JP2014060629A - Light source system, image reading device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption while supplying stable power to a plurality of light source elements constituting a light source unit without generating noise.SOLUTION: A light source unit 1 includes a plurality of LED arrays 11 in which a plurality of LEDs 11a are connected in series; a constant input voltage Vin is applied to each of the plurality of LED arrays 11 of the light source unit 1; and a constant current Ic is caused to flow in each of the LED arrays 11 by a constant current source 2 so as to drive each of the LEDs 11a. Voltages of connections between each of the plurality of LED arrays 11 and the constant current source 2 are detected, so as to switch between a first state in which the number of serially connected LEDs 11a of each of the LED arrays 11 is larger than the number of the LED arrays 11 and a second state in which the number of LED arrays 11 is larger than the number of serially connected LEDs 11a of each of the LED arrays 11, by switches S1 and S2 according to the detected voltage level.

Description

  The present invention relates to a light source system, an image reading apparatus including the light source system, and an image forming apparatus including the image reading apparatus.

As a light source of an image reading apparatus such as a scanner apparatus, a light source using a light source in which a large number of LEDs (light emitting diodes) having a large energy saving effect compared to a conventional Xe (xenon) lamp or the like is arranged in an array is known. .
When a large number of LEDs are driven, the following two types of methods are generally put into practical use as a method for generating power to be supplied to each LED.
(1) Power generation method for supplying input voltage after voltage conversion by a DC / DC converter or the like by buck-boost switching (2) Method for directly supplying the voltage of the reference power supply

Each power supply system has the following advantages and disadvantages.
The power generation method using the step-up / step-down switching can generate an arbitrary power supply voltage. Therefore, there is an advantage that power consumption can be minimized.
However, the influence of switching noise is inevitable, and there is a demerit that the influence may spread over a wide range, for example, the influence on peripheral circuits and the emission of noise to the outside of the machine.
On the other hand, the method of directly supplying a reference power supply (+ 24V or the like) does not generate switching noise or ripple, and can stably supply power. Further, there is an advantage that the configuration is simple and can be easily implemented.
However, in consideration of variations in the forward voltage of the LED, it is necessary to always apply a voltage that can be driven even when the forward voltage of the LED is assumed to be the largest. For this reason, there is a demerit that power consumption in the standard state becomes larger than necessary.

As described above, each power supply method has advantages but disadvantages, and there is a problem that measures such as radiation noise and local power consumption (heat generation) are required.
Further, as a conventional light source system, for example, there is one disclosed in Patent Document 1. The light source system aims to reduce power consumption in LED driving. Then, the sum of the forward voltages of the plurality of LEDs connected in series is detected, and the switching control of a plurality of power sources having different supply voltages is automatically performed according to the detected voltage. Thereby trying to reduce the power loss in the LED.

However, in this light source system, it is necessary to generate a plurality of power supplies having different supply voltages. Therefore, it is assumed that each power source is generated by either the step-up / step-down switching system or the series regulation system.
In that case, according to the step-up / step-down switching system, the switching circuit must be configured by the required number of power supplies, so that there is a problem that the occupied area becomes wide and a plurality of sources of switching noise are generated.

In addition, according to the series regulation method, a necessary power supply voltage is generated due to heat loss, so generation of wasteful power consumption is inevitable. Therefore, even when compared with the conventional method of directly supplying the reference power supply, the power consumption in the LED constituent unit (constant current source unit) is merely transferred to the power generation unit. Therefore, the power consumption of the entire LED drive system is not substantially reduced.
In any case, the disadvantages of the conventional power generation method are not eliminated.

  The present invention has been made in view of the above points. A constant voltage is applied to a light source section provided with a plurality of light source element arrays in which a plurality of light source elements are connected in series, and a constant current is applied to each light source element array. In a light source system that drives each light source element by supplying a constant current depending on the source, it is possible to reduce power consumption even in a standard state, and stable to a plurality of light source elements constituting the light source unit without generating noise An object is to reduce power consumption while supplying power.

  In order to achieve the above-described object, the present invention provides a light source unit provided with a plurality of light source element columns in which a plurality of light source elements are connected in series, and a plurality of light source element columns of the light source unit to which a constant voltage is applied, In a light source system comprising a constant current source for driving each light source element by flowing a constant current, voltage detecting means for detecting a voltage at a connection portion between each of the plurality of light source element arrays and the constant current source, Each of m and n is an integer greater than or equal to 2 such that m> n, and the configuration of the light source unit is determined according to the level of the voltage detected by the voltage detection means, and the number of light source elements for each light source element array is m. A first state in which the number of light source element rows is n, and a second state in which the number of light source elements for each light source element row is n and the number of light source element rows is m. And a configuration switching means for switching between.

  In the light source system according to the present invention, the voltage at the connection portion between each of the light source element rows of the plurality of rows constituting the light source section and the constant current source, that is, the voltage that changes depending on the sum of the voltage drop by each light emitting element for each light source element row. Depending on the detected voltage level, the number of light emitting elements in each light source element array constituting the light source unit and the number of light source element arrays can be switched. Therefore, it is not necessary to give a sufficient margin to the supply voltage of the power source, and the power consumption can be reduced by switching to an arrangement of light source elements suitable for the voltage drop state of each light source element array. That is, it is possible to reduce power consumption while supplying stable power to each light source element constituting the light source unit. In addition, since no switching circuit is used for power generation, no noise is generated.

It is explanatory drawing which shows the example of a switching of the structure state of the light source part in the light source system by this invention. It is a circuit diagram which shows the example of the switching circuit for switching the structure of the light source part to a 1st state and a 2nd state. FIG. 3 is a circuit diagram illustrating the configuration when each switch illustrated in FIG. 2 is in a switching state illustrated in an easy-to-understand manner. FIG. 3 is a circuit diagram showing the configuration when each switch shown in FIG. 2 is in a switching state opposite to that shown in the figure.

FIG. 3 is a circuit diagram illustrating a specific configuration example of each switch in FIG. 2 and a circuit that controls switching thereof. FIG. 3 is a circuit diagram illustrating another specific configuration example of each switch and a circuit that controls the switching in FIG. 2. FIG. 6 is a circuit diagram of an example in which a circuit for maintaining and releasing the state holding function is added to the switch drive / latch circuit.

FIG. 3 is a circuit diagram corresponding to FIG. 2, showing another embodiment of a light source system according to the present invention.

1 is an overall configuration diagram showing a mechanism part of an embodiment of an image reading apparatus according to the present invention. FIG. 2 is a block diagram showing a configuration example of a part of an image signal processing unit of the image reading apparatus. 1 is an overall configuration diagram showing a mechanism part of an embodiment of an image forming apparatus according to the present invention.

Hereinafter, embodiments for carrying out the present invention will be specifically described with reference to the drawings.
[Embodiment of Light Source System]
First, an embodiment of a light source system according to the present invention will be described. Prior to that, an outline thereof will be described.

A light source system (apparatus) that is an object of the present invention includes a light source unit provided with a plurality of light source element arrays in which a plurality of light source elements are connected in series, and a plurality of light source element arrays of a light source unit to which a constant voltage is applied. And a constant current source for driving each light source element by passing a constant current.
In the following description, all examples will be described using light-emitting diodes (hereinafter referred to as “LEDs”) as light source elements. However, the present invention is not limited to this, and other semiconductor light emitting elements or other light emitting elements may be used.

FIG. 1 is an explanatory diagram showing an example of switching the configuration state of the light source unit in the light source system according to the present invention.
In this example, in the normal state (standard state), the light source unit 1 is configured in a first state in which five LED rows 11 in which six LEDs 11a are connected in series are provided as shown in FIG. doing. This is referred to as a “6 series × 5 column” configuration.
The anode side of each LED row 11 of the light source unit 1 is commonly connected, and a constant voltage is applied thereto from a reference power source. This voltage is set as the input voltage Vin. The cathode side of each LED row 11 is individually connected to the constant current source 2. Then, the constant current source 2 supplies a constant current Ic to each of the five LED rows 11, and drives each LED 11a to light it.

  And the voltage of the connection part c with the cathode side of each LED row | line | column 11 of this light source part 1, ie, the constant current source 2, is detected. When the voltage falls below a predetermined value, the configuration of the light source unit 1 is set to five LEDs 11a connected in series in each LED row 11 as shown in FIG. Switch to the 6th row in the 2nd state. This is referred to as a “5 × 6 columns” configuration. This is because the five LEDs 11a surrounded by the broken line in the first state shown in FIG. 1A are surrounded by the broken line in the second state shown in FIG. That is, each LED row 11 in the row is changed.

Therefore, the voltage drop in each LED array 11 which is the sum of the forward voltages of each LED 11a is reduced by the amount of the LEDs 11a connected in series constituting the LED array 11, and the connection with the constant current source 2 is reduced. The voltage of the part c rises. Thereby, even when the forward voltage of each LED 11a is large, it becomes possible to drive each LED 11a normally by supplying a constant current Ic to each LED row 11.
In any state, since the number of LEDs 11a constituting the light source unit 1 is not changed by 30, the light emission quantity as a whole of the light source unit 1 does not change.

  The power consumption as this light source system is calculated by the input voltage Vin × the input current Iin. Since the input voltage Vin is a constant voltage supplied from the reference power supply and the current Ic for each LED column 11 is also constant, “power consumption = input voltage Vin × Ic × the number of columns in the LED column 11”. Therefore, the power consumption in the first state shown in FIG. 1A is 5 rows / 6 rows≈83 with respect to the power consumption in the second state shown in FIG. .3%, about 17% less.

As described above, in the light source system according to the present invention, in the light source system in which a voltage is directly applied from the reference power source to the light source unit, the configuration of the light source unit is the first state described above in the standard state where the occurrence frequency is high and the standard state. Thus, power consumption can be reduced.
Since no switching circuit is used for power generation, no noise is generated and there is no adverse effect on peripheral circuits.
Further, since the switching target is only the connection of the voltage and current supply lines to the LEDs as will be described later, there is no electrical drive condition of each LED or physical switching of the LED to be lit, and the optical system of the illumination system. It does not affect the properties.

In the example shown in FIG. 1, the number of light source elements for each light source element array is six, the number of light source element arrays is five, and the number of light source elements for each light source element array is five. In the second state, the number of light source element arrays is five and the number of light source element arrays is six.
When this is generalized, the first number in which m and n are each an integer of 2 or more such that m> n, the number of light source elements for each light source element array is m, and the number of light source element arrays is n. The state and the second state in which the number of light source elements for each light source element array is n and the number of light source element arrays is m may be switched.

Normally, when the light source unit 1 is driven in the first state where the number of series is large and the number of parallels is small, and the voltage at the connection portion c between each LED row 11 and the constant current source 2 becomes less than a predetermined value, It is desirable to switch to the second state where the number of series is small and the number of parallel is large.
However, when driving in the first state, when the voltage at the connection portion c between each LED row 11 and the constant current source 2 becomes greater than or equal to a predetermined value due to a change in use environment or a change in power supply voltage, It is also possible to switch from the second state to the first state.

A specific embodiment of a light source system (apparatus) according to the present invention will be described below.
FIG. 2 is a circuit diagram showing an example of a switching circuit for switching the configuration of the light source section between the first state and the second state as described above. In FIG. 2 and FIGS. 3 to 8 to be described later, portions corresponding to those in FIG.

  In this example, one LED 11a on the side connected to the constant current source 2 of each of the plurality of LED rows 11 of the light source unit 1 is cut off. Then, changeover switches (hereinafter simply referred to as “switches”) S1 and S2 are inserted between the one LED and the immediately preceding LED and between the constant current source 2 and connected as shown in the figure. . Each changeover switch S1, S2 has a movable contact C and two fixed contacts A, B.

  Each switch S1, S2 is in a state in which the movable contact C is connected to the fixed contact A (A: ON, B: OFF) and a state in which the movable contact C is connected to the fixed contact B (B: ON, A: OFF). Switch. Thereby, the configuration of the light source unit 1 is switched. The switching operations of the switches S1 and S2 are all linked, and A: ON and B: ON are not partially mixed.

Each switch S1, S2 is normally in the switching state of A: ON and B: OFF as shown in FIG. 2, and as shown in FIG. 3, it is easy to understand. This state is the same as the first state of 6 × 5 columns shown in FIG.
When the respective switches S1 and S2 are switched to B: ON and A: OFF, it becomes easy to understand in FIG. This state is the same as the second state of 5 × 6 columns shown in FIG. At this time, five LEDs 11a separated from the five LED rows 11 are connected in series to form a sixth LED row 11 ′.
In this manner, each switch can be easily switched between the first state and the second state by interlocking switching of S1 and S2.

  In this way, since only the driving configuration is switched without changing the LED to be driven by the light source unit 1, the optical characteristics are not affected before and after the switching, and only the power consumption can be optimized. This switching is performed based on the voltage level of the connection portion of each LED row 11 with the constant current source 2 on the cathode side when the light source unit 1 is driven.

FIG. 5 is a circuit diagram showing a specific configuration example of each switch in FIG. 2 and a circuit for controlling the switching.
In FIG. 5, 3 is a minimum voltage detection circuit, 4 is a switch drive / latch circuit, and 5 is a switch circuit.

The minimum voltage detection circuit 3 includes the cathode terminals of six diodes D1 each having an anode terminal connected to a point a to which an input voltage Vin from a reference power supply is applied through a resistor R1, and each LED array 11 and constant current source 2 Are connected to six lines L1 to L6.
Each of the lines L1 to L6 is connected to the cathode side end of each LED row 11 and the constant current source 2 in the light source unit 1 shown in FIG. 2, that is, the movable contact C and the constant current source 2 of each switch S2. It is a line that connects However, only the line L6 is effective only when the sixth LED row 11 'is formed in the second state shown in FIG.

When the diode D1 whose cathode terminal is connected to the line with the lowest voltage among the lines L1 to L6 (only when L6 is valid) among the lines L1 to L6, the minimum voltage detection circuit 3 has the lowest voltage at the point a. It becomes almost the same. For this reason, the diode D1 whose cathode terminal is connected to a higher voltage line is reverse-biased and thus becomes non-conductive. Therefore, the minimum voltage (more precisely, the minimum voltage + the forward voltage of the diode D1) among the voltages of the lines L1 to L6 is detected at the point a.
That is, the minimum voltage detection circuit 3 functions as a voltage detection unit that detects a voltage at a connection portion between the LED array 11 that is a plurality of light source element arrays and the constant current source 2.

  The detection voltage Va is input to the switch drive / latch circuit 4 through the resistor R2 and applied to the base of the NPN transistor Tr2. That is, the ON / OFF state of the NPN transistor Tr2 is determined by the detection voltage Va. When the NPN transistor Tr2 is ON, the point b of the switch circuit 5 at the subsequent stage is set to low (Low), and when it is OFF, the point b is set to high (High).

For setting the threshold value of the detection voltage Va, it is desirable that the voltage of each of the lines L1 to L6 be set to a level at which it can be determined whether or not the voltage level is sufficient for the constant current operation by the constant current source 2. In the following example, the operation when the threshold is set to the voltage level will be described.
The switch drive / latch circuit 4 has a function of determining a voltage level for turning on / off each switch of the switch circuit 5 in the subsequent stage and holding the state after switching.
Accordingly, the subsequent operation changes depending on whether the value of the detection voltage Va at the point a described above is equal to or higher than the threshold value or lower than the threshold value.

The switch drive / latch circuit 4 includes a PNP transistor Tr1 and an NPN transistor Tr2 (hereinafter simply referred to as “transistors”) and resistors R3 to R3 connected between a positive voltage power supply terminal E and a ground terminal G. It is constituted by R5.
This circuit also has a latch function, and once the transistor Tr2 is turned on, the state is maintained. When the transistor Tr2 is turned on, current is drawn from the power supply and the transistor Tr1, so that the transistor Tr1 is also turned on. As a result, current continues to be supplied to the base of the transistor Tr2, so that the transistor Tr2 continues to be turned on regardless of the state of the detection voltage Va. That is, once one of the transistors is turned on, it functions as a state holding means that keeps driving each other.

The switch circuit 5 includes an N-MOS FET (hereinafter simply referred to as “FET”) Qa group 51 and a P-MOS FET (hereinafter simply referred to as “FET”) Qb group 52, and one end connected to each point b. It is comprised by resistance R6, R7.
Each gate of each FETQa in group 51 is connected to point b through resistor R6, and each gate of each FETQb in group 52 is connected to point b through resistor R7. Since the point b is either high (≈power supply voltage level or arbitrary voltage level) or low (≈ground level), the FET Qa and the FET Qb are not simultaneously turned ON.
Therefore, when one of FETQa and FETQb is ON, the other is OFF. That is, when the point b is high, the FETs Qa are all turned on and the FETs Qb are all turned off. Conversely, when point b is low, all FETs Qa are turned off and all FETs Qb are turned on.

The FETQa of the group 51 and the FETQb of the group 52 are paired to constitute an analog switch.
Each FET Qa performs an opening / closing function between the movable contact C and the fixed contact A of each switch S1, S2 shown in FIG. 2, and each FET Qb is between the movable contact C and the fixed contact B of each switch S1, S2. Performs opening and closing functions. Therefore, FETQa and FETQb constitute one set and constitute one of the switches S1 or S2. Therefore, the terminals A, B, and C of the FET Qa and the FET Qb in FIG. 5 are connected to the connection lines of the fixed contacts A and B and the movable contacts C of the switches S1 and S2 in FIG. Since there are ten switches S1 and S2 in both, ten sets of FETQa and FETQb in FIG. 5 are necessary, but only three sets are shown for convenience of illustration.

Accordingly, when the FET Qa is ON, the switches S1 and S2 shown in FIG. 2 are switched to A: ON / B: OFF, and the configuration of the light source unit 1 is set to the first state shown in FIG. . When the FET Qb is ON, the switches S1 and S2 shown in FIG. 2 are switched to B: ON / A: OFF, and the configuration of the light source unit 1 is switched to the second state shown in FIG.
Here, the relationship between the level of the detection voltage Va at the point a, the state of the NPN transistor Tr2, the low / high voltage of the point b, and the states of the FETs Qa and Qb in the switch circuit 5 is as follows. Table 1 shows.

  In this embodiment, the switch drive / latch circuit 4 is provided, and when the switch circuit 5 switches the configuration of the light source unit 1, as described above, it functions as a state holding unit that holds the state after the switching. I am doing so. This is to prevent the switching operation from being repeated thereafter when the configuration of the light source unit 1 is switched as described above. For example, when the driving of the light source unit 1 is started in the first state (FET Qa: ON, Qb: OFF) shown in FIG. 3 and the detection voltage Va at the point a is less than the threshold value, It is determined that the voltage is insufficient, and the second state (FET Qb: ON, Qa: OFF) shown in FIG. 4 is switched.

  However, when the voltage at the end of the cathode side of each LED array rises and the detection voltage Va at the point a changes to a threshold value or more, the first state (FET Qa: ON, Qb: OFF) is again switched. To do. Then, there is a risk that this switching operation may be continued without convergence. However, once the NPN transistor Tr2 is turned ON, the switch drive / latch circuit 4 maintains the ON state regardless of the level change of the detection voltage Va. Therefore, the switch circuit 5 also maintains the FETQb: ON and Qa: OFF states. . Thereby, the configuration of the light source unit 1 maintains the state after switching.

  However, this state holding means is not essential. For example, it is possible to prevent the switching operation from being repeated by providing a comparator or a Schmitt trigger circuit having hysteresis instead of the switch driving / latch circuit 4. it can. In addition, after the switch to the second state, when the detection voltage Va increases greatly, it is possible to switch back to the first state again.

Next, another specific configuration example of each switch in FIG. 2 and a circuit for controlling the switching will be described. FIG. 6 is a circuit diagram thereof.
This circuit is modified as follows from the circuit described above with reference to FIG.
As a voltage detection means for detecting the voltage of the lines L1 to L5 of the connection portion between the LED row 11 which is each light source element row and the constant current source 2, a mean voltage detection circuit is used instead of the minimum voltage value detection circuit 3. 13 is provided.

That is, the resistors Rs having the same resistance value are connected between the point a where the input voltage Vin from the reference power source is applied through the resistor R1 and the lines L1 to L5 connecting the LED strings 11 and the constant current source 2. doing. In this case, since the resistor Rs is not connected to the sixth line for the LED row, the illustration is omitted.
And the voltage of the point a which connected the end of each resistance Rs and the end of resistance R1 turns into a voltage corresponding to the average value of the voltage of the lines L1-L5. The voltage at the point a is input to the switch drive / latch circuit 4 through the filter circuit 6 as the detection voltage Va.

The average value voltage detection circuit 13 is lower in detection accuracy than the minimum voltage detection circuit 3, but can be configured with only a chip resistor, so that cost and space can be reduced.
In order to minimize interference and influence on the voltages of the lines L1 to L5, it is desirable to increase the resistance value of each resistor Rs. For example, the resistance value is about several hundred kΩ to MΩ.
A filter circuit 6 including a resistor R8 and a capacitor C6 is provided between the average value voltage detection circuit 13 and the switch drive / latch circuit 4. It has enhanced resistance to malfunctions due to instantaneous voltage changes and noise during driving.

Further, the switch circuit using the MOS FET in FIG. 5 is changed to a switch circuit 15 using a bipolar transistor. In this switch circuit 15, an analog switch corresponding to one switch S1 or S2 shown in FIG. 2 is constituted by a pair of PNP transistors (hereinafter simply referred to as “transistors”) Tr3 and Tr4.
The base of the transistor Tr3 is connected to a positive voltage power supply terminal E via a resistor R13 together with the collector of an NPN transistor (hereinafter simply referred to as “transistor”) Tr5 whose emitter is grounded via a resistor R14. The base of the transistor Tr5 is connected to the point b via resistors R11 and R6. On the other hand, the base of the transistor Tr4 is connected to the point b via resistors R12 and R7.

Also in this case, when one of the transistors Tr3 and Tr4 is ON, the other is OFF.
The terminals A, B, and C of the transistors Tr3 and Tr4 in FIG. 6 are respectively connected to the connection lines of the fixed contacts A and B and the movable contacts C of the switches S1 and S2 in FIG. . Since there are 10 switches S1 and S2 in both, 10 sets of circuits other than the resistors R6 and R7 shown in the figure including the transistors Tr3 and Tr4 in FIG. 5 are necessary, but only one set is shown for the sake of illustration. Yes.
Compared with the switch circuit using the MOS FET in FIG. 5, the switch circuit 13 increases the number of parts, but it is possible to construct a system with a lower total cost.

FIG. 7 is a circuit diagram of an example in which a circuit for maintaining and canceling the state holding function is added to the switch driving / latch circuit 4 shown in FIGS.
As described above, the switch drive / latch circuit 4 is a circuit in which the transistor Tr1 and the transistor Tr2 continue to drive each other. In order to cancel this driving state, one of the current paths may be cut to cut off current supply or drawing.

  Therefore, in the circuit shown in FIG. 7, a switching NPN transistor (hereinafter simply referred to as “transistor”) Tr6 is interposed between the transistor Tr2 and the ground terminal G. Since the transistor Tr6 is ON while a high level signal is input to the base of the transistor Tr6 through the resistor R10, the switch drive / latch circuit 4 maintains the state holding function.

However, when a low level signal is input to the base of the transistor Tr6, the transistor Tr6 is turned off. As a result, the current path of the transistor Tr2 is cut off, so that the switch driving / latch circuit 4 releases (resets) the state holding function.
At that time, since the transistor Tr2 is turned off, the point b becomes high. Accordingly, the FET Qa is turned on in the switch circuit 5 of FIG. 5, and the transistor Tr3 is turned on in the switch circuit 15 of FIG. Therefore, the process returns to the first state (initial state) shown in FIG.

Control signal (LED for controlling ON / OFF of driving of the light source unit 1
If the ON / OFF signal) is input to the base of the transistor Tr6, the state holding function can be maintained and released in synchronization with the driving ON / OFF. As a result, the configuration of the light source unit 1 is automatically switched from the voltage detection and the state is maintained and released every time driving is started, and each LED of the light source unit 1 can always be driven with an optimal configuration.

FIG. 8 is a circuit diagram corresponding to FIG. 2, showing another embodiment of the light source system according to the present invention.
In this embodiment, the functions of the switches S1 and S2 in FIG. 2 and the switch circuit 5 in FIG. 5 or the switch circuit 15 in FIG. 6 are performed by a general-purpose logic IC (analog multiplexer: function model No. 4053) 20. It is an example. Since a plurality of functions of the ten changeover switches in FIG. 2 are mounted on the four logic ICs 20C, space saving can be realized.

[Embodiment of Image Reading Apparatus]
Next, an embodiment of an image reading apparatus according to the present invention will be described.
FIG. 9 is an overall configuration diagram showing a mechanism portion of the image reading apparatus.
The image reading apparatus 200 is a scanner apparatus or a single scanner apparatus mounted on an image forming apparatus such as a digital copying machine, a digital multifunction peripheral, or a facsimile machine.

  As shown in FIG. 9, the image reading apparatus 200 includes a contact glass 201 on which an original is placed, and a first carriage 206, a second carriage 207, and a lens unit 208 as a reading optical system. The first carriage 206 is provided with a light source 41 for document exposure and a first reflection mirror 203. The second carriage 207 is provided with a second reflection mirror 204 and a third reflection mirror 205. A CCD linear image sensor (hereinafter simply referred to as “CCD”) 209 is also provided.

Then, the first carriage 206, the second carriage 207, and the lens unit 208 form an image on the original on the CCD 209 and read it.
Further, a white reference plate 210 used for shading correction and a sheet-through reading slit 211 are also provided.
The light source 41 may use the LED array corresponding to the light source unit 1 or the LED array 11 in each embodiment of the light source unit according to the present invention described above, but may be another light source element array.

An automatic document feeder (hereinafter abbreviated as “ADF”) 220 is mounted on the upper part of the image reading apparatus 200, and a hinge or the like (not shown) is provided so that the ADF 220 can be opened and closed with respect to the contact glass 201. Are connected through.
The ADF 220 includes a document tray 221 on which a document bundle composed of a plurality of documents can be placed. Further, separation / feeding means including a feeding roller 222 that separates documents one by one from a bundle of documents placed on the document tray 221 and automatically feeds them toward the sheet-through reading slit 211 is also provided. .

  In the image reading apparatus 200 configured as described above, in the scan mode in which the image surface of the document placed on the contact glass 201 is scanned (scanned) and the image of the document is read, the first carriage 206 is scanned. The second carriage 207 scans the document in the arrow A direction (sub-scanning direction) by a stepping motor (not shown). At this time, the second carriage 207 moves at a speed half that of the first carriage 206 in order to keep the optical path length from the contact glass 201 to the CCD 209 constant.

  At the same time, the image surface, which is the lower surface of the document placed on the contact glass 201, is illuminated (exposed) by the irradiation light of the light source 41 of the first carriage 206. Then, the reflected light from the image plane passes through the first reflection mirror 203 of the first carriage 206, the second reflection mirror 204 and the third reflection mirror 205 of the second carriage 207, and the lens unit 208, and then on the CCD 209. Is imaged. Then, an analog signal by photoelectric conversion is output from the CCD 209 and converted into a digital signal by a signal processing unit at the subsequent stage. Thereby, the image of the original is read and digital image data is obtained.

  On the other hand, in the sheet-through mode in which the document is automatically fed and the image of the document is read, the first carriage 206 and the second carriage 207 move to a fixed position below the sheet-through reading slit 211. Thereafter, the document placed on the document tray 221 is automatically fed in the arrow B direction (sub-scanning direction) by the feeding roller 222, and the document is scanned at the position of the sheet through reading slit 211.

  At this time, the lower surface (image surface) of the automatically fed document is illuminated by the irradiation light of the light source 41 of the first carriage 206. Therefore, the reflected light from the image plane is coupled on the CCD 209 via the first reflecting mirror 203 of the first carriage 206, the second reflecting mirror 204 and the third reflecting mirror 205 of the second carriage 207, and the lens unit 208. Imaged. Then, an analog signal by photoelectric conversion is output from the CCD 209 and converted into a digital signal by a signal processing unit at the subsequent stage. Thereby, the image of the original is read and digital image data is obtained. The document whose image has been read in this manner is discharged to the document collection unit.

In the scan mode or the sheet through mode, the reflected light from the white reference plate 210 is converted into an analog signal by the CCD 209 by the illumination of the light source 41 that is started before image reading, and is converted into a digital signal by the signal processing unit in the subsequent stage. Converted. As a result, the white reference plate 210 is read, and shading correction at the time of reading the document is performed based on the read data. Since this shading correction is a well-known technique, a detailed description thereof will be omitted.
Further, when the ADF 220 is provided with a conveyance belt, the document can be automatically fed to the reading position on the contact glass 201 by the ADF 220 and the image of the document can be read even in the scan mode.

FIG. 10 is a block diagram illustrating a configuration example of a part of an image signal processing unit that constitutes an image reading unit together with the reading optical system of the image reading apparatus 200 illustrated in FIG. 9.
In this image signal processing unit 250, the analog image signal photoelectrically converted by the CCD 209 is output to the analog processing circuit unit 251.
The analog processing circuit unit 251 performs various image processing such as sample hold processing and black level correction on the analog image signal input from the CCD 209, and then outputs the analog image signal to the A / D conversion circuit unit 252.

The A / D conversion circuit unit 252 converts the analog image signal input from the analog processing circuit unit 251 into a digital image signal (image data), and further converts the digital image signal into an appropriate transmission pattern using the signal interface conversion unit 253. To the image signal processing unit.
Various timing clock signals input to the CCD 209, the analog processing circuit unit 251, the A / D conversion circuit unit 252, the signal interface conversion unit 253, and a stepping motor (not shown) or a load driving circuit (not shown) in the image signal processing unit 250. The timing clock generator 254 generates and supplies the clock based on the reference clock from the oscillator 255.

  The timing clock generation unit 254 generates and outputs a light source drive signal synchronized with the reading line as a drive signal for the light source 41. Then, the light source 41 using an LED array (LED array) or the like is driven to light by the above-described light source system according to the present invention. As a result, it is possible to save power for driving the light source.

[Embodiment of Image Forming Apparatus]
Next, an embodiment of an image forming apparatus according to the present invention will be described.
FIG. 11 is an overall configuration diagram showing a mechanism part of the image forming apparatus, and parts corresponding to those in FIG. 9 are denoted by the same reference numerals, and description thereof is omitted.
The image forming apparatus 300 is a digital copying machine equipped with the image reading apparatus 200 shown in FIG.

As shown in FIG. 11, the image forming apparatus 300 has an ADF 400 mounted on the contact glass 201 on which a document is placed. A hinge or the like (not shown) is provided so that the ADF 400 can be opened and closed with respect to the contact glass 201. It is connected through.
The ADF 400 includes a document tray 401 on which a document bundle composed of a plurality of documents can be placed. Further, when a print key on an operation unit (not shown) is pressed, the originals are separated one by one from the original bundle placed on the original tray 401 with the image surface facing upward, and automatically fed, and the sheet through reading slit 211 is provided. Alternatively, separation / feeding means including a feeding roller 402 and a conveying belt 403 that are conveyed toward the contact glass 201 is provided. A document set detection sensor 405 detects whether a document bundle is set on the document tray 401.

As described with reference to FIG. 9, the document fed by the feeding roller 402 and the conveying belt 403 is read by the image reading apparatus 200, and is then placed on the upper surface of the ADF 400 by the conveying belt 403 and the discharging roller 404. Discharged.
Here, the operation of the controller (not shown) and the ADF 400 in the scan mode in which the document is conveyed to the reading position of the contact glass 201 by the ADF 400 will be described.

  The feeding motor of the ADF 400 is driven by an output signal from the controller. The controller drives the feed motor if the document set detection sensor 405 detects a document when a feed start signal generated by pressing a print key on the operation unit is input. When the feeding motor is driven, the feeding roller 402 rotates clockwise in FIG. 11 to automatically feed the document located at the uppermost position from the document stack on the document tray 401 toward the contact glass 201. Transport.

  When the document set detection sensor 405 detects the trailing edge of the document, the controller also counts a rotation pulse of a conveyance belt motor (not shown) from this detection point, and when the rotation pulse reaches a predetermined value, the conveyance belt 403. Is stopped and the conveying belt 403 is stopped, whereby the document is stopped at the reading position on the contact glass 201.

When the document stops at the reading position on the contact glass 201, the image reading device 200 reads the image of the document. When this image reading is completed, a signal indicating that is input to the controller. Based on the signal, the controller drives the conveyor belt motor, and causes the conveyor belt 403 to carry out the document from the contact glass 201 toward the discharge roller 404.
At the same time, the feeding motor is driven again to rotate the feeding roller 402 and the next document is automatically fed and conveyed toward the contact glass 201.

  On the other hand, one of the three paper feed trays 301, 302, and 303 provided in the lower part of the main body is selected, and the transfer paper that is a recording medium stacked on the three paper feed trays 311, 312 and 313 is selected. Are conveyed to a position where they are in contact with the photosensitive drum 315 as an image carrier by the vertical conveyance unit 314.

  The image data read by the image reading device 200 is temporarily stored in the image memory. Thereafter, the stored image data is read out, the laser light emitted from the writing unit 350 disposed on the upper part of the main body is modulated, and the photosensitive drum 315 charged in advance by a charging unit (not shown) by optical scanning with the laser light. An electrostatic latent image is formed on the surface. When the electrostatic latent image passes through the developing unit 327, the electrostatic latent image is developed with toner to form a toner image.

An image for forming an image on a recording medium by a photosensitive drum 315 that performs the image formation, a charging unit (not shown), the writing unit 350, the developing unit 327, and a conveyance belt 316 and a fixing unit 317 described later. The formation part 310 is comprised.
As described above, the transfer paper fed from the selected paper feed tray is transferred by the conveyor belt 316 at the same speed as the rotation of the photosensitive drum 315, and the toner image on the photosensitive drum 315 is transferred. Further, the transfer paper is sent to the fixing unit 317 to fix the toner image, and is then discharged by a paper discharge unit 318 to a paper discharge tray 319 outside the apparatus.

  At this time, for example, in order to reverse the transfer paper on which the toner image is formed on one side in order to discharge face-down (the image surface faces downward in order to align the transfer paper in the page order), the transfer paper is discharged. The paper is transported to the reverse transport path 320 by the unit 318, switched back by the reverse unit 321, and then discharged to the paper discharge tray 319 through the reverse paper transport path 322.

When images are formed on both sides of the transfer paper, the transfer paper on which the image is formed on one side is conveyed to the reversal conveyance path 320 by the paper discharge unit 318 and switched back by the reversal unit 321. After that, it is sent to the duplex conveying unit 323.
The transfer sheet sent to the duplex conveying unit 323 is conveyed by the vertical conveying unit 314 to a position where it comes into contact with the photosensitive drum 315 again in order to transfer the toner image formed on the photosensitive drum 315 again. Then, after the toner image is transferred to the other surface, the toner image is fixed by the fixing unit 317 and discharged to the paper discharge tray 319 by the paper discharge unit 318.

  The photosensitive drum 315, the conveyance belt 316, the fixing unit 317, the paper discharge unit 318, and the development unit 327 are driven by a main motor (not shown), and the driving power of the main motor is transmitted to each of the paper feeding units 311 to 313 by a paper feeding clutch. To be driven. The vertical conveyance unit 314 is driven by the driving force of its main motor being transmitted via an intermediate clutch.

  The writing unit 350 includes a laser output unit 351, an imaging lens 352, a mirror 353, and the like. The laser output unit 351 includes a laser diode that is a laser light source and a rotating polygon mirror (polygon mirror) or a vibrating mirror that scans the laser beam. Laser light emitted from the laser output unit 351 is deflected and scanned by a polygon mirror or a vibrating mirror, passes through an imaging lens 352, is folded by a mirror 353, and is focused on the surface of the photosensitive drum 315.

The image forming apparatus (digital copying machine) 300 includes the above-described image reading apparatus 200, and forms an image on a recording medium based on image data read by the image reading apparatus 200. You can plan.
The image forming apparatus of this embodiment is an application of the present invention to a digital copying machine. However, the image forming apparatus according to the present invention is not limited to this, and may be an analog copying machine, a digital multifunction peripheral, a facsimile machine, or the like. .
In the case of a digital image forming apparatus such as a digital copying machine, an image reading apparatus including a light source system according to the present invention and an image forming means for forming an image on a recording medium based on image data read by the image reading apparatus. And.

However, in the case of an analog image forming apparatus such as an analog copying machine, an original is illuminated with light emitted from a light source, and a precharged image carrier is directly exposed by reflected light from the original. Image forming means for imaging is provided.
Further, the load drive deviation, the image reading apparatus, and the image forming apparatus according to the present invention are not limited to the above-described embodiments, and may be appropriately changed within the scope of the technical matters described in the claims. Needless to say, addition, omission, or combination can be made.

1: Light source unit 2: Constant current source 3: Minimum voltage detection circuit
4: Switch drive / latch circuit 5, 15: Switch circuit 6: Filter circuit 11, 11 ′: LED array (light source element array)
11a: Light emitting diode (LED: light source element)
13: Average value voltage detection circuit 20: Logic IC

200: Image reading device 209: CCD
220, 400: Automatic document feeder (ADF) 250: Image signal processor
251: Analog processing circuit unit 252: A / D conversion circuit unit 253: Signal interface conversion unit 300: Image forming apparatus
301 to 303: Paper feed tray 310: Image forming unit (image forming unit)
311 to 313: paper feed unit 314: vertical transport unit
315: Photosensitive drum 317: Fixing unit
327: Development unit 350: Writing unit

S1, S2: Changeover switch D1: Diode Qa: N-MOS FET
Qb: P-MOS FET Rs: Resistors L1 to L6 for detecting the average value voltage: Lines Tr1, Tr3, Tr4 for connecting each LED string and a constant current source: PNP transistors
Tr2, Tr5, Tr6: NPN transistors
Vin: Input voltage (constant voltage) Iin: Input current Ic: Constant current Va: Detection voltage

JP 2009-157189 A

Claims (10)

A light source unit provided with a plurality of light source element arrays in which a plurality of light source elements are connected in series, and each light source by passing a constant current through each of the plurality of light source element arrays of the light source unit to which a constant voltage is applied. In a light source system comprising a constant current source for driving an element,
Voltage detection means for detecting a voltage at a connection portion between each of the light source element rows of the plurality of rows and the constant current source;
According to the level of the voltage detected by the voltage detection means, where m and n are each an integer of 2 or more such that m> n, the number of the light source elements for each of the light source element arrays is m. A first state in which the number of light source element rows is n, and a second state in which the number of light source elements for each light source element row is n and the number of light source element rows is m. A light source system comprising: a configuration switching means for switching between states. The light source system according to claim 1,
A light source system comprising: a state holding unit that holds a state after the configuration of the light source unit is switched by the configuration switching unit.   The state holding means maintains a function of holding the state after the switching while the light source unit is driven, and releases the function of holding the state after the switching when the light source unit is not driven. The light source system according to claim 2, wherein:   The state holding means switches between maintaining and canceling the function of holding the state after the switching in synchronization with a control signal for controlling on / off of driving of the light source unit. The light source system described.   The voltage detection means detects the lowest voltage among the voltages at the connection portions between the light source element arrays of the light source section and the constant current source. The light source system according to item.   The said voltage detection means detects the average value of each voltage of the connection part of each said light source element row | line | column of the said light source part, and the said constant current source, The Claim 1 characterized by the above-mentioned. Light source system. The light source system according to any one of claims 1 to 6,
A filter circuit for removing high-frequency components of the voltage detected by the voltage detection means;
The configuration switching means switches the configuration of the light source unit according to a voltage level from which a high frequency component has been removed by the filter circuit.   The light source system according to claim 1, wherein the light source element is a light emitting diode. The light source system according to any one of claims 1 to 8,
An image reading apparatus comprising: an image reading unit that reads an image of a document using illumination by the light source unit in the light source system. An image reading apparatus according to claim 9,
An image forming apparatus comprising image forming means for forming an image on a recording medium based on image data read by the image reading apparatus.

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