Abstract:
A method for detecting the status of the toner in a laser printer uses a photosensor. The method includes sampling a signal generated from the photosensor during a specified time, increasing or decreasing the value of a counter in accordance with an integral algorithm, and comparing the resultant counter value with a reference value, and displaying the status of the toner in the printer on a display device, depending on a result of such comparison. This method can accommodate relatively inexpensive photosensors. As the noise-ridden signal generated by such a photosensor is effectively filtered, this method is advantageous in cost and reliability.

Description:
CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for METHOD FOR DETECTING THE STATUS OF TONER USING A PHOTOSENSOR earlier filed in the Korean Industrial Property Office on the 15 th  day of May 1996 and there duly assigned Serial No. 16063/1996, a copy of which application is annexed hereto. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a method for detecting the level of printing material in a printer, and more particularly to accurately detecting the status of toner in a laser printer by a more efficient use of a photosensor. 
     2. Description of the Prior Art 
     In general, exemplars of the contemporary practice of printers are frequently concerned with detecting the current level of printing material that is left in the printer. In particular, laser printers are provided with toner sensing apparatus for detecting the status of toner powder in those printers. Among exemplars of the contemporary practice, Tachihara et al. (U.S. Pat. No. 5,617,121, Ink Jet Recording With Ink Detection, Apr. 1, 1997) discusses a recording head that includes discharge ports for discharging ink. An ink detection element is provided in the liquid chamber for detecting the presence of ink. Murray et al. (U.S. Pat. No. 5,610,635, Printer Ink Cartridge With Memory Storage Capacity, Mar. 11, 1997) discusses a printer ink cartridge including a memory storage element. The memory storage element is capable of storing information regarding the amount of ink remaining in the cartridge. The memory storage element is connected to the control and driver circuit to enable information to be retrieved and stored from the memory storage element. The control and driver circuit can also include a counter for counting the number of times the heating elements on the cartridge are energized. The approximate number of times the heating elements have been energized indicates the approximate number of drops of ink that have been applied by the cartridge. Stapleton (U.S. Pat. No. 5,596,351, Ink Level Sensing On A Pen Carriage In A Pen Plotter, Jan. 21, 1997) discusses an apparatus for sensing whether a liquid with a turbulent surface and contained within a vessel has fallen to a level where the liquid is substantially expended. Cowger (U.S. Pat. No. 5,574,484, Level Detection For Ink Cartridges Of Ink-Jet Printers, Nov. 12, 1996) discusses a sensor that detects the level of ink present in an inksupply cartridge of an ink-jet type printer. The sensor moves with the reciprocating pen carriage of the printer. Ogiri et al. (U.S. Pat. No. 5,508,786, Image Forming Apparatus, Apr. 16, 1996) discusses determining the number of copies which can be outputted corresponding to the defined capacity of the developer. Takayanagi et al. (U.S. Pat. No. 5,488,395, Liquid Jet Recording Apparatus, Jan. 30, 1996) discusses a liquid jet recording apparatus having a pair of electrodes provided to be immersed in the ink in the container. By applying a voltage between the electrodes, the remainder of the ink is detected by a change in the electric resistance between the electrodes. Gu (U.S. Pat. No. 5,485,191, Image Forming Apparatus Having Tone Correction Function, Jan. 16, 1996) discusses an image forming apparatus including an electrophotographic photosensitive member. For tone controls, a detector detects a state of the tone control image, and the controller controls the electrostatic latent image forming device on the basis of a datum from the detector and predetermined tone correcting information. Accatino et al. (U.S. Pat. No. 5,414,452, Recognition Of Ink Expiry In An Ink Jet Printing Head, May 9, 1995) discusses ink jet printers in which the print head is connected to an ink reservoir, such as can be used in teleprinter or facsimile apparatuses. A logic circuit is used to count the number of drops gradually expelled, and with any necessary correction, compares this number with the maximum number of drops equivalent to a known volume of ink contained on average in the reservoir. Expiry of the ink is indicated as in dependence upon the result of the comparison. Gatten (U.S. Pat. No. 5,068,806, Method Of Determining Useful Life Of Cartridge For An Ink Jet Printer, Nov. 26, 1991) discusses a computer program in the microcontroller of an ink jet printer-plotter that counts the ink dots fired by the carriage of the printer. El Hatem et al. (U.S. Pat. No. 4,853,718, On Chip Conductive Fluid Sensing Circuit, Aug. 1, 1989) discusses a situation in which the ink in an ink jet is sensed by a capacitor, one plate of which is coupled to the ground through the ink. From my study of these exemplars of the contemporary practice and art, I find that there is a need for an effective and improved device for accurate toner detection that does not require an overly accurate (and hence expensive) photosensor. 
     SUMMARY OF THE INVENTION 
     Thus, an object of the present invention is to provide an improved method for detecting the level of printing material in a printer. 
     A further object of the present invention is to provide an improved method for accurately detecting the status or level of toner in a laser printer by a more efficient use of a photosensor. 
     Another object of the present invention is to provide a method for detecting the status or level of the toner in the developing device which is advantageous in costs and reliability. 
     To achieve these and other objects, a photosensor is employed to measure the amount of the toner in the developing device. This photosensor does not have to be apiezoelectric detector. Thus, it may be relatively inexpensive compared with a piezoelectric detector. The noise-ridden signal generated from such a photosensor is sampled in accordance with the integral algorithm and filtered to enable the presence or absence of the toner in the developing device to be detected with accuracy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
     FIG. 1 is a schematic block diagram of a contemporary toner sensing apparatus; 
     FIG. 2A shows a circuitry of another contemporary toner sensing apparatus employing a photosensor as can be used with a CPU/counter and a display device in the present invention; 
     FIG. 2B depicts how the toner sensing apparatus of FIG. 2A is mounted in the developing device; 
     FIG. 2C shows a waveform of an output terminal B of the toner sensing device of FIG. 2A when the toner is properly enough or full in the developing device; 
     FIG. 2D shows a waveform of an output terminal B of the toner sensing device of FIG. 2A when the toner is short or empty in the developing device; 
     FIG. 3 is a flowchart illustrating a series of steps for detecting the status of toner using a photosensor according to one embodiment of the present invention; 
     FIG. 4 is a flowchart illustrating a series of steps for detecting the status of toner using a photosensor according to another embodiment of the present invention; 
     FIG. 5A shows a waveform obtained by sampling the signal of the output terminal B of the toner sensing apparatus of FIG. 2A in accordance with the flowchart of FIG. 3; 
       15 FIG. 5B shows a waveform obtained by filtering the waveform of FIG. 5A using a reference value for a specified duration of time; 
     FIG. 6A is a waveform obtained by sampling the signal of the output terminal B of the toner sensing apparatus of FIG. 2A in accordance with the flowchart of FIG. 4; 
     FIG. 6B is a waveform obtained by filtering the waveform of FIG. 6A using a first and a second reference value for a specified duration of time; and 
     FIG. 6C is a waveform obtained by filtering the waveform of FIG. 6A using a first and second reference value for a specified duration of time. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the drawings, specifically to FIG. 1, a contemporary toner sensing apparatus is schematically illustrated, wherein a piezoelectric detector  10  measures the weight of the toner powder in a developing device not shown and outputs the measured value as digital data. A data decoder  11  reads the digital data inputted from the piezoelectric detector  10 . A CPU or controller  12  determines whether of the status of the toner in the developing device on the basis of the data inputted from the data decoder  11  and outputs the resultant of determination to a display device not shown. 
     FIG. 2A illustrates a circuitry of another toner sensing apparatus employing a photosensor  25 . An anode of a photodiode is connected to a power source Vcc via a resistance R 1  and its cathode is connected to ground. Another component of the photosensor can be a phototransistor  21  of which a base receives light from the photodiode  20 , a collector terminal A is connected to the power source Vcc via a resistance R 2  and an emitter is connected to ground. The photosensor can also include a transistor  22  of which a base is connected to the collector terminal A of the phototransistor  21  via a resistance R 3 , a collector terminal B is connected to the power source Vcc via a resistance R 4  and an emitter is connected to ground. In this configuration, the photosensor  25  is composed of the photodiode  20  for emitting light and the phototransistor  21  for receiving the light from the photodiode  20  as shown in the dotted line in that view. 
     FIG. 2B shows how the toner sensing apparatus of FIG. 2A is mounted in the developing device. In arrangement, the photodiode  20  and the phototransistor  21  are in opposing relation with each other, having the developer such as toner powder therebetween in a toner container  23   a  two light transmitting films  22  made of transparent insulating material are provided to make isolation of the photodiode  20  and the phototransistor  21  from the toner having conductivity so as to prevent the two elements from being short-circuited by such toner. A toner removing blade  23  is fixed to a rotational shaft  24  and scrapes the toner powder adhered to the surfaces of the light transmitting films  22  as it rotates, so that the light from the photodiode  20  can be transmitted to the phototransistor  21  without interruption. 
     Hereinafter, such a toner sensing apparatus is described in more detail with reference to FIGS. 2A and 2B. In the developing device, the toner powder is provided between the photodiode  20  and the phototransistor  21  by a specified height in toner container  23   a  both being arranged to face with each other as mentioned before. The photodiode  20  can emit light since it is connected to the power source Vcc in forward direction and thus current flows therethrough all the time. 
     In such a set of devices, at least two situations can arise: one is when the toner is properly full enough in the developing device and the other is when the toner is short or empty. 
     First, in case of the former (enough toner), the toner in toner container  23   a  existing in the developing device by a specified height can block the light from the photodiode  20  to be transmitted to the base of the phototransistor  21 . In this case, the phototransistor  21  is turned off and the collector terminal A outputs the signal of high level. This signal is then transmitted to the base of the transistor  22  through the resistance R 3 , so that the transistor  22  is turned on. Next, the signal is inversed and amplified at the last output terminal B of the toner sensing apparatus  3 , resulting in low level. 
     In contrast, when the toner is nearly short or empty in the lather case (low/empty toner), it is possible that the light from the photodiode  20  is transmitted to the base of the phototransistor  21  with no problem, whereby the phototransistor  21  is turned on and the collector terminal A outputs the signal of low level. This signal is then transmitted to the base of the transistor  22  through the resistance R 3  and the transistor  22  is turned on. As a result, the signal at the terminal B becomes high level. 
     Thus, it is possible to judge the status or level of the toner in the developing device by means of the output signal of the terminal B in a manner that the low signal signifies that the toner is properly enough or full and the high signal signifies that the toner is short or empty. Nevertheless, this contemporary apparatus is disadvantageous in various aspects. The piezoelectric detector is very expensive and since replacement is limited to the same model of any specific manufacturer for the reliable operation, to buy such replacement may be not easy. For these reasons, the relatively cheaper photosensors have often been used instead of the piezoelectric detector. This can often bring problems in reliability because the toner removing blade or the like can make noise as shown in FIGS. 2C and 2D and filtering of such noise is also not easy. 
     The flowchart of FIG. 3 explains how to detect the status or level of the toner in the developing device. As shown in this flowchart, the printer is initialized when a printer engine is on, an upper and lower limit values of a toner empty counter and a reference value are determined These values give standard points in judging the presence or absence of the toner in toner container in the developing device (S 1 ). After the initialization step, the next step (S 2 ) is followed by judging whether the signal of the last output terminal B of this toner sensing apparatus is low or high. Based on the result of judgment, the next step is performed by counting up the counter values by ones if the output signal is high (S 3 ) and counting down the counting values by ones if low (S 4 ). Then, the status or level of the toner is displayed on any display device as a series of characters “TONER EMPTY” (S 6 ) when the counter value is equal to or larger than the reference value, or as a series of characters “TONER FULL” (S 7 ) when the counter value is smaller than the reference value. 
     The flow chart of FIG. 4 explains another method according to this invention, wherein the printer is initialized when a printer engine is on. Then, there exists the steps of determining an upper and lower limit values of a toner empty counter and a first reference value and a second reference value which function as standard points in judging the amount of the remaining toner in a toner container in the developing device. After the initialization, the next step is implemented by judging whether the signal of the last output terminal B of this toner sensing apparatus is low or high. Based on the result of judgment, the next step is performed by counting up the counter value by ones if the output signal is high and counting down the counter value by ones if low. Then, comparison of the counter value and the first reference value is implemented and the resultant toner level is displayed on any display device as a series of characters “TONER EMPTY” when the counter value is equal to or larger than the first reference value. However, if the counter value is smaller than the first reference value, an additional comparison is implemented between the counter value and the second reference value and the resultant toner level is displayed on any display device as a series of characters “TONER LOW” when the counter value is equal to or larger than the second reference value, or as a series of characters “TONER FULL” when the counter value is smaller than the second reference value. 
     The two preceding embodiments of this invention can also be explained as follows referring to FIGS. 2A and 2B illustrating a toner sensing apparatus used with a CPU/counter  28  and a display device  29  in the present invention. At first, as in FIG. 3, the printer is initialized (S 1 ) immediately when a printer engine is on, and at the same time the photodiode  20  emits light since it is connected to the power source Vcc in the forward direction as shown in FIGS. 2A and 2B to allow the current to flow therethrough all the time. Simultaneously, the toner empty counter of CPU/counter  28  is programmed to have the upper limit value and the lower limit value, which is designed to be operated in response to the output from the photosensor, and the reference value which functions as a standard point for judging the presence or absence of the toner in the developing device. 
     In the absence of the toner in the toner container  23   a  the light from the photodiode  20  is applied to the base of the phototransistor  21  so that the phototransistor  21  is turned off and the last output terminal B of this toner sensing apparatus outputs the signal of high level as shown in FIG.  2 D. In contrast if the toner level in toner container  23   a  is properly enough or full, the light transmission from the photodiode  20  to the phototransistor  21  is blocked by the existence of toner, so that the phototransistor  21  is turned on and the last output terminal B of this toner sensing apparatus outputs the signal of low level as shown in FIG.  2 C. 
     Next, the CPU  28  judges whether the output signal of the terminal B is high or low (S 2 ). Based upon the result of judgment, the next step is selected in either of two ways (low or high signal). The high signal signifies what the toner level is short or empty, so that the toner empty counter of CPU/counter  28  increases the counting value by 1 (S 3 ). The low signal signifies that the toner level in the toner container  23   a  is properly enough or full, so that the counter decrease the counting value by 1 (S 4 ). In the steps of S 2  to S 4 , the waveform of FIG. 5A can be obtained by sampling the counter during a specified time T. 
     After the increase or decrease of the counter value, the resultant value is compared with the reference value (S 5 ). As a result, if the counter value is equal to or larger than the reference value, the high signal is outputted from the terminal B as shown in FIG. 5B and a series of characters “TONER EMPTY” is displayed on the display device  29  to indicate that the toner in toner container  23   a  must be refilled to the user (S 6 ), and however if the counter value is smaller than the reference value, the low signal is outputted from the terminal B as shown in FIG. 5B and a series of characters “TONER FULL” is displayed on the display device  29  to confirm that the toner level in toner container  23   a  is properly enough in the developing device to the user (S 7 ). 
     Another embodiment of this invention is described below with reference to FIG. 4 again also referring to FIGS. 2A and 2B. In the same manner with the preceding embodiment, the printing system is initialized (S 1 ) immediately when the printer engine is turned on, and at the same time the photodiode  20  emits light since it is connected to the power source Vcc in forward direction as shown in FIGS. 2A and 2B to allow the current to flow therethrough all the time. The toner empty counter of CUP/counter  28  which is designed to perform the counting operation in accordance to the output signal of the photosensor, is programmed to have the upper limit value and lower limit value, the first reference value and the second reference value which both will be standard points in judging the presence or absence of the toner in the developing device. 
     The light from the photodiode  20  is applied to the base of the phototransistor  21  in the absence of the toner, so that the phototransistor  21  is tuned off and the last output terminal B of this toner sensing apparatus outputs the signal of high level as shown in FIG.  2 D. However if the toner in toner container  23   a  is properly enough or full, the light transmission from the photodiode  20  to the phototransistor  21  is blocked by the existence of toner, so that the phototransistor  21  is tuned on and the last output terminal B of this toner sensing apparatus outputs the signal of low level as shown in FIG.  2 C. 
     Then, the CPU  28  judges whether the output signal of the terminal B is high or low (S 2 ). Based upon the result of judgment, the next step is selected in either of two ways. That is, the high signal signifies what the toner level in toner container  23   a  is short or empty, so that the toner empty counter of CPU/conter  28  increases the counting value by 1 (S 3 ), and the low signal signifies that the toner level in toner container  23   a  is properly enough or full, so that the counter decreases the counting value by 1 (S 4 ). In the steps of S 2  to S 4 , the waveform of FIG. 6A can be obtained by sampling the counter during a specified time t. 
     After such a step (S 3  or S 4 ), the counter value is compared with the first reference value (S 5 ) As a result, if the counter value is equal to or larger than the first reference value, a first signal of high level is outputted from the terminal B as shown in FIG. 6B and a series of characters “TONER EMPTY” is displayed on the  29  display device to indicate that the toner in toner container  23   a  must be refilled to the user (S 6 ), and however if the counter value is smaller than the first reference value, that value is again compared with the second reference value (S 7 ). After the comparison of S 7 , if the counter value is equal to or larger than the second reference value, a first signal of high level and a second signal of low level are outputted from the terminal B as shown in FIGS. 6B and 6C and a series of characters “TONER LOW” is displayed on the  29  display device to indicate that the toner in toner container  23   a  must be refilled before long to the user (S 8 ). 
     However, if the counter value is smaller than the second reference value, a first signal and a second signal of low level are outputted from the terminal B as shown in FIGS. 6B and a series of characters “TONER FULL” is displayed on the  29  display device to confirm that the toner level in toner container  23   a  is properly enough in the developing device (S 9 ). 
     As mentioned above, this invention detects the status of the toner in the developing device by means of using a photosensor that can be obtained relatively cheaply. The noise generated from such a photosensor is sampled in accordance with the integral algorithm and is filtered, bringing an improvement in reliability. 
     It will be recognized by those skilled in the art that changes or modifications can be made to the above-described embodiments without departing from the broad inventive concept of the invention. It should therefore be understood that this invention is not only applicable to the LASER printers described herein but also to page printers, as another example.