FR2546083A1 - Device for detecting multiple pickups of objects - Google Patents

Abstract

The invention relates to a device for detecting multiple pickups of objects comprising a destacker 1, a conveyor 2 and a sorting centre 3. In order to detect multiple pickups, a video camera 29 is placed in line with the window 40 formed beneath the conveyor 2. The lower portions 32, 33 of the flat objects 13, 14 that have been wrongly picked up together are perceived by the camera 29 whose video signal comprises two peaks representing this double pickup. This video signal is processed 5 to produce a reject signal (OR).

Description

DEVICE FOR DETECTING MULTIPLE TAKES OF QBJETS
The invention relates to a device for -detection of multiple objects taken used in particular in postal sorting installations. In such installations, the handling of flat objects, such as letters or postal envelopes, involves a certain number of distinct phases. In particular flat objects, stored in a stack, are presented opposite a destacker which extracts these objects from the stack one by one and introduces them into a conveyor. This conveyor routes the various flat objects to a set of receptacles. The conveyor also comprises control means for delivering each of the flat objects to the receptacle which is intended for it as a function of the postal address carried by this object.

 Each object being individualized by its destination and the processing being carried out in an automatic manner, it is understood that it is of the first importance that the flat objects are well differentiated from each other. Thus two consecutive objects must not remain attached to each other which would have the effect of assigning this pair of objects to a receptacle which would only be suitable for one of the two. In addition to these errors d assignment which are inconvenient for the misdirected object, it should be noted that the gripping by the conveyor of a couple of artificially attached objects to one another is not done in the optimal conåiltloels of operation of this conveyor. The couple of objects thus transported can be the cause of frequent jams or untimely breakdowns. We can finally note that these incidents can occur in particular at the exit of the destackers whose operation is most delicate. 3 Until now, apart from human surveillance, which is carried out in an excessively forbidding and restrictive manner due to the speed of travel of objects in the conveyors, there is no double catch detection system and more generally catch catch. multiple. There are only alarm systems that go off in case of breakdowns or jams, that is to say when the damage is done and when it is too late.

 To remedy such drawbacks, Invention proposes a detection device provided with a camera for monitoring the movement of objects. The existence and installation of this camera constitutes the invention.

 The invention relates to a device for detecting multiple catches of objects, of the type comprising a means for unstacking stacked flat objects and a means for conveying to a means for receiving flat unstacked objects, characterized in that it comprises - image-taking means arranged in line with the conveying means downstream from the unstacking means for developing a video signal representative of the image of the edges of the flat objects in movement and means for processing the video signal developed to produce a signal presence or absence of multiple sockets.

 The invention will be better understood on reading the description which follows and on Peamen of the accompanying figures. This description is given for information and is in no way limitative of the invention. In the figures, the same references designate: the same elements. These figures represent: - Figure 1, a block diagram of all the means of the device of the invention; - Figure 2, the highlighting of certain features of this device; - Figure 3, a block diagram of an example of video signal processing means; - Figure 4, time diagrams of the signals involved in the device of the invention.

 Thus, in the invention when two flat objects are unfortunately unstacked at the same time by a destacker and grabbed by a conveyor, these two objects are pressed against each other.

By having a device for taking pictures facing the edges of these two objects, it can be seen that the video signal produced by this device for taking pictures presents at each line scanning period a series of two peaks corresponding to the bright images of the sections examined. while the rest of the signal is weak. If only one object is presented, only one light peak appears at each scanning time. Consequently, by using means for counting the peaks of the video signal, it is possible to produce a signal of presence or absence of multiple sockets.

 In FIG. 1, a device for detecting multiple shots according to the invention is distinguished, comprising a depilating means 1, a conveying means 2, and a receiving means 3. It also includes means for taking pictures. 4 and means 5 for processing the video signal produced by these shooting means.

 The unstacking means 1 can be any, in particular manual, but it will in particular be of a type comprising a vacuum box 4 ?, and a drum 6 rotating continuously, and connected to a source of suction not shown. This unstacking means is more particularly described in French patent application NO 82 02794 of the applicant. Flat objects to be unstacked 7 are approached parallel to a generator of the drum 6 by displacement means 8 in the direction of the arrow 9.

During this movement, the objects 7 are supported by a bottom 10 and are guided by a jogging edge 11. In this way all the objects 7, arranged on edge, are aligned with each other by two sections, their lower section resting on the bottom 10 and one of their vertical edges pressing against the jogging edge 11. To unstack an object the suction exerted through the holes 50 made in the boot 49 attracts the first object against the face 51 of unstacking who faces him; then certain orifices 12 of the drum 6 are suddenly put in contact with the suction source and thus attract this first object towards them. In its rotating movement, the drum then extracts the first object and introduces it into the conveying means 2.

 The incidents which may occur and which the invention proposes to detect are then in the form of two flat objects 13 and 14 seized at the same time by the drum 6 and also introduced at the same time into the conveying means 2. In the 'example described, the conveyor means 2 comprise two bands, respectively 15 and 16, driven and pressed one against the other by pulleys such as 17 and 18. These pulleys are driven by motor means not shown, and rotate respectively in the direction of the arrows 19 and 20. The conveying means 2 could comprise, sets of rollers coming into direct contact with flat objects unstacked in place of the strips 15 and 16. Finally, they could have any other known shape.

 The conveying means 2 convey the flat objects to a receiving means 3 which in a sorting application comprises for example several receptacles denoted 21 to 24. In this application the objects to be sorted are deposited in the corresponding receptacle under the effect of sorting orders issued by control members 25 to 28 respectively. The features of receptacles 21 to 24 and control members 25 to 28 are independent of the invention.

 The shooting device 4 essentially comprises a video camera 29 provided with its detector 30 and a lens 31.

 The purpose of the objective 31 is to focus the camera 29 at the distance d separating in use the objective 31 from the lower sections 32 and 33 of the objects 13 and 14 respectively.

This adjustment makes it possible to avoid taking account of phenomena other than the passage of the slices of the objects in scrolling in the image plane of the camera 29. The signal produced by the detector 30 is introduced into the processing means 5 which develop in in case of detection of a multiple take a scrap order.

The scrap order can be entered on the invalidation inputs of the control members 25 to 28 to prevent these members from assigning the multiple outlet to one of the receptacles designated by the address of the first object taken into account. This waste order is introduced at the input of a control member 34 imposing the dejection of the multiple outlet in a waste receptacle 35. In the example presented the waste receptacle 35 is located at the start of the sorting chain, in another example it is located at the end to also receive all the flat objects whose assignment to a receptacle has been missed. Putting it in place at the start of the sorting chain thus makes it possible to avoid any jams or breakdowns that could cause the multiple take.

 To improve the contrast of the image captured by the camera 29, complementary lighting is set up symbolized by the lamps 36 and 37 by choosing the color of the light emitted by these lamps so that it corresponds to the length d wave of better sensitivity of the detector 30. The contrast of the captured image can be further improved by moving the slice 32 of the object 13 away from the slice 33 of the object I 4 To do this, air is injected by a nozzle 38 disposed under these sections. You can also do this differently, by placing a suction nozzle oriented perpendicular to the plane of flat objects in transit. Its effect is to vacuum the flat object that is closest to it. In this way, the effective separation of the lower sections of the objects conveyed together is ensured. However, thanks to the separating power of the detector 30 and its associated optics, this additional device is not essential in the majority of cases.

Objects which have undergone a multiple take are often of different sizes. Furthermore, the malfunction of the unstacking means 1 also has the consequence of shifting the objects 13 and 14 relative to one another. Also, to focus a sharp image on the detector 30 of the camera 29, it is important to have the latter facing a place where the trajectories of the slices examined of flat objects in movement are common and invariable. In
The example presented shows that the trajectory of the upper slices of flat objects is not invariable Indeed, it varies from one object to another depending on their respective size. Also Invention plans to place the camera 29 opposite of the lower edge of the flat unstacked objects. A support plate 39 holds the flat objects on edge to the right of the shooting device 4.

This plate 39 is preferably arranged in the same plane as the bottom 10 of the unstacking means. A continuous path can even be provided between this bottom 10 and this support plate 39.

It is not drawn in FIG. 1 so as not to overload the drawing.

 In FIG. 2, there is a special feature of the operation of the conveying means 2 in line with the shooting device 4. Firstly the support plate 39 is pierced by a window 40 reducing the field of examination of the camera to useful dimensions . Furthermore, by means which are not shown, compressions are applied which tend to bring the belts 15 and 16 closer together and subsequently to pinch the objects carried by these belts with negligible slip. The compression means can be any. Under the effect of these compressions, the objects 13 and 14 which are inserted between the belts tend to warp each on their side. This warping, possibly combined with the action of a suction nozzle or blowing, has the effect of spreading the lower sections 32 and 33 respectively from one another. It follows that the image captured by the camera 29 will then comprise two clearly differentiated peaks and brightness.

 In one application, the detector 30 is a strip of a charge transfer device. This bar is placed orthogonally to the direction of transit of the objects 13 and 1 and it can comprise 1000 cells in steps of 25 micronsimeter. The time for charge transfer from one cell to another is of the order of a microsecond. This means that the line sweep frequency provided by the circuit is of the order of Kilohertz. Taking into account the speed of passage of flat objects in front of the window 40 which is of the order of several meters per second and taking into account an average overlap of ten centimeters of a flat object 13 on a flat object 14 it is deduced therefrom that the camera 29 will have scanned the phenomenon to be detected several tens of times during the time when it is significant.

 The processing means 5 are shown in FIG. 3 and their operation is examined by means of the time diagrams in FIG. 4. The video signal SV delivered by the camera 29 is introduced at the input of a threshold comparator 41 having the object of which is to reshape the video signal SV to develop a so-called binary video signal SVB oscillating between two characteristic levels. The trigger threshold of the comparator 41 can be fixed in advance, it can also be adjusted to be equal to half the maximum of the video signal SV measured at the output of the camera. In doing so, the SV signal self-adjusts according to the brightness received, since the signal can vary significantly depending on whether the flat objects to be detected are light or dark in color. The means 48 for adjusting the threshold of the comparator 41 are known means, which may include, for example, an RC circuit with a time constant greater than the scanning period and the resistance R of which is constituted by a resistive divider bridge. The midpoint of this dividing bridge delivers the set threshold signal.

 In FIG. 4, a distinction is made between the scanning signal SB specific to the camera 29, equal to 1 during each scanning period and canceling out at each end of the period. From this signal, two other signals are developed, a Test signal which is the complement to 1 of the signalSB presented, and a reset signal, called RESET, delayed with respect to the Test signal of a duration t. Obtaining these signals can be done by any known means. The SVB signal appears below the RESET signal. This SVB signal presents during a first scanning period a single pulse II, during the second and the third scanning period a double pulse 12.32 and I.33.33 during the fourth scanning period. single pulse scan 14, and during the fifth scan period no pulse. This means that during the first scanning period only one letter slice is detected, which means that one of the flat objects was ahead of the other. During the second and third scanning period, the double pulse indicates that there are two objects 13 and 14 joined together. During the fourth scanning period, only one slice is visible again and during the fifth scanning period, the double socket is completely passed, the video signal then remains zero.

In the exemplary embodiment of the processing means 5 which will be described, use is made of a D flip-flop. These D flip-flops have the particularity of locking and delivering at their output Q, a signal identical to that present at their input D upon reception on their input H of the rising edge of a clock pulse authorizing this transfer. These flip-flops also contain a Q output complementary to the Q output, as well as an input
Reset used to reset the Q output. The invention cannot however be limited to the use of such flip-flops. This realization is given only by way of example; the same operation of the processing means could also be obtained by any other means, in particular by means of a microprocessor which would manage the control members 25 to 28 and 34.

 The signal SVB is introduced on the input HI of a first flip-flop D 42. On the input D1 of this flip-flop 42 a logic level symbolized by a positive voltage generator 43 is permanently introduced. The reset signal is introduced on the input RAZ1 of this flip-flop 42 whose output Q1 delivers the signal SQ1 visible in FIG. 4. By examining this signal SQ1 we note that during the first scanning period, very shortly after the start of this period the signal1 is imposed on O by a pulse of the RESET signal. Consequently, the duration t is adjusted experimentally so as not to encroach on the useful scanning part while sufficiently distinguishing itself from the moment of passage of the pulse of the Test signal. During this first scanning period, during the appearance of the pulse 11 of the signal SVB on the clock input of the flip-flop 42, the logic level introduced in D1 is transferred to the output Q1 and therefore the signal SQ1 is equal to I from the appearance of l impulse It.

 During the second scanning period, the reset signal resets the signal SQ1 to zero, which goes back to 1 when the pulse 12 of the double pulse 12, 32 mentioned previously appears.

Then the signal SQ1 is reset to zero by pulse of the RESET signal appearing during the third scanning period. Thus, the signal SQ1 goes up to 1 on the first detected pulse and goes down to zero shortly after the start of the next scanning period.

 This signal SQ1 is introduced on re-entry D2 of a second flip-flop D 44 while the test signal is introduced on the input H2 of this flip-flop 44. The signal SQ2 delivered by the output Q2 appears under the signal SQ1 in FIG. 4. At the end of the first scanning period, the signal SQ1 equal to 1, being admitted on the input D2 of the flip-flop 44, is transferred by the pulse of the Test signal to the output Q2. The signal SQ2 is therefore equal to 1 from this moment on. It can be seen that the preceding signal SQ1 is equal to I at each end of the scanning period since it is only reset after the start of the following scanning period. Ln eonsequence9 lQimpulsòn Test will transfer the signal SQI to Q2 when it is equal to 1.

This continues to occur until the end of the fifth scanning period. At this instant, the pulse T5 of the test signal forces the transfer of a zero signal SQ1 to the output Q2, the signal SQ2 therefore drops to zero. It can thus be seen that the detector 30 a detects the presence of an object during the first four scanning periods, that is to say between the dates of the signal pulses
Test TO and T4, and that the signal SQ2 representative of this information is brought to 1 between the dates of the pulses T1 and T5. The signal SQ2 is called the "presence of object" signal because, apart from a scanning period close to which one can easily manage, it indicates, by being brought to level 1, the duration during which at least one object flat is visible through window 40.

 A third flip-flop D numbered 45 receives on its input D3 the signal SQ1, receives on its input H3 the signal SVB and receives on its input RAZ3 the signal delivered by the output 42 which is the complementary to 1 of the signal SQ2. The signal SQ3 delivered by the output Q3 of this flip-flop 45 is visible in FIG. 4. During the first scanning period, the signal SQI, initialized by the pulse I1 of the signal SVB, cannot be transmitted to the Q3 output because the clock signal authorizing this transmission is the same as that which was used to generate the Sapa signal. As the transit times through the D flip-flops, while being very low, are not negligible from this point of view it follows that when the pulse I1 arrives at the input H3 the signal SQ1 is not yet present at l entry Fui3.

Consequently, the Q3 output remains at zero.

 On the other hand, during the second scanning period, the second pulse 32 of the pair of pulses 12, 32 arrives with sufficient delay so that the signal SQ1 has had time to be brought to level 1 by the pulse 12. Consequently, the signal SQ3 rises to 1 at the time of the pulse 32. This is the opposite of what occurs at the start of the next pair of pulses 13.33. Indeed, when 13 paratt SQ I is zero slightly before the appearance of 13 and is plagued at 1, to the nearest transit time, only after the appearance of 13.

As 13 is also applied to the clock input H3 of flip-flop 45, this pulse has the effect of lowering the output SQ3. However, this rises very shortly afterwards at the moment of the appearance of the pulse 33. This oscillation continues until the appearance of a pulse of the single SVB signal 14 which definitively resets the signal SQ3.

 The output Q3 of the flip-flop 45 is introduced on the input H4 of a fourth flip-flop D 46 whose input D4 is permanently brought to a logic level 1 by a positive voltage generator 47.

In addition, input RAZ4 of flip-flop 46 is connected to output> 2 of flip-flop 44- which delivers a signal complementary to the signal
SQ2. The signal delivered by output Q4 is the OR signal "reject order" mentioned above. When the first pulse of the signal SQ3 appears, during the second scanning period, the logic level 1 introduced in D4 is transmitted in Q4 and the OR signal rises to 1. I1 remains at 1 until 'it receives a positive pulse on its RESET 4 input, this is delivered by the Q2 output and therefore the OR signal drops to zero at the same time as the SQ2 signal. Under these conditions it can be seen that the processing means 5 have issued a reject order setting to 1 as soon as the first signs of the presence of a double take appear. This reject signal disappears as soon as the objects in question have passed. The orders of presence of object and the orders of scrap can be exploited in various ways by the reception means 3.

 The operation described for a double socket is of course the same if one is in the presence of a multiple socket.

The invention applies in particular to postal sorting, it also applies in all cases where the handling of flat objects in large numbers is envisaged, in particular in publishing.

Claims (10)

 1. Device for detecting multiple catches of objects, of the type comprising a means (1) for unstacking stacked flat objects and a means (2) for conveying towards a means (3) for receiving unstacked flat objects, characterized in that that it comprises means (4) for taking pictures, arranged in line with the conveying means downstream of the unstacking means, for developing a video signal (SV) representative of the image of the slices (32,33) of the objects moving dishes and means (5) for processing the video signal developed to produce a signal (OR) of the presence or absence of multiple sockets.  2. Detection device according to claim I characterized in that the means (4) for taking pictures are arranged opposite a place (39) where the trajectory of the section examined of flat objects in movement is invariable.  3. Detection device according to any one of claims 1 to 2 characterized in that the shooting means comprise a lens (31) for focusing on a predetermined distance (d).  4. Detection device according to any one of claims I to 3 characterized in that the means (4) for taking pictures comprise a bar (30) of a charge transfer device oriented orthogonally to the direction of travel of the objects .  5. Detection device according to any one of claims 1 to 4 characterized in that the means (4) for taking pictures comprise means (36, 37) for lighting to improve the contrast of the captured image.  6. Detection device according to any one of claims 1 to 5 in which the receiving means (3) comprises a set (21 to 28) for sorting conveyed objects, characterized in that this sorting set comprises a box (35 ) discarded to receive flat objects (13,14) having undergone a multiple grip.  7. Detection device according to any one of claims 1 to 6 characterized in that the processing means (5) comprise means (41) for converting the video signal into impulse signal (SVB), and means (42 to 47) to count the pulses of the converted signal on demand.  8. Device according to any one of claims I to 7 characterized in that the means (5) for processing comprise means (48) for carrying out a self-correction of the amplitude of the detected video signal.  9. Device according to any one of claims 1 to 8 characterized in that the conveying means (2) comprises means (38) for separating from one another the edges of the flat objects having undergone a multiple grip and thus improving the contrast of the captured image.  10. Device according to any one of claims 1 to 9 characterized in that the means (2) for conveying comprises a window (40) for aiming to take the picture.