Mix mail feeder

Abstract

A feeder (12) for feeding envelopes in a mail handling machine comprising a transport deck (30) for receiving a stack of envelopes, feed rollers (34) for conveying downstream envelopes towards a reference wall (32) leaving a clearance path for the envelopes; a stack sensor (48) for detecting the presence of the stack of envelopes at a predetermined height threshold; and a control unit (46) configured for decreasing acceleration of the feed rollers when the stack of envelopes goes below the predetermined height threshold.

Claims

1. A feeder for feeding envelopes in a mail handling machine comprising a transport deck for receiving a stack of envelopes, feed rollers for conveying downstream envelopes towards a reference wall leaving a clearance path for the envelopes, a stack sensor for detecting the presence of said stack of envelopes at a predetermined height threshold, and a control unit for activating the feed rollers, wherein the control unit is configured for applying a determined acceleration to said feed rollers and for decreasing said determined acceleration of said feed rollers when the stack of envelopes goes below said predetermined height threshold in order to separate remaining envelopes of the stack.

2. The feeder of claim 1, wherein said acceleration is decreased from a first acceleration to a second acceleration.

3. The feeder of claim 2, wherein said first acceleration is a higher acceleration of 100 m/s2 and said second acceleration is a lower acceleration of 20 m/s2.

4. The feeder of claim 1, wherein said control unit is further configured for maintaining a top speed of said feed rollers when the stack of envelopes goes below said predetermined height threshold.

5. The feeder of claim 1, wherein said control unit is further configured for limiting a top speed of said feed rollers when the stack of envelopes goes below said predetermined height threshold.

6. The feeder of claim 1, wherein said reference wall extends vertically from said transport deck.

7. The feeder of claim 6, wherein said stack sensor is placed in said reference wall just above said clearance path.

8. The feeder of claim 1, wherein said stack sensor is a contact sensor protected by an articulated lever or an optical reflective sensor.

9. The feeder of claim 1, wherein it further comprises a feed sensor located below said transport deck and near said reference wall.

10. The feeder of claim 9, wherein said control unit is further configured for, in an initialization phase, if said envelopes are detected by said feed sensor, activating said feed rollers to advance the entire stack of envelopes towards the reference wall.

11. The feeder of claim 1, wherein it further comprises friction pads facing separation rollers for ejecting one by one said envelopes from said stack.

12. A mail handling machine, comprising: feeder for feeding envelopes, the feeder comprising: a transport deck sized, dimensioned and positioned to receive a stack of envelopes; a number of feed rollers positioned and operable to convey envelopes downstream towards a reference wall leaving a clearance path for the envelopes; a stack sensor positioned to detect a presence of said stack of envelopes at a predetermined height threshold; and a control unit communicatively coupled to selectively activate the feed rollers, wherein the control unit determines an acceleration to be applied to said feed rollers and decreases said determined acceleration of said feed rollers in response to the stack of envelopes being below said predetermined height threshold in order to separate remaining envelopes of the stack.

13. The mail handling machine of claim 12, wherein the controller decreases said acceleration from a first acceleration to a second acceleration in response to the stack of envelopes being below said predetermined height threshold.

14. The mail handling machine of claim 13, wherein said first acceleration is a higher acceleration of about 100 m/s2 and said second acceleration is a lower acceleration of about 20 m/s2.

15. The mail handling machine of claim 12, wherein when the stack of envelopes is below said predetermined height threshold, said control unit maintains a top speed of said feed rollers.

16. The mail handling machine of claim 12, wherein when the stack of envelopes goes below said predetermined height threshold, said control unit limits a top speed of said feed rollers.

17. The mail handling machine of claim 12, wherein said reference wall extends vertically from said transport deck and said stack sensor is placed in said reference wall just above said clearance path.

18. The mail handling machine of claim 12, wherein said stack sensor is a contact sensor protected by an articulated lever or an optical reflective sensor.

19. The mail handling machine of claim 12, wherein the feeder further comprises a feed sensor located below said transport deck and near said reference wall, and wherein, in an initialization phase, if said envelopes are detected by said feed sensor, said control unit activates said feed rollers to advance the entire stack of envelopes towards the reference wall.

20. The mail handling machine of claim 12, wherein the feeder further comprises a number of friction pads facing separation rollers that eject said envelopes from said stack, one by one.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The embodiments of the invention can be better understood in reading the following detailed description accompanied by illustrative and non-limiting examples with reference to the drawings, in which:

(2) FIG. 1 is a view of a franking machine in which the invention can be implemented,

(3) FIGS. 2A, 2B and 2C are schematic views of a feeder according to the invention containing respectively a high, intermediate and low stack, and

(4) FIG. 3 shows several motion profiles that can be applied to the feed rollers of said feeder.

DETAILED DESCRIPTION

(5) The embodiments of the invention will be better understood with a brief explanation of the forces acting on the envelopes in the stack. The model presented here is extremely simplified and shall serve only as an illustration of the main principles governing the separation of mail. In the following, the drive rollers located in the upstream part of the feeder are called feed rollers.

(6) The feed rollers acting on the bottommost envelope have a static coefficient of friction μs.sup.re. The dynamic coefficient of friction is considered equal to the static one insofar that there is no significant differential speed between the rollers and the bottommost envelope.

(7) The friction pads retaining the envelopes just above the bottommost one have a static coefficient of friction μs.sup.pe and a kinetic coefficient of friction μk.sup.pe. They form an angle θ with the horizontal plane. They apply a vertical downward force S to the envelopes.

(8) The envelopes have mutual static and kinetic coefficient of friction μs.sup.ee and μk.sup.ee.

(9) The stack has a weight W, which varies during the separation process.

(10) We consider μs.sup.ee=0.6; μk.sup.ee=0.5; θ=18°; S=600 gr; μs.sup.pe=μk.sup.pe=1; μs.sup.re=μk.sup.re=2.

(11) Double Feed

(12) A double (or multiple) feed occurs when two (or more) envelopes are bound in a block and pass together through the separation mechanism. The friction between envelopes belonging to the block is greater than the separation forces acting on the block boundaries.

(13) The force driving the uppermost envelope of the block is D=W*(μs.sup.ee−μk.sup.ee) where the weight of the entire stack W is considered much bigger than the weight of envelopes in the block.

(14) The uppermost envelope of the block shall lift the friction pad thus W*(μs.sup.ee−μk.sup.ee)>S*tan θ.

(15) Then the uppermost envelope of the block shall not be retained by the friction pad, thus W*(μs.sup.ee−μk.sup.ee)>S*(μk.sup.pe−μs.sup.ee). These conditions are more likely to be met with heavy stacks.

(16) The first condition is: W*0.1>600*0.325 thus W>1950 grams (gr).

(17) The second condition is: W*0.1>600*0.4 thus W>2400 gr.

(18) The last one gives a realistic value of the weight where double feeds start occurring.

(19) The maximum capacity of the feeder is therefore limited by the weight of the stack.

(20) Miss-Feed

(21) A miss-feed occurs when the very last envelopes of the stack cannot be extracted. This is the case because there is not enough friction generated by the stack against the drive rollers.

(22) The force driving the bottommost envelope is then D=W*(μs.sup.re−μk.sup.ee). In order to pass the friction pads the driving force shall be greater than S*tan θ. The condition is met for a weight such that W*1.5>600*0.325 thus W>130 gr, corresponding to a dozen of envelopes. (In practice, an additional grip is generated by the compression of the envelopes engaging under the friction pads. The above value is therefore overestimated, but the extraction of the very last letters often remains problematic).

(23) These simple calculations show that the weight of the stack, and thus the capacity or the feeder is limited. Furthermore it can be easily demonstrated that modifying a parameter to increase the capacity of the feeder, for instance increasing the angle θ or the separation load S, may have a detrimental effect on the feeding of the envelopes when the stack becomes smaller. Moreover, as automatic franking machines operate at high speed and acceleration, typically 1 m/s and 100 m/s.sup.2, the inertia of the envelopes is not negligible. The force required to accelerate a mass of 10 gr at 100 m/s.sup.2 is D=1 N or ˜100 gr. In comparison, the force acting on the bottommost envelope can be lower than 50 gr when the stack is down to a few letters, and the rollers may very well start slipping before the bottommost envelope is driven through the separation mechanism.

(24) Conventionally, a franking machine 10 as illustrated in FIG. 1 comprises disposed from upstream to downstream in the direction of advance of the envelopes: a receiving deck 12 designed to receive a stack of mail items (typically envelopes of the mixed type, i.e., of different sizes and weights); a selector and conveyor module 14 for selecting the envelopes and conveying them one-by-one (both forming the feeding module of the franking machine); preferably a dynamic weighing module 16 for determining the weight and optionally the size of each selected envelope; a franking module 18 designed to print the franking mark on each of the envelopes selected one-by-one and weighed on the fly in this way; and a stacker or a tray 20 for receiving the franked envelopes. The franking module classically has a user interface that makes it possible, in particular, to select the class of mail and other postal services. Preferably, and also as is known, said franking module is connected to a remote server 22 of a dealer of the franking machine, which machine is also connected to a server (not shown) of a postal authority or of a private carrier who delivers the mail items.

(25) As illustrated in FIGS. 2A to 2C, the feeding module or feeder 12 is conventionally composed of a transport deck 30, a reference wall 32, a plurality of rollers 34, 36, 38 (successively in the envelope flow direction: feed, separation and extraction rollers), a separation mechanism comprising for instance one or several friction pads 40, one or several drive motors 42, and one or several sensors 44. The feeder is controlled by a control unit 46 which can be dedicated to the feeding module or the entire franking machine. Except for the feeding of envelopes which will be described hereafter, the feeder operates in a standard manner and the successive activation of the various rollers during the process of separating and conveying the envelopes do not need to be described here.

(26) In operation, at the beginning of this process, a stack of envelopes is disposed in the feeder. The stack resides on the horizontal transport deck 30 sensibly aligned with the feed rollers 34, their upper part protruding slightly from the deck. The stack is then in front of a reference wall 32, extending vertically from the deck but leaving a clearance path for the envelope to enter the separation area with the friction pads 40 facing the separation rollers 36.

(27) Once the machine is ready to operate, the presence of envelope in the feeder is checked in a conventional manner by the feed sensor 44 located below the transport deck 30 and near the reference wall 32. In this initialization phase if envelopes are detected, the feed rollers 34 are activated to advance the entire stack towards the reference wall at moderate speed, in order to check the height of the stack.

(28) A stack sensor 48 is located in the reference wall 32, preferably just above the clearance path for detecting the presence of envelopes at a predetermined height threshold (reference level). This sensor can be, for instance, a contact sensor protected by a small articulated lever or an optical reflective sensor, also called proximity sensor, which has a detection range of a few centimeters focused around its optical axis. The vertical distance between the stack sensor and the deck is for instance 20 mm. This distance corresponds roughly to a stack of 20 envelopes or 200 gr. As the stack is advanced by the feed rollers 34, the stack sensor checks the presence of envelopes above this reference level. Then, if the stack is higher than the reference level, a higher acceleration (typically 100 m/s.sup.2) is applied to the feed rollers to separate the bottommost envelope. Otherwise, a lower acceleration (typically 20 m/s.sup.2) is applied to the feed rollers.

(29) As envelopes are extracted, the stack becomes lower and its upper part reaches the level of the stack sensor as illustrated in FIGS. 2A, 2B and 2C that show the feeder with respectively a high, intermediate and low stack. A low stack is detected when the stack sensor 48 is cleared but not the feed sensor 44, indicating that there are still a few envelopes in the feeder. The detection of a low stack triggers the control unit 46 of the franking machines to apply the lower acceleration to the feed rollers (typically 20 m/s.sup.2) for the separation of the remaining envelopes.

(30) At any time before the feed sensor is cleared, if envelopes are reloaded on the fly, the stack sensor 48 immediately detects the presence of envelopes above the reference level and the initial, higher, value of the acceleration can be restored.

(31) More particularly, the control unit 46 receives signals from the feed sensor 44 and the stack sensor 48, and selects the motion profile to be applied to the motor 42 driving the feed rollers 34, according to the desired speed and acceleration of the envelopes. For instance, as illustrated on FIG. 3 that shows the various motion profiles to be applied in the various phases, moderate speed and acceleration (typically 0.2 m/s and 20 m/s.sup.2) may be used at initialization (curve 50). Then if a stack higher than the predetermined height threshold is detected, high speed and acceleration (typically 1 m/s and 100 m/s.sup.2) are used for the separation process (curve 52). Adversely, when a low stack is detected, the same speed but a lower acceleration (typically 20 m/s.sup.2) is used (curve 54).

(32) It shall be noted that the separation process may start during the initialization phase (while the stack is moving towards the reference wall) as soon as the height of the stack is determined. The top speed can also differ for high or low stacks, in a manner independent from the selected acceleration. A lower or the same top speed may be preferred for a low stack, depending on other parameters and/or requirements.

(33) It must also be noted that the invention is not limited to the illustrations and that for example other means may be used for driving and separating the envelopes. For instance transport belts may be used instead of feed or separation rollers, and separation belts or rollers may be used instead of friction pads; without departing from the nature of the invention.