JPS63167226A - Spectrophotometer - Google Patents

Abstract

PURPOSE:To increase resolution without using any speed reducing mechanism by driving and rotating a diffraction grating by an encoder direct-coupled DC servomotor, and counting output pulses of an encoder and calculating the wavelength of projection light. CONSTITUTION:The diffraction grating is mounted at the rotational center position of a rotary drum 2 and this diffraction grating 6 is driven and rotated by the motor at an equal speed to scan homogeneous light which has such a waveform that it is incident from an incident slit 7 and projected on a projection slit 8. The rotary drum 2 is provided with the rotary encoder consisting of a magnetic recording medium 3, a magnetic sensor 4, and a comparator 5 and rotational position detection pulses from this rotary encoder are utilized to calculate the wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a wavelength scanning mechanism for a spectrophotometer.

(Prior Art) In conventional spectrophotometers, a so-called sine bar mechanism has been used as a mechanical wavelength scanning mechanism. This has the advantage that the relationship between the rotation speed of the motor and the wavelength of the emitted monochromatic light is linear, making it easy to calculate the wavelength, but on the other hand, the mechanism is complex, the number of parts is large, and there is a limit to the scanning speed. There was a drawback. In addition, recently, by using a microprocessor, the diffraction grating can be directly rotated by a pulse motor without using a sine bar mechanism, and the wavelength can be calculated using C.
Although it has become possible to use a calculation method using a PU, in order to obtain a certain level of wavelength accuracy, the rotation angle of the diffraction grating per step of the pulse motor must be made small, which requires a deceleration mechanism. The problem was that the structure ended up becoming complicated.

(Problems to be Solved by the Invention) In view of the above-mentioned problems, it is an object of the present invention to provide a wavelength scanning mechanism for a spectrophotometer that is compact and capable of high-speed scanning.

(Means for Solving the Problems) In order to achieve the above object, the spectrophotometer according to the present invention includes a recording medium 3 provided on the circumferential surface of a rotating drum 2 directly connected to a rotating shaft of a small DC servo motor. A sensor 4 installed opposite to the recording medium 3 generates pulses for detecting rotational position, a diffraction grating 6 is placed at the center of rotation on the rotating drum 3, a counter 12 counts the pulses, and output light is output from the counter output. A calculation circuit 13 for calculating the wavelength of the wavelength is provided.

(Function) As the rotation mechanism of the diffraction grating, a so-called encoder-directly connected DC servo motor is used, so the resolution can be sufficiently increased without using a deceleration mechanism, and the rotational position detection pulse from the encoder can be It can be used to calculate
Furthermore, since a sine bar mechanism and a speed reduction mechanism are no longer necessary, the device can be made smaller, and has less noise and vibration, improving reliability.

(Embodiment) Fig. 1 shows an embodiment of the present invention, in which a flat type DC servo motor is fixed to the back surface of a motor control printed circuit board 1, and a motor shaft extends through the printed circuit board 1 and protrudes from the top surface. A rotary drum 2 is coupled to the rotary drum 2, and a low-resolution encoder detects a magnetic recording medium 3 provided on the circumferential surface of the rotary drum 2, a magnetic sensor 4 provided opposite to the magnetic recording medium 3, and a rotational position and direction. A comparator circuit 5 generates two-phase pulse outputs for the purpose.

The diffraction grating 6 is mounted at the center of rotation on the rotating drum 2, and when the diffraction grating 6 is rotated at a constant speed by a motor, the wavelength of the monochromatic light that enters the input slit 7 and exits the output slit 8 is is now scanned.

Figure 2 shows the motor control circuit, with encoder E
The pulse output from the rotation direction detection circuit 11 and the counter 12 are inputted, and the counter 12 adds or subtracts the pulses according to the output from the rotation direction detection circuit 11.
The output is manually input to the arithmetic circuit I3. In the arithmetic circuit 13, based on the outputs of the rotation direction detection circuit 11 and the counter 12,
The current rotational position and direction are detected, and a control signal is sent to the motor drive circuit 15 according to a command from the operation circuit 14 to control the motor M, and the current rotational angle, the grating constant of the diffraction grating, and the geometry of both slits are The wavelength of the emitted monochromatic light is calculated from the target arrangement, displayed on the display circuit 16, and stored in the memory circuit I7.

FIG. 3 shows a method for determining the wavelength using the above configuration, and wavelength scanning is performed by rotating the motor at a constant speed.

Theta-order light λ serves as the reference for the emitted light. Since it has sufficient intensity compared to other diffracted lights, it can be detected by monitoring the emitted light with a photodetector. A gap is provided on the magnetic recording surface as a reference point for pulses from the encoder, and pulses are counted from the end point L0 of the gap. 0th order light λ. If the rotational position of is determined as the count number N0, the count number N or the wavelength λ1 or λ corresponding to N can be calculated by the arithmetic circuit 13.

(Effects of the Invention) As described above, the spectrophotometer according to the present invention rotates the diffraction grating using a direct current servo motor connected directly to an encoder.
Since the wavelength of the emitted light is calculated by counting the output pulses of the encoder, the resolution can be sufficiently increased without using a deceleration mechanism compared to the conventional method using a step motor. In addition, the output pulses from the encoder can be used directly to calculate the wavelength, which simplifies the circuit and increases calculation speed. Also, since a sine bar mechanism and deceleration mechanism are not required, the device can be made smaller. It has the advantage of being able to reduce noise and vibration.

In this embodiment, a magnetic type encoder is used as the low-return encoder, but a photoelectric type can also be used.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the present invention, FIG. 2 is a circuit diagram of a main part of the same, and FIG. 3 is an explanatory diagram of the operation of the same. ■...Printed circuit board, 2...Rotating drum, 3...
Recording medium, 4... Sensor, 5... Comparator, 6
... Diffraction grating, 7... Input slit, 8... Output slit.

Claims (1)

[Claims] (1) A recording medium is provided on the circumferential surface of a rotating drum that is directly connected to the rotating shaft of a small DC servo motor, and a pulse for detecting the rotational position is generated by a sensor installed opposite to the recording medium, and the rotation center position on the rotating drum is A spectrophotometer characterized in that a diffraction grating is arranged, a counter for counting the pulses, and an arithmetic circuit for calculating the wavelength of emitted light from the output of the counter.