EP0589789B1 - Device for separating flat articles from a pile, including a front aligning device - Google Patents

Description

The invention relates to a device for unstacking flat articles, such as closed or open mail folds. This type of device is in particular used in automatic mail sorting machines or the like.

US Pat. No. 4,357,007 discloses a device for unstacking flat articles including first and second suction nozzles arranged on one side of a jogging edge, a perforated endless band running continuously in front of the nozzles. suction and the free face of the first article of a stack of articles, a passage forming an outlet between the jogging edge and the strip, a first and a second sensor arranged on the other side of the jogging edge. The second suction nozzle is spaced downstream of the first suction nozzle in the direction of travel of the endless belt and the second sensor is spaced downstream of the first sensor in the direction of travel of this belt. The second sensor operates the first or second suction nozzle depending on whether the first sensor is in the condition of detecting or not detecting an article, respectively.

This known device makes it possible to single out articles taken from a pile of articles in order to distribute them one by one towards the outlet even when, in a pile of articles on edge abutting against a jogging edge, some of the articles have a defect in 'alignment.

A problem encountered in article unstacking devices is that two consecutive articles in a stack of articles to be singled out are not always arranged with their edge leading into contact with the jogging edge, which leads to errors in operation of the unstacking device. Indeed, when for example a first article of the stack has an edge leading back from the jogging edge and beyond the trailing edge of a suction nozzle and a second article has its edge leading into contact with the jogging edge, the second article, and not the first article, is first taken by the suction nozzle when activated and is conveyed to the outlet by the endless belt before the first article. If the first article in the stack is not moved towards the jogging edge, it will never be unstacked.

In the document cited above, a control means is provided for selectively actuating the suction nozzles in response to the signals supplied by the sensors. The operation of the control means is as follows. If at an instant t = 0, the sensors detect the absence of an article at the outlet, the control means actuates the first suction nozzle until the first sensor detects the presence of the article which causes the deactivation of the first suction nozzle and the actuation of the second suction nozzle. The article held against the endless belt by the second suction nozzle is moved towards the outlet until the second sensor detects the presence of the article which causes the deactivation of the second suction nozzle.

This known device has drawbacks. First, the tolerated misalignment between the leading edges of the articles is equal to the distance between the trailing edge of the first suction nozzle and the plane of the jogging edge. However, the maximum distance between the trailing edge of the first suction nozzle and the first sensor is equal to the size of the smallest item in the stack. Because the sensors and the suction nozzles are disposed respectively on either side of the jogging edge, it follows that the maximum tolerable misalignment is less than the dimension of the smallest article in the stack. Then, in normal operation, that is to say when no item of the stack is cracked back, the control means simultaneously actuates the first then the second suction nozzle. As a result, the unstacking rate is lower than that which would be obtained if the control means activated a single suction nozzle. Hereinafter, an item with a backward crack will be designated an article which has its edge leading back from the jogging edge beyond the trailing edge of the second suction nozzle. The term re-tapping will mean the action of bringing the leading edge of a tackled article against the tapping edge.

The object of the invention is to remedy these drawbacks by proposing in particular an unstacking device which tolerates rear stripping larger than the dimension of the smallest article in a stack of articles.

To this end, the subject of the invention is a device for unstacking flat articles as defined in claim 1.

In this way, the maximum tolerable distance between the trailing edge of the second gripping means and the sensor is equal to the dimension of the smallest article in the stack. Furthermore, the maximum tolerable distance between the trailing edge of the first gripping means and the leading edge of the second gripping means is equal to the smallest dimension of an article in the stack. The gripping means and the sensor being arranged on either side of the jogging edge, therefore the maximum tolerable rear impact is equal to the distance between the trailing edge of the first gripping means and the jogging edge. This distance can therefore be greater than the dimension of the smallest item in the stack. Furthermore, the first gripping means is actuated only in the case where a rear tackle is detected by the control means which guarantees, in the absence of tackled articles back in the stack, an optimal unstacking rate.

According to a particular embodiment, the control means controls a timer which is triggered simultaneously with the actuation of the second gripping means by the control means during the unstacking cycle and which is stopped on detection of the presence of an article by the sensor, and is arranged to initiate the re-tracking cycle if said timer has not been stopped before the expiration of a set time. This timer can be set for more than one set point so that you can detect backstroke items with different characteristics. Such a timer is easy to realize in the form of a program loaded in a microcomputer and the control means can also consist of a program loaded in this microcomputer.

According to another embodiment, the unstacking device comprises a vacuum sensor which monitors the vacuum level prevailing in a vacuum tank connected to the gripping means constituted by suction nozzles. The vacuum sensor provides a rear tackle detection signal to the control means when the detected vacuum level is lower than a set vacuum level.

According to another embodiment, the unstacking device comprises a low vacuum chamber disposed between the two gripping means whose function is to attract the first article of the stack close to the endless belt which allows to increase the rate of unstacking items from the stack.

An exemplary embodiment of the invention is described in detail below with reference to the drawings.

FIG. 1A schematically represents a top view of the unstacking device.

FIG. 1B is a block diagram of the control circuit of the device.

Figure 2 is a flow diagram illustrating a depilation cycle.

FIG. 3 is a flow diagram illustrating a pickling detection cycle.

Figure 4 is a flowchart illustrating a re-tapping cycle.

Referring to Figures 1A and 1B, the device includes an input stage 1 for receiving a stack of folds 2 on edge abutting against a jogging edge 3. The stack is brought against the jogging edge 3 by a path d substantially horizontal or inclined feed formed by conveyor belts 4. In the figure, three folds are shown such as L1, L2, L3. The fold L1 is tacked back, its leading edge not being in contact with the jogging edge 3.

It also includes a destacking stage 5 disposed in front of the front face of the first ply L1 of the stack and on the side of the plane of the jogging edge on which the stack of plies is supported. This stage comprises an endless strip 6 perforated continuously scrolling in front of the free face of the first ply of the stack in the direction designated by the arrow D. This strip is guided and driven by pulleys and defines with the jogging edge 3 an outlet for folds.

The unstacking stage also includes a first suction nozzle 7 and a second suction nozzle 8 mounted along the endless strip facing the top of the stack, the endless strip running between the nozzles suction and the folds of the stack 2. The suction nozzles 7,8 have their outputs connected to a vacuum tank 9 via solenoid valves not shown. The vacuum tank is connected to a depressor not shown which maintains a permanent vacuum in the tank of the order of 300mbars below atmospheric pressure. The suction nozzles are actuated selectively by means of their respective solenoid valves by a microcomputer 10 to take an article from the pile and hold it against the endless strip and therefore to separate it from the pile of plies to be singled out.

The unstacking stage 5 also includes a low vacuum chamber 11 disposed between the two suction nozzles and acting permanently to keep the first fold of the stack close to or in contact with the endless belt. As shown in the figure, the endless belt 6 has a path which frees up a space between the two nozzles 7,8 to allow the vacuum chamber to act directly on the folds of the stack.

A vacuum sensor 12 is provided inside the vacuum tank 9 to provide the microcomputer 10 with a signal when it detects that the vacuum prevailing inside the vacuum tank is lower or greater than a set value equal for example to 250mbars below atmospheric pressure.

The unstacking device also includes a distribution stage 13 disposed on the side of the plane of the jogging edge opposite the support plane of the stack of plies. This stage comprises a suction nozzle 14 connected to the vacuum reservoir 9 which acts on the rear face of a depilated ply presenting itself at the outlet, a singularized ply transfer member constituted by two endless bands 15, 16 guided and driven by pulleys and acting by pinching singularized folds. The role of the nozzle 14 is to prevent double sockets. Sensors 17, 18, 19 are provided in the distribution stage to supply the microcomputer 10 with signals for detecting the presence or absence of a fold at the exit from the unstacking stage. These sensors are conventionally constituted by light diodes and photosensitive cells. The sensor 17 is placed immediately at the exit of the unstacking stage between the strip 6 and the strip 16 and downstream of the jogging edge 3. The sensor 18 is placed downstream of the sensor 17 in the direction of travel of the strip (arrow referenced D) but preferably upstream of the pinch point P. The sensor 19 is placed downstream of the sensor 18 near the pinch point of the bands 15, 16.

The operation of the unstacking device is now described with reference to Figures 2 to 4.

Unstacking cycle (Figure 2)

The cycle begins with an initialization phase 50 in which the nozzles 7,8,14 are deactivated, the strip 6 and the rollers 20 driven and the low vacuum chamber 11 put into action. The microcomputer 10 actuates the nozzle 8 (V1) at 51 to unstack a fold of the stack. As soon as the sensor 18 (C1) detects the presence of the fold at 52, it sends a signal to the microcomputer 10 which actuates the nozzle 14 (V2) at 53 after a time delay allowing the fold to reach the pinch point. As soon as sensor 19 (C2) detects the presence of the fold at 54, it sends a signal to the microcomputer 10 which deactivates the nozzle V1 at 55 and as soon as the sensor 17 (C0) detects the absence of the fold at 56, it sends a signal to the microcomputer which deactivates the nozzle V2 at 57. The unstacking cycle resumes at 51 for a new ply after a time delay making it possible to obtain the desired difference between each singularized ply supported by the bands 15,16.

It is clear that, due to the position of the sensor C2, the maximum distance between the trailing edge of the nozzle V1 and the sensor C2 is equal to the dimension of the smallest fold to be treated by the destacker.

Pickling detection cycle (Figure 3)

This cycle begins from the actuation of the nozzle V1 in step 51. Two alternative detection steps are implemented which begin with the setting of a timer (microcomputer clock) for two delays T1 and T2 , the delay T1 being for example equal to 50 ms and the delay T2 being equal for example to 150ms.

The cycle can consist in controlling the time between the instant when the nozzle V1 is actuated and the instant of detection by the sensor C1 of a fold during unstacking. In fact, if a fold such as L1 is cracked, it more or less closes the chamber with permanent low vacuum 11 and prevents the second fold L2 of the stack from pressing against the strip 6.

If before the expiration of the delay T1 at 64, the sensor C1 detects at 61 the presence of the fold, there is no untagged fold and the microcomputer continues the detection cycle with the unstacking cycle at 53.

If the sensor C1 detects the presence of the fold at 61 after the expiration of the delay T1 at 64, the microcomputer increments a counter at 65. The cycle continues at 53 as long as the value of the counter has not reached at 66 a predetermined count value, for example equal to 3. If the counter has reached this count value in 66, the cycle continues with a re-tapping cycle R.

This detection step is intended for thin, folded folds and / or which partially obstruct the chamber 11.

If after the expiration of the delay T2 at 62, the sensor C1 has still not detected the presence of the fold at 61, the cycle continues with a re-tracking cycle R.

This detection step is intended for thick stapled folds and / or which completely obstruct the chamber 11.

The pickling detection cycle can also consist in monitoring the vacuum level in the vacuum tank during the actuation of the nozzle V1.

Thus, if during one of the delays T1, T2 after 60, the vacuum sensor 12 detects at 63 that the vacuum in the vacuum tank is less than a set vacuum, the pickling detection cycle continues with a cycle R, the cycle continues at 61.

When the solenoid valve controlling the nozzle V1 is opened by the microcomputer 10, the vacuum tank fills with air until the ply L1 is pressed against the strip 6. This short time results in a temporary decrease in vacuum in the vacuum tank. If a thick fold is cracked back, it disturbs the operation of the nozzle V1 enough to bring down the vacuum level in the vacuum tank which is detected by the sensor 12. The control of the vacuum level has the advantage of rapid detection of a rear tackle and maintains the order of unstacking the folds.

Jogging cycle (Figure 4)

The jogging cycle begins with the deactivation of the nozzle V1 at 70.

Alternative re-tracking steps are implemented starting from the detection of the presence or absence of a fold by the sensor C0 at 71.

Case 1 .:

If the sensor C0 detects the absence of a fold in 71, the microcomputer actuates the nozzle V0 in 72 and triggers in 73 the timer for a TRMAX delay equal for example to 100 ms. The microcomputer 10 then deactivates the nozzle V0 and simultaneously activates the nozzle V1 at 77 if the sensor C0 detects the presence of a fold at 74, or if the depression sensor 12 detects a drop in depression at 75 or if the delay TRMAX has elapsed in 76. In 78, the microcomputer triggers the timer again for a TRMAX delay equal for example to 150 ms. If the sensor C1 detects the presence of a fold in 79 before the expiration of the TRMAX delay in 81, then the microcomputer continues the unstacking cycle in 53. If the sensor C1 does not detect the presence of a fold in 79 before the expiration of the TRMAX delay or if the sensor 12 detects a drop in vacuum at 80, then the microcomputer deactivates the nozzle V1 and simultaneously actuates the nozzle V0 at 82 then triggers the timer at 83 for a new time TRMAX by example equal to 300ms. At the end of the TRMAX delay in 84, the microcomputer continues the cycle in 77 as before. If again the sensor C1 does not detect a fold at 79, the microcomputer starts the timer at 83 for a TRMAX delay of 500 ms and then continues the cycle at 77 as before. If again the sensor C1 does not detect a fold at 79, the microcomputer starts the timer at 83 for a TRMAX delay of 500 ms and then continues the cycle at 77 as before. If finally the sensor C1 does not yet detect a fold at 79, the destacker is stopped.

Case 2 .:

If the sensor C0 detects the presence of a fold at 71, a first letter L1 is tapped back and a second letter L2 is tapped forward. The microcomputer then checks the value of the counter at 85. If the value of the counter is equal to the predetermined count value (in this case 3), the microcomputer initializes the counter at 86, then continues the cycle with a cycle of unstacking starting at 51 and ending at 57. If at the end of the unstacking cycle, the C0 sensor detects the presence of a fold in 87, the unstacking cycle is resumed from 51 to 57. As soon as the C0 sensor detects the absence of a fold in 87, the re-tracking cycle continues in 72. If the counter value is not equal to the predetermined count value in 85, the microcomputer actuates the nozzle V0 at 88 and triggers the timer in 89 for a TRMAX delay equal for example to 150 ms. If the sensor C1 detects the presence of a fold in 90 or if the sensor 12 detects a drop in depression in 91 or if the TRMAX delay has expired in 92, the microcomputer deactivates the nozzle V0 and actuates the nozzle V1 in 93 The re-tracking cycle then continues with a destacking cycle at 52.

It is clear that the distance between the trailing edge of the nozzle V0 and the sensor C0 can be greater than the dimension of the smallest fold to be treated. But the maximum distance between the trailing edge of the nozzle V0 and the leading edge of the nozzle V1 is equal to the dimension of the smallest fold to be treated. As a result, the maximum tolerable rear stopping is equal to the distance between the leading edge of the nozzle V0 and the jogging edge. This tolerable rear coating may be more or less important depending on whether the leading edge of the nozzle V1 is far from the jogging edge.

The destacker according to the invention is particularly suitable for mail folds having dimensions and a weight varying in a wide spectrum. The rear stripping tolerated by the destacker can go up to 150mm for a dimension of the smallest fold equal to 125mm.

Of course, the invention is not limited to the embodiment described above, and other variants can be provided without departing from the scope of the invention according to claims 1-13.

Claims (13)

1. Unstacking apparatus for unstacking flat items, in particular mail items, the apparatus comprising an alignment plate (3) having an abutment surface against which a stack (2) of flat items (L1, L2, L3) on edge abuts, an endless belt (6) continuously advancing past the free face of the first item in the stack so as to convey the items from the stack towards an outlet, first gripping means (7) disposed on the abutment surface side of the alignment plate so that when actuated they take the items from the stack and hold them against the endless belt, second gripping means (8) disposed between the first gripping means and the alignment plate so that when actuated they take the items from the stack and hold them against the endless belt, at least one sensor (18) disposed on that side of the alignment plate which is opposite from the abutment surface so as to supply a signal in response to the presence or the absence of an article being detected at the outlet, control means (10) for selectively actuating the second gripping means in response to the signal supplied by the sensor (18) so as to perform an unstacking cycle, said apparatus being characterized in that the control means are organized so as to detect that the first item in the stack is backwardly misaligned from said second gripping means by monitoring the operation of the second gripping means (8) during the unstacking cycle, and so as to respond to detection only of backward misalignment by performing a realignment cycle during which said control means actuate the first gripping means (7) and the second griping means (8) both selectively and successively.
2. Apparatus according to claim 1, in which apparatus the control means control a timer which is triggered at the same time as the second gripping means (8) are actuated during the unstacking cycle, and which is stopped when said sensor detects the presence of an item, and in which apparatus the control means are organized so as to perform the realignment cycle if said timer has not been stopped before the end of a reference duration.
3. Apparatus according to claim 2, the control means are organized to perform a misalignment detection cycle starting at time t=0, which is defined as being the time at which the control means (10) actuate the second gripping means (8) for an unstacking cycle when the sensor (18) detects the absence of an item, the misalignment detection cycle comprising the following alternative steps:

   a) if, after a first duration T1 that is shorter than a second duration T2, the sensor detects the presence of an item, the control means increment a counter and continue the unstacking cycle, and if said counter reaches a predetermined count value after a plurality of successive unstacking cycles, then the control means perform a realignment cycle; or

   b) if, after the second duration T2, the sensor has not detected the presence of an item, the control means perform a realignment cycle.
4. Apparatus according to claim 2, including a first sensor (17) disposed on that side of the alignment plate which is opposite from the abutment surface, and a second sensor (18) spaced apart from the first sensor downstream in the advance direction of the endless belt, so as to supply signals in response to the presence or the absence of an item being detected at the outlet, and in which apparatus the control means (10) are organized to perform a realignment cycle starting at time t'=0, which is defined as being the time at which the control means deactivate the second gripping means, the realignment cycle comprising the following alternative steps:

   a) if the first sensor (17) detects the absence of an item, the control means (10) actuate the first gripping means (7) so as to take at least one item from the stack and so as to hold it against the endless belt until:

   the first sensor (17) detects the presence of an item; or

   a waiting duration TRMAX has elapsed;

      whereafter the control means (10) deactivate the first gripping means (7) and simultaneously actuate the second gripping means (8); or

   b) if the first sensor (17) detects the presence of an item, the control means (10) actuate the first gripping means (7) until:

   the second sensor (18) detects the presence of an item; or

   a waiting duration TRMAX has elapsed;

      whereafter the control means (10) deactivate the first gripping means (7) and simultaneously actuate the second griping means (8).
5. Apparatus according to claim 4, in which the control means are organized to continue step a) of the realignment cycle with an unstacking cycle if the second sensor detects the presence of an item before the end of a waiting duration TRMAX that starts at the time at which the control means actuate the second gripping means, and otherwise with at least one new realignment cycle.
6. Apparatus according to claim 4, the control means are organized to perform an unstacking cycle when the presence of an item is detected by the first sensor and if the counter has reached said count value, and so long as the first sensor detects the presence of an item, the control means then performing a realignment cycle.
7. Apparatus according to claim 4, in which the control means are organized to continue step b) of the realignment cycle with an unstacking cycle.
8. Apparatus according to claim 3, in which said gripping means comprise a first suction nozzle (7) and a second suction nozzle (8) that is spaced apart from the first suction nozzle downstream in the advance direction of the endless belt, said suction nozzles being connected to a vacuum tank (9), and being actuated selectively by the control means (10) so as to take the items from the stack and so as to hold them against the endless belt, said apparatus further including a suction sensor (12) disposed inside the vacuum tank so as to supply a signal in response to the suction inside the vacuum tank being detected to be less than or greater a reference suction, and in which apparatus the misalignment detection cycle further includes an alternative step c) in which the control means are organized to perform a misalignment cycle if the suction sensor (12) detects that the suction in the vacuum tank is less than the reference suction.
9. Apparatus according to claim 4 or 8, in which, in step a) of the misalignment cycle, the control means actuate the first suction nozzle so as to take at least one item from the stack and so as to hold it against the endless belt until the suction sensor detects that the suction in the vacuum tank is less than the reference suction.
10. Apparatus according to claim 4 or 8, in which, in step b) of the misalignment cycle, the control means actuate the first suction nozzle so as to take at least one item from the stack and so as to hold it against the endless belt until the suction sensor detects that the suction in the vacuum tank is less than the reference suction.
11. Apparatus according to any one of claims 3 to 10, in which the first duration T1 is equal to 50 ms and the second duration T2 is equal to 150 ms.
12. Apparatus according to any one of claims 4 to 11, in which the waiting duration TRMAX varies in the range 100 ms to 500 ms.
13. Apparatus according to claim 8, said apparatus further including a low-suction chamber (11) disposed between the two suction nozzles.

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