Patent Publication Number: US-2023141085-A1

Title: Actuation of pick mechanisms for media stack height sensing based on number of printed sheets

Description:
BACKGROUND 
     During printing processes, printers may report media stack heights of print media contained in media trays. Some types of printers may use pick mechanisms to sense the media stack heights. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features of the present disclosure are illustrated by way of example and not limited in the following figure(s), in which like numerals indicate like elements, in which: 
         FIG.  1    depicts a block diagram of an example apparatus that may update a pick mechanism activation counter value and, based on a determination that the updated pick mechanism activation counter value is greater than or equal to a threshold value, may cause a pick mechanism to be actuated to sense a media stack height of print media; 
         FIG.  2    depicts a block diagram of an example system within which the example apparatus depicted in  FIG.  1    may be implemented; 
         FIG.  3    depicts a flow diagram of an example method for updating a pick mechanism activation counter value based on a number of printed sheets and activating a pick mechanism to sense a media stack height based on the updated pick mechanism activation counter value; 
         FIG.  4    depicts a flow diagram of an example method for updating a pick mechanism activation counter value based on a number of printed sheets and preventing an operation of a pick mechanism to determine a media stack height of print media; and 
         FIG.  5    depicts a block diagram of an example non-transitory computer-readable medium that may have stored thereon computer-readable instructions to update a pick mechanism activation counter value and, based on the updated pick mechanism activation counter value relative to a threshold value, may allow or prevent an operation of a pick mechanism to sense a media stack height of print media. 
     
    
    
     DETAILED DESCRIPTION 
     For simplicity and illustrative purposes, the present disclosure is described by referring mainly to examples. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be readily apparent however, that the present disclosure may be practiced without limitation to these specific details. In other instances, some methods and structures have not been described in detail so as not to unnecessarily obscure the present disclosure. 
     Throughout the present disclosure, the terms “a” and “an” are intended to denote at least one of a particular element. As used herein, the term “includes” means includes but not limited to, the term “including” means including but not limited to. The term “based on” means based at least in part on. 
     Generally, with increasing adoption of a print-anywhere paradigm, printing devices may increasingly report levels of print media remaining in the input trays of printing devices. Printing devices, such as desktop printers, may use mechanical pick mechanisms, or pick arms, to sense a media stack height of the print media remaining in the input trays. Concerns associated with implementations of mechanical pick mechanisms to sense media height may be that, in some instances, the structural reliabilities and/or the life spans of the mechanical components of the pick mechanisms may be degraded, oftentimes to be less than the expected life spans of the pick mechanisms when the pick mechanisms are not used for media stack height measurements and/or the life spans of other components of the printing devices. 
     By way of particular example, the pick mechanisms may perform a hard stop homing move in order to zero a measurement system, which may impart a relatively large amount of mechanical stress to components of the pick mechanism. In some examples, pick mechanisms may be used to sense the media stack height based on movements of the pick mechanism relative to the print media in an input tray. In order to measure accurate media stack heights, the pick mechanism may establish a reliable reference position, also referred to herein as a home position or a “0” position, along an operation of the pick mechanism. For instance, the pick mechanism may establish the reference position at one end of a range of motion of the pick mechanism, such as at a fully lifted position. The pick mechanism may determine the media stack height based on movement of the pick mechanism from the reference position to a top of the media stack in the input tray. 
     In this regard, accuracy of media stack height measurements based on the pick mechanisms may depend on a reliability of the reference position. Pick mechanisms may include various types of mechanisms, such as rotary type pick mechanisms or linear type pick mechanisms. For each of the various types of pick mechanisms, in order to establish reliable reference positions, the pick mechanisms used may push to a hard stop. In this regard, the homing moves may be performed with relatively large amounts of force, or torque, to provide reliable reference positions. Insufficient amounts of force in the homing moves may result in insufficient biasing against hard stops, which may produce unreliable reference positions. 
     In some examples, such hard stop homing moves may be performed each time the media stack height is to be sensed, which may be after each print job. In some printing device implementations, the average number of pages per print job may be relatively low, for instance around 2 pages per print job. In such instances, the average number of sheets per print job may be as low as 1 sheet per print job, particularly since 2 pages may be printed on 1 sheet in cases of duplex printing. As a result, relatively large numbers of mechanical actuations per printed sheets may occur. The relatively large numbers of mechanical stresses to the pick mechanisms over many print jobs may lead to premature mechanical failure of the pick mechanisms and/or other components in the printing devices. 
     Disclosed herein are apparatuses, systems, methods, and computer-readable media in which rates of mechanical media stack height sampling may be reduced. The reduction in the rates of mechanical medial stack height sampling may improve failure rates and may extend the service lives of mechanical components for sensing media stack height as well as other functions in printing devices. In some examples, a processor may reduce rates of media stack height sampling by using a pick mechanism activation counter to control an operation of a pick mechanism. For instance, the processor may receive a sheet count before and after execution of a print job, and may determine a number of sheets printed for the print job based on the received sheet counts. The processor may update a pick mechanism activation counter value based on the determined number of printed sheets. In some examples, based on a determination that the updated pick mechanism activation counter value is greater than or equal to a predetermined threshold value, the processor may cause the pick mechanism to be actuated to sense a media stack height of print media. 
     By enabling control of pick mechanisms as disclosed herein, which may include causing the pick mechanisms to be actuated for media stack height measurements based on a predetermined threshold number of printed sheets, a number of actuations of the pick mechanisms may be reduced. This may improve the service lives of the pick mechanisms and reduce costs associated with re-design and/or repair of components that may be susceptible to premature failure. Additionally, the processor may cause a sampling rate for media stack height sensing to be controlled, which may improve flexibility and enable balancing between improved service life of the pick mechanisms and accuracy of the media stack height measurements. This may also improve efficiency and speed of the printing devices as a fewer number of media stack height measurements may be needed, which in turn may reduce consumption of computing resources and/or energy resources. 
     Reference is made to  FIGS.  1  and  2   .  FIG.  1    depicts a block diagram of an example apparatus  100  that may update a pick mechanism activation counter value and, based on a determination that the updated pick mechanism activation counter value is greater than or equal to a threshold value, may cause a pick mechanism to be actuated to sense a media stack height of print media.  FIG.  2    depicts a block diagram of an example system  200  within which the example apparatus  100  depicted in  FIG.  1    may be implemented. It should be understood that the apparatus  100  depicted in  FIG.  1    and the system  200  depicted in  FIG.  2    may include additional features and that some of the features described herein may be removed and/or modified without departing from the scopes of the apparatus  100  and/or the system  200 . 
     In some examples, the apparatus  100  may be implemented in a computing device, a printing device (such as an inkjet printer, a laser printer, a photo printer, or the like), a server, a scanner, and/or the like. As shown, the apparatus  100  may include a processor  102  and a non-transitory computer-readable medium, e.g., a memory  110 . The processor  102  may be a semiconductor-based microprocessor, a central processing unit (CPU), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), and/or other hardware device. Although the apparatus  100  is depicted as having a single processor  102 , it should be understood that the apparatus  100  may include additional processors and/or cores without departing from a scope of the apparatus  100  and/or system  200 . In this regard, references to a single processor  102  as well as to a single memory  110  may be understood to additionally or alternatively pertain to multiple processors  102  and/or multiple memories  110 . 
     As depicted in  FIG.  2   , the apparatus  100  may be implemented in a system  200 , which may include a server  204  that is connected to a data store (not shown). The apparatus  100  may be in communication with the server  204  via a network  202 . 
     The memory  110  may be an electronic, magnetic, optical, or other physical storage device that contains or stores executable instructions. The memory  110  may be, for example, Read-Only Memory (ROM), flash memory, solid state drive, Random-Access memory (RAM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), a storage device, an optical disc, or the like. The memory  110  may be a non-transitory computer-readable medium. The term “non-transitory” does not encompass transitory propagating signals. 
     As shown in  FIG.  1   , the processor  102  may execute instructions  112 - 122  to cause an operation of a pick mechanism within the apparatus  100  to be controlled. The instructions  112 - 122  may be computer-readable instructions, e.g., non-transitory computer-readable instructions. In other examples, the apparatus  100  may include hardware logic blocks or a combination of instructions and hardware logic blocks to implement or execute functions corresponding to the instructions  112 - 122 . 
     The processor  102  may fetch, decode, and execute the instructions  112  to receive a first sheet count  208  before execution by a printing device (e.g., the apparatus  100  or a printing device connected to the apparatus  100 ) of a print job  206 . In some examples, the printing device may maintain a print count that represents a running total or a cumulative number of sheets printed in the printing device. The first sheet count  208  may be a value of the print count at a particular point in time, e.g., before execution by the printing device of the print job  206 . The print count as well as the first sheet count  208  may be stored in the memory  110 , for instance, in a non-volatile memory on a main board (now shown) of the printing device. e.g., a motherboard, or the like of the printing device. In some examples, the print job  206  may include a file or a set of files that may be submitted to the printing device (e.g., apparatus  100  or a printing device connected to the apparatus  100 ) for printing. The print job  206  may include information regarding an image to be printed, media size, number of copies, priority, and/or the like. In some examples, the processor  102  may maintain the print count for the running total of sheets printed based on sheet count information included in the received print job  206 , based on sheet detection through the printing device, and/or the like. 
     The processor  102  may fetch, decode, and execute the instructions  114  to receive a second sheet count  210  after execution by the printing device of the print job  206 . In some examples, the first sheet count  208  and the second sheet count  210  may be numerical values, which are greater than one. The second sheet count  210  may be a value of the print count maintained at the printing device at a particular point in time, e.g., after execution by the printing device of the print job  206 . The second sheet count  210  may be stored in the memory  110 , for instance, in a non-volatile memory on a main board (not shown) of the printing device, e.g., a motherboard, or the like of the printing device. 
     The processor  102  may fetch, decode, and execute the instructions  116  to determine a number of sheets printed  212  for the print job  206  based on the first sheet count  208  and the second sheet count  210 . The processor  102  may calculate the number of sheets printed  212  based on a difference between the second sheet count  210  and the first sheet count  208 . The processor  102  may end the print job  206 . 
     The processor  102  may fetch, decode, and execute the instructions  118  to update a pick mechanism activation counter value  214  based on the determined number of sheets printed  212 . In some examples, the pick mechanism activation counter value  214  may be a counter value that represents a number of sheets printed since a previous media stack height sensing event. The processor  102  may increment the pick mechanism activation counter value  214  by the determined number of sheets printed  212  for the print job  206  to update the pick mechanism activation counter value  214 . 
     In some examples, the pick mechanism activation counter value  214  may be a value that is carried forward from a previous print job. In these instances, the processor  102  may increment the carried forward value of the pick mechanism activation counter value  214  from the previous print job by the determined number of sheets printed  212  in the print job  206 . 
     The processor  102  may fetch, decode, and execute the instructions  120  to determine whether the updated pick mechanism activation counter value  214  is greater than or equal to a predetermined threshold value  216 . In some examples, the predetermined threshold value  216  may represent a minimum number of sheets to be printed before performing a media stack height measurement. A relatively greater value for the predetermined threshold value  216  may reduce a rate of media stack height sensing. The processor  102  may determine whether the updated pick mechanism activation counter value  214  is greater than or equal to the predetermined threshold value  216  or, equivalently, less than the predetermined threshold value  216 . 
     The processor  102  may fetch, decode, and execute the instructions  122  to cause a pick mechanism  218  to be actuated to sense a media stack height  220  of print media based on a determination that the updated pick mechanism activation counter value  214  is greater than or equal to the predetermined threshold value  216 . By way of particular example and for purposes of illustration, the predetermined threshold value  216  may be set to 5 sheets printed, and based on a determination that the updated pick mechanism activation counter value  214  is greater than 5, such that more than 5 sheets have been printed since the previous actuation of the pick mechanism  218 , the processor  102  may cause the pick mechanism  218  to be actuated. In some examples, the apparatus  100  may include a print media tray  222 , and the processor  102  may cause the pick mechanism  218  to sense the media stack height  220  present in the print media tray  222 . 
     In some examples, the predetermined threshold value  216  may be set to balance structural reliability of the pick mechanism  218  versus accuracy of the media stack height measurements. For instance, a relatively lower rate of media stack height sensing may reduce the total number of actuations and may thus increase the life span of the pick mechanism  218 . In contrast, a relatively higher rate of media stack height sensing may increase the accuracy of the media stack height measurements, buy may also increase a number of fatigue cycles in the pick mechanism  218 , which may lead to a lower life span. The predetermined threshold value  216  may be determined through testing, developer knowledge, modeling, real-world determinations, and/or the like. 
     Once the pick mechanism  218  is actuated, the processor  102  may determine the sensed media stack height  220  using the pick mechanism  218 . In some examples, the sensed media stack height  220  may represent a raw stack height reading, and the processor  102  may generate a corrected value for the media stack height  220  using the data fusion model based on the raw stack height reading, previous stack height readings, and recent printed sheets since the last stack height reading. The data fusion model may be a linear regression model, or the like. In some examples, the processor  102  may correct the sensed media stack height  220  by accounting for the number of sheets printed  212  since a previous stack height reading, using the linear regression model. The data fusion model may be referred to herein as a media stack height correction model. The processor  102  may output the corrected media stack height  220 , for instance, to UI clients or to print services that may reside on the server  204 . 
     In some examples, the processor  102  may initialize the updated pick mechanism activation counter value  214  to a predetermined initial value when the pick mechanism  218  is actuated. For instance, the processor  102  may reset the pick mechanism activation counter value  214  to 0. Initialization of the pick mechanism activation counter value  214  with each actuation of the pick mechanism  218  may reduce errors, such as missed pick mechanism actuation events. By way of particular example and for purposes of illustration, in a case in which the pick mechanism activation counter value  214  is not initialized when the pick mechanism  218  is actuated, the processor  102  may use a rolling printed sheet counter value, such as the print count as previously described, or the like. For instance, the processor  102  may apply a modulus operation to the rolling printed sheet counter value and may actuate the pick mechanism  218  based on a comparison of a modulus to the predetermined threshold value  216 . However, in these instances, some pick mechanism actuation events may be missed in cases where the modulus equals 0, such as when the number of sheets printed  212  may equal the predetermined threshold value  216 . In order to avoid such errors, the processor  102  may initialize the updated pick mechanism activation counter value  214  with each actuation of the pick mechanism  218 . Once the updated pick mechanism activation counter value  214  is initialized, the processor  102  may proceed to the next print job with the pick mechanism activation counter value  214  set to 0. 
     Based on a determination that the updated pick mechanism activation counter value  214  is less than the predetermined threshold value  216 , the processor  102  may prevent operation of the pick mechanism  218  to sense the media stack height  220  of the print media. In some examples, the processor  102  may cause a state of the pick mechanism  218  to be set in a standby mode to prevent operation of the pick mechanism  218 . The processor  102  may carry forward the updated pick mechanism activation counter value  214  for use in a subsequent print job. Returning to the previous example in which the predetermined threshold value  216  is set to 5, in a case in which the updated number of sheets printed  212  is 3, which is less than the predetermined threshold value  216 , the processor  102  may carry forward this value as the pick mechanism activation counter value  214  for a subsequent print job. In this example, the processor  102  may prevent operation of the pick mechanism  218  until the number of sheets printed  212  in the subsequent print job(s) is 2 or greater, so that the pick mechanism activation counter value  214  is incremented to be greater than or equal to the threshold value  216  of 5. 
     In some examples, the processor  102  may initialize the pick mechanism activation counter value  214  based on a predetermined event. For instance, based on a determination of a printing device start-up, the processor  102  may initialize the pick mechanism activation counter value  214  to a predetermined initial value, such as 0. 
     In some examples, the processor  102  may adjust a rate in which the pick mechanism  218  is to be actuated. The predetermined threshold value  216  may correlate to an accuracy of the media stack height measurement and a life span of the pick mechanism  218 . In some examples, the processor  102  may decrease the predetermined threshold value  216  to increase a rate at which the pick mechanism  218  may be actuated, which may increase the accuracy of the media stack height measurement. In some examples, the processor  102  may increase the predetermined threshold value  216  to decrease the rate in which the pick mechanism  218  may be actuated, which may increase the life span of the pick mechanism  218 . 
     In some examples, based on a predetermined event that may cause a model to be generated, the processor  102  may override the pick mechanism activation counter value  214  by causing the pick mechanism  218  to be actuated to sense the media stack height  220  of print media in an input tray while the updated pick mechanism activation counter value  214  is less than the predetermined threshold value  216 . The model may be referred to herein as a media stack height correction model. 
     For instance, the processor  102  may cause the pick mechanism  218  to be actuated to sense the media stack height  220  of the print media in the input tray regardless of the value of the pick mechanism activation counter value  214 . As previously described, the processor  102  may generate a corrected media stack height using a model, such as a linear regression model, which may account for the number of sheets printed  212  in the print job  206  to the media stack height  220 . The media stack height  220  may be a raw sensed height value determined using the pick mechanism  218  and the model may adjust this value based on the number of sheets printed  212  and previous media stack height measurements. In some examples, the model may be reset, for instance, when an input tray is removed from and re-inserted into the apparatus  100 , in which case a media stack height may be unknown since a user may fill the print media tray to any level. In these instances, the processor  102  may override the pick mechanism activation counter value  214  in order to obtain additional data points to rebuild the model for stack height correction. The processor  102  may cause the pick mechanism  218  to be actuated to sense the media stack height  220  of print media while the updated pick mechanism activation counter value  214  is less than the predetermined threshold value  216 . The processor  102  may override the pick mechanism activation counter value  214  for a predetermined number of actuations of the pick mechanism  218 . 
     Various manners in which the processor  102  may operate are discussed in greater detail with respect to the methods  300  and  400 , respectively depicted in  FIGS.  3  and  4   .  FIG.  3    depicts a flow diagram of an example method  300  for updating a pick mechanism activation counter value based on a number of printed sheets and activating a pick mechanism to sense a media stack height based on the updated pick mechanism activation counter value.  FIG.  4    depicts a flow diagram of an example method  400  for updating a pick mechanism activation counter value based on a number of printed sheets and preventing an operation of a pick mechanism to determine a media stack height of print media. It should be understood that the methods  300  and  400  respectively depicted in  FIGS.  3  and  4    may include additional operations and that some of the operations described therein may be removed and/or modified without departing from the scope of the methods  300  and  400 . The descriptions of the methods  300  and  400  are made with reference to the features depicted in  FIGS.  1  and  2    for purposes of illustration. 
     Referring first to  FIG.  3   , at block  302 , the processor  102  may start a print job  206 . The processor  102  may start the print job  206  at a printing device, which may be the apparatus  100  or a printing device connected to the apparatus  100 . At block  304 , the processor  102  may receive a first sheet count before execution of the print job  206 . At block  306 , the processor  102  may execute the print job  206 , and at block  308 , once the print job  206  has been executed and all of the sheets in the print job  206  have been printed, the processor  102  may receive a second sheet count  210 . The first sheet count  208  and the second sheet count  210  may correlate to a number of sheets printed in the printing device at a given point in time. 
     At block  310 , the processor  102  may determine a number of sheets printed  212  for the print job  206  based on the first sheet count  208  and the second sheet count  210 . The processor  102  may determine the number of sheets printed  212  based on a difference between the second sheet count  210  and the first sheet count  208 . At block  312 , the processor  102  may end the print job  206 . 
     At block  314 , the processor  102  may update a pick mechanism activation counter value  214  based on the determined number of sheets printed  212 . The processor  102  may increment the pick mechanism activation counter value  214  by the determined number of sheets printed  212  during the execution of the print job to update the pick mechanism activation counter value  214 . 
     At block  316 , the processor  102  may determine whether to override the pick mechanism activation counter value  214 , which may cause the pick mechanism  218  to activate. In some examples, the processor  102  may generate a corrected media stack height using a model, such as a linear regression model that may fine tune the media stack height  220  based on the number of sheets printed  212  in the print job  206  and previous media stack height values. In some examples, the model may be reset based on certain events, for instance, when a print media tray is removed from and re-inserted into the apparatus  100 , in which case a media stack height may be unknown since a user may fill the print media tray to any level. In these instances, the processor  102  may override the pick mechanism activation counter value  214  in order to obtain additional data points to rebuild the model for stack height correction. For instance, the processor  102  may cause the pick mechanism  218  to be actuated to sense the media stack height  220  of print media while the updated pick mechanism activation counter value  214  is less than the predetermined threshold value  216 . The processor  102  may override the pick mechanism activation counter value  214  for a predetermined number of actuations of the pick mechanism  218 . 
     At block  318 , the processor  102  may determine whether the updated pick mechanism activation counter value  214  is greater than or equal to a predetermined threshold value  216 , or less than the predetermined threshold value  216 . 
     At block  320 , the processor  102  may initialize the updated pick mechanism activation counter value  214  to a predetermined initial value. For instance, the processor  102  may reset the pick mechanism activation counter value  214  to 0, or some other value. The processor  102  may initialize the updated pick mechanism activation counter value  214  based on a determination that the updated pick mechanism activation counter value  214  is greater than or equal to the predetermined threshold value  216 . In some examples, the processor  102  may initialize the updated pick mechanism activation counter value  214  based on a determination to override the pick mechanism activation counter value  214 . 
     At block  322 , the processor  102  may cause a pick mechanism  218  to be actuated to sense a media stack height  220  of print media. 
     At block  324 , the processor  102  may generate a corrected value for the media stack height  220  using a data fusion model. The media stack height  220  may be a raw media stack height reading based on movement of the pick mechanism  218 . The processor  102  may use the data fusion model to improve an accuracy of the media stack height  220  based on the raw media stack height reading for the print job  206 , previous media stack height readings, and the number of sheets printed  212  during the print job  206 . In some examples, the data fusion model may be a linear regression model, or the like. At block  326 , the processor  102  may output the corrected media stack height  220 , for instance, to UI clients or to print services that may reside on the server  204 . 
     Based on a determination that the updated pick mechanism activation counter value  214  is less than the predetermined threshold value  216 , at block  318 , the processor  102  may prevent operation of the pick mechanism  218  to sense the media stack height  220  of the print media. In some examples, the processor  102  may cause a state of pick mechanism  218  to be set in a standby mode. At block  328 , the processor  102  may carry forward the updated pick mechanism activation counter value  214  for use in a subsequent print job. 
     At block  330 , the processor  102  may determine that a predetermined event has occurred, such as a printing device start-up, or the like. At block  332 , the processor  102  may initialize the pick mechanism activation counter value  214  to a predetermined initial value, such as 0, or some other value. The processor  102  may initialize the pick mechanism activation counter value  214  prior to starting the print job in block  302 . 
     Referring to  FIG.  4   , the processor  102  may update a pick mechanism activation counter value  214  based on a number of sheets printed  212  and may prevent an operation of a pick mechanism  218  to determine a media stack height  220  of print media. At block  402 , the processor  102  may receive a print job  206 . At block  404 , the processor  102  may receive a first sheet count  208  before printing of the print job  206 . At block  406 , the processor  102  may receive a second sheet count  210  after printing of the print job  206 . 
     At block  408 , the processor  102  may determine a number of sheets printed  212  during the print job  206  based on a difference between the first sheet count  208  and the second sheet count  210 . At block  410 , the processor  102  may update a pick mechanism activation counter value  214  based on the determined number of sheets printed  212 . The pick mechanism activation counter value  214  may represent a number of sheets printed since a previous actuation of the pick mechanism  218 . 
     At block  412 , the processor  102  may determine whether the updated pick mechanism activation counter value  214  is greater than or equal to a predetermined threshold value  216 . At block  414 , based on a determination that the updated pick mechanism activation counter value  214  is less than the predetermined threshold value  216 , the processor  102  may prevent an operation of a pick mechanism  218  to determine a media stack height  220  of print media in a print media tray  222 . 
     In some examples, based on a determination that the updated pick mechanism activation counter value  214  exceeds or equals the predetermined threshold value  216 , the processor  102  may cause the pick mechanism  218  to determine the media stack height  220  of the print media in the print media tray  222 . The processor  102  may initialize the updated pick mechanism activation counter value  214  to a predetermined initial value, such as to 0, after the pick mechanism  218  is actuated. 
     In some examples, the processor  102  may increment the pick mechanism activation counter value  214  by the determined number of sheets printed  212  during printing of the print job  206  to update the pick mechanism activation counter value  214 . 
     In some examples, based on a determination that the updated pick mechanism activation counter value  214  is less than the predetermined threshold value  216 , the processor  102  may carry forward the updated pick mechanism activation counter value  214  for a subsequent print job. In some examples, based on a determination of a printing device start-up, the processor  102  may initialize the pick mechanism activation counter value  214  to a predetermined initial value, such as to 0. 
     In some examples, the processor  102  may override the updated pick mechanism activation counter value  214  based on certain events. For instance, based on a predetermined event, such as re-insertion of a print media tray  222 , the processor  102  may cause the pick mechanism  218  to be actuated while the updated pick mechanism activation counter value  214  is less than the predetermined threshold value  216 . 
     In some examples, the processor  102  may use a model to improve an accuracy of the media stack height  220 , which may account for actual sensed values of the media stack height  220  from the pick mechanism  218 , previous media stack height values, and the number of sheets printed in the print job  206 . Certain events, such as re-insertion of the print media tray  222 , may cause the processor  102  to rebuild the model. For instance, based on a predetermined event that may cause the model to be generated, the processor  102  may allow the actuation of the pick mechanism  218 , while the updated pick mechanism activation counter value  214  is less than the predetermined threshold value  216 . The processor  102  may override the updated pick mechanism activation counter value  214  for a predetermined threshold number of actuations of the pick mechanism  218 . In some examples, the processor  102  may decrease the predetermined threshold value  216 , which may increase a rate in which the pick mechanism  218  is actuated. Alternatively, the processor  102  may increase the predetermined threshold value  216 , which may decrease the rate in which the pick mechanism  218  is actuated. 
     Some or all of the operations set forth in the methods  300  and  400  may be included as utilities, programs, or subprograms, in any desired computer accessible medium. In addition, the methods  300  and  400  may be embodied by computer programs, which may exist in a variety of forms both active and inactive. For example, they may exist as computer-readable instructions, including source code, object code, executable code or other formats. Any of the above may be embodied on a non-transitory computer-readable storage medium. 
     Examples of non-transitory computer-readable storage media include computer system RAM, ROM, EPROM, EEPROM, and magnetic or optical disks or tapes. It is therefore to be understood that any electronic device capable of executing the above-described functions may perform those functions enumerated above. 
     Turning now to  FIG.  5   , there is shown a block diagram of a non-transitory computer-readable medium  500  that may have stored thereon computer-readable instructions to update a pick mechanism activation counter value and, based on the updated pick mechanism activation counter value relative to a threshold value, may allow or prevent an operation of a pick mechanism to sense a media stack height of print media. It should be understood that the computer-readable medium  500  depicted in  FIG.  5    may include additional instructions and that some of the instructions described herein may be removed and/or modified without departing from the scope of the computer-readable medium  500  disclosed herein. The computer-readable medium  500  may be a non-transitory computer-readable medium. The term “non-transitory” does not encompass transitory propagating signals. 
     The computer-readable medium  500  may have stored thereon computer-readable instructions  502 - 514  that a processor, such as the processor  102  depicted in  FIGS.  1  and  2   , may execute. The computer-readable medium  500  may be an electronic, magnetic, optical, or other physical storage device that contains or stores executable instructions. The computer-readable medium  500  may be, for example, Random-Access memory (RAM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), a storage device, an optical disc, or the like. 
     The processor may fetch, decode, and execute the instructions  502  to receive a pick mechanism activation counter value  214 . The pick mechanism activation counter value  214  may represent a number of sheets printed since a previous actuation of a pick mechanism  218 . In some examples, the pick mechanism activation counter value  214  may be carried forward from a previous print job or the pick mechanism activation counter value  214  may be an initialized value, for instance, reset to 0 after a printing device start-up. 
     The processor may fetch, decode, and execute the instructions  504  to receive a first sheet count  208  before execution of a print job  206 . The first sheet count  208  may be a count of printed sheets before execution of the print job  206 . 
     The processor may fetch, decode, and execute the instructions  506  to receive a second sheet count  210  after execution of the print job  206 . The second sheet count  210  may be a count of printed sheets after execution of the print job  206 . 
     The processor may fetch, decode, and execute the instructions  508  to determine a number of sheets printed  212  for the print job  206  based on a difference between the second sheet count  210  and the first sheet count  208 . 
     The processor may fetch, decode, and execute the instructions  510  to update the pick mechanism activation counter value  214  by incrementing the pick mechanism activation counter value  214  by the determined number of sheets printed  212 . 
     The processor may fetch, decode, and execute the instructions  512  to allow an operation of a pick mechanism  218  to sense a media stack height  220  of print media based on a determination that the updated pick mechanism activation counter value  214  is greater than or equal to a predetermined threshold value  216 . 
     The processor may fetch, decode, and execute the instructions  514  to prevent the operation of the pick mechanism  218  to sense the media stack height  220  of the print media based on a determination that the updated pick mechanism activation counter value  214  is less than the predetermined threshold value  216 . 
     In some examples, based on the determination that the updated pick mechanism activation counter value  214  may be greater than or equal to the predetermined threshold value  216 , the processor may cause the pick mechanism  218  to be actuated to sense the media stack height  220  of the print media in a print media tray  222 . Based on a determination to actuate the pick mechanism  218 , the processor may initialize the updated pick mechanism activation counter value  214  to a predetermined initial value, such as to 0. In some examples, the processor may initialize the updated pick mechanism activation counter value  214  prior to actuation of the pick mechanism  218 . The processor may carry forward the initialized pick mechanism activation counter value  214  for a subsequent print job. 
     Although described specifically throughout the entirety of the instant disclosure, representative examples of the present disclosure have utility over a wide range of applications, and the above discussion is not intended and should not be construed to be limiting, but is offered as an illustrative discussion of aspects of the disclosure. 
     What has been described and illustrated herein is an example of the disclosure along with some of its variations. The terms, descriptions and figures used herein are set forth by way of illustration and are not meant as limitations. Many variations are possible within the scope of the disclosure, which is intended to be defined by the following claims—and their equivalents—in which all terms are meant in their broadest reasonable sense unless otherwise indicated.