Abstract:
A method for sensing paper on a paper roll is disclosed. The method comprises transmitting an ultrasonic signal into the paper roll and detecting an ultrasonic return echo transmit signal from the paper roll, the ultrasonic return echo transmit signal resulting from the ultrasonic signal interacting with the paper roll. Moreover, the method comprises determining an amount of paper remaining on the paper roll in response to the ultrasonic return echo transmit signal. Furthermore, the method may comprise indicating that the paper roll needs to be replaced in response to determining the amount of paper remaining on the paper roll.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a system and method for sensing a paper roll, and particularly to a system and method for ultrasonically sensing an amount of paper remaining on a paper roll. 
   2. Description of Background 
   Receipt printer paper, such as are commonly found with point of sale devices, usually comes in rolls. Before our invention, it has been difficult to for a printer to estimate the amount of paper remaining on a roll. This is in part due to the various roll sizes and varied diameters of the hollow center carriers on which the rolls are mounted. In other words, even if two rolls have the same overall outside diameter, one may have a hollow center carrier with a greater outer diameter, thereby resulting in less paper on that roll. 
   Currently, the last few feet of the paper on a roll are marked with colored ink. When the operator of the point of sale device notices the colored ink on the paper receipts being dispensed, they know to replace the paper roll, as it will soon run out. This tends to work satisfactorily for point of sale devices that are operated by a staff person of an establishment. However, for self-service devices that dispense receipts, the user (when seeing the colored ink on their receipt) does not reliably notify (if at all) a staff person that the paper roll needs to be replaced. 
   SUMMARY OF THE INVENTION 
   A method for sensing paper on a paper roll is disclosed. The method comprises transmitting an ultrasonic signal into the paper roll and detecting an ultrasonic return echo transmit signal from the paper roll, the ultrasonic return echo transmit signal resulting from the ultrasonic signal interacting with the paper roll. The method further comprises determining an amount of paper remaining on the paper roll in response to the ultrasonic return echo transmit signal. Furthermore, the method may comprise indicating that the paper roll needs to be replaced in response to determining the amount of paper remaining on the paper roll. 
   Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with advantages and features, refer to the description and to the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
       FIG. 1  diagrammatically illustrates one example of a system for sensing a paper roll ultrasonically; and 
       FIG. 2  illustrates one example of a return echo signal plotted as a function of amplitude and time. 
   

   The detailed description explains the preferred embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
   DETAILED DESCRIPTION OF THE INVENTION 
   Turning now to the drawings in greater detail, it will be seen that in  FIG. 1  there is a paper roll  10  such as is commonly found in point-of-sale devices for use in printing receipts, which includes a continuous sheet of paper  30  rolled onto a hollow carrier  40 . The hollow carrier  40  is typically composed of a cardboard or plastic material. Paper roll  10 , and, more particularly, the carrier  40 , is typically disposed on a spindle  12  of a point of sale device (not shown), as is well known. A feeder  14  of the point of sale device dispenses paper receipts, also as is well known. An ultrasonic transducer  16  is positioned, by a biased holder  18 , to be in contact with the outer surface of the paper roll  10 . The biased holder  18  is simply a holder receptive to supporting the ultrasonic transducer  16  that is mounted within the point of sale device with a force applied to maintain contact of the ultrasonic transducer  16  with the outer surface of the paper roll  10 . The biased holder  18  further includes a pair of rollers  20  that permit the paper roll  10  to easily rotate relative to the ultrasonic transducer  16  while maintaining the aforementioned contact with the paper roll  10 . The ultrasonic transducer  16  can be a piezoelectric ceramic ultrasonic transducer. 
   The ultrasonic transducer  16  is electrically connected by lines  22  to an electronic circuit assembly  24 , which is disposed within the point of sale device. A transmitter circuit  26  provides a transmit signal to the transducer  16  for generating an ultrasonic signal  34  to be transmitted into the paper roll  10 . A receiver circuit  28  measures a detected return echo  36  from the transducer  16 , of the ultrasonic signal. A microprocessor  32  is provided to process the measured return echo to determine an estimated amount of paper remaining on the paper roll  10 . Once it is determined that the paper is about to run out, an output signal is generated to indicate that the paper roll needs to be replaced. The amount of paper remaining when the signal to replace the paper roll is generated can be set at the processor  32 . This output signal may simply activate a visual display (such a lamp, not shown), drive an audible alarm (not shown), generate a systems management alert to another computer, or generate a prompt at a screen, for detection by a staff person. 
   In the present example, the ultrasonic signal generated by the transducer  16  is a 100 nanosecond (nsec.) pulse. The pulse travels through the paper roll  10  resulting in a return echo. The return echo over time reveals the amount of paper (P) between the outer surface (outer diameter=D o ) and the inner carrier (inner diameter=D i ) of the paper roll  10 , by multiplying the speed of sound (i.e., 1432 mm./ms. (millimeters per millisecond)) by the edge feature times. Edge feature times or Echos (E) are the times, in milliseconds, between particular edges of the reflected ultrasonic waveform. Thus:
 
 P =( D   o   −   D   i )/2=( E mm.)(1432 mm/ms)
 
The unit of P is mm.
 
   Turning now to  FIG. 2 , a plot of a detected return echo from the paper roll  10  is shown for the 100 nsec. pulse ultrasonic signal. The first portion of the plot, i.e., from 0 to 0.0014 ms. (=1.4 us), reveals an amount of paper at one side on the paper roll (P (between an outer surface of the paper roll  10  (outer diameter=D o ) and an outside surface of the carrier  40  (inner diameter=D i )) to be 2.0 mm. (0.0014 ms. multiplied by 1432 mm./ms). Further, knowing the outside diameter of the carrier  40 , which is in this example 22 mm. results in an outside diameter of the paper roll  10  of 26 mm.
 
 P =( D   o   −   D   i )/2 →D   o =2 P+D   i  
 
   A description of a method of determining the thickness of the paper on the roll follows. After determining a first paper roll diameter (as described above) and printing several receipts that total 1.5 meters (i.e., the length of paper fed in a printer is easily determined), a second ultrasonic pulse detects an echo after 0.0007 ms. Now the amount of paper on one side of the paper roll  10  is 1.0 mm. (i.e., 0.0007 ms. multiplied by 1432 mm./ms.) and the second outside diameter of the paper roll  10  is 24 mm. (i.e., 22 mm., the outside diameter of the carrier  40  plus 2 times 1 mm. amount of paper). The thickness of one layer of the paper can be calculated by dividing the cross sectional area of the roll between the first outer diameter (D o =26 mm.) and the second inner diameter (D i =24 mm.) by the length of paper printed (L=1.5 meters) resulting in a paper thickness of 0.05 mm. Thus the equation for thickness (T) is:
 
 T =(π( D   o /2) 2− π( D   i /2) 2 )/ L =( D   o   2−   D   i /4)π/ L  
 
   An example of an actual calculation of T would be (((26 squared minus 24 squared)/4) multiplied by 3.1416 divided by 1500 mm.). 
   In determining when to signal for replacement of the paper roll  10 , one exemplary approach would signal that the paper supply is low when the desired remaining paper length is specified. To provide this signal, the desired outside diameter of the paper roll  10  is calculated by rearranging the equation for paper thickness to solve for D o =the first outer diameter: 
   From above: T=(D o   2− D i   2 /4)π/L
 
→ TL /π=( D   o   2−   D   i   2 /4)→4 TL/π=D   o   2−   D   i   2 →4 TL/π   +   D   i   2   =D   o   2  
 
→ D   o =(4 TL/π   +   D   i   2 ) 1/2  
 
   Thus the preceding calculation of D o  takes the square root of the sum of 4 times the thickness of the paper times the specified length divided by 3.1416 and the outer diameter of the carrier 40 squared. Here the thickness of the paper can be determined by the method described previously or it may be known. 
   The calculated outside diameter of the paper roll 10 less the known inside diameter of the paper roll  10  (i.e., the outside diameter of the carrier  40 ) divided by 2 yields the amount of paper that should be on one side of the paper roll  10  to signal that paper should be replaced. In other words, this is the minimum amount of paper (P) that the ultrasonic must pass through without low paper being indicated.
 
 P =( D   o   −   D   i )/2
 
   The corresponding echo time (E) is now calculated by dividing this distance (P) by 1432 mm./ms.: E=(P mm.)/1432 mm./ms. The unit of E is ms. 
   For example: if the signal for replacement of the paper is desired to occur when there are 5 meters of paper left on a carrier having a 22 mm. outer diameter and using the paper thickness calculated previously of 0.05 mm, the desired outside diameter of the paper roll  10  is 28.3 mm. (i.e., square root of (4 times 0.05 mm. times 5000 mm. divided by 3.1416 plus 22 mm. squared)). The desired amount of paper on the paper roll  10  is 3.15 mm. (i.e., 28.3 minus 22 divided by 2) and the desired echo time is 0.0022 ms. (i.e., 3.15 mm. divided by 1432 mm./ms.). 
   Once the outer diameter (D o ), the inner diameter (D i ) and paper thickness are known, the length of paper remaining on the paper roll (L) can be easily determined by rearranging the equation for paper thickness to solve for L:
 
From above:  T =(D o   2−   D   i   2 /4)π/ L  
 
→ TL =( D   o   2−   D   i   2 /4)π→ L =( D   o   2=   D   i   2 )π/4 T  
 
   The capabilities of the present invention can be implemented in software, firmware, hardware or some combination thereof. 
   As one example, one or more aspects of the present invention can be included in an article of manufacture (e.g., one or more computer program products) having, for instance, computer usable media. The media has embodied therein, for instance, computer readable program code means for providing and facilitating the capabilities of the present invention. The article of manufacture can be included as a part of a computer system or sold separately. 
   Additionally, at least one program storage device readable by a machine, tangibly embodying at least one program of instructions executable by the machine to perform the capabilities of the present invention can be provided. 
   There may be many variations to the steps (or operations) described therein without departing from the spirit of the invention. For instance, the steps may be performed in a differing order, or steps may be added, deleted or modified. All of these variations are considered a part of the claimed invention. 
   While the preferred embodiment to the invention has been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.