Method and apparatus for inner diameter measurement of transparent tube

• US 10,458,779 B2
• Filed: 08/03/2018
• Issued: 10/29/2019
• Est. Priority Date: 03/01/2018
• Status: Active Grant

• Current Assignee: Mitutoyo Corporation
• Original Assignee: Mitutoyo Corporation
• Inventors: Haitjema, Han, Ketelaars, Hendrik
• Primary Examiner(s): Akanbi, Isiaka O
• Application Number:
  US16/054,340
• Publication Number:
  US 20190271535A1
• Time in Patent Office: 452 Days
• Field of Search: 356601-624, 356632, 356660, 356517
• CPC Class Codes: G01B 11/12 internal diameters
• CPC Class Codes: G01B 11/255 for measuring radius of curvature measuring diameter G01B11/08
• CPC Class Codes: G01J 1/4257 applied to monitoring the characteristics of a beam, e.g. laser beam, headlamp beam monitoring arrangements for lasers in general H01S3/0014
• CPC Class Codes: G01N 21/41 Refractivity; Phase-affecting properties, e.g. optical path length G01N21/21 takes precedence

Abstract

In a method and apparatus for measuring a property of a transparent tubular object, a laser beam scans the object, and laser light originating from the object is detected in a first detection direction parallel to the laser beam direction, or in the first and in a second detection direction at an angle thereto, in particular at 90°. The inner radius of the object may be calculated from the refractive index, scanning speed, outer diameter detected in the first detection direction, and, in the second detection direction, the time difference between laser light reflected from the outer surface of the object and laser light refracted into the object and reflected at the inner surface thereof. If the time of detecting laser light refracted into the object and reflected at the inner surface thereof in the first detection direction is known, the refractive index is not required.

Claims

1. An apparatus for measuring a property of a transparent tubular object having a refractive index, n, and a longitudinal axis, the apparatus comprising:

a laser beam scanner that scans a laser beam in a scanning direction with a constant scanning speed, v_s, along a scanning path at right angles to the longitudinal axis of the object, wherein the scanning laser beam is directed in a first laser beam direction to the object at right angles to the scanning direction and at right angles to the longitudinal axis of the object;

a detector assembly that detects an intensity of laser light originating from the object in a first detection direction parallel to the first laser beam direction, and that detects an intensity of laser light originating from the object in a second detection direction at a detection angle, a, greater than zero to the first detection direction;

a processor; and

one or more memories which store an executable set of instructions, which when executed by the processor, cause the processor to execute operations including;

determining a first time, τ

(0), and a second time, τ

(2R_D), from the intensity of the laser light detected in the first detection direction by the detector assembly, τ

(0) being representative of the laser beam being tangential to the outer surface of the object at a first point of the object, and τ

(2R_D) being representative of the laser beam being tangential to the outer surface of the object at a second point of the object diametrically opposite the first point;

determining a third time, τ

(x_D2), and a fourth time, τ

(x_d2), from the intensity of the laser light detected in the second detection direction by the detector assembly, τ

(x_D2) being representative of the laser beam being reflected at the outer surface of the object at a third point of the object, and τ

(x_d2) being representative of the laser beam being refracted at the outer surface of the object and reflected at the inner surface of the object at a fourth point of the object; and

calculating an inner radius, R_d, of the object based on n, v_s, a, τ

(0), τ

(2R_D), τ

(x_D2), and τ

(x_d2), wherein calculating R_d comprises calculating a difference between τ

(2R_D) and τ

(0), and a difference between τ

(x_d2) and τ

(x_D2).

2. The apparatus according to claim 1, wherein the processor calculates R_d based on the equation:

3. The apparatus according to claim 1 wherein a is between 45°

and 135°

.

4. The apparatus according to claim 1, wherein the detector assembly comprises:

a first detector that detects the intensity of laser light originating from the object in the first detection direction; and

a second detector, different from the first detector, and that detects the intensity of laser light originating from the object in the second detection direction.

5. The apparatus according to claim 4, wherein the detector assembly further comprises a reflector arranged between the object and the second detector, the reflector configured to reflect laser light originating from the object in the second detection direction towards the second detector.

6. The apparatus according to claim 5, wherein the reflector is further configured to reflect laser light originating from the object in the second detection direction to be in the first detection direction, the apparatus further comprising:

a laser beam polarizer arranged between the laser beam scanner and the object, the polarizer configured to polarize the laser beam;

a half-lambda plate, arranged between the object and the reflector, the half-lambda plate configured to rotate the polarization direction of the laser light originating from the object; and

a polarizing beam splitter arranged and configured to split the laser light from the object and the reflector in the first detection direction, to the first detector and the second detector based on the polarization state of the laser light.

7. The apparatus according to claim 5, wherein the reflector comprises one of a pentagon prism or a mirror.

8. The apparatus according to claim 1, wherein the detector assembly comprises:

a reflector that reflects laser light originating from the object in the second detection direction to be in the first detection direction; and

a first detector that detects the intensity of laser light originating from the object in the first detection direction, and that detects the intensity of laser light originating from the object in the second detection direction and being reflected by the reflector to be in the first detection direction.

9. The apparatus according to claim 1, further comprising at least one of:

a first polarizer having a 45°

polarizing direction, and being arranged in the path of the scanning laser beam;

a second polarizer having a (−

45+δ

)°

polarizing direction, and being arranged in the path of the laser light originating from the object in the first detection direction, wherein |δ

|>

0;

or

a third polarizer having a (45+ε

)°

polarizing direction, and being arranged in the path of the laser light originating from the object in the second detection direction, wherein |ε

|>

0.

10. An apparatus for measuring a property of a transparent tubular object having a refractive index, n, and a longitudinal axis, the apparatus comprising:

a laser beam scanner that scans a laser beam in a scanning direction with a constant scanning speed, v_s, along a scanning path at right angles to the longitudinal axis of the object, wherein the scanning laser beam is directed at right angles to the longitudinal axis of the object, wherein the scanning laser beam is directed in a first laser beam direction to the object at right angles to the scanning direction in a first part of the scanning path, and redirected via a reflector in a second laser beam direction to the object at a scanning angle, β

, greater than zero to the first laser beam direction in a second part of the scanning path;

a detector assembly that detects an intensity of laser light originating from the object in a first detection direction parallel to the first laser beam direction, and that detects an intensity of laser light originating from the object in a second detection direction at a detection angle, a, to the first detection direction;

a processor; and

one or more memories which store an executable set of instructions, which when executed by the processor, cause the processor to execute operations including;

determining a first time, τ

(0), and a second time, τ

(2R_D), from the intensity of the laser light detected in the first detection direction, τ

(0) being representative of the laser beam being tangential to the outer surface of the object at a first point of the object, and τ

(2R_D) being representative of the laser beam being tangential to the outer surface of the object at a second point of the object diametrically opposite the first point;

determining a third time, τ

(x_D2), and a fourth time, τ

(x_d2), from the intensity of the laser light detected in the second detection direction, τ

(x_D2) being representative of the laser beam being reflected at the outer surface of the object at a third point of the object, and τ

(x_d2) being representative of the laser beam being refracted at the outer surface of the object and reflected at the inner surface of the object at a fourth point of the object; and

calculating an inner radius, R_d, of the object based on n, v_s, a, β

, τ

(0), τ

(2R_D), τ

(x_D2) and τ

(x_d2), wherein calculating R_d comprises calculating a difference between τ

(2R_D) and τ

(0), and a difference between τ

(x_d2) and τ

(x_D2).

11. The apparatus according to claim 10, wherein the processor calculates R_d based on the equation:

12. The apparatus according to claim 10 wherein α

+β

is between 45° and

135°

.

13. An apparatus for measuring a property of a transparent tubular object having a longitudinal axis, the apparatus comprising:

a laser beam scanner that scans a laser beam in a scanning direction with a constant scanning speed, v_s, along a scanning path at right angles to the longitudinal axis of the object, wherein the scanning laser beam is directed in a first laser beam direction to the object at right angles to the scanning direction and at right angles to the longitudinal axis of the object;

a detector assembly that detects an intensity of laser light originating from the object in a first detection direction parallel to the first laser beam direction, and that detects an intensity of laser light originating from the object in a second detection direction at a detection angle, a, greater than zero to the first detection direction;

a processor; and

one or more memories which store an executable set of instructions, which when executed by the processor, cause the processor to execute operations including;

determining a first time, τ

(0), and a second time, τ

(2R_D), from the intensity of the laser light detected in the first detection direction, τ

(0) being representative of the laser beam being tangential to the outer surface of the object at a first point of the object, and τ

(2R_D) being representative of the laser beam being tangential to the outer surface of the object at a second point of the object diametrically opposite the first point;

determining a third time, τ

(x_D2), and a fourth time, τ

(x_d2), from the intensity of the laser light detected in the second detection direction, τ

(x_D2) being representative of the laser beam being reflected at the outer surface of the object at a third point of the object, and τ

(x_d2) being representative of the laser beam being refracted at the outer surface of the object and reflected at the inner surface of the object at a fourth point of the object;

determining a fifth time, τ

(x_d1), from the intensity of the laser light detected in the first detection direction, τ

(x_d1) being representative of the laser beam being refracted at the outer surface of the object and reflected at the inner surface of the object at a fifth point of the object; and

calculating an inner radius, R_d, of the object based on v_s, α

, τ

(0), τ

(2R_D), τ

(x_D2), τ

(x_d2) and τ

(x_d1), wherein calculating R_d comprises calculating a difference between τ

(2R_D) and τ

(0), and a difference between τ

(x_d2) and τ

(x_D2).

14. The apparatus according to claim 13, wherein the processor calculates R_d based on the equation:

15. An apparatus for measuring a property of a transparent tubular object having a longitudinal axis, the apparatus comprising:

a laser beam scanner that scans a laser beam in a scanning direction with a constant scanning speed, v_s, along a scanning path at right angles to the longitudinal axis of the object, wherein the laser beam is directed at right angles to the longitudinal axis of the object, wherein the scanning laser beam is directed in a first laser beam direction to the object at right angles to the scanning direction in a first part of the scanning path, and redirected via a reflector in a second laser beam direction to the object at a scanning angle, β

, greater than zero to the first laser beam direction in a second part of the scanning path;

a detector assembly that detects an intensity of laser light originating from the object in a first detection direction parallel to the laser beam direction, and that detects an intensity of laser light originating from the object in a second detection direction at a detection angle, a, to the first detection direction;

a processor; and

one or more memories which store an executable set of instructions, which when executed by the processor, cause the processor to execute operations including;

determining a first time, τ

(0), and a second time, τ

(2R_D), from the intensity of the laser light detected in the first detection direction, τ

(0) being representative of the laser beam being tangential to the outer surface of the object at a first point of the object, and τ

(2R_D) being representative of the laser beam being tangential to the outer surface of the object at a second point of the object diametrically opposite the first point;

determining a third time, τ

(x_D2), and a fourth time, τ

(x_d2), from the intensity of the laser light detected in the second detection direction, τ

(x_D2) being representative of the laser beam being reflected at the outer surface of the object at a third point of the object, and τ

(x_d2) being representative of the laser beam being refracted at the outer surface of the object and reflected at the inner surface of the object at a fourth point of the object;

determining a fifth time, τ

(x_d1), from the intensity of the laser light detected in the first detection direction, τ

(x_d1) being representative of the laser beam being refracted at the outer surface of the object and reflected at the inner surface of the object at a fifth point of the object; and

calculating an inner radius, R_d, of the object based on v_s, α

, β

, τ

(0), τ

(2R_D), τ

(x_D2), τ

(x_d2) and τ

(x_d1), wherein calculating R_d comprises calculating a difference between τ

(2R_D) and τ

(0), and a difference between τ

(x_d2) and τ

(x_D2).

16. The apparatus according to claim 15, wherein the processor calculates R_d based on the equation: