Note: Descriptions are shown in the official language in which they were submitted.
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ROTARY ABRASIVE TOOL
Background of the Invention
This invention relates to the coupling of in-situ measurement devices with
rotary abrasive tools. Major advantages in the use and operation of abrasive
tools can be gained by real time feedback to the operator or machine tool
controlling the abrasive tool. The type of real-time feedback that has major
significance are, for example, temperature, surface roughness, workpiece
position during the abrading, grinding, or finishing, or surface roughness.
Hitherto this has depended on the use of experienced operators or interrupted
operations in which the abrading is interrupted more or less frequently for
measurement. In this document the term "abrading" is to be understood to refer
not only to processes in which substantial amounts of material are removed
from
a surface but also, and perhaps more importantly, to processes in which the
operation is considered to be fine finishing, polishing or lapping.
A rotary abrasive tool has now been devised that can be controlled in a
plurality of ways to respond to critical parameters automatically and to
adjust
the operation in response to variation in these parameters without the need
for
interruption of the operation.
Brief Descr~tion of the Drawina
The Figure is a schematic side view diagram of a rotary abrading tool with
at least one non-contact sensor aligned to evaluate the condition of a
workpiece
surface through holes in the abrasive disk as it rotates. The drawing is not
necessarily to scale, emphasis instead being placed upon illustrating the
principles of the invention.
Description of the Invention
The present invention provides a rotary abrading tool which comprises:
a) an abrasive disk having holes pierced through the disk at intervals
permitting a view of the surface during the abrading operation, the disk
being mounted on
b) a rotatable shaft actuated by a motor; and
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c) at least one non-contact sensor aligned to view and/or measure the
condition of a workpiece surface through holes in the abrasive disk as it
rotates.
An example of a rotary abrading tool is shown in the Figure. Tool 10 is
useful for abrading workpiece 12. Tool 10 has rotatable shaft 14 that is
actuated
by motor 16. Abrasive disk 18 has abrasive disk holes 20 pierced through the
disk at intervals permitting a view of the workpiece surface 22 of workpiece
12
during an abrading operation. Abrasive disk 18 can be supported on backup pad
24 having backup pad holes 26. Non-contact sensor 28 is attached to tool 10
in alignment along path 30 to view or measure, or view and measure the
condition of workpiece surface 20 through backup pad holes 26 and abrasive
pad holes 20 as abrasive disk 18 rotates.
The abrasive disk can be rigid, (that is self-supported), but usually more
conveniently it is supported on a backup pad which comprises holes in the body
of the pad corresponding In location to those in the disk supported thereon
such
that, upon rotation, it is possible to view a workpiece as it is undergoing
abrasion
through both the disk and the backup pad.
Abrasive disks with viewing holes or apertures are known in the art for the
purpose of allowing the operator to assess the state of the surface being
abraded as it happens. Such abrasive disks are described for example in
WO/US96l19191. The present invention goes much further however in adapting
a rotary abrading tool not only to view the workpiece surface but also to
measure
its condition in application-specific ways.
In one embodiment of the invention the non-contact sensor is a laser
device adapted to measure the surtace finish of the workpiece andlor the
distance between the abrasive disk and the surface of the workpiece. Thus in
an
is automated operation such a sensor can, for example, advance the abrasive
disk towards the workpiece in a rapid but controlled fashion so as to avoid
both
delays and workpiece damage resulting from excessively abrupt initial contact.
Then, having initiated abrading, the laser can monitor the surface of the
workpiece and, through appropriate feedback mechanisms, control the grinding
pressure or withdraw the tool when the appropriate surface finish has been
generated. Making this a part of the rotary abrasive tool ensures that the
abrasive operation is conducted efficiently with a minimum of lost time.
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In another embodiment the non-contact sensor is one specifically adapted
to measure the temperature of the surface, for example using an infra-red
sensor device. This is particularly important when the surface been treated is
a
painted surface. Modern automobile paints, for example, above a certain
temperature determined by the chemistry of the polymer matrix, tend to "ball
up",
(that is to partially melt or soften and form small balls or globules of
polymer),
during abrasion. This of course destroys the abrasive function of the disk and
it
is therefore critical to monitor the surface temperature during
2a
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WO 00/64634 PCT/US00/09576
abrasion. The temperature sensing device can be separate from, or
incorporated into, a laser sensing device such that both modes of surface
condition sensing mechanism are available.
Other non-contact sensors can respond to tight waves, (both UV and visible),
s sound waves and any other desired variety of electromagnetic radiation.
The abrading disk is conveniently provided with from 3 to 6 apertures located
at a uniform radial distance from the axis of the disk. The size of the
apertures is preferably large enough to ensure that, when the tool is in use
the surface condition sensors are able to receive sufficient data to give a
io useful reading. The shape of the apertures is not critical but generally
round
holes are preferred since these afford maximum visibility with minimum
disruption to the cohesiveness of the disk under grinding conditions. It is
also preferred that sensing devices are located to view through the disk in
the radial position on the disk of maximum aperture area.
ns Since the most relevant information relates to the surface of the workpiece
actually being abraded, the viewing apertures are preferably located in the
radially outer half of the disk since this is the portion that is most heavily
used. In some forms of abrasive disk, it is known to remove portions of the
circumference of a disk so as to afford a view of the surface right to the
edge
Zo of the abrasive disk.. Such removed peripheral portions are likewise
considered to be "apertures" since they perform the same function as holes in
the body of the disk but in a different location on the disk.
The sensor devices operate by transmitting and/or receiving electromagnetic
radiation , (the nature of which depends on the condition being sensed as
2s above indicated), through the apertures in the disk. In practice this means
that one would synchronize the detection systems to the rotational speeds of
the disc and to the frequency of the holes passing the detector system. This
ensures that maximum information is received by the sensing device.
Where the disk is rigid, as would be the case for example if the disk were a
30 °flap-disk" in which quadrilateral flaps of coated abrasive material
are
attached by one edge to a rigid usually cupped disk in overlapping fashion
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around one surface of the disk. Such disks generally need no backup pad and
are used for grinding down welds or joint lines.
The surface of the abrasive disk can be of the conventional type in which
abrasive grain is bonded to a backing material by the usual maker and size
s coat combinations, with or without a supersize coat conferring special
grinding properties or characteristics. However it can also have an
engineered surface comprising micro-replicated structures, such as pyramids
or lines of parallel ridges, each of which comprises abrasive particles
dispersed in a binder and adhered to a backing material.
io Finally the surface can comprise a layer of a formulation comprising
abrasive
particles dispersed in a binder resin and deposited in a relatively uniform
layer
or in a contoured structure on a backing.
The abrasive particles used can be any of those typically made available for
such purposes and range from alumina, alumina-zirconia and silicon carbide in
is the general purpose grinding area, to diamond, CBN, ceria, gamma alumina,
,and microcrystalline alpha alumina in the more specialized abrading
applications.
The binder component of the abrasive disk can be selected from those known
in the trade for such applications. These include thermosetting resins such as
Zo phenolic and epoxy-based resins, and radiation-curable resins such as
acrylates, epoxy-acrylates, urethane-acrylates resins and similar resins that
are curable by visible or UV light as well as electron-beam radiation. Also
included are moisture-curable resins.
The means by which the abrasive disk is made to rotate can be any suitable
Zs motor means and the whole tool can be a basic adaptation of an angle
grinder, off hand grinder, fixed grinder and the like.
Advantageously the condition-sensing mechanism is linked to control systems
on the tool which regulate parameters such as the position of the tool with
respect to a workpiece, the force with which the abrasive disk contacts a
3o workpiece and the speed of rotation of the disk. Alternatively or
additionally
the condition sensing device can be linked to a notification mechanism such
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as a light, a bell or a buzzer indicating that a desired end-point or limit
condition has been reached. Clearly if the tool is used in an off-hand
grinding
mode, the linkage is preferably of the notification type.
A preferred application is in the automobile industry wherein automation of
s finishing processes is well advanced. The rotary abrasive tool of the
invention
is particularly well adapted to the removal of finish defects where the
workpiece is a painted automobile panel. An example of a tool adapted for
this application is equipped with two sensors: one a laser device to read out
the surface finish of the workpiece as it is polished and to terminate the
work
io when the desired finish has been attained; and the second is a temperature
sensor which is set to interrupt or moderate the polishing when the
temperature of the surface approaches the point at which "balling-up" of the
paint polymer becomes a problem. The preferred disk for the tool has a three
round hole pattern with the holes equally spaced around the disk and each is
~s located about two thirds of the radial distance from the center of the disk
to
,the circumference. The diameter of the holes is from about 15 to 30% of the
radius of the
disk. The abrading surface is conventional for this application and is not
critical to the tool itself.
s
