Method and apparatus for controlling the depth of an agricultural work unit mounted to a frame that can be raised and lowered by a cylinder assembly

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.

We claim: 
     
       1. An agricultural machine, comprising:
 a central frame configured to carry a plurality of farming related work units; 
 left and right wheel sets pivotally mounted to the central frame; 
 a left wheel actuator interconnecting the left wheel set and the central frame and being configured to raise and lower the central frame to adjust a depth of the work units, the left wheel actuator including a hydraulic cylinder and a piston extendable and retractable from the hydraulic cylinder; 
 a right wheel actuator interconnecting the right wheel set and the central frame and being configured to raise and lower the central frame to adjust a depth of the work units, the right wheel actuator including a hydraulic cylinder and a piston extendable and retractable from the hydraulic cylinder of the right wheel actuator; 
 a depth control system controlling the a flow of hydraulic fluid to and from the hydraulic cylinders of the left and right wheel actuators; 
 a left position sensor integrally formed with the hydraulic cylinder and the piston of the left wheel actuator, the left position sensor configured to measure a linear displacement of the piston of the left wheel actuator and provide a signal to the depth control system indicative of a depth of a first portion of the central frame; 
 a right position sensor integrally formed with the hydraulic cylinder and the piston of the right wheel actuator, the right position sensor configured to measure a linear displacement of the piston of the right wheel actuator and provide a signal to the depth control system indicative of a depth of a second portion of the central frame; 
 
       wherein:
 at least one of the left and right position sensors is a linear potentiometer instrument that is configured to output a signal having a voltage that changes with linear displacement of the piston of the corresponding hydraulic cylinder; 
 the depth control system including a controller that receives the signal from the linear potentiometer and can store the voltage of the signal to define a baseline voltage upon selection of a depth of the plurality of farming related work units by an operator, the controller controlling flow of hydraulic fluid to the hydraulic cylinders so as to automatically control pressures in the hydraulic cylinders of the left and right wheel actuators in response to the signals received from the left and right position sensors relative to the baseline voltage to raise and lower the central frame such that the depth of the plurality of farming related work units is maintained at the depth of the plurality of farming related work units that was selected by the operator. 
 
     
     
       2. The agricultural machine of  claim 1  wherein the work units are seed or fertilizer dispensers. 
     
     
       3. The agricultural machine of  claim 1  wherein the work units are soil preparation devices. 
     
     
       4. The agricultural machine of  claim 1  wherein the controller is further configured to control the flow of hydraulic fluid to the cylinders to minimize a difference between an instantaneous values of parameters measured by the sensors and set point values for the parameters. 
     
     
       5. The agricultural machine of  claim 1  further comprising a fluid reservoir fluidly connected to the hydraulic cylinders and solenoids communicatively connected to the controller, wherein the controller controls operation of the solenoids to deliver hydraulic fluid to the hydraulic cylinders based on outputs of the linear potentiometers. 
     
     
       6. The agricultural machine of  claim 5  wherein the fluid reservoir contains hydraulic oil. 
     
     
       7. The agricultural machine of  claim 1  further comprising an operator cab remote from the central frame and comprising operator controls that allow an operator to vary the depth of the work units from within the operator cab. 
     
     
       8. A farming machine comprising:
 a central frame, wherein said central frame includes first and second fore-and-aft extending members; 
 a left and right wheel set pivotally mounted on said first and second fore-and-aft extending members; respectively; 
 a front and back side member connected to said fore-and-aft members; 
 a left and right bearing mounted on each of said fore-and-aft members; 
 a rockshaft having opposing ends extending laterally across said central frame, wherein said left and right bearings constrain said rockshaft to rotate about a longitudinal axis with respect to said central frame; 
 a left bracket mounted on one of the outer ends of said rockshaft; 
 a right bracket mounted on opposing end of said rockshaft; 
 a plurality of work units coupled to the central frame; 
 a left hydraulic cylinder coupled to the first fore-and-aft member at one end and at the left bracket; 
 a right hydraulic cylinder coupled to the second fore-and-aft member at one end and at the said right bracket; 
 said left and right hydraulic cylinder operative to raise and lower the central frame; 
 a depth control system controlling the a flow of hydraulic fluid to and from the hydraulic cylinders, the hydraulic cylinders being depth control hydraulic cylinders; 
 pistons extendable and retractable from the depth control hydraulic cylinders; 
 sensors that measures linear displacement of the pistons with respect to the depth control hydraulic cylinders, the sensors integrally formed with the depth control hydraulic cylinders and the pistons so that each sensor outputs a signal with a voltage that corresponds to a position of relative extension or retraction of the piston with respect to the respective depth control hydraulic cylinder; and 
 a controller that receives the signals of the sensors, the controller including a memory and a set-depth control that can be activated by an operator when the plurality of work units has achieved a first depth that is set by the operator such that, upon activation of the set-depth control, the controller receives the signals from the sensors and stores the voltages of the signals in the memory so as to define a baseline voltage that is indicative of the position of relative extension or retraction of the piston with respect to the respective depth control hydraulic cylinder that corresponds to the first depth of the plurality of work units, and wherein the controller iteratively receives signals from the sensors and independently controls pressure in the depth control hydraulic cylinders based on the outputs of the sensors to raise and lower the central frame so as to attenuate deviation of the voltages from the baseline voltage and maintain the first depth of the plurality of work units. 
 
     
     
       9. The farming machine of  claim 8  wherein the sensors are contained within the hydraulic cylinders. 
     
     
       10. The farming machine of  claim 8  wherein the work units are one of seed or fertilizer dispensers and soil preparation tools.