Abstract:
A conveyor unit for conveying flat objects includes at least first, second and third endless belts, together with a cylinder. The first endless belt extends along a part of the circumference of the cylinder and forms, with the cylinder circumference, a section of a path of conveyance for the objects. The second and third belts define another section of the path of conveyance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a division of U.S. application Ser. No. 10/494,045, filed May 11, 2004, now U.S. Pat. No. 7,007,603, issued Mar. 7, 2006. That application was the U.S. National Phase, under 35 U.S.C. 371 of PCT/DE2002/04106, filed Nov. 6, 2002; published as WO 2003/045826 on Jun. 5, 2003, and claiming priority to DE 10160754.7, filed Nov. 14, 2001, the disclosures of which are expressly incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention is directed to a conveyor unit for flat objects. The conveyor unit has at least first and second endless belts and a cylinder embodied as a collection cylinder. 
   BACKGROUND OF THE INVENTION 
   Conveyor units are typically employed in folding apparatus, for example, for conveying signatures which had been previously cut from a web of an imprinted material. 
   The signatures each consist of a variable number of sheets which are not connected to each other. For conveying the signatures, it is therefore of great importance that the two endless belts and the cylinder of the conveyor unit move at exactly matched speeds in order to avoid any shearing forces acting on signatures clamped between them, which shearing forces could lead to deformation and to fanning of the signatures in the course of their being transported. 
   In conventional conveyor units of the above-mentioned type, the first endless belt, which partially loops around the surface of the cylinder, is driven by the cylinder, by friction. Therefore, if no objects are conveyed between them, the path speed of the first belt corresponds to the circumferential speed of the cylinder. If conveyed objects are located in the area of the loop between the cylinder and the first belt, this has an effect on the speed of the first belt, which acts as it would with an increase of the diameter of the cylinder. Therefore, the speed of the first belt increases in accordance with the thickness of the objects to be conveyed. The movement of the second belt is coupled to the rotation of the cylinder at a fixedly set transmission ratio via a speed-transforming gear. Therefore, the speed of the second belt is constant. This results in the two belts only running exactly at the same speed at a defined thickness of the objects to be conveyed, so that the objects are not subjected to shearing forces only during this operating condition. 
   DE 94 17 127 U1 and EP 0205143 A2 both describe a collection cylinder, against whose circumference a belt system rests and which is provided with sheets via two further cooperating belt systems. 
   U.S. Pat. No. 5,405,126 describes a folding apparatus with belts driven by an electric motor. 
   U.S. Pat. No. 3,363,520 discloses a collection cylinder for sheets, having several belts. One belt is driven by the collection cylinder. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is directed to providing a conveyor unit for flat objects. 
   In accordance with the present invention, this object is attained by the provision of a conveyor unit for conveying flat objects and having at least first and second endless belts and a cylinder which is embodied as a collection cylinder. The conveyor unit is located downstream of a cutter unit. A conveying path is defined, on one side, by at least the first endless belt, and on the other side by a portion of the circumference of the cylinder and the second endless belt. The first endless belt extends around a portion of the circumference of the cylinder. The conveying path is defined, with respect to the second endless belt, by a third endless belt. 
   The advantages which can be gained by the present invention consist, in particular, in that it is possible to provide synchronous running between both sides of the conveying path over their entire length even in case of different thicknesses of the object to be conveyed. Objects can thus be conveyed gently and free of shearing forces. 
   For this purpose, it has been provided that the conveying path of the conveyor unit is divided into two sections which follow each other. In one section, a portion of the circumference of the cylinder and the first conveyor belt lie opposite each other. A second conveyor belt and a third conveyor belt lie opposite each other in a second section. 
   It is possible by the use of a coupling, and in particular by the use of a mechanical coupling, to reduce deviations in the speed of the movement of the second and third endless belts to exactly zero. Accordingly, regardless of the length of the section of the conveying path delimited by these endless belts, no shearing of the conveyed products can occur. 
   In accordance with a first, simple preferred embodiment of the present invention, the second and the third endless belts are coupled to the rotating movement of the cylinder by a speed-transforming gear. The transmission ratio of the speed-transforming gear is fixed in such a way that the speeds of the second and third endless belts coincide exactly with the circumferential speed of the cylinder. 
   In accordance with a more elaborate preferred embodiment of the present invention, a drive mechanism for the second and third endless belt can be regulated independently of the rotary speed of the cylinder. By this, it is possible to adjust the speed of the second and third belts in response to the respective thickness of the conveyed product, and to adjust the speed of the first endless belt resulting from this. Small deviations from a speed of the second and third belts, which would be optimal in view of the deformation-free conveyance of the products and in view of their actual speed, can be tolerated more easily than in connection with the above explained conveyor unit. With the conveyor unit in accordance with the present invention, such a deviation leads to only a slight tensional stress or to a slight transient compression of the products in the course of their transfer from one section of the conveyor unit to the other, depending on which one is the faster. No shearing can occur. For such shearing to occur, it would be necessary that the belts of different speeds be located opposite each other. 
   The optimum speed must equal the speed of the first endless belt or must equal the circumferential speed of the cylinder, or must lie between these two values. The mean value of the speeds of the first belt and of the cylinder, in particular, can be used as the optimal speed. This corresponds to the position of the neutral fiber of the product, i.e. to a position of a fictional line in the product located exactly in the center of the product which neutral fiber, in the course of the product being conveyed on the cylinder, is neither stretched nor compressed. 
   A regulating device is usefully assigned to this drive mechanism, and works toward accomplishing a matching of the speeds of the second and third belts with the optimal speed. This regulating device preferably proportionally regulates the speed of the second belt by a variable proportionality factor in relation to the speed of rotation of the cylinder. 
   By adjusting the proportionality factor, as a function of the thickness of the conveyed objects, the stretching or compression stress imparted to the conveyed objects, during the transfer of the conveyed objects from one section of the conveying path to the other, is minimized. 
   For determining the proportionality factor, the regulating device can be coupled with a sensor for measuring the speed of the first belt. The speed of the first belt varies linearly with the thickness of the conveyed object. Freedom from stretching or compression stresses can be achieved by a simple matching of the speeds of all belts. 
   A further option lies in coupling a sensor, which is usable for detecting the thickness of the objects, with the regulating device. Such a sensor can be arranged, in particular, prior to the inlet of the conveyor unit. The belt speeds of the conveyor unit can then be matched to a changed product thickness even before the object on which the thickness measurement was performed, reaches the conveyor unit. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     A preferred embodiment of the present invention is represented in the sole drawing and will be described in greater detail in what follows. 
     The sole drawing FIGURE represents a schematized section through a conveyor unit in accordance with the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The conveyor unit of the present invention, as shown in the sole drawing FIGURE, is arranged following a cutter unit that is formed of a cutter cylinder  02  and a grooved cylinder  03  located opposite it. By the operation of this cutter unit, a web  01  of material, for example a paper web  01 , which has been cut in a superstructure located above the cutter unit, and not shown in the sole drawing, into strands with the aid of several rotating linear cutters, which strands are placed one above the other, and the web of material  01  is cut into individual signatures in the cutter unit. Therefore, the signatures consist of a different number of sheets of paper lying on top of each other, which sheets of paper are not firmly attached to each other and which are therefore open at all four sides. 
   The path along which the signatures are conveyed in the conveyor unit located after the cutter unit can be divided into two sections. A first section  08 , is one in which the signatures are conveyed, pressed against each other, between two endless belts  06 ,  05 , called a second and third endless belt here. A second section  09 , is one in which the signatures are conveyed between a first endless belt  04  and a cylinder  07 , for example a collection cylinder  07  of a rotary printing press. 
   In a transition zone between the first section  08  and the second section  09 , the signatures are conducted through a wedge-shaped tongue  17 , which is situated on the side facing the collection cylinder  07 . A lower deflection roller  18 , which carries the third endless belt  05 , has been mounted, which lower deflection roller  18  is pivotable around a pivot shaft  19  and which maintains the tension of the third endless belt  05 , and in this way provides access to the tongue  17  for exchanging or for performing maintenance on tongue  17 . 
   The collection cylinder  07  is driven by a motor, which is not specifically represented in the drawings. The first endless belt  04 , which forms the second section  09  of the conveyor unit and which loops around the collection cylinder  07  over an angle area of approximately 180°, is driven by friction resulting from its contact with the peripheral surface of the collection cylinder  07 . When the signatures are conveyed in the second section  09 , they transfer the driving force from the collection cylinder  07  to the first endless belt  04 . 
   Because of their greater relative distance from the center of rotation of the collection cylinder  07 , with respect to the inside portion of the signatures, the outside portion of the signatures, i.e. the signature portion facing away from the collection cylinder  07  have a slightly greater path speed than the surface area of the collection cylinder  07  itself. The speed difference is proportional to the thickness of the signatures. Therefore, the speed of the first endless belt  04  is automatically adapted to the changing thickness of the signatures. 
   The second endless belt  06 , and the third endless belt  05  are together driven at the same speed via an intermediate drive wheel  11  by a drive mechanism  12 , which drive mechanism  12  may be, for example, a frequency-regulated motor  12 . In this way, no shearing at all can occur during the transport of the signatures in the first section  08  of the conveyor unit. The speed of the motor  12  is regulated by a regulating device  13 , whose job is to maintain the path speeds of the two endless belts  05 ,  06  at a suitable value which is matched to the transport speed of the signatures in the second section  09  of the conveyor unit, and in this way, to prevent the sheets of the signatures from being displaced, in relation to each other, during their transition from the first section  08  to the second section  09 , or to prevent the signatures from being compressed, so that the signatures become unsightly or unusable. 
   A first option for controlling the path speed of the three endless belts  04 ,  05 ,  06  is to match the speed of the second and third endless belt  06  or  05  to that of the first endless belt  04 . The result is that a signature which is transferred from the first section  08  to the second section  09  of the conveying path is not subjected to any stretching or compression, at least on their side facing the third and first endless belts  05  or  04 . Since, as described above, the speed of the first endless belt  04  is a function of the speed of the collection cylinder  07  and of the thickness of the signatures to be conveyed, an active regulation of the speed of the various endless belts is necessary. 
   In accordance with the present invention, the regulating device  13  is connected with two speed sensors for sensing the path speeds of the third and the second endless belts  05 , or  06 , and acts toward the matching of these two path speeds. The speed sensors can be angle of rotation sensors, for example, which are respectively arranged at a deflection roller  14  or  16  of the third or second endless belt  05 ,  06 , and which transmit a pulse to the regulating device  13  every time the deflection rollers  14 ,  16  have traveled over a fixed angle of rotation. These angle of rotation sensors are preferable identically constructed and are mounted on the deflection rollers  14 ,  16  which rollers  14 ,  16  are of identical radii. In this case, the regulating device  13  can assure an identical path speed of the two endless belts  05 ,  06  by maintaining a constant, and preferably diminishing phase offset between the pulses provided by the two sensors. In that case, the speed of the second and third endless belts  06 ,  05  is proportional to the speed of the collection cylinder  07  in accordance with a proportionality factor, wherein the proportionality factor is determined by the thickness of the signatures conveyed between the collection cylinder  07  and the first endless belt  04 . 
   Another option for regulating the speed of the second endless belt  06  is to connect the regulating device  13  on the one side with a sensor for the speed of the first endless belt  04  or for the rotational speed of the collection cylinder  07 , and on the other side with a sensor for the thickness of the signatures to be conveyed. The regulating device  13  then calculates a speed to be maintained by the motor  12  from the measured speed of the first endless element  04 , corrected by a proportionality factor which is determined depending on the measured thickness of the signatures to be conveyed. A sensor, for determining the thickness of the signatures to be conveyed or for determining a value proportional to the signature thickness, can be arranged at a location which is arbitrary, to a large extent, in the conveyor unit or, even better, at a location adjacent the web  01  of material prior to the intake of the web of material into the conveyor unit. 
   It is also conceivable that an operator can set a known thickness of the signatures, the number of sheets in the signature, and their basis weight, or other arbitrary equivalent combinations of parameters in a control unit of the regulating device. 
   An operator can also perform subsequent corrections with such a control unit if it is noticed that the signatures conveyed by the conveyor unit are being sheared or have been sheared. 
   In accordance with a simplified second preferred embodiment of the present invention, the intermediate drive wheel  11 , which drives both the two endless belts  05 ,  06 , is coupled by a gear which is not specifically represented, and having a fixed gear ratio, to the rotation of the collection cylinder  07 . The gear ratio of the not depicted gear has been selected to be such that the path speed of the two endless belts  05 ,  06  is equal to the circumferential speed of the collection cylinder  07 . With this embodiment, the third endless belt  05  runs slightly slower than the first endless belt  04  following it in the conveying path. As a result of the equality of the path speeds of the endless belts  05 ,  06  and the circumferential speed of the collection cylinder  07 , a signature is not subjected to any shearing or compression forces at the transition between the first conveyor section  08  and the second conveyor section  09 , at least at the signature side facing the second endless belt  06  and the collection cylinder  07 . A slight stretching stress can occur at the opposite side of the substrate in contact with the endless belts  05 ,  04 , since the endless belt  04  moves slightly faster than the endless belt  05 . 
   Such a stretching stress can be acceptable in the situation of small thicknesses of the signatures, and therefore in the case of small differences between the speeds of the first endless belt  04  and of the remaining endless belts  05 ,  06 . However, if the thickness of the signatures becomes too great, and if therefore the speed difference between the collection cylinder  07  and the first endless belt  04  becomes too great, a slight shearing force might occur on the signatures during the transfer of a signature between the two conveyor sections  08  and  09 . 
   In contrast thereto, with the use of the above-described first embodiment, only a compression force acts on the signature at the moment of transfer. This compression force cannot result in a sliding of individual sheets of the signature. In the situation of processing thick signatures the technically more elaborate first embodiment might be preferred over the simpler, and more cost-effective second one. 
   In principle it is, of course, possible to set any arbitrary speed, which arbitrary speed lies between the circumferential speed of the collection cylinder  07  and the path speed of the first endless belt  04 , as the conveying speed of the conveying endless belts  05 ,  06  of the first section  08 . If, for example, the average value of the circumferential speed of the collection cylinder  07  and the path speed of the endless belt  04  in the second conveying section is selected as the path speed of the first conveying section  08 , a slight compression or speed reduction acts on the surface of the signature facing the collection cylinder  07  during the transfer to the second section, while the oppositely located surface of the signature facing the endless belts  05 ,  04  is stretched or accelerated. 
   While preferred embodiments of a conveyor unit for conveying flat objects, in accordance with the present invention, have been set forth fully and completely hereinabove, it will be apparent to one of skill in the art that various changes in, for example, the size of the collection cylinder, the type of web being conveyed, and the like could be made without departing from the true spirit and scope of the present invention which is accordingly to be limited only by the following claims.