Patent Publication Number: US-6213011-B1

Title: Loading and offloading systems for printing machine

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns a loading system and an offloading system for a printing table. 
     It generally concerns the loading of objects presented as groups of objects in an entry support. The objects are taken from their entry support for printing one by one on a printing table. 
     It also concerns, in a symmetrical manner, the offloading of such objects after printing them to enable a new disposition in groups in an exit support. 
     2. Description of the Prior Art 
     In printing machines, the printing table co-operates with a transfer system which puts objects to be printed down one by one on the printing table and then picks them up one by one. This transfer system co-operates in turn with a loading system and an offloading system which respectively present the objects to be printed and recover the printed objects. 
     The production rate of a printing machine of the above kind depends on that of the transfer system associated with the loading and offloading systems. 
     To avoid reducing the rate of production, it is therefore essential for the loading and offloading systems to be able to present and recover the objects at a high rate which is relatively close to the printing rate of the printing table. 
     An aim of the present invention is to propose loading and offloading systems which in particular enable a good rate of production to be maintained. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, a system for loading a printing table with objects presented in groups in an entry support, the objects of the group being distributed with an entry spacing, and the printing table co-operating with a transfer system disposed between the printing table and the loading system, the transfer system being adapted to transfer the objects one by one from the loading system onto the printing table, includes an intermediate support adapted to support the group of objects disposed with a predetermined spacing, holding means adapted to take up simultaneously and to move a group of objects between the entry support and the intermediate support, and spacing modification means adapted to modify the spacing of the group of objects from the entry spacing to the predetermined spacing, the transfer system being adapted to transfer the objects onto the printing table from the intermediate support. 
     Accordingly, by using an intermediate support between the entry support and the transfer system the objects can be disposed with a predetermined spacing and in accordance with a disposition suitable for the transfer system to take them up. 
     The invention solves the problem of positioning the objects on the intermediate support by means of the holding means and the spacing modification means which enable the objects to be placed correctly on the intermediate support. Taking the objects in groups to place them on the intermediate support eliminates the constraint of the limit on the speed at which the objects can be moved from the entry support to the intermediate support, as it were. The rate of operation of the holding means and the spacing modification means is equal to a sub-multiple of the rate of operation of the transfer system. To be more precise, the rate of operation of the holding means and the spacing modification means is equal to the operating rate of the transfer system divided by the number of objects in the group of objects. 
     The loading system in accordance with the invention therefore eliminates the constraints of positioning the objects in the entry support and the constraints of the limit on the speed of the holding means and the spacing modification means necessary for correct positioning of the objects before they are taken up by the transfer system. 
     In a preferred version of the invention, the holding means include separate holding members adapted to take respective objects from the group of objects and to move between the entry support and the intermediate support in co-operation with the spacing modification means. 
     By using separate holding members for the objects of the same group it is possible to modify the spacing of the objects, i.e. the distance between the objects, while the objects are being moved toward the intermediate support, which represents a time saving which also improves the rate of transfer of the objects. 
     According to an advantageous feature, which provides for relatively simple co-operation of the holding means and the spacing modification means, the spacing modification means include guide grooves adapted to guide the respective separate holding members and the guide grooves have intersecting directions in a common plane. 
     In another preferred version of the invention, the holding means include at least one clamp adapted to grasp the group of objects, the objects are presented in a vertical position in the entry support, and the clamp is adapted to move the group of objects from the vertical position to a horizontal position. 
     The clamp simultaneously modifies the position of the objects in the same group to place them in a horizontal position, which is the position in which they are processed on the printing table. 
     A holding clamp of the above kind also eliminates constraints associated with the position of the objects in their entry support. 
     In accordance with another preferred feature of the invention, the intermediate support includes a circular contour turntable adapted to rotate stepwise and comprising a series of support members for the objects disposed along the circular contour turn-table at a spacing equal to the predetermined spacing. 
     An intermediate support of the above kind provides a simple way of presenting the objects to the transfer system continuously, by stepwise rotation of the circular contour turntable. 
     In this case, and in an advantageous version that facilitates subsequent centering of the objects to be printed, the holding means co-operate with orientation means adapted to orient the objects during their movement toward the intermediate support so that the objects are placed on respective support members with the same orientation relative to the center of rotation of the circular contour turntable. 
     In another advantageous version, if the intermediate support comprises a circular contour turntable, the printing table and the transfer system are adapted to rotate stepwise and drive means are adapted to drive their stepwise rotation synchronously with the printing table, the transfer system and the intermediate support. 
     Synchronized driving of the various members provides a simple way of loading the printing machine continuously. 
     In accordance with an analogous aspect of the present invention, a system for offloading from a printing table objects presented in groups and distributed with an exit spacing in an exit support, the printing table co-operating with a transfer system disposed between the printing table and the offloading system, the transfer system being adapted to transfer the objects one by one from the printing table to the offloading system, includes an intermediate support adapted to support the group of objects disposed with a predetermined spacing, holding means adapted to take up simultaneously and to move a group of objects between the intermediate support and the exit support and spacing modification means adapted to modify the spacing of the group of objects from the predetermined spacing to the exit spacing, the transfer system being adapted to transfer the objects from the printing table to the intermediate support. 
     In a manner that is symmetrical with respect to the loading system in accordance with the first aspect of the invention, and using an intermediate support between the exit support and the transfer system, an offloading system of the above kind disposes the objects with a predetermined spacing and in a disposition suitable for their transfer by the transfer system. The objects are positioned on the exit support by the holding means and the spacing modification means which enable the objects to be placed correctly on the exit support. Placing the objects on the exit support in groups eliminates the constraint of the limit on the speed of movement of the objects from the intermediate support toward the exit support. The rate of operation of the holding means and the spacing modification means is equal to a sub-multiple of the rate of operation of the transfer system. To be more precise, the rate of operation of the holding means and the spacing modification means is equal to the rate of operation of the transfer system divided by the number of objects in the group of objects. 
     The offloading system of the invention therefore eliminates constraints associated with positioning of the objects in the exit support and the constraints of the limit on the speed of the holding means and the spacing modification means necessary for proper positioning of the objects in the exit support. 
     In a preferred version of this analogous aspect of the invention, the holding means include separate holding members adapted to take respective objects from the group and to move between the intermediate support and the exit support in co-operation with the spacing modification means. 
     By using separate holding members for the objects of the same group, the spacing of the objects can be modified while the objects are moving toward the exit support, which represents a time saving which also improves the rate of transfer of the objects. 
     In an advantageous version of the invention, which simplifies co-operation of the holding means and the spacing modification means, the spacing modification means include guide grooves adapted to guide the respective separate holding members and the guide grooves are disposed in intersecting directions in a common plane. 
     In another preferred version of this analogous aspect of the invention, the holding means include at least one clamp adapted to grasp the group of objects, the objects are presented in a horizontal position, the clamp is adapted to move the group of objects from the horizontal position toward a vertical position, and the objects are presented in the vertical position in the exit support. 
     The clamp enables the position of the objects in the same group to be modified simultaneously in order to place them in a vertical position in their exit support. 
     In accordance with another preferred feature of this analogous aspect of the invention, the intermediate support includes a circular contour turntable adapted to rotate stepwise and comprising a series of support members for the objects disposed along the circular contour turn-table at a spacing equal to the predetermined spacing. 
     An intermediate support of the above kind provides a simple way to take up the objects continuously from the transfer system by stepwise rotation of the circular contour turntable. 
     In this case, and in an advantageous version which facilitates subsequent positioning of the objects to be disposed in the exit support, the holding means cooperate with orientation means adapted to orient the objects during their movement toward the exit support so that the objects are placed on the exit support with the same orientation. 
     In another preferred version of this analogous aspect of the invention, independent drive means are adapted to drive the stepwise rotation of the intermediate support, the rotation causes the support members to move in succession to a transfer station to which the transfer system is adapted to transfer an object, and a sensor senses an object on the support member at the transfer station and co-operates with the independent drive means so that the intermediate support turntable is driven in rotation only if the sensor senses an object on the support member at the transfer station. 
     Independent driving of the rotation of the intermediate support in this way, under the control of a sensor sensing an object, guarantees that all the adjoining support members are actually supporting an object so that complete groups of objects can be formed at the exit from the intermediate support by taking up the objects on a group of adjoining support members. 
     This disposition is particularly advantageous if objects are lost or removed while printing them on the printing table or if the printing table is not fed regularly with objects to be printed. 
     In a further preferred version of this analogous aspect of the invention, which also guarantees that the holding means actually take up complete groups of objects, the rotation of the intermediate support causes the support members to move successively to exit stations, the number of exit stations being equal to the number of objects in a group of objects, sensors sense objects on the support members at the exit stations and co-operate with drive means for the holding means so that the holding means take a group of objects placed on the support members at exit stations only if the sensors sense an object on each support member at the exit stations. 
     In accordance with the invention, the loading system and the offloading system are particularly well suited to co-operate with a printing table if the objects are screens of the type equipping a liquid crystal or similar display system. 
     In accordance with a third aspect of the invention, a printing machine for objects presented in groups in entry and exit supports is characterized in that it includes a loading system and an offloading system in accordance with the invention. 
     A machine of this kind can print objects and package them at the exit in a similar manner to how they are packaged at the entry, possibly in identical entry and exit supports. 
     Other features and advantages of the invention will become apparent in the course of the following description, which is given by way of non-limiting example and with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a printing machine in accordance with one aspect of the invention. 
     FIG. 2 is a partial elevation view of the machine from FIG. 1, as seen from the loading system side. 
     FIG. 3 is a diagrammatic view showing one embodiment of the holding means of a loading or offloading system of the invention. 
     FIG. 4 is a partial plan view of a loading cr offloading system of the machine shown in FIG.  1 . 
     FIG. 5 is an elevation view to a larger scale showing a detail of the offloading system from the machine shown in FIG.  1 . 
     FIGS. 6 and 7 are respectively partial top and bottom views of an intermediate support of a loading or offloading system constituting one embodiment of the invention. 
     FIG. 8 is a partial view in section taken along the line VIII—VIII in FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One embodiment of a printing machine in accordance with the invention is described below with reference to FIG.  1 . 
     A machine of this kind generally comprises a printing table  1 , a transfer system  2 , a loading system  3  and an offloading system  4 . 
     An entry conveyor  5  conveys the objects to be printed to the vicinity of the loading system  3 . In a symmetrical fashion, an exit conveyor  6  takes up the objects downstream of the offloading system  4 . 
     A machine of the above kind is suitable for printing objects  7  (see FIG. 3, for example) presented in the form of groups of objects  7  at the entry and at the exit in entry supports  8  and exit supports  9 . 
     By way of non-limiting example, the objects can be screens for a display system as routinely used in portable telephones. More generally, the objects can be in the form of flat parts with small dimensions (a few centimeters on each side) and made from a synthetic material, for example a transparent plastics material. Because of their dimensions and the material from which they are made, such parts are relatively fragile and difficult to handle. 
     During their manufacture, the parts  7  are routinely presented in supports which package them in groups in a plurality of rows. The entry supports  8  and exit supports  9  are typically thermoformed trays in the bottom of which locations for positioning the various flat parts  7  are formed. To save space in packaging them, the parts  7  are generally disposed vertically in the entry supports  8  and exit supports  9 . 
     The printing table  1  has a circular contour. It includes a plurality of object stations  10  regularly distributed at its periphery and each adapted to receive one object  7  to be printed. The table  1 , part of which is shown in FIG. 1, is adapted to rotate stepwise about a vertical rotation axis. This rotation moves the object stations  10  to a loading station  11 , various workstations (not shown) in which the objects  7  are printed, and an offloading station  12 . 
     The printing table  1  co-operates with the transfer system  2  to transfer the objects  7  one by one. The transfer system  2  is also in the form of a turntable  20  adapted to rotate stepwise. It includes take-up members  21 , of which there are six in this example, regularly distributed along the periphery of the transfer system. 
     The rotation of the transfer system  2  moves the take-up members  21  to a take-up station  22  facing the loading system  3 , to a station  23  feeding the printing table and facing the loading station  11  of the printing table  1 , to a take-up station  24  facing the offloading station  12  of the printing table  1  and to a release station  25  facing the offloading system  4 . 
     As shown in FIG. 2, the turntable  20  of the transfer system  2  lies in a horizontal plane above the printing table  1  and the loading system  3 . Likewise it lies above the offloading system  4 . In addition to its stepwise rotation, the turntable  20  also moves in vertical translation, parallel to its rotation axis X—X, when the take-up members  21  are respectively in their take-up stations  22 , feed stations  23 , take-up stations  24  and release stations  25 . The turntable  20  therefore reciprocates between a low position and a high position on each rotation step, so that the flat parts  7  to be transferred are taken up or put down at each of the aforementioned stations of the transfer system  2 . 
     In this example, the take-up members  21  are suction nozzles connected in a conventional way to a vacuum pump by a pneumatic circuit. These suction nozzles are very suitable for transporting the flat parts  7  by suction. 
     The structure of the loading system  3  and the offloading system  4  in one embodiment of the present invention will now be described. The structures of the systems are substantially identical and they are symmetrically disposed about the transfer system  2 . 
     In this example, as seen most clearly in FIG. 3, the flat parts  7  are disposed vertically in the entry supports  8  and exit supports  9 , in rows each comprising four parts  7  (see FIG.  1 ). 
     The loading system  3  and offloading system  4  include clamps  30 ,  40  for grasping the flat parts  7  and moving the parts  7  between a vertical position shown in dashed line and a horizontal position shown in continuous line in FIG.  3 . 
     The number of clamps  30 ,  40  is preferably equal to the number of parts  7  in each group in order to take up the latter individually and simultaneously. Thus in this example there are four clamps. 
     The clamps  30 ,  40  are mounted on respective piston rods  31 ,  41  which reciprocate them vertically. The clamps  30 ,  40  are also associated with rollers  32 ,  12  which move in guide grooves  33 ,  43 . The guide grooves  33 ,  43  define a curved path enabling each clamp  30 ,  40  associated with the rollers  32 ,  42  to pivot through one quarter-turn. The vertical movement of the clamps  30 ,  40  associated with the pivoting of the rollers  32 ,  42  moves the clamps between the vertical position and the horizontal position. 
     The loading system  3  and offloading system  4  further include suction nozzles  34 ,  44  similar to the take-up members  21  of the transfer system  2  and which form separate holding members, the number of which is equal to the number of parts  7  in each group. 
     The separate holding members  34 ,  44  in each loading system  3  and offloading system  4  are adapted to move the objects  7  in co-operation with spacing modification means  35 ,  45  between an intermediate support  36 ,  46  described below and clamps  30 ,  40 . 
     In this example, and as shown in FIG. 4, the spacing modification means include guide grooves  35 ,  45  disposed in intersecting directions in the same horizontal plane. In this example, in which the entry spacing between the objects  7  of the same group in the entry support  8  is less than the spacing of the objects placed on the intermediate support  36 , the guide grooves  35  of the loading system  3  extend toward the intermediate support  36  in respective diverging directions (see FIG.  1 ). 
     In a symmetrical fashion, the exit spacing between the objects  7  in the same row in the exit support  9  being less than the spacing of the objects on the intermediate support  46  of the offloading system  4 , the guide grooves  45  of the offloading system  4  extend toward the intermediate support  46  in respective diverging directions. 
     The suction nozzles  34 ,  44  are adapted to slide in the respective guide grooves  35 ,  45  with a horizontal reciprocating movement between the clamps  30 ,  40  and the intermediate support  36 ,  46 . This reciprocating movement can be conventionally produced by pneumatic jacks  39 ,  49  associated with each suction nozzle  34 ,  44 . The latter are mounted on a circuit connected to a vacuum pump and used to pick up the objects  7  by suction. 
     As shown in FIG. 6, the intermediate support  36 ,  46  includes a circular contour turntable  360 ,  460  which rotates stepwise about a vertical rotation axis. It includes a series of support members  361 ,  461  adapted to support the objects  7 . The support members  361 ,  461  are disposed along the circular contour of the turntable  360 ,  460  at a predetermined regular spacing. 
     The stepwise rotation of the intermediate support  36  of the loading system  3  moves the support members  361 . to entry stations  362  facing the separate holding members  34  when the latter are at one end of the guide grooves  35 . obviously, the number of entry stations  362  is equal to the number of objects  7  in each group. 
     In a symmetrical fashion, the stepwise rotation of the intermediate support  46  of the offloading system  4  moves the support members  461  to exit stations  462  facing the separate holding members  44  when the latter are at one end of the guide grooves  45 . The number of exit stations  462  is equal to the number of objects  7  in each group to be placed in the exit support  9 . 
     In this embodiment the guide grooves  35 ,  45  are different lengths so that the objects  7  of the same group are moved between a position in which they are aligned in the entry support  8  or the exit support  9  and a position in which they are arranged along a circular arc facing the support members  361 ,  461  at the entry stations  362  of the intermediate support  36  of the loading system  3  or the exit stations  462  of the intermediate support  46  of the offloading system  4 . 
     The suction nozzles  34  of the holding members preferably co-operate with orientation means  37 ,  38 ,  47 ,  48  to orient the objects while they are moving, as shown in more detail in FIG.  4 . 
     To perform this orientation, in this particular embodiment, each suction nozzle  34 ,  44  is mounted at the end of a bar  37 ,  47  whose other end is adapted to slide in a second guide groove  38 ,  48  associated with the guide groove  35 ,  45  in which the suction nozzle  34 ,  44  slides. The two guide grooves  35 ,  45  and  38 ,  48  are disposed in non-parallel directions so that sliding of the bar  37 ,  47  in the associated two grooves  35 ,  45  and  38 ,  48  is accompanied by relative rotation about the end sliding in said second guide groove  38 ,  48  to modify the orientation of the suction nozzle  34 ,  44  sliding in the first guide groove  35 ,  45 . 
     The objects  7  are thus placed on the support members  361  of the intermediate support  36  of the loading system  3  with the same orientation relative to the rotation center of the turntable  360  of the intermediate support  36  and the objects  7  are placed in the exit support  9  with the same orientation on leaving the offloading system  4 . 
     The support members  361 ,  461  of the intermediate supports  36 ,  46  are preferably also suction nozzles  361 ,  461 . 
     In this example, and as shown in FIG. 3, the turntable  360 ,  460  of the intermediate support  36 ,  46  of the loading and offloading systems  3  and  4  lies in a horizontal plane under the horizontal plane in which the suction nozzles  34 ,  44  of the holding members move. At the entry or exit stations  362 ,  462  of the intermediate support  36 ,  46 , the support members  361 ,  461  are reciprocated vertically to come close to the holding members  34 ,  44  so that the objects  7  are transferred at the entry or exit stations  362  or  462  by suction applied alternately to one face or the other of each object. 
     As shown in detail in FIG. 8, this reciprocating movement can be produced by a jack  367 ,  467  at each entry or exit station  362 ,  462  of the intermediate support  36 ,  46 , for example. The upward movement of the support member  361 ,  461  is shown in FIG. 3, for example, in which the support member  361 ,  461  is shown in dashed outline in its high position. 
     A guide plate  368 ,  468  facilitates positioning the support members  361 ,  461  above the jacks  367 ,  467  on each rotation of the turntable  360 ,  460 . The guide turntable  368 ,  468  fixed to the jack  367 ,  467  defines an upward and then downward path on the circular path of movement of the support members  361 ,  461  on stepwise rotation of the turntable  360 ,  460 . 
     The support members  368 ,  468  are further adapted to be spring-loaded into a low position by return spring means such as springs  369 ,  469 . 
     Furthermore, each entry or exit station  362 ,  462  is also associated with a jack  363 ,  463  adapted to actuate switches  364 ,  464  mounted on the pneumatic circuit of the suction nozzles  361 ,  461  (see FIG. 7) so that the suction nozzles  361 ,  461  are connected to the vacuum pump when they are in the entry stations  362  and disconnected when they are in the exit stations  462 . 
     The intermediate support  36  of the loading system  3  further includes a transfer station  365  facing the take-up station  22  of the transfer system at which each object is taken up by the transfer system  2 . 
     In a similar manner, the intermediate support  46  of the offloading system  4  includes a transfer station  465  facing the release station  25  of the transfer system  2  at which each object  7  is taken up by the intermediate support  46 . 
     As shown in FIG. 2 for the loading system  3  and in FIG. 5 for the offloading system  4 , a jack  367 ,  467  identical to the jacks of the entry or exit stations  362 ,  462  is provided at the transfer station  365 ,  465  to raise the support member  361 ,  461  toward the take-up member  21  of the transfer system  2 . A cam  368 ,  468  likewise facilitates positioning the support members  361 ,  461  on the jack  367 ,  467  of the transfer station  365 ,  465  on each rotation of the turntable  360 ,  460  of the intermediate support  36 ,  46 . 
     As shown in FIG. 1, a jack  366 ,  466  at the transfer station  365 ,  465  actuates the switches  364 ,  464  associated with each suction nozzle  361 ,  461  to disconnect the suction nozzles  361  from the pneumatic circuit and thereby to cut off the suction by the vacuum pump which holds the objects onto each support member  361  of the intermediate support  36  in the case of the loading system  3  and connects the suction nozzles  461  to a vacuum pump on the pneumatic circuit to enable the objects to be held by suction on each support member  461  of the intermediate support  46  in the case of the offloading system  4 . 
     A centering system  70  can be provided at the transfer station  365  of the loading system  3  to perfect the position of each object  7  before it is transferred onto the printing table  1 . This type of centering system is well known in itself and is not described in detail here. It can conventionally comprise two jaws whose inside contour in the closed position is identical to the contour of the object  7 , so that each jaw closes around the object  7 . 
     Conventional drive means  13 ,  14 ,  15  which are not described in detail here drive the synchronized stepwise rotation of the printing table  1 , the turntable  20  of the transfer system  2  and the turntable  360  of the intermediate support  36  of the loading system  3 . A direction changer  13 , for example, connects a shaft of the indexing system of the printing table  1  to a shaft line that drives a Maltese cross  15  associated with a roller system  14  to rotate the intermediate support  36  stepwise via a transmission belt  16 . 
     Drive means  17 ,  18 ,  19  are provided for the offloading system and are independent of those driving rotation of the printing table  1  and the transfer system  2 . They drive stepwise rotation of the intermediate support and comprise, for example, a motor  17  associated with a Maltese cross  18  driving stepwise rotation of the turntable  460  of the intermediate support  46  via a transmission chain  19 . 
     Sensor means  50  controlling rotation of the turntable  460  of the intermediate support  46  of the offloading system  4  will now be described. 
     As shown in FIG. 5, a sensor  51 ,  52  sensing an object on the support member  461  at the transfer station  465  co-operates with the independent drive means  17 ,  18 ,  19  so that the turntable  460  of the intermediate support  46  is rotated only if the sensor  51 ,  52  senses an object  7  on the support member  461  at the transfer station  465 . This prevents any of the support members  461  remaining empty, which would produce incomplete groups of objects at the exit from the intermediate support  46 . 
     The sensor  51 ,  52  can be mounted on the pneumatic circuit and include, for example, bellows  51  each associated with the pneumatic circuit of one of the circuit members  461  and adapted to deform according to the status of the pneumatic circuit, which is closed if there is an object  7  on the support member  461  or open if there is no object  7  on the support member  461 . The bellows  51  are mounted on a sensor plate  54  constrained to rotate with the turntable  460  of the intermediate support  46 . The number of bellows  51  is therefore the same as the number of support members  461  and the rotation of the sensor plate  54  causes the bellows  51  to pass under a displacement sensor  52  which senses the movement of the bellows  51 , which varies according to the open or closed status of the pneumatic circuit on which they are mounted. The displacement sensor  52  is at a fixed position determined so that each bellows  51  coming face to face with the displacement sensor  52  is the one associated with the support member  461  which is then positioned at the transfer station  465 . The motor  17  of the means driving rotation of the intermediate support  46  is therefore under the control of the displacement sensor  52 . A sensor  51 ,  52  of this kind and its operation are described in detail in the Applicant&#39;s French patent application No. 96 06797, the content of which is hereby incorporated in this description by reference. 
     In a similar manner, sensors  51 ,  53  sensing objects on the support members  461  at the exit stations  462  co-operate with drive means, here the jacks  41  and  49 , of the holding means  40 ,  44  so that the holding means take up a group of objects  7  placed on the support members  461  only if the sensors  51 ,  53  sense an object  7  on each support member  461  at the exit stations  462 . 
     The sensors  51 ,  53  consist of the same bellows  51  as those described above and displacement sensors  53  in fixed positions above the sensor plate  54 , said positions corresponding for each rotation step to the positions of the bellows  51  associated with the support members  461  at the exit stations  462 . 
     The number of displacement sensors  53  is preferably equal to the number of exit stations  462 , which is four in this example. 
     In this example, the sensor means  50  comprise a plate  54 , bellows  51 , a displacement sensor  52  and four displacement sensors  53  and could naturally include other displacement sensors for driving or monitoring the operation of the offloading system  4 . 
     Furthermore, identical sensor means could be associated with the intermediate supports  36  of the loading system  3 . Accordingly, as shown in FIGS. 1 and 2, a displacement sensor  62  associated with bellows  61  can sense an object  7  on the support member  361  at the transfer station  365  and control the operation of the centering system  70 , for example, so that it operates only when there is an object  7  on this member. 
     Similarly, displacement sensors  63  can be adapted to sense an object on the support members  361  at the respective input stations  462 , for example to count the parts introduced into the printing machine. 
     The operation of the printing machine will now be described. 
     The objects  7  in the entry support  8  advance stepwise on the conveyor  5  under the clamps  30  which are initially vertical. The clamps  30  grasp the objects and are then raised and pivoted to present the objects  7  horizontally. During this movement of the clamps  30 , the suction nozzles  34  of the holding means are standing by at one end of the guide grooves  35 , substantially in line with the clamps  30 . They are adapted to take up by suction the group of objects  7  placed in the horizontal position by the clamps  30 . The clamps  30  then open to release the objects. The suction nozzles  34  then move in the guide grooves  35 , in association with the bars  37 , and at the end of their stroke locate in the guide grooves  35 , opposite entry stations  362  of the intermediate support  36 , simultaneously orienting the objects relative to the center of the turntable  360  of the intermediate support  36 . 
     The support members  361  at the entry stations  362  are raised by the jacks  367  to pick up the objects  7  by suction, applied to their bottom face in this position, and the jacks  363  actuate the switches  364  to connect the suction nozzles of the support members  361  to the vacuum. pump in the pneumatic circuit. The objects  7  are therefore supported by the support members  361  and the rotation of the turntable  360  moves the objects  7  stepwise toward the transfer station  365 . 
     During this time, the clamps  30  move to a vertical. position to grasp a new group of objects  7  and the suction nozzles  34  of the holding means are moved in the opposite direction in the guide grooves  35  and return to their original position substantially in line with the clamps  30 . 
     At the transfer station  365 , and on each rotation of the transfer system  2 , the turntable  20  of the latter is lowered and a take-up unit  21  takes up by suction the objects  7  at the transfer station  365 . Simultaneously, at the transfer station, the jack  367  pushes the support member  361  up toward the take-up member  21 . This high position is shown in FIG. 2 at the transfer station  365  in particular. At the same time, the jack  366  disconnects the vacuum from the suction nozzle of the support member  361  at the transfer station  365 . The object  7 , which is no longer held onto the support member  361  by suction, is then taken up by suction by the take-up member  21  and is then moved stepwise by the transfer system  2  toward the printing table  1 . 
     The object  7  is then fed in the conventional way to a loading station  11  of the printing table  1  and printed. 
     Afterward, it is taken up by a take-up member  21  of the transfer system at the offloading station  12  of the printing table and is moved to the release station  25  facing the intermediate support  46  of the loading system. 
     The associated jack  467  lowers the turntable  20  and raises the support member  461  to bring the object  7  into contact with the support member  461  and the transfer station  465  of the intermediate support  46 . Simultaneously, the jack  466  associated with the support member  461  actuates the switch  464  to connect the suction nozzle of the support member  461  to the vacuum pump to enable the object to be picked up by the intermediate support  46 . 
     If there is an object on the support member, the sensor  51 ,  52  enables the turntable  460  to rotate one step to receive the next object. On the other hand, if no object has been put down, the turntable  460  does not move but the printing table  1  and the turntable  20  of the transfer system  2  rotate one step. 
     At the exit stations  462  of the intermediate support  46 , if the sensors  53  sense four objects on the support members  461  at the respective four exit stations, the support members  461  are moved vertically upward by the jacks  467  toward the suction nozzles  44  of the holding members and the jacks  463  disconnect the support members  461  from the vacuum pump so that the suction nozzles  44  take up the objects by suction on an opposite side, the top side in this position. The nozzles are then moved in guide grooves  45 , each associated with a bar  47  mounted in a guide groove  48 , toward the clamps  40  which are standing by in a horizontal position. 
     At the end of the stroke of the suction nozzles  44  the objects are aligned with the same orientation. The clamps  40  then grasp the group of objects presented in the horizontal position by the suction nozzles  44 . The objects grasped by the clamps  40  are moved downward, simultaneously rotating through one quarter-turn so that they are positioned vertically in the exit support  9 . When the objects are in place in the exit support  9  the clamps  40  return to their horizontal position to take up a new group of objects  7 . 
     The exit support  9  then moves forward one step on the exit conveyor  6  to enable the clamps to receive the next group of objects. 
     Clearly the clamps  30 ,  40  and the nozzles  34 ,  44  of the holding members perform one to-and-fro movement while the turntable  360  of the intermediate support  36 , the turntable  20  of the transfer system  2 , the printing table  1  and where applicable the turntable  460  of the intermediate support  46  of the offloading system  4  rotate through four indexing steps. 
     The objects  7  can therefore be loaded and offloaded in accordance with the invention without slowing the rate of production of the printing machine, which can be as high as 3 600 printed objects per hour. 
     Of course, many modifications can be made to the examples described above without departing from the scope of the invention. 
     Thus the printing machine may comprise only a loading system in accordance with the invention at its entry, the objects exiting in any manner, or the printing machine can include only an offloading system, the objects entering differently. 
     The clamps of the holding members described in the above example could equally be replaced by a single clamp adapted to grasp a group of objects. 
     Furthermore, the objects can be presented in a horizontal position at the entry, respectively at the exit, so that the clamps for modifying the position of the objects can be dispensed with, only suction nozzles moving in a horizontal plane and co-operating with spacing modification means able to move the objects between the intermediate support and the entry, respectively exit, support.