GB2090003A - Electrophotographic Copier - Google Patents

Abstract

An image forming apparatus, a light quantity controller and an input device are disclosed. The image forming apparatus has a reciprocally movable member for forming an image on a record medium. The reciprocally movable member carries mirrors 3 and 21 for scanning an original 25 and is set to a predetermined home position before a first image is formed. An error sensor is associated with the moving and setting operation of the reciprocally movable member. The light quantity controller comprises a light source, a photosensor to detect a light quantity of the light source, a signal source for generating a reference signal, a comparator for comparing the detected light amount with the reference signal, and control circuit to control a duty ratio of the energization to the light source in accordance with the compare result to maintain the light quantity of the light source at a constant level. The light quantity controller further comprises a comparator to compare the energization signal to the light source with a reference signal to detect the degradation of the light source. The input device has a key matrix including a plurality of input ports and a plurality of output ports of a control unit interconnected through switches. A signal source independent from the output ports of the key matrix is connected to at least one of the input ports through switches. <IMAGE>

Description

SPECIFICATION Image Forming Apparatus Background of the Invention Field of the Invention The present invention relates to an image forming apparatus.

Description of the Prior Art In a conventional image forming apparatus, a copying process including charging image scan, exposure, developing, transfer and fixing steps is sequence-controlled by control signals from a number of cams and microswitches or by a microcomputer which processes those signals.

In addition to those used for the sequence control, many sensors for detecting error conditions of the apparatus are also included in the image forming apparatus.

Accordingly, in an apparatus which satisfies a high level of control and detection, the configuration of the signal generation and signal processing tends to be complicated.

As a performance of a microcomputer is improved and as size thereof is reduced, various controls are carried out by the microcomputer.

However, since the number of input/output ports of the microcomputer is limited, if a number of input signals are to be used as control information, a multiplexor or a key matrix circuit is usually used to process a large amount of control information with a small number of input ports.

Fig. 1 shows a control circuit which uses an input device having a key matrix circuit. Numeral 10 denotes a control unit having a microcomputer, 01-04 denote output ports, 11-14 denote input ports, R denotes a resistor, and M1--M16 denote switches arranged between the input ports and the output ports which constitute the key matrix circuit. An operator actuates one of the switches M -M 16 to enter control information. The control unit 1 produces time-divided repetitive pulse HIGH signals at the output ports 0144, detects which one of the input ports 11-14 a HIGH signal is applied to, determines the actuated switch and reads a status of the key into a memory.With such a key matrix circuit, a maximum number of switches that can be arranged is mxn where mis the number of output ports and n is the number of input ports. Thus, only mxn control information can be processed. When the multiplexor is used, the input and output ports can be saved but a cost increases.

In a copying machine, an image of a text is exposed by a light source in the machine to form a copy of the text.

A halogen lamp or a fluorescent lamp has been widely used as the light source, but the halogen lamp has defects in that it has a poor conversion efficiency, generates much heat to raise a temperature of the machine and adversely affect to components of the machine and a power consumption is high. The fluorescent lamp has a defect in that a light quantity various with a surrounding temperature (temperature of a tube wall of the fluorescent lamp). In the copying machine, the affect of the defects of the light source to the tone of the copy is substantial as described above.

An approach to stabilise the light quantity of the light source has been proposed. In the proposed approach, the amount of energisation of the light source is increased when the light quantity decreases so that the light quantity in increased to a desired level. The proposed approach also operates when the change in the light quantity is caused not by the phenomenon described above but by the degradation of the light source per se. Accordingly, if the degradation of the light source is such that the desired light quantity is not attained by increasing the amount of energisation, a power is wasted and the machine may be overheated by an overcurrent, which may lead to fire.

The present invention aims to alleviate the above difficulties.

In one aspect the present invention aims to simplify the construction of the apparatus by providing a plurality of control and detection functions of detection means which is activated by a movable member for forming an image.

In another aspect of the present invention a movable member of the apparatus is positioned to a predetermined home position when the apparatus is powered on in order to allow rapid and exact image producing operation.

In a further aspect of the present invention an image forming apparatus is provided having a light quantity controller which provides a stabilised light quantity from a light source.

In a still further aspect the present invention provides an image forming apparatus having a light quantity controller which has a function to detect the degradation of a light source and indicate it to an operator.

In another aspect the present invention provides an image forming apparatus having an input device which utilises a limited number of input/output ports of a control unit of a control circuit in an economic and effective way.

In yet another aspect the present invention provides a light quantity controller suitable for obtaining desired light quantity from a light source.

Brief Description of the Drawing Fig. 1 shows a control circuit having an input device in accordance with a prior art key matrix circuit; Fig. 2 shows a schematic view of a copying machine of the present invention; Fig. 3 shows a schematic diagram of a signal generating unit of the copying machine shown in Fig. 2; Fig. 4 shows a perspective view of the signal generating unit of the copying machine shown in Fig. 2; Fig. 5 shows a block diagram of a control circuit of the present invention; Figs. 6A and 6B, and 8A and 88 which are arranged as shown in Fig. 6 and 8, respectively, show control flow charts; Figs. 7, 9 and 10 show operation timing charts.

Fig. 11 shows a block diagram of a light quantity controller in accordance with the present invention; Fig. 12 shows a circuit diagram of a H.F.

fluorescent lamp stabilizer; Fig. 1 3 shows an operation time chart of the circuit of Fig. 12; Figs. 14 and 17 show circuit diagrams of control circuits; Figs. 15, 16, and 18 show operation time charts of the control circuits; Fig. 1 9 shows a control circuit which uses an input device of the present invention; Fig. 20 shows a control flow chart in accordance with the present invention; Fig. 21 shows an external view of a copying machine in which the input device of the present invention is embodied; Fig. 22 shows a control circuit of another embodiment of the present invention; Fig. 23 shows an external view of a copy density setter; Fig. 24 shows a block diagram of a light quantity control circuit;; Fig. 25 shows a graph iliustrating a relation between a light quantity of a CdS photo-sensitive element and a copy tone; Fig. 26 shows a circuit diagram of a light quantity controller in accordance with the present invention; and Fig. 27 shows a graph illustrating a relation between a position of an output terminal and a control voltage.

Detailed Description of the Preferred Embodiments Fig. 2 shows a schematic view of a copying machine in accordance with one embodiment of the present invention. In the present embodiment, the present invention is implemented in a stationary text table type copying machine. The present invention may be readily applied to a movable text table type copying machine.

A surface of a photosensitive drum 20 comprises photo-sensitive material of photoconductor. the drum 20 is rotatably supported by a shaft 41 and starts to rotate in the direction of an arrow in response to a copy instruction.

As the photosensitive drum 20 rotates to a predetermined position, a text mounted on a text table glass 24 and fixed in position by a text table cover 25 is illuminated by a light ray emanated from an illumination lamp 22 integrated with a first mirror 3 and reflected by a main reflection plate 23. The reflected light is scanned by the first mirror 3 and a second mirror 21. The first mirror 3 and the second mirror 21 are moved at a velocity ratio of 1 to 1/2 so that the text is scanned with an optical path length in front of a lens 26 being kept constant.

The reflected optical image transmits through the lens 26 and is reflected by a third mirror 27 and a fourth mirror 30 and focused on the photosensitive drum 20 at an exposing station 29.

The photosensitive drum 20 is charged (for example, positively) by a primary charger 28 and slit-exposed by the image irradiated by the illumination lamp 22 at the exposing station 29.

At the same time, the photosensitive drum 20 is discharged by A.C. or to the opposite polarity (for example, negative) to the primary charging by a discharger 42, and then it is flat-exposed by a flat exposure lamp 43 to produce a high contrast electrostatic latent image on the photosensitive drum 20. The electrostatic latent image on the photosensitive drum 20 is then visualized as a toner image by a developer 32.

A transfer paper P, not shown, in a cassette 13 is transported into the machine by a paper feed roller 14 and fed to register rollers 1 7 and 1 8 by conveyor rollers 1 5 and 1 6. It is exactly timed by the register rollers 17 and 18 and then fed toward the photosensitive drum 20.

While the transfer paper P passes through a gap between a transfer charger 33 and the photosensitive drum 20, the toner image on the photosensitive drum 20 is transferred onto the transfer paper.

After the transfer, the transfer paper is separated from the photosensitive drum 20 by a separation roller 1 9 and guided to a conveyor belt 35, which is provided with a paper pressing roller 34. The transfer paper is further guided to fixing roller pair 36 and 37 where it is pressed and heated to effect fixing. Then, it is ejected to a tray 40 by paper ejection rollers 38 and 39.

After the transfer, the surface of the photosensitive drum 20 is cleaned by a cleaner having an elastic blade 31 and then the next cycle starts. Numeral 46 denotes a blank shutter which selects an image exposure or a blank exposure to the photosensitive drum 20.

In order to detect a moving position of the optical system including the first mirror 3, the illumination lamp 22 and the second mirror 21 for exposing to and scanning the text, a photointerrrupter serving as a signal source is mounted at a fixed position.

The position of the photo-interrupter may be moved along the direction of movement of the mirror 3.

In order to time the copying operation, a timing disc 11 which is rotated in synchronism with a main motor, not shown, and a photo-interrupter 12 for detecting the rotation of the timing disc 11 are also provided. Signals from the photointerrupters 2 and 12 are supplied to a microcomputer, not shown, which controls the copying operation in response to the supplied signals.

Fig. 3 shows a schematic diagram of a signal generation unit in the movable optical system.

Numeral 1 denotes a light screen mounted on the movable mirror 3, numeral 2 denotes the photo-interrupter serving as the signal source fixed at a predetermined position, numeral 3 denotes the first mirror of the movable optical system, numeral 4 denote a wire for moving the mirror 3 on which the light screen 1 is mounted, numeral 5 denotes a wire pulley for driving the wire 4 and numerals 6, 7, 8 and 9 denote pulleys for guiding the wire 4. As the wire 4 is pulled by the rotation of the wire pulley 5, the mirror 3 is advanced (in the direction of an arrow F) or retracted (in the direction of an arrow B).

Fig. 4 shows a detail of the signal generation unit.

Numeral 1 denotes the light screen, numeral 2 denotes the photo-interrupter, numeral 22 denotes the illumination lamp, numeral 24 denotes the text table glass and numeral 44 denotes an illumination lamp table of the optical system which is moved on a rail 45 by the wire 4.

The light screen 1 comprises two plates as shown in Fig. 4, one being fixed to the illumination lamp table 44 while the other being movable along the direction of the movement of the mirror 3. Thus, by moving the movable plate the overall length of the light screen may be varied.

The operation of the signal generation by the photo-interrupter 2 is now explained.

In the present embodiment, a stationary text table type copying machine is explained, although a similar effect can be attained by a movable text table type copying machine.

The photo-interrupter 2 fixed at the predetermined position produces a LOW signal (hereinafter referred to as L) when the apparatus is powered on so that a predetermined voltage is supplied and an LED is turned on. As the copying machine operates and the movable optical system moves such that the light screen 1 mounted on the mirror 3 is positioned at the photo-interrupter 2, the LED is interrupted and the photo-interrupter 2 produces a HIGH signal (hereinafter referred to as H). Thus, the photo-interrupter signal S1 changes depending on the presence or absence of the light screen 1 in the photo-interrupter 2.

Fig. 5 shows a block diagram of a control circuit which receives the signal S1 of the photointerrupter 2 and a timing signal S2 derived from the timing disc 11 and the photo-interrupter 12, as control signals.

Numerals 2 and 12 denote the photointerrupters, S1 denotes the photo-interrupter signal from the photo-interrupter 2, S2 denotes the timing signal from the photo-interrupter 12, numeral 10 denotes a microcomputer, for example, uCOM44, numeral 4-1 denotes a register roller drive circuit, numeral 4-6 denotes a register solenoid SLl,numeral 4-2 denotes a blank shutter drive circuit, numeral 4-7 denotes a blank solenoid SL3, numeral 4-3 denotes a main motor drive circuit, numeral 4-8 denotes a main motor MM, numeral 4-4 denotes a forward clutch drive circuit, numeral 4-9 denotes a forward clutch CL1, numeral 4-5 denotes a backward clutch drive circuit and numeral 4-10 denotes a backward clutch CL2.

The photo-interrupter signal S1 and the timing signal S2 are applied to input terminals IN 1 and iN2 of the microcomputer 10 as shown in Fig. 5 and the microcomputer 10 responds to the input signals to control the operations of the register rollers 1 7 and 18, the blank shutter 46, the main motor MM, not shown, and the forward and backward clutches of the optical system in accordance with a control program prestored in a ROM of the microcomputer 10.

The respective controls are explained below in detail.

A first function of the photo-interrupter signal is a detection of the position of the movable optical system during an initialization operation which is carried out after the power on and before the copying operation starts. The initialization operation is referred to as an operation for preparing the copying machine to the copying operation, including the erasure of memory remaining on the drum, pre-heating of a heater and the detection of the position of the optical system. As described above, in order to start the copying operation, the optical system must be positioned at a predetermined position (hereinafter referred to as a home position). In a normal operation, the optical system is controlled and driven so that it returns to the home position at the end of the copying operation.However, the movable optical system may be stopped at non-home position when a trouble such as jam takes place or a power supply is turned off. In such a case it is necessary to return the optical system to the home position to prepare for the next copying operation, after the jam process has been completed or the power supply is turned on again. To this end, the position of the optical system is detected and returned to the home position when the power is turned on.

Fig. 6 shows a control flow chart of the microcomputer 10 for detecting the home position of the optical system when the power is turned on or during the initialization operation.

Fig. 7 shows a time chart of the operation for detecting the home position. In the following description, clock counts t1-t12 are based on the timing signal S2 from the photointerrupter 12.

In the present embodiment, the home position of the movable optical system or the first mirror 3 is at the position shown in Fig. 3. In a step 100, the copying machine is powered on. After a predetermined tl clock count in a step 101, the forward clutch CL1 is driven in a step 102 to advance the optical system in the direction of an arrow F to detect the position of the mirror 3. In this case, the optical system may take one of three positions when the forward clutch CLi is turned on, as described above. In the first case, the mirror 3 is off the photo-interrupter 2 toward the pulley 7 (including a case where the mirror 3 is at the home position), in the second case the mirror 3 is off the photo-interrupter toward the pulley 6, and in the third case the mirror 3 is on the photo-interrupter 2.The three mirror positions are detected in steps 103, 104 and 120. The first case where the light screen 1 is off the photointerrupter 2 toward the pulley 7 is first explained.

In the step 102, the forward clutch CLi is turned on and the optical system start to advance. The photo-interrupter signal S1 is L at this time and the process proceeds to a step 11 9. In the step 119, t2 clock is counted for a time to allow the light screen 1 advances from the home position of the optical system beyond the photo-interrupter 2. In a step 120, if the light screen 1 advanced during the t2 clock count interrupts the photointerrupter 2, the photo-interrupter signal S1 changes to H and the process proceeds to a step 1 04. In the step 104, if the advancing light screen 1 moves past the photo-interrupter 2 and the photo-interrupter signal S1 changes to L, the process proceeds to a step 105.In the step 105, the forward clutch CLi is turned off to stop the optical system, and the process proceeds to a step 106. In the step 106, t3 clock is counted, and in a step 107 the backward clutch CL2 is turned on to retract the optical system in the direction of the arrow B. The process then moves to a step 108. In the step 108, if the photointerrupter signal S1 changes to H, the process proceeds to a step 1 09. In the step 109, if the photo-interrupter signal S1 changes to L, the process proceeds to a step 110. In the step 110, the backward clutch CL2 is turned off to stop the optical system and the process proceeds to a step 111.In the step 111, t4 clock is counted and in a step 112 to forward clutch CL1 is again turned on to advance the optical system, and the process proceeds to a step 113.

In the step 113, t5 clock is counted and in a step 114 the forward clutch CLi is turned off to stop the optical system. The process then proceeds to a step 11 5. In the step 11 5, t6 clock is counted and in a step 11 6 the backward clutch CL2 is turned on to retract the optical system, and in a step 117, t7 clock is counted. In a step 118, the backward clutch CL2 is turned off to stop the optical system. Through the series of steps described above, the optical system including the mirror 3 is returned to the home position. (See time chart in Fig. 7A).

The second case where the light screen 1 is off the photo-interrupter toward the pulley 6 is now explained. In the step 102, the forward clutch CLI is turned on and the optical system starts to advance. The photo-interrupter signal is L at this time. Thus, the process proceeds from the step 3 to the step 119. In the step 119, t2 clock is counted and in the step 120 a change in the photo-interrupter signal is examined. Since the light screen 1 does not interrupt the photointerrupter 2 during the advancement, the photointerrupter signal remain L and the process proceeds to the step 105. In the step 105, the forward clutch CLi is turned off to stop the optical system and the process proceeds to the step 106. Thus, the timing of the turn-off of the forward clutch CL1 is different from that of the first case.The subsequent steps are same as those in the first case. (See time chart in Fig. 7B).

In the third case, the light screen 1 interrupts the photo-interrupter 2 when the power is turned on. In the step 102, the forward clutch CL1 is turned on to advance the optical system. The photo-interrupter signal S1 is H at this time, and the process proceeds from the step 103 to the step 1 04. In the step 104, if the photo-interrupter signal S1 changes to Las the optical system advances, the process proceeds to the step 105 and the forward clutch CL1 is turned off to stop the optical system, and the process proceeds to the step 106. The subsequent steps are same as those of the first case. (S;ee time chart in Fig. 7C).

Thus, by moving the optical system when the power is turned on to detect the position of the optical system and the optical system is controlled to return to the home position in accordance with the detected position.

A second function of the photo-interrupter signal S1 is the sequence control in the copying operation. A control flow chart therefore is shown in Fig. 8, and an operation time chart therefor is shown in Fig. 9.

In a step 127, when a copy start instruction is supplied by a user through a copy start button, not shown, t8 clock is counted in a step 128 and the main motor MM is energized in a step 129 so that the photosensitive drum 20 starts to rotate. In a step 130, t9 clock is counted and in a step 131 a paper feed solenoid SL2, not shown, is energized so that the transfer paper P is taken out of the cassette 13 by the paper feed roller 14. The transfer paper P passes through the conveyor rollers 15 and 1 6 and fed to the register rollers 17 and 1 8 where it is stopped. In a step 132, ti 0 clock is counted, and in a step 133 the forward clutch CL1 is turned on to scan the text so that the optical system starts to advance.In a step 1 34, if the photo-interrupter signal S1 changes to H as the optical system advances, the process proceeds to a step 135. In the step 135, the blank solenoid SL3 is energized to carry out the blank exposure and the process proceeds to a step 136.

In the step 136, if the photo-interrupter signal S1 changes to L, the process proceeds to a step 137.

in the step 137, the blank solenoid is deenergized and the process proceeds to a step 138. In the step 138, the register solenoid SL2 is turned on to drive the register rollers 1 7 and 1 8 for transferring the image on the photosensitive drum 20 with the transfer paper P being in registration therewith. A time point at which the photo-interrupter signal changes from H to L is used as a timing point.

Thus, the transfer paper P is fed to the transfer station in synchronism with the photosensitive drum. In a step 139, t1 1 dlock is counted and in a step 1 40 the forward clutch is turned off to terminate the seen of the text. In a step 141, the backward clutch is turned on to return the optical system to the home position. In a step 142, if the photo-interrupter signal S1 changes to H, the process proceeds to a step 143. In the step 143, if the photo-interrupter signal S1 changes from H to L, the backward clutch SL2 is turned off and the process proceeds to a step 145 where the copying operation is terminated The transfer paper P having the image transferred thereon is ejected to the paper ejection tray 40 through the fixing station 36 and 37.

As described above, during the copying operation, the photo-interrupter signal S1 controls the blank solenoid SL3, the register solenoid SL2, the forward clutch CL1 and the backward clutch CL2.

A third function of the photo-interrupter signal is the detection of errors in the movement of the optical system. The photo-interrupter signal S1 diagnoses two types of errors during the advancement and the retraction of the optical system or the mirror 3. An operation timing chart therefore is shown in Fig. 10.After the forward clutch CL1 has been turned on, if the photointerrupter signal S1 remains L for more than t1 2 clock count as shown in a step 134 of Fig. 8 (error type I) or if the photo-interrupter signal S1 remains H for more than t12 clock count after the photo-interrupter signal S1 has changed from L to H as shown in a step 104 in Fig. 6 and a step 136 of Fig. 8 (error type II), it is determined that an error has occurred in the optical system which otherwise is advancing, and the step 134 goes to a step 147 through a step 146, the step 104 goes to the step 122 through the step 121 and the step 136 goes to a step 149 through a step 148 so that all outputs are turned off to stop the copying machine.If the photo-interrupter signal S1 remains L for more than t1 2 clock count after the backward clutch CL2 has turned on as shown in the step 108 of Fig. 6 and the step 142 of Fig.

8 (error type Ill) or if the photo-interrupter signal S1 remains H for more than t12 clock count after the photo-interrupter signal S1 has changed from L to H as shown in the step 109 of Fig. 6 and the step 1 43 of Fig. 8 (error type IV), it is determined that error has occurred in the optical system which otherwise is retracting, and the step 108 goes to the step 124 through the step 123, the step 142 goes to the step 1 51 through the step 150, the step 109 goes to the step 126 through the step 125, and the step 143 goes to the step 1 53 through the step 1 52 so that all outputs are turned off to stop the copying machine.

As described above, the signal generated by the combination of the photo-interrupter 2 which detects the movement of the optical system or the mirror 3, and the light screen 1 has the functions of detecting and restoring the home position of the optical system, controlling the sequence of the copying operation and detecting the error in the movement. The length of the light screen is variable so that a required timing is obtained.

The above signal may be used as a plurality of different control signals depending on the operational conditions of the apparatus.

Accordingly, means for producing the signal in the apparatus is simplified and the image forming apparatus of low cost can be provided.

A light quantity controller for controlling a light quantity of an illumination lamp 22 in the copying machine of Fig. 2 to a desired level is now explained.

Fig. 11 shows a block diagram of one embodiment of a light quantity controller of the present invention.

Numeral 51 denotes a fluorescent lamp light source, numeral 52 denotes a photo-sensor for detecting light quantity of the light source 52, numeral 53 denotes a light quantity setter having a potentiometer for setting a desired light quantity of the light source 51, numeral 54 denotes a control circuit for controlling the light quantity of the light source 51 by input signals from the photo-sensor 52 and the light quantity setter 53, and numeral 55 denotes a H.F.

fluorescent lamp stabilizer which controls the energization of the fluorescent lamp of the light source 51 by a clock signal produced by the control circuit 54.

When a desired light quantity is set by the light quantity setter 53, the control circuit 54 provides the clock signal to the H.F. fluorescent lamp stabilizer 55 to attain the desired light quantity so that the H.F. fluorescent lamp stabilizer 55 causes the light source 51 to emit light in accordance with the clock signal. The photo-sensor 52 detects the light quantity of the light source 51 and supplies the detected signal to the control circuit 54. The control circuit 54 determines if the light source 51 emits the desired light quantity set by the light quantity setter 53, by the light amount detection signal from the sensor 52 which is indicative of the light quantity of the light source 51, and if the desired light quantity is not emitted, the clock signal to the H.F. fluorescent lamp stabilizer is corrected to attain the desired light quantity from the light source 51.Through the light quantity control described above, the desired light quantity set by the light quantity setter 53 can be attained from the light source 51.

Fig. 12 shows a detailed circuit diagram of the H.F. fluorescent lamp stabilizer 55 shown in Fig.

11.

Such a H.F. fluorescent lamp stabilizer 55 is commercially available and can be readily obtained. (For example, Tokyo Shibaura Electric Co. Ltd. 30TL-1 004). R1--R4 denotes fixed resistors, C1-C7 denote capacitors, DS-1 and DS-2 denote diode rectifiers, D1-D4 denote diodes, CH denotes a choke coil, TR1-TR3 denote transistors, PC denotes a photocoupler, T denotes a transformer, OT denotes an output transformer, IN 10 denotes an input terminal to be connected to the control circuit 54, and OUT10 denotes an output terminal to be connected to the light source 51.

Fig. 13 shows an operation timing chart of the circuit of Fig. 12. The operation is now explained with reference to the timing chart.

When the clock signal (of a frequency of approximately 1 KHz) is applied to the input terminal INlO (Fig. 3a) from the control circuit 54 (Fig. 11), the photo-coupler PC turns on and off in .

synchronism with the turn-on and the turn-off of the clock signal. The turn-on and the turn-off of the photocoupler PC determines the turn-on and the turn-off of the transistor TR4 and the turn-on and the turn-off of the transistor TR3. That is, the transistor TR3 turns on and off in synchronism with the turn-on and the turn-off of the clock signal to the input terminal IN 10 (Fig. 1 3b). A push-pull circuit comprising the transistors TR1 and TR2 oscillates while the transistor TR3 is on.

As it oscillates, a current flows to the output terminal OUT10 through the output transformer OT (Figure 13c) so that the light source 51 connected to the output terminal OUT10 is energized to emit the light (Fig. 1 3d). When the light source 51 is the flurorescent lamp, a substantially uniform light quantity is attained due to an afterglow characteristic of phosphor material even when the on-off interval of the energization is approximately one millisecond.

In the time chart of Fig. 13, a ratio of the on time (T-on) of the clock signal from the control circuit 54 to the off time (t-off) that is, a duty ratio is given by the following equation: (t-on) duty ratio= (t-o n) + (t-off) By changing the dury ratio, the energization time of the light source 51 (Fig.11) can be controlled.

That is, by changing the on time and the off time of the clock signal from the control circuit 54, the light quantity of the light source 51 can be controlled. (In an experiment, when the duty ratio was 10%, a tube current to the light source 1 was approximately 40mA, and when the duty ratio was 90%, the tube current was approximately 800mA).

Fig. 14 shows a detailed circuit diagram of the control circuit 54, the sensor 52 and the light quantity setter 53 of Fig. 11.

OP 1 -OP3 denote operational amplifiers, R8-R 1 6 denote fixed resistors, C7-C9 denote capacitors, Q1-Q2 denote IC's, VR1 and VR2 denote potentiometers, Vcc denotes a positive voltage source and OUT20 denotes an output terminal to be connected to the H.F. fluorescent lamp stabilizer 55.

The IC Q1 ,the fixed resistors R15 and R1 6 and the capacitors C8 and C9 forms an oscillation circuit which produces an oscillation output OUT-A shown in Fig. 1 5a. The oscillation output OUT-A is supplied to a tigger terminal 2 of the IC Q2. The IC Q2 operates as a monostable multivibrator and a duty ratio of the output clock signal OUT-B thereof is determined by the potentiometer VR2, the capacitor C7 and a voltage V,, applied to a control terminal 5. The voltage VIN is explained below.A setting voltage VS from the light quantity setter 53 for setting the light quantity of the light source 51 is applied to a 23 terminal of the operational amplifier OP2 which is a differential amplifier and the operational amplifier OP3 which is a summing circuit. The output of the sensor 52 is applied to a G) terminal of the operational amplifier OP2 through the operational amplifier OP 1 which is an amplifier. (An output of the operational amplifier OP1 is Vf).Assuming that a gain of the differential amplifier is G (which is in the order of 100200), the output voltage VD of the operational amplifier OP2 is given by VD=G(VsVf). The output voltage VD is supplied to the operational amplifier OP3 together with the setting voltage Vs from the light quantity setter 53 described above and the summing circuit of the operational amplifier OP3 produces the voltage VIN. (VIN=VS+VD and hence V1N=Vs+G(VsVf)).

In an experiment, when VIN (volts) and the positive voltage Vcc (volts) applied to the IC Q2 have a relation of V,,=Vcc--2 and the capacitor C7 and the potentiometerVR2 are selected such that the clock signal output OUT-B at the terminal OUT2 has a duty ratio of 85%, the clock signal OUT-B having a duty ratio of less than 10% as shown in Fig. 1 6b appears at the output terminal OUT2 when the voltage VIN is approximately one volt.

In this manner, by changing the output voltage VIN of the operational amplifier OP3 applied to the IC Q2, the duty ratio of the clock signal OUT-B at the output terminal OUT2 can be changed as desired.

Accordingly, by comparing the setting voltage Vs of the light quantity setter 53 with the output voltage Vf of the operational amplifier OP1 which amplifies the output of the sensor 52 which detects the light quantity of the light source 51, and amplifying the difference by the operational amplifier OP2, the output voltage VD is produced.

In the operational amplifier OP3, the output VD of the operational amplifier OP2 is added to the light quantity setting voltage Vs to compensate for the difference between the set light quantity and the actual light quantity in order to correct the output voltage VIN applied to the IC Q2. Consequently, the output to the H.F. fluorescent lamp stabilizer 55 and hence the duty ratio of the clock signal OUT-B is corrected in the IC Q2 by the output voltage VIN, and the duty ratio of the energization of the light source 51 is also corrected. As a result, the light source 51 can emit the preset light quantity.

By setting the gain G of the operational amplifier OP2 to be much greater than unity (G 1), the control circuit 54 changes the output VIN to the IC Q2 such that the light quantity setting voltage Vs and the output voltage Vf of the operational amplifier OP 1 which amplifies the output of the sensor 52 are always equal. Thus, the light quantity controller which allows the light source 51 to emit the desired light quantity set by the light quantity setter 53 is provided.

When the present light quantity controller is used to control the light quantity of the light source for scanning a text of an image forming apparatus, the light amount set by the light amount setter can be always emitted.

Consequently, the tone of the image formed is uniform and the image of any desired tone as set by an operator can be formed.

A control circuit shown in Fig. 17 includes an additional function of detecting the degradation of the light source, in addition to the control circuit shown in Fig. 14. The like numerals to those shown in Fig. 14 denote the elements of like functions and they are not explained here.

In Fig. 17, OP1--OP3 denote operational amplifiers, R8-R1 6, RT and RC denote fixed resistors C7--C10 and CT denote capacitors, Q1--03 denote IC's, VR1 and VR2 denote potentiometers, Vcc denotes a positive voltage source, LED denotes a light emitting diode, D denotes a diode and OUT2 denotes an output terminal to be connected to the H.F. fluorescent lamp stabilizer 5.

The iC Ql,the fixed resistors R15 and R16 and the capacitors C8 and C9 form an oscillation circuit which produces an oscillation output OUT-A as shown in Fig. 1 8a. The oscillation output OUT-A is supplied to trigger terminals 2 of the IC Q2 and the IC Q3.

Like in the circuit of Fig. 14, the light quantity is controlled to maintain the light quantity set by the light quantity setter 53.

Like the IC 02, the IC 03 operates as a monostable multivibrator, and the duty ratio of the output clock signal OUT-C thereof is determined by the resistor RT and the capacitor CT. The rise timings of the clock signals OUT-B and OUT-C of the IC Q2 and IC Q3 are synchronized with the oscillation output OUT-A of the oscillation circuit formed by the IC Q1 (See Fig. 18) The duty ratio of the clock signal OUT-C of the IC 03 is set, for example, to 70%. (This is an upper limit of the energization current of the light source). As a result, when the duty ratio of the clock signal OUT-B of the IC 02, that is, the clock signal OUT-B applied to the H.F.

fluorescent lamp stabilizer 55 exceeds 70% (as described above, the H.F. fluorescent lamp stabilizer 55 energizes the light source 51 in accordance with the duty ratio of the clock signal OUT-B), the current of the clock signal OUT-B flows to the IC Q3 through the light emitting diode LED, the diode D and the fixed resistor RC.

As shown in Fig. 18, when the duty ratio of the clock signal OUT-B from the IC Q2 is larger than that of the clock signal OUT-C which is preset to 70%, a current corresponding to a difference between the duty ratios flows through the light emitting diode LED so that the light emitting diode LED emits light to indicate to an operator that the duty ratio of the clock signal OUT-B from the IC Q2 is too large.If the duty ratio of the clock signal OUT-B from the IC Q2 is smaller than the preset 70% duty ratio of the clock signal OUT-C from the IC 03, the current corresponding to the difference between the duty ratios of the clock signals OUT-B and OUT-C is prevented from flowing through the light emitting diode LED because the diode D is connected in series with the light emitting diode LED. Accordingly, the light emitting diode LED does not emit light. In this manner, as the light source 51 degrades and the light quantity therefrom decreases, the output voltage Vf of the sensor 52 reduces and hence the output voltage VIN of the operational amplifier OP3 increases.Consequently, the duty ratio of the clock signal OUT-B from the IC 02 increases to exceed the preset duty ratio of the clock signal OUT-C from the IC 03. When this happens, the light emitting diode LED emits light so that the operator can identify the degradation of the light source 51.

In this manner, an error operation which apts to take place as the light source degrades in the automatic light quantity control circuit can be detected. It should be understood that the present invention is also applicable to a manual operation.

The light quantity controller of the present invention is applicable to not only the copying machine but also automatic light quantity control in an apparatus which requires a stabilized light quantity of the light source.

An input device for inputting information relating to the operation of the copying machine, such as instructions of number of copies, start of operation and stop of operation, is now explained.

Fig, 1 9 shows an embodiment of a control circuit which utilizes the input device of the present invention. Numeral 10 denotes a control unit having a counter function and a microcomputer having a ROM and a RAM, 0104 denote output ports, 11-14 denote input ports, R denotes a resistor, D denotes a diode, Vcc denotes a power supply and Ml -M20 denote switches. As shown in Fig. 10, a key matrix circuit is formed by the output ports 01-04 and the input ports 11-14 of the control unit 10, and the power supply is connected to the input ports Il- 14 through the switches M1, M6, Ml 1 and M16.

When the switch M1 is actuated, the power supply is connected to the input port 11 through the switch M1 so that a potential thereof is applied to the input port 11 as a HIGH signal.

Similarly, when the switches M6, Ml 1 and M16 are actuated, the HIGH signals are applied to the input ports 12, 13 and 14, respectively. In this manner, by actuating the switches M1, M6, Ml 1 and Ml 6, the signals similar to the HIGH signal generated by the actuation of the switches in the key matrix circuit are applied to the input ports 11-14.

Fig. 20 shows a control flow chart of the control unit 10 of the input device of the present invention. Control information is stored in the ROM of the control unit 10.

The operation will now be explained in detail with reference to Figs. 1 9 and 20.

In a step 10, the control unit is powered on and the control unit (CPU) 10 starts the operation. In a step 11, a counter of the control unit 10 is reset to zero and the process proceeds to a step 1 2. In the step 12, if the content n of the counter of the control unit 10 is no larger than 4, the process proceeds to a step 13, and if it is larger than 4, the process goes back to the step 11. Since the content n of the counter is O in this particular example, the process proceeds to the step 13. In the step 13, the output signals at the output ports 01-04 of the control unit 10 are rendered to LOW level and the process proceeds to a step 14.

in a step 14, if the content n of the counter of the control unit 10 is 0, the process proceeds to a step 16, and if it is not 0, the process proceeds to a step 1 5. Since the content n is O in this example, the process proceeds to the step 1 6. In the step 16, if the HIGH signal is being applied to the input port 11, the process proceeds to a step 21 where it is determined that the switch M1 is on and the key status is read into the RAM. If the HIGH signal is not being applied to the input port 11 , the process proceeds to a step 1 7. In the step 17, if the HIGH signal is being applied to the input port 12, the process proceeds to a step 22 where it is determined that the switch M6 is on and it is read into the RAM.If the HIGH signal is not being applied to the input port 12, the process proceeds to a step 18. In the step 18, if the HIGH signal is being applied to the input port 13, the process proceeds to a step 23 where it is determined that the switch Ml 1 is on and it is read into the RAM.

If the HIGH signal is not being applied to the input port 13, the process proceeds to a step 1 9.

In the step 19, if the HIGH signal is being applied to the input port 14, the process proceeds to a step 24 where it is determined that the switch Ml 6 is ON and it is read into the RAM. If the HIGH signal is not being applied to the input port 14, the process proceeds to a step 20. In the step 20, the content n of the counter is incremented by one. Since the content n of the counter is O in this example, the content n of the counter is set to 1 and the process goes back to &commat;). If the on-state of either one of the switches M1, M6, M1 1 and M 6 is detected in the step 21, 22, 23 or 24, the key status is read into the RAM to complete the first key scan and the process goes back to (!).When the count n of the counter is 0, the HIGH signal is not produced from any of the output ports 01- 04 and the HIGH signals at the input ports i 1 H4 due to the on/off states of the switches M1, M6, M1 1 and M 6 are determined. If the on-state of any of the switches M1, M6, M1 T and M1 6 is detected, the key status is read in to the RAM and the process goes back to the step 11 to determine the on/off state of the switches M1, M6, M1 1 and Ml 6 with the content n of the counter being 0.If the on-state is not detected for the switches M1, M6, Ml 1 and M16 when the content n of the counter is 0, the content n of the count is set to 1 and the process proceeds to the step 12. In the step 12, since the content n of the counter is 1 in this example and is smaller than 4, the process proceeds to the step 13. In the step 13, all outputs at the output ports 01--04 are rendered to LOW level and the process proceeds to the step 14. In the step 14, since the count n of the counter is 1, the process proceeds to the step 1 5.

In the step 15, the output at the output port 01 is rendered to HIGH level and the process proceeds to the step 1 6. In the subsequent steps, the input signal status of the input ports 11-14 are sequentially examined and the on/off states of the switches M2, M7, M12 and M17 are determined in the same manner as is done in the case that the content n of the counter is 0. If the on-state of the switch M2, M7 Ml 2 or Ml 7 is detected, the process goes back to (E) and the content n of the counter is set to O to determine the on/off states of the switches M1, M6, M1 1 and M 16 with the content n of the counter being 0.If the ON state of the switch M2, M7, M 12 or M 17 is not detected, the content n of the counter is set to 2 and the process goes back to &commat;). When the content n of the counter is 1, only the output port Ol produces the HIGH signal and the on/off states of the switches M2, M7, Ml 2 and Ml 7 are determined.Similarly, when the content n of the counter is 2, the on/off states of the switches M3, M8, M13, and M18 are determined, when the content n of the counter is 3, the orÇoff states of the switches M4, M9, Ml 4 and Ml 9 are determined, and when the content n of the counter is 4, the on/off states of the switches M5, MlO, Ml 5 and M20 are determined. When the content n of the counter is 5, the process goes back from the step 1 2 to the step 11 where the content n of the counter is again set to O to continue the detection of the on/off states of the switches.

In the input device which utilizes the prior art key matrix circuit, only (mxn) control information can be entered to the control unit, where m is the number of the output ports and n is the number of the input ports. In accordance with the present invention in which the power supply is connected to the input ports through the switches, ((m+i)xnl control information can be entered and there is no need for addition of a multiplexor circuit. Accordingly, the limited number of input/output ports of the control unit can be utilized economically and effectively.

While four output ports and four input ports have been shown in the illustrated embodiment, it should be understood that the same effect is attained when different number of ports are used.

It is not necessary to connect the power supply to all of the input ports through the switches, and the number of switches for entering the control information may be increased or decreased as required.

Fig. 21 shows an external view of an input panel when the input device of the present invention is embodied in a copying machine. K1, K2 and K3 denote reduced copy setting keys, K4 denotes an equal scale copy instruction/reduced copy release key, K5 and K6 denote upper and lower tray selection buttons, K7-Ki 6 denote numeric keys for setting the number of copies, K17 denotes a clear key for clearing the number set by the numeric keys K7--K 16, K18 denotes a stop key for interrupting the copying operation, K19 denotes an interruption copy key and K20 denotes a copy start key. The copying machine has many functions and the number of functions will increase in future. Accordingly, the number of control information to the control unit which controls the machine will increase.Consequently, a number of input/output ports are required in the control unit. In accordance with the present invention, the switching means or the keys can be added without adding the input/output ports, merely by connecting the power supply to the input ports through the switching means and altering the control information of the control unit 10.

While the power supply is connected to the additional switching means in the illustrated embodiment, the power supply may be replaced by signals other than those from the key matrix produced by the control unit, such as a latch signal for controlling the drive of a motor of the image forming apparatus. When the motor drive control signal is used, it is possible to inhibit the entry by the switch because the read-in of the status of the additional switches is in synchronism with the drive of the motor.

The switches Ml -M20 shown in Fig. 19 may be implemented by transistor switching means. Fig.

22 shows an embodiment in which a portion of the switches of Fig. 1 9 is replaced by the transistor switching means. TR 11 -TR 14 denote transistor. For example, when a voltage is applied to the switch My 6, the voltage is applied to a base of the transistor TR4 so that the transistor TR4 turns on. As a result, the same effect as that when the switch Ml 6 of Fig. 19 is on is attained.

A light quantity controller for setting a light quantity of the illumination lamp 22 in the copying machine of Fig. 2 is now explained.

In a copying machine of this type, an operator controls the light quantity of the tight source for exposing the image by manipulating copy density setting means of the machine such as a knob 64 of a copy density setter as shown in Fig. 23 so that the light quantity of the light reflected from the text and impinging to the photo-sensitive element is changed to set a desired density of the image reproduced on the transfer medium.

Fig. 24 shows a block diagram of a circuit for controlling the light quantity of the light source by the copy density setter. Numeral 61 denotes a light source, numeral 62 denotes a control circuit, numeral 63 denotes a density setter and numeral 70 denotes a light source. In such a circuit, when the light quantity of the light source 61 linearly changes relative to a control voltage Vc produced from the density setter 63, that is, when the control circuit 62 controls the amount of energization from the power supply 70 to the light source 61 linearly relative to the control voltage Vc applied to the control circuit 62 and the light quantity changes linearly relative to the amount of energization, and when the light from the light source 61 is directed to the CdS photosensitive element to produce a latent image and a copy is made in accordance with the latent image, a relation between the light quantity of the light source 61 and the copy density is not linear but logarithmic as shown in Fig. 25 because of a characteristic of the CdS photo-sensitive element to the light. In other words, the relation between the control voltage Vc and the copy density is not linear. Accordingly, if the control voltage Vc of the density setter 63 is linear relative to the change of the knob 64, a relation between the amount of movement of the knob 64 of the tone setter 63 and the change of the copy density is not linear.

This means that the operator finds a difference between a density setting of the copy density setter 63 having equi-spaced indices as shown in Fig. 23 and an actual copy density and feels it inconvenient.

The inconvenience due to the characteristic of the photo-sensitive element is also encountered in the photo-sensitive elements other than CdS photo-sensitive element.

Fig. 26 shows an embdodiment of the light quantity controller in accordance with the present invention. Numeral 61 denotes a light source, numeral 62 denotes a control circuit for linearly changing the light quantity of the light source 61 by a control voltage Vc, VR2 denotes a potentiometer having a linear characteristic, R20, R21 and R22 denote fixed resistor, Vcc denotes a positive voltage source, numerals 64, 65, 66 and 68 denote terminals, numeral 67 denotes a movable output terminal, numeral 70 denotes a power supply, and MP denotes a center point of the potentiometer VR2.A copy density desired by the operator is set by changing the control voltage Vc to the control circuit 62 by moving the output terminal 67 which is coupled to and movable with the knob 64 so that the control circuit 62 controls the amount of energization from the power supply 70 to the light source 61. As shown in Fig. 26, the terminal 64 at the center point MP of the potentiometer VR2 and the terminal 65 between the potentiometer VR2 and the fixed resistor R22 are connected in parallel with a portion of the potentiometer VR2 through the resistor R2 1. The fixed resistors R20 and R22 define a voltage across the terminals 66 and 65.

Assuming that a resistance between the terminal 66 and 68 of the potentiometer VR2 is 2r and a resistance of the resistor R21 is r21, a ratio of a changing rate AV66 when the output terminal 67 for the control voltage Vc, which is produced in accordance with the movement of the terminal 67 in the density setter 63, is moved between the center point MP and the terminal 66 to a changing rate AV68 when the output terminal 67 is moved between the center point MP and the terminal 68 is given by: r21 AV66/AV68=r/ r+r21 Consequently the relation between the position of the output terminal 67 and the control voltage Vc is represented by two-segment line as shown in Fig. 27 in which the changing rates changes at the center point MP in the range of movement of the output terminal 67.Thus, by using the relation in changing the control voltage Vc in accordance with the movement of the knob 64 in the density setter 63, the relation between the position of the knob 64 and the control voltage Vc can be approximated to a logarithmic function.

Accordingly, when this control voltage Vc is applied to the control circuit 62, the relation between the light quantity, which is determined by the amount of energization to the light source 61 which in turn is controlled by the control circuit 62, and the position of the knob 64 is similar to the relation between the position of the knob 64 and the control voltage Vc. Thus, by forming the latent image by the light quantity thus controlled and seiecting a relation between the copy density resulting from the latent image and the position of the knob 64 by appropriately setting the fixed resistors R20, R21 and R22 and the potentiometer VR2 of Fig. 26, an essentially linear relation is attained.

As described above, in accordance with the present invention, an essentially linear relation is attained between the setting position of the knob of the density setter and the copy density determined by the knob without requiring a potentiometer having a special resistance characteristic or a logarithmic amplifier.

The illustrated embodiment contemplates to attain the essentially linear relation between the copy density and the changed of the knob 64 over the entire range of movement of the knob 64 of the density setter. Alternatively, the range of the movement of the knob 64 which assures the linear relation may be restricted to a vicinity of index 5 which is most frequently used, shown in Fig. 23.

As described above, in accordance with the present invention a copy machine having a light quantity controller which is inexpensive and readily set by an operator is provided. The light quantity controller of the present invention can also be used in an exposure device of an illumination apparatus or a photographing apparatus in which control of light quantity is desired.

Claims (9)

Claims

1. An image forming apparatus comprising; a reciprocally movable member for forming an image on a record medium; means for reciprocally moving said reciprocally movable member, and control means for moving said reciprocally movable member and then setting said reciprocally movable member at a predetermined position before a first image is produced.

2. An image forming apparatus according to Claim 1 wherein said control means is operative to change the direction of the movement of said reciprocally movable member after said movement to set said reciprocally movable member to said predetermined position.

3. An image forming apparatus according to Claim 1 further comprising a sensor associated with the moving or setting operation.

4. An image forming apparatus according to claim 3 further comprising timer means for clocking in synchronism with said control means and means for determining an error if said sensor does not sense within a predetermined time.

4. An image forming apparatus according to Claim 3 further comprising timer means for clocking in synchronism with said control means and means for determining an error if said sensor does not sense within a predetermined time.

5. An image forming apparatus according to Claim 3 wherein said sensor is used to control the sequence for forming the image.

6. An image forming apparatus comprising; a movable member for forming an image on a record medium, and detection means for detecting the position of said movable member, said detection means being operable to control the return of said movable member to a predetermined position and the feed of said record medium.

7. An image forming apparatus according to Claim 6 wherein said movable member is a reciprocally movable member for scanning a text.

8. An image forming apparatus according to Claim 6 wherein said control of the return of said movable member to said predetermined position is effected before a first image is formed.

9. An image forming apparatus comprising: a movable member for forming an image on a rotating photosensitive body, and detection means for detecting a position of said movable member, said detection means controlling the feed of a transfer medium and the exposure to said rotating photo-sensitive body.

1 0. An image forming apparatus according to Claim 9 wherein said movable member is a reciprocally movable member for scanning a text.

11. A light quantity controller comprising; a light source adapted to emit light upon energization; means for detecting light quantity of said light source, means for generating a reference signal, means for comparing the light quantity detected by said detecting means with said reference signal, and means responsive to said compare means to control the energization to said light source, said reference signal generating means controlling said control means.

1 2. A light quantity controller according to Claim 11 wherein said control means controls a duty ratio of the energization to said light source.

1 3. A light quantity controller according to Claim 11 wherein said control means processes the output of said compare means and the output of said reference signal generating means.

1 4. A light quantity controller according to Claim 1 2 wherein said process is addition process.

1

5. A light quantity coritroller according to Claim 11 wherein said compare means differentially amplifies the output of said detection means and said reference signal.

1

6. A light quantity controller comprising; a light source adapted to emit light upon energization, control means for generating a signal to control the energization to said light source, and means for determining a status of said signal to detect the degradation of said light source.

1

7. A light quantity controller according to Claim 1 6 wherein said detection means includes means for generating a reference signal and compares said control signal with said reference signal to detect the degradation.

1

8. A light quantity controller according to Claim 1 6 wherein said detection means includes indication means for indicating the degradation of said light source.

1

9. A light quantity controller according to Claim 1 6 wherein said control means controls a duty ratio of said signal.

20. A light amount controller comprising; a light source adapter to emit light upon energization, means for detecting light quantity of said light source, means for setting a light quantity to be maintained by said light source, control means responsive to said detection means and said setting means for generating a first signal having a duty ratio to control the energization to said light source, means for generating a second signal having a predetermined duty ratio, and means for comparing to duty ratios of said first signal and said second signal to determine the degradation of said light source.

21. A key matrix type input device having a plurality of input ports and a plurality of output ports of a control unit inteconnected through switching means, comprising; means for supplying a signal independent from said output ports of the key matrix to at least one of said input ports through switching means.

22. A key matrix type input device according to Claim 21 wherein said control unit controls the operation of an image forming apparatus.

23. A copying machine comprising; exposure means for producing a copying image, copy density setting means, and means responsive to said copy density setting means for controlling the amount of energization to said exposure means, said control means being operative to maintain an essentially linear relation between setting of said setting means and copy density within a predetermined adjustable range of said setting means.

24. A copying machine according to claim 23 wherein said control means controls the amount of energization in accordance with an output voltage of said setting means.

25. A copying machine according to claim 23 wherein said setting means includes a potentiometer and a fixed resistor connected in partially parallel with said potentiometer.

26. A light quantity controller comprising; a light source adapted to emit upon energization, a control unit for controlling the light quantity of said light source by changing the amount of energization to said light source, a potentiometer for adjusting the light quantity, a fixed resistor connected in partially parallel to said potentiometer, and a variable voltage output terminal connected to said potentiometer, said control unit being responsive to the variable voltage from said variable voltage output terminal to control the light quantity of said light source.

27. An image forming apparatus substantially as hereinbefore described with reference to the accompanying drawings.

28. A light quantity controller substantially as hereinbefore described with reference to the accompanying drawings.

29. A key matrix type input device substantially as hereinbefore described with reference to the accompanying drawings.

New Claims or Amendments to Claims filed on 28 Jan 82 Superseded Claims 1-4 New or Amended Claims:

1. An apparatus for performing an image forming operation in which an image of an original is formed on a recording medium, the apparatus comprising: scanning means, including a reciprocal member and operable during a said image forming operation for scanning a said original; driving means for causing said reciprocal member to move reciprocally in a forward direction for original scanning and a reverse direction; and control means for controlling said driving means so as to position said reciprocal member in a predetermined position before the performance of an initial said image forming operation by a setting operation involving movement of the reciprocal member in both said forward and said reverse directions, said control means being arranged to determine as an improper state of the apparatus the failure of said reciprocal member to become so positioned in said setting operation.

2. An image forming apparatus according to claim 1 wherein the control means is arranged to cause the setting operation of said reciprocal member to the predetermined position to be initiated when a power switch of the apparatus is turned-on.

3. An image forming apparatus according to claim 1 further comprising a sensor associated with the moving or setting operation.