Abstract:
Offset printing plates are usually supplied from the manufacturer as a plate stack with intermediate paper layers. For further processing, the plate stack is placed in a magazine cassette. A suction plate lifts a top plate off from the stack and, after removal of the intermediate paper layer by means of blowing air, conducts it for further processing. Also by means of blowing air, the respective upper plates of the remaining stack are isolated, so that they no longer firmly adhere to the stack. Undesired dislocations of the plates thus arising are mechanically corrected.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an apparatus by means of which plates input as a stack are isolated in modern processing machines for offset printing plates such as, for example, exposure machines, and wherein intermediate paper layers which are usually present are removed. 
     There is a desire in modern machines of the graphics trade, particularly in exposure machines for offset printing plates, to individually remove the plates from a magazine. The unexposed offset plates are normally supplied in packages of 50 to 100 articles, whereby the individual plates are protected by intermediate layers of thin paper due to their sensitive surface. Insofar as possible, the plate stack should be inserted into the magazine in the same way in which it was removed from the outer packaging. From the magazine, the plates should be individually removed, for instance by means of a suction plate or gripper, and should then be supplied for further processing. 
     This operation, which may seem rather simple at first, is complicated by a number of conditions in view of current practices. 
     The light-sensitive layer side of the plates is extremely sensitive to scratches. The plates, therefore, dare not slide on other surfaces, for instance parts of the conveyor means, or on one another in any situation. 
     In the condition in which they are delivered, the plates are usually separated from one another by intermediate layers of paper so that they cannot rub against one another. This intermediate paper layer, however, must be respectively removed after a plate is taken from the stack. 
     In the condition in which they are delivered, the plates of the stack adhere greatly to one another. In order for the uppermost plate to be reliably taken from the stack without disruption, it is necessary to first loosen it from the plate stack by means of an isolating operation. 
     Plates having different formats should be processed with one and the same magazine. 
     The lifting element should always grasp the individual plates in the same position. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to specify an apparatus which meets all of the above conditions. 
     According to the invention, a cassette means is provided for containing the stack of plates, the cassette means having at least one open end. A vacuum suction plate means is positioned over the stack for lifting an upper-most plate from the stack. Means for lifting the suction plate means is provided such that in a first work phase a channel having a rectangular cross section is opened between an underside of the lifted, upper-most plate and a top of the remaining plate stack. Adjustment means are provided for laterally limiting the channel given differing plate formats. At least two detent pins are positioned such that an end face of the plate stack abuts thereagainst when inserted into the apparatus. The detent pins are hollow and have vertically situated radial slots facing the adjacent plate stack. The detent pins have means for permitting blowing air to be blown from the detent pin slots against the end face of the plate stack and into the channel. Resilient caps which partially cover the slots are situated on the detent pins. Means are provided coupled to the suction plate for actuating the resilient caps. The means for lifting, in a second work phase, lifts the suction plate sufficiently so that it stands free from the cassette on all sides. At least one movable pin is situated in a floor of the cassette at a side of the plate stack opposite the detent pins. Means are provided for pivoting the movable pin away such that it lies beneath the cassette floor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of the apparatus of the invention with a suction plate applied; 
     FIG. 2 is a side view of the apparatus of the invention with a blowing channel open; 
     FIG. 3 illustrates resilient partitions in the apparatus of FIGS. 1 and 2; and 
     FIG. 4 is a front elevation of the apparatus of FIGS. 1 and 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     After being removed from their outer packaging, the unexposed offset printing plates with intermediate paper layers are inserted as a plate stack 1 into a box-shaped cassette with open end faces. At least two detent pins 3 are screwed into the cassette floor at one of the open end faces, the plate stack 1 being applied against these detent pins. The detent pins 3 are hollow-bored and comprise a vertical slot 4 in the direction toward the plate stack 1. Blowing air supplied from below at 5 is capable of being blown against the end face of the plate stack 1 from this vertical slot 4. Proceeding from above, a cap 6 slides on a guide 7 over the slotted part of the detent pins 3, this pressing upward against a detent 9 in its idle position on the basis of a spring 8. When the cap 6 is pressed down, it partially covers the slot 4. 
     The clearance between the lateral walls of the cassette 2 is kept such that the plate stack having the largest format to be processed just fits in. Resilient sidewalls 10 are situated in the floor of the cassette 2 for smaller formats--as shown in FIG. 3. These are conducted in guides 11 and are drawn up by springs 12. Given larger plate formats, they are pressed down under the weight of the plate stack until their upper edge is flush with the floor of the cassette. The spacing between these resilient side walls is also adapted to the respective plate format. 
     A suction plate 13 having an engageable and disengageable vacuum is situated above the cassette 2 on guides 31a, 31b in a movable fashion. Among other things, these guides allow the suction plate 13 to lower via a control rod 30 onto the plate stack 1 in a precisely defined position and also allow it to assume defined distances from the plate stack 1 in a vertical direction as well. Fork-shaped detents 14 are situated on the upper side of the suction plate 13 such that they press against the upper side of the caps 6 when the suction plate 13 is lowered and press these caps 6 against the spring 8. The lower edges of the caps 6 cover the slots 4 to a greater or lesser degree. The degree of coverage is determined by the height of the remaining plate stack 1 when the suction plate 13 lowers down onto the plate stack. 
     Pivotably situated pins 15 are further situated in the floor of the cassette 2 such that, in the vertical position, they press against that narrow side of the plate stack 1 which lies opposite the detent pins 3. These pins 15 can be pivoted by means of a lever mechanism 16 so that they disappear through slots 17 in the cassette floor, and thus disappear below the level thereof. 
     The functioning of the apparatus is as follows. 
     As shown in FIG. 1, the suction plate 13 is lowered down onto the plate stack 1. The detents 14 press against the springs 8 and thus press the caps 6 down. The pins 15 are situated in the vertical position. After the vacuum is switched on in the suction plate 13, this vacuum seizes the uppermost plate of the stack. After this, the suction plate 13 is lifted a few millimeters together with the uppermost plate held by suction (FIG. 2), so that a flat channel 18 opens between the underside of the lifted plate and the remaining stack. This flat channel 18 is laterally limited by the side walls of the cassette 2 and by the respective, resilient side walls 10, given smaller plate formats. Due to the detents 14, the caps 6 proceed into such a position that the slots 4 in the detent pins 3 are covered such that they terminate exactly with the upper edge of the channel 18. After the pins 15 are pivoted away by the lever mechanism 16, the detent pins 3 are supplied with blowing air proceeding from the air supply 5. This emerges from the slots 4 and blows into the opened channel 18 and against the end face of the plate stack 1. The use of blowing air is as low as conceivably possible because this can only freely emerge from the slots 4 at the level of the opened channel 18. The remaining slot is substantially closed by the plate stack 1. Given an appropriate dimensioning of the height of the channel 18 and the quantity of blowing air, the following occurs. 
     An intermediate paper layer 19 usually lying between the individual plates of the stack, and serving to protect the surface thereof, slides in the direction of the air stream, guided by the lateral walls. It slides out between the lifted plate and plate stack, and is conducted into a collecting container via a channel, which is not shown here. The air stream also penetrates from the end face of the plate stack between the plates lying at the top. These are slightly lifted off from one another, i.e. &#34;isolated&#34;. Only after this is the following, undisturbed lifting of the next plate by the suction plate 13 possible because the individual plates usually adhere greatly to one another when the stack is delivered. In the described isolating operation, it occurs that the uppermost 3 or 4 plates dislocate slightly in the direction of the air stream, as shown in FIG. 2. They must be returned into the exact position (detent against the detent pins 3) because the further processing of the plates requires that these are always seized by the suction plate 13 in the same position and are later also exactly deposited. After the intermediate paper layer 19 has been blown out, the isolation of the uppermost plates of the stack has been carried out and the blowing air has been shut off, the suction plate 13 is therefore further lifted into a position 20 (FIG. 2). The pins 15 are now pivoted back into the vertical position by means of the lever mechanism 16. The dislocated uppermost plates thus shift against the detent pins 3 into their correct initial position. The suction plate 13 conducts the seized plate away (for instance laterally) for further processing via guides 31a, 31b, deposits it elsewhere when the vacuum is disconnected, and returns into the position 20 shown in FIG. 2. After the suction plate 13 is lowered onto the plate stack 1, the operation begins anew, as described, on the basis of executive sequencing. 
     The invention is not limited only to application given offset plates. On the contrary, it can be employed anywhere where materials such as films, foils, plates or the like with protective intermediate layers of paper or similar material are supplied as a stack to be individually moved from a magazine together with removal of the intermediate layer. They are then supplied for further processing. 
     Although various minor changes and modifications might be proposed by those skilled in the art, it will be understood that we wish to include within the claims of the patent warranted hereon all such changes and modifications as reasonably come within our contribution to the art.