Paper status indicator

Abstract: An imprinting mechanism (10) includes a sheet tray (22) and comprises a housing (14) and a spring bias device (28) within the housing (14). A sheet stack support (24) is positioned within the housing (14) and in contact with the spring bias (28), the spring bias (28) forcing the sheet stack support (24) towards a first position, the sheet stack support (24) being forced (against the spring bias (28)) to a second position when a stack of sheets is positioned thereon. A pivotally mounted indicator (20) is positioned within the housing (14) and includes first and second arm portions (30, 32), a first portion (30) being in contact with a surface of the sheet stack support (24) and a second portion (32) movable between visible and invisible locations, as viewed by a user. The first portion (30) is movable about the pivot (34) to position the second portion (32) to the visible location when a predetermined size stack of sheets remain in the sheet stack support (24). The indicator (20) is constructed of a single piece of molded plastic and its second portion (32) exhibits greater mass than its first (30) so that no spring or other bias device is required in its operation.

Description: Field Of The Invention This invention relates to sheet imprinting mechanisms, and more particularly to a device for indicating when a supply of sheets in the imprinting mechanism diminishes to a predetermined level. BACKGROUND OF THE INVENTION Copiers, laser printers, ink jet printers and other imprinting mechanisms today incorporate an ability to store and supply sheets of paper from a stack stored within their covers. As such, the sheet stack is invisible to the user. Normally, the only indication the user receives of a paper-out status is a signal when the paper supply has actually been exhausted. In many cases, that signal issues during a printing or copying job and requires that the job be interrupted to re-supply the paper stack. It is preferable that such a signal be given at a time that enables the user to interrupt the copying or print job at a convenient point, replenish the stack and continue the job. Some prior art sheet status indicators display the sheet supply status by means of an indicator in or behind a slot in the wall of a cassette that supports the sheets. This type of indicator is continually visible to the operator and is often ignored due to its continuous visibility. JP-A-57170338 relates to a residual-amount indicator comprising a cassette, a spring and support means in contact with the spring, wherein the spring bears upon a lower surface of a sheet stack and forces the support means towards a first position, wherein the support means is forced against the spring to a second position when a sheet stack is positioned thereon. An optical-electrical indication means for indicating the residual amount of paper in a paper cassette is provided comprising a residual-amount of paper indicator using green light-emitting elements and red light-emitting elements controlled by an electronic circuit which is adapted to indicate the residual amount of paper and to show same by turning on the respective number of green light-emitting elements and to provide an alarm indication when no more paper is available by turning on the red light-emitting element. JP-A-60262733 relates a sheet feed cassette for a photoelectronic copying machine comprising a cassette body which is loaded with stacked sheets and covered at its overpart with a cassette cover. Further a residual amount sensing/displaying device comprising an actuator piece, a sensing/displaying piece which in turn is formed by a sensor part and a displaying part is provided. The sensing/displaying piece is arranged such that the display part and the sensor part are able to rotate. The sensor part is in contact with the top of the sheets. When the copying machine is operating papers will be used and the residual amount of sheets is going to decrease. In this case, the sensor part in contact with the top of the sheets will rotate in a direction and accordingly the display part will rotate to show the display elements one after another. Accordingly, it is an object of this invention to provide an improved sheet supply status indicator for an imprinting mechanism. It is another object of this invention to provide a sheet supply status indicator that provides a visible indication when a sheet supply falls to a predetermined level. It is still another object of this invention to provide a sheet supply status indicator that provides an ability to indicate an incipient supply exhaustion at any desired level of remaining sheets. It is still another object of this invention to provide a sheet supply status indicator that is of simple construction and does not effect the operation of a sheet cassette tray with which it is associated even when it is inadvertently moved by a user. SUMMARY OF THE INVENTION An imprinting mechanism includes a sheet tray and comprises a housing and a spring bias device within the housing. A sheet stack support is positioned within the housing and in contact with the spring bias, the spring bias bearing upon a lower surface of said sheet stack means and forcing the sheet stack support towards a first position, the sheet stack support being forced (against the spring bias) to a second position when a stack of sheets is positioned thereon. A pivotally mounted indicator is positioned within the housing and includes first and second arm portions, a first portion being in contact with the lower surface of the sheet stack support and a second portion movable between visible and invisible locations, as viewed by a user. The first portion is movable about the pivot to position the second portion to the visible location when a predetermined size stack of sheets remain in the sheet stack support. The indicator is constructed of a single piece of molded plastic and its second portion exhibits greater mass than its first so that no spring or other bias device is required in its operation. DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of a print mechanism showing the relationship of a sheet tray to the overall mechanism; FIG. 2 is a plan view of the sheet tray; FIG. 3 is a schematic sectional view of the sheet tray of Fig. 2 taken along line A-A; FIG. 4A is an isometric view of the indicator mechanism; FIG. 4B is a plan view of the indicator mechanism; and FIG. 4C is a side view of the indicator mechanism. DETAILED DESCRIPTION OF THE INVENTION Hereafter, the invention will be described in the context of a laser printer having a removable paper tray, however, it is to be understood that the invention is usable with any imprinting or sheet handling mechanism wherein a sheet supply status indication is desired. Furthermore, while the invention will be described in the context of a paper handling mechanism, it is to be understood that any type of sheet stock may be included therewith. Referring now to Fig. 1, a printer 10 includes a cassette tray 12 that is slidable in relationship to housing 14. In order to replace a paper stack within paper tray 12, a user grasps upper portion 16 of tray 12 and pulls it in the direction of arrow 18. The withdrawal of tray 12 from housing 14 exposes the paper stack and enables its replenishment. When the paper stack reaches a predetermined level within paper tray 12, an indicator 20 drops down from behind upper portion 16 and becomes visible to the user. Indicator 20 signals the user that the paper supply has reached a predetermined level. Referring to Figs. 2 and 3, details of paper tray 12 will be described. Paper tray 12 comprises a frame portion 22 in which a movable sheet stack support 24 is positioned. Support 24 is pivotally mounted at axis 26 (see Fig. 3) and is adapted to support a stack of paper thereon. A spring bias 28 (schematically shown in Fig. 3) biases support 24 in an upward direction so that whatever sheets of paper are present thereon are brought into engagement with a sheet feed mechanism within printer 10 (not shown). In Fig. 3, the position of support 24 is shown when it is loaded with zero sheets of paper, fifty sheets of paper, and two hundred fifty sheets of paper. An Indicator 20 is a pivotally mounted, molded plastic piece that is shown in greater detail in Figs. 4a-4c. Indicator 20 comprises three portions, a curved arm 30, an arcuately shaped portion 32, and pivots 34. The mass of portion 32 is greater than that of arm 30 so that when indicator 20 is mounted by pivots 34, the weight of portion 32 moves arm 30 in a clockwise direction. As shown in Figs. 2 and 3, indicator 20 is pivotally mounted within tray 12 so that arm 30 bears upon the underside of stack support 24. Portion 32 of indicator 20, when mounted as shown in Fig. 3, rotates about pivots 34 so as to expose its lower extremity 36 through a window (not shown) in the underside of upper portion 16 of tray 12. The shaded version of indicator 20 shows its orientation when stack support 24 is fully depressed by a full stack of paper. In such a state, tip 36 is hidden from view behind upper portion 16 of tray 12. When tray 24 is elevated by spring 20 as a result of a depletion of the paper stack, the greater weight of portion 32 of indicator 20 causes arm 30 to follow the movement of stack support 24. As can be seen, tip 36 of indicator 20 becomes exposed when the position of stack support 24 reaches a predefined inclination with respect to axis 26. By properly adjusting the shapes of arm 30 and portion 32 of indicator 20, tip 36 can become visible at any desired level of remaining sheet supply. Preferably, it becomes visible when some paper still remains on stack support 24. It is to be noted that the weight distribution of indicator 20 about pivot 34 enables elimination of any spring bias or other mechanism. Furthermore, should the user attempt to lift tip 36, such action merely brings arm 30 out of contact with stack support 24 and does not affect its operation. It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.

Claims: A mechanism (10) having a sheet supply tray (22), the mechanism comprising: a housing (14); spring bias means (28) within said housing (14); sheet stack support means (24) within said housing (14) in contact with said spring means (28), said spring bias means (28) bearing upon a lower surface of said sheet stack support means (24) and forcing said sheet stack support means (24) towards a first position, said sheet stack support means (24) being forced against said spring bias means (28) to a second position when a sheet stack is positioned thereon; and characterized by pivotally mounted indicator means (20) having first and second arm portions (30,32), a first arm portion (30) in contact with said lower surface of said sheet stack support means (24) and a second portion (32) movable between visible and invisible locations as viewed by a user, said first arm portion (30) being movable to position said second portion (32) to said visible location when a predetermined size stack of sheets is present on said sheet stack support means (24). The mechanism (10) as claimed in claim 1 wherein said spring bias means (28) bears upon a lower surface of said sheet stack support means (24) and said first arm portion (30) of said indicator means (20) also bears upon said lower surface. The mechanism (10) as claimed in claim 2 wherein said second portion (32) of said indicator (20) is of greater mass than said first arm portion (30) and creates a moment about a pivot (34) to cause said first portion (30) to bear upon said lower surface of said sheet stack support means (24). The mechanism (10) as claimed in claim 3 wherein said indicator means (20) is pivotally mounted in a fixed relation with respect to movements of said sheet stack support means (24). The mechanism (10) as claimed in claim 4 wherein said second portion (32) is arcuately shaped and exhibits an end tip (36), said end tip (36) extending through an aperture in said housing (14) when said predetermined sheet stack size is present on said sheet stack support means (24). The mechanism (10) as claimed in claim 5 wherein said indicator means (20) comprises a molded unitary plastic part, said indicator means (20) including pivots (34) extending therefrom for mounting in said sheet supply tray (22).

Inventors: FETHEROLF WILLIS G, YERGENSON ROBIN P, FETHEROLF, WILLIS G., YERGENSON, ROBIN P.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1993
Main classification: B65H1
IPC codes: B41J11, B41J29, B65H1, B65H7