US3198513A - Stacking devices for sheet articles - Google Patents

Description

Aug. 3, 1965 c. FAREZ 3,198,513

STAGKING DEVICES FOR SHEET ARTICLES Filed June 28, 1963 2 Sheets-Sheet 1 Q wag INVENTOR BY M ATTORNE E Aug. 3, 1965 c. FAREZ 3,198,513

STAGKING DEVICES FOR SHEET ARTICLES Filed June 28, 1963 2 Sheets-Sheet 2 INVENTOR 00mm may BY ww w United States Patent C) 3,198,513 STACKMJG DEVICES 56R SHEET ARTLCLES Claude Farez, Saint Maui, France, assignor to Qharvo, Grenoble (isere), France, a French joint-stock company Filed lune 28, 1963, Ser. No. 231,333 7 Claims. (Cl. 271-1) This invention relates to automatic stacking machines for flexible sheet'articles such as hides or skins.

Hides or skins are frequently treated in a continuous process on endless conveyors by being disposed on the conveyor at the inlet end thereof so as to pass through successive treating stations. At the outlet end of the conveyor the hides or skins are stacked either on a flat supporting table or more generally on a pallet or horse and'it is frequently required that they be alternately disposed with the grain side up and with the flesh side up, this being known as Marry stackingbecause adjacent hides are in grain side to grain side or flesh side to flesh side contact. The automatic stacking device conveniently comprises a movable depositing member by means of which the successive hides or skins are fed so as to be properly positioned on the stack support.

A first diificulty to be solved in such stacking machines is that the hides or skins are disposed more or less at random at the inlet of the conveyor. It is therefore impossible to synchronize the operation of the depositing member with the advance of the conveyor and some means must be devised to detect the arrival of the hides or skins at the outlet end of the conveyor and to time in correspondence the operation of the depositing member. For instance the passage of each hide may be detected by feelers disposed a short distance upstream of the outlet end of the conveyor (such conveyor being generally made of parallel strings or cables through which the feelers may project) and the depositing member may begin to operate a pre-determined time after actuation of the feelers by the incoming hide.

Another difiiculty encountered is that hides or skins are articles of widely varying shapes and dimensions. If therefore the detector means and the delayed actuation of the depositing member have been so adjusted that a hide of average shape and dimensions be properly disposed on the supporting pallet with its center of gravity substantially in registration with the midpoint or top line of the pallet, an abnormally long or short hide will be liable to slip and to fall to the floor.

It has been proposed to separately detect the passage of the leading edge and of the trailing edge of each hide and to operate the depositing member in such a manner that a point situated midway between the leading and the trailing edge be deposited on the midpoint of the support. But this solution would only be correct if the hides were in the form of regular geometrical surfaces (as for instance of rectangles) and if they were disposed on the conveyor with one of their axes parallel to the longitudinal axis of the conveyor. Since these conditions are not fulfilled, the center of gravity of the hide may widely differ from the midpoint deduced from the leading and the trailing edge thereof and therefore the stacking is not correctly effected.

It is an object of the present invention to provide a machine which will obviate these disadvantages and which will stack regularly sheet articles such as hides or skins as they reach the outlet end of an endless conveyor irrespective of their varying shapes and/ or dimensions.

In accordance with the present invention in a machine for stacking flexible sheet articles of irregular shapes and dimensions which are fed by an endles conveyor of substantially transparent nature (as for instance by an endless conveyor made of spaced parallel strings, cables or the like), the article is caused to pass between a pair of ice to be stacked, and a pair of photo-electric cells respectively associated with each surface, a signal is derived from the said cells when they receive the same quantity of light, this meaning that the center of gravity of the article to be stacked is substantially situated on the above-mentioned transverse line, and this signal is used to cause delayed operation of the movable depositing member.

. Of course in the absence of any article between the light-emitting surfaces and the cells, the latter receive an equal quantity of light and in autmatic operation without any attendant the device which compares the voltages received from the cells would emit a continuous spurious signal if no particular means were provided. Such means may preferably consist of an auxiliary detector which only permit effective operation of this comparing device when an article is present between the light-emitting surfaces and the cells. This auxiliary detector may be in the form of a narrow intermediate auxiliary light-emitting surface disposed between the above-mentioned or main lightemitting surfaces and associated with an auxiliary cell. The voltage emitted by thi auxiliary cell may actuate a relay or the like which opens an appropriate electric circuit to render the automatic comparing device ineffective as long as the quantity of light received by the auxiliary cell exceeds a pre-determined limit.

The movable depositing member is preferably in the form of a reciprocating carriage disposed under the outlet end of the endless conveyor (which will behereinafter designated as the main conveyor) and movable substantially in parallel relation therewith, the said carriage supporting an auxiliary conveyor which is permanently driven in the reverse direction with respect to the main conveyor and in such a manner that its absolute velocity, i.e. its velocity with respect to the stationary frame of the machine, remains always equal to the velocity of the main conveyor, irrespective of the displacements of the carriage. The carriage itself may be actuated in any appropriate manner, as for instance by a double clutch with reversing gearing, by a reversible electric motor, by a pneumatic or hydraulic ram, etc.

In the annexed drawings:

FIG. 1 is a digrammatical side view illustrating the main constituents of a stacking machine according to this invention.

FIG. 2 is a cross-section of a light-emitting surface with its associated parts.

FIG. 3 is a plan view showng a hide at its passage on the light-emitting surfaces.

FIG. 4 is a general diagram of the electric circuits associated to the photo-electric cells.

FIGS. 5 to 10 are simplified side views showing the successive steps of a full operating cycle of the movable depositing carriage.

FIG. 11 is a diagrammatical perspective view illustrating a possible embodiment of the carriage actuating mechanism.

FIG. 12 is a diagram of the electric circuits which con trol the double clutch of this mechanism.

FIG. 1 shows the outlet end of the endless conveyor 1 of a machine for the treatment of sheet articles such as hides and skins, this conveyor (which will be hereinafter referred to as the rnain conveyor) beingformed of a large number of parallel endless strings or cables stretched between end drums such as 2. Close below the effective upper run of conveyor 1 and some what upstream of the end drum 2 are disposed three light-emitting surfaces 3, 4 and 5'. Each surface such as 3 comprises a fiat box 6 (FIG. 2) having a rectangular horizontal contour with the inside painted in white, this box enclosing a number of tubular luminescent electric tubes 7 and being closed by a ground plate glass 8. These light-emitting surfaces extend transversely along the full width of conveyor 1. Surfaces 3 and 5, which form the main light-emitting surfaces of the machine, are disposed each side of surface 4 and they extend longitudinally along a length at least equal to half the length of the longest hide which may have to be stacked, while surface 4, or auxiliary light-emitting surface, is quite narrow, its dimension in the longitudinal irection of conveyor 1 being negligible with respect to surfaces 3 and 5. A photo-electric cell is associated to each main or auxiliary light-emitting surface, these cells, referenced respectively 66, 6'7 and 68, being disposed above conveyor 1, each at the top of a light collecting hood 9, 1G and 11.

When no hide is present between the light emitting surfaces 3, 4, and the corresponding cells 66, 67, and 68, the main cells 66 and 68 (i.e. those corresponding to the main light-emitting surfaces 3 and 5) are equally illuminated and the auxiliary cell 67 (corresponding to the auxiliary light-emitting surface 4) is fully illuminated. When a hide such as 12 (FIG. 3) passes on the lightemitting surfaces it succesisvely influences cells 66, 67 and 63 by reducing the quantity or intensity of light received by each cell. When the hide is simultaneously on both main surfaces 3 and 5 (as illustrated in FIG. 3) the light received by cell 66 increases progressively (since the hide is leaving surface 3), while the light received by cell 68 decreases progressively (the hide coming on surface 5). When both cells are equally illuminated the area of the portion of the hide which covers surface 3 is exactly equal to the portion thereof which covers surface 5, which means that the center of gravity of the hide, considered as a mere geometrical surface, is exactly situated on the transverse line of symmetry of the illuminating unit, as indicated at G, the influence of the quite narrow intermediate auxiliary surface 4 being negligible. It may besides be remarked that if the portion of the hide which covers surface 4 is substantially rectangular, the presence of this auxiliary surface has no influence whatever on the position of point G. 7 Now a hide is generally of substantially uniform thickness and density, and therefore its center of gravity fairly corresponds with the center of gravity of its contour considered as a geometrical surface.

It results from the above description that the passage of the center of gravity of the hide across the transverse axis of symmetry of the illuminating unit may be detected by the equality of the voltages emitted by the main cells 66 and 68, and by a simultaneous substantial reduction of the voltage from the auxiliary cell 67.

FIG. 4 illustrates an arrangement of electric circuits whereby a signal may be derived from the above operation of cells 66-68. The main cells 66 and 68 act in one and the other direction on an amplifier 13 which emits a resultant outlet voltage proportional to the difference be tween the inlet voltages received from cells 66 and 68. This resultant voltage is applied to a polarized relay or galvanometer 14 the movable member 15 of which forms a contact cooperating with two fixed contacts 16 connected with the coil of a relay 17 having its contacts normally closed. This relay is inserted in an electric line 18 which is connected with a registering device or memory 19. In line 18 is inserted another relay 20 the coil of which is energized by the auxiliary cell 67. This relay is also of the type having its contacts normally closed and it is further so arranged that it is only actuated (i.e. that its contacts are only open) when cell 67 is almost fully illuminated. This may be obtained in any appopriate manner, as for instance by properly adpusting its biassing spring, or by inserting a Zener diode in series with its coil.

In the absence of any hide between the auxiliary lightemitting surface 4 and the auxiliary cell 67, the latter is fully illuminated, relay 20 is therefore open and no voltage movable member or contact 15 is at the neutral position between contacts 16. Relay 17 is unenergized and its.

contacts are closed. When the leading edge of an incoming hide such as 12 (FIG. 3) reaches the first main light-emitting surface 3, the main cells 66 and 63 are no more equally illuminated, the movable contact 15 deviates and engages one of the fixed contacts 16 so that relay 17 is energized and that it opens its contacts. When the leading edge of hide 12 reaches the auxiliary surface 4, the voltage emitted by the auxiliary cell 67 is substantially reduced and therefore relay 2t) closes its contacts, but memory 19 cannot receive any current from line 18 since the contacts of relay 17 are open. But when the center of gravity G of hide 12 passes across the transverse line of symmetry of the illuminating unit the voltages emitted by the main cells 66 and 68 are momentarily equal, the movable contact 15 of galvanometer 14 returns to its neutral position (or more exactly it moves from one fixed contact 16 to the other one and therefore passes through the neutral position) and relay 17 being unenergized, its contacts close for a short time. Memory 19 thus receives a current pulse. This memory is so arranged as to start a movable depositing carriage, still to be described, a predetermined time after it has received such a pulse.

The horizontally movable depositing carriage 21 is disposed immediately below the outlet end of conveyor 1, this carriage being guided by appropriate guides, not illustrated. Carriage 21 supports an auxiliary conveyor 22 which may be formed, as the main conveyor 1, of a number of parallel strings stretched between end drums 23 and 24, though it may be of any appropriate form. The end drum 23 which. is upstream with respect to the main conveyor 1 (i.e. the left-hand end drum in FIG. 1) has a lateral sprocket 25 which cooperates with an endless chain 26 which passes on a sprocket 27 carried by the corresponding end of the end drum 2 of the main conveyor 1, on a returning sprocket 28 supported .by the frame of the machine (not illustrated) and finally on a second returning sprocket 29 supported by carriage 21 itself. Sprockets 25 and 27 have the same number of teeth and of course the same diameter.

It will be understood that assuming that carriage 21 is at a standstill, the sprocket 25 of the end drum 23 of the auxiliary conveyor 22 rotates at the same speed as the sprocket 27 of the end drum 2 of the main conveyor 1. If both end drums 2 and 23 have the same diameter, the linear velocity of the auxiliary conveyor 22 will be exactly equal to that of the main conveyor 1, but in the reverse direction. Alternatively sprockets 25 and 27 could have different number of teeth provided the ratio of the numbers of drums 23 and 2 be equal to the ratio of these diameters. When carriage 21 moves, this equality of the linear velocities of conveyors 22 and 1 is not perturbed provided the velocity of conveyor 22 is considered with respect to the stationary frame of the machine (absolute velocity) and not with respect to the movable frame of the carriage (relative velocity). It is clear for instance that if conveyor 1 is at standstill (velocity Zero), the absolute velocity of conveyor 22 will be zero whatever may be the movement of the carriage.

It is now possible to describe the general operation of the stacking machine before going into the details of its controlling and actuating devices.

The beginning of an operating cycle may for instance correspond to the position diagrammatically illustrated in FIG. 5. The depositing carriage is at standstill at the right-hand end of its stroke with its left-handend drum 23 slightly upstream of the end drum 2 of the main conveyor 1 (the term upstream being used here with reference to the main conveyor). The stacking pallet or horse 30 is in position to receive the hides in flesh side to flesh side contact. In practice this pallet is mounted on a wheeled carriage and its proper position is carefully indicated on the floor or is determined by positive positioning means such as lateral guides and transverse abutments.

When a hide 12 reaches the outlet end of the main conveyor 1, it passes on the auxiliary conveyor 22 which moves it towards the left (i.e. upstream with respect to the main conveyor) until it hangs vertically from the lefthand end drum 23, as shown. At an appropriate time carriage 21 is started by the above-described memory ll? of PEG. 4 to effect its stroke towards the left and the hide is progressively deposited on horse 36 as indicated in FIG. 6. It is to be observed that the regular transfer of the hide 12 from the main conveyor 1 onto the auxiliary conveyor 22 is only possible because the absolute velocities of both conveyors are equal. Further the advancing speed of the depositing carriage 21 should be lower than the absolute velocities of both conveyors, since otherwise the relative velocity of the auxiliary conveyor 22 with respect to its supporting carriage 21 would'be negative (i.e. directed towards the right) and the hide would hang and fall from end drum 24.

It is to be noted that the side of the hide which rests on the stacking horse 3% is the same as that which was on the main conveyor 1. In other words the hide has not been inverted.

When the hide has thus been deposited, carriage 21 continues its stroke and stops at the position shown in FIG. 7, for which its right-hand end drum 24 is just slightly downstream of the end drum 2 of the main conveyor (the term downstream being here again used with reference to the main conveyor).

When another hide 12' reaches the outlet end of the main conveyor 1, it is again transferred onto the auxiliary conveyor 22 on which it moves upstream with respect to the main conveyor 1, i.e. towards the left, as illustrated in FIG. 7. The hide 12' therefore reaches end drum 23 and it hangs therefrom as indicated in FIG. 8. The carriage is then again started by the memory 19 to effect its stroke towards the right and the hide is regularly deposited on the horse or pallet 39, as indicated in FIG. 9. The depositing carriage stops when it reaches its initial position, as indicated in FIG. (which is to be compared with PEG. 5). The side of hide 12 which rests on horse (or more exactly on the previously stacked hide 12) is the side which was facing upwardly on the main conveyor 1. In other words the hide 12 has been inverted and the successive hides will be stacked in grain to grain and flesh to flesh contact.

It is further to be noted that proper operation requires that the depositing carriage 21 moves at a sufficiently high speed since otherwise the hide would fall from the end drum 23 before reaching the stacking horse 3d. Carriage 21 should therefore be driven alternately at a low speed towardsthe left and at a high speed towards the right.

FIG. 11 diagrammatically illustrates a possible driving mechanism for this purpose. A shaft 31 is connected in any appropriate manner with the main conveyor 1 or with the driving gearing thereof. Shaft 31 has a bevel pinion 32 which meshes with two opposed bevel gears 33 and 34 carried by alined shafts 35 and 36. On each shaft 35 or 36 is mounted a sprocket wheel, respectively 37, 33, connected by a chain 39, 4% with another sprocket wheel 40, 41, wheels 44 and 41 being loosely mounted on a common shaft 43. Shaft 43 supports a double clutch 44, as for instance of the electromagnetic type, by means of which wheels 4t) and 41 may be selectively coupled with shaft 43. Shaft 43 has a pinion 45 which meshes with a rack 46 carried by the depositing carriage 21.

It will be apparent that the double clutch 44 permits to drive carriage 21 in one or the other direction at two different speeds, as determined by the relative diameters of sprockets 37-41 and 38-42.

FIG. 12 shows an embodiment of a device to control operation of carriage 21. The memory 19 of FIG. 4 has been illustrated as in the form of an endless member capable of registering signals emitted by the relay 17 of FIG. 4. Memory 19 may for instance be formed ofa drum carrying an annular row of needles which are frictionally slida ole in longitudinal holes of the drum. This form of mechanical memory being conventional in the art, it has not been described nor illustrated in greater details. In FIG. 12 reference numeral 19 may be considered as designating a portion of the drum, the needles being not illustrated. Reference numeral 43 indicates the solenoid which pushes the needles longitudinally with respect to the drum (i.e. downwardly in FIG. 12) under control of relay 17 of FIG. 4 so as to register in the memory (i.e. on the drum) the pulses received from the said relay. Reference numerals 49 and 5t designate two successive needle feeler switches respectively corresponding to the upstream and to the downstream stroke of carriage 21 (upstream and downstream referring to the movement of the main conveyor 1). Each feeler switch closes an electromagnetic switch or contactor switch, respectively 51, 52, which in turn controls one of thecircuits of the double clutch 44. In order to avoid that both circuits of clutch 44 be simultaneously energized, each contactor switch comprises an auxiliary contact 53, 54 inserted in the actuating circuit of the other contactor switch so as only tobe closed when the first contactor switch is open, in such a manner that when once a contactor switch such as 5'1 is closed, the other one 52 cannot be closed before the first one has returned to the open position. \Contactor switches 51 and 52 are'of the self-retaining type and in their retaining circuit 55, respectively 56, is inserted a normally closed end switch 57, 58 actuated by carriage 21 when same reaches the end of one of its strokes.

' There is further provided a restoring device 59 (such as a stationary cam surface) which returns the needles of the memory drum 1-9 to their inoperative position.

Drum 1-9 may be rotated in any appropriate manner, as for instance by a separate constant speed motor, but it is preferable'to derive its drive from the machine it self, as for instance from the end drum 2 of the main convey-or l, in order that its rotational speed be always proportional to the linear speed of the conveyors.

Supposing that the depositing carriage 21 is at its lefthand end stroke, it maintains switch 57 at the open position and therefore feeler switch 49 cannot close con.- tactor switch '51. When a hide passes on the illuminating unit, relay 17 of FIG. 4 registers its passage in memory 19 by causing solenoid 48 to displace one or several suc cessive needles thereof. These needles thereafter actuate feeler switch 49 but, as above explained, this actuation has no elfect on contactor switch 51, switch 57 being open. But when the first needle displaced by solenoid 48 reaches feeler switch 5%, the latter close contactor switch 52 which in turn actuates the double clutch 44 in such a manner as to displace carriage 21 towards the right at the proper speed. At the end of its stroke carriage 21 opens switch 56 and therefore returns contactor switch 52 to the open position. When the passage of the next hide is registered in memory 19, switch 57 will be closed and switch 53 will be open. Fee er switch 49 will therefore be effective while feeler switch 5% will be inetfective. When the first needle displaced by solenoid 48 reaches feeler switch 49, the latter will close contactor switch 51 and carriage 21 will move towards the left until it opens switch 57 at the end of its stroke.

It will be observed that the time elapsed between passage of the center of gravity of the hide on the illuminating unit, as indicated in FIG. 4, and the starting of the depositing carriage 21 may be adjusted at will for each stroke of the carriage by merely displacing feeler switches 49 and/or 50 with respect to the memory drum or carrier 19. The displacements of the carriage may thus be so timed that the center of gravity of the hide be always disposedon the top of horse or pallet so whatever may be the shape or dimensions of the hide since the signal registered in memory 19 corresponds to passage of the center of gravity of the hide across a fixed transverse line of the frame.

It will be observed that the device of FIG. 12 may operate with any kind of memory and with any kind of carriage driving gear, the double clutch of FIG. 11 being only illustrative of one of the many possibilities of the present invention.

For instance the driving shaft 43 of FIG. 11 could be connected by gears, pulleys or otherwise with a reversible two speed electric motor, contactor switches 51 and 52 being so arranged as to actuate this motor respectively in one direction at a first speed and in the reverse direction at the other speed.

The pinion-and-rack gearing 4546 of FIG. 11 could be replaced by a drum on which would be wound in one and the other direction the ends of an endless cable, belt or like flexible member attached to the carriage and appropriately guided by idle pulleys. Alternatively the carriage could be attached to an endless belt stretched between two end pulleys, one of the latter being driven by a reversible two-speed motor, or by a double clutch such as clutch 44 of FIG. 11.

In another embodiment the depositing carriage 21 could be reciprocated by a pneumatic or hydraulic ram to the ends of which fluid under pressure would be supplied through two electromagnetic valves controlled by contactor switches 51 and 52 of FIG. 12. The advancing speed could be adjusted by pressure regulators or throttling members respectively associated with each valve. 'Each valve would be double in order that when actuated it would inject fluid under pressure into one end of the ram and at the same time connect the other end with an exhaust line.

I claim:

1. A machine for stacking opaque flexible sheet articles, such as hides and skins, comprising a main endless conveyor with a substantially flat article-carrying portion having a first side and a second side and an outlet end, and being at least in part transparent to light in the vicinity of said outlet end, said articles being disposed at random on one of said first and second sides of said article-carrying portion of said main conveyor to be carried thereby towards said outlet end at a given linear speed; two stationary main lightemitting surfaces disposed on the first side of said article-carrying portion of said main conveyor in the vicinity of the outlet end thereof and extending across the full width thereof substantially symmetrically with respect to a line transverse to said article-carrying portion of said main conveyor and close to said line so as to illuminate the articles carried by same, said surfaces having a substantially uniformly distributed luminosity and said surfaces each having a dimension longitudinally of said article-carrying portion of said main conveyor at least equal to half the maximum length of the articles to be stacked; two main photoelectric cells disposed on the second side of said articlecarrying portion of said main conveyor, each to receive light substantially from one only of said main lightemitting surfaces; comparing means to compare the voltages emitted by said main photo-electric cells and to deduce from such comparison the passage across said transverse line of the approximate center of the surface of an article carried by said main article-carrying portion of said main conveyor between said main light-emitting surfaces and said cells; a stacking support disposed in the vicinity of the outlet end of said article-carrying portion of said main conveyor and on which the articles carried by said conveyor are to be stacked; depositing means to receive the articles from the outlet end of said articlecarrying portion of said main conveyor and to deposit same on said support; driving means to drive said depositing means; and means to actuate said driving means a pre-determined time after said comparing means have detected passage of the approximate center of the surface {3 0 of an article across said transverse line to. substantially regularly stack same on said support.

2. In a machine as claimed in claim 1, means to detect the presence of an article between said main lightemitting surfaces and said main photo-electric cells to avoid spurious operation of said depositing means under the action of said comparing means in the absence of any article on said article-carrying portion of said main conveyor between said main light-emitting surfaces and said main photo-electric cells.

3. In a machine as claimed in claim 1, an auxiliary lightemitting surface disposed between said main lightemitting surfaces, said auxiliary surface extending substantially across the full width of said article-carrying portion of said main conveyor and being of small dimension with respectto said main surfaces longitudinally of said main conveyor, and said auxiliary surface being disposed on one of said first and second sides of said article-carrying portion of said main conveyor; an auxiliary photo-electric cell disposed on the other side of said article-carrying portion of said conveyor to receive light substantially exclusively from said auxiliary lightemitting surface; and means under control of voltage from said auxiliary photo-electric cell to prevent said driving means from being actuated when the voltage from said auxiliary cell exceeds a pre-determined limit.

4. In a machine as claimed in claim 1, said depositing means comprising a carriage reciprocatable under said article-carrying portion of said main conveyor in the vicinity of the outlet end thereof and substantially in parallel relation thereto; an auxiliary endless conveyor supported by said carriage; and means to move said auxiliary conveyor at an absolute linear speed equal to the linear speed of said article-carrying portion of said main conveyor and in the reverse direction with respect thereto independently of the movement of said carriage.

5. A machine for stacking opaque flexible articles such as hides and skins, comprising a main endless conveyor with an article-carrying portion having an outlet end, said articles being disposed at random on said articlecarrying portion of said conveyor to be carried thereby at a given linear speed; a depositing carriage reciprocatable under said article-carrying portion of said main conveyor in the vicinity of the outlet end thereof and in substantially parallel relation thereto; an auxiliary endless conveyor supported by said carriage, said auxiliary conveyor also having an article-carrying portion; means to move said article-carrying portion of said auxiliary conveyor at an absolute linear speed equal to the linear speed of said article-carrying portion of said main conveyor and in the reverse direction with respect thereto independently of the movement of said carriage; first carriage driving means to cause said depositing carriage to effect a first stroke in the reverse direction with respect to the movement of said article-carrying portion of said main conveyor at a speed lower than the linear speed thereof; second carriage driving means to cause asid depositing carriage to effect a second stroke in the same direction as the movement of said article-carrying portion of said main conveyor at a speed higher than the linear speed thereof; means to detect the passage of the approximate center of the surface of an article across a line transverse to said article-carrying portion of said main conveyor and situated at a distance upstream of the outlet end thereof; and means to alternately actuate said first carriage driving means and said second carriage driving means a pre-determined time after passage of the approximate center of the surface of an article across said line.

6. An apparatus to detect the passage of the approximate center of the surface of an opaque flexible sheet article moving across a substantially linear path across a stationary line transverse to said path, comprising two stationary main light-emitting surfaces disposed on a first side of said path, symmetrically with respect to said line and close to same, and extending across the full width of said path in such manner that said article fully passes in front of them, each of said surfaces having a dimension longitudinally of said path at least equal to half the length of said article, and said surfaces further having a substantially uniformly distributed luminosity; two photo-electric cells disposed on the second side of said path each to receive light from one only of said light-emitting surfaces; and means to compare the voltages from said cells during passage of said articles in front of said light-emitting surfaces.

7. A method to detect the passage of the approximate center of the surface of a moving opaque flexible sheet article across a line transverse to the path thereof which comprises, the steps of passing a sheet article in front of two spaced light-emitting surfaces both located on one side of said sheet article; detecting the light emitted by each of said light-emitting surfaces which pass to the other side of said sheet article; comparing the light emit- -10 ted which passes to the other side from one light-emitting surface wtih the light emitted which passes to the other side from the other light-emitting surface; and ascertaining the moment when the light emitted which passes to the other side from both surfaces are the same.

References Cited by the Examiner UNITED STATES PATENTS HENSON WOOD, JR., Primary Examiner.

ROBERT B. REEVES, Examiner.

Claims (1)

1. A MACHINE FOR STACKING OPAQUE FLEXIBLE SHEET ARTICLES, SUCH AS HIDES AND SKINS, COMPRISING A MAIN ENDLESS CONVEYOR WITH A SUBSTANTIALLY FLAT ARTICLE-CARRYING PORTION HAVING A FIRST SIDE AND A SECOND SIDE AND AN OUTLET END, AND BEING AT LEAST IN PART TRANSPARENT TO LIGHT IN THE VICINITY OF SAID OUTLET END, SAID ARTICLES BEING DISPOSED AT RANDOM ON ONE OF SAID FIRST AND SECOND SIDES OF SAID ARTICLE-CARRYING PORTION OF SAID MAIN CONVEYOR TO BE CARRIED THEREBY TOWARDS SAID OUTLET END AT A GIVEN LINEAR SPEED; TWO STATIONARY MAIN LIGHT-EMITTING SURFACES DISPOSED ON THE FIRST SIDE OF SAID ARTICLE-CARRYING PORTION OF SAID MAIN CONVEYOR IN THE VICINITY OF THE OUTLET END THEREOF AND EXTENDING ACROSS THE FULL WIDTH THEREOF SUBSTANTIALLY SYMMETRICALLY WITH RESPECT TO A LINE TRANSVERSE TO SAID ARTICLE-CARRYING PORTION OF SAID MAIN CONVEYOR AND CLOSE TO SAID LINE SO AS TO ILLUMINATE THE ARTICLES CARRIED BY SAME, SAID SURFACES HAVING A SUBSTANTIALLY UNIFORMLY DISTRIBUTED LUMINOSITY AND SAID SURFACES EACH HAVING A DIMENSION LONGITUDINALLY OF SAID ARTICLE-CARRYING PORTION OF SAID MAIN CONVEYOR AT LEAST EQUAL TO HALF THE MAXIMUM LENGTH OF THE ARTICLES TO BE STACKED; TWO MAIN PHOTOELECTRIC CELLS DISPOSED ON THE SECOND SIDE OF SAID ARTICLECARRYING PORTION OF SAID MAIN CONVEYOR, EACH TO RECEIVE LIGHT SUBSTANTIALLY FROM ONE ONLY OF SAID MAIN LIGHTEMITTING SURFACES; COMPARING MEANS TO COMPARE THE VOLTAGES EMITTED BY SAID MAIN PHOTO-ELECTRIC CELLS AND TO DEDUCE FROM SUCH COMPARISON THE PASSAGE ACROSS SAID TRANSVERSE LINE OF THE APPROXIMATE CENTER OF THE SURFACE OF AN ARTICLE CARRIED BY SAID MAIN ARTICLE-CARRYING PORTION OF SAID MAIN CONVEYOR BETWEEN SAID MAIN LIGHT-EMITTING SURFACES AND SAID CELLS; A STACKING SUPPORT DISPOSED IN THE VICINITY OF THE OUTLET END OF SAID ARTICLE-CARRYING PORTION OF SAID MAIN CONVEYOR AND ON WHICH THE ARTICLES CARRIED BY SAID CONVEYOR ARE TO BE STACKED; DEPOSITING MEANS TO RECEIVE THE ARTICLES FROM THE OUTLET END OF SAID ARTICLECARRYING PORTION OF SAID MAIN CONVEYOR AND TO DEPOSIT SAME ON SAID SUPPORT; DRIVING MEANS TO DRIVE SAID DEPOSITING MEANS; AND MEANS TO ACTUATE SAID DRIVING MEANS A PRE-DETERMINED TIME AFTER SAID COMPARING MEANS HAVE DETECTED PASSAGE OF THE APPROXIMATE CENTER OF THE SURFACE OF AN ARTICLE ACROSS SAID TRANSVERSE LINE TO SUBSTANTIALLY REGULARLY STACK SAME ON SAID SUPPORT.

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