Hover control system for a submersible buoy

A compressed fluid hover control system for a submersible buoy in which the water level in a buoyancy chamber is controlled in accordance with external water pressure and predetermined levels of water in the buoyancy chamber. More specifically, a submersible buoy having a fluid-containing chamber containing a compressed fluid is connected to a buoyancy chamber by a gas inlet valve. A gas exhaust valve connects an upper portion of the buoyancy chamber to the surrounding water and a relief duct connects a lower portion of the buoyancy chamber to the surrounding water. Both the gas inlet and gas exhaust valves are controlled by a valve control circuit which opens and closes the valves in accordance with predetermined criteria related to water levels within the buoyancy chamber and the depth of the buoy as determined by a water pressure transducer. The valve control circuit thus causes the buoy to oscillate between predetermined depth levels, those levels changing as the compressed fluid is expended in order to maximize operating life of the buoy. In the specific embodiment described, four level sensors are utilized in the buoyancy chamber and four predetermined depths are programmed in the valve control circuit.

BACKGROUND OF THE INVENTION 
The invention relates to hover control systems for submersible buoys. 
Conventional control systems frequently utilize an externally generated 
signal to transfer a pressurized buoyant fluid from a fluid storage 
chamber to a buoyancy chamber, the buoyancy chamber containing water to be 
displaced by the buoyant fluid. These systems are adequate for locating 
the buoy at a predetermined depth but are not readily adaptable for 
automatic depth adjustment because of weight changes due to loss of the 
buoyant fluid. In order to effect an automatic transfer of buoyant fluid 
to a buoyancy chamber in order to maintain hovering at a predetermined 
depth, other conventional control systems sense the level of water in the 
buoyancy chamber and maintain an appropriate level for the depth being 
desired. These systems typically use analog measuring techniques, or flood 
the buoyancy chamber with buoyancy fluid for a predetermined time when a 
predetermined depth is reached. Such systems tend to excessively oscillate 
about the predetermined depth and thus are wasteful of the buoyancy fluid. 
The hover control system of the present invention solves the above 
problems by providing a simplified control system that responds only to 
predetermined water levels within the buoyancy chamber and depth of the 
buoy as measured by a water pressure transducer. 
SUMMARY OF THE INVENTION 
The invention provides a hover control means for submersible buoys having a 
fluid-containing chamber member for containing a pressurized fluid and a 
buoyancy chamber member having a bottom portion in fluid communication 
with a surrounding liquid such as a body of water. A first valve means 
interconnects the fluid-containing chamber to the buoyancy chamber and a 
second valve means interconnects an upper portion of the buoyancy chamber 
to the surrounding liquid. Pressure sensing means for determining liquid 
pressure external to the buoy is provided; and a level sensing means for 
determining discrete liquid levels in the buoyancy chamber is also 
provided. A control means responsive to the pressure sensing means and the 
level sensing means controls the first and second valves so as to maintain 
the buoy in a hovering condition. 
In a specific embodiment of the invention, four water level sensors are 
provided in the buoyancy chamber, the first sensor being located just 
below a water level which would provide neutral buoyancy when the 
fluid-containing chamber is fully pressurized with a compressed buoyancy 
fluid. The second sensor is located just above a water level in the 
buoyancy chamber which would provide neutral buoyancy when the 
fluid-containing chamber is no longer pressurized with respect to the 
surrounding body of water. The third and fourth water level sensors are 
located between the first and second sensors. A valve control circuit 
controls the first and second valves in accordance with inputs from the 
four water level sensors and a water pressure transducer. Four 
predetermined water depths are provided to the valve control circuit, 
these depths being compared to actual water depth as measured by the 
pressure transducer. Each of the predetermined depths corresponds to one 
of the four water level sensors in the buoyancy chamber. The valve control 
circuit is mechanized so that the buoy will slowly oscillate at depths 
related to the four predetermined depths. 
The valve control circuit is basically a digital device which incorporates 
a means for comparing discrete water levels within the buoyancy chamber 
and the actual buoy depth with respect to the four predetermined depths. 
The first and second valves are opened and closed in accordance with this 
comparison. This simplified approach for the valve control circuit allows 
implementation with a minimal amount of electronic circuitry, thereby 
resulting in low cost, ruggedness, long operating life, and a long shelf 
life. The average compressed fluid consumption for each hover cycle 
between two of the predetermined depths, and the average hover cycle time 
is greatly reduced with respect to conventional systems when the third and 
fourth water level sensors are located much closer together than are the 
first and second water level sensors associated with the neutral buoyancy 
levels. In addition, the lower compressed fluid consumption results in a 
smaller acoustic signature than that associated with conventional hover 
control systems.

DETAILED DESCRIPTION 
A detailed illustrative embodiment of the invention disclosed herein 
exemplifies the invention and is currently considered to be the best 
embodiment for such purposes. However, it is to be recognized that other 
means for altering the buoyancy of the buoy in accordance with discrete 
water levels in a buoyancy chamber and predetermined buoy depths could be 
utilized. Accordingly, the specific embodiment disclosed is only 
representative in providing a basis for the claims which define the scope 
of the present invention. 
As previously explained, the invention provides a hover control system for 
a submersible buoy in which various water levels within a buoyancy chamber 
and the water pressure surrounding the buoy are used to alter its buoyancy 
as water in the buoyancy chamber is cycled within predetermined limits. 
Although the exemplary embodiment is described in terms of a buoy 
submersed in water, the hover control system could be utilized in 
conjunction with other liquids such as oil or the like. 
Referring to FIG. 1, a submersible buoy 10 is shown having a compressed 
fluid-containing chamber 12, a buoyancy chamber 14 and a payload section 
16 which could contain sound detection equipment, explosives, or the like. 
The compressed fluid chamber 12 is connected to the buoyancy chamber 14 by 
a gas inlet duct 18. Flow of the compressed fluid, which could be gaseous 
in form, through the gas inlet duct 18 is regulated by a gas inlet valve 
20. A gas exhaust duct 24 connects an upper portion of the buoyancy 
chamber 14 to the surrounding water W. Flow through the gas exhaust duct 
24 is controlled by a gas exhaust valve 26. A relief duct 28 connects a 
bottom portion of the buoyancy chamber 14 to the surrounding water. A 
pressure transducer 30 provides a signal related to the surrounding water 
pressure to a valve control circuit 34 whose operation will be explained 
in further detail below. In addition, there are four water-level sensors 
located in the buoyancy chamber 14. The sensors are designated as a first 
level sensor L1, a second level L2, a third level sensor L3 and a fourth 
sensor L4. These sensors are of the type that provides one output voltage 
when the water level in the buoyancy chamber 14 is above an associated 
predetermined level, and another voltage when the water level is below the 
predetermined level. 
The various components of the submersible buoy 10 are located so as to keep 
the centers of mass, buoyancy, and vertical drag on the vertical axis of 
the buoy 10, and the center of buoyancy always above the center of mass. 
The four level sensors L1-L4 can be of any suitable type, examples of 
which include seawater switches or float actuated microswitches. The first 
water level sensor L1 is vertically located just below a water level 
within the buoyancy chamber 14 which will result in a neutral buoyancy 
when the fluid chamber 12 is completely charged with compressed fluid. 
This neutral buoyancy level is shown as a dotted line 36. The second water 
level sensor L2 is vertically located just above a water level within the 
buoyancy chamber 14 which will result in a neutral buoyancy when the fluid 
chamber 12 is no longer pressurized with respect to the pressure of the 
surrounding water. This neutral buoyancy is shown as a dotted line 38. The 
location of the water level switches L1 and L2 in the above manner will 
compensate for the buoy's loss of mass as compressed fluid is expended, 
and assures control system stability. The other two level sensors L3 and 
L4 are located between the first two level sensors L1 and L2. Each of the 
water level sensors L1-L4 is associated with a predetermined reference 
depth. These four reference depths are set into the valve control circuit 
34 and, in a manner to be explained below, are utilized in conjunction 
with output signals from the water level sensors L1-L4 within the buoyancy 
chamber 14 to control the hover depth of the submersible buoy. Thus, a 
reference depth D1 is associated with the first sensor L1, D2 with L2, D3 
with L3, and D4 with L4. The two depths D3 and D4 are chosen to bracket a 
desired depth DD. The reference depths may be offset from each other by 
fixed depth increments or fixed percentages of the desired depth DD, or by 
any other scheme so long as D1&gt;D3&gt;DD&gt;D4&gt;D2&gt; and the depth increment 
between D2 and D1 is less than a desired peak-to-peak depth keeping 
tolerance. By means of the valve control circuit 34 to be explained below, 
high pressure fluid from the compressed fluid-containing chamber 12 is 
admitted to the buoyancy chamber 14 through the gas inlet valve 20 when a 
buoyancy increase is desired. This fluid displaces water from the buoyancy 
chamber 14 which passes out through the relief duct 28, thereby causing 
the buoy to rise. 
As previously explained, the valve control circuit 34 has four 
predetermined reference depths D1-D4 set in prior to deployment of the 
buoy. The water pressure transducer 30 provides another input to the valve 
control circuit 34 so that the actual pressure surrounding the buoy can be 
continually compared to the four predetermined reference depths or 
pressure D1-D4. The four water level sensors L1-L4 are also connected to 
the valve control circuit 34 so that four specific water levels within the 
buoyancy chamber can be ascertained. The valve control circuit 34 is 
chosen to control the gas inlet valve 20 and the gas exhaust valve 24 in 
accordance with five predetermined control states. These five control 
states are: 
(1) If the actual buoy depth is greater than the first predetermined depth 
D1, and the buoyancy chamber water level as shown at 40 is above L1, open 
the gas inlet valve 20 (increase buoyancy). 
(2) If the actual buoy depth is greater than the third predetermined depth 
D3 and the buoyancy chamber water level is above L3, open the gas inlet 
valve 20 (increase buoyancy). 
(3) If the actual buoy depth is less than the second predetermined depth D2 
and the buoyancy chamber water level is below L2, open the gas exhaust 
valve 26 (decrease buoyancy). 
(4) If the actual buoy depth is less than the fourth predetermined depth D4 
and the buoyancy chamber water level is below L4, open the gas exhaust 
valve 26 (decrease buoyancy). 
(5) If none of the test conditions in control states 1 through 4 are 
satisfied, close both the gas inlet valve 20 and the gas exhaust valve 26. 
Operation of the buoy in accordance with the five control states previously 
explained can be understood by reference to FIG. 2. The four predetermined 
reference depths D1, D2, D3 and D4 can be seen. The figure shows typical 
depth versus time profiles which illustrate operation of the valve control 
circuit 34 as a function of buoy depth and loss of compressed fluid. 
Assuming the buoy 10 is launched near the water surface at 42 with the 
buoyancy chamber 14 full of water, it begins to sink and soon achieves a 
terminal velocity shown at 44 which is related to its drag coefficient and 
the negative buoyancy inherent in its structure. The buoy continues to 
sink at a constant rate until it reaches the third predetermined depth D3 
shown at 46. At this point, the second control state is activated because 
the buoy depth is now below the third predetermined depth D3 and water in 
the buoyancy chamber 14 is above the third water level sensor L3. At this 
point, gas flowing from the fluid-containing chamber 12 to the buoyancy 
chamber 14 forces water in the buoyancy chamber 14 out the relief duct 28 
until its level is below the third water level sensor L3. When the water 
is below the third water level sensor L3, as shown at 48, the fifth 
control state is implemented, thus closing the gas inlet duct 20. The buoy 
10 now has an increased buoyancy which results in a lower vertical 
velocity. Since none of the compressed fluid has yet been lost to the 
surrounding body of water, the new water level in the buoyancy chamber 14 
does not result in a positive buoyancy, and the buoy depth continues to 
increase at a slower velocity until the first predetermined depth D1 is 
reached, as shown at 50. When the buoy 10 is below the first predetermined 
level D1, the first control state is activated and the gas inlet valve 20 
is again opened until the buoyancy chamber water level is forced below the 
first level sensor L1. As previously explained, since L1 is below the 
neutral buoyancy water line 36 when the fluid chamber 12 is full of 
compressed fluid, a slight positive buoyancy is developed and the buoy 10 
begins to rise. When the buoyancy chamber water level reaches L1 as shown 
at 52, the fifth control state is again activated and the gas inlet valve 
20 is closed. The buoy 10 continues to slowly rise until it reaches the 
fourth predetermined depth D4 as shown at point 54. At this point the 
fourth control state is activated because the buoy is at a depth less than 
that of the fourth predetermined depth D4 and the water level is below the 
fourth water level sensor L4. At this point, the gas exhaust valve 26 is 
opened and the buoyancy fluid passes from the buoyancy chamber 14 to the 
surrounding water until the water level within the buoyancy chamber 14 
rises to that of the fourth water level sensor L4. This new water level 
results in the buoy again having a negative buoyancy as shown at 56 and 
the buoy 10 slowly begins to descend. This cycle then repeats itself with 
the buoy oscillating with a nominal overshoot and undershoot between the 
first and fourth predetermined depths D1 and D4. 
During each of the above-described oscillation cycles the buoy 10 loses an 
increment of compressed fluid, thus reducing its total mass. However, the 
oscillations continue until enough of the compressed fluid has been lost 
so that a buoyancy chamber water level at the third level sensor L3 no 
longer results in a negative buoyancy, but rather in a positive buoyancy 
as indicated at point 60. This results in a second oscillation phase in 
which the buoy 10 oscillates between the third and fourth predetermined 
depths D3 and D4. This second oscillation phase may be accompanied by a 
greatly reduced compressed fluid consumption per oscillation cycle if the 
third and fourth water level sensors L3 and L4 are closer to each other 
than to the first and second water level sensors L1 and L2, respectively. 
Oscillation between the third and fourth predetermined depths D3 and D4 
will continue until sufficient compressed fluid is lost so that a buoyancy 
chamber water level at the fourth water level sensor L4 no longer results 
in a negative buoyancy, but rather in a positive buoyancy as indicated at 
point 62. This results in a third oscillation phase in which the buoy 10 
continues upwardly until it reaches the second predetermined depth D2 and 
the third control state is activated. The gas exhaust valve 26 is then 
opened as shown at 64 and remains open until the buoyancy chamber water 
level reaches the second water level sensor L2 as shown at 66. This cycle 
continues with the buoy oscillating between the second and third 
predetermined depths until the buoy is out of compressed fluid. 
Referring now to FIG. 3, logic in the valve control circuit 34 for 
implementing the five predetermined control states can be seen. Signals 
corresponding to the predetermined reference depths or pressures D1-D4 are 
provided by a pressure indicator unit 80. The signal 82 corresponding to 
reference depth D1 goes from a low state to a high state whenever the 
actual buoy depth as measured by the pressure transducer 30 exceeds the 
first predetermined depth D1. Similarly, signals 84, 86 and 88 also go 
from a low state to a high state whenever the actual buoy depth exceeds 
the second, third and fourth predetermined depths D2, D3 and D4, 
respectively. The four level sensors L1-L4 are also chosen to provide 
output signals 90, 92, 94 and 96, respectively, that go from a low state 
to a high state whenever the water level in the buoyancy chamber 14 
exceeds the level being monitored by its associated level sensor. A first 
AND gate 100 provides a high output signal to open the gas inlet valve 20 
when D1 and L1, signals 82 and 90, respectively, are high; and a second 
AND gate 102 provides a high output signal to open the gas inlet valve 
when D3 and L3 are high. A NOR gate 104 provides a high signal to close 
the gas inlet valve when neither output signal from the two AND gates 100 
and 102 are high. Two additional NOR gates 106 and 108 and NOR gate 110 
are used to similarly control the gas exhaust valve 26. 
Although the above description and accompanying figures utilize four 
predetermined reference depths and four water level sensors, it should be 
clear that the concept can be applied to larger or smaller numbers of 
reference depth/level sensor pairs. However, it is important that 
regardless of the number of depth/sensor pairs utilized, the upper-most 
water level sensor should be above the neutral buoyancy line 38 when the 
compressed fluid-containing chamber is empty, and the lower-most water 
level sensor should be below the neutral buoyancy line 36 when the 
fluid-containing chamber is full. 
It should now be apparent that a hover control system for a submersible 
buoy has been described in which the depth of the buoy is continually 
adjusted in response to water pressure external to the buoy and to 
discrete water levels within a self-contained buoyancy chamber. In the 
embodiment described, four water level sensors and four predetermined 
depths are utilized, the buoy alternating between various of the 
predetermined depths as the compressed fluid is depleted.