U.S. patent number 3,801,071 [Application Number 05/295,758] was granted by the patent office on 1974-04-02 for towing winch control system.
This patent grant is currently assigned to Byran Jackson, Inc.. Invention is credited to Charles D. Barron.
United States Patent |
3,801,071 |
Barron |
April 2, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
TOWING WINCH CONTROL SYSTEM
Abstract
A towing winch control system in which the winch for the towing
cable is driven through a slipping clutch to apply a substantially
constant tension to the towing cable, and a position sensor and a
tensiometer are operated to control the length of the tow cable
between the towing winch and the object being towed and to limit
the load on the cable to prevent parting of the cable.
Inventors: |
Barron; Charles D. (Huntington
Beach, CA) |
Assignee: |
Byran Jackson, Inc. (Long
Beach, CA)
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Family
ID: |
23139125 |
Appl.
No.: |
05/295,758 |
Filed: |
October 6, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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110695 |
Jan 28, 1971 |
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Current U.S.
Class: |
254/267; 114/254;
254/273; 254/358; 254/367; 254/368; 254/900 |
Current CPC
Class: |
B66D
1/14 (20130101); B66D 1/48 (20130101); B63B
21/56 (20130101); B66D 2700/0108 (20130101); Y10S
254/90 (20130101) |
Current International
Class: |
B63B
21/56 (20060101); B66D 1/14 (20060101); B66D
1/48 (20060101); B66D 1/28 (20060101); B66D
1/02 (20060101); B66d 001/48 () |
Field of
Search: |
;254/172R,173B,185R,173R,187R,175.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1,158,229 |
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Nov 1956 |
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DT |
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1,138,908 |
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Nov 1959 |
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DT |
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864,182 |
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Mar 1961 |
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GB |
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646,279 |
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Apr 1933 |
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DD |
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1,294,078 |
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Feb 1969 |
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DT |
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Primary Examiner: Aegerter; Richard E.
Assistant Examiner: Lane; H. S.
Attorney, Agent or Firm: Banner; Donald W.
Parent Case Text
This application is a continuation of application Ser. No. 110,695,
filed Jan. 28, 1971, now abandoned.
Claims
I claim:
1. In a winch system including a winch drum having a line thereon
connectable to a load, drive means for driving said drum to wind
said line on said drum, to hold said line, and to allow said line
to be stripped away from said drum, said drive means including a
continuously operable slip clutch having continuously variable
actuator means operable to adjust the torque transmitted to said
drum by said drive means, settable control means for establishing a
predetermined line position at a preselected line tension, said
control means comprising: line position sensing means responsive to
the deviation of said line away from said predetermined line
position for producing an output signal proportional to said
deviation, line tension sensing means responsive to the tension in
aid line for producing an output signal proportional to the
deviation of said tension from said preselected tension, said
control means including computer means comprising means for
receiving both said output signals and producing a continuously
variable clutch control signal which is a function of the
integration of said output signals, and means for varying said
actuator means as a function of said clutch control signal to
adjust said actuator means for causing said line to be stripped
away from, held on, or returned to said drum in response to said
clutch control signal to continuously control the deviation of said
line from said predetermined line position in proportion to said
deviation of the tension in said line.
2. In a winch system as defined in claim 1, speed sensing means
operable by said drum, said control means including means operable
by said speed sensing means to adjust said actuator means and
control the speed of movement of said drum.
3. In a winch system as defined in claim 1, said actuator means
comprising an air pressure responsive device, a source of air
connected to said device, and said control means varying the supply
of air to said device from said source.
4. In a winch system as defined in claim 1, said control means
comprising means for producing a variable air signal pressure to
adjust said actuator means.
5. In a winch system as defined in claim 4, speed responsive means
operable by said drum to adjust said air signal pressure to limit
the speed of movement of said drum.
6. In a winch system as defined in claim 1, said line tension
sensing means comprising tensiometer means engaged with said line,
said position sensing means engaged with said line, and said
control means comprising computer means for receiving said output
signals and producing a clutch control signal at a constant value
determined by the difference between said output signals.
7. In a winch system as defined in claim 6, speed responsive means
to produce an output signal determined by the speed of movement of
said line, said computer means receiving said output signal of said
speed responsive means and being operable to produce a clutch
control signal determined by the difference between the sum of said
output signal of said position sensing means and said output
signals of said speed responsive means, and the output signal of
said tensiometer means.
8. In a winch system as defined in claim 1, said line tension
sensing means comprising tensiometer means engaged with said line,
said position sensing means engaged with said line, said control
means comprising computer means for receiving said output signals
and producing a clutch control signal at a constant value
determined by the difference between said output signals, and speed
responsive means operable upon winding of line on said drum and
stripping of line from said drum to produce a speed responsive
output signal, said computer means receiving the latter output
signal and adding the same to said position control signal in
producing said clutch control signal.
9. In a winch system as defined in claim 1, said line tension
sensing means comprising tensiometer means engaged with said line,
said position sensing means engaged with said line, and said
control means comprising computer means for receiving said output
signals and producing a clutch control signal determined by the
difference between said output signals, said control means
including a pressure controller operable in response to said output
signal of said tensiometer means to maintain said output signal
determined by the load on said line at a constant value.
10. In a winch system as defined in claim 1, said line tension
sensing means comprising tensiometer means engaged with said line,
said position sensing means engaged with said line, and said
control means comprising computer means for receiving said output
signals and producing a clutch control signal determined by the
difference between said output signals, said control means
including a pressure controller operable in response to said output
signal of said tensiometer means to maintain said output signal
determined by the load on said line at a constant value, and speed
responsive means operable upon winding and unwinding of line on
said drum to produce a speed responsive output signal, said
computer means receiving the latter output signal, said speed
responsive output signal being added to said output signal from
said position sensing means by said computer means in producing
said clutch control signal.
11. In a winch system as defined in claim 1, said actuator means
comprising an air pressure responsive device, a source of air
connected to said device, said control means varying the supply of
air to said device from said source, said control means comprising
a pressure computer for receiving variable input pressure signals
representative of load on said line, the deviation of said line,
and a reference pressure, and said computer producing an output
pressure signal determined by the equation
X = 2P - R - T,
where X is the computer output signal pressure, P is the input
pressure signal determined by the deviation of said line, R is the
reference input pressure signal, and T is the input signal pressure
determined by load on said line, said tension sensing means sensing
the load on said line and said position sensing means sensing the
deviation of said line and supplying said variable input pressure
signals to said computer means representative of load on said line
and the position of said line, and means for supplying a selected
reference signal pressure to said computer means.
12. In a winch system as defined in claim 11, said computer means
comprising a control valve assembly having an air inlet, an air
outlet, and an exhaust port, and valve means for controlling the
flow of air from said inlet to said outlet and said exhaust port to
maintain said output pressure signal substantially constant at a
selected pressure.
13. In a winch system as defined in claim 1, said clutch actuator
means comprising an air pressure responsive device, a source of air
connected to said device, said control means varying the supply of
air to said device from said source, said control means comprising
a pressure computer for receiving variable input pressure signals
representative of load on said line, the deviation of said line,
and a reference pressure, and said computer producing an output
pressure signal determined by the equation
X = 2P - R - T
where X is the computer output signal pressure, P is the input
pressure signal determined by the deviation of said line, R is the
reference input pressure signal, and T is the input signal pressure
determined by load on said line, said tension sensing means sensing
the load on said line and said position sensing means sensing the
deviation of said line and supplying said variable input pressure
signals to said computer means representative of load on said line
and the position of said line, means for supplying a selected
reference signal pressure to said computer means, and controller
means for receiving the computer output signal and variably
transmitting a constant output signal to control said clutch of a
magnitude determined by said computer output signal.
14. In a winch system as defined in claim 1, said clutch actuator
means being pneumatically operable, said line tension sensing means
comprising hydraulic load sensing means for producing a hydraulic
pressure signal determined by the load on said line, controller
means having an air inlet, an air outlet, and control valve means
operable by said hydraulic pressure signal to cause a constant
output pressure signal at said outlet, said sensing means also
comprising pneumatic sensing means operable in response to
deviation of said line and including an air inlet, an air outlet,
and control valve means operable to cause a constant output
pressure signal at the latter outlet, additional controller means
having an air inlet, an air outlet, and control valve means
operable to cause a constant output pressure signal at the
last-mentioned outlet, pneumatic computer means having an air
inlet, an air outlet and control valve means for maintaining a
constant output pressure signal at the outlet of said computer
means at a pressure determined by a comparison of said output
pressure signals from said controllers, and means for supplying air
to said clutch actuator means at a pressure determined by said
output pressure signal from said computer means.
15. In a winch system as defined in claim 14, speed responsive
means operable in response to rotation of said drum to produce an
air pressure signal determined by the speed of said drum, said
computer means receiving the last-mentioned pressure signal to
adjust the output pressure signal from said computer means.
Description
BACKGROUND OF THE INVENTION
The towing of a vessel to sea, such as well drilling barges, cargo
barges, or, indeed any vessel, by a tug or other towing vessel,
poses problems which are difficult of solution. Heretofore, the
towing cable by which the towing vessel tows the towed vessel has
been relied upon to compensate for changes in load on the cable due
to changes in tidal, wave, or wind action on the vessels, and, as a
result, an extremely long run of cable or line has been employed.
The cable sags between the vessels, generally beneath the water and
provides a long arcuate cable section which can be more or less
tensioned as the towing vessel and the towed vessel experience
different influences of tide, waves, or wind, or combinations
thereof.
Such long tow lines or cables make control of the towed vessel very
difficult, particularly when entering or navigating narrow channels
or waterways. A heavy barge may require a length of tow line or
cable on the order of one quarter mile, for example, to afford a
safe bow in the line or cable, whereby the towing and towed vessels
may react differently to different influences without parting the
tow line or cable. A typical problem in this connection involves
the opposite reactions caused by the towed vessel's tending to slow
down when on the trailing slope of a wave and the towing vessel's
tending to accelerate when picked up by the forward slope of a
wave. Such long tow lines or cables also produce a navigational
hazard, particularly, when visibility is poor, and the pilot of
another vessel may not be aware of the existence of the tow line,
due to his inability to see the towed vessel, or, perhaps, either
vessel.
Ordinarily, the towing line or cable is on a towing winch and is
played off as may be required by the relative conditions of the sea
and the weight of the towed vessel. When desired, the winch is
operated to pull in the line or cable to shorten the distance
between the two vessels. However, if, due to wave, tide or wind
influence on the vessels, the line is over loaded it may part,
allowing the towed vessel to then drift free, with potentially
dangerous results.
SUMMARY OF THE INVENTION
The present invention provides a towing winch system which obviates
the problems and hazards of the above-described towing
practices.
More particularly, the present invention is a towing winch system
which may be employed on a towing vessel to tow another vessel, or
string of vessels, in a more closely adjacent relation than has
been practical heretofore.
The towing winch system, in general, involves a winch adapted to be
driven by a power source through a clutch which is capable of
constantly slipping to apply a substantially constant tension on
the towing line or cable. When the load on the line or cable
increases above a pre-set capacity, the line or cable will be
stripped from the winch, but when the tension is thereafter reduced
the line or cable will be rewound by the winch until the towed
vessel is in the pre-selected spaced relation to the towing
vessel.
In accomplishing the foregoing, a position sensor and a tensiometer
are engaged with and operated by the tow line or cable to control
the slip clutch so as to maintain the tension on the line or cable
and to maintain the relative positions of the vessel, so long as
different influences on the vessels permit the maintenance of the
relative positions of the vessels, and to re-establish the tension
on the line or cable and the relative positions of the vessels when
the influences on the vessels, or either of them, permit.
Constant tension winches, driven by a fluid pressure actuated slip
clutch are well known, as exemplified in United States Letters
Patent No. 3,373,972, dated March 19, 1968. Preferably, however, to
effect better cooling of the slip clutch with resultant improved
efficiency, the clutch may be cooled as disclosed in the pending
application for United States Letters Patent of C. D. Barron, Ser.
No. 19,601, filed Mar. 16, 1970. The position sensor referred to
above is adapted to cause a change in the fluid pressure acting on
the slip clutch, and is preferably made in accordance with the
disclosure of the pending application for United States Letters
Patent of C. D. Barron, Ser. No. 19,564, filed Mar. 16, 1970.
This invention possesses many other advantages, and has other
purposes which may be made more clearly apparent from a
consideration of a form in which it may be embodied. This form is
shown in the drawings accompanying and forming part of the present
specification. It will now be described in detail, for the purpose
of illustrating the general principles of the invention; but it is
to be understood that such detailed description is not to be taken
in a limiting sense, since the scope of the invention is best
defined by the appended claims. In this connection, while the
invention is herein disclosed as being incorporated in a towing
winch system, it will be understood that the invention is
applicable to other dynamic systems in which the tension on a line
and the position of a line must be controlled or adjusted to
prevent overloading of the line and to reposition a load in
response to changes in load condition.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective, generally illustrating a towing vessel and
a towed barge to which the towing winch control system of the
invention is applied;
FIGS. 2a and 2b, together constitute a diagrammatic illustration of
the towing winch control system, FIG. 2b constituting a downward
continuation of FIG. 2a;
FIG. 3 is a longitudinal section through a computing relay or
pressure transmitter employed to vary the drive of a slip clutch in
response to variations in the load conditions on the towing winch
line;
FIG. 4 is a longitudinal section through a line position sensing
device for varying a pressure signal supplied to the computer of
FIG. 3, in response to changes in position of the towing winch
line; and
FIG. 5 is a view partly in elevation and partly in longitudinal
section, showing a slip clutch assembly for driving the towing
winch.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As seen in the drawings, with reference first to FIG. 1, a towing
vessel or tug boat V is shown as having a towing winch W from which
a tow cable or line L extends sternward for connection to a towed
vessel or barge B.
While a rock barge is shown as illustrative, it will be understood
that the problem of overload on a towing line L exists in any
similar situation involving a towed vessel or barge, such as, for
examples, an offshore well drilling platform, a disabled ship, or
the like.
The towing vessel or tug is shown as having the winch W disposed
above-deck, for clarity, and a suitable drive or motor source M is
shown below-deck, but as a practical matter, it may be preferred
that the entire apparatus or any portion thereof be located below
deck, with the cable or line L passing through a fairlead or guide
at the stern of the vessel V.
More particularly, the illustrative drive M includes a suitable
drive connection in the form of a chain 10 adapted to effect
rotation of a counter shaft 11 through a slip clutch assembly C,
which, as is more particularly seen in FIG. 5 and described
hereinafter, is adapted to transmit torque to the shaft 11 under
the control of the control system of the invention, whereby to
limit the tension on the line L and to adjust the relative
positions of the towing vessel V and the barge B. Thus, a drive
connection, say the illustrative chain drive 12 provides means for
applying torque to the drum 13 of the winch W, whereby the line L
will be pulled in if the selected line tension overcomes the load
of the barge B, but the line L may be stripped from the drum 13 if
the barge exceeds the pre-set line tension. Associated with the
line L are sensing means TP, incorporated in the system and
adapted, as will be later described, to sense the load or tension
on the line L and to sense changes in position of the line L so as
to effect control of the line.
Referring to FIG. 2a, the sensing means TP is generally shown to
comprise a typical hydraulic tensiometer 15 and a position senser
16. The tensiometer 15 is adapted to be applied to the line L in
such a manner that the line engages and extends between a pair of
spaced rollers 17 and 19 which are rotatable on shafts 19 and 20,
respectively, supported in a frame 21. A third roller 22 engages
the line L between the rollers 17 and 18 to deflect the
intermediate portion of the line, the roller 22 being carried on a
shaft 23 which is mounted for movement relative to the frame 21,
whereby such movement is applied to the hydraulic sensing unit 24,
to produce a hydraulic signal the magnitude of which is a function
of tension on the line L. Such devices 15 are well known and
require no further description herein. An example of such a line
tension no responsive device is the Tensiometer Model UD12 of
Martin-Decker Corp., of Santa Ana, Calif. The position sensor unit
16 of the sensing means TP is more particularly illustrated in FIG.
4 and will be latter described.
In order to control the speed at which the line L may change
position, speed control means including a tachometer signal
generator 25 is adapted to be driven by the winch drum 13 to supply
a variable signal to an electro-pneumatic transducer 26, say the
Model T-10 electro-pneumatic, transducer of Conoflow Corporation of
Blackwood, N.J. The output from the hydraulic unit 15, the position
sensor 16 and the transducer 26 are compared by computer means 27,
the details of which are shown in FIG. 3, to control the clutch C,
as will be more fully described below.
The clutch C, as best seen in FIG. 5, is associated with an end 37
of the counter shaft 11, and the drive chain 10 engages a sprocket
50 which is revolvable relative to the shaft end 37 on bearings 52.
Affixed to the sprocket 50, is a disc 54 which is in turn affixed
by fasteners 55 to the outer periphery of the back-up plate 56 of
the slip clutch means C.
This slip clutch means C includes an outer annular body 57 to which
an annular flange 58 is connected by fasteners 59 in opposed
relation to the plate 56. Internally thereof, the body 57 has a
splined connection 60 with the outer periphery of an axially
shiftable clutch pressure plate 61. Between the clutch plates 56
and 61 is a clutch friction disc 62 having friction facing 63 on
opposite sides thereof and having, as at 64, a splined connection
with a hub 65 which is disposed upon the shaft end 37 and is keyed
thereto by a key 66. Thus, rotation from the sprocket 50 will be
transmitted to the tensioning hoist shaft 11 when the slip clutch
means C is engaged to transmit rotation from the clutch body 57 and
its plates 56 and 61 to the friction disc 62.
Engagement of the slip clutch means C is accomplished by an annular
expansible actuator tube 67 having an air inlet 68. The actuator
tube 67 engages an annular body of insulating material 69
interposed between the tube 67 and the clutch pressure plate 61.
Each of the clutch plates 56 and 61 has a number of annular,
radially spaced and concentric coolant passages 56a and 61a to
which a coolant is supplied to dissipate the heat of friction
caused by slippage of the clutch C. These passages 56a and 61a are
defined respectively between the clutch plates and a wear disc 56b
carried by the plate 56 and a wear disc 61b carried by the plate
61, the friction material on the friction disc 62 being engaged
with the wear discs 56b, 61b.
Such cooled, slip clutches are well known, and generally are
provided with a coolant circulating system including a stationary
coolant connector 71 through which coolant flows to and from a
rotary connector 72 which is connected, as by fasteners 72a, to the
clutch flange 58 and which has conduit means 73 for supplying
coolant to the passages 56a and 61a, as well as conduit means for
the return flow of coolant to the connector 71 and thence to a heat
exchanger. Preferably, in order to more effectively cool the
clutch, it is constructed in accordance with the aforementioned
application for patent. In addition, the rotary connector 72
provides a connection for air conduit means 74 which leads to the
air inlet 68 for the clutch actuator tube 67 from a stationary air
inlet fitting 75. As is well known, the torque transmitting
capacity of such slip clutches varies with the pressure of air in
the actuator tube 67.
Thus, the tension applied to the line L will be determined by the
magnitude of the air pressure supplied to the actuator tube 67
through the coupling 75 under the control of the computing relay
27, as will be more fully described below.
The preferred line position sensing unit 16, of the sensing meant
TP, is shown in greater detail in FIG. 4, and is more specifically
disclosed in the aforementioned pending patent application. It
comprises an elongated housing 81 having at one end a closure or
cap 82 and having at the other end an assembly which provides an
air inlet or supply port 84, an outlet 85 for a controlled air
pressure signal, a port 86 for bias pressure fluid, and a port 87
communicating with the atmosphere.
Included within the assembly are actuator means generally denoted
at 88, fluid pressure responsive piston means 89 operatively
connected to the actuator means 88, orifice means 90 operable in
response to the application of fluid pressure to the piston means
89 and to the application of force from the actuator means 88 for
opening and closing the orifice means 90, and combined inlet and
outlet valve means 91 for controlling the flow of air from the
supply port 84 to the output port 85 and for controlling the
exhaust of air from the outlet port to the atmosphere through the
port 87.
In general, it is the purpose of the position sensing pneumatic
control device to regulate the output signal pressure to a constant
value which is determined by the net force applied to the piston
means 89, whereby the orifice means 90 is either opened or closed
for a period sufficient to balance the piston means 89, so that the
pressure drop through the orifice means 90 remains constant,
resulting in a constant output signal pressure at the port 85 which
leads to the computer relay 27, as will be later described.
More particularly, the actuator means 88 comprises a shaft 92 which
extends longitudinally of the housing 81 and has an end 93 which
extends axially from the end cap 82 through a suitable bearing 94
and a suitable seal 95. Disposed upon the shaft 92 within the
housing 81 is a spring seat 96 having a reduced central section 97
on which is piloted the upper end of a coiled compression spring
98. The shaft 92 is threaded as at 99, and the spring seat 96 and
the reduced pilot portion 97 thereof are complementally threaded,
whereby rotation of the shaft 92 will effect longitudinal movement
of the spring seat 96 on the shaft, since the seat 96 is held
against rotation by a key 100 carried thereby and extending into a
lateral slot 101 in the housing 81. At its inner end the spring 98
seats on a spring seat 103 having a reduced pilot portion 104. This
spring seat 103 is connected by fasteners 105 to the circular upper
body portion 106 of the piston 107 of the piston means 89, the seat
103 and the body 106 being held in axially spaced relation by
tubular spacers 108 interposed therebetween and through which the
fasteners 105 extend. The lower end of the shaft 92 extends through
the seat 103 and is journalled in a bearing 109 which is mounted in
a supporting spider 110 having circumferentially spaced openings
111 to accommodate the spacers 108, whereby the piston means 89 is
axially movable.
The assembly also comprises, in addition to the spider 110, an
annular spacer 112, an annular cylinder 113 for the piston 107 and
an annular cylinder 114 which houses a piston 115, an annular body
116 containing the nozzle means 90, and an end member 117. The
spider 110, spacer 112, cylinders 113 and 114, annular body 116,
and end member 117 are interconnected together and to the
cylindrical body 81 by tie-bolts or the like, requiring no
illustration.
Between the spacer 112 and the cylinder 113 is clamped the outer
marginal portion of a diaphragm 119, and between the cylinder 113
and the cylinder 114 is clamped the outer marginal portion of
another diaphragm 120. Still another diaphragm 121 has its outer
marginal portion clamped between the cylinder 114 and the annular
body 116. In the illustrative embodiment, the body portion 106 of
the piston 107, as well as the piston 107 and the piston 115 are
interconnected by a stem 122 having an enlarged head 123 at one end
which clamps the inner periphery of the diaphragm 121 against the
adjacent portions of the piston 115, and a nut 124 is threaded onto
the other end of the stem 122 to effectively clamp the piston 117,
including its upper body portion 106, and the piston 107 together.
The inner periphery of the diaphragm 119 is like-wise clamped
between the upper body portion 106 and the piston 107, and the
inner periphery of the diaphragm 120 is clamped between the piston
107 and the piston 115. Thus, the piston means 89 comprises both
the piston 107 and the piston 115. More particularly, the piston
107 has an enlarged portion 125 which is exposed to the pressure in
a chamber 126 provided in the cylinder 113 between the diaphragms
119 and 120. The piston 115 is exposed to the pressure in a chamber
127 provided in the annular body 116 across substantially the
entire cross-sectional area of the piston 115. Within the cylinder
114, the piston 115 is disposed in a chamber 128 which is vented to
the atmosphere through radial ports 129.
Interposed between the annular body 116 and the end member 117, and
clamped at its outer margin is a double diaphragm assembly
including an upper diaphragm 130 and a lower diaphragm 131 spaced
apart by an outer material spacer 132 in which is formed one or
more of the radial outlet ports 87, previously referred to, which
communicate the space between the diaphragms 130 and 131 with the
atmosphere. In the annular body 116 above the upper diaphragm 130
is a chamber 134 and centrally of the body 116 is a threaded bore
having therein a nozzle 136, the port through which communicates
with the chamber 134, and the outlet of which is opposed by a
nozzle seat 137 suitably carried by the lower end of the stem 122.
Air is supplied to the chamber 134 and thence to the nozzle 136
from the supply port 84 through a passage 138 which extends through
the margin of the diaphragms 130 and 131 and the spacer 132 and
connects with a passage 139 leading into the chamber 134. Disposed
in the passage 139 is a flow restrictor 140 having a reduced
passage therethrough. This flow restrictor is replaceable through
an opening in the body 116 which is closed by a threaded closure
plug 141. At the outer side of the diaphragm 131 in the end member
127 is a chamber 142 which communicates with the output port 85.
The output port 85 also communicates through a passage 143 with the
chamber 127 in the body 116 below the diaphragm 121.
The inlet and outlet valve means 91, previously referred to,
includes a valve seat 144 carried by a plate 145 below the
diaphragm 131 and having a valve port 146 leading from the outlet
chamber 142 into the space between the diaphragms 130 and 131. A
coiled compression spring 145a is provided beneath the plate 145
which applies a normal inward bias to the diaphragm 131 and to the
outlet valve seat 144. A valve stem 147 is reciprocably mounted in
a port 147a in the end member 117, which port leads from the inlet
84 to the outlet 85. The stem is normally biased inwardly by a
coiled compression spring 148 which seats in a plug 149 in the end
member 117 and acts inwardly on a spherical valve head 150 to bias
the same against an inlet valve seat 151.
As previously indicated, the position sensing pneumatic control
device functions to regulate the output signal pressure at the port
85 to a value which is proportional to sensed movement.
Accordingly, the outer end 93 of the shaft 92, in the illustrative
embodiment, has mounted thereon the sheave or roller 17 of the
tensiometer 15 which is engaged by the cable or line L, to effect
rotation of the shaft 92 in response to relative movement between
the line L and the sensing device. Movement of the line L is
transmitted to the shaft 92 to effect rotation of the latter in one
direction or the other depending upon the direction of movement of
the line L. It is apparent that rotation of the shaft 92 in one
direction or the other will impose more or less compression on the
spring 98 to provide more or less force acting on the piston means
89 which will either cause the nozzle seat 137 to close the nozzle
136 or to open the nozzle 136 for communication with the chamber
127, and hence the discharge or signal output port 85. Such spring
force is opposed by the pressure of air in the chamber 127 acting
on the cross-sectional area of the piston 115 and the pressure of
fluid in the chamber 126 acting on the effective area of the piston
107. Thus, the fluid admitted through the port 86 to the chamber
126 may be supplied from a remote set point to quickly and easily
calibrate the motion sensor, so that the signal output pressure is
at a desired level, less than the input pressure, under the
conditions that the shaft 92 is in the neutral or non-moving
condition.
With the foregoing details in mind, the operation of the motion
sensor is such that the spring 98 is operative to apply a variable
force in a direction tending to move the piston means 89 variable
force in a direction tending to move the piston means 89
downwardly. Opossing the force derived from the actuator means is
the force derived from the application of pressure from a remote
set point to the bias or calibrating chamber 126, which pressure is
effective over the area of the enlargement 125 of the piston means
89 to provide a force tending to move the piston means 89 upwardly.
Also providing a force tending to move the piston means 89 upwardly
is the pressure in the piston chamber 127 which acts upon the
piston 115 of the piston means 89, the other side of the piston 115
being exposed to the atmosphere in the chamber 128.
The effective signal outlet pressure in the piston chamber 127 is a
function of the reduction in the inlet pressure caused by the
passage of air from the inlet 84 through the flow restrictor 140
into the pilot pressure chamber 134 and the reduction in pressure
resulting from the passage of air from the pilot pressure chamber
134 through the orifice means 136, as indicated by the arrows, into
the piston chamber 127. When the device is in the condition shown
in FIG. 4, the effective signal outlet pressure at the outlet 85 is
the same as that in the piston chamber 127, and under the condition
shown the pressure drop from the inlet 84 to the outlet 85 will
remain constant, unless the force derived from the actuator means
88 is varied or the force derived from the remote set point
pressure is varied.
Assuming that the force derived from the actuator means tending to
shift the piston means 89 downwardly is reduced, the net force
acting on the piston means will cause the piston means to move
upwardly, allowing greater flow from the pilot pressure chamber 134
into the piston chamber 127. Such action will result in an
instantaneous decrease in the pilot pressure in the chamber 134. As
a consequence, pressure applied to the diaphragm 131 and the force
of the spring 145a will move the exhaust valve seat 144 upwardly
and off of the end of the valve stem 147, to allow the exhaust of
fluid pressure from the outlet chamber 142 and the piston chamber
127 through exhaust port 87, until the device again assumes the
condition shown in FIG. 4 at which the exhaust valve port 146 is
again closed. At this time, the pressure at the outlet 85 will
again be stabilized at a value determined by the fluid pressures
acting on the actuator means 88 and the decreased spring force of
the spring 98. A larger volume of air will flow past the orifice
closure 137, and the signal outlet pressure will be at a lower
value.
Assuming that the force derived from the actuator means tending to
move the piston means 89 downwardly is increased, overcoming the
effect of the signal outlet pressure in the chamber 127, then the
orifice closure disc 137 will engage the end of the orifice means
136, thereby shutting off the passage of air from the pilot
pressure chamber 134 into the piston chamber 127. Under these
circumstances, the pilot pressure in the pilot chamber 134 will
build up, forcing the diaphragm 130 and the diaphragm 131
downwardly, thereby unseating the valve 150, so that inlet pressure
will transfer through port 147a of the inlet-outlet valve 91,
resulting in an increase in the signal outlet pressure in the
outlet chamber 142 and in the piston chamber 127 which will be
effective to again condition the apparatus as shown in FIG. 4, so
that the pressure at the outlet 85 again remains constant, but
greater.
It will now be understood that variation of the remote set point
pressure in the chamber 126 will have the same effect as variation
of force derived from the actuator means. In other words, as the
remote set point pressure is increased, the force tending to move
the piston means 89 upwardly will also be increased, but if the
remote set point pressure is decreased, the force tending to move
the piston means 89 upwardly will be decreased. The supply of air
to the chamber 126 through the port 86 is shown in FIG. 2a, as
being via a conduit 86a leading from a suitable valve 86b which
controls the pressure derived from a source conduit 86c which leads
from a suitable pressure source, not shown. The outlet port 85 is
in communication with a conduit 85a which leads to the computer
means 27, now to be described.
This computer means 27, as seen in FIG. 3, comprises a support 200
adapted to be mounted at a suitable location. Carried by the
support 200 is an end cup 201 having a marginal flange 202 for
connecting the cup 201 with an assembly which comprises a stack of
discs 203, 204, 205, 206 and 207 and a body 208, all connected at
the outer peripheries by a suitable number of tie bolts, one of
which is shown at 209. The disc 203 includes a rigid central
section 203' and a flexible annular diaphragm 203" supporting the
central section 203' and a flexible annular diaphragm 203"
supporting the central section 203' within the disc 203. Similarly,
each of the discs 204, 205, 206 and 207 comprises a rigid central
section 204' to 207' and an annular diaphragm 204" to 207".
Intermediate, the discs 203 to 207 are annular, outer peripheral
spacers 210 and central spacers 211. The outer spacers 210 are
connected in the assembly by the tie bolts 209. The central spacers
211 are interconnected at the respective central sections 203' to
207' by a pin 212 having a head 213 at its lower end and a nut 214
at its upper end for clamping the piston sections and central
spacers together.
Fluid under pressure, say air, is supplied to the computer means 27
above and below the stack of diaphragms and between the diagrams
from various sources, whereby to provide an output pressure signal
which is a function of the various input signals and the constant
force of an adjustable coiled spring K which is disposed in the cap
201 and seats, at one end, on a seat 215 above the disc section
203' and at the other end on a spring seat 216 carried by an
axially shiftable adjuster pin 217. The pin 217 is shiftable by an
adjuster screw 218 threaded in a nut 219 which is suitably affixed
to the support 200. Below the disc 207 is another coiled spring K'
which seats at one end in a seat 208' and engages at its other end
beneath the disc section 207' in opposition to the spring K. Thus,
the spring K is adjustable to provide a selected force on the
stacked disc sections 203' to 207', determined by the relationship
between springs K and K'.
Air pressure is supplied to a chamber P1 in the cup 201, from the
position sensor 16 via conduit 85a, by suitable means, such as an
inlet fitting 220, to provide a downward force on the effective
piston area of the central section 203' of disc 203. In order to
increase the magnitude of the force derived from air pressure
supplied to the computer 27 from the position sensor 16 via conduit
85a, a branch conduit 85b leads to a chamber P2 defined between the
diaphragms 203" and 204", say through a pressure inlet 221, so that
such pressure also acts downwardly on the effective annular piston
area of the central section 204' of the disc 204, which extends
radially beyond the spacer 211 thereabove.
Below the annular piston area of the disc section 204' is a chamber
R having an inlet 222 to which pressure fluid is supplied, as will
be later described, at a value determined by the computer 27, the
pressure in chamber R acting upwardly on the effective annular
piston area of the disc section 204' in opposition to the downward
force derived from pressure in the chambers P1 and P2.
Between the discs 205 and 206 is defined a pressure chamber S to
which air is supplied through an inlet 223 via a conduit 26a, at a
pressure determined by the speed of rotation of the drum 13, under
the control of the electro-pneumatic transducer 26, previously
referred to. The disc section 206' provides an annular piston area
projecting radially outwardly of the spacer 211 thereabove, this
piston area being responsive to pressure in chamber S to provide a
downward force. Below the disc section 206' is another chamber T to
which air is supplied via a port 224 at a pressure determined, as
will be later described, by the tension on the line L. Such
pressure acts upwardly on the effective annular piston area of the
disc section 206'.
Below the disc 207, and in the body 208, is a chamber X which
constitutes an output chamber communicating with an outlet port 225
via porting 226. The pressure in the chamber acts upwardly on the
lower disc section 207', and this pressure is derived from on inlet
conduit 27a (FIG. 2a) connected to an inlet port 227, under the
control of the computer.
Interposed between the body 208 and an end member 228 having the
ports 225 and 227 therein, and clamped at its outer margin is a
double diaphragm assembly 229 including an upper diaphragm 230 and
a lower diaphragm 231 spaced apart by an outer marginal spacer 232
in which is formed one or more radial outlet ports 232a, which
communicate the space between the diaphragms 230 and 231 with the
atmosphere. In the body 208 above the upper diaphragm 230 is a
threaded bore having therein a nozzle 236, the port through which
communicates with the chamber X, and the outlet of which is opposed
by a valve head 237 suitably carried by the lower end of the stem
212. Air is supplied to the chamber 234 and thence to the nozzle
236 from the supply port 227 through a passage 238 which extends
through the margin of the diaphragms 230 and 231 and the spacer 232
and connects with a passage 239 leading into the chamber X.
Disposed in the passage 239 is a flow restrictor 240 having a
reduced passage therethrough. This flow restrictor is replaceable
through an opening in the body 208 which is closed by a threaded
closure plug 241. At the underside of diaphragm 231 in the end
member 228 is a chamber 241 which communicates with the output port
225. The output port 225 also communicates through the passage 226,
previously referred to, with the chamber X in the body 208 below
the piston or disc section 207'.
Inlet and outlet valve means are provided to control the admission
of fluid from the inlet 227 to the chamber 242 and the exhaust of
such fluid through the vent port 232a. This valve means includes a
valve seat 244 carried by a plate 245 below the diaphragm 231 and
having a valve port 246 leading from the outlet chamber 242 into
the space between the diaphragms 230 and 231. A coiled compression
spring 245a is provided beneath the plate 245 and applies a normal
upward bias to the diaphragm 231 and to the outlet valve seat 244.
A valve stem 247 is reciprocably mounted in a port 247a in the end
member 228, which port leads from the inlet 227 to the outlet
chamber 242. The stem is normally biased inwardly by a coiled
compression spring 248 which seats in a plug 249 in the end member
228 and acts inwardly on a spherical valve head 250 to bias the
same against an inlet valve seat 251.
As previously indicated, the computer means functions to regulate
the output signal pressure at the port 225 to a value which is
proportional to load on or position of the line L, as well as speed
of the drum 13, and in addition, the computer may be adjusted to
modify the output pressure by varying either the effective constant
force of spring K or the reference set point pressure in the
chamber R. Thus, as will be understood, the output pressure in
chamber X is determined by the various pressures in the various
chambers P1, P2, R, S and T, acting on the various piston areas of
the discs 203 to 207. The equation may be stated:
X = P1 + P2 - R + S - T + or - K,
where P1 and P2 are the pressure derived from the position sensor
16 tending to close the nozzle 236, R is the pressure derived from
a reference pressure source tending to open the nozzle 236, S is
the pressure derived from the speed of the drum 13 tending to close
the nozzle 236, T is the pressure derived from the tension sensing
means 15 tending to open the nozzle 236, and K is the spring
constant.
The effective signal outlet pressure in the outlet chamber 242 is a
function of the reduction in the inlet pressure caused by the
passage of air from the inlet 227 through the flow restrictor 240
into the pilot pressure chamber 234, and the reduction in pressure
resulting from the passage of air from the pilot pressure chamber
234 through the orifice means 236, as indicated by the arrows, into
the pressure chamber X. When the device is in the condition shown
in FIG. 3, the effective signal outlet pressure at the outlet 225
is the same as that in the chamber X, and, under the condition
shown, the pressure drop from the inlet 227 to the outlet 225 will
remain constant, unless the force derived from any of the position
sensing means TP, the tachometer 25, or the reference pressure is
varied, and, accordingly, as will be later more fully described,
the actuating pressure supplied to the clutch C will remain
constant.
Assuming that the force tending to shift the stacked disc sections
causes the valve head 237 to move upwardly allowing greater flow
from the pilot pressure chamber 234 into the chamber X, such action
will result in a decrease in the pilot pressure in the chamber 234.
As a consequence, pressure applied to the diaphragm 231 and the
force of the spring 145a will move the exhaust valve seat 244
upwardly and off of the end of the valve stem 247 to allow the
exhaust of fluid pressure from the outlet chamber 242 and the
chamber X through exhaust port 232a between the diaphragms 230 and
231, until the device again assumes the condition shown in FIG. 3
at which the exhaust valve port 246 is again closed. At this time,
the pressure at the outlet 255 will again be stabilized at a lower
value, determined by the change in forces acting on the stack of
disc sections 203' to 207'.
Assuming that the net force tending to move the stacked discs 203'
to 207' downwardly is increased, overcoming the effect of the
signal outlet pressure in the chamber X, then the orifice valve 237
will close the orifice means 236, thereby shutting off the passage
of air from the pilot pressure chamber 234 into the chamber X.
Under these circumstances, the pilot pressure in the pilot chamber
234 will build up, forcing the diaphragm 230 and the diaphragm 231
downwardly, thereby unseating the valve 250, so that inlet pressure
will transfer through port 247a of the inlet-outlet valve means,
resulting in an increase in the signal outlet pressure in the
outlet chamber 241 and in the chamber X, which will be effective to
again condition the apparatus as shown in FIG. 3, so that the
pressure drop therethrough again remains constant, but greater,
since there is less flow through the orifice means 236.
The conduit 300 leads from the outlet port 225 of the computing
relay 27 to the control pressure inlet 301 of a pressure controller
C1 of a conventional type adapted to control the pneumatic pressure
at an outlet 302 supplied from a suitable source (not shown)
through an inlet 303, whereby, as will be later described the slip
clutch C is adapted to apply a controlled constant torque to the
drum 13 which is a function of the output signal pressure of the
computer or transmitter means 27.
More particularly, the controller C1 may be Model 50 Controller of
Moore Products Co., of Spring House, Pennsylvania or a Model 2516
Controller of Fisher Governer Company of Marshalltown, Iowa, as
examples, the controller, generally shown in FIG. 2b, being the
latter and more specifically illustrated in Bulletin D-2506A of
that company.
The controller C1 is supplied a reference pressure at an inlet 304
from a conduit 305 connected to a source (not shown) by a regulator
valve 306, the same reference pressure being supplied to the
reference chamber R of the computer or transmitter means 27. This
reference pressure is admitted to a bellows 307 of the controller
which cts downwardly on a plate 308. Pressure supplied to the inlet
301 from the computer 27 causes an increase in acts in a bellows
309 which is opposed to the bellows 307 and acts upwardly on the
plate 308. The position of the plate 308 relative to a nozzle 310
to which controlled fluid pressure is supplied from the source
inlet 303, is determined by the difference in pressures in the
bellows 307 and 309. If the output pressure from the computer means
27 increases, the pressure increases in bellows 309 causing the
plate 308 to move closer to the nozzle 310, restricting flow
through the nozzle to cause an increase in the pressure in a
chamber 311 of a control valve 312, causing an increased downward
force on a diaphragm assembly comprising spaced diaphragms 313 and
314, which carries a valve seat 315, the passage through which
communicates with the atmosphere through a port 316 between the
diaphragms 313 and 314. The valve seat 315 engages and pushes
downwardly, under the circumstances now being described, on an
inlet and outlet valve having a head 317 for closing the exhaust
passage through the valve seat 315 and a head 318 which is moved
away from a seat 319 to allow increased supply pressure into the
valve outlet chamber 320 which acts on the diaphragm 314 until the
valve seat 315 is again moved upwardly to allow return upward
movement of the inlet-outlet valve head 318 towards its seat.
During the same time, pressure is increasing in the chamber 320,
such pressure is supplied to the outlet 302, and, thus, to the
clutch C, as well as to an adjustable proportioning valve 321 and,
depending on the adjustment of the latter, to an adjustable re-set
control valve 322 which controls the build up of pressure in a
bellows 323. This bellows 323 acts downwardly on the plate 308
tending to move the latter away from the nozzle 310 to decrease
pressure at the outlet 302 and in control valve chamber 320, and is
opposed by the upward action of a bellows 324 to which pressure is
supplied from the valve 322 at a slower rate, depending on the
adjustment of the valve 322, until the plate 308 is moved toward
the nozzle to again increase pressure at the outlet 302 and in the
valve chamber 320.
If a chamge in the system causes a decrease in pressure at the
inlet 301 to the controller C1, then, the reverse action will occur
in the controller, the tendency being in either case to attempt to
return to a pre-established, constant pressure at the outlet 302
which pressure is a function of the outlet pressure from chamber X
of the above-described computer means.
The outlet pressure from the controller means C1 is supplied via a
conduit 325 to cause actuation of the clutch C, but preferably a
typical booster 326 is employed, whereby the actual pressure source
(not shown) for the clutch includes an inlet to the booster 326
from a relatively high pressure source, and the pressure in conduit
325 acts on the usual pilot valve of the booster, so that the
outlet 328 of the booster is at a greater pressure than the signal
pressure from the controller C1. In addition, is preferred that a
selector valve 329 be provided, so that the air connector 75 of the
clutch C may be connected either to the booster outlet 328 or,
alternatively, to a separate source conduit 330 including a manual
control valve for operating the clutch C independently of the
control system.
A second controller means C2 is employed, as previously indicated,
to vary the pressure supplied to the chamber T of the computer or
transmitter means 27, as a function of line tension, and, thus, to
vary the output signal pressure from the computer according to the
above equation for the pressure of the chamber X.
Accordingly, leading from the hydraulic load cell 24 of the
tensiometer 15 of the sensing means TP, to the controller means C2
is a conduit 331 through which a hydraulic pressure signal
depending upon load or tension of the line L is transmitted to the
controller C2 to control the pneumatic pressure supplied to the
controller outlet 332 from an inlet 333. This controller C2, for
example, may be the Model 4151 remote set proportional controller
or transmitter of the Fisher Governor Company, as illustrated in
Bulletin D-4150C.
In the illustrative controller C2 is a hydraulic pressure
responsive means in the form of a Bourdon tube 334, an increase in
pressure in which forces a plate 335 toward an exhaust nozzle 336
of the control valve means 337, and a decrease in pressure in which
moves the plate 335 away from the nozzle 336 to vary the pressure
in the valve chamber 338 as the sensed hydraulic pressure signal is
varied to cause a decrease or increase in the outlet pressure at
outlet 333 and in the chamber T of the computer means 27, whereby
the net result is the application of a pressure to clutch C
dependent upon the tension on line L.
The control valve means 337 is similar to the control valve means
312 previously described, and includes a diaphragm assembly
comprising a diaphragm 339 exposed to pressure in the chamber 338
derived from the inlet 333, and a diaphragm 340 exposed to pressure
in the valve chamber 341 which communicates with the outlet 332.
This diaphragm assembly carries a valve seat 342, the passage
through which communicates with the atmosphere through a port 343.
A combined inlet and outlet valve has a head 344 engageable with
the seat 342 to prevent exhaust of pressure from chamber 341 and a
head 345 engageable with a seat 346, the passage through the latter
communicating between the inlet 333 and the chamber 341.
Thus, if pressure in the Bourdon tube 334 is increased, due to an
increase in tension on line L, the exhaust of pressure from chamber
338 will be restricted, causing an increase in pressure acting on
the diaphragm 339, so that the valve seat 342 will engage valve
head 344, preventing exhaust of air from the chamber 341 through
the exhaust port 343, and, at the same time, the valve head 345
will be moved off of its seat, allowing an increase in pressure in
chamber 341 which tends to return the diaphragm to its original
position.
Such increased pressure in the chamber 341 is conducted to an
adjustable valve 347, and thence to a bellows 349 which acts on the
plate 335 to move the same away from the nozzle 336 to effectively
reduce the pressure in the chamber 338. Resisting such movement of
the plate 335 is a bellows 350 having an inlet 351 to which a set
point pressure is supplied from a remote point, such as a regulator
valve 352 to which fluid is supplied from a suitable source (not
shown), as for example, the same source as supplies reference
pressure to the controller C1 and the computer or transmitter means
27.
Reduction in hydraulic signal pressure from the tensiometer 15 to
the controller C2 will cause the plate 335 to move away from the
nozzle 334 and a reduction in pressure in the control valve chamber
338, resulting in opening of the passage through valve seat 342 and
reduction in the signal at outlet 332 and computer chamber T. This
is to say that in the latter case, the operation of the controller
is the reverse of that described above, as will be understood
without need for further explanation.
For convenience, a gauge panel G is preferably provided, as seen in
FIG. 2b, whereby to indicate the effective pressures determined by
the position sensing means 16, the speed responsive means 26, and
the line tension or load responsive means 15, as well as the
reference pressure, the set-point pressure for controller C2, and
the ultimate clutch actuating pressure supplied to the slip clutch
C, respectively, such gauges being designated by the legends
"POS.", "REF.", "SPEED", "LOAD", SET-POINT", and "CLUTCH".
The "POS," gauge is connected to the output of the position sensing
means 16 by a conduit 400 which joins with the conduit 85a leading
to the computer chambers P1 and P2. The "REF." gauge is connected
by a conduit 401 to the conduit 305 which leads to both the inlet
304 of controller C1 and the chamber R of the computer 27. The
"SPEED" gauge is connected by a conduit 402 with the conduit 26a
leading to the chamber S of the computer 27 from the drum speed
responsive electro-pneumatic transducer means 26. The "LOAD" gauge
is connected by a conduit 403 and a conduit 404 with the outlet 332
from the load or tension responsive controller means C2 and the
chamber T of the computer 27. The "SET-POINT" gauge is connected by
a conduit 405 between the set-point inlet 351 of the load
responsive controller C2 and the supply regulator valve 352. The
"CLUTCH" gauge is connected by a conduit 406 with the air inlet
connector 75 of the clutch C and the outlet of the selector valve
329.
From the foregoing, it is believed that the operation of the
present invention clearly involves the controlling of the slip
clutch drive means for the drum 13 to apply a tension to the line L
controlled such that the tension is maintained substantially
constant below a value established by the load "SET-POINT"
pressure, but the air pressure supply to the clutch is, in the
automatic mode, controlled by changes in load or position sensed by
the sensing means TP, whereby under added load, the line will be
stripped from the drum in a predetermined ratio of feet of line to
increased load until the line tension resumes the established
value, and the line will then be wound on the drum to reposition
the load relative to the towing vessel. The speed and extent of
line movement in either direction is sensed by the speed responsive
means 25, 26 and the position sensing means 16 to vary the clutch
operation to maintain a pre-established tension on the line to an
established position at a controlled rate.
Thus, under all conditions encountered by a towed vessel or barge B
being towed by a towing vessel V, such as waves and wind or other
forces, the barge may be positioned closely to the towing vessel
without fear of parting the line L.
If it is assumed that a speed reference signal of 9 p.s.i. is
supplied to the computer chamber S when the drum is static, the
reference pressure of 5 p.s.i. is supplied to the inlet 304 of
controller C1 and to the chamber R of the computing relay 27, the
controller C2 supplies a load or tension reference pressure to the
chamber T of 9 p.s.i. at a predetermined line tension, and the
position sensor 16 supplies a position signal of 5 p.s.i. to the
chambers P1 and P2 of the computer 27, then the equation
representing the computer output pressure is
X = p1 + p2 - r + s - t
x = 5 + 5 - 5 + 9 - 9
x = 5
under these conditions, the output signal to the inlet 301 of
controller C1 from the computing relay is the same as the reference
input pressure signal at the inlet 304, and, therefore, the clutch
actuating signal pressure transmitted to the booster 326 remains
constant, and the line tension caused by the torque transmitted by
the clutch C remains constant.
Now, if the load on line L decreases, due to the tendency of the
towed vessel and the towing vessel to move towards one another, for
example, so that the load signal pressure derived from the load
sensor 15 and the controller C2 is reduced to 8 p.s.i., then the
equation reads:
X = p1 + p2 - r + s - t
x = 5 + 5 - 5 + 9 - 8
x = 6
under these conditions, the output signal to the inlet 301 of the
controller C1 is 6 p.s.i., but the reference pressure is 5 p.s.i.,
resulting in an increase in the pressure in the chamber 311 of the
control valve 312 and a resultant increase in the pressure in the
outlet 302 of the controller C1 and in the pressure applicable to
the clutch actuator to tend to wind in the line. Conversely, if the
load on the line increases, the clutch actuating signal pressure
will be decreased.
Under these conditions, however, line position changes are
reflected in the pressure signal derived from the position sensor
operated controller C2, so that as the line moves in or out the
effective pressure in the chamber P1 and P2 of the computer 27 is
varied by the position sensing means 16, and the effective pressure
in the chamber S of the computer is varied by the speed of drum
movement, resulting in a control system which is capable of
maintaining position of the towed vessel, under constant line
tension conditions, but enables the line to be stripped from the
drum in a predetermined ratio of feet of line to increased load on
the line above the set-point. Indeed, the system can be at
equilibrium when subjected to loads on the line different than the
load which the system is adjusted for by the set-point. The system
automatically returns the line to a pre-established position when
the line is subjected to the pre-established tension.
* * * * *