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Description  |
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BACKGROUND AND DISCUSSION OF THE INVENTION
The present invention relates to a device for the automatic processing of
differently shaped workpieces which has a controlled tool-changing
capability. The tool changing device of the present invention is
particularly useful for the spot-welding of parts or workpieces.
Previous tool-changing devices typically consist of a frame having several
different tools which are brought into use alternatively accordingly to
the operational steps in an existing program or processing routine.
Several of these devices can be arranged and interconnected by
intermediate conveyors one after the other which transport the parts to be
processed to the devices, thereby forming a production line.
An object of the present invention is to develop an improved processing and
tool-changing device which provides for a quick change of the complete set
of tools in the device as well as in the workpiece receiving fixture. The
present invention, provides a device having an improved adaptability to
accommodate different workpieces and wherein a quick tool change and an
optimum adjustment of the tools outside the production line can be made in
an economical manner, even under operating conditions.
Preferably, the tool-changing device comprises a lower frame and a
plurality of tool frames which are of identical construction and are
placed onto the lower frame. Fortunately many identical parts can be used
in the tool-changing device of the present invention even though it is
capable of accommodating workpieces of very different shapes. Alternately,
the tool frames can be displaced on the lower frame along a longitudinal
guide into a central working position. In this central working position,
the workpieces are fed to the tool frame and are processed by the variety
of tools arranged in the tool frame. If there is a workpiece of a
different shape or if a workpiece of the same type is to be processed in
another manner, the current tool frame is moved to one side and a
different tool frame which is now required is displaced from the other
side into the central working position. By this design, it is possible, in
the case of workpieces of considerably different shapes or requiring
varying processing operations, to change the tools very quickly. Moreover,
if a plurality of these devices are arranged one after the other in a
production line or even if devices of this type are used at various
locations or by various manufacturers, the same lower frames and the same
tool frames can always be used with the result that the manufacturing
costs are considerably reduced.
Preferably, the individual tool frames are equipped only with different
tools enabling one to adjust the tools externally thereby reducing the
adjustment time needed during production. Positioning new tools or
arranging them in conjunction with a new part no longer needs to be done
in the production line Also, the tool frames can be easily exchanged by
means of a crane or a fork lift truck, since, in contrast to previous tool
changing devices, the frame and the tools are completely separate.
The present invention is especially useful in spot-welding operations using
electrode holders or production sequences with low counterpressure.
Pinning is appropriate when working with large pressures. Although the
present invention, in principle, can be used for parts of the most varied
orders of magnitude, it is especially useful in the case of medium-sized
parts.
In contrast to the present tool-changing devices which are designed as a
unit, and in particular such devices used for welding, the lower frame,
the tool frames and the conveying mechanism of the present invention can
be reused and are fully reutilized. For example, after an initial
production run, it is possible for tool frames having the tools fixed
therein to be removed and used later for a production run for spare parts
without any modification.
The tool frames in the present invention are moved into the working
position over the central section of the lower frame by a displacing unit.
A variety of devices known to one skilled in the art can be used. For
example, a pneumatic device which has a rodless cylinder that enables
strokes of over 2 meters can be used advantageously as the displacing
unit. Another feature of the present invention is that the tool frames can
be centered in position above the central section of the lower frame (i.e.
the working position) by a centering unit and then fastened by means of a
clamping unit.
The tool frames themselves comprise a base plate and a head plate which are
connected to one another by a plurality of columns. The tools are fastened
to either the head plate, the columns, or both. In order to permit the
easy installation and removal of the tools and to combine a plurality of
devices one after the other in a production line, it is preferable if the
workpieces can be passed through the device from one side. The free
accessibility thereby created not only enables improved insertion and
removal of the workpieces, but also facilitates maintenance work, such as
the replacement of electrode caps in a device having welding tools.
Provided in the base plate of the tool frame is a recess into which the
bottom plate of a workpiece holder is inserted. In the area of this bottom
plate, a lifter is arranged in the central section of the lower frame. A
table closing off the lifter at the top can be connected to the bottom
plate of the workpiece holder by a second centering and clamping device.
By the two centering and clamping devices, one for securing the tool frame
to the lower frame and the other for securing the workpiece holder to the
lifter, an arrangement is created which permits precision work to be
performed on the workpiece.
The table connected to the bottom plate of the workpiece holder can be
moved by a controlled drive (e.g. a three-phase flat-geared motor) from a
lower insertion position into an upper processing position enabling the
tools to act on the workpiece. The workpiece holder can be lifted in the
reverse direction to such an extent that when the centering devices and
clamping devices are released, it is possible to displace the tool frames
on the longitudinal guide to beyond the table.
The tool frames in the present invention can have a variety of
arrangements. The first arrangement consists of only one tool frame
mounted over the central section of the lower frame. With this
arrangement, there is no direct means of changing the tool frame, however,
the advantage of this device is that it can be used in conjunction with
other similar single tool frame devices by linking several of them
together. The result is the same as if a device having a simple changing
means for the tool frames is used. The second arrangement utilizes a lower
frame having a central section, a left hand section and a right hand
section which are arranged next to one another in a row and provided
thereon are two tool frames for alternating use. When not in use, the tool
frames are stored in the left and right hand sections. The third
arrangement consists of a central section, two left hand sections and two
right hand sections. This arrangement permits the alternative use of three
tool frames.
This third arrangement is particularly advantageous since it enables the
alternate use of the three tool frames. In this arrangement, the lower
frame and the displacing unit are extended beyond the left hand section
and the right hand section of the two-tool frame arrangement for forming
the additional locating surfaces for the third tool frame. Preferably, the
individual sections are arranged in a U-shape rather than a straight line
which makes it more convenient to alternately use the three tool frames.
It is of course also possible, by enlarging the lower frame, to increase
the number of tool frames which can be alternatively used, however, this
does not necessarily create any advantages which could not also be gained
by interlinking a plurality of these devices one after the other with a
conveying means between them.
In all these arrangements, the same tool frames can be used and exchanged
one for the other. In addition, the central section having the lifter can
be used in any of these arrangements. Similarly, the outer sections in the
second and third arrangements conveniently are made using identical
elements which are joined by a suitable connecting means.
Each tool frame can be provided with a separate conveying means by which
the workpiece can be automatically picked up, inserted into the workpiece
holder and moved out of the device after processing is complete. In a
further development of this feature, each tool frame can have a separate
drive for each conveying means arranged thereon. The conveying means
enables a workpiece to be picked up, inserted into the workpiece holder,
and once processing is complete, moved out of the device. Many different
types of conveying means can be used as one skilled in the art would know.
Fully automatic conveying is also possible in the present invention if the
conveying means of the tool frame receives the workpiece from one conveyor
and after the processing is finished places it onto another conveyor. When
a plurality of devices according to the present invention are coupled, it
is also possible for the preceding conveyer to deposit the workpiece on a
lifter between the two devices in such a way that the conveyor of the
following tool frame can pick it up. An intermediate conveyor having a
lifter (for example, a translational rocking arm) may be necessary with
lower frames having the U-shaped configuration.
The power supply and the means for controlling the tools in the tool frames
of the present invention can be effected by lines or cables preferably
from one or more locations above the tool frames. Cable-trailing devices
can also be used to enable the tool frames to be moved. Thus, contact
reels and complicated transmission devices can be avoided. Moreover, when
the cables are secured on each tool frame in such a way as to be easily
releasable (for example, by connectors or quick-acting couplings), the
tool frames can be dismantled very quickly and cost-effectively. Further
work for replacing a tool frame is not really necessary.
Preferably, the tool frames of the present invention are easily
displaceable with the help of a support means such as spring-mounted ball
castors located on the lower frame. With this arrangement, the springs are
designed in such a way that they apply, as a whole, a larger upward force
than the force due to the weight of the tool frame. Consequently, when the
tool frame is being clamped down, it is only necessary for the clamping
device to overcome the difference between both forces. This difference in
force can be accurately established by the selection of the springs so
that only small forces are required for the clamping itself.
The tool-changing operation of the present invention using an automatic
control will now be described. Starting with a device having a lower frame
comprising a central section, a left hand section and a right hand
section, the tool frames each occupying an outer position on the left hand
and right hand sections, the displacing unit is first moved toward the
selected tool frame. Once the end position is reached, pinning takes
place, i.e. a positive connection is made between the tool frame and the
driver of the displacing unit. Once pinning is effected, the displacing
unit pulls or pushes the tool frame over the central section of the lower
frame. Next, the centering units move out of the lower frame and then the
clamping units which pull the tool frame against the central section of
the lower frame.
Once the tool frame is fixed on the central section of the lower frame, the
workpiece holder arranged on the tool frame is centered with the lifter
located in the lower frame. For this purpose, the table of the lifter is
provided with a corresponding centering device which interacts with the
bottom plate of the workpiece holder. Following the centering operation,
both parts are fastened by means of a separate clamping device.
The operation of mounting the workpiece and the subsequent processing can
now begin. During this procedure, the part or workpiece to be processed is
placed in front of the working station into the conveyor located in the
tool frame and moved by the conveyor into the workpiece holder which is in
the receiving position. The workpiece holder is then raised by the lifter
to take the part to be processed out of the conveyor and move it up into
the processing position. While the part is being processed, the conveyor
can return so that, once processing is complete and the workpiece holder
has been lowered, it can move the processed part out of the tool frame and
also introduce a new part into the tool frame.
If the tool frame is to be changed for carrying out another processing
phase or for processing a workpiece of a different configuration, this is
done by releasing the clamping device, the centering devices of the lifter
and the lower frame, by the displacing unit moving the tool frame which is
no longer required to the side and then moving the new tool frame onto the
central section of the lower frame. It is more convenient if the
displacing unit has to perform only rectilinear movements. A plurality of
displacing units, (air cylinders for example), are needed for movement in
more than one direction such as in the case of the lower frame with
sections arranged in a U-shape.
Other details, objects and advantages of the present invention will become
more readily apparent from the following description of a presently
preferred embodiment thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, a preferred embodiment of the invention is
illustrated, by way of example only, wherein:
FIG. 1 shows a front view of a device for the automatic processing of
differently shape workpieces;
FIG. 2 shows a plan view of the device shown in FIG. 1; and,
FIG. 3 shows a side view of the device shown in FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A device for the automatic processing of differently shaped workpieces
preferably consists of a frame 5 having a central section 7, a left hand
section and a right hand section 11. Tool frames 13 and 15 are placed onto
the lower frame 5. In their dimensions and connections, both tool frames
13 and 15 are of identical construction. They preferably consist of a base
place 17, a head place 19 and also perpendicular columns 21 connecting the
base plate 17 and the head plate 19. A variety of tools 23 for processing
a workpiece are fastened to the head plates 19. In the present device,
which is designed for spot-welding, the tools 23 can also be fastened to
the columns 21. These are mainly electrode holders.
On their underside, the base plates 17 of the tool frames 13 and 15 are
provided with spring-mounted ball castors 25 whose springs are designed in
such a way that they apply, as a whole, a larger upward force than the
force due to the weight of the complete tool frame so that the tool frame
can be easily moved and clamped down with little force. Here, a force
which corresponds to the difference between the spring force and the force
due to the weight is sufficient to clamp down the tool frame.
As shown in FIG. 2, a rectangular recess 27 is provided in the center area
of the base plate 17 of the tool frame 15, shown in greater detail in this
figure. The bottom plate 29 of a workpiece holder 31 is mounted in this
recess 27 in a floating manner on disk-spring stacks in conjunction with
coarse-centering devices.
In the area beneath the workpiece holder 31, the central section 7 of the
lower frame 5 is equipped with a lifter 33. The lifter 33 is closed off at
the top by a table 35.
Referring to FIG. 2, the lower frame 5 is of a U-shaped construction and
includes a total of five locations at which tool frames can be mounted,
thus enabling three tool frames to be moved in such a way that each tool
frame can alternatively be brought into use over the central section 7 of
the lower frame 5. In the drawing, the tool frames 13 and 36 are only
indicated, whereas the tool frame 15 is reproduced in detail without head
plate 19 and tools 23.
To enable the tool frames to be moved in a desired manner over the central
section 7, a total of four displacing units 37, 39, 41 and 42 are
provided. These displacing units are characterized by a rodless cylinder
having a pneumatic actuation, permitting larger strokes (over 2 m) to be
achieved without problem. Each displacing unit has a driver 43 to engage
allocated bores in the base plate 17 of the tool frames. For this purpose,
each driver 43 consists of two pneumatic cylinders 49, a driving plate 51
and connecting pins 53. To move the tool frames, the driver 43 is first
moved toward the tool frame up to its bores 45 and 47, respectively. The
connecting pins 53 are then extended, inserted into the bores 45 and 57,
respectively, and moved into the desired position by the displacing unit,
whose main component is a pneumatically acting rodless cylinder.
If this position is not the central section 7, in which the processing is
carried out, but another section of the lower frame 5, the tool frame is
secured in this position by means of two pinning units 55 each. The
pinning units comprise hydraulic cylinders 57 and centering points 59, the
points interacting with bores 61 in the base plates of the tool frames. If
tool frame 15 is located above the central section 7 of the lower frame 5,
the tool frames are accurately secured in their working position by
centering units. The tool frames are additionally clamped down in the
working position by means of four hydraulically driven swivelling clamping
cylinders 63. Only a small force is necessary to clamp down the tool
frames mounted on spring-mounted ball castors, so that swivelling clamping
cylinders 63 of relatively small dimensions can be used.
If the tool frame 15 is centered and firmly connected to the lower frame,
the bottom plate 29 of the tool holder 31 mounted in the recess 27 of the
base plate 17 is connected in a similar manner to the table 35 of the
lifter 33. Here, too, centering devices 65 are provided which, with their
tips, engage bores 67 in the bottom plate 29. A central clamping device
69, likewise formed by a swivelling clamping cylinder, is provided to
clamp the bottom plate 29 down onto the table 35.
The actual operation of the tool-changing device will now be described.
First, the workpiece is inserted into the workpiece holder 31. This can be
done by a worker as shown in FIG. 3 or it can be performed automatically
by means of a suitable apparatus. The workpiece is then moved up into its
processing position. The lifter 33 located in the central section 7 of the
lower frame 5 is provided for this purpose. The lifter 33, preferably,
comprises an electric-motor drive in the form of a three-phase
flat-spur-gear motor and a crank. The lifting movement is controlled by
means of a precision switching mechanism. Once the operating height is
reached, the tools 23 start the programmed processing of the workpiece. In
the embodiment shown in the drawings, the tools 23 are mainly formed by
electrode holders.
Once the processing of the workpiece has been carried out, the lifter 33
lowers the table 35 and with it the workpiece holder 31. During this
movement, the processed part is deposited in the return conveyor device 71
and is then conveyed out of the tool frame 15 where it is received by an
intermediate conveyor which deposits the part onto the conveying device of
the next processing station. In the meantime, the workpiece holder 31 can
receive another workpiece.
Just as each tool frame has a workpiece holder for accommodating a certain
workpiece and its adapted tools, each workpiece frame is also equipped
with separate conveying device 71. The drive of the conveying device 71
preferably consists of a change-pole worm-gear motor 75, conveying members
with roller blocks 77, and also cam strips 79 which interact with a
camshaft gear 81 for controlling the conveying step.
If other processing operations are to be carried out on the same workpiece
in the same device or if the processing of a workpiece of a different
shape should be desired, the device of the present invention does not need
to be converted. To the contrary, another tool frame only needs to be
moved into the working position over the central section 7 of the lower
frame 5. For this purpose, it is first necessary for the tool frame 15
located in this position to be moved out, such as to the right in FIG. 2.
Before this can be done, however, the clamping device 69 must be released,
the centering device 65 must be retracted such that the workpiece holder
is free from lifter 33, the swivelling clamping cylinders 63 must be
released and the pinning units 55 must be retracted such that base plate
17 of the tool frame 15 is free from the lower frame 5. The connecting
pins 53 of the driver 43 can now engage the bores 47 in the base plate 17
and the displacing unit 39 can move tool frame 15. Once the right hand
position has been reached, tool frame 15 is secured by the pinning units
55, which again engage the bores 61 of the base plate 17. With displacing
unit 37, it is possible to move the tool frame 15 at right angles to the
step just described and into a waiting position further away.
The displacing unit 42 now moves up to the tool frame 13, couples onto it
and pulls it into the processing position above the central section 7. The
centering and clamping operations described above are then carried out in
this position so that, subsequently, a new processing phase with changed
tools can be carried out.
The tool frames can be easily moved by means of the displacing units 37,
39, 41 and 42 on the lower frame 7 in such a way that one of the three
tool frames can always be brought into the working position. It is also
possible to remove the tool frames from the lower frame by lifting them
off using lugs 83. The tool frames can then be used in other similar
devices either at the present site or at other sites. The tool frames can
also be lifted off when the tools 23 have to be changed or replaced for a
new workpiece. Since the tool frames always contain all tools for a
particular phase of processing and also the conveying device for
transporting the workpiece, it is now possible with the present invention,
to carry out the positioning of tools for a new workpiece outside the
actual production line (i.e. the center section) so that the actual
production sequence is not disturbed.
In order to permit an easy exchange of the tool frames, all lines for
supplying power and control signals to the device are preferably made via
plug connections (not shown) on the tool frames which are constructed so
as to be easily releasable. So that easy displacement of the tool frames
on the lower frame is ensured without great expense, the power and control
lines are fed to the individual tool frames from above, preferably through
cable-trailing means.
The actual control signals for the device has not been discussed in detail
because they can easily be realized by one skilled in the art from the
information provided herein. If a specific program is specified, the
device including the required changes of the tool frames can operate fully
automatically. If used in combination with an operator, it is possible for
the operator to not only insert the workpieces but also to give the
commands for changing the tool frames.
While a presently preferred embodiment of practicing the invention has been
shown and described with particularity in .connection with the
accompanying drawings, the invention may otherwise be embodied within the
scope of the following claims.
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