JPS6337969A - Light emitting control circuit - Google Patents

Abstract

PURPOSE:To provide printing quality free from density irregularity by making the exposure energy on a photosensitive drum due to an LED element constant, by providing a register storing the value proportional to the current applied to a light emitting element and a memory element storing the value stored in the register and storing a proper value in said memory element. CONSTITUTION:A printing control circuit 1 informs that a power source is made ON to a light quantity correction circuit 10. The light quantity correction circuit 10 receives said information to initially set the address of a memory element 9 and reads a data value to write the same in the register circuit 11 of a left side. Then, the address of the memory element 9 is increased to read a data value which is, in turn, written in the register circuit 11 second from the left end. By this method, the data values are written in all of register circuits 11. Thereafter, a printing control circuit 1 outputs printing information and a shift clock to a latch circuit 2 through the light quantity correction circuit 10 and sends a light emitting signal to DAC12 after all of printing informations are outputted. DAC12 outputs the analogue voltage proportional to the value stored in the register circuit 11 corresponding to AND of the light emitting signal and the output of the latch circuit 2 and VIC13 allows the current proportional to the input voltage thereof to flow to an LED element 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light emission control circuit, and more particularly to a light emission control circuit that controls light emission of an LED that exposes a photosensitive drum of an electrophotographic printing device.

[Conventional technology]

Conventionally, this type of LED light emission control circuit, as shown in FIG. 2, a resistor 4 connected to the output of the switch element 3, and an LED element 5 whose anode is connected to the resistor 4 and whose cathode is grounded. Element 3, resistor 4, and LED
A plurality of elements 5 are connected in parallel between the output of a power source 6 and ground, and the output light of the LED elements 5 passes through a self-off lens 7 and reaches a photosensitive drum 8.

Next, its operation will be explained.

The print control circuit 1 outputs print information and a shift clock to the latch circuit 2. Information from the print control circuit 1 is shifted between a plurality of latch circuits 2, and after the print information is output to all the latch circuits 2, the print control circuit 1 transfers the information to the switch element 3.
sends a light emission signal to.

Switch element 3 connects the output of latch circuit 2 and print control circuit 1
A logical product is performed with the light emission signal from the resistor 4 and the power source 6, and conduction is established between the resistor 4 and the power source 6 based on the logical product value. LED in conductive position
The element 5 emits light and applies exposure energy to the photosensitive drum 8 through the self-off lens 7, lowering the surface potential and creating a latent image.

[Problem that the invention seeks to solve]

In the conventional LED light emission control circuit described above, the current flowing through the LED element 5 is determined by the output value of the power supply 6, the saturation voltage value of the switch element 3, the resistance value of the resistor 4, and the forward voltage value of the LED element 5. However, there are variations in all of these factors, and as a result, they are not constant.Furthermore, the light emission energy with respect to the current flowing through the LED elements 5 also varies among the LED elements 5. Due to variations in light transmittance depending on the position of the self-off lens 7, the emission energy varies even more at the position where it reaches the photosensitive drum 8.

The above results have the disadvantage that the surface potential on the photosensitive drum 8 varies, resulting in uneven printing density and deterioration of printing quality.

[Means for solving problems]

The light emission control circuit of the present invention includes a plurality of latch circuits to which information is transferred, a plurality of light emitting elements that emit light according to information transferred to each of the latch circuits provided correspondingly, and each of the light emitting elements. a correcting means for applying a current to the light emitting element in proportion to the value stored in the register when emitting light; and a memory element for storing in advance the value to be stored in each of the registers. It consists of:

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. a print control circuit 1, a memory element 9, and a light amount correction circuit 10 whose inputs are the output of the print control circuit 1 and the output of the memory element 9;
and a latch circuit 2 whose input is the output of the light amount correction circuit 10.
, a register circuit 11, a digital-to-analog conversion circuit (hereinafter referred to as DAC) 12 whose inputs are the outputs of the latch circuit 2, the light amount correction circuit 1o, and the register circuit 11, and the DAC1.
It has a voltage-current conversion circuit (hereinafter referred to as IC) 13 whose input is the output of VIC 13, and an LED element 5 whose anode is connected to the output of VIC 13 and whose cathode is grounded. DACl2 and VIC13 and L
A plurality of ED elements 5 are connected in parallel between a light amount correction circuit 10 and ground, and the output of the LED elements 5 passes through a self-off lens 7 and reaches a photosensitive drum 8.

Next, the operation of this embodiment will be explained.

First, the print control circuit 1 notifies the light amount correction circuit 1o that it is time to start up the apparatus, such as by turning on the power. Upon receiving this notification, the light amount correction circuit 1o initializes the address of the memory element 9, reads the data value, writes the data value to the leftmost register circuit 11 shown in FIG. The address is incremented, the data value indicated by the address is read, and the data value is written into the second register circuit 11 from the left end shown in FIG.

In this way, all register circuits 11 are connected to memory elements 9.
Write the data value stored in .

After that, the print control circuit 1 outputs the print information and shift clock to the latch circuit 2 through the light amount correction circuit 10, and after all the print information is output, it sends a light emission signal to the DAC 12. The VIC 13 outputs an analog voltage proportional to the value stored in the register circuit 11 according to the logical product of the output of the latch circuit 2.
A current proportional to the input voltage flows through the LED element 5, L
The ED element 5 emits light and applies exposure energy to the photosensitive drum 8 through the self-off lens 7, lowering the surface potential and creating a latent image. Here, the values stored in each register circuit 11 from the light amount correction circuit 10 are as follows. , is a unique value for each LED element 5, and is stored in advance in the memory element 9.

The values stored in the memory element 9 to be stored in each register circuit 11 are set in such a way that a certain amount of exposure energy is detected at the surface position of the photosensitive drum 8 when each LED element 5 emits light. This is a value that is proportional to the voltage value that is necessary for the AC 12 to output, and is a value that is measured in advance using a light amount measuring device or the like. By storing such pre-measured values in the memory element 9, it is possible to keep the exposure energy on the photosensitive drum constant and obtain print quality without unevenness in density.

〔Effect of the invention〕

As explained above, the present invention provides a register that stores a value proportional to the current applied to the light emitting element, and a memory element that stores the value to be stored in the register, so that an appropriate value can be stored in the memory element in advance. If this is done, the light emitting elements can output an appropriate amount of light regardless of variations in the performance of the light emitting elements.

If the present invention is applied to an electrophotographic printing device, the variation in exposure energy due to variation in LED elements and self-off lenses can be measured in advance, and the current value flowing through the LED element can be determined to compensate for it. By storing a value corresponding to this current value in a memory element, L
By keeping the exposure energy on the photosensitive drum by the ED element constant, it is possible to provide printing quality without unevenness in density.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional light emission control circuit.

Claims (1)

[Claims] A plurality of latch circuits to which information is transferred, a plurality of light emitting elements that emit light according to the information transferred to each of the latch circuits provided correspondingly, and a register provided corresponding to each of the light emitting elements. and a correction means for applying a current proportional to the value stored in the register to the light emitting element when emitting light, and a memory element that stores in advance the value to be stored in each of the registers. circuit.