U.S. patent number 3,731,435 [Application Number 05/114,023] was granted by the patent office on 1973-05-08 for polishing machine load plate.
This patent grant is currently assigned to Speedfam Corporation. Invention is credited to Stephen A. Boettcher, Joseph V. Cesna, Raymond E. Dumentat.
United States Patent |
3,731,435 |
Boettcher , et al. |
May 8, 1973 |
POLISHING MACHINE LOAD PLATE
Abstract
A load plate having depending pedestals with vacuum passage
means communicating with the lower surfaces of the pedestals, and
valve means for effecting a negative pressure on work pieces
mounted on the pedestals for retaining the work pieces thereon
during finishing. A mask plate establishes work piece receiving
pockets with the pedestals, and sealing means maintain the negative
pressure mounting and prevent leakage between the work pieces and
the pedestal mounting surfaces. BACKGROUND OF THE INVENTION The
present invention relates to load plates having novel means for
retaining work pieces thereon for finishing the work pieces on
polishing machines and the like. The general type of machine with
which the present invention is used includes an abrading, lapping,
or polishing wheel assembly which is rotatably driven about a
vertical axis such that work pieces may be engaged with the upper
surface of the wheel assembly and polished or abraded by means of
an abrasive slurry. It is known to employ load plates with such
machines which are connected to vertically movable spindles and are
adapted to have work pieces mounted on the lower surfaces thereof
for engagement with the polishing wheel assemblies. In the
finishing of relatively thin wafer plates or discs such as used in
photo transfer processes and lens constructions, a plurality of
discs are generally mounted on the lower surface of a load plate at
a loading station removed from the polishing wheel and the loaded
plate is then placed on the polishing wheel for finishing the work
pieces. One known method of securing the wafers or discs to the
load plate is to apply a hot paraffin coating to the lower surface
of the load plate and embed the wafers or discs into the paraffin
coating where they are retained upon hardening of the paraffin.
This method has presented numerous drawbacks among which are that
it is difficult to provide a uniform thickness of paraffin or wax
on the mounting surface of the load plate with the result that the
work pieces are not uniformly spaced from the mounting surface. The
presence of foreign particles in the paraffin coating further
prevents uniform spacing of the discs from the lower mounting
surface of the load plate. In addition, after finishing the mounted
wafers or discs, the paraffin must be re-melted to allow removal of
the discs and cleaning of the mounting surface preparatory to
mounting the next group of wafers or discs. The use of paraffin to
mount the work pieces and removal of the paraffin from the load
plate mounting surfaces is time consuming and thereby substantially
increases manufacturing costs. The present invention overcomes the
disadvantages in the prior art methods of mounting and retaining
work pieces on a load plate by providing an improved load plate
construction whereby work pieces may be readily mounted and
retained on the load plate for finishing, and thereafter easily
removed without further cleaning of the load plate mounting
surface. Summary of the Invention One of the primary objects of the
present invention is to provide a load plate for use with a
polishing machine and the like which includes novel work piece
retaining means operative to retain one or more work pieces on the
load plate. Another object of the present invention is to provide a
load plate which may be readily assembled and disassembled and
which employs a plurality of work piece mounting surfaces which may
be readily re-finished to insure coplanar relation of the mounting
surfaces. Another object of the present invention is to provide a
load plate having novel means for retaining work pieces on the load
plate by negative pressure, the load plate having means for
connecting vacuum passage means to a vacuum source during mounting
of the work pieces and during operation on a finishing machine. A
feature of the present invention is the provision of a sealing ring
member about each of a plurality of work piece mounting pedestals
to retain the vacuum mounting of the work pieces and prevent
abrasive slurry from getting between the work pieces and the
mounting surfaces of the associated pedestals. Another feature of
the present invention is the provision of a mask plate cooperative
with the mounting pedestals to provide a work piece retaining
pocket on the lower surface of each pedestal. Another feature of
the present invention is the provision of pressure disc assembly
means for effecting cooperation between the load plates and the
vertically movable pistons, the pressure disc assemblies having
novel means for allowing swivel movement of the associated load
plates. In carrying out the objects and advantages of the present
invention, there is provided a load plate having a plurality of
downwardly depending pedestals the lower surfaces of which are
adapted to have work pieces mounted thereon. Vacuum passage means
are disposed within the load plate in communication with the lower
mounting surfaces of the pedestals. A normally closed vacuum
connector valve is supported on the upper surface of the load plate
for connection to a vacuum source whereby to retain work pieces on
the pedestals by negative pressure. A mask plate is secured to the
lower surface of the load plate and has a plurality of openings
therein to receive the depending pedestals and establish work piece
retaining pockets on the lower mounting surfaces of the pedestals.
Resilient sealing rings are mounted on the annular peripheral
surfaces of the pedestals for sealing engagement with the work
pieces. A central opening in the upper surface of the load plate
receives the center spindle portion of a pressure disc assembly and
communicates with the vacuum passage means through a flow passage
having a normally closed control valve therein operable to effect
communication between the vacuum passage means and a source of
vacuum during finishing of the work pieces. The pressure disc
assembly is connected to the lower end of a vertically movable
spindle and is adapted to apply a downward force on the load plate
while providing a swivel connection between the load plate and the
spindle. Further objects and advantages of the present invention,
together with the organization and manner of operation thereof, may
best be understood from the following detailed description when
taken in conjunction with the accompanying drawings wherein like
reference numerals designate like elements throughout the several
views.
Inventors: |
Boettcher; Stephen A.
(Deerfield, IL), Cesna; Joseph V. (Niles, IL), Dumentat;
Raymond E. (Roselle, IL) |
Assignee: |
Speedfam Corporation (Des
Plaines, IL)
|
Family
ID: |
22352939 |
Appl.
No.: |
05/114,023 |
Filed: |
February 9, 1971 |
Current U.S.
Class: |
451/288; 451/289;
451/388 |
Current CPC
Class: |
B24B
37/102 (20130101) |
Current International
Class: |
B24B
37/04 (20060101); B24b 007/04 () |
Field of
Search: |
;51/129,131,235 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Whitehead; Harold D.
Claims
We claim:
1. In a polishing machine and the like having a polishing wheel
assembly mounted for rotation about a vertical axis, and at least
one vertically movable spindle supported above the polishing wheel
assembly, the combination therewith of load plate means having at
least one depending pedestal the lower surface of which is adapted
to have a work piece mounted thereon, said load plate means having
vacuum passage means therein communicating with said lower surface
of said pedestal, vacuum connection means supported by said load
plate means and communicating with said vacuum passage means
intermediate the center and outer peripheral edge of said load
plate means, said vacuum connection means being releasably
connectible to a source of vacuum for effecting a vacuum within
said passage means and retaining a work piece on the lower surface
of said pedestal by negative pressure, said connection means
including self-closing valve means for maintaining said negative
pressure after disconnection of said connection means from the
vacuum source such that the load plate may be transferred to and
from the machine with a work piece mounted on said pedestal for
engagement with the polishing wheel assembly.
2. The improvement of claim 1 including means supported by said
spindle and releasably cooperable with said load plate means to
selectively exert a downward pressure on the mounted work piece
against the wheel assembly.
3. The improvement of claim 1 including mask plate means secured to
said load plate means adjacent said depending pedestal, said mask
plate means having an opening therethrough to receive said pedestal
therein and being positioned such that the lower surface of said
mask plate lies in a plane spaced below the plane of the lower
surface of said pedestal to form a work piece receiving pocket with
the lower surface of said pedestal.
4. The improvement of claim 1 including a resilient ring member
secured to the peripheral surface of said pedestal adjacent said
lower surface thereof, said resilient member having a lower surface
disposed below the lower surface of said pedestal for sealing
engagement with a work piece when mounted on the lower surface of
said pedestal.
5. In a polishing machine and the like having a polishing wheel
assembly mounted for rotation about a vertical axis, and at least
one vertically movable spindle supported above the polishing wheel
assembly, the combination therewith of load plate means having at
least one depending pedestal the lower surface of which is adapted
to have a work piece mounted thereon, said load plate means having
vacuum passage means therein communicating with said lower surface
of said pedestal, vacuum connection means supported by said load
plate means and communicating with said vacuum passage means, said
vacuum connection means being connectible to a source of vacuum for
retaining a work piece on the lower surface of said pedestal by
negative pressure, said connection means being further adapted to
maintain said negative pressure after disconnection from the vacuum
source such that the load plate may be transferred to and from the
machine with a work piece mounted on said pedestal for engagement
with the polishing wheel assembly, means supported by said spindle
and releasably cooperable with said load plate means to selectively
exert a downward pressure on the mounted work piece against the
wheel assembly, said load plate means having a central opening in
the surface thereof opposite said depending pedestal, said load
plate means having second passage means in communication with said
vacuum passage means and said central opening, normally closed
valve means disposed within said second passageway means, said
central opening being connectible to a source of vacuum pressure,
and said valve means being operable to connect said vacuum passage
means to said central opening to effect negative pressure retention
of a work piece mounted on the lower surface of said pedestal
during finishing of the work piece when said load plate means is
supported on the polishing wheel assembly in cooperating relation
with said releasable cooperating means supported by said
spindle.
6. The improvement of claim 1 wherein said load plate means
includes a plurality of depending pedestals the lower surfaces of
which are coplanar and adapted to receive work pieces thereon, said
vacuum passage means communicating with the lower surface of each
of said pedestals, and said vacuum connection means being
connectible to a vacuum source for effective a negative pressure
operative to retain the work pieces on the lower surfaces of said
pedestal during transfer of said load plate means to and from the
polishing machine.
7. The improvement of claim 6 including a mask plate secured to
said load plate means adjacent said downwardly depending pedestals,
said mask plate having a plurality of openings therethrough
corresponding to said pedestals and each adapted to receive a
pedestal therein with slight clearance therebetween, said mask
plate having a lower surface lying in a plane below the plane of
the lower surfaces of said pedestal to provide work piece receiving
pockets with said pedestals.
8. The improvement as defined in claim 7 wherein said mask plate
has at least one jack screw therein operative to effect separation
of said mask plate from said load plate means for disassembling the
same.
9. The improvement of claim 7 including a resilient ring member
supported on the peripheral surface of each of said depending
pedestals adjacent the lower surface thereof, each of said
resilient members having a sealing surface lying in a plane spaced
below the lower surface of the associated pedestal for sealing
engagement with a work piece mounted on the associated
pedestal.
10. The improvement of claim 6 wherein said pedestals comprise
cylindrical members secured to the lower surface of said load plate
means, each of said pedestals being laterally positionable relative
to the axis of said load plate means.
11. The improvement of claim 2 wherein said load plate means has an
annular groove in the upper surface thereof opposite said depending
pedestals, and wherein said means supported by said spindle and
cooperable with said load plate means includes pressure disk means
having depending engagement means cooperable with said annular
groove in said load plate means for exerting a downward pressure on
said load plate means upon vertical downward movement of the
associated spindle.
12. The improvement of claim 2 wherein said means supported by said
spindle and releasably cooperable with said load plate means
includes pressure disc means connected to the spindle through
swivel connection means.
13. A load plate for retaining work pieces during finishing thereof
on a polishing machine and the like, comprising plate means having
at least one depending pedestal the lower surface of which is
adapted to have a work piece mounted thereon, said plate means
having vacuum passage means communicating with said lower surface
of said pedestal, and vacuum connection means supported by said
plate means and communicating with said vacuum passage means
intermediate the center and outer peripheral edge of said plate
means, said vacuum connection means being releasably connectible to
a source of vacuum pressure for effecting a vacuum within said
passage means and retaining a work piece on the lower surface of
said pedestal by negative pressure, said connection means including
self-closing valve means for maintaining said negative pressure
after disconnection of said connection means from the vacuum
source.
14. A load plate as defined in claim 13 wherein said plate means
has a plurality of depending pedestals thereon the lower surfaces
of which are coplanar and adapted to have work pieces mounted
thereon, and wherein said vacuum passage means communicates with
the lower surface of each of said pedestals for retaining work
pieces thereon by negative pressure.
15. A load plate as defined in claim 14 wherein said plate means
includes upper and lower plate portions which define said vacuum
passage means therebetween, and wherein said pedestals comprise
generally cylindrical pedestal members secured to said lower plate
portion in a manner to allow lateral positioning of said pedestals
relative to the axis of the load plate.
16. A load plate as defined in claim 14 including a mask plate
secured to said plate means adjacent said pedestals, said mask
plate having openings therethrough to receive said pedestals
therein and being positioned such that the lower surface of said
mask plate is spaced below the plane of the lower surfaces of said
pedestals so as to define work piece receiving pockets with said
pedestals.
17. A load plate as defined in claim 13 including sealing means
secured to the peripheral surface of said pedestal, said sealing
means having an annular surface portion spaced below the plane of
the lower surface of said pedestal for sealing engagement with a
work piece mounted on the lower surface of said pedestal.
18. A load plate for retaining work pieces during finishing thereof
on a polishing machine and the like, comprising, plate means having
at least one depending pedestal the lower surface of which is
adapted to have a work piece mounted thereon, said plate means
having vacuum passage means communicating with said lower surface
of said pedestal, vacuum connection means supported by said plate
means and communicating with said vacuum passage means, said vacuum
connection means being releasably connectible to a source of vacuum
pressure for effecting a vacuum within said passage means and
retaining a work piece on the lower surface of said pedestal by
negative pressure, said plate means having a central opening in the
surface thereof opposite said depending pedestal, said plate means
including second passageway means communicating between said vacuum
passage means and said central opening, and normally closed valve
means disposed within said second passageway means and operable to
effect open communication between said vacuum passage means and
said central opening such that connection of said central opening
to a source of vacuum pressure effects a negative pressure within
said vacuum passage means for retaining a work piece on said
pedestal.
19. The improvement of claim 12 wherein said swivel connection
means includes resilient washer means operatively associated with
said pressure disc means and the spindle, said resilient washer
means allowing swivel movement of said load plate means relative to
the axis of the associated spindle.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial perspective view of a polishing machine having
load plates in accordance with the present invention associated
therewith;
FIG. 2 is a bottom view of one of the load plates shown in FIG.
1;
FIG. 3 is a partial vertical sectional view through a load plate
mounted on the polishing machine of FIG. 1;
FIG. 4 is an enlarged bottom view of a work piece support
spindle;
FIG. 5 is a partial sectional view of the load plate of FIG. 3 with
the pressure disc assembly removed to show the center vacuum
control valve in a closed position;
FIG. 6 is a top plan view of a load plate removed from the
polishing machine; and
FIG. 7 is a partial sectional view taken substantially along the
line 7--7 of FIG. 3, looking in the direction of the arrows.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring now to the drawings, and in particular to FIG. 1, the
present invention is illustrated, by way of illustration, as being
embodied in a polishing machine indicated generally at 10. The
polishing machine 10 includes a framework having a generally
cylindrical lower base portion 12 which supports two diametrically
opposed upstanding columns or channels 14 between which is
supported a horizontal bridge member 16. Four pneumatic cylinder
assemblies 18 are supported by the bridge member 16 so as to
substantially vertically overlie four quadrants of a circular
polishing wheel assembly, indicated generally at 20. The pneumatic
cylinder assemblies 18 are of known construction and include
vertically movable pistons 22. The polishing wheel assembly 20 is
also of known construction and includes a plurality of coplanar
wedge shaped segments 24 supported by a back-up wheel 26 (FIG. 3)
which is supported by the framework for rotational movement about a
vertical axis. Suitable means (not shown) are supported within the
base portion 12 for effecting selective rotational movement of the
wheel assembly 20. A staging table or apron 28 is supported to
substantially surround the polishing wheel assembly with its upper
surface generally coplanar with the upper surface of the polishing
wheel segments. The staging table provides a station for mounting
and removing work pieces before and after polishing or finishing
the work pieces. A plurality of tubular conduits 30 extend
downwardly from the bridge member 16 to overlie the polishing wheel
segments 24 for feeding a free flowing polishing or abrading
mixture to the upper surface of the polishing wheel assembly 20.
The polishing or abrading mixture may comprise any suitable
polishing or abrasive slurry such as one having an abrasive base of
iron oxide, cerium oxide or zirconium oxide suspended or mixed in
water.
Noting FIG. 1, taken in conjunction with FIG. 3, pressure disc
assembly means, indicated generally at 32, is secured to the lower
end of each of the vertically movable piston rods 22. Load plate
means, indicated generally at 34, is operatively associated with
each of the pressure disc assembly means 32. The load plate means
34 are adapted to have work pieces affixed thereto for engagement
with the upper surface of the polishing wheel assembly 20 as will
be more fully described hereinbelow. Each of the pressure disc
assemblies 32 include a cylindrical spindle 36 having a threaded
upper end portion 38 for connection to one of the piston rods 22.
Each of the spindles 36 has reduced diameter lower end portions 40
and 42 upon which are mounted pressure discs means. The pressure
disc means comprises an inner annular support member 44 and an
outer annular pressure transmitting member 46 interconnected by a
radial and axial thrust bearing 48 retained between members 44 and
46 by retainer rings 60 and 62.
The inner support member 44 has a lower radially inwardly directed
annular lip portion forming an annular shoulder surface 50 which
abuts the lower surface of an annular relatively hard rubber washer
52 received over the lower portion 42 of the spindle 36. The rubber
washer 52 has a durometer rating of approximately 60 and has its
upper surface seated against an annular surface 54 formed between
the stepped portions 40 and 42 of the spindle. The inner peripheral
surface of the support member 44 adjacent the washer 52 has a
diameter substantially equal to that of the cylindrical portion 40
of the spindle 36 so as to capture and enclose the annular
peripheral surface of the rubber washer and prevent expansion or
extrusion thereof when subjected to compressive forces. The inner
peripheral surface of the support member 44 above and below the
washer 52 is spaced outwardly from the spindle surfaces 40 and 42,
as at 56 and 58, to allow swivel motion of the support member 44
relative to the axis of the spindle 36 through the action of the
rubber washer 52. The annular support member 44 is retained axially
on the lower end portions of the spindle 36 by a conically shaped
retainer ring 64 received within an annular groove in the lower
portion 42 of the spindle. An annular cap or shroud 66 is suitably
supported on the spindle 36 to overlie the thrust bearing 48 and
shield the bearing from polishing or abrasive slurry and other
foreign materials, the shroud being spaced slightly upwardly of the
bearing and associated support members to allow swivel action
thereof relative to the axis of the spindle 36.
The outer pressure transmitting member 46 has a downwardly
extending annular flange or rib 68 adapted to engage the load plate
means 34 and exert a downward force thereagainst upon downward
movement of the associated spindle 22 as will be described more
fully hereinbelow.
The load plate means 34 includes upper and lower circular plate
portions 72 and 74, respectively, which are secured together in
sealed relation by a plurality of cap screws 76. The upper and
lower load plate portions 72 and 74 define a generally annular
vacuum passage 78 therebetween which communicates with a plurality
of cylindrical recesses 80 formed in the lower plate portion 74.
Secured to the lower planar surface of the load plate portion 74
beneath each of the recesses 80 is a cylindrically shaped pedestal
82 having upper and lower parallel planar surfaces. Each of the
pedestals 82 is secured to the lower load plate portion 74 through
suitable means such as a threaded stud 84 which is fixed centrally
to the pedestal and received upwardly through an enlarged opening
86 in the lower plate portion. A nut 88 and washer 90 are secured
on the upper end of each stud 84 to retain the pedestals against
the lower surface of the plate portion 74. The openings 86 which
receive the studs 84 of the pedestals 82 are of sufficiently
greater diameter than the studs to allow lateral positioning of the
pedestals for cooperation with a mask plate to be described. The
lower surfaces of the pedestals 82 are coplanar and provide
mounting surfaces for work pieces, shown at 92 in FIG. 3, which are
retained on the lower surfaces of the pedestals during finishing of
the work pieces. Noting FIG. 4, the lower mounting surface of each
of the pedestals 82 has an annular groove 94 and cross grooves 96
formed therein which are in communicating relation with the annular
vacuum passage 78 through passages 98 and a circular recess 100
formed in each of the pedestals, and through the associated opening
86 and a cross V-shaped groove 102 (FIG. 7) formed in the lower
surface of the associated recess 80 in the lower load plate portion
74.
Each of the cylindrical pedestals 82 has a relatively hard rubber
ring or sleeve 104 secured to its annular peripheral surface. The
lower annular edge surface of each resilient sleeve 104 projects
downwardly below the lower surface of the associated pedestal 82
approximately .001 inch to establish sealing engagement with a work
piece when mounted on the lower surface of the pedestal and prevent
abrasive slurry from getting between the upper surface of the work
piece and the lower mounting of the pedestal.
Noting FIGS. 2 and 3, a circular mask plate 106 is secured to the
lower surface of the lower load plate portion 74 through a
plurality of set screws 108. The mask plate 106 has upper and lower
parallel planar surfaces and further has a plurality of circular
openings 110 therethrough each of which is adapted to receive a
pedestal 82 therein with the outer peripheral surfaces of the
sealing sleeves 104 being snugly received within the associated
openings in the mask plate. The mask plate 106 is spaced downwardly
from the lower surface of the load plate portion 74 by spacer shims
112 disposed about the cap screws 108 such that the lower surface
of the mask plate lies in a plane spaced below the lower surfaces
of the pedestals 82. In this manner, a work piece receiving pocket
is formed adjacent the lower surface of each of the pedestals 82.
The mask plate is preferably positioned such that its lower surface
is spaced below the lower surfaces of the pedestals 82 a distance
equal to approximately two-thirds of the desired finished thickness
of the work pieces after polishing or abrading. A plurality of jack
screws 114 are threadedly received in the mask plate 106 and may be
threaded upwardly, as considered in FIG. 3, to force separation of
the mask plate from the lower load plate portion 74 during
disassembly after the set screws 108 have been removed.
The load plate means 34 has a self-closing valve 116 of
conventional construction supported on the upper plate portion 72
generally intermediate the center and outer peripheral edge of the
load plate. The valve 116 communicates with the annular vacuum
passage 78 such that connection of the valve to a vacuum source
effects a vacuum within the passage 78 when work pieces are mounted
on the pedestals 82 to retain the work pieces on the pedestals by
negative pressure. The load plate 34 finds particular application
in the finishing of the work pieces 92 which comprise relatively
thin wafer plates or discs which require high accuracy in
finishing. The unfinished work pieces 92 may be mounted on the
pedestals 82 of the load plate means 34 at a work station removed
from the polishing wheel assembly 20, such as on the staging table
28. In accomplishing mounting of the work pieces on the load plate,
the load plate is inverted and the work pieces are placed on the
lower surfaces of the pedestals 82 with the outer peripheral edge
portions of the work pieces engaging the annular seal members 104.
After so mounting the work pieces on the lower surfaces of the
pedestals, the self-closing vacuum valve 116 is connected to a
suitable vacuum source and the vacuum passage 78 evacuated to
effect retention of the work pieces on the lower surface of the
pedestal through negative pressure. Disconnection of the valve 116
from the vacuum source effects self-closing of the valve whereby to
maintain the negative pressure retention of the work pieces.
Thereafter, the load plate 34 is inverted to its normal upright
position and positioned to underlie one of the pressure disc
assemblies 32 secured to the lower end of one of the pistons
22.
As noted, each of the pressure disc assemblies 32 is adapted to
engage a load plate means 34 and effect downward pressure thereon
whereby to effect selective pressure engagement of the work pieces
against the upper surface of the polishing wheel assembly 20. To
this end, the upper plate portion 72 of each load plate means 34
has an annular pressure disc engaging member 118 secured within a
central opening in the upper plate portion by a radial flange 120
formed on the member 118 and a retaining ring 122 cooperable with
member 118. Each pressure disc engaging member 118 has an annular
groove 126 in the upper surface thereof adapted to receive the
depending rib 68 on the pressure transmitting member 46 carried by
the associated spindle 36 upon downward movement of the
corresponding piston 22 from a raised position. The pressure disk
engaging member 118 further has a stepped central bore 128
therethrough which retains a lip seal 130 for sealing engagement
with the lower end portion 42 of the associated spindle 36 upon
engagement of the pressure disc means with the load plate means 34.
The lip seal 130 has an annular garter spring 132 to urge the lip
seal radially inwardly against the peripheral surface of the lower
end of the spindle, as is known.
The lower load plate portion 74 has a central chamber 134 therein
which is adapted for communication with the annular vacuum passage
78 through second passage means comprising an inclined passage 136,
a second chamber 138 provided in the lower load plate, a vertical
bore 139 in the member 118 underlying the groove 126, and a
horizontal passage 140 formed in the radial flange 120 of member
118. Valve means including an upwardly biased valve member 142
carrying a seal ring 144 is normally urged to a closed position by
a compression spring 146 whereby to normally prevent communication
between the chamber 134 and the annular vacuum passage 78 as shown
in FIG. 5. When the pressure disc assembly means 32 and load plate
means 34 are brought into cooperating relation as shown in FIG. 3,
the annular depending rib 68 opens the valve 142 whereby to effect
communication between the central chamber 134 and the annular
vacuum passage 78. An axial passage 148 is provided in the spindle
36 and intersects the lower end surface of the spindle and a
radially disposed passage 150 in the spindle. A tubular elbow
connection 152 is suitably secured to the spindle 36 such that its
central passage intersects the radial passage 150. Connection of
the elbow 152 to a suitable vacuum source through flexible tubular
conduits 154, as shown in FIG. 1, serves to assure that a vacuum or
negative pressure is maintained within the passage means 78 when
the pressure disc assembly means 32 and the load plate means 34 are
in cooperating relation as shown in FIG. 3. In this manner, work
pieces mounted on the lower surfaces of the pedestals 82 are
retained thereon by negative pressure derived from both the initial
vacuum mounting and after connection of the load plate means 34 to
a pressure disc assembly means 32 during finishing of the work
pieces.
Thus, in accordance with the described embodiment of the present
invention, load plate means are provided upon which a plurality of
disc-like work pieces can be mounted at a work station removed from
the polishing wheel assembly, and retained on the load plate by
negative pressure during transfer to and from the polishing wheel
assembly and also during finishing of the work pieces. Swivel
movement of a load plate means relative to the axis of its
associated piston 22 during operation is readily accommodated by
the rubber ring 52 as described. By providing the vacuum connection
154 to the spindle 36, the vacuum passage 78 may be continually
subjected to a vacuum source during finishing of the work pieces
should a small leak reduce the initial vacuum retention of the work
pieces.
The load plate means 34 may be readily disassembled and cleaned to
remove any clogging from the abrasive slurry mixture as may result
during operation. In addition, the lower work piece mounting
surface of the pedestals may be easily refinished to insure
coplanar relation.
While a preferred embodiment of the invention has been shown and
described, it will be obvious to those skilled in the art that
changes and modifications may be made therein without departing
from the invention in its broad aspects.
* * * * *