The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2011-140400 filed in Japan on Jun. 24, 2011.
1. Field of the Invention
The present invention relates to an image forming apparatus, a power supply control method, and a computer-readable storage medium.
2. Description of the Related Art
Conventionally, image forming apparatuses including a secondary battery as a power supply source have been proposed. The secondary battery is charged with electric power generated by a power generation unit such as a solar cell. Such an image forming apparatus is designed to reduce electric power consumption by blocking the main power supply and supplying electric power to an apparatus main body from the secondary battery in an energy saving mode.
In the image forming apparatus of this type, if a state of charge (SOC) of the secondary battery is lowered significantly due to discharge in the energy saving mode, there arises a risk that electric power cannot be supplied appropriately. Then, a power supply control technique as described in Japanese Patent No. 4365052 has been proposed, for example. In the technique as described in Japanese Patent No. 4365052, if an output voltage of a secondary battery drops to be equal to or lower than a predetermined threshold in the energy saving mode, the power supply source is switched from the secondary battery to the main power supply. Thereafter, if the SOC of the secondary battery is recovered by getting a charge of electric power generated by the power generation unit and the output voltage of the secondary battery becomes higher than the threshold, the power supply source is switched from the main power supply to the secondary battery.
However, in this conventional technique, the threshold for switching the power supply source from the secondary battery to the main power supply is equal to the threshold for switching the power supply source from the main power supply to the secondary battery. Therefore, if the threshold is defined to be lower with reference to the lowest level of SOC that makes it possible to supply electric power appropriately, when the power supply source is switched from the main power supply to the secondary battery, the secondary battery starts discharging in a state where the SOC thereof is not sufficient so that the output voltage drops drastically to be equal to or lower than the threshold soon. As a result, the power supply source is switched frequently and electric power is consumed wastefully. On the other hand, if the threshold is defined to be higher with reference to a sufficient SOC under which the voltage immediately after the start of discharge does not drop drastically, time during which electric power is supplied from the secondary battery becomes shorter, resulting in an increase in electric power consumption.
Therefore, there is a need for an image forming apparatus and a power supply control method that can ensure time during which electric power is supplied from a secondary battery sufficiently while effectively preventing frequent switching of power supply sources so as to reduce electric power consumption appropriately.
It is an object of the present invention to at least partially solve the problems in the conventional technology.
According to an embodiment, there is provided an image forming apparatus that includes a main power supply configured to receive electric power from a commercial power supply; a power generation unit configured to generate electric power with natural energy; a secondary battery configured to serve as a power supply source while the electric power is not supplied from the main power supply, the secondary battery being charged with the electric power generated by the power generation unit; a voltage detector configured to detect an output voltage of the secondary battery; and a switching unit configured to switch the power supply source from the secondary battery to the main power supply when the output voltage becomes equal to or lower than a first threshold while the electric power is supplied from the secondary battery, and switch the power supply source from the main power supply to the secondary battery when the output voltage becomes equal to or higher than a second threshold that is higher than the first threshold while the electric power is supplied from the main power supply. The second threshold is set such that the output voltage, when the second battery has not been charged and a set time has passed after the power supply source is switched from the main power supply to the secondary battery, is higher than the first threshold.
According to another embodiment, there is provided a power supply control method performed in an image forming apparatus that includes a main power supply configured to receive electric power from a commercial power supply, a power generation unit configured to generate electric power with natural energy, and a secondary battery configured to serve as a power supply source while the electric power is not supplied from the main power supply, the secondary battery being charged with the electric power generated by the power generation unit. The power supply control method includes detecting an output voltage of the secondary battery; switching the power supply source from the secondary battery to the main power supply when the output voltage becomes equal to or lower than a first threshold while the electric power is supplied from the secondary battery; switching the power supply source from the main power supply to the secondary battery when the output voltage becomes equal to or higher than a second threshold that is higher than the first threshold while the electric power is supplied from the main power supply. The second threshold is set such that the output voltage, when the second battery has not been charged and a set time has passed after the power supply source is switched from the main power supply to the secondary battery, is higher than the first threshold.
According to still another embodiment, there is provided a non-transitory computer-readable storage medium with an executable program stored thereon and performed in an image forming apparatus that includes a main power supply configured to receive electric power from a commercial power supply, a power generation unit configured to generate electric power with natural energy, and a secondary battery configured to serve as a power supply source while the electric power is not supplied from the main power supply, the secondary battery being charged with the electric power generated by the power generation unit. The program instructs a processor of the image forming apparatus to perform detecting an output voltage of the secondary battery; switching the power supply source from the secondary battery to the main power supply when the output voltage becomes equal to or lower than a first threshold while the electric power is supplied from the secondary battery; switching the power supply source from the main power supply to the secondary battery when the output voltage becomes equal to or higher than a second threshold that is higher than the first threshold while the electric power is supplied from the main power supply. The second threshold is set such that the output voltage, when the second battery has not been charged and a set time has passed after the power supply source is switched from the main power supply to the secondary battery, is higher than the first threshold.
The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.
Hereinafter, preferable embodiments of an image forming apparatus and a power supply control method according to the invention are described in detail with reference to accompanying drawings.
The image forming apparatus 1 according to the embodiment includes the engine unit 10, the controller unit 20, and the power supply unit 30 as illustrated in
As illustrated in
In the image forming apparatus 1 according to the embodiment, electric power is supplied to the engine unit 10 from the power supply unit 30 with the power supply system of the D system Sd. When the operation mode of the image forming apparatus 1 is shifted to an energy saving mode, the power supply system of the D system Sd is blocked so that supply of electric power to the entire engine unit 10 is stopped.
As illustrated in
In the image forming apparatus 1 according to the embodiment, electric power is supplied to the IO ASIC 24, the external I/F 25 and the sensor 26 of the controller unit 20 from the power supply unit 30 with the power supply systems of the A system Sa and the B system Sb. Furthermore, electric power is supplied to the controller CPU 21, the DRAM 22, and the controller ASIC 23 of the controller unit 20 from the power supply unit 30 with the power supply system of the C system Sc. When the operation mode of the image forming apparatus 1 is shifted to the energy saving mode, the power supply system of the C system Sc is blocked so that supply of electric power to the controller CPU 21, the DRAM 22, and the controller ASIC 23 of the controller unit 20 is stopped. On the other hand, even when the operation mode of the image forming apparatus 1 is shifted to the energy saving mode, the power supply systems of the A system Sa and the B system Sb are not blocked so that supply of electric power to the IO ASIC 24, the external I/F 25, and the sensor 26 of the controller unit 20 is continued. It is to be noted that the power supply system of the A system Sa is a power supply system of 3.3 V that is commonly used for a power supply voltage of an IC, for example. The power supply system of the B system Sb is a power supply system of 1.1 V that is commonly used for a core voltage of an IC, for example. It is to be noted that the classification of the power supply system is an example and can be varied variously. For example, the power supply system may be classified into much more power supply systems in one power supply voltage.
As illustrated in
The AC power supply 31 is a power supply to which electric power is supplied from a commercial power supply. The main power supply circuit 32 AC-DC-converts and DC-DC-converts the AC power supply 31 and generates a desired direct voltage (5 V, 24 V, 3.3 V, 1.1 V, or the like) so as to supply the direct voltage to the engine unit 10 and the controller unit 20.
The power generator 33 is a power generation module that generates electric power with natural energy such as light and heat. As the power generator 33, a solar cell or a thermoelectric conversion element is preferable, for example. It is to be noted that because the solar cell and the thermoelectric conversion element are power generation units that are widely known, they are not described in detail.
The secondary battery 34 is charged with electric power generated by the power generator 33. When the operation mode of the image forming apparatus 1 is shifted to the energy saving mode and electric power is not supplied from the main power supply circuit 32 to the engine unit 10 and the controller unit 20, the secondary battery 34 serves as a power supply source to the controller unit 20.
When the operation mode of the image forming apparatus 1 is the energy saving mode, the switching circuits 35a and 35b selectively switch the power supply source to the controller unit 20 between the main power supply circuit 32 and the secondary battery 34 under control by the switching controller 37. The switching circuit 35a switches the power supply source of the A system Sa and the switching circuit 35b switches the power supply source of the B system Sb. It is to be noted that when the power supply system to the controller unit 20 is classified into much more systems, a switching circuit is provided for each power supply system.
The detecting circuit 36 detects an output voltage of the secondary battery 34. The output voltage of the secondary battery 34 that is detected by the detecting circuit 36 is transmitted to the switching controller 37.
The switching controller 37 controls switching of the power supply sources to the controller unit 20 by the switching circuits 35a and 35b based on an operation mode notification signal from the controller unit 20 and the output voltage of the secondary battery 34 that has been detected by the detecting circuit 36.
To be more specific, if the switching controller 37 receives an operation mode notification signal indicating that the operation mode of the image forming apparatus 1 is shifted to the energy saving mode from the controller unit 20, the switching controller 37 operates the switching circuits 35a and 35b so as to switch the power supply sources of the A system Sa and the B system Sb to the controller unit 20 from the main power supply circuit 32 to the secondary battery 34. With this, electric power of the AC power supply 31 is not consumed, thereby achieving electric power consumption of 0 W.
Furthermore, if an output voltage of the secondary battery 34 becomes equal to or lower than an A system first threshold Vth1
Furthermore, after the power supply source of the A system Sa has been switched from the secondary battery 34 to the main power supply circuit 32, if the output voltage of the secondary battery 34 further lowers to be equal to or lower than a B system first threshold Vth1
It is to be noted that in the embodiment, because the A system Sa is the power supply system of 3.3 V, the A system first threshold Vth1
If the power supply sources of the A system Sa and the B system Sb to the controller unit 20 are switched from the secondary battery 34 to the main power supply circuit 32, the secondary battery 34 is charged with electric power generated by the power generator 33 and the SOC thereof is recovered. Therefore, the output voltage of the secondary battery 34 is gradually increased. Then, if the output voltage of the secondary battery 34 becomes equal to or higher than a B system second threshold Vth2
Furthermore, after the power supply source of the B system Sb has been switched from the main power supply circuit 32 to the secondary battery 34, if the output voltage of the secondary battery 34 is further increased to be equal to or higher than an A system second threshold Vth2
For the A system first threshold Vth1
Next, power supply control when the image forming apparatus 1 is in the energy saving mode is described in detail with reference to
When the operation mode of the image forming apparatus 1 is shifted to the energy saving mode, the power supply sources of the A system Sa and the B system Sb to the controller unit 20 are switched from the main power supply circuit 32 to the secondary battery 34 as described above. With this, as illustrated in
Then, if the output voltage of the secondary battery 34 further lowers to be equal to or lower than the A system first threshold Vth1
Then, if the output voltage of the secondary battery 34 further lowers to be equal to or lower than the B system first threshold Vth1
As described above, in the image forming apparatus 1 according to the embodiment, if the output voltage of the secondary battery 34 lowers with the lowering of the SOC thereof due to discharge of the secondary battery 34 in the energy saving mode, the power supply sources to the controller unit 20 are switched from the secondary battery 34 to the main power supply circuit 32 stepwisely in the A system Sa and the B system Sb. A threshold for the output voltage of the secondary battery 34 for switching the power supply source of the A system Sa from the secondary battery 34 to the main power supply circuit 32 corresponds to the A system first threshold Vth1
If the power supply sources to the controller unit 20 are switched to the main power supply circuit 32 in both of the A system Sa and the B system Sb, the secondary battery 34 is charged with electric power generated by the power generator 33 and the SOC thereof is recovered. Then, if the SOC of the secondary battery 34 has been recovered sufficiently, the power supply sources to the controller unit 20 are switched from the main power supply circuit 32 to the secondary battery 34 in order to reduce electric power consumption in the energy saving mode. In this case, there arises the following problem if switching from the main power supply circuit 32 to the secondary battery 34 is performed using the thresholds (Vth1
For example, in a case of the B system Sb, if the power supply source of the B system Sb is switched from the main power supply circuit 32 to the secondary battery 34 immediately at a stage where the output voltage of the secondary battery 34 reaches the VVth1
On the other hand, when the Vth1
In order to solve the above-described problem, in the image forming apparatus 1 according to the embodiment, the thresholds (A system second threshold Vth2
A difference between the A system first threshold Vth1
V
th2
a
=V
th1
a
+ΔV
th
a
V
th2
b
=V
th1
b
+ΔV
th
b
If the secondary battery 34 is charged with electric power generated by the power generator 33 and the SOC thereof is recovered, the output voltage of the secondary battery 34 is gradually increased as illustrated in
Then, the output voltage of the secondary battery 34 is further increased to be equal to or higher than the A system second threshold Vth2
The B system second threshold Vth2
To be more specific, when the B system set time ΔTb has passed from the start of electric power supply from the secondary battery 34, the output voltage of the secondary battery 34 lowers with the lowering of the SOC thereof due to discharge of the secondary battery 34. A lowering amount of the output voltage of the secondary battery 34 during the B system set time ΔTb is assumed to be a voltage drop amount ΔVb. As the B system second threshold Vth2
Furthermore, the A system second threshold Vth2
To be more specific, when the A system set time ΔTa has passed from the start of electric power supply from the secondary battery 34, the output voltage of the secondary battery 34 lowers with the lowering of the SOC thereof due to discharge of the secondary battery 34. A lowering amount of the output voltage of the secondary battery 34 during the A system set time ΔTa is assumed to be a voltage drop amount ΔVa. As the A system second threshold Vth2
The A system set time ΔTa and the B system set time ΔTb are previously set in accordance with a set input by a user using an operation panel (not illustrated) included in the image forming apparatus 1, for example. Specifically, if a user performs the set input for setting an A system set time ΔTa and a B system set time ΔTb using the operation panel, the controller unit 20 receives the set input so as to set the A system set time ΔTa and the B system set time ΔTb. Furthermore, the controller unit 20 selects optimum values of the A system second threshold Vth2
Hereinafter, a specific method in which the controller unit 20 selects an optimum value of the B system second threshold Vth2
The discharge amount ΔCb of the secondary battery 34 during the B system set time ΔTb can be obtained in the following manner based on an electric power consumption amount (B system) Pb of the controller unit 20 per unit time in the energy saving mode, the B system set time ΔTb, and the supply voltage Vb (for example, 1.1 V) of the B system Sb.
ΔCb═Pb×ΔTb/Vb
The electric power consumption amount Pb of the controller unit 20 per unit time in the energy saving mode is a value estimated at a design stage. Because the number of devices to which power supply is supplied is limited in the energy saving mode, the estimation can be performed with relatively high accuracy.
It is to be noted that the power supply source of the B system Sb has been already switched from the main power supply circuit 32 to the secondary battery 34 at a time at which the power supply source of the A system Sa is switched from the main power supply circuit 32 to the secondary battery 34. Accordingly, when a discharge amount ΔCa of the secondary battery 34 during the A system set time ΔTa is obtained, not only the electric power consumption in the A system Sa but also that in the B system Sb are required to be taken into consideration. The discharge amount ΔCa of the secondary battery 34 during the A system set time ΔTa can be obtained in the following manner based on the above-described Pb and Vb, an electric power consumption amount (A system) Pa of the controller unit 20 per unit time in the energy saving mode, the A system set time ΔTa, the supply voltage Va (for example, 3.3 V) of the A system Sa.
ΔCa=(Pa×ΔTa/Va)+(Pb×ΔTa/Vb)
Furthermore, the voltage drop amount ΔVa of the secondary battery 34 during the A system set time ΔTa can be obtained based on the discharge amount ΔCa of the secondary battery 34 during the A system set time ΔTa and the discharge characteristic of the secondary battery 34.
As the B system second threshold Vth2
The A system second threshold Vth2
As described above, the A system second threshold Vth2
Furthermore, it is known that the discharge characteristic of the secondary battery 34 changes depending on a temperature of the secondary battery 34. Accordingly, a temperature sensor that detects an ambient temperature of the secondary battery 34 is provided as the sensor 26 of the controller unit 20. In addition, a plurality of discharge characteristics corresponding to a plurality of temperatures are previously held as information and the voltage drop amount ΔVa and the voltage drop amount ΔVb of the secondary battery 34 are obtained using a discharge characteristic corresponding to a temperature detected by the temperature sensor so as to select the A system second threshold Vth2
Furthermore, the discharge characteristic of the secondary battery 34 also changes depending on a discharge current of the secondary battery 34. In general, as the discharge current is larger, an influence by an internal resistance of the secondary battery 34 is larger and a lowering degree of the output voltage of the secondary battery 34 is larger. Accordingly, intensities of the discharge currents in the A system Sa and the B system Sb are previously obtained roughly, and the A system second threshold Vth2
Furthermore, errors of the A system second threshold Vth2
As described in detailed above with specific examples, in the image forming apparatus 1 according to the embodiment, after the power supply source to the controller unit 20 has been switched from the main power supply circuit 32 to the secondary battery 34 in the energy saving mode, if the output voltage of the secondary battery 34 becomes equal to or lower than the first threshold (A system first threshold Vth1
The specific embodiment of the invention has been described. However, the invention is not limited to the above-described embodiment as it is and can be embodied by varying constituent components in a range without departing from a scope of the invention at an execution stage. For example, the configuration and the operation of the image forming apparatus 1 according to the embodiment are merely examples and can be varied variously in accordance with an intended use or object.
The image forming apparatus 1 described above may be configured to have a hardware configuration using a normal computer including a control device, such as a central processing unit (CPU); a storage device, such as a read only memory (ROM) or a random access memory (RAM); and an external storage device, such as a hard disk drive (HDD) or a compact disc (CD)-drive.
The above processing performed by the image forming apparatus 1 may be provided as a computer program by being recorded in a computer-readable recording medium, such as a CD-ROM, a flexible disk (FD), a CD-R, or a digital versatile disk (DVD), in a computer-installable or a computer-executable file format.
The computer program performed may be stored in a computer connected to a network, such as the Internet, so as to be provided by being downloaded via the network. The computer program executed by the image forming apparatus 1 may be provided or distributed via a network, such as the Internet.
The present invention can achieve the effect of sufficiently ensuring time during which electric power is supplied from a secondary battery while effectively preventing frequent switching of power supply sources so as to reduce electric power consumption appropriately.
Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.
Number | Date | Country | Kind |
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2011-140400 | Jun 2011 | JP | national |