Image forming apparatus and initialization control method therefor

An immediate printing type image forming apparatus is provided of which the warm-up time is sufficiently shortened without causing any trouble to occur in the execution of image reading processing and/or image forming processing. The image forming apparatus is configured to determine a time required to raise the current temperature of the surface of a heating roller in a fixing unit to a predetermined temperature and increase the duty ratio of a power waveform to be fed to each of a copy lamp and a motor driving a polygon mirror when the time required thus determined is shorter than each of a time required to increase the current light quantity of the copy lamp to a predetermined light quantity and a time required to raise the current rotational speed of the motor to a predetermined speed, thereby turning each of the copy lamp and the motor into respective predetermined condition before the elapse of the determined time required.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to image forming apparatus for forming images electrophotographically such as copying machines and to an initialization control method for turning function devices included in such an image forming apparatus into their respective predetermined operable conditions after energization thereof.

2. Description of the Related Art

A certain length of time is required for function devices included in an electrophotographic image forming apparatus such as a fixing unit, light-source lamp unit and laser scanning unit to reach their respective operable conditions from the starting of energization thereof. The fixing unit, which functions to fuse a toner image and pressure-bond the fused toner image to a recording medium by heating and pressurizing the recording medium after a transfer step, needs to be heated to a predetermined temperature that allows the toner image to be fused from the starting of image forming processing. The light-source lamp unit, which functions to emit light for reading image information from an original document placed on a platen, needs to emit a predetermined quantity of light for obtaining image data of a proper density from the starting of image reading processing. The laser scanning unit, which functions to scan the surface of a photosensitive member with laser light modulated according to image data, has a polygon mirror for scanning with laser light in a primary scanning direction, which polygon mirror needs to rotate at a predetermined speed from the starting of the image forming processing.

Thus, such an electrophotographic image forming apparatus waits for the function devices of the apparatus to turn into their respective predetermined operable conditions (inclusive of the aforementioned predetermined temperature, predetermined light quantity and predetermined speed) after the starting of energization of the function devices and then starts the image reading processing and the image forming processing. When the units included in the apparatus turn into their respective predetermined operable conditions after the image forming apparatus has been powdered on or re-powered on following settlement of jam or the like, a ready lamp in a display section of the apparatus is turned on to notify the user that the image forming apparatus becomes ready for use.

Heretofore, the time required for the function devices of an image forming apparatus to turn into their respective predetermined operable conditions from the powering-on of the apparatus has been determined by the time required for the fixing unit to reach the predetermined temperature. The time required for the fixing unit to reach the predetermined temperature is what is called “warm-up time”. During the warm-up time of the image forming apparatus, preparations for the starting of image reading processing and image forming processing are made including operations such as to check and adjust the thickness of toner and to initialize the processing parts including the photosensitive member, .while the light-source lamp unit and the polygon mirror of the laser scanning unit are caused to reach the predetermined light quantity and the predetermined rotational speed, respectively. Controls exercised to effect these operations constitute initialization control of the image forming apparatus.

With the development of power-saving image forming apparatus proceeding in these years, the number of apparatus that require a few minutes' warm-up time like conventional apparatus is decreasing, while on the other hand the development of image forming apparatus of the immediate printing type which is capable of starting the image forming operation at substantially the same time with power-on is proceeding. In such an immediate printing type image forming apparatus, the efficiency in raising the temperature of a fusing roller (heating roller) included in the fixing unit by means of a heat source is improved by rendering the fusing roller thinner or by like means, thereby shortening the warm-up time. However, the following problems arise with such immediate printing type image forming apparatus if the warm-up time is determined only by the time required to raise the temperature of the fixing unit up to the predetermined temperature.

That is, as the case may be, a relatively long time is needed not only to raise the temperature of the fixing unit up to the predetermined temperature but also to turn other function devices such as the light-source lamp unit and laser scanning unit into their respective predetermined operable conditions during the warm-up time of the image forming apparatus. This is because the quantity of light emitted from a cold cathode tube that is used as the light-source lamp unit for power saving depends on the bulb temperature of the cold cathode tube and, hence, a prolonged time is required for the cold cathode tube to reach the predetermined light quantity, and because the rotational speed of the polygon mirror included in the laser scanning unit is rising with rising resolution and, hence, a sufficient acceleration time is required to raise the rotational speed of the motor driving the polygon mirror sufficiently.

For this reason, if the warm-up terminates in a short time from power-on at the time when the fixing unit reaches the predetermined temperature, the ready lamp in the display section is turned on even though other function devices of the apparatus than the fixing unit are not ready to operate and, hence, it is possible for the apparatus to accept an instruction from the user to start image reading processing and image forming processing despite the apparatus not in a ready-to-operate state as a whole.

If the image reading processing and image forming processing are executed with the apparatus not in the ready-to-operate state, troubles occur in the image reading processing and image forming processing such that images on an original document are not read normally due to an insufficient quantity of light emitted from the light-source lamp unit and that such images are written inaccurately on the photosensitive member due to the polygon mirror of the laser scanning unit rotating at an insufficient rotational speed. Thus, proper image formation becomes impossible.

In attempt to overcome the foregoing problem, a prior-art image forming apparatus disclosed in Japan Patent Laid Open sho No. 62-6277 is configured to terminate the warm-up after .detection is made of both of the two facts that: the temperature of the fixing unit has reached a predetermined temperature that allows a toner image to fuse; and the light quantity of the light-source lamp unit has reached a predetermined light quantity that allows images on an original document to be read accurately. Also, there have been proposed a number of configurations to terminate the warm-up after the satisfaction is made of both of the two conditions that: the temperature of the fixing unit has reached a predetermined temperature that allows a toner image to fuse; and the rotational speed of the polygon mirror in the laser scanning unit has reached a predetermined speed that allows images to be accurately written on the photosensitive member with laser light.

However, with such prior-art configurations to terminate the warm-up at the time when both of the temperature of the fixing unit and the light quantity of the light-source lamp unit have reached the predetermined temperature and the predetermined light quantity, respectively, or when both of the temperature of the fixing unit and the rotational speed of the polygon mirror in the laser scanning unit have reached the predetermined temperature and the predetermined speed, respectively, the warm-up time cannot be shortened sufficiently, but the warm-up is merely terminated upon elapse of the time required for the temperature of the fixing unit to reach the predetermined temperature, the time required for the light quantity of the light-source lamp unit to reach the predetermined light quantity, or the time required for the rotational speed of the polygon mirror in the laser scanning unit to reach the predetermined speed, whichever the longest. This does not lead to the realization of an immediate printing type image forming apparatus.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to realize an immediate printing type image forming apparatus which is capable of sufficiently shortening its warm-up time without causing any trouble to occur in image reading processing and/or image forming processing by turning all other function devices than a fixing unit into respective predetermined operable conditions before the time when the temperature of the fixing unit reaches the predetermined temperature.

With a view to resolving the foregoing problem, the present invention provides an image forming apparatus comprising:

a fixing unit operative to heat a recording medium bearing a toner image transferred thereto at a predetermined temperature;

at least one function device other than the fixing unit for use in image formation;

a first memory storing information on a relationship between a current temperature of the fixing unit and a time required for the fixing unit to reach a predetermined temperature; and

a controller operative to determine a time required corresponding to a current temperature of the fixing unit measured immediately after starting of energization from the information on the relationship stored in the first memory and modify control over the at least one function device to turn the at least one function device into a predetermined condition within the determined time required.

The image forming apparatus of this configuration measures a current temperature of the fixing unit immediately after energization of function devices, determines the time required corresponding to the current temperature from the information on the relationship stored in the memory, and modifies control over the function devices so that the function devices are turned into respective predetermined conditions suited for the execution of image forming processing within the time required thus determined. Accordingly, the time required for each of other function devices than the fixing unit to turn into respective predetermined condition is adjusted depending on the time required for the fixing unit to reach the predetermined temperature from the starting of energization and, when the fixing unit reaches the predetermined temperature suited to heat the recording medium after energization of the function devices, the other function devices have been turned into their respective predetermined conditions suited for the execution of image forming processing. As a result, the warm-up time can be shortened without any trouble in image reading processing and/or image forming processing.

The foregoing and other objects, features and attendant advantages of the present invention will become apparent from the reading of the following detailed description in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first toFIG. 1, there is shown an image forming apparatus100including an image reading section110in an upper part thereof, an image forming section210in a central part thereof, and a sheet feeding section250in a lower part thereof. A platen111of transparent glass is disposed on top of the image forming apparatus100, and an automatic document feeder112is provided on the platen111for automatically feeding a plurality of original documents one by one onto the platen111. A post-processing unit260is fitted on one side of the image forming section210, and a multi-tier sheet feeding unit270serving also as a pedestal is provided under the sheet feeding section250.

The image reading section110located under the platen111has a first scanning unit113, a second scanning unit114, an optical lens115, and a CCD line sensor116, which is a photoelectric converter. In cooperation with the operation of the automatic document feeder112, the image reading section110reads an image on an original document placed on the platen111by relatively scanning the original document at a predetermined exposure position. The first scanning unit113is equipped with an light-source lamp unit1for illuminating the surface of the original document to light, and a first mirror2afor reflecting a reflected light image from the original document toward a predetermined direction. A light quantity sensor3detects the quantity of light emitted from the light-source lamp unit1. The second scanning unit114is equipped with a second mirror2band a third mirror2cfor guiding the reflected light from the original document having being reflected by the first mirror2ato the CCD line sensor116. The optical lens115causes the reflected light from the original document to form an image on the light-receiving surface of the CCD line sensor116.

The image forming section210includes an electrostatic charger223for charging a photosensitive drum.222to a predetermined potential, a laser scanning unit (hereinafter referred to as “LSU”)227for forming an electrostatic latent image on the photosensitive drum222by emitting laser light according to image data transferred from the image reading section110or from an external device, a developing unit224for developing the electrostatic latent image formed on the photosensitive drum222into a tangible toner image by feeding toner to the electrostatic latent image, a transfer device225for transferring the toner image formed on the photosensitive drum222onto a recording sheet(used as the recording medium defined by the invention), a cleaner226for recovering toner that remains on the photosensitive drum222after completion of the transfer step, and a peeler229for peeling-off the recording sheet from the photosensitive drum222after the completion of the transfer step.

The laser scanning unit227includes therein a semiconductor laser11for emitting laser light modulated according to the image data, a polygon mirror12for deflecting laser light in a primary scanning direction by its rotation, and a group of lenses not shown. The polygon mirror12is driven by means of a motor13, the rotational speed of which is detected by a speed sensor14.

The image forming section210is provided with a fixing unit217for fusing the toner image to the recording sheet by heating and pressurizing the recording sheet bearing the toner image transferred thereto. The fixing unit217includes a pair of upper and lower rollers, the upper one being a heating roller21, lower one being a pressurizing roller22. A temperature sensor23detects the temperature of the heating roller21. Further, the fixing unit217is formed on the ejecting side thereof with a switch-back path221for reversing the advancing direction of the recording sheet in a double-sided image formation mode for forming images on both sides of the recording sheet.

The recording sheet to which the toner image has been fused at the fixing unit217is guided to the post-processing unit260by means of sheet ejecting rollers219, optionally passing through the switch-back path221. At the post-processing unit260the recording sheet is subjected to post-processing such as stapling or punching and then ejected into a tray261.

The sheet feeding section250comprises a manual feed tray254fitted on one side of the apparatus body, a double-sided feed unit255, a sheet feeding tray251, and sheet feeding trays252and253provided in the multi-tier sheet feeding unit270. These trays251to254each hold plural recording sheets as stacked. The sheet feeding section250is provided with conveyor means, such as rollers, for conveying recording sheets fed from the trays251to254to an image transfer position between the photosensitive drum222and the transfer device225in the image forming section210. The double-sided feed unit255, which communicates with the switch-back path221adapted to reverse recording sheets, stores turned-over recording sheets temporarily in the double-sided image formation mode. The double-sided feed unit255is replaceable with an ordinary sheet feeding tray.

It is to be noted that the light-source lamp unit1and the LSU227are each equivalent to the function device defined in the present invention.

In copy-mode processing (including the image reading processing for reading an image on an original document and the image forming processing for copying the image read onto a recording sheet) of the image forming apparatus100thus constructed, a copying operation including the image reading processing and the image forming processing is started when the user depressed a start key after having inputted desired conditions (including the number of copies and a magnification) via a condition entry key provided on a control panel not shown following placement of an original document to be copied on the platen111of the image reading section110.

In the image forming apparatus100, which starts processing in the manner described above, a main driving motor not shown is first actuated substantially simultaneously with the depressing of the start key to cause associated driving gears to rotate. Subsequently, sheet feeding rollers256rotate to feed a recoding sheet the recoding sheet which is then conveyed through a conveyance path up to resist rollers257at which the recording sheet is stopped temporarily to synchronize with a leading end portion of the image carried on the photosensitive drum222and the leading edge of the recording sheet is pressed against the resist rollers257for correction of the position thereof.

In reading image information from the original document at the image reading section110, the copy lamp of the light-source lamp unit1is turned on and the scanning unit113moves in the direction indicated by arrow A to start exposure scanning. Light emitted from the light-source lamp unit1and then reflected by the image-carrying surface of the original document is received by the CCD line sensor116via the mirrors2ato2cand optical lens115, so that the reflected light thus received is read as image information. The image information thus read is converted into digital image data by the image processing circuit of a control section to be described later. The image data is subjected to image processing under established conditions, stored in an image memory temporarily, and then transferred to the LSU227.

The surface of the photosensitive drum222rotating at a predetermined speed becomes uniformly charged to a predetermined potential by the electrostatic charger unit223giving electric charge thereto. The LSU227drives the semiconductor laser11on the basis of the image data transferred from the control section and exposes the surface of the photosensitive drum222with laser light modulated according to the image data via the polygon mirror12rotating at a predetermined speed. The illumination with laser light by the LSU227causes an electrostatic latent image to be formed on the surface of the photosensitive drum222on the basis of the image data. The surface of the photosensitive drum222on which the electrostatic latent image has been formed is supplied with toner from the developing unit224, so that the electrostatic latent image is developed into a tangible toner image.

The recording sheet is conveyed to a position between the photosensitive drum222and the transfer device225by means of the resist rollers256which start rotating in synchronism with the rotation of the photosensitive drum222. The toner image carried on the surface of the photosensitive drum222is transferred to the recording sheet at that position by the transfer device225. Toner remaining on the surface of the photosensitive drum222after completion of the transfer is removed and recovered together with paper dust and the like by the cleaner226.

The recording sheet bearing the transferred toner image is conveyed to the fixing unit217where the recording sheet is heated and pressurized while passing between the heating roller21and the pressurizing roller22. The transferred toner image on the recording sheet is fused and fixed firmly to the surface of the recording sheet due to heating and pressurization by the pair of rollers21and22. The recording sheet bearing the toner image thus fused thereto is ejected to the post-processing unit260by means of sheet ejecting rollers219.

Referring toFIG. 2, control section40of the image forming apparatus100is configured by connecting a CPU41provided with a ROM42and a RAM43to such components as image memory44, light quantity sensor3, speed sensor14, temperature sensor23, drivers45to47, image processing circuit48. The CPU41, which is the controller defined by the present invention, unifies and controls the associated components according to the program prestored in the ROM42and temporarily stores data inputted to and outputted from the associated components in a predetermined memory area of the RAM43. The image memory44stores image data outputted from the image processing circuit48.

The light quantity sensor3detects the quantity of light emitted from the copy lamp la of the light-source lamp unit1and inputs the light quantity data thus obtained to the CPU41. The speed sensor14detects the rotational speed of the motor13driving the polygon mirror12in the LSU227and inputs the speed data thus obtained to the CPU41. The temperature sensor23detects the temperature of the heating roller21in the fixing unit217and inputs the temperature data thus obtained to the CPU41.

The driver45drives the copy lamp la of the light-source lamp unit1on the basis of control data outputted from the CPU41The driver46drives the motor in the LSU227on the basis of control data outputted from the CPU41. The driver47drives heater21aincorporated in the heating roller21of the fixing unit217on the basis of control data outputted from the CPU41.

Besides the associated components described above, a multiplicity of components adapted to operate in the image reading processing and image forming processing, including a main motor, other motors, clutches, solenoids and sensors in the image forming apparatus100, are connected to the CPU41. The CPU41reads data detected by each sensor with predetermined timing in the image reading processing and image forming processing and drives a pertinent motor or the like on the basis of the data thus detected.

Referring to the flowchart atFIG. 3, description will be made of a part of the processing procedure at the control section of the above-described image forming apparatus100. In the image forming apparatus100, the heating roller21of the fixing unit227for fusing a toner image and pressure-bonding it to a recording sheet by heating and pressurizing the recording sheet needs to be heated to the predetermined temperature that allows the toner image to fuse from the starting of the image forming processing. The copy lamp la of the light-source lamp unit1for illuminating an original document placed on the platen111to read image information from the original document needs to emit the predetermined quantity of light sufficient to obtain image data of a proper density from the starting of the image reading processing. The polygon mirror12of the LSU227for scanning the surface of the photosensitive drum222with laser light modulated according to image data needs to rotate at the predetermined speed commensurate with the writing speed from the starting of the image forming processing.

In order to turn such function devices into respective predetermined operable conditions (inclusive of the aforementioned predetermined temperature, predetermined light quantity and predetermined speed) prior to the starting of the image reading processing and the image forming processing and immediately after the starting of energization of the function devices in response to power-on of the image forming apparatus100or immediately after the resuming of energization of the function devices following the completion of settlement of a trouble such as jam, the control section40of the image forming apparatus100executes the following initialization processing.

When the image forming apparatus100is powered on, the CPU41outputs initial control data to the drivers45to47(step s1) to start driving the copy lamp1a, motor14and heater21a. Subsequently, the CPU41reads the temperature of the surface of the heating roller21of the fixing unit217detected by the temperature sensor23(step s2) and judges whether the temperature thus read is the predetermined temperature that allows toner to fuse (step s3). If the surface temperature of the heating roller21has reached the predetermined temperature, the CPU41judges that the apparatus100is in a state ready to start the image forming processing, and continues driving the copy lamp1a, motor14and heater21aaccording-to the initial control data to maintain their respective predetermined conditions (step s4). Then, the CPU41turns on the ready lamp of the control panel (step s5) and waits for the user to depress the copy switch to give the apparatus100an instruction to start the image forming processing (step s6). The CPU41starts executing the image reading processing and the image forming processing in response to the depressing of the copy switch (step s7).

If the surface temperature of the heating roller21has not reached the predetermined temperature yet, the CPU41continues driving the heater21aaccording to the initial control data (step S8) and reads the time required corresponding to the temperature (current temperature) of the heating roller21from information stored in the ROM42on the relationship between the current temperature of the heating roller21and the time required (step s9). The ROM42, which serves as the first memory and second memory defined by the present invention, stores the information on the relationship between the current temperature of the heating roller21and the time required, an example of which is plotted with the broken line in FIG.4. The “time required”, as used herein, is the time required for the temperature of the heating roller21to reach the predetermined temperature, for example 175° C., from the current temperature of the heating roller21. It is possible that a relational expression representing the relationship shown inFIG. 4is prestored in the ROM42and the time required corresponding to the current temperature is calculated at the step s9.

Thereafter, the CPU41reads light quantity data of the copy lamp1adetected by the light quantity sensor3as the current light quantity (step s10) and reads correction data consistent with the current light quantity and with the time required from information stored in the ROM42on the relationship of correction data to the current light quantity and to the time required (step s11). Subsequently, the CPU41outputs corrected control data to the driver45(step s12), the corrected control data being obtained by correcting the initial control data according to the correction data thus read. When the current light quantity of the copy lamp la reaches the predetermined light quantity, the CPU41restores the control data to be outputted to the driver45to the initial control data (steps s13and s14).

The correction data stated above is data for determining an electric energy to be added to the electric energy that is supplied to the copy lamp1aaccording to the initial control data in order for the light quantity of copy lamp1ato reach the predetermined light quantity by the time when the predetermined time required elapses. For example, in adjusting the electric energy for driving the copy lamp1aby varying the duty ratio of driving pulses according to the control data inputted to the driver45from the CPU41, the initial duty ratio corresponding to the initial control data is increased by an amount of correction corresponding to the correction data. The ROM42stores the information on such a relationship of correction data to the current light quantity and the time required that the correction data decreases with increasing current light quantity and increases with decreasing time required. While this relationship can be determined experimentally, the correction data need not necessarily vary continuously with varying current light quantity and with varying time required and it is sufficient for the ROM42to store at least one correction data item selected consistently with the current light quantity and with the time required.

When the light quantity of the copy lamp1aand the temperature of the heating roller21of the heating unit217have reached the predetermined light quantity and the predetermined temperature, respectively, within the time required, the light-source lamp unit1is in a condition capable of properly reading the image carried on the original document in the image reading section110.

In the case where the copy lamp1ais a cold cathode tube, the time required for the light quantity of the copy lamp1ato reach the predetermined light quantity depends on the bulb temperature of the copy lamp1a. The bulb temperature of the copy lamp1ais influenced by the temperature of the heating roller21disposed in the image forming apparatus100together with the copy lamp1a, as plotted with the solid line in FIG.4. As a result, the time required for the light quantity of the copy lamp1ato reach the predetermined light quantity depends also on the temperature of the heating roller21. For this reason, the correction data stored in the ROM42may be data prepared taking the current temperature of the heating roller21into consideration.

Further, the CPU41reads speed data of the motor13detected by the speed sensor14as the current speed (step s15) and reads correction data consistent with the current speed and with the time required from information stored in the ROM42on the relationship of correction data to the current speed and to the time required (step s16). Subsequently, the CPU41outputs corrected control data to the driver45(step s17), the corrected control data being obtained by correcting the initial control data according to the correction data thus read. When the current rotational speed of the motor13reaches the predetermined speed, the CPU41restores the control data to be outputted to the driver45to the initial control data (steps s18and s19).

The correction data stated above is data for determining an electric energy to be added to the electric energy that is supplied to the motor13according to the initial control data in order for the rotational speed of the motor13to reach the predetermined speed by the time when the time required elapses. For example, in adjusting the electric energy for driving the motor13by varying the duty ratio of driving pulses according to the control data inputted to the driver46from the CPU41, the initial duty ratio corresponding to the initial control data is increased by an amount of correction corresponding to the correction data. The ROM42stores the information on such a relationship of correction data to the current speed and to the time required that the correction data decreases with rising current speed and increases with decreasing time required. While this relationship can be determined experimentally, the correction data need not necessarily vary continuously with varying current speed and with varying time required and it is sufficient for the ROM42to store at least one correction data item selected consistently with the current light quantity and with the time required.

When the rotational speed of the motor14and the temperature of the heating roller21of the fixing unit217have reached the predetermined speed and the predetermined temperature, respectively, within the time required, the polygon mirror12of the LSU227rotates at a speed that allows image data to be written on the photosensitive drum222at a proper writing speed.

As shown inFIG. 5A, in the case where the current temperature of the heating roller21of the fixing unit217is relatively low and, hence, the time required Ta for the temperature of the heating roller21to reach the predetermined temperature is relatively long at the time immediately after the starting of energization of the function devices in response to power-on of the image forming apparatus100or immediately after the resuming of energization of the function devices following the completion of settlement of a trouble such as jam, the light quantity of the copy lamp1aand the rotational speed of the motor13reach the predetermined light quantity and the predetermined speed, respectively, prior to the elapse of the time required Ta even if the copy lamp la and the motor13are driven continuously according to the initial control data. For this reason, the CPU41continues feeding the initial control data to the driver45driving the copy lamp la and to the driver46driving the motor13during the warm-up time up to the time when the temperature of the heating roller21reaches the predetermined temperature.

As shown inFIG. 5B, on the other hand, in the case where the current temperature of the heating roller21of the fixing unit217is relatively high and, hence, the time required Tb for the temperature of the heating roller21to reach the predetermined temperature is relatively short at the time immediately after the starting of energization of the function devices in response to power-on of the image forming apparatus100or immediately after the resuming of energization of the function devices following the completion of settlement of a trouble such as jam, the light quantity of the copy lamp1aand the rotational speed of the motor13do not reach the predetermined light quantity and the predetermined speed, respectively, prior to the elapse of the time required Tb if the copy lamp1aand the motor13are driven continuously according to the initial control data. For this reason, the CPU41feeds corrected control data having a higher duty ratio than does the initial control data to the driver45driving the copy lamp1aand to the driver46driving the motor13during the warm-up time up to the time when the temperature of the heating roller21reaches the predetermined temperature. By so doing, the predetermined light quantity of the copy lamp1aand the predetermined speed of the motor13can be reached within the warm-up time up to the time when the temperature of the heating roller21reaches the predetermined temperature, irrespective of the current temperature of the heating roller21.

Thus, the image forming apparatus100is configured to determine the time required for the temperature of the heating roller21to reach the predetermined temperature from the temperature of the heating roller21of the fixing unit217measured at the time the apparatus100is powered on and modify control over other function devices, such as the light-source lamp unit1and the LSU227, on the basis of the time required thus determined so as to turn the other function devices into their respective predetermined conditions suited for the image forming processing, whereby all the other function devices are already turned into their respective predetermined operable conditions when the temperature of the heating roller21of the fixing unit217reaches the predetermined temperature. In this way the present invention is capable of realizing an immediate printing type image forming apparatus by sufficiently shortening the warm-up time without causing any trouble to occur in the image forming operation.

It is to be noted that the CPU41may be configured to cause the steps s15to s19to be performed at the same time with respective steps s10to s14.

In determining correction data at each of the steps s11and s16, it is possible to employ a configuration such as to determine the time required to raise the light quantity of the copy lamp1afrom the current light quantity to the predetermined light quantity or the time required to raise the rotational speed of the motor13driving the polygon mirror12from the current speed to the predetermined speed and then select or calculate correction data such that the time required thus determined becomes shorter than the predetermined time required.

Where the developing unit224of the image forming apparatus100is adapted to contain a two-component developer comprising toner and carrier, a toner replenishing operation for maintaining the toner concentration in the two-component developer at a predetermined concentration level or higher needs to have been completed prior to the starting of the image forming processing in order to form a toner image having a proper density at the developing step of the image forming processing. In view of this, control data for controlling a motor driving a toner-replenishing roller may be corrected depending on the current concentration of toner in the two-component developer and on the time required in a manner similar to the procedure from the step s15to the step s19.

Where the image forming apparatus100operates in a power-saving mode in which the temperature of the heating roller21, the light quantity of the copy lamp la and the rotational speed of the motor13are limited lower than their respective predetermined conditions if a predetermined period of time from the turning-on of the ready lamp has elapsed without manipulation of the copy switch, the present invention may be applied to a reset operation during the period of time from the manipulation of the copy switch in the power-saving mode up to the starting of the image forming processing so that control data to be fed to each of the drivers45and46is corrected.

The present invention provides the following advantages.

By employing the configuration adapted to measure the current temperature of the fixing unit immediately after energization of function devices, determine the time required corresponding to the current temperature from the information on the relationship stored in the first memory, and modify control over the function devices so that the function devices are turned into respective predetermined conditions suited for the execution of image forming processing within the time required thus determined, it becomes possible that the time required for each of the function devices other than the fixing unit to turn into respective predetermined condition is controlled depending on the time required for the temperature of the fixing unit to reach the predetermined temperature from the starting of energization, and that when the temperature of the fixing unit reaches the predetermined temperature suited to heat the recording medium after energization of each function device, the other function devices also are already turned into their respective conditions suited for the execution of image forming processing. As a result, no trouble occurs in the image forming processing even though the warm-up time is shortened. Since the required warm-up time can be shortened sufficiently, the present invention can realize an immediate printing type image forming apparatus.

Since the time required for each of the other function devices to turn into respective predetermined condition from the starting of energization of the other function devices varies with varying efficiency in energizing each of the other function devices, control over the other function devices to turn into their respective predetermined conditions within the time required for the temperature of the fixing unit to reach the predetermined temperature from the starting of energization can be exercised easily and accurately by adjusting the efficiency in energizing each of the other function devices depending on the time required for the temperature of the fixing unit to reach the predetermined temperature from the starting of energization.

By determining an energization efficiency consistent with the current condition and the predetermined condition of each of the other function devices and with the time required from information stored in the second memory on the relationship between the energization efficiency and the rate of change of condition in adjusting the efficiency in energizing each of the other function devices depending on the time required for the temperature of the fixing unit to reach the predetermined temperature from the starting of energization, an energization efficiency to be set for each of the other function devices to turn into respective predetermined condition within the time required for the temperature of the fixing unit to reach the predetermined temperature from the starting of energization can be determined accurately.

By exercising normal control over the other function devices once the temperature of the fixing unit has reached the predetermined temperature and the other function devices have turned into their respective predetermined conditions after the starting of energization, each of the function devices can be maintained in a condition that enables the image forming processing to be performed properly after the image forming apparatus has turned into a state allowing the execution of the image forming processing.

By modifying control over the light-source lamp unit illuminating an original document with light for reading image information from the original document or the laser scanning unit scanning with laser light according to the image information by means of the polygon mirror depending on the time required for the temperature of the fixing unit to reach the predetermined temperature, the warm-up time can be shortened sufficiently without any trouble in the execution of the image reading processing or the image forming processing since, when the temperature of the fixing unit reaches the predetermined temperature suited for heating of a recording medium after energization of the function devices, the light quantity of the light-source lamp unit has reached the predetermined light quantity suited for reading of the image information from the original document or the rotational speed of the polygon mirror of the laser scanning unit has reached the predetermined speed suited for scanning with laser light according to the image information. Thus, an immediate printing type image forming apparatus can be realized.

While only a certain presently preferred embodiment of the present invention have been described in detail, as will be apparent for those skilled in the art, certain changes and modifications may be made in embodiments without departing from the spirit and scope of the present invention as defined by the following claims.