Retroreflector covered by window

• US 7,388,654 B2
• Filed: 02/17/2005
• Issued: 06/17/2008
• Est. Priority Date: 02/24/2004
• Status: Active Grant

• Current Assignee: Faro Technologies Incorporated
• Original Assignee: Faro Technologies Incorporated
• Inventors: Brown, Lawrence B., Raab, Simon, Bridges, Robert E.
• Primary Examiner(s): Toatley, Jr.; Gregory J.
• Assistant Examiner(s): Nur; Abdullahi
• Application Number:
  US11/060,244
• Publication Number:
  US 20050185182A1
• Time in Patent Office: 1,216 Days
• Field of Search: 356/625, 356/628, 356/634, 356/152.2, 356/152.3, 250/559.49
• US Class Current: 356/4.01
• CPC Class Codes: G01S 17/74 Systems using reradiation of electromagnetic waves other than radio waves, e.g. IFF, i.e. identification of friend or foe
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: G02B 27/0025 for optical correction, e.g. distorsion, aberration
• CPC Class Codes: G02B 5/122 cube corner, trihedral or triple reflector type

Abstract

Embodiments may comprise methods, apparatuses, systems, and one or more computer-readable media having computer-readable instructions thereon for adjusting a laser retroreflector to compensate for passing laser light through a window of the retroreflector comprising: determining an adjustment factor to compensate for propagation errors due to passing laser light through the window of the retroreflector; and adjusting a location of a reflection point of the retroreflector to minimize the propagation errors based on the adjustment factor.

Claims

1. A method for adjusting the depth of a cube-corner reflector apex location within a spherically mounted retroreflector (SMR) to partially compensate for radial and transverse errors caused by passing a laser light-beam through a window of the SMR comprising:

selecting a number of values of depth d to be evaluated, where depth d is defined as a distance from a center of the SMR to the cube-corner apex;

a selecting a range of angles of incidence A₁ of the laser beam on the window;

calculating, for each value d, a radial error Δ

R and a transverse error Δ

D resulting from the window as a function of the angle of incidence A₁ over the selected range of angles of incidence;

selecting a value of depth d that provides a smallest absolute value of errors for both the radial error Δ

R and the transverse error based on results of the calculation; and

adjusting the depth of the cube-corner apex within the spherically mounted retroreflector (SMR) to the selected value of d.

2. The method of claim 1 wherein the calculation of the radial error Δ

R for a particular depth d and a particular angle of incidence A₁ further comprises;

starting with a first equation Δ

R=2[nT/cos(A₂)+H/cos(A₁)−

(nT+H+L)] where T is a thickness of the window, n is an index of refraction of the window; and

H is a distance from an inside edge of the window to the cube-corner apex;

eliminating L from the first equation by substituting a second equation L=(T+H−

d)/cos(A_q)−

(T+H−

d);

eliminating the quantity A₂ from the combination of the first and second equations using third equation sin(A₂)=sin(A₁)/n to obtain a resulting equation for Δ

R in which the quantity H cancels out; and

substituting values for T, n, A₁ and d into the resulting equation to obtain a value for Δ

.

3. The method of claim 1 wherein the calculation of the transverse error Δ

D for a particular depth d and a particular angle of incidence A₂ further comprises;

starting with a first equation Δ

D=T sin(A₁−

A₂)/cos(A₂)−

d sin(A₁);

eliminating the quantity A₂ from the first equation by substituting a second equation sin(A₂)=sin(A₁)/n to obtain a resulting equation for Δ

D; and

substituting values for T, n, A₁ and d into the resulting equation to obtain a value for Δ

D;

where T is a thickness of the window, and n is an index of refraction of the window.

4. The method of claim 1 wherein the depth d is set equal to T (1−

1/n)k, where k is an adjustable parameter between 1.0 and 1.2; and

where T is a thickness of the window, and n is an index of refraction of the window.

5. The method of claim 4 wherein T=1 mm, n=1.51509, k=1.0908, and d=0.3708 mm.