Note: Descriptions are shown in the official language in which they were submitted.
CA 02251858 1998-10-26
This invention relates to an automated method of
trimming and finishing moulded plastic articles.
Moulded plastic articles, such as for example,
automobile bumpers, automobile front grilles and other
articles are removed from the moulds with an appreciable
amount of "flash", i.e. excess plastic material from
crevices or irregularities in the mould or from cracks
between two mould parts. Such flash is inevitable in
injection moulding. It must be trimmed away from the
article cleanly to provide a finished surface.
Conventionally trimming and finishing is carried out
manually and may require the use of several tools for
example, an Exacto knife, a swirl knife, an orbital sander,
a drill. Some parts may require hand sanding. Different
techniques may be required consecutively on some parts of
the article or on different parts of the article.
Such manual trimming and finishing is very labour and
time intensive and completely uniform parts are not
achievable. Human error may result in undue wastage
especially as it may sometimes be necessary to scrap an
entire article when a mistake is made.
It is a problem that no automated method for trimming
and finishing moulded plastic articles exists, which method
is sufficiently accurate to provide finished uniform
articles.
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It is known to operate tools using robots programmed to
follow a preset path but it has not been thought possible to
use a robot to trim and finish a complex plastic moulding,
such as, for example an automobile front grille due to the
complexity of the various paths to be followed and, due to
the fact that the article would have to be presented to tool
at various different angles to allow the tool to access all
necessary surfaced, the angle of approach of the tool.
According to the invention there is provided an
automated method of trimming a workpiece moulded from
plastics material and having a complex three dimensional
shape comprised of various differently angled planes, edges
and/or surfaces, comprising: supporting the workpiece
firmly on a support therefor to present one aspect of the
article to a trimming tool mounted on a robotic arm;
operating the robotic arm according to a first trimming
program to move the tool along at least a first trimming
path for the tool to trim the workpiece along said first
trimming path; tilting said support through a preset angle
to present a second aspect of the workpiece to said tool;
and operating the robotic arm according to a second trimming
program to move the tool along at least a second path for
the tool to trim the article along said second path.
Preferably the preset angle is computer calculated in
dependence on the shape of the workpiece and the first
trimming program.
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The invention includes apparatus for automated trimming
of a workpiece moulded from plastics material and having a
complex three dimensional shape comprised of differently
angled planes, edges and/or surfaces comprising: a support
for the workpiece and a robotically operable trimming tool;
the trimming tool being robotically operable to move along
trimming paths according to trimming programs to trim the
workpiece along each of the paths; and the support being
tiltable through preset angles to present different aspects
l0 of the workpiece to the tool for operation of the tool along
a respective trimming path.
The trimming paths need not be continuous. The robotic
arm may lift the tool away from the workpiece and return the
tool to the workpiece to trim discontinuous lengths along
the workpiece. Such discontinuous lengths may be, for
example, parts of a square grid grille.
The angle of the tool to the workpiece may be altered
as desired within the capability of the robotic arm by means
of the program for the path.
The tool utilized with the robotic arm may be any
conventional tool but a diamond router may give a fine,
accurate finish.
The support may be a positive image of the workpiece
which may be fixed thereto by any convenient means which
does not foul the passage of the trimming tool.
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Tilting of the support may be through any conventional
accurate mechanism in three dimensions. Computer control of
the mechanism must be precise and should be preferably be
implemented by a tilting program itself dependent upon the
trimming program to be operated. Thus, when the first
trimming path is completed, the tilting mechanism may be
automatically operated by means of the tilting program to
set the support, and hence the workpiece, in precise
position for the start of the second trimming path.
The first trimming program, the second trimming program
and the tilting program may be component parts of an
integrated program for interdependent trimming and tilting
program. However, practically, it is likely that the
trimming program for the robotic arm may be separate from
the tilting program which may utilize a personal computer.
An embodiment of the invention will now be described by
way of example with reference to the drawings in which:
Figure 1 illustrates an automobile front grille on a
controllably tiltable support for trimming by a tool mounted
on a robotic arm;
Figure 2 shows one design of controllably tiltable
stand; and
Figure 3A and 3B show different moulded bumpers which
may be trimmed according to the invention.
Figure 1 shows an automobile front grille 10 held
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firmly on a stand 12 for trimming by a diamond router 14
operated through a Motoman KlOS Routing Robot 16.
The robot 16 is programmed so that the diamond router
14 follows a first path to trim flash from all available
surfaces of a grille 10 in a first position of stand 12.
The amount of available surface is dependent both upon the
complexity of the grille 10 and the manoeuvrability of robot
16. The Motoman K10S is a robot of the vertical jointed arm
type with 6 degrees of freedom and wide range of wrist
action for both pitch/yaw movement and for twist movement.
Thus good access to the grille 10 is possible.
The stand 12 (illustrated in more detail in Figure 2)
comprises a pair of tiltable supports 20 to which the grille
10 is firmly attached. The supports 20 comprise elongate
members pivoted about a tilt axis at lower ends 22 to extend
generally upwardly. They should be spaced apart by a
suitable distance to hold an automobile grille or bumper.
For many automobiles such distance may be about 52".
Distal ends 24 of the supports 20 are provided with
bearing surfaces 26 attached to positive image buck 11.
Positive image buck 11 is shown in Figure 2 having
adjustable side supports 13 on extensible and retractable
supports 15. However, it is to be noted that adjustment may
be achieved by various means. Bearing surfaces 26 may be
steel plates welded onto supports 20 and bolted to buck 11.
They should be located such that they do not obstruct
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interior trim surfaces of grille 10. For this reason
bearing surfaces 26 should be as small as reasonable while
holding grille 10 firmly. Actual attachment of grill 10 to
the bearing surfaces 26 may be by any convenient means for
example by screws.
The lower ends 22 of supports 20 are fixed on axles 28
in pillow blocks 30 mounted on respective pillars 32. The
axles 28 are driven from chain drive 34 on driven axle 36.
A support bar 38 may also be present connecting the pillars
32 for additional stability.
The driven axle 38 is located at or near floor level
well away from the vicinity of grille 10.
When robot 16 has finished its primary task, i.e. the
trimming and finishing of all available surface of the
workpiece when in its first position, the driven axle 36 is
activated to rotate by motor 37 and thereby drive the chain
drive 34 to rotate axle 32 to alter the angle of supports
20. Axle 38 is rotated just sufficiently to twist the
supports 20 into a prechosen position for the robot 16 to
access further surface of grille 10 so that it may perform a
second programmed path for the diamond router 14 to trim
further flash from the grille 10.
If all the surface to be trimmed of grille 10 has not
been trimmed in two positions of grille 10, the drive shaft
38 may be rotated further to move the supports 20 and hence
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grille 10 into yet another position. Robot 16 may be
programmed to carry out yet another trimming path on grille
10.
Conveniently, the robot is preprogrammed for as many
trimming paths as are necessary for any particular work
piece to be trimmed at respective preset presentation angles
of the work piece to the robot. The drive shaft 38 may be
automatically controlled through a computer to move the
workpiece to its new presentation angle as soon as the robot
has finished its trimming path in the previous position of
the work piece. The presentation angle of the work piece to
the robot are precalculated independence on the complexity
of the workpiece and the three dimensional orientation of
the various planes and surfaces of the work piece which are
to be trimmed.
Figures 3A and 3B show different aspects of automobile
bumpers for trimming and finishing according to the
invention.
Such bumpers may require to be set into a variety of
different positions to allow the robot to access all planes
and surfaces to be trimmed. Possible different trimming
paths are indicated on the drawings of Figures 3A and 3B in
broken lines.
The relatively simple bumper of Figure 3A requires
trimming along 8 trim paths and around all attachment holes.
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The trim paths are marked a - h. Paths a, c, and d run
along the front edge of the bumper while path b runs along
the rear edge of an upper rearwardly extending flange.
Paths a and g run vertically (or generally vertically) along
rear inner vertical edges of the bumper. Path f runs along
a front lower edge of the bumper and path h runs along the
inside edge of a lower inwardly directed flange. By tilting
of the bumper supported on the tiltable support all of these
paths may be accessed by the robotic tool which for these
paths may suitably be a diamond router. It is also possible
to use an orbital sander on the robotic arm to sand outer
vertical rear edges of the bumper.
The bumper of Figure 3B is more complex but again all
of trim paths A - J may be accessed by a tool on a robotic
arm. Path A runs along the front top edge of the bumper.
Path B runs along a rear edge of a rearwardly extending top
flange of the bumper. Path C runs along GOP flanges and
side retainer. Path D runs along the bottom valance inside
the rearwardly extending flange. Path E runs along the
outer edge of the bottom valance. Path F and G run
generally vertically along inside rear vertical edges of the
wheel flanges. Path H runs around the grille opening. Path
I runs around the various attachment holes. Path J runs
around the signal light. All of these paths may be accessed
a tool on a robotic arm when the support is tilted in
various positions.
Programming of the robot 16 to follow a particular
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trimming path for a particular work piece is conventional
for whatever robot is used and such programming will not be
addressed here. Once the robot has been programmed and, as
a result it has been established what particular angles of
presentation are required for the workpiece, these angles
may be entered into a computer so that movement of the
workpiece from one position to the next angle of
presentation is automated.
