Abstract:
A propulsion system is provided that includes one or more pumps that form a jet for propulsion. A number of Coanda jet devices (CJDs) are coupled to the one or more pumps. The CJDs are arranged so to allow for a multi-axis underwater control of an underwater robot.

Description:
PRIORITY INFORMATION 
     This application claims priority from provisional application Ser. No. 61/482,272 filed May 4, 2011, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention is related to the field of underwater vehicle propulsion and maneuvering, and in particular to a system for propelling and orienting an underwater robot without the use of conventional propeller thrusters. 
     Since the 1990s, underwater vehicles have become a very popular approach for a number of industrial applications. For example underwater robots have played a major role in the search for undersea wrecks and in the repair of damaged underwater oil risers. Recently there has emerged a new application for such robots: industrial piping systems such as those used for the cooling cycle in nuclear reactor systems. For these applications, the robot must carry a camera or other sensor array and be able to maneuver precisely within the confines of the pipe. For these types of inspections the speed of the robot is actually quite slow. This is to ensure that the robot operator is able to carefully and thoroughly examine the images in real time. 
     Typical underwater robots use a set of five separate propeller thruster devices. These thrusters are driven by electric motors and have proven quite robust and useful for many applications. However, for certain applications this approach is not desirable. The large number of motors adds considerable mass and volume to the robot. In addition, thrusters exhibit nonlinearities which make them difficult to control when operating at very low speeds or when required to turn on and off rapidly. Finally, reversing the direction of a propeller (something that would be required for fine maneuvers) exerts substantial reaction moments on the body of the vehicle. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, there is provided a propulsion system. The propulsion system includes one or more pumps that form a jet for propulsion. A number of Coanda jet devices (CJDs) are coupled to the one or more pumps. The CJDs are arranged so to allow for a multi-axis underwater control of an underwater robot. 
     According to another aspect of the invention, there is provided a method of forming a propulsion system. The method includes providing one or more pumps that form a jet for propulsion. Moreover, the method includes coupling a plurality of CJDs to the one or more pumps. The CJDs are arranged so to allow for a multi-axis underwater control of an underwater robot. 
     According to another aspect of the invention, there is provided a method of performing the operation of a propulsion system. The method includes forming a jet for propulsion using one or more pumps. Also, the method includes providing multi-axis underwater control using a plurality of CJDs. The CJDs are coupled to the one or more pumps. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a Coanda effect valve used in accordance with the invention; 
         FIGS. 2A-2B  are schematic diagrams illustrating a CJD formed in accordance with the invention; 
         FIG. 3  is a schematic diagram illustrating a multi-axis architecture used in accordance with the invention; 
         FIG. 4  is a schematic diagram illustrating a valve architecture having a set of reversible pumps and CJDs; 
         FIG. 5  is a schematic diagram illustrating a valve architecture having a set of reversible pumps and CJDs for use in three dimensional motion; 
         FIG. 6  is a schematic diagram illustrating a valve architecture having a set of reversible pumps and CJDs in a null configuration; 
         FIG. 7  is a schematic diagram illustrating a tree structure using CJDs in accordance with the invention; 
         FIG. 8  is a schematic diagram illustrating a valve architecture with a set of non reversible pumps and tree structures formed in accordance with the invention; 
         FIG. 9  is a schematic diagram illustrating a valve architecture with a set of non reversible pumps and tree structures in a null configuration formed in accordance with the invention; 
         FIG. 10  is a graph illustrating experimental results of the invention using the tree structures described in  FIG. 9 ; and 
         FIGS. 11A-11B  are schematic diagrams illustrating an actuator skin and robot formed in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is a jet based approach to multi-axis underwater propulsion and maneuvering, but incorporates a set of custom high speed and compact valves based on well known fluidics technology. Like the previous work on water jet actuation, the underwater vehicle contains an onboard pump and several exit ports. A valve system enables the operator to choose which direction and axis to apply force and moments. Specifically vehicle translation and rotation can be controlled in several axes. Several maneuvering architectures are described herein. 
     However for the inventive design, a different type of valve is used. A Coanda effect valve based on fluidics technology is used as a valve, allowing the direction of the exit jet to be controlled in a high speed yet compact way. 
     This invention is unique in several key ways. Most significantly, the invention is specifically designed for multi-axis underwater vehicle control instead of simply switching between two outputs. This architecture uses a number of valves to create forces and moments that can result in translations and rotations along multiple axes. Additionally, the use of a diffuser nozzle to create a null configuration is novel. This allows the pump to remain on while applying zero force or moment to the vehicle. Also, the vehicle to remain stationary momentarily without dealing with the implications of switching the rotary pump on and off repeatedly. 
     Finally, the specific implementation of the Coanda effect valve is unique. First, the device was designed for use in water alongside a micropump. The geometry of the device therefore differs substantially from the prior art. Additionally, a mechanical design was incorporated that enables the switching of the jet with a single solenoid. This innovation reduces size, weight, and complexity. For the sake of simplicity this entire device is chosen as a CJD. The CJD structure can even be implemented as part of a robot structure itself. 
       FIG. 1  shows a schematic diagram illustrating a Coanda effect valve  2 . A high pressure water supply (volume flow rate Q) is supplied to inlet I which goes through a nozzle  4  of area A n . Depending on the pressures at the two control ports (C 1 , C 2 ), the water jet attaches to either the left or right wall and then exits through either exit (Exits  1  and  2 ) having an area A e . The control ports (C 1 , C 2 ) use the Coanda effect to switch the direction of the water jet between Exits  1  and  2 . When a control port C 1  or C 2  is opened, ambient fluid is entrained causing the jet to move towards the opposite wall. This process eventually causes the jet to attach to the opposite wall. Therefore, if control port C 1  is opened (C 2  must remain closed) the water jet can bend towards the right wall, attach to the wall, and exit through Exit  2 . It should be noted that these valves do have pressure losses associated with them due to the exit area being larger than the nozzle area. The theoretical flow coefficient (C v ) for these valves (˜0.55) substantially exceeds those of comparable conventional solenoid valves. 
       FIGS. 2A-2B  illustrates a CJD  20 .  FIG. 2A  shows fluid flowing into the device  20  through the inlet  23 . A custom designed plastic piece  22  is used to cover one control port  25  while exposing the other control port  24  to ambient pressure. This pressure differential is sufficient to cause the jet to switch directions. When a solenoid  21  is activated the push rod  27  moves forward and the situation is reversed. With respect to the figure, when the solenoid  21  is inactive the control port  25  facing the reader  26  is covered, the fluid jet exits out of the page. When the solenoid  21  is activated the control port  24  facing away is covered while the control port  25  is opened, as shown in  FIG. 2B . Therefore the jet exits into the page. This simple design enables the switching of the jet with a compact solenoid  21  and at high speed. The simplicity of this approach should not be underestimated; the weight of the entire CJD  20  is ˜25 grams. 
       FIG. 3  is a schematic diagram illustrating a multi-axis architecture  30  used in accordance with the invention. A single reversible pump  32  is used in tandem with two CJDs  34 ,  36  to enable the water jet to be switched at high speed between the four exit ports (Exits  1 - 4 ). Water is ingested through inlet I and then depending on the direction of the pump  32  and the configuration of the CJDs  34 ,  36 , water can be ejected through Exits  1 ,  2 ,  3 , or  4 . Note that switching between Exits  1  and  2  or Exits  3  and  4  can be done simply by switching a solenoid. Other switches, such as Exits  1  to  3  or Exits  2  to  4 , require the reversal of the pump  32 . 
       FIG. 4  is a schematic diagram illustrating a valve architecture  40  with a set of reversible pumps P 1 , P 2  and Coanda Jet Devices (CJDs)  42 ,  44 ,  46 ,  48 . The valve architecture  40  is used to achieve maneuvering within the plane of a vehicle (xy plane). The pumps P 1 , P 2  are assumed to be reversible pumps. The jets  1 ,  2 , A, B, can be used for motion in the x direction and for control of the orientation (yaw) of the vehicle. Note that this mode can be controlled without reversing the direction of either pump P 1  or P 2 . This means that the while the solenoids can be switching back and forth at a high frequency to achieve precise control, the pumps P 1 , P 2  cannot. This is desirable because a pump like a propeller has undesirable qualities when switched back and forth. To control motions in the y direction, the jets  3 ,  4 , C, D can be used. Note that in this mode the orientation can still be controlled. 
       FIG. 5  is a schematic diagram illustrating a valve architecture  50  with a set of reversible pumps P 1 , P 2  and CJDs  52 ,  54 ,  56 ,  58 . This design is intended for three dimensional motions. The pumps P 1 , P 2  are assumed to be a reversible pumps. The jets  1 ,  2 , A, B, can be used for motion in the x direction and for control of the orientation (yaw) of the vehicle. Note that this mode can be controlled without reversing the direction of either pump P 1  or P 2 . This means that the while the solenoids can be switching back and forth at a high frequency to achieve precise control, the pumps P 1 , P 2  cannot. This is desirable because a pump like a propeller has undesirable qualities when switched back and forth. To control motions in the z direction, the jets  3 ,  4 , C, D can be used. In addition rotations about the y axis (pitch) can also be controlled. 
       FIG. 6  is a schematic diagram illustrating a valve architecture  80  with a set of reversible pumps P 1 , P 2  and CJDs  82 ,  84 ,  86 ,  88 . This valve architecture  80  is used to achieve maneuvering within the plane of the vehicle (xy plane). The pumps P 1 , P 2  are assumed to be reversible pumps. The difference in jet  4  and jet D is the use of a diverging nozzle  90  on the jet outlet to indicate that a large exit area exists that reduces the force of the jet to be approximately zero. This arrangement is a null configuration that can be used to impose zero force without having to turn the pump off. The reason for this is that some pumps introduce nonlinear and dynamic effects when turned on and off, and this could complicate control. The jets  1 ,  2 , A, B, can be used for motion in the x direction and for control of the orientation (yaw) of the vehicle. 
     This mode can be controlled without reversing the direction of either pump P 1 , P 2 . This means that the while the solenoids can be switching back and forth at a high frequency to achieve precise control, the pumps P 1 , P 2  cannot. This is desirable because a pump like a propeller has undesirable qualities when switched back and forth. To control translational motions in the y direction, the jets  3 ,  4 , C, D can be used. Note that the key difference in this architecture that when the vehicle is in y translation mode the orientation cannot be controlled by the outlets  3 ,  4 , C, D. 
       FIG. 7  is a schematic diagram illustrating a tree structure  100  using CDs (Device A, Device B). A high pressure water supply (volume flow rate Q) is supplied to Device A at inlet I. Depending on the pressures at the two control ports C A1  or C A2 , the jet either exits through Exit A 1  or enters Device B. If the jet enters Device B the control ports C B1 , and C B2  can be used to switch between Exit B 1  and Exit B 2 . Note one of the exits of Device A is connected to one of the exits of Device B. Therefore with this tree structure  100 , three distinct choices now exist for the water jet. A third device can be added at Exit A 1  and increase this number to four. 
       FIG. 8  is a schematic diagram illustrating a valve architecture  120  with a set of non reversible pumps P 1  and P 2  and four tree structures  138 ,  140 ,  142 ,  144 . The valve architecture  120  is used to achieve maneuvering within the plane of the vehicle (xy plane). In this case the pumps P 1 , P 2  are assumed to be one way (not reversible). This condition is considered because most simple pumps P 1 , P 2 , such as centrifugal pumps, are not designed to be reversible. The tree structures  138 ,  140  are formed by coupling the exits of the CJD  126  to one of the exits of the CJD  122 ,  124 . The tree structures  142 ,  144  are formed by coupling the exits of the CJD  132  to one of the exits of both CJD  128 ,  130 . The jets  1 ,  2 , A, B, can be used for motion in the x direction and for control of the orientation (yaw) of the vehicle. To control translational motions in the y direction, the jets  3 ,  4 , C, D can be used. The chief benefit to this design is that the pumps P 1 , P 2  do not need to be reversible. 
       FIG. 9  is a schematic diagram illustrating a valve architecture  152  with a set of non reversible pumps P 1 , P 2  and 4 tree structures  166 ,  168 ,  170 ,  172 . The valve architecture  152  achieves maneuvering within the plane of the vehicle (xy plane). In this case the pumps P 1 , P 2  are assumed to be one way (not reversible). This condition is considered because most simple pumps, such as centrifugal pumps, are not designed to be reversible. The tree structures  166 ,  168  are formed by coupling the two exits of the CJD  158  to one of the exits of the CJDs  154 ,  156 . The tree structures  170 ,  172  are formed by coupling the two exits of the CJD  164  to one of the exits of both CJD  160 ,  162 . This architecture  152  includes the null configuration having diverging nozzles  174 ,  176  on jets  4  and D. The jets  1 ,  2 , A, B, can be used for motion in the x direction and for control of the orientation (yaw) of the vehicle. To control translational motions in the y direction, the jets  3 ,  4 , C, D can be used. The chief benefit to this design is that the pumps do not need to be reversible. 
       FIG. 10  is a graph illustrating experimental results of the invention using the tree structures  166 ,  168 ,  170 ,  172  described in connection with  FIG. 9 . A simple floating vehicle was used for these measurements and a gyroscope integrated circuit was used to measure the yaw rate. This experiment illustrates that the output forces from the nested tree structure are still sufficient to maneuver a vehicle. 
       FIGS. 11A-11B  are schematic diagrams illustrating an actuator skin  200  and robot  202  formed in accordance with the invention. A CJD structure can be incorporated into a skin or shell of an underwater robot.  FIG. 11A  illustrates the smooth shaped actuator skin or shell  200  where a CJD can be positioned inside.  FIG. 11B  shows an actual robot  202  formed using the smooth shaped actuator skin or shell  200  where a CJD can be positioned in the interior region of the robot  202 . This type of geometry is now possible due to advances in 3D printing technology. 
     The invention provides for multi-axis underwater vehicle control by simply switching between two outputs. The inventive architecture uses a number of valves to create forces and moments that can result in translations and rotations along multiple axes while also allowing for the use of a diffuser nozzle to create a null configuration. This allows a pump to remain on while applying zero force or moment to the vehicle. 
     Although the present invention has been shown and described with respect to several preferred embodiments thereof, various changes, omissions and additions to the form and detail thereof, may be made therein, without departing from the spirit and scope of the invention.