Calibration of an intraoral scanner

Patent metadata

Field	Value
Publication number	US-10952827-B2
Application number	US-202016823156-A
Country	US
Kind code	B2
Filing date	Mar 18, 2020
Priority date	Aug 15, 2014
Publication date	Mar 23, 2021
Grant date	Mar 23, 2021

Abstract

A method of generating a three-dimensional virtual model of an intraoral object includes capturing, by an intraoral scanner for performing intraoral scans, surface scan data of the intraoral object while changing a position of at least one lens of focusing optics of the intraoral scanner, wherein the surface scan data comprises depth data for a plurality of points of the intraoral object. The method further includes adjusting the depth data for one or more of the plurality of points based at least in part on a value associated with a temperature of at least a portion of the imaging apparatus. The method further includes generating the three-dimensional virtual model of the intraoral object using the adjusted depth data.

First claim

What is claimed is:

1. A method of calibrating an intraoral scanner having a non-flat focal surface, comprising:
measuring a calibration object by the intraoral scanner at one or more focusing setting of the intraoral scanner to determine measured depth values for a plurality of points on the calibration object, wherein each of the plurality of points on the calibration object has a known depth value in a reference coordinate system;
determining, for each point of the plurality of points on the calibration object, a difference between the measured depth value for the point and the known depth value for the point;
applying the determined difference between the measured depth value and the known depth value for each point of the plurality of points on the calibration object to a smooth function to generate a compensation model that compensates for the non-flat focal surface of the intraoral scanner; and
storing the compensation model, wherein the compensation model is usable to correct errors in depth measurements caused by the non-flat focal surface.

2. The method of claim 1 , wherein a magnification of the non-flat focal surface changes with a focusing setting of the intraoral scanner, and wherein a measured x value and a measured y value are determined for each of the plurality of points on the calibration object, the method further comprising:
determining, for each of the plurality of points having a measured x value and a measured y value, a matching known point on the calibration object, the matching known point having a known x value and a known y value;
determining, for each pair of a measured point and a matching known point, a) a first difference between the measured x value and the known x value for that point and b) a second difference between the measured y value and the known y value for that point;
applying the determined difference between the measured x value and the known x value for each point of the plurality of points on the calibration object to the smooth function or to an additional smooth function to generate the compensation model or a first additional compensation model; and
applying the determined difference between the measured y value and the known y value for each point of the plurality of points on the calibration object to the smooth function or to the additional smooth function to generate the compensation model, the first additional compensation model, or a second additional compensation model;
wherein at least one of the compensation model, the first additional compensation model or the second additional compensation model is usable to compensate for changes in the magnification of the non-flat focal surface caused by changes with the focusing setting.

3. The method of claim 1 , wherein the calibration object comprises a known x value, a known y value and a known z value for each of the plurality of points to within 0.5 microns of accuracy.

4. The method of claim 1 , further comprising:
moving the calibration object to at least one of multiple different x positions, multiple different y positions or multiple different depth positions for each of the one or more focusing setting of the intraoral scanner; and
measuring the calibration object for each position of the calibration object and for each focusing setting of the intraoral scanner.

5. The method of claim 4 , wherein different compensation models are generated for different focusing settings of the intraoral scanner.

6. The method of claim 1 , wherein the smooth function is a bi-variate quadratic polynomial, and wherein the differences between the measured depth value and the known depth value for each point of the plurality of points on the calibration object are applied to the smooth function to solve for constraints in the bi-variate quadratic polynomial.

7. The method of claim 1 , wherein the calibration object is measured at each focusing setting of the intraoral scanner, the method further comprising:
generating a separate compensation model for each focusing setting.

8. The method of claim 1 , wherein the calibration object is measured at each focusing setting of the intraoral scanner, and wherein the compensation model accounts for changes in the focusing setting.

9. The method of claim 1 , wherein the compensation model compensates for the non-flat focal surface and further compensates for at least one of magnification change caused by changes in the focusing setting, optical distortions or optical aberrations.

10. The method of claim 1 , further comprising:
performing the measuring of the calibration object at multiple different temperatures of the intraoral scanner over a temperature operating range of the intraoral scanner;
determining differences in the measured depth values for the points at the multiple different temperatures; and
performing at least one of:
a) applying the differences to the compensation model to create a thermal state correction model;
b) determining a temperature dependent adjustment factor to be applied to the compensation model based on the differences; or
c) generating separate compensation models for a plurality of temperatures.

11. An intraoral scanning system, comprising:
an intraoral scanner having a non-flat focal surface, wherein the intraoral scanner is to scan a calibration object at one or more focusing setting of the intraoral scanner to determine measured depth values for a plurality of points on the calibration object, wherein each of the plurality of points on the calibration object has a known depth value in a reference coordinate system; and
a computing device to:
receive scan data from the intraoral scanner, the scan data comprising the measured depth values for the plurality of points on the calibration object;
determine, for each point of the plurality of points on the calibration object, a difference between the measured depth value for the point and the known depth value for the point;
apply the determined difference between the measured depth value and the known depth value for each point of the plurality of points on the calibration object to a smooth function to generate a compensation model that compensates for the non-flat focal surface of the intraoral scanner; and
store the compensation model, wherein the compensation model is usable to correct errors in depth measurements caused by the non-flat focal surface.

12. The intraoral scanning system of claim 11 , wherein a magnification of the non-flat focal surface changes with a focusing setting of the intraoral scanner, and wherein a measured x value and a measured y value are determined for each of the plurality of points on the calibration object, wherein the computing device is further to:
determine, for each of the plurality of points having a measured x value and a measured y value, a matching known point on the calibration object, the matching known point having a known x value and a known y value;
determine, for each pair of a measured point and a matching known point, a) a first difference between the measured x value and the known x value for that point and b) a second difference between the measured y value and the known y value for that point;
apply the determined difference between the measured x value and the known x value for each point of the plurality of points on the calibration object to the smooth function or to an additional smooth function to generate the compensation model or a first additional compensation model; and
apply the determined difference between the measured y value and the known y value for each point of the plurality of points on the calibration object to the smooth function or to the additional smooth function t

Assignees

• Align Technology Inc

Inventors

• Verker Tal
• Levin Adi
• Saphier Ofer
• Moshe Maayan

Classifications

• G02B23/2446

  of the image relay (G02B23/26 takes precedence) · CPC title

• G02B23/2461

  Illumination · CPC title

• G02B23/26

  using light guides {(for illumination G02B23/2469)} · CPC title

• G02B27/0025 Primary

  for optical correction, e.g. distorsion, aberration · CPC title

• G01B11/24

  for measuring contours or curvatures · CPC title