Method and apparatus for limiting torque in a feeder

Abstract: A method and device for reducing the maximum torque to rollers (16) mounted on a drive shaft (12) of a drive roller assembly. By using a plurality of slip clutches (20), each for engaging an individual roller (16) to the drive shaft (12) and setting a maximum torque for the individual rollers (16), each roller (16) is coupled to the drive shaft (12) when the tangential force exerted on the roller (16) does not exceed the maximum torque, and each roller (16) is mechanically decoupled from the drive shaft (12) when the tangential force exerted on the roller (16) exceeds the maximum torque. Because each roller (16) has a separate slip clutch (20), each roller (16) can be mechanically decoupled from the drive shaft (12) without affecting the other rollers (16) coupled to the drive shaft (12).

Description: The present invention relates generally to a sheet or envelope feeder and, more specifically, to the feeding mechanism of a feeder. Sheet and envelope feeders are commonly used in an envelope insertion system where envelopes are fed, one at a time, into an envelope inserting station, and enclosure documents are released into a gathering device for collation before the enclosure documents are inserted into the envelope at the envelope inserting station. They are also used in many different types of printers, photo copiers, print presses, and so forth. In those feeders, the most commonly used feeding mechanism is a drive roller assembly having a plurality of rollers mounted on a common shaft to be driven by a motor for rotation. A sheet feeder is described in EP-A-0 737 589. A typical envelope printer 100 is shown in Figure 1. As shown, the printer 100 has a rack 102 for supporting a stack of envelopes 104 to be fed into the printing area 106 . The feeding mechanism of the printer 100 comprises a set of six (6) drive rollers 108 for moving the envelopes 104 , one at a time, into the printing area 106 . On top of each drive roller 108 is a separator 110 forming a separation gap 112 to admit one (1) envelope 104 at a time into the printing area 106 . The separation gap 112 Is adjustable according to the thickness of the envelope 104. In a prior art drive roller assembly 120 , as shown in Figure 2 , the drive rollers 108 are fixedly mounted on a drive shaft 114 . The drive shaft 114 is operatively connected to a motor 116 for rotation. A torque limiting device 118 is mounted between the motor 116 and the drive shaft 114 to set a maximum torque such that when the tangential force 122 exerted on the periphery 124 of one or more of the rollers 108 exceeds the maximum torque, all the rollers 108 , along with the drive shaft 114 , are mechanically decoupled from the motor 116 . In order to accommodate envelopes having certain ranges of thickness, the maximum torque for a feeding mechanism in a printer Is set to usually about 10 pounds (about 44.5 N). Accordingly, when the motor 116 is turning, the rollers 108 are stopped only when the tangential force 122 exceeds ten (10) pounds (44.5 N). If an operator accidentally inserts a finger Into one of the separation gaps 112 , this would result in discomfort or even injury to the operator. In order to reduce this safety hazard, it would be necessary to substantially reduce the maximum torque. However, with the driving assembly 120 as shown, it would be impractical to reduce the maximum torque far beyond the ten (10) pound (44.5 N) limit for this would adversely affect the feeding function of the feeding mechanism. It is, therefore, desirable to provide a method and a device for reducing the maximum torque of the driving rollers without adversely affecting the feeding function of the drive roller assembly while greatly reducing the safety hazard to the operator. The present invention provides a method and a device for reducing the maximum torque to the rollers in a feeder for feeding substantially flat items such as printed documents, envelopes, cardboards and so forth. While the maximum torque to the individual rollers of the feeder is substantially reduced so as to greatly reduce the safety hazard to the operator, the feeding function of the feeder is not adversely affected. The device for reducing maximum torque, according to the present invention, comprises a drive roller assembly which includes: a drive shaft having a longitudinal axis operatively connected to a driving device for rotation about the longitudinal axis; a plurality of rollers mounted on the drive shaft for motion; and a plurality of torque limiting devices, each separately engaged with a roller for mechanically coupling the roller to the drive shaft and setting a maximum torque to the roller so that the roller is driven along with the drive shaft when the torque produced by the tangential force exerted on the roller does not exceed the maximum torque and the roller is mechanically decoupled from the drive shaft when the torque produced by the tangential force exerted on the roller exceeds the maximum torque, while such decoupling is accomplished without affecting the motion of the other rollers. Accordingly, the method for reducing the torque to the drive rollers mounted on a common drive shaft in a drive roller assembly, according to the present invention, comprises the step of engaging a separate torque limiting device to each roller for mechanically coupling the roller to the drive shaft and setting a maximum torque to the roller so that the roller is driven along with the drive shaft when the torque produced by the tangential force exerted on the roller does not exceed the maximum torque and the roller is mechanically decoupled from the drive shaft when the torque produced by the tangential force exerted on the roller exceeds the maximum torque. Because each roller has a separate torque limiting device for setting the maximum torque, a roller can be mechanically decoupled from the drive shaft without adversely affecting the motion of the other rollers. In other words, the method and device for reducing the torque to the drive rollers mounted on a common drive shaft in a drive roller assembly, according to the present invention, replaces a single torque limiting device for the entire drive roller assembly with a plurality of torque limiting devices, one for each roller. With each roller having a separate torque limiting device, the rollers will share the torque required for the entire feeding mechanism to function properly. Therefore, the maximum torque set for each of the rollers is only a fraction of the maximum torque when a single torque limiting device is used for the entire drive roller assembly. The method and device, according to an embodiment of the present invention, will become apparent upon reading the description taken in conjunction with Figure 3 to Figure 8. Figure 1 is a perspective view of a typical printer having a feeder to move the materials to be printed into the printing area. Figure 2 is a schematic illustration of a prior art drive roller assembly which can be used in the feeder as shown in Figure 1. Figure 3 is a schematic illustration of the drive roller assembly, according to an embodiment of the present invention, which can also be used in the feeder as shown in Figure 1 and other feeders. Figure 4 is a top view of part of a drive shaft to be used in the drive roller assembly, according to the preferred embodiment of the present invention, showing four pin holes axially drilled through the drive shaft. Figure 5 is a top view of part of the drive roller assembly, according to the preferred embodiment of the present invention, showing two pairs of rollers with slip clutches. Figure 6 is a cross sectional view of a roller showing the pulley and the hub of a roller. Figure 7 is a side view of a roller showing the groove on one of the hub side-surfaces. Figure 3 illustrates a drive roller assembly 10 which can be used in a feeder for feeding substantially flat items. The drive roller assembly 10 comprises a common drive shaft 12 operatively connected to a driving device 14 for rotating motion, a plurality of rollers 16 mounted on the common drive shaft 12 , with a gap 15 separating two adjacent rollers 16 , and a plurality of slip clutches 20 , each mounting on the drive shaft 12 to mechanically couple a roller 16 to the drive shaft 12 so that the roller 16 is driven by the drive shaft 12 . Each slip clutch 20 also separately sets a maximum torque for a respective roller 16 so that when torque produced by a tangential force 112 exerted on the periphery 22 of a roller 16 exceeds the maximum torque, the roller 16 is mechanically decoupled from the drive shaft 12 . When decoupled, the roller 16 does not rotate along with the drive shaft 12. Because the maximum torque on each roller 16 is set by a separate slip clutch 12 , the disengagement of one roller 16 does not affect the rotating motion of other rollers 16 , if the tangential force 112 exerted on the periphery 22 of the other rollers 16 does not exceed the maximum torque set by the respective slip clutches 20 . With each roller 16 being torque limited by a separate slip clutch 20 , the total maximum torque to the entire drive roller assembly 10 is substantially proportional to the number of the rollers 16 on the common drive shaft 12 . For example, if the required feeding torque of the drive roller assembly 10 is ten (10) pounds, and there are four (4) rollers 16 mounted on the drive shaft 12 with each roller 16 having a separate slip clutch 20, then the required maximum torque for each roller 16 is substantially equal to two and one-half (2.5) pounds (about 11 N). It is unlikely that this maximum torque to each roller creates a safety hazard to an operator. Accordingly, the limiting torque reduction method includes in a drive roller assembly 10 a plurality of drive rollers 16 mounted on a common drive shaft 12 , with each roller 16 operatively connected to a separate slip clutch 20 in order to mechanically couple the roller 16 to the drive shaft 12 . Each slip clutch 20 separately sets a maximum torque to a respective roller 16 so that when the tangential force 112 exerted on the periphery 22 of a roller 16 exceeds this maximum torque, the roller 16 is mechanically decoupled from the drive shaft 12 without affecting the motion of the other rollers 16 . It should be noted that the drive roller assembly 10 shown in Figure 3 is for illustrative purposes only. In practice, there are many embodiments that can be used to carry out the method of the present invention. The preferred embodiment of the present invention is illustrated in Figures 4 through Figure 7. Figure 4 shows part of the drive shaft 12 to be used in the drive roller assembly 10 . As shown, a plurality of holes 23 are axially drilled through the drive shaft 12. Each of the holes 23 is used for fitting a dowel pin 32 as shown in Figure 5. In Figure 5, there are shown four (4) drive rollers 16 mounted on a section of the drive shaft 12 . As shown, the rollers 16 are grouped into two (2) pairs ( 16a, 16b ), ( 16c, 16d ), with a gap 18 between the rollers of the same pair, and a gap 17 between the pairs. Each roller 16a - 16d has a hub 30 having a V-shape groove 34 (see Figure 5) to be engaged with a dowel pin 32 to prevent the rollers 16a - 16d from moving along the longitudinal axis 13 of the drive shaft 12 in normal operation. A compression spring 36 is mounted on the drive shaft 12 within the gap 18 to provide an urging force against the rollers 16a - 16d of the same pair. When the dowel pin 32 is seated in the V-shape groove 34 on the hub 30 of a roller 16a - 16d , the urging force applied by the compression spring 36 creates a frictional force between the dowel pin 32 and the groove 34 . When the drive shaft 12 rotates, the dowel pin 32 couples the respective roller 16a - 16d to the shaft 12 . However, when the tangential force 112 (Figure 3) exerted on a roller 16a - 16d exceeds the frictional force, the dowel pin 32 rides up and out of the groove 34 of the respective roller 16a - 16d, mechanically decoupling the respective roller 16a - 16d from the shaft 12 . As the drive shaft 12 continues to rotate, the dowel pin 32 either briefly bumps through the groove 34 and allows the roller 16a - 16d to keep slipping, or returns to the groove 34 to drive the roller 16a - 16d if the tangential force has been reduced to below the frictional force between the dowel pin 32 and the groove 34 . In this respect, the dowel pin 32 in the groove 34 acts as a slip clutch 20 (Figure 3) which mechanically couples the respective roller 16a - 16d to the drive shaft 12 and sets the maximum torque to the respective roller 16a - 16d . The maximum torque is determined partially by the friction between the dowel pin 32 and the groove 34 and partially by the urging force of the compression spring 36 . Because each roller 16a - 16d has a separate slip clutch (dowel pin 32 and groove 34 ), the motion of one (1) roller 16a - 16d is not affected by whether any of the other rollers 16a- 16d are mechanically decoupled from the drive shaft 12 . Each roller 16a - 16d is mechanically coupled by the respective dowel pin 32 to the drive shaft 12 so long as the torque produced by the tangential force exerted on that roller 16a - 16d does not exceed the maximum torque. Optionally, a washer 44 can be placed between the spring 34 and the engaging roller 16a - 16d so as to provide a smooth sliding surface for the rollers 16a - 16d during slipping. Figure 6 shows a cross-sectional view of the rollers 16a - 16d . As shown, the rollers 16a - 16d comprise a pulley 37 with the hub 30 which is concentric about a mounting center hole 42 . The pulley 37 also has a concentric outer rim 38 to secure a roller surface 40 for moving a fed item. There is also shown the V-shaped groove 34 on the hub 30 with an inclusive angle α. Preferably, the angle α is substantially equal to ninety (90) degrees. Figure 7 is the side view of the rollers 16a - 16d showing the groove 34 located on a side surface 46 of the hub 30 . The side surface 46 is substantially perpendicular to the axis of the center hole 42. Thus, when the rollers 16a - 16d are mounted to the drive shaft 12, the groove 34 and the side surface 46 are substantially perpendicular to the longitudinal axis 13 of the drive shaft 12 . Although the invention has been described with respect to a preferred embodiment thereof, it will be understood by those skilled In the art that the foregoing and various other changes, omissions and deviations in the form and detail thereof may be made without departing from the scope of this invention, as defined by the claims.

Claims: A method of reducing the torque to a plurality of drive rollers (16) mounted on a drive shaft (12) in a drive roller assembly (10), wherein the drive roller assembly (10) encounters a tangential force during a feeding operation of substantially flat objects, said method comprising the step of: engaging a separate torque limiting device (20) on each roller (16) for mechanically coupling the roller (16) to the drive shaft (12) and setting a maximum torque so that the roller (16) is driven along with the drive shaft (12) when the torque produced by the tangential force exerted on the roller (16) does not exceed the maximum torque and the roller (16) is individually mechanically decoupled from the drive shaft (12) when the torque produced by the tangential force exceeds said maximum torque. The method of Claim 1, wherein the torque limiting device for each roller is a slip clutch (20). The method of Claim 1, wherein each roller (16) is mechanically decoupled from the drive shaft (12) without adversely affecting other rollers that are mechanically coupled to the drive shaft. A drive roller assembly (10) in a feeder which encounters a tangential force during a feeding operation of substantially flat objects (104), said drive roller assembly (10) comprising: (a) a drive shaft (12) having a longitudinal axis operatively connected to a driving device (14) for rotation about the longitudinal axis; (b) a plurality of rollers (16) mounted on the drive shaft (12) for motion; and (c) a plurality of torque limiting devices (20) each for mechanically coupling an individual roller (16) to the drive shaft (12) and setting a maximum torque for the roller (16) so that the roller is driven along with the drive shaft (12) when the torque produced by the tangential force exerted on the respective roller does not exceed the maximum torque and the roller (16) is individually mechanically decoupled from the drive shaft (12) when the torque produced by said tangential force exceeds the maximum torque. The drive roller assembly of Claim 4, wherein the torque limiting device comprises a slip clutch (20). The drive roller assembly of Claim 4 or 5, wherein each roller has a groove (34) substantially perpendicular to the longitudinal axis of the drive shaft, said drive roller assembly further comprising: (a) a plurality of pins (32) axially located on the drive shaft (12) with each pin seated in a groove of a corresponding roller; and (b) means (36) for providing an urging force on each roller (16) against the respective pin (32) in order to create a frictional force between the pin (32) and the groove (34) for setting the maximum torque for the respective roller (16) so that the pin (32) mechanically couples the respective roller (16) to the drive shaft (12) when the torque produced by the tangential force exerted on the roller does not exceed the maximum torque and the pin (32) rides up and out of the groove (34) of the roller thereby mechanically decoupling the respective roller from the drive shaft when the torque produced by the tangential force exerted on the roller exceeds the limiting force. The drive roller assembly of Claim 6, wherein the rollers are grouped into pairs with a gap (18) between each roller pair and wherein the force urging means comprises at least a compression spring (36) mounted in the gap (18) of the roller pair so as to provide the urging force in a direction substantially perpendicular to the longitudinal axis of the drive shaft (12). The drive roller assembly of Claim 6, wherein each roller (16) has a hub (30) having a side surface substantially perpendicular to the longitudinal axis of the drive shaft for forming the groove (34) in the roller. The drive roller assembly of Claim 6, wherein each roller (16) has a pulley (37) connecting the hub (30) to an outer rim (38) concentric to the drive shaft (12), the outer rim (38) providing a roller surface for feeding the substantially flat objects. The drive roller assembly of Claim 6, wherein the groove (34) in each roller is V-shaped. The drive roller assembly of Claim 10, wherein the groove (34) has an inclusive angle substantially equal to ninety (90) degrees. The drive roller assembly of Claim 6, further comprising a plurality of washers (44) each placed between a respective roller (16) and the force urging means (36) so as to provide a smooth surface for smooth slipping when the roller is mechanically decoupled from the drive shaft (12).

Inventors: KULPA WALTER J, PRITCHETT WAYNE W, SETTE PAUL R, SLOAN RICHARD A JR, KULPA, WALTER J., PRITCHETT, WAYNE W., SETTE, PAUL R., SLOAN, RICHARD A., JR.
Applicants: PITNEY BOWES INC, PITNEY BOWES INC.
Application year: 2000
Main classification: B65H3
IPC codes: B65H3