Note: Descriptions are shown in the official language in which they were submitted.
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380-78-0140
COORDINATE MEASURING MACHINE HAVING LOW
FRICTION CURTAINS TO PROTECT THE WAY SURFACES
TECHNICAL FIELD
The present invention relates to coordinate measuring
machines of the type having a horizontally-movable
carriage mounted to move along way surfaces carried on a
machine base. More particularly, the present invention
relates to a low-friction system for way surface
protection which isolates the way surfaces from external
debris and damage.
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380-78-0140
BACKG20UND AND SUMMARY OE THE INVENTION
Coordinate measuring machines are well known of the
type having a base upon which a part to be measured is
fixed. A horizontally movable carriage is mounted to the
base to move along horizontal way surfaces to measure the
part, frequently in ten-thousnadths of an inch.
In one measuring technique, the movable carriage and
the fixed base each include a grating having a plurality
of spaced parallel lines. The movement of the carriage
moves the grating attached to the carriage. Movement of
the grating on the carriage with respect to the grating on
the fixed base moving creates a "fringe effect" which is
detected and measured to provide an indicati~n of the part
measurement. This is commonly referred to as a Moire
fringe measurement technique.
In such measuring machines, it is desirable to keep
the way surfaces as free from debris as possible to
prolong the life of the machine, maintain the accuracy of
the machine and prevent damage to it. It is also
desirable that the measuring grating be free from debris
to avoid distorting the fringe. The measurement machines,
however, are designed to be used in a manufacturing
environment in which particulate material is frequently
encountered from machining operations. Such factory
operations are also a source of various other industrial
materials s~hich advantageously should be kept away from
the way surface and the gratings.
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The prior art has proposed to mount a flexible fabric
material or curtain to either end of the carriage and to
provide a support at either end of the base for receiving
and supporting the curtain. The movement of the carriage
with respect to the base moved the curtains creates
considerable friction and inertia when the supports are
machined surfaces.
The prior art has also suggested reducing friction
and inertia by using a mechanical bearing as a support.
I0 The bearing rotates with the movement of the curtain to
reduce the friction and inertia generated by the relative
movement between the curtain and the support.
Such curtain support systems, however, are still
undesirable in that there is significant friction and
inertia between the curtain and the support. The friction
creates less accurate measurements. Also, the
repeatability of a part measurement in such systems is
often poor.
The friction of such curtain support systems is also
undesirable in that a significantly larger force is
required to start initial movement of the carriage. In
one coordinate measuring machine, initial movement of the
carriage with respect to the base could be accomplished
with approximately three ounces of force when no curtain
is used. The use of curtains and mechanical bearing
supports raises the force required to start movement to
six ounces (double the no curtain force.)
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According to the present invention there is
provided an apparatus for performing an operation on a workpiece,
the apparatus having a base with means for engaging the
workpiece, the means including a member mounted for movement
along a surface of the base. Means is provided for covering
at least a portion of the surface of the base, the covering
means being mounted to one of the base and the movable member.
A support member is coupled to the other of the base and
movable member for supporting the cover means away from
its mounting. Means is associated with the support member
for receiving and directing a source of pressurized fluid
between the covering and the support member to produce a fluid
cushion therebetween, so that when a source of pressurized
fluid is supplied to the support member, a fluid cushion is
created between the covering means and the support member.
The present invention overcomes the limitations and
undesirable features of the prior art coordinate measuring
machines by providing a way surface protection system which may
include a curtain supported for low-friction movement by a layer
of pressurized air directed between a curtain support and the
curtain.
The system of present invention provides a minimal
(or negligible) inertial load on the carriage. The small
inertial load results in dimensional measurements having
greater accuracy with greater repeatability.
The low inertia of the present invention is also
advantageous in that the curtain support system requires
only a small force (approximately one-third ounce) above the
force which is necessary to start the movement of the
carriage without any curtains or support.
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The present invention also has the advantage that the
curtains may be used to protect the ways and the gratings
without any significant inertial disadvantage.
The foregoing other features and objects of the
present invention will become apparent to those skilled in
the art, in view of the following description and claims
and the appended drawings.
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380-78-0140
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a front view of a portion of the
coordinate measuring machine of the present invention,
showing a carriage mounted to a base and an air curtain
and support system.
FIGURE 2 is an enlarged view of the curtain support
of the present invention, along with a portion of the
curtain.
FIGURE 3 is a top view of the support, with the
curtain removed to expose the structure of the curtain
support.
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DETAILED DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a front view of a portion of a coordinate
measuring machine 10 including the present invention. The
coordinate machine 10 includes a base 12 and a movable
carriage 14.
The carriage 14 advantageously includes a vertically
movable probe 15 which is adapted to engage a part 5 for
measuring features on the part 5.
The carriage 14 is mounted to the base 12 by bearings
16 which move along way surfaces 17 on the top portion of
the base. The bearings 16 are preferably mounted to the
carriage and have low-friction and high precision to allow
accuracy of measurements on the part 5 and minimal loading
on the system.
Associated with the carriage 14 is a movable grating
fixed thereto. A second grating is fixed to the base 12.
The gratings, which are not shown, are known in the art
and form no basis of the present invention. The movement
of one grating with respect to the other is sensed to
provide an indication of the distance through which the
carriage is moved to engage the feature of the part 5, and
thus the location of the feature.
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At each end of the horizontal way surface 17 is a
support 200. The support 200 is mounted to the top of the
base 12. The support 200 includes a mounting bracket 210
and a tubular piece 220, shown in its cross section in
FIGURE 1.
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380-78-0140
One flexible curtain 300 is mounted to each end 14a,
14b of the carriage 14. The curtain 300 is mounted near
one curtain end 310 to the end 14a of the carriage.
mounting member 330. The curtian extends over (around)
the tubular support piece 220 and then is weighted at an
other end 320 of the curtain by a small weight 400.
The weight 400 provides a tenslon on the curtain 300
all the way to the mounted end 310 at the attachment to the
carriage 14a. The curtain 300 is this in tension from the
end 310, over the support 200 and down to the weight 400.
Advantageously, the curtain 300, between the curtain
end 310 mounted to the end 14a of the carriage and the
portion which extends over the support 200, is
substantially horizontal with the top of the tubular
member 220 being at the same height as the mounted curtain
end 310.
Also, advantageously, the tubular member 220 is
rounded so that the curtain extends over and around a
section which is approximately one-quarter of a circle.
The weight 400 pulls the curtain substantially
vertically downward from the outside edge of the tubular
member 220.
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The weight 400 on either side of the carriage
approximately are equal in weight with each other.
The curtains on either side are also advantageously
equal in length and weight. The equality of weight
on either size of the carriage assures that the car-
riage will be balanced and not have a preferred
direction of movement. If the right weight were sig-
nificantly larger than the left weight, the force to
move the carriage to the right would be decreased
while the force to move the carriage to the left
would be increased. The equal length of curtains
additionally allows a uniform distance of carriage
movement in each direction.
The curtain 300 covers the way surfaces 17 and
also the measuring gratings in a Moire-fringe effect
measuring system.
The curtain 300 is a thin, light weight sheet
of flexible material which is relatively impervious
to passage of the pressurized fluid and the par-
ticulate material from manufacturing. The pre-
ferred materials for the curtain are fluorglass or
polyester film, such as that sold under the trade
mark "Mylar".
FIGURE 2 is an enlarged front view of a por-
tion of the base 12 and the carriage 14 of the co-
ordinate measuring machine. The curtain 300 is shown
attached to the carriage the member 300 and weighted
by the weight 400.
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A pressurized air delivery system 500 is partially
shown in FIGURE 2. A flexible hose 510, which is coupled
to a pressurized air source (not shown), is mounted to a
fitting 520 which is fixed to the tubular member 220 to
communicate with a central axial passage 222 in the member
220. A plurality of rows of radial passages 225, 226, 227
through the member 220 communicate with the axial passage
220 to provide an egress route for the pressurized air.
Advantageously and for best results each row of
passages is spaced by the adjacent row by a uniform angle
~ and the end rows (top and side) are spaced by the same
angle ~ from the end of the portion of the tubular member
which supports the curtain (e.g. horizontal and vertical
on the member). Since there are three rows of passages
shown as the preferred embodiment~ each row is spaced by
an angle 0 of 22 1/2, although the passage spacing need
not be uniform nor in three rows.
The pressurized air forms a thin film across the
surface of the support member 220 between it and the
curtain. Such a film, even in very thin proportion,
serves to reduce friction of the moving curtain over the
member to a negligible amount.
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FIGURE 3 shows a top view of a portion of the base 12,
the support member 220 and bracket 210. The curtain has
been removed from the top of the support member, although
a downwardly-extending curtain portion 300 is shown. End
caps 221, 229 on the tubular member make the tubular
member 220 with the relatively large central axial passage
222 into a pressure chamber having only an entrance
through the fitting 520 and egress through the rows of
radial passages 225, 226, 227.
Other objects and advantages of the present invention
will be apparent to those skilled in the art in view of the
foregoing description. For example, in some embodiments,
the curtain might be mounted to the base and the support
member mounted to the carriage. Further, other
configurations of the support member and fluid passages
might be employed to advantage. Other pressurized fluids
might be used to create the friction-reducing film. The
foregoing description, accordingly, should be considered
as illustrative of the invention only should not be
interpreted to limit the scope of the present invention,
which is defined solely by the following claims.
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