Note: Descriptions are shown in the official language in which they were submitted.
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ABRASIVE FLOW MACHINING APPARATUS AND METHOD
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention is related to abrasive flow machining and, more
particularly, to an abrasive flow machining apparatus capable of processing an
orifice
within a part by carefully controlling the media flow rate. The invention is
also
directed to a method for such processing.
DESCRIPTION OF THE RELATED ART
Abrasive flow machining is the process of polishing or abrading a
workpiece by passing a viscous media having abrasive particles therein under
pressure
over the workpiece or through an orifice extending through the workpiece.
Conventional abrasive flow machining processes are designed to maintain
a constant media extrusion pressure which often results in significant changes
in media
temperature, flow rate and viscosity which adversely impacts the system
capability to
accurately predict abrasive flow machine (AFM) processing tiines and,
consequently,
overall process results.
As an example, the media temperature increases as the flow rate of the
media increases through an orifice. When the orifice is subjected to media
under a
constant pressure, the flow rate of the media through the orifice increases as
the orifice
walls becomes smoother and the orifice diameter increases. As a result, not
only does
the media temperature increase, but such an increase is localized to the media
that passes
through the orifice at a higher flow rate. This produces both excessively high
temperatures and a non-uniform temperature distribution throughout the media.
High
temperatures and variations in temperatures throughout the media prevent the
media
from working in a consistent and effective fashion. Therefore, an apparatus
and method
that may effectively utilize the media while at the same time maintain the
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temperature of the media within a relatively narrow temperature band is
desired.
United States Patent No. 3,634,973, which is assigned to the assignee of
the present invention, discloses a reciprocal machining structure utilizing
abrasive media
but operating in a fashion which does not provide for direct control of the
media flow
rate through an orifice. While this apparatus is capable of affective abrasive
flow
machining, such machining would be of a higher quality and the media would
last longer
if the flow rate were controlled.
BRIEF SUMMARY OF THE INVENTION
In accordance with an aspect of the present invention, there is provided
an abrasive flow machine for moving abrasive media through the orifice of a
workpiece
comprising:
a) a workpiece holder, wherein the holder is adapted to securely
retain the workpiece, and wherein one side of the holder defines an upstream
side and the
other side of the holder defines a downstream side;
b) a first positive displacement pump positioned on the upstream
side and connected to the upstream side of the holder for forcing media under
a
predetermined pressure to the downstream side of the holder;
c) a media opposer positioned on the downstream side and
connected to the downstream side of the holder for opposing the flow of the
media to the
downstream side;
d) a media flow rate measurement device to determine flow rate of
media past the holder; and
e) a controller for controlling the media opposer to limit the media
flow to a predetermined flow rate from the upstream side to the downstream
side of the
holder while the first positive displacement pump maintains the predetermined
upstream
pressure.
In accordance with another aspect of the present invention, there is
provided an abrasive flow machine for moving abrasive media through the
orifice
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of a workpiece comprising:
a) a workpiece holder, wherein the holder is adapted to securely
retain the workpiece, and wherein one side of the holder defines a first side
and the other
side of the holder defines a second side;
b) a first positive displacement pump positioned on the first side
and connected to the first side of the holder;
c) a second positive displacement pump positioned on the second
side and connected to the second side of the holder;
d) wherein in a first mode the first positive displacement pump
forces media from the first side to the second side of the holder while the
second
displacement pump resists flow thereby controlling flow to the second side of
the holder;
e) wherein in a second mode the second positive displacement
pump forces media from the second side to the first side of the holder while
the first
displacement pump resists flow thereby controlling flow to the first side of
the holder:
f) a media flow rate measurement device to determine the flow
rate of media past the holder; and
g) a controller for controlling the first positive displacement pump
and the second positive displacement pump to limit the media flow to a
predetermined
flow rate as it travels back and forth past the holder.
In accordance with a further aspect of the present invention, there is
provided a method for abrasive flow machining using an abrasive media through
the
orifice of a workpiece, wherein the orifice defines an upstream side and a
downstream
side, comprising the steps of:
a) moving media through the orifice from the upstream side to the
downstream side at a predetermined constant pressure on the upstream side;
b) monitoring the flow rate; and
c) selectively throttling the flow of media to the downstream side
to control the flow rate of the media passing through the orifice while
maintaining the
predetermined constant pressure on the upstream side.
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In accordance with another aspect of the present invention, there is
provided a method for abrasive flow machining using an abrasive media through
the
orifice of a workpiece, wherein the orifice defines a first side and a second
side,
comprising the steps of
a) moving media through the orifice from the first side to the
second side at a predetermined constant pressure on the first side;
b) monitoring the flow of media through the orifice;
c) selectively throttling the flow of media to the second side to
control the flow rate of the media passing through the orifice while
maintaining the
predetermined constant pressure on the first side;
d) moving media through the orifice from the second side to the
first side at the predetermined constant pressure on the second side; and
e) selectively throttling the flow of media to the first side to
control the flow rate of the media passing through the orifice while
maintaining the
predetermined constant pressure on the second side.
In accordance with a further aspect of the present invention, there is
provided a method for abrasive flow machining using an abrasive media through
the
orifice of a workpiece, wherein the orifice defines an upstream side and a
downstream
side, comprising the steps of:
a) moving media through the orifice from the upstream side to the
downstream side at a pressure on the upstream side;
b) monitoring the flow rate of media through the orifice and
c) adjusting the pressure on the upstream side to provide a constant
flow rate of the media passing through the orifice.
In accordance with another aspect of the present invention, there is
provided a method for abrasive flow machining using an abrasive media through
the
orifice of a workpiece, wherein the orifice defines a first side and a second
side,
comprising the steps of:
a) moving media through the orifice from the first side to the
second side by applying pressure at a first side and relieving pressure at the
second side;
b) monitoring the flow rate of media through the orifice;
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c) adjusting the pressure at the first side to provide a constant flow
rate of the media passing from the first side through the orifice;
d) moving media through the orifice from the second side to the
first side by applying pressure at the second side and relieving pressure at
the first side;
and
e) adjusting the pressure at the second side to provide a constant
flow rate of the media passing from the second side through the orifice.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a simplified sketch illustrating two opposing positive
displacement pumps urging abrasive media through the orifice of t workpiece.
Figure 2 is a simplified sketch of a single positive displacement pump
displacing media through the orifice of a workpiece and opposing the flow of
the media
thereafter;
Figure 3 illustrates opposing positive displacement pumps for moving
media back and forth through an orifice whereby the drivers of the pumps are
linear
actuators;
Figure 4 is a simplified sketch of two opposing positive displacement
pumps and the control systems which operate them;
Figure 5 is a sketch of an operating system illustrating two opposing
positive displacement pumps and the associated hardware;
Figure 6 is a simplified sketch of single positive displacement pump
which provides media through an orifice where by the media is release to an
open
environment; and
Figure 7 is a perspective view of an in-line heat exchanger that may be
used to control the temperature of the media.
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DETAILED DESCRIPTION OF THE INVENTION
In one embodiment of the subject invention abrasive media is subjected
to a constant pressure and forced through an orifice of a workpiece. The flow
rate
discussed with this embodiment will be equal to or less than the maximum flow
rate
capability with the downstream side of the orifice open to the atmosphere. In
particular,
a flow rate of less than this maximum value is obtained by limiting the flow
of the media
at the down stream side of the orifice.
Directing attention to Fig. 1, a simplified schematic of an abrasive flow
machine 10 for moving abrasive media 15 through the orifice 18 of a workpiece
20 is
illustrated. For purposes of this discussion, media will be discussed as
having viscosity
in the range between 1 to 50 million centipoise. One example of a relatively
high
viscosity media is a visco-elastic plastic media such as a semisolid polymer
composition.
One example of a media having a lower viscosity is a liquid abrasive slurry
that includes
abrasives suspended or slurried in fluid media such as cutting fluids of
honing fluids.
The fluid may have a rheological additive, and finely divided abrasive
particles
incorporated therein. The rheological additive creates a thixotropic sluny.
The abrasive
flow machine 10, as an entity on its own, will not include the workpiece 20
having the
orifice 18 therein but will include a workpiece holder 25 which is adapted to
securely
retain the workpiece 20 wherein one side 27 of the holder 25 defines an
upstream or first
side and the other side 29 of the holder 25 defines a downstream or second
side.
A first positive displacement pump 35 is positioned on the upstream side
27 and connected to the upstream side 27 of the holder 25 for forcing media 15
under
a predetermined pressure through the orifice 18 of the workpiece 20 to the
downstream
side 29 of the holder 25.
Unencumbered flow of the media through the orifice 18 is prevented by
a media opposer 45 positioned on the downstream side 29 of the holder 25 for
opposing
the flow of the media 15 to the downstream side 29, thereby controlling the
media flow
rate from the upstream side 27 to the downstream side 29 of the holder 25.
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As illustrated in Fig. 1, the first positive displacement pump 35 is
comprised of a piston 37 within a cylinder 39, wherein the piston 37 is
operable to urge
media 15 from the cylinder 39 toward the downstream side 29 of the holder 25.
The
piston 37 is moved by a driver 41. As will be illustrated, the driver 41 for
the piston 37
may be a hydraulic actuator (Fig. 4) or as illustrated in Fig. 3, the driver
41 may be a
linear motor actuator 42 which utilizes for example, a worm gear 43 which
engages a
mating gear 44 on a rod 38 extending from the piston 37. It should be
appreciated that
while only two types of drivers have been mentioned, any number of drivers
known to
those skilled in the art of hydraulic machinery may be utilized for the
positive
displacement pumps in accordance with the subject invention.
Returning to Fig. 1, one method to control both the pressure of the media
and the flow rate of the media 15 involves reducing the flow rate through the
orifice
18 by restricting the amount of media permitted to travel to the downstream
side 29 of
the holder 25. In particular, a second positive displacement pump 55 may be
utilized as
15 the media opposer 45 to accomplish this. The second positive displacement
pump 55
has a piston 57 within a cylinder 59. The piston 57 is operable to resist and
thereby
control the media flow to the downstream side 29 of the holder 25.
Other mechanisms are available to act as a media opposer 45. Directing
attention to Fig. 2, an arrangement similar to that in Fig. 1 is presented,
however, the
media opposer 45 now takes the form of a relief valve 60. The media 15 flows
directly
through the relief valve 60 and the release pressure of the relief valve 60 is
controlled
based upon the desired media flow rate.
In a preferred embodiment, the relief valve 60 is a proportional electric
relief valve (PER). A control device monitors the flow rate and decreases a
voltage
output to the proportional electric relief valve 60 when the actual flow rate
is greater
than a target flow rate. This causes the relief valve 60 to allow less media
15 to pass
through. In the alternative, the voltage output to the valve 60 may be
increased which
allows more media 15 to pass through when the actual flow rate is less than a
target flow
rate. Other relief valves described herein may operate in a similar fashion.
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To accurately determine the media flow rate, a media flow rate
measurement device 65 is utilized. One such device is illustrated in Fig. 1.
When the
first positive displacement pump 35 is comprised of a piston 37 within a
cylinder 39, the
piston 37 may have a rod 38. An encoder 66 may be used as the flow rate
measurement
device 65 to measure the linear motion of the rod 38 to determine the media
flow rate.
Knowing the volume within the cylinder 39, and the rate of travel of the
piston 37,
which is provided by the encoder 66, the volume flow rate of the media 15
through the
orifice 18 may be used to determine the media flow rate and in turn the
controller may
adjust the media opposer 45 to increase or decrease the flow rate of the media
15
through the orifice 18.
When the media opposer 45 is comprised of the second positive
displacement pump 55, which as previously discussed has a piston 57 within a
cylinder
59, the piston 57 has a rod 58 and under such circumstances the media flow
measurement device 65 may be an encoder 67 that measures the linear motion of
the rod
58 to determine the media flow rate. It should be apparent therefore that the
measurement of the media flow rate may occur at either the upstream side 27 or
downstream side 29 of the holder 25.
Encoders 66, 67 may each be either a linear encoder or a rotary encoder,
both of which are well known to those skilled in the field of measurement
equipment.
The discussion so far has been limited to flow of media 15 in a single
direction from the upstream side 27 of the holder 25 to the downstream side 29
of the
holder 25. In the abrasive flow machine 10 embodiment illustrated in Fig. 2,
this is the
only manner in which the media 15 may flow through the orifice 18 of the
workpiece
20. However, as illustrated in Fig. 1, when the media opposer 45 is a second
positive
displacement pump 55, the roles of the first displacement pump 35 and second
displacement pump 55 may alternate such that in a first mode the first
displacement
pump 35 may force media 15 through the orifice 18 while the second positive
displacement pump 55 acts as the media opposer 45 to control the flow rate of
the media
15. In a second mode of operation, the second positive displacement pump 55
may be
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used to force the media 15 toward the first positive displacement pump 35
while the first
positive displacement pump 35 is used as a media opposer to control flow in
the
opposite direction. It is apparent from this description that with these
alternating modes
media 15 may be moved back and forth through the orifice 18 in a reciprocating
fashion.
Directing attention once again to Fig. 1, each of the first positive
displacement pump 35 and the second positive displacement pump 55 are
comprised of
pistons 37, 57 within cylinders 39, 59 wherein the pistons 37, 57 are moved by
drivers
41, 61. Just as before, each driver 41, 61 may be a hydraulic actuator, which
will be
described or in the alternative, may be a linear motor actuator as illustrated
in Fig. 3.
When the abrasive flow machine 10 is operating such that media 15 is
moved only in a single direction through the orifice 18 of the workpiece 20,
the media
is moved through the orifice 18 from the upstream side 27 to the downstream
side 29
at a predetermined constant pressure. The flow of media 15 to the downstream
side 29
is then selectively throttled to control the flow rate of the media 15 passing
through the
15 orifice 18 while at the same time maintaining the predetermined constant
pressure.
In an alternative embodiment when the abrasive flow machine 10 is
utilized in a reciprocating fashion, media 15 is moved through the orifice 18
from the
upstream side 27, which is now referred to as the first side 27, to the
downstream side
29, which is now referred to as the second side 29, at a predetermined
constant pressure.
The flow of media 15 to the second side 29 is selectively throttled to control
the flow
rate of the media 15 passing through the orifice 18 while maintaining the
predetermined
constant pressure. Thereafter, the media 15 is moved through the orifice 18
from the
second side 29 to the first side 27 at a predetermined constant pressure.
However, the
flow of media 15 to the first side 27 is now selectively throttled to control
the flow rate
of the media 15 passing through the orifice 18 while maintaining the
predetermined
constant pressure. Just as before, the amount the media selectively throttled
is
determined by the media flow rate through the orifice 18, and this is
determined by
monitoring the flow rate utilizing one or both of the linear encoders 66, 67.
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Fig. 4 illustrates a more comprehensive schematic view of the abrasive
flow machine 10, wherein each positive displacement pumps 35, 55 has a driver
41, 61
and each driver 41, 61 may be a hydraulic actuator.
In particular, Fig. 4 includes many elements previously discussed, and
the reference numbers for these elements will be retained. However, additional
details
associated with the driver 41 and the driver 61 in conjunction with the
operation of the
abrasive flow machine 10 will now be discussed.
In the single stroke mode, whereby the first positive displacement pump
35 moves media 15 through the orifice 18 of the workpiece 20 to the media
opposer 45,
which is the second positive displacement pump 55, the driver 41 acts to force
the media
through the orifice 18 while the driver 61 acts as a media opposer 45 to
resist and
control such flow. Directing attention to the hydraulic actuator 70 associated
with driver
41, a hydraulic pump 72 moves media through a supply line 74 at which point
the
hydraulic fluid 76 encounters a poppet valve 78, which may be a solenoid
operated
15 poppet valve (SOP), which for purposes of our discussion is a valve which
permits full
flow or no flow. The hydraulic fluid 76 also encounters a proportional
electric relief
valve 80, which as previously mentioned is capable of adjusting its resistance
to flow
therethrough. When the hydraulic actuator 70 is being used as a driver 41, the
poppet
valve 78 is in the full open position and the relief valve 80 is completely
closed.
Therefore, the hydraulic cylinder 82 is pressurized with hydraulic fluid 76 at
whatever
pressure the pump 72 can provide. This may be a predetermined pressure that
remains
constant throughout the stroke of the first positive displacement pump 35. A
piston 84
in the hydraulic cylinder 82 is acted upon by the pressurized hydraulic fluid
76 such that,
through the common piston rod 38, the piston 37 is advanced against the media
15,
thereby forcing the media 15 through the orifice 18 of the workpiece 20.
When the first positive displacement pump 35, with the hydraulic
actuator 70, acts as a driver 41, the second positive displacement pump 55,
with the
hydraulic actuator 90, acts as a media opposer 45. In particular, the
hydraulic actuator
90 has similar components to the hydraulic actuator 70 including a hydraulic
pump 92,
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supply line 94, and hydraulic fluid 96, wherein the hydraulic fluid is
directed to a poppet
valve 98 and a relief valve 100. The hydraulic actuator 90 is further
comprised of a
hydraulic cylinder 102 having a piston 104 therein connected to the piston rod
58 of the
positive displacement pump 55. When the driver 41 urges media 15 through the
orifice
18 media 15 is also urged against the piston 57, thereby transferring a force
to the piston
104 which acts against the hydraulic fluid 96 in the hydraulic actuator 90.
When the
second positive displacement pump 55 acts as a media opposer 45 the poppet
valve 98
is completely closed such that the hydraulic fluid 96 must pass through the
relief valve
100.
It should be noted in Fig.4 that a single pump utilizing directional valves
and a hydraulic fluid reservoir may be used in lieu of the two pumps 72, 92.
The media flow rate through the orifice 18 is determined by one of the
encoders 66, 67 and transmitted to a controller. Utilizing the media flow
rate, and
comparing it to a target media flow rate, the voltage in the proportional
electric relief
valve 100 is adjusted to permit hydraulic fluid 96 past the relief valve 100
in such a
manner that the retraction of the piston 104 is controlled, thereby
controlling the media
flow rate. In this manner, when the first positive displacement pump 35 acts
as the
driver 41, the poppet valve 78 associated with the hydraulic actuator 70 is
fully opened
thereby bypassing the relief valve 80. With respect to the hydraulic actuator
90 of the
second positive displacement pump 55, the poppet valve 78 is fully closed
thereby
forcing hydraulic fluid 96 through the relief valve 100, which throttles the
hydraulic
fluid flow to control the media flow rate.
In the second mode the same configuration exists, but in a reversed
arrangement. In particular, when the second positive displacement pump 55 acts
as a
driver 61, the first positive displacement pump 35 acts as a media opposer. In
particular,
in this configuration the poppet valve 98 is fully opened such that the full
pressure
produced upon the hydraulic fluid 96 by the pump 92 is transferred to the
piston 104,
which in turn acts upon the piston 57 through the piston rod 58 and forces the
media 15
through the orifice 18 toward the first positive displacement pump 35. Acting
as a
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media opposer, the hydraulic actuator 70 is configured such that the poppet
valve 78 is
fully closed thereby forcing the hydraulic fluid 76 through the relief valve
80. The
release pressure of the relief valve 80 may be electronically controlled by
the controller
based upon the media flow rate determined by one of the encoders 66, 67. In
this
fashion, the operation of the abrasive flow machine may be alternated between
the first
mode and the second mode to provide a reciprocating motion of the media 15
through
the orifice 18 of the workpiece 20.
Fig. 5 represents a sketch of the hardware utilized to implement at least
one embodiment of the subject invention described hereto. Just as before, like
reference
numerals are repeated. However, some additional elements are illustrated in
this
drawing. In particular, there is a pressure sensor 105 in the form of a
pressure transducer
associated with the hydraulic supply line 74 to determine the pressure in that
line.
Additionally, there is a pressure sensor 108 associated with supply line 94 to
determine
pressure in that line. It should be appreciated the pressure in the supply
lines 74, 94 will
be transmitted to the media 15 by the respective pistons 37, 57. Additionally,
a
temperature sensor 110 may be utilized to determine the temperature of the
media 15.
The pressure of the hydraulic fluid, which translates into the pressure of
the media 15, along with the linear position of each piston 37, 57 is
processed by a
controller 112 which in turn acts to modify the release pressure of the
pressure relief
valve 80 for the positive displacement pump acting as the media opposer.
By more closely controlling the flow rate of the media 15 through the
orifice 18, the temperature may be held within a relatively narrow temperature
band in
contrast to when the flow rate is not controlled. Nevertheless, it may still
be desirable
to remove heat from the media 15 during the abrasive flow machining process.
For that
reason there may be a cooling collar 115 associated with the first positive
displacement
pump cylinder 39 and a cooling collar 117 associated with the secoiid positive
displacement pump cylinder 59. Each of these cooling collars 115, 117 may have
a
plurality of cooling tubes 116, 118 capable of transferring heat from the
media 15 when
necessary. Under certain circumstances these cooling collars 115, 117 may also
be
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utilized to heat the media 15 such as, for example, when the media 15 must
begin the
abrasive process at a minimum temperature. The cooling collars 115, 117 are
externally
positioned and do not interfere with the flow of media 15. However, their
effectiveness
is limited because heat transfers from the media 15 to the collars 115, 117
occurs by
conduction through the walls of the cylinders 39, 59.
It is possible to introduce an in-line heat exchanger directly within the
flow path of the media 15. Fig. 7 illustrates one such heat exchanger 200
having hollow
cooling fins 202 within an internal passageway 205 through which the media 15
flows.
Coolant passes through a coolant inlet 207, enters the hollow fins 202 and
exits at the
coolant outlet (not shown). Bolts may extend through peripheral holes 209 in
the collar
210 to secure the heat exchanger 200. The heat exchanger 200 may be attached
to one
or both cylinders 39, 59 and may be adjacent to the holder 25. While this heat
exchanger
200 provides a greater heat transfer rate with the media 15, it also partially
obstructs the
flow of media 15 such that the cylinder size may need to be increased to
accommodate
a given flow rate.
The controller 112 (Fig. 5) may be a programmable logic controller such
as the Micologics 1200 model, which is commercially available from the Allen
Bradley
Company. Additionally, the proportional electric relief valve may be type TS
10-26,
which is commercially available from Hydra Force, Inc. Additionally, the
poppet valves
may be type SV 10-23 two way nonnally open valves commercially available from
Hydro Force, Inc.
The signals from the encoders 66, 67 are used by the controller 112 to
calculate the actual flow rate of the media 15. A suitable encoder is the
Quadrature type,
which is commercially available from Automation Direct, Inc. The use of the
encoders
66, 67 and the poppet valves 78, 98 and the relief valves 80, 100 allow the
controller 112
to maintain a desired consistent media flow rate. This consistent flow rate
allows the
media to remain within a-narrow temperature band, as measured by the
temperature
sensor 110, which in turn maintains consistent media viscosity. By maintaining
the
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media viscosity essentially constant, the controller 112 may more accurately
predict the
processing time to achieve the desired machining of the orifice 18.
What has so far been described are drivers 41, 61 which alternately urge
media 15 under constant pressure through the orifice 18 of the workpiece 20
while the
flow rate of the media 15 is controlled by the retraction or resistance of the
media
opposer 50 which may be a pressure relief valve or the other driver.
It is possible to eliminate the media opposer 45 and still maintain a
constant media flow rate. This is accomplished by varying the pressure
provided by the
driver 41 to the media 15. As the abrasive flow machining process proceeds,
given a
constant media pressure, the flow rate of the media 15 through the orifice 18
tends to
increase. Therefore, to maintain the same media flow rate, it is necessary to
decrease
the pressure imparted to the media 15 by the driver 41. This may be
accomplished in
a single direction, or just as before, in a reciprocating motion.
Directing attention to Fig. 6, in a single direction media 15 is moved
through the orifice 18 from the upstream side 27 to the downstream side 29 at
a
particular pressure. Utilizing encoder 66 the flow rate may be monitored and
the
pressure provided to the media may be adjusted to provide a constant flow rate
of the
media 15 passing through the orifice 18. In particular, the encoder 66 may
monitor the
linear motion of the piston rod 38 associated with piston 37 to determine the
flow rate.
The pump 72 delivers hydraulic fluid under pressure to the hydraulic cylinder
82, where
the fluid acts upon the hydraulic piston 84. With respect to the arrangement
illustrated
in Fig. 4, it is entirely possible for the downstream side 29 of the holder 25
to discharge
into the atmosphere as illustrated in Fig. 6. In the alternative, and again
directing
attention to Fig. 4, it is possible to coordinate the motion of piston 37 with
that of piston
57 such that the flow of media 15 applied under pressure at the first side 27
through the
orifice 18 is neither hindered nor assisted by piston 57 but that pressure on
the second
side 29 side is relieved. It is also possible to coordinate the motion of
piston 57 with
that of piston 37 such that the flow of media 15 applied under pressure at the
second side
57 through the orifice 18 is neither hindered nor assisted by piston 37 but
that pressure
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on the first side 37 is relieved. Such an arrangement will permit the abrasive
flow
machine 10 illustrated in Fig. 4 to operate in a reciprocating fashion whereby
in a first
mode that the first positive displacement pump 35 forces the media 15 though
the orifice
18 while the second positive displacement pump 55 is passive, and in the
second mode
the second positive displacement pump 55 forces the media 15 through the
orifice 18
while the first positive displacement 35 is passive.
The invention has been described with reference to the preferred
embodiments. Various modifications and alterations will occur upon reading and
understanding the preceding detailed description. It is intended that the
invention be
construed as including all such modifications and alterations insofar as they
come within
the scope of the appended claims or the equivalents thereof.
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