Patent Publication Number: US-10308334-B2

Title: Self-draining oil buoyancy regulating device for underwater robots

Description:
CROSS REFERENCE OF RELATED APPLICATION 
     This is a U.S. National Stage under 35 U.S.C 371 of the International Application PCT/CN2015/092177, filed Oct. 19, 2015. 
     BACKGROUND OF THE PRESENT INVENTION 
     Field of Invention 
     The present invention relates to a buoyancy regulating device, and more particularly to a self-draining oil buoyancy regulating device for underwater robots. 
     Description of Related Arts 
     Underwater robots and other underwater appliances work in different depth under the water, which requires a control over the movement and depth in the water. The underwater environment makes the energy supply hard so control the buoyancy by active propelling is impossible, which makes the buoyancy regulating device necessary for the appliances to regulate the buoyancy and move up and down. 
     The conventional methods for regulating the buoyancy are mechanical transmission, active oil pumping, load rejection, water drainage and phase change. 
     Mechanical transmission method adopts a series of mechanical transmission to adjust the volume of the appliance by changing the position of the execution parts to regulate the buoyancy, which needs mechanical self-locking structure to keep the volume of the appliance unchanged during a period of time. To overcome the static friction caused by maintaining the self-locking consumes energy, which wastes the energy and cause low efficiency. Compared to other methods the mechanical transmission adopts transmission parts, which is heavier in weight and bigger in volume when regulating same buoyancy. Besides changing the relative position of the rigid bodies by piston makes the sealing underwater a difficult problem to solve compared to other methods and reduces the reliability. For example the basic theory of a most commonly used method for regulating the buoyancy is to drive the piston to change the volume of the liquid (sea water or oil) inside the piston cylinder by motor through screw rod. The reciprocating motion of the piston inside the cylinder undermines the reliability due to the sealing problem. 
     The active oil pumping method is to pump the hydraulic oil into the oil bag through oil channel and change volume of displacement by changing the volume of the oil bag, which further regulates the buoyancy. Same as the mechanical transmission method the active oil pumping also needs the self-locking to maintain the volume of the appliance unchanged during a period of time. The conventional hydraulic system has complex valve system which increases the weight and volume of the appliance. All the oil channels are acting during the oil draining, which is passive oil drainage and is classified as active oil return and passive oil return according to whether the adopted pump is one-way or two-way. The problem of the passive oil drainage and active oil return plan is when the water is shallow and the external pressure is lower than the friction loss the active oil return fails. The problem of passive oil drainage and passive oil return is that a two-way pump is needed. Under the same flow pressure the cost, weight and volume of the two-way pump are bigger than that of the one-way pump. The hydraulic pump is on during the oil return and oil drainage, which consumes the energy. The two-way pump is unable to quick switch between forward and reversal rotation, which affects the control performance. 
     The method of load rejection is to control the buoyancy by throwing away the weight to reduce the self-gravitation, which is irreversible and makes the appliance moves up one time. The method of water drainage is to adjust the water displacement and suction by releasing or compressing the high-pressure gas. The compression of high pressure gas is accomplished by water pump, which is hard to control due to the process of gas compression is nonlinear and tend to be affected by many factors. The water pump is not reliable and has short service life if stay in the sea for a long time. The method of phase change is to regulate the buoyancy by the change in volume of specific medium during the process of phase change. The phase change is a complex nonlinear thermodynamic process and the gas generated is easy to be compressed, which is hard to control. 
     SUMMARY OF THE PRESENT INVENTION 
     An object of the present invention is to provide a self-draining oil buoyancy regulating device for underwater robots, which is a buoyancy regulating solution has the advantages of stable, easy to control, quick switch between oil drainage and oil return, low energy consumption, compact structure, light weight and small volume. The present invention is applied in the buoyancy and depth control for underwater appliance. 
     In order to accomplish the above object, the present invention provides a self-draining oil buoyancy regulating device for underwater robots, comprising: an accumulator, a lower hatch cover, a lower valve block, a hydraulic-operated check valve, an upper valve block, a pump outlet pressure sensor, an accumulator pressure sensor, a depth-pressure sensor, a hydraulic pump motor assembly, a directional valve, a relief valve, a control circuit board, a hatch shell, an upper hatch cover, a bladder, a water-proof connector and host computer, wherein 
     the accumulator, the lower hatch cover, the hatch shell, the upper hatch cover and the bladder are fixedly connected in sequence; the water-proof connector is fixed on the upper hatch cover; 
     The depth-pressure sensor is settled on the lower hatch cover to check the underwater pressure; the upper valve block, the hydraulic-operated check valve and the lower valve block is connected though piping in sequence; the lower valve block is fixed on the lower hatch cover; 
     The pump outlet pressure sensor and the accumulator pressure sensor are settled on the lower valve block; the directional valve and the upper valve block are connected through piping; the hydraulic pump motor assembly and the relief valve are both connected with the lower valve block through piping; 
     The depth-pressure sensor, the pump outlet pressure sensor and the accumulator pressure sensor are all connected with the control panel; the control panel is connected with the external power supply and the host computer respectively by the water-proof connector; 
     Furthermore on a top surface of the lower valve block there are a lower valve block 10 th  port, a lower valve block 11 th  port and a lower valve block 12 th  port; on sides of the lower valve block there are a lower valve block 2 nd  port, a lower valve block 3 rd  port, a lower valve block 4 th  port, a lower valve block 5 th  port, a lower valve block 6 th  port, a lower valve block 7 th  port, a lower valve block 8 th  port and a lower valve block 9 th  port; on the bottom surface of the lower valve block there is a lower valve block 1 st  port; inside the lower valve block there are runners, wherein the lower valve block 2 nd  port, the lower valve block 3 rd  port, the lower valve block 9 th  port and the lower valve block 12 th  port are connected by a first runner; the lower valve block 1 st  port, the lower valve block 7 th  port, the lower valve block 8 th  port and the lower valve block 11 th  port are connected by a second runner; the lower valve block 4 th  port, the lower valve block 5 th  port, the lower valve block 6 th  port and the lower valve block 10 th  port are connected by a third runner; 
     wherein the lower valve block 1 st  port is connected with the accumulator through the lower hatch cover; the lower valve block 2 nd  port is connected with an oil draining outlet of the hydraulic pump motor assembly; the lower valve block 3 rd  port is connected with an oil inlet of the relief valve; the lower valve block 4 th  port is connected with an oil outlet of the relief valve; the lower valve block 5 th  port is connected with an oil return outlet of the hydraulic pump motor assembly; the lower valve block 6 th  port is connected with the bladder; the lower valve block 7 th  port, the lower valve block 8 th  port and the lower valve block 9 th  port are blocked; the lower valve block 10 th  port is connected with an oil return outlet of the hydraulic-operated check valve; the lower valve block 11 th  port is connected with a first working port of the hydraulic-operated check valve; the lower valve block 12 th  port is connected with an oil inlet of the hydraulic-operated check valve; 
     Furthermore on the upper valve block there are an upper valve block 1 st  port, an upper valve block 2 nd  port, an upper valve block 3 rd  port, an upper valve block 4 th  port; wherein a second working port of the directional valve is connected with a second working port of the hydraulic-operated check valve through the upper valve block 1 st  port; an oil outlet of the directional valve is connected with an oil return outlet of the hydraulic-operated check valve through the upper valve block 2 nd  port; a first working port of the directional valve is connected with the first working port of the hydraulic-operated check valve through the upper valve block 3 rd  port; an oil inlet of the directional valve is connected with the oil inlet of the hydraulic-operated check valve through the upper valve block 4 th  port; 
     The control panel further comprising: a first power supply module, a second power supply module, a communication drive module, a voltage reference stabilizing module, a first filter module, a second filter module, a third filter module, AD converter module and single-chip microcomputer; wherein the first power supply module transfers an external 12V power supply to an internal 12V power supply inside the control panel; the second power supply module transfers an internal 12V power supply inside the control panel to a 5V power supply for the single-chip microcomputer; the first power supply module is connected to the second power supply module and the voltage reference stabilizing module respectively; input ends of a power supply of the pump outlet pressure sensor, the accumulator pressure sensor, the depth-pressure sensor, the hydraulic pump motor assembly and the directional valve are all connected with the second power supply module; a signal cable of the depth-pressure sensor is connected with the first filter module; a signal cable of the pump outlet pressure sensor is connected with the second filter module; a signal cable of the accumulator pressure sensor is connected with the third filter module; the first filter module, the second filter module, the third filter module and the voltage reference stabilizing module are all connected with the AD converter module; the AD converter module is connected with an input end of the single-chip microcomputer; control cables of the hydraulic pump motor assembly and the directional valve ( 23 ) are connected with an output end of the single-chip microcomputer; the communication drive module is connected with the single-chip microcomputer; the first power supply module is connected with the external power supply through a power cord of the water-proof connector; the communication drive module is connected with the host computer through a signal cable of the water-proof connector. 
     Compared to the conventional technology the present invention has following benefits:
         1. By adopting a whole hydraulic plan, there are no other movement components except the pump and motor. All the key sealing parts are static seal, which makes the mechanical transmission has reliable sealing and has long service life.   2. Realize the active oil drainage and passive oil return by taking the advantage of the accumulator, which reduces the energy consumption and increases the energy efficiency. At the mean time the problem of the active oil return failure if the water is shallow and the external pressure is lower than the friction loss. Compared to the conventional hydraulic solution by adopting the present invention the working duration under the water is prolonged; the stability is improved; and the quick switch between the oil drainage and oil return is fulfilled. The accumulator is a standard component which is low in cost and easy to find.   3. By adopting the directional valve and the relief valve, the oil channel is simplified. By using the hydraulic-operated check valve and building a self-locking oil channel accordingly the leakage of the accumulator inside the oil channel is reduced without compromise the function, which enhances the security. The valve block assembly reduces the whole assembling volume of the oil channel and makes the appliance compact.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective appearance of the present invention; 
         FIG. 2  is an axonometric explosive view of the assembling of the present invention (except oil pipe) 
         FIG. 3  is an external sectional view of the lower hatch cover of the present invention; 
         FIG. 4  is an external sectional view of the upper hatch cover of the present invention; 
         FIG. 5  is an external sectional view of the hatch shell of the present invention; 
         FIG. 6  is an external view of the lower valve block of the present invention; 
         FIG. 7  is a top sectional view of the lower valve block of the present invention; 
         FIG. 8  is an external sectional view of the upper valve block of the present invention; 
         FIG. 9  is a connection diagram of the modules on the control panel of the present invention; 
         FIG. 10  is the working diagram of the present invention; 
         FIG. 11  is the connection diagram of the hydraulic oil channel; 
     
    
    
     Element reference: accumulator  1 , lower hatch cover  2 , lower valve block  3 , hydraulic-operated check valve  4 , upper valve block  5 , 1 st  oil pipe connector  6 , 2 nd  oil pipe connector  7 , 3 rd  oil pipe connector  8 , 4 th  oil pipe connector  9 , 5 th  oil pipe connector  10 , 6 th  oil pipe connector  11 , 7 th  oil pipe connector  12 , 8 th  oil pipe connector  13 , 9 th  oil pipe connector  14 , 10 th  oil pipe connector  15 , 1 st  oil channel plug  16 , 2 nd  oil channel plug  17 , 3 rd  oil channel plug  18 , pump outlet pressure sensor  19 , accumulator pressure sensor  20 , depth-pressure sensor  21 , hydraulic pump motor assembly  22 , directional valve  23 , relief valve  24 , control panel  25 , 1 st  bolt  26 , 2 nd  bolt  27 , 3 rd  bolt  28 , 4 th  bolt  29 , hatch shell  30 , upper hatch cover  31 , bladder  32 , water-proof connector  33 , nut  34 , lower valve block 1 st  port  35 , lower valve block 2 nd  port  36 , lower valve block 3 rd  port  37 , lower valve block 4 th  port  38 , lower valve block 5 th  port  39 , lower valve block 6 th  port  40 , lower valve block 7 th  port  41 , lower valve block 8 th  port  42 , lower valve block 9 th  port  43 , lower valve block 10 th  port  44 , lower valve block 11 th  port  45 , lower valve block 12 th  port  46 , upper valve block 1 st  port  47 , upper valve block 2 nd  port  48 , upper valve block 3 rd  port  49 , upper valve block 4 th  port  50 . 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1  to  FIG. 11  of the drawings, according to a preferred embodiment of the present invention is illustrated, comprising: accumulator  1 , lower hatch cover  2 , lower valve block  3 , hydraulic-operated check valve  4 , upper valve block  5 , 1 st  oil pipe connector  6 , 2 nd  oil pipe connector  7 , 3 rd  oil pipe connector  8 , 4 th  oil pipe connector  9 , 5 th  oil pipe connector  10 , 6 th  oil pipe connector  11 , 7 th  oil pipe connector  12 , 8 th  oil pipe connector  13 , 9 th  oil pipe connector  14 , 10 th  oil pipe connector  15 , 1 st  oil channel plug  16 , 2 nd  oil channel plug  17 , 3 rd  oil channel plug  18 , pump outlet pressure sensor  19 , accumulator pressure sensor  20 , depth-pressure sensor  21 , hydraulic pump motor assembly  22 , directional valve  23 , relief valve  24 , control panel  25 , 1 st  bolt  26 , 2 nd  bolt  27 , 3 rd  bolt  28 , 4 th  bolt  29 , hatch shell  30 , upper hatch cover  31 , bladder  32 , water-proof connector  33 , nut  34  and several oil pipes; wherein an overlay hydraulic-operated check valve  4  with a model MPCV-02W is adopted while other model type is also applicable; a water-proof connector  33  with a model BH5F is adopted while other model type is also applicable; a diaphragm accumulator with a model type Careland AD1.4-140-2x is adopted; Pressure transmitters with a model type KYB2003-04M1P3C1-I (0-1.6 MPa) made by Kang Yu-control are adopted as the pump outlet pressure sensor  19 , the accumulator pressure sensor  20  and the depth-pressure sensor  21  while other model type is also applicable; a bladder  32  for accumulator model NXQ1 is adopted while other type is also applicable. 
     As illustrated in  FIG. 3 , the lower hatch cover  2  is in flange plate shape. On the geometry center of the bottom of the lower hatch cover there is a male threaded cylinder. On the top surface of the lower hatch cover  2  there are 4 threaded blind holes, a pipe taper threaded through hole to fix the depth-pressure sensor  21  and a through-hole at the geometry center of the top surface. There is a groove on the side of the upper part of the lower hatch cover  2  containing a sealing ring. There are 8 through holes and 4 through holes for external connection distributed evenly in circumferential direction of the flange shaped lower hatch cover  2 . The accumulator  1  is connected with the male threaded cylinder on the bottom of lower hatch cover  2 . 
     As illustrated in  FIG. 4 , the upper hatch cover  31  is in flange plate shape. On the geometry center of the top of the upper hatch cover there is a male threaded cylinder. There is a groove on the side of the bottom of the upper hatch cover  31  containing a sealing ring. There are 8 through holes and 4 through holes for external connection distributed evenly on the flange shaped upper hatch cover  31 . The bladder  32  is connected with the male threaded cylinder on the top of upper hatch cover  31 . On the geometry center of the upper hatch cover  31  there is threaded hole to fix the 10 th  oil pipe connector  15 . There is an embossment on the top of upper hatch cover  31 . On the geometry center of the embossment there is a through hole to fix the water-proof connector  33 . 
     As illustrated in  FIG. 5 , the two ends of the hatch shell  30  are in flange plate shape. There are grooves containing sealing rings on the flange plates at the two ends. On each of the flange plates there are 8 through holes. The 8 through holes on the top flange plate are match with the 8 through holes on the upper hatch cove  31 . The 8 through holes on the bottom flange plate are match with the 8 through holes on the lower hatch cove  2 . 
     As illustrated in  6  and  7 , there are four positioning through holes on the lower valve block  3 , on the top surface of the lower valve block  3  there are two pipe taper threaded holes to fix the pump outlet pressure sensor  19  and the accumulator pressure sensor  20 ; 
     On a top surface of the lower valve block  3  there are a lower valve block 10 th  port  44 , a lower valve block 11 th  port  45  and a lower valve block 12 th  port  46 ; on sides of the lower valve block  3  there are a lower valve block 2 nd  port  36 , a lower valve block 3 rd  port  37 , a lower valve block 4 th  port  38 , a lower valve block 5 th  port  39 , a lower valve block 6 th  port  40 , a lower valve block 7 th  port  41 , a lower valve block 8 th  port  42  and a lower valve block 9 th  port  43 ; on the bottom surface of the lower valve block  3  there is a lower valve block 1 st  port  35 ; inside the lower valve block  3  there are runners, wherein the lower valve block 2 nd  port  36 , the lower valve block 3 rd  port  37 , the lower valve block 9 th  port  43  and the lower valve block 12 th  port  46  are connected by a first runner; the lower valve block 1 st  port  35 , the lower valve block 7 th  port  41 , the lower valve block 8 th  port  42  and the lower valve block 11 th  port  45  are connected by a second runner; the lower valve block 4 th  port  38 , the lower valve block 5 th  port  39 , the lower valve block 6 th  port  40  and the lower valve block 10 th  port  44  are connected by a third runner; 
     The lower valve block 1 st  port  35  is connected with the accumulator  1  through the through hole on the geometry center of the lower hatch cover  2 ; the lower valve block 2 nd  port  36  is connected with the 1 st  oil pipe connector  6 ; the lower valve block 3 rd  port  37  is connected with the 2 nd  oil pipe connector  7 ; the lower valve block 4 th  port  38  is connected with 3 rd  oil pipe connector  8 ; the lower valve block 5 th  port  39  is connected with the 4 th  oil pipe connector  9 ; the lower valve block 6 th  port  40  is connected with the 5 th  oil pipe connector  10 ; the lower valve block 7 th  port  41  is connected with the 1 st  oil channel plug  16 ; the lower valve block 8 th  port  42  is connected with the 2 nd  oil channel plug  17 ; and the lower valve block 9 th  port  43  is connected with the 3 rd  oil channel plug  18 ; the lower valve block 10 th  port  44  is connected with an oil return outlet of the hydraulic-operated check valve  4 ; the lower valve block 11 th  port  45  is connected with a first working port of the hydraulic-operated check valve  4 ; the lower valve block 12 th  port  46  is connected with an oil inlet of the hydraulic-operated check valve  4 . 
     As illustrated in  FIG. 8 , there are four positioning through holes on the upper valve block  5 ; on the upper valve block  5  there are an upper valve block 1 st  port  47 , an upper valve block 2 nd  port  48 , an upper valve block 3 rd  port  49 , an upper valve block 4 th  port  50 . There are four runners on the upper valve block  5 . The first runner on the upper valve block  5  is connected with the upper valve block 1 st  port  47 ; the second runner on the upper valve block  5  is connected with the upper valve block 2 nd  port  48 ; the third runner on the upper valve block  5  is connected with the upper valve block 3 rd  port  49 ; the fourth runner on the upper valve block  5  is connected with the upper valve block 4 th  port  50 ; There are embossments on the outlets of the four runners on the upper valve block  5 . 
     The upper valve block 1 st  port  47  is connected with the 9 th  oil pipe connector; the upper valve block 2 nd  port  48  is connected with the 8 th  oil pipe connector  13 ; the upper valve block 3 rd  port  49  is connected with the 7 th  oil pipe connector  12 ; the upper valve block 4 th  port  50  is connected with the 6 th  oil pipe connector  11 . 
     As illustrated in  FIG. 1  and  FIG. 2 , the accumulator  1  is connected with the lower hatch cover  2  by the male threaded cylinder on the bottom; the upper hatch cove  31  is fixed on the top of the hatch shell  30  by a bolt; the lower hatch cover  2  is fixed on the bottom of the hatch shell  30  by a bolt. Both end-face sealing and radial sealing are adopted for the sealing of the upper hatch cover  31  and the lower hatch cover  2  with the hatch shell  30  respectively. The bladder  32  is connected with the upper hatch cover  31  through the male threaded cylinder on the top. The water-proof connector  33  is fixed on the embossment on the top surface of the upper hatch cover  31  by the bolt  34 . The 10 th  oil pipe connector  15  is fixed on the geometry center of the bottom of the upper hatch cover  31 ; 
     The depth-pressure sensor  21  is fixed on the pipe taper threaded hole on the lower hatch cover  2 . The first bolt  26 , the second bolt  27 , the third bolt  28  and the fourth bolt  29  are threaded through the upper valve block  5  in sequence. The hydraulic-operated check valve  4  and the positioning through hole on the lower valve block  3  are fixed on the lower hatch cover  2 . After the upper valve block  5 , the hydraulic-operated check valve  4  and the lower valve block  3  are pressed and fixed together, the lower valve block 1 st  port  35  is connected with the through hole on the geometry center of the lower hatch cover  2 ; the upper valve block 1 st  port  47  is connected with the second working port of the hydraulic-operated check valve  4  through the first runner on the upper valve block  5 ; the upper valve block 2 nd  port  48  is connected with the oil return outlet of the hydraulic-operated check valve  4  through the second runner on the upper valve block  5 ; the upper valve block 3 rd  port  49  is connected with the first working port of the hydraulic-operated check valve  4  through the third runner on the upper valve block  5 ; the upper valve block 4 th  port  50  is fourth runner on the upper valve block  5 . The pump outlet pressure sensor  19  and the accumulator pressure sensor  20  are both fixed on the pipe taper threaded hole on the lower valve block  3 . The hydraulic pump motor assembly  22 , the directional valve  23  and the relief valve  24  are all settled on the upper valve block  5 . 
     The oil draining outlet of the hydraulic pump motor assembly  22  is connected with the 1 st  oil pipe connector  6  through an oil pipe; the oil return outlet of the hydraulic pump motor assembly  22  is connected with the 4 th  oil pipe connector  9  through an oil pipe; the oil inlet of the relief valve  24  is connected with the 2 nd  oil pipe connector  7  through an oil pipe; the oil outlet of the relief valve  24  is connected with the 3 rd  oil pipe connector  8  through an oil pipe; the 5 th  oil pipe connector  10  and the 10 th  oil pipe connector  15  are connected through a oil pipe; the 6 th  oil pipe connector  11  is connected with the oil inlet of the directional valve  23 ; the 7 th  oil pipe connector  12  is connected with the first working port of the directional valve  23 ; the 8 th  oil pipe connector  13  is connected with the oil outlet of the directional valve  23 ; the 9 th  oil pipe connector  14  is connected with the second working port of the directional valve  23 ; the control panel  25  is fixed on the lower hatch cover  2 . 
     As illustrated in  FIG. 9 , the control panel  25  comprising: a first power supply module, a second power supply module, a communication drive module, a voltage reference stabilizing module, a first filter module, a second filter module, a third filter module, AD converter module and single-chip microcomputer; wherein the first power supply module is for separation and transfers an external 12V power supply to an internal 12V power supply inside the control panel; the second power supply module transfers an internal 12V power supply output by the first power supply module inside the control panel to a 5V power supply for the single-chip microcomputer; the first power supply module is connected to the second power supply module and the voltage reference stabilizing module respectively; input ends of a power supply of the pump outlet pressure sensor  19 , the accumulator pressure sensor  20 , the depth-pressure sensor  21 , the hydraulic pump motor assembly  22  and the directional valve  23  are all connected with the second power supply module; a signal cable of the depth-pressure sensor  21  is connected with the first filter module; a signal cable of the pump outlet pressure sensor  19  is connected with the second filter module; a signal cable of the accumulator pressure sensor  20  is connected with the third filter module; the first filter module, the second filter module, the third filter module and the voltage reference stabilizing module are all connected with the AD converter module; the first filter module, the second filter module and the third filter module are for depressing the high frequency noise and allows the wanted low frequency noise to pass through, which improves the accuracy of the test; the voltage reference stabilizing module feeds accurate reference voltage to the AD converter module; the AD converter module is connected with an input end of the single-chip microcomputer; control cables of the hydraulic pump motor assembly  22  and the directional valve  23  are connected with an output end of the single-chip microcomputer; the communication drive module is connected with the single-chip microcomputer; the communication drive module receives signals from the single-chip microcomputer; the first power supply module is connected with the external power supply through a power cord of the water-proof connector  33 ; the communication drive module is connected with the host computer through a signal cable of the water-proof connector  33 ; the first power supply module and the second power supply module adopts the DCDC power supply module from GODSEND with the model type WD12-12S12 and WD12-12S05 while other model type is also applicable; the voltage reference stabilizing module adopts REF5050 chip from TI while other model type is also applicable; the communication drive module adopts DS275 from MAXIM; the first filter module, the second filter module and the third filter module adopts MAX291 from MAXIM while other model type is also applicable; the AD converter module adopts THS107 from TI while other model type is also applicable. 
     The working process the self-draining oil buoyancy regulating device for underwater robots is as below: 
     As illustrated in  FIG. 10  and  FIG. 11 , the test result of the accumulator pressure sensor  20  is input to the single-chip microcomputer after converted to digital by the AD converter module and calculated into the volume of the bladder  32  based on the gas equation; as the depth of the sea is proportional to the pressure, the test result of the depth pressure sensor  21  is input to the single-chip microcomputer after converted to digital by the AD converter module and calculated into depth; Based on the two test result, the single-chip microcomputer decide whether to increase, decrease or maintain the volume of the bladder  32  to regulate the buoyancy by changing the displacement. 
     When to reduce the volume of the bladder  32 , the control panel  25  output the control signal to the hydraulic pump motor assembly  22  and the directional valve  23 ; the hydraulic pump motor  22  is started and pump the oil (if the pump is already started then keep it unchanged); switch the directional valve  23  to the left position; the bladder  32  is connected with oil return outlet of the hydraulic pump assembly  22 ; the oil outlet of the hydraulic pump assembly  22  is connected with the accumulator  1 ; the flow of the hydraulic oil is in the same direction with the hydraulic-operated check valve  4 ; the hydraulic-operated check valve  4  is switched on; the oil inside the bladder  32  is pumped into the accumulator  1  by the hydraulic pump assembly  22 ; the volume of the bladder is reduced; 
     When to reduce the volume of the bladder  32 , the control panel  25  output the control signal to the hydraulic pump motor assembly  22  and the directional valve  23 ; the hydraulic pump motor assembly  22  is started and pump the oil (if the pump is already started then keep it unchanged); switch the directional valve  23  to the right position; the oil outlet of the hydraulic pump motor assembly  22  is plugged and connected with the hydraulic-operated check valve  4 ; the relief valve  24  is parallel with the hydraulic pump assembly  22 ; the bladder  32  is connected with the accumulator  1  through the hydraulic-operated check valve  4 ; the hydraulic pump motor assembly  22  is started and generates pressure; when switch on the hydraulic-operated check valve  4  and the bladder  32  is connected with the accumulator  1 , the oil inside the accumulator  1  flows into the bladder  32  under the gas pressure and the volume of the bladder is increased; the oil return to the hydraulic pump motor assembly  22  through the relief valve  24  due to the oil outlet is plugged. 
     There are two ways to keep the volume of the bladder  32  unchanged for varied situation. One is to control the directional valve  23 . When the directional valve is switched to middle, the connection between the accumulator  1  and other oil channels is cut off and the oil is not able to enter the accumulator  1 . With the assistance of the hydraulic-operated check valve  4  the oil leakage through the crevice of the valve core is reduced. The other way is to control the hydraulic pump motor assembly  22 . When the hydraulic pump motor assembly  22  is stopped, the oil inside the bladder  32  is not able to flow into the accumulator  1  due to no pressure generated. The hydraulic-operated check valve  4  is not able to reversely be switched on when there is no pressure and the oil is not able to flow from the accumulator to the bladder  32 . 
     Furthermore, under the process of reducing the volume of the bladder the control panel  25  keeps adjusting the rotational speed of the hydraulic pump motor assembly  22  according to the feedback from the pump outlet pressure sensor  19  to maintain the outlet pressure of the hydraulic pump motor assembly  22 . Meanwhile in order to ensure the security, when the feedback from the pump outlet pressure sensor  19  exceeds rated value, the control panel  25  urgently idles all the current tasks, stops the hydraulic pump motor assembly  22 , switches the directional valve  23  to middle position and report the abnormal to the host computer.