to dimensions of image regions of the three-dimensional images.

9. The method according to claim 1,

wherein each three-dimensional image partially overlaps with a preceding three-dimensional image in a circuit direction, and

wherein the method further comprises:

registering each three-dimensional image with the preceding three-dimensional image and with a second preceding three-dimensional image that precedes the preceding three-dimensional image in the circuit direction.

10. A dental measuring system, comprising:

a dental camera configured to record a plurality of three-dimensional images from a plurality of different image directions in a circuit along a reference object, wherein an object region of the reference object is imaged twice, at a start of the circuit and at an end of the circuit; and

a computer configured to;

receive the three-dimensional images;

register each of the three-dimensional images with another of the three-dimensional images using a registration algorithm for the dental measuring system so that the three-dimensional images are combined into an overall image;

determine a distance in the overall image between a first position of the object region in a three-dimensional image from the start of the circuit and a second position of the object region in a three-dimensional image from the end of the circuit;

determine a total measuring error based on the distance in the overall image;

determine a registration error of the dental measuring system from a deviation between an ideal virtual three-dimensional model of the reference object and another virtual model of the reference object generated by applying the registration algorithm for the dental measuring system to a plurality of virtual sub-regions of the ideal virtual three-dimensional model of the reference object; and

determine a calibration error by subtracting the registration error from the total measuring error.

11. The dental measuring system according to claim 10, wherein an image direction of the three-dimensional image from the end of the circuit corresponds to an image direction of the three-dimensional image from the start of the circuit.

12. The dental measuring system according to claim 10, wherein a first image region of the three-dimensional image from the start of the circuit corresponds, at least partially, to an image region of a following three-dimensional image in the circuit.

13. The dental measuring system according to claim 10, wherein dimensions of the plurality of virtual sub-regions correspond to dimensions of image regions of the three-dimensional images.

14. The dental measuring system according to claim 10,

wherein each three-dimensional image partially overlaps with a preceding three-dimensional image in a circuit direction, and

wherein the computer is further configured to:

register each three-dimensional image with the preceding three-dimensional image and with a second preceding three-dimensional image that precedes the preceding three-dimensional image in the circuit direction.