JPH0321966A - Exposure controller for copying machine - Google Patents

Abstract

PURPOSE:To allow a copy lamp voltage to rise speedily by providing a full- power control voltage generating circuit which outputs a full-power control voltage to a voltage control circuit without intervening PWM control circuit when the copy lamp voltage rises. CONSTITUTION:A copy lamp control part 1 is equipped with a PWM control circuit 22, a remote circuit 2, a voltage control circuit 24, and a full-power control voltage generating circuit 3. When the copy lamp voltage rises, the full-power control voltage generating circuit 3 outputs the full-power control voltage to the voltage control circuit 24 without intervening the PWM control circuit 22. Namely, a DC control voltage corresponding to full power is inputted directly to the voltage control circuit 24 without intervening any extra circuit. Consequently, a copy lamp can be controlled with the full power from the initial stage and a speedy rise can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to an improvement in an exposure control device for controlling the voltage supplied to a copy lamp of a copying machine.

(b) Conventional technology FIG. 3 is a block diagram showing a conventional exposure control device.

The copy lamp control unit 21 is PWM! It has an II control circuit 22, a remote circuit 23, and a voltage control circuit 24. The main control section 25 sets a duty ratio according to the detection data (amount of light reflected from the document) of the AE sensor 28, etc., and outputs it to the exposure lamp control section 2l as a voltage amount control signal VA. The exposure lamp control section 21 receives the voltage amount control signal ■. The voltage applied to the copy lamp 26 is controlled accordingly. That is, the PWM control circuit 22 converts the voltage amount control signal VA into a DC control voltage VII""VD and outputs it to the voltage control circuit 24. The voltage control circuit 24 applies a voltage corresponding to the DC control voltage VD to the copy lamp 26 to light the copy lamp. Note that the remote circuit 23 controls the main control unit 25 in response to a copy start command from the operation unit 27.
This gate section outputs the DC control voltage vl from the PWM fil7 control circuit 22 to the voltage control circuit 24 as the DC control voltage V when CL is output from the PWM fil7 control circuit 22.

By the way, when starting copying, it is desirable that the voltage applied to the copy lamp reach a steady value as quickly as possible. Therefore, conventionally, when the copy lamp starts up, the duty ratio set by the main control section 25 is set to approximately 100% (full power) so that the voltage can be raised quickly. The duty ratio in steady state is max 80-90%.
That's about it.

(C) The problem that the invention seeks to solve is PWM! Since the II control circuit 22 includes an integrating circuit therein, the response to the input pulse is delayed by the time constant thereof, and there is a problem in that it takes time for the copy lamp voltage to rise at the start of copying.

That is, as shown in FIG. 4, even if the main control unit 25 outputs the full power exposure control signal VA at the copy start point td, the PWM control circuit 22
The corresponding DC control voltage v! Since the output of + is delayed by the time constant T, the voltage of the copy lamp 26 cannot be raised quickly. Furthermore, when canceling full power, it is necessary to take the delay time of the PWM control circuit 22 into account and bring down the control pulse VA by T2 time earlier, which ultimately shortens the time during which full power can be controlled for the copy lamp. It took a long time T3 for the light intensity to rise.

SUMMARY OF THE INVENTION An object of the present invention is to provide an exposure control device that can rapidly raise a copy lamp voltage when copying is started.

(Means for Solving Problems d1) This invention provides a PWM control circuit that generates a DC control voltage according to an exposure control signal, and a voltage control circuit that controls the voltage supplied to a copy lamp according to the DC control voltage. The exposure control device for a copying machine is equipped with a full-power control voltage generation circuit that outputs a full-power control voltage to the voltage control circuit without going through the PWMI+ control circuit when the copy lamp voltage rises. shall be.

(e) Effect In this invention, the DC control voltage corresponding to full power is directly inputted to the voltage control circuit without going through an extra circuit (PWM control circuit), so the copy lamp can be controlled at full power from the initial stage. It is possible to achieve rapid start-up.

(f) Embodiment FIG. 1 is a block diagram of an exposure control device for a copying machine which is an embodiment of the present invention. In the figure, the same parts as in FIG. 3 are indicated by the same numbers.

The copy lamp control section 1 includes a PWM control circuit 22, a remote circuit 2, a voltage control circuit 24, and a full power control voltage generation circuit 3. The full power control voltage generation circuit 3 is constructed of a simple circuit including, for example, a transistor Tr, and when it receives a Full signal, it outputs the full power control voltage V, to the remote circuit 2.
Output to. The full power control voltage V is a value corresponding to 100% duty of the copy lamp 26.

The remote circuit 2 constitutes a voltage OR circuit with a wired OR circuit of diodes D, D2, and the voltage is the higher of v8 and ■o. is output to the voltage control circuit 24 via the gate G. Gate G opens when the CL signal is manually operated. The main control section 4 outputs an exposure amount control signal V corresponding to the duty ratio to the PWM control circuit 22, and also outputs a FuI1 signal to the full power control voltage generation circuit 3 when a copy start command is input from the operation section 27. Outputs the CL signal to the remote circuit 2.

FIG. 2 is a diagram showing output signal waveforms from each circuit section. Hereinafter, copy lamp control will be explained with reference to this figure.

The main control unit 4 PWMs the exposure amount control signal vA with a duty ratio according to the output data of the AE sensor 28, etc.
It is constantly output to the control circuit 22. In this duty ratio, maχ is set to 80 to 90%, and does not increase to a value corresponding to full power. Therefore PWM
DC control voltage v! output from the control circuit! l is always at a steady-state value level. When a copy start command is input from the operation unit 27, the main control circuit 4 outputs a full signal to the full power control voltage generation circuit 3, and the remote circuit 2 outputs a process signal. The full power generation circuit 3 generates the full power control voltage V by the signal
, which is input to the voltage control circuit 24 as the DC control voltage VD. The voltage control circuit 24 turns on the copy lamp 26 based on the full power control voltage vc=Vo.

Furthermore, when the full power control is stopped, if the ULL signal is turned off, the steady DC control voltage V8 from the PWM control circuit 22 is manually input to the voltage control circuit 24, and the DC control voltage is immediately lowered. There is no need to apply early braking in anticipation of a time constant like in the past. As a result, the copy lamp voltage rise time can be shortened to T4.

As described above, since the circuit 3 is provided only for generating the full power control voltage (2), the response of the full power control voltage output is improved and the voltage rise time can be shortened. Note that the timing t2 for stopping the Ful signal is set after a predetermined time has elapsed from the copy start timing t1, when the amount of light detected by the AE sensor reaches a predetermined value, when the copy lamp voltage reaches a predetermined value, etc. .

(0) Effects of the Invention As described above, if this device is used, the voltage can be rapidly raised to reach a steady state when the copy lamp starts up, so the preliminary time until the copy lamp stabilizes at the start of copying can be shortened, Copy processing time can also be shortened.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an exposure control apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram showing output signal waveforms in the same apparatus. FIG. 3 is a block diagram of the conventional device, and FIG. 4 is its output signal waveform diagram. Calyx 1 Figure 1 - Exposure lamp control section, 2 - Remote circuit, 3 - Full power control voltage generation circuit.

Claims (1)

[Claims] (1) Exposure control device for a copying machine equipped with a PWM control circuit that generates a DC control voltage according to an exposure amount control signal, and a voltage control circuit that controls the voltage supplied to a copy lamp according to the DC control voltage. An exposure control device for a copying machine, comprising: a full power control voltage generation circuit that outputs a full power control voltage to the voltage control circuit without going through the PWM control circuit when the copy lamp voltage rises.