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BACKGROUND OF THE INVENTION
The present invention relates to an arrangement for control of a hydraulic
motor, the two opposite faces of which to be impinged by pressure fluid
are operatively connected with a first valve means for controlling the
direction of movement of the motor, in which second valve means are
connected in a hydraulic circuit with the first valve means for
controlling the speed of the motor and in which further control means are
provided which are actuated from a movable member of the motor to
influence the change of the speed of the motor dependent on the position
of the movable member.
In a known arrangement of this type for control of the advancing movement
of a member of a machine tool, a separate block is provided for
controlling the speed in which for two advancing movements of a
reciprocating drive two fluid stream controllers, a four-way solenoid
operated valve, as well as a roller actuated delay valve are provided. The
roller actuation is necessary in order to assure a smooth deceleration of
large masses between exactly determined end positions. The roller
actuation requires, however, to space the block for control of the speed a
certain distance from the block for control of the direction of the
movable member of the tool machine, in which the two blocks have to be
connected by conduits with each other. Such an arrangement requires
therefore a relatively large space. In addition the adaptation of the
arrangement for different load conditions is cumbersome.
It is also known to use in a control arrangement of the aforementioned kind
an electrohydraulic servo valve and external electronic signal receivers.
The disadvantage of this known arrangement is, however, that its operating
safety is far from perfect and also that it is very expensive to produce.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a control arrangement
of the aforementioned kind which avoids the mentioned disadvantages of
such control arrangements known in the art.
It is a further object of the present invention to provide for such control
arrangements which can be produced at very reasonable cost, while
providing at the same time an optimal operating safety.
With these and other objects in view, the control arrangement of the
invention for controlling the direction of movement and speed of a
hydraulic motor, having a movable member with a pair of opposite faces to
be alternately impinged by pressure fluid, mainly comprises first valve
means for controlling the direction of movement of the movable member,
second valve means for controlling the speed of the movable member in
dependence on the position thereof and comprising a throttle valve in one
of the conduits feeding pressure fluid to a respective one of the opposite
faces, in which the throttle valve includes a valve slide movable between
a plurality of positions respectively controlling the amount of pressure
fluid passing therethrough, a pressure reducing valve upstream of the
throttle valve in the aforementioned conduit, and a proportional magnet
connected to the valve slide for moving the same between the positions
thereof. The control arrangement includes further a first inductively
operating transducer connected with the proportional magnet into a
feedback position control circuit, a first electrical control device
coordinated with the feedback position control circuit, control means
actuated by the aforementioned movable member and influencing change of
the speed of the latter in dependence on the position thereof, which
control means includes at least a second inductively operating position
transducer for indicating the actual value of displacement of the movable
member, and in which the control means forms part of a second feedback
circuit.
In this way a control arrangement is derived which is relatively simple in
its construction and which assures a high degree of safety, whereby the
valves for controlling the direction of movement and speed of the movable
member can be arranged closely to each other. In addition, the control
arrangement will operate relatively fast and exact.
An especially high degree of operational safety is derived, which can be
produced with relatively small additional cost, if a third inductively
operating position transducer is provided which forms with the second
position transducer a redundant control circuit and which is operatively
connected with a second electrical control device, which in turn is
operatively connected with the first electrical control device and a
differential amplifier into the second feedback circuit.
The novel features which are considered as characteristic for the invention
are set forth in particular in the appended calims. The invention itself,
however, both as to its construction and its method of operation, together
with additional objects and advantages thereof, will be best understood
from the following description of specific embodiments when read in
connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic illustration of the control arrangement according to
the invention for controlling a hydraulic motor; and
FIG. 2 is a partially sectioned side view of the throttle valve of the
control arrangement with the pressure reducing valve, the proportional
magnet and the first inductively operated position transducer directly
connected thereto.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 illustrates an arrangement which includes a hydraulic motor having a
cylinder 11 in which a piston 51, to which a piston rod 51' is connected,
is arranged for reciprocating movement in axial direction. The piston 51
divides the interior of the cylinder 11 into a cylinder compartment 12 to
the right side of the piston 51 and a piston rod compartment 14 to the
left side of the piston through which the piston rod 51' extends. A first
working conduit 13 communicates with the cylinder compartment 12 and a
second working conduit 15 communicates with the piston rod compartment 14.
A first valve means 16 for controlling the direction of movement of the
movable member of the motor, that is the piston 51 and the piston rod 51'
connected thereto, is interconnected with the conduits 13 and 15, for
controlling the direction of movement of the movable member. The valve
means 16 is movable between three positions and is connected by a feed
conduit 17 to a pump 18, providing the pressure fluid for the hydraulic
motor, and by a return conduit 19 to a tank 21, containing the fluid for
the pump 18. To assure maintainance of a predetermined pressure in the
piston rod compartment 14, a pressure gradient valve 22 is arranged in the
second working conduit 15, which reduces the fluid pressure imparted
thereto at the inlet end by a predetermined amount. A first branch circuit
23 with a first check valve 24 is arranged in parallel to the pressure
gradient valve 22. The check valve 24 is arranged to prevent outflow of
fluid from the piston rod compartment 14 over the first branch conduit 23.
A second branch conduit 25 is connected in parallel to the pressure
gradient valve 22 and the first valve means 16, in which a second check
valve 26 is arranged, preventing direct flow of pressure fluid from the
pump 18 through the second branch conduit 25 into the second working
conduit 15 to permit a rapid traverse motion of the movable member 51,
51'.
A throttle valve 27 and a pressure reducing valve 28 upstream of the
throttle valve are located in the first working conduit 13. The pressure
reducing valve 28 is additionally impinged over a control conduit 29 with
the fluid pressure prevailing between the cylinder compartment 12 and the
throttle valve 27 and cooperates with the latter as fluid stream
regulator. A second control conduit 31 leads from the first working
conduit 13 to the pressure gradient valve 22. The throttle valve 27
includes, as shown in FIG. 2, a housing 32 and a valve slide 33
reciprocable in axial direction in a bore of the housing and movable
between a plurality of positions thereof by the armature of a proportional
magnet 34. The proportional magnet 34 is to be understood as a magnet in
which the armature thereof will take different positions depending on the
magnitude of the voltage or the current applied to the magnet winding. A
first inductively operating position transducer 35 is, as shown in FIG. 2,
directly connected to one end of the proportional magnet 34, and the
output 36 of the transducer 35 is connected to a first input 37 of a
differential amplifier 38 for transmitting to the latter signals depending
on the position of the armature of the proportional magnet 34. A second
input 39 of the differential amplifier 38 receives signals from the output
41 of a first electrical control device 42, whereas the output 43 of the
differential amplifier 38 is connected in circuit with the input 44 of the
porportional magnet 34. The proportional magnet 34 is therewith connected
into a feedback position circuit 45. The fluid connections for the unit
comprising the throttle valve 27 and the pressure reducing valve 28 are
designated in FIG. 2 with the reference numerals 20 and 30.
The first electrical control device 42 has five inputs 46, 47, 48, 49, and
50, and the first input 46 is connected with a second inductively
operating position transducer 52, which serves during outward movement of
the piston rod 51' as an actual valve transducer for regulation of the
change of the speed of the piston rod 51'. The second input 47 is
connected with a limit switch 53, the third input 46 and the fourth input
49 are respectively connected with desired value setting means 54 and 55
for two different advancing speeds of the piston rod 51', and the fifth
input 50 is connected with retardation course setting means 56. The
throttle valve 27 is therefore located in a second feedback circuit to
which the actual position values are applied from the second position
transducer 52 and the desired values from the setting means 54, 55 and 56.
In order to obtain a redundant control circuit, a third inductively
operating position transducer 58 operable from the piston rod 51' is
provided in addition to the second transducer 52 and the output of the
third position transducer 58 is connected in circuit with the input 59 of
a second electrical control device 61, the second input 62 of which is
connected in circuit with the control output 63 of the differential
amplifier 38. In addition, an operative connection 64 is provided between
the electrical devices 42 and 61. The output 65 of the second electrical
control device 61 is connected with the setting means 66, which controls
the magnets 67 and 68 of the valve 16 for moving the latter between the
positions thereof. The output 65 is further connected with an additional
magnet 69 provided on the throttle valve 27. As schematically shown in
FIG. 1, the second and third inductively operating position transducer
means include each a cam 52', respectively 58', which are operatively
connected in a manner not shown in FIG. 1, to the piston rod 51' for
movement therewith in longitudinal direction and respectively cooperating
with roller follower means to displace the latter in the direction as
indicated by the double-headed arrows, to thereby produce inductively, in
a manner known per se, signals depending on the position of the follower
means which signals, as mentioned before, are respectively transmitted to
the first and second electrical control devices 42 and 61.
The throttle valve 27 comprises, as shown in further detail in FIG. 2, a
housing 32 formed with a longitudinal bore therethrough which is
intersected by a plurality of fluid passages. The valve slide 33 is
axially movable in the longitudinal bore of the throttle valve 27, and the
valve slide 33 has a first and a second control edge 71, respectively 72
which overlap the fluid passages formed in the housing 32 to different
degrees. The throttle valve 27 is thereby connected to the pressure
reducing valve 28 in such a manner that it can be flown through with
pressure fluid in parallel at both control edges 71 and 72. As shown in
FIG. 2, the fluid enters the housing 73 of the pressure reducing valve 28
through the inlet 20 passes then through a plurality of bores 75 and an
annular groove communicating therewith in the bushing 74 fixedly arranged
in a bore of the housing 73 through an opening 77 in the peripheral wall
of the cup-shaped valve member 76 into the interior of the latter and from
there into the axial bore of the housing 73 to the right side of the valve
member 76. From there the fluid passes through bore 78 in the housing 73
and an aligned bore portion in the housing 32 of the throttle valve 27
into a passage 79 surrounding the land 85 of the valve slide or valve
spool 33 of the throttle valve 27. At the same time, fluid from the axial
bore in the housing 73 of the pressure reducing valve 28 passes also
through a passage 80, shown in dotted lines in FIG. 2, into the annular
passage 81 formed in the housing 32 between the two lands 85 and 86 of the
valve spool 33. In the position of the valve spool 33 as shown in FIG. 2
which corresponds to the position shown in FIG. 1, pressure fluid does not
flow from the inlet 20 to the outlet 30 of the pressure reducing valve 28.
However, if the valve slide 33 is moved by the proportional magnet 34 to a
first position in which the control edge 71 enters into the annular
passage 79, then a restricted flow of fluid will pass from the annular
passage 79 past the control edge 71 into the curved passage 83 formed in
the housing 32 and from there through the bore portion 84 shown in dotted
lines to the outlet 30.
It will be noted that the land 86 is longer than that of the land 85 and
that in the above-described first position of the valve slide 33 the flow
connection between the annular passage 81 and the outlet 30 is still
interrupted.
However, if valve slide 33 is now moved by the proportional magnet 34
further to the right, as viewed in FIG. 2, to a second position so that
the control edge 72 enters into the annular passage 87 a second flow path
will be opened and additional fluid will flow from the annular passage 81
into the annular passage 87 and from there through the bore 88 into the
outlet 30 of the pressure reducing valve 28 while the first described flow
path remains open. The various cross sections are so dimensioned that the
valve 27 controls with its first control edge 71 the fine regulating
region for small fluid streams (for instance about 10 liters per minute),
whereas for larger fluid streams fluid may also pass past the second
control edge 72.
The proportional magnet 34 together with the first position transducer 35
are connected to one end face of the housing 32. The additional magnet 69,
not shown in FIG. 2, is connected to the opposite end face of the housing
32.
The above described arrangement will operate as follows:
If the arrangement 10 is not actuated, the first working conduit 13 is
interrupted by the throttle valve 27, when the latter is in the position
as shown in FIG. 1, and the piston 51 with its piston rod 51' is thereby
hydraulically blocked in the cylinder 11.
In order to move the piston rod 51' out of the cylinder 11, the valve slide
of the valve 16 is moved by means of the direction setting means 66 and
the magnet 67 towards the right, as viewed in FIG. 1, so that pressure
fluid from the pump 18 flows over the first working conduti 13 into the
cylinder compartment 12. At the same time, pressure fluid flows from the
piston rod compartment 14 over the second working conduit 15, the second
branch conduit 25 with the check valve 26, into the feed conduit 17
resulting in a rapid traverse speed control. The pressure gradient valve
22 is thereby not yet active since the prevailing pressure level is still
too small. The setting means 54 for the rapid traverse speed is actuated
simultaneously with the direction setting means 66, whereby the first
electrical control device 42 acts over the differential amplifier 38 unto
the proportional magnet 34. The valve slide 33 of the throttle valve opens
thereby widely so that a large pressure fluid stream, necessary for the
fast transverse speed, may flow in parallel past both control edges 71 and
72, from the pressure reducing valve 28 into the cylinder compartment 12.
The thereby prevailing position of the armature of the proportional magnet
34 and therewith that of the control slide 33 is inductively determined by
the first position transducer 35 and is transmitted by corresponding
electrical signals to the differential amplifier 38. The displacement time
for the armature of the position regulated proportional magnet is thus
below the switching time of normal magnet valves. In order to obtain an
exact speed regulation independent of the load, the pressure reducing
valve 28 is connected in series with the throttle valve 27 and this valve
combination acts therewith as electrically stepless adjustable fluid
stream regulator with a highly progressive characteristic curve.
If the arrangement is used in a machine tool, the piston rod 51' moving out
of the cylinder 11 moves a workpiece as fast as possible closely adjacent
to a tool, whereafter the workpiece has to be decelerated within an
exactly determined short stroke from the rapid traverse speed to a working
speed. The outwardly moving piston rod 51' actutates thereby by means of
the cams 52' and 58', after a fast traversed partial stroke, the second
and third position transducers 52 and 58 simultaneously. The second
position transducer 52 transmits thereby electrical signals proportional
to its stroke to the first electrical control device 42 which,
corresponding to the signal transmitted, controls, by means of the
amplifier 38 and the position controlled proportional magnet 34, the
position of the valve slide 33 in the throttle valve 27 and therewith the
amount of pressure fluid passing therethrough, for instance by closing the
flow path controlled by edge 72. The signals at the output 41 of the first
electrical control device 42 are thereby also influenced by the
preprogrammed value of the setting means 55 for the working speed, as well
as from the preprogrammed retardation course of the setting means 56, in
order to control the transition from the fast traverse speed to the
working speed corresponding to the signals of the second transducer means
52. By means of the reterdation course setting means 56, the retardation
course can thus be influenced in such a manner that, withouth displacement
of the cam 52' , different retardation courses and therewith an optimal
retardation of even large masses connected to the piston rod 51' may be
obtained.
The signals form the third position transducer 58, which is operated in
synchronism with the second position transducer 52, are transmitted to the
second electrical control device 61 and there compared with the desired
value signals from the first electrical control device 42 and/or with a
difference signal from the amplifier 38. If this comparison shows that the
actual retardation at the piston rod 51' differs too much from the desired
value of the retardation, then a fast disconnection is actuated. Thereby,
the second control device 61 may, by means of the direction setting means
66, act on the valve 16 and return the control slide thereof to the middle
position, as shown in FIG. 1. A retardation is thereby obtained which will
depend on the actuating time of the magnet 67 and on the throttle cross
section of the throttles provided in the valve 16. In addition thereto,
the throttle valve 27 is quickly disconnected by the first electrical
control device 61 over an additional magnet 69 and therewith the first
working conduit 13 will be more or less throttled or interrupted. As long
as the piston rod 51' moves out with a working speed from the cylinder 11,
the amount of pressure fluid flowing through the cylinder compartment 12
is so small that it will be controlled by the first control edge 71 of the
throttle valve 27. In this especially advantageous manner it is possible
to control pressure fluid streams of largely varying size (for instance
one to hundred) with the same valve.
If the piston rod 51', which moves with working speed out of the cylinder
11, finally actuates the limit switch 53, further advance of the piston
rod is stopped by the first electrical control device 42. During the time
the piston rod 51' moves with its working speed out of the cylinder 11,
pressure fluid from the piston rod compartment 14 flows, in a manner known
per se, over the pressure gradient valve 22 to the valve 16 and further to
the tank 21.
In order to move the piston rod 51' into the cylinder 11, the magnet 68 is
energized by means of the direction setting means 66, to thereby actuate
the valve slide of the valve 16 in such a manner that the pump 18 is
connected over the first branch conduit 23 and the second working conduit
15 with the piston rod compartment 14 and the cylinder compartment 12 over
the first working conduit 13 and the valve 16 with the tank 21. Thereby
the inward movement of the piston rod may be controlled either by the
throttle valve 27 or only by the amount of pressure fluid pumped by the
pump 18.
The arrangement 10 assures thereby, even by breakdown of one element, with
maximum safety and small expenditure a quick disconnection of the drive
especially to prevent abutment of a tool at high speed onto a workpiece.
In addition, all hydraulic valves of the arrangement may be connected in
advantageous manner into a single block. Advantageous is further that an
exact electrically controlled deceleration function, as well as adjustment
to any desired speed can be carried out with a throttle valve and
corresponding setting means for preprogramming. Advantageous is also the
avoidance of bouncing during the start of the arrangement since the
pressure reducing valve is already in its working position during speed
changes. The arangement is further immune against fauling since it
requires no small hydraulic control streams. By actuating the valve 16 and
the throttle valve 27 simultaneously it is also possible to obtain soft
switching transitions.
It will be understood that each of the elements described above, or two or
more together, may also find a useful application in other types of
arrangements for control the speed of hydraulic motors differing from the
types described above.
While the invention has been illustrated and described as embodied in an
arrangement for controlling the speed and direction of a hydraulic motor,
it is not intended to be limited to the details shown, since various
modifications and structural changes may be made without departing in any
way from the spirit of the present invention.
Thus, for instance, it is possible to use only one of the above described
possible arrangements for the quick disconnection. The comparison between
desired value and actual value in the second electric control device may
also be carried out in different ways. Of course, it is also possible to
adapt the disclosed arrangement for more than two working speeds. The
division of the different fluid streams at different speeds by the two
control edges of the throttle valve is also variable.
Without further analysis, the foregoing will so fully reveal the gist of
the present invention that others can, by applying current knowledge,
readily adapt it for various applications without omitting features that,
from the standpoint of prior art, fairly constitute essential
characteristics of the generic or specific aspects of this invention.
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