JP6182773B2 - Charge / discharge system - Google Patents

Description

  The present invention relates to a charge / discharge system that temporarily accumulates electric power generated by a power generation element in a secondary battery and then supplies electric power from the secondary battery to a load.

  As is well known, the power generation element has a maximum power point at which the product of the output voltage and the output current is maximum according to the amount of power generation. This maximum power point fluctuates with changes in the amount of power generation. Therefore, from the viewpoint of efficient use of the power generation element, it is necessary to perform tracking control for fluctuations in the maximum power point by so-called maximum power point tracking control (hereinafter referred to as MPPT). There exists a thing of patent document 1 as a charging / discharging system using such MPPT.

  As another example of MPPT, a voltage tracking method is known. In the voltage tracking method, the open circuit voltage of the power generation element is confirmed, and the power generation element generates power at an optimum operating point that is about 50% of the open circuit voltage. The voltage tracking method described above is excellent in that the function can be realized with a simple circuit configuration and control, and that the maximum power point of the power generating element can be quickly tracked.

  For secondary batteries, the voltage at full charge is determined for each type. If charging of the secondary battery is continued after full charge, the performance of the secondary battery deteriorates. Further, a voltage increase due to the internal resistance is observed during the charging of the secondary battery. However, in general, it is said that the voltage in the charging halt state is a true value.

  Therefore, a pulse charging method is known in which a rechargeable battery is fully charged based on the voltage (that is, the true value) of the secondary battery during the charging suspension period by repeating a very short time charging and charging suspension. It has been. According to this pulse charging method, since charging control with a true value is possible, it is advantageous for the life of the secondary battery and the secondary battery can be charged in a time-sharing manner. Excellent when accumulating in secondary batteries.

JP 2010-015317 A

  However, in the charge / discharge system, the power generation element cannot supply power to the secondary battery during the period of checking the open circuit voltage. Further, the secondary battery cannot store the power from the power generation element during the charging suspension period.

  Therefore, in the charge / discharge system, if the open voltage confirmation period and the charge suspension period are shifted, the period during which the power generated by the power generation element cannot be stored in the secondary battery is prolonged, and the power loss is increased. There was a problem.

  Therefore, an object of the present invention is to provide a charge / discharge system capable of reducing power loss.

  In order to achieve the above object, one aspect of the present invention is directed to a charge / discharge system. This charge / discharge system is connected to a power generation element capable of generating power at a maximum power point, and the power generation element via a power transmission path, and can store power generated by the power generation element and supply power to a load. A dischargeable secondary battery, a control circuit that obtains an open-circuit voltage of the power generating element during a predetermined first period, and derives a current maximum power point of the power generating element; and A take-out unit for taking out the electric power generated by the power generation element outside the first period based on the derived maximum power point.

The control circuit further obtains a voltage value of the secondary battery for charge control during a second period in which charging to the secondary battery is suspended, and outside the second period, The charging of the extracted power to the secondary battery is controlled, and the first period and the second period overlap in time, and the control circuit is based on the amount of change in the power generation amount of the power generation element. was superposed on the second period the first period is selected, based on the voltage value of the secondary battery, Ru together by selecting said first time period overlapping with the second time period.

  According to each said form, it becomes possible to provide the charging / discharging system which can reduce an electric power loss.

1 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. It is a block diagram which shows the structure of the charging / discharging system of FIG. It is a figure which shows an example of the attachment location of the electric power generation element of FIG. It is a graph which shows the characteristic of the electric power generation amount and output current with respect to an output voltage in case the electric power generation element of FIG. 1 is a thermoelectric conversion element. It is a graph which shows the time-dependent change of the voltage value which shows the outline | summary of the charge system (namely, pulse charge system) to the secondary battery of FIG. It is the figure which contrasted the charging / discharging system which concerns on a comparative example, and the charging / discharging system of FIG. 2 from the viewpoint of the loss (namely, power loss) of a charging opportunity. It is a schematic diagram which shows the attachment position of the temperature sensor to the fixing device of FIG. FIG. 2 is a diagram illustrating a change in the operation mode of the image forming apparatus in FIG. 1 and a time change of the temperature of the fixing device. FIG. 3 is a diagram showing the measurement frequency of the open-circuit voltage for each operation mode of the image forming apparatus 1 in FIG. 1 and at the time of transition to another operation mode. FIG. 3 is a main flow diagram of the control circuit of FIG. 2. It is a flowchart which shows the 1st example of the detailed process of S02 of FIG. It is a flowchart which shows the 2nd example of the detailed process of S02 of FIG. It is a flowchart which illustrates the detailed process of S03 of FIG.

<Embodiment>
Hereinafter, an image forming apparatus including a charge / discharge system according to an embodiment of the present invention will be described in detail with reference to the drawings. Prior to that, first, in the drawings or in the following description, the lowercase letters a, b, c, and d described after the reference numerals are yellow (Y), magenta (M), cyan (C), black (Bk ). For example, the photosensitive drum 51a means the yellow photosensitive drum 51.

<< Configuration and operation of image forming apparatus >>
First, refer to FIG. The image forming apparatus 1 is, for example, a copying machine, a printer, a facsimile machine, or a multifunction machine having these functions. (Film). The image forming apparatus 1 generally includes a supply unit 2, a registration roller unit 3, an image forming unit 4, a fixing device 6, a discharge tray 7, and a control circuit 8.

  The supply unit 2 generally includes a supply tray and a supply roller. The supply tray is configured so that unprinted sheets Sh can be stacked. The supply roller rotates under the control of the control circuit 8 and picks up the sheets Sh one by one from the supply tray. The sheet Sh is sent out from the supply unit 2 to a conveyance path FP indicated by a broken line in FIG. 1, and is then conveyed toward the registration roller unit 3 on the conveyance path FP.

  The registration roller unit 3 includes, for example, a pair of two rollers. The roller pairs are in contact with each other to form a registration nip, and are configured to be rotatable under the control of the control circuit 8. While the roller pair is stopped, the sheet Sh from the supply unit 2 hits the registration nip and stops temporarily. Thereafter, the roller pair starts to rotate for secondary transfer, and sends the sheet Sh to the secondary transfer area (details will be described later).

  The image forming unit 4 generally includes image forming units 41a to 41d, an exposure device 42, an intermediate transfer belt 43, a driving roller 44, a driven roller 45, primary transfer rollers 46a to 46d, and secondary transfer. And a roller 47.

  The image forming units 41a to 41d are arranged on the frame (not shown) of the image forming apparatus 1 so as to be linearly arranged from left to right. The image forming unit 41a includes a photosensitive drum 51a of a corresponding color. Around the photosensitive drum 51a, at least a charger 52a and a developing device 53a are provided in this order from the upstream side to the downstream side in the rotation direction (that is, the sub-scanning direction). Similarly, the image forming units 41b to 41d also include photosensitive drums 51b to 51d, chargers 52b to 52d, and developing units 53b to 53d.

  In the image forming unit 4, the chargers 52a to 52d are typically chargers using corona discharge (corotron or scorotron) or chargers using proximity discharge (charging roller or charging brush). These chargers 52a to 52d uniformly charge the peripheral surfaces of the rotating photosensitive drums 51a to 51d (charging process). The exposure device 42 can typically use a so-called laser scanning method or an LED array method. When the exposure device 42 receives image data of each color from the control circuit 8 described later, the exposure device 42 generates light beams Ba to Bd modulated with the image data for each color. Then, the exposure device 42 sequentially scans the peripheral surfaces of the photosensitive drums 51a to 51d charged by the chargers 52a to 52d for each line in the main scanning direction for each line (exposure process). By the above charging / exposure process, electrostatic latent images of corresponding colors are formed on the peripheral surfaces of the photosensitive drums 51a to 51d.

  In the image forming unit 4, the developing devices 53a to 53d supply toners of corresponding colors to the electrostatic latent images formed on the photosensitive drums 51a to 51d (development process). By this development process, Y, M, C, and Bk toner images are formed on the peripheral surfaces of the photosensitive drums 51a to 51d. Here, in the following description, the process from the charging process to the development process may be referred to as an image forming process.

  The intermediate transfer belt 43 is an endless belt stretched between the drive roller 44 and the driven roller 45 so that the outer peripheral surface of the intermediate transfer belt 43 is in contact with the upper end portions of the photosensitive drums 51a to 51d. It is configured to rotate in the direction shown.

  The primary transfer rollers 46a to 46d are arranged so as to press the outer peripheral surface of the intermediate transfer belt 43 and push the inner peripheral surface of the intermediate transfer belt 43 into the photosensitive drums 51a to 51d by a certain amount. Hereinafter, a portion where the intermediate transfer belt 43 and the photosensitive drums 51a to 51d are in contact with each other is referred to as a primary transfer region. A primary transfer voltage having a polarity opposite to that of the toner is applied to each of the primary transfer rollers 46a to 46d. The toner images on the photosensitive drums 51 a to 51 d are transferred onto the intermediate transfer belt 43 by such a primary transfer process. Here, the toner images of the respective colors are sequentially transferred to the same area on the outer peripheral surface of the intermediate transfer belt 43 by appropriately adjusting the rotational speed and arrangement of the intermediate transfer belt 43 and the photosensitive drums 51a to 51d. As a result, a full-color composite toner image is formed on the intermediate transfer belt 43. Such a composite toner image is conveyed to a secondary transfer region described later while being held on the intermediate transfer belt 43 by the rotation of the intermediate transfer belt 43.

  The secondary transfer roller 47 is disposed so as to face the drive roller 44 from the lateral direction with the intermediate transfer belt 43 stretched and supported by the drive roller 44 and the like, and is pushed into the intermediate transfer belt 43 on the transport path FP. Arranged to be. Thereby, the intermediate transfer belt 43 and the secondary transfer roller 47 form a secondary transfer region. The sheet Sh is sent from the registration roller unit 3 to the secondary transfer area. A secondary transfer voltage is applied to the secondary transfer roller 47. The composite toner image on the intermediate transfer belt 43 is transferred onto the sheet Sh sent to the secondary transfer area. The sheet Sh is sent out from the secondary transfer nip toward the fixing device 6.

  The fixing device 6 typically includes two rotating bodies that are in contact with each other to form a fixing nip. The sheet Sh fed to the fixing nip is heated by one rotating body and the other rotating body. Pressurize with your body. By this fixing process, the synthetic toner image on the sheet Sh is fixed. The sheet Sh is discharged as a printed product Sh to a discharge tray 7 provided on the downstream side of the conveyance path FP with respect to the fixing device 6.

  The control circuit 8 controls each component of the image forming apparatus 1.

<Configuration and operation of charge / discharge system>
As is well known, the temperature around the fixing device 6 is very high. The metal frame 66 for fixing the fixing device 6 is heated by the waste heat of the fixing device 6. The image forming apparatus 1 includes a charge / discharge system 9 that generates power from the heat of the metal frame 66. As shown in FIGS. 1 and 2, the charge / discharge system 9 includes a power generation element 91, a secondary battery 92, a power transmission path 93, a switch unit 94, a takeout unit 95, a load, in addition to the control circuit 8. 96.

The control circuit 8 includes a CPU 84, a ROM 85, a RAM 86, an ADC 87, and an I / F 88. The CPU 84 operates according to the program stored in the ROM 85 while controlling the configuration of the charge / discharge system 9 while using the RAM 86 as a work area. The processing of the CPU 84 generally includes the following.
The switch unit 94 is turned off / on by the control signal to switch between the open voltage measurement period (that is, the first period) of the power generation element 91 and the other period.
The maximum power point of the power generation element 91 is derived based on the open circuit voltage of the power generation element 91.
A current value indicating the maximum power point is set in the constant current circuit 952, and the power from the power generation element 91 is taken out at the maximum power point.
Switching between the charging suspension period (that is, the second period) of the secondary battery 92 and the chargeable period.
-The voltage value of the secondary battery 92 is acquired during the second period.

  In the control circuit 8, the ADC 87 converts the open-circuit voltage obtained as analog information from the power generation element 91 into digital information. The ADC 87 further converts a voltage value obtained as analog information from the secondary battery 92 into digital information. The ADC 87 transmits these digital information to the CPU 84. The I / F 88 is an interface circuit that connects the control circuit 8 and the switch unit 94 or the extraction unit 95, and transmits various control signals generated by the CPU 84 to each unit.

The power generation element 91 is illustratively a thermoelectric conversion element that applies the Seebeck effect. The thermoelectric conversion element is configured, for example, by connecting two different thermoelectric conversion materials (for example, an n-type semiconductor and a p-type semiconductor) in series, and arranging these thermoelectric conversion materials substantially in parallel in a direction in which a temperature difference occurs. The By making the joint part of such two thermoelectric conversion materials high temperature with respect to both ends, for example, a thermoelectromotive force due to the Seebeck effect is generated between both ends. In the present embodiment, the joint portion of the thermoelectric conversion element is attached to a location that satisfies the following conditions (1) and (2) in the image forming apparatus 1.
(1) The operation of the image forming apparatus 1 is not affected. For example, it does not affect the temperature of the fixing nip.
(2) Quickly follow the temperature change accompanying the change of the operation mode of the image forming apparatus 1. For example, when the mode is changed from the power saving mode (sleep mode or low power mode) to the printing mode, the temperature quickly increases.

  In the present embodiment, the power generation element 91 is provided in the vicinity of the most downstream position of the transport path FP as a place that satisfies the above conditions (1) and (2). More specifically, as shown in FIGS. 1 and 3, the power generating element 91 includes a placement surface of the printed product Sh in the discharge tray 7 and a most downstream portion of the transport path FP (that is, a discharge portion of the printed product Sh). Between the two, a frame 66 is provided. The power generation element 91 is attached to the left side surface of the frame 66 such that a semiconductor (or conductor) connection portion is in physical contact. Specifically, as shown in the lower part of FIG. 3, the left side surface of the frame 66 has a height of 60 mm in the vertical direction (that is, vertical) of the image forming apparatus 1 and the front-rear direction (that is, horizontal) of the image forming apparatus 1. ) Has a length of 380 mm. 3 shows a plurality of power generation elements (that is, thermoelectric conversion elements) 91 having a size of 18 mm in length × 14 mm in width in plan view. The power generation elements 91 are arranged in a matrix (for example, two in the vertical direction of the image forming apparatus 1 and about 25 in the front-back direction) so as to physically contact the left side surface of the frame 66.

  Although not shown in FIG. 3, the fixing device 6 is disposed on the right side of the frame 66. Therefore, when the image forming apparatus 1 transitions to the printing mode, the frame 66 is heated by the temperature rise of the fixing device 6. The power generation element 91 generates power using the frame 66 as a heat source, and outputs the generated power from both output terminals.

  In addition to the above, the thermoelectric conversion element may be attached to a heat generating component such as a power supply circuit or a motor.

  Here, as described above, MPPT is known as a method for extracting power from the power generation element 91. In MPPT, the maximum power point (that is, the product of the voltage value and the current value) of the power generation element 91 is automatically determined, and power is extracted from the power generation element 91 based on the determined maximum power point. As a result, the power generation amount of the power generation element 91 can be maximized. Here, the maximum power point varies depending on the surrounding environment of the power generation element 91. Therefore, in order to use at the maximum efficiency of the power generation element 91, it is preferable to dynamically control the MPPT so as to follow the fluctuation of the maximum power point.

  Here, FIG. 4 is a graph showing characteristics of the amount of power generation with respect to the output voltage and characteristics of current with respect to the output voltage when the power generation element 91 is a thermoelectric conversion element. These characteristic curves are obtained under conditions where the ambient temperature is 25 ° C. and the temperature difference of the power generation element 91 is 30 ° C. Further, the characteristic curve of the power generation amount is indicated by a solid line, and the characteristic curve of the current is indicated by a broken line.

  First, as shown in FIG. 4, the characteristics of the power generation amount are represented by a convex quadratic function curve. Therefore, the maximum power point is the apex of this characteristic curve. The voltage value at the maximum power point (hereinafter referred to as the maximum power point voltage) is generally said to be about one half of the value of the open circuit voltage. Here, the open circuit voltage is a voltage between terminals when both output terminals of the thermoelectric conversion element are opened. As described above, there is a correlation between the open-circuit voltage and the maximum power point voltage. If the open-circuit voltage can be obtained, the maximum power point voltage can be roughly estimated.

  Next, as shown in FIG. 4, the current characteristic is represented by a straight line having a negative slope. The current value becomes zero in the case of an open circuit voltage.

  MPPT using the above correlation is well known as a power tracking method. Hereinafter, the power tracking method will be described in more detail. First, the open circuit voltage of the power generation element 91 is periodically measured. Next, a voltage value (that is, a maximum power point voltage value) and a current value (that is, a maximum power point current value) that can obtain the maximum power point are derived from the open circuit voltage. Electric power is extracted from the power generation element 91 with these voltage value and current value.

  According to the voltage tracking method described above, since it is possible to quickly follow the fluctuation of the maximum power point, there is an advantage that it is possible to efficiently extract power from the power generation element 91. On the other hand, since it is necessary to open between output terminals in order to measure an open circuit voltage, there exists a demerit that electric power cannot be taken out from an output terminal during the measurement period.

  In the present embodiment, the description is continued assuming that the power generation element 91 is a thermoelectric conversion element. However, not limited to this, the power generation element 91 may be a solar cell. Since a solar cell does not require a heat source for power generation, it does not necessarily have to be installed at a place satisfying the above (1) and (2). Rather, it is preferably installed in a place where an appropriate amount of illuminance is expected. The MPPT (voltage tracking method) can also be applied to solar cells.

  With respect to the secondary battery 92, the voltage at full charge is determined for each type of secondary battery (for example, a lithium ion battery or a nickel metal hydride battery). If charging is continued after reaching this full-charge voltage, the temperature of the secondary battery 92 rises and its performance deteriorates. Further, when compared with the voltage value during the charging suspension period, an increase in the voltage value due to the internal resistance is observed in the voltage value during the charging period. Therefore, in general, it is said that the voltage value in the charging suspension state is a true value.

  From the above background, the pulse charging method is adopted as the charging method of the secondary battery 92. In the pulse charging method, as shown in FIG. 5, charging and charging suspension are repeated, and the voltage value during the charging suspension period is measured. Then, the measured voltage value is compared with a predetermined threshold voltage for completion of charging to determine whether the battery has been fully charged.

  In the present embodiment, the control circuit 8 periodically switches between a charging suspension period as the second period and a chargeable period outside the second period. During the chargeable period, the power generated by the power generation element 91 is supplied to the secondary battery 92 via the power transmission path 93. The secondary battery 92 stores the supplied power. On the other hand, in the secondary battery 92 during the charging suspension period, for example, the built-in remaining amount detector 921 detects the voltage between the terminals of the secondary battery 92 by the voltage measurement method, and controls the voltage value as analog information. Output to the circuit 8. Here, in this embodiment, the voltage measurement method is adopted as a method for detecting the remaining amount of the secondary battery. However, there are various techniques for realizing the remaining amount detection, and other known methods (for example, impedance track method) are used. It is also possible to adopt. Further, the built-in remaining amount detector 921 can also be realized by an IC.

  According to the above pulse charging method, charging control by the true voltage value is possible, which is advantageous in terms of life and can be charged in a time-sharing manner. It is advantageous.

  The power transmission path 93 is provided between the power generation element 91 and the secondary battery 92. In the present embodiment, in the power transmission path 93, the power generation element 91 side is referred to as upstream, and the secondary battery 92 side is referred to as downstream. The power transmission path 93 is provided with a switch portion 94 on the upstream side and a take-out portion 95 on the downstream side.

  The switch unit 94 is, for example, an FET, and is turned on / off by a switching signal that is a kind of control signal. The off period is the first period, and the on period is the period outside the first period. When the switch unit 94 is turned off (that is, opened), the output terminals of the power generation element 91 are opened. On the other hand, when the switch unit 94 is turned on (that is, in the closed state), the electric power generated by the power generation element 91 is supplied to the take-out unit 95 via the switch unit 94.

  The extraction unit 95 includes a constant voltage circuit 951 and a constant current circuit 952. The constant voltage circuit 951 converts the output voltage of the power generation element 91 into a voltage value suitable for charging the secondary battery 92. The constant current circuit 952 is set to output a maximum power point current in accordance with a control signal from the control circuit 8. Thus, the constant current circuit 952 supplies power corresponding to the maximum power point to the secondary battery 92. Thus, outside the first period, the power generation element 91 can generate power at the maximum power point and supply the generated power to the secondary battery 92.

  Reference is again made to FIG. The load 96 is, for example, an operation panel (not shown) provided in the image forming apparatus 1 or a CPU 84 provided in the control circuit 8 and driven by power supplied from the secondary battery 92 via the power supply path 97. To do. In FIG. 2, the load 96 and the CPU 84 are shown at different positions for convenience.

<< Synchronous control in charge / discharge system >>
In the known voltage tracking method, as described above, the power generation element cannot store power in the secondary battery during the open voltage measurement period (that is, during the first period). In the known pulse charging method, as described above, since the voltage value of the secondary battery is measured during the charging suspension period (that is, during the second period), charging cannot be performed. In a charge / discharge system (hereinafter simply referred to as a comparative example) in which these are simply combined, the first period P1 and the second period P2 do not overlap in time as shown in the upper part of FIG. Therefore, in the comparative example, charging from the power generation element to the secondary battery cannot be performed during the period obtained by adding both periods P1 and P2. As a result, the loss of power that can be charged in the secondary battery increases.

  In view of the above problems, in the present charging / discharging system 9, the first period P1 and the second period P2 overlap in time as shown in the lowermost part of FIG. More preferably, one of the first period P1 and the second period P2 includes the other period of the first period P1 and the second period P2. More preferably, the first period P1 and the second period P2 coincide with each other. In this case, only the secondary battery 92 cannot be charged during the first period P1. Therefore, in this charging / discharging system 9, it becomes possible to suppress the loss of the electric power charged from the power generating element 91 to the secondary battery 92 as compared with the comparative example.

  In the example in the lower part of FIG. 6, the frequencies of the first period and the second period are set to be the same. However, the present invention is not limited to this, and any one of the first period and the second period may be set to a different frequency as long as either one is superimposed on the other.

<Variations>
Here, as described above, the maximum power point varies not only according to the surrounding environment (for example, temperature or humidity), but also changes in the maximum power point per unit time. It is desirable that the control circuit 8 increase the measurement frequency of the open circuit voltage during a period when the amount of change is large, and decrease the measurement frequency of the open circuit voltage during a period when the change amount is not large. When such control is performed, the first period is shifted on the time axis from the second period. Therefore, when the measurement frequency of the open circuit voltage is increased, the control circuit 8 sets the second period to the first period. It is preferable to superimpose in time. Conversely, when the measurement frequency is lowered, it is preferable to overlap the first time with the second period.

  Also, with respect to the secondary battery 92, the charging rate is not constant with respect to time. The control circuit 8 may reduce the frequency of measuring the voltage of the secondary battery 92 and increase the frequency of measurement during other periods because the charging speed may be increased when there is a margin until full charge. Is desirable. When such control is performed, the second period is shifted from the first period on the time axis, so at least the control circuit 8 sets the first period to the second period when there is no allowance until full charge. It is preferable to superimpose in time.

  As described above, the control circuit 8 preferably obtains the change amount of the maximum power point per unit time and the difference between the current voltage value of the secondary battery 92 with respect to the full charge voltage, and the change amount of the maximum power point is If so, select the second period and overlap it with the first period. On the other hand, when the difference with respect to the full charge voltage is small, the first period is selected so as to overlap the second period.

  As described above, when the surrounding environment of the power generation element 91 changes, the power generation amount changes. The ambient environment is a temperature difference in the case of a thermoelectric conversion element, and an illuminance amount in the case of a solar cell. As the surrounding environment changes, the maximum power point of the power generation element 91 also changes. Therefore, in order to efficiently charge the secondary battery 92, the voltage tracking method is used in the charge / discharge system 9. Yes. A disadvantage of the voltage tracking method is that, as already mentioned, power cannot be taken out during the measurement of the open circuit voltage (that is, during the first period). Here, in order to make the explanation easy to understand, the initial value of the open-circuit voltage measurement period in the charge / discharge system 9 is 10 seconds. Specifically, the first period is 1 second, and the remaining 9 seconds are used for power extraction.

  After the operation of the charge / discharge system 9 starts, when the amount of change in the amount of power generation becomes greater than a predetermined reference value due to changes in the surrounding environment (that is, when the amount of change per unit time of the maximum power point increases), the control circuit 8 Makes the measurement period of the open-circuit voltage relatively short, for example, 5 seconds. As described above, the frequency at which the first period arrives is relatively increased, and thereby, the power can be efficiently extracted from the power generation element 91 by quickly following the fluctuation of the maximum power point. Further, when the arrival frequency of the first period is increased as described above, the control circuit 8 selects the second period and overlaps it with the first period.

  On the other hand, when the change amount of the power generation amount becomes small, the control circuit 8 makes the open voltage measurement period relatively long, for example, 30 seconds. Thereby, since the frequency at which the first period arrives can be relatively reduced, it is possible to suppress a loss of charging opportunity from the power generation element 91 to the secondary battery 92, and to extract power from the power generation element 91 with high efficiency. Is possible.

  Further, regarding the secondary battery 92, when the charging is continued after full charging, the temperature of the battery gradually increases. This temperature increase occurs because the supplied electric power is not used for charging but is converted into heat. As a result, the performance of the secondary battery 92 is deteriorated, which affects its life. Therefore, it is important to avoid overcharging the secondary battery 92. For this purpose, the charge / discharge system 9 uses a pulse charging method.

  However, in the pulse charging method, since the voltage value of the secondary battery 92 is measured during the charging suspension period (that is, during the second period), the charging opportunity is lost. Here, in order to make the following explanation easy to understand, it is assumed that the measurement period of the voltage value of the secondary battery 92 in the charge / discharge system 9 is initially 30 seconds. Specifically, the second period is 1 second, and the remaining 29 seconds are used for charging.

  When the voltage value of the secondary battery 92 is small (that is, the amount of charge is small) after the start of the operation of the charge / discharge system 9 and the possibility that the battery is fully charged is low, the control circuit 8 The measurement period of the voltage value is set relatively long, for example, 60 seconds. Thereby, since the frequency with which the second period arrives relatively decreases, it becomes possible to efficiently charge the secondary battery 92 with the power from the power generation element 91. Further, when the arrival frequency of the second period is reduced as described above, the control circuit 8 selects the first period and overlaps it with the second period.

  On the other hand, when there is a high possibility that the battery will be fully charged soon, the control circuit 8 sets the measurement period of the voltage value of the secondary battery 92 to be relatively short, for example, 15 seconds. Thereby, since the frequency with which the second period arrives can be relatively increased, the possibility of overcharging can be suppressed. Further, even when the arrival frequency of the second period is increased as described above, the control circuit 8 selects the first period and overlaps it with the second period.

《Specific application examples》
By the way, in the present charge / discharge system 9, the thermoelectric conversion element as the power generation element 91 generates power using waste heat generated in the image forming apparatus 1. This electric power is temporarily stored in the secondary battery 92 and then supplied to the load 96. In general, the image forming apparatus 1 transitions from a power saving mode (that is, a sleep mode or a standby mode) to a print mode to execute printing. Due to the transition to the printing mode, the temperature of the fixing device 6 greatly changes, so the maximum power point of the thermoelectric conversion element also varies.

  As shown in FIG. 7, the present inventor attached temperature sensors Se <b> 1 to Se <b> 3 (specifically, thermocouples or thermistors) to predetermined positions of the fixing device 6 of the image forming apparatus 1. Specifically, the mounting positions of the sensors Se1, Se2, Se3 are near the front end, the center, and the rear end of the fixing device 6. Then, as shown in FIG. 8, the image forming apparatus 1 was operated in the order of power-off mode → continuous printing mode → sleep mode. Temporal changes in temperature detected by the sensors Se1, Se2, and Se3 during operation are indicated by solid lines, thin broken lines, and sparse broken lines in the lower part of FIG. In order to roughly represent the temperature difference of the thermoelectric conversion elements, the time change of the temperature in the atmosphere outside the fixing device 6 is also indicated by a dashed line in the lower part of FIG. Specifically, the temperature difference is an absolute value of the difference between the temperature of the fixing device 6 and the temperature in the atmosphere.

  As can be seen from FIG. 8, in the image forming apparatus 1, the temperature of the fixing device 6 rises or falls due to the transition of the operation mode, and the maximum power point of the power generating element 91 changes due to the temperature change. In addition, since the speed of temperature change varies depending on the mounting location of the power generation element 91, the maximum power point changes. However, how the temperature changes in accordance with the transition of the operation mode of the image forming apparatus 1 can be estimated to some extent by repeating the experiment. Therefore, in the time interval where the temperature rising rate or the temperature decreasing rate is large, such as time intervals T1 and T3 in FIG. 8, the control circuit 8 is programmed to increase the arrival frequency of the first period and measure the open circuit voltage at short intervals. The Further, every time the open circuit voltage is measured, the maximum power point of the power generation element 91 is derived, and then the constant voltage circuit 951 converts the voltage value of the power generation element 91 into the charging voltage of the secondary battery 92, and the constant current circuit 952. The current value (see FIG. 2) is programmed to be updated to match the maximum power point. As a result, the secondary battery 92 is efficiently charged.

  On the other hand, in the time interval where the temperature increase rate or temperature decrease rate is small as in time intervals T2 and T4 in FIG. 8, the control circuit 8 is programmed to reduce the arrival frequency of the first period and measure the open circuit voltage at long intervals. Is done. Thereafter, the secondary battery 92 is efficiently charged by the same method as described above.

  In the above description, the temperature change in the case of transition from the power-off mode to the continuous printing mode to the sleep mode has been described as an example. However, the present invention is not limited to this, but has been described as a change, but may be a combination of other operation modes (for example, a copy mode, a single print mode, a scan mode, and a standby mode).

  In addition, even if some temperature fluctuation is assumed during an operation mode in which the temperature change is assumed to be gradual, voltage follow-up can be achieved by increasing the frequency of open-circuit voltage measurement and preparing for temperature fluctuation. The performance degradation of the law can be prevented.

  In addition to changing the operation mode, the open-circuit voltage measurement frequency is increased according to the type of sheet Sh (for example, plain paper, thick paper, etc.), the number of printed pages, and the size of the sheet Sh (for example, A4, A3, etc.). May be.

  As described above, when the temperature difference of the thermoelectric conversion element can be predicted to some extent, by changing the measurement frequency of the open circuit voltage and the measurement frequency of the voltage value of the secondary battery 92 to the secondary battery 92, Efficient charging is performed. Here, FIG. 9 is a diagram illustrating the measurement frequency of the open-circuit voltage (voltage value of the secondary battery 92) for each operation mode of the image forming apparatus 1 and at the time of transition to another operation mode. As shown in FIG. 9, in the sleep mode, in the power-off mode and in the standby mode, the temperature difference between the thermoelectric conversion elements is predicted to be stable and small, so the frequency of measurement of the open circuit voltage is relatively reduced. Further, at the time of transition to another mode, as described above, the measurement frequency of the open circuit voltage or the like is made variable.

  In the continuous printing mode, the temperature difference differs between when the sheet Sh is passing through the fixing device 6 and when it is not. That is, in the continuous printing mode, the open voltage is predicted to fluctuate irregularly immediately after the sheet Sh passes through the fixing device 6 or immediately after being introduced into the fixing device 6, so that the measurement frequency of the open voltage or the like is variable. . In other periods, the temperature difference between the thermoelectric conversion elements is predicted to be stable and large, and therefore the frequency of measurement of the open-circuit voltage or the like is relatively reduced. In this case, the control circuit 8 further overlaps the first period with the second period.

  Further, when changing to another mode, for example, when changing from the continuous printing mode to the standby mode, an instruction to change the operation mode is sent to the control circuit 8. Here, the standby mode is an operation mode in which the image forming apparatus 1 can immediately shift to a state in which a printing operation can be performed by a change instruction. In this standby mode, since the preliminary temperature adjustment of the fixing device 6 is performed, the temperature difference between the thermoelectric conversion elements is expected to be stable and large, and therefore the frequency of measuring the open-circuit voltage is reduced. In this case, the control circuit 8 makes the first period overlap with the second period.

  The image forming apparatus 1 can also include a dye-sensitized solar cell that can generate power with room light as the power generation element 91. Such an image forming apparatus 1 is installed in an office, for example. Here, Table 1 below is a diagram showing an example of office operating hours.

  It is considered that the amount of power generated by the power generation element 91 is large because the image forming apparatus 1 is irradiated with illumination light during the normal working hours. Therefore, in the normal working hours, it is preferable to superimpose the voltage follow-up method on the first period, which is the open voltage measurement period, and the second period, which is the charging suspension period of the secondary battery 92.

  On the other hand, in the midnight time zone, it is highly possible that the image forming apparatus 1 is not irradiated with illumination light. Therefore, in the midnight time zone, it is preferable to prioritize charging of the secondary battery 92 and to match the first period with the second period.

  In addition, during the early morning work, overtime, or break time period, the amount of illumination light is detected by the illuminance sensor built in the image forming apparatus 1, and if this detected value exceeds a predetermined reference value, the first period is given priority. Otherwise, priority is given to the second period. Such control may be executed during normal work hours.

  Further, the image forming apparatus 1 can be configured not to perform the above-described processing according to time zones on holidays. Alternatively, if the image forming apparatus 1 is irradiated with illumination light exceeding a predetermined reference value, the secondary battery 92 is charged with the electric power of the power generation element 91 while overlapping the second period with the first period. It doesn't matter. When the voltage value of the secondary battery 92 is close to full charge or full charge, the image forming apparatus 1 forcibly charges the second period while overlapping the first period. The charging operation may be stopped in some cases.

  The case where solar electrons are used as the power generation element 91 has been described above. However, the present invention is not limited to this. For example, even when another type of power generation element 91 such as a piezoelectric element or a thermoelectric conversion element is used, the second period is overlapped with the first period in consideration of the office operating time. Or the second period may overlap the first period.

  In the above description, the installation space is an office. However, the present invention is not limited to this. For example, even when the image forming apparatus 1 is installed in another space such as a factory or a store, the second period is set in the first period in consideration of the operation time in each installation space. The periods may be overlapped, or the second period may be overlapped with the first period.

  Further, as shown in Table 2 below, the sunshine hours for each season vary depending on the installation area of the image forming apparatus 1. Therefore, in a season with long sunshine hours, it is preferable to prioritize the voltage tracking method and overlap the second period, which is the charging suspension period of the secondary battery 92, with the first period, which is the measurement period of the open circuit voltage. On the other hand, in a season with little sunshine hours, it is preferable to prioritize charging of the secondary battery 92 and to match the first period with the second period.

  Even in the season when the sunshine hours are short, the light intensity is detected by the illuminance sensor built in the image forming apparatus 1, and the first period is given priority if the detected value exceeds a predetermined reference value. Otherwise, the second period takes precedence. In this case, if a sufficient amount of light cannot be obtained, the charging of the secondary battery 92 may be stopped. Such control may be executed in a season with a long sunshine time.

  Further, depending on the installation environment of the image forming apparatus 1, the light source of the main incident light to the solar cell may change. Specifically, when the image forming apparatus 1 is installed near the window, the main incident light is sunlight, but when it is installed at a location away from the window, the main incident light is illumination light. Assuming such a situation, the light amount is detected by an illuminance sensor built in the image forming apparatus 1, and if this detection value exceeds the reference value determined for each installation location, the first period is given priority. Otherwise, priority is given to the second period.

  In addition, when the secondary battery 92 is fully charged or close to it, the control circuit 8 forcibly superimposes the first period on the second period regardless of the time zone and the installation environment. Stop charging control.

<Example of specific processing of control circuit>
Next, an example of specific charging control of the control circuit 8 of FIGS. 1 and 2 will be described with reference to the flowchart of FIG. In FIG. 10, if the power generating element 91 is capable of generating power (S01), the control circuit 8 temporarily sets the open voltage measurement period (that is, the frequency of the first period) by the voltage tracking method (S02). Next, the control circuit 8 temporarily sets the measurement period (that is, the frequency of the second period) of the voltage value of the secondary battery 92 by the pulse charging method (S03). Thereafter, the control circuit 8 sets the first period and the second period by superimposing either one of the frequencies temporarily set for the first period and the second period on the other (S04). Next, the control circuit 8 controls the charging of the power generated by the power generation element 91 to the secondary battery 92 (S05). In S05, the control circuit 8 measures the open circuit voltage and the voltage value of the secondary battery 92 in the first period and the second period set in S04. The control circuit 8 sets the maximum voltage point current of the constant current circuit 952 according to the measured open circuit voltage. Further, the control circuit 8 compares the measured voltage value of the secondary battery 92 with a predetermined reference value to determine whether or not the fully charged voltage has been reached (S06).

  Here, FIG. 11 is a flowchart showing a first example of detailed processing of S02 of FIG. In FIG. 11, the control circuit 8 first determines whether or not there is an instruction to change the operation mode of the image forming apparatus 1 (S11). If there is no change instruction, the frequency of the first period is temporarily set to a relatively long 10 seconds (S12). At this time, fine adjustment may be added to 10 seconds, which is the frequency of the first period, according to the increase rate or decrease rate of the open circuit voltage. This fine adjustment is the same for S14, S17, S18, and S110.

  If there is a change instruction in S11, the control circuit 8 determines whether the changed operation mode is the power-off mode or the sleep mode (S13). When it is determined Yes, the frequency of the first period is temporarily set to a relatively short 5 seconds (S14).

  When it is determined No in S13, the control circuit 8 determines whether or not the changed operation mode is the standby mode (S15). When it is determined Yes, the control circuit 8 determines whether or not it is a transition from the power-off mode or the sleep mode (S16). When it is determined Yes, the frequency of the first period is temporarily set to a relatively short 5 seconds (S17). When it is determined No, the frequency of the first period is temporarily set to a relatively short 5 seconds (S18).

  If it is determined No in S15, the control circuit 8 determines whether or not the print mode is changed (S19). When determining Yes, the control circuit 8 temporarily sets the frequency of the first period to a relatively short 5 seconds (S110).

  After execution of S12, S14, S17, S18, and S110, the control circuit 8 exits S02 of FIG. 10 and performs S03. If it is determined No in S19, the control circuit 8 displays an error, etc., assuming that a trouble has occurred.

  In the above description, the frequency of the first period is uniformly 5 seconds in S14, S17, S18, and S110. However, the present invention is not limited to this, and another value may be assigned.

  FIG. 12 is a flowchart showing a second example of detailed processing in S02 of FIG. In FIG. 12, the control circuit 8 determines whether the power generation amount of the power generation element 91 is a time zone in which a constant amount can be expected or an environmental condition (S21). If determined No, the control circuit 8 temporarily sets the frequency of the first cycle to a relatively long 10 seconds (S22). On the other hand, if the determination is Yes, the control circuit 8 temporarily sets the frequency of the first cycle to a relatively short 5 seconds (S23). In S22 and S23, fine adjustment may be added to the temporarily set frequency of the first period according to the increase rate or decrease rate of the open circuit voltage. After execution of S22 and S23, the control circuit 8 exits S02 of FIG. 10 and performs S03.

  FIG. 13 is a flowchart illustrating the detailed process of S03 of FIG. In FIG. 13, the control circuit 8 determines whether or not the voltage value of the secondary battery 92 has reached a reference value indicating full charge (S31). If determined No, the control circuit 8 temporarily sets the frequency of the second cycle to a relatively long 30 seconds (S32). On the other hand, if the determination is Yes, the control circuit 8 temporarily sets the frequency of the second period to a relatively short 15 seconds (S33). After execution of S32 and S33, the control circuit 8 exits S03 of FIG. 10 and performs S04.

  The charge / discharge system according to the present invention can reduce the loss of electric power generated by the power generation element, and is suitable for a copying machine, a printer, a facsimile machine, and a multifunction machine having these functions.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 8 Control circuit 9 Charging / discharging system 91 Power generation element 92 Secondary battery 93 Power transmission path 94 Switch part 95 Extraction part 96 Load

Claims (13)

A power generating element capable of generating power at the maximum power point;
A secondary battery connected to the power generation element via a power transmission path, capable of storing the power generated by the power generation element, and capable of discharging to supply power to a load;
A control circuit for obtaining an open voltage of the power generation element during a predetermined first period and deriving a current maximum power point of the power generation element;
Based on the maximum power point derived by the control circuit, a take-out unit for taking out the power generated by the power generation element outside the first period,
The control circuit further obtains a voltage value of the secondary battery for charge control during a second period in which charging to the secondary battery is suspended, and outside the second period, Control the charging of the extracted power to the secondary battery,
The first period and the second period overlap in time,
The control circuit includes:
Based on the amount of change in the power generation amount of the power generation element, select the second period and overlap the first period,
Based on the voltage value of the secondary battery, Ru superposed on said second time period by selecting the first period, the charge and discharge system. Wherein the control circuit, based on the amount of change in power generation by the power generating device, when you change the arrival frequency of the first period, superimposed on the first period and select the second period, according to claim 1 Charging and discharging system. Wherein the control circuit, based on said voltage value of the secondary battery, when you change the arrival frequency of the second period, superimposed on the said selected first time period the second period, according to claim 1 or 2 Charging and discharging system. In the case where the charge / discharge system is mounted on a predetermined device,
2. The control circuit overlaps the second period with the first period when the open circuit voltage of the power generating element is assumed to fluctuate irregularly due to the operation of the predetermined device. The charge / discharge system according to any one of to 3 . In the case where the charge / discharge system is mounted on a predetermined device,
The control circuit overlaps the first period with the second period when it is assumed that the open circuit voltage of the power generating element does not substantially vary due to the operation of the predetermined device. The charging / discharging system in any one of 1-4 . The predetermined apparatus is an image forming apparatus that individually prints images on a plurality of sheets in a continuous printing mode,
When it is assumed that the open circuit voltage of the power generating element does not substantially vary by continuously executing the continuous printing mode as the operation of the predetermined device, the control circuit sets the first period to the first period. The charge / discharge system according to claim 5 , wherein the charge / discharge system overlaps with the second period. In the case where the charge / discharge system is mounted on an image forming apparatus capable of executing an operation mode capable of shifting to an operable state by a predetermined return request,
Wherein said control circuit, when in the image forming apparatus is executing said operation mode is superimposed the first period to the second period, the charge and discharge system according to any of claims 1-3. The charge / discharge system according to claim 7 , wherein the operation mode is a standby mode in which preliminary temperature adjustment of a fixing device provided in the image forming apparatus is performed. Wherein the control circuit, wherein the time period is large power generation amount by the power generation device, superimposing the second period to the first period, the charge and discharge system according to any of claims 1-8. The charge / discharge system according to any one of claims 1 to 9 , wherein the control circuit overlaps the first period with the second period in a time zone in which the amount of power generated by the power generation element is small. Wherein the control circuit comprises at by the power generation opportunities noisy environments the power generation element, superposing the second period to the first period, the charge and discharge system according to any of claims 1-8. The charge / discharge system according to any one of claims 1 to 11 , wherein one of the first period and the second period is overlapped with the other and set at the same frequency. The charge / discharge system according to any one of claims 1 to 11 , wherein one of the first period and the second period is overlapped with the other, but is set to a different frequency.

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