JP2625832B2 - Spectrophotometer wavelength drive mechanism - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a wavelength driving mechanism for rotating a diffraction grating in a spectrophotometer.

(Prior Art) As a wavelength driving mechanism, a sine bar method is used in most spectrophotometers.

 FIG. 5 shows a sine-bar type wavelength driving mechanism.

Reference numeral 1 denotes a diffraction grating which is rotated by a sine bar 2. The tip ball 3 of the sine bar 2 comes into contact with a slider 4, and the slider 4 is moved by a screw 5 rotated by a drive motor. For example, when the slider 4 at the position 4a indicated by the chain line moves by the distance x by the rotation of the screw 5 and moves to the position of the solid line 4, the sine bar 2 also rotates by θ from the position 2a, and the diffraction grating 1 also moves Rotate θ from 1a.

As another example of the wavelength driving mechanism, there is a system having a reduction mechanism using a gear and a pulley as shown in FIG.

The rotation of the pulley 6 rotated by the drive motor is transmitted to the pulley 8 via the belt 7, and the gear 8a rotating integrally with the pulley 8 meshes with the gear 9, whereby the diffraction grating 1 is reduced and rotated.

(Problems to be Solved by the Invention) In the sine bar method, adjustment for emitting the zero-order light when the surface of the slider 4 is parallel to the bar 2 and adjustment of the length L of the bar 2 are troublesome, and time is required. It takes.

The flatness of the surface of the slider 4 is required, and the wavelength accuracy deteriorates due to wear due to long-term use.

 High-speed wavelength scanning is difficult due to high frictional resistance.

In a wavelength driving mechanism using a gear and a pulley, the eccentricity of the gear and the pulley and the processing accuracy of the teeth directly affect the wavelength accuracy, so that it is difficult to drive the wavelength with high wavelength accuracy.

In the wavelength driving mechanism of the spectrophotometer, the rotation of the driving motor must be accurately transmitted to the rotation of the diffraction grating at a reduced speed.

 FIG. 7 shows the principle of the spectroscope.

The opening angle between the input optical axis 10 and the output optical axis 11 is 2K, the bisector of the opening angle is l, the normal to the grating surface of the diffraction grating 1 is P, and l and P
Let δ be the angle formed by the following equation (1).

λ = (2d / m) cosKsinδ (1) where m is the order of the diffracted light, and d is the lattice spacing.

As a general example, m = 1, d = 1/1600 (mm), K =
Considering the case of 10 °, in order to send the wavelength every 0.1 mm, δ must be sent every about 0.005 ° or less. When a stepping motor is used as the drive motor, if the feed angle per pulse of the stepping motor is, for example, 0.36 °, a transmission mechanism having a reduction ratio of 1/72 or less is required.

An object of the present invention is to solve the problems of the sine bar method and the method using a gear and a pulley, and to provide a wavelength driving mechanism with good wavelength accuracy and capable of high-speed scanning.

(Means for Solving the Problems) FIG. 1 schematically shows the present invention.

1 is a diffraction grating, 12 is a drive motor, and the drive motor 12
A harmonic drive mechanism is provided as a deceleration mechanism between the first and second diffraction gratings. Reference numeral 14 denotes a drive circuit of the drive motor 12. Reference numeral 15 denotes storage means for storing a parameter for correcting a periodic error of the harmonic drive mechanism 13, and reference numeral 16 denotes wavelength calculation means for calculating a spectral wavelength in which the error of the harmonic drive mechanism 13 has been corrected using the parameter.

(Operation) The harmonic drive mechanism is a type of a speed reduction mechanism.
FIG. 2 shows the result of measuring the accuracy of an example harmonic drive mechanism. A stepping motor, which is a drive motor, has a feed angle per pulse of 0.36 ° and a harmonic drive mechanism with a reduction ratio of 1/100, and rotates every 300 pulses. The rotation angle at 300 pulses is 0.0036 mm x 300 = 1.08 mm. As a result of measuring the shift amount of the output rotation angle, the maximum value ± Xmax was about 60 seconds (= 0.017 °). This corresponds to ± 0.34 nm from the equation (1) when converted into a wavelength.
Intermediate class or higher spectrophotometers require a wavelength accuracy of ± 0.3 nm and cannot be used as is.

It can be seen from the principle of the harmonic drive mechanism and the measurement results of FIG. 2 that errors occur periodically. Therefore,
The present invention obtains an accurate wavelength output by correcting an error from an error shape of one cycle. The parameter storage means 15 stores a parameter indicating an error shape as shown in FIG. 2, and the wavelength calculation means 16 corrects the error based on the parameter.

(Embodiment) FIG. 3 shows a cross-sectional view of an example of the harmonic drive mechanism 13.

Harmonic drive mechanism 13 is a wave generator
20, flex spline 21 and circular spline 22
The three basic elements are provided.

The wave generator 20 includes an elliptical cam 20a and a bearing ball 20b fitted around the cam 20a. The inner ring of the bearing is fixed to the cam 20a,
The outer ring is elastically deformed via the ball 20b.

The flex spline 21 is a thin, cup-shaped metal elastic body having teeth cut on the outer periphery of the opening.

Circular spline 22 is rigid and ring-shaped, with teeth of the same pitch as flexspline 21 engraved on the inner circumference, and the number of teeth is two more than the number of teeth of flexspline 21. I have.

The flexspline 21 is bent into an elliptical shape by the wave generator 20, and the circular
The spline 22 meshes with the teeth, and the teeth are completely separated from each other at the short axis. For example, when the circular spline 22 is fixed and the wave generator 20 is turned, the flex spline 21 is elastically deformed, and the circular spline 21 is deformed.
The position of engagement with 22 moves sequentially. When the wave generator 20 makes one revolution, the flex spline 21 has two fewer teeth than the circular spline 22.
Accordingly, the wave generator 20 moves in the direction opposite to the rotation direction. In this case, the movement of the flex spline 21 is extracted as an output.

Further, if the flex spline 21 is fixed, the movement of the circular spline 22 can be extracted as an output.

Assuming that the number of teeth of the flex spline 21 is Zf and the number of teeth of the circular spline 22 is Zc (= Xf + 2), the reduction ratio when the circular spline 22 is fixed is (Zf−Zc) / Zf = −2 / Zf And the reduction ratio when the flexspline 21 is fixed is (Zc−Zf) / Zc = 2 / Zc.

In FIG. 4, a 5-phase stepping motor having a feed angle per pulse of 0.36 ° is used as the drive motor 12,
An example of measurement of an error shape when the wave generator 20 of the harmonic drive mechanism 13 makes one rotation (1000 pulses = 3.6 °) by rotating every 20 pulses (0.072 ° in output) is shown.

From this error shape, δ when N pulses are sent from δ = 0 in equation (1) can be approximated by the following equation (2).

δ = 3.6 × a + (0.0036 + θi × k) × (b−100 × n)
...... (2) (when A or A + 1000 is _{320~519) θ 1 = 0.88 × 10} -4 ( when A or A + 1000 is _{0~319) θ 2 = -1.14 × 10} -4 θ 3 = 0.80 × 10 ^-4 (when A or A + 1000 is 520 to 799) θ ₄ = −1.36 × 10 ^-4 (when A or A + 1000 is 800 to 999) where A = (b−100 × n) and a, b is a, b when N ÷ 1000 = a too much b. θi (i = 1 to 4) and its application range are constants determined from FIG. 4, and k and n are parameters that vary depending on the device. n can take ten values from 0 to 9. k can take three values, 0.8, 1, and 1.2.

 The determination of k and n is performed as follows.

Using a light source (e.g., a mercury lamp) having many known emission line spectra, the wavelength of the emission line is measured while sequentially changing k and n, and the combination of k and n with the smallest wavelength shift is determined. The determination of k and n is automatically searched by a program, and the types of k and n are stored in, for example, an EEPROM (Electrically Erasable Read-Only Memory) as the parameter storage means 15 so that the wavelength accuracy can be determined without using a remote controller. Adjustment can be performed.

The important point here is that the cycle of the error curve shown in FIG. 4 will be determined if the equipment to be used is determined. Therefore, the correction function can be applied by a relatively simple method only by appropriately selecting k as the error amplitude and n as the phase as the parameters of each device.

(Effect of the Invention) In the present invention, a harmonic drive mechanism is used as a speed reduction mechanism for transmitting the rotation of the drive motor to the diffraction grating.
High-speed wavelength scanning is possible, accuracy is not deteriorated even when used for a long time, and a large space is not required.

Since the error of the harmonic drive mechanism is corrected using the stored parameters, automatic adjustment is possible, and high wavelength accuracy can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing the present invention, FIG. 2 is a diagram showing a measurement result of an error of the harmonic drive mechanism, FIG. 3 is a cross-sectional view showing the harmonic drive mechanism, and FIG. 4 is one cycle of the harmonic drive mechanism. FIG. 5 is a configuration diagram showing a conventional wavelength drive mechanism of a sine bar method,
FIG. 6 is a schematic configuration diagram showing a conventional wavelength drive mechanism using gears and pulleys, and FIG. 7 is a diagram showing the principle of a spectroscope. 1 ... Diffraction grating, 12 ... Drive motor, 13 ... Harmonic drive mechanism, 14 ... Drive circuit, 15 ... Parameter storage means, 16 ... Wavelength calculation means.

Claims (1)

(57) [Claims] A harmonic drive mechanism is provided between a drive motor and a diffraction grating as a speed reduction mechanism, and storage means for storing a parameter for correcting a periodic error of the harmonic drive mechanism, and an error of the harmonic drive mechanism using the parameter. A wavelength driving mechanism for a spectrophotometer, comprising: a wavelength calculating means for calculating a spectral wavelength in which the wavelength is corrected.