Sheet feed mechanism

Abstract: A sheet feed mechanism for feeding sheets (P) one at a time, comprising a hopper (1) loaded with a stack of sheets (P), a feed roller (2) disposed near the outlet of the hopper (1), and a resilient tongue (3) held in resilient contact with the central section (8) of the feed roller (2). The central section (8) of the feed roller (2) is provided with an alternate circumferencial arrangement of low friction portions (9-1, 9-2, 9-3) and high friction portions (10-1, 10-2, 10-3). The friction coefficient between the sheet (P) and the low friction portions (9-1, 9-2, 9-­ 3) is smaller than that between the sheet (P) and the tongue (3), and the friction coefficient between the sheet (P) and the high friction portions (10-1, 10-2, 10-3) is greater than that between the sheet (P) and the tongue (3).

Description: The present invention relates to a sheet feed mechanism for feeding a plurality of stacked sheets one at a time. Facsimile equipment and printers have each a hopper for accommodating a stack of a plurality of sheets, and a sheet feed mechanism for feeding the sheets one at a time from the hopper to feed the sheet for reading characters printed on the sheets or for printing characters on the sheet. British Patent No. 1,225,883 discloses such a sheet feed mechanism, which comprises a hopper, a feed roller disposed adjacent to the outlet of the hopper so as to be in contact with the lowermost sheet, and a sheet restricting member disposed opposite to the feed roller. In feeding the sheets, the feed roller drives the lowermost sheet while the sheet restricting member restrains the rest of the sheets lying on the lowermost sheet in contact with the feed roller. The sheet restricting member can be moved substantially perpendicularly to the sheets placed in the hopper. Accordingly, the width of a gap formed between the sheet restricting member and the feed roller at the outlet of the hopper can be varied according to the thickness of the sheets. This sheet feed mechanism, however, has a problem that, in some cases, a sheet warped sideways driven by the feed roller interferes with the sheet restricting member. The width of the gap between the sheet restricting member and the feed roller must be increased to avoid the interference between the sheet and the sheet restricting member. However, increase in the width of the gap affects adversely the restricting function of the sheet restricting member, excessive increase in the width of the gap entails the feed of a plurality of superposed sheet at a time, which makes the normal printing operation of the printer or the normal character reading operation of the facsimile impossible. FR-A-2588538 discloses a sheet feed mechanism suitable for paper sheets, utilising a resilient tongue arrangement which engages spaced friction rings on a feed roller. US-A-2705636 discloses a sheet feed mechanism suitable for rigid cardboard sheets in which a tongue is resiliently pressed against the central section of a feed roller, which is provided with an alternate circumferential arrangement of axial low friction and high friction portions, for producing an intermittent feed. It is an object of the present invention to provide an improved sheet feed mechanism capable of surely separating the sheets and transporting them without curling. To this end, the sheet feed mechanism according to the present invention is characterised in that the feed roller has sheet drag sections with substantially uniform circumferential frictional properties, respectively disposed at opposite ends of the central section and outwardly of the tongue, said drag sections in use, continuously frictionally engaging the sheet outwardly of the central section. Thus, the sheet feed mechanism of the present invention is able to feed sheets smoothly without interfering with the sheet. Furthermore, the sheet feed mechanism of the present invention separates superposed sheets surely and feeds them one at a time. Still further, the sheet feed mechanism of the present invention is capable of feeding various kinds of sheets without requiring any adjustment of the component parts. The above and other objects, features and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawing, wherein; Figure 1 is a schematic perspective view of a sheet feed mechanism embodying the present invention; Figure 2 is a perspective view of a feed roller shown in Figure 1; Figure 3 is a sectional view taken on line A-A' in Figure 2; Figure 4 is a fragmentary sectional view of the sheet feed mechanism of Figure 1, loaded with sheets P; Figure 5 is a fragmentary sectional view similar to Figure 4, showing a state in which the leading edge P a of the lowermost sheet P₀ is caught between the feed roller and a tongue; Figure 6A is a fragmentary sectional view of the sheet feed mechanism of Figure 1, showing a state in which the sheet P₀ is in contact with a low friction portion of the feed roller; Figure 6B is a fragmentary sectional view similar to Figure 6A, showing a state in which the sheet P₀ is in contact with a high friction portion of the feed roller; Figure 6C is a fragmentary sectional view similar to Figure 6A, showing a state in which the sheet P₀ is in contact with another low friction portion of the feed roller; and Fig. 6D is a fragmentary sectional view similar to Fig. 6A, showing a state in which the sheet P₀ is in contact with another high friction portion of the feed roller. With reference to Fig. 1, a hopper 1 has a bottom wall declining toward the front edge 1a thereof. The hopper 1 is loaded with sheets P. The sheets P are caused to slide downward by the force of gravity and the leading edges of the sheets P are in contact with a feed roller 2 disposed near the front edge 1a of the bottom wall of the hopper 1 or with a resilient tongue 3 placed in contact with the central portion of the feed roller 2. The tongue 3 has one end pressed against the feed roller 2 with a pressing member 5 pressed against the tongue 3 with a spring 4 having one end attached to a frame, not shown. A portion of the tongue 3 in contact with the feed roller 2 presses the sheet P drawn out from the hopper 1 by the feed roller 2 against the feed roller 2 and applies a frictional resistance against the advancement of the sheet P. Another portion of the tongue 3 not in contact with the feed roller 2 holds the sheet P not in contact with the feed roller 2 in place on the hopper 1. Guide plates 6-1 and 6-2 are extended with a gap therebetween after the feed roller 2 to guide the sheet P fed from the hopper 1 by the feed roller 2. A pair of drive rollers 7-1 and 7-2 each having an elastic circumference are disposed in slots formed in the guide plates 6-1 and 6-2 so as to be in contact with each other within the gap between the guide plates 6-1 and 6-2. The drive roller 7-1 is rotated in the same direction as the feed roller 2 while the drive roller 7-2 is rotated in a direction opposite the direction of rotation of the feed roller 2. The feed roller 2, the drive rollers 7-1 and 7-2 are rotated synchronously at the same surface speed to feed and convey the sheet P. The feed roller 2 will be described in detail with reference to Figs. 2 and 3. As shown in Fig. 2, the feed roller 2 has a central section 8 engaging the tongue 3. The circumference of the central section 8 has an alternate arrangement of axial low friction portions 9-1, 9-2 and 9-3 and axial high friction portions 10-1, 10-2 and 10-3. The low friction portions 9-1, 9-2 and 9-3 are formed of a low friction material, such as polyacetal. The high friction portions 10-1, 10-2 and 10-3 are formed of a high friction material, such as rubber. Sheet drag sections 11-1 and 11-2 are formed contiguously with the opposite ends of the central section 8, respectively. The circumferences of the sheet drag sections 11-1 and 11-2 are formed, for example, of silicon rubber. When the leading edge P a of the sheet P reaches the rotating feed roller 2, the sheet drag sections 11-1 and 11-2 direct the leading edge P a of the sheet P toward the tongue 3. Sheet support sections 12-1 and 12-2 are formed contiguously with the respective outer ends of the sheet drag sections 11-1 and 11-2, respectively. The circumferences of the sheet support sections 12-1 and 12-2 are formed, for example, of polyacetal. The sheet support sections 12-1 and 12-2 prevent the sheet P from curling and guides the sheet P into the gap between the guide plates 6-1 and 6-2. The central section 8, the sheet drag sections 11-1 and 11-2 and the sheet support sections 12-1 and 12-2 are substantially the same in diameter. Referring to Fig. 3, axial fine furrows 13 are formed in the contact surfaces of the high friction portions 10-1, 10-2 and 10-3. The furrows 13 are formed in the contact surfaces to secure a sufficient frictional driving action of the high friction portions 10-1, 10-2 and 10-3 even if powdered paper sticks to the high friction portions 10-1, 10-2 and 10-3. The low friction portions 9-1, 9-2 and 9-3, the high friction portions 10-1, 10-2 and 10-3, and the tongue 3 are formed of materials meeting a relation expressed by µ₁ < µ t < µ₂ where µ₁ is the friction coefficient between the low friction portions 9-1, 9-2 and 9-3 and the sheet P, µ₂ is the friction coefficient between the high friction portions 10-1, 10-2 and 10-3 and the sheet P, and µ t is the friction coefficient between the tongue 3 and the sheet P. The operation of the sheet feed mechanism will be described hereinafter. As shown in Fig. 4, the sheet P placed on the bottom wall of the hopper 1 are caused to slide downward by the force of gravity and the leading edges P a of the sheets P are in contact with the feed roller 2 or the tongue 3. As the feed roller 2 is rotated in the direction of an arrow R, the sheet drag sections 11-1 and 11-2 urges the lowermost sheet P₀ so that the leading edge P a of the lowermost sheet P₀ enter between the feed roller 2 and the tongue 3 as shown in Fig. 5. In this state, the tongue 3 applies a frictional resistance to the sheet P₀. When the low friction portion 9-1, 9-2 or 9-3 engages the sheet P₀ as shown in Fig. 6A, the sheet P₀ remains stationary, because µ₁ < µ t and hence the frictional resistance of the tongue 3 is greater than the frictional driving force of the feed roller. When the high friction portion 10-1, 10-2 or 10-3 engages the sheet P₀ as shown in Fig. 6B, the sheet P₀ is advanced, because µ t < µ₁ and hence the frictional driving force of the feed roller 2 is greater than the frictional resistance of the tongue 3. The pair of drive rollers 7-1 and 7-2 disposed after the feed roller 2 are rotated synchronously with the feed roller 2 at the same surface speed as the feed roller 2 respectively in directions indicated by arrows R₁ and R₂ in Fig. 5. The sheet separating function of the sheet feed mechanism will be described hereinafter. When the low friction portion 9-1 is in contact with the sheet P₀ and the preceding sheet P₁ is caught between the drive rollers 7-1 and 7-2 as shown in Fig. 6A, the succeeding sheet P₀ is held stationary by the frictional resistance of the tongue 3 while the preceding sheet P₁ is advancaed by the drive rollers 7-1 and 7-2, and hence the distance d₁ between the leading edge of the succeeding sheet P₀ and the trailing edge of the preceding sheet P₁ increases gradually as the drive roller 7-1 and 7-2 rotate. In a state where the high friction portion 10-2 is in contact with the sheet P₀ and the preceding sheet P₁ is caught between the drive rollers 7-1 and 7-2 as shown in Fig. 6B, the succeeding sheet P₀ is advanced by the feed roller 2 while the preceding sheet P₁ is advanced by the drive rollers 7-1 and 7-2 and hence the distance between the leading edge of the succeeding sheet P₀ and the trailing edge of the preceding sheet P₁ is kept substantially at a constant distance d₂ (d₁ < d₂). In a state where the low friction portion 9-2 is in contact with the sheet P₀ and the preceding shaet P₁ is caught between the drive rollers 7-1 and 7-2 as shown in Fig. 6C, the succeeding sheet P₀ is held stationary by the frictional resistance of the tongue 3 while the preceding sheet P₁ is advanced by the drive rollers 7-1 and 7-2 and hence the distance d₃ between the leading edge of the succeeding sheet P₀ and the trailing edge of the preceding sheet P₁ increases gradually. In a state where the high friction portion 10-3 is in contact with the sheet P₀ and the trailing edge of the preceding sheet P₁ has advanced beyond the drive rollers 7-1 and 7-2 as shown in Fig. 6D, the sheet P₀ is advanced by the feed roller 2 while the prceding sheet P₁ is advancad at the same speed as the succeeding sheet P₀ by another sheet feed mechanism, not shown, and hence the distance between the leading edge of the succeeding sheet P₀ and the trailing edge of the preceding sheet P₁ is kept substantially at a constant distance d₄ (d₃ < d₄). Thus, the sheet feed mechanism of the present invention separates the sheets P from each other to feed the sheets P surely one at a time. While the sheets P are fed successively, the sheet support sections 12-1 and 12-2 prevent the sheets P from curling so that the curled portion of the sheet P will not be folded between the drive rollers 7-1 and 7-2 and the sheet P will not be checked by the drive rollers 7-1 and 7-2. Although the invention has been described in its preferred form with a certain degree of particularly, it is to be understood that many variations and changes are possible in the invention without departing from the scope of the claims.

Claims: A sheet feed mechanism comprising: a hopper (1) loaded with a stack of sheets (P), a feed roller (2) disposed near the outlet (1a) of the hopper (1) and in contact with the sheets (P) stacked in the hopper (1), and a tongue (3) resiliently pressed against a central section (8) of the feed roller (2) on a sheet conveying path, the central section (8) of the feed roller (2) being provided with an alternate circumferential arrangement of axial low friction portions (9-1, 9-2, 9-3) and axial high friction portions (10-1, 10-2, 10-3) meeting a relation expressed by µ1 < µt < µ2 where µ1 is the friction coefficient between the sheet (P) and the low friction portions (9-1, 9-2, 9-3), µ2 is the friction coefficient between the sheet (P) and the high friction portions (10-1, 10-2, 10-3), and µt is the friction coefficient between the sheet (P) and the tongue (3), characterised in that the feed roller has sheet drag sections (11-1, 11-2) with substantially uniform circumferential frictional properties, respectively disposed at opposite ends of the central section (8) and outwardly of the tongue (3), said drag sections in use, continuously frictionally engaging the sheet outwardly of the central section. A sheet feed mechanism according to claim 1, wherein the feed roller (2) has sheet support sections (12-1, 12-2) respectively outside the sheet drag sections (11-1, 11-2). A sheet feed mechanism according to claim 1 or 2, wherein the contact surfaces of the high friction portions (10-1, 10-2, 10-3) are provided each with axial furrows (13). A sheet feed mechanism according to any preceding claim, wherein a pair of drive rollers (7-1, 7-2) are disposed on the sheet conveying path after the feed roller (2) with respect to a sheet feed direction. A sheet feed mechanism according to claim 4, wherein the surface speed of the drive rollers (7-1, 7-2) is substantially the same as that of the feed roller (2).

Inventors: KONISHI HIROSHI OKI ELECTRIC I, NOGUCHI MATSUSABURO OKI ELECTR, OTAKI NOBORU OKI ELECTRIC INDU, TADOKORO JOJI OKI ELECTRIC IND, KONISHI, HIROSHI OKI ELECTRIC INDUSTRY CO., LTD., NOGUCHI, MATSUSABURO OKI ELECTRIC IND. CO., LTD., OTAKI, NOBORU OKI ELECTRIC INDUSTRY CO., LTD., TADOKORO, JOJI OKI ELECTRIC INDUSTRY CO., LTD.
Applicants: OKI ELECTRIC IND CO LTD, OKI ELECTRIC INDUSTRY COMPANY, LIMITED
Application year: 1989
Main classification: B41J13
IPC codes: C08G69, B65H3, B41J13