Method and device for controlling toner density of an electrostatic printing apparatus employing toner

Abstract: In an electrostatic recording apparatus according to the present invention, while a photosensitive drum (1) and a drum cleaner (4) are enabled but an electrostatic latent image is not formed on the drum and a developing unit is not operated yet, a light emission level of a LED (3a) which is controlled so as to keep a received light level of a photodiode (3b) which receives the LED's light reflected from the drum is measured as a first light emission level. If the first light emission level exceeds a predetermined level it is judged that the detector (3) composed of the LED and the photodiode is contaminated and requires cleaning. Next, the developer is enabled while the latent image is not formed yet, the light emission level to keep the same received light level is measured as a second light emission level. If a difference between the first and second light emission levels exceeds a predetermined limit level, it is judged that the photosensitive drum (1) and/or carrier in developer is deteriorated. Thus, an interval for cleaning the detector is extended, and the deterioration of the drum and/or the carrier is distinguished from the contamination of the detector.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a recording apparatus employing a toner image produced on an electrostatic latent image forming medium, such as an electrophotographic printing apparatus, and particularly relates to a method of detecting the end of life of the image forming media, as well as the developer carrier. Description of the Related Art In an apparatus utilizing toner development, such as an electro-photographic apparatus, the toner is consumed for the development, and it is therefore necessary to supply toner into a developing unit to keep the toner density constant. In order to control this toner density, there exists a method employing a special toner mark formed on a latent image forming medium, i.e. on a photosensitive drum, cooperating with an optical detector composed of a light emitting device projecting a light spot on the surface of the photosensitive drum and a light receiving device receiving light reflected from where the projected spot impinges the photosensitive drum. The optical detector detects the toner mark so as to measure its toner density. According to this measured toner density, a supply of the toner to the developer in the developing unit is controlled so that a uniform toner darkness is achieved in the printed image. The optical detector is also employed for detecting whether a developer (carrier) in the developing unit has deteriorated,having reached its life end, as well as for detecting the end of life of the photosensitive drum itself, resulting from contamination, such as generation of filming, etc. When the carrier has deteriorated, the toner clings to the carrier causing an increase in electrical resistivity thereof. Accordingly, toner stays on the photosensitive drum where no toner should remain. This undesirable toner deteriorates the contrast of printed images. When the photosensitive drum has deteriorated, it loses its electric charging capability, allowing undesirable toner to remain on areas where no light has been projected; accordingly, contrast is also deteriorated. Thus, decreased reflection from the drum surface causes a decrease in the received light level as well as in an amplitude of the toner mark in the received light. The optical detector must be located close to the photosensitive drum if it is to detect both the toner mark and the contamination of the drum itself. But this means that the light emitting window as well as the light-receiving window of the detector is likely to be contaminated with the toner floating out from the photosensitive drum. When the window of the optical detector is contaminated, the light receiving level of the detector declines, leading to errors in the detection of toner density, etc. When the optical detector is contaminated, the detector must be cleaned. Conventionally, air is blown onto the detector in order to remove the contaminating toner thereon. However, the air blowing method has a problem in that the narrowness of the gap between the photosensitive drum and the detector makes it difficult to blow air directly onto the light receiving surface. Furthermore, there is also a problem in that the strong air flow disturbs the toner image on the photosensitive drum. When the level of the received light reflected from the photosensitive drum - except from the toner mark - declines to a certain level, it is judged that the detector has become contaminated, and its cleaning operation is then carried out. The problem with this method, however, is not only that the degree of contamination is not correctly evaluated, but also that a rapid contamination from many print operations shortens the interval of the cleaning operations, resulting in an increase in maintenance labour. Furthermore, even though the rate of deterioration of the drum or the carrier is much slower than that of the detector's contamination, the above method makes it impossible to determine, once the drum or the carrier has deteriorated, whether the fall in the received light level is caused by the detector's contamination, the deterioration of the photosensitive drum or the deterioration of the toner carrier. Accordingly, it is impossible to compensate correctly the variation of the toner density. Still furthermore, there has been proposed a method of detecting the toner density by a differential output of a pair of detectors, as disclosed in Japanese Patent Publication, No. Sho 63-14348, etc. The problem with this method, which involves providing a pair of detectors, is that an additional detector is required, which in turn calls for additional space and installation costs. There is also a problem with the difficult alignment of the optical detector to the toner mark, and it is still impossible to determine whether the fall in received light level is caused by the detector's contamination, the deterioration of the photosensitive drum or from the deterioration of the toner carrier. SUMMARY OF THE INVENTION It is a general object of the invention, therefore to provide a method of detecting deteriorations in an electrostatic image forming medium and carrier in developer according to claim 1, independently of a contamination of an optical detector employed therein, and a recording apparatus comprising means for performing said method as claimed in claim 10. It is another object of the invention to provide a method according to claim 3 of detecting contamination of an optical detector which detects the toner density of a toner mark provided on an electrostatic image forming medium, and a recording apparatus comprising means for performing said method as claimed in claim 12. According to the present invention, when on the one hand a rotation of a photosensitive drum and operation of its pre-charger are enabled, and on the other the magnetic roll, its bias charger and the toner mixer in the developing unit are not yet enabled, a received light level of an optical detector is fed back to control a light emission of the optical detector so that the received light level attains a predetermined reference level, and then the light emission level is measured as a first light emission level. If the first light emission level exceeds a predetermined level, it is judged that the optical detector is contaminated to a degree where cleaning is required. Next, while the magnetic roll, its bias charger and the toner mixer are enabled, a light emission level, which keeps the received light level equal to the predetermined reference level, is measured as a second light emission level. A difference between the first and second light emission levels indicates a degree of deterioration of the photosensitive drum and/or the carrier in the developer. If this difference exceeds a predetermined limit level, it is judged that the photosensitive drum and/or the carrier must be changed. If the difference is smaller than or equal to the limit level, the light emission level is kept at the second light emission level, and a printing procedure is started. According to the above-described procedure, a contamination of the optical detector and the deterioration of the photosensitive drum and/or the developer carrier can be distinguished. An increase in the first light emission level correctly indicates a degree of the contamination of the optical detector, and accordingly the appropriate moment for cleaning the optical detector can be detected. Therefore, the interval between detector cleanings can be extended more appropriately compared with a conventional method where the declined received light level is also due to the deterioration of the photosensitive drum and/or deterioration of the carrier. The above-mentioned features and advantages of the present invention, together with other objects and advantages, which will become apparent, will be more fully described hereinafter, with reference to the accompanying drawings which form a part hereof, wherein like numerals refer to like parts throughout. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 schematically illustrates the constituent elements of an embodiment of the electrophotographic printing apparatus according to the invention. Fig. 2 schematically illustrates an optical detector and a toner mark used for the present invention. Fig. 3 is a block diagram of a detector control circuit employed in an embodiment of the present invention. Fig. 4 (A) is a flow chart showing steps of an embodiment of the present invention. Fig. 4 (B) is a flow chart of a step for toner density control. Fig. 5 is a timing chart of the steps of an embodiment of the present invention shown in Fig. 4 (A). Figs. 6 (A) and (B) are waveforms of a received light signal indicating reflection from a surface of a photosensitive drum and a toner mark according to the present invention. Fig. 7 explains the alignment of the optical detector to the toner mark. Fig. 8 is a circuit diagram of a detector control circuit of an embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS A laser printer is schematically illustrated in Fig. 1 as an example of a preferred embodiment of the present invention. At first, a general operation of the laser printer is hereinafter described. A photosensitive drum 1 rotates along the direction of the arrow shown in the figure. A cleaner 4 comprising a brush wipes off toner remaining on the surface of the rotating photosensitive drum 1. A pre-charger 6 electrically charges the photosensitive drum, typically with + 600 volts. A light modulator 11 comprising a laser oscillator sequentially outputs a laser light LL according to information data to be printed on a paper sheet PP. The laser light LL is scanned along the axial direction of the photosensitive drum 1 and focused on the surface of the photosensitive drum by means which are not shown in the figure. A light spot projected on the photosensitive drum 1 locally discharges the electric charge of the spot area. Thus, a latent image is electrostatically formed on the photosensitive drum 1. A developing unit 2 comprises a magnetic roll 2a, a toner supplier 2b, and a toner mixer (not shown in the figure) and contains a two-component developer therein, which is composed of a carrier and a toner. Magnets installed in the magnetic roll 2a coaxially rotate therein. The magnetic roll 2a, together with the toner thereon, is electrically charged with a bias voltage VB, typically + 100 volts, via a bias switch 2c. The carrier, which is a powder of magnetic material mixed with the toner, is attracted by the magnets onto the surface of the magnetic roll 2a, and is conveyed, i.e. supplied, towards the photosensitive drum 1 by the rotation of the magnets. The toner, thus charged with + 600 volts, and facing the photosensitive drum 1, is attracted by a spot area previously electrically discharged by the laser light, and is transferred onto the spot of the photosensitive drum 1. Thus, a toner image is developed on the photosensitive drum 1. An optical detector 3 comprises a light emitting device 3a (Fig. 2), such a light emitting diode (referred to hereinafter as an LED), which projects a light spot onto the surface of the photosensitive drum 1, and a light receiver 3b (Fig. 2), such as a photodiode, which receives a light reflected from the light spot by the photosensitive drum 1. The optical detector will be described in more detail further on. The toner image on the photosensitive drum 1 is conveyed towards a sheet of paper PP. Behind the sheet PP there is provided a transfer charger 7, which charges the sheet PP with typically ± 5kV. Accordingly, the toner image in face-to-face contact with the sheet PP is electrostatically transferred from the photosensitive drum 1 onto the sheet PP. The sheet PP is introduced by rollers 8 and driven out by rollers 8′. While the sheet having the toner image thereon is pinched by the drive-out rollers 8′, the toner is fused to be permanently fixed onto the sheet. A control circuit 5 comprises a microprocessor (referred to hereinafter as MPU) 55, a detector controller 3c and a toner mark generating circuit 10. The functions of MPU 55 will be described in detail further on. Fig. 3 shows a block diagram of a detector control circuit 3c. A D/A (digital/analog) converter 50, typically of 8 bits, i.e. having 254-step resolution, receives from the MPU 55 a digital level Dout to determine the light emission level of LED 3a, and converts it into an analog voltage. A voltage-current converter 30 converts this analog voltage into a current Id to drive LED 3a. A photodiode 3b generates a photocurrent Ip as a function of a light level reflected and received thereto. A current-voltage converter 31 converts the photocurrent Ip into an analog voltage V DRM . An A/D (analog/digital) converter 51, typically of 8 bits, converts this voltage into a digital received light level Din, which is then input to the micro processor MPU 55. The MPU 55 is programmed to execute ON/OFF controls of : the rotation of the photosensitive drum 1, the rotation of the magnetic roll 2a and toner mixer in the developing unit 2, the bias charger 2c, the pre-charger 6, as well as a supply control of the toner from the toner supplier 2b, and a level control of light emission of the LED 3a. Operation of the laser printer according to the present invention is hereinafter described in reference to flow chart of Fig. 4(A) and a timing chart of Fig. 5. Numbers in circles in Figs. 4 correspond to the number given to each step in the below description. Numbers in squares in Figs. 4 indicate each sequence of the flow chart. (1) When the laser printer is about to start, the MPU 55 initiates rotation of the photosensitive drum 1, while disabling the pre-charger 6, the laser light LL, the magnetic roll 2a, the supply of the bias voltage VB, the sheet feed, and the transfer charger 7. Then, MPU 55 sets an appropriate value Dsc in Dout to determine the light emission level of the LED; eg., 10 mA input to the LED. Next, the pre-charger 6 is enabled. While the photosensitive drum 1 thus rotates for a period t₁, eg., 30 seconds, which is equivalent to 11 rotations of the drum, all the toner existing between the magnetic roll 2a and the photosensitive drum 1 becomes electrostatically attracted and transferred onto the photosensitive drum 1, since there is no longer any toner supplied thereto and no bias voltage VB is applied thereto. The toner on the photosensitive drum 1 is wiped away by the cleaner 4. Thus, the surface of the photosensitive drum becomes clean without any toner thereon. (2) MPU 55 reads a received light level Din of the photodiode 3b, from the A/D converter 51, as a drum level V DRM . MPU compares the drum level V DRM with a predetermined reference level V DRMO , which is for example 10 V. (3) When it is determined that V DRM ≠ V DRMO , it is judged that the received light level is low, because the light emission level has been set at a relatively low Dsc, which corresponds to, eg. 10 mA to LED 2a. Next, MPU 55 checks whether the magnetic roll 2a is not driven, MPU 55 instructs an increase in the light emission level Dout, which was hitherto Dsc, to Dout+1. After waiting, over a response period t₅, during which the result of Dout+1 appears in the output Din, the process goes back to step (2), and repeats until V DRM becomes equal to V DRMO over a period t₂ of eg. 2 seconds. This step is indicated additionally by route 1 in the flow chart. (4) Hence, after thus increasing the light emission level, if it is then judged that V DRM has reached the predetermined reference level V DRMO , then MPU 55 checks whether the magnetic roll 2a is driven. If the magnetic roll 2a is not driven, the process goes to step (5). (5) The light emission level Dout is measured by MPU 55 and stored in its register 55a as a first light emission level DS1, which is a non-driven developer state level. The value of DS1 corresponds to, eg. 11 mA in this case. The first light emission level DS1 indicates the degree of the detector contamination, and increases as the LED 3a and/or the photodiode 3b is contaminated with toner, etc. The value of DS1 is compared with a predetermined limit level Dcont, eg., corresponding to 20 mA in this example. If DS1 exceeds the limit level Dcont, MPU 55 issues an alarm signalling that the detector window is to be cleaned. Cleaning of the detector is generally carried out by manually wiping the window surfaces while the photosensitive drum 1 is detached from the printer chassis. (6) When DS1 is below the limit Dcont in step (5), MPU 55 instructs to drive the magnetic roll 2a and the toner mixer, and to close the bias switch 2c so as to apply the bias voltage VB to the magnetic roll 2a. There is then a waiting period t₃ during which developer in the developing unit 2 is uniformly mixed up. These steps (5) and (6) are indicated additionally by route 2. Then, the step goes back to (2). (7) Because the developing unit 2 is now in operation, some of the toner is present on the photosensitive drum 1, if the photosensitive drum 1 and/or the carrier in the developer has become deficient. Therefore, V DRM decreases with the toner on the photosensitive drum 1. Accordingly, V DRM ≠ V DRMO . Thus, the step goes along route 3. MPU 55 instructs an increase in the light emission level from Dout to Dout+1. If V DRM > V DRMO , MPU 55 instructs a decrease in the light emission level from Dout to Dout-1. Then, after a waiting period t₅ during which the result of increasing/decreasing the amount of Dout appears in the output Din, the step goes back to (2). This step repeats until V DRM becomes equal to V DRMO . Thus, if it is determined that V DRM = V DRMO , MPU 55 checks whether the magnetic roll 2a is driven. If the magnetic roll 2a has been enabled, the step goes to (8). (8) The amount of the light emission level Dout is measured and stored by MPU 55 in its register 55b as a second light emission level DS2, which is a driven-developer state level for the same received light level V DRMO . The value of DS2 corresponds, eg., 12 mA in this example. This step to (8) is indicated additionally with route 4. (9) MPU 55 checks next whether a difference between the first and second light emission levels, i.e. between the non-driven developer state level DS1 and the driven-developer state level DS2 (DS2 - DS1), is larger than a predetermined limit level Co, corresponding to, for example, 3 mA. If (DS2 - DS1) > Co, that is, if DS2 becomes larger than 13 mA in this example, it is judged that the photosensitive drum 1 and/or the carrier has reached its/their end of life. Accordingly, MPU 55 outputs an alarm so that a printing operation is inhibited, allowing an operator to change the necessary items. The above-described automatic light emission level control and the automatic checks of the drum/developer deteriorated according to step 2 through 9 may be periodically carried out either at the time of starting up the system, i.e. power supply is switched on, or according to a predetermined period, such as an operation time of the system since the power supply has been on, an operation time of the photosensitive drum rotation, or number of printed sheets, measured or counted by MPU 55. (10) When it is determined that (DS2 - DS1) is equal to or less than Co, it means that the photosensitive drum 1 and the carrier are not yet worn; therefore, the printer is ready for the printing process. During the stand-by for the printing process, the drum may be generally stopped while the second light emission level DS2 is stored. Printing processes are independently shown in Fig. 4(B). (11) For starting the printing process, MPU 55 enables the drum rotation, the light modulator 11, the scanning device (which is not shown in the figure), a toner mark generator 10 in the control circuit 5, a transfer charger 7, and the feeding of the sheet PP. The toner mark generator 10 outputs to the light modulator 11 a signal which produces a toner mark TNM typically 5mm square, outside a print area PT on the photosensitive drum 1, as shown in Fig. 2. When either a continuous or cut sheet is used to be printed thereon, the toner mark TNM is located beside the print area PT denoted with dotted lines and is detected by LED 3a and photodiode 3b, both of which are connected to the control circuit 5 (the connection line is not shown in the figure). When only a cut sheet is used, the toner mark TNM′ may be located between the end and the start of print area PT and is detected by LED 3a′ and photodiode 3b′, each connected to the control circuit 5. (An alignment procedure of the optical detector to the toner mark TNM or TNM′ will be described later in detail). (12) The received light signal drops when the detector detects the toner mark TNM, as shown in Fig. 6(A), depending on the degree of the density of the toner in the toner mark TNM, since the dark toner reduces the light reflection therefrom. A detection circuit 33 provided in the detector control circuit 3c (shown in Fig. 8) detects the above-described drop, i.e. a change, in the received light as shown in Fig. 6(A) and outputs a toner mark level (i.e. an amplitude) V MRK , which is then input to MPU 55. (Dotted line in Fig. 6(A) shows a received light signal and a toner mark level V MRK ′ for the case where the optical detector 3 is contaminated). (13) MPU 55 checks whether the toner mark level V MRK is smaller than a predetermined limit level Vs, eg., 5V in this case. If V MRK < Vs, MPU 55 stores this information, and repeats this check for a predetermined number of cycles, eg., for printing a hundred sheets. MPU 55 determines how many times the information of V MRK < Vs appears among the stored hundred data. When this number exceeds a predetermined number, such as fifty one, it is judged that the toner is running short. (14) Then, MPU 55 instructs the toner supplier 2b to add toner into the developer in the developing unit 2. This step is repeated until the average value of V MRK exceeds Vs. (15) If V MRK is equal to or larger than Vs, it is judged that the toner is adequate; accordingly, the printing operation is continued without adding toner into the developer. According to the above-described preferred embodiment of the present invention, the current to drive the LED can be increased up to its upper limit until cleaning of the detector is required. This contrasts with a conventional method, where the limit Vs of the toner mark level must be decreased according to the decrease of the received light level. Therefore, the interval between the detector cleanings can be extended, resulting in a reduction of maintenance labour. Furthermore, according to the invention, the reliable level of received light, having no effect of detector contamination, and not requiring blowing of air or additional detector, allows the printed image to keep its constant toner darkness over long periods, and with different drums. The above-described method of keeping the receiving light level constant is advantageous, over the conventional analog feedback method, in that the light emission control circuit can be made such that light emission control is not affected by the toner image, even when the light emission control is carried out during the printing operation. In the above-described preferred embodiment, steps 2 through 7 for keeping the receiving light level is carried out at the time of starting up the system. However, this automatic received-light level control may also be carried out later, at a predetermined period, eg. during operation of the system, or drum rotation or after a number of printed sheets, after a printing operation is initiated. A preferred embodiment of a control circuit for aligning the optical detector is shown in Fig. 8, where the same parts are denoted with the same numerals as those of previous figures. An analog output from the D/A converter 30 is input via a switch 9b to the voltage-current converting circuit 20, which comprises an amplifier M1 to amplify the signal input from the switch 9b, a transistor Tr to supply a current Id to the LED 3a, and a resistor R2. The current-voltage converter circuit 31 comprises a resistor R3 which generates a voltage depending on the detected current Ip of the phototransistor 3b, and an amplifier M2. When the detector control circuit of Fig. 8 is used for the above-described steps (1) through (10) and/or in (11) through (15), the switch 9b is connected to "a" position so that a feedback loop for keeping a constant receiving light level is enabled. The numeral 32 denotes an integration circuit, which is composed of a capacitor C1, a resistor R7, an amplifier M3, and input resistors R6 and R8. The integration circuit 32 has a time constant long enough to integrate, i.e. smooth, the voltage dip, in the output of the current-voltage converting circuit, caused from the toner mark having a pulse duration as short as, eg., 5 to 20 ms, so that its output, the drum surface level V DRM , can be handled as a substantially DC (direct current) voltage. Numeral 33 denotes a detection circuit, which comprises a diode, a capacitor and a resistor (none of which are shown in the figure). The circuit 33 detects an amplitude of an instantaneous voltage change in the output of the current-voltage converting circuit 31, so as to output a DC voltage indicative of the detected amplitude. The numeral 51′ is an A/D converter similar to that of the numeral 51, but which further receives the toner mark level V MRK . When a new apparatus is assembled in a factory, or the optical detector 3 is exchanged for servicing in field, the position of the optical detector must be adjusted so as to align the toner mark along the axial direction of the photosensitive drum 1. For this alignment, the toner mark may be modified to become a strip fully surrounding the photosensitive drum 1, and the photosensitive drum is generally prevented from rotating as a safety precaution. During this adjustment, the received light level is observed with an oscilloscope or a voltmeter (neither of which are shown in the figure) connected to the output terminal of the current-voltage converting circuit 31. If the optical detector detects a portion deviated from the toner mark TNM, as shown with dotted line in Figure 7, amplitude of the toner mark level decreases as shown by V MRK′ in Figure 6(B). At this time, if the feedback loop to determine the light emission level is enabled by connecting the "a" position in the switch 9b, the light emission level varies so as to oppose the received light level, resulting in a difficulty in finding a right position setting for the detector. Therefore, switch 9b is provided to be able to select the "b" position, through which a predetermined DC voltage level is input from a level generator 9a to the voltage-current converting circuit 30, so that the light emission level of the LED is set constant, being released from the feedback operation. Thus, the constant light emission level allows an easy and correct alignment of the optical detector 3 to the toner mark TNM by simply searching for a maximum amplitude of the toner mark level V MRK . Though in the above-described preferred embodiments a switch 9b and the level generator 9a are provided in the detector control circuit in order to disable the feedback loop and to provide a constant light emission level, it is apparent that these functions may be performed by a firmware provided in MPU 55 instead of the switch 9b and the level generator 9a. Although in the above-described preferred embodiments a single set of optical detectors 3 or 3′ is referred to, a plurality of optical detectors may be employed to detect the first and second light emission levels. Also, in the above-described preferred embodiments a laser printer employing a scanned laser light are referred to, but it is apparent that the present invention may be embodied in other electrostatic printing or copying apparatus employing an LED array or liquid crystal shutter. Finally, in the above-described preferred embodiments a photosensitive drum is referred to, it is apparent that the latent image forming medium is not limited to the drum-shape medium.

Claims: A method of controlling a recording apparatus comprising : an image forming medium (1) for electrostatically forming a latent image thereon according to an image information to be recorded; developing means (2) for developing said latent image as a toner image on said image forming medium; cleaning means (4) for removing residual toner from said image forming medium after developing said toner image; a detector (3), comprising a light emitting means (3a) projecting a light spot onto a predetermined area on said image forming medium; and a light receiving means (3b) for receiving a light reflected from said light spot; and a control circuit (5) for controlling a light emision level of said light emitting means and measuring a level of the light received by said light receiving means, comprising the steps of : (1) enabling said image forming medium and said cleaning means while disabling an input of said image information and said developing means; (2) measuring a light emission level (Dout) from said light emitting means (3a) which keeps said light level received by said light receiving means (3b) at a predetermined level, as a first light emission level (DS1); (3) measuring a light emission level (Dout) from said light emitting means (3a) which keeps said light level received by said light receiving means (3b) at said predetermined level, as a second light emission level (DS2), after said developing means is enabled; (4) discriminating whether a difference between said first light emission level and said second light emission level is larger than a predetermined limit level, whereby a deterioration of said image forming means and/or said toner is detected if said difference exceeds said predetermined limit level; and (5) starting a recording procedure of said recording apparatus only when no severe deterioriation is detected. A method of controlling a recording apparatus, according to claim 1, further comprising the step of : discriminating whether said first light emission level (DS1) is larger than a predetermined limit level, whereby a contamination of said detector (3) is detected separately from the deterioration of said image forming means and/or said toner. A method of controlling a recording apparatus comprising : an image forming medium (1) for electrostatically forming a latent image thereon according to an image information to be recorded; developing means (2) for developing said latent image as a toner image on said image forming medium; cleaning means (4) for removing residual toner from said image forming medium after developing said toner image; a detector (3), comprising a light emitting means (3a) for projecting a light spot onto a predetermined area on said image forming medium; and a light receiving means (3b) for receiving a light reflected from said light spot; and a control circuit for controlling a light emission level of said light emitting means and measuring a level of the light received by said light receiving means, comprising the steps of : (1) enabling said image forming medium and said cleaning means while disabling an input of said image information and said developing means; (2) measuring a light emission level (Dout) from said light emitting means (3a) which keeps said light level received by said light receiving means (3b) at a predetermined level, as a first light emission level (DS1); and (3) discriminating whether said first light emission level is larger than a predetermined limit level (Dcont), whereby a contamination of said detector is detected if said predetermined level is exceeded; and (4) issuing an alarm signal if a contamination of said detector is detected. A method of controlling a recording apparatus, according to claim 3, further comprising the step of : outputting an alarm signal for cleaning said optical detector (3) when it is discriminated that said first light emission level (DS1) is larger than a predetermined limit level. A method of controlling a recording apparatus according to any one of claims 1 to 4, where said apparatus is further provided with toner mark generating means (10) for outputting a toner mark signal to said image information, said toner mark being produced outside a print area on a predetermined area on said image forming medium, said toner mark being detected by said detector; and a control circuit (5) comprising a feedback loop for controlling a light emission level of said light emitting means so as to keep a level of the light received by said light receiving means at a predetermined level, the method further comprising the steps of : (1) forming said toner mark on said image forming medium; and (2) adjusting a location of said detector by observing a toner mark signal in the received light while said feedback loop is disabled and said light emission level is kept constant. A method of controlling a recording apparatus according to any one of claims 1 to 5, further comprising the steps of : (1) converting an analog value of said received light level into a digital value; (2) discriminating whether said digital received light level is equal or larger than a predetermined reference level; (3) increasing a light emission level when said digital received light level is discriminated to be smaller than said predetermined reference level; (4) repeating steps (2) and (3) until said digital received light level is discriminated to be equal to said predetermined reference level. A method of controlling a recording apparatus according to claim 6, wherein said steps are carried out before said developing means is operated. A method of controlling a recording apparatus, according to claim 6, wherein said steps are carried out before an image forming operation is carried out while said developing means is operating. A method of controlling a recording apparatus according to claim 6, wherein said steps are carried out while an image forming operation is carried out. A recording apparatus comprising : an image forming medium (1) for electrostatically forming a latent image thereon according to an image information to be recorded; developing means (2) for developing said latent image as a toner image on said image forming medium; cleaning means (4) for removing residual toner from said image forming medium after developing said toner image; a detector (3), comprising a light emitting means (3a) projecting a light spot onto a predetermined area on said image forming medium; and a light receiving means (3b) for receiving a light reflected from said light spot; and a control circuit (5) for controlling a light emission level of said light emitting means and measuring a level of the light received by said light receiving means, characterised in that said control circuit comprises : (1) control means for selectively enabling or disabling said image forming medium, said cleaning means, an input of said image information and said developing means; (2) means for measuring a light emission level (Dout) from said light emitting means (3a) which keeps said light level received by said light receiving means (3b) at a predetermined level, as a first light emission level (DS1) when said image forming medium and said cleaning means are enabled, and said input of said image information and said developing means are disabled by said control means; (3) means for measuring a light emission level (Dout) from said light emitting means (3a) which keeps said light level received by said light receiving means (3b) at said predetermined level, as a second light emission level (DS2), after said developing means is enabled by said control means; (4) means for discriminating whether a difference between said first light emission level and said second light emission level is larger than a predetermined limit level, whereby a deterioration of said image forming means and/or said toner is detectable if said difference exceeds said predetermined limit level; and (5) means for starting a recording procedure of said recording apparatus only when no severe deterioration is detected. A recording apparatus according to claim 10, wherein said control unit further comprises means for : discriminating whether said first light emission level (DS1) is larger than a predetermined limit level, whereby a contamination of said detector (3) is detectable separately from the deterioration of said image forming means and/or said toner. A recording apparatus comprising : an image forming medium (1) for electrostatically forming a latent image thereon according to an image information to be recorded; developing means (2) for developing said latent image as a toner image on said image forming medium; cleaning means (4) for removing residual toner from said image forming medium after developing said toner image; a detector (3), comprising a light emitting means (3a) for projecting a light spot onto a predetermined area on said image forming medium; and a light receiving means (3b) for receiving a light reflected from said light spot; and a control circuit for controlling a light emission level of said light emitting means and measuring a level of the light received by said light receiving means, characterised in that said control circuit comprises : (1) control means for said image forming medium, said cleaning means, selectively enabling or disabling an input of said image information and said developing means; (2) means for measuring a light emission level (Dout) from said light emitting means (3a) which keeps said light level received by said light receiving means (3b) at a predetermined level as a first light emission level (DS1) when said image forming medium and said cleaning means are enabled, and said input of said image information and said developing means are disabled by said control means; and (3) means for discriminating whether said first light emission level is larger than a predetermined limit level (Dcont), whereby a contamination of said detector is detectable if said predetermined level is exceeded; and (4) means for issuing an alarm signal if a contamination of said detector is detected. A recording apparatus, according to claim 12, wherein said control circuit further comprises means for outputting an alarm signal for cleaning said optical detector (3) when it is discriminated that said first light emission level (DS1) is larger than a predetermined limit level. A recording apparatus according to any one of claims 10 to 13, further comprising: toner mark generating means (10) for outputting a toner mark signal to said image information, said toner mark being produced outside a print area on a predetermined area on said image forming medium, said toner mark being detected by said detector; and wherein said control circuit (5) further comprises a feedback loop for controlling a light emission level of said light emitting means so as to keep a level of the light received by said light receiving means at a predetermined level, said apparatus comprising : (1) means for forming said toner mark on said image forming medium; and (2) means for adjusting a location of said detector by observing a toner mark signal in the received light while said feedback loop is disabled and said light emission level is kept constant. A recording apparatus according to claim 14, wherein said control circuit further comprises switch means by which an input to said light emitting means (3a) is selected to one of: a feedback from said received light level and a constant voltage. A recording apparatus according to claim 15, wherein said switch means is composed of a mechanical switch and said constant voltage is supplied from a direct current power source. A recording apparatus according to claim 15, wherein said switch means and said constant voltage are composed of a firmware of a microprocessor.

Inventors: SETO FUMIAKI, TAKENAKA YUTAKA, SETO, FUMIAKI, TAKENAKA, YUTAKA
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1989
Main classification: G03G15
IPC codes: G03G15