U.S. patent application number 13/386593 was filed with the patent office on 2012-11-01 for vacuum-gripper.
This patent application is currently assigned to ZIMMERMANN & SCHILP HANDHABUNGSTECHNIK GMBH. Invention is credited to Michael Schilp, Josef Zimmermann, Adolf Zitzmann.
Application Number | 20120274011 13/386593 |
Document ID | / |
Family ID | 43466897 |
Filed Date | 2012-11-01 |
United States Patent
Application |
20120274011 |
Kind Code |
A1 |
Schilp; Michael ; et
al. |
November 1, 2012 |
VACUUM-GRIPPER
Abstract
The present invention relates to a vacuum gripper and in
particular to a vacuum gripper for gently gripping work-pieces
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).
Inventors: |
Schilp; Michael;
(Regensburg, DE) ; Zimmermann; Josef; (Regensburg,
DE) ; Zitzmann; Adolf; (Teunz, DE) |
Assignee: |
ZIMMERMANN & SCHILP
HANDHABUNGSTECHNIK GMBH
Regensburg
DE
|
Family ID: |
43466897 |
Appl. No.: |
13/386593 |
Filed: |
July 22, 2010 |
PCT Filed: |
July 22, 2010 |
PCT NO: |
PCT/DE10/00860 |
371 Date: |
May 7, 2012 |
Current U.S.
Class: |
269/21 |
Current CPC
Class: |
B25J 15/0616 20130101;
H01L 21/6838 20130101; B65G 47/91 20130101; B65G 49/061 20130101;
B65G 47/911 20130101 |
Class at
Publication: |
269/21 |
International
Class: |
B25B 11/00 20060101
B25B011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 22, 2009 |
DE |
10 2009 039 474.8 |
Claims
1. Vacuum gripper for gripping a work-piece (1), the vacuum gripper
comprising the following features: a plan or curved gripper plate
(2), at least one suction port (3; 3a) which the gripper plate (2)
is provided with, wherein a work-piece suction throttling zone (6)
is formed around the suction port (3), at least one recess (4)
provided in the gripper plate (2) at that side thereof directed the
work-piece and arranged beyond the work-piece suction throttling
zone (6) formed around the suction port (3), and at least one vent
hole (5) formed within each of the recesses (4).
2. Vacuum gripper according to claim 1, characterized in that the
cross sections of the vent holes (5) are variable. 25
3. Vacuum gripper according to claim 1, characterized in that
several vent holes (5) are formed within each of the recesses,
which can be closed selectively.
4. Vacuum gripper according to claim 1, characterized in that the
vent holes (5) are filled with a porous material.
5. Vacuum gripper according to claim 4, characterized in that the
porous material is a foamed plastic having open pores and shaped
into a plug.
6. Vacuum gripper according to claim 1, characterized in that the
vent holes (5) comprise exchangeable air filters.
7. Vacuum gripper according to claim 1, characterized in that the
vent holes (5) are tap-holes for screwing in nozzles having
different geometries.
8. Vacuum gripper according to claim 1, characterized in that the
vent holes (5) comprise controllable flow valves.
9. Vacuum gripper according to claim 1, characterized in that the
volumes of the recesses (4) are variable.
10. Vacuum gripper according to claim 1, characterized in that
several work-piece suction throttling zones (6) are provided within
a gripper plate (2).
11. Vacuum gripper according to claim 1, characterized in that the
gripper plate (2) is formed as air bearing having air exit
nozzles.
12. Vacuum gripper according to claim 1, characterized in that the
gripper plate (2) is mechanically coupled to at least one
ultrasonic vibrator, 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
several suction ports (3) are provided, wherein a work-piece
suction throttling zone (6) is formed around each of the suction
ports (3).
Description
[0001] The present invention relates to a vacuum gripper and, in
particular, to a vacuum gripper for gently gripping work-pieces
having sensitive surfaces, such as solar cells, wafers or panels
for flat screens, and for gripping heavy glass plates or plates
made of a material having a very smooth surface, which are stacked
on top of each other and are to be removed from above.
[0002] Vacuum grippers are generally known and are constructively
adapted to each case of application, that is, to the work-piece to
be gripped. If work pieces having sensitive surfaces are to be
gripped, special measures must be taken to prevent that surfaces
from being damaged.
[0003] On principle, there are two kinds of vacuum grippers: On the
one hand, there are vacuum grippers which are put onto the
work-piece and, at the beginning of the gripping procedure, are
mechanically brought into contact with the surface of work-piece,
that is, the gripper is provided with a sealing the lips of which
effect a sealing action between the surface of work-piece and the
gripper so that, when a vacuum is generated within the gripper, the
barometric pressure causes the work-piece to be pressed against the
sealing lips. However, due to the high contact pressure, the
surface of work-piece can be changed undesirably.
[0004] On the other hand, there are vacuum grippers which are
constructed such that they suck the work-piece to the gripper head
from a certain distance and hold it in a non-contact way close to
the gripping surface of the gripper. This effect is gained when the
surface of the gripper is formed as an air bearing, for example. An
air bearing can be generated by a field of nozzles from which
compressed air flows out or by an oscillating plate such as
described in the document EP 1387808 B1 which is completely
included in the following description.
[0005] When the work-piece is sucked, it is urged to the gripper
surface by the atmospheric pressure and keeps hanging at it.
However, contacting of the gripper surface by the work-piece is
prevented by the air bearing. That is, the work-piece is kept
levitating under the gripper surface in a predetermined distance
without contacting it. However, this functional description is in
force only for the stationary state. Therefore, during the
procedure of gripping, there is a problem which will be explained
below:
[0006] In order to lift a work-piece by sucking, an increased
suction power is required. However, it would be desirable to reduce
the suction power before the work-piece reaches its final position,
because otherwise, there is the danger that, caused by its mass
force of inertia, the accelerated work-piece overcomes the force
generated by the air bearing and hits against the surface of
gripper.
[0007] In practice, it is often necessary to chose a maximum
suction force 10 times greater than the holding force actually
required, which, in turn, must slightly be greater than the weight
of work-piece, that is, the mass thereof.
[0008] Also, there are gripping actions where the maximum suction
force must still be greater. This is the case when glass plates
have to be lifted separately from a stack or a glass plate has to
be lifted from a table having a very smooth surface, for example.
In such a case, almost no air is present between the glass plate
and the surface of table. When the glass plate is lifted up, first
if all, during lifting, the surrounding barometric pressure must be
overcome to form a small gap into which air can enter. When the gap
is completely filled with air und, thus, the pressure in the gap
corresponds to the barometric pressure, the contact pressure
initially generated becomes zero so that merely the weight of
work-piece has to be overcome. The additional force necessary for
separating smooth plates is called breakaway force in the
following.
[0009] Therefore, a vacuum suction gripper sucking work-pieces
without contacting them mechanically, has to be designed so that
the suction force of the gripper overcomes the breakaway force and
then, accelerates the work-piece towards the surface of gripper,
against the gravitational force. It would be desirable to
decelerate the work-piece and thus, to reduce its mass force of
inertia as soon as it reaches a predetermined distance to the
surface of gripper to prevent it from hitting against the
gripper.
[0010] In an automatic process, as the work-pieces to be lifted
have the same size and the same weight, it is theoretically
possible to arrange a fast-reacting valve control means behind the
suction nozzle, which, after the breakaway force has been overcome,
reduces the suction flow in a first action so that the work-piece
in the shape of a plate is decelerated to the technologically
optimum speed. A second throttling action can be carried out after
the plate has already been lifted a predetermined distance, in
order to decelerate the plate such that it reaches its final
position at the surface of gripper.
[0011] An expert knows that the control of such highly dynamic
processes is extremely complex and thus costly, because it is
difficult to control gaseous media, conditioned by the
compressibility thereof.
[0012] Therefore, subject matter of the invention is to provide a
reliable and low-cost device enabling also smooth plates requiring
a great breakaway force to be lifted in a non-contact way.
[0013] This subject matter is solved by a vacuum gripper according
to claim 1, wherein the vacuum gripper comprises the following
features: a flat or an arched gripper plate. The gripper plate can
be flat to hold plane plates, it can be arched one-dimensionally to
hold tubes, for example, or can be arched two-dimensionally to hold
ball-shaped work-pieces, for example. Also, the gripper plate can
have a shape adapted to the surface of a work-piece to be gripped,
provided that the technical science described below is convertible
in fluidic respect.
[0014] The gripper plate is provided with at least one suction port
in which a vacuum can be generated. The suction port is surrounded
by a work-piece suction throttling zone. The work-piece suction
throttling zone is an area section which, together with the surface
of the work-piece, forms a defined gap when the work-piece is
sucked. As soon as the work-piece has reached its final position,
it is kept hanging at the gripper plate predominantly through this
gap. Therefore, the work-piece suction throttling zone is
dimensioned so that the suction force generated around this zone is
greater than the force caused by the mass-dependant weight of
work-piece and acting in the opposite direction.
[0015] In addition, the gripper plate is provided with at least one
recess, on that side thereof directed to the work-piece. According
to the technical science of the invention, this recess is always
arranged beyond the work-piece suction throttling zone. In other
words, the air sucked in from the edge of the gripper plate flows
along the gripper plate up to the suction port, thereby passing the
recess assigned to and positioned in front of it. The recess is
provided with at least one vent hole.
[0016] The function of the vacuum gripper will be described below.
As soon as the bottom side of the gripper has reached a position
about 2 mm to 0.5 mm away from the top side of work-piece, the
vacuum gripper acts like a common vacuum gripper, that is, air is
sucked in at the edge of the gripper and flows up to the suction
port. Thereby, a negative pressure is generated along the entire
gripper surface, the altitude of which lowering in the direction to
the edge of gripper. The negative pressure has a constant height
within the recess. A predetermined quantity of air is also sucked
in through the vent hole. However, this quantity of air is
relatively small compared with that sucked in through the 2 mm to
0.5 mm wide gap along the gripper surface.
[0017] With this constellation, with a given constant suction
pressure and the given area of the gripper plate, the gripper
generates its maximum lifting force.
[0018] The more the work-piece approaches to the gripper surface,
the narrower the gap and ,thus, the smaller the cross section
through which air can flow from the edge of gripper plate. However,
the cross section of the vent hole remains constant. The result is
that a negative pressure can not be generated any longer within the
recess because air permanently flows through the vent hole into it
from the outside. This effect is increased when the cross section
through which air is sucked in from the edge of gripper becomes
smaller. Therefore, the area of the recess does not contribute any
longer to the suction force being the product of effective suction
area and suction pressure. In other words: With this constellation,
the effective suction area is essentially restricted to the
work-piece suction throttling zone and thus, is smaller than that
formed with a greater distance between the gripper surface and the
surface of work-piece, by a multiple. Thus, the suction force also
is smaller by a multiple.
[0019] Therefore, the wanted effect is gained, that is, the vacuum
gripper generates a very great suction force with a greater
distance to the surface of the work-piece to be gripped, which,
however, strongly decreases when the surface of work-piece
approaches the vacuum gripper, so that, with proper dimensioning of
gripper, the work-piece can be prevented from hitting against
it.
[0020] Thus, the suction force is reduced automatically. When the
vacuum gripper is competently dimensioned dependant on the weight
of work-piece and the height of suction pressure, the work-piece
can be kept levitating without contacting it. In this case, a force
balance, that is, a balance between the suctions force lifting the
work-piece and the weight of work-piece, which acts downwardly, is
gained. When the suction force is changed, that is, is reduced, for
example, the work-piece slightly sags. Thereby, the effective
suction area is increased, with the result, that the suction force
is increased and, thus, the work-piece is drawn upwardly again.
[0021] This levitation state is always regulated and is independent
on the surface condition of work-piece. Therefore, not only glass
plates having smooth surfaces, but also wooden plates having coarse
surfaces can be gripped by this gripper.
[0022] With a further advantageous embodiment of the vacuum gripper
according to claim 2, the vent holes are executed variably. This
enables the suction force to be adjusted to a predetermined
distance between the surface of work-piece and the gripper in a
simple way.
[0023] With a further advantageous embodiment of the vacuum gripper
according to claim 3, each of the recesses is provided with several
vent holes which can be closed by choice. This enables the suction
force to be adjusted to a predetermined distance between the
surface of work-piece and the gripper in a simple way.
[0024] With a further advantageous embodiment of the vacuum gripper
according to claim 4, the vent holes are filled with a porous
material having the function of a throttle. Thus, the cross section
of the vent hole can be dimensioned greater, which enables
small-sized grippers to be made more advantageously.
[0025] With a further advantageous embodiment of the vacuum gripper
according to claim 5, the porous material is a foamed plastic
having open pores and being shaped into a plug. Such plugs can
easily be made and exchanged.
[0026] With a further advantageous embodiment of the vacuum gripper
according to claim 6, alternatively to the porous material, the
vent holes are provided with air filters which function as
throttles and can also be exchanged easily.
[0027] With a further advantageous embodiment of the vacuum gripper
according to claim 7, the vent holes are executed as tap-holes into
which nozzles having different geometries and thus, predetermined
flow profiles can be screwed.
[0028] With a further advantageous embodiment of the vacuum gripper
according to claim 8, the vent holes comprise controllable flow
valves. Thus, when the work-piece is sucked in, the rate of air
flow can be controlled effectively and thus, the suction and
holding characteristics of the vacuum gripper can be improved.
[0029] With a further advantageous embodiment of the vacuum gripper
according to claim 9, the volume of the recess is alterable so that
the gripper can be adjusted to an other work-piece more quickly. An
alteration of this volume can be effected by inserting any material
into the recess. When the gripper is made of steel, for example,
magnets can be inserted into the recesses without requiring
additional fixing means. It is also possible to screw bolts into
the recesses so that the heads thereof contribute to the volume
reduction within the recesses.
[0030] With a further advantageous embodiment of the vacuum gripper
according to claim 10, the gripper plate is provided with several
work-piece suction throttling zones. Such an arrangement is chosen
when a plate to be lifted is to be held at several points.
[0031] An expert knows that the work-piece suction throttling zones
must not have an annular shape unconditionally, but can extend
rectilinearly, which will be explained in more detail with the
description of the exemplified embodiments.
[0032] With a further advantageous embodiment of the vacuum gripper
according to claim 11, the gripper plate is designed as air bearing
having air exit nozzles. Thus, an additional measure for preventing
any contact between the work-piece and the gripper is provided.
[0033] According to claim 12, as an alternative to the embodiment
according to claim 11, the gripper plate is mechanically coupled to
at least one ultrasonic vibrator and dimensioned so that an
ultrasonic air bearing such as described in EP 1387808 B1, for
example, is formed.
[0034] With a further advantageous embodiment of the vacuum gripper
according to claim 13, the gripper plate is provided with several
suction ports, wherein a work-piece suction throttling zone is
formed around each of the suction ports. Such an arrangement can be
used advantageously for lifting a work-piece having an even
surface, for example, which the gripper applies to, but being
different in thickness. The suction ports can be admitted with
different suction pressures, which enable a work-piece to be lifted
uniformly and in horizontal position.
[0035] In the following, the invention will be described by means
of exemplified embodiments in connection with the drawings
enclosed.
[0036] FIG. 1a,b show a first embodiment of the vacuum gripper.
[0037] FIG. 2a,b show a second embodiment of the vacuum
gripper.
[0038] FIG. 3a,b show a third embodiment of the vacuum gripper.
[0039] FIG. 4a,b show a fourth embodiment of the vacuum gripper
[0040] FIGS. 1a,b show a cross-sectional view of a circular vacuum
gripper for carrying a work-piece 1, wherein the vacuum gripper
comprises the following features: a disk-shaped round gripper plate
2 provided with a suction port 3 in its center. A round annular
work-piece throttling zone 6 is formed around the suction port 3,
the operating characteristics of which being explained in the
consecutive section. The gripper plate 2 is also provided with an
annular recess 4 extending towards the margin of plate, which has
two vent holes 5 dislocated to each other by 180 degrees, that is,
the entire recess 4 is connected with the atmosphere.
[0041] FIG. 1a shows the work-piece 1 still in its initial
position. By the suction action of the gripper, air is sucked from
the outside of gripper through the gap 7 usually having a width of
about 2 mm to 0.8 mm and flows through the suction port 3. In this
position, the vacuum gripper generates its maximum suction force
being greater than the weight of the work-piece 1.
[0042] Thereby, the work-piece 1 lifted. In other words: When the
bottom side of the gripper approaches the surface of work-piece,
the vacuum gripper acts like a common vacuum gripper, that is, air
is sucked via the edge of gripper plate and flows towards the
suction port. Thus, a negative pressure is generated along the
entire gripper surface, the height of which decreasing towards the
edge of gripper. However, in the region of the recess 4, the
negative pressure P is constant, represented by the plateau line 8
in the diagram A below this figure. Also, a predetermined volume of
air is sucked through the vent hole. However, this volume of air is
relatively small compared with that sucked through the 2 mm to 0.5
mm wide gap.
[0043] In the diagram B, in addition to the pressure distribution
indicated in diagram A, a pressure distribution 9 is indicated,
which would arise without the recesses 4.
[0044] As shown in FIG. 1b, the more the work-piece approaches the
gripper surface, the smaller the gap 7 through which air flows from
the outside, that is, from the edge of gripper plate. Thus, the
cross section of the gap, through which air can flow from the edge
of gripper plate, is reduced remarkably. However, the cross
sections of the vent holes remain constant. Because air in an
adequate amount can permanently flow from the outside through the
vent holes, a negative pressure is not generated any longer in the
recess 4. This effect is intensified with the reduction of the
cross section of the gap 7 through which air flows from the
outside. Therefore, the area of the recess does not contribute any
longer to the suction force being the product of effective suction
area and suction pressure. In other words: With this constellation,
the effective suction area is essentially restricted to the
work-piece suction throttling zone 6 and thus, is smaller than that
formed with a greater distance between the gripper surface and the
surface of work-piece, by a multiple. Thus, the suction force also
is smaller by a multiple.
[0045] Therefore, the wanted effect is gained, that is, the vacuum
gripper generates a very great suction force with a greater
distance to the surface of the work-piece to be gripped, which,
however, is decreased remarkably when the surface of work-piece
approaches the vacuum gripper so that hitting of the work-piece
against the gripper is prevented, provided that the gripper is
dimensioned properly.
[0046] The diagrams A and B drawn below figure lb represent the
pressure distribution with and without a recess 4,
respectively.
[0047] Thus, the suction force is reduced automatically. When the
vacuum gripper is competently dimensioned based on the weight of
work-piece and the height of suction pressure, the work-piece can
be held in a levitation state without contacting the vacuum
gripper. In this case, a force balance is gained between the
suction force lifting the work-piece and the weight drawing the
work-piece downwardly. When the suction force is somewhat lowered,
for example, the work-piece 1 slightly sags. However, as the
effective suction area is increased at this moment, the suction
force is also increased so that the work-piece 1 is drawn upwardly
again.
[0048] Nozzle geometry and negative pressure required are
determined by the properties of the work-piece to be gripped. With
numerous technological processes, work-pieces of the same kind are
used so that nozzle and pressure parameters can be kept constant.
As the nozzle and pressure parameters are dependant on the size,
the weight, the surface and some further features of work-piece, it
is not meaningful to specify shapes of nozzles and other
parameters.
[0049] Further embodiments of the vacuum gripper are shown in the
corresponding figures mentioned above, all of which working
according to the technical science described in connection with
FIG. 1. Therefore, in the following, the new features of each of
these embodiments will be described only, but not the general
technical science again.
[0050] FIGS. 2a,b show a circular gripper plate having a suction
port 3 and four suction ports 3a, in which a vacuum is generated,
wherein the suction ports 3a are connected with each other by an
annular groove. With this embodiment, as the sum of the cross
sections of the suction ports 3a is remarkably smaller than the
cross section of the suction port 3, the suction effect thereof is
also smaller than that of the suction port 3. If necessary, the
cross sections of the suction ports 3a can be increased such that
the suction effect thereof is almost the same as that of the
suction port 3.
[0051] FIGS. 3a,b show a rectangular gripper plate for optimum
gripping of work-pieces preferably being rectangular in shape. With
this embodiment, the suction port 3 has a rectangular cross section
and the groove-like recesses 4 are arranged in parallel with each
other.
[0052] FIGS. 4a,b show a gripper plate like that represented in
FIG. 3, but designed for gripping a tube. For this purpose, the
shape of gripper plate is proportioned to the radius of tube.
* * * * *