U.S. patent application number 14/380887 was filed with the patent office on 2015-01-15 for method for operating a hydraulic pump arrangement, and hydraulic pump arrangement.
This patent application is currently assigned to LUKAS HYDRAULIK GMBH. The applicant listed for this patent is Dietmar Lindner, Carsten Sauerbier. Invention is credited to Dietmar Lindner, Carsten Sauerbier.
Application Number | 20150017021 14/380887 |
Document ID | / |
Family ID | 45833382 |
Filed Date | 2015-01-15 |
United States Patent
Application |
20150017021 |
Kind Code |
A1 |
Lindner; Dietmar ; et
al. |
January 15, 2015 |
METHOD FOR OPERATING A HYDRAULIC PUMP ARRANGEMENT, AND HYDRAULIC
PUMP ARRANGEMENT
Abstract
A hydraulic pump arrangement of a portable hydraulic tool
operates by an autonomous power supply or is releasably connected
to the hydraulic tool by a hose and driven by an electrical power
source. A load-dependent control of the hydraulic pump switches
between a loaded state and a non-loaded state. A higher electrical
power supply is implemented for the loaded state and a lower
electrical power supply is implemented for the non-loaded state. To
provide energy savings and problem-free operation even in different
system pressure conditions, a method fixes a control variable for
the load-dependent control that is dependent on work being
performed by the hydraulic pump motor. A first threshold value at
which switching from the non-loaded state to the loaded state takes
place and a second threshold value at which switching from the
loaded state to the non-loaded state takes place are assigned to
the control variable.
Inventors: |
Lindner; Dietmar;
(Eckersdorf, DE) ; Sauerbier; Carsten; (Lauf an
der Pegnitz, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lindner; Dietmar
Sauerbier; Carsten |
Eckersdorf
Lauf an der Pegnitz |
|
DE
DE |
|
|
Assignee: |
LUKAS HYDRAULIK GMBH
Erlangen
DE
|
Family ID: |
45833382 |
Appl. No.: |
14/380887 |
Filed: |
February 29, 2012 |
PCT Filed: |
February 29, 2012 |
PCT NO: |
PCT/EP2012/053473 |
371 Date: |
August 25, 2014 |
Current U.S.
Class: |
417/44.1 |
Current CPC
Class: |
F04B 49/22 20130101;
F04B 49/002 20130101; F04B 49/06 20130101 |
Class at
Publication: |
417/44.1 |
International
Class: |
F04B 49/00 20060101
F04B049/00; F04B 49/22 20060101 F04B049/22 |
Claims
1. A method for operating a hydraulic pump arrangement of a
portable hydraulic tool operated by an autonomous power supply,
wherein the hydraulic pump arrangement is releasably connected to
the hydraulic tool by a hose connection and is driven by an
electrical power source and a load-dependent control of the
hydraulic pump takes place by switching from a loaded state to a
non-loaded state and vice versa, wherein a first higher electrical
power supply is implemented for the loaded state and a second lower
electrical power supply is implemented for the non-loaded state,
the method comprising: establishing at least one control variable
for the load-dependent control of the hydraulic pump arrangement
and said control variable is dependent as an input value on work
that to be performed by a motor of the hydraulic pump arrangement,
assigning to the control variables a first threshold value at which
switching from the non-loaded state to the loaded state takes
place, and where necessary assigning to the control variables a
second threshold value at which switching from the loaded state to
the non-loaded state takes place.
2. The method as claimed in claim 1, wherein two control variables
and are established for the load-dependent control of the hydraulic
pump arrangement and said control variables are dependent as input
values on the work to be performed by the motor of the hydraulic
pump arrangement, a first threshold value at which switching from
the non-loaded state to the loaded state takes place is assigned to
the first control variables, and a second threshold value at which
switching from the loaded state to the non-loaded state takes place
is assigned to the control variables.
3. The method as claimed in claim 1, wherein after switching on the
hydraulic pump arrangement but before the tool moves, the control
process maintains the supply of power to the electric motor from
the electrical power source at the second, lower electrical power
supply level, as the tool begins to move under no external load,
the control process switches the supply of power to the motor from
the electrical power source to the first, higher electrical power
supply level.
4. The method as claimed in claim 1, wherein as movement of the
tool under load is stopped, a process of switching from the loaded
state to the non-loaded state takes place and if the movement of
the tool is continued, in turn a switching process from the
non-loaded state to the loaded state takes place.
5. The method as claimed in claim 1, wherein the second threshold
value is a variable value and is updated during the operation.
6. The method as claimed in claim 1, wherein a third threshold
value is assigned to the control variables and a process of
switching from the loaded state to the non-loaded state takes place
in dependence upon the second threshold value and the third
threshold value.
7. The method as claimed in claim 1, wherein the control variable
is the motor current.
8. The method as claimed in claim 1, wherein the control variable
is the pressure and/or the motor torque.
9. The method as claimed in claim 1, wherein the control variable
is a value related to time.
10. A hydraulic pump device for driving a portable hydraulic tool
comprising: a housing, a hydraulic pump, an electric motor for the
purpose of driving the hydraulic pump, a coupling device for the
purpose of connecting the hydraulic pump device to flexible
connecting lines for supplying the hydraulic tool with hydraulic
fluid, a control device for the load-dependent control of
rotational speed of the motor; means for detecting at least one of
the control variables and said control variable is dependent as an
input value upon work to be performed by the motor of the hydraulic
pump arrangement, means for comparing the detected control
variables with a first threshold value, where necessary means for
comparing the detected control variables with a second threshold
value, means for switching the power supply of the motor for a
loaded state or non-loaded state in dependence upon the detected
control variables.
11. The hydraulic pump device as claimed in claim 10, wherein the
control variable is the motor current and/or the pressure and/or
the motor torque.
12. The hydraulic pump device as claimed in claim 11, wherein the
process of determining the drop in voltage at a resistor comprises
means for detecting the motor current.
13. The hydraulic pump device as claimed in claim 11, wherein a
current measuring device comprises means for detecting the motor
current.
14. The hydraulic pump device as claimed in claim 10, further
comprising a storage medium in which the second threshold value is
continuously updated.
15. The hydraulic pump device as claimed in claim 10, wherein the
control variable is measured over a time interval.
16. The hydraulic pump device as claimed in claim 10, wherein the
load state switching of the hydraulic pump arrangement comprises a
pulse width modulation of the motor voltage.
Description
[0001] The present invention relates to a method for operating a
hydraulic pump arrangement in accordance with the preamble of claim
1 and the invention also relates to a hydraulic pump arrangement in
accordance with the preamble of claim 9.
TECHNICAL FIELD
[0002] Hydraulic pump arrangements of the type described above are
used for a variety of applications. They are generally portable and
are therefore equipped with an autonomous power supply for example
a battery or the like. On the one hand, they are used as a
component of hydraulically driven rescue tools such as so-called
spreading or cutting tools that are used by emergency services for
rescuing people who are trapped or buried in wrecks of vehicles. On
the other hand, they are also used in tool technology, for example
to reduce the size of pieces of scrap etc. Generally, the switching
valves for operating the hydraulically driven tools are located
directly on the tool so that the operator can directly control the
tool as required by way of the switching valves. The hydraulic pump
arrangements that are necessary for the drive are therefore
generally connected to the individual tools by way of flexible
hydraulic hoses. Hydraulic hoses can have a variety of lengths
depending upon individual applications and this leads to a variety
of pressure ratios. In addition, there are a variety of different
rescue tools for different individual applications and said
different rescue tools are to be changed where necessary on site if
the situation demands it. Different rescue tools in turn lead to
different power levels, for example different motor idle pressures.
In order to extend the service life of the tools, every effort is
made to extend the service life of the power source as much as
possible. In the past, a system of providing energy saving modes
was adopted. An energy saving mode of this type is achieved by way
of example by means of switching from a loaded state to a
non-loaded state (switching the operating state), if it is not
necessary for the tool to perform further work.
PUBLISHED PRIOR ART
[0003] A portable hydraulic system in accordance with the preamble
of claim 1 is disclosed in U.S. Pat. No. 5,678,982. This hydraulic
system already comprises a process of controlling the operation in
a loaded state and a non-loaded state accordingly with the aid of a
switch that is switched between the loaded state and the non-loaded
state in dependence upon a pressure threshold value. This pressure
threshold value becomes an absolute pressure and is established by
means of a pressure sensor that taps the pressure at the output of
the pump and controls a switching unit. The switching unit is
actuated in dependence upon the absolute pressure at the output of
the pump, said output pressure being established by the pressure
sensor, and the system is switched from a non-loaded state to a
loaded state or vice versa. This known hydraulic system functions
well as long as the components of the system, namely the hydraulic
pump arrangement, the hose line and also the tool, match one
another. However, replacing tools with different motor idle
pressures and/or using different hose lengths leads to
malfunctions.
OBJECT OF THE PRESENT INVENTION
[0004] The object of the present invention is to provide a new
method for operating a hydraulic pump arrangement and also to
provide a new hydraulic pump arrangement that on the one hand,
ensures that energy is saved and on the other hand, renders
possible a problem-free operation even in the case of different
system pressure ratios.
ACHIEVING THE OBJECT OF THE INVENTION
[0005] The present object is achieved in the case of the method in
accordance with the generic type by means of the features of the
characteristic part of claim 1 and also in the case of the
hydraulic pump arrangement in accordance with the generic type by
means of the features of the characteristic part of claim 9.
[0006] Expedient embodiments of the method in accordance with the
invention and also of the hydraulic pump arrangement in accordance
with the invention are described in the dependent claims.
[0007] By virtue of the fact that at least one input value is
established for control purposes as a control variable S and said
control variable is dependent upon the work that is to be performed
by the motor of the hydraulic pump arrangement, malfunctions as a
result of the changing pressure ratios in the case of varying the
hose length, in the case of changing tools, in the case of
fluctuating temperatures etc., are effectively eliminated because
the relevant control variable is directly dependent upon the work
that is to be performed by the motor. The first and also the second
threshold value W1 or rather W2 are different. In particular, the
first threshold value W1 is lower than the second threshold value
W2. The control process renders it possible, even in the case of
stopping the movement of the tool while the tool is under load, for
example if the emergency doctor requires even further space in
order to care for a person who is trapped in a vehicle and it is
necessary therefore once again to control the rescue tool (for
example a spreader) to change from the loaded state to the
non-loaded state and also to subsequently switch from the
non-loaded state to the loaded state during a further movement of
the tool while the tool is under load.
[0008] In particular, it is also possible to establish two control
variables S1 and S2, for example the motor current and the
pressure, in an expedient manner for the load-dependent control of
the hydraulic pump arrangement and said two control variables are
dependent as input values on the work that is to be performed by
the motor of the hydraulic pump arrangement, wherein a first
threshold value W1, at which switching from the non-loaded state to
the loaded state takes place, is assigned to the first control
variables S1 (motor current), and a second threshold value W2, at
which switching from the loaded state to the non-loaded state takes
place, is assigned to the control variables S2. As a consequence,
in the case of problems defining the signal of one of the control
variables, the other control variable is drawn upon as an auxiliary
variable and vice versa. This renders possible a precise switching
process.
[0009] The operation of the hydraulic pump arrangement is suitable
for multiple operating situations by virtue of the fact that the
second threshold value is preferably a variable value that is
continuously updated, in other words a storage medium is
overwritten, during operation of the hydraulic pump
arrangement.
[0010] In accordance with one expedient embodiment of the method in
accordance with the invention, a third threshold value W3 is
preferably also assigned to the control variable S, wherein
switching from the loaded state to the non-loaded state takes place
in dependence upon both the second threshold value W2 and also the
third threshold value W3. As a consequence, an excessively rapid
switch from the loaded state to the non-loaded state is
avoided.
[0011] In the case of the third threshold value W3, said threshold
value is preferably a fixed predefined value of the control
variables S.
[0012] The motor current is drawn upon in an expedient manner as a
control variable S, in other words the current consumption of the
motor of the hydraulic pump and said current consumption represents
a measurement for the work that is to be performed by the motor of
the hydraulic pump arrangement. The process of determining the
motor current can be performed in various ways.
[0013] Alternatively, it is also possible for this purpose to draw
upon the pressure or the motor torque as the control variable
S.
[0014] In all cases, the values are preferably time related, in
other words values that represent the change of the control
variables S over a predefined time interval.
[0015] In an expedient manner, the hydraulic pump device in
accordance with the invention detects the motor current by means of
measuring a drop in voltage across a resistor and it is possible to
deduce the value of the motor current from said measurement.
[0016] Alternatively, it also possible to provide a current
measurement device, such as for example an ampere meter or the
like, for measuring the current in the motor line.
[0017] A rewritable storage medium of the type RAM or EEPROM is
expediently used as a storage medium.
[0018] In the case of a drop in load, the rotational speed of the
motor is reduced by means of changing the motor voltage in its
rotational speed. For this purpose, a voltage is applied at the
motor as a voltage pulse, preferably having a uniform pulse height,
in other words intensity, however having a different pulse width.
The voltage is consequently modulated. The current adjusts in
response to the external load.
DESCRIPTION OF THE INVENTION WITH REFERENCE TO EXEMPLARY
EMBODIMENTS
[0019] Expedient embodiments of the invention are further explained
hereinunder with reference to figures. In the drawings:
[0020] FIG. 1 schematically illustrates a first embodiment of the
present invention;
[0021] FIG. 2 illustrates a flow diagram of the process of
controlling the hydraulic pump arrangement in accordance with the
embodiment in accordance with FIG. 1;
[0022] FIG. 3 illustrates a diagrammatic illustration of the curve
of the motor current of the hydraulic pump arrangement in
accordance with FIG. 1;
[0023] FIG. 4 illustrates a further diagrammatic illustration of
the curve of the motor current of the hydraulic pump arrangement in
accordance with FIG. 1 with a break in the operation;
[0024] FIG. 5 schematically illustrates a further embodiment of the
present invention;
[0025] FIG. 6 schematically illustrates the use of the hydraulic
pump arrangement in accordance with the invention in the case of
different hose lengths, and also
[0026] FIG. 7 schematically illustrates the use of the hydraulic
pump arrangement in the case of different types of hydraulic
tools.
[0027] The reference numeral 1 describes in its entirety the
hydraulic pump arrangement in accordance with the invention. It is
portable and is connected by way of preferably flexible hose lines
15 to an exchangeable hydraulic tool 18. Coupling arrangements 14
and 16 respectively can be provided at the output of the hydraulic
pump arrangement 1 and also at the input of the hydraulic tool 18
for a rapid coupling and accordingly decoupling of the hydraulic
pump arrangement.
[0028] The hydraulic pump arrangement 1 comprises a pump 2 and also
an electric motor 4 that drives the pump 2. The electric motor 4 is
supplied with electrical power from a battery 19 or rather a power
supply network. The pump 2 comprises a tank 3 for the hydraulic
fluid. A pressure line leads from the pump 2 and the tank line
leads from the tank 3 out of the hydraulic pump arrangement 1 to
the respective coupling arrangement 14.
[0029] The reference numeral 10 describes a control device for the
sequence control of the hydraulic pump arrangement 1. This control
device comprises in particular a microcontroller 6, a storage
medium 7, a generator 8 for the purpose of pulse width modulation
and also an analogue/digital converter 9. The above-mentioned
components are attached to a circuit board. The microcontroller 6
is preferably connected to a main switch 5. The electrical circuit
from the battery 19 to the microcontroller 6 is either closed or
interrupted by means of said main switch. The electric motor 4 can
be directly connected to the main switch 5 so that the former is
supplied with electrical power from the battery 19 in the case of
switching on the main switch 5.
[0030] In accordance with the present invention, in particular the
motor current, in other words the current that the electric motor 4
consumes during the operation of the hydraulic pump arrangement, is
measured as a control variable S for the load switching (switching
the operating state). This switching process is performed in the
case of the embodiment that is illustrated in FIG. 1 in an
expedient manner with the aid of a resistor 13. The resistor 13 is
connected via a signal line 23 to the analogue/digital converter 9.
The latter converts the analogue signals into digital signals for
the purpose of further signal evaluation.
[0031] The process of determining the current is preferably
performed indirectly by way of the drop in voltage across the
resistor 13. This drop in voltage is amplified by means of the
amplifier 21 and is provided by way of the signal line 23 as an
input into the analogue/digital converter 9. The digital data are
processed by the microcontroller 6 and are compared with the data
in the storage medium 7 (threshold values from the control logic).
As a consequence, the corresponding pulse width is output in the
generator 8 for the pulse width modulation and the power transistor
11 (for example a MOSFET) transistor is correspondingly connected.
If the power transistor 11 is disconnected, the current flows by
way of the free-wheeling diode 12 that is connected in parallel to
the motor 4. The minus terminal of the motor 4 is so-to-speak
pulsed. Likewise, however, it is also possible that the plus
terminal is pulsed.
[0032] The abovedescribed embodiment of the present invention has
two operating states, namely a loaded operation and also a
non-loaded operation. During a loaded operation the electric motor
4 is supplied with the full electrical power (for example 24V), and
during a non-loaded operation the electric motor is supplied with a
reduced electrical power (for example 2V). The switching process is
performed by means of the control unit 10 by means of the generator
8 for the pulse width modulation and said generator cooperates with
the power transistor 11 as described above. The generator 8 for the
pulse width modulation process together with the power transistor
11 preferably forms continuous, periodic current signals that only
differ in their pulse width in dependence upon the respective
loaded state. The pulse width during the loaded state is greater in
relation to a unit of time and the pulse width during the
non-loaded state is smaller.
[0033] The respective hydraulic tool 18 comprises a hydraulic
cylinder 20 that is connected by way of a switching valve 17 to the
hose lines 15. In the case of the switching valve 17, said valve is
preferably a so-called 4/3 directional valve with which it is
possible to establish the two movement directions (forwards and
backwards) of the hydraulic cylinder 20 and also a motor idle
position (medium position of the switching valve 17). The switching
valve 17 is provided by way of example in the form of a so-called
star-grip directly on the tool 18.
[0034] The function sequence of the hydraulic pump arrangement 1 in
accordance with the invention is further explained hereinunder with
reference to FIG. 2. If the hydraulic pump arrangement 1 in
accordance with the invention is set in operation by means of
switching on the main switch 5, the electric motor 4 is supplied
with electrical power (in this case for example with 2V) in the
non-loaded region. Simultaneously, in the manner that is described
in the introduction, the current that is consumed by the electric
motor 4 is continuously determined. In this case, a difference
current, in other words a current difference, is determined by way
of a fixed defined time interval. A first threshold value W1 is
stored in the control device 10. The determined value of the
current consumption of the electric motor 4 is compared with the
first threshold value W1 in the logic of the microcontroller 6. If
the determined value of the current consumption is lower than the
first threshold value W1, the hydraulic pump arrangement remains in
the non-loaded region. Provided that the determined value of the
current consumption is greater than the first threshold value W1,
the hydraulic pump arrangement switches into the loaded region. In
the loaded region, the electric motor 4 is operated with a voltage
of for example 24V.
[0035] Directly after switching up into the loaded region, the
current is determined and is stored as the threshold value W2 in
the storage medium 7. The last value that relates to this is
overwritten in the storage medium. An individual threshold value W2
that is dependent upon the actual factors (temperature, connected
hose length, type of the rescue tool) is consequently always stored
in the storage medium 7 after the process of switching into the
loaded region.
[0036] Furthermore, a third threshold value W3 that represents a
fixed value is provided in the control process. If the continuously
measured consumed current of the electric motor 4 remains greater
than the second threshold value W2 or third threshold value W3, the
control process remains in the loaded state. If the continuously
measured current that is consumed by the electric motor 4 is lower
than the second threshold value W2 and is also lower than the third
threshold value W3, the control process switches to the non-loaded
state (2 V).
[0037] FIG. 3 illustrates the control process of the motor drive
with reference to a current curve I that is plotted over the time
axis t. In the case of actuating the main switch 5, the electric
motor is at first supplied with a voltage of 2 V. After a specific
time interval, the control valve 17 is actuated by the operator at
which point the hydraulic cylinder 20 of the tool 18 is moved
forwards under no external load. The measured current I exceeds the
first threshold value W1 so that the control device 10 converts the
operation from 2 V to 24 V. As long as no external load is present
on the movement of the tool, the electric motor 4 (after a specific
transient response) only requires an essentially constant current.
As soon as an external load affects the tool movement, the current
that is required by the electric motor 4 considerably increases
until a release as a result of the terminated deformation or
severing of a relevant item or component or the like. After the
control valve 17 has been brought into the neutral position (motor
idle), the amount of current that is required by the electric motor
4 considerably decreases. As soon as the current falls below the
third threshold value W3 and also below the second threshold value
W2, the control process switches to the non-loaded operation (2
V).
[0038] The illustration in accordance with FIG. 4 differs from that
in accordance with FIG. 3 by virtue of the fact that a break in the
operation is implemented during the operation. The break in the
operation can occur, as in FIG. 4, for example if the operator
becomes unsure, briefly releasing the star-grip, in order then to
continue working. In this case, the control valve 17 is brought
into the neutral position (motor idle position) by the operator.
The amount of current that is required by the electric motor 4
rapidly decreases. If the current consumption has fallen below both
the third threshold value W3 and also the second threshold value
W2, the control process switches from the loaded operation to the
non-loaded state. As soon as the working cycle is re-commenced, the
operator actuates the control valve 17 again so that current is
once again drawn by the electric motor 4. As a result of the break
in the operation, switching takes place from the non-loaded state
to the loaded operation, as a consequence of which a new threshold
value W2 is established and stored in the storage medium 7. Since
the break in the operation takes place in the proximity of the peak
of the current curve, a very high threshold value W2 is stored. In
order to avoid an immediate switching process, the third threshold
value W3 is provided. Only if the determined motor current has also
fallen below the third threshold value W3 does the control process
switch from the loaded operation to the non-loaded state.
[0039] An alternative embodiment of the present invention is
disclosed in FIG. 5. In contrast with the embodiment according to
FIG. 1, this embodiment of the invention has a current measuring
device 22 by way of example in the form of an ampere meter in lieu
of an electrical resistor. Said current measuring device measures
the current in the motor line. The current measuring device 22 is
likewise connected to the analogue/digital converter 9 by way of a
signal line 23. In the case of the embodiment according to FIG. 5,
two further connectors T and also P are provided.
[0040] In addition, during the process of controlling the load, the
pressure and/or the temperature can also be drawn upon as an
additional control variable, for example the pressure as a leading
variable and the current as an auxiliary variable for the purpose
of ensuring a precise switching process by means of a higher signal
resolution. By virtue of detecting the temperature, it is rendered
possible to use an additional deciding criterion in order to
evaluate the main variables. These variables are described in FIG.
5 with the input values T (temperature) and also P (pressure) at
the analogue/digital converter 9.
[0041] As is illustrated in FIG. 6, it is possible to connect the
hydraulic pump arrangement 1, depending upon the desired purpose,
to the same tool 18 by way of coupling arrangements 14 and 16
respectively and also by way of variable hose lengths 15a and 15b
respectively. The pressure ratios that are present in the system
change as a result of the use of different hose lengths. However,
this change in pressure ratios does not lead to malfunctions since
the process of controlling the operation of the hydraulic pump
arrangement 1 is provided in accordance with the invention by way
of the motor current as a control variable S and said variable is
directly dependent on the work that is to be performed by the motor
of the hydraulic pump arrangement 1.
[0042] If the pressure ratios change as a result of a comparably
longer hose line 15 then the motor current also changes. However,
said motor current is compared with at least in part variable
current thresholds (adaptive control process).
[0043] The same also applies when exchanging the tools 18a to 18c,
as is also illustrated in FIG. 7. The operating pressure ratios
also change in this case. By way of example, a tool 18a in the form
of a cutter has a different current consumption in the motor idle
mode than a spreader (tool 18b). This difference also applies as a
consequence in the process of controlling the hydraulic pump
arrangement 1.
[0044] The same also applies for a change of the length of the hose
lines in the case of a simultaneous change of the type of tool 18a
to 18c.
[0045] Alternatively, the pressure and/or the torque can also be
drawn upon as a control variable S, in other words as a control
parameter, in lieu of the motor current.
LIST OF REFERENCE NUMERALS
[0046] 1 Hydraulic Pump Arrangement [0047] 2 Pump [0048] 3 Tank
[0049] 4 Motor [0050] 5 Main Switch [0051] 6 Microcontroller [0052]
7 Storage Medium [0053] 8 Generator for Pulse Width Modulation
[0054] 9 Analogue/Digital Converter [0055] 10 Control Device [0056]
11 Power Transistor [0057] 12 Free-Wheeling Diode [0058] 13
Resistor [0059] 14 Coupling Arrangement [0060] 15 Hose Line [0061]
16 Coupling Arrangement [0062] 17 Switching Valve [0063] 18 Tool
[0064] 19 Battery or rather Power Supply Network [0065] 20
Hydraulic Cylinder [0066] 21 Amplifier [0067] 22 Current Measuring
Device [0068] 23 Signal Line
* * * * *