EP2456694A2

EP2456694A2 - Vacuum gripper

Info

Publication number: EP2456694A2
Application number: EP10768366A
Authority: EP
Inventors: Michael Schilp; Josef Zimmermann; Adolf Zitzmann
Original assignee: Zimmermann and Schilp Handhabungstechnik GmbH
Current assignee: ZS-HANDLING GMBH
Priority date: 2009-07-22
Filing date: 2010-07-22
Publication date: 2012-05-30
Also published as: US20150015013A1; TW201116468A; KR20120051025A; CN102639415A; JP5752119B2; CN102639415B; WO2011009446A2; US20120274011A1; TWI571418B; US9266686B2; JP2012533491A; WO2011009446A3; KR101759357B1

Abstract

The present invention relates to a vacuum gripper and in particular to a vacuum gripper for gently gripping workpieces having sensitive surfaces, such as solar cells, wafers, or panels for flat screens, and for gripping heavy glass plates or plates made of other material having a very smooth surface that are stacked on top of each other and should be removed from above, wherein the vacuum gripper has the following characteristics: a straight or curved gripper plate (2), at least one suction opening (3; 3a), which is provided in the gripper plate (2), wherein a workpiece throttle surface (6) is formed around the suction opening (3), at least one recess (4), which is provided in the side of the gripper plate (2) facing the workpiece, outside of the workpiece throttle surface (6) relative to the suction opening (3), and at least one ventilation hole (5), which is provided within each recess (4).

Description

Vacuum gripper

The present invention relates to a vacuum gripper and more particularly to a vacuum gripper for gently gripping surface sensitive workpieces such. As solar cells, wafers or panels for flat screens, as well as for gripping heavy glass plates or plates made of other material with a very smooth surface, which are stacked on each other and should be removed from above.

Vacuum grippers are well known and are suitable for use, i. H. adapted to the workpiece to be gripped constructively. If the task is to grip surface-sensitive workpieces, special measures must be taken not to damage the workpiece surface when gripping.

There are basically two types of vacuum grippers:

There are vacuum grippers, which are placed on the workpiece and mechanically brought into contact with the workpiece surface at the beginning of the gripping process, d. H. the gripper is provided with sealing lips which provide a seal between the workpiece surface and the gripper such that upon creation of a vacuum within the gripper, the external air pressure presses the workpiece against the sealing lips. The high surface pressure can lead to undesirable changes in the workpiece surface.

There are also vacuum grippers, which are designed to suck the workpiece from a distance to the gripper head and close to the Gripper surface to keep contact-free. This effect is z. B. achieved in that the gripper surface is designed as an air bearing. An air bearing can be produced by a nozzle field, from which compressed air flows or by means of a vibrating plate, as described in the document EP 1387808 B1, which is hereby fully incorporated into the description.

When the workpiece hangs on the surface of the vacuum gripper, it is pressed against the gripper surface by the external air pressure. However, a contact of the gripper surface is prevented by the air bearing. Thus, the workpiece floats at a predetermined distance below the gripper surface, so that the workpiece surface is not touched. However, this functional description only applies to the static state. During gripping, however, there is the following problem: suction requires increased suction power to lift the workpiece. It would be desirable to reduce the suction power before the workpiece has reached its final position, because otherwise there is a risk that the accelerated workpiece overcomes the counterforce of the air bearing due to the inertia force and strikes against the gripper surface.

In practice, it is often necessary to choose the maximum suction force 10 times greater than the actually required holding force, which only has to be slightly larger than the weight force, which is determined by the mass of the workpiece. There are also gripping operations where the maximum suction force has to be selected even higher. This is the case when z. B. glass plates on a stack or on a table with a very smooth surface. In this case, there is almost no air between the glass plate and the table surface. When the glass plate is raised, the surrounding air pressure must be overcome initially to create a small gap when lifting to allow air to flow into it. Only when the gap is filled with air and thus the pressure in the gap corresponds to the outer air pressure, and the initially acting contact pressure is zero, so that only the weight force overcome. The additional force required to separate smooth plates is hereinafter referred to as tear-off force.

A vacuum suction gripper, which sucks the workpieces without mechanical contact, must therefore be designed such that the suction force of the gripper first overcomes the breaking force, then accelerates the workpiece towards the gripper surface against the gravitational force. If the workpiece has a predetermined distance from the gripper surface, it would be desirable to decelerate the workpiece so that it does not hit the gripper surface because of the inertial force.

Since in an automatic process, the workpieces to be lifted are the same and thus have the same weight, it is theoretically possible to arrange a fast-reacting valve control behind the suction nozzle, which throttles the Saugström after overcoming the tearing force for the first time, so that the suction force for technologically optimal acceleration of the plate is tuned. A second throttling could occur when the plate has already been raised a predetermined distance to decelerate its speed enough for the plate to reach its final position on the gripper surface.

It is clear to the person skilled in the art that the control of such highly dynamic processes is extremely complicated and therefore expensive, since gaseous media are difficult to control because of their compressibility. It is therefore the object of the invention to provide a reliable and cost-effective device, with the particular smooth plates that require high tear-off, can be lifted without contact.

The object is achieved with a vacuum gripper according to claim 1, wherein the vacuum gripper has the following features: a straight or curved gripper plate. The gripper plate can be flat to accommodate flat plates, it can be bent one-dimensionally, for. B. but can also be curved two-dimensional, for example, spherical workpieces on increase. The gripper plate may have a form adapted to the workpiece surface shape, as far as the technical teaching described below can be implemented in terms of fluid mechanics. In the gripper plate is provided at least one, acted upon by a predetermined negative pressure suction port. A workpiece throttle area is formed around the suction port. As a workpiece throttle area, a surface portion is designated, which forms a defined gap when sucking the workpiece with the workpiece surface. Predominantly at this gap, the workpiece hangs on the gripper plate when it has reached its final position. Accordingly, this workpiece throttle area is dimensioned such that the suction force that arises at this workpiece throttle area is greater than the oppositely directed weight force of the workpiece, which depends on the mass of the workpiece.

Furthermore, at least one recess is provided in the workpiece-facing side of the gripper plate. This recess is arranged according to the technical teaching of the invention so that it is always outside the workpiece throttle area. In other words, sucked air flows from the edge of the gripper plate along the gripper plate to the suction port, passing through the suction opening associated with this, d. H. upstream recess. In the recess at least one vent hole is present.

The following describes the function of the vacuum gripper:

When the bottom of the gripper approaches approx. 2 mm to 0.5 mm of the workpiece surface, the vacuum gripper acts like a conventional vacuum gripper, ie the air is drawn in from the gripper edge and flows towards the suction opening. Over the entire gripper surface forms a negative pressure, the height of which drops towards the gripper edge. In the area of the recesses, the negative pressure is constant. A predetermined volume flow of air is also drawn through the vent hole. However, this volume flow is relatively small compared to the volume flow, which is sucked into the gripper surface within the 2 mm to 0, 5 mm wide gap. The gripper has in this constellation its maximum load capacity at a predetermined constant suction pressure and the predetermined surface of the gripper plate.

The closer the workpiece approaches the gripper surface, the narrower is the gap, and thus the smaller the flow cross-section, through which the outside, d. H. from the edge of the gripper plate, air can flow. However, the cross section of the vent hole remains constant. This leads to the fact that in the recess no negative pressure can build up, as always flows through the vent hole outside air. This effect intensifies the smaller the flow cross section through which the air can flow from the edge. As a result, the surface of the recess no longer contributes to the suction force. In other words, since the suction force is the product of effective suction area and suction pressure - and the effective suction area is essentially limited to the area of the workpiece throttle area, the effective suction area is thus many times smaller than with one greater distance of the gripper surface from the workpiece surface. Thus, the suction force is many times smaller than at a greater distance of the gripper surface of the workpiece surface. This produces the desired effect that the vacuum gripper has a very high suction force at a greater distance from the surface of the workpiece to be gripped, which drops sharply as the workpiece surface approaches the vacuum gripper, so that, with suitable dimensioning, striking of the workpiece against the gripper is avoided can.

The lowering of the suction force is thus automatic. With appropriate professional dimensioning of the vacuum gripper as a function of the workpiece weight and the height of the suction pressure, levitation of the workpiece can be achieved, ie without the workpiece surface touching the vacuum gripper. In this case, an equilibrium of forces arises between the suction force which lifts the workpiece and the weight force which pulls the workpiece downwards. When the suction power changes, for. B. becomes slightly weaker, the workpiece would lower slightly. This increases but the effective suction surface, so that the suction increases and the workpiece is pulled up again.

This floating state always sets in and is independent of the surface condition of the workpiece. Thus, not only glass plates with a very smooth surface, but also wood plates with a rough surface can be detected with this gripper.

In an advantageous embodiment of the vacuum gripper according to claim 2, the opening cross sections of the vent holes are variably formed. As a result, a simple adjustment of the suction force to a predetermined distance between the workpiece surface and the gripper is possible.

In an advantageous embodiment of the vacuum gripper according to claim 3 more vent holes per recess are provided, which are selectively closed. As a result, a simple adjustment of the suction force to a predetermined distance between the workpiece surface and the gripper is possible.

In an advantageous embodiment of the vacuum gripper according to claim 4, the vent holes are filled with a porous material which acts as a throttle. As a result, the cross section of the vent hole can be made larger, which can lead to advantages in the production of small grippers.

In an advantageous embodiment of the vacuum gripper according to claim 5, the porous material is a plug made of an open-cell plastic foam. These plugs are easy to produce and easy to replace.

In an advantageous development of the vacuum gripper according to claim 6, the vent holes are provided with air filters as an alternative to a porous material, which act as a throttle and are also easily replaceable.

In an advantageous embodiment of the vacuum gripper according to claim 7, the vent holes are designed as threaded holes in which nozzles with different geometries, ie can be screwed with predetermined flow profiles.

In an advantageous development of the vacuum gripper according to claim 8, the vent holes have steerable flow control valves. As a result, the air flow rate during the suction of the workpiece can be actively controlled, which leads under certain conditions to an improvement of the suction and holding properties of the vacuum gripper. In an advantageous embodiment of the vacuum gripper according to claim 9, the volume of the recess is variable, whereby a faster adaptation of the gripper to another workpiece can be achieved. The volume change can be effected by inserting material. If the gripper z. B. made of steel, magnets can be inserted into the recesses, which then hold without further attachment. It can also be screwed screws whose heads contribute to the reduction in volume within the recess.

In an advantageous embodiment of the vacuum gripper according to claim 10, a plurality of workpiece throttle surfaces are provided within a gripper plate. This arrangement is chosen if the board to be removed is to be worn at several points.

It is clear to the person skilled in the art that the workpiece throttle surfaces do not necessarily have to be ring-shaped, but can also extend in a straight line, which will be explained in greater detail in the exemplary embodiments.

In an advantageous embodiment of the vacuum gripper according to claim 11, the gripper plate is designed as an air bearing with air outlet nozzles. This creates an additional safeguard against touching the gripper by the workpiece.

As an alternative to the development according to claim 11, the gripper plate is mechanically coupled to at least one ultrasonic oscillator according to claim 12. at the gripper plate is dimensioned so that it forms an ultrasonic air bearing, as z. As described in EP 1387808 B1.

In an advantageous development of the vacuum gripper according to claim 13, a plurality of suction openings are provided, wherein a workpiece throttle area is formed around each of these suction openings. This arrangement can be advantageously used when a workpiece z. B. has a straight surface to which the gripper attaches, but the workpiece is of different thickness. The suction openings can be operated with different suction pressures, which allows a uniform and horizontal lifting of the workpiece.

The invention will be described in more detail below with reference to exemplary embodiments in conjunction with appended drawings. Fig. 1a, b show a first embodiment of the vacuum gripper.

Fig. 2a, b show a second embodiment of the vacuum gripper.

Fig. 3a, b show a third embodiment of the vacuum gripper.

Fig. 4a, b show a fourth embodiment of the vacuum gripper. 1a, b show the cross section of a circular vacuum gripper for picking up a workpiece 1, the vacuum gripper having the following features: A circular disk-shaped gripper plate 2 has a suction opening 3 at its center. A circular-shaped workpiece is arranged around the suction opening 3 Throttle surface 6 is formed, whose operation is explained in the following section. In the direction of the gripper plate edge, an annular recess 4 is provided, which in the present case has two ventilation holes offset by 180 degrees, ie, the entire recess 4 is connected to the external atmosphere. FIG. 1a shows the workpiece 1 still in the starting position. By means of the suction hole 3 air is sucked, which flows laterally via the gap 7, which is usually between about 2 mm to 0, 5 mm. In this position, the vacuum gripper its highest suction force, which is greater than the weight of the workpiece. 1

As a result, the workpiece 1 is raised. In other words, as the gripper bottom approaches the workpiece surface, the vacuum gripper acts like a conventional vacuum gripper, i. H. the air is drawn in from the gripper edge and flows towards the intake opening. Over the entire gripper surface forms a negative pressure, the height of which drops towards the gripper edge. In the region of the recess 4, however, the negative pressure P is constant, which can be seen in the underlying diagram A as a plateau line 8. A predetermined volume flow of air is also drawn through the vent hole. However, this volume flow is relatively small compared to the volume flow, which is sucked into the gripper surface within the 2 mm to 0, 5 mm wide gap. In the diagram B, in addition to the pressure curve of the diagram A, the pressure curve 9 is additionally shown, as it would appear without the recesses 4.

The closer the workpiece approaches the gripper surface, as shown in Fig. 1b, the narrower is the gap 7 through which air can flow from the outside, ie from the edge of the gripper plate. The flow cross section, through which the air can flow from the edge, decreases greatly. However, the cross-section of the vent holes remains constant. This leads to the fact that in the recess 4 no negative pressure builds up, as can always flow through the vent holes outside air in sufficient quantity. This effect intensifies the smaller the flow cross-section of the gap 7, through which the air can flow from the edge. As a result, the surface of the recess 4 no longer contributes to the suction force. In other words, since the suction force is the product of effective suction surface and suction pressure - and the effective suction surface is essentially limited only to the area of the workpiece throttle surface 6, the effective suction surface has thus become many times smaller than in a greater distance of the gripper surface from the workpiece surface. Thus, the suction force is many times smaller than at a greater distance of the gripper surface from the workpiece surface.

This produces the desired effect that the vacuum gripper has a very high suction force at a greater distance from the surface of the workpiece to be gripped, which drops sharply as the workpiece surface approaches the vacuum gripper, so that, with suitable dimensioning, striking of the workpiece against the gripper can be avoided. The diagrams A and B below the figure show the pressure gradients with or without recess. 4

The lowering of the suction force thus takes place automatically. With appropriate professional dimensioning of the vacuum gripper as a function of the workpiece weight and the height of the suction pressure, it is possible to levitate the workpiece; H. without the workpiece surface touching the vacuum gripper. In this case, an equilibrium of forces arises between the suction force which lifts the workpiece and the weight force which pulls the workpiece downwards. When the suction power changes, for. B. becomes slightly weaker, the workpiece 1 would lower slightly. However, this increases the effective suction surface, so that the suction increases and the workpiece 1 is pulled back up.

The nozzle geometry and the required pressure and vacuum are determined by the properties of the workpiece to be gripped. In many technological processes, the workpieces are the same, so that the nozzle and pressure parameters can remain constant. Since the nozzle and pressure parameters depend on the size, weight, surface, and a number of other features of the workpiece, it does not make sense to specify specific nozzle shapes and other parameters.

The following figures show further embodiments of the vacuum gripper, all according to the same in Fig. 1 described technical teaching work. Therefore, a repetition of the description of the general technical teaching will be omitted hereinafter and only the new features of the respective embodiment will be described. FIGS. 2a, b show a circular gripper plate with two intake openings 3, 3a. The second suction port 3a is an annular groove having 4 holes to which vacuum is applied. In the present embodiment, since the sum of the cross sections of the 4 holes is substantially smaller than the cross section of the suction port 3, the suction effect of the suction groove 3a is also less than the suction effect of the suction port 3. If necessary, the suction cross section of the suction groove 3a may be larger be selected so that the suction is at least as large as that of the suction port. 3

Figs. 3a, b show a rectangular gripper plate for optimal gripping of preferably rectangular workpieces. In this embodiment, the suction port 3 is rectangular and the groove-shaped recesses 4 are parallel to each other.

Figs. 4a, b show a gripper plate according to Fig. 3 for lifting a pipe. For this, the gripper plate is adapted to the curvature of the pipe diameter.

Claims

claims

A vacuum gripper for receiving a workpiece (1), the vacuum gripper having the following features:

a straight or curved gripper plate (2),

at least one suction opening (3; 3a) provided in the gripper plate (2), a workpiece throttle surface (6) being formed around the suction opening (3),

- At least one recess (4) which is provided in the workpiece-facing side of the gripper plate (2) with respect to the suction port (3) outside the workpiece throttle surface (6) and

- At least one vent hole (5) which is provided within each recess (4).

2. Vacuum gripper according to claim 1, characterized in that the opening cross-sections of the vent holes (5) are variable.

3. Vacuum gripper according to claim 1, characterized in that a plurality of vent holes (5) are provided per recess, which are selectively closable.

4. vacuum gripper according to claim 1, characterized in that the vent holes (5) are filled with porous material.

5. Vacuum gripper according to claim 4, characterized in that the porous material is a plug made of an open-cell plastic foam.

6. vacuum gripper according to claim 1, characterized in that the vent holes (5) have interchangeable air filters.

7. Vacuum gripper according to claim 1, characterized in that the vent holes (5) have threaded holes for screwing in nozzles with different geometries.

8. vacuum gripper according to claim 1, characterized in that the vent holes (5) have controllable flow valves.

9. vacuum gripper according to claim 1, characterized in that the volume of the recess (4) is variable.

10. vacuum gripper according to claim 1, characterized in that a plurality of workpiece throttle surfaces (6) within a gripper plate (2) are provided.

11. Vacuum gripper according to claim 1, characterized in that the gripper plate (2) is designed as an air bearing with air outlet nozzles.

12. Vacuum gripper according to claim 1, characterized in that the gripper plate (2) is mechanically coupled to at least one ultrasonic oscillator, wherein the gripper plate (2) is dimensioned so that it forms an ultrasonic air bearing.

13. Vacuum gripper according to claim 1, characterized in that a plurality of suction openings (3) is provided, wherein each of these suction openings (3) around a workpiece throttle area (6) is formed.