Note: Descriptions are shown in the official language in which they were submitted.
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GRIPPING AND TRANSPORT CLAMP MOUNTED AT THE END OF A ROBOTIC
ARM AND METHOD FOR OPERATING THE SAME
FIELD OF THE INVENTION
The present invention relates to a depalletizing tool for an industrial robot,
and more
particularly to a gripping and transport clamp mounted at the end of a robotic
arm.
Furthermore, the present invention also relates to a method for operating the
above-
mentioned depalletizing tool.
BACKGROUND OF THE INVENTION
Several manufacturing industries need to pack their product into boxes. These
boxes
are often shipped by the manufacturers, in an unfolded and stacked manner, on
pallets. The piles of boxes need to be handled manually in order to transfer
them
from the pallet to a machine whose function is to form the boxes and to insert
the
product therein. The main problems to which are confronted these industries
are the
costs related to the use of manual labor and the industrial illnesses related
to the
repetitive handling of moderately heavy loads. Confronted to this type of
problem,
industrialists are turning themselves more and more towards automated
solutions
which replace human beings by an automated system.
An automated solution is generally defined as a set of mechanisms governed by
a
control system accomplishing a specific functionality. There exist on the
market
specialized systems capable of accomplishing depalletization work but only
under
very specific constraints. These constraints are such that the industries must
consider
robotized solutions which are much less constraining.
A robotized solution is defined as a system using an industrial robot with at
least four
degrees of freedom, as well as a tool specifically designed to be affixed on
the robot
and accomplish a very well defined task. There exist on the market robotized
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solutions capable of accomplishing depalletization work but the latter have
certain
constraints. These constraints are:
= the pallets must always be placed at the same location;
= the set of articles on the pallet must always be at the same location on the
pallet;
= the articles must be of the same dimension;
= the piles of articles must be fastened individually, or the article must be
a formed
box; and
= the tool of the robot or the downstream machine must remove the fasteners of
the
piles and dispose adequately of the fasteners (e.g. straps).
One can find on the market vision systems allowing the digitalization of
objects in
three dimensions. It is possible to adapt such a system to an industrial robot
tool and
to produce a computer program capable of processing the digital images and
allowing
a tridimensional tracing. Unfortunately, the costs involved would be
prohibitive for an
industrial application intended for a very competitive market.
Prehension is a very complex function even for human beings and there is no
industrial robot tool presently on the market which is capable of carrying
out, at a
reasonable cost, such a complex task while remaining independent of the
physical
dimensions of the articles.
Known in the art, are, for example, US patents Nos. 4,993,915 and 5,169,284 by
Berger disclosing a row of claws for unstacking objects pilled up on a pallet.
The
claws are mounted on a carriage assembly movable horizontally on a guide rail.
However, the use of this carriage assembly and guide rail reduces the
independence
with respect to the physical dimension and positioning of the articles.
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SUMMARY OF THE INVENTION
An object of the present invention is to provide a tool for a robot and a
method for
operating the tool which satisfy at least some of the above-mentioned needs
and
which are thus an improvement over what is known in the prior art.
According to the present invention, there is provided an object transporting
tool
mountable at an end of a robotic arm movable towards an object to be
transported,
the object transporting tool comprising: a support member to be mounted at the
end
of the robotic arm; a first lower plate mounted to the support member for
insertion
under the object to be transported; a first actuator mounted between the first
lower
plate and the support member for moving the first lower plate between a
retracted
position and an extended position; a reaction force sensor for detecting a
reaction
force exerted on the first lower plate upon displacement thereof; a second
lower
plate mounted to the support member below the first lower plate and being
movable
between a retracted position and an extended position; a second actuator
mounted
between the second lower plate and the support member for moving the second
lower plate between the retracted position and the extended position; and a
controller connected to the reaction force sensor and to the first and second
actuators for receiving detection signals from the reaction force sensor and
for
operating the first and second actuators.
According to an illustrative embodiment, the object transporting tool further
comprises an upper plate mounted to the support member and being movable
toward the object to be transported between an open position and a gripping
position, and a third actuator mounted between the upper plate and the support
member for moving the upper plate between the open position and the gripping
position.
According to the present invention, there is also provided a method for
transporting
an object with an object transporting tool mounted at an end of a robotic arm,
the
object transporting tool having a first lower plate and second lower plate
below the
first lower plate, the method comprising: sequentially moving the end of the
robotic
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arm in horizontal step movements toward the object to be transported and in
vertical
up and down step movements until the first lower plate touches a separator
positioned under the object to be transported; inserting the first lower plate
under the
object to be transported; inserting the second lower plate under the object to
be
transported after the first lower plate has been inserted under the object to
be
transported.
According to an illustrative embodiment, the object transporting tool further
comprises an upper plate and the method further comprises lowering the upper
plate
toward the object to be transported, thereby gripping the object between the
upper
and lower plates.
According to the present invention, there is further provided a method for
transporting an object with an object transporting tool mounted at an end of a
robotic
arm, the object transporting tool having a first lower plate and a second
lower plate
below the first lower plate, the method comprising: moving the end of the
robotic arm
toward the object to be transported until the first lower plate is in the
proximity of the
object to be transported; partially inserting the first lower plate under the
object to be
transported; detecting if a reaction force exerted on the first lower plate is
below a
predetermined threshold; further inserting the first lower plate under the
object to be
transported if the reaction force exerted on the first lower plate is below
the
predetermined threshold; and inserting the second lower plate under the object
to be
transported after the first lower plate has been further inserted under the
object to be
transported.
According to an illustrative embodiment, the object transporting tool further
comprises an upper plate and the method further comprises lowering the upper
plate
toward the object to be transported, thereby gripping the object between the
upper
and lower plates.
The foregoing and other objects, advantages and features of the present
invention
will become more apparent upon reading of the following non-restrictive
description
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of an illustrative embodiment thereof, given by way of example only, with
reference
to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
5
In the appended drawings:
Figure 1 a perspective view of a pile of articles tacked on a pallet that are
to be
gripped with a clamp mounted on a robotic arm according to an illustrative
embodiment of the present invention;
Figure 2 is a perspective view of a portion of the clamp according to an
illustrative
embodiment of the present invention;
Figures 3, 4, 5 and 6 are side views illustrating the steps of a method for
operating
the clamp shown in Figure 2 with respect to the pile shown in Figure 1,
according to
an illustrative embodiment of the present invention; and
Figure 7 is a perspective view of the clamp shown in Figure 2, mounted at the
end of
a robotic arm, said clamp being shown in its entirety.
DETAILED DESCRIPTION OF THE INVENTION
In the following description, the same numerical references refer to similar
elements. The embodiments shown in the figures are illustrative.
Moreover, although the present invention can be designed for use with an
industrial
robot for depalletizing purposes, it could be used with other types of objects
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of different fields for other purposes, e.g. sorting applications, etc., as
apparent to a
person skilled in the art. For this reason, expressions such as
"depalletizing" and/or
"articles" and any other references and/or other expressions equivalent
thereto
should not be taken as to limit the scope of the present invention and include
all other
objects with which the present invention could be used and may be useful.
Furthermore, it is to be understood that the expression "articles" as used in
the
context of the present description refers to various different objects which
may be
used with the present invention, whether these objects are of substantially 2-
D and
3-D form, such as metal sheets, cardboards, unfolded boxes, formed boxes,
plastic
containers, etc., as apparent to a person skilled in the art.
Referring to figure 1, there is shown a preferred pile of articles 1 that are
to be
handled by a gripping and transport clamp 20 (shown in Figure 7) of the
present
invention. These articles 1 are stacked one over the other on a pallet 3,
without
fasteners, and separated into layers by means of separators 2 used mostly to
add
stability to the set of articles 1 on the pallet 3. The separators 2
preferably exceed on
the side of the pile facing the clamp 20 by about an inch. It is also
preferable that the
piles not be too inclined or twisted.
Referring to figure 7, there is shown the gripping and transport clamp 20
mounted at
an end 22 of a robotic arm 24 according to a preferred embodiment of the
present
invention. The robotic arm 24 is designed so as to be movable towards the
object to
be gripped, such as the article 1 shown in Figure 1. The clamp 20 is held by a
support plate 25, which is mounted at the end 22 of the robotic arm 24. As it
will be
further described below, the clamp 20 is mainly formed of two superposed lower
pressing plates 8, 9 and an upper pressing plate 10, which are mounted on
support
members 26.
Referring to figure 2, the first lower pressing plate 8 is shown mounted on a
support
plate 4, which is part of the support members 26 holding the clamp 20. The
lower
pressing plate 8 is shaped so that it can be inserted under the object 1 to be
gripped.
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For example, the lower pressing plate 8 can have the shape of a spatula and it
is
preferably made of a flat, thin and flexible metal plate. However, the lower
pressing
plate 8 may have other suitable shapes, such as forks, arms, claws, etc.
Adjacent to the lower pressing plate 8, there is shown a sensor 7 that is
adapted for
detecting a reaction force that is exerted on the lower pressing plate 8 upon
displacement thereof. Preferably, the sensor 7 is a tactile sensor that
detects a
deformation of the lower pressing plate 8 when it touches an obstacle. In
particular,
the tactile sensor can be an inductive proximity sensor. As will be described
below,
the preferred purpose of the tactile sensor is to detect the presence of the
separator
2 between the articles 1.
An actuator, such as a pneumatic cylinder and piston arrangement 30 ( see
Figure
7), is used for inserting the lower pressing plate 8 under the object 1 to be
gripped in
response to a detection of the reaction force by the sensor 7. Preferably, the
actuator
30 is mounted between the lower pressing plate 8 and the support plate 4 so as
to
move the lower pressing plate 8 between a retracted position and an extended
position. At the extended position, the lower pressing plate 8 is inserted
under the
object 1 to be gripped. Of course, those skilled in the art will appreciate
that the same
can be accomplished without the lower pressing plate 8 being retractable as
this
same insertion movement can also be done by means of a forward displacement of
the robotic arm 24. The purpose of the first lower pressing plate 8 is to
slightly lift the
object 1 to be gripped in order to slide in the second lower pressing plate 9.
The second lower pressing plate 9 is mounted below the lower pressing plate 8
on
the support plate 4. This lower pressing plate 9 is movable between a
retracted
position and an extended position by means of another actuator, such as a
pneumatic cylinder and piston arrangement 31 (see Figure 7), that is mounted
between the lower pressing plate 9 and the support plate 4. This actuator 31
moves
the lower pressing plate 9 between the retracted position and the extended
position,
and thereby inserts the lower pressing plate 9 under the object 1 to be
gripped in
response to the lower pressing plate 8 being inserted under the object 1 to be
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gripped. As will be appreciated by those skilled in the art, the second lower
pressing
plate 9 should be rigid enough to support the weight of the object 1 to be
gripped and
preferably be shaped in the form of a spatula. Also, the second lower pressing
plate
9 may have other suitable shapes, such as forks, arms, claws, etc.
The upper pressing plate 10 is mounted on a support plate 28, which is part of
the
support members 26, and is movable toward the object 1 to be gripped between
an
open position (as shown in Figure 7) and a gripping position. The support
plate 28 is
rigidly fixed onto the support plate 4 at a right angle. Similarly as
explained above in
the case of the lower pressing plates 8, 9, the upper pressing plate 10 may
have
several suitable shapes, such as forks, arms, claws, etc. An actuator, such as
a
pneumatic piston and cylinder arrangement 32 (see Figure 7), is mounted
between
the upper pressing plate 10 and the support plate 28. This actuator 32 moves
the
upper pressing plate 10 between the open position and the gripping position,
and
thereby grips the object 1 between the upper and lower pressing plates 8, 9,
10.
Of course, as it will be apparent to those skilled in the art, many
modifications can be
done on the configuration described above. Indeed, the position of the
different
support members 26 can be varied according to other design configurations.
The clamp 20 and robotic arm 24 of the present invention are further coupled
to a
controller or a computer module so as to receive detection signals from the
sensors
and for operating the actuators, as will be described below.
Preferably, and as is known in the art, detectors may be included in the
robotic
system for detecting abnormalities of operation and for stopping the robotic
arm 24
in the event of false movements or damage of an object.
Referring to figures 3, 4, 5 and 6, the clamp 20 and robotic arm 24 is
operated to
perform the following basic steps in order to grip the object 1:
sequentially moving the end 22 of the robotic arm 24 in horizontal step
movements toward the object 1 to be gripped and in vertical up and down step
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movements until the first pressing plate 8 touches a separator 2 positioned
under the
object 1 to be gripped;
inserting the first lower pressing plate 8 under the object 1 to be gripped;
inserting the second lower pressing plate 9 under the object 1 to be gripped
after the first lower pressing plate 8 has been inserted under the object 1 to
be
gripped; and
lowering the upper pressing plate 10 toward the object 1 to be gripped,
thereby
gripping the object 1 between the upper and lower pressing plates 8, 9, 10.
Preferably, the clamp 20 can also be provided with an optical sensor 5 and a
laser
sensor 6. These sensors 5, 6 are used for approaching the end of the robotic
arm 24
towards the object 1 to be gripped. In effect, by means of the optical sensor
5, the
robotic arm 24 carries out a vertical tracing over the left corner of the
pallet 3 (see
figure 1). This tracing routine allows a robotic system to read the height
along the Z
direction over the pile and to deduce the X and Y positions by means of its
internal
references. The approximate dimensions of the pile of articles 1 on the
separator 2
being known parameters, a controller coupled to the robotic arm 24 calculates
the
position of the separator 2 and positions its clamp 20 approximatefy as shown
in
figure 3 so that the edge of the first lower pressing plate 8 is close to the
separator
2. Then, by means of the laser sensor 6, the robotic system validates the
horizontal
position of the pile and approaches the first lower pressing plate 8 of the
clamp 20
towards the pile, while always remaining away from the separator 2.
Preferably, once the robotic arm 24 is thus positioned, the robotic system
begins a
precise search routine for the separator 2 as described above. This routine
consists
in making, as shown in figure 3, a small movement horizontally towards the
pile
followed by a small movement vertically from top to bottom. After this last
movement,
the robotic system verifies if the proximity sensor 7 is activated by the
deformation
of the edge of the first lower pressing plate 8 touching the separator 2, as
shown in
figure 4. If the proximity sensor 7 is not activated, the robotic arm 24
brings up the
clamp 20 to the initiating height and repeats the search routine until the
proximity
sensor 7 is activated.
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Preferably, after the precise localization of the separator 2, the robotic arm
24 brings
forward the first lower pressing plate 8 of the clamp 20 by means of the
pneumatic
piston and cylinder arrangement 30 in order to insert it under the pile,
between the
5 last article 1 of the pile and the separator 2, as shown in figure 5. The
robotic system
then actuates the second lower pressing plate 9 of clamp 20 by means of the
pneumatic cylinder and piston arrangement 31 in order to insert it under the
first
lower pressing plate 8, as shown in figure 6. At the same time that the second
lower
pressing plate 9 is inserted, the robotic system actuates the clamping plate
10 shown
10 in figure 7 by means of the pneumatic cylinder and piston arrangement 32 in
order
to apply a certain pressure on the top of the pile in order to maintain the
articles 1 in
place and prevent unwanted displacements. Once the robotic arm 24 has
completed
the prehension cycle with its clamp 20, it can then displace the article 1, or
pile of
articles 1, and lay it down at a precise location.
Preferably, since there may be several rows of articles on the separator 2,
the
prehension cycle is repeated until the robotic arm 24 has removed all the
articles 1
lying on the separator 2. When there are no more piles on the separator 2, the
robotic
arm 24 removes and discards the separator 2 by means of the suction cups 11 of
the
clamp 20. In order to do so, the robotic arm 24 positions the clamp 20 over
the
separator 2 and elevates the clamp 20 by means of another cylinder and piston
arrangement 33 mounted on a movable support plate 27 which is slidably
connected
to support plate 28. When the clamp 20 is elevated by the cylinder and piston
arrangement 33, the suction cups 11 can touch the separator 2 by lowering the
robotic arm 24. Using suction, the suction cups raise the separator 2. The
robotic arm
24 can then displace the separator 2 and lay it down at a precise location.
These
steps are repeated until there are no more articles 1 on the pallet 3.
As will be apparent of those skilled in the art, and similarly to what is
disclosed in US
patent No. 4,993,915 by Berger, several clamps 20 according to the present
invention
may be mounted on a robotic arm in order to grab an entire row of articles
simultaneously. In addition, the robotic arm 24 of the present invention is
also
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intended to cover such carriage assembly and support rail of US patent No.
4,993,915 by Berger.
In an alternative embodiment of the present invention, the objects to be
gripped are
not separated by separators 2, but are separated by a space sufficiently large
to
allow insertion of the first lower pressing plate 8 under the object. These
objects can
be for example corrugated cardboard boxes which, when piled up, have spaces in
between them. The clamp 20 is modified because there is no need for the
tactile
sensor 7, but instead a force sensor coupled to the actuator 30 of the first
lower
pressing plate 8 is used. This sensor measures a horizontal reaction force
exerted
on the first lower pressing plate 8. If the lower pressing plate 8 touches the
object 1
head on, the sensor detects a very large force as compared to when the first
lower
pressing plate 8 is inserted in between two cardboards where almost no force
is
detected.
Accordingly, referring to figures 1 and 7, a second method of operating the
clamp 20
and robotic arm 24 is performed by the following steps in order to grip the
objet 1:
moving the end of the robotic arm 24 toward the object 1 to be gripped until
the first pressing plate 8 is in proximity of the object 1 to be gripped;
partially inserting the first lower pressing plate 8 under the object 1 to be
gripped;
detecting if a reaction force exerted on the first lower pressing plate 8 is
below
a predetermined threshold;
further inserting the first lower pressing plate 8 under the object 1 to be
gripped if the reaction force exerted on the first lower pressing plate 8 is
below the
predetermined threshold;
inserting the second lower pressing plate 9 under the object 1 to be gripped
after the first lower pressing plate 8 has been further inserted under the
object 1 to
be gripped; and
lowering the upper pressing plate 10 toward the object 1 to be gripped,
thereby
gripping the object 1 between the upper and lower pressing plates 8, 9, 10.
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In another alternative embodiment used when the objects to be gripped are not
separated by separators 2, a positioning sensor or horizontal displacement
sensor
is fixed to the pneumatic cylinder arrangement 30 of the first lower pressing
plate 8
and the proximity sensor 7 is kept. Thereby, the position of the first lower
pressing
plate 8 in the pile can be known by the robotic system by means of this
positioning
sensor. The robotic system can determine the penetration distance of the first
lower
pressing plate 8 in the pile during the insertion and determine if the
insertion is
successful or not. In a first step, the first lower pressing plate 8 is moved
toward the
object 1 with a small force or speed so as not to bend or damage the first
lower
pressing plate 8 if it hits the object head on. If the insertion is not
successful, the
robotic arm 24 removes the first lower pressing plate 8 from the pile, raises
or lowers
the clamp 20 with a certain increment and restarts the insertion of the first
lower
pressing plate 8. If the positioning sensor on the pneumatic cylinder and
piston
arrangement 30 detects that a certain distance has been reached and that the
proximity sensor 7 did not detect a deformation of the first lower pressing
plate 8 or
is within an acceptable threshold, then a stronger force can be exerted on the
first
lower pressing plate 8 in order to extend it to its maximum. This particular
embodiment also allows not using the separators 2 between the layers of the
piles,
provided that the articles forming the pile are of a minimal thickness. The
positioning
sensor and proximity sensors accomplish the same object as the force sensor
mentioned above as both will detect the results of a reaction force being
exerted on
the first lower pressing plate 8.
The present invention provides a depalletizing tool that is more efficient
than manual
methods for unstacking objects and that does not put workers' health at risk.
In
particular, the depalletizing tool eliminates repetitive manual movements that
may
cause back problems and chronic illnesses such as bursitis and tendinitis.
Furthermore, the present invention provides a depalletizing tool that is less
costly to
operate than most other prior art devices.
Although a preferred embodiment of the present invention has been described in
detail herein and illustrated in the accompanying drawings, it is to be
understood that
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the invention is not limited to this embodiment and that various changes and
modifications may be effected therein without departing from the scope or
spirit of the
present invention.
