Shredder with mechanical sensor

Abstract: A shredding machine (10) comprising a housing (11) containing cutting shafts (14,15) adapted to shred paper as the paper is passed through a shredding gap (13) between them, and a motor to cause rotation of the cutting shafts, having an operating means comprising first (17) and second (18) switching means to control supply of power to the motor, the first switching means (17) being operable through contact with the material and the second switching means (18) having an operating member which bears upon a guide surface (24) associated with one of the cutting shafts. The guide surface may be cam like such that the operating member (19) which bears upon it reciprocates as the guide surface (24) rotates, thus alternately opening and closing a switch which controls power to the motor. The shredder provides advantages over those currently known since the switching means allowing power to the motor are both mechanical, with no photoelectric or any other electronic sensors being required.

Description: This invention relates to an operating means for a shredding machine. Shredding machines such as paper shredders conventionally comprise a housing comprising a cutting mechanism, conventionally comprising two rotatable cutting shafts closely adjacent one another, there being defined a gap therebetween into which paper or other material to be shredded (hereinafter to be referred to as "paper" for convenience) may be fed when shredding is required. Such a shredding machine is hereinafter referred to as being of the kind specified. The cutting shafts are generally powered by an electric motor and it is desirable that operation of the motor be controlled in a manner such that a shredding operation is automated as much as possible. Accordingly, many paper shredders now comprise an electronic sensor, for example a photo-electric sensor, located at a position adjacent a duct through which paper is passed prior to engagement with the cutting rollers, and which causes the motor to operate when paper is sensed. A timing means is often provided in conjunction with the sensor such that when the paper has passed the sensor the motor continues to operate for a preset time thereafter, such that all the paper is shredded and none is left protruding from the nip when the motor stops. However, such sensors are relatively expensive and in the case of photo-electric sensors, are often susceptible to problems caused by dust or other matter blocking the path of light to the sensor. Mechanical switches have also been used but suffer from the problem that once the paper has passed the switch, the motor stops, leaving paper protruding from the nip. A shredding machine and operating means comprising first and second mechanical switches as in the preambles of claims 1 and 10 are known from DE-A-20 45 280. Accordingly, it is an object of the present invention to provide an improved operating means which overcomes or minimises the problems outlined above. According to one aspect of this invention there is provided a shredding machine comprising a housing, a cutting mechanism comprising two rotatable cutting shafts closely adjacent one another, adapted to shred material as the material is passed through a shredding gap between them, an inlet to guide the material to the shredding gap and a motor to cause rotation of the cutting shafts, first mechanical means adjacent to the inlet which is responsive to the presence of material to be shredded to move to an operative position in which power is supplied to the motor, the first mechanical means adopting an inoperative position in the absence of such material, and second mechanical means operative to delay cessation of the supply of power to the motor when the first mechanical means adopts its inoperative position, characterised in that the second mechanical means includes an operating member which bears upon a guide surface associated with one of the cutting shafts. Conveniently the first mechanical means comprises a sensing member which is physically moved to its operative position by paper in the inlet. Conveniently the second mechanical means is operative on most occasions to delay cessation, but not need be so operative on all occasions. Thus the second mechanical means may comprise a second sensing member moved to a closed position (corresponding to the supply of power to the motor) during the majority part of a cycle of the machine, for example being controlled by the drive shaft of the machine, or another member which rotates during operation of the machine. According to another aspect of the invention, there is provided an operating means for a shredding machine of the kind comprising a housing, a cutting mechanism comprising two rotatable cutting shafts closely adjacent one another, adapted to shred material as the material is passed through a shredding gap between them, an inlet which guides the material to the shredding gap, and a motor to cause rotation of the cutting shafts, the operating means comprising first and second mechanical means moveable between inoperative and operative positions to control supply of power to the motor, the first mechanical means being moveable by contact with the material, characterised in that the second mechanical means has an operating member which is adapted to bear upon a guide surface associated with one of the cutting shafts. The first and second mechanical means are conveniently arranged such that movement of one or both of the mechanical means to an operative position causes power to be supplied to the motor such that the cutting shafts rotate. Preferably the first mechanical means is operable through contact with the paper such that when paper is brought into contact with the first switching means, the first mechanical means is moved to an operative position, and power is supplied to the motor. Conveniently, the first mechanical means comprises a lever or other suitable member linked to a microswitch having a sensitivity suitable for such movement to be permitted. The lever is preferably located near the inlet but away from the shredding gap such that the microswitch is closed and power is supplied to the motor before any part of the paper enters the shredding gap. Conveniently, there are provided guides adjacent the lever to constrain the paper for movement towards the lever to ensure that passage of paper past the lever closes the associated microswitch. Conveniently, the lever is pivotally mounted, having a first end in a path of the paper and a second end associated with the microswitch. Preferably, the operating member of the second mechanical means bears upon a guide surface attached to or integral with one of the cutting shafts, such a guide surface being for example, a disc or plate. The operating member is also preferably pivotable, and may be pivotable about the same pivot point as the lever of the first mechanical means. The guide surface preferably has a configuration such that on rotation of the shaft, the operating member bearing upon the guide surface is displaced relative to and away from the axis of the shaft, preferably in a direction generally perpendicular to the axis. Accordingly, the guide surface may be of cam like configuration such that rotation of the shaft induces reciprocation in the operating member relative to the shaft, which in turn causes a microswitch associated with the operating member to move between inoperative and operative positions. As with the lever of the first mechanical means, the operating member of the second mechanical means may bear directly on the associated microswitch, but there may be provided an additional member associated with and pivotable with the operating member, which causes opening and closing of the associated microswitch. Conveniently, the guide surface is contoured when viewed in cross-section to provide a first part adapted to displace the operating member in a first direction to cause the associated microswitch to close, and a second part adapted to displace the operating member in a second direction to cause the microswitch to open or to permit the microswitch to open. Preferably, the length of the first part is greater than the length of the second part, such that the operating member is displaced in the first direction for a greater proportion of the time taken to complete one revolution of the cutting shaft than it is displaced in the second direction. Conveniently, the ratio of length of the first part to the second part is at least 3:1, preferably greater than 4:1. Preferably the guide surface is generally circular in cross-section, but having a generally chordal linear portion, the curved surface corresponding to the first part, and the generally chordal linear portion corresponding to the second part. Conveniently, the operating member is resiliently biased towards the guide surface, such that the operating member remains in good contact with the guide surface. The first and second mechanical means may comprise separate microswitches which are arranged in a supply circuit in parallel, such that if either of the microswitches is closed, power is supplied to the electric motor. Preferably however the first and second mechanical means share a common microswitch, such that the microswitch may be closed by the operating member of either of said mechanical means, to cause power to be supplied to the electric motor. Accordingly, when paper is introduced through the inlet and is brought into contact with the lever of the first mechanical means, power is supplied to the motor and the cutting shafts rotate. As the rotation continues, the guide surface also rotates and displaces the operating member in a reciprocating manner. Since the first and second mechanical means are in parallel relationship with each other, the mircroswitch of the second mechanical means may be opened when the operating member bears upon the second part of the guide surface, but power is maintained to the motor by virtue of the first mechanical means, provided that paper is maintained in contact with the lever of the first mechanical means. When an end of the paper passes past the lever of the first mechanical means, the associated microswitch opens, but there is a relatively high probability (at least 3:1) that the operating member of the second mechanical means will at that point be bearing on the first part of the guide surface, since the length of the first part is considerably greater than the second part. Accordingly, power is maintained to the motor by the microswitch until the cutting shaft carrying the guide surface rotates to a position wherein the operating member bears upon the second part of the guide surface. As such a point, the microswitch opens and the power supply to the motor is stopped. Preferably, the relative lengths of the first and second parts of the guide surface are such that momentum of the cutting shaft carrying the guide surface is insufficient to cause the shaft to rotate, after power to the motor has been stopped, from a position where the operating member bears upon the second part to a position where the operating member bears upon the first part. Accordingly, the cutting shaft always comes to rest at similar rotational positions. The microswitch may arranged in circuitry which is operative to effectively connect a resistance wire between the terminals of the motor when it moves to its open position, thus causing the electric motor to operate as a generator, and applying regenerative braking, causing the shafts to cease rotation more quickly than would be the case were the electric motor circuitry simply to be opened. It will be appreciated however, that the resistance should not be too high, since in such a case, the regenerative braking effect would be insufficient to bring the motor to rest before the operating member again bears upon the first part of the guide surface, thus closing the switch and resuming supply of power to the motor. The invention will now be described by way of example only, by reference to the accompanying drawings, wherein: FIGURE 1 is a cross-sectional view of a shredder in accordance with the invention viewed along the axes of the cutting shafts, and FIGURES 2A and 2B illustrates schematically the cam like operation of the guide surface and operating member. Referring first to Figure 1, there is shown a paper shredder 10 comprising a housing 11, in which there is provided an inlet duct 12 to enable paper to be fed to a shredding gap 13 between cutting shaft 14 and 15. The cutting shafts are powered in generally conventional manner by an electric motor (not shown), there being provided an operating means having a first, mechanical switching means 17 comprising an operating member 20 and a second, mechanical switching means 18 comprising an operating member 19. The first switching means 17 is mechanically operable through contact of paper and is located between the inlet duct 12 and the shredding gap 13 such that when paper is introduced through the inlet duct towards the shredding gap, the paper bears upon a member 20, conveniently afforded by a lever pivotable about a pivot point 21, which induces movement of the lever to close the microswitch 16 at button 16a and accordingly allows power to be supplied to the motor. The operating member 19 is preferably also afforded by a lever which pivots about pivot point 21, and bears upon a guide surface 24 which is attached to axle 25 of the first cutting shaft 14. The guide surface is generally circular in cross-section, having a generally curved portion 26 and a generally chordal linear portion 27 whose length is considerably less than that of the curved portion 26. Accordingly, rotation of the cutting shaft 14 and associated guide surface 24 induces reciprocating movement of the operating member 19 in a direction towards and away from the axle 25 and generally perpendicular thereto. Conveniently both the operating member 20 of the first switching means 17, and the operating member 19 of the second switching means 18 are arranged to operate on the same microswitch 16. Thus, the microswitch may be closed either by the action of the operating member 20, caused by the introduction of paper into the inlet duct 12 of the machine, or by the operating member 19 caused by the engagement between the operating member 19 and the surface 24 of the axle 25. Thus as paper passes through the inlet duct beyond the first operating member 20, the microswitch will be maintained closed as long as the operating member 19 is in contact with the guide surface 24. The applicants have found that a ratio of at least 4:1 for the relative length of the curved portion and chordal linear portion is particularly suitable to provide such a probability, and the applicants have found that in approximately 90% of cases, the cutting shafts will continue to rotate to a sufficient degree for complete paper shredding to be accomplished. Of course if desired separate microswitches for the two switching means may be utilised, the two microswitches being wired in parallel. Alternatively, by the use of a single microswitch, the circuit may be such that when the microswitch is opened. there is provided an electrically conductive bridge comprising a resistance wire between the live and neutral terminals thereof, causing continued rotation of the electric motor under the impetus of its momentum to act as a generator, and thus causing the electric motor to cease rotation more quickly than would be the case were the circuit simply opened. The shredder provides advantages over those currently known since the switching means are both purely mechanical, with no photo-electric or other electronic sensors being required.

Claims: A shredding machine (10) comprising a housing (11), a cutting mechanism comprising two rotatable cutting shafts (14,15) closely adjacent one another, adapted to shred material as the material is passed through a shredding gap (13) between them, an inlet (12) to guide the material to the shredding gap (13) and a motor to cause rotation of the cutting shafts, first mechanical means (17) adjacent to the inlet which is responsive to the presence of material to be shredded to move to an operative position in which power is supplied to the motor, the first mechanical (17) means adopting an inoperative position in the absence of such material, and second mechanical means (18) operative to delay cessation of the supply of power to the motor when the first mechanical means adopts its inoperative position; characterised in that the second mechanical means (18) includes an operating member (19) which bears upon a guide surface (24) associated with one of the cutting shafts (14, 15). A shredding machine (10) according to claim 1 wherein the guide surface (24) has a cam like configuration such that rotation thereof induces reciprocation in the operating member (19). A shredding machine (10) according to claim 1 or claim 2 wherein the guide surface (24) has a first part (26) adapted to displace the operating member (19) in a first direction to cause an associated microswitch (16) to close, and a second part (27) adapted to displace the operating member (19) in a second direction to cause the associated microswitch (16) to open or to permit the associated microswitch (16) to open. A shredding machine (10) according to claim 3 wherein the length of the first part (26) of the guide surface (24) is greater than the length of the second part (27) of the guide surface (24), such that the operating member (19) is displaced in the first direction for a greater proportion of the time taken to complete one revolution of the cutting shaft (14, 15) upon which it bears, than it is displaced in the second direction. A shredding machine (10) according to claim 4 wherein the ratio of the length of the first part (26) to the second part (27) is at least 3:1. A shredding machine (10) according to any one of the preceding claims wherein the guide surface (24) is generally circular, but also has a generally chordal linear portion (27). A shredding machine (10) according to any one of the preceding claims wherein the guide surface (24) is attached to or integral with one of the cutting shafts (14, 15). A shredding machine (10) according to any one of the preceding claims wherein the operating member (19) is pivotable. A shredding machine (10) according to claim 8 wherein the first mechanical means (17) comprises a pivotally mounted lever (20), and wherein the lever (20) is pivotable about the same pivot point as the operating member (19). An operating means for a shredding machine (10) of the kind comprising a housing (11), a cutting mechanism comprising two rotatable cutting shafts (14,15) closely adjacent one another, adapted to shred material as the material is passed through a shredding gap (13) between them, an inlet (12) which guides the material to the shredding gap, and a motor to cause rotation of the cutting shafts (14, 15), the operating means comprising first and second mechanical means (17, 18) moveable between inoperative and operative positions to control supply of power to the motor, the first mechanical means (17) being moveable by contact with the material, characterised in that the second mechanical means (18) has an operating member (19) which is adapted to bear upon a guide surface (24) associated with one of the cutting shafts (14,15). An operating means according to claim 10 wherein the first and second mechanical means (17, 18) are arranged. such that movement of one or both of the mechanical means to an operative position causes power to be supplied to the motor such that the cutting shafts (14, 15) rotate. An operating means according to claim 10 or claim 11 wherein the first mechanical means (17) comprises a lever (20) linked to a microswitch (16) and wherein there are provided guides adjacent the lever (20) to constrain the material for movement towards the lever (20) to ensure that passage of material past the lever (20) closes the associated microswitch (16). An operating means according to any one of claims 10 to 12 wherein the guide surface (24) is attached to or integral with one of the cutting shafts (14, 15). An operating means according to claim 13 wherein the guide member (24) forms part of a disc or plate. An operating means according to any one of claims 10 to 14 wherein the operating member (19) of the second mechanical means (18) is pivotable. An operating means according to any one of claims 12 to 15 wherein the operating member (19) of the second mechanical means (18) is pivotable about the same pivot point as the lever (20) of the first switching means (17). An operating means according to any one of claims 10 to 16 wherein the guide surface (24) has a configuration such that on rotation of the associated cutting shaft (14, 15), the operating member (19) bearing upon the guide surface (24) is displaced relative to and away from the axis of the cutting shaft (14, 15). An operating means according to claim 17 wherein the guide surface (24) is of cam-like configuration such that rotation of the cutting shaft (14, 15) induces reciprocation of the operating member (19) relative to the cutting shaft (14, 15). An operating means according to any one of claims 10 to 18 wherein the guide surface (24) is contoured when viewed in cross section to provide a first part (26) adapted to displace the operating member (19) in a first direction to cause an associated microswitch (16) to close, and a second part (27) adapted to displace the operating member (19) in a second direction to cause the associated microswitch (16) to open or to permit the associated microswitch (16) to open. An operating means according to claim 19 wherein the length of the first part (26) of the guide surface (24) is greater than the length of the second part (27) of the guide surface (24), such that the operating member (19) is displaced in the first direction for a greater proportion of the time taken to complete one revolution of the associated cutting shaft (14, 15) than it is displaced in the second direction. An operating means according to claim 20 wherein the ratio of the length of the first part (26) to the second part (27) is at least 3:1. An operating means according to any of claims 10 to 21 wherein the guide surface (24) is generally circular in cross section, but also has a generally chordal linear portion (27). An operating means according to any one of claims 10 to 22 wherein the operating member (19) is resiliently biased towards the guide surface (24).

Inventors: ARIES PAUL ARTHUR, WATKINS STEPHEN CHRISTOPHER, ARIES, PAUL ARTHUR, WATKINS, STEPHEN CHRISTOPHER
Applicants: ACCO REXEL GROUP SERVICES PLC, ACCO-REXEL GROUP SERVICES PLC
Application year: 1997
Main classification: B02C18
IPC codes: B02C18