GB2097960A - An exposure controller for a copying machine - Google Patents

Abstract

A copying machine, which includes a light source (6) for supplying light used for the purpose of exposure, is provided with an exposure controller (3) which allows the intensity of the source (6) to be varied to adjust the optical density of the final copy. The source (6) is supplied with a voltage which is proportionally related to a selected optical density. The exposure controller (3) applies a voltage, which is different from a voltage to be established, upon initiating the illumination of the light source, in order to achieve a uniform rise time to the required light intensity which is independent of the selected optical density. <IMAGE>

Description

SPECIFICATION An exposure controller for a copying machine The invention relates to an exposure controller for a copying machine in which the amount of light supplied from an exposure light source is controlled to adjust the optical density of a copy image.

In a copying machine of the type in which a photosensitive member is exposed to a light image of an original while a light source used for exposure and movable optics, and the original, move relative to one another and the amount of light supplied from the light source is controlled to adjust the optical density of the copy image, the magnitude of the voltage supplied to the light source depends upon the adjustment of the optical density, resulting in a change in the rise time of the light amount supplied from the source.

Accordingly, the timing to initiate the activation of the light source is determined by the maximum value of the rise time. In a copying machine of the type described, the rise time will increase when a low voltage is applied to the light source, resulting in an insufficient amount of illumination supplied to the leading edge of the original. If this is compensated for by increasing the length of time allowed from the initiation of the light source to the illumination of the leading edge of the original, a reduction in the copying speed results.

Conversely, when the voltage applied to the light source is increased as a result of an adjustment of the optical density of the copy image, the rise time reduces to cause overheating and excess power dissipation due to unnecessary irradiation of parts other than the original.

According to the present invention there is provided an exposure controller for a copying machine including a light source which is used for the purpose of exposure and first means for varying a voltage applied to the light source and second means for controlling the magnitude of the voltage applied to the light source upon onset of operation of the light source, whereby substantially to suppress a change in the rise time of the light source resultant from the variation in the voltage applied to the light source by the first means.

The invention further provides an exposure controller for a copying machine in which a light source and an original to be copied move relative to one another to produce an optical image on a photosensitive surface comprising means whereby the optical density of the resultant copy can be adjusted by varying the voltage applied to the light source to set the light intensity, and means operable such that on selection of a particular density setting the appropriate voltage for the required light intensity is reached by applying to the source a related initial, timedependent, voltage which results in a substantially constant predetermined rise time before the required light intensity is reached irrespective of the value of the said appropriate voltage.

The invention also includes a method of controlling the exposure of a copy produced by a photocopying machine in which an original is illuminated by a light source of variable intensity to produce an image of the original on a photoconductive surface, the method comprising the steps of selecting a required optical density, supplying independence on the value of the voltage required to produce the intensity of the light source equivalent to the selected density, an initial time-dependent voltage to the light source which results in the rise time in which the source reaches its required intensity having a predetermined value.

In order that the invention may be understood some embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings in which: Figures 1 and 2 graphically show the rising response of the amount of light supplied from an exposure lamp or lamps; Figures 3(a) and 3(b) are graphs which illustrate the light output in response to various applied voltage; Figure 4 is a block diagram of an exposure controller; Figure 5 is a circuit diagram of one form of lamp regulator; Figures 6 to 8 are a chart a graphical illustrations for describing the operation of the lamp regulator of Fig. 5; Figure 9 is a circuit diagram of another form of lamp regulator; Figure 10 graphically shows the timing of operation of the lamp regulator of Figure 9;; Figure 11 is a plan view of one form of control panel for a copying machine fitted with an exposure controller; Figure 12 is a flow chart of a key control routine for adjusting the optical density of a copy; and Figure 13 is a flow chart of part of an operation sequence performed by a copying machine.

A copying machine usually employs a tungsten lamp as a light source to be used for the purpose of exposure. Figs. 1 and 2 illustrate the rise time of an amount of light supplied from such a light source as the voltage applied to the light source is manually changed to Vr, V2 or V3. In a copying machine of the type in which a photosensitive member is exposed to an optical image of an original while the light source and optics and the original move relative to one another, it may be assumed that the time at which exposure of the original is initiated by the movement of the light source and optics or the original coincides with the time at which the amount of light supplied from the light source achieves its final value, with a voltage V2 applied thereto, for example.When the voltage applied to the light source is changed to V3 in order to reduce the optical density of the copy image (dark image), there will be an insufficient amount of light supplied from the light source at the time when the leading edge of the original is to be exposed. Accordingly, the leading edge of the original is illuminated insufficiently so as to cause a non-uniformity in the optical density of the copy image in the region of the leading edge. Conversely, when the voltage applied to the light source is changed to Vr in order to increase the optical density of the copy image, the amount of light supplied from the source rises before the leading edge of the original is exposed, thus causing an unnecessary irradiation or heating of parts other than the original. In addition, the rush current increases to Produce noises.

To overcome these problems, a voltage different from a voltage which is used to establish a desired optical density is temporarily applied when activating a light source which is used for the purpose of exposure, in order to maintain a constant time interval from the initiation of activation of the light source to the completion of the rising of the light quantity.

Referring to Fig. 3, when the voltage which is chosen to provide a desired optical density is low, a high voltage is initially applied to the light source. On the other hand, when the voltage chosen to provide a selected optical density is high, the initial voltage applied to the light source is less than such voltage and is subsequently increased in a gradual manner.

Figure 4 shows a copying machine which is of the type in which a photosensitive member is exposed to a light image of an original during relative scanning of an exposure light source and optics and an original. A control unit 1 controls the entire copying machine, and may be formed by a microcomputer or the like. The machine also includes a control panel 2 which allows selection of a copy mode and the optical density of a copy image and provides a display of the machine conditions. A lamp regulator 3 of the type which is adapted to adjust the optical density of a copy image includes a digital-analog converter 4 and a regulator circuit 5, and receives a density control signal from the control unit 1 to generate and stabilize a voltage to be applied to an exposure lamp 6.When a particular optical density of a copy image is chosen by a user on the control panel 2, a corresponding signal is stored in the control unit 1 and is also displayed by the control panel 2. By way of example, when an optical density corresponding to a lamp voltage of V3 is chosen, at the initiation of a copying operation, a voltage higher than V3, for example, a density control signal corresponding to V2, for example, is produced at the output of the lamp regulator 3 in order to accelerate the rising change in the amount of light supplied from the lamp 6. The density control signal is subsequently switched stepwise or continuously to reduce the voltage applied to the lamp 6 to the value V3.Conversely, when the optical density of a copy image corresponding to a lamp voltage of V is chosen, the control unit 1 outputs a density control signal less than V1 and correspondsing to V2, for example, and the control signal is subsequently switched either stepwise or continuously to increase the voltage applied to the lamp 6 to the value V.

One form of the lamp regulator 3 is shown in Fig. 5. The regulator 5 includes an output voltage detector 5-1 formed by a feedback transformer T2 and diodes D17--D20. The output voltage supplied to the exposure lamp 6 is detected by the transformerT2, which steps it down and the diode bridge D17--D20 rectifies it for conversion into a d.c. voltage. The regulator also includes a comparison and control circuit 5-2 formed by a comparator IC1, transistor Q3, diodes Dl 1, D12, D15, D16, capacitors C5, C6, resistors R5--R8 and RAY2 1 -RAY26. It operates to convert an output voltage from the output voltage detector 5-1 into a control voltage Vc by means of the diode D15 and capacitor C6.The comparator IC1 compares the control voltage Vc against a reference voltage from the digital-analog converter 4 in order to provide a triggering phase control so that an output voltage corresponding to the reference voltage is developed for application to the lamp 6 as a phase control voltage. For example, when the output voltage supplied to the lamp 6 increases to thereby increase the control voltage Vc, the comparator IC1 produces a reduced output to thereby retard the triggering phase, thus preventing the output voltage to the lamp 6 from increasing. Conversely, when the reference voltage Vs from the digital-analog converter 4 increases, the comparator IC1 produces an increased output to thereby advance the triggering phase, allowing the output voltage to the lamp 6 to be increased.As the reference voltage Vs decreases, the output from the comparator IC1 also decreases, retarding the triggering phase to thereby reduce the output voltage supplied to the lamp 6.

A trigger circuit 5-3 is formed by programmable unijunction transistor PUT1 (hereafter referred to as PU transistor), transistors Q1, Q2, a pulse transformer PT1, diodes D6 D10, D13, D14, resistors R4, RAYl l-RAY16, and capacitors C3, C4, C13. A trapezoidal voltage is applied to the gate of the transistor PUT1 to reset it for each half-cycle of an a.c. source S.

When a trigger signal or a lamp illumination signal supplied from the control unit is off or assumes a floating H level, the transistor Q2 is turned on, preventing the capacitor C3 from charging. When the trigger signal assumes an on level or a low level which is approximately equal to zero volt, the transistor Q2 is turned off, allowing the capacitor C3 to begin charging. The capacitor C3 continues to be charged through the transistor Q1 to a level which is close to the output voltage of the comparator IC1, and then continues to be charged gradually through the resistor RAY13.

When the voltage across the capacitor C3 exceeds the gate voltage of the transistor PUT1, the latter is turned on. This allows the capacitor C3 to discharge through the pulse transformer PT1 , thereby turning a triac TRC on. When the comparator IC1 produces a high output, it takes a lesser time for the voltage across the capacitor C3 to exceed the gate voltage of the transistor PUT1, thus producing a trigger pulse at an earlier point in time. When the comparator IC1 produces a low output, it takes a longer time for voltage across the capacitor C3 to exceed the gate voltage of the transistor PUT1, whereby a trigger pulse is produced at a retarded phase.

A drive circuit 5-4 is formed by the triac TRC, diode D1, capacitors C1, C2, C15, resistor R1, contact Xl -1, coil L1 and a surge killer SK1. The triac TRC is turned on in response to a pulse from the pulse transformer PTl, thus supplying the voltage from the a.c. source to the exposure lamp 6. In the event the trigger signal continues to be present as a result of a failure of the control unit, or the exposure lamp 6 continues to be illuminated as a result of short-circuiting of the triac TRC, it is detected by a timer circuit 5-5, which operates to open the relay contact Xl -1 of a safety circuit, ceasing to supply the voltage to the exposure lamp 6.The capacitor C1 forms an extraneous noise filter, and the combination of the capacitor C2 and the coil L1 forms a filter which filters out noises produced by the triac TRC. The surge killer SK1 prevents an adverse firing of the triac TRC.

The timer circuit 5-5 is formed by a comparator 1C2, transistors O4-Q8, relay X1, diodes D2l- D28, capacitors C8--C12, C14, resistors R9, R10, RAY3 1--RAY3 5, RAY41-RAY44, RAYS 1--RAY54. An output from the output voltage detector 5-1 turns transistors Q8, Q7 on, whereby the transistor Q6 is turned off, allowing the capacitor C10 to begin charging. When the duration of the output from the output voltage detector 5-1 exceeds a time length determined by the time constant of the capacitor C10 and resistor R9, the output of the comparator IC2 assumes a low level, whereby the transistor Q4 is turned off to thereby deenergize the relay X1, opening its contact X1-l.Simultaneously, the transistor Q5 is turned on, and its output is supplied to the control unit.

A power supply circuit 5-6 is formed by a transformer Tl, diodes D2--D5, D8, resistors R2, R3, RAY27, Zener diodes ZD1, ZD2 and capacitor C7. The voltage supplied from the source S is transformed by the transformer T1 and is rectified by the diode bridge D2--D5, the resulting voltage being stabilized by the combination of the Zener diodes ZD1, ZD2 and the capacitor C7. The voltage developed at the anode of the diode D8 represents a trapezoidal voltage which resets the trigger circuit 5-3 for each half cycle.

The digital-analog converter 4 includes a decoder DEC which decodes an encoded signal from the control unit 1 to drive one of analog switches S1-Sn. These analog switches are connected to select part or all of a resistor network R1 1-R(1n-l) to provide a reference voltage which is supplied to the comparison and control circuit 5-2. The decoder DEC and the analog switches S1-Sn may comprise CMOS MC14051 as supplied from Motorola, for example. The decoder DEC can be omitted if the analog switches S1-Sn are directly driven by the control unit 1.

A control over the rise time of the exposure lamp 6 will now be described. A user chooses a particular optical density of a copy image on the control panel 2. When the optical density chosen is high, the lamp regulator 3 produces an output voltage of a reduced magnitude. In this instance, the lamp 6 will have a longer rise time, and the control unit 1 reduces the rise time by providing a control such that a high output voltage is supplied immediately after the trigger signal is turned on.

By way of example, assume that an output voltage corresponding to the optical density chosen is equal to 55 volts. In response to the trigger signal, the output voltage is sequentially changed in the manner of 70 e 67 o64 o61 o58 at 55. Fig. 6 shows the relationship between the density control signal from the control unit 1 and the activated analog switch or the output voltage chosen. As shown, there are fifteen levels designated by No. 1 to No. 15. The control unit 1 operates to change the density control signal in the manner from No.8 -t No. 7 -t ... No.4. No.

3. Fig. 7 graphically shows a corresponding timing chart.

When the particular optical density chosen is bright, or when an output voltage corresponding to the optical density chosen is equal to 85 volts, the output voltage is sequentially changed in the mannerof70e73e76e79e82e85voltsin response to the trigger signal. At this end, the control unit 1 successively changes the density control signal in the manner of No. 8 No. < . . .

No. 12 at No. 13. Fig. 8 graphically shows a corresponding timing chart.

In the described arrangement, the rise time of the lamp 6 has been maintained constant.

However, it is also possible to increase the voltage applied to the lamp stepwise or continuously by changing the density control signal in combination with a "soft start technique" which is commonly used in order to suppress the rush current of the lamp 6.

Fig. 9 shows another form of lamp regulator 3 which is adapted to adjust the optical density. In this arrangement, the rise time is internally controlled, and the density adjustment is vacated and an output voltage of a constant magnitude is produced for a given time interval after the initiation of lamp activation. A principal difference between this arrangement and that shown in fig.

5 can be stated as follows: In the arrangement of Fig. 5, the density control signal is utilized by the control unit 1 to control the rising time of the lamp 6 in a software manner. By contrast, in the arrangement of Fig. 9, the regulator 5 includes hardware which operates as a rising time control circuit 7, which is activated for a given time interval in response to the trigger signal. Thus, in this arrangement, the functioning of the control unit 1 is reduced. Another difference relates to the insulation between the primary circuit to which 100 volt a.c. is applied and the secondary circuit connected to the control unit. In Fig. 5, the transformers T1, T2 and the pulse transformer PT1 have been used.But in the arrangement of Fig. 9, the regulator circuit is incorporated into the primary cirucit, and a photoconductor is provided in the interface to provide an isolation between the primary and secondary circuit while allowing the trigger signal and the density control signal to be transmitted therebetween. Reference character IC3 shown in Fig. 9 represents an integration of the functions performed by the blocks 5-1,5-2 (partially), 5-3 and 5-5 shown in Fig. 5, and the basic functions of the various components are essentially the same as those illustrated and described above in connection with Fig. 5.

In the arrangement of Fig. 9, a digital-analog converter 4 is formed by photocouplers PC1- PC6, decoder DEC2, analog switches Sl1-S18, diodes D29, D30 and resistors R21-R41. A density control signal from the control unit 1 is fed through the photoconductors PC3-PC6 to the decoder DEC2, which decodes it to select one of the analog switches Sll-Sl8 to select a particular resistance presented by the resistor network R32-R41,thus establishing a reference voltage Vs.A comparison and control circuit 5-2 is formed by operational amplifiers Al, A2, a constant current source CCl,transistor Q9, diodes D31, D32, capacitors Cm 6, Cm 7, resistors R42-R56, RAY6 1 and inverter N 1. It responds to the trigger signal which turns the photocoupler PC1 on, by deriving a difference between an output from the output voltage detector 5-1 and the reference voltage Vs and controlling the firing position of triacs TRCl , TRC2 so that an output voltage corresponding to the density control signal is developed for application to the lamp.When the reference voltage Vs is low, the triacs TRC1, TRC2 are fired at an advanced phase, increasing the output voltage supplied to the lamp 6. Conversely, when the reference voltage Vs is high, the triacs TRC1, TRC2 are fired at a retarded phase, decreasing the output voltage to the lamp 6.

The rising time control circuit 7 is formed by transistors Ql 0-Qi 3, capacitors C19, C20, diodes D34, D35 and resistors R58-R66. When the photocoupler PC1 is turned on by the trigger signal, the transistor Q12 is turned off as is the transistor Q1 1, thus rendering the transistor Q10 non-conductive to maintain the transistor Q13 off for a time interval T determined by the time constant of the resistor R58 and capacitor Cl 9, thus vacating the analog switch circuit within the digital analog converter 4 which produces the reference voltage in accordance with the density control signal. Accordingly, the reference voltage Vs assumes its minimum value, increasing the output voltage supplied to the lamp 6 to its maximum value.After the time T has passed, the transistor Q13 is turned on to render the analog switch circuit effective, whereby an output voltage is produced which corresponds to the density control signal. Fig. 10 graphically shows a corresponding timing chart. In the example shown, the rising time of the lamp which results from the maximum value of the output voltage supplied to the lamp 6 is chosen as the basis, and the output voltage to the lamp 6 is controlled to a high value in order to reduce the rise time whenever the trigger signal is applied.

An output voltage detector 5-1 is formed by operational amplifiers A3-A5, diodes D36 D38, resistors RAY62-RAY66, and a constant current source CC2. The purpose of the detector is to detect an output voltage supplied to the lamp 6. A trigger circuit 5-3 is formed by operational amplifiers A6-A8, transistors Q14- Q1 6, constant current sources CC3--CC5, diodes D33, D39-D49, resistors R57, RAY67 and capacitor C18. It triggers triac TRC2 in a drive circuit 5-4 in response to the output signal from the comparison and control circuit 5-2.The drive circuit 5-4 is formed by triacs TRC1 , TRC2, capacitors C21-C25, coil Ll, relay contactXl-1, and resistors R58-R62. The drive circuit is triggered by an output signal from the trigger circuit 5-3 to provide a phase control over the voltage applied to the lamp 6. A timer circuit 5-5 is formed by operational amplifiers A9, Al 0, NOR circuit NOR, transistors QI 7-Q26, constant current sources CC6-CC9, photocoupler PC7, relay X1, diodes DSO-D59, inverter N2, resistors RAY68--RAY70, R63-R68, and capacitors C26, C27.In response to a prolonged on-condition of the trigger signal or a short-circuiting of triacs TRC1, TRC2, the timer operates to cease the supply of the voltage to the lamp 6. A power supply circuit 5-6 is formed by Zener diodes ZD3, ZD4, diodes DSO-D64, capacitors C28-C3 1 and resistors R69-R65, and operates to convert a voltage from the source S into a corresponding d.c. voltage and effects a voltage stabilization.

These circuits 5-1, 5-3 to 5-6 function in the similar manner as described above in connection with Fig. 5.

Fig. 11 shows a control panel used in a copying machine. As shown, the control panel is provided with various keys including a set of keys 11 which are utilized to preset a desired number of copies, a pair of cassette selection keys 12 which are used to select a cassette of a desired size, a pair of magnification selection keys 1 3 which allow a choice between a unity magnification and a reduced magnification operation, an interrupt key 14 which instructs an interrupt copy mode, a pair of density adjusting keys 1 5 including a light key 15a and a dark key 1 sub which are used to establish a desired optical density of a copy image, a clear/stop key 1 6 for resetting the number of copies to unity and for interrupting a copying operation, and a print key 17 which instructs the initiation of a copying operation. It will be noted that these keys are arranged in a manner to facilitate their operation. In addition, the control panel is provided with display means in the form of a number of copy display 18 which indicates the number of copies to be produced, another number of copy display 1 9 which indicates the number of copies which have already been produced, a pair of size displays 20 which indicate the size of transfer sheets which are loaded in the upper and the lower cassette, a pair of lights 21 which are selectively lit to indicate a selected magnification, an interrupt indicator lamp 22 which is lit when an interrupt mode is established, a density indicator 23 which indicates a sequential grade of the optical density of a copy image established, and an abnormality indicator 24.The print key 1 7 is formed as a switch which is automatically illuminated to provide a green indication whenever a copying operation is possible and a red indication whenever a copying operation is disabled.

Fig. 12 is a flow chart showing a density adjusting key control routine performed by the control unit 1. Each time either the dark key 1 sub or the light key 1 5a is depressed, the control unit 1 increments or decrements data representing a density control signal and stored in a four-bit register L by one. The data stored in the register L are binary data representing a numeral from 1 to 1 5. In the event either key 1 spa or 1 sub is held depressed, the data in the register L are decremented or incremented for each time interval of 0.3 second.

Fig. 13 is part of a flow chart representing an operational sequence performed by the copying machine incorporating the lamp regulator shown in Fig. 5. The control unit 1 initially determines if the machine is ready to initiate a copying operation, and produces an indication that a copying operation is enabled or disabled. If the machine is ready to initiate a copying operation and the print key 1 7 is depressed, a copying sequence is initiated by turning a drive motor and a cleaner solenoid on. When the drive motor is energized, a photosensitive drum is set in motion, and a pulse generator produces pulses in synchronism with the rotation of the drum. The resulting pulse is counted, and when a count of 65 is reached, the control unit output "8" corresponding to a standard exposure, as a density controlling output supplied to the exposure lamp 6. Subsequently, the density controlling output is either incremented or decremented by one for each time interval of 50 milliseconds, and when the density controlling output becomes equal to data stored in the register L, namely, the density control signal, which is established by the depression of the key 15, the control unit proceeds to the following step.

Claims (11)

Claims

1. An exposure controller for a copying machine including a light source which is used for the purpose of exposure and first means for varying a voltage applied to the light source and second means for controlling the magnitude of the voltage applied to the light source upon onset of operation of the light source, whereby substantially to suppress a change in the rise time of the light source resultant from the variation in the voltage applied to the light source by the first means.

2. An exposure controller as claimed in claim 1, in which the first means comprises operating means which is used to adjust the optical density of a copy image, and voltage regulator means for adjusting the voltage applied to the light source in response to a signal from the operating means, the second means comprising control means for applying a voltage which is different from that established by the voltage regulator means to the light source for a given time interval from the onset of operation thereof.

3. An exposure controller as claimed in claim 2, in which the control means serves gradually to change the voltage applied to the light source from a given value to the voltage established by the voltage regulator means.

4. An exposure controller for a copying machine in which a light source and an original to be copied move relative to one another to produce an optical image on a photosensitive surface comprising means whereby the optical density of the resultant copy can be adjusted by varying the voltage applied to the light source to set the light intensity, and means operable such that on selection of a particular density setting the appropriate voltage for the required light intensity is reached by applying to the source a related, initial, time dependent voltage which results in a substantially constant predetermined rise time before the required light intensity is reached irrespective of the value of the said appropriate voltage.

5. An exposure controller as claimed in claim 4, in which a means for applying the initial voltage comprises means for applying a fixed voltage and subsequently stepping ths voltage in a discrete manner towards the appropriate voltage for the required light intensity.

6. An exposure as claimed in claim 4, in which a means for establishing the appropriate voltage for the required light intensity is inhibited from applying that voltage for a fixed time interval during which a predetermined voltage at least equal to that appropriate to the highest optical density selectable is supplied to the light source.

7. An exposure controller as claimed in any one of claims 4 to 6, in which means for selecting the required optical density comprises a digital to analogue converter which outputs the appropriate voltage for supplying to the light source in response to an input keyed from a control panel of the copying machine.

8. An exposure controller substantially as herein described with reference to any of the accompanying drawings.

9. A copying machine incorporating an exposure controller as claimed in any one of the preceding claims.

10. A method of controlling the exposure of a copy produced by a photocopying machine in which an original is illuminated by a light source of variable intensity to produce an image of the original on a photoconductive surface, the method comprising the steps of selecting a required optical density, supplying, in dependence on the value of the voltage required to produce the intensity of the light source equivalent to the selected density, an initial time-dependent voltage to the light source which results in the rise time in which the source reaches its required intensity having a predetermined value.

11. A method of exposure control for a photocopying machine substantially as herein described with reference to any of the accompanying drawings.