FR2679824A1 - Device for separating/folding individual sheets and apparatus for manufacturing bags including such a separating/folding device - Google Patents

Abstract

The bag machine includes a separating/folding device (28) and produces individual folded bags (22) made from plastic material. Two high-speed separation rollers actuated by a cam mechanism driven by a servomotor seize a continuous strip (12) of plastic material in order to separate individual bags (22) made from plastic material which are formed in the strip. Two parallel wide strips and two similar superposed strips seize the two sides of the separated bags (22) and transport the bags towards several folding stations. A two-speed deceleration mechanism at the exit end of the separating/folding device (28) slows down the folded bags in order to facilitate downstream handling. An optional stacking and indexing transporter (conveyor) automatically stacks predetermined numbers of folded bags, aligns them and compresses them in order to form a stack.

Description

 This invention relates generally to bag making machines, and more particularly to separation / folding mechanisms for separating and folding plastic bags in a bag making operation.

 Plastic bags of various types are widely used around the world. These bags can be economically produced in large quantities from extruded plastic films, and a large number of machines have been developed to automate the bag making process. Every advancement that makes it possible to produce bags with higher speed and efficiency results in greater savings for manufacturers and users of plastic bags.

 Plastic bags are typically formed from a continuous strip of plastic which may be in the form of a flattened continuous tube or a continuous folded sheet. Individual bags are defined by forming bottom welds, in the case of a tubular strip, or side welds, in the case of a folded sheet. Typically, a perforation adjacent to the bottom or side welds allows separation of the individual bags.

Until separation, the bags remain tied together in the form of a continuous ribbon.

 For many reasons, additional processing is often necessary before the bags can, from a practical point of view, be offered for sale. For example, a typical series of bags may include many more bags than any consumer could expect. In addition, the need to separate the bags manually could affect the convenience of the bags and their overall usefulness. Finally, in the case of larger bags, such as garbage or grass bags, the total size of each bag makes handling and packaging difficult, unless the bags are first folded to a more suitable size. . Therefore, many machines have been developed to automatically separate, fold and stack bags formed from continuous strips of plastic.

 In a prior machine, the separation of the bags is carried out by operating a downstream assembly of pinch or separation rollers at a higher speed than that of an upstream assembly of rollers.

When the perforated strip meets the downstream separation rollers, the higher speed of the rollers pulls the strip, thus tearing it along the perforations
A pneumatic cylinder periodically brings the high speed separation rollers into contact with each other in order to start the separation sequence. Although this is effective, the use of a pneumatic cylinder to cyclically move the separation rollers limits the maximum operating speed of the machine and leads to inaccuracies in the separation spacing.

 In a prior machine, several cables are used to transport the separate bags between the separation nip rollers and several folding stations downstream. During operation, it is not unusual for the side edge of a bag to wrap itself around one of the cables. This results in jams and requires the machine to be stopped until the jam is cleared. Profitable production time is thus lost.

 In view of the foregoing, it is a general object of the present invention to provide a new and improved machine intended to separate and fold objects formed from a continuous strip of plastic material.

 It is another object of the present invention to provide a new and improved separation and folding apparatus which can achieve separations with precision and at high speeds.

 It is yet another object of the present invention to provide a new and improved separation and folding mechanism which can handle a large number of product widths without frequent stuffing.

 The invention provides a separator for separating individual sheets from a continuous strip of plastic material in which transverse perforations are formed. The separator has a feed mechanism for advancing the plastic strip at a predetermined speed, and further comprises a pair of pinch rollers disposed downstream of the feed mechanism and mounted so as to move in a movement back and forth to come into contact with each other and move away from each other. The pinch rollers act when in contact to advance the plastic web at a speed greater than the predetermined speed to cause the continuous plastic web to separate along the next adjacent transverse perforation located between the pinch rollers and the feed mechanism. A mechanism comprising an eccentric is connected to at least one of the pinch rollers in order to bring the pinch rollers in reciprocating contact with each other in response to the rotation of the eccentric . A motor is provided to drive the eccentric in rotation so as to bring the pinch rollers back and forth in contact with each other, and thus to cause the strip of plastic to separate along the next adjacent downstream perforation.

 The invention also provides a separator / folder for separating individual sheets from a continuous strip of plastic material in which transverse perforations are formed, and for folding the individual sheets separated along at least one predetermined fold line. The separator / folder has a separator mechanism for separating individual sheets from the continuous web of plastic, and further includes a plurality of folding stations operable to fold the separate individual sheets along predetermined fold lines. Several strips are provided for transporting the separate individual sheets between the separating mechanism and the folding stations. Each of the strips defines a transport surface having a width greater than the width of the separate individual sheets, and has a continuous side edge which extends beyond the adjacent side edge of the individual sheets being transported.

 The invention also provides a separator / folder for separating individual sheets from a continuous strip of plastic material in which transverse perforations are formed, and for folding the individual sheets separated along at least one predetermined fold line. The separator / folder has a separation mechanism for separating individual sheets from the continuous web of plastic material, and further includes a plurality of folding stations operable to fold the individual sheets separated along predetermined fold lines. The separator / folder further includes a set of strips for transporting the individual sheets separated between the separator mechanism and the folding stations. The strip assembly includes a first strip having a lower surface and an upper surface and for supporting, on the upper surface, the separate individual sheets.

The strip assembly further includes a second strip having a lower surface covering the first strip so as to enclose the individual sheets separated between the upper surface of the first strip and the lower surface of the second strip. Means are provided for simultaneously moving the first and second strips together with each other so as to transport the separate individual sheets between the first and second strips with substantially no relative longitudinal movement between the upper surface of the first strip and the separate individual sheets, and between the bottom surface of the second strip and the separate individual sheets.

The displacement means comprise a first roller in contact with the lower surface of the first strip, and further comprise a second roller offset from the first roller and in contact with the lower surface of the second strip. The first and second rollers are provided to change the direction of the first and second strips and to separate the first and second strips during the change of direction so that relative differences in the longitudinal surface velocities of the first and second strips during the change are not transmitted to the separate individual sheets carried.

 The invention further provides a separator / folder for separating individual sheets from a continuous strip of plastic material in which transverse perforations are formed, and for folding the separate individual sheets along at least one predetermined fold line. . The separator / folder has a separator mechanism for separating individual sheets from the continuous web of plastic, and further includes a plurality of folding stations operable to fold the separate individual sheets along predetermined fold lines. A set of strips is provided for transporting the separate individual sheets between the separating mechanism and the folding stations. A slowing mechanism is positioned downstream of the folding stations and operates so as to slow the transport speed of the separate individual sheets when the sheets are unloaded from the separator / folder. The slowing mechanism includes a pair of nip rollers positioned to grip the separate individual sheets when the sheets are unloaded from the separator / folder. The retarding mechanism further comprises drive means connected to the nip rollers in order to operate the nip rollers at a first predetermined speed when one of the separate individual sheets begins to engage between the nip rollers, and to reduce the speed of the pinch rollers to a second predetermined speed lower than the first predetermined speed when each of the sheets passes between the pinch rollers.

Following the discharge of the sheet, the drive means increase the speed of the pinch rollers to the first predetermined speed before the engagement of the next sheet between the pinch rollers.

The invention, with the other aims, particularities and advantages thereof, will be better understood by referring to the following detailed description made in conjunction with the appended drawings, in which identical references identify identical elements, and in which
Figure 1 is a simplified side view of a production line for the manufacture of bags, comprising a separator / folder implementing various features of the invention.

 FIG. 2 is a simplified perspective view of the separation, transport and folding mechanisms of the separator / folder shown in FIG. 1.

 FIG. 3 is a side view of the separator / folder shown in FIG. 1.

 FIG. 4 is a partial and enlarged side view of the folding stations included in the separator / folder shown in FIG. 1.

 FIG. 5 is a simplified perspective view of drive mechanisms intended to actuate different elements of the separator / folder shown in FIG. 1.

 Figure 6 is a top view of a conveyor belt incorporated in the separator / folder and constructed in accordance with one aspect of the invention.

 FIG. 7 is a schematic representation of the folding sequence produced by the separator / folding machine shown in FIG. 1.

 Figure 8 is a simplified perspective view of a stacking and transport mechanism for handling separate and folded bags developed by the separator / folder.

 Figure 9 is a perspective view of part of the stacking mechanism shown in Figure 8, useful for understanding the operation of the stacking finger mechanism which operates to lower a stack of folded bags on a conveyor .

 Figure 10 is a perspective view of part of the stacking mechanism useful for understanding the structure and operation of a compression mechanism for compressing a stack of folded bags.

 FIG. 11 is a side view of the bag stacking mechanism shown in FIGS. 8 to 10.

 Figure 12 is a simplified perspective view showing the drive mechanism for actuating the stacking finger mechanism.

 Figure 13 is a perspective view showing the drive mechanism for actuating the battery conveyor.

 Referring to the drawings, and in particular to FIG. 1, a production line 10 for the manufacture of bags is illustrated there. In the illustrated embodiment, the production line 10 operates so as to transform a continuous tubular strip 12 of plastic material into stacks of individual folded plastic bags 22. The production line comprises a driven reeling machine 14 of known structure which contains a supply reel 16 of tubular continuous strip of plastic material. The unwinding machine 14 unwinds the strip from the spool and discharges it into a tension adjustment mechanism 18 which operates so as to maintain a substantially constant tension on the discharged strip.

 From the reeling machine, the strip 12 is brought into a rotary bag machine 20 of known structure. The rotary bag machine forms transverse and evenly spaced bottom welds across the strip. Individual bags 22 are defined between the spaced bottom welds. Following the formation of the bottom welds, the strip passes through several fold panels which fold inwards and along fold lines extending parallel to the longitudinal axis of the strip the lateral edges of the strip. bandaged. The width of the strip when it leaves the bag machine is thus considerably reduced. A perforation mechanism or knife adjacent to the outlet of the bag machine 20 punctures the strip 12 immediately downstream of each bottom weld in order to allow the separation of the individual bags 22. The bags remain however connected in a continuous tape or strip 12 when they leave the bag machine 20.

 From the bag machine 20, the welded, folded and perforated strip 12 is brought to a separation / folding machine 28 constructed according to different aspects of the invention. The separator / folder 28 operates so as to separate into individual bags 22 the continuous strip of plastic material 12 along the perforations, and then to fold the individual bags 22 along predetermined fold lines extending along the width of each bag. 22. From the separator / folder 28, the folded bags 22 are brought to a bag stacking and indexing conveyor 30. The bag stacking and indexing conveyor 30 stacks the folded bags 22 into predetermined numbers and transfers bags downstream for further processing.

 Referring to Figure 2, the separation / folding machine 28 comprises, in combination, a separation mechanism 32 intended to separate the individual bags, several folding stations 34, 36, 38 intended to fold the bags 22 along predetermined fold lines, and a conveyor mechanism for transporting the bags 22 between the separator mechanism 32 and the fold stations 34, 36 and 38.

 Referring to Figures 2 and 3, the separating mechanism 32 includes a feeding mechanism operable to advance the plastic strip at a predetermined speed. In the illustrated embodiment, the feed mechanism comprises a pair of pinch rollers 42. Downstream of the pinch rollers 42, the separating mechanism 32 further comprises an additional pair of pinch or separation rollers 44, 46. The separation rollers 44, 46 operate at a higher speed than the supply nip rollers 42, and are mounted so as to move back and forth to come into contact with each other. other and move away from each other. In particular, the upper pinch roller 46 is mounted on a support 48 which, in turn, pivots substantially up and down relative to the fixed lower roller 44. The pivoting support 48, in turn, is connected by via an eccentric mechanism 50 to a drive motor 52 so that the operation of the motor 52 results in a reciprocating movement of the upper roller 46 to bring it into contact with the lower roller 44 and move it away from it. The lower roller 44, in turn, is connected via several transmission belts 54 to a supply drive motor 56 which also drives the supply rollers 42. By reducing the size of the pulley drive 58 connected to the lower separation roller 44, the separation rollers 44, 46 operate at a higher speed than that of the supply rollers 42. In one embodiment, the separation rollers 44, 46 are actuated at a speed 25% higher than the speed of the feed rollers 42. In addition, the separation rollers 44, 46 are mounted such that the maximum space between the upper and lower separation rollers is approximately 0.32 cm. When the supply and separation rollers are simultaneously in contact with the strip 12, the speed differential between the rollers creates in the strip 12 a tension directed longitudinally. If a line of perforations 60 marking the junction between adjacent bags 22 is located between the supply and separation rollers 42, 44 and 46, the tension thus developed is sufficient to tear the strip along the perforations 60 and thus separate the individual bags 22.

 In order to ensure correct separation of the bags 22, it is necessary for the reciprocating movement of the separation rollers 44 and 46 to bring them into contact with each other to occur only when the perforations 60 between adjacent bags 22 are correctly positioned between the supply and separation rollers 42, 44 and 46. Preferably, in order to ensure correct guiding of the separate bags 22 through the rest of the separation / folding mechanism 28, the separation takes place when the perforations 60 are adjacent to and slightly downstream from the separation rollers 44, 46. For this purpose, the motor 52 intended to actuate the eccentric mechanism 50 is preferably a servomotor which operates according to band position information coming from the bag making machine 20 upstream. In particular, a position indicator connected to the perforation knife 26 of the bag machine 20 upstream provides strip position information to the servomotor 52, and the motor 52 then operates so as to communicate to the separation rollers 44 and 46 a back and forth movement so that the rollers grip the strip 12 when the next adjacent strip perforation 60 downstream is between the supply and separation rollers 42, 44 and 46.

 Referring further to Figures 2, 3 and 4, the separation / folding mechanism 28 has three separate folding stations 34, 36 and 38. Each of the folding stations is capable of folding an individual bag 22 once along a fold line extending along the width of the bag perpendicular to the side edges thereof. As illustrated, each folding station 34, 36 and 38 includes a pair of pinch rollers 62, 64 and 66, respectively, which rotate in the directions shown by the arrows in Figure 3. A cable conveyor 68 and guides 70 and 72 adjacent to each of the folding nip rollers 62, 64 and 66 serve to transport and guide the bags past the nip rollers. Air jets 74, 76 and 78 are located behind the conveyor and guides, respectively, and are directed through the cables and guide rods toward the gap between the folding rollers. When the air jet 74, 76 and 78 is activated, the bag 22 carried by the conveyor 68 or the adjacent guide 70, 72 is gripped between the folding rollers 62, 64 and 66, as best seen in the figure 2. A pickup detector 80 with optical fiber mounted adjacent to the conveyor 68 and the guides 70, 72 detects the front edge of each bag 22 when this edge passes. The pickup detector 80 actuates a counter which delays the actuation of the air jets 74, 76, 78 so that the actuation occurs when the middle of the bag is opposite the jet 74. This causes the bag to be folded in half as it passes between the folding rollers 62. At the next folding station 36, the process is repeated, thereby folding the bag 22 again in half. At the next folding station 38, the bag 22 is folded again in half. At this location, the bag 22 has been folded three times to one eighth of its original length. This is best seen in Figure 7. As best seen in Figure 4, one roller in each pair of folding rollers is preferably spring loaded so that the folding rollers automatically adjust for thickness of the bag that is folded.

 Once the bag has passed through the final folding station 38, it is ready for transfer to the stacking mechanism 30. In a high speed bag making operation, each bag 22 can move at considerable speed when 'it passes through the separation / folding mechanism 28. Such a high speed can make it difficult to stack the folded bags with precision and regularity 22. Consequently, the separator / folding 28, according to one aspect of the invention, comprises a mechanism which reduces the speed of each folded bag as it exits from the separation / folding mechanism 28. The retarding mechanism comprises a motor 82 and a pair of retarding rollers 84, 86 connected to the motor 82 by means of a two-speed clutch mechanism 88. When the clutch is not engaged, the rollers 84, 86 operate at a speed which substantially corresponds to the speed of the bags in the separation / folding mechanism 28. When the clutch is engaged, the speed of the rollers deceleration 84, 86 is reduced to approximately one third. An optical sensor 90 detects when each folded bag 22 emerges from the third folding station 38. The sensor 90 triggers a counter which controls the actuation of the clutch so that when approximately one third of the folded bag 22 still has to pass between the slowing rollers 84, 86, the slowing rollers switch to lower speed operation. This has the effect of slowing the speed at which the folded bags are discharged from the separation / folding mechanism 28.

 According to one aspect of the invention, a transport system 40 substantially without jamming is provided for transporting the bags between the separating mechanism 32 and the various folding stations 34, 36 and 38. In the illustrated embodiment, the transporter 40 comprises several wide synchronizing bands 92, 94 generally arranged so that the transported bags 22 are sandwiched between the upper surface of a lower band 92 and the lower surface of an adjacent upper band 94 overhanging the band 92. Preferably, the upper and lower strips 92 and 94 each have two parallel strips 96, 98 and 100, 102 arranged side by side and separated by a small space.

In one embodiment, each of the strips 96 to 102 is approximately 25.4 cm wide, and the space between adjacent strips 96, 98 or 100, 102 is approximately 1.27 cm. This results in a transport surface which is approximately 52.1 cm wide, which is wider than any of the bags 22 which have been planned to be handled with the particular separator / folder 28. As a result, the Tapes 92, 94 extend below and beyond these side edges of the transported bags 22, thereby reducing the risk of a bag wrapping around the edge of the tape and causing a jam.

 According to another aspect of the invention, the jam-free conveyor 40 is arranged such that the relative longitudinal displacement between the upper and lower strips 92, 94 when the direction of the strips changes is not transferred to the transported bags 22 and n is not perceived by them. In particular, a change in the direction of movement of the conveyor is achieved by passing the upper strip 94 over a first roller 104 while the lower strip 92 passes over a pair of additional rollers 106, 108 which are laterally offset from the first roller 104.

When so arranged, the upper and lower bands 92, 94, which are normally adjacent to each other, are separated while undergoing a change of direction. In addition, the bands 92, 94 are in close proximity to each other only when the travel of the conveyor 40 is substantially straight. In operation, the transported bags 22, which are normally sandwiched between the upper and lower bands 92, pass over the first roller 104 and under the overhanging bands 100, 102, while the underlying bands 96, 98 pass over the rollers interiors 106, 108 being separated from both the bag 22 and the overhanging strips 100, 102. After the change of direction is made, the strips are brought back together again. An air jet directed upwards 110, and an air jet directed downwards 112, placed between the offset rollers, ensure that the transported bag 22 remains against the underside of the upper strip 94 when it passes over the roller 104. The advantage of this arrangement of the rollers and the strip is that it avoids deformation of the bags which could occur if the two strips and the bag enclosed between them passed over a single roller.

 According to yet another aspect of the invention, a tension regulation mechanism 114 is provided upstream of the feed rollers 42. The tension regulation mechanism 114 detects the tension of the plastic strip 12 when it enters the separator / folder 28, and provides feedback to the feed motor 56 so as to ensure that the feed speed corresponds to the output speed of the bag machine upstream. A tension roller 116 has a relatively small range of movement limited to about 0.16 to 0.32 cm. The small range of movement of the tension roller 116 avoids shifting the perforation 60 in the web relative to the separation rollers 44, 46, which can occur when tension rollers with greater movement are used. The use of the low displacement tension roller 116 avoids such offset or phase errors and ensures that the perforations remain correctly positioned with respect to the separation rollers 44, 46 during the separation sequence.

 The frame of the separation / folding mechanism is provided in two parts 118, 120 which are movable relative to each other around a pivot 122. The frame elements 118, 120 and different rollers are arranged so that, when the frame elements are pivoted apart, adjacent rollers separate along the path followed by the bags 22 in the separation / folding mechanism 28. This makes it very easy to rearrange the machine in the event a jam. A pneumatic cylinder 124 actuated by the operator is preferably provided to pivot the frame halves 118, 120 relative to each other.

 In order to improve the flexibility of use, the separator / folding device 28 can operate in such a way that the separating mechanism 32 operates independently of the folding mechanism 34, 36, 38. For this purpose, separate motors 56 and 126 are provided for actuating separation and folding sections of the machine. In addition, a downward-directed air jet 128 is positioned adjacent to the downstream end of the separating mechanism 32.

When activated, the air jet 128 diverts the separate bags 22 from the main conveyor 40 and sends them to the ground under the machine 28. In this way, the separating mechanism 32 can continue to operate in synchronism with the machine 20 manufacturing bags upstream while the folding mechanism is stopped in order, for example, to eliminate a jam. This avoids stopping the entire production line 10. An additional upwardly directed air jet 130 used to deactivate the next downstream air jet so that the bag is thus diverted from the normal path. In this way, the separator / folding mechanism can have an automatic scrap characteristic.

 The bag stacking mechanism is illustrated in more detail in Figures 8 to 13. As shown, the bag stacking and indexing conveyor 30 basically operates to stack a predetermined number of folded bags 22, to compress the bags in order to reduce the size of a stack 130 of folded bags 22, and to transfer each of the resulting stacks 130 to a conveyor 132 for further processing.

 Referring to Figures 8 and 9, the bag stacking mechanism 30 includes two sets of stacking fingers 134, 136 on which folded bags 22 delivered by the separator / folding mechanism 28 are initially deposited. The stacking fingers 134, 136 cooperate with a pair of lateral guides 138, 140, several rear stop bars 142 and a front guide 144 in order to define a rectangular chamber intended to receive the folded bags 22. The use of the lateral guides , rear stop bars and front guide ensures that the bags remain perfectly aligned inside the stack 130.

 The two sets of stacking fingers 134, 136 operate in displacement generally at a right angle so that bags stacked on the stacking fingers are lowered onto the underlying indexing conveyor 146. When a predetermined number of bags has been accumulated on one of the stacking finger sets 134, 136, this stacking finger set lowers the stack on the conveyor 146 while the other stacking finger set moves into position to receive the following series of folded bags delivered by the separator / folder 28. Continuous operation of the stacking fingers in this way avoids having to interrupt the flow of the folded bags coming from the separator / folder 28.

 After each stack of bags has been delivered to the indexing conveyor 146, the stack 130 is then transferred to a compression station 148 shown in detail in FIG. 10. The compression station 148 comprises several guides 150 which support the sides of the stack 130 and ensure that the bags 22 in the stack 130 remain perfectly aligned during the compression operation. Preferably, two compression stations are included so that each stack is compressed twice to expel the air between the bags.

 Each compression station comprises, in addition to the guides 150, a pneumatic cylinder 152 connected to a compression plate 154. When the cylinder 152 is actuated, the plate 154 is pressed down on the top of the stack 130, thereby driving out the air between the bags and reducing the size of the total stack 130. After being compressed at the first compression station, the stack is again compressed at the next downstream station which operates in the same way.

 Downstream of the double compression station, the stacking mechanism comprises a stack transfer mechanism 156 shown in FIG. 13. The conveyor 132 of the packaging machine, which leads downstream to an additional packaging machine, is located just in front of the stack 130. Two toothed wheels 160, 162 which can rotate around a horizontal shaft 164 are positioned behind the stack 130, and two other toothed wheels 166, 168, which can also rotate around a horizontal shaft 170 , are positioned in front of the stack 130 on the conveyor 132 of the packaging machine. Two parallel transfer chains 172 form a loop around the opposite toothed wheels so as to extend above the stack 130 and of the conveyor 132 of the packaging machine and substantially parallel to these. A motor 174 is connected by means of a transmission belt 176 to the toothed wheels, thereby driving each transfer chain 172 in a continuous loop. Opposite pairs of transfer fingers 178 are mounted on the parallel transfer chains 172 and extend down behind the stack 130 during normal movement of the chains 172.

When the chains continue to circulate, the transfer fingers 178 push the stack 130 onto the conveyor 132 of the packaging machine. The next stack 130 is then delivered to the unloading zone against the stop 158, after which the next pair of fingers 178 pushes the stack onto the packaging conveyor 132.

 Although a particular embodiment of the invention has been described and shown here, it is obvious to a person skilled in the art that modifications can be made without departing from the scope of the invention, which is by no means limited to this embodiment.

 Of course, a rotary bag making machine, which comprises a drive motor intended to actuate said machine and a separation / folding mechanism as described above itself comprising a drive motor intended to actuate said mechanism , usually comprises means associated with the drive mechanism of the separation / folding mechanism in order to synchronize said separation / folding mechanism with the bag machine so that the separation / folding mechanism separates and folds the bags at a corresponding speed at the speed at which the bag machine develops the bags.

Claims (4)

 1. Separator / folder (28) for separating individual sheets (22) from a continuous strip of plastic (12) in which transverse perforations (60) are formed, and folding the separate individual sheets (22) along at least one predetermined fold line, the separator / folder (28) comprising  a separating mechanism (32) for separating individual sheets (22) from the continuous strip of plastic (12);  a plurality of fold stations (34, 36, 38) operable to fold the separate individual sheets (22) along predetermined fold lines;  a set of bands for transporting the separate individual sheets (22) between the separating mechanism (32) and the folding stations (34, 36, 38);  characterized in that it further comprises  a slowing mechanism positioned downstream of the folding stations (34, 36, 38) so as to slow down the transport speed of the separate individual sheets (22) when the sheets are unloaded from the separator / folder (28);  said slowing mechanism comprising a pair of nip rollers (84 <86) positioned to grip the separate individual sheets (22) when the sheets are discharged from the separator / folder (28);  the slowing mechanism further comprising drive means (82, 88) connected to the pinch rollers (84, 86) to operate the pinch rollers (84, 86) at a first predetermined speed when each of the individual sheets separated (22) begins to engage between the pinch rollers (84, 86), to reduce the speed of the pinch rollers (84, 86) to a second predetermined speed lower than the first predetermined speed when each of the sheets ( 22) passes between the pinch rollers (84, 86), and in order to increase the speed of the pinch rollers (84, 86) to the first predetermined speed before the engagement of the next sheet (22) between the pinch rollers (84, 86).  2. Separator / folder (28) according to claim 1, characterized in that the drive means (82, 88) comprise a clutch (88) operable to ensure the second predetermined speed lower than the first predetermined speed .  3. Separator / folder (28) according to claim 2, characterized in that the second predetermined speed is substantially one third of the first predetermined speed.  4. Bag making apparatus (10), comprising  a rotary bag making machine (20) comprising a drive motor for actuating said machine, which can operate so as to develop a continuous strip of plastic material (12) in which several bags (22) are formed ;  separation / folding means (28) operable to separate and fold the bags (22) developed by the bag making machine (20), the separation / folding mechanism (28) comprising a drive motor for to activate said mechanism  means associated with the drive motor of the separation / folding mechanism (28) in order to synchronize said separation / folding mechanism (28) with the bag machine (20) so that the separation / folding mechanism (28 ) separates and folds the bags (22) at a speed corresponding to the speed at which the bag machine (20) develops the bags (22),  characterized in that the separation / folding means (28) comprise a separator / folding (28) according to any one of claims 1 to 3.