Abstract:
An agricultural implement has a depth control system in which a position sensor directly measures linear translation of a hydraulic cylinder that lifts and lowers the implement frame to set and adjust the depth of the implement frame. The position sensor may be positioned adjacent to or integrally formed with the hydraulic cylinder, and provides a voltage to a controller remote from the implement. The controller automatically adjusts the flow of hydraulic fluid to and from the hydraulic cylinder to maintain the depth of the implement frame at an operator-selected level.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to farm and agricultural related machinery and, more particularly, to a method and system for controlling the depth of a work unit mounted to a frame that is raised and lowered by a hydraulic cylinder. 
     BACKGROUND OF THE INVENTION 
     An agricultural implement is generally composed of a number of work units, such as seed or fertilizer dispensers, or soil preparation tools, e.g., discs, tillers, cultivators, plows, and the like, that are typically carried by an implement frame that is hitched to and towed by a tractor, combine or similar wheeled device. The implement frame is generally supported above the ground by a pair of frame supporting wheels, which are mounted to wheel mounting spars that are rigidly attached to a rockshaft. The rockshaft may be rotated by a hydraulic cylinder to effectively raise and lower the implement frame and thus the work units. 
     For many agricultural implements, it is necessary for an operator to manually raise and lower the implement frame and the hydraulic cylinder holds the implement frame at the position set by the operator. More particularly, conventional depth control systems utilize a poppet valve to stop the flow of hydraulic fluid to the hydraulic cylinder to set the depth of the implement frame and thus the work units. Such stop valves have been found to be inconsistent in setting the depth of the implement frame and the valve is set until hydraulic fluid flow is reversed. 
     More recently, implements have been designed whereby the depth of the implement frame is monitored and hydraulic fluid flow to the hydraulic cylinder is controlled accordingly. U.S. Pat. No. 6,076,611 to Rozendaal et al. discloses an implement mounted depth control system whereby an electronic position sensor is mounted to the implement frame and senses the rotational position of the rockshaft. The rotational position of the rockshaft is used by a monitor to derive a depth of the work units and control the hydraulic cylinder to raise or lower the implement frame to raise or lower the work units to an operator-selected depth. The depth control system further allows an operator to raise and lower the implement frame using controls within the operator cab. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an agricultural implement towed by a tractor or other vehicle and having a depth control system in which a position sensor directly measures linear translation of a hydraulic cylinder that lifts and lowers the implement frame to set and adjust the depth of the implement frame. The position sensor may be positioned adjacent or integrally formed with the hydraulic cylinder, and provides a signal to a controller remote from the implement. In one implementation, the controller automatically adjusts the flow of hydraulic fluid to and from the hydraulic cylinder to maintain the depth of the implement frame at an operator-selected level. 
     Thus, in one embodiment, an operator raises or lowers the implement frame to a desired depth. The operator may then depress or otherwise activate a set depth selector that causes the controller to read the output of the position sensor. The output of the position sensor has a voltage level that establishes a baseline voltage to which subsequent voltage readings of the position sensor are compared. More particularly, as the implement is towed along the field, voltage signals are output by the position sensor and those readings are compared by the controller to the baseline voltage. The controller then controls the flow of hydraulic fluid to and from the cylinder so that the cylinder raises or lowers the implement frame. As the frame is raised or lowered, new readings are provided by the position sensor and used by the controller to control hydraulic pressure to minimize the difference between the real-time readings of the position sensor and the baseline voltage. The present invention also allows the operator to manually adjust the depth of the implement frame remotely from within the operator cab. 
     Therefore, in accordance with one aspect of the invention, an agricultural machine includes a frame configured to carry a plurality of farming related work units. A cylinder is coupled to the frame and configured to raise and lower the frame to adjust the depth of the work units. A sensor is associated with the cylinder and measures the linear displacement of the cylinder. The output of the sensor is a value indicative of the linear displacement and thus is indicative of the depth of the frame. 
     In accordance with another aspect of the invention, a method of controlling the depth of an agricultural work unit is provided. The method includes providing a set-point value based on an initial position of the work unit and measuring a linear translation of a hydraulic cylinder coupled to the work unit. The method further includes providing a measured value based on the linear translation of the hydraulic cylinder and comparing the measured value to the set-point value. The method also includes controlling hydraulic fluid flow to and from the hydraulic cylinder based on the comparison to reduce a difference between the measured value and the set-point value. 
     According to a further aspect of the invention, a farming machine includes a frame and a plurality of work units coupled to the frame. A hydraulic cylinder is coupled to the frame and operative to raise and lower the frame. A sensor is proximate the cylinder and measures the linear displacement of the cylinder. A control receives the output of the sensor and automatically controls pressure in the hydraulic cylinder based on the output of the sensor. 
     Other objects, features, and advantages of the invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred exemplary embodiments of the invention are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout. 
       In the drawings: 
         FIG. 1  is a top view of an agricultural machine and an agricultural implement hitched to the agricultural machine and having a depth control system according to one embodiment of the invention; 
         FIG. 2  is a partial isometric view of the agricultural implement of  FIG. 1 ; 
         FIG. 3  is a schematic diagram of a depth control system according to the present invention; and 
         FIG. 4  is a flow chart setting forth the steps of a method of setting the depth of the agricultural implement of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is directed to an agricultural implement having a frame that carries a number of farming related tools, such as discs, tillers, sweeps, or dispensers, whose depth is controlled by a depth control system. As will be described, the depth control system includes a sensor, such as a linear potentiometer, that outputs a signal having characteristics that are a function of the linear displacement of a hydraulic cylinder that raises and lowers the implement frame. As known in the art, the hydraulic cylinder includes an extendable piston or ram that when extended lifts the implement frame and when retracted lowers the implement frame. In one embodiment, the sensor includes an integrated linear position sensor, such as those described in U.S. Pat. Nos. 7,307,418, 7,259,553, and 7,034,527, the disclosures of which are incorporated herein by reference. 
     In  FIG. 1 , an implement  10  is illustrated having a central frame  12 , two wings  14  and  16  pivotally coupled to the central frame, lift actuators  18  and  20  for lifting the wings above the frame, wheel actuators  22 ,  24 ,  26 , and  28  for raising and lowering wheel sets  30 ,  32 ,  34 , and  36 , front tool gang  38  fixed to the front of the frame and wings, rear tool gang  40  fixed to the rear of the frame and wings. The implement may optionally have a leveling mechanism for leveling the implement, as described in U.S. Pat. No. 7,063,167. 
     Front tool gang  38  includes inner forward gang tubes  44  and  46  which are bolted to central frame  12  and extend laterally away from the central frame. These gang tubes have pivotal couplings  48  and  50  disposed at their outer ends to which outer forward gang tubes  52 ,  54 , respectively, are pivotally connected. 
     Rear tool gang  40  includes inner rear gang tubes  56  and  58  which are bolted to central frame  12  and extend laterally away from the central frame. These gang tubes have pivotal couplings  60  and  62  disposed at their outer ends to which outer rearward gang tubes  64  and  66 , respectively, are pivotally connected. 
     A plurality of ground engaging tools, here shown as discs  68 , are fixed to and disposed below each of the gang tubes. Like each pair of inner and outer gang tubes themselves, these discs are arranged in a substantially straight line. 
     The gang tubes on each side of the implement are bolted to a wing frame on that side of the implement. Outer gang tubes  52  and  64  are coupled to wing frame  70 , and outer gang tubes  54  and  66  are coupled to wing frame  72 . 
     The outer gang tubes are pivotally coupled to the inner gang tubes to permit them to be lifted above and over the central frame to permit the implement to be folded up for clearance when towed over the road. This lifting is provided by lift actuators  18  and  20 , here shown as hydraulic cylinders. Lift actuator  18  is coupled between central frame  12  and wing frame  70  to lift wing  14 , and lift actuator  20  is coupled between central frame  14  and wing frame  72  to lift wing  16 . When lift actuators  18  and  20  are retracted, they pull their associated wings  14  and  16  upward and over the top of central frame  12  about pivotal couplings  48 ,  60 , and  50 ,  62 , respectively. 
     Wing  14  includes wing frame  70 , front and rear gang tubes  52  and  64 , respectively, and the ground engaging tools attached to those tubes. Wing  16  includes wing frame  72 , front and rear gang tubes  54  and  66 , and the ground engaging tools attached to those tubes. 
     Referring to  FIG. 2 , central frame  12  includes two fore-and-aft extending members  74  and  76  to which wheel sets  32  and  34 , respectively, are pivotally mounted. Side-to-side members  78  and  80  are disposed at the front and rear, respectively, of the frame and are coupled to members  74  and  76  to form a substantially rectangular framework. A tongue  82  is coupled to central frame  12  and allows the implement to be hitched to a tractor in a known manner. 
     A rockshaft  84  extends laterally across central frame  12  and is supported in rotation at each end by bearings  86  and  88  that are mounted on fore-and-aft members  74  and  76 , respectively. Bearings  86  and  88  constrain rockshaft  84  to rotate about its longitudinal axis with respect to central frame  12 . Four wheel supports  90 ,  92 ,  94  and  96  extend downward and rearwardly from rockshaft  84  to which they are attached. Wheel supports  90  and  92  are disposed on the inside and the outside, respectively, of bearing  86  and member  74  to which bearing  86  is attached. Wheel supports  94  and  96  are disposed on the inside and outside, respectively, of bearing  88  and fore-and-aft member  76  to which bearing  86  is attached. Thus, when rockshaft  84  rotates, it causes the outer ends of wheel supports  90 ,  92 ,  94  and  96  to simultaneously and equally raise or lower with respect to central frame  12 . Two axles  98  and  100  are provided to which wheel sets  32  and  34  are mounted for rotation. Axle  98  is mounted to the outer ends of wheel supports  90  and  92 , and axle  100  is mounted to the outer ends of wheel supports  94  and  96 . Wheel set  32  has two wheels that are mounted to opposing ends of axle  98 , and wheel set  34  has two wheels that are mounted to opposing ends of axle  100 . The wheels in each wheel set are disposed on opposite sides of their associated fore-and-aft member, one inside and one outside. Wheel actuators  24  and  26  are pivotally coupled to fore-and-aft members  74  and  76 , at one end, and at the other end to brackets  102  and  104 . Brackets  102  and  104  are mounted to rockshaft  84  to rotate with rockshaft  84 . 
     When wheel actuators  24  and  26  are retracted, the wheels are raised thereby causing a lowering of the implement and the work units coupled thereto. When actuators  24  and  26  are extended, they push the upper ends of brackets  102  and  104  away from the actuators toward the rear of the implement. The lower ends of brackets  102  and  104  are coupled to rockshaft  84 , which causes rockshaft  84  to rotate clockwise. This clockwise rotation causes wheel supports  90 ,  92 ,  94  and  96  to also rotate clockwise. As the wheel supports rotate clockwise, the outer ends of the wheels supports and the two wheels sets coupled to the wheel supports also lower. As a result, the wheels pivot about rockshaft  84  as they are lowered thereby lifting the implement. 
     In one embodiment, the actuators  24  and  26  are hydraulic cylinders, with one of the cylinders including an integrated linear position sensor, such as those described in U.S. Pat. Nos. 7,307,418, 7,259,553, and 7,034,527, the disclosures of which are incorporated herein by reference. It is contemplated however that both cylinders may include a position sensor. 
     The depth control system  106  is schematically illustrated in  FIG. 3  and controls the flow of hydraulic fluid to and from depth control hydraulic cylinder  108 . Piston  110  is extendable and retractable from cylinder  108  and has an integrated linear potentiometer that provides a signal to a controller  114  of the tractor T. As will be described, the controller  114  selectively energizes a raise solenoid  116  and a lower solenoid  118 . Hydraulic fluid is supplied to the cylinder  108  through supply port  120  and is returned through a return port  122 . The solenoids  116  and  118  are fluidly connected to a fluid reservoir  124  that includes a pump  126 . 
     When raise solenoid  116  is energized, hydraulic fluid is supplied to the cylinder  108  along a fluid path between reservoir  124  and cylinder  108 , thereby causing an extension of piston  110  that is coupled to bracket  102 ,  FIG. 2 . As the piston is extended, the bracket  102  rotates rearwardly or in a counterclockwise direction thereby causing the implement to lift. Conversely, when solenoid  118  is energized, a fluid path is open between the cylinder  108  and the reservoir  124  resulting in fluid being drawing from the cylinder  108 . This causes a retraction of the piston  110  and thus a lowering of the implement. 
     The controller  114  selectively energizes the solenoids  116 ,  118  to maintain the depth of the implement at an operator selected level, which is selected using appropriate operator controls  128  within the operator cab of the tractor. The operator cab may also include various displays  130  to provide feedback regarding operation of the depth control system and other systems of the implement or tractor. 
     The feedback provided by the integrated potentiometer  112  is used by the controller  114  to derive a relative depth of the implement  10 . More particularly, and referring now to  FIG. 4 , the operator manually sets the implement to a desired depth. The depth can be set remotely using controls within the operator cab of the tractor if so equipped or at the implement itself. Once the depth has been selected, the operator activates a set-depth control which is detected by the controller at block  132 . Responsive thereto, the controller  114  reads and stores the output of the potentiometer  112  integrally formed with the cylinder  108 . The output of the potentiometer provides a baseline voltage that is stored in memory at block  134 . As the implement is towed along the field, the controller  114  iteratively reads the output of the potentiometer  112 . Any leakage of hydraulic fluid as the implement is being towed, which can cause a change in the depth of the implement, is detected by a change in the voltage output of the potentiometer  112 . That is, as the piston  110  is retracted and extended as a result of unintended changes in the flow of hydraulic fluid to and from the cylinder  108 , the output of the potentiometer  112  will also change. Those changes are detected by the controller at block  136  and compared to the baseline voltage at block  138 . If the position of the piston  110  has changed, which would result in a change in the depth of the implement, the voltage output of the potentiometer  112  will differ from the baseline voltage. Thus, if the voltage is different, the controller selectively energizes one of the solenoids at block  140  to either extend or retract the piston  110  until the output voltage of the potentiometer  112  equals, within some tolerance, the baseline voltage. If the voltage substantially equals the baseline voltage, the controller  114  returns to block  136  with continued monitoring of the potentiometer. 
     In the above described embodiment, one of the wheel actuators includes a cylinder with an integrated potentiometer. Thus, changes in depth readings are measured at that cylinder and any changes in hydraulic flow to maintain the depth of the implement at the operator selected level are made in that and the other wheel actuators. It is also contemplated however that each wheel actuator may have a cylinder with an integrated potentiometer and that the hydraulic pressure in the cylinders can be independently controlled to independently vary the position of the wheel actuators. 
     In a preferred embodiment, the position sensor is integrally formed with the hydraulic cylinder and its piston, but it is understood that other types of sensors could be used to directly measure the position of the piston and cylinder relative to one another. Moreover, sensors that measure voltage changes as a function of the displacement of a cylinder is representative and as such sensors that measure other types of parameters, such as sound, current, force, and the like, may be used and are considered within the scope of the invention. 
     Additionally, it is recognized that the output of the sensor could be provided to the controller in a wired or wireless transmission. 
     Many changes and will modifications could be made to the invention without departing from the spirit thereof. The scope of these changes will become apparent from the appended claims.