U.S. patent number 3,774,641 [Application Number 05/239,396] was granted by the patent office on 1973-11-27 for electrohydraulic control arrangement for hydraulic actuators.
Invention is credited to Karl-Heinz Adler, Heinz Flaschar, Reinhard Mindner, Klaus Schneider.
United States Patent |
3,774,641 |
Mindner , et al. |
November 27, 1973 |
ELECTROHYDRAULIC CONTROL ARRANGEMENT FOR HYDRAULIC ACTUATORS
Abstract
A control arrangement for hydraulic actuators in which two
hydraulic transmission lines communicating with the actuator are
closed when the control slide of a control valve is in neutral
position. Inlet and return lines communicate with the hydraulic
transmission lines in alternate operative positions of the control
slide. The control slide is actuated by a piston moving within a
control cylinder. Working fluid is applied to the control cylinder
through electromagnetically actuated valves. A remote control lever
provides an adjustable input parameter through a transducer. The
electromagnetically actuated valves are operated by a regulating
amplifier as a function of the input parameter established by the
remote control lever. Two flow lines communicate with the control
cylinder and are connected to the inlet and return lines by two
electromagnetically actuated valves. Threshold switching circuits
are connected between the signal amplifiers used to energize the
electromagnetically actuated valves and the regulating
amplifier.
Inventors: |
Mindner; Reinhard (Gutenberg,
DT), Adler; Karl-Heinz (Leonberg, DT),
Flaschar; Heinz (Asperg, DT), Schneider; Klaus
(Ludwigsburg, DT) |
Family
ID: |
5802811 |
Appl.
No.: |
05/239,396 |
Filed: |
April 11, 1972 |
Foreign Application Priority Data
|
|
|
|
|
Mar 26, 1971 [DT] |
|
|
P 21 14 639.4 |
|
Current U.S.
Class: |
137/625.64 |
Current CPC
Class: |
B66C
13/54 (20130101); B64C 13/00 (20130101); F15B
9/09 (20130101); Y10T 137/86614 (20150401); B66C
2700/085 (20130101) |
Current International
Class: |
B64C
13/00 (20060101); B66C 13/00 (20060101); B66C
13/54 (20060101); F15B 9/09 (20060101); F15B
9/00 (20060101); F16k 011/00 () |
Field of
Search: |
;137/625.64,625.66,625.65,625.69,554,487.5
;251/131,130,14,25,63,78 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Klinksiek; Henry T.
Assistant Examiner: Miller; Robert J.
Claims
What is claimed as new and desired to be protected by Letters
Patent is set forth in the appended claims:
1. An electrohydraulic control arrangement for hydraulic operating
means operative in two directions comprising, in combination, a
control valve with control slides; two hydraulic transmission lines
communicating with said operating means and closed by said control
slide when in neutral position in said control valve; inlet line
means communicating with one of said hydraulic transmission lines
when said control slide is in a first operative position; return
line means communicating with the other one of said hydraulic
transmission lines when said control slide is in a second operative
position; control piston means movable within a control cylinder
and actuating said control slide; electromagnetically actuated
valves for applying working fluid to said control cylinder; remote
control lever means for providing an adjustable input parameter;
regulating amplifier means actuating said electromagnetic valves as
a function of said input parameter; two flow lines communicating
with said control cylinder and connected to said inlet line means
and said return line means by two of said electromagnetically
actuated valves; signal amplifying means connected to said
electromagnetically actuated valves for actuating said
electromagnetically actuated valves; and threshold switching means
connected between said signal amplifying means and said regulating
amplifying means.
2. The arrangement as defined in claim 1 wherein a first one of
said electromagnetically actuated valves is connected between said
inlet line means and said two electromagnetically actuated valves,
said first one of said electromagnetically actuated valves being
closed when said remote control lever means is in 0 position.
3. The arrangement as defined in claim 2 including a close control
lever for actuating said control slide when said first one of said
electromagnetically actuated valves is closed and said two
electromagnetically actuated valves are open.
4. The arrangement as define in claim 2 including a dead center
circuit; an input parameter transducer actuated by said remote
control lever means; and a first amplifier in said signal
amplifying means connected to said first one of said
electromagnetically actuated valves, the input of said first
amplifier being connected through said dead center circuit to said
input parameter transducer.
5. The arrangement as defined in claim 4 wherein said dead center
circuit comprises two threshold switching circuits having different
threshold levels, the input of one threshold switching circuit
being connected with a first input of the other threshold switching
circuit, the output of said one threshold switching circuit being
connected to a second input of the other threshold switching
circuit.
6. The arrangement as defined in claim 4 including AND-gates
connected to a second amplifier and a third amplifier in said
signal amplifying means; a threshold switching circuit connected to
a first input of each AND-gate, the second inputs of said AND-gates
being connected to said dead center circuit.
7. The arrangement as defined in claim 6 including an AND-gate
connected to the input of said first amplifier, a first input of
said AND-gate connected to said first amplifier being connected to
said dead center circuit, said AND-gate connected in front of said
first amplifier being a first AND-gate and said AND-gates connected
to said second and third amplifiers being respectively second and
third AND-gates; a fourth AND-gate connected between the second
input of said first AND-gate and the outputs of said second and
third AND-gates.
8. The arrangement as defined in claim 4 including an amplifying
stage connected in series with the input of said dead center
circuit.
9. The arrangement as defined in claim 1 including output parameter
transducer means actuated by said control slide; input parameter
transducer means actuated by said remote control lever means; and
summing means with inputs connected to said input and output
parameter transducer means, the output of said summing means being
connected to said regulating amplifying means.
10. The arrangement as defined in claim 7 wherein said threshold
switching circuits and said AND-gates are two-stage, positive
feedback-coupled transistor amplifiers with two transistors of
complementary conductivity type.
11. The arrangement as defined in claim 10 including base voltage
divider means connected to a first one of said two transistors in
said threshold switching circuits for setting the threshold voltage
of said threshold switching circuit; and diode means for applying
to the emitter of said first transistor the input voltage
signal.
12. The arrangement as defined in claim 10 including diode means
connected to the emitter of a first transistor of said AND-gates
for applying input voltage signals to the emitter of said first
transistor of said AND-gates.
13. The arrangement as defined in claim 4 including second and
third AND-gates connected to second and third amplifiers in said
amplifying means; and pulse stretcher modulator means connected to
first inputs of said second and third AND-gates, the second inputs
of said AND-gates being connected to said dead center circuit, said
pulse stretcher modulator means controlling intermittently said
electromagnetically actuated valves when the output signals of said
regulating amplifier means are substantially small, said
electromagnetically actuated valves being continuously unactuated
when the output signals of said regulating amplifier means are
substantially large.
14. The arrangement as defined in claim 13 wherein said pulse
stretcher modulator comprises an operational amplifier with a first
resistor connected between the output of said amplifier and one
input thereof, and a second resistor connected between the output
of said operational amplifier and a circuit input thereof; an input
resistor connected to the inverting input of said operational
amplifier, on terminal of said input resistor being the input
signal terminal; and a capacitor connected between said input
resistor and ground potential.
15. The arrangement as defined in claim 9 including a third
threshold switch connected to the output of said output parameter
transducer means; and a forth threshold switching circuit connected
to the output of said summing means.
16. The arrangement as defined in claim 15 including a first
OR-gate and a second OR-gate, the output of said third threshold
switching circuit being connected to said second OR-gate and to
said first OR-gate; a first inverter circuit connected between said
output of said third threshold switching circuit and said first
OR-gate; a second inverter circuit connected between the output of
said fourth threshold switching circuit and said second OR-gate,
the output of said fourth threshold switching circuit being also
connected to said first OR-gate, the outputs of said OR-gates being
connected to the inputs of said first AND-gate.
17. The arrangement as defined in claim 7 wherein said fourth
AND-gate comprises a NAND-gate.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an electrohydraulic control
arrangement for use in conjunction with a hydraulic actuator which
is operable in two directions. A control valve is provided with a
control slider which closes two lines to the actuator when in
neutral position. A regulating amplifier controls the precontrol
valves as a function of an input parameter set by a remote control
lever.
A control arrangement of the preceding known species is already
known in the art for actuating the altitude rudder or flaps of an
aircraft. In such an arrangement known in the art, the output
parameter or value from the deflection angle of the rudder is
applied to a second input of the regulating amplifier, so that for
every position of the remote control lever, a predetermined
deflection angle of the rudder is attained. In other hydraulic
actuators, as for example in automotive cranes, which are driven by
double acting hydraulic cylinders or by a hydraulic motor with
radial head, it is desired, however, to regulate the velocity
rather than the final position.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a control
arrangement in which a predetermined velocity of the hydraulic
actuator corresponds to every position of the remote control lever.
In the use of an automotive crane, for example, the velocity of the
load fork or distributor is to be set or established.
Another object of the present invention is to provide an
arrangement for controlling a hydraulic actuator, as set forth,
which is simple and design and may be readily fabricated.
A still further object of the present invention is to provide an
arrangement of the foregoing character which may be economically
manufactured and economically maintained in service.
Another object of the present invention is to provide an
arrangement of the foregoing character which is reliable in
operation.
The objects of the present invention are achieved by providing that
the control cylinder is in the form of a double acting cylinder
with two communicating lines. A second and a third precontrol valve
connect the two communicating lines with inlet and return lines.
Each precontrol valve may be actuated through a magnetic winding
which, in turn, is energized by a signal amplifier. The signal
amplifiers are connected, through threshold switching circuits, to
the output of the regulating amplifier.
In an automotive crane it is advantageous when the operating
personnel of the crane, can operate the crane directly when on the
vehicle for the crane, as well as from a remote location through a
cable. Such possibility is realized with a further embodiment of
the present invention, in which a first precontrol valve lies
between the inlet line and the two other precontrol valves. The
first precontrol valve is closed when the remote control lever is
in its 0 position. When the first precontrol valve is closed,
furthermore, the control slide may be actuated by a close control
lever.
The velocity of the hydraulic actuator or operating arrangement may
be precisely regulated or set, in accordance with a further
embodiment of the present invention, by providing that an output
parameter or value transducer may be actuated by the control slide.
The output transducer and the input transducer are both connected
to a summing device in front of the regulating amplifier.
The novel features which are considered as characteristic for the
invention are set forth in particular in the appended claims. 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 drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic diagram of the hydraulic arrangement in
conjunction with the electronic control circuitry, in accordance
with the present invention;
FIGS. 2-4 are electrical circuit diagrams of operating circuits
shown in block form in FIG. 1;
FIG. 5 is a block diagram of a second embodiment of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawing and in particular to FIG. 1, a hydaulic
operating unit has a double-acting cylinder 11 in which a piston
head 12 moves with a piston rod 13. The cylinder 11 is connected to
a control valve through lines 14 and 15. Within a housing 16 of the
control valve, is a slider bore 17 which guides closely a control
slide 23. The slide bore 17 communicates with five chambers 18, 19,
20, 21, 22 and a control cylinder 27. The central chamber 20 is
connected with an inlet line 57 through a check valve 33. The two
chambers 19, 21 on both sides of a central chamber 20, are
connected with the lines 14, 15, while the outer chambers 18, and
22 are connected to the return line 37.
The control slide 23 is subdivided into three slider sections by
two necked-down portions 24, 25. In the neutral position of the
control slide 23, the three slider sections lie closely opposite
the chambers 18 to 22, as shown in FIG. 1. At the right end of the
control slide 23, is a control piston head 26 which is designed in
the embodiment in the form of a differential piston, and is movable
within the control cylinder 27. At the left end of the control
slide 23, is an extension 29 which actuates, on the one hand, a
double-acting return or resetting arrangement. This extension 29
also is connected, on the other hand, mechanically with a control
lever 30 and an output transducer 47.
The inlet line 57 is provided with pressurized fluid from a storage
reservoir 31, by means of a pump 32. A hydraulic series-connected
circuit between the inlet line 57 and the return line 37, consists
of the series combination of a first control valve 34, a first
throttle 35, a second control valve 36, a third control valve 38,
and a second throttle 39. The control cylinder 27 is, on one hand,
connected through a first line 58, to the connecting line between
the first control valve 34 and the first throttle 35. The control
cylinder 27 is also connected, on the other hand, through a line
59, to the connecting line between the second control valve 36 and
the third control valve 38.
The control valves 34, 36 and 38 become actuated by the
electromagnet windings 34a, 36a and 38a. Each winding becomes
controlled from an amplifier 40, 41, 42, respectively.
A remote control lever 55 actuates an input transducer 48 which has
an output connected to a dead-center element 50, through an
amplifier stage 49. Connected with the output of the dead-center
element 50, are the first inputs of three AND-gates 43, 44 and 45.
These AND-gates are, in turn, connected to amplifiers 40, 41 and
42, with their outputs. The second input of the first AND-gate 43
is connected, through a fourth AND-gate 46, with the outputs of the
second and third AND-gates, 44 and 45, respectively. The AND-gate
46 is constructed in the form of a NAND-gate.
The second inputs of the second and third AND-gate 44, 45 are
connected each, by way of threshold switches 53, 54, to the output
of a regulating amplifier 52. A summing device 51 is connected to
the input of this regulating amplifier 52. The input transducer 48
and the output transducer 47 are connected to the inputs of the
summing device 51.
FIG. 2 shows the circuit diagram of the second threshold switch 54,
the third AND-gate 45 and the third amplifier 42. The second
threshold switch 54 is designed in the form of a two-stage,
feedback-coupled amplifier with two transistors 540, 541 of
opposite conductivity type. The first transistor 540 has a base
voltage divider 546, 547, an emitter-resistor 544, and a collector
resistor 542. The collector of the first transistor 540 is
connected to the base of the second transistor 541. The collector
of the second transistor 541 is connected, through a feedback
resistor 545, to the base of the first transistor 540. This
collector of the second transistor 541 is also connected, through a
collector resistor 543, to the positive voltage supply line 60. The
emitter of the first transistor 540 forms the input of the second
threshold switch 54, and is connected, through a diode 548, to the
output terminal 52a of the regulating amplifier 52.
The third AND-gate 45 is similar to the second threshold switch 54
in the form of a feedback-coupled amplifier with two transistors of
opposite conductivity type. Modifications in the circuit design are
realized in the respect that the third AND-gate 45, as shown in
FIG. 1, is designed in the form of a blocking or inhibiting gate
which has a noninverting and one inverting input. In addition, the
second transistor 451 in the third AND-gate 45, has two collector
resistors 453, 453a connected in series. The junction of these two
resistors is connected to the second noninverting input of the
third AND-gate 45. This junction, furthermore, is connected through
a diode 458, to the output of the second threshold switch 54. All
remaining components are the same as in the second threshold switch
54, and are thereby not further described. The reference numerals
are lower by 90, than in the second threshold switch 54.
The third amplifier 42 has a transistor 420 and a power transistor
421. The preamplifying transistor 420 is connected with its base,
to the output of the third AND-gate 45. The emitter of the
preamplifying transistor 420, is connected, through a diode 424, to
the negative voltage supply line 62. The collector of this
transistor 420, furthermore, is connected through two resistors
422, 423, to a nonstabilized positive voltage supply line 61. The
base of the power transistor 421 is connected to the junction
between the resistors 422 and 423. The emitter of the transistor
421 is connected directly with the non-stabilized voltage supply
line 61. The collector of the power transistor 421 is connected,
furthermore, through a resistor 425 and electromagnetic winding
38a, to the negative voltage supply line 62. A series circuit,
moreover, leads from the collector of the power transistor 421, to
a diode 428 and a resistor 427, and from there to the negative
voltage supply line 62, as well as a junction to the feedback
resistor 455 within the third AND-gate 45. Connected in parallel
with the resistor 425, is a storage capacitor 426.
The remaining AND-gates 42, 44 and 46, as well as the first
threshold switch 53 are constructed precisely the same as the
second threshold switch 54. The latter is universally insertable,
since it is possible to connect as many inputs as desired, to the
emitter of the first transistor, through diodes. At the same time,
the threshold level can be set simultaneously with the aid of the
base voltage divider of the first transistor.
The dead-center circuit 50, shown in FIG. 3, consists of two
threshold switches 505, 506 which are also constructed and designed
in the form described above. The threshold level of the switch 505
is set at 7 volts, in the embodiments, and the other threshold
switch is set to 5 volts. The output of the switch 505 is
connected, through a diode 503, to a second output of the other
threshold switch 506. With this arrangement, a positive signal is
emitted at the output terminal 50a of the dead-center circuit 50,
when the input voltage at the terminal 49a is either below 5 volts
or above 7 volts. Within this region, the output terminal 50a is
substantially at the potential of the negative voltage supply line
62.
FIG. 4 shows the circuit diagram of a pulse stretcher modulator,
which can be used in place of the threshold switch 53 or 54. an
operational amplifier 530 serves as the active component, and has a
noninverting input at the junction of two resistors 533, 534, which
form a voltage divider. The inverting input of this operational
amplifier 530, is connected, through an input resistor 537, to an
input terminal 52a. A resistor 531 is connected between the output
of the operational amplifier 530 and the inverting input of the
amplifier. A resistor 532, furthermore, is connected between the
output of the operational amplifier 530, and the noninverting
input. The output of the operational amplifier 530 is, furthermore,
connected directly to an output terminal 53a, and to the positive
voltage supply line 60, through a resistor 536. A capacitor 535 is
connected between the inverting input of the operational amplifier
530, and the negative voltage supply line 62.
The second embodiment shown in FIG. 5, is extensively the same as
the first embodiment. The components and circuits that are the same
in FIG. 5, as they are in FIG. 1, have the same reference numerals,
and are also not further described. In the second embodiment, the
first AND-gate 43 has four inputs, of which two are connected the
same as in the first embodiment. The other two inputs of the first
AND-gate 43 are connected with the outputs of a first OR-gate 73
and a second OR-gate 75. A third threshold switch 70 is connected
to the output of the output transducer 47, and a fourth threshold
switch 71 is connected to the output of the summing device 51. A
first inverter 72 is connected to the output of the third threshold
switch 70, and a second inverter 74 is connected to the fourth
threshold switch 71. The two inputs of the first OR-gate 73, are
connected with the output of the first inverter 72 and the output
of the fourth threshold switch 71. In a similar manner, the two
inputs of the second OR-gate 75 are connected to the output of the
third threshold switch 70 and the output of the second inverter
74.
For the purpose of describing the functional operation of the
electro-hydraulic control arrangement, the arrangement of the
hydraulic valves is described first. Each position of the control
slide 23 corresponds to a predetermined fluid flow from the inlet
line 57 to one of the lines 14, 15. With this arrangement, a
predetermined speed or velocity of the piston head 12 can be
established corresponding to a predetermined position of the
control slide.
The control valves 34, 36, 38, each have two controlled connections
and two positions, and are thereby constructed in the form of
2/2-way valves. In the normal inoperative position, the first
control valve 34 is closed, and the two other control valves 36, 38
are open. It is possible, thereby, to bring the control slide 23
into any desired position, with the aid of the control lever 30. As
a result, any desired velocity of the operating piston head 12 may
be attained. Should the control slide 23 be actuated through the
electro-hydraulic remote control unit with the aid of the remote
control lever 55, then the first control valve 34 becomes opened.
When the control piston 26 is to be moved toward the left, then the
third control valve 38 must be closed, and the second control valve
36 must be opened. In the reverse situation, the second control
valve 36 must be closed and the third control valve 38 must be
opened, in the case that the control piston 26 is to be moved
toward the right. When, finally, the control piston 26 is to be
held at a predetermined position outside of its neutral position,
then the second control valve 36 and the third control valve 38
must be closed.
These four different valve positions are set or established by the
electronic circuit in dependency on the position of the remote
control lever lever 55 and the output signal of the output
transducer 47. In the following description of the functional
operation, the digital circuitry is described in conjunction with
the designations of a 1 signal and 0 signal as in common usage.
When an AND-gate provides a 1 signal, it is implied that its output
is substantially at the potential of the positive supply line 60.
Conversely, when the output of the AND-gate emits a 0 signal, then
the potential of the output of the AND-gate is substantially at the
negative voltage supply line 62. The output transducer 47, the
input transducer 48, the amplifying stage 49 and the regulating
amplifier 52, all provide analog signals. These analog signals are
converted to digital signals in the dead center circuit 50, as well
as in the two threshold switches 53, 54. The remaining circuitry
operates, then, on the basis of only digital signals.
The summing device 51 is designed so that the output signal of the
input transducer 48 is negative, and the output signal of the
output transducer 47 is positive. This summing device 51,
therefore, computes the difference between the input value and the
output value as provided by the transducers. In a practical design,
the input transducer 48 and the output transducer 47 are connected
to the two inputs of a difference amplifier, which serves
simultaneously as the regulating amplifier 52. It is also possible
to design the regulating amplifier 52 so that the latter has an
input, as shown in FIG. 1. With such an arrangement, an inverting
stage must be connected to either the output of the input
transducer 48 or the output of the output transducer 47. Such
inversion is required in the event that the transducer does not
provide already such an inverted signal, relative to the other
transducer. Once such inversion has been realized the two signals
from the two transducers may be applied, through summing resistors,
to the input of the regulating amplifier 52.
The input transducer 48 and the output transducer 47 are designed
so that their output potentials become shifted in the negative
region, when the associated control lever is moved toward the left.
The dead-center circuit 50 provides a 0 signal within a small
region about the 0 position of the remote control lever 55 --within
the so-called dead zone. In all other positions of the remote
control lever 55, a 1 signal is emitted. In the embodiment, the
threshold level of the first threshold switch 53 is set to 5 volts,
and the second threshold switch 54 is set to 7 volts. At the same
time, the output voltage from the regulating amplifier 52 is
established at 6 volts, provided the difference between the input
value and output value is zero. When the input value is equal to
the output value, the first threshold switch 53 provides a 1
signal, and the second threshold switch 54 provides a 0 signal.
When the remote control lever 55 is moved toward the right, then
the dead-center circuit 50 provides a 1 signal, when the dead zone
is exceeded. The output voltage from the regulating amplifier 52 is
shifted, thereby, in the positive direction to the extent that the
threshold level of the second threshold switch 54 becomes exceeded.
At this point, the three circuits 50, 53, 54 each provide a 1
signal. At the output of the second AND-gate 44 is a 1 signal and
at the output of the third AND-gate 45 is a 0 signal. At the output
of the NAND-gate 46, is, thereby, a 1 signal which is applied to
the second input of the first AND-gate 43. A 1 signal is,
henceforth, also available at the output of the AND-gate 43. As a
result, the first two control valves become actuated by the
amplifiers 40 and 41. The control piston 26 moves, consequently, in
the same direction as the remote control lever 55--namely toward
the right.
In view of this arrangement, the output potential of the output
transducer 47 is shifted in the positive direction, and the output
potential of the regulating amplifier 52 is shifted in the negative
direction, until the threshold level of the second circuit 54 is
higher. Then the third AND-gate 45 also provides a 1 signal which,
in turn, actuates the third control valve 38 and, at the same time,
the AND-gate 43 by way of the NAND-gate 46. The first amplifier 40
of the first control valve is thereby switched off. As a result,
some control valves are now closed, so that the control piston 26
becomes blocked in its position. A predetermined velocity of the
operating piston 12 is thereby established, and this piston 12
corresponds precisely to the position of the remote control lever
55, as is required.
If, now, the remote control lever 55 is moved toward the left,
then, after passage through the 0 region and the dead zone, the
threshold level of the first switch 53 becomes the higher value.
Both threshold switches provide, thereby, 0 signals. Since the
third AND-gate 45 is constructed in the form of a blocking or
inhibiting gate and is provided with an inverting input, the output
of this AND-gate 45 provides a 1 signal which is applied to the
third amplifier 42 and thereby the third control valve 38. As a
result, this valve 38 is closed. Since the second control valve 36
becomes simultaneously opened, through the AND-gate 44 and the
amplifier 41, and the first control valve 34 also becomes opened
through the NAND-gate 46, the AND-gate 43 and the amplifier 40, the
control piston 26 is moved toward the left.
In summary, the functional operation of the first embodiment can be
described with the following characteristics: When the remote
control lever 55 is deflected past the dead zone, either the second
control valve 36 or the third control valve 38 is closed, depending
upon the direction of deflection of the lever. Aside from this, the
first control valve 34 becomes opened, through the AND-gate 43 and
the NAND-gate 46. When the remote control lever 55 is deflected,
the first control valve 34 is again closed, through the NAND-gate
46, only until the two other control valves 36 and 38 are
simultaneously closed, when the input value is equal to the output
value and the control piston 26 is to be held in its position.
A particular advantageous of the control arrangement described
above resides in the condition that all digital components of the
circuitry can be constructed from the same circuit elements, as
shown in FIGS. 2 and 3. In the second threshold switch 54,
according to FIG. 2, the base voltage divider 546, 547 of the first
transistor 540, is adjusted so that a voltage of 7 volts is
available at the tap. The first transistor 540 becomes then turned
off, as soon as the potential of the input terminal 52a drops below
7 volts. The voltage drop across the diode 548 and the emitter-base
diode of the first transistor 540 become compensated. As a result
of the positive feedback coupling of the resistor 545, no
continuous collector current of the first transistor is available
when the potential of the input terminal 52a is slowly taken off.
Instead, a rapid switching takes place in the threshold voltage
established by the base voltage divider. From the circuit of the
threshold switch 54, a NAND-gate can be produced in a simple
manner, in that several input terminals can be connected to the
emitter of the first transistor 540, by way of several diodes. Such
a NAND-gate 506 is shown in FIG. 3 as a component of the
dead-center circuit 50. A blocking or inhibiting gate with an
inverting and a noninverting input, as required for the third
AND-gate 45, is obtained when the emitter of the first transistor
450 is used as the first input and the collector of the second
transistor 451 is used as the second input, as shown in FIG. 2 with
respect to the blocking gate 45.
The emitter potential of the transistor 420 in the second power
amplifier 42 is raised by substantially 0.7 volts, through the
diode 424, relative to the potential of the negative voltage line
62. In this manner, the transistor 420 is securely turned off when
the transistor 451 conducts. Power transistor 421 is also turned
off, since the latter is of opposite conductivity type relative to
the transistor 420. In front of the electromagnetic winding 38a, is
the parallel circuit including the resistor 425 and the capacitor
426. Upon turning on the power transistor 421, full operating
voltage is applied, through the capacitor 426, to the winding 38,
until the capacitor 426 has become charged. As a result, a rapid
energizing of the magnet winding 38a is realized. After switching
off the power transistor 421, the energy stored within the winding
38a is dissipated in the two resistors 427 and 425, and the
resistance within the winding 38a. This results from the condition
that the turn-off current of the winding 38a can flow further
through the diode 428.
The dead zone is the allowable deviation or difference between the
input value and output value, or is the region in which the output
signal from the switch 53 is a 1 signal and the output from the
switch 54 is a 0 signal. The dead zone is provided so that
continuous switching or oscillation of the valves is prevented. The
dead zone together with the dead time of the control valves,
determines the maximum allowable displacement velocity of the
control slide 23. This velocity is dependent on the pressure in the
inlet line 57, the dimensions of the throttles 35 and 39, and on
the surfaces of the control pistons. The displacement velocity and
thereby the acceleration of the operating piston 12, is thereby
constant. As a result, reverse accelerations or delays arise under
predetermined conditions, when the remote control lever 55 is
deflected, or when the input value is attained by the output value.
These displacement transitions become softer when the two threshold
circuits 53, 54 become replaced by pulse stretcher modulators.
Such a pulse stretcher modulator is shown in FIG. 4. When the input
terminal 52a has applied to it the potential of the negative
voltage supply line 62, the capacitor 535 is extensively
discharged, and the input potential of the inverting input of the
operational amplifier 130 is below the potential of the
noninverting input, so that the output of the operational amplifier
530 is at positive potential. Thus, the output of the operational
amplifier provides a 1 signal. The potential of the non-inverting
input of the operational amplifier 530 is high, and is determined
through the resistors 532, 533, 534, whereby the resistor 532 is in
parallel, in this case, with the resistor 533. The resistor 536 is
substantially small in relation to the resistors 532, 533 and 534.
When a predetermined potential prevails at the input terminal 52a,
the capacitor 535 becomes charged to the potential of the positive
voltage supply line, through the resistors 536, 531 and 537. As a
result, the potential of the inverting input of the operational
amplifier 530 rises. When this potential exceeds the potential
prevailing at the non-inverting input, the operational amplifier
530 switches state through the coupling resistor 532, and a 0
signal prevails at the output of this amplifier. At the same time,
the potential at the noninverting input shifts in the direction
toward a negative value which is, in turn, determined by the
resistors 533, 534 and 532, whereby the resistor 532 is, in this
case, in parallel with the resistor 534. The capacitor 535
discharges from the original input potential of the input terminal
52a in direction to the potential of the negative voltage supply
line 62, through the resistors 537 and 531. When the potential at
the inverting input is below the potential of the noninverting
input, then the operational amplifier 530 switches again state, and
provides at its output a 1 signal.
This process is repeated periodically, whereby the pulse repetition
frequency of the output pulses of the operational amplifier 530 is
dependent upon the magnitude of the input potential prevailing at
the terminal 52a. When this input potential is sufficiently high,
then the capacitor 535 can no longer discharge sufficiently through
the resistor 531, so that the output of the operational amplifier
530 remains continuously at negative potential.
The pulse stretcher modulator in accordance with FIG. 4 operates
similarly to a threshold switch. Thus, when the input voltage drops
below a predetermined threshold level, then the output provides a
continuous 1 signal. When, on the other hand, the output voltage
exceeds an upper threshold level, then the output provides a
continuous 0 signal. When the input voltage lies between the lower
and upper threshold levels, the pulse stretcher modulator provides
pulses having a repetition frequency dependent upon the magnitude
of the input voltage. The potential difference between the lower
and upper threshold levels is determined through the relationship
between the two resistors 531 and 537. The absolute magnitude of
the two threshold levels is, on the other hand, determined by the
voltage divider 533, 534, 532.
When two pulse stretcher modulators in accordance with FIG. 4, are
used in place of the two threshold switches 53, 54, then the three
control valves 34, 36 and 38 are controlled in a pulse-wise manner
when the output value differs by small amounts from the input
value. As a result, the displacement velocity of the control slide
23 and thereby the acceleration of the operating piston 12 become
essentially smaller. With this arrangement, softer transitions in
the motion are realized. For a smaller dead zone and corresponding
larger positional accuracy, larger final velocities of the control
slides are possible. The rest of the functional operation is
precisely the same as when using the threshold switches.
The dead zone is to be as small as possible for attaining a large
positional accuracy of the control slide 23. At the same time, the
displacement velocity of the control slide is to be, on the other
hand, as large as possible. In order that a stable operation of the
arrangement may be obtained, the dead zone and the dead time of the
valves must be matched. The two requirements of maximum possible
displacement velocity and smallest possible dead zone are in
conflict.
In the first embodiment of FIG. 1, the displacement velocity of the
control slide 23 is larger than the velocity when the control slide
is moved from its 0 position in direction of greater deflection, in
the return process. This results from the condition that upon
deflection or movement from the 0 position, the spring force is
opposed against the hydraulic force in the return arrangement 28,
whereas the spring force adds to the hydraulic force during the
return process. The displacement velocity in the return process
must, therefore, take into account the dead zone.
In order to make possible a smaller dead zone, other force
relationships are selected in the circuit embodiment of FIG. 5.
Thus, the hydraulic force acts on the differential piston 26 only
upon deflection or movement from the 0 position, but not during the
return process. This may be attained because in the return process
the first control valve 34 is basically closed.
To determine whether a deflection process or a return process
prevails, the components 70 to 75 are used. The third threshold
switch 70 determines whether the control slide 23 is either to the
right or to the left of the 0 position, whereas the fourth
threshold switch 71 determines whether the regulating deviation is
either positive or negative, i.e., whether the output value has
already attained the input value or not.
In order that the first control valve 34 becomes opened, all four
inputs of the first AND-gate 43 must have 1 signals. The manner in
which the 1 signals at the first two inputs are derived, is already
described above. These first two inputs are connected with the
outputs of the dead center circuit 50 and the third AND-gate 56.
Assume, now, as an example, that the control slide 23 becomes moved
towards the left, and has not as yet attained the input value. Then
the third threshold switch 70 provides a 0 signal and the fourth
threshold switch 71 also provides a 0 signal, since the output
voltage of the output transducer 47 as well as from the summing
device, are negative. In this case, both inverters 72 and 74
provide 1 signals which are transmitted, through the OR-gates 73
and 75, to the two remaining inputs of the first AND-gate 43. As
soon as the input value is attained, the regulating error or
deviation becomes 0 or positive, and the fourth threshold switch 71
provides a 1 signal. At this point, a 0 signal lies at the third
input of the AND-gate 43, which is connected with the second
OR-gate 75, whereas a 1 signal still lies at the fifth input. As a
result, the first control valve 34 becomes closed. This closing of
the valve also remains when the remote control lever 55 is again
returned to the 0 position. Upon return of the control slide 23,
the control cylinder 27 can thereby have applied fluid from the
first control valve 34.
In the second embodiment of FIG. 5, it is also possible to use
pulse stretcher modulators in accordance with FIG. 4, instead of
the first two threshold switches 53 and 54.
The control arrangement described above, fulfills, consequently,
all of the imposed requirements. The velocity of the operating
piston 12 is set to a constant value through the remote control
lever 55 as well as through the control lever 30. This constant
value depends on the deflection or displacement of the remote
control lever or of the lever 30. When using both stretcher
modulators, it is possible to avoid furthermore accelerations or
delays which are too large for small regulating errors or
deviations. When the remote control lever 55 is at its normal
inoperative position, then the control slide 23 can be actuated
with the aid of the control lever 30. An output value-return is
then made possible to maintain precisely the velocity for the
operating piston 12, which is set by the remote control lever. The
control arrangement is, thereby, particularly adaptable for
automotive cranes, although its area of application is not limited
to this field.
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 electro-hydraulic control arrangements differing from the
types described above.
While the invention has been illustrated and described as embodied
in an electro-hydraulic control arrangement, 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.
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 and, therefore such adaptations should
and are intended to be comprehended within the meaning and range of
equivalence of the following claims.
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