Toner quantity detecting system for an image recording apparatus, a method of detecting the quantity of toner and a developing device for the image recording apparatus

Abstract: A toner quantity detecting system has a toner quantity detector (4c) and is capable of accurately detecting the decrease of the quantity of toner contained in the toner container of the developing unit of an image recording apparatus to an upper threshold quantity and to a lower threshold quantity regardless of the inherent output characteristic of the toner quantity detector (4c) and determining a prewarning voltage (E nep ) representing the upper threshold quantity and a warning voltage (E emp ) representing the lower threshold quantity so that the difference between the prewarning voltage (E nep ) and the warning voltage (E emp ) is sufficiently large. The prewarning voltage (E neP ) and the warning voltage (E emP ) are determined on the basis of the inherent output characteristic of the toner quantity detector (4c). The output voltage (E s ) of the toner quantity detector (4c) is compared with the prewarning voltage (E nep ) and the warning voltage (E emp ) to provide a prewarning signal (NAL) upon the reduction of the quantity of the toner to the upper threshold quantity and to provide a warning signal (EAL) upon the reduction of the quantity the toner to the lower threshold quantity.

Description: The present invention relates to developing devices for use in image recording apparatus. The invention also relates to a method of detecting the quantity of toner in an image recording apparatus including such a developing device, which method is capable of detecting the exhaustion and virtual exhaustion of toner, i.e., residual amount of toner in the storage, on the basis of the output voltage of a toner quantity detector provided on the outer surface of the casing of a toner container of the developing device. An electrophotographic printer or a copying machine first forms an electrostatic latent image of the original document to be copied or printed on a photoconductive drum; and thereafter prints or copies it by developing the electrostatic latent image to form a toner image, transferring the toner image to a recording sheet, and fixing the toner image on the recording sheet. Fig. 1 shows such an electrophotographic printer. The electrophotographic printer has a photoconductive drum 1, a charger 2 for charging the entire circumference of the photoconductive drum to a uniform potential, and a scanning unit 3 for longitudinally scanning the circumference of the photoconductive drum 1 (in the main scanning direction) with a laser beam RB emitted by a laser diode (not shown), a developing unit 4 for developing the electrostatic latent image with toner, a transfer charger 5 for transferring the toner image to the recording sheet, a fixing unit 6 for fixing the toner image on the recording sheet, and sheer transporting passage 7. The scanning unit 3 comprises a polygonal rotating mirror 3a, an f lens 3b, a mirror 3c and a cylindrical lens 3d. During the scanning operation, the laser beam RB is turned on and off according to image data to form an electrostatic latent image on the photoconductive drum 1. As shown in Fig. 2, the developing unit 4 comprises a toner stirring unit 4a for frictionally charging toner TN by stirring toner TN with a toner stirring member 4a-1, a toner feeder 4b and a toner quantity detector 4c for detecting the quantity of toner TN remaining in the developing unit 4. The toner TN is stirred by the toner stirrer 4a-1 and the frictionally charged toner TN is fed to a rotating magnet roller 4b-1 included in the toner feeder 4b. Surplus toner TN is scraped off with a doctor's blade 4b-2 to form a toner layer of toner TN in a predetermined thickness on the circumference of the magnet roller 4b-1 so that the toner layer touches the circumference of the photoconductive drum 1. A bias voltage is applied between the magnet roller 4b-1 and the photoconductive drum 1. The toner TN is transferred from the magnet roller 4b-1 to the electrostatic latent image formed on the circumference of the photoconductive drum 1 by the agency of the potential difference between the magnet roller 4b-1 and the photoconductive drum 1 to develop the electrostatic latent image in a toner image. As shown in Fig. 3(A), the toner quantity detector 4c is placed fixedly in contact with a detector seat 4a-3, formed on a frame 4a-2 of the developing unit 4 to detect the quantity of toner TN remaining in the developing unit 4. Since it is impossible to print a sharp image on a recording sheet if the quantity of toner TN in the developing unit 4 decreases excessively during operation, the quantity of toner TN is detected by the toner quantity detector 4c during operation and, if necessary, a warning is given to prompt the operator to replenish the developing unit 4 with toner or to replace the developing unit with another. As shown in Fig. 3(B), the toner quantity detector 4c is of a differential transformer construction comprising a driving coil L1, a reference coil L2 and a detecting coil L3, which are mounted on a core. A high-frequency signal of 500 kHz is applied to the driving coil L1. A developer, in general, is a mixture of a small amount of magnetic carrier particles and a magnetic toner. As toner is consumed, the magnetic resistance of the toner varies according to an upper level of the developer relative to the position of the toner quantity detector 4c, whether that upper level remains above, below or near a surface defined by the detector 4c and hence the output voltage of the detecting coil L3 varies with the variation of the level of the developer as shown in Fig. 3(C). That is, the output voltage of the toner quantity detector 4c remains constant at a high level while the quantity of toner is greater than a threshold quantity. When the quantity of toner decreases below the threshold quantity, the output voltage of the toner quantity detector 4c starts falling, and the output voltage of the toner quantity detector 4c settles at a low level after the toner has almost been exhausted. A prewarning voltage E nep corresponding to a state where the toner is nearly exhausted, or a warning voltage E emp , corresponding to a state where the toner is virtually exhausted, is set, or both the prewarning voltage E nep and the warning voltage E emp are set, the output voltage E s of the toner quantity detector 4c is compared with the prewarning voltage E nep and/or the warning voltage E emp to detect if the quantity of the toner has decreased below a predetermined near-exhaustion quantity or if the toner has virtually been exhausted as the case may be, and the condition is identified by an alarm. Incidentally, DE-A-3940517 mentions one example of toner quantity detecting circuitry that generates a prewarning signal when the detected quantity of toner remaining is less than a level corresponding to near-exhaustion of the toner supply, and another warning signal when the detected quantity of toner remaining is less than a further, lower level corresponding to virtual exhaustion of the toner supply. The electrophotographic apparatus of such a construction uses a single-component developer comprising only a toner made of carbon particles containing a magnetic component therein, a two-component developer containing a nonmagnetic container and a magnetic carrier, or a two-component developer containing a small amount of magnetic carrier and a magnetic toner. In image recording apparatus including a toner container having a toner quantity or density detector, one problem that arises is accumulation of toner particles near to the location on the toner container at which the detector is provided. Such accumulation may prevent the detector from operating accurately. To address this problem JP-A-2216167 discloses a developing device that is suitable for use in image recording apparatus including a main frame, a photoconductive drum supported for rotation on the said main frame, charging means for charging the circumference of the said photoconductive drum, electrostatic latent image forming means for forming an electrostatic latent image on the said circumference of the photoconductive drum, the said developing device serving to develop the electrostatic latent image with toner so as form a toner image on the photoconductive drum, transfer charging means for charging a recording medium so that the toner image formed on the circumference of the photoconductive drum is transferred to the recording medium, and fixing means for fixing the toner image to the recording medium. This developing device comprises: a toner stirring unit having a toner container for holding a supply of toner and also having a toner stirring member rotatable within the said toner container for stirring toner held in the toner container so as to charge the toner frictionally, the toner container having a seat portion at which, in use, toner detecting means are arranged for producing an output voltage representing the quantity or density of toner remaining in the said toner container; and a cleaning member connected with the said toner stirring member for cleaning away toner from the said seat portion during rotation of the stirring member. In this prior developing device the cleaning member projects from the stirring member, and the cleaning performance and durability of the cleaning member are not always satisfactory. A developing device embodying a first aspect of the present invention is characterised in that the said seat portion has an outer surface that is arranged to be in contact with such toner detecting means when the device is in use, and also has an inner surface that, when viewed in a plane perpendicular to the axis of rotation of the toner stirring member, is circular and proud of the level of the surrounding areas of the inner surface of the toner container, and in that a portion of an extremity of the toner stirring member, which portion passes across the seat portion inner surface during rotation of the toner stirring member, is formed with a recess of a width, measured parallel to the said axis, greater than that of the seat portion inner surface so that the said toner stirring member does not collide against that inner surface during the said rotation thereof, the said cleaning member being attached to the said toner stirring member in the said recess such that a working surface of the cleaning member is substantially flush with surface portions of the said extremity adjacent to the said recess, and the dimensions and arrangement of the toner stirring member and the said seat portion being such that during rotation of the toner stirring member the working surface of the cleaning member contacts the seat portion inner surface so as to clear therefrom toner adhered thereto, but does not contact said surrounding areas of the inner surface of the toner container. According to a second aspect of the present invention there is provided image recording apparatus including: a developing device embodying the aforesaid first aspect of the present invention; toner quantity detecting means arranged, when the apparatus is in use, in a working disposition in which the toner quantity detecting means are in contact with the said outer surface of the seat portion of the said toner container for producing an output voltage representative of the quantity of toner remaining in the toner container, and movable, relative to the said toner container, from the said working disposition to a measuring disposition in which the toner quantity detecting means are spaced from the toner container such that the said output voltage thereof changes to a characteristic value for the toner quantity detecting means concerned; and toner quantity detecting circuitry connected with the said toner quantity detecting means for receiving therefrom the said output voltage and including: comparator means operable, when the said toner quantity detecting means are in the said working disposition relative to the toner container, to compare the said output voltage with a reference voltage, representing a threshold quantity of toner, so as to detect when the said quantity of toner remaining in the toner container falls below the said threshold quantity; output characteristic determining means, operable, when the said toner quantity detecting means are in the said measuring disposition relative to the toner container, to measure the said characteristic value of the said output voltage; and reference voltage setting means operable to set the said reference voltage in dependence upon the measured characteristic value. According to a third aspect of the present invention there is provided a method of detecting the quantity of toner in image recording apparatus having a developing device embodying the aforesaid first aspect of the present invention and also having toner quantity detecting means for producing an output voltage representative of the quantity of toner remaining in the toner container, which method comprises: an output characteristic determining step in which the said toner quantity detecting means are arranged in a measuring disposition relative to the said toner container in which the toner quantity detecting means are spaced from the toner container such that the said output voltage changes to a characteristic value for the toner quantity detecting means concerned, and the said characteristic value of the said output voltage is measured; and a reference voltage setting step in which a reference voltage, representing a threshold quantity of toner, is set in dependence upon the characteristic value measured in the said output characteristic determining step; whereafter, when the said toner quantity detecting means are arranged in a working disposition in which those means are in contact with the outer surface of the seat portion of the said toner container, the said output voltage is compared with the said reference voltage to detect when the said quantity of toner remaining in the toner container falls below the said threshold quantity. Such image recording apparatus embodying the second aspect of the present invention and such a toner quantity detecting method embodying the third aspect of the present invention can enable the reference voltage (prewarning voltage E nep and/or warning voltage E emp ) to be set to a level correct for the particular toner quantity detector even though the output voltage characteristics of the different detectors vary from one another due to the variations in the their sensitivity and the adjusting operation precision. Preferably, the comparator means are operable to compare the said output voltage with two reference voltages, one reference voltage being a prewarning voltage representing a first threshold quantity of toner at which the supply of toner in the toner container is nearly exhausted, and the other reference voltage being a warning voltage representing a second threshold quantity of toner, lower than the said first threshold quantity, at which the said supply is virtually exhausted, the said reference voltage setting means being operable to set both the prewarning voltage and the warning voltage in dependence upon the said measured characteristic value. This embodiment enables the setting of a prewarning voltage and a warning voltage, and is capable of securing a sufficiently long time between the detection of the decrease of the quantity of toner to a prewarning level and the detection of the decrease of the same to a warning level. Reference will now be made, by way of example, to the accompanying drawings, in which: Fig. 1 is a schematic sectional view of an electro-photographic printer; Fig. 2 is a schematic sectional view of a developing unit included in the Fig. 1 printer; Figs. 3(A), 3(B) and 3(C) are a fragmentary sectional view, a circuit diagram and a graph, respectively, for use in explaining operation of a toner quantity detector; Figs. 4(A) and 4(B) are fragmentary schematic sectional views of a developing device embodying the present invention; Figs. 5(A) and 5(B) are fragmentary schematic sectional views of another developing embodying the present invention; Fig. 6 is a plan view of a toner stirrer included in the Figure 5 developing device; Figs. 7(A) and 7(B) are fragmentary schematic sectional views for use in explaining a cleaning range of the Figure 5 developing device; Fig. 8 is a graph showing the output characteristics of a plurality of toner quantity detectors having different respective properties; Figs. 9(A) and 9(B) are a schematic sectional view and a graph, respectively, for use in explaining a principle underlying a preferred toner quantity detecting system suitable for use with a developing device embodying the present invention; Fig. 10 is a block diagram of the preferred toner quantity detecting system; Fig. 11 is a flowchart for use in explaining a method of determining a prewarning voltage and a warning voltage in the Fig. 10 system; Fig. 12 is an exploded perspective view of an image recording apparatus when a developing device thereof is taken out; Fig. 13 is a graph for use in explaining the Figure 11 method of determining a prewarning voltage and a warning voltage; and Fig. 14 is a flowchart of a control program for use in a preferred method of detecting the quantity of toner. As mentioned in the introduction, if toner TN accumulates on the inner surface of the toner container 4a-2 of the developing unit of Figure 2 (particularly in an area corresponding to the toner quantity detector 4C), the toner quantity detector 4c is unable to detect accurately the quantity of toner TN remaining in the toner container 4a-2 and provide a warning when the quantity of toner TN decreases below a predetermined threshold value. Therefore, a developing unit embodying the present invention is designed so as to remove the toner adhering to the inner surface of the toner container 4a-2 to ensure the accurate detection of the quantity of toner remaining in the toner container 4a-2. Preferably, a developing unit embodying the present invention is provided with a cleaning member capable of smoothly coming into contact with a wide area of a portion (seat portion), corresponding to the toner quantity detector, of the inner surface of the toner container 4a-2 and removing the toner adhering to that portion of the inner wall of the toner container 4a-2 without applying shocks to the toner container 4a-2. Referring to Figs. 4(A) and 4(B) showing a developing unit embodying the present invention, there are shown a toner stirring unit 111, a rotary stirring member 112 for frictionally charging the toner by stirring, a toner container 113, a toner quantity detector 114, which may be a toner density detector, a detector seat 115 on which the toner quantity detector 114 is seated, and a cleaning member 116 for cleaning a portion of the inner surface of the toner container 113 corresponding to the detector seat 115. When viewed in a plane perpendicular to the axis of rotation of the toner stirring member 112, as in Figure 4(A) for example, the inner surface of the detector seat 115 is raised on a circular inner surface from the inner surface of the toner container 113 so that the inner surface of the detector seat 115 interferes with the extremity 112b-1 of the toner stirring member 112. A recess of a width (measured parallel to the axis of rotation of the toner stirring member) wider than the width of the circular inner surface of the detector seat 115 is formed in the extremity of the toner stirring member 112, and the cleaning member 116 is attached to the toner stirring member 112 in the recess so that its surface is substantially flush with the extremity 112b-1 of the toner stirring member 112. When the toner stirring member 112 is rotated, the cleaning member 116 wipes off the toner adhering to the circular inner surface of the detector seat 115 to enable the toner quantity detector 114 to detect the quantity of toner accurately. The radius of a circle having a center A and corresponding to the circular inner surface of the detector seat 115 is equal to or slightly greater than the radius of a circle having a center B along which the extremity 112b-1 of the toner stirring member 112 moves, and the center A is dislocated from the center B away from the inner surface of the toner container 113 on a line passing through the center B and the middle of the circular inner surface of the detector seat 115. Accordingly, the cleaning member 116 comes smoothly into contact with the circular inner surface of the detector seat 115 at a point C, the pressure acting between the cleaning member 116 and the circular inner surface of the detector seat 115 increases as the toner stirring member 112 rotates to enable the cleaning member 116 to remove the toner adhering to the circular inner surface of the detector seat 115, the pressure acting between the cleaning member 116 and the circular inner surface of the detector seat 115 decreases gradually as the toner stirring member 112 rotates further, and then the cleaning member 116 separates smoothly from the circular inner surface of the detector seat 115 at a point D. Thus, the cleaning member 116 is able to clean a wide area of the circular inner surface of the detector seat 115. Figs. 5(A) and 5(B) show another developing unit 110 embodying the present invention, in which parts like or corresponding to those of the developing unit shown in Figs. 4(A) and 4(B) are denoted by the same reference characters. The remaining construction of the developing unit 110 is substantially the same as that of the conventional developing unit shown in Fig. 2. Referring to Figs. 5(A) and 5(B), there are shown a toner stirring unit 111, a rotary toner stirring device 112 for frictionally charging the toner, a toner container 113, a toner quantity detector 114, which may be a toner density detector, for detecting the quantity of toner contained in the toner container 113, a detector seat 115, and a cleaning member 116, such as a sponge pad, for removing the toner adhering to the circular inner surface of the detector seat 115. As shown in Fig. 6, the toner stirring device 112 comprises a rotary shaft 112a, and two stirring members 112b and 112c having a shape substantially resembling the letter U and attached to the rotary shaft 112a. The stirring member 112b (112c) has arms 112b-2 (112c-2) radially projecting from the rotary shaft 112a and having a shape resembling a blade as shown in Fig. 5, and a stirring rod 112b-1 (112c-1) having a round cross section and held between the extremities of the arms 112b-2 (112c-2). The inner surface of the detector seat 115 formed in the toner container 113 is raised in a circular inner surface as shown in Fig. 5(A). The radius Ra of a circle corresponding to the circular inner surface of the detector seat 115 is equal to or greater than the radius Rb of a circle along which the extremities of the toner stirring device 112 move, and the center A of the circle having the radius Ra is dislocated (spaced) from the center B of the circle having the radius Rb so that the circular inner surface of the detector seat 115 interferes with the stirring rod 112b-1 of the stirring member 112b by a maximum depth a of interference. If the inner surface of the detector seat 115 is flat as shown in Fig. 7(A), the cleaning member 116 is capable of contacting a portion of the inner surface of a length L1. However, since the detector seat 115 has the circular inner surface as shown in Fig. 5(A), the cleaning member 116 is capable of contacting a portion of the circular inner surface of a length L2, which is greater than the length L1, as shown in Fig. 7 (B). A recess of a width wider than that of the circular inner surface of the detector seat 115 is formed on the surface of the stirring rod 112b-1 of the stirring member 112b facing the inner surface of the toner container 113, and a cleaning member 116 is attached adhesively to the stirring rod 112b-1 in the recess so that the surface of the cleaning member 116 is substantially flush with the surface of the stirring rod 112b-1 as shown in Fig. 5(B). When the toner stirring device 112 is rotated, the cleaning member 116 is compressed between the stirring rod 112b-1 and the circular inner surface of the detector seat 115 and pressed firmly against the circular inner surface of the detector seat 115 to wipe off the toner adhering to the circular inner surface of the detector seat 115. The cleaning member 116 comes smoothly into contact with the circular inner surface of the detector seat 115 at a point C (Fig. 5(A)), is compressed gradually by a thickness corresponding to the maximum depth a of interference as the toner stirring device 112 rotates, is allowed to expand gradually after the same has been compressed by the thickness corresponding to the maximum depth a of interference, and then separates smoothly from the circular inner surface of the detector seat 115 at a point D (Fig. 5(A)) after wiping off the toner adhering to the circular inner surface of the detector seat 115. Consequently, the toner quantity detector 114 is capable of detecting the quantity of toner accurately. Since the cleaning member 116 is able to come smoothly into contact with the circular inner surface of the detector seat 115 and separate smoothly from the circular inner surface of the detector seat 115, no shock is applied to the developing unit 110; the circular inner surface of the detector seat 115 is not damaged and the stirring member 116 is not broken. A preferred toner quantity detecting system, suitable for use with a developing device embodying the present invention, will now be described with reference to Figures 8 to 13(C). This system is intended to address the following problem. In the apparatus described hereinbefore with reference to Figures 1 to 3(C) the output characteristic of the toner quantity detector is not constant due to a variation of the adjusting operation thereof and the sensitivity thereof. The variation arising from the adjustment operation (in which an output of a magnetic resistance sensor portion of the detector is adjusted) occurs because the adjustment is performed with variable degrees of carefulness. Accordingly, the output characteristic of the toner quantity detector is represented by: (1) a curve A (Fig. 8) when the sensitivity thereof is maximum and the setting of the adjusting operation is maximum, (2) a curve B (Fig. 8) when the sensitivity thereof is maximum and the setting of the adjusting operation is minimum, (3) a curve C (Fig. 8) when the sensitivity thereof is minimum and the setting of the adjusting operation is maximum or (4) a curve D (Fig. 8) when the sensitivity is near to the standard sensitivity and the setting of the adjusting operation is minimum. If the output characteristic of the toner quantity detector varies according to the sensitivity and the adjustment setting, the actual quantity of toner corresponding to the prewarning voltage E nep and the toner quantity corresponding to the warning voltage E emp vary widely depending on the output characteristics represented by the output characteristic curves A, B, C and D. Accordingly, the number of copies that can be produced before the toner quantity detector provides an output voltage E s corresponding to the warning voltage E emp varies depending on the output characteristic of the toner quantity detector. Therefore, all the possible output characteristics of the toner quantity detector must be taken into consideration in determining the prewarning voltage E nep and the warning voltage E emp ; that is, the prewarning voltage E nep must be set at a level below a voltage E1 defined by the output characteristic curve D, in which both the sensitivity and adjusting operation setting are at minima, and the warning voltage E emp must be set at a level higher than a voltage E2 defined by the output characteristic curves A and C in which the adjusting operation setting is maximum. If the prewarning voltage E nep and the warning voltage E emp are determined in such a manner, the difference between the prewarning voltage E nep and the warning voltage E emp is small, and hence the toner quantity detector will provide the warning voltage E emp a very short time after providing the prewarning voltage E nep , so that only a very short time is available for preparing a fresh supply of toner, after a prewarning has been given, before a warning prompting the operator to replenish the developing unit with toner is given. If the operator is unable to prepare the fresh supply of toner before the warning is given, the operation of the electrophotographic apparatus must be interrupted. Although toner quantity detectors have different output characteristics respectively due to errors in the toner quantity detector manufacturing processes and in the quality of the component parts, the toner quantity detectors are adjusted uniformly by a standardized adjusting method after mounting the toner quantity detectors respectively on electrophotographic apparatus before shipping the electrophotographic apparatus. Accordingly, the present state of the art is that the output voltage E s of the toner quantity detector does not necessarily represent the accurate quantity of toner remaining in the developing unit. As is obvious from Fig. 8, although the difference between the output voltages E s of the toner quantity detectors having different output characteristics near the warning voltage E emp is relatively small, the output voltages E s change sharply in greatly different modes from the upper output voltages above the prewarning voltage E nep to the lower output voltages near the warning voltage E emp , respectively. Thus, the mode of change of the output voltage E s from the upper output voltage to the lower output voltage is dependent on the inherent output characteristic of each toner quantity detector. Accordingly, the output characteristic of the toner quantity detector must be measured accurately to determine accurately the quantities of toner respectively corresponding to the prewarning voltage E nep and the warning voltage E emp of the toner quantity detector. Referring now to Fig. 9(A), there are shown a photoconductive drum 1, a developing unit 4, a toner stirring unit 4a, a toner feeder 4b, a toner quantity detector 4c, an AD converter 13 for converting the output voltage of the toner quantity detector 4c to a corresponding digital signal, and a signal processing unit 15 for setting a prewarning voltage E nep and a warning voltage E emp and for controlling and monitoring the quantity of toner. The signal processing unit 15 is set, taking into consideration the output characteristic of the toner quantity detector 4c, for a warning voltage E emp (E emp ') representing the virtual exhaustion of toner below a predetermined lower limit and a prewarning voltage E nep (E nep ') representing a decrease of the quantity of toner below a predetermined threshold quantity. The signal processing unit 15 compares the output voltage E s of the toner quantity detector 4c with the warning voltage E emp (E emp ') and the prewarning voltage E nep (E nep '), and provides a warning signal EAL when the output voltage E s is not higher than the warning voltage E emp (E emp ') or provides a prewarning signal NAL when the output voltage E s is not higher than the prewarning voltage E nep (E nep '). Thus, the warning voltage E emp (E emp ') and the prewarning voltage E nep (E nep ') are respectively set for each individual toner quantity detector 4c, so that when any one of the warning voltages E emp (E emp ') and the prewarning voltages E nep (E nep ') is generated, the variation in the amount of toner can be suppressed and decreased even though different toner quantity detectors 4c have different output characteristics as shown by curves A, B, C or D in Fig. 9 (B). Since it is possible to determine warning voltage E emp (E emp ') and the prewarning voltage E nep (E nep ') so that the difference between the warning voltage E emp (E emp ') and the prewarning voltage E nep (E nep ') is relatively large, a time interval between the coincidence of the output voltage E s of the toner quantity detector 4c with the prewarning voltage E nep (E nep ') and the coincidence of the same with the warning voltage E emp (E emp ') is relatively long. The warning voltage E emp (E emp ') is determined by adding a first fixed value S 1 to a minimum output voltage E smin of the toner quantity detector 4c, which is provided when the toner stirring unit 4a is removed from the image recording apparatus, and the prewarning voltage E nep (E nep ') is determined by adding a second fixed value S 2 (S 2 > S 1 ) to the minimum output voltage of the toner quantity detector 4c. The output voltage E s of the toner quantity detector 4c may be displayed on a display to facilitate the operator in detemining the warning voltage E emp (E emp ') and the prewarning voltage E nep (E nep ') by operating a keyboard or the like. Thus, when the toner quantity detector 4c is replaced with a new toner quantity detector, a new warning voltage and a new prewarning voltage can readily be determined for the new toner quantity detector. Such a toner quantity detecting system as incorporated into an image recording apparatus will be described in detail hereinafter. Referring to Fig. 10 showing the general construction of the developing unit 4, the toner quantity detecting system comprises: the toner quantity detector 4c held on a main frame of the image recording apparatus in contact with the outer surface of the toner container of a toner stirring unit 4a detachably mounted on the main frame of the image recording apparatus; a toner output characteristic determining unit 20 for determining an inherent output characteristic of the toner quantity detector 4c and determining the warning voltage E emp and the prewarning voltage E nep ; an AD converter 13 for converting the analog output signal of the toner quantity detector 4c into a corresponding digital signal; and a signal processing unit 15 that compares the output voltage E s of the toner quantity detector 4c with the warning voltage E emp and the prewarning voltage E nep and determines the quantitative condition of toner in the toner container. The toner output characteristic determining unit 20 comprises, as principal components, an output characteristic measuring device 21 for measuring the output characteristic of the toner quantity detector 4c, a first storage device 22 for storing the measured output characteristic of the toner quantity detector 4c, a second storage device 23 for storing the predetermined (fixed )values S 1 and S 2 , an adder 24 or adding the fixed values S 1 and S 2 to the stable minimum output voltage E smin of the toner quantity detector 4c to determine the prewarning voltage E nep , i.e., an upper reference voltage, and the warning voltage E emp , i.e., a lower reference voltage, a third storage device 25 for storing the prewarning voltage E nep and the warning voltage E nep provided by the adder 24, and a fourth storage device 26 for storing a reference warning level and a reference prewarning level corresponding respectively to the warning voltage E emp and the prewarning voltage E nep . Referring again to Fig.10, there are shown the photoconductive drum 1, the developing unit 4, a motor 11 for rotating a stirrer 4a-1, a speed detector 12 which detects the rotating speed of the motor 11 and provides a set speed signal CVE upon the coincidence of the rotating speed of the motor 11 with a set rotating speed, the AD converter 13, a display 14, such as a liquid crystal display, for displaying the output voltage E s of the toner quantity detector 4c, the signal processing unit 15, and a printer operating unit 16. The stirrer 4a-1 of the toner stirring unit 4a of the developing unit 4 is rotated by the motor 11 to stir the toner TN contained in a toner container 4a-2. The toner feeder 4b has a magnet roller 4b-1 for transferring the toner TN to the photoconductive drum 1, and a doctor's blade 4b-2 for regulating the thickness of the layer of toner TN on the circumference cf the magnet roller 4b-1. The toner quantity detector 4c is disposed in contact with the outer surface of the toner container 4a-2 of the toner stirring unit 4a. The toner quantity detector 4c provides an output voltage E s corresponding to the quantity of toner TN contained in the toner container 4a-2. The signal processing unit 15 comprises a microprocessor 15a, a data memory 15b for storing data, and a program memory, not shown. The warning voltage E emp , the prewarning voltage E nep , and the fixed values S 1 and S 2 are stored in the data memory 15b. A procedure of measuring the output characteristic of the toner quantity detector 4c will be described hereinafter. Since the respective output characteristics of toner quantity detectors are different from each other, the output characteristic unique to the toner quantity detector 4c of the toner quantity detecting system must be measured and defined in advance of the detector's use. As mentioned above, the output voltage E s of the toner quantity detector 4c is stabilized and variation thereof between different detectors is small at the lowest level which occurs when the toner container 4a-2 is empty or contains a small amount of the toner. Therefore, the output characteristic of the toner quantity detector 4c is represented by measuring its minimum output voltage E smin (provided when the developing unit 4 is separated from the main frame of the apparatus and by adding a predetermined first fixed value S 1 to the minimum output voltage E smin so measured to determine the warning voltage E emp , and by adding a predetermined second fixed value S 2 to the minimum output voltage E smin to determine the prewarning voltage E nep . The minimum output voltage E smin is stored in the first storage device 22. To separate the toner quantity detector 4c from the developing unit 4, in the case in which the toner quantity detector 4c is fixedly provided on the developing unit 4, the detector is removed therefrom, or in the case in which the detector is fixedly mounted on the main frame of the image recording apparatus and the developing unit 4 is removably mounted on the main frame of the apparatus, the developing unit 4 is removed from the image recording apparatus. In the latter case, the developing unit 4 is detachably mounted on the main frame of the image recording apparatus, and the toner quantity detector 4c is held fixedly on the main frame of the image recording apparatus, which facilitates the measurement of the output characteristic of the toner quantity detector 4c and enables the accurate connection of the toner quantity detector 4c and the developing unit 4. The first fixed value S 1 and the second fixed value S 2 are read from the second stcrage device 23, the adder 24 calculates E smin + S 1 = E emp and E smin + S 2 = E nep , and the warning voltage E emp and the prewarning voltage E nep thus calculated are stored in the third storage device 25. The first fixed value S 1 and the second fixed value S 2 are stored previously in the second storage device 23. For example, the first ixed value S 1 is 0.6 V and the second fixed value S 2 is 1.2 V. Although there is no particular restriction on the predetermined first fixed value S 1 and the second ixed value S 2 , the fixed values S 1 and S 2 must selectively be determined so that the lower reference voltage is not lower than the warning voltage E emp (Fig. 9(B))and the upper reference voltage is not higher than the prewarning voltage E nep (Fig. 9(B))when the toner quantity detector 4c has an output characteristic represented by the curve A or C, and the fixed values S 1 and S 2 must selectively be determined so that the lower reference voltage is not lower than the warning voltage E emp ' (Fig. 9(B))and the upper reference voltage is not higher than the prewarning voltage E nep ' (Fig. 9(B)) when thetoner quantity detector 4c has an output characteristic represented by the curve B or D. Fig. 11 is a flowchart showing steps of a reference voltage determining procedure for automatically determining the warning voltage E emp and the prewarning voltage E nep . In determining the warning voltage E emp and the prewarning voltage E nep , the toner stirring unit 4a is removed from the main frame of the image recording apparatus. In Fig. 12, the photoconductive drum unit 1' and the developing unit 4' including the toner stirring unit 4a are removed from the main frame of the image recording apparatus, and the detecting head of the toner quantity detector 4c is expcsed. When the developing unit 4' is removed from the image recording apparatus, and there is no metallic part in the vicinity of the toner quantity detector 4c, the output voltage of the toner quantity detector 4c is substantially equal to that obtained when the toner is virtually exhausted. A check is made in step 101 to see if an instruction requesting the determination of the warning voltage E emp and the prewarning voltage E nep has been given by operating the operating unit 16. If the response in step 101 is affirmative, the reference voltage determining unit 20 reads the output voltage E s of the toner quantity detector 4c through the AD converter 13 in step 102. The adder 24 of the output characteristic determining unit 20 reads the first fixed value S 1 and the second fixed value S 2 from the second storage device 23 and calculates the warning voltage E emp and the prewarning voltage E nep by using the expressions: E emp = E smin + S 1 E nep = E smin + S 2 in step 103, and stores both results in the third storage device 25 as the warning voltage E emp and the prewarning voltage E nep , respectively, before ending the reference voltage determining procedure. The reference warning voltage and the reference prewarning voltage will be explained with reference to Fig.13. The reference warning voltage and the reference prewarning voltage for the toner quantity detector 4c are E emp and E nep when the toner quantity detector 4c has an output characteristic represented by the curve A or C, and E emp ' and E nep ' wren the toner quantity detector 4c has an output characteristic represented by the curve B or D. The operation of the toner quantity detecting system will be described hereinafter with reference to Fig. 14. The period of sampling operation of the toner quantity detecting system, for example, 1.2 sec, is an integral multiple of a stirring period. The sampling rate is 200 cycles /1.2 sec, for example. The microprocessor 15a of the signal processing unit 15 monitors the rotating speed of the motor 11 continuously (step 201), and the speed detector 12 provides the set speed signal CVE. A check is made at a sampling time in step 202 to see if a count TNEMPC, which is zero in the initial state, stored in the data memory 15b is 0. In the initial state, the court TNEMPC is 0 and hence the response in step 202 is affirmative. In step 203 the output ADCR of the AD converter is read (sampled) and in step 204 the output is stored in the data memory 15b as TNSBUF. In step 205, the content of the counter is incremented by one (TNEMPC+1), and then a check is made in step 206 to see if the count of the counter is 200 or greater, i.e. if the sampling period (set at 1.2 sec for example) is over. If the response in step 206 is negative, steps 201 to 206 are executed repeatedly. If the response in step 202 is negative, namely, if the count of the counter is not 0, the output ADCR of the AD converter 13 is sampled at a sampling time and held in the register (accumulator) A, and then TNSBUF, i.e., the quantity of toner, is updated by the following conversion formula namely, A ← A+TNSBUF and TNSBUF ← A/2, in step 207; that is, the moving average of data is calculated every time the output ADCR of the AD converter 13 is sampled. Then, steps 205 and 206 are executed. Steps 201, 207, 205 and 206 are executed repeatedly until the count exceeds 200. The response in step 206 is affirmative when TNEMPC ≥ 200. In step 208 a check is made to see if TNSBUF, representing the quantity of toner, is smaller than the prewarning voltage E nep . If the response in step 208 is negative, a prewarning flag STNR is reset to 0 in step 209, a warning flag STEND is reset to 0 in step 210, the content of the counter is cleared in step 211, and then the routine returns to step 201 to execute the same steps again. As the toner is consumed with the progress of the image recording operation, TNSBUF, representing the quantity of toner, decreases gradually. Upon the decrease of TNSBUF below the prewarning voltage E nep , the response in step 208 is affirmative. Then, the prewarning flag STNR is set to 1 to generate the prewarning signal NAL and to display a warning sign on the display. In step 213, a query is made to see if TNSBUF is lower than the warning voltage E emp . If the response in step 213 is negative, step 210 and the following steps are executed repeatedly. When the TNSBUF, representing the quantity of toner, is lower than the warning voltage E emp , namely, when the quantity of toner remaining in the toner container is less than a lower threshold quantity, the response in step 213 is affirmative. Then, a warning flag STEND is set to 1 to generate the warning signal EAL and a warning sign is displayed on the display in step 214. Then, the count TNEMPC of the counter is cleared in step 215 and the procedure is repeated. In the above-described method, the prewarning voltage E nep and the warning voltage E emp are determined on the basis of the output voltage of the toner quantity detector 4c in a removed state corresponding to the state in which the toner has virtually been exhausted. It is also possible to take into consideration the output voltage of the toner quantity detector 4c in a state in which the toner container is filled with toner to its full capacity when determining the prewarning voltate E nep and the warning voltage E emp , which can reduce the variation of the quantity of tonic from the lower threshold quantity corresponding to the warning voltage E emp . Furthermore, although the above-described method determines the prewarning voltage E nep and the warning voltage E emp automatically, it is also possible to display the output voltage of the toner quantity detector 4c provided when the toner stirring unit is removed from the image recording apparatus on the display to make the operator set the prewarning voltage E nep and the warning voltage E emp by operating the operating unit 16 whilst referring to the output voltage of the toner quantity detector 4c displayed on the display 14. Thus, the prewarning voltage E nep and the warning voltage E emp are determined on the basis of the output voltage of the toner quantity detector 4c in a specific state corresponding to the virtual exhaustion of toner, so that the prewarning voltage E nep and the warning voltage E emp correspond accurately to the desired quantities of toner remaining in the toner container, respectively. Furthermore, since the difference, i.e., S 1 -S 2 , between the prewarning voltage E nep and the warning voltage E emp is sufficiently large, sufficient time is available for replenishing the toner container with toner after the output voltage E s of the toner quantity detector 4c has coincided with the prewarning voltage E nep before the output voltage E s drops to the warning voltage E emp . Still further, in the above-mentioned example which displays the output voltage of the toner quantity detector 4c on the display 14 to enable the operator to set the prewarning voltage E nep and the warning voltage E emp by operating the keyboard, the prewarning voltage E nep and the warning voltage E emp can readily be set when the toner quantity detector 4c is replaced with a new one. A developing unit embodying the present invention is capable of enabling the toner quantity detecting system described above to function effectively. Although the invention has been described in its preferred form with a certain degree of particularity, obviously many changes and variations are possible therein, and it is therefore to be understood that the present invention may be practiced otherwise than as specifically described herein without departing from the scope thereof as defined in the claims.

Claims: A developing device (110) for use in image recording apparatus including a main frame, a photoconductive drum (1) supported for rotation on the said main frame, charging means (2) for charging the circumference of the said photoconductive drum (1), electrostatic latent image forming means (3) for forming an electrostatic latent image on the said circumference of the photoconductive drum (1), the said developing device (4) serving to develop the electrostatic latent image with toner so as form a toner image on the photoconductive drum, transfer charging means (5) for charging a recording medium so that the toner image formed on the circumference of the photoconductive drum is transferred to the recording medium, and fixing means (6) for fixing the toner image to the recording medium; the developing device (110) comprising: a toner stirring unit (111) having a toner container (113) for holding a supply of toner and also having a toner stirring member (112) rotatable within the said toner container (113) for stirring toner held in the toner container so as to charge the toner frictionally, the toner container (113) having a seat portion (115) at which, in use, toner detecting means (114) are arranged for producing an output voltage representing the quantity or density of toner remaining in the said toner container (113); and a cleaning member (116) connected with the said toner stirring member (112) for cleaning away toner from the said seat portion (115) during rotation of the stirring member; characterised in that the said seat portion (115) has an outer surface that is arranged to be in contact with such toner detecting means (114) when the device (110) is in use, and also has an inner surface that, when viewed in a plane perpendicular to the axis of rotation (B) of the toner stirring member, is circular and proud of the level of the surrounding areas of the inner surface of the toner container (113), and in that a portion of an extremity (112b-1) of the toner stirring member (112), which portion passes across the seat portion inner surface during rotation of the toner stirring member (112), is formed with a recess of a width, measured parallel to the said axis, greater than that of the seat portion inner surface so that the said toner stirring member (112) does not collide against that inner surface during the said rotation thereof, the said cleaning member (116) being attached to the said toner stirring member (112) in the said recess such that a working surface of the cleaning member (116) is substantially flush with surface portions of the said extremity (112b-1) adjacent to the said recess, and the dimensions and arrangement of the toner stirring member (112) and the said seat portion (115) being such that during rotation of the toner stirring member (112) the working surface of the cleaning member (116) contacts the seat portion inner surface so as to clear therefrom toner adhered thereto, but does not contact the said surrounding areas of the inner surface of the toner container. A device as claimed in claim 1, wherein, when viewed in the said plane, the said seat portion inner surface forms part of a first circle having a radius (Ra) greater than or equal to the radius (Rb) of a second circle described by the said extremity of the toner stirring member (112) as it rotates, the centre (A) of the said first circle being located on a side of the centre (B) of the said second circle opposite to the said seat portion (115) along a line passing both through the centre (B) of the said second circle and through a central point of the said seat portion inner surface. Image recording apparatus including: a main frame; a photoconductive drum (1) supported for rotation on the said main frame; charging means (2) for charging the circumference of the photoconductive drum (1); electrostatic latent image forming means (3) for forming an electrostatic latent image on the said circumference of the photoconductive drum (1); a developing device (4) as claimed in claim 1 or 2, for developing the electrostatic latent image with toner to form a toner image on the photoconductive drum; a transfer charging means (5) for charging a recording medium so that the toner image is transferred from the photoconductive drum (1) to the recording medium; and fixing means (6) for fixing the toner image to the recording medium. Image recording apparatus including: a developing device (4) as claimed in claim 1 or 2; toner quantity detecting means (4c) arranged, when the apparatus is in use, in a working disposition in which the toner quantity detecting means are in contact with the said outer surface of the seat portion of the said toner container (4a-2) for producing an output voltage (E s ) representative of the quantity of toner remaining in the toner container (4a-2), and movable, relative to the said toner container (4a-2), from the said working disposition to a measuring disposition in which the toner quantity detecting means are spaced from the toner container such that the said output voltage (E s ) thereof changes to a characteristic value (E smin ) for the toner quantity detecting means concerned; and toner quantity detecting circuitry (13-16, 20) connected with the said toner quantity detecting means (4c) for receiving therefrom the said output voltage (E s ) and including: comparator means (15) operable, when the said toner quantity detecting means (4c) are in the said working disposition relative to the toner container (4a-2), to compare the said output voltage (E s ) with a reference voltage (E emp ; E nep ), representing a threshold quantity of toner, so as to detect when the said quantity of toner remaining in the toner container falls below the said threshold quantity; output characteristic determining means (20), operable, when the said toner quantity detecting means (4c) are in the said measuring disposition relative to the toner container (4a-2), to measure the said characteristic value (E smin ) of the said output voltage (E s ) ; and reference voltage setting means (20) operable to set the said reference voltage (E emp ; E nep ) in dependence upon the measured characteristic value (E smin ). Apparatus as claimed in claim 4, in which the said toner stirring unit (4a) is mounted removably on a main frame of the apparatus and the said toner quantity detecting means (4c) are fixed relative to that main frame such that when the toner stirring unit (4a) is installed in the apparatus the toner quantity detecting means (4c) are arranged at the said outer surface of the said seat portion (115) of the toner container (4a-2), so as to be in the said working disposition relative thereto, and when the said toner stirring unit (4a) is removed from the apparatus the toner quantity detecting means are in the said measuring disposition relative to the said toner container. Apparatus as claimed in claim 4 or 5, wherein the said reference voltage of said circuitry is a prewarning voltage (E nep ) representing a threshold quantity of toner at which the said supply of toner in the toner container is nearly exhausted. Apparatus as claimed in claim 4 or 5, wherein the said reference voltage of said circuitry is a warning voltage (E emp ) representing a threshold quantity of toner at which the said supply of toner in the toner container is virtually exhausted. Apparatus as claimed in claim 4 or 5, wherein the said comparator means of said circuitry are operable to compare the said output voltage (E s ) with two reference voltages (E nep , E emp ), one reference voltage being a prewarning voltage (E nep ) representing a first threshold quantity of toner at which the supply of toner in the toner container is nearly exhausted, and the other reference voltage being a warning voltage (E emp ) representing a second threshold quantity of toner, lower than the said first threshold quantity, at which the said supply is virtually exhausted, the said reference voltage setting means (20) being operable to set both the prewarning voltage (E nep ) and the warning voltage (E emp ) in dependence upon the said measured characteristic value (E smin ). Apparatus as claimed in claim 8, wherein the measured characteristic value is the minimum stable value (E smin ) of the output voltage (E s ) produced by the toner quantity detecting means (4c), and the said reference voltage setting means (20) set the warning voltage (E emp ) to a value equal to the sum of the said characteristic value (E smin ) and a first predetermined value (S 1 ) and set the prewarning voltage (E nep ) to a value equal to the sum of the said characteristic value (E smin ) and a second predetermined value (S 2 ) greater than the said first predetermined value (S 1 ). Apparatus as claimed in any one of claims 4 to 9, further including means for displaying the said characteristic value (E smin ) on a display (14) of the apparatus, the said reference voltage setting means (16, 20) being selectively controllable by an operator of the apparatus to set the or each said reference voltage (E nep ; E emp ) with reference to the displayed characteristic value. Apparatus as claimed in any of claims 3 to 10, in which the toner quantity detecting means (4c) produce the said output voltage (E s ) in analog form, and the said toner quantity detecting circuitry further includes an analog-to-digital converter (13) connected to the said toner quantity detecting means (4c) for converting the analog output voltage (E s ) into corresponding digital values. Apparatus as claimed in claim 11 when read as appended to claim 9, wherein the said output characteristic determining means (20) include: measuring means (21) for measuring the said characteristic value (E smin ) of the output voltage (E s ) of the toner quantity detecting means (4c); first storage means (22) for storing the measured characteristic value (E smin ) ; second storage means (23) for storing the said first and second predetermined values (S 1 , S 2 ); third storage means (25) for storing the said sum of the said characteristic value (E smin ) and the said first predetermined value (S 1 ) and for storing the said sum of the said characteristic value (E smin ) and the said second predetermined value (S 2 ) ; and fourth storage means (26) for storing the said sum of the said characteristic value (E smin ) and the said first predetermined value (S 1 ) as the said warning voltage, and for storing the said sum of the said characteristic value (E smin ) and the said second predetermined value (S 2 ) as the said prewarning voltage. Apparatus as claimed in claim 11 or 12, further including: average calculating means (15) for sampling a plurality of such digital values provided by the said analog-to-digital converter (13) and for calculating an average value of the sampled digital values, the said comparator means (15) being connected to the said average calculating means for receiving therefrom the calculated average value and being operable to compare that average value with both the said prewarning voltage and the said warning voltage; first warning means for generating a prewarning signal prompting the operator to replenish the toner container with toner when the said average value is lower than the said prewarning voltage; and second warning means for generating a warning signal warning the operator of the virtual exhaustion of the said supply of toner in the toner container when the said average value is lower than the said warning voltage. A method of detecting the quantity of toner in image recording apparatus having a developing device as claimed in claim 1 or 2 and also having toner quantity detecting means (4c) for producing an output voltage (E s ) representative of the quantity of toner remaining in the toner container of the developing device; which method comprises: an output characteristic determining step in which the said toner quantity detecting means (4c) are arranged in a measuring disposition relative to the said toner container (4a-2) in which the toner quantity detecting means are spaced from the toner container such that the said output voltage changes to a characteristic value (E smin ) for the toner quantity detecting means (4c) concerned, and the said characteristic value (E smin ) of the said output voltage (E s ) is measured; and a reference voltage setting step in which a reference voltage (E nep ; E emp ), representing a threshold quantity of toner, is set in dependence upon the characteristic value (E smin ) ) measured in the said output characteristic determining step; whereafter, when the said toner quantity detecting means (4c) are arranged in a working disposition in which those means are in contact with the outer surface of the seat portion of the said toner container (4a-2), the said output voltage (E s ) is compared with the said reference voltage (E nep ; E emp ) to detect when the said quantity of toner remaining in the toner container falls below the said threshold quantity. A method as claimed in claim 14, employed in such image recording apparatus in which the said toner stirring unit (4a) of the developing device is mounted removably on a main frame of the apparatus and the toner quantity detecting means (4c) are fixed relative to that main frame such that, when the toner stirring unit (4a) is installed in the apparatus, the toner quantity detecting means are arranged at the said outer surface of the toner container seat portion (115), so as to be in the said working disposition relative to the toner container, and when the toner stirring is removed from the apparatus the toner quantity detecting means (4c) are in the said measuring disposition relative to the said toner container; in which method in the said output characteristic determining step the toner stirring unit (4a) is removed from the apparatus so that when the said characteristic value of the output voltage is measured, the said toner quantity detecting means (4c) are in the said measuring disposition relative to the said toner container (4a-2).

Inventors: ISHII MASATO, TOKUHISA MASANORI, ISHII, MASATO, TOKUHISA, MASANORI, Ishii, Masato, c/o Fujitsu Limited, Tokuhisa, Masanori, c/o Fujitsu Limited
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1992
Main classification: G03G15
IPC codes: G03G15