JPH0820685B2 - Automatic exposure control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an apparatus for adjusting the exposure amount of a copy lamp of a copying machine.

(B) Prior Art FIG. 3 is a diagram showing the configuration of a general automatic exposure control device in a copying machine.

In the figure, the original 1 placed on the original table on the upper surface of the main body of the copying machine is scanned by the copy lamp 2 moving in the arrow A direction. The light reflected from the document by the copy lamp 2 is guided by the mirror 4 onto the photosensitive drum 3 to form a latent image, as shown by the broken line in the figure, and the AE sensor 5
Incident on. The incident light amount VAE to the AE sensor 5 is MPU (Micro
Processing Unit) reads and calculates the appropriate amount of light for the copy lamp according to the document density VAE, and the CLR (Copy Lamp Regul
ator) to automatically adjust the light intensity of the copy lamp. As a result, the reproducibility of fine lines in the copied image is ensured and background fogging is prevented.

(C) Problem to be Solved by the Invention By the way, the output voltage of the AE sensor has ripples (swells) in the power supply frequency even when the copy lamp output voltage is constant. Therefore, in the conventional device, the influence of the ripple on the output voltage is prevented by setting the zero cross point of the copy lamp driving power source as the sampling timing of VAE reading. However, in this case, the document density can be sampled only every half cycle, and the copy lamp control is delayed with respect to the document density change.
This phenomenon was remarkable especially in recent high-speed copying machines.

It is an object of the present invention to provide an automatic exposure control device capable of preventing a delay in density adjustment and improving the quality of a formed image by increasing the number of sampling points for density detection.

(D) Means for Solving the Problems The present invention relates to an automatic exposure control device for controlling the light quantity of a copy lamp in accordance with the detected reflected light of an original document, and a plurality of copy lamp driving power sources are provided between zero cross points. Set the sampling point of
The present invention is characterized in that means is provided for correcting the document reflected light amount at each sampling point based on the document reflected light amount for the reference density document at each sampling point.

(E) Operation In the present invention, the sampling point for the reflected light amount of the document is provided between the zero cross points, so that the light amount of the copy lamp can be controlled at a fine interval. At this time, the detected document reflected light amount is corrected based on the document reflected light amount with respect to the reference document at each sampling point, so that the copy lamp light amount control can be performed without being affected by the ripple of the power supply frequency.

(F) Embodiment FIG. 2 is a block diagram of an automatic exposure control device.

The reflected light of the original from the copy lamp 2 is detected by the AE sensor 5. The MPU A / D converts this detection value and captures it
L (copy lamp control voltage) is calculated, and this data is output to CLR as a PWM (Pulse Width Modulation) value. In CLR, the copy lamp 2 is phase-controlled based on this value and is turned on.

FIG. 1 is a diagram showing an example of sampling of AE sensor output.

The reference reflected light amounts D _{0 to} D _{9 with} respect to the reference density original document at the 10 sampling points S _{0 to} S ₉ between the zero-cross points P ₀ and P _{1 of the} half cycle are measured in advance and stored in the MPU. From the reference reflected light amounts D _{0 to} D ₉ to the sampling points S _n
By correcting the AE sensor output value VAE _n in, the VAE excluding the effect of ripple can be obtained.

VAE = VAE _n × (D ₀ / D _n ) Although 10 points of sampling are provided between the zero cross points P ₀ and P _{1 in} this embodiment, this number is arbitrary. The drive power supply cycle for ripple correction may be set to a half cycle or more. Furthermore, the correction formula may take into consideration the variation characteristics of the copy lamp, the photoconductor, the control system, and the like.

(G) Effect of the Invention As described above, according to the present invention, the copy lamp control can be performed by shortening the document density detection interval without being affected by the ripple of the power supply frequency. It is possible to respond quickly and improve the quality of the formed image.

[Brief description of drawings]

FIG. 1 is a diagram showing sampling points of AE sensor output in an automatic exposure control apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram of the apparatus, and FIG. 3 is a general automatic exposure apparatus configuration. FIG.

Claims (1)

[Claims] 1. An automatic exposure control device for controlling the light intensity of a copy lamp according to the detected reflected light of an original, wherein a plurality of sampling points are set between zero cross points of a copy lamp driving power source and each sampling point is set. An automatic exposure control apparatus comprising means for correcting the original reflected light amount at each sampling point based on the original reflected light amount for a reference density original at a point.