Patent Publication Number: US-11376868-B2

Title: Capacitance sensor

Description:
BACKGROUND 
     Capacitance is the ability of a system to store an electric charge. Put another way, capacitance is the ratio of the change in an electric charge in a system to the corresponding change in its electric potential. Capacitance may also include capacitance that occurs between two charge-holding objects in which the current passing through one passes over into the other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a diagram of an example of a device including a sensor and a controller according to the present disclosure. 
         FIG. 2  illustrates a diagram of an example of a printing device including a first metal piece and a second metal piece according to the present disclosure. 
         FIG. 3  illustrates a diagram of another example of a printing device including a first metal piece and a second metal piece according to the present disclosure. 
         FIG. 4  illustrates a diagram of an example paper tray including a spring component according to the present disclosure. 
         FIG. 5  illustrates a diagram of another example paper tray including a spring component according to the present disclosure. 
         FIG. 6  illustrates a diagram of an example first metal piece and an example second metal piece separated by an insulator according to the present disclosure. 
         FIG. 7  illustrates a diagram of another example first metal piece and second metal piece separated by an insulator according to the present disclosure. 
         FIG. 8  illustrates a diagram of an example first metal piece and an example second metal piece according to the present disclosure. 
         FIG. 9  illustrates a diagram of another example printing device including a paper tray, rack, first metal piece, and second metal piece according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Printing devices such as printers and scanners, among others, can have paper width guides to position paper entering the printing device. In some instances, it may be desirable to know the width, length, and/or overall shape of the paper that will be printed or scanned before it enters the printing device. For example, this enables margins to be set to prevent printing off the edge of the paper, as well as allowing clipping of a scanned image to reduce non-image defects at an edge of the paper. Additionally, for example, a user may want to print something of a particular size (e.g., envelope), so the user may want to know if that particular size of paper is currently in a paper tray of the printing device. 
     Some approaches to determining a paper size can include using multiple discreet sensors that correspond to common paper sizes (e.g., letter and A4). For instance, determinations about a limited number of paper sizes may be made in such an example. Such an approach uses multiple sensors, which can increase cost, and may not allow for detection of non-standard or less common paper sizes (e.g., card or letter envelope). Other approaches prompt users to enter a paper size ahead of printing. Such approaches can result in incorrect paper sizes to be set due to human error. In addition, for simple printing devices without a user interface (e.g., a graphical user interface), it may be challenging to prompt a user to enter and/or select a paper size. 
     Still other approaches can include the use of linear displacement sensors and/or rotary sensors for detecting paper width, but these sensors and/or rotary sensors can be expensive, especially as resolution increases. Additionally, such approaches use additional cabling to connect the sensors and/or rotary sensors to electronics of the printing device. 
     In contrast, examples of the present disclosure can include a capacitance sensor for determining a paper size that can detect a plurality of paper sizes, including common and uncommon paper sizes, without user input and at a reduced cost as compared to other approaches. In addition, examples of the present disclosure can include fewer and less complicated components as compared to other approaches. For instance, capacitance can be detected between conductive materials (e.g., metal pieces) coupled to the printing device at particular locations. This capacitance can be used to determine a paper size in a paper tray of the printing device. 
       FIG. 1  illustrates a diagram of an example of a device  100  including a sensor  101  and a controller  102  according to the present disclosure. Controller  102  can be coupled to sensor  101  and can include a processor  103  in communication with a memory resource  104  (e.g., a non-transitory machine-readable medium) including instructions  105  executable by processor  103  to perform the operations as described herein (e.g., by executing the instructions store on memory resource  104 ). As used herein, coupled can include coupled via various wired and/or wireless connections between devices such that data can be transferred in various directions between the devices. The coupling need not be a direct connection, and in some examples, can be an indirect connection. 
     The operations are not limited to a particular example described herein and may include additional operations such as those described with respect to  FIGS. 2-9 . Memory resource  104  can be any type of volatile or non-volatile memory or storage, such as random-access memory (RAM), flash memory, read-only memory (ROM), storage volumes, a hard disk, or a combination thereof. 
     Sensor  101  may determine a capacitance between a first metal piece coupled to a paper tray of a printing device and a second metal piece coupled to a paper width adjuster of the printing device. As used herein, “paper width adjuster” can include an adjuster of paper width, paper length (e.g., a length guide), and/or a combination of the two, among others. For instance, the first metal piece may be a conductive material such as a flexible flat cable (FFC), and the second metal material can be a conductive material strip, such that as the paper width adjuster is moved to fit a paper size, the second metal piece changes from where it is barely covering a small strip of the FFC to where it is covering a larger portion of the FFC coupled to the paper tray. Based on the capacitance, memory resource  104  can store instructions  105  executable by the processor  103  to determine a size of the paper in the paper tray. 
     For instance, in some examples memory resource  104  can store instructions  105  executable by the processor  103  to determine a size of paper in a paper tray based on the determined capacitance. In some instances, determining the capacitance between the first and the second metal pieces by measuring the capacitance at the two positions of the first and the second metal pieces and correlating them to fixed distances can allow for interim positions to be calculated. For example, to reduce error in detecting a paper size, the paper width adjuster can be moved to a widest and a narrowest position. Measuring the capacitance at these two positions and correlating them to fixed distances can allow for interim positions to be calculated using linear interpolation since capacitance will change linearly between these two points. For instance, a sensor can be calibrated when a piece of paper is fed by measuring an output of the sensor, and as paper is fed, verifying that the sensor output matches the paper size that is fed. 
     A determination of a paper size can be used to determine if a print process can proceed, in some examples. For instance, if a user attempts to send a print job that does not align with a paper size currently in the printing device, an alert may be sent to the user that the paper size is incorrect. Additionally or alternatively, a user may be able to see what paper size is in the printing device before sending a print job, such that they know whether they need to adjust the paper size based on their desired print job. 
     Put another way, based on the size of paper in the paper tray as determined by controller  102 , a job such as a print job or scan job can be allowed in response to a determination that the job requested of the printing device can be performed. A source of the request (e.g., a user, administrator, source computing device, graphical user interface, etc.) can be alerted in response to a determination that a job requested of the printing device cannot be performed. 
       FIG. 2  illustrates a diagram of an example of a printing device  206  including a first metal piece  209  and a second metal piece  207  according to the present disclosure.  FIG. 2  illustrates a paper width adjuster  212  in different positions  210  and  211 . Paper width adjustor can be used to adapt a paper tray  213  to a particular size of paper. While the paper width adjuster  212  illustrated in  FIG. 2  includes a gear  220  and rack  219  mechanism for adjustment, other paper width adjustor mechanisms may be used. 
     In the example illustrated in  FIG. 2 , a paper tray  213  (seen from below in  FIG. 2 ), has a paper width adjuster  212  coupled thereto for adjustment and/or centering of paper on the paper tray  213 . In position  210 , paper width adjuster  212  is in a letter paper position. In position  211 , paper width adjuster  212  is in a narrower paper position (e.g., a narrowest paper position). In some examples, positions such as positions  210  and  211  can be used to determine the width of paper in paper tray  213  using capacitive sensing. 
     For instance, printing device  206  can include a first metal piece  209  coupled to paper tray  213  and a second metal piece  207  coupled to paper width adjuster  212 . First metal piece  209  can be connected (e.g., via a sensing trace) to an electronics portion of printing device  206 , for instance an electronics board (e.g., printed circuit board (PCB), application specific integrated circuit (ASIC), digital ASIC, etc.). By connecting directly to an electronics board, costs can be reduced because additional cables and/or other connection components can be avoided. The first metal piece  209  can include components for connection to the electronics board without addition connections. Such an example can include the first metal piece being an FFC including flat cables covered by an insulator. An FFC can include components for directly connecting to an electronics board. 
     Second metal piece  207  may be a metal strip in some instances and may be grounded by grounding tab  208 . Grounding tab  208  can allow for movement of second metal piece  207  (e.g., over grounding tab  208 ). Other grounding mechanisms may be used to ground second metal piece  207  in some examples. While the first metal piece  209  and the second metal piece  207  are referred to herein as metal pieces, other conductors or semiconductors may be used. 
     As paper width adjuster  212  is adjusted, second metal piece  207  moves with paper width adjuster  212 , and different amounts of first metal piece  209  and second metal piece  207  overlap (but may not touch) one another. An insulator separates first metal piece  209  and second metal piece  207 ; for instance, an insulator surrounding a portion of first metal piece  209  (e.g., plastic surrounding cables within an FFC) acts as a separating insulator. As the first metal piece  209  and the second metal piece  207  overlap one another, a capacitance can be determined. For instance, in position  211 , a smaller amount of overlap between the first metal piece  209  and the second metal piece  207  occurs as compared to position  210 . The different amounts of overlap result in different capacitances. A sensor, for instance as illustrated in  FIG. 1 , can determine the capacitance between the first metal piece  209  and the second metal piece  207  and determine a paper width based on the determination. 
     In the example illustrated in  FIG. 2 , position  210  can be considered a widest position of paper width adjuster  212  (e.g., letter size paper) and position  211  can be considered a narrowest position of paper width adjuster  212 . In some examples, to reduce error in detecting a paper size, paper width adjuster can be moved to widest position  210  and narrowest position  211  and capacitance at the two positions can be determined. The determined capacitances at positions  210  and  211  can be correlated to fixed distances allowing interim positions to be determined. 
     In some examples, a capacitance sensor can be calibrated when paper is fed into a paper tray by measuring an output of the sensor, and as paper is fed verifying that the sensor output matches the paper size that is fed. In some examples, this can be done by detecting the paper length using a leading edge and/or a trailing edge sensor that may be found in print devices. In examples in which paper sizes are known, knowing the paper length can enable verification of the paper width. 
       FIG. 3  illustrates a diagram of another example of a printing device  306  including a first metal piece  309  and a second metal piece  307  according to the present disclosure. Because a printing device may contain conductive materials other than first metal piece  309  and second metal piece  307 , guard traces  314  may be used to prevent other conductive materials from affecting a capacitance determination. 
     For instance, first metal piece  309  can include a sensing trace  315  surrounded by guard traces  314 - 1  and  314 - 2  (referred together herein as guard traces  314 ). Guard traces  314  can shield the first metal piece  309  (and sensing trace  315 ) from conductors other than the second metal piece  307 , for example. Guard traces  314  can be driven to be an approximately same voltage as sensing trace  315  to block field current from leaking. For instance, to sense the capacitance, a voltage and current can be driven into a triangle waveform. By driving a constant current, frequency can be measured, and capacitance can be determined. By driving guard traces  314  with a same waveform, guard traces  314  can block field current from leaking into other grounded conductive materials in printing device  306 . Put another way, if guard traces  314  have approximately a same voltage as sensing trace  315 , field current can be terminated in guard traces  314 . In some examples, driving guard traces  314  at a same rate as sensing trace  315  can result in no voltage change between sensing trace  315  and guard traces  314 , which in turn can result in no current effects. For instance, sensing trace  315  can be shielded from the effects of other conductors. 
     While the example illustrated in  FIG. 3  illustrates one sensing trace  315  surrounded by two guard traces  314 , more sensing and/or guard traces can be used. For instance, two sensing traces may double an amount of capacitance in first metal piece  309 , which may increase sensing capability, sensitivity, and/or accuracy. In such an example, a pattern of guard trace, sensing trace, guard trace, sensing trace, guard trace may occur. Guard and sensing traces may be increased in number until a desirable sensing signal is reached. The pattern of guard trace, sensing trace (with guard traces on the ends) can be repeated. In some instances of the present disclosure, no guard traces are present. 
       FIG. 4  illustrates a diagram of an example paper tray  413  including a spring component according to the present disclosure. The image on the left illustrates paper tray  413  having a cut-out  416  to house a spring component. The image on the right illustrates paper tray  413  including rack  419 , first metal piece  409 , second metal piece  407 , and foam material  418 . Components such as first metal piece  409  and second metal piece  407  may have impurities (e.g., not uniform, have irregularities, etc.) and because capacitance is dependent on a distance between two conductors, the spring component may be used to maintain a spacing variation below a particular threshold between first metal piece  409  and second metal piece  407 . 
     For instance, the particular threshold can include a space between first metal piece  409  and second metal piece  407  below a distance of two millimeters or less. Two millimeters, as used herein, is an example and other threshold amounts may be used. In some instances, a particular threshold may include a particular number of gaps between first metal piece  409  and second metal piece  407 . For instance, the spring component can reduce gaps between first metal piece  409  and second metal piece  407  to achieve a more uniform distance between the two. In some instances, the distance between the first metal piece  409  and the second metal piece  407  is zero, such that they are firmly pressed against one another. 
     For instance, cut-out  416  may house foam material  418  which acts as the spring component to press the first metal piece  409  against the second metal piece  409  to reduce variation in capacitance due to a spacing variation between the first metal piece  409  and the second metal piece  407 . Foam material  418  can include, for instance, a foam material having sufficient force to deflect and keep uniform pressure on first metal piece  409 , reducing gaps between first metal piece  409  and second metal piece  407 . Foam material  418 , in some examples can be fitted into cut-out  416  using an interference fit. In some instances, a spring component other than a foam material may be used, such that it provides sufficient force to deflect and keep uniform pressure on first metal piece  409 , reducing gaps between first metal piece  409  and second metal piece  407 . In examples of the present disclosure in which a foam material acts as a spring component, an insulator can be present between the first metal piece  409  and the second metal piece  407 . 
       FIG. 5  illustrates a diagram of another example paper tray  513  including a spring component according to the present disclosure. The image on the left illustrates paper tray  513  without a rack, while the image on the right illustrates paper tray  513  with rack  519 . In some examples, second metal piece  507  can include folds  522  to act as the spring component to provide a spring force against rack  519  to keep second metal piece  507  tightly against first metal piece  509 . The length of second metal piece  507  can have the folds  522 , reducing gaps between first metal piece  509  and second metal piece  507 . In examples of the present disclosure in which folds  522  act as a spring component, an insulator can be present between the first metal piece  509  and the second metal piece  507 . 
       FIG. 6  illustrates a diagram of an example first metal piece  609  and an example second metal piece  607  separated by an insulator  623  according to the present disclosure. In some instances, first metal piece  607  can include metal sensing traces separated from second metal piece  607  by an insulator such as an insulating sheet. For example, if an increased capacitance is desired, a first metal piece  607  that is not an FFC may be used to avoid a set size of the FFC (e.g., cannot change FFC width). In such an example, metal (or other conductive material) sensing traces can be used in place of the FFC, with an insulator  623  being used in place of an insulating material that surrounds an FFC. 
     In some examples, first metal piece  609  can include an insulator having a metal layer deposited thereon. For instance, first metal piece  609  can be a metalized plastic material. Insulator  623  may still be present between the metal layer and the second metal piece  607 . Such an approach may allow for increase in capacitance, similar to the use of metal sensing traces as the first metal piece  609 , in some examples. 
       FIG. 7  illustrates a diagram of another example first metal piece  709  and second metal piece  707  separated by an insulator  723  according to the present disclosure. The image on the left illustrates first metal piece  709  (e.g., FFC, metal traces, metalized plastic, etc.) separated by insulator  723  from second metal piece  707 . The image on the right illustrates first metal piece  709  directly connected to electronics board  724 . A sensing trace of first metal piece  709  can be directly connected to electronics board  724 , for instance via a spring, carbon foam, etc. As first metal piece  709  and second metal piece  707  are further from a sensor, stray capacitance may be detected by the sensor. The sensor may sense capacitance from other conductors in the printing device, for instance. By directly connecting a sensing trace of first metal piece  709  to electronics board  724 , stray capacitance detection can be reduced. In such an example, guard traces may be used (e.g., the outside traces  726  are guard traces) or may not be used (the outside traces  726  are additional sensing traces or they are not present). 
     In some examples of the present disclosure, keeping the first metal piece  709  and the second metal piece  707  near the electronics board  724  can reduce stray and/or incorrect capacitance that resulted from unstable and/or moving cables within a printing device. In some instances, guard traces can reduce this stray and/or incorrect capacitance. 
     Electronics board  724 , in some instances, can be located a threshold distance away from the paper width adjuster to reduce variation in capacitance due to long traces between an area comprising the capacitive sensor and a remote printer controller electronics board. As used herein, a threshold distance away from the paper width adjuster can include a distance close enough such that a desired lower limit of capacitance variation is reached. In some instances, the first metal piece  707  and the second metal piece  709  and/or the paper width adjuster being a threshold distance away and/or directly connected to electronics board  724  can reduce costs, as connector costs can be reduced or eliminated. 
       FIG. 8  illustrates a diagram of an example first metal piece  809  and an example second metal piece  807  according to the present disclosure. The top image illustrates a first position of a paper width adjuster (e.g., letter paper position for second metal piece  807 ), and the bottom image illustrates a second position of the paper width adjuster (e.g., A4 paper position for second metal piece  807 . Because a width difference between letter paper size and A4 paper size is not large (e.g., about 6 millimeters), a determined capacitance change may be very small and potentially undetectable. In the example illustrated in  FIG. 8 , a size of a sensing trace can be increased at  825 , which corresponds to a threshold at which the paper width adjuster moves between A4 and letter size paper. By increasing the sensing trace size, there can be an increased transition between the two paper size positions, so even with a very small size difference, a capacitance change can be large enough to be detected. As the first metal piece  809  and the second metal piece  807  overlap one another, a slope of the sensing trace and a size of the sensing trace can change depending on location, which can improve accuracy of a paper size determination based on a capacitance determination. 
     Put another way, first metal piece  809  can include a plurality of sensing traces having modifiable shapes to amplify the capacitance between the first metal piece  809  and the second metal piece  807  as a function of linear motion of paper guides of the paper adjuster in sizes corresponding to paper size such as paper width, paper length, and/or paper shape differences, among others. While examples described with respect to  FIG. 8  include A4 and letter paper sizes, other paper sizes may be acknowledged with sensing trace size and/or slope changes. Sensing trace  809 , in some instances, can be surrounded by traces  826 , which can be additional sensing traces or guard traces. 
       FIG. 9  illustrates a diagram of another example printing device including a paper tray  913 , rack  919 , first metal piece  909 , and second metal piece  907  according to the present disclosure. In some examples, paper tray  913  may be a conductive material. In such an example, an insulator, such as insulating sheet  923  can be used to insulate first metal piece  909  and second metal piece  907  from paper tray  913 . 
     In the foregoing detailed description of the present disclosure, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration how examples of the disclosure may be practiced. These examples are described in sufficient detail to enable those of ordinary skill in the art to practice the examples of this disclosure, and it is to be understood that other examples may be utilized and that process, electrical, and/or structural changes may be made without departing from the scope of the present disclosure. 
     The figures herein follow a numbering convention in which the first digit corresponds to the drawing figure number and the remaining digits identify an element or component in the drawing. Elements shown in the various figures herein can be added, exchanged, and/or eliminated so as to provide a number of additional examples of the present disclosure. In addition, the proportion and the relative scale of the elements provided in the figures are intended to illustrate the examples of the present disclosure and should not be taken in a limiting sense. Further, as used herein, “a” element and/or feature can refer to one or more of such elements and/or features.