Hinged-arm pick mechanism

A pick mechanism includes a hinged pick arm which moves between a retracted position and a varying, operating position. The pick arm is anchored about a pivot axis and hinged along its length. Rotation of a pick roller along the arm while in contact with a media sheet induces a moment on the pick arm causing the pick arm to pivot and hinge. A first stop limits the pivoting motion. A second stop limits the hinging motion, Such pivoting and hinging is desirable to create an effective normal force enabling reliable picking of thick media sheets. Such motions are limited to prevent the pick roller from translating too far from a media separation ramp. If the pick roller translates too far, undesirable media buckling may occur during the pick operation.

BACKGROUND

This invention relates generally to media sheet feed mechanisms, and more particularly, to a media sheet pick and feed system which operates effectively regardless of media tray content and which enables easy re-loading of the media tray.

Print recording devices, such as printers, fax machines and copy machines, and print scanning devices often include an input media tray. A media sheet is picked from the input tray and fed along a media path to receive print recording or to undergo print scanning. One common mechanism for picking and feeding a media sheet employs a D-shaped wheel. During rotation of the wheel the curved portion contacts and picks a media sheet. Subsequent to the pick action the flat portion of the D-shaped wheel is adjacent to the picked media sheet, but out of contact with the media sheet. The media sheet is fed from the media tray while the flat portion of the wheel is adjacent but out of contact with the media sheet.

Another known pick mechanism includes a drive gear mounted on a shaft which in turn is coupled to a drive motor. The drive motor turns the shaft and drive gear during a pick operation. The drive gear engages a driven gear to which is rigidly connected a pick roller. Thus, the drive motor rotates the pick roller. The pick mechanism is moved into and out of contact with a media sheet to be picked by the rotation of the drive gear. When the drive gear rotates in one direction the driven gear and pick roller move into contact with a media sheet. Continued rotation in such direction causes the media sheet to be picked and moved onto a media feed path. Typically, rotation in the opposite direction causes the drive gear and pick roller to move out of contact with the media sheet. A shortcoming of this mechanism is that a spring-loaded tray is needed to bias the media sheets toward the pick range of the pick roller. Further, the media tray needs to be removed during reloading (or alternatively a mechanism is needed during reloading to depress the spring-loading plate which raises a media sheet into the pick range).

In U.S. Pat. No. 5,547,181 issued Aug. 20, 1996 to Underwood for “Media Sheet Pick and Feed System,” Underwood discloses a clutch mechanism which allows the pick roller to remain in contact with the media sheet as the media

e media tray along the feed path. In particular, the clutch disengages the drive gear from the drive motor allowing the pick roller (along with the drive gear and driven gear) to “free” wheel. This approach eliminates the need for a spring-loaded media tray.

DETAILED DESCRIPTION

Overview

The pick arm mechanism of this invention is implemented in a print recording system or a print scanning system, such as a printer, a fax machine, a copy machine, or an optical scanning device. Referring toFIG. 1, such a system10includes an operative device12, such as a print recording device or a print scanning device, along with an operations controller14and a media transport assembly16. The system10responds to commands input at a user interface panel (not shown) or input from a host device (e.g., a computer) to which the system10is coupled. In response to the command, the operations controller14generates signals which are sent to the media transport system16to move a media sheet into position for an operation (e.g., print recording; media scanning) by the operative device12.

Typically the system10includes an input tray including a stack of media sheets. A media sheet is picked from the stack and then fed along a feed path. Accordingly, the media transport assembly16includes mechanisms for a pick function18and mechanisms for a feed function20.

Referring toFIG. 2, in one embodiment the media transport assembly16includes one or more feed rollers22driven by a feed drive motor24through a feed transmission26. The transmission26typically includes a gear chain for mechanically coupling the feed rollers22to the drive motor24. The media transport assembly16also includes a pick roller30driven by a pick drive motor32through a pick transmission33. The feed drive motor24and the pick drive motor32respond to signals received from the operations controller14. In addition, sensors34are included which provide information to the operations controller14to allow desired control of operations. For example, a media position sensor is often included which enables the operations controller14to determine when to signal one of the drive motors24,32to stop or reverse directions.

Referring toFIG. 3, in an alternative embodiment the pick roller30is driven by the same drive motor24as the feed rollers22. In such embodiment a transmission26′ links both the feed rollers22and the pick roller30to the common drive motor24.

Hinged Pick Arm

Referring toFIG. 4, a pick arm assembly40is shown mounted to a frame42which also supports an input tray44. The pick arm assembly40includes one or more pick rollers46, the pick drive motor32and the pick transmission33, mounted to a distal portion48of a hinged pick arm50. Wires (not shown) or other signal transport medium couple the motor32to the operations controller14.

The pick arm assembly40is mounted to the frame42at an axle52which extends along a transverse section54of the assembly40. In one embodiment the pick arm assembly40is free to rotate about the axle52within a given rotational range of motion. In another embodiment the axle52may be coupled to a transmission which also is coupled to the pick rollers46. The pick arm50includes a first portion55(also referred to as the proximal portion) located proximal to the transverse section54and a second portion48(also referred to as the distal portion) located distally from the transverse section54.

The pick arm50is hinged at a hinge axis56. The distal portion48moves with one degree of freedom relative to the proximal portion55about the hinge axis56. In other embodiments additional degrees of freedom are implemented to also allow the distal portion to slide or translate longitudinally relative to the proximal portion55. In a preferred embodiment the distal portion48is spring-biased to maintain the distal portion48at a first orientation relative to the proximal portion55. In the best mode embodiment the first orientation is straight, although an angular orientation may be implemented instead. Various spring-like mechanisms may be used to implement the spring biasing. Referring toFIG. 5, in one embodiment a torsion spring60provides the bias to maintain the hinged pick arm50in the first orientation. In other embodiments, a compression spring, tension spring, leaf spring or sheet metal spring may be used. Still other known spring-like mechanisms may be used instead.

Pick Arm Movement Between Retracted Position and Operative Position

Referring again toFIG. 5, the hinged pick arm50rotates about an axis defined by the axle52. The pick arm50moves into an operative position adjacent to a media sheet58during a pick operation. It also is desirable that the pick arm50be retracted when the input tray44is removed, so that the tray44does not bump the pick arm50upon re-insertion. There are various known methods for moving a pick am between a retracted position and an operative position. Referring toFIGS. 4,6,7,8, and9, in one embodiment, a cam61is included to control the retraction of the pick arm50. The cam61is biased (seeFIG. 8) to maintain the pick arm50in a retracted position64. The cam60moves about an axis62and includes two contact points66,68. One contact point66enters physical communication with the pick arm assembly40at an area70as the cam60is biased to move the pick arm into the retracted position64. The other contact point68receives physical communication from the input tray44along a rail72when the input tray is inserted into frame42. In some embodiments the cam60is spring-biased as shown inFIGS. 8 and 9. In other embodiments the cam61is biased into the retracted position64, instead, by having a balance point away from axis62.

As the input tray44is inserted, the rail72contacts the point68of the cam60. The rail72has an inclined portion74where contact first occurs. As the tray44is pushed into the frame42, the point68moves up the inclined portion74of the rail72, then along a flat portion76. As the contact point68moves up the incline74, the cam60rotates about axis62in direction67. Cam60is a rigid structure so contact point66rotates with the cam60moving the contact point66in a direction away from the pick arm50. The pick arm50under its own weight falls, or more specifically rotates about axle52, to stay supported by the contact point66. During the rotation of the cam60, the pick arm50eventually rotates enough for the pick roller46to make contact with the media sheet58. The pick arm50is entering an operative position. As rotation of the cam60continues, the contact point66separates from the portion70, as shown in FIG.9. While the tray44remains installed the contact point66is kept away from the pick arm. In some embodiments the pick arm section70rotates back into contact with the contact point66with the picking of the last media sheet from the input tray44. As a result, the normal force applied by the pick roller46on the empty tray44is reduced. This avoids damage to the pick arm and pick roller46in the event that a pick operation is attempted while the input tray is empty. In other embodiments a sensor is used to signal that the tray44is empty, so that a pick operation does not occur.

Upon removal of the input tray44, the cam60rotates in direction69which causes the contact point66to contact section70and left the pick arm into the extracted position. The cam60is biased to rotate in the direction68either by a spring or another biasing method (e.g., relative weights of cam links about the axis62).

Hinging of the Pick Arm

During the pick operation, the operations controller14signals the pick drive motor32to rotate the pick roller46in a pick direction78(see FIG.10). When the pick roller begins to move, it applies a translation force to the media sheet. Ignoring acceleration of the roller, this translation force is resisted by equal and opposite forces consisting of a separation force and the friction between the sheet being picked and the sheet below it. The separation force, in the example described, is a force acting on the leading edge of the sheet being picked, applied by the separation ramp when the sheet runs into it. The translation force applied by the roller will continue to increase until the sheet bends at the ramp, allowing it to picked out of the tray. Referring toFIG. 12, horizontal and vertical components, Rxand Ry, of a reaction force act upon the roller46at roller bearings. These forces are reaction forces balancing the forces N and f applied by the sheet58to the roller46.

The resisting forces, applied by the sheet to the roller induce a moment at the pivot point52. When the moment exceeds the spring force that biases the pivot arm50into the first orientation, the distal portion48and proximal portion55hinge at the hinge axle56, as shown in FIG.10. Because the pick arm is fixed at the axle52, the proximal portion55rotates about the axle52in the direction82. As a result the pick roller46translates slightly in the direction84away from a media separation ramp86. When the input tray44is filled with media sheets the proximal portion55rotates in the direction82until it reaches a mechanical stop88. In one embodiment the mechanical stop88is positioned so as to allow the proximal portion55to return to the same place as when the entire arm50is retracted. In one embodiment this is a position which extends generally parallel to the media sheet58. Due to the hinging at hinge point56, however, the pick arm has a second orientation different than the first orientation, in which the distal portion48is out of the retracted position.FIG. 10shows the pick arm50in an operative position for picking a media sheet58.

Referring toFIG. 13, an angle α is defined as 180 degrees minus the angle formed between the proximal portion55and the distal portion48. Angle β is defined as the angle formed between the distal portion48and the media sheet58. In an embodiment in which the mechanical stop88is positioned to keep the proximal portion55parallel to the media sheet58, angle α equals angle β as long as the proximal portion55is in contact with the mechanical stop88.

In some embodiments the angle α is limited by another stop mechanism90(see FIG.5). The distal portion48can only rotate to a limited angle relative to the proximal portion55before being stopped by stop mechanism90.

As the media sheets are picked from the input tray44, the height of the media stack decreases. While the stack is high, the angle a increases as the media stack height decreases. Eventually angle a reaches a maximum angle where the mechanical stop90prevents further increases in angle a As the media stack continues to be reduced in height, the pivot arm50then rotates about the axle52keeping angle a fixed at the maximum angle. In other embodiments the spring constant for the spring60biasing the hinge point56is selected so as to overcome the moment exerted on it by the translation force when angle α reaches a prescribed angle. In such embodiment the spring60serves as the stop mechanism90which limits angle α to some maximum angle.

An advantage of hinging the pick arm50is that picking becomes more effective as angle a is increased to some maximum angle. Referring toFIGS. 10 and 12, the normal force N acting on the pick roller46increases as angle a increases. As the normal force increases, the available pick force (μN) also increases. Accordingly, as the normal force N acting on the pick roller46increases, it becomes easier to pick heavier media sheets. Stated another way, picking of heavier media sheets is more effective as the normal force N increases. Correspondingly, picking of heavier media sheets is more effective as angle α increases.

There is also a trade-off, however. As the angle α increases the pick roller46translates away from the media separation surface86. As the pick roller gets farther from the media separation surface86there is more likelihood of undesirable media sheet buckling. Accordingly, it is desirable to limit the amount of translation. One manner of doing so is to limit the angle α to a maximum angle using the angle stop mechanism90or by appropriately selecting a spring constant for spring60. Once the maximum of angle α is reached, the pick arm no longer hinges at axle56, but instead pivots at axle52. As a result, there is relatively less translation of the pivot roller46per unit drop in height while the media stack continues to decrease in height toward an empty input tray44.

In an alternative embodiment the translation is minimized not by limiting angle α but instead by limiting angle β. To do so, a stop mechanism is mounted to stay in the same horizontal position relative to the input tray while dropping vertically by the same amount as the paper stack decreases in height. Thus, regardless of the stack height, the stop mechanism limits angle β to a maximum angle.

Method for Picking a Media Sheet

In one embodiment the pick arm50is lowered adjacent to a media sheet58when the media input tray44is inserted into frame42, as shown inFIGS. 8 and 9. With the pick arm50in the position shown inFIG. 9, the operations controller14signals the pick drive motor32to rotate the pick roller46. In an alternative embodiment the driving of the pick roller causes the pick arm to lower into position to begin a pick operation. In such alternative embodiment, the pick arm retracts after the pick operation (or after the media sheet is fed along the media path).

With the pick roller rotating while in contact with the media sheet58, the translation force applied by the roller to the media sheet causes the media sheet to move in direction27toward a media separation ramp86. The separation ramp resists the motion of the sheet, causing the translation force to increase and allowing only the top sheet to be picked. The top media sheet moves into contact with a feed roller22and a pinch roller23. When the leading edge of the media sheet58is captured between the feed roller22and pinch roller23, the media sheet is pulled out of the input tray44onto a media path25. The media sheet58then is driven along the media path by one or more feed rollers22.

As the pick roller46rotates while in contact with the media sheet58, the forces applied by the media sheet to the roller, opposing the translational force, cause a moment to act upon the pick arm50which causes the pick arm50to hinge at hinge point56. As a result the arm pivots about axle52and hinges about hinge point56until the proximal portion55of the arm50reaches a mechanical stop88. As the media stack gets lower (see FIG.11), a second mechanical stop90limits the angle formed between the proximal portion55and the distal portion48. As a result, the proximal portion55rotates away from the mechanical stop88as the weight of the arm50acts to keep the pick roller46in contact with the media sheet58.

In some embodiments the pick arm is retracted after a picking operation. In the embodiment illustrated, the pick arm50remains in contact with the media stack until the input tray44is removed (see FIG.8).

Meritorious and Advantageous Effects

One advantage of the invention is that media sheets of varying weights are effectively picked from a media sheet stack without media buckling.

Although a preferred embodiment of the invention has been illustrated and described, various alternatives, modifications and equivalents may be used. Therefore, the foregoing description should not be taken as limiting the scope of the invention which are defined by the appended claims.