Image formation apparatus and associated method of storing power

A power storage apparatus is disclosed, which includes a charge-able and discharge-able capacitor unit, discharged power being supplied to an electrical load. The power storage apparatus includes a detection unit configured to determine whether an amount of power stored by the capacitor unit falls less than a predetermined magnitude at a predetermined voltage. Degradation of the power storage apparatus is determined based on a detection result of the detection unit, and a setting value concerning charging and discharging is adjusted.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a power storage apparatus that can be charged, and can supply power to a load, a fixing apparatus serving as the load of the supplied power, and an image formation apparatus equipped with the fixing apparatus, such as a copying machine, a printer, a facsimile apparatus, and a multifunctional machine capable of any combination of copying, printing, and facsimile operations.

2. Description of the Related Art

Conventionally, a technology of providing an auxiliary power storage apparatus in addition to a main power supply has been known (for example, Patent Reference 1). The technology aims at improving operability of the image formation apparatus by shortening a time required for the temperature of the fixing apparatus to rise when starting operations, the image formation apparatus using electrophotography methods. The technology also aims at reducing the power consumption of the fixing apparatus for energy savings.

The fixing apparatus is usually constituted by a fixing roller that includes a heating member, and a pressurization roller that contacts the fixing roller with pressure.

In the image formation apparatus, a toner image is formed on the surface of a recording medium that is conveyed along a conveyance path of the image formation apparatus. The recording medium that supports and carries the toner image, which toner image is yet to be fixed, further travels along the conveyance path at a predetermined conveyance speed, and reaches the fixing apparatus. Then, the recording medium travels between the fixing roller and the pressurization roller (called a nip), the fixing roller applies heat to the recording medium, and both rollers apply pressure to the recording medium such that the toner image is fixed. The recording medium carrying the fixed image is sent out from the nip, and is discharged from the image formation apparatus.

The image formation apparatus includes a main power supply that is connected to commercial main power, and provides power to loads, such as the fixing apparatus, of the image formation apparatus. In addition to the main power supply, the image formation apparatus includes an auxiliary power supply consisting of a power storage apparatus that provides auxiliary power by discharging stored power to the fixing apparatus as required.

The power storage apparatus includes

one or more capacitor units (cell units) that are capable of charging and discharging,

a switching unit that switches between charging and discharging states of the capacitor units,

a converting unit that rectifies alternating current power (AC) provided from the commercial main power supply into direct current (DC) power, the DC power being provided to the capacitor units,

devices, such as a FET, and

connection terminals for providing power to the loads, all of which are electrically connected as required.

When the main power supply of the image formation apparatus is turned on (i.e., when the image formation apparatus is started), while the main power supply connected to the commercial main power supplies power to the fixing apparatus, the power storage apparatus serving as the auxiliary power supply also supplies power to the fixing apparatus. Accordingly, power that is greater than rated (e.g., 100V 15 A of the commercial main power) can be provided to the fixing apparatus, the power supplied by the power storage apparatus being added in. In this manner, the fixing roller can reach a desired temperature (fixing temperature) in a short time. Therefore, the image formation apparatus can become operational in a short time even after the main power has been disconnected for a long time, and the temperature of the fixing roller can be held low during a standby mode. In this way, the operability of the image formation apparatus is improved; and since the temperature of the fixing roller can be set up lower while in standby, the power consumption of the image formation apparatus is reduced.

Further, in addition to when the image formation apparatus is to start up initially, when there is great power consumption (for example, when image formation is continuously performed, when a document reading unit is operating, and when resuming operation after a prolonged standby state), the power storage apparatus provides the additional power to the fixing apparatus. In the cases such as exemplified above, the power storage apparatus supplements the insufficient power provided from the main power supply to the fixing apparatus. In this manner, stable and sufficient power is provided to the fixing roller of the fixing apparatus irrespective of the operation modes of the image formation apparatus, and the fixing temperature of the fixing roller can be properly maintained. Accordingly, even if the heat capacity of the fixing roller is small, the time required for the fixing roller to reach the operational temperature can be shortened while the fixing nature of an output image is always maintained at a proper level. In this manner, the fixing temperature while at standby can be lowered, the standby power consumption can be reduced, the heat dissipation loss is reduced, and as a result, energy savings are attained.

In addition, the capacitor unit of the power storage apparatus can be charged at any time as required after the image formation apparatus is started, when the image formation apparatus is operating at power less than the power available from the main power, and a part of the main power can be supplied to the power storage apparatus.

DESCRIPTION OF THE INVENTION

Problem(s) To Be Solved By the Invention

Conventionally, when the capacitor unit is degraded with the passage of time, the power (discharging power) that can be supplied to the fixing apparatus becomes insufficient, and the power storage apparatus cannot perform as desired. In this case, problems are in that it takes more time for the temperature of the fixing apparatus to rise, the fixing nature of the fixing apparatus is degraded, and the energy savings of the fixing apparatus cannot be attained.

The problems are common to generic power storage apparatuses, not being peculiar to the power storage apparatus for supplying the auxiliary power to the fixing apparatus of the image formation apparatus. That is, when the capacitor unit of the power storage apparatus is degraded, generally, power that can be provided to the load runs short, and the function the power storage apparatus is not attained as desired.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a power storage apparatus, a fixing apparatus therewith, and an image formation apparatus therewith that substantially obviate one or more of the problems caused by the limitations and disadvantages of the related art, the power storage apparatus of the present invention properly detecting a status of degradation of a capacitor unit of the power storage apparatus.

To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the inventors hereto have determined after research as follows.

That is, when the capacitor unit of the power storage apparatus is degraded, main phenomena are that its electrostatic capacity falls, and that its internal resistance increases. When the electrostatic capacity of the capacitor unit falls, power discharged from the capacitor unit declines. When the internal resistance of the capacitor unit increases, a part of the power is consumed inside the capacitor unit, and the power available to the fixing apparatus declines.

Specifically, if the power storage apparatus is controlled for constant-current charging or constant power charging, a charge time and discharge time for the same voltage of a degraded capacitor unit become shorter than those in early stages of the service life of the capacitor unit.

The present invention is based on the knowledge as described above.

To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides as follows.

An aspect of the present invention provides a power storage apparatus that includes a capacitor unit that is capable of being charged and discharging, discharged power being provided to a load, and a detection unit that detects that power stored by the capacitor unit falls below a predetermined level at a predetermined voltage.

Another aspect of the present invention provides the power storage apparatus, wherein the above-mentioned detection unit serves as a degradation detection unit that detects degradation of the power storage apparatus.

Another aspect of the present invention provides the power storage apparatus, wherein the detection unit includes a voltage detection unit to detect the voltage of the above-mentioned capacitor unit, and a time detection unit to measure an elapse of time.

According to another aspect of the present invention, the power storage apparatus includes an adjustment unit configured to adjust setting values concerning charging and discharging of the above-mentioned capacitor unit based on a result of the detection by the above-mentioned detection unit.

Another aspect of the present invention provides the power storage apparatus, wherein controls are carried out such that discharging is made possible when a charged voltage becomes greater than a predetermined value for a discharge start, and the above-mentioned adjustment unit increases a setting value of the above-mentioned discharge starting voltage, when the above-mentioned power is determined to be below a predetermined value.

Another aspect of the present invention provides the power storage apparatus, wherein the discharge starting voltage is adjusted to be no greater than a withstand voltage of the power storage apparatus.

Another aspect of the present invention provides the power storage apparatus, wherein discharge is stopped when a discharging voltage becomes below a predetermined value for stopping discharge, and the above-mentioned adjustment unit reduces the value the above-mentioned discharge stopping voltage, when the above-mentioned detection unit detects that the above-mentioned power becomes below a predetermined value.

Another aspect of the present invention provides the power storage apparatus, wherein the discharge stopping voltage is set at no less than a reverse potential generating voltage of the power storage apparatus.

Another aspect of the present invention provides the power storage apparatus, wherein charging is controlled so that the charging voltage reaches a predetermined target charge voltage, and the above-mentioned adjustment unit raises the predetermined target charge voltage, when the detection unit detects that the power becomes below the predetermined value.

Another aspect of the present invention provides the power storage apparatus, wherein the above-mentioned target charge voltage is adjusted no greater than the withstand voltage.

Another aspect of the present invention provides the power storage apparatus, wherein the detection unit determines that the power is below the predetermined value by determining whether one of a period between a first charging voltage and a second charging voltage, and a period between a first discharging voltage and a second discharging voltage, is less than a predetermined period.

Another aspect of the present invention provides the power storage apparatus, wherein the power is determined to be below a predetermined value by determining whether one of a charging voltage change and a discharging voltage change in a predetermined period is greater than a predetermined value.

Another aspect of the present invention provides the power storage apparatus, wherein degradation of the capacitor unit is determined by the detection unit detecting that the power falls below the predetermined value under the predetermined voltage, and in consideration of information concerning an operating environment.

Another aspect of the present invention provides the power storage apparatus, wherein degradation of the capacitor unit is determined by the detection unit detecting that the power falls below the predetermined value under the predetermined voltage two or more times.

Another aspect of the present invention provides the power storage apparatus, wherein a load, to which the power storage apparatus provides power, is a heating member.

Another aspect of the present invention provides the power storage apparatus, wherein the heating member is installed in a fixing apparatus that heats a toner image on a recording medium such that the toner image is fixed to the recording medium.

Another aspect of the present invention provides the fixing apparatus configured to fix the toner image to the recording medium by heating the toner image on the recording medium, the fixing apparatus being configured to receive power from the power storage apparatus of the present invention.

Another aspect of the present invention provides the image formation apparatus that includes the power storage apparatus of the present invention.

Another aspect of the present invention provides the image formation apparatus that includes a display unit that is configured to display a message that the power storage apparatus is degraded, when the detection unit detects that the power becomes below the predetermined value.

Another aspect of the present invention provides the image formation apparatus that includes an operating unit capable of adjusting the setting value concerning charging and discharging of the capacitor unit by an external input based on the displayed message.

Another aspect of the present invention provides the image formation apparatus that includes the fixing apparatus configured to thermally fix the toner image to the recording medium, and the power storage apparatus configured to provide power to the image formation apparatus.

Another aspect of the present invention provides the image formation apparatus that includes a changing unit that changes the number of sheets of the recording medium that are continuously conveyed to the fixing apparatus per unit time, and the changing unit reduces the number of sheets to be conveyed per the unit time when the detection unit detects that the power becomes below the predetermined value.

Another aspect of the present invention provides the image formation apparatus, wherein the changing unit reduces the conveyance number of sheets per the unit time by increasing intervals between conveyances of the sheets of the recording medium.

Another aspect of the present invention provides the image formation apparatus, wherein the changing unit reduces the conveyance number of sheets per the unit time by reducing the speed of the conveyance.

Here, in this specification of the present invention,

“charge power” represents the electrical energy stored in the power storage apparatus when charging, and

“discharge power” represents the electrical energy discharged from the power storage apparatus when discharging.

“power of charge power (charge power amount)” represents a product of the charge power and charge time, and is a synonym of “stored power”. Similarly,

“power of discharge power (discharge power amount)” represents a product of the discharge power and discharge time. Accordingly, in the case that the power storage apparatus is charged by constant current control or constant power control, the charge power amount is small if the charge time for reaching a predetermined charging voltage is short, and the discharge power amount is small if the discharge time from a predetermined discharging voltage is short.

EFFECT OF THE INVENTION

According to the present invention, it is detected whether the stored power of the capacitor unit becomes below the predetermined value at a predetermined voltage. In this manner, the present invention provides the power storage apparatus, the fixing apparatus, and the image formation apparatus that can detect degradation of the capacitor unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention are described with reference to the accompanying drawings. In the drawings, the same reference numbers indicate the same or corresponding components, and explanations thereof are not repeated, except that simplified explanations may be presented.

In the following, Embodiment 1 of the present invention is described with reference toFIG. 1throughFIG. 5.

First, the overall structure and operations of a copying machine1serving as the image formation apparatus1are described with reference toFIG. 1.

The image formation apparatus1includes a document reading unit2that optically reads image information of a document D, an exposure unit3that irradiates an exposure light L to a photo conductor drum5based on the image information read by the document reading unit2, an imaging unit4that forms a toner image on the photo conductor drum5, an imprint unit7that imprints the toner image formed on the photo conductor drum5to a recording medium P, a document conveyance unit (ADF)10that conveys the document D to the document reading unit2, feed units12,13, and14that store recording media P such as sheets of imprint paper, a fixing apparatus20that fixes the toner image to the recording medium P, a fixing roller21that is installed in the fixing apparatus20, a pressurization roller24that is installed in the fixing apparatus20, a main power supply40that supplies power to the fixing apparatus20and the like, and a power storage apparatus41that supplies auxiliary power to the fixing apparatus20.

With reference toFIG. 1, operations of normal image formation by the image formation apparatus are explained.

First, the document D is conveyed in the direction of an arrow inFIG. 1by the conveyance roller of the document conveyance unit10from a document stand, and passes on the top of the document reading unit2. At this time, the document reading unit2optically reads image information of the document D.

Then, the optical image information read by the document reading unit2is converted into an electrical signal, and is provided to the exposure unit3(write-in unit). Then, the exposure unit3emits the exposure light L, such as a laser beam, based on the electrical signal representing the image information, the exposure light L being emitted to the photo conductor drum5of the imaging unit4.

On the other hand, in the imaging unit4, the photo conductor drum5rotates clockwise as shown inFIG. 1, and the toner image corresponding to the image information is formed on the photo conductor drum5through predetermined imaging processes (an electrification process, an exposure process, a development process, and the like).

Then, the imprint unit7imprints the toner image formed on the photo conductor drum5on the recording medium P conveyed by the resist roller.

Further, operations concerning the recording medium P being conveyed to the imprint unit7are as follows.

First, one of the feed units12,13, and14is chosen either automatically or manually. In the following, the feed unit12is assumed as being chosen.

The top sheet of the recording medium P stored by the feed unit12is conveyed toward the position of a conveyance path K.

Then, the recording medium P passes the conveyance path K, and arrives at the position of a resist roller. Then, the recording medium P that arrives at the position of the resist roller waits for a proper timing such that the timing and position match with the toner image formed on the photo conductor drum5, and travels again toward the imprint unit7.

The recording medium P after the imprint process reaches the fixing apparatus20through the conveyance path K, after passing through the position of the imprint unit7. The recording medium P that reaches the fixing apparatus20is fed between the fixing roller21and the pressurization roller24, and the toner image is fixed by heat received from the fixing roller21and pressure received from both fixing roller21and pressurization roller24. The recording medium P, on which the image is fixed, is sent out from between the fixing roller21and the pressurization roller24and is discharged from the image formation apparatus1.

In this way, the image formation processes are completed.

Next, the structure and operations of the fixing apparatus20installed in the image formation apparatus1are explained in detail with reference toFIG. 2.

As shown inFIG. 2, the fixing apparatus20includes a thermistor37, a separation nail38, and a guide board35in addition to the fixing roller21, the pressurization roller24.

Here, the fixing roller21is constituted by a thin-walled cylinder that rotates in the direction of an arrow shown inFIG. 2, and two heaters22and23that serve as heating members and are fixed inside the thin-walled cylinder. The surface of the thin-walled cylinder of the fixing roller21is fluorocarbon-resin processed such that the mold-release characteristic of toner T is obtained. The heaters22and23of the fixing roller21are cylindrical heaters, each of which has a heating wire inside, with both ends being fixed to side plates of the fixing apparatus20. The heaters22and23, to which electric power is provided, apply heat to the thin-walled cylinder, which heat is then applied to the toner T on the recording medium P from the surface of the thin-walled cylinder.

Here, the main power supply40supplies power to the heater22(as indicated by a dotted line arrow Y1), and the power storage apparatus41supplies power to the heater23(as indicated by a dotted line arrow Y2). Further details are described below.

Further, the thermistor37is provided so as to contact the surface of the fixing roller21such that the temperature of the surface of the fixing roller21is measured. Magnitudes of power provided from the main power supply40and the power storage apparatus41are adjusted based on the roller surface temperature measured by the thermistor37.

Further, as shown inFIG. 2, the separation nail38is arranged rocking-free, touching the surface of the fixing roller21. The tip of the separation nail38touches the surface of the fixing roller21such that winding (coiling) of the recording medium P around the fixing roller21along with rotation of the fixing roller21is prevented from occurring, the recording medium P being sent out from between the fixing roller21and the pressurization roller24.

Here, the pressurization roller24that contacts and pressures the fixing roller21(through a pressurization mechanism that is not illustrated) is structured by a core metal, and two or more elastic layers formed around the perimeter of the core metal through an adhesion layer. The elastic layers of the pressurization roller24are 1 through 10 mm thick, and are made of a fluororubber, silicone rubber, foaming silicone rubber, etc. A mold release layer, thickness of which is 300 micrometers or less, is prepared on the surface of the elastic layers. The mold release layer is made of poly-imide, polyether imide, PES (polyether sulphide), PFA (4 fluoride ethylene perfuloro arkyl vinyl ether copolymer resin), etc.

Further, guide boards35are arranged on the entrance and the exit sides of the nip constituted by the fixing roller21and the pressurization roller24such that the recording medium P is properly guided for proper conveyance. The guide boards35are fixed to the side plate of the fixing apparatus20.

The fixing apparatus20as described above operates as follows.

First, when a main power switch of the image formation apparatus1is turned on, the main power supply40and the power storage apparatus41of the image formation apparatus1start supplying power to the heaters22and23, respectively, of the fixing roller21. Specifically, the main power supply40supplies power to the heater22, the power being based on the rated commercial main power supplied from a socket that is outside of the image formation apparatus1, and the power storage apparatus41discharges and supplies power to the heater23.

In this manner, the surface of the fixing roller21reaches a desired temperature (for example, 180 degrees C.) in a short time, and the image formation apparatus1becomes operational.

When the image formation apparatus1is operational, and a user pushes a copy start button, the fixing roller21and the pressurization roller24start rotating, being driven by a drive unit (not illustrated) in the directions of the arrows in FIG.2. The imaging processes as described above are performed such that

the recording medium P carrying the toner image T is guided by the guide boards35,

the recording medium P carrying the toner image T is fed between the fixing roller21and the pressurization roller24(movement in the direction of arrow Y10),

the toner image T is fixed to the recording medium P by the heat received from the fixing roller21and the pressure received from both fixing roller21and pressurization roller24, and

the recording medium P is discharged from between the fixing roller21and the pressurization rollers24(movement in the direction of arrow Y11).

Further, when the image formation apparatus1is consuming high power, the power storage apparatus41supplies power to the heater23.

Specifically, for example, when the document reading unit2is performing a scanning operation, the power consumption increases as compared with the time when the scanning operation is not performed, and the power storage apparatus41supplies power to the heater23. Further, when image formation is continuously performed, and the heat of the fixing roller21is taken by the recording media P that are continuously conveyed, the power storage apparatus41also supplies power to the heater23. Further, when the image formation apparatus1resumes operating after a prolonged standby state while the energy-saving mode functions and the temperature of the fixing roller40has become low, the power storage apparatus41also supplies power to the heater23. In this manner, insufficiency of the power provided to the fixing apparatus20from the main power supply40is supplemented by discharge power of the power storage apparatus41.

When the temperature of the fixing roller40is stabilized at about a saturation state, a small amount of power is intermittently supplied from the main power supply40to the heater22, and the power from the power storage apparatus41to the heater23is not necessary. At this time, remaining capacity of the power of the main power supply40is provided to charge the power storage apparatus41as shown by arrow Y3inFIG. 2for future discharging.

Next, the structure and operations of the power storage apparatus41of the image formation apparatus1are explained in full detail with reference toFIG. 3.

As shown inFIG. 3, the power storage apparatus41includes

a capacitor unit42(cell unit), to which power is charged and from which power is discharged,

a charging unit43configured to charge the capacitor unit42,

a switching unit44configured to switch between charging and discharging states of the capacitor unit42,

a voltmeter50serving as a voltage detection unit configured to detect the voltage of the capacitor unit42, and

a main power switch51.

As the capacitor unit42of the power storage apparatus41, an electric double layer capacitor, a nickel-cadmium battery, etc., can be used. When the switching unit44is turned on to the discharging side as illustrated inFIG. 3, the capacitor unit42discharges and supplies power to the heater23. When the switching unit44is turned on to the charging side, the charging unit43charges the capacitor unit42, the charging unit43rectifying the AC power provided from the main power supply40into DC power. Here, the change of the switching unit44is performed based on a change signal sent from a CPU48based on a predetermined control program stored in a memory of a control unit45. In addition, other than the structure of Embodiment 1 as described above, the switching unit44may be configured by an FET, etc., such that the capacitor unit42, which is a secondary heater, discharges and provides the power to the heater23.

Further, the control unit45controls the magnitude of the discharging power based on detection information of the thermistor37. Further, the power storage apparatus41is charged at constant current or constant power. That is, the power storage apparatus41is controlled so that constant-current charging or constant power charging is carried out.

Further, the CPU48of the control unit45receives information concerning the voltage of the capacitor unit42from the voltmeter50, and information concerning time from a timer49, the timer49serving as a time detection unit. The CPU48, the voltmeter50and the timer49serve as a degradation detection unit to detect degradation of the capacitor unit42by detecting that the power stored by the capacitor unit42falls below a predetermined value at a predetermined voltage. Details are described below.

The main power supply40is connected to the power storage apparatus41, the heater22that serves as the main heater, the main power switch51, a control switch47, and other loads (not illustrated) of the image formation apparatus1. When the main power switch51is closed, the power supply to the main heater22, the charge of the power storage apparatus41, and the like become possible. Here, the power supply to the heater22and the charge of the power storage apparatus41are performed based on a signal supplied by the control unit45based on the predetermined control program stored in the memory of the control unit45. That is, when the control switch47is closed, the power is supplied to the heater22. Further, when the switching unit44of the power storage apparatus41is connected to the charging unit43, the power storage apparatus41is charged.

Next, controls that characterize Embodiment 1 are described with reference toFIG. 4andFIG. 5.

According to Embodiment 1, the discharge power amount that the power storage apparatus41discharges is detected. Specifically, at the time of discharge, a time (discharge time), during which the voltage (discharging voltage) that remains in the capacitor unit42drops from a first discharging voltage (for example, 30V) to a second discharging voltage (for example, 20V) is measured using the voltmeter50and the timer49. Since a constant-current charge or constant-resistance discharge is carried out, in the case that the first discharging voltage (discharge starting voltage) is the same (under the condition of the same voltage), the shorter the measured discharge time is, the smaller the discharge power amount is.

When the discharge time (which can be directly translated into the discharge power amount) detected in this way becomes below a predetermined value, the control unit45determines that the capacitor unit42is degraded. If the capacitor unit42is degraded, in comparison with the early stages of the service life, the discharge time becomes shorter. The discharge power that the capacitor unit42can provide to the heater23decreases, and the desired heating effect cannot be obtained. Further, if the capacitor unit42is degraded, compared with the early stages of the service life, the charge time become shorter. Therefore, the charge power (stored power) that is charged to the capacitor unit42decreases.

In this manner, degradation of the capacitor unit42can be detected comparatively simply by detecting the shortened discharge time by the voltmeter50and the timer49.

In addition, it is desirable that the control unit45finally determines the degradation of the capacitor unit42after carrying out the detection of the discharge time being below the predetermined value two or more times. In this manner, incorrect detection of the degradation state can be prevented from occurring.

Further, determination of the degradation state of the capacitor unit42by the control unit45is desirably carried out in consideration of an operating environment of the power storage apparatus41. For example, when the power storage apparatus41is used under a high temperature environment and the discharge time is short, based on predetermined compensation data, the detected discharge time is compensated for and converted to a normal temperature environment. In this manner, the shortening of the discharge time due to the environment can be separated from what is due to degradation. In addition, the information concerning the operating environment is obtained by an operating environment detection unit such as a thermometer, a hygrometer, and the like.

According to Embodiment 1, setting values concerning charging/discharging are adjusted such that the discharge power amount is increased, based on degradation detection of the capacitor unit42, the detection being carried out by the CPU48, the timer49, and the voltage meter50serving as the degradation detection unit. Reference is made toFIG. 4.

Specifically, when the control unit45determines that a discharge time T1is less than a predetermined time T2, a predetermined discharge starting voltage is adjusted to 33V from 30V.

Details follow with reference toFIG. 4.

FIG. 4gives a graph that shows change of the discharge time when adjusting the discharge starting voltage based on the degradation detection. InFIG. 4, the horizontal axis shows the time (detected by the timer49), and the vertical axis shows the discharging voltage (which is in agreement with the charging voltage, and detected by the voltmeter50) of the capacitor unit42. Further, a dashed line S shows the discharge property of the capacitor unit42in the early stages of the service life of the capacitor unit42, a solid line R1shows the discharge property of the capacitor unit42that is degraded before adjusting the discharge starting voltage, and a solid line R2shows the discharge property of the degraded capacitor unit42after adjusting discharge starting voltage.

Here, the “discharge starting voltage” is a voltage at which the discharge from the capacitor unit42is enabled, and it is a value set up for controlling purposes. That is, when the charging voltage of the capacitor unit42has not reached the discharge starting voltage, the capacitor unit42does not supply the discharge power to the heater23. In other words, when the voltmeter50detects that the charging voltage of the capacitor unit42becomes greater than the discharge starting voltage, the switching unit44can be turned on to the discharging side.

Further, the charging voltage inFIG. 4is a “target charge voltage” (the charging voltage of the capacitor unit42targeted when charging), and is a value set up for controlling purposes. That is, when there are no instructions from the control unit45to start discharging, and when the charging voltage exceeds the discharge starting voltage, the capacitor unit42is charged until the charging voltage reaches the target charge voltage.

Further, the “discharge stopping voltage” is a voltage at which the discharge from the capacitor unit42is stopped, and is a value set up for controlling purposes. That is, the capacitor unit42does not have to stop supplying the discharged power to the heater23while the discharging voltage of the capacitor unit42has not reached the discharge stopping voltage. Specifically, when the voltmeter50detects that the discharging voltage of the capacitor unit42is below the discharge stopping voltage, the switching unit44turns off the connection to the heater23.

The dashed line S inFIG. 4shows the case wherein the discharge starting voltage is set at 30V, and the discharge time is a period from when the discharging voltage is equal to the discharge starting voltage (30 V) until the discharging voltage becomes the discharge stopping voltage (20 V), which represents the case of the early stages of the service life of the capacitor unit42, and is expressed by T1. The discharge power amount at this time is sufficient to supply the power to the heater23of the fixing roller21.

With the passage of time, degradation of the capacitor unit42is detected as described above. At this time, as shown by the solid line R1, the discharge time becomes T2, which is less than T1. The discharge power amount at this time is insufficient to properly supply the power to the heater23of the fixing roller21.

Accordingly, when the discharge time becomes below a predetermined value, and the degradation of the capacitor unit42is detected, the control unit45(serving as an adjustment unit) raises the setting value of the discharge starting voltage from 30 V to 33 V (in the direction indicated by a white arrow inFIG. 4). Then, as shown by the solid line R2, the discharge time from 33 V to 20 V becomes equal to the early stages discharge time T1. The discharge power amount at this time becomes almost equal to the initial available power amount, i.e., is sufficient to supply the power to the heater23.

In addition, the setting value of the discharge starting voltage after adjustment is arranged to be no greater than the withstand voltage (the maximum voltage to be used) of the capacitor unit42. Accordingly, reliable operation of the power storage apparatus41is ensured.

FIG. 5gives graphs showing state transitions of the fixing apparatus20, the power storage apparatus41, and the main power supply40when the image formation apparatus1of Embodiment 1 carries out image formation.

Here, the capacitor unit42of the power storage apparatus41is assumed be in a degradation state.

At (A) ofFIG. 5, a time change of the fixing temperature of the surface of the fixing roller21detected by the thermistor37is shown. Therein, a solid line M shows the fixing temperature change in the case where the discharge starting voltage is adjusted for degradation, and a dashed line N shows the fixing temperature change in the case where the adjustment is not performed.

At (B) ofFIG. 5, a time change of the supply power of the main power supply40and the power storage apparatus41is shown. Therein, a solid line Q1shows the supply power change of the main power supply40to the image formation apparatus1(i.e., to all the loads including but not limited to the heater22), and a dashed line Q2shows the supply power change to the heaters22and23from the main power supply40and the power storage apparatus41, respectively (note that this is the total of the supply power to the heaters22and23).

At (C) ofFIG. 5, a time change of a power amount remaining in the capacitor unit42of the power storage apparatus41is shown.

In all the graphs ofFIG. 5, the horizontal axis shows the time. Specifically, time W0is a preparation time, i.e., from the time when the image formation apparatus1is started after a state where the main power switch51is turned off for a long time. Time W1is time wherein scanning of the document D by the document reading unit2and image formation are carried out. Time W2is time wherein image formation is carried out based on the image information provided by the document reading unit2during the time W1. During the time W2, the document reading unit2does not perform scanning. Time W3is time during which the image formation apparatus1is in the standby mode without performing image formation, while the main power switch51is kept turned on following the time W2.

Further, time W0′ is time during which the image formation apparatus1is preparing for operation from the standby state. Time W1′ is time during which scanning of the document D by the document reading unit2and image formation are carried out. Time W2′ is time during which image formation is carried out without performing the scan by the document reading unit2.

If the power storage apparatus41is degraded, unless the discharge starting voltage is adjusted as explained above with reference toFIG. 4, the power storage apparatus41cannot provide sufficient power during the times W1and W1′ for supplementing the power from the main power supply40to the fixing apparatus20, with the operation of the document reading unit2ongoing, as shown by the dashed lines N at (A) ofFIG. 5. For this reason, in the times W1and W1′, poor fixing due to temperature drop of the fixing roller21occurs. In addition, a dashed line that is parallel to the horizontal axis at (A) ofFIG. 5represents the minimum fixing temperature, below which poor fixing is produced.

On the other hand, as shown by the solid lines M at (A) ofFIG. 5, even if the power storage apparatus41is degraded, by adjusting the discharge starting voltage as explained above with reference toFIG. 4, the power storage apparatus41is capable of supplementing the power from the main power supply40to the fixing apparatus20during the times W1and W1′. That is, during the times W1and W1′, as shown at (C) ofFIG. 5, the power storage apparatus41discharges, and as shown by the dashed lines Q2at (B) ofFIG. 5, the power supplied to the fixing apparatus20is increased. In this manner, during the times W1and W1′, the temperature dropping below the minimum fixing temperature can be prevented from occurring, and satisfactory fixing is obtained.

Since the drop of the discharge power amount accompanying the shortened discharge time is detected by the detection unit according to Embodiment 1 as explained above, the degradation state of the power storage apparatus41can be reliably managed. Furthermore, when the power storage apparatus41is degraded, the shortened discharge time is restored to the early stages level by adjusting the discharge starting voltage. The service life of the power storage apparatus41is prolonged by suppressing the discharge power drop and maintaining the performance of the power storage apparatus41, even if the power storage apparatus41is degraded.

As described above, according to Embodiment 1, time of the residual voltage of the capacitor unit42descending from the first discharging voltage to the second discharging voltage when discharging is detected, and based on this, the degradation of the capacitor unit42is determined. On the other hand, the degradation of the capacitor unit42can also be determined by detecting a voltage change of the capacitor unit42in a fixed time. That is, since the discharging voltage drop per unit time when discharging becomes greater when the capacitor unit42is degraded as compared with the early stages, an amount of voltage drop (discharging voltage change) per unit time represents the degree of the degradation. When the discharging voltage change becomes greater than a predetermined value, it is determined that the capacitor42is degraded, and the setting value of the discharge starting voltage is adjusted upward as described above. This variation provides the same effect as Embodiment 1.

As described above, according to Embodiment 1, the change of the discharge power amount of the power storage apparatus41when discharging is detected, and the degradation of the capacitor unit42is determined based on this. A different method is possible. That is, a change of the charge power amount of the power storage apparatus41when charging may be detected, and the degradation of the capacitor unit42may be determined based on this. Furthermore, the changes of both charge amount and discharge amount may be detected, and the degradation of the capacitor unit42may be determined based on the changes. Since the power storage apparatus41is charged by a constant current control, if the capacitor unit42is degraded, the charge time becomes short, and a charged power amount declines. Therefore, a time (charge time) for the charging voltage of the capacitor unit42to rise to a second charge voltage from a first charge voltage is detected, and if the charge time becomes shorter than a predetermined value, it is determined that the capacitor unit42is degraded. Then, the control unit45serving as the adjustment unit raises the discharge starting voltage as at Embodiment 1. This variation also gives the same effect as Embodiment 1.

Embodiment 2 of the present invention is described in detail with reference toFIG. 6.

FIG. 6is a graph that shows an adjustment control that is carried out when the power storage apparatus41is degraded according to Embodiment 2. In the case that the capacitor unit42of the power storage apparatus41is degraded, the discharge stopping voltage is adjusted according to Embodiment 2, which is different from Embodiment 1 wherein the discharge starting voltage is adjusted.

FIG. 6is a graph that shows a change of the discharge time when adjusting the discharge stopping voltage based on the same degradation detection carried out by the same degradation detection unit as Embodiment 1, the degradation detection unit being constituted by the CPU48, the timer49. InFIG. 6, the horizontal axis shows the time and the vertical axis shows the voltage of the capacitor unit42. Further, a dashed line S shows the discharge property of the capacitor unit42in the early stages of the service life, a solid line R1shows the discharge property of the capacitor unit42that is degraded before the discharge stopping voltage is adjusted, and a solid line R2shows the discharge property of the degraded capacitor unit42after the discharge stopping voltage is adjusted.

As shown by the dashed line S, in the early stages, the discharge stopping voltage is set at 20 V, and the discharge time from the discharge starting voltage (30 V) to the discharge stopping voltage 20 V is T1. The discharge power amount at this time is sufficient to provide power to the heater23of the fixing roller21.

With the passage of time, the capacitor unit42is degraded, which is detected as described above. At this time, the discharge time becomes shorter as shown by T2(refer to the solid line R1). The discharge power amount at this time is insufficient to provide power to the heater23of the fixing roller21.

At this instance (i.e., when the discharge time becomes shorter than a predetermined value at the same voltage, and degradation of the capacitor unit42is detected), the setting value of the discharge stopping voltage is adjusted downward to 18 V from 20 V by the control unit45as indicated by a white arrow inFIG. 6. Accordingly, as shown by the solid line R2, the discharge time from 30 V to the adjusted 18 V is made as long as T1. The discharge power amount at this time becomes almost equivalent to that of the early stages, and sufficient power can be supplied to the heater23.

In addition, the setting value of the discharge stopping voltage is adjusted to be no less than the reverse voltage generating voltage (i.e., the minimum voltage to be used) of the capacitor unit42. In this manner, the power storage apparatus41being reliable is offered.

Since the drop of the discharge power amount accompanying the shortened discharge time is detected by the degradation detection unit according to Embodiment 2 as explained above, the degradation state of the power storage apparatus41can be reliably managed. Furthermore, when the power storage apparatus41is degraded, the shortened discharge time is restored to that of the early stages by adjusting the discharge stopping voltage. In this manner, the service life of the power storage apparatus41is prolonged with the discharge power drop being suppressed, and the performance of power storage apparatus41being maintained, even if the power storage apparatus41is degraded.

Embodiment 3 of the present invention is described in detail with reference toFIG. 7.

FIG. 7is a graph that shows an adjustment control of Embodiment 3, which adjustment control is carried out when the power storage apparatus41is degraded. Embodiment 3 differs from Embodiments 1 and 2 in that Embodiment 3 adjusts a target charge voltage when the capacitor unit42of the power storage apparatus41is degraded, and that degradation of the capacitor unit42is also detected when charging in addition to when discharging.

According to Embodiment 3, the degradation of the capacitor unit42is detected, when charging and discharging, by the same degradation detection unit that includes the CPU48, the timer49, and the voltage meter50as Embodiments 1 and 2.FIG. 7is a graph that shows changes of the charge time and the discharge time when the target charge voltage is adjusted based on the degradation state of the capacitor unit42. InFIG. 7, the horizontal axis shows the time and the vertical axis shows the charging voltage and discharging voltage of the capacitor unit42.

Further, a dashed line s shows the charging property of the capacitor unit42in the early stages of the service life, a solid line r1shows the charging property of the capacitor unit42that is degraded before adjusting the target charge voltage, and a solid line r2shows the charging property of the degraded capacitor unit42after adjusting the target charge voltage. Furthermore, a dashed line S shows the discharging property of the capacitor unit42in the early stages, a solid line R1shows the discharging property of the capacitor unit42that is degraded before adjusting the target charge voltage, and a solid line R2shows the discharging property of the degraded capacitor unit42after adjusting the target charge voltage.

As shown by the dashed line s, in the early stages, the target charge voltage is set at 40 V, and the charge time required to raise the voltage from the discharge stopping voltage (20 V) to the target charge voltage (40 V) is expressed by t1. The charge power amount at this time is sufficient as the amount of charge to be stored in the capacitor unit42.

Further, as shown by the dashed line S, in the early stages, the target charge voltage is set at 40 V, and the discharge time during which the voltage drops from the target charge voltage 40 V to the discharge stopping voltage 20 V is expressed by T1. The discharge power amount at this time is sufficient to supply power to the heater23of the fixing roller21.

The degradation of the capacitor unit42is detected based on the charge time being shortened at the time of charging, and the discharge time being shortened at the time of discharging. When the capacitor unit42is degraded, as shown by the solid line r1, the charge time t2from the discharge stopping voltage (20V) to the target charge voltage (40V) becomes shorter than t1. The charged power amount at this time is insufficient as the amount of charge stored in the capacitor unit42. Further, as shown by the solid line R1, the discharge time from the target charge voltage (40V) to the discharge stopping voltage (20V), which discharge time is expressed by T2, becomes shorter than T1. The discharge power amount at this time is insufficient to supply the power to the heater23of the fixing roller21.

Thus, when at least one of the charge time and the discharge time becomes below respectively predetermined values at the same voltage, and degradation of the capacitor unit42is detected, the control unit45raises the setting value of the target charge voltage from 40 V to 43 V (the adjustment in the direction of the white arrow inFIG. 7). That is, as shown by the solid line r2, the charge time from the discharge stopping voltage 20 V to the adjusted target charge voltage 43 V becomes equivalent to t1, which is the charge time at the early stages. The charge power amount at this time becomes almost equivalent to that of the early stages, and is sufficient as the amount of charge stored in the capacitor unit42. Further, as shown by the solid line R2, the discharge time from the target charge voltage after adjustment, i.e., 43 V, to the discharge stopping voltage 20 V becomes equivalent to T1, which is the discharge time of the early stages. The discharge power amount at this time is almost equivalent to that of the early stages, and is sufficient to supply the power to the heater23.

In addition, the setting value of the target charge voltage is adjusted to be no greater than the withstand voltage (the maximum voltage to be used) of the capacitor unit42. In this manner, the power storage apparatus41offered provides high reliability.

As described above, according to Embodiment 3, the drop of the charge power amount and the drop of the discharge power amount accompanying the short charge time and discharge time, respectively, are detected by the detection unit (which includes the CPU48, the timer49, and the voltage meter50), and the degradation state of the power storage apparatus41is properly managed. Furthermore, when the power storage apparatus41is degraded, the shortened charge time and the shortened discharge time are restored to those at the early stages of the service life of the power storage apparatus41by adjusting the target charge voltage. In this manner, even when the capacitor unit42is degraded, the service life of the power storage apparatus41is prolonged, the charge power amount drop and the discharge power amount drop are prevented from occurring, and the performance of the power storage apparatus41is maintained.

As described above, according to Embodiments 1, 2 and 3, the control unit45controls based on the control program such that the degradation detection unit including the CPU48, the timer49, and the voltage meter50detects the degradation of the capacitor unit42, and adjusts the setting values of such as the discharge starting voltage so that the discharge power amount is adjusted. In contrast to this, the adjustment can be manually performed. That is, when the degradation detection unit (the CPU48, the timer49, and the voltage meter50) detects the degradation of the capacitor unit42, a message to that effect is displayed on a display (not illustrated) of the image formation apparatus1such that a person, e.g., a service-person, is notified of the fact. The service-person adjusts the setting value of the discharge starting voltage of the power storage apparatus41by manually operating (external input) an operations unit (not illustrated) according to the displayed message.

Further, according to Embodiments 1, 2 and 3, the degradation of the capacitor unit42is detected by the degradation detection unit (the CPU48, the timer49, and the voltage meter50serving as the degradation detection unit), and the setting value of the discharge starting voltage, etc., is adjusted such that the shortened discharge time is restored. If the degradation of the capacitor unit42progresses further, and if the discharge time cannot be restored to that of the early stages of the service life by adjusting the discharge starting voltage, etc., the number of sheets of the recording medium P that are conveyed per unit time (CPM) to the fixing apparatus20can be controlled downward. Specifically, in order to reduce the CPM, an interval of sheet conveyance can be controlled while keeping the conveyance speed; or alternatively, the conveyance speed can be reduced while keeping the sheet conveyance interval. In this manner, the heat consumption (dissipation) of the fixing roller21per unit time is reduced, and the degraded power storage apparatus41can continue to provide services.

Further, Embodiments 1, 2 and 3 describe the power storage apparatus41serving as an auxiliary power supply at the time of starting the image formation apparatus1, and when otherwise required. However, the present invention is not limited to this, but can be applied to any power storage apparatus that supplies power to any electrical load, providing the same highly efficient and long-life power storage apparatus as embodied as above.

Furthermore, it is evident that the present invention can be suitably modified within the limits of the technical thought of the present invention, besides as embodied above and as suggested above. The present invention is not limited to Embodiments described above. Further, the structure, the number of members, the position, the form, etc., as described above are not limited to what are described as Embodiments, but the present invention can be implemented with a suitable structure, a suitable number, a suitable position, a suitable form, etc.

The present application is based on Japanese Priority Application No. 2004-027796 filed on Feb. 4, 2004 with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.