CN102928078A - Spectrophotometer scanning mechanism - Google Patents

Abstract

The invention provides a spectrophotometer scanning mechanism. The invention discloses a device in which the cam rotary angle and the wavelength output are in linear proportion. The device comprises a cam, a push rod, a concave face diffraction grating (the concave face diffraction grating is a reflecting grating), an entrance slit and an exit slit. The entrance slit and the exit slit are fixed; a parallel light beam is emitted into the concave face diffraction grating from the entrance slit, and reflected light is emitted out from the exit slit and is received by a receiving device; one end of the push rod is fixedly and rigidly connected with the center of a grating platform, and the other end of the push rod is contacted with the cam in a tangent manner; the cam uniformly rotates, and the grating is pushed to rotate by the push rod so as to change the generation of exit light; and the output wavelength is in linear change according to the rotary angle displacement and the position displacement of the cam.

Description

A kind of spectrophotometer scanning mechanism

Technical field

The invention belongs to raster scanning light splitting technology field, especially be fit to be applied to the spectrophotometer measurement system and use.

Background technology

Spectrophotometer can directly record the relation between wave number or wavelength and transmitance or the absorption.By rotating dispersion element-grating, make spectrum after the dispersion by certain wave number or wavelength interval, in order by with respect to the radiation of monochromator exit slit.

The rotation of dispersion element and wave number or wavelength are the spectral scan of unit, and be normally nonlinear.For the wave number that obtains even linearity or the record of wavelength, generally by cosecant rod mechanism or sinusoidal excellent mechanism linearization process, realize spectrum etc. wave number or equiwavelength's the scanning of the even speed spectrogram that obtains recording.But sinusoidal rod or cosecant rod exist error greatly, the inadequate shortcoming such as precision and mechanism's complexity.The present invention has designed a linear change simple, that cam easily processing is realized spectral scan wavelength and the cam anglec of rotation, and its cam radius vector is also with the rotational angle linear change.Still nobody proposes this method and designs cam at present, and the cam of this method design has greatly reduced the complexity of processing, and detects easily in process.The inventive method is applicable to any cam mechanism that is rotated by the lever drives driven machine, but because very easily wearing and tearing of some contact generally are used for the little low speed mechanism of power transmission.

Summary of the invention

The object of the invention is to solve the rotation of dispersion element and the nonlinear problem of wavelength, propose a kind of simple and easy Cam Design method that realizes linearization process, greatly reduced the processed complex degree.

Spectrophotometer scanning mechanism provided by the invention comprises, some contact cam, push rod, concave diffraction grating, entrance slit and exit slit; Putting position as shown in Figure 1, entrance slit and exit slit are fixed, push rod one end is fixed with the grating platform center that concave diffraction grating is installed and is rigidly connected, the push rod other end contacts with cam is tangent, the radius vector R of cam of the present invention and the cam anglec of rotation

Between the pass be linear relationship so that cam processed complex degree reduces greatly, relational expression is

R is the cam radius vector,

Be the cam anglec of rotation, between the 0-270 degree, rotate.

Parallel beam incides concave diffraction grating from entrance slit, and described concave diffraction grating adopts reflection grating, and reflected light penetrates and received by receiving trap from exit slit; Cam is evenly rotated, drive concave diffraction grating by push rod and rotate, thereby emergent light is changed, the radius vector of setting cam according to anglec of rotation displacement and the position displacement of cam changes, and making output wavelength is linear change.

Technical Analysis of the present invention:

1. the relation of plane diffraction grating corner and wavelength

As shown in Figure 2, can find out that the diffraction grating equation is

d(sini±sinθ)=mλ m=0,±1,±2,... （1）

When the diffraction spectrum of investigation and incident light the same side, following formula is got positive sign; When the diffraction spectrum of investigation and incident light heteropleural, following formula is got negative sign.D is grating constant, and i is incident angle, and θ is angle of diffraction, and λ is wavelength, and m is spectral order, generally gets in the spectral measurement ± 1 grade.

Spectrophotometer scanning mechanism of the present invention adopts the heteropleural receiving trap ,+1 grade of reception, so following formula (1) but abbreviation be

$\mathrm{\λ}-2d\sin \frac{i-\mathrm{\θ}}{2}\cos \frac{i+\mathrm{\θ}}{2}---\left(2\right)$

Because entrance slit and exit slit are fixed, so i+ θ fixes, i-θ is the grating rotating angle, makes i+ θ=Q, β=Q/2-θ, and then (2) formula becomes

λ＝2dsinβcos(Q/2) (3)

β is the grating rotating angle, and Q is the mechanical angle of entrance slit and exit slit.

Can find out that by (3) formula wavelength X and grating corner β are not proportional relations.

2. the relation of cam radius vector and plane grating corner

Along with the variation of the cam anglec of rotation, radius vector changes, thereby causes the grating rotating angle to change.

Can be got by Fig. 3:

cosβ=(L ²+H ²-R ²)/2LH （4）

L is the push rod fixed length, is invariant, and H is raster center and cam center distance, is constant, changes with R thereby can obtain cos β, and then obtains sin β and change with R.

That is:

sinβ=sinarccos ^-1[(L ²+H ²-R ²)/2LH] （5）

Again because λ=2dsin β cos (Q/2), thereby wavelength X is with the variation of cam radius vector R as can be known, and then definite cam face, makes cam angle and wavelength linear.

Advantage of the present invention and beneficial effect:

The cam of the present invention's design can greatly reduce the complexity of processing, and detects easily in process.The inventive method is applicable to any cam mechanism that is rotated by the lever drives driven machine, but because very easily wearing and tearing of some contact generally are used for the little low speed mechanism of power transmission.

Description of drawings

Fig. 1 is spectrophotometer scanning mechanism synoptic diagram.

Fig. 2 is plane diffraction grating corner and wavelength relationship synoptic diagram.

Fig. 3 is cam radius vector and plane grating angle relation synoptic diagram.

Fig. 4 is that wavelength X is with cam angle

Change curve.

Embodiment

Embodiment

As shown in Figure 1, a kind of spectrophotometer scanning mechanism comprises cam 1, push rod 2, concave diffraction grating (reflection grating) 3, entrance slit 4 and exit slit 5.

Fixedly entrance slit 4 and exit slit 5, parallel beam incides concave diffraction grating (reflection grating) 3 from entrance slit 4, reflected light penetrates and is received by receiving trap from exit slit 5, push rod 2 one ends and grating platform (being used for fixing the device of grating one end) center O is fixed and is rigidly connected, the other end contacts with cam is tangent, cam is evenly rotated, driving grating 3 by push rod 2 rotates, thereby emergent light is changed, according to anglec of rotation displacement and the position displacement of cam, making output wavelength is linear change.

Cam radius vector and the cam anglec of rotation relational expression of the inventive method design are

Wherein, R is the cam radius vector,

Be the cam anglec of rotation, between the 0-270 degree, rotate.

Can get,

Push rod 2 one ends and raster center are fixed and are rigidly connected, and the other end contacts with cam is tangent.Cam and grating are connected, can draw cos β=(L by Fig. 2 ²+ H ²-R ²)/2LH, push rod length L are 67mm, and raster center and cam center distance are 60mm, thereby can draw grating rotating angle beta and cam radius vector relation, β=cos ^-1(L ²+ H ²-R ²)/2LH, the substitution data can get:

Concave diffraction grating 3 adopts reflection grating, and drives rotation by described push rod.Grating equation is λ=2dsin β cos (Q/2).Entrance slit and exit slit angle Q are 0.1237mm, and grating constant is 1000/mm, and wavelength is 200nm-700nm, can draw the relation of wavelength and grating corner β, Fig. 4 is that wavelength X is with cam angle

Change curve.

Entrance slit 4 is fixing, and parallel beam incides described plane diffraction grating through entrance slit.

Exit slit 5 is also fixing, and receiving trap receives the light that exit slit penetrates at the exit slit place.

Claims (2)

1. a spectrophotometer scanning mechanism is characterized in that the point in this scanning mechanism contacts the relative position of cam, push rod, concave diffraction grating, entrance slit and exit slit; Entrance slit and exit slit are fixed, and push rod one end is fixed with the grating platform center that concave diffraction grating is installed and is rigidly connected, and the push rod other end contacts with cam is tangent, the radius vector R of its cam and the cam anglec of rotation

Between the pass be linear relationship, between the 0-270 degree, rotate, so that cam processed complex degree reduces greatly;

Parallel beam incides concave diffraction grating from entrance slit, and reflected light penetrates and received by receiving trap from exit slit; Cam is evenly rotated, drive concave diffraction grating by push rod and rotate, thereby emergent light is changed, set cam profile according to anglec of rotation displacement and the position displacement of cam, making output wavelength is linear change.

2. spectrophotometer scanning mechanism according to claim 1 is characterized in that described concave diffraction grating is reflection grating.

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