US20090108520A1

US20090108520A1 - Apparatus and method for breaking open and aerating sheet material stacks

Info

Publication number: US20090108520A1
Application number: US12/288,470
Authority: US
Inventors: Frank Stemmer
Original assignee: Adolf Mohr Maschinenfabrik GmbH and Co KG
Current assignee: Adolf Mohr Maschinenfabrik GmbH and Co KG
Priority date: 2007-10-24
Filing date: 2008-10-21
Publication date: 2009-04-30
Also published as: DE502007004027D1; ATE469852T1; EP2053001B1; JP2009102171A; EP2053001A1

Abstract

An apparatus and a method for separating and aerating sheet material arranged in a stack include a support to receive the sheet material stack thereon before the same is separated and aerated. A roll mechanism clamps the sheet material stack between an upper rotatable roll and a lower drivable roll. The sheet material stack is conveyed into a position between the upper and lower rolls when the same are in an open position. A ram converges the upper and lower rolls to clamp the sheet material stack therebetween. A drive rotates the lower roll in the conveying direction of the sheet material stack, and a gripper selectively grips the front end of the sheet material stack.

Description

CLAIM TO PRIORITY

Applicant hereby claims the priority benefits under the provisions of 35 U.S.C. §119, basing said claim of priority on European Patent Application Serial No. 07020794.9, filed Oct. 24, 2007. In accordance with the provisions of 35 U.S.C. §119 and Rule 55(b), a certified copy of the above-listed European patent application will be filed before grant of a patent.

BACKGROUND OF THE INVENTION

The invention relates to a method and apparatus for breaking open and aerating or venting material stacks formed from sheets, such as paper stacks.
A method and an apparatus for breaking open and aerating or venting a material stack which is formed from sheets, in particular a paper stack, are generally known from DE 10 2004 003 455 A1. In the prior art devices, a part stack of sheet material is separated from the overall stack, and is pushed outwardly over a rotatable guide roll. The front end of the separated material stack is gripped by means of a gripper, and is pulled obliquely downward through a passage which is formed between two rolls between which the material can be fed. The material stack is positioned in the passage when the rolls have been moved apart. Immediately after tongs have pulled the front end of the material stack into the passage, the two rolls are moved toward one another, and the material stack is thereby clamped. The gripper pulls the material stack between the rolls which are situated in the clamping position. The deflection of the material stack in the region of the guide roll results in the sheets of the material stack being broken open, such that air can pass between the adjacent sheets. In addition to the gripper pulling the material stack, the upper or the lower roll can be driven, wherein the two rolls have different circumferential speeds.
One drawback with this prior art method is that the material stack has to be pulled by the tongs in order to be broken up. As a result, only insufficient results are achieved with regard to the relative displacement of the individual sheets with respect to one another and, furthermore, with regard to the bulging of the material stack, and therefore with regard to the passing of air between the individual sheets. Also, breaking open of the material stack is also ineffective because the material stack is pulled downward at an angle through the passage, and therefore the conveying of the material stack between the two clamping rolls results in an insufficient amount of wraparound of the rolls, which is important for advantageous results during breaking open the material stack.
Further methods for breaking open and venting sheet material stacks are known from DE 32 19 693 A1 and EP 0 021 396 A1. However, in such devices, a gripper is not used to grip the material stack, but rather the sheet layers are conveyed by means of a conveyor belt, which interacts either with another conveyor belt or with a roll on the other side of the stack. Since the material stack is not gripped by a gripper before it is broken open, a positional change of the individual sheets of the material stack in the region of one stack side is permitted while the stack is being broken open. To this extent, the methods which are described in said documents are not only distinguished by an insufficient result of breaking open, but disadvantages are also to be noted which relate to the following process of vibrating of the vented material stack.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and an apparatus for breaking open and venting a material stack which is formed from sheets, in particular a paper stack, which achieve an optimum result of breaking open the material stack and venting the same for further processing in an optimum manner.
The invention proposes a method for breaking open and venting a material stack which is formed from sheets, in particular a paper stack, having the following features:

- advancing a cuboidal material stack beyond a support, between a roll arrangement, and gripping the material stack in the region of its front end by means of a gripper,
- directly clamping the material stack adjacent to the gripper between an upper rotatable roll and a lower drivable roll of the roll arrangement, wherein the material stack wraps around the upper roll over a part of its circumference in front of the clamping region of the two rolls,
- advancing the material stack by driving the lower roll while simultaneously moving the gripper in order to hold the material stack between the gripper and the rolls which clamp the material stack, and
- depositing the material stack, which is conveyed out of the clamping region of the rolls by means of the lower roll, on a support by means of the gripper and releasing the clamping action of the gripper.

It is important in the method according to the present invention that both rolls make direct contact with the material stack, and that the lower roll serves to transport the material stack which is clamped between the roll arrangement. The gripper has the task of holding the front free end of the material stack, which end moves further and further away from the roll arrangement during the transport of the material stack by means of said roll arrangement. In the present invention, the material stack is not pulled by the gripper, but rather the stack sags or is arched downward in the region between the gripper and the rolls which clamp the material stack. This makes it possible to form a bulge in the material stack in this region, and permits air to pass between the individual sheets of the material stack. In order to improve the venting or aerating of the material stack in this region, air can additionally be blown in from the side between the sheets of the material stack which are separated from one another. While the material stack is being broken up, the gripper fixes the position of the front end of the material stack. Accordingly, the material stack is fixed securely in this region of the stack, such that the individual sheet layers cannot be displaced in that region with respect to one another. After breaking open and venting, the material stack can therefore be deposited in cuboidal form on a support, such as a vibrating table. All that is required then is to orient the material stack, which was substantially cuboidal before breaking open and venting, exactly as a cube on the vibrating table, with the vibrating being carried to shift the stack into one corner of the vibrating table which has lateral guides.
The diameter of the upper roll is preferably smaller than the diameter of the lower roll.
Since the material stack, which is gripped by means of the gripper in the region of the front end, has a substantially flat end edge, and the sheets of the material stack at the subject end edge cannot be displaced with respect to one another in this region, the compression effect of the two rolls during clamping, and the fact that the material stack wraps around a part of the circumference of the upper roll in front of the clamping region, cause the two rolls of the material stack to be conveyed at a higher speed at its lower region than at its upper region. This effect leads to the lower sheets of the material stack bulging to a more pronounced extent than the upper sheets. In relation to the upper roll, the sheets on the outside of the bulge or curve therefore cover a greater distance than the sheets on the inside of the bulge or curve. The circumferential speed and therefore the conveying speed of the sheets thus increases toward the outside of the bulge. This is the reason why the individual sheets slide off of one another. A further effect which is important for optimum breaking open of the material stack is that the upper roll has a smaller diameter, and the conveying forces are introduced into the material stack via the lower roll that has a larger diameter. If the lower roll is driven and the upper roll co-rotates passively, the paper layer which lies on top will be driven to a less pronounced extent on account of the slip which occurs.
The result of breaking open is optimized in a surprising manner by the described effects. The overlapping of the sheets in the region of the clamping or pinching point between the rolls results in a pronounced stack bulge between the roll arrangement and the gripper, with the individual sheets separating from one another, and permitting sufficient air to pass between the individual sheets.
The gripper is moved at most at a speed which corresponds to the circumferential speed of the upper roll. In this case, the upper sheet layers, in particular the uppermost sheet of the material stack, are not pulled. However, no bulge is formed at this portion of the stack. In every case, on account of the described effects, a bulge is formed, in this case in the region of the lower sheet layers of the material stack. In order to ensure that the gripper does not pull the material stack, it is considered advantageous that the gripper is moved at a speed which is lower, in particular slightly lower, than the circumferential speed of the upper roll. The gripper is given the task of ensuring that the front end is fixed securely, and accordingly does not sag downward freely. As a result of the coordinated movement of the upper roll and the gripper, the material stack does not have to be pulled, but rather, the material stack is advanced by driving the lower roll.
In order to coordinate the circumferential speed of the upper roll and the moving speed of the gripper, a rotary encoder interacts with the upper roll, and detects the conveying path and the conveying speed of the upper roll and therefore of the upper sheet of the material stack which bears against said upper roll, and actuates movement means of the gripper via a controller. The gripper movement path and the gripper speed are then selected accordingly. The intention is to prevent the paper from being pulled.
Furthermore, one aspect of the invention proposes an apparatus for carrying out the method, having the following features:

- a support for receiving the material stack before it is broken open and vented,
- a roll arrangement for clamping the material stack between an upper rotatable roll and a lower drivable roll,
- a mechanism for conveying the material stack into the region between the opened roll pair,
- a device for converging the rolls relative to one another,
- a drive for driving the lower roll in the conveying direction of the material stack, and
- a gripper for holding the material stack in the region of its front end.

The mechanism for conveying the material stack in the region between the opened roll pair is a gripper.
The diameter of the upper roll is preferably smaller than the diameter of the lower roll.
The rolls of the roll arrangement can preferably be diverged or moved apart from one another only to such an extent that the material stack, in a still unclamped state, can be conveyed freely between the two rolls. It is therefore not necessary to provide a particularly large opening between the two rolls, which opening would be suitable for passage by a gripper.
According to one advantageous aspect or development of the invention, there is provision for the material stack, which rests on a support, to be advanced horizontally, and for the degree of wraparound of the smaller roll to result from the positioning of the front end of the support with respect to the upper roll, taking into consideration the thickness of the material stack.
The upper roll should be wrapped around over an angle of greater than 30 degrees. A wraparound angle of from 30 degrees to 50 degrees is considered advantageous. This angle is sufficient to achieve the positive effect of the overlapping of the material stack in the region of the clamping or pinching point.
In one example of the invention, the upper roll can be rotated freely, and the lower roll can be driven by an electric motor.
The circumferential face of the upper roll is preferably hard. The circumferential face of the lower roll is preferably soft. These properties of the circumferential faces of the rolls have a positive influence, in particular, on the described compression effect.
According to a significant aspect or development of the apparatus according to the invention, there is provision for the connecting plane of the two bearing axes of the two rolls to be directed from the top at the rear to the bottom at the front at a predetermined angle with respect to the horizontal and with respect to the vertical. On account of this oblique orientation of the connecting plane, the material stack can be conveyed substantially horizontally to the roll arrangement, and can also be conveyed substantially horizontally away from the roll arrangement. It is not necessary to provide movement of the material stack in an obliquely downward direction, apart from the region of the roll arrangement which is arranged at the angle.
The inclined connecting plane makes it possible to position the top of the lower roll level with the support, for example of a supporting face of a table for the material stack, or to arrange the top of the lower roll below the supporting face of the stack in a manner which corresponds at most to the size of the radius of the lower roll. Moreover, it is also possible to arrange the supporting face of the material stack on the support in such a way that said supporting face and the connecting plane of the two rolls intersect between the rolls when the stack is clamped between the rolls.
The oblique arrangement of the connecting plane has the advantage that the material stack can be conveyed substantially horizontally to the roll arrangement, wherein the desired degree of wraparound of the upper roll is achieved immediately in the region of the upper roll.
Moreover, the lower roll and the support can certainly be moved horizontally and/or vertically relative to one another.
Further features of the invention are shown in the sub-claims, the description of the figures and in the figures themselves, wherein it is noted that all the individual features and all the combinations of individual features represent further inventive refinements.
These and other advantages of the invention will be further understood and appreciated by those skilled in the art by reference to the following written specification, claims and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the method and apparatus for breaking open and venting a material stack which is formed from sheets are explained in greater detail in the following text with reference to the drawings, in which:

FIG. 1 is a side view of the apparatus, and

FIGS. 2 to 5 are side views of the apparatus showing various method sequences for breaking open and venting a paper stack which is formed from sheets.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For purposes of description herein, the terms “upper”, “lower”, “right”, “left”, “rear”, “front”, “vertical”, “horizontal ” and derivatives thereof shall relate to the invention as oriented in FIG. 1. However, it is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise.
The apparatus according to the illustrated embodiments for carrying out the method according to the invention has a table 1 with a receiving face 2 for supporting a paper stack 4 which is formed from a plurality of sheets 3. While only some sheets 3 are shown in the drawings for illustrative reasons, in reality, the stack comprises a multiplicity of sheets, in particular considerably more than 100 sheets.
The receiving face 2 of the table 1 is arranged horizontally. The table 1 can be moved to and fro, or fore to aft, in the direction of the double arrow 5. FIG. 1 shows the advanced or extended end position of table 1. FIG. 4 shows the withdrawn or retracted end position of table 1.
Furthermore, the apparatus has an upper roll 6 with a relatively small diameter and a lower roll 7 with a relatively large diameter. The two rolls 6 and 7 can be rotated about horizontal axles 8 and 9, which extend parallel to one another and are arranged parallel to the front edge 10 of the table 1. The axle 9 is mounted in a stationary bearing part 11 of the apparatus. Furthermore, a stationary constituent part of the apparatus also includes a pneumatic cylinder 12 having a piston rod 13 which receives in the region of its free end the axle 8 for the upper roll 6. In relation to its longitudinal center axis, the piston rod 13 is arranged at an angle with respect to the horizontal and with respect to the vertical. The connecting plane 14, which extends perpendicularly with respect to the sheet plane of the figure, connects the two axles 8 and 9 and is directed from the top at the rear to the bottom at the front. In the exemplary embodiment, the connecting plane 14 extends at an angle of 45 degrees with respect to the horizontal, that is to say 45 degrees with respect to the receiving face 2 of the table 1.
The upper roll 6 is mounted on the axle 8 such that it can be rotated freely. The lower roll 7 can be driven by means of an electric motor 15, in the direction of the arrow 16. In the illustrated example, the electric drive includes electric motor 15, a step-down gear mechanism 17 and a belt 18, which transmits the movement of the output shaft of the step-down gear mechanism 17 to the lower roll 7.
A rotary encoder 19 determines the rotary angle and the rotational speed of the upper roll 6.
A gripper 20 is arranged in its rear position in front of the connecting plane 14 adjacent to the table 1 when table 1 is in the extended position shown in FIG. 1. Gripper 20 can be moved horizontally to and fro, or fore to aft, in the direction of the double arrow 21. The clamping face 22 of the tongs' lower part 23, and the receiving face 2 of the table 1 which forms the support for the paper stack 4, are situated at the same vertical level. The tongs' upper part 24 can be moved vertically in the direction of the double arrow 26 by means of a pneumatic drive. The clamping face of the tongs' upper part 24 is denoted by the reference numeral 27. The tongs' lower part 23 is of an angular configuration, and has a front, vertically oriented stop plate 28.
In relation to the initial position which is shown in FIG. 1, the lower roll 7 is arranged directly below a tapered thickness section 29 of the table 1 when table 1 is situated in the extended end position. The pneumatic cylinder 12 is actuated in such a way that the piston rod 13 is retracted to form a relatively large passage 30 between the two rolls 6 and 7, and also between the upper roll 6 and the receiving face 2 of the table 1. The maximum passage height is somewhat larger than the maximum stack height.
Proceeding from the state shown in FIG. 1, a cuboidal paper stack 4, for example a part stack which is separated from an overall stack in a customary manner, is placed onto the table 1, and is advanced by means of a conveying mechanism, which is not shown in greater detail, for example a gripper 35, which grips the paper stack 4 at the rear end thereof, until the maximum advanced position is reached, at which point, the paper stack 4, which is still cuboidal, makes contact with the stop plate 28 of the opened gripper 20. This condition is shown in FIG. 2.
Subsequently, the gripper 20 is transferred into its gripping position, that is to say the tongs' upper part 24 is moved against the paper stack 4, with the result being that the paper stack 4 is clamped between the tongs' lower part 23 and the tongs' upper part 24. The gripper 35 is opened and moved back. This state is illustrated in FIG. 3. Then table 1 is moved back into the retracted end position shown in FIG. 4. This results in a relatively wide gap being formed between the front edge 10 of the table 1 and the gripper 20. In the illustrated example, the spacing of the table 1 in its withdrawn or retracted end position from the upper roll 6 corresponds to approximately twice the thickness of the stack 4 of the sheets 3. The pneumatic cylinder 12 is then activated, and the piston rod 13 is extended. The upper roll 6 makes contact with the upper sheet 3 of the paper stack 4, and clamps the paper stack 4 between the upper roll 6 and the lower roll 7. In this condition, in front of the clamping region of the two rolls 6 and 7, the paper stack 4 wraps around the upper roll 6 over a part of the circumference of the upper roll, and, in particular, an angle of greater than 30 degrees. The circumferential face 31 of the upper roll 6, with the relatively small diameter, is preferably of a hard configuration. Accordingly, the upper roll 6 compresses the paper stack 4 to a relatively pronounced extent in the region of the upper sheets 3 of stack 4. The upper roll 6 therefore shapes the paper stack 4 in this region in accordance with the radius of upper roll 6. The lower roll 7, with the relatively large diameter, has a circumferential face 32 which is preferably relatively soft. Accordingly, the lower roll 7 presses into the paper stack 4 only a relatively small amount in the region of the lower sheets 3 of paper stack 4. After the paper stack 4 is clamped between the two rolls 6 and 7, the lower roll 7 is driven by means of the electric motor 15 in the direction of the arrow 16 according to FIG. 1, and the paper stack 4 is thereby conveyed away from the table 1, toward the gripper 20. On account of the different compression effects of rolls 6 and 7, the sheets 3 in the lower region of the paper stack 4 are moved more quickly than the sheets 3 in the upper region of the paper stack 4. This effect is reinforced or augmented by the introduction of the conveying force to the lower region of the paper stack 4 by means of the lower roll 7. Finally, as best shown from a comparison of FIG. 5 with FIGS. 1 to 4, that region of the paper stack 4 which rests on the table 1 has the end edges of the sheets 3 arranged in an angled, splayed or overlapping relationship. This separating or fanning of sheets 3 results from the different conveying speeds of the sheets 3 in the paper stack 4. Those sheets 3 which are arranged closer to the axle 8 of the upper roll 6 have to cover a shorter path than those sheets 3 which are arranged at a greater distance from the axle 8.
On account of the conditions which are described in the preceding text, a downwardly bulging shape 33 is formed in the paper stack 4 in front of the lower roll 7 during conveying of the sheet stack 4 by the driven lower roll 7. The bulge 33, which is deformed downward to a pronounced extent, and the individual sheets 3, which have separated or detached from one another, are shown in FIG. 5. Air can then pass between said sheets 3. There is certainly the possibility of arranging air nozzles to the sides of the paper stack 4 in the region in which the bulge 33 is formed, and also to blow blown air into the paper stack 4 from the side.
The conveying path of the upper roll 6 and its rotational speed are detected by the rotary encoder 19, which is connected via a controller to the mechanism (not shown) for moving the gripper 20 horizontally. Therefore, if the paper stack 4 is pushed forward by the driven lower roll 7, the gripper 20 is then also moved forward. The movement path and the movement speed of the gripper 20 are coordinated with regard to the kinematics of the upper roll 6, such that the gripper 20 only holds the front end of the paper stack 4 firmly, but does not pull it. The movement path and the speed of gripper 20 are preferably selected in such a way that the upper sheet 3 of the paper stack 4, as can be seen in FIG. 5, sags downward slightly, and the bulge 33 is formed in a downward direction from this point to an ever more pronounced extent.
The driven lower roll 7 conveys the paper stack 4, until its rear end leaves the clamping region between the two rolls 6 and 7. At this instant, the paper stack 4 is held above a support 34 only by the gripper 20. The gripper 20 moves further a little, pulls the paper stack 4 onto the support 34 completely, and is then opened to deposit the paper stack 4 on the support 34. The support 34 forms, in particular, a constituent part of a vibrating table, which is otherwise not illustrated in greater detail. This support can be arranged horizontally, as shown, or can be positioned in an inclined manner, as is customary in the case of a vibrating table. The broken open and vented cuboidal paper stack 4 can therefore be fed by the gripper 20 to the side guides of the vibrating table in order to deposit the paper stack on the table of the vibrating table, and to shake it into a corner of the vibrating table for the purpose of absolutely accurate orientation of the edges of the paper stack 4, and thus for the purpose of the formation of the paper stack 4 as an exact cube. In this regard, it is to be understood that as long as the cuboidal paper stack is gripped by the gripper 20, the shape of the stack can deviate slightly from that of an exact cube, thereby requiring that the stack be arranged exactly as a cube for subsequent processing operations, such as cutting or punching processes.
In the foregoing description, it will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed herein. Such modifications are to be considered as included in the following claims, unless these claims by their language expressly state otherwise.

Claims

1. A method for separating and aerating sheets of material arranged in a stack having forward and rearward ends, comprising the steps of:

positioning the sheet material stack on a first support;

advancing the sheet material stack such that the forward end thereof extends beyond the first support;

positioning a rotatable upper roll above the first support and the sheet material stack;

positioning a drivable lower roll below the first support and the sheet material stack;

gripping the forward end of the sheet material stack in a gripper;

converging the upper roll and the lower roll to clamp therebetween that portion of the sheet material stack disposed adjacent to the gripper at a clamping region, whereby at least a portion of the sheet material stack wraps around a predetermined portion of the circumference of the upper roll at a location forward of the clamping region;

advancing the sheet material stack by driving the lower roll, and simultaneously shifting the gripper to retain the material stack between the gripper and the upper and lower rolls until the rearward end of the sheet material stack passes out of the clamping region, thereby separating and aerating the sheets in the sheet material stack;

further shifting the gripper to position the separated sheets in the sheet material stack on a second support; and

releasing the gripper to ungrip the forward end of the sheet material stack.

2. A method as set forth in claim 1, wherein:

said upper and lower roll positioning steps include selecting the diameter of the upper roll smaller than the diameter of the lower roll.

3. A method as set forth in claim 1, wherein:

said advancing step includes positioning the sheet material stack on the first support and advance the same horizontally; and wherein

said converging step includes positioning the first support with respect to the upper roll as a function of the thickness of the sheet material stack to vary the degree of wraparound of the upper roll.

4. A method as set forth in claim 3, wherein:

said converging step further comprises converging the upper roll and lower roll to a point where the sheet material stack wraps around the upper roll over an angle in the range of 30 to 50 degrees in front of the clamping region.

5. A method as set forth in claim 1, including:

coordinating the circumferential speed of the upper roll relative to the movement speed of the gripper.

6. A method as set forth in claim 5, including:

shifting the gripper at a speed which is slightly lower than the circumferential speed of the upper roll.

7. A method as set forth in claim 1, including:

shifting the material stack substantially horizontally, apart from its deflection in the region of the upper and lower rolls.

8. A method as set forth in claim 1, including:

blowing air in from the side of the material stack between the individual sheets at the fanned open region of the material stack in front of the lower roll.

9. An apparatus for separating and aerating sheets of material arranged in a stack, comprising:

a support shaped to receive thereon a sheet material stack before the same is separated and aerated;

a roll mechanism configured for clamping the sheet material stack between an upper rotatable roll and a lower drivable roll;

a conveyor mechanism converging the sheet material stack into a position between said upper and lower rolls when the same are in an open position;

a ram converging and diverging said upper and lower rolls;

a drive rotating the lower roll in the converging direction of the sheet material stack; and

a gripper selectively gripping a front end of the sheet material stack.

10. An apparatus as set forth in claim 9, wherein:

said upper roll has an outside diameter that is smaller than the outside diameter of said lower roll.

11. An apparatus as set forth in claim 9, wherein:

said conveyor mechanism comprises a gripper.

12. An apparatus as set forth in claim 9, wherein:

said upper roll is mounted such that it can be freely rotated.

13. An apparatus as set forth in claim 9, wherein:

said drive rotating said lower roll comprises an electric motor.

14. An apparatus as set forth in claim 9, wherein:

said upper roll includes a hard circumferential face.

15. An apparatus as set forth in claim 9, wherein:

said lower roll includes a soft circumferential face.

16. An apparatus as set forth in claim 9, wherein:

said upper and lower rolls are arranged such that a plane passing through the pivot axes of said upper and lower rolls is disposed at an angle in the range of 40 to 50 degrees with respect to the horizontal.

17. An apparatus as set forth in claim 9, including:

a rotary encoder operably connected with and detecting the rotary angle and/or rotational speed of said upper roll.

18. An apparatus as set forth in claim 17, including:

a controller operably connected with said rotary encoder and including a drive for moving said gripper.