Copying machine exposure adjustment device

A copying machine exposure adjustment device, including an operation panel that converts user operations into digital signals, a digital operation circuit that processes operational data from the operation panel and computes exposure data, a D/A converter that converts exposure data sequentially transmitted from the digital operation circuit into analog exposure data, a copy-lamp control circuit that adjusts the light volume of a copying lamp in response to the exposure data from the D/A converter, an image density circuit that detects light reflected from the original document, and a data correction circuit that corrects the exposure data from the D/A converter in response to the image density data from the image density detector circuit while the automatic exposure mode is in operation.

BACKGROUND OF THE INVENTION 
The present invention relates to a copying machine exposure adjustment 
device for properly adjusting the exposure before it is applied to copying 
papers. Conventional copying machines require that the user determine the 
exposure amount and adjust to the desired level through the manual 
operation of a switch to control the exposure. Even when utilizing 
automatic exposure systems, operators are obliged to set the exposure 
level initially, which is an inconvenience. Furthermore, since 
conventional copying machine exposure adjustment devices use analog means, 
in which the data analyzing is inferior, to process all of the operational 
input data, the exposure setting generally falls short of satisfactory 
results. Using such conventional means, operators cannot choose the 
optimum exposure amount which precision before copying, especially under 
adverse conditions such as copying a photograph. 
SUMMARY OF THE INVENTION 
To eliminate the disadvantages described above, the present invention aims 
at providing an extremely useful copying machine exposure adjustment 
device capable of digitally processing and serially transmitting the 
operational data to a D/A (digital to analog) converter. The exposure 
adjustment device embodied by the present invention also features an 
automatic exposure mode which is capable of determining the optimum 
exposure amount based on data obtained by monitoring the original. As a 
result, the exposure adjustment device of the present invention involves 
simple operations for easier handling in addition to simplified hardware 
which enables operators to precisely adjust the exposure. 
Other objects and further scope of applicability of the present invention 
will become apparent from the detailed description given herein. It should 
be understood, however, that the detailed description and specific 
examples, while indicating preferred embodiments of the invention, are 
given by way of illustration only, since various changes and modifications 
within the spirit and scope of the invention will become apparent to those 
skilled in the art from the following detailed description. 
Specifically, the copying machine exposure adjustment device embodied by 
the present invention is comprised of the following: An operation panel 
converting user operations into digital signals, digital equipment that 
computes data from the operation panel to determine the exposure data, a 
D/A converter that converts exposure data as it is transmitted 
sequentially from said digital equipment into analog exposure data, a 
copy-lamp control circuit that adjusts the copy lamp in accordance with 
exposure data from the D/A converter, an image density circuit that 
detects light reflecting from the original, and a data compensation 
circuit that corrects the exposure data from the D/A converter during the 
automatic exposure mode in response to the image density data from the 
image density detector circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a simplified block diagram of the entire circuit of the copying 
machine exposure adjustment device embodied by the present invention. The 
reference numeral 1 indicates a central processing unit (i.e., digital 
equipment) made of a single LSI chip, which processes data in an 8-bit 
unit. The reference numeral 2 indicates an operation panel of the copying 
machine, which is provided with copy button and number keys. The operation 
panel 2 converts the user input operation into digital signals for 
transmittal to the central processing unit (CPU). The CPU 1 then processes 
the received data to compute the reference exposure data D. Since the 
exposure data is substantially composed of 8-bit data, it can be provided 
with a maximum of 256 steps ranging from zero (0) to 255. The reference 
numeral 3 indicates a D/A converter to which the reference digital 
exposure data D computed by the CPU 1 is sequentially transmitted, and 
which converts reference digital exposure data D into analog exposure data 
D for delivery to an operational amplifier 4. As shown in FIG. 2, the CPU 
1 sequentially transmits the reference digital exposure data D to the D/A 
converter 3 in the state of an 8-bit serial data SI together with clock 
pulse SCK. The CPU 1 latches a serial data SI whenever the clock pulse SCK 
rises. The CPU 1 delivers the strobe pulse STB immediately after it reads 
the 8th serial data SI. Simultaneous with the rise of the strobe pulse 
STB, the D/A converter 3 outputs the reference analog exposure data D to 
the operational amplifier 4. On receipt of the reference analog exposure 
data D from the D/A converter 3, the operational amplifier 4 outputs 
reference analog exposure data D' which then becomes (Vo +D.i). The 
reference numeral 5 indicates a resistor that provides the reference value 
Vo, whereas the reference numeral 6 indicates a resistor that adjusts the 
value of constant "i". The reference numeral 7 indicates an analog switch 
which transmits the reference analog exposure data D' to a copy-lamp 
control circuit 8 in response to a switching signal from the CPU 1 when 
the exposure is manually executed. The analog switch 7 transmits the 
reference analog exposure data D' to the copy-lamp control circuit 8 
through a subtraction circuit (i.e., the data compensation circuit) 9 when 
the copier is in the automatic reference exposure mode . In accordance 
with the level of the exposure data D', the copy-lamp control circuit 8 
feeds a trigger pulse to a triac switch 10. This causes the phase of AC 
power source 11 to be controlled so that the light volume of the copying 
lamp 12 can be adjusted to an optimum level. In addition, the copy-lamp 
control circuit 8 properly compensates for the varied voltages of the AC 
power source 11 to constantly maintain a beneficial exposure. The 
reference numeral 13 indicates an image density detector circuit which is 
comprised of a silicon blue cell 14, and operational amplifiers 15 and 16. 
The silicon blue cell 14 is the photo sensor that detects the amount of 
light reflected from the original and outputs a specific voltage 
proportional to the received light volume. Operational amplifier 15 acts 
as a buffer, whereas operational amplifier 16 amplifies the voltage output 
from the silicon blue cell 14 by the operational amplifier 15 and 
transmits the amplified voltage as the original image density data VA. The 
reference numeral 17 indicates a resistor that adjusts the amplitude of 
the operation amplifier 16. By keeping the exposure data D constant, the 
resistor 17 performs adjustments so that the difference between the 
voltage fed to copying lamp 12 after detection of an original with high 
image density and the voltage fed to the copying lamp 12 after detection 
of an original with low image density remains the optimum value. When the 
automatic exposure mode is in operation, the image density data VA is 
delivered to the subtraction circuit 9 together with the exposure data D'. 
The subtraction circuit 9 corrects the exposure data D' by applying the 
image density data VA, and as a result, the exposure data D" to be denoted 
as (Vo+D.i-VA) is delivered to the copy-lamp control circuit 8. 
Consequently, the less dense the image on the original, the greater the 
value of VA, thus diminishing the value (Vo+D.i-VA) to reduce the 
exposure. The automatic exposure mode thereby executes its function fully. 
When the exposure data D is to be kept constant, the value (Vo+D.i-VA) 
present during the automatic exposure mode is lower than the value 
(Vo+D.i) which is present in the manual exposure mode. Therefore, the CPU 
1 outputs a greater exposure value during the automatic exposure mode than 
it delivers during the manual exposure mode to compensate for this 
difference. If the exposure level is to be modified during the automatic 
exposure mode, the exposure value D may be either increased or decreased 
by the user. The copying machine exposure adjustment device incorporating 
the preferred embodiments of the present invention causes the CPU 1 to 
digitally execute the operations from the operation panel 2 as instituted 
by the user to optimize the exposure, thus making it possible for the 
copying machine to precisely adjust the exposure in accordance with 
specific exposure conditions. In addition, since the exposure adjustment 
device embodied by the present invention serially transmits the digital 
exposure data D from the CPU 1 to the D/A converter 3, the system can 
reduce the number of input lines of the D/A converter 3, thus simplifying 
the necessary hardware. Furthermore, the device corrects the exposure data 
D' in response to the image density of the original VA while the automatic 
exposure mode is underway. The corrected data is then transmitted to the 
copy-lamp control circuit 8 as exposure data D", and as a result, 
operations on the part of the user are minimized and simplified. The 
system of the copying machine exposure adjustment device embodied by the 
present invention allows digital processing of the operational data, thus 
allowing the exposure amount to be precisely adjusted according to the 
required exposure conditions. In addition, since the exposure data from 
digital circuit is sequentially transmitted to the D/A converter, the 
number of input lines and the complexity of the hardware are decreased. 
Furthermore, since the exposure amount can be precisely determined by 
correcting the exposure data while the automatic exposure mode is 
underway, user operation are minimized and simplified. 
While only certain embodiments of the present invention have been 
described, it will be apparent to those skilled in the art that various 
changes and modifications may be made therein without departing from the 
spirit and scope of the present invention as claimed.