JPS6139023A - Controlling method of light - Google Patents

Abstract

PURPOSE:To remove the loss of diffracted light and to improve control accuracy by detecting the quantity of reduction of light on the non-diffracted light side at the time of diffraction and controlling the distribution ratio of the diffracted light to the non-diffracted light in accordance with the detected quantity. CONSTITUTION:A difference between an output signal obtained at the OFF of diffracted light of an optical sensor PD and an output signal obtained at the ON of the diffracted light is extracted by a coupling capacitor C1 and detected and smoothed by diodes D1, D2 and a capacitor C2. The voltage is applied to one side of voltage determining resistors R3, VR for a constant voltage circuit consisting of TRs Q1-Q5, a Zener diode ZD, a variable resistor VR and resistors R3-R7 and the output voltage of the constant voltage circuit controls a voltage to be applied to a modulating means 2. Consequently, the reduced quantity of light of the non-diffracted light side at the time of diffraction is detected and the distribution ratio of the diffracted light to the non-diffracted light is controlled in accordance with the detected quantity, so that the diffracted light is not lost and the control accuracy can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a light amount control method used in a laser printer or the like.

(Prior Art) A laser printer and the like are examples of devices that utilize the diffracted light by dividing output light from a light source into diffracted light and non-diffracted light using a distributing means such as a modulating means. In addition, the light intensity control methods in this device include: (1) guiding a portion of the diffracted light to a light intensity sensor using a half mirror or partial mirror, and controlling the distribution ratio of diffracted light and undiffracted light according to the output; There is a method of detecting the amount of diffracted light and controlling the distribution ratio of diffracted light and undiffracted light according to this amount of light.

However, although the method (2) has good control accuracy, a part of the diffracted light to be used is lost in the half mirror or partial mirror, so the light utilization efficiency is poor. Even if this is not the case, there will be a loss of about 30% due to the output light from the light source passing through the distribution means, so this is not a good method for users who want to use as much light as possible. In addition, although 100% of the diffracted light can be used in the method (2), the control accuracy is poor and it is not suitable for very precise control of the amount of light.

(Objective) It is an object of the present invention to provide a light amount control method with no loss of diffracted light and high control accuracy.

(Structure) The present invention is a device that divides output light from a light source into diffracted light and non-diffracted light and utilizes the diffracted light. The distribution ratio of diffracted light and undiffracted light is controlled accordingly.

Next, examples of the present invention will be described.

FIG. 1 shows the circuit used in this example. This embodiment was implemented in a laser printer, and the light source 1 is, for example, a gas laser tube whose light intensity cannot be controlled.

The output light from the light source 1 is modulated by a high-frequency image signal by the modulation means 2, and is converted into diffracted light (first-order light or higher) and non-diffracted light (0
The diffracted light is used for image recording. For example, an acousto-optic element is used as the modulating means 2, and the amount of the undiffracted light is detected by the light amount detector 3. The light amount difference extraction circuit 4 extracts the difference between the output signal voltages of the light amount detector 3 when the modulating means 2 performs diffraction and when it does not perform diffraction. By lowering the power supplied to the modulating means 2--, the distribution ratio between the diffracted light and the non-diffracted light is lowered to reduce the amount of diffracted light, and conversely, if the voltage difference is low, the voltage supplied to the modulating means 2 is increased. This increases the distribution ratio and increases the amount of diffracted light. Therefore, when using this method, it is necessary to turn off the diffracted light from time to time when the light intensity detector 3 detects the undiffracted light and the light intensity difference extraction circuit 4 extracts the difference between the diffracted and non-diffracted outputs. . However, in a laser printer, although the recorded portion of the diffracted light is turned on and off, there is always a non-recorded portion of the diffracted light, so it is better to turn it off to prevent scattered light. In this embodiment, means is provided for turning off the diffracted light in the non-recording portion (the modulating means 2 does not diffract the light due to the modulation signal).

FIG. 2 shows a specific example of an implementation circuit of the present invention.
, C2 is a capacitor, DI, D2 is a diode, z
D is a Zener diode, Q1 to Q5 are transistors,
VR is a variable resistance. The difference between the output signal of the light quantity sensor PD when the diffracted light is off and the output signal when the diffracted light is off is picked up by the compling capacitor C1 and then sent to the diode DI,
The detected voltage is smoothed by D2 and capacitor C2, and this voltage is applied to transistors Ql-Q5 and Zener diode Z.
D, variable resistance VR.

A resistor R for determining the voltage of a constant voltage circuit consisting of resistors R3 to R7
3. The voltage applied to the modulation means 2 is controlled by this constant voltage circuit (output voltage) applied to one side of the VR. In a device that utilizes diffracted yellow by distributing it into diffracted light and non-diffracted light, the amount by which the amount of light on the non-diffracted light side decreases during diffraction is detected, and the distribution ratio between the circular light and non-diffracted light is determined according to this amount. Since it is controlled, there is no loss of diffraction waves and the control accuracy is high.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a circuit for implementing the present invention. FIG. 2 is a block diagram showing an example of a circuit for implementing the present invention. 3 light amount detector, 4... light amount difference extraction circuit, 5...
- Control means. Be

Claims (1)

[Claims] In a device that divides output light from a light source into diffracted light and non-diffracted light and uses the diffracted light, it detects the amount by which the amount of light on the non-diffracted light side decreases during diffraction, and divides the output light into diffracted light and non-diffracted light according to this amount. A light amount control method characterized by controlling a distribution ratio of.