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FIELD OF THE INVENTION 
     The present invention relates to a system for sensing and automatically controlling the orientation of a work tool. 
     Background of the Invention 
     A variety of work machines can be equipped with tools for performing a work function. Examples of such machines include a wide variety of loaders, excavators, tele-handlers, and aerial lifts. A work vehicle such as backhoe loader may be equipped with a tool, such as a backhoe bucket or other structure, for excavating and material handling functions. A swing frame pivotally attaches to the frame of the vehicle, a boom pivotally attaches to the swing frame, a dipperstick pivotally attaches to the boom, and the tool pivotally attaches to the dipperstick about a bucket pivot. A vehicle operator controls the orientation of the tool relative to the dipperstick by a tool actuator. The operator also controls the rotational position of the boom relative to the vehicle frame, and the dipperstick relative to the boom, by corresponding actuators. The aforementioned actuators are typically comprised of one or more double acting hydraulic cylinders and a corresponding hydraulic circuit. 
     During a work operation with a backhoe bucket, such as lifting or excavating material, it is desirable to maintain an initial orientation relative to gravity to prevent premature dumping of material, or to obtain a constant excavation shear angle. To maintain the initial backhoe bucket orientation relative to gravity, the operator is required to continually manipulate the backhoe bucket command input device to adjust the backhoe bucket orientation as the backhoe boom and dipperstick are moved during the work operation. The continual adjustment of the backhoe bucket orientation, combined with the simultaneous manipulation of a backhoe boom command input device and a dipperstick command input device inherent in movement of the backhoe boom and dipperstick, requires a degree of operator attention and manual effort that diminishes overall work efficiency and increases operator fatigue. 
     A number of mechanism and systems have been used to automatically control the orientation of a tool such as a backhoe bucket. Various examples of electronic sensing and control systems are disclosed in U.S. Pat. Nos. 4,923,326, 4,844,685, 5,356,260, and 6,233,511. Control systems typical of the prior art utilize position sensors attached at various locations on the work vehicle to sense and control tool orientation relative to the vehicle frame. Unlike the typical prior art, the present invention makes use of an angular velocity sensor attached to the tool to sense and maintain a fixed work tool orientation relative to an initial orientation, independent of vehicle frame orientation. The result is a simpler control system and improved tool orientation control relative to gravity. 
     A number of angular velocity sensors suitable for use in the present invention are commercially available. Examples of these types of angular velocity sensor are disclosed in U.S. Pat. Nos. 4,628,734, 5,850,035, 6,003,373. One example of such an angular velocity sensors is the BEI GYROCHIP® Model AQRS, marketed by the Systron Donner Internal Division of BEI Technologies of California. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide for an improved system for sensing and automatically controlling the orientation of a tool pivotally attached to a dipperstick of a backhoe or excavator. 
     The system automatically controls work tool orientation by making use of an angular velocity sensor attached to the tool to sense angular velocity of the tool relative to a global earth reference. A controller maintains the tool at a selected angular velocity. 
     The illustrated invention comprises a backhoe, a swing frame pivotally attached to the frame of the backhoe, a boom pivotally attached to the swing frame, a dipperstick pivotally attached to the boom, a tool pivotally attached to the dipperstick, an actuator for controllably moving the tool about its pivot, and the aforementioned angular velocity sensor. A controller processes data from the angular velocity sensor and commands movement of the tool actuator in response thereto. The illustrated embodiment also includes a tool command input device to affect movement of tool actuator, and a tool auto-hold command input device to enable a tool auto-hold function for maintaining the tool in an initial orientation. 
     When the tool auto-hold function is enabled, the controller maintains the tool orientation by commanding the tool actuator to move the tool such that the angular velocity sensed is zero. The controller is adapted to discontinue the tool auto-hold function when the operator manipulates the tool command input device to affect tool movement. The controller resumes tool auto-hold function once the operator discontinues manipulation of the tool command input device, reestablishing the initial tool orientation at the new orientation affected by the operator. Additionally, the operator may manipulate an auto-hold command input device to selectively enable and disable the tool auto-hold function. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a backhoe loader. 
     FIG. 2 is a schematic diagram of a loader bucket orientation sensing and automatic control system. 
     FIG. 3 is a schematic diagram of a backhoe bucket orientation sensing and automatic control system. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a self-propelled work vehicle, such as a backhoe loader  10 . A backhoe loader  10  has a frame  12 , to which are attached ground engaging wheels  14  for supporting and propelling the vehicle. Attached to the front of the vehicle is a loader assembly  16 , and attached to the rear of the vehicle is a backhoe assembly  18 . Both the loader assembly  16  and backhoe assembly  18  each perform a variety of excavating and material handling functions. An operator controls the functions of the vehicle from an operator&#39;s station  20 . 
     The loader assembly  16  comprises a loader boom  22  and a tool such as a loader bucket or other structure  24 . The loader boom  22  has a first end  26  pivotally attached to the frame  12  about a horizontal loader boom pivot  28 , and a second end  30  to which the loader bucket  24  pivotally attaches about a horizontal loader bucket pivot  32 . 
     A loader boom actuator, having a loader boom hydraulic cylinder  36  extending between the vehicle frame  12  and the loader boom  22 , controllably moves the loader boom  22  about the loader boom pivot  28 . A loader bucket actuator  38 , having a loader bucket hydraulic cylinder  40  extending between the loader boom  22  and the loader bucket  24 , controllably moves the loader bucket  24  about the loader bucket pivot  32 . In the illustrated embodiment, the loader bucket actuator  38  comprises a loader bucket electro-hydraulic circuit  42  hydraulically coupled to the loader bucket hydraulic cylinder  40 . The loader bucket electro-hydraulic circuit  42  supplies and controls the flow of hydraulic fluid to the loader bucket hydraulic cylinder  40 . 
     The operator commands movement of the loader assembly  16  by manipulating a loader bucket command input device  44  and a loader boom command input device  46 . The loader bucket command input device  44  is adapted to generate a loader bucket command signal  48  in response to manipulation by the operator, proportional to a desired loader bucket movement. A controller  50 , in communication with the loader bucket command input device  44  and loader bucket actuator  38 , receives the loader bucket command signal  48  and responds by generating a loader bucket control signal  52 , which is received by the loader bucket electro-hydraulic circuit  42 . The loader bucket electro-hydraulic circuit  42  responds to the loader bucket control signal  52  by directing hydraulic fluid to the loader bucket hydraulic cylinder  40 , causing the hydraulic cylinder  40  to move the loader bucket  24  accordingly. 
     During a work operation with the loader bucket  24 , such as lifting or transporting material, it is desirable to maintain an initial loader bucket orientation relative to gravity to prevent premature dumping of material. To maintain the initial loader bucket orientation as the loader boom  22  is moved relative to the frame  12  during a lifting operation, and as the vehicle frame  12  changes pitch when moving over uneven terrain during a transport operation, the operator is required to continually manipulate the loader bucket command input device  44  to adjust the loader bucket orientation. The continual adjustment of the loader bucket orientation requires a degree of operator attention and manual effort that diminishes overall work efficiency and increases operator fatigue. 
     FIG. 2 illustrates an improved actuator control system adapted to automatically maintain an initial loader bucket orientation. The present invention makes use of an angular velocity sensor  54  attached to the loader bucket  24 , in communication with the controller  50 . The loader bucket angular velocity sensor  54  is adapted to sense angular loader bucket velocity relative to an earth based coordinate system and to continuously generate a corresponding angular velocity signal  56 . The controller  50  is adapted to receive the angular loader bucket velocity signal  56  and to generate a loader bucket control signal  52  in response, causing the loader bucket actuator  38  to move the loader bucket  24  to achieve a desired loader bucket angular velocity. Where the object of the invention is an auto-hold function to maintain the initial loader bucket orientation set by the operator, relative to gravity, the desired angular loader bucket velocity is zero. Additionally, the controller  50  is adapted to suspend the auto-hold function when the operator commands movement of the loader bucket  24  when receiving the loader bucket command signal  48 , and reestablishing the initial loader bucket orientation as the orientation of the loader bucket  24  immediately after the loader bucket command signal  48  terminates. 
     In applications requiring greater precision in maintaining the initial loader bucket orientation, the controller  50 , having computational and time keeping capabilities, is adapted to solve the integral for the loader bucket angular velocity as a function of time to determine deviation from the initial loader bucket orientation. The controller  50  is adapted to generate a loader bucket control signal  52  in response to deviation exceeding a desired loader bucket orientation deviation, causing the loader bucket actuator  38  to move the loader bucket  24  to achieve the desired loader bucket orientation deviation. Where the object of the invention is an auto-hold function to maintain the initial loader bucket orientation set by the operator, relative to gravity, the desired loader bucket orientation deviation is approximately zero. Additionally, the controller  50  is adapted to discontinue responding for the desired angular loader bucket velocity when responding for the desired loader bucket orientation deviation. 
     In the illustrated embodiment, the present invention also utilizes a loader auto-hold command switch  58  in communication with the controller  50 . The loader auto-hold command switch  58  is adapted to generate a loader auto-hold command signal  60  corresponding to a manipulation of the loader auto-hold command switch  58  by the operator to enable operation of the auto-hold function for the loader bucket  24 . The controller  50  is adapted to ignore the angular loader bucket velocity signal  56  unless receiving the loader auto-hold command signal  60  from the loader auto-hold command switch  58 . 
     The backhoe assembly  18  comprises a swing frame  62 , a backhoe boom  64 , a dipperstick  66 , and a tool such as a backhoe bucket or other structure  68 . The swing frame  62  has a first end  70  pivotally attached to the frame  12  about a vertical pivot  72 , and a second end  74 . The backhoe boom  64  has a first end  76  pivotally attached to the second end  74  of the swing frame  62  about a horizontal backhoe boom pivot  78 , and a second end  80 . The dipperstick  66  has a first end  82  pivotally attached to the second end  80  of the backhoe boom  64  about a horizontal dipperstick pivot  84 , and a second end  86  to which the backhoe bucket  68  pivotally attaches about a horizontal backhoe bucket pivot  88 . 
     A swing frame actuator, having a swing frame hydraulic cylinder  90  extending between the vehicle frame  12  and the swing frame  62 , controllably moves the swing frame  62  about the vertical pivot  72 . A backhoe boom actuator, having a backhoe boom hydraulic cylinder  92  extending between the swing frame  62  and the backhoe boom  64 , controllably moves the backhoe boom  64  about the backhoe boom pivot  78 . A dipperstick actuator, having a dipperstick hydraulic cylinder  94  extending between the backhoe boom  64  and the dipperstick  66 , controllably moves the dipperstick  66  about the dipperstick pivot  84 . A backhoe bucket actuator  96 , having a backhoe bucket hydraulic cylinder  98  extending between the dipperstick  66  and the backhoe bucket  68 , controllably moves the backhoe bucket  68  about the backhoe bucket pivot  88 . In the illustrated embodiment, the backhoe bucket actuator  96  comprises a backhoe bucket electro-hydraulic circuit  100 , in connection the backhoe bucket hydraulic cylinder  98 , which supplies and controls the flow of hydraulic fluid to the backhoe bucket hydraulic cylinder  98 . 
     The operator commands movement of the backhoe assembly  18  by manipulating a backhoe bucket command input device  102 , a dipperstick command input device  104 , a backhoe boom command input device  106 , and a swing frame command input device. The backhoe bucket command input device  102  is adapted to generate a backhoe bucket command signal  108  in response to manipulation by the operator, proportional to a desired backhoe bucket movement. The controller  50 , in communication with the backhoe bucket command input device  102 , dipperstick command input device  104 , backhoe boom command input device  106 , and backhoe bucket actuator  96 , receives the backhoe bucket command signal  108  and responds by generating a backhoe bucket control signal  110 , which is received by the backhoe bucket electro-hydraulic circuit  100 . The backhoe bucket electro-hydraulic circuit  100  responds to the backhoe bucket control signal  110  by directing hydraulic fluid to the backhoe bucket hydraulic cylinder  98 , causing the hydraulic cylinder  98  to move the backhoe bucket  68  accordingly. 
     During a work operation with the backhoe bucket  68 , such as lifting or excavating material, it is desirable to maintain an initial backhoe bucket orientation relative to gravity to prevent premature dumping of material or to obtain a constant excavation shear angle. To maintain the initial backhoe bucket orientation relative to gravity, the operator is required to continually manipulate the backhoe bucket command input device  102  to adjust the backhoe bucket orientation as the backhoe boom  64  and dipperstick  66  are moved during the work operation. The continual adjustment of the backhoe bucket orientation, combined with the simultaneous manipulation of the backhoe boom command input device  106  and the dipperstick command input device  104  inherent in movement of the backhoe boom  64  and dipperstick  66 , requires a degree of operator attention and manual effort that diminishes overall work efficiency and increases operator fatigue. 
     FIG. 3 illustrates an improved actuator control system adapted to automatically maintain an initial backhoe bucket orientation. The present invention makes use of an angular velocity sensor  112  attached to the backhoe bucket  68 , in communication with the controller  50 . The backhoe bucket angular velocity sensor  112  is adapted to sense angular backhoe bucket velocity relative to an earth based coordinate system and to continuously generate a corresponding angular velocity signal  114 . The controller  50  is adapted to receive the angular backhoe bucket velocity signal  114  and to generate a backhoe bucket control signal  110  in response, causing the backhoe bucket actuator  96  to move the backhoe bucket  68  to achieve a desired angular backhoe bucket velocity. Where the object of the invention is an auto-hold function to maintain the initial backhoe bucket orientation set by the operator, relative to gravity, the desired angular backhoe bucket velocity is zero. Additionally, the controller  50  is adapted suspend the auto-hold function while the operator commands movement of the backhoe bucket  68  when receiving the backhoe bucket command signal  108 , and reestablishing the initial backhoe bucket orientation as the orientation of the backhoe bucket  68  immediately after the backhoe bucket command signal  108  terminates. 
     The present invention also utilizes a backhoe auto-hold command switch  116  in communication with the controller  50 . The backhoe auto-hold command switch  116  is adapted to generate a backhoe auto-hold command signal  118  corresponding to a manipulation of the backhoe auto-hold command switch  116  by the operator to enable operation of the auto-hold function for the backhoe bucket  68 . The controller  50  is adapted to ignore the angular backhoe bucket velocity signal  114  unless receiving the backhoe auto-hold command signal  118  from the backhoe autohold command switch  116 . 
     In the alternate embodiment, where a backhoe work operation is typically performed only when the vehicle is stationary, adjustments to maintain the initial backhoe bucket orientation normally result only from a corresponding movement of the backhoe boom  64  or the dipperstick  66 . To minimize the period of auto-hold function for the backhoe bucket  68 , the controller  50  may be adapted to ignore the angular backhoe bucket velocity signal  114  unless receiving a backhoe boom command signal  122  from the backhoe boom command input device  106 , or a dipperstick command signal  120  from the dipperstick command input device  104 . 
     Having described the illustrated embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.

Summary:
The invention comprises a backhoe with a tool pivotally attached to a dipperstick, an actuator for controllably moving the tool about its pivot, and an angular velocity sensor for sensing the angular velocity of the tool relative to an earth based coordinate system. A controller is adapted to perform a tool auto-hold function, automatically maintaining an initial tool orientation by processing the angular velocity data and commanding movement of the tool actuator to hold the angular velocity at zero. The controller is adapted to discontinue the tool auto-hold function when the operator manipulates a tool command input device affecting tool actuator movement, and resume the tool auto-hold function at the new orientation affected by the operator. Manipulation of an auto-hold command input device allows the operator to selectively enable and disable the tool auto-hold function.