Abstract:
The invention relates to a conveyor device for a modularly arranged machine line for manufacturing containers, in particular tubs. A system of clamps which brings the tubs step-by-step to each work station is operated by means of a crank drive.

Description:
BACKGROUND 
     The present invention relates to a conveyor device for a modular machine line for manufacturing containers, and especially for manufacturing tubs or drums, according to the preamble of claim  1 . 
     Machine lines for manufacturing containers usually comprise a plurality of processing machines arranged in sequence with which the container preforms can be brought into their definitive shape. For manufacturing cylindrical or tapered containers, in particular tubs or drums, with a capacity of approx. 3 to 70 liters, welded tubular bodies are exactly positioned by means of a suitable conveyor device in a first machine, and in particular in an expansion machine, where they are formed and in particular tapered. For the next process step, the expanded bodies are picked up by means of the conveyor device and are precisely positioned in the next processing machine. In this manner the body preforms can be transferred step-by-step to the individual machines, which continue forming the preforms, applying a beaded edge, applying a curl bead, forming a flange and/or providing them with a bottom. In order to be able to do this, it is necessary to place the preforms exactly in predetermined positions of the processing machines. The processing precision largely depends on the positioning accuracy of the conveyor systems used. Conveyor systems with pairs of reciprocating bars have proved effective for manufacturing containers. 
     Suitable conveyor devices with pairs of reciprocating bars are known to the expert, for example from GB 2169531. The conveyor device disclosed by this publication comprises a pair of bars which are reciprocatingly moved by means of a first drive mechanism. This drive mechanism is coupled via complicated mechanical gearing to a second drive mechanism, which moves the pair of bars apart, and back towards each other. Grippers are attached at suitable points to this mechanically moved pair of bars with which the preforms to be processed are picked up and transferred in the direction of the bars to a processing machine. The movement of the grippers generated by the drive mechanism causes these to move towards each other in a first movement phase in order to pick up the preforms, displaces the grippers in a second movement phase parallel with the bars and, in a third movement phase, causes the grippers to move apart and return to their original position. Such conveyor devices not only have a complicated drive mechanism but also make access for maintenance work difficult, are not easily adaptable for processing preforms of various sizes, are very noisy in operation, and cause undesirably strong vibrations. In particular these conveyor devices are not very efficient, because the vibrations generated by the jolting movements during transfer make precise and rapid positioning of the preforms difficult. 
     SUMMARY OF THE INVENTION 
     It is therefore the aim of the present invention to provide an efficient conveyor device which does not have the drawbacks of the known devices and in particular, which is able to rapidly transfer preforms with minimal vibration and noise levels and with high positioning accuracy. 
     In particular the aim is to provide a conveyor device whose transfer movements and cycle can easily be adapted to differently sized container preforms, thereby optimizing conveyor performance. 
     The conveyor device should therefore allow an efficient utilization of the individual processing machines, i.e. should allow a simple, rapid and precise positioning of the container preforms. Furthermore, this conveyor device should be easily adjustable to the processing speed of the individual machines and to the properties of the transferred items, and should be easily accessible for maintenance work and change-overs. 
     According to the invention this is achieved with a conveyor device according to claim  1  and in particular by means of a pair of bars which are axially displaced and rotated by a conveyor drive unit in a synchronized and suitable manner. In a preferred embodiment the bars carry clamp sets which are aligned with each other and are fixed to the respective bars. These clamp sets are synchronously tilted out of their initial position towards each other in order to grasp the container preforms. At the same time these clamp sets begin to shift axially to their end position, i.e. into the processing position of the next following processing machine. On reaching this end position the clamp sets are tilted away from each other, thereby releasing the container preforms for processing. In a last movement stage the parted clamp sets shift back into their original starting position. 
     The movement cycle of these clamp sets is brought about simply by means of suitable axial and turning motions of the bars, and according to the invention is effected by a single, continuously driven conveyor drive. This conveyor drive comprises a cam drive with a cam pivotably mounted between the pair of bars and linked to a continuously operating crank drive. 
     In a preferred embodiment the crank drive is fixed to the machine base and comprises a drive unit with a continuously operating drive motor which drives the crank of the crank gear via a drive gear and a drive shaft. Preferably, an electric motor is used for this continuous drive. The advantages of this crank gear essentially lie in the quiet running of the continuous drive. Moreover, this drive allows the conveyor device to be simply controlled by regulating the drive speed of the motor. In this way the speed of the cycle of movements of the clamp sets, or if need be the speed of individual phases of the cycle can easily be varied and/or optimized. 
     The crank of this crank drive is linked with the cam gear. In this preferred embodiment the cam gear comprises a cam which can be turned about an axle by means of a lever arm. This axle is mounted on a slide which is slidably supported on the bars. The rotary motion of the crank and the link between crank and lever arm cause the cam to move to and fro parallel with the bars and at the same time to pivot in alternate directions. Parts of the rim of the cam form a track for deflection rollers. Each of these deflection rollers is mounted in a roller-block which is, in turn, fixed to one of the bars. This has the effect that a deflection of the rollers caused by movement of the cam disk results in an axial turning movement of the bars. It can be seen that the cam disk can be shaped so as to cause a synchronized rotating motion of the bars in opposite directions. In particular, the shape of the cam disk can influence this rotating motion of the bars and of the clamp sets attached thereto in such a way that the clamping motion of the clamp sets is faster than the releasing motion. 
     The articulated coupling of the crank and cam, and the fixing of the axle of the cam to the slide have the effect that a rotational movement of the crank causes the slide to move to and fro along the bars. As the roller-blocks which are mounted on the bars are always moved with the slide, the bars themselves are thereby moved to and fro. It will be understood that the amplitude of this reciprocating motion can easily be adjusted by changing the length of the crank and/or the length of the lever arm of the cam. 
     Thus the outstanding features of this device are the extreme simplicity of its construction and therefore its operational reliability. Its construction allows periodical maintenance work to be carried out without the necessity of any special technical interventions. Should malfunctions occur at one of the processing machines, the machine is freely accessible for rectification. 
     The device according to the invention can be easily modified and, in particular, adapted to different dimensions of the container preforms to be processed. Thus, for example, for transfer of container preforms with larger diameters it is merely necessary to utilize deflection rollers of a larger diameter. 
     This simple mode of construction enables the conveyor device according to the invention to be used in modularly designed machine lines, because the conveyor device does not need to be removed when replacing or converting these machine lines. It is advantageous to mount the conveyor device in the machine base. 
     In particular, the movement cycle of the clamp sets is easily adaptable to the properties, i.e. to the size and weight, of the container preforms to be processed. The profile of the cam disk can be designed so that the movement of the clamps meets the requirements in an optimal manner. In particular in their forward position the clamps should open smoothly and without causing any notable vibrations, and in their rear position should close as rapidly as possible. This special way of controlling the movement cycle of the clamp sets makes it possible to transfer the container preforms rapidly into an exact position at the machine while preventing them from skidding further along or even tipping over when they are released by the clamp units. Obviously, the expert will design the envelope curve of the cam disk determining the movement cycle so as to utilize the processing machines to their optimum capacity. 
     The suggested embodiment has a continuous drive which plays an important part in the smooth and quiet operation of the conveyor device. Vibrations are further reduced by mounting the conveyor device in the machine base. 
     The use of an electric motor to drive the crank mechanism makes it possible to synchronize the clamp sets with the individual processing machines in a simple manner, and to electronically control the speed of the movement cycle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in detail with reference to an embodiment given by way of example and with the aid of the drawings, in which 
     FIG. 1 is a schematic view of a machine line for manufacturing containers; 
     FIG. 2 is a three-dimensional view of the conveyor device according to the invention; 
     FIG. 3 is a section through the conveyor device according to the invention; 
     FIGS. 4 a  to  4   d  are detailed drawings showing the movement cycle of the conveyor device; and 
     FIG. 5 is a diagram showing the speed curve of the clamp sets. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The machine line  1  shown in FIG. 1 comprises a number of modularly arranged processing machines  2  to  7  and is suitable for manufacturing tubs with a capacity of 3 to 15 liters. Similar machine lines can manufacture containers with capacities of 15 to 30 liters or 50 to 70 liters. These 3 to 15 litre containers usually have a diameter of 160 mm to 230 mm and a height of 150 mm to 300 mm. With a modern machine line it is possible to produce approx. 3600 such containers per hour. Such high production rates impose special requirements on the conveyor devices. The machine line  1  shown in FIG. 1 has a first processing module  2  for tapering cylindrical container preforms, and in particular container shell preforms. At the second machine module  3  the containers are provided with a beaded top rim and with curl beads. The next machine module  4  forms an outwardly projecting flange and a seam. Module  5  turns the container part over, i.e. stands it upside down. In the machine module  6  the turned-over container part is again provided with a flange and a beaded edge and can be clinched with a bottom part. The last machine module  7  attaches a bail to the finished tub. 
     The conveyor device  8  shown in FIG. 2 has a pair of bars  9 , 9   b , which are connected to a cam gear  11  and are guided in guiding elements  12  of the machine base. The cam gear  11  is connected to a crank gear  14  by a linkage  13  (not shown). Clamp sets  15  are mounted in pairs on the bars  9   a , 9   b , which clamp sets comprise a plurality of interconnected clamps  16  and clamp carriers  17  which are fixed to the bars. These clamp sets  15  can be tilted away from each other or towards each other by rotational movements of the bars  9   a , 9   b  in opposite directions. A conveyor drive  10  controls these opposite rotational movements and, at the same time, causes an axial displacement of the bars  9   a , 9   b . The crank gear  14  is fixed to the guiding elements  12  and comprises a motor  19 , a drive gear  21 , a drive shaft  22  and crank  23 . The crank  23  of the crank gear  14  is linked to the cam gear  11 . The cam gear  11  has a cam disk  34  which, in the present embodiment, can be rotated about its axle  35  by means of a lever arm  32 . The axle  35  is mounted in a slide which is slidably carried on the bars  9   a , 9   b . The cam  34  is moved linearly to and fro and, at the same time, turned back and forth, both motions being caused by the rotational movement of the crank  23  and the pivot connection  13  between this crank  23  and the lever arm  32 . Parts of the rim  33  of the cam  34  form a track for deflection rollers  36 . These deflection rollers  36  are each fitted in a roller block  37  in such a way that a deflection of the rollers  36  by the cam  34  leads to an axial rotation of the bars  9   a , 9   b . For transfer of container preforms the clamp sets  15 , which are opened in their initial position, are tilted towards each other in order to grasp the container preforms. The container preforms are transferred to the next processing module by the axial displacement of the bars  9   a , 9   b . The clamp sets  15  are tilted away by an opposite axial rotation of the bars  9   a , 9   b . The container preforms can then be processed by the processing machines. During this processing time the bars  9   a , 9   b  while still in their rotated position are pushed backwards into their initial position. The cam disk  34  is of course designed so that the rotational movement of the bars is synchronized and is performed in opposite directions. In particular the design of the cam disk  34  can set up this rotational movement of the bars  9   a , 9   b  and the clamp units  15  attached to these bars  9   a , 9   b  so that, for example, the closing movement of the clamp set  15  is faster than the opening movement. 
     FIG. 3 shows a section through a preferred embodiment of the conveyor device according to the invention. In order to prevent the abovementioned deflection rollers  36  of the cam gear  11  from losing contact with the cam disk  34  during a rapid rotational movement of this cam disk  34 , a closure unit  24  is preferably provided between the bars  9   a , 9   b  which exerts a permanent, inwardly directed torque on these. In this embodiment, a pair of clamping shoes  20  are fixed to the pair of bars  9   a , 9   b , and are linked together by this closure unit  24 . This closure unit  24  is preferably driven by a hydraulic or pneumatic pressure system. A plurality of clamp carriers  17  are fixed to these clamping shoes  20 . In a preferred embodiment, each clamp carrier  17  carries e.g. five to eight clamps  16 . 
     FIGS. 4 a  to  4   d  show the mode of operation of the conveyor drive. This drive comprises a crank gear  14 , whose drive shaft  22  has a crank  23 . This crank  23  is connected by a pivot  13  to a lever arm  32  of the cam  34 . The axle  35  of this cam  34  is mounted in a slide  29  which is slidably carried on the bars  9   a , 9   b . As shown in FIG. 4b, the cam  34  is for example rotated anti-clockwise about its axle  35  by the clockwise-rotating crank  23 , and at the same time the axle  35  is pushed away from the drive shaft  22  in a direction parallel with the bars  9   a , 9   b . As shown in FIG. 4 c , upon further rotation of the crank  23  the cam  34  is rotated further in an anti-clockwise direction and, at the same time, the axle  35  of the cam disk  34  is drawn back again. As rotation of the crank  23  continues, the cam  34  is turned back in a clockwise direction and at the same time the axle  35  is drawn closer to the drive shaft  22 . Concurrently with the movement of the cam  34  the bars  9   a , 9   b  are displaced in their longitudinal direction and also rotated about their longitudinal axis, by the action of the deflection rollers  36  and roller blocks  37 . 
     As can be seen from FIG. 5, the course of the rotational movement of the bars  9   a , 9   b  and the course of the releasing and clamping action of the clamp sets  15  fixed to these bars can be modified by giving the cam disk a suitable profile. This FIG. 5 shows a diagram of the movement of the clamps  16  from their forward position to their rearward position. In the course of this movement the clamps  16  are simultaneously opened and moved to the rearward position. From the movement curve B of these clamps  16  one can see that the releasing movement A is performed more slowly than the clamping movement C near the rearward position. In accordance with the invention the rim  33  of the cam disk  34  is designed so that the velocity of the releasing movement A is adapted to the articles to be transferred, i.e. jerks are avoided. In particular the clamps  16  are not released until after the conveyor device has stopped at the processing position. Of course, the velocity profiles of the clamping movement C and the releasing movement A may differ, i.e. in particular the velocity of the clamping movement may be higher than that of the releasing movement.