Abstract:
A method and apparatus for operating a pool cleaner body in a manner to maximize the time spent on cleaning relative to the time spent on repositioning. More particularly, the invention is directed to a control subsystem for operating a cleaner body to enable it to primarily travel in a forward direction (i.e., forward state) along a travel path but operable also in a backup/redirect state to translate and or rotate the body to enable it to escape from obstructions while also minimizing the formation of conduit tangles. The control subsystem is configured to perform reposition operations without increasing incidents of conduit tangling by:
   1—avoiding an excessive rotation of the body, e.g., approximately 180° or more, when attempting to free the body from an obstruction; and/or   2—avoiding the initiation of a timed reposition operation while the body is transitioning between a travel path at the wall surface and a travel path at the water surface.

Description:
RELATED APPLICATIONS 
     This application is a CIP of PCT/US2006/017283 filed on 4 May 2006 which claims priority based on U.S. Application 60/678,499 filed on 5 May 2005. This application claims priority based on the aforecited applications which my reference are incorporated herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to automatic swimming pool cleaners of the type which use a cleaner body for traveling through a water pool to clean the water and/or containment wall surfaces and more particularly to such cleaners in which the cleaner body is tethered to a conduit which supplies power (e.g., positive pressure water flow, negative pressure (i.e., suction) water flow, electricity, etc.) for propelling the body through the water pool. 
     BACKGROUND OF THE INVENTION 
     Well known automatic pool cleaners utilize a cleaner body coupled to a flexible conduit which supplies power to propel the body forwardly along a substantially random travel path though the pool. For example, U.S. Pat. Nos. 6,090,219 and 6,365,039 (reissued as RE 38,479) describe automatic pool cleaners which use a body powered by supplied positive pressure water for cleaning the interior surface of a pool containment wall and the upper surface of a water pool contained therein. Other U.S. patents describe cleaner bodies which are powered by a negative pressure water source and/or electric power. Regardless of the particular body configuration and power source a number of known cleaners include some type of timer mechanism for periodically initiating a timed “back-up” or “repositioning” operation to allow the body to escape form being trapped by an obstruction in the pool and/or enhance randomization of the body&#39;s travel path. Additionally, some available patent documents (e.g., U.S. Pat. No. 6,365,039; U.S. Pat. No. 6,398,878; PCT/US2004/016937) suggest the inclusion of a motion sensor for sensing when the rate of forward motion of the cleaner body diminishes below a certain threshold rate. This can occur, for example, when the body gets trapped by an obstruction. The sensed decrease in the rate of forward motion can be used to initiate the repositioning operation to free the body. 
     Aforementioned U.S. Pat. No. 6,398,878 describes an automatic swimming pool cleaner which includes a propulsion subsystem for producing a force F P  for propelling a cleaner body in a forward direction, a motion sensor for reporting when the body&#39;s rate of forward motion is less than a certain threshold rate, and a repositioning subsystem for producing a force F R  for redirecting the body&#39;s forward motion along a different travel path. The preferred repositioning subsystem described in said &#39;678 patent redirects the body by applying the force F R  ( FIGS. 1A ,  1 B) in a direction to translate the body rearwardly and rotate it around an axis oriented substantially perpendicular to the direction of the body&#39;s forward motion. Aforementioned International application PCT/US2004/016937 describes an enhanced propulsion subsystem. 
     Although the application of the repositioning force F R  as described in said &#39;878 patent is generally effective to free a cleaner body trapped by an obstruction, it has been observed that excessive body rotation can contribute to the formation of tangles, e.g., persistent coils and/or knots, in the conduit supplying power to the body. The formation of such tangles is undesirable because tangles tend to impede the free travel of the body and increase the time dedicated to repositioning at the expense of the time available for cleaning. It has also been observed that tangles are more likely to occur when a timed repositioning operation is initiated while the body is transitioning between a travel path at the wall surface. (i.e., wall surface mode) and a travel path at the water surface (i.e., water surface mode). 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a method and apparatus for operating a pool cleaner body in a manner to maximize the time spent on cleaning relative to the time spent on repositioning. More particularly, the invention is directed to a control subsystem for operating a cleaner body to enable it to primarily travel in a forward direction (i.e., forward state) along a travel path but operable also in a backup/redirect state to translate and/or rotate the body to enable it to escape from obstructions while also minimizing the formation of conduit tangles. A control subsystem in accordance with the invention is configured to perform repositioning operations without increasing incidents of conduit tangling by:
     1—avoiding an excessive rotation of the body, e.g., approximately 180° or more, when attempting to free the body from an obstruction; and/or   2—avoiding the initiation of a timed repositioning operation while the body is transitioning between a travel path at the wall surface and a travel path at the water surface.   

     In accordance with the invention, a reposition operation is initiated in response to an “event” which can be time dependent (e.g., expiration of a timed interval) and/or condition dependent (e.g., rate of forward body motion falling below a certain threshold). In a preferred embodiment, the reposition operation is comprised of a sequence of one or more “redirect actions” where each such action redirects the body for forward motion along a new path and involves first applying a limited duration repositioning force F R , then applying a forward propelling force F P , and then determining the consequence of those forces on the cleaner body forward motion; i.e., have the applied forces produced sustained cleaner body forward motion? If sustained forward motion is recognized, the reposition operation is terminated. If sustained forward motion is not recognized, then the reposition operation continues with a further redirect action. 
     In a preferred control subsystem embodiment, the magnitude, or effectiveness, of each succeeding redirect action in a reposition operation is progressively increased. For example, an initial redirect action can apply the repositioning force F R  for a first interval (e.g., about four seconds) to rotate the cleaner body approximately 90° to redirect it for forward motion along a different travel path. Then a second redirect action can apply the force F R  for a second interval (e.g., about six seconds) to rotate the body approximately 135° to redirect it for forward motion along a still different path. Additional redirect actions can be sequentially executed if necessary to apply the force F R  for increasing durations. In most situations, the body will be free of the obstruction after the first and/or second redirect actions, thereby avoiding the necessity of a third redirect action and the additional rotation which can promote conduit tangles. 
     Embodiments of the invention are compatible with many types of pool cleaners which use a conduit to supply power to a cleaner body. The power can be supplied in the form of positive or negative fluid pressure (e.g., water) or electricity. Moreover, embodiments of the invention can be used with cleaner bodies which travel solely along the containment wall surface or with bodies which alternately travel at the containment wall surface and at the water surface. In the latter type of cleaner (e.g., U.S. Pat. No. 6,365,039), to minimize forming conduit tangles, it has been found preferable to avoid initiating a timed repositioning operation while the cleaner body is transitioning from the wall surface to the water surface, or vice versa. 
     A control subsystem in accordance with the invention can be implemented in various ways to execute a reposition operation comprised of a sequence of one or more redirect actions. For example, a control subsystem in accordance with the invention can employ a mechanical, e.g., hydraulic, controller, using cams driven by the supplied power, or can employ an electronic controller, using a microprocessor, to respond to certain inputs for appropriately producing the aforementioned repositioning force F R . 
     A control subsystem in accordance with the invention can operate “open loop”, in the sense that the repositioning force F R  can be applied for a certain interval, e.g., four seconds, to produce the desired body rotation, e.g., approximately 90°. Alternatively, the control subsystem can operate “closed loop”, in the sense that the force F R  is applied until a rotation sensor reports that the desired rotation magnitude has been achieved. More particularly, a preferred closed loop embodiment preferably includes means for monitoring the net rotation of the body accumulated during a reposition operation. The magnitude of the accumulated rotation can, for example, be derived by detecting the body&#39;s heading at the start of a reposition operation and comparing it to headings subsequently detected during the operation. The difference, of course, represents the net angle of rotation of the body. This information can then be used by the control subsystem controller to determine further actions. A suitable heading detector can employ a directional sensor such as a magnetic compass yaw device, GPS sensor, etc. 
     In a preferred embodiment of the invention, the cleaner body includes a housing having vent openings at the front and rear for allowing pool water to move (relative to the housing) therethrough as the cleaner body travels through the pool. The cleaner body includes a motion sensor which preferably channels the moving water through a window interior to the housing. The preferred motion sensor also includes a paddle mounted adjacent to the window for movement by the channeled water. When the velocity of the water relative to the housing (i.e., forward body motion) exceeds a threshold rate, the motion sensor paddle is forced to a first position causing it to close a relief port. On the other hand, when the relative water velocity is below the threshold rate, the paddle defaults to a second position to open the relief port and permit the initiation of a reposition operation. 
     The execution of a reposition operation in accordance with a preferred embodiment of the invention involves performing one or more successive redirect actions. In a preferred hydraulic embodiment, each redirect action uses one of multiple state cams driven by a common mechanism, for example, the shaft of a turbine powered by a supplied positive pressure water flow. A first of the state cams has one or more discontinuities, e.g., lobes, each of which opens a state valve to produce the reposition force F R  for a first duration, e.g., four seconds. A second of the state cams has discontinuities which produce the force F R  for a second duration, e.g., six seconds. A cam selector is provided so that the initial redirect action of each reposition operation uses the first state cam, i.e., the cam having the shortest duration lobes. The reposition operation is terminated when sustained forward motion greater than a threshold rate is sensed by the aforementioned motion sensing mechanism. If sustained forward motion is not recognized, then the repositioning operation continues to a second redirect action using the second state cam. 
     As previously mentioned, in a preferred embodiment, a reposition operation is initiated as a consequence of the motion sensor recognizing that the rate of forward motion is less than a certain threshold. Additionally, the reposition operation is preferably also initiated by a timed event to enhance randomization of the body&#39;s travel path even if its forward motion is being sustained. In a preferred embodiment, the timed event is defined by a state cam lobe arranged to force the paddle to the aforementioned second position to open the relief port. 
     In order to reduce the likelihood of conduit tangles, it is preferable to avoid, or inhibit, the initiation of a timed reposition operation while the cleaner body is transitioning between wall surface travel (i.e., wall surface mode) and water surface travel (i.e., water surface mode). In a preferred embodiment, this is accomplished by properly phasing a cam defining the operating state (i.e., state cam) which defines either a forward state or a backup/redirect state. A preferred mode cam is mounted for rotation and has cam surfaces which define the respective durations of the wall surface and water surface modes. A follower bears against the mode cam surfaces to control a mode valve to produce a vertical force (e.g., F +V , F −V ) to place the body proximate to the water surface or wall surface. 
     A manually operable mode override mechanism is preferably provided to enable a user to assure operation (a) solely in the wall surface mode or (b) solely in the water surface mode or (c) alternately in the wall surface and water surface modes. The manually operable override mechanism in a first position holds the mode valve open to keep the cleaner body in the water surface mode, in a second position holds the mode valve closed to keep the body in the wall surface mode, and in a third position permits the valve to be controlled by the mode cam for operating alternatively in the water surface and wall surface modes. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  corresponds to FIG. 1 of U.S. Pat. No. 6,365,039 and schematically depicts an automatic pool cleaner including a cleaner body for traveling along and cleaning the containment wall surface and/or the water pool surface; 
         FIG. 2  corresponds to FIG. 2 of U.S. Pat. No. 6,365,039 and schematically depicts an exemplary cleaner body showing multiple outlets which can be selectively activated to discharge water flows to establish the body&#39;s operating mode (i.e., wall surface or water surface) and state (i.e., forward or backup/redirect); 
         FIGS. 3A ,  3 B,  3 C,  3 D schematically illustrate respective top, side, front, and rear views of a cleaner body showing an exemplary configuration of nozzles for discharging respective water flows to propel the body forwardly along a travel path at the wall surface or at the water surface; 
         FIGS. 4A ,  4 B,  4 C,  4 D schematically illustrate respective top, side, front, and rear views of the pool cleaner of  FIG. 3  showing an exemplary configuration of nozzles for discharging respective water flow for redirecting the body&#39;s travel path in the backup/redirect state; 
         FIG. 5  is a block diagram of an automatic pool cleaner in accordance with the invention showing a control subsystem including a controller responsive to various inputs for controlling a force generator to selectively apply various forces to the cleaner body to establish its operating mode/state. 
         FIG. 6  is a flow chart describing the operation of the controller of  FIG. 5  in accordance with an embodiment of the invention in which the cleaner body operates solely in a wall surface mode; 
         FIG. 7  is a flow chart describing the operation of the controller of  FIG. 5  in accordance with an alternative embodiment of the invention in which the cleaner body alternately operates in a wall surface mode and a water surface mode; 
         FIG. 8  is a timing chart device depicting the relationship between various events associated with the initiation and execution of an exemplary repositioning operation. 
         FIG. 9A  is a schematic diagram of a first exemplary control subsystem implementation in accordance with the invention which can use an electronic controller to control a rotary valve and  FIG. 9B  is a perspective exploded view of a suitable rotary valve; 
         FIG. 10  is a schematic diagram of a second exemplary control subsystem implementation in accordance with the invention employing a hydraulic controller; 
         FIGS. 11A ,  11 B,  11 C depict a preferred motion sensing mechanism useful in the subsystem of  FIG. 10 ; 
         FIGS. 12A and 12B  respectively comprise a top view and a side sectional view of a preferred configuration of multiple state cams useful in the subsystem of  FIG. 10 ; 
         FIG. 12C  is an enlarged fragmentary perspective view showing exemplary lobes on the state cam configuration of  FIGS. 12A and 12B , together with a follower mechanism for selecting which of multiple state cams to use; 
         FIG. 13A  illustrates a simple manual override mechanism which permits a user to restrict operation to solely wall surface, solely water surface or alternatively wall surface/water surface; 
         FIGS. 13B and 13C  respectively comprise side and top sectional views of a preferred mode cam configuration and manual override mechanism, useful in the cleaner of  FIG. 10 , showing the override mechanism in a position to permit the cleaner body to automatically operate alternately in the wall surface and water surfaces modes; 
         FIGS. 13D and 13E  comprise side sectional view of the mode cam of  FIGS. 13A and 13B  respectively showing the cam in the (1) wall surface only and (2) water surface only rotary positions; 
         FIGS. 14A ,  14 B show the relative positioning of the state and mode cams to assure that a timed reposition operation is not initiated during a mode transition; 
         FIGS. 15A and 15B  depict a fixture useful during the assembly of a gear train of the preferred hydraulic controller of  FIG. 10  to assure proper relative phasing of the state and mode cams as depicted in  FIGS. 14A ,  14 B. 
         FIGS. 16A and 16B  respectively comprise side and front views of an alternative motion sensor mechanism for producing an electric output signal representing forward body motion; and 
         FIGS. 17A and 17B  respectively comprise isometric and front views of an additional alternative motion sensor mechanism for producing an electric output signal representing forward body motion. 
     
    
    
     DETAILED DESCRIPTION 
     Attention is initially directed to  FIG. 1  which duplicates a corresponding figure shown in U.S. Pat. No. 6,365,039.  FIG. 1  illustrates a method and apparatus for cleaning a water pool  1  contained in an open vessel  2  defined by a containment wall  3  having a bottom  4  and side  5  portions. The apparatus includes a unitary structure or body  6  configured for immersion in the water pool  1  for selective operation to the interior wall surface  8  in a wall surface cleaning mode. 
     The unitary body  6  preferably comprises an essentially rigid structure having a hydrodynamically contoured exterior surface for efficient travel through the water pool  1 .  FIG. 1  depicts a heavier-than-water body  6  which in its quiescent or rest state typically sinks to a position (represented in solid line) proximate to the bottom of the pool  1 . For operation in the water surface cleaning mode, a vertical force F +V  is produced to lift the body  6  to proximate to the water surface  7  (represented in dash line). Alternatively, body  6  can be configured to be lighter than water such that in its quiescent or rest state, it floats proximate to the water surface  7 . For operation in the wall surface cleaning mode, a vertical force F −V  is produced to cause the lighter-than-water body to descend to the pool bottom. In either case, the vertical force is produced as a consequence of energy/power (e.g., a positive pressure water flow) supplied via a conduit  9  from an energy/power source, e.g., an electrically driven motor and hydraulic pump assembly  10 . The exemplary assembly  10  defines a pressure side outlet  11  preferably coupled via a pressure/flow regulator  12 A and quick disconnect coupling  12 B to the conduit  9 . The conduit  9  can be formed of multiple sections coupled in tandem, e.g., by hose nuts and swivels  13 . Further, appropriately placed floats and/or weights  14  can be distributed along the conduit length. 
     As represented in  FIG. 1 , the body  6  generally comprises a top portion or frame  6 T and a bottom portion or chassis  6 B, spaced in a nominally vertical direction. The body also generally defines a front or nose portion  6 F and a rear or tail portion  6 R spaced in a nominally horizontal direction. The body is supported on a traction means such as wheels  15  whose orientation defines the body&#39;s direction of forward motion. A sweep hose  16  trails from the body  6  for sweeping the wall surface. 
     Attention is now directed to  FIG. 2  which substantially corresponds to FIG. 2 of U.S. Pat. No. 6,365,039 and schematically depicts an exemplary cleaner body  100  having a positive pressure water supply inlet  101  and multiple water outlets which can be variously used by the body  100  in its different operating modes and states. The outlets active during the forward state and during the backup/redirect state are respectively shown in  FIGS. 3A-3D  and  FIGS. 4A-4D . 
     With reference to  FIG. 2 , the following exemplary water outlets are depicted: 
       102 —Forward Thrust Nozzle; provides forward propulsion and a downward force in the wall surface cleaning mode to assist in holding the wheels  15  against the wall surface  8 . 
       104 —Backup/Redirect Thrust Nozzle; provides backward propulsion and rotation of the body around a substantially vertical axis when in the backup/redirect state; 
       106 —Forward Thrust/Lift Nozzle; provides thrust to lift the cleaner body to the water surface and to hold it there and propel it forwardly when operating in the water surface cleaning mode; 
       108 —Vacuum Jet Pump Nozzle; produces a high velocity jet to create a suction at the vacuum inlet opening  109  to pull in water and debris from the adjacent wall surface  8  in the wall surface cleaning mode; 
       110 —Skimmer Nozzles; provide a flow surface water and debris into a debris container  111  when operating in the water surface cleaning mode; 
       112 —Debris Retention Nozzles; provides a flow of water toward the mouth of the debris container  111  to keep debris form escaping when operating in the backup/redirect state; 
       114 —Sweep Hose; discharges a water flow through hose  115  to cause it to whip and sweep against wall surface  8 . 
     Attention is now directed to  FIGS. 3A ,  3 B,  3 C and  3 D which are similar to like numbered Figures in PCT/US2004/016937 and which schematically illustrate top, side, front, and rear views of an exemplary cleaner body  120 . These figures show a power supply conduit  121  and the primary water nozzles for discharging water jets during wall surface and/or water surface cleaning modes for forward propulsion. Note initially that  FIGS. 3A ,  3 B, and  3 D illustrate a forward thrust nozzle  102  oriented to discharge a water jet rearwardly and downwardly substantially along the longitudinal centerline of the body  120  to produce a force F P  for propelling the body in the forward direction defined by wheels  15  and a force F −V  for holding the wheels against the wall surface. 
       FIGS. 3B and 3D  illustrate a forward/lift discharge nozzle  106  mounted at the rear of body  120  below the nozzle  102  but also substantially aligned with the longitudinal center line of the body  120 . Note that the nozzle  106  is oriented to discharge a water jet rearwardly and downwardly to produce a vertical force F +V  for lifting the body  120  to the water surface and a forward thrust F P  for propelling the body  120  along the water surface. The jet discharged from nozzle  106  acts to maintain the body  120  at the water surface while propelling it forwardly in the forward/water surface travel state. 
     Attention is now directed to  FIGS. 4A ,  4 B,  4 C, and  4 D which also are similar to like numbered Figures in PCT/US2004/016937 and which schematically illustrate the top, side, front, and rear views of the cleaner body  120  showing a front backup/redirect nozzle  104  and an additional rear backup/redirect nozzle  122 . The nozzles  104  and  122  are used during backup/redirect state to execute a reposition operation to redirect the travel path of the body  120 . More particularly, note in  FIG. 4A  that nozzle  104  mounted at the front of body  120  is oriented to discharge a water jet having a horizontal component extending to the left and that nozzle  122  mounted at the rear of body  120  is oriented to discharge a water jet having a horizontal component extending to the right. The forces F R  attributable to these oppositely directed horizontal components discharged from spaced nozzles  104  and  122  act cooperatively to produce a turning moment around the body&#39;s center of gravity to rotate the body in a clockwise direction and enable it to resume forward travel along a different redirected path. In order to facilitate rotation of the body  120  when operating in the wall surface mode with wheels  15  engaged against wall surface  8 , it is preferable that the body be lifted slightly to disengage the wheels  15  from the wall surface. Accordingly, it is preferable that at least one of the nozzles  104 ,  122  be oriented so that the jet discharged therefrom has a vertical component acting to life the body and wheels from the wall surface. It should also be noted in  FIG. 4A  that the nozzle  104  is oriented so that the jet discharged therefrom has a forward component to produce a force acting to cause the body to move rearwardly, i.e., backup, to facilitate the body extricating itself from behind an obstruction. 
     The present invention is directed primarily to a control subsystem for controlling the respective water discharges from the nozzle outlets depicted in  FIGS. 3A-3D  and  4 A- 4 D to optimize the performance of the cleaner body.  FIG. 5  comprises a functional block diagram depicting such a control subsystem and illustrates a controller  140  for responding to certain input conditions for causing a force generator  142  to selectively generate the aforementioned forces F P , F +V , F −V , F R  to produce the desired cleaner body motion. 
     More particularly, controller  140  is responsive to multiple conditional inputs, as depicted in  FIG. 5 . The depicted inputs include (1) a timed mode change input which switches operation from the wall surface mode to the water surface mode or visa versa. In accordance with an exemplary embodiment to be discussed herein, it will be assumed that a typical operational cycle is comprised of thirteen minutes of wall surface mode operation and seven minutes of water surface mode operation. Controller input (2) in  FIG. 5  comprises a timed state change input which in the exemplary embodiment assumed herein occurs at 2.5 minute intervals and typically initiates a reposition operation. Input (3) depicted in  FIG. 5  is derived form the position of a manually set mode cam override mechanism. The override mechanism can be manually set by a user to any one of three conditions; i.e., (a) wall surface mode only; (b) water surface mode only; (c) alternating between wall surface mode and water surface mode. Input (4) in  FIG. 5  comprises a motion sensor input which will be assumed to be a binary signal indicating whether the rate of cleaner body forward motion is greater than (&gt;) or less than (&lt;) a predetermined threshold rate (T). Input (5) depicted in  FIG. 5  is identified as an event sensor and contemplates several alternative input signals which can be derived, for example, from a rotation sensor, a direction sensor, an attitude sensor, etc. 
     The controller  140  can be electronically and/or mechanically (including hydraulic and pneumatic) implemented. Regardless of the implementation, the controller  140  functions to respond to the set of inputs to generate command signals for the force generator  142 . More particularly, the controller can generate a forward water surface command  144  to cause the force generator to produce forward/lift force components  146  (F P , F +V ). Alternatively, the controller  140  can generate a forward/wall surface command  148  to cause the force generator  142  to produce forward/descend force components  150  (F P , F −V ). Additionally, the controller  140  can generate a reposition command  152  to cause the force generator  142  to produce backup/redirect force components  154  (F R ). 
     Attention is now directed to  FIG. 6  which comprises a flow chart depicting an exemplary routine executable by the controller  140  for a cleaner body operating solely at the wall surface. Execution of the flow chart of  FIG. 6  is initiated by a start signal (e.g., supplying positive pressure water to the controller) which enables block  160  to establish a forward state to propel the cleaner body in a forward direction. Thereafter, decision block  162  is executed which determines whether a timed reposition signal has occurred. If NO, operation proceeds to decision block  164  which queries the motion sensor to determine whether the forward motion rate is less than the threshold rate (T). If NO, operation loops back to block  162  and the cleaner body&#39;s operation remains in forward state. 
     On the other hand, if block  162  produces a YES, operation proceeds to block  166  which initiates a reposition operation. Similarly, if the decision block  164  determines that the forward motion rate is less than T, operation would also branch to block  166 . In accordance with the present invention, a reposition operation initiated by block  166  is comprised of one, two, or more sequential redirect actions. That is, a first redirect action (RA 1 ) is executed in block  168  to rotate the cleaner body through a first angle. Thereafter, operation proceeds to decision block  170  which asks whether the rate of forward motion is less than the threshold T. If the cleaner body has extricated itself after RA 1  and is now exhibiting sustained forward motion, decision block  170  delivers a NO output causing operation to loop back to block  162 . On the other hand if decision block  170  delivers a YES, indicating that forward motion has not been sustained, i.e., the cleaner body is likely still trapped by an obstruction, then operation branches to block  172  to execute a second redirect action (RA 2 ). Thereafter, operation branches back to decision block  170  to again check for sustained forward motion. 
     As will be discussed hereinafter, in accordance with the invention, the initial redirect action (RA 1 ) resulting from block  168  is of a lesser net magnitude than the second redirect action (RA 2 ) resulting from block  172 . For example, RA 1  can cause the cleaner body to initially rotate 90° whereas RA 2  can cause the cleaner body to rotate further to a net angle of 135° 
     Whereas the flow chart of  FIG. 6  contemplates cleaner body operation solely at the wall surface, the flow chart of  FIG. 7  contemplates operation alternately at the wall surface and at the water surface and functions to assure that a timed reposition operation is not initiated during a transition between the wall surface and the water surface modes. The flow chart of  FIG. 7  assumes a start signal which leads to block  180  which, as an example, initializes the system to the wall surface mode and the forward travel state. Decision block  182  is then executed which determines whether a timed mode change input has occurred. If YES, operation proceeds to block  184  to switch the operating mode. Thereafter, decision block  186  is executed to determine whether the mode transition has been completed. For the sake of simplicity, it will be assumed that the transition has been completed within a predefined transition interval, e.g., 75 seconds, after the mode is switched in block  184 . Accordingly, operation will loop around decision block  186  until the transition interval has expired. Once the transition interval expires, then operation branches from block  186  to decision block  188 . Similarly, if decision block  182  delivers a NO to indicate that a timed mode change input has not occurred, operation will branch to decision block  188 . It should be recognized that decision block  188  corresponds to decision block  162  of  FIG. 6 . The subsequent blocks in  FIG. 7  and resulting actions are substantially identical to those discussed in  FIG. 6  except for one important distinction. In  FIG. 7 , after execution of a certain number of redirect actions, e.g., RA 2  in block  172 , if forward motion is not sustained (sensed in block  190 ), then operation loops back to block  184  to switch the operating mode. 
     Attention is now directed to  FIG. 8  which comprises a timing chart to help explain the operation of a preferred control subsystem operating in accordance with  FIG. 7 .  FIG. 8  assumes an exemplary subsystem having a 20 minute operational cycle during which the water surface mode is defined for 7 minutes and the wall surface mode is defined for 13 minutes. Line (b) of  FIG. 8  depicts mode change triggers  200  which occur at the 7 and 20 minute marks of each cycle to switch cleaner body modes as represented in line (a). Also, note that line (a) represents mode transition intervals, e.g.,  202 ,  204 , which will be assumed to have a 75 second duration, during which time initiated reposition operations are to be avoided. Line (c) depicts timed reposition triggers  206  which in the exemplary embodiment are spaced by 2.5 minutes. Except during a mode transition interval, each of these timed reposition triggers initiates a reposition operation to facilitate randomization of the body&#39;s travel path. To prevent the initiation of a reposition operation during a mode transition interval, the timed reposition triggers  206  (line (c)) have been intentionally phased relative to the timed mode change triggers  200  (line (b)) to assure that no reposition triggers occurs during a mode transition interval, e.g.,  202 ,  204 . Lines (d) and (e) respectively show the propulsion force intervals  208  which occur normally as a consequence of the timed reposition triggers  206  outside of the mode transition intervals. 
     Line (f) of  FIG. 8  shows the outlet of a motion sensor which indicates whether the body&#39;s rate of forward motion is greater than a threshold rate (&gt;T) or less than the threshold rate (&lt;T). It will be recalled form  FIGS. 6 and 7 , that a reposition operation is initiated when the &lt;T condition is recognized. This situation is depicted at  210  in  FIG. 8 , line (f). As a consequence, a first redirect action RA 1  is initiated to suspend the propulsion force F P  (at  212 ) and produce the reposition force F R  (at  214 ). It will be recalled that RA 1  is intended to produce a relatively small angular rotation, e.g., 90° which can typically be produced, for example, by a short duration force, e.g., 4 seconds. RA 1  is then terminated after the desired rotation is achieved or at the end of the specified short duration. If sustained forward motion fails to occur after RA 1 , a second redirect action RA 2  is executed to suspend the force F P  (at  216 ) and produce a larger angular rotation, e.g., net 135° which can typically be produced by a longer duration force F R  (at  218 ), e.g., 6 seconds. RA 2  is then terminated after the desired rotation is achieved or the specified duration has expired. In most circumstances, the first and second redirect actions will free the body form the obstruction to produce sustained forward motion. However, the system can be configured to execute one or more further redirect actions, e.g., reposition force F R  (at  220 ) having an 8 second duration, can be produced. If sustained forward motion fails to occur after a certain number (e.g., 2, 3, or 4) of redirect actions, then the mode is switched (shown at  221 ) as has been explained in connection with  FIG. 7 . 
     Attention is now directed to  FIGS. 9A and 9B  which illustrate a first exemplary implementation of a control subsystem in accordance with the invention as depicted in  FIGS. 5-8 .  FIG. 9A  depicts a controller  240  corresponding to controller  140  of  FIG. 5 . Controller  240  preferably includes microprocessor based electronics which can be powered by battery  242 . The battery can be charged by a generator  244  driven by a turbine  246  rotated by a water jet  248  derived from a positive pressure source, e.g., pump  10  of  FIG. 1 . The controller  240  responds to multiple inputs (see  FIG. 5 )  249  to control a motor  250  to selectively set a three position rotary valve  252 . The valve  252  is comprised, as shown in  FIG. 9B  of a valve body  254  defining three isolated chambers  256 ,  258 ,  260 . The chambers respectively communicate with outlets  262 ,  264   266 . A valve element  268  overlays and seals the chambers and is mounted for rotation around axis  267 . Motor  250  rotates valve element  268  via gear reducer  269  to position valve port  270  over a selected one of the chambers. Position sensor  271  can report the position of element  268  back to the controller  240 . The valve port  270  opens the selected chamber to a power source, e.g., positive pressure water supplied via tube  272  through shroud  274 . The outlets  262 ,  264 ,  266  respectively produce water jets to develop the three respective force sets represented at the output of the force generator  142  in  FIG. 5 . 
     Attention is now directed to  FIG. 10  which schematically illustrates an exemplary control subsystem  300  using a hydraulic controller  302 . The subsystem  300  is supplied with high pressure water at inlet  303  (e.g., from pump assembly  10  of  FIG. 1 ). The water flow at inlet  303  is directed to the inlet  304  of a two port state valve assembly  305 . The assembly  305  includes a valve actuator  306  configured to move a valve element  308  between a first position (to the right as viewed in  FIG. 10 ). When in the left position, the valve element  308  closes port  310  and opens port  312 . Water flow from inlet  304  through port  312  is delivered to a backup/redirect nozzle  313  for producing the backup/redirect force F R . When in the right position, the valve element  308  opens port  310  and closes port  312 . Water flow through port  310  is delivered to the inlet  315  of a two port mode valve assembly  314 . 
     The assembly  314  includes a valve actuator  316  configured to move a valve element  318  between a left position and a right position. When in the right position, port  320  is open and port  322  is closed. Port  320  delivers water flow for producing the lift/propulsion force components (F +V , F P ) for operation in the forward state water surface mode. When the valve element  318  is in the left position, port  320  is closed and port  322  is open. Port  322  delivers water flow for producing the forward/descend force components (F −V , F P ) for operation in the forward state wall surface mode. 
     The state valve actuator  306  includes a piston mounted for reciprocal linear motion. The piston has oppositely directed first and second faces  330 ,  332  with the area of face  330  being larger than the area of face  332 . Thus, as is explained in aforementioned application PCT/US2004/16937, a positive pressure applied only to face  332  will move the valve element  308  to the left but positive pressure applied to face  330  will move the valve element  308  to the right. In operation, positive pressure water is continually applied to face  332  via inlet  304  from supply inlet  303 . On the other hand, positive pressure water is selectively applied to face  330  via control port  336  by controller  302 . When positive pressure water is applied to control port  336 , the valve element  308  moves right to supply, via port  310 , positive pressure water to inlet  315  of the mode valve assembly  314 . This positive pressure flow into inlet  315  is directed out though either port  320  or  322  dependent on the position of valve element  318  mounted on mode valve element  318  mounted on mode valve actuator  316 . 
     The mode valve actuator  316  similarly includes a piston mounted for reciprocal linear motion and similarly has oppositely directed first and second faces  340 ,  342  with the area of face  340  being larger than the area of face  342 . When positive pressure water is supplied to control port  344 , the valve element  318  moves left to open port  322  to produce an outflow at exit  345  for forward propulsion in the wall surface mode. When positive pressure is not available at control port  344 , the valve element  318  moves right to open port  320  to produce an outflow at exit  346  for forward propulsion in the water surface mode. 
     Control ports  336  and  344  are controlled by controller  302 . Controller  302  is schematically depicted in  FIG. 10  with exemplary implementation details being shown in  FIGS. 11-15 . The controller  302  is comprised of a turbine  350  driven by a jet  352  supplied with positive pressure water via line  354 . The turbine  350  rotates a shaft  356  carrying a timed redirect cam  358  and a bank  359  of two or more motion redirect cams, e.g.,  360 ,  362 ,  364 . A gear train (not shown) in housing  366  is also driven by the turbine  350  to rotate shaft  367  carrying a mode cam  368 . Thus, the cams  358 ,  360 ,  362 ,  364 ,  368  all rotate synchronously. Unless otherwise stated, it will be assumed herein that the exemplary embodiment to be discussed, 
     a) the mode cam  368  has a 20 minute cycle and two spaced discontinuities for generating timed trigger signals at the beginning/end of each cycle and at the 7 minute mark; 
     b) the timed redirect cam  358  has a 2.5 minute cycle and a single discontinuity for generating trigger signals spaced by 2.5 minutes; and 
     c) each motion redirect cam  360 ,  352 ,  264  has a 2.5 minute cycle and eight lobes. 
     A preferred mode cam  368  implementation will be discussed in detail in connection with  FIGS. 13A ,  13 B,  13 C,  13 D. It will suffice at this point to understand that as cam  368  rotates, it opens a normally closed mode control valve  370  for 7 minutes of each 20 minute cycle. When valve  370  is closed, the positive pressure water form supply inlet  303  is applied to control port  344  to move valve element  318  left. This supplies a positive pressure flow out of exit  345  for producing force components for forward propulsion in the wall surface mode. When valve  370  is open, the control port  344  is deprived of positive pressure water from inlet  303  thus enabling the valve element  318  to move right for supplying a flow out of exit  346  to produce force components for forward propulsion in the water surface mode.  FIG. 10  also shows a user override control mechanism  371  which can be manually set to permit operation (1) solely in the wall surface mode or (2) solely to the water surface mode or (3) alternately in the wall surface and water surface modes. 
     The state valve control port  336  selectively receives positive pressure water from check valve  380  and flow path  384 . Positive pressure water is supplied to the check valve  380  via flow path  382 . In order to initiate a reposition operation and supply positive pressure water to the backup/redirect nozzle  313 , the flow to or out of the check valve  380  is diverted. More particularly, note flow path  390  extending from the output of check valve  380  to a relief port  392 . As will be discussed with reference to  FIGS. 11A ,  11 B,  11 C the relief port  392  is held closed when the cleaner body is traveling at a forward rate &gt;T by a motion sensor mechanism  395 . With relief port  392  closed, check valve  380  can supply positive pressure to control port  336  to maintain the state valve in the forward state. The timed redirect cam  358  (by virtue of lever arm  396 ) opens the relief port  392  every 2.5 minutes to interrupt the positive pressure at control port  336  and thus initiates a reposition operation as previously discussed in connection with  FIGS. 6-8 . 
     As previously noted, flow path  384  supplies a positive pressure via check valve  380  to control port  336  to move valve element  308  right to place valve  305  in the forward state. This path includes a small orifice  397  which communicates pressure but limits the magnitude of water flow. A ball valve  398  is coupled to the upstream side of check valve  380 . If the ball  398  opens and motion sensor relief port  392  opens (which will occur if cleaner body motion is &lt;T), then the check valve  380  will fail to deliver sufficient positive pressure to control port  336  to maintain the actuator to the right, i.e., the forward state. 
     More particularly, consider the situation in which the cleaner body is moving forward at a rate &gt;T with relief port  392  closed. Now assume that the body encounters an obstruction which reduces its forward rate to &lt;T thus opening the relief port  392 . This action alone is insufficient to deprive control port  336  of positive pressure. However, when ball valve  398  is next opened, e.g., by a lobe on cam  360 , then the control port  336  will be deprived of pressure and the state valve  305  will switch to initiate a reposition operation. 
     As will be discussed in greater detail in connection with  FIGS. 12A ,  12 B,  12 E, a cam selector  400  is associated with the ball valve  398  to assure that each reposition operation is initiated using the first motion redirect cam  360  to execute a first redirect action RA 1 . The cam  360  has the shortest duration lobes, e.g., sufficient to hold the ball valve  398  open for 4 seconds. If this first redirect action RA 1  is sufficient to produce a sustained forward motion rate &gt;T, the motion sensor mechanism  395  will close relief port  392  thus terminating the reposition operation. However, if the body&#39;s forward motion is insufficient to close port  392 , then the cam selector  400 , controlled by a pressure online  402  from state valve port  312 , will associate ball valve  398  with the next motion redirect cam  362  to perform a second redirect action RA 2 . Cam  362  has longer duration lobes than cam  360 , e.g., sufficient to hold the ball valve open for 6 seconds, to increase the body&#39;s turning angle. 
     Attention is now directed to  FIGS. 11A ,  11 B,  11 C, which show a preferred implementation of the timed redirect cam  358  and the motion sensor mechanism  395  schematically depicted in  FIG. 10 .  FIG. 11A  is a prospective representation of the bottom portion  6 B of a cleaner body housing having a front or nose portion  6 F and a rear or tail portion  6 R. Note that inlet vents  410  are provided on the housing front portion  6 F and outlets vents  412  are provided on the housing rear portion  6 R. As a consequence, as the cleaner body moves through the pool in a forward direction, pool water will move rearwardly through the body cavity  414  below the deck from the inlet vents to the outlet vents  412 . 
     In accordance with a preferred implementation of the motion sensor mechanism  395 , a channeling means, e.g., a partition  416  having a window  418 , is provided in the body cavity  414  to channel most of the water moving through the cavity through the window  418 . A motion sensor arm  420  is mounted for pivotal movement around pin  422 . The arm  420  includes a long front portion  423  which carries a paddle  424  aligned with the window  418 . 
     When the body is moving forward at a rate greater than a threshold T, water movement through the body cavity  414  will bear on the paddle  424  to pivot arm  420  to the clockwise position shown in  FIG. 11B . The arm  420  also includes a short rear portion  426  which carries a seal  428  which is aligned with the aforementioned relief port  392  ( FIG. 10 ). 
     When the body&#39;s rate of forward motion is sufficient to force the paddle  424  and arm  420  to the clockwise position ( FIG. 11B ), the arm rear portion  426  presses the seal  428  against the relief port  392  to close it. The long length of arm front portion  423  relative to the short length of arm rear portion  426  affords a sufficient moment arm to assure that relief port  392  can be well sealed. 
     It will be recalled that the timed redirect cam  358  in  FIG. 10  is operable to open relief port  392  every 2.5 minutes.  FIGS. 11A ,  11 B,  11 C show a preferred implementation wherein the cam  358  carries a protruding lobe  434  located to engage lever arm  396  attached to the motion sensor arm  420 . As the cam  358  rotates clockwise ( FIGS. 11B ,  11 C), the lobe  434  will engage a projection  437  on lever arm  396  to pivot arm  420  counterclockwise ( FIG. 11C ) to move the seal  428  and thus open relief port  392 . After the lobe  434  moves past projection  437 , the position of the arm  420  will again be determined by the water bearing against paddle  424  in cavity  414 . 
     Attention is now directed to  FIGS. 12A ,  12 B,  12 C which illustrates a preferred implementation  450  of the motion redirect cam bank  359  and cam selector  400  of  FIG. 10 . Whereas the schematic diagram of  FIG. 10  depicts the cam bank  359  as including two ( 360 ,  362 ) or more (e.g.,  364 ) cams mounted on a common drive shaft  356 , the implementation  450 , for simplicity in explanation, shows only cams  360  and  362 . 
     It will be recalled that the cam  360  in an exemplary embodiment is comprised of eight short duration lobes each of which defines a four second interval whereas the cam  362  has eight longer duration lobes each of which defines a six second interval. In the implementation  450  of  FIGS. 12A ,  12 B,  12 C, each of these cams is defined on the periphery of a different level of multilevel cam assembly  452  which can be integrally formed. The cam assembly  452  is mounted on and rotated by shaft  356  in a clockwise direction as viewed in  FIG. 12A . 
     The assembly  452  includes a lower level shelf  454  having radial slots  456  extending inwardly from a peripheral edge  458 . Eight slots  456  are provided uniformly spaced around the peripheral edge  458 . The assembly  452  further includes a middle level peripheral edge  460  having eight uniformly spaced lobes  462  projecting radially outward therefrom. Each lobe  462  includes an entrance ramp surface  464 , a valve activating surface  466 , and an exit ramp  468 . The valve activating surface  466  is located to engage ball  470  to open valve  398 . The length of the surface  466  along the peripheral edge  460  defines the interval duration during which the ball valve  398  stays open (six seconds in the exemplary embodiment). 
     The assembly  452 , as shown in  FIGS. 12A ,  12 B,  12 C also includes an upper level peripheral edge  474  having eight uniformly spaced lobes  476  projecting radially outward therefrom. Each lobe  476  includes an entrance ramp surface  478 , a valve activating surface  480 , and an exit ramp surface  482 . The valve activating surface  480  has a length along the peripheral edge  474  to engage ball  470  to hold the valve  398  open for an assumed four second interval. 
     The cam selector mechanism  400  is provided to initially align the ball  470  with the upper level peripheral edge  474  for executing a first redirect action RA 1  of a reposition operation. If RA 1  fails to provide sustained forward motion, then the mechanism  400  moves the ball  470  into alignment with the middle level peripheral edge  460  to execute a second redirect action RA 2 . The cam selector mechanism  400  includes a right angle link  481  comprised of first and second arms  482 ,  484 . The first arm  482  carries the ball valve  398 . The second arm  484  is attached to shaft  488  of piston  490 . The link  481  is mounted for pivotal movement about the vertex  486  between a normal (counterclockwise) position shown in solid line in  FIG. 12B  and an activated (clockwise) position shown in phantom line. When in its normal solid line position, the ball  470  is positioned to engage the upper level lobes  476  which form the cam  360  of  FIG. 10 . When in the clockwise phantom line position, the ball  470  is positioned to engage the middle level lobes  462  which form the cam  362  of  FIG. 10 . 
     The piston  490  is normally held to the right as viewed in  FIG. 12B  by spring  492  to position the link  481  in the normal solid line position. However, pressure from port  312  ( FIG. 10 ) applied to piston  490  via tube  494  produces a force on arm  484  tending to pivot the link  481  to its phantom line position to align ball  470  with the middle level lobes  462 . A projecting finger  496  mounted on the front end of link arm  482  bears against the upper surface of shelf  454  and prevents the link  481  from pivoting to the phantom line position until a slot  456  moves into alignment with the finger  496 . When this occurs, the finger  496  falls through the slot  456  and allows the link  481  to pivot clockwise ( FIG. 12C ) to move ball  470  into alignment with the middle level lobes  462  which are used to initiate the second redirect action RA 2 . If RA 2  produces sustained forward body motion, the pressure from port  312  is relieved allowing the spring  392  to pivot the link  480  counterclockwise to return to the normal full line position when a slot  456  next moves into alignment with finger  496 . 
     Attention is now directed to  FIG. 13A  which illustrates a simplified manual override control  371  ( FIG. 10 ) for controlling the mode control valve, i.e., ball valve  370 . Briefly, the override control  371  in  FIG. 13A  is comprised of a member  497  which can be linearly manually moved to any one of three vertical positions. In the middle position as shown in  FIG. 13A , member  497  positions an actuator element  498  held captive in recess  499 , in alignment with control element  504  of the ball valve  370 . In this middle position, a high portion  503  of the rotatable mode cam  368  is able to periodically engage the actuator element  498  to force it against control element  504  to open the valve  370 . Member  497  can be manually pulled down to a second position (not shown) to align a protuberance  505  with the control element  504  to hold the valve  370  open regardless of the action of the mode cam  368 . Alternatively, the member  497  can be manually moved upward from the position shown in  FIG. 13A  so that nothing bears against control element  504  thereby leaving the valve  370  in its normally closed condition. 
     Attention is now directed to  FIGS. 13B ,  13 C,  13 D,  13 E which illustrate a preferred implementation of the manual override control  371  ( FIG. 10 ) for controlling the ball valve  370 . The ball valve  370  is normally closed by spring  502  bearing against ball  504  to seat it against ridge  506 . As will be recalled from  FIG. 10 , when valve  370  is closed, the body  6  operates in the wall surface mode. When valve  370  is open, the body operates in the water surface mode. The mode cam  368  is mounted on and rotated by shaft  367 . Cam  368  defines an annular periphery  510  comprised of a low portion  512  and a high portion  514 . In order to produce thirteen minutes of wall surface mode operation and seven minutes of water surface mode operation during each 20 minute cycle, the low portion  512  extends over 65% of the periphery  510  and high portion extends over 35%. 
     A rotatable ring cage  520  is mounted concentrically around mode cam  368  for retaining a ball  522  in cage opening  523 . The rotational positional of the cage  520  is set by a manually operable user handle  524 . A cylindrical housing  526  is mounted around the cage  520  to contain the ball  522  in opening  523 . 
       FIGS. 13B ,  13 D,  13 E respectively show the three distinct rotational positions of cage  420  which can be set by a user to respectively cause the body  6  to (1) operate alternately in the water surface mode and wall surface modes, (2) operate solely in the water surface mode, or (3) operate solely in the wall surface mode. 
     More particularly,  FIG. 13B  shows the ring cage  420  positioned to align ball  522  with ball  504  of valve  370 . In this position of the cage, when the periphery high portion  514  of cam  368  rotates ball  522 , it moves ball  504  axially to open valve  370 . However, as cam  368  rotates to move the periphery low portion  512  adjacent ball  522 , it permits spring  502  to force ball  504  against ridge  506  to close the valve  370 . Thus, with the cage position depicted in  FIG. 13B , the state of the ball valve alternately opens and closes as the mode cam  368  rotates. 
     Attention is now directed to  FIG. 13D  which shows the cage  520  in a position to assure that the valve  370  remains open regardless of the orientation of the mode cam  368 . More particularly, note that the periphery of cage  520  includes a protrusion or bulge  530  which engages ball  504  to axially move the ball to open valve  370 . Thus with the cage set by handle  524  to the position shown in  FIG. 13D , the valve  370  will remain open causing the body  6  to operate solely in the water surface mode. 
       FIG. 13E  shows the cage  520  in a position which permits spring  502  to force ball  504  against housing ridge  506  to maintain valve  370  closed regardless of the rotational position of mode cam  369 . When in the position illustrated in  FIG. 13E , the valve  370  remains closed thereby restricting the operation of body  6  to the wall surface mode. 
     It should now be recognized that the timed mode change triggers  200  of  FIG. 8  coincide with the opening and closing of valve  370  ( FIG. 13A ) as a consequence of the rotation of the mode cam  368 . It should also be recognized that the timed reposition triggers  206  of  FIG. 8  occur when a lobe ( 462 ,  476 ) of cam assembly  452  ( FIG. 12A ) presses against ball  470 . 
     It will be recalled from the discussion of  FIG. 8  that it is preferable to phase the timed reposition triggers  206  relative to the timed mode change triggers  200  to assure that no timed reposition trigger occurs during a mode change interval. This preferred phasing is achieved in accordance with the present invention by appropriate installation of the mode cam  368  relative to the state cam assembly  452  at the time of manufacture. More particularly, as shown in  FIG. 14A , the mode cam  368  is provided with a registration hole  552  and the shaft  356  which is used to drive the state cam assembly  452  is keyed at  556  to only accept the assembly  452  ( FIG. 12A ) in a particular rotational orientation. By properly phasing the shaft key  556  relative to the registration hole  552 , the timed reposition triggers  206  ( FIG. 8 ) will fall outside of the mode change intervals, e.g.,  202 ,  204 . 
     In order to properly phase hole  552  and shaft key  556 , a fixture  572  ( FIGS. 15A ,  15 B) is provided containing a keyed shaft recess  574  and carrying a registration pin  576 . In use ( FIG. 15A ), the cam  368  is manually rotated until fixture  572  accepts keyed shaft  356  in recess  574  and pin  576  is accepted into registration hole  572 . This relative phasing of mode cam  368  and shaft  356  will assure proper phasing to avoid the occurrence of timed reposition triggers during mode change intervals. Once the shaft position has been set, fixture  572  can be removed and the keyed state cam assembly  452  can be mounted on the shaft and it will automatically be properly phased relative to mode cam  368 . 
     Although only a limited member of electronic and hydraulic controller implementations have been specifically described, it is recognized that various alternative implementations and modification may occur to those skilled in the art falling within the spirit and intended scope of the invention as defined by the appended claims. For example only, the motion sensor mechanism  95  can be implemented in a variety of alternative ways to detect the relative motion of the body through the water. As one example, attention is directed to  FIGS. 16A and 16B  which show a motion sensor  600  including a paddle  602  mounted for pivoting about shaft  604 . The paddle  602  is normally urged by spring  606  to the solid line counter clockwise position  608  shown in  FIG. 16A . The paddle  602  is carried by the cleaner body in a manner to cause the paddle to move to the dashed line clockwise position  610  shown in  FIG. 16A  as the cleaner body moves in a forward direction at a rate greater than T. In the position  610 , the paddle contacts pin  612  to close switch  614  which supplies an input to controller  140  ( FIG. 5 ). Another example of an alternative motion sensor  620  is shown in  FIGS. 17A and 17B . The motion sensor  620  includes a turbine wheel  622  which is carried by the cleaner body so as to rotate at a rate proportional to the body&#39;s forward motion through the water. The wheel  622  carries at least one marker  624 , e.g., magnet, reflector, aperture, which can be sensed by a suitable detector  626  as the marker moves therepast. The pulse output rate produced by detector  626  thus represents the speed of wheel  622  and the rate of forward motion of the cleaner body through the water.