Method of detecting amount of remaining sheets of paper

Abstract: A method of detecting the amount of sheets of paper remaining in a paper feeding cassette of a printing apparatus by calculating a difference in the number of operations of a lifting means (300) for lifting a knock-up plate (201) toward a pickup roller (120) when the maximum number of sheets of paper is loaded in the cassette and when only one sheet of paper is left in the cassette and calculating the amount of consumed paper per one operation of the lifting means as a set value; lifting the knock-up plate (201) when the cassette enters in the printing apparatus until the loaded paper closely contacts the pickup roller and counting the number of operations of the lifting means then; and calculating the amount of paper remaining in the cassette considering the number of operations counted and the set value. Thus, the amount of sheets of paper remaining in the cassette can be easily determined without opening the cassette so that a printing job can be prevented from being stopped due to lack of paper.

Description: The present invention relates to a method of automatically detecting the amount of sheets of paper remaining in a paper feeding cassette of a printing apparatus. For instance, a cassette 20 containing a plurality of sheets of paper S is detachably installed in a printing apparatus such as a printer or copier, as shown in Figure 1. A pickup roller 11 is provided closely contacting the uppermost surface of a paper S in the cassette 10 when the cassette 20 is coupled to a main body 10 of the printing apparatus so that paper S is provided one by one though a paper feeding path according to rotation of the pickup roller 11. However, in the conventional printing apparatus, when a paper S in the cassette 20 is gradually consumed during a printing job, a user cannot see how many sheets of paper S are left in the cassette 20 unless the cassette 20 is drawn out of the main body 10. Thus, there frequently are cases in which the printing job is stopped due to lack of paper. Also, it is inconvenient to check the amount of remaining paper by drawing the cassette 20 out, prior to a printing job, to prevent the above problem. Therefore, a method for detecting the amount of paper remaining in the cassette 20 without drawing the cassette 20 out of the main body 10 is required. It is an aim of the present invention to provide a method of detecting the amount of sheets of paper remaining in a cassette without drawing the cassette out of the main body of a printing apparatus. JP-A-10-161 376 describes a method for detecting the amount of paper remaining in a cassette using a lifter for the whole cassette. According to the present invention there is provided a method as set forth in claim 1 appended hereto. Preferred features of the present invention will be apparent from the dependent claims and the description which follows. According to a first aspect of the present invention there is provided a method of detecting the amount of sheets of paper remaining in a paper feeding cassette of a printing apparatus, comprising the steps of: preparing a knock-up plate installed in the cassette to be capable of pivoting, on which paper is placed, a pickup roller installed in the printing apparatus to be capable of elastically moving up and down within a predetermined range, rotating in close contact with the paper loaded in the printing apparatus so that the paper can sequentially enter a paper feeding path of the printing apparatus, a lifting means for lifting the knock-up plate step by step according to consumption of paper to locate the loaded paper within a range of closely contacting the pickup-roller; calculating a difference in the number of operations of the lifting means for lifting the knock-up plate toward the pickup roller when the maximum number of sheets of paper is loaded in the cassette and when only one sheet of paper is left in the cassette and calculating the amount of consumed paper per one operation of the lifting means as a set value; lifting the knock-up plate when the cassette enters in the printing apparatus until the loaded paper closely contacts the pickup roller and counting the number of operations of the lifting means then; and calculating the amount of paper remaining in the cassette considering the number of operations counted and the set value. Preferably, said lifting means comprises: a rotation shaft installed in said printing apparatus to rotate under said knock-up plate such that a lift lever installed at one side thereof can lift said knock-up plate during rotation; a cam gear connected to said rotation shaft for rotating said rotation shaft a predetermined amount per one turn by being rotated by a predetermined driving source; and a solenoid for locking said cam gear at each turn by selectively being interfered with a locking step formed on said cam gear, wherein the number of operations of said lifting means is calculated by counting the number of operations of said solenoid. For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: Figure 1 is a perspective view showing a typical printing apparatus; Figures 2 and 3 are a perspective view and an exploded perspective view showing a paper feeding structure adopted in a preferred method of detecting the amount of sheets of paper remaining in a cassette; Figure 4 is a simplified view showing the paper feeding structure showing in Figure 2; and Figure 5 is a flow chart for explaining a preferred method of detecting the amount of sheets of paper remaining in a cassette. Figures 2 and 3 show an example of a paper feeding structure suitable for the method of detecting the amount of sheets of paper remaining in a cassette according to the preferred embodiment of the present invention. As shown in the drawing, a knock-up plate 201 where sheets of paper are placed is installed in a cassette 200 to be capable of pivoting. A lifting means for lifting the knock-up plate 201 to allow the paper stacked on the knock-up plate to closely contact a pickup roller 120 is provided in a printing apparatus 100. The lifting means includes a rotation shaft 130 disposed under the knock-up plate 201 when the cassette 200 is installed in the printing apparatus 100. A lift lever 150 is coupled to the rotation shaft 130 so that the lift lever 150 lifts the knock-up plate 201 during rotation to allow the stacked paper to closely contact the pickup roller 120. To rotate the rotation shaft 130 a predetermined amount, there is provided a lift gear 310 engaged with a gear member 110 coupled to the rotation shaft 130, a cam gear 330 rotated in engagement with a driving gear 320 and having a predetermined cam surface 331 and a locking step 332 formed at one side thereof, a pivot lever 340 pivoting according to the rotation of the cam gear 330 while closely contacting the cam surface 331, a connection shaft 350 connecting the lift gear 310 and the pivot lever 340, a first forward direction bearing 371 coupled to the outer circumference of the connection shaft 350 and inserted in a holder 360, a second forward direction bearing 372 coupled to the outer circumference of the connection shaft 350 and inserted in the pivot lever 340, a tension spring 380 for elastically pulling the pivot lever 340, and a solenoid 390 for locking the rotation of the cam gear 330 by selectively interfering with the locking step 332 of the cam gear 330. The pickup roller 120 is elastically biased downward by a predetermined elastic member 121 and installed to be capable of moving up and down within a range of its elasticity. Reference numeral 351 denotes a coupling pin and reference numeral 400 denotes a supporting body for supporting the lifting means. Figure 4 shows a simplified paper feeding structure for convenience of explanation. In the above structure, when the knock-up plate 201 is lifted, a hooking piece 391 of the solenoid 390 hooked at the locking step 332 escapes therefrom and the locking is released. At this time, as the cam gear 330 is rotated slightly by the power converting spring 333, the cam gear 330 is engaged with the driving gear 320 connected to a driving source (not shown). Next, the cam gear 330 rotates one turn by the driving gear 320. Here, the pivot lever 340 closely contacting the cam surface 331 is moved along the curved surface of the cam surface 331 to rotate a predetermined amount and returns to its original position by the tension spring 380 thereafter. At the instant the pivot lever 340 rotates along the cam surface 331, the lift gear 310 connected to the connection shaft 350 rotates a predetermined amount. However, when the pivot lever 340 returns to the original position by the tension spring 380, the lift gear 310 does not rotate together and only the pivot lever 340 returns to its original position. The lift gear 310 is rotated together, or not rotated, according to the rotational direction of the pivot lever 340 because the second forward direction bearing 372 is installed. That is, when the pivot lever 340 is rotated in a direction of being pushed, the second forward direction bearing 372 rotates the connection shaft 350 connecting the lift gear 310 together, while being rotated in a return direction, the pivot lever 340 is idle. The first forward direction bearing 371 functions to prevent reverse rotation due to the weight of the paper after the lift gear 310 is rotated with the pivot lever 340. When the lift gear 310 is rotated, the gear member 110 of the rotation shaft 130 engaged with the lift gear 310 is rotated. Accordingly, the lift lever 150 of the rotation shaft 130 lifts the knock-up plate 210 to a predetermined height. That is, at every one rotation of the cam gear 330, the knock-up plate 201 is raised to a predetermined height by the power transferred through the pivot lever 340 and the lift gear 310. Thus, when the cassette 200 is first inserted, the knock-up plate 201 is lifted step by step by rotating the cam gear 330 until the paper loaded on the knock-up plate 201 closely contacts the pickup roller 120. Then, after close contact is completed, the pickup roller 120 maintains the position as it is within a range of elastically pressing the paper down, for example, until 25 sheets of paper are consumed. When over 25 sheets of paper are consumed, the cam gear 330 rotates one turn to lift the knock-up plate 201 one more step so that the paper closely contacts the pickup roller 120 again. As a result, after the cassette 200 is inserted and the pickup roller 120 closely contact the paper, the knock-up plate 201 is lifted by one step by rotating the cam gear 320 one turn at each predetermined amount of consumed paper. Here, the solenoid 390 repeats on/off actions per one time for locking and locking releasing per one turn of the cam gear 330. For example, in the case of a cassette 200 accommodating a maximum of 500 sheets of paper and the maximum amount is loaded, assuming that the cam gear 330 must be basically rotated three turns to make the pickup roller 120 contact the paper and also rotated twenty two turns until one sheet of paper is left, the number of rotations of the cam gear 330 until 500 sheets of paper are all consumed is 20, counting from the point when the paper contacts the pickup roller 120 by the initial basic rotation number. Thus, 25 sheets of paper are consumed per one turn of the cam gear 330 in the above example. However, as the solenoid 390 operates once for each turn of the cam gear 330, the number of rotations of the cam gear 330 can be obtained by checking the number of operations of the solenoid 390, which means how many times the knock-up plate 201 are lifted. The present method is to detect the above so that the amount of the paper remaining in the cassette 200 can be calculated. To sequentially summarize the detection method, as shown in Figure 5, the paper feeding structure above is prepared (S1) and the amount of sheets of paper consumed whenever the knock-up plate 201 is lifted by the above-mentioned lifting means is calculated as a set value (S2). That is, as described above, the difference in the numbers of operation of the solenoid 390 for lifting the knock-up plate 201 toward the pickup roller 120 when the maximum amount of sheets of paper is loaded in the cassette 200 and when only one sheet of paper is left in the cassette 200 is calculated and the amount of consumed paper per one operation of the solenoid 390 is calculated and set. Then, when the cassette 200 enters the printing apparatus 100, the knock-up plate 201 is lifted until the loaded paper closely contacts the pickup roller 120 and the number of operations of the solenoid 390 are counted (S3). Here, counting is performed in consideration of the basic rotation. Next, the amount of paper remaining in the cassette 200 is calculated considering the counted number of operations and the set value above (S4). Then, when printing proceeds and as many sheets of paper is consumed as the number of the set value, the knock-up plate 201 is lifted one more step and it is detected that as many sheets of paper is consumed as the set value than the previous step. However, as the position of the knock-up plate 201 is the same until 25 sheets of paper are consumed in the present example, the amount of paper calculated has as large an error as the above. However, although not an accurate number of sheets of paper, what percentage of the maximum loading amount can be roughly seen. Thus, by displaying the amount of paper remaining calculated as above on a monitor, a user can determine whether a sufficient amount of paper is left in the cassette 200 without opening it. Thus, a user can always determine how many sheets of paper are left in the cassette 200 so that a printing job can be prevented from being stopped due to lack of paper. According to the method and paper feeding apparatus of a printing apparatus described above, the amount of sheets of paper remaining in the cassette can be easily identified in the state in which the cassette is installed at the printing apparatus.

Claims: A method of detecting the amount of sheets of paper remaining in a paper feeding cassette (200) of a printing apparatus, comprising the steps of: preparing a knock-up plate (201) pivotably located in said cassette on which paper is placed, a pickup roller (120) located in said printing apparatus to be capable of moving up and down within a predetermined range, rotating in close contact with the paper loaded in said printing apparatus so that the paper can sequentially enter a paper feeding path of said printing apparatus, a lifting means (300) for lifting said knock-up plate (201) step by step according to consumption of paper to locate the loaded paper within a range of closely contacting said pickup-roller (120); calculating a difference in the number of operations of said lifting means (300) for lifting said knock-up plate (201) toward said pickup roller when the maximum number of sheets of paper is loaded in said cassette (200) and when only one sheet of paper is left in said cassette and calculating the amount of consumed paper per one operation of said lifting means as a set value; lifting said knock-up plate (201) when said cassette enters in said printing apparatus until the loaded paper closely contacts said pickup roller and counting the number of operations of said lifting means then; and calculating the amount of paper (S) remaining in said cassette (200) considering the number of operations counted and said set value. The method as claimed in claim 1, wherein said lifting means (300) comprises: a rotation shaft (130) installed in said printing apparatus to rotate under said knock-up plate (201) such that a lift lever (150) installed at one side thereof can lift said knock-up plate during rotation; a cam gear (330) connected to said rotation shaft for rotating said rotation shaft a predetermined amount per one turn by being rotated by a predetermined driving source; and a solenoid (390) for locking said cam gear at each turn by selectively being interfered with a locking step (320) formed on said cam gear (330), wherein the number of operations of said lifting means is calculated by counting the number of operations of said solenoid (390).

Inventors: LIM KWANG-TAEK, LIM, KWANG-TAEK
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 1999
Main classification: G03G15
IPC codes: B65H7, G03G15, B65H1