CN101881606B - Laser straightness interferometer light path system - Google Patents

Abstract

The invention relates to a laser straightness interferometer light path system which solves the problem of low measuring sensitivity of the traditional straightness interferometer. The laser straightness interferometer light path system comprises a laser head (1), an assembly (A), a double optical wedge (11) and a biplane reflecting mirror (12). The assembly (A) is formed by binding a polarizing beam splitter (6), a reflecting mirror (7), a pyramid prism (8) and quarter wave plates (9) and (10) into an integer. The double optical wedge (11) is formed by binding an upper wedge and a lower wedge, and the bottom surface of the upper wedge is opposite to that of the lower wedge. f1 light and f2 light emitted by the laser head (1) respectively pass through the upper wedge and the lower wedge of the double optical wedge (11) after beam splitting by the assembly (A), vertically irradiate the two reflecting planes of the biplane reflecting mirror (12), and go back the same way. A measured object and the double optical wedge (11) move along the Y direction; when a displacement is generated in the Z direction, i.e. a straightness error exits, the f1 light and the f2 light produce opposite optical path differences, and thus, the straightness error value can be calculated out. The invention has high measuring sensitivity, compact structure, low cost and convenient assembly.

Description

Laser straightness interferometer light path system

Technical field:

The present invention is a kind of laser straightness interferometer light path system, and is relevant with the straight line degree measurement of precision equipment guideway.

Background technology:

Laser straightness interferometer adopts the method for differential interference to measure straightness error, because precision height, range are big, the guideway linearity that is widely used in the precision equipments such as lathe, coordinate measuring machine detects.

Laser straightness interferometer light path system is made up of laser head and straightness interferometer, Fig. 1 is the straight line degree measurement annex of Agilent company, orthogonal linearly polarized light f1 in the polarization direction that laser head 1 sends and f2 divide according to certain angle at wllaston prism 3, directive double mirror 4.Laser head 1 and double mirror 4 are fixing, because the light path conjugation before the wllaston prism 3, wllaston prism 3 moves not influence of optical path difference along the Y direction, then produce the rightabout frequency drift Δ f1 and the Δ f2 of f1 light and f2 light along moving of Z direction, through dioptric apparatus 2 return laser light heads, calculate along the linearity of Z direction.

Dioptric apparatus 2 is made up of a beam divider (being coated with semi-transparent semi-reflecting film) and a completely reflecting mirror, because light can lose 50% energy during by beam divider, and need twice process beam divider 2 to return by laser head 1 shoot laser, if do not consider other energy losses, the back light that carries metrical information is 25% of an emergent light energy, because the gain of two-frequency laser interferometer system is very big, such loss can be disregarded, but in the single frequency laser interferometer system, this shortcoming is fatal.

Summary of the invention:

The purpose of this invention is to provide a kind of simple in structurely, be convenient to install and adjust, cost is low, measures highly sensitive laser straightness interferometer light path system.

The present invention is achieved in that

Laser straightness interferometer light path system of the present invention, by laser head 1, assembly A, two wedges 11 and biplane catoptron 12 are formed, assembly A is by polarization spectroscope 6, catoptron 7, prism of corner cube 8, quarter- wave plate 9,10 bonding being integral, wherein polarization spectroscope 6 is made up of along the inclined-plane bonding two right-angle prisms, on the inclined-plane of right-angle prism, be coated with polarization beam splitter, catoptron 7 is right-angle prisms that are coated with the depolarization reflectance coating on the inclined-plane, the inclined-plane of catoptron 7 is parallel with the inclined-plane of the right-angle prism of polarization spectroscope, quarter-wave plate 9, the 10 right angle faces along two right-angle prisms are bonded to a plane, three pyramidal planes of prism of corner cube 8 are coated with total reflection film, the right angle face of the right-angle prism of its bottom surface and polarization spectroscope 6 is bonding, the f2 polarisation of light direction that the optical axis of quarter-wave plate 9 and laser head send is that the angle of S polarization is 45 °, the f1 polarisation of light direction that the optical axis of quarter-wave plate 10 and laser head send is that the angle of P polarization is 45 °, the top wedge that two wedges 11 are faced mutually by two right angle faces and the bottom wedge is bonding forms, top wedge and bottom wedge are right-angle triangle, two is connected to the quarter-wave plate of the right angle face facing assembly A on a plane, laser head 1 during measurement, assembly A and biplane catoptron 12 stationkeeping, two wedges 11 place between assembly A and the biplane catoptron 12, and be fixed on the measured body, the f1 light P polarized light that laser head 1 sends separates according to the polarization direction on the polarization spectroscope 6 of assembly A with f2 big gun S polarization, the bottom wedge of the two wedges 11 of f1 light transmission polarization spectroscope 6 and quarter-wave plate 10 directives, f2 light passes through the top wedge of the two wedges 11 of quarter-wave plate 9 directives in polarization spectroscope 6 and catoptron 7 reflection backs, the f1 of two wedge 11 outgoing, f2 light intersects, and be vertically projected to biplane catoptron 12, when measured body moves together with two wedge 11 along continuous straight runs (Y direction), when measured body produces displacement (being straightness error) at vertical direction (Z direction), f1, the position that f2 light incides two wedges 11 changes and produces optical path difference, this optical path difference retroeflection is to laser head 1, by obtaining straightness error after the processing of circuit of laser straightness interferometer and the Computing.

When there was straightness error in measured body, the two wedges 11 vertically straightness error Δ of (Z direction) were obtained by following formula:

$\mathrm{\Δ}=\frac{\mathrm{\δ}}{8\tan \mathrm{\α}(n-\cos (\arcsin (n\·\sin \mathrm{\α})-\mathrm{\α}))}$

δ is the optical path difference of light single by two wedges (11), and α is the wedge angle of wedge, and n is the refractive index of wedge.

The present invention is simple in structure, and all elements of assembly A are bonded as one, and is convenient to install adjust; Two wedges reduce the length of biplane catoptron, reduce cost; Because f1, f2 light are producing a translational movement by prism of corner cube 8 reflection backs, back light all enters laser head, increases the measurement sensitivity of instrument.

Description of drawings:

Fig. 1 is the light path system composition diagram of existing laser interferometer.

Fig. 2 is a light path system composition diagram of the present invention.

Fig. 3 is computing method figure of the present invention.

Embodiment:

This patent is a kind of laser straightness interferometer light path system, as shown in Figure 2, reflects 12 mirrors by laser head 1, assembly A, two wedge 11 and biplane and forms.

Assembly A concerns bonding forming by polarization spectroscope 6, catoptron 7, prism of corner cube 8, quarter- wave plate 9 and 10 by position shown in Figure 2.Catoptron 7 is coated with the depolarization reflectance coating, does not influence the polarization of reflected light direction.The optical axis of quarter-wave plate 9 and f2 polarisation of light direction are 45 degree, and the optical axis of quarter-wave plate 10 and f1 polarisation of light direction are 45 degree.

Two wedges 11 are by the relative top wedge in two bottom surfaces and the bottom wedge is bonding forms, the f1 of laser head 1 outgoing and f2 light are after the polarization spectroscope 6 of assembly A separates, project two wedges 11 respectively, because it is relative to constitute the bottom surface of 11 two wedges of wedge, outgoing f1 and f2 light intersect, under certain measuring straightness error range, the length of biplane catoptron 12 is reduced.

The present invention can be used for dual-frequency laser interferometer system and single-frequency laser interference system.

In dual-frequency laser interferometer system, orthogonal linearly polarized light f1 in the polarization direction that laser head 1 sends and f2 directive straightness interferometer assembly A, f1 is a p direction polarized light, see through polarization spectroscope 6 and quarter-wave plate 10, become circularly polarized light and in 11 refractions of two wedges, directive biplane catoptron 12 at a certain angle, because biplane catoptron 12 is vertical with deflecting light beams, the reflection back is returned along former road, by quarter-wave plate 10, make f1 polarisation of light direction become s once more, reflex to prism of corner cube 8 through polarization spectroscope 6, in prism of corner cube 8, produce a translational movement and return, after polarization spectroscope 6 reflection, repeat above-mentioned light path track again, but the translational movement that has a prism of corner cube 8 to cause in the Z direction, back light reverts to the p polarization by quarter-wave plate 10, sees through polarization spectroscope 6 and turns back to laser head 1.

The f2 that is sent by laser head 1 is a s direction polarized light, through polarization spectroscope 6 and catoptron 7 reflections, by quarter-wave plate 9, become circularly polarized light and in 11 refractions of two wedges, directive biplane catoptron 12 at a certain angle, because biplane catoptron 12 is vertical with deflecting light beams, the reflection back is returned along former road, once more by quarter-wave plate 9, make f1 polarisation of light direction become p, see through polarization spectroscope 6 through catoptron 7 reflection back, in prism of corner cube 8, produce a translational movement and return, pass through polarization spectroscope 6 once more after, repeat above-mentioned light path track, but at the translational movement that the Z direction has a prism of corner cube 8 to cause, back light reverts to the s polarization by quarter-wave plate 9, turns back to laser head 1 through polarization spectroscope 6 reflections.

The path of the f1 light that is sent by laser head 1 is polarization spectroscope 6, quarter-wave plate 10, two wedge 11, biplane catoptron 12, two wedge 11, quarter-wave plate 10, polarization spectroscope 6, prism of corner cube 8, polarization spectroscope 6, quarter-wave plate 10, two wedge 11, biplane catoptron 12, two wedge 11, quarter-wave plate 10, polarization spectroscope 6, laser head 1; The path of the f2 light that is sent by laser head 1 is polarization spectroscope 6, catoptron 7, quarter-wave plate 9, two wedge 11, biplane catoptron 12, two wedge 11, quarter-wave plate 9, catoptron 7, polarization spectroscope 6, prism of corner cube 8, polarization spectroscope 6, catoptron 7, quarter-wave plate 9, two wedge 11, biplane catoptron 12, two wedge 11, quarter-wave plate 9, catoptron 7, polarization spectroscope 6 return laser light heads 1.

In said process, f1 light comes and goes the bottom wedge by two wedges 11 twice, it is four times that single passes through optical path difference that the bottom wedge produces, f2 light comes and goes the top wedge by two wedges 11 twice, it also is four times that single passes through optical path difference that the top wedge produces, again because the change in optical path length that f1 light and f2 light produce is reverse, so the total optical path difference is single produces optical path difference by wedge a octuple, amplify optical path difference, improved measurement sensitivity.

In single frequency laser interferometer, the linearly polarized light that laser head 1 sends incides polarization spectroscope 6 with the 45 degree, its minute optical mode split into the f1 light of p polarization direction and the f2 light of s polarization direction, optical path afterwards is ditto described.

During measurement, laser head 1, assembly A and biplane catoptron 12 are fixing, two wedges 11 place on the measured body, because f1 light and the light path conjugation of f2 light before two wedges 11, two wedges 11 move not influence of measurement result along the Y direction, and at measured body when promptly there is straightness error in moving of Z direction, the position of inciding two wedges 11 owing to f1 and f2 light changes and produces optical path difference, this optical path difference is being carried the linearity information return laser light head 1 of measured body in the Z direction, obtains the straightness error value after processing of circuit and Computing.

Fig. 3 is the top wedge of two wedges 11, and when there was straightness error in measured body, wedge moved Δ along the Z direction, the optical path difference δ that produces is the poor of wedge glass interior change in optical path length δ 1 and airborne change in optical path length δ 2, if the refractive index of two wedges is n, the wedge angle of wedge is α, then:

δ＝n·δ1-δ2

＝8Δtanα(n-cos(arcsin(n·sinα)-α)) (1)

$\mathrm{\Δ}=\frac{\mathrm{\δ}}{8\tan \mathrm{\α}(n-\cos (\arcsin (n\·\sin \mathrm{\α})-\mathrm{\α}))}---\left(2\right)$

If S is the ratio of optical path difference δ and straightness error Δ:

$S=\frac{\mathrm{\δ}}{\mathrm{\Δ}}=8\tan \mathrm{\α}(n-\cos (\arcsin (n\·\sin \mathrm{\α})-\mathrm{\α}))---\left(3\right)$

The product of the displayed value of length interferometer and S value is actual straightness error value.

Select different optical glass to obtain different S values with the wedge angle of wedge:

Example 1: two wedge materials: K9 glass

Refractive index: n=1.51630

The wedge angle of wedge: α=2.64 °

Calculate according to formula 2: S=0.191

Example 2: two wedge materials: ZF7 glass

Refractive index: n=1.80600

The wedge angle of wedge: α=4 °

Calculate according to formula 2: S=0.504.

Claims (2)

1. laser straightness interferometer light path system, it is characterized in that by laser head (1), assembly (A), two wedges (11) and biplane catoptron (12) are formed, assembly (A) is by polarization spectroscope (6), catoptron (7), prism of corner cube (8), first, two quarter-wave plates (9), (10) bonding being integral, wherein polarization spectroscope (6) is made up of along the inclined-plane bonding two right-angle prisms, on the inclined-plane of right-angle prism, be coated with polarization beam splitter, catoptron (7) be one be coated with on the inclined-plane depolarization reflectance coating right-angle prism, the inclined-plane of catoptron (7) is parallel with the inclined-plane of the right-angle prism of polarization spectroscope, first, two quarter-wave plates (9), (10) the right angle face along two right-angle prisms is bonded to a plane, three pyramidal planes of prism of corner cube (8) are coated with total reflection film, the right angle face of the right-angle prism of its bottom surface and polarization spectroscope (6) is bonding, the f2 polarisation of light direction that the optical axis of first quarter-wave plate (9) and laser head send is that the angle of S polarization is 45 °, the f1 polarisation of light direction that the optical axis of second quarter-wave plate (10) and laser head send is that the angle of P polarization is 45 °, two wedges (11) are by the relative top wedge of two right angle faces and the bottom wedge is bonding forms, top wedge and bottom wedge are right-angle triangle, two is connected to the quarter-wave plate of the right angle face facing assembly (A) on a plane, laser head during measurement (1), assembly (A) and biplane catoptron (12) stationkeeping, two wedges (11) place between assembly (A) and the biplane catoptron (12), and be fixed on the measured body, the f1 light that laser head (1) sends is that the P polarized light is that the S polarized light upward separates according to the polarization direction at the polarization spectroscope (6) of assembly (A) with f2 light, the bottom wedge of the two wedges (11) of f1 light transmission polarization spectroscope (6) and second quarter-wave plate (10) directive, f2 light passes through the top wedge of the two wedges (11) of first quarter-wave plate (9) directive in polarization spectroscope (6) and catoptron (7) reflection back, the f1 of two wedges (11) outgoing, f2 light intersects, and be vertically projected to biplane catoptron (12), when measured body together with two wedges (11) when horizontal Y direction is moved, measured body is when vertically the Z direction produces displacement, f1, the position that f2 light incides two wedges (11) changes and produces optical path difference, this optical path difference retroeflection is to laser head (1), by obtaining straightness error after the processing of circuit of laser straightness interferometer and the Computing.

2. the light path system of laser straightness interferometer according to claim 1 is characterized in that the path of the f1 light that sent by laser head (1) is followed successively by polarization spectroscope (6), second quarter-wave plate (10), two wedges (11), biplane catoptron (12), two wedges (11), second quarter-wave plate (10), polarization spectroscope (6), prism of corner cube (8), polarization spectroscope (6), second quarter-wave plate (10), two wedges (11), biplane catoptron (12), two wedges (11), second quarter-wave plate (10), polarization spectroscope (6), laser head (1); The path of the f2 light that is sent by laser head (1) is followed successively by polarization spectroscope (6), catoptron (7), first quarter-wave plate (9), two wedges (11), biplane catoptron (12), two wedges (11), first quarter-wave plate (9), catoptron (7), polarization spectroscope (6), prism of corner cube (8), polarization spectroscope (6), catoptron (7), first quarter-wave plate (9), two wedges (11), biplane catoptron (12), two wedges (11), first quarter-wave plate (9), catoptron (7), polarization spectroscope (6) return laser light head (1).

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