Patent Publication Number: US-6661979-B2

Title: System and method for detecting low paper in a printer using continuously variable measurements

Description:
FIELD OF THE INVENTION 
     This invention relates generally to methods and systems for detecting low paper in a printer and, more particularly, to methods and systems for detecting multiple levels of paper supply in a printer. 
     BACKGROUND OF THE INVENTION 
     Printers are used for depositing indicia on paper to produce documents and the like. The paper on which the indicia are deposited or printed may be provided to the printer in separate sheets or in continuous form such as a roll or fan-folded sheets. The paper on which the indicia are printed is typically provided in a supply unit such as a well, cassette, recess, or the like as is well known. To prevent the operation of the printer when no paper is available for receiving the indicia, detectors were developed that sensed the absence of available paper in a supply unit and provided an indicator of the paper unavailable condition so an operator could replenish the supply. Because the condition of the paper supply is sensed prior to the printing mechanism for depositing the indicia, the paper unavailable condition could occur during the printing of a multiple page document. Also, printing of a document on a roll of paper might also commence before detection of the end of the paper roll by the supply detector. To prevent the likelihood that a paper supply would be exhausted during a printing operation, low paper condition detectors were developed. 
     Low paper condition detectors monitor the paper supply unit and determine when the paper supply has reached a predetermined threshold and signals a low paper condition without terminating an ongoing printing operation. At the conclusion of the ongoing printing operation, if it finishes before the supply is exhausted, the operator may then replenish the paper supply to prevent the subsequent interruption of a later printing operation for the lack of paper. Thus, low paper condition detectors facilitate the scheduling of paper supply replenishment at a time that is not likely to interfere with an ongoing printing operation. To further facilitate paper supply replenishment scheduling or to assist an operator in determining whether sufficient paper is available for the printing of a multiple page document or a long document, detectors for providing multiple indications of the paper supply level were developed. These detectors typically include multiple sensors that detect the presence or absence of paper in the vicinity of a sensor. When the multiple sensors are arranged along the depth of a stack of paper sheets in a supply or along the radius of a paper roll supply, the two adjacent sensors that detect opposite conditions provide an indication of the paper supply condition. That is, a sensor indicating no paper is present and an adjacent sensor that indicates paper is present demarcates an approximate boundary of the paper supply. For example, four sensors equally spaced in longitudinal array along the depth of a paper supply or the radius of a paper roil may have second and third sensors indicating opposite conditions. From the signals from the sensors, a controller or processor may determine that the paper supply is between 50% and 75% full. When all four of the sensors indicate the presence of paper, the supply is full, while all four sensors indicating the absence of paper indicates the supply is below the last sensor in the array. This last condition is typically used to signal a low paper condition and the other possible signals from the detector are used to determine the approximate level of the paper supply for determining whether substantial printing operations may be performed without exhausting the available paper supply. 
     While the detectors that provide multiple indications of the status of a paper supply are useful, they do not provide a continuous indication of the level of the paper supply available. To address this deficiency, a low-paper sensing device was disclosed in U.S. Pat. No. 5,960,230 to Peter. The device of that paper uses a sensor of the type described above to indicate more than one level of paper supply and supplements this paper level indication by counting the number of sheets of paper delivered to a printer from the supply between detection of level indications. This data may then be used to count down to an empty condition or to calculate an approximate number of sheets left in the supply. Thus, this device requires the addition of a counting mechanism to the printer paper supply unit to more accurate assess the status of the printer paper supply between level indications. 
     One limitation of the above-described device is the requirement for a sheet counter. In printers that use paper sheets, additional counter circuitry and software for adjusting the sheet count through averaging and the like to compensate for some measurement errors is required. For printers that use paper roll supplies, the counter does not successfully indicate the amount of paper remaining because it is not provided in a sheet by sheet manner. 
     Consequently, what is needed is a way of continuously indicating the status of the paper supply. 
     What is need is a way of refining measurements of available paper for printing without requiring the counting of sheets. 
     SUMMARY OF THE INVENTION 
     The above-noted limitations of previously known systems and methods for indicating the level of available paper in a paper supply for a printer have been overcome by a system and method that operate in accordance with the with principles of the present invention. The system of the present invention comprises a signal emitter for emitting a signal into a paper supply and a variably activated receiver for generating a paper supply level signal, the variably activated receiver is mounted at a location for selectively receiving the emitted signal from the signal emitter in relation to the level of paper in the supply. The signal emitter may be an infrared (IR) or electrical source. The variably activated receiver is preferably a photoresistor having a resistor value that changes in accordance with the amount of infrared radiation received at the surface of the photoresistor. The photoresistor is coupled to a signal circuit that generates a continuously variable signal across a range and the signal variation follows the resistance value of the photoresistor. The variably activated receiver has sufficient length such that only a portion of the receiver is exposed to the signal emitter as the paper supply between the emitter and receiver diminishes. When the length of the receiver is fully exposed to the signal emitter, the receiver generates a saturation signal that defines one end of the range of the signal generated by the receiver. 
     In an alternative embodiment of the present invention, a light guide is interposed between the variably activated receiver and the signal emitter. The light guide collects the infrared signal emitted by an optical signal emitter and transmits the light to a variably activated sensor. As a longer section of light guide is exposed to the optical signal emitter, more light is delivered to the surface of the variably activated receiver. The intensity of the delivered light causes a parameter of the receiver to vary and generate a continuously variable signal indicating the relationship between the signal emitter, light guide, and paper in the paper supply. 
     The method of the present invention includes emitting a signal into a paper supply and generating a continuously variable signal indicative of the amount of emitted signal being received by a variably activated receiver coupled to a paper supply. Preferably, the emitted signal is an infrared signal and the continuously variable signal is indicative of the amount of light incident upon the variably activated receiver. The method of the present invention may also include coupling the emitted signal through a light guide to the variably activated receiver. A length of light guide, a continuous light source, or array of discrete light sources may be provided along the length of the paper to continuously provide an amount of light indicative of the amount of available paper in a paper supply. 
     Because the system and method of the present invention may be used to generate a continuously variable signal indicative of the paper supply level, a user may specific a low paper condition level anywhere along the range of the supply capacity. Thus, the low paper condition detector need not be physically arranged to correspond to the desired level for generation of a low paper condition signal. Instead, a user may enter the low paper condition through a software interface and the control program for the printer may store the low paper condition parameter for comparison with the signal indicative of the paper supply level. Additionally, with data regarding the length of a standard roll or thickness of a sheet, the system and method of the present invention may be used to compute a remaining number of sheets or roll length for display to an operator. In this manner, a continuous indication of the paper supply is provided for operator control of the printer and printer supply replenishment. 
     It is an object of the present invention to provide a continuously variable signal indicative of paper supply level in a printer. 
     It is an object of the present invention to support user definition of the low paper condition level without requiring mechanical adjustment of the paper supply sensors. 
     It is an object of the present invention to provide continuously variable indicator of the remaining paper supply in a printer. 
     These and other advantages and features of the present invention may be discerned from reviewing the accompanying drawings and the detailed description of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may take form in various system and method components and arrangement of system and method components. The drawings are only for purposes of illustrating an exemplary embodiment and are not to be construed as limiting the invention. 
     FIG. 1 depicts a side view of a receipt printer in which the present invention may be used; 
     FIG. 2A depicts the receipt printer of FIG. 1 with the signal emitter and receiver of the present invention mounted therein; 
     FIG. 2B depicts an alternative arrangement of the signal emitter array and receiver of the present invention; 
     FIG. 2C depicts another alternative arrangement of the signal emitter array and receiver of the present invention; 
     FIG. 3 depicts a circuit diagram of the low paper detector of the present invention; and 
     FIG. 4 is a flowchart of an exemplary method for indicating the status of paper within a paper supply for the printer of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A receipt printer incorporating the system and method of the present invention is shown in FIG.  1 . Printer  10  includes a housing  14 , and a paper supply cover  18 . Mounted to extend from housing  14  is a power cord  20  for coupling printer  10  to a power source for operation of the printer. Power cord  20  is coupled to a power card  24  for stepping down and rectifying the voltage of the power source for use with the electronics of printer  10 . The electronics for controlling the operation of printer  10  are mounted on printed circuit card  30 . The electronics may include an application specific integrated circuit (ASIC) or a microcontroller having volatile and programmed memory. The electronics are coupled to printer mechanism  38  through signal cable  34 . Formed within housing  14  is a paper well  40  for holding a paper roll  44 . Paper roll  44  may be dropped into well  40  so it freely spins about its axis or paper roll  44  may be formed about a spindle and mounted within spindle holders on each side of well  40 . Free end  46  of roll  44  is moved proximate printer mechanism  38  so indicia may be placed on the surface of the paper facing printer mechanism  38 . Printer  10  also includes a cable connector mounted to housing  14  so printer  10  may be coupled to a host computer for receiving control signals and a datastream for printing. Internal to housing  14 , the connector is coupled to PC card  30  so the microcontroller or ASIC may respond to the control signals and deliver the datastream to printer mechanism  38  through signal cable  34  so the datastream may be printed on the paper or media disposed in well  40 . 
     The system and method of the present invention may be incorporated in printer  10  by mounting a signal emitter  50  in well  40  in conjunction with an variably activated receiver  54  as shown in FIG.  2 A. The signal emitter may be an optical or electrical signal generator comprised of an array of such emitters or a single emitter. Preferably, the emitter is an infrared source, such as a light emitting diode (LED), for directing a light or other infrared signal into a paper supply when paper well  40  contains a full paper roll. Preferably, the emitter or emitter array extends from the center of roll  44  and is aligned along the radius of paper roll  44 . Mounted on the opposing wall of well  40  in horizontal alignment with emitter  50  is a variably activated receiver  54 . Variably activated receiver  54  is any infrared receiver that alters an electrical parameter in proportion to the amount of incident infrared energy that contacts the receiver surface. Preferably, receiver  54  is a photoresistor that alters the electrical resistance of the receiver in proportion to the amount of light sensed by receiver  54 . Receiver  54  may also be an array of multiple receivers  54   a - 54   n  that covers substantially all of the radius of paper roll well  44  or the depth of a paper stack well. 
     If the photoresistor is an elongated receiver having a length that covers a substantial portion of the radius between two signal emitters  50   a  and  50   b  (FIG.  3 ). The amount of light incident on such a receiver  54  is proportional to the amount of photoresistor exposed to the emitter directly across from the receiver. As roll  44  is used, its perimeter retracts towards its center and exposes more of receiver  54  to the light from emitter  50 . As the amount of light incident on receiver  54  increases, the electrical parameter associated with the receiver is altered, as explained below, this alteration generates a signal indicative of the paper level in well.  40 . The generated signal has a magnitude that is proportional to the infrared or other emitted signal incident on receiver  54 . For emitters and receivers that are more aptly described as point sources and receivers, the receivers are mounted in a staggered arrangement so they are located between two adjacent emitters as shown in FIG.  2 B. Preferably, the receivers are mounted at a location approximately halfway between the two emitters although other staggered arrangements may be used. As light spreads out from emitter  50   a , it increasingly impinges upon receiver  54   a  as paper roll  44  retracts. When the perimeter of roll  44  is just past the receiver  54   a , light spreading from emitter  50   a  is striking the receiver without any blockage from paper roll  44 . However, the light striking receiver  54   a  is at an angle and the amount of energy in such angled light does not saturate receiver  54   a . As paper roll  44  further retracts, light from emitter  50   b  begins to strike the receiver until roll  44  fully exposes emitter  50   b . At that point, the receiver  54   a  is receiving angled light from the two most recently exposed emitters,  50   a  and  50   b . The sum of this incident energy is sufficient to saturate the point receiver so its contribution to the paper level signal is maximized. 
     A circuit diagram depicting an exemplary system of the present invention is shown in FIG.  3 . Emitters  50   a ,  50   b , and  50   c  are coupled together in a parallel circuit so they continually emit light while printer  10  is being powered. Each receiver  54   a ,  54   b , and  54   c  are in coupled in series with a fixed resistor R. One end of all the receivers are coupled to power and each resistor R is coupled to system ground. The node between a resistor R and a receiver provides a voltage divider signal that is proportional to the resistance of a receiver  54 . As described above, the resistance of receiver  54  is proportional to the incident energy on its surface. As this resistance changes so does the level of the signal at the voltage divider node. The signal from each such node is provided to summing amplifier  60  to generate a single signal that represents the sum of the node signals. This summing signal has a magnitude that is proportional to the amount of energy incident on receiver  54  and this signal is provided to an analog/digital converter that supplies a digital value to microcontroller  68  or other control component used to operate printer  10 . 
     If receivers  54   a ,  54   b , and  54   c  are photoresistors that alter a resistance from a high value with little incident energy to a low value at its maximum energy input, then the signals at the nodes are approximately equal to zero at low energy and equal to some percentage of the source level at high energy levels. The level of the signal at high energy levels depends upon the ratio of the resistor R to the low resistance of the photoresistor at the high energy levels. For example, the value of R and the range of resistance for the photoresistors may be selected so that ⅓ of the source voltage is present at a node when the maximum energy is incident on the surface of a receiver. Thus, when all of the receivers have maximum energy incident on their surfaces, three signals equal to one third of the source voltage are provided to amplifier  60 . These signals cause amplifier  60  to generate a signal that is approximately equal to the source voltage, although the output of summing amplifier  60  may be offset so the range of its output signal varies over the range defined by the positive and negative values of the source voltage. 
     One advantage of the present invention is the detection of a paper roll loading by detecting the fully exposed condition of receiver  54  when roll  44  is removed and the initial condition of receiver  54  when a supply roll is placed well  40 . Typically, the replacement roll is a full supply roll and receiver  54  is fully blocked from emitter  50 . Thus, the range of the signal generated by summing amplifier  60  represents the level of paper present in well  44  from a full roll to an empty roll. However, when a partially full roll is placed in well  44 , the output of amplifier  60  represents the “full” supply condition. The system of the present invention permits microcontroller  68  to adjust the range of operation of amplifier  60  so the full range of its operation is mapped to the full and empty conditions of the paper supply currently in well  44 . This permits partially used rolls to be saved and later used. For example, if a user sets the low paper condition at 20% of a roll, the operator may change out the roll when the low paper condition is signaled. Later, the 20% roll may be loaded in printer  10  and microcontroller  68  may adjust the operation of amplifier  60  so that a low paper condition is signaled when only 20% of the partially used roll is left. 
     In an alternative embodiment, a single receiver  54  may be provided at the end of an emitter signal conduit. The conduit is arranged to oppose emitter  50  as described above. As the conduit is exposed by the retracting paper roll, more emitted signals impinge upon the conduit that conducts the emitted signals to receiver  54  for altering the electrical parameter. The conduit may be any known material that permits light to enter the conduit through its sidewall and then reflect the light through a passageway internal to the conduit so it may be delivered to the selectively activated receiver. One example of a conduit that may be used to provide infrared energy in the visible light spectrum to a photoresistor or the like is a light guide such as that manufactured by CUDA Fiberoptics and having part number S8-36FS-G. 
     In yet another alternative embodiment, receiver  54  may be mounted on the same side of well  40  as emitter  50 . In this arrangement, shown in FIG. 2C, signals from emitter  50  are reflected off of roll  44  into receiver  54 . As paper roll  44  retracts, less radiant energy is reflected from roll  44  into receiver  54 . Accordingly, the total radiant energy impinging upon receiver  54  is greatest at a full roll condition and least at an empty roll condition. Again, this energy range may be used to alter an electrical parameter such as the resistance of a photoresistor that is used to vary a signal indicative of the paper level in well  44 . Also, the initial value of the radiant energy at receiver  54  following an exhausted supply condition may be used to map the radiant energy range over the operational range of amplifier  60  for more refined measurement of the remaining capacity of roll  44 . 
     The method of the present invention uses the continuously varying signal indicative of the paper supply to signal a low paper condition for printer  10 . The software executing the method may be programmed in the instructions for controlling microcontroller  68  or an ASIC. The method follows initialization of printer  10  (block  100 ) and is periodically executed during operation of printer  10 . Following initialization (block  100 ), the signal indicative of the paper supply level is input (block  104 ) and a determination is made as to whether a new roll is being installed or printer  10  has been powered up with a supply roll in well  44  (block  108 ). If a new roll has been loaded, the initial signal indicating the “full” supply condition is mapped to the operational range of the paper level signal converter (block  112 ). The operator may then identify a low paper condition value (block  116 ). The low paper condition value may be entered through a computer or terminal coupled to printer  10 , a switch selectable option on the panel of printer  10 , or through a digital display of printer  10 . To receive the low paper condition value from a computer, the computer is coupled to the connector of printer  10  for receiving control signals and datastreams. The printer control program in the computer may be adapted to receive a low paper condition from a user. Preferably, this value is expressed as a percentage of the media supply although it may be specified in linear units of measurement, number of sheets, or media supply units. This value may then be included in the control signals for processing by the microcontroller. In response, the microcontroller uses the received value to set the low paper condition for printer  10  operation and may display the low paper condition value in the display at printer  10  to provide a visual confirmation signal to the user. The program controlling the microcontroller or ASIC may also include instructions for responding to a request from the computer coupled to printer  10  for a media remaining value. Because the microcontroller or ASIC monitors the paper level signal as described below, it may compute the amount of remaining paper or other media and send a data message to the computer that contains the remaining paper level value. The computer may use this value for scheduling print jobs or other computer operations. This operation also allows the computer to alter the low paper condition value to efficiently control usage of the paper supply in well  40 . 
     Alternatively, the low paper condition value may be entered at printer  10 . In this embodiment, microcontroller  68  may display a default low paper condition value as a number representing a percentage of a full supply in a digital display (not shown). A user may then use a up/down switch to increment or decrement the displayed value to a percentage other than the one displayed. Alternatively, the low paper condition may be defined as a linear measurement of remaining paper provided microcontroller  68  includes a program for calculating remaining paper in linear measurement units. Such a program would have to correlate the range of the signal indicative of the paper supply level to the range of available paper length from zero to its maximum length. 
     Once the operational range and low paper condition are defined, the paper level signal is monitored (block  120 ) and compared to the low paper condition value (block  124 ). This operation continues until the paper level signal indicates the low paper condition has been reached or exceeded (block  124 ). When the low paper condition is reached, a determination is made as to whether the paper supply has been exhausted (block  128 ). If it has not been exhausted, the low paper signal is illuminated or sounded (block  132 ) and the monitoring of the paper level signal continues (block  120 ). Otherwise, a flag is set to indicate a new paper roll is required (block  136 ). Once a new roll is detected (block  140 ), the initial paper roll condition is read (block  104 ) and used to reset the operational range of the low paper detector and any change in the low paper condition may also be set by the operator. 
     While the present invention has been illustrated by the description of exemplary processes and system components, and while the various processes and components have been described in considerable detail, it is not the intention of the applicant to restrict or in any limit the scope of the appended claims to such detail. Additional advantages and modifications will also readily appear to those skilled in the art. For example, the present invention has been described as using infrared emitters and receivers but the invention may also be implemented by measuring a capacitance between an electrode contacting the perimeter of the roll and an electrode at the core of the roll. Another alternative within the scope of the present invention is to generate a continuously varying signal in accordance with the deflection of a piezoelectric device operatively coupled to the paper roll. Also, the principles of the present invention may be applied to printer supplies that contain paper sheets rather than a paper roll or to other media than paper. The invention in its broadest aspects is therefore not limited to the specific details, implementations, or illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant&#39;s general inventive concept.