U.S. patent number 3,726,334 [Application Number 05/075,968] was granted by the patent office on 1973-04-10 for electrohydraulic ram velocity control circuit.
This patent grant is currently assigned to Koehring Company. Invention is credited to Walter E. Meyer, David W. Sallberg.
United States Patent |
3,726,334 |
Sallberg , et al. |
April 10, 1973 |
ELECTROHYDRAULIC RAM VELOCITY CONTROL CIRCUIT
Abstract
An electrohydraulic control circuit for controlling the velocity
of a ram driving a fluid into a die cavity is disclosed. In
accordance with the control method disclosed, the position of the
ram is sensed by a pulse generator and sensed ram positions are
used to provide electric signals which vary in accordance with the
sensed positions and flow of hydraulic ram drive fluid is varied in
accordance with the electric signals provided to vary the velocity
of the ram. The electric signals may be further varied in
accordance with one or more of the positions of a metering member
in a hydraulic valve supplying ram drive fluid, the pressure of the
fluid in the shot cylinder, the velocity of the ram and the
pressure in the die cavity. Control of the ram may be directly from
a large electrohydraulic servo valve or a pilot electrohydraulic
servo valve may be used to control a larger hydraulic valve
supplying ram drive fluid.
Inventors: |
Sallberg; David W. (Farmington,
MI), Meyer; Walter E. (Ferndale, MI) |
Assignee: |
Koehring Company (Milwaukee,
WI)
|
Family
ID: |
22129067 |
Appl.
No.: |
05/075,968 |
Filed: |
September 28, 1970 |
Current U.S.
Class: |
164/155.3;
425/145; 164/457; 164/155.4; 164/155.5 |
Current CPC
Class: |
B22D
17/32 (20130101) |
Current International
Class: |
B22D
17/32 (20060101); B22d 017/32 (); B29b
005/04 () |
Field of
Search: |
;164/4,113,155,303,314
;18/3CR ;425/145 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Annear; R. Spencer
Claims
What we claim as our invention is:
1. In conjunction with a die having a cavity therein, a shot
cylinder, means for feeding fluid into the shot cylinder and for
passing fluid out of the shot cylinder into the die cavity, a ram
for forcing the fluid from the shot cylinder into the die cavity
and means for driving the ram into the shot cylinder, the
improvement comprising means for sensing the position of the ram in
the shot cylinder over substantially the entire length of the shot
cylinder and means operable in response to the sensed position of
the ram for controlling the movement of the ram into the shot
cylinder over substantially the entire length of the shot cylinder
to provide optimum fluid flow from the shot cylinder into the die
cavity during filling of the die cavity.
2. Structure as set forth in claim 1 wherein the means for sensing
the position of the ram comprises a pulse generator for producing a
separate pulse in response to arrival of the ram at a plurality of
predetermined positions within the shot cylinder which positions
are spaced apart over substantially the entire length of the shot
cylinder.
3. Structure as set forth in claim 1 wherein the means for
controlling the driving of the ram comprises a multiple slidewire
resistance circuit for providing different electric output signals
and a switching circuit connected to the multiple slidewire
resistance circuit for passing separate ones of the different
electric output signals in response to different sensed positions
of the ram.
4. Structure as set forth in claim 3 wherein the means for
controlling the driving of the ram further includes a main
hydraulic valve controlling flow of hydraulic fluid to the ram.
5. Structure as set forth in claim 4 and further including means
for controlling the driving of the ram into the cylinder in
accordance with at least one of the additional parameters velocity
of a portion of the main hydraulic valve, the pressure of the fluid
in the shot cylinder, the velocity of the ram, and the pressure of
the fluid in the die cavity.
6. Structure as set forth in claim 5 wherein the means for
controlling the driving of the ram further includes a pilot
electrohydraulic servo valve positioned between the switching
circuit and main hydraulic valve for controlling fluid flow through
the main hydraulic valve.
7. In combination, a die cavity, a shot cylinder into which molten
metal is placed for movement into the die cavity positioned
adjacent to the die cavity, a reciprocally movable ram positioned
within the shot cylinder for moving the molten metal from the shot
cylinder into the die cavity in accordance with the movement of the
ram into the shot cylinder, a ram cylinder in which the ram is
mounted for reciprocal movement, a main hydraulic valve connected
to the ram cylinder operable to produce movement of the ram within
the ram cylinder and shot cylinder, an electrohydraulic servo valve
connected to the main hydraulic valve for metering hydraulic fluid
through the main hydraulic valve in accordance with an electric
signal applied to the servo valve, a source of electrical energy, a
multiple slidewire resistance circuit connected to the source of
electrical energy for providing a plurality of different output
electrical signals, a switching circuit connected to the multiple
slidewire resistance circuit for providing an output from the
switching circuit in accordance with one of the output signals of
the multiple slidewire resistance circuit in accordance with
programming of the switching circuit, means for sensing the
position of the ram and programming the switching circuit in
accordance with the position of the ram whereby the output signal
from the switching circuit reflects the position of the ram, means
connected to the switching circuit for modifying the output signal
from the switching circuit in accordance with at least one of the
pressure in the shot cylinder, the velocity of the ram, and the
pressure in the die cavity to provide a modified output signal,
means for further modifying the modified output signal in
accordance with the position of the main hydraulic valve and means
for actuating the electrohydraulic servo valve with the further
modified output signal whereby the placing of the molten metal in
the die cavity is accomplished under optimum conditions.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to electrohydraulic servo controls and
methods and refers more specifically to a control circuit for and
method of controlling the flow of fluid into a die cavity in die
casting to provide a most efficient flow rate, using sensors
monitoring different parameters of the die casting operation and
providing an electric control signal corresponding to the sensed
parameters to an electrohydraulic servo valve controlling the
actual movement of the ram in accordance with a predetermined
velocity program.
2. Description of the Prior Art
In the past, feeding fluid into cavities in die casting operations
and the like has been deficient in that in general a single speed
of fluid fed into the cavity has been used on application of a
single hydraulic pressure to a ram forcing the fluid into the
cavity. Such operation, if the ram speed is too fast, wears the die
cavity opposite the inlet port and may produce air bubbles in
finished castings. If the ram speed is too slow, improper cooling
and filling of the cavity will produce unacceptable castings.
SUMMARY OF THE INVENTION
In accordance with the present invention, an electrohydraulic
control circuit is provided to control the velocity of the ram
forcing casting material such as molten metal out of a cylinder
into a die cavity in accordance with the position of the ram to
provide most efficient metal flow at all times during casting. In
accomplishing this result, the position of the ram is sensed at a
plurality of points and an electric signal is supplied to hydraulic
servo means corresponding to each position of the ram for varying
the hydraulic drive for the ram in accordance with the position of
the ram.
The electric signal may also be changed in accordance with a
plurality of other parameters including the position of the
hydraulic valve metering fluid to drive the ram, the pressure in
the shot cylinder from which the molten metal is forced, the
velocity of the ram, and the pressure of the metal in the casting
cavity. Control of the ram velocity may be either from a single
large electrohydraulic servo valve or a large hydraulic main valve
may be controlled by a smaller pilot electrohydraulic servo
valve.
BRIEF DESCRIPTION OF THE DRAWING
The FIGURE is a partly block, partly diagrammatic illustration of
the electrohydraulic control circuit of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The electrohydraulic control circuit 10 illustrated in the FIGURE
includes a multiple slidewire resistance circuit 12, a switching
circuit 14, a first comparator 16, a first amplifier 18, a second
comparator 20, a second amplifier 22, an electrohydraulic servo
valve 24, a main hydraulic valve 26, a ram cylinder 25, a ram 27
and a shot cylinder 28 for forcing molten aluminum into a die 30
having a die cavity 32 therein.
Control circuit 10 further includes a ram position electric pulse
generator 34, a die cavity pressure to electric signal transducer
36, a ram velocity to electric signal transducer 38, a shot
cylinder pressure to electric signal transducer 40 and a main
hydraulic valve position to electric signal transducer 42.
More specifically, the multiple slidewire resistance circuit 12
which is a purchased item of commerce includes a resistance network
44 connected across a power source, and a plurality of separate
slides 46 associated with different output conductors 48. The
slides 46 may be moved vertically as indicated in the FIGURE to tap
off a greater or lesser signal from the resistance network 44 which
will appear at the output terminal 48 associated with the
particular slide.
Thus, in use a plurality of selected voltages may be provided at
the output terminals 48 of the multiple slidewire resistance
circuit 12 which are selected in accordance with a predetermined
velocity program for the ram 27 in the shot cylinder 28. Further,
the velocity program for the ram 27 will be graphically indicated
on the multiple slidewire resistance circuit 12 by the position of
the slides thereon. Thus, a slide position closer to the power
source indicated in the FIGURE would provide a greater output
signal from the multiple slidewire resistance circuit on the output
conductor associated therewith and thus produce a greater hydraulic
fluid flow and more rapid movement of the ram 27, as will be seen
subsequently.
The selection of a signal from a particular output terminal of the
multiple slidewire resistance circuit 12 by the switching circuit
14 may be by any convenient means such as a rotary stepping switch
responsive to each count of a counter, if desired. In practice, the
switching circuit 14 has included a binary counter in conjunction
with a plurality of separate amplifiers and appropriate logic
circuitry to actuate a different field effect transistor associated
with each of the output signals and thus pass each of the output
signals represented by the positions of the slides on the multiple
slidewire resistance circuit in response to a corresponding
position of the ram 27. Other switching circuits are possible
actuated by the pulse generator 34 and operable to pass the output
signals from the switching circuit 14 in accordance with the
program of the multiple slidewire resistance network in response to
pulses from the pulse generator 34 indicating the position of the
ram 27.
The signals from the switching circuit 14 are passed to a
conventional comparator 16 where they are changed in accordance
with the pressure in the shot cylinder 28, the velocity of the ram
27 and the pressure in the die cavity 32, if desired. Control in
accordance with these additional parameters is not essential to the
operation of the control circuit 10. Control in accordance with
these additional parameters is, however, useful wherein control of
the velocity of the ram in accordance with the position of the ram
does not optimize the other indicated parameters.
The signal from the amplifier 18 is then passed into an additional
comparator wherein the signal is altered in accordance with the
velocity of the spool of the main hydraulic valve 26. The final
control signal from the comparator 20 is fed through the amplifier
22 and in the embodiment of the invention illustrated is used to
control an electrohydraulic servo valve 24.
The electrohydraulic servo valve 24 is a pilot valve and is used to
control the position of the spool in the main hydraulic valve 26.
The main hydraulic valve 26 in turn controls the flow of hydraulic
fluid to the ram cylinder 25 and thus the velocity of the ram 27 in
accordance with the signal received by the electrohydraulic servo
valve 24 from the switching circuit 14 through the comparators 16
and 20 and associated amplifiers 18 and 22.
The pulse generator 34 which may be, for example, an
electromagnetic structure positioned adjacent ram 27 for
determining the position thereof or may be a photoelectric cell 35
operable in conjunction with mechanical means 37 carried by the ram
to provide pulses of energy representing the position of the ram is
effective to provide an output signal to the switching circuit 14
in accordance with the position of the ram 27. Thus, if for
example, the ram 27 has a 48-inch travel and it is desired to
change the velocity of the ram every 2 inches, 24 mechanical
actuating means 37 may be positioned every 2 inches along the path
of the ram operable in conjunction with one photoelectric cell to
produce an electric pulse each time the ram moves 2 inches.
In overall operation, the ram 27 is backed up past the inlet gate
52 of the shot cylinder 28 and liquid metal such as aluminum is
placed in the shot cylinder. When the shot cylinder has the
required charge therein, the ram 27 is caused to move toward the
die 30. Movement of the ram is slow past the inlet gate 52. The
velocity of the ram is controlled in accordance with the settings
of the slides on the multiple slidewire resistance circuit 12 and
is changed with each pulse from generator 34 since the pulses from
generator 34 change the effective output conductor from the
multiple slidewire resistance circuit 12 through switching circuit
14 to provide a single electric output signal to the comparator 16
which varies in accordance with the position of the ram 27.
The single output signal from switching circuit 14 modified by the
signals from the main hydraulic valve spool position to electric
signal transducer 42, the shot cylinder pressure to electric signal
transducer 40, the ram velocity to electric signal transducer 38
and the die cavity pressure to electric signal transducer 36
through comparators 16 and 20 and amplifiers 18 and 22 actuates the
electrohydraulic servo valve 24 to position the main hydraulic
valve 26, thus providing the desired control of the velocity of ram
27.
While one modification of the invention has been considered in
detail, it will be understood that modifications and other
embodiments of the invention are contemplated. Thus, for example,
other structures may be used for the multiple slidewire resistance
circuit 12 to establish a program for the velocity of the ram 27
and other switching circuits than those disclosed may be
substituted for the switching circuit 14. It is the intention to
include all embodiments and modifications suggested by the above
disclosure within the scope of the appended claims.
* * * * *