WO2000058565A1

WO2000058565A1 - Variable float system

Info

Publication number: WO2000058565A1
Application number: PCT/US2000/008146
Authority: WO
Inventors: David J. Rocke
Original assignee: Caterpillar Inc.
Priority date: 1999-03-31
Filing date: 2000-03-28
Publication date: 2000-10-05

Abstract

Methods and apparatuses for controlling a work implement on an operating machine (100) having a hydraulic cylinder (30) coupled with the work implement and operable to move the work implement. A sensor measures a first physical quality exerted on the hydraulic cylinder (30) and transmits a first signal as a function of the first physical quality exerted on the hydraulic cylinder (30). A controller (16) receives the first signal, and determines if a net physical quality is within a predetermined range, the net physical quality being a function of the first signal. If the net physical quality is not within the predetermined range, the controller (16) transmits an adjustment signal to a fluid pump system (18). The fluid pump system (18) receives the adjustment signal and actuates the actuator to change the position of the work implement as a function of receiving the adjustment signal.

Description

VARIABLE FLOAT SYSTEM

Technical Field

This invention relates generally to controlling a work implement on an operating machine, and more specifically to a method and apparatus for controlling the drag pressure of the work implement.

Background Art

Many conventional operating machines consist of a motorized chassis, such as a tractor or loader, and a hydraulically controlled work implement, such as a bucket or a blade. A hydraulic cylinder, or more typically a pair of hydraulic cylinders control the position and motion of the work implement.

The hydraulics of some operating machines include a "float" mode. Float mode may be used to scrape a layer of debris off of the ground, or to locate the work implement on the ground in preparation for digging into a pile of material . In the float mode, the hydraulic system opens hydraulic paths to and from the hydraulic cylinders, allowing for a relatively unrestricted flow of hydraulic fluid to and from the hydraulic cylinders. As a consequence, the hydraulic cylinders no longer exert a controlling force on the work implement, and the position of the work implement freely changes as external forces are exerted on the work implement. The most common example is the bucket of a loader resting on a surface of the ground. When the loader is in motion, the bucket is pushed up by rising terrain and pulled down by gravity with falling terrain, effectively "floating" on the surface of the ground.

The weight of a typical work implement may be considerable. Bucket weights for some heavy- equipment range from 2,800 lbs. to 50,000 lbs. When the work machine is operating in float mode, the weight of the work implement may press itself into the ground with a significant drag pressure, and may cause the implement to gouge into the ground, plowing it. As a result, the work implement removes a layer of the ground in addition to the intended material . This is undesirable, as it unintentionally changes the surface of the ground and may decrease the volume of the work implement available for the intended payload.

Disclosure of the Invention The present invention provides methods and apparatuses for controlling the position of a work implement on an operating machine having a hydraulic cylinder coupled with the work implement and operable to move the work implement . The apparatus includes a first sensor coupled with the hydraulic cylinder. The first sensor measures a first physical quality exerted on the hydraulic cylinder and transmits a first signal as a function of the first physical quality exerted on the hydraulic cylinder. A controller is coupled with the first sensor to receive the first signal, and to determine if a net physical quality is within a predetermined range, the net physical quality being a function of the first signal. If the net physical qualityis not within the predetermined range, the controller transmits an adjustment signal to a fluid pump system. The fluid pump system pressurizes hydraulic fluid as a function of receiving the adjustment signal. An actuator is coupled with the fluid pump system to receive the pressurized fluid, and changes the position of the work implement as a function of receiving the pressurized fluid.

Brief Description of the Drawings

Figure 1 is a functional block diagram of a float control apparatus according to one embodiment of the invention, installed on a forward portion of an operating machine.

Figure 2 is a side view and block diagram of one embodiment of the float control apparatus installed on a wheel loader.

Figure 3 is a flowchart of a control algorithm according to one embodiment of the invention.

Best Mode for Carrying Out the Invention

Figure 1 is a functional block diagram of a float control apparatus 10 according to one embodiment of the invention, installed on a forward portion of an operating machine, such as a wheel loader 100. The float control apparatus 10 includes a first sensor, such as a first pressure sensor 12, a second sensor, such as a second pressure sensor 14, a controller 16, an actuator, such as a hydraulic cylinder 30, coupled with a fluid pump system 18, as described below, and an input device, such as an infinitely variable dial 20. Although operating machines typically use at least two pairs of hydraulic cylinders 30 to exercise a work assembly, only one of each pair is shown for purposes of simplicity. A greater or lesser number of hydraulic cylinders 30 may, of course, also be used. Further, although a wheel loader 100 is illustrated here, other types of operating machines, such as graders, skidders, track loaders, and tractors may also use the float control apparatus 10. The first and second pressure sensors 12, 14 are coupled with the hydraulic cylinder 30 having a first area 32, a second area 34, and a piston 36 having a first face 38 and a second face 40. The first and second sensors respectively monitor the hydraulic pressure of a hydraulic fluid (not shown) within the first and second areas 32, 34. It should be noted that the second area 34 surrounds a cylinder rod 56. The first and second pressure sensors 12, 14 respectively transmit a first and second pressure signal corresponding to the hydraulic pressure within the respective first and second areas 32, 34. The first and second sensors 12, 14 may be any of a variety of appropriate sensors that are capable of providing a signal indicative of a physical quality, such as pressure or force, including pneumatic pressure .

The controller 16 is coupled with the first and second pressure sensors 12, 14 to receive the first and second pressure signals. The controller 16 determines a cylinder force (F_cyι) , as described below, that corresponds to a drag pressure of a bucket assembly 50. The cylinder force (F_cyι) is determined as a function of the first and second pressure signals. The drag pressure is the pressure that the bucket assembly 50 applies to the ground. In float mode, the drag pressure typically corresponds to the weight of, or a percentage of the weight of the bucket assembly 50. The bucket assembly 50 includes a work implement, such as a bucket 52 or blade (not shown), and a lift arm 54 that is coupled with the hydraulic cylinder 30.

As the bucket assembly 50 rests a greater portion of its weight on the surface of the ground (resulting in a greater drag pressure) , the weight of the bucket assembly 50 transmitted through the cylinder rod 56, and born by the piston 36 decreases, and vice versa. As the weight of the bucket assembly 50 born by the piston 36 decreases, the piston 36 exerts a lesser force on the hydraulic fluid within the first area 32, thereby decreasing the pressure of the hydraulic fluid within the first area 32. Similarly, as the portion of weight of the bucket assembly 50 born by the piston 36 increases, the piston 36 exerts a greater force on the hydraulic fluid within the first area 32, increasing the pressure of the hydraulic fluid within the first area 32.

The precise mathematical relationship between the drag pressure of the bucket assembly 50 and the pressure within the first and second areas 32, 34 will vary with the specifications of the bucket assembly 50 and the hydraulic cylinder 30. This relationship may be approximately calculated based on the known geometries and weights, for example, or may be determined by experiment. Once determined, the relationship may be programmed into the controller 16.

Three primary forces exist within the cylinder 30: the force transmitted through the cylinder rod 56 from a pin onto which the lift arms 54 are mounted (created by the weight of the bucket assembly 50) ; the force of the hydraulic fluid within the second area 34 on the second face 40 of the piston 36 (F_h2) ; and the force of the hydraulic fluid within the first area 32 on the first face 38 of the piston 36 (F_hi) • Assuming that the piston 36 is not accelerating, the forces on the piston 36 will be balanced, thereby producing the following equations:

and because force equals pressure times area,

F_h2 = A₂* P₂ where Ai is the area of the first face 38 of the piston 36 and P_α is the pressure of the hydraulic fluid on the first face 38, i.e., in the first area 32, and where A₂ is the area of the second face 40 of the piston 36 and P₂ is the pressure of the hydraulic fluid in the second area 34. Combining the equations,

The quantities Ai and A₂ are known from the cylinder 30 geometry, and P_x and P₂ are measured with pressure sensors 12, 14. It should be noted that the quantities A_x and A₂ remain constant, and therefore measuring pressures P_α and P₂ is tantamount to measuring forces F_ω and F₂.

As explained above, the drag pressure of the bucket assembly 50 is a function of the force of the cylinder (F_cyι) applied to the fluid within the first area 32. Thus, by measuring Pi and P₂, an approximation of the drag pressure of the bucket assembly 50 may be determined.

Although the use of two sensors 12, 14 is described above, a single sensor 12 may be used instead to determine the drag pressure in the float control apparatus 10. The force exerted on the second face 40 by the fluid within the second area 34 is ignored, and therefore,

The float control apparatus 10 otherwise functions similarly to what is described above, and will not be repeated in the interest of brevity. The drag pressure calculated using a single pressure sensor 12 will generally not be as accurate as the float control apparatus 10 having two pressure sensors 12, 14, but for small values of P₂, the amount of deviation from the two sensor float control apparatus 10 will be low.

The controller 16 is operable to determine F_cyι and to generate an adjustment signal when F_cyι is not within a predetermined range. The adjustment signal indicates whether the drag pressure is too high or too low. If the drag pressure is above the predetermined range, the controller 16 transmits an adjustment signal having first characteristics, such as being a relatively high voltage, such as V_cc. If the drag pressure is below the predetermined range, the controller 16 transmits an adjustment signal having second characteristics, such as being a relatively low voltage, such as ground. Other characteristics and/or types of adjustment signals known to those skilled in the art, such as pulse width or frequency modulation, or using a current, may also be used to denote the drag pressure being too high or low.

The adjustment signal may also be generated strictly as a function of the first and second pressure signals, without calculating the force of the piston 36 (F_cyι) . Thus, the adjustment signal is generated when the pressure of fluid within the first area 32 is within a predetermined range and/or the pressure within the second area 34 is within another predetermined range. Again, the predetermined ranges may be determined by calculation or experiment. The hydraulic pump system 18 is coupled with the controller 16 to receive the adjustment signal, and is operable to cause the hydraulic cylinder 30 to change the position of the bucket assembly 50 as a function of receiving the adjustment signal. In one embodiment, the hydraulic pump system 18 includes a tank 19, a main pump 21, a pilot pump 23, a main manifold 25 having a valve 27, and a pilot manifold 29. A variety of other fluid pump and cylinder configurations known to those skilled in the art may also be used, as appropriate. The functioning of hydraulic systems using hydraulic pumps and cylinders is known to those skilled in the art, and will not be discussed in the interest of brevity.

When the adjustment signal has the first characteristics, the hydraulic pump system 18 causes the hydraulic cylinder 36 to raise the bucket assembly 50, decreasing the drag pressure of the bucket assembly 50. When the adjustment signal has the second characteristics, the hydraulic pump system 18 causes the hydraulic cylinder 36 to lower the bucket assembly 50, increasing the drag pressure. Thus, the hydraulic pump system 18 adjusts the position of the bucket assembly 50 to keep the drag pressure within a predetermined range. Figure 2 is a side view and block diagram of one embodiment of the float control apparatus 10 installed on the wheel loader 100. The wheel loader includes a conventional chassis 112, an engine 114 coupled with the chassis 112 and operable to generate a propelling force, a propulsion system 116, such as a transmission, drive shaft, and a wheel or a track, coupled with the engine to receive the propelling force and to drive the loader 100, a work implement, such as the bucket 52, coupled with the chassis 112, and the hydraulic cylinder 30 coupled with the bucket 52 and chassis 112.

In operation, as the wheel loader 100 moves over the surface of the ground, the percentage of the weight of the bucket assembly 50 supported by the ground may vary. For example, if the bucket 52 encounters an upslope, the weight of the bucket assembly 50 born by the ground will increase as the ground presses against the bucket 52. The additional supporting pressure from the ground will decrease the weight of the bucket assembly 50 born by the hydraulic cylinder 30, thus decreasing the pressure exerted by the weight of the bucket assembly 50 through the cylinder rod 56 on the piston 36 of the hydraulic cylinder 30. The decrease in pressure on the piston 36 is detected by the first and second pressure sensors 12, 14 and may be calculated as described above. When the pressure on the piston 36 decreases below the predetermined range, the controller 16 transmits the adjustment signal to the hydraulic pump system 18, causing the hydraulic pump system 18 to effect a fluid flow to/from the hydraulic cylinder 30 that raises the bucket assembly 50. Thus, when the bucket 52 encounters an upslope, the bucket 52 is automatically raised.

As the bucket 52 is raised, the pressure on the hydraulic cylinder 30 increases, and is detected by the first and second pressure sensors 12, 14. When the pressure is within the predetermined range, the controller 16 stops transmitting the adjustment signal, thereby stopping the upward movement of the bucket 52 in a position that causes the desired drag pressure .

Similarly, if the bucket 52 encounters a downslope, the percentage of weight of the bucket assembly 50 born by the ground will decrease as the ground falls away from the bucket 52. As the percentage of weight born by the ground decreases, the percentage of weight of the bucket assembly 50 born by the piston 36 of the hydraulic cylinder 30 increases. The increase in pressure is detected by the first and second pressure sensors 12, 14, and may be calculated as described above. When the pressure on the piston 36 increases above of the predetermined range, the controller 16 transmits the adjustment signal to the hydraulic pump system 18, causing the hydraulic pump system 18 to effect a fluid flow to/from the hydraulic cylinder 30 that lowers the bucket assembly 50. Thus, when the bucket 52 encounters a downslope, the bucket 52 is automatically lowered. As the bucket 52 is lowered, the pressure on the hydraulic cylinder 30 decreases, and is detected by the first and second pressure sensors 12, 14. When the pressure is within the predetermined range, the controller 16 stops transmitting the adjustment signal, thereby stopping the downward movement of the bucket 52 in a position that causes the desired drag pressure .

Thus, by selection of an appropriate predetermined range, the bucket 52 can be made to float over the surface of the ground without digging into and plowing the ground, regardless of the weight of the bucket assembly 50 or the contours of the ground. Alternately, the bucket 52 may be made to remove a layer of the ground by selecting an appropriately high drag pressure.

An input device, such as the infinitely variable dial 20 or a multi-position switch (not shown) may be used to input a desired drag pressure to the float control apparatus 10. The dial 20 transmits a desired drag pressure signal to the controller 16 as a function of the position of the dial 20. The desired pressure signal may correspond to a single pressure or a range of pressures. Thus, a float control apparatus 10 has a programmable, and variable drag pressure, i.e., a variable float system.

The desired drag pressure may also be programmed into the controller 16 during manufacturing of the controller 16, including being hard-wired or burned into a memory (not shown) .

Alternately, an operator may place the bucket 52 in a position to cause a desired drag pressure. With an appropriate input (not shown), the controller 16 reads the pressure signals from the first and second pressure sensors 12, 14. The controller calculates, as described above, a baseline pressure equal to the current force on the piston 36, and thereafter regulates the pressure to the sampled baseline pressure. A button or switch (not shown) is typically coupled with the controller 16 to provide a signal indicating that the controller 16 should read the baseline pressure. In one embodiment, the hydraulic pump system

18 is capable of variable flow rates, and the adjustment signal transmitted by the controller 16 has varying characteristics as a function of how far out of the predetermined range the cylinder force (F_cyι) , and therefore the drag pressure, is. When the drag pressure deviates from the predetermined range by only a relatively small quantity, the adjustment signal causes the hydraulic pump system 18 to pump at a relatively low rate, moving the bucket assembly 50 at a relatively low speed. However, when the drag pressure deviates from the predetermined range by a relatively large quantity, the adjustment signal causes the hydraulic pump system 18 to pump at a relatively high rate, moving the bucket assembly 50 at a relatively high speed. The greater the deviation from the predetermined range, the faster the hydraulic pump system 18 moves the bucket assembly 50. Other relationships between the extent to which the drag pressure deviates from the desired drag pressure and the speed at which the bucket assembly 50 moves are also possible.

In one embodiment, as shown in Figure 1, a position sensor, such as a rotary potentiometer 62, is coupled with the cylinder 30. The rotary potentiometer 62 transmits a position signal as a function of the position of the piston 36 within the hydraulic cylinder 30. The controller 16 is coupled with the rotary potentiometer 62 to receive the position signal. When the cylinder 30 is fully or nearly fully collapsed, the controller 16 reads this condition from the position signal, and ceases transmitting the adjustment signal causing the hydraulic pump to lower the bucket assembly 50. This prevents the hydraulic pump 16 from trying to move the cylinder 30 when the cylinder has reached a stop. Although using a rotary potentiometer 62 for the position sensor has been discussed above, other devices known to those skilled in the art may also be used. Figure 3 shows a flowchart 200 of a preferred embodiment of a control algorithm, such as software control, implemented in connection with one embodiment of the invention. Those skilled in the art may easily write software code implementing the control algorithm. In block 210 a desired cylinder force (F_cyι) corresponding to a desired drag pressure is determined. In block 220 the cylinder force (F_cyl) is measured. If, as determined in block 230, the cylinder force (F_cyι) is within the range of desired forces from block 210, the process returns to block 220. If the cylinder force (F_cyi) is not within the range of desired forces determined in block 210, the process proceeds to block 240. In block 240, it is determined whether the cylinder force (F_cyι) is too high, i.e., is above the predetermined range from block 210. If so, the bucket assembly is lowered (in block 250), increasing the drag pressure. The process then returns to block 220. Because block 230 has determined that the cylinder force (F_cyι) is not within the predetermined range, if the cylinder force (F_cyι) is not above the predetermined range, then it must be below the predetermined range. Therefore, in block 260 the bucket assembly 50 is raised, decreasing the drag pressure. From the foregoing it will be appreciated that although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.

Claims

1. An apparatus (10) for controlling a work implement on an operating machine (100) , the operating machine (100) having a hydraulic cylinder (30) coupled with the work implement and operable to move the work implement, the apparatus (10) comprising : a first sensor (12) coupled with the hydraulic cylinder (30), the first sensor (12) operable to measure a first physical quality exerted on the hydraulic cylinder (30) , and to transmit a first signal as a function of the first physical quality exerted on the hydraulic cylinder (30) ; a controller (16) coupled with the first sensor (12) to receive the first signal, the controller (16) operable to determine if a net physical quality is within a predetermined range, the net physical quality being a function of the first signal, and to transmit an adjustment signal when the net physical quality is not within the predetermined range ; a fluid pump system (18) coupled with the controller (16) to receive the adjustment signal and operable to pressurize a fluid as a function of receiving the adjustment signal; and an actuator coupled with the fluid pump system (18) to receive the pressurized fluid, the actuator operable to change the position of the work implement as a function of receiving the pressurized fluid.

2. The apparatus (10) of claim 1 wherein the net physical quality comprises a physical quality corresponding to the first signal .

3. The apparatus (10) of claim 1 wherein the adjustment signal comprises a signal having first characteristics when the net physical quality is greater than a first predetermined value and having second characteristics when the net physical quality is less than a second predetermined value, the first and second predetermined values defining the predetermined range.

4. The apparatus (10) of claim 3 wherein the first predetermined value is a value greater than the second predetermined value.

5. The apparatus (10) of claim 3 wherein one of the first and second characteristics comprises being a relatively low voltage and the other of the first and second characteristics comprises being a relatively high voltage.

6. The apparatus (10) of claim 5 wherein the relatively low voltage comprises ground and the relatively high voltage comprises V_cc .

7. The apparatus (10) of claim 1 wherein the fluid pump system (18) is operable to pressurize the fluid to a relatively low pressure as a function of receiving the adjustment signal having first characteristics and is operable to pressurize the fluid to a relatively high pressure as a function of receiving the adjustment signal having second characteristics .

8. The apparatus (10) of claim 3 wherein the actuator is operable to lower the work implement as a function of receiving the pressurized fluid having the relatively low pressure and operable to raise the work implement as a function of receiving the pressurized fluid having the relatively high pressure .

9. The apparatus (10) of claim 1 wherein the actuator is operable to change the position of the work implement at a rate that is a function of the extent to which the net physical quality is outside of the predetermined range.

10. The apparatus (10) of claim 9 wherein the rate of change increases as the net physical quality is farther outside of the predetermined range.

11. The apparatus (10) of claim 1 wherein the first sensor (12) comprises a pressure sensor (12) , the first physical quality comprise a pressure, and the pressure sensor (12) is operable to measure a hydraulic pressure within the hydraulic cylinder (30) , and to generate a pressure signal as a function of the measured hydraulic pressure, and the first signal comprises the pressure signal .

12. The apparatus (10) of claim 1 wherein the hydraulic cylinder (30) comprises: a first area (32) operable to receive hydraulic fluid; and a piston (36) having a first face (38) forming a border to the first area (32), the first force comprising the pressure of the hydraulic fluid within the first area (32) on the first face (38) of the piston (36) multiplied by the area of the first face (38) .

13. The apparatus (10) of claim 1, further comprising an input device coupled with the controller (16) , the input device operable to allow data to be input to the controller (16) , the controller (16) operable to determine the predetermined range as a function of the data.

14. The apparatus (10) of claim 13 wherein the input device comprises an infinite position dial (20) having a plurality of positions corresponding to a respective plurality of predetermined ranges, the input device operable to transmit a position signal as a function of the position of the dial (20) , the controller (16) operable to receive the position signal and to determine the predetermined range as a function of the position signal.

15. The apparatus (10) of claim 13 wherein the input device comprises a multi-position switch having a plurality of positions corresponding to a respective plurality of predetermined ranges, the input device operable to transmit a position signal as a function of the position of the switch, the controller (16) operable to receive the position signal and to determine the predetermined range as a function of the position signal.

16. The apparatus (10) of claim 1 wherein the fluid pump system (18) comprises a fluid pump.

17. The apparatus (10) of claim 1 wherein the fluid pump system (18) comprises: a storage tank (19) operable to store a volume of the fluid; a main pump (21) coupled with the storage tank (19) to receive the fluid, the main pump (21) operable to pressurize a first portion of the fluid; a main manifold (25) coupled with the main pump (21) to receive the pressurized first portion of fluid, the main manifold (25) having a valve (27) , the valve (27) operable to control fluid flow out of the main manifold (25) to the actuator as a function of receiving a second portion of pressurized fluid; a pilot pump (23) coupled with the storage tank (19) to receive the fluid, the pilot pump (23) operable to pressurize the second portion of the fluid; a pilot manifold (29) coupled with the pilot pump (23) to receive the pressurized second portion of the fluid, coupled with the controller (16) to receive the adjustment signal, and coupled with the main manifold (25) , the pilot manifold (29) operable to control the valve (27) within the main manifold (25) as a function of receiving the adjustment signal.

18. The apparatus (10) of claim 1 wherein the work implement comprises a bucket (52) .

19. The apparatus (10) of claim 1 wherein the work implement comprises a blade.

20. The apparatus (10) of claim 1 wherein the operating machine comprises a tractor.

21. The apparatus (10) of claim 1 wherein the operating machine comprises a loader (100) .

22. The apparatus (10) of claim 1, further comprising : a second sensor (14) coupled with the hydraulic cylinder (30) to monitor a second physical quality exerted on the hydraulic cylinder (30) , the second physical quality comprising a physical quality exerted by a hydraulic system of the operating machine on the hydraulic cylinder (30) , and the second sensor (14) is operable to transmit a second signal as a function of the second physical quality exerted on the hydraulic cylinder (30) ; and the controller (16) is coupled with the second sensor (14) to receive the second signal, and the net physical quality is a function of the first signal and the second signal.

23. The apparatus (10) of claim 20 wherein the net physical quality comprises the first signal minus the second signal .

24. An operating machine, comprising: a chassis (112) ; an engine (114) coupled with the chassis (112) , the engine (114) operable to generate a propelling force; a propulsion system (116) coupled with the engine (114) to receive the propelling force and operable to propel the operating machine as a function of receiving the propelling force; a work implement coupled with the chassis (112) ; a hydraulic cylinder (30) coupled with the work implement and the chassis (112) , the hydraulic cylinder (30) operable to move the work implement; a first sensor (12) coupled with the hydraulic cylinder (30) , the first sensor (12) operable to measure a first physical quality exerted on the hydraulic cylinder (30), and to transmit a first signal as a function of the first physical quality exerted on the hydraulic cylinder (30) ; a controller (16) coupled with the first sensor (12) to receive the first signal, the controller (16) operable to determine if a net physical quality is within a predetermined range, the net physical quality being a function of the first signal, and to transmit an adjustment signal when the net physical quality is not within the predetermined range ; a fluid pump system (18) coupled with the controller (16) to receive the adjustment signal and operable to pressurize a fluid as a function of receiving the adjustment signal; and an actuator coupled with the fluid pump system (18) to receive the pressurized fluid, the actuator operable to change the position of the work implement as a function of receiving the pressurized fluid.

25. The apparatus (10) of claim 24 wherein the net physical quality comprises a physical quality corresponding to the first signal.

26. The apparatus (10) of claim 24 wherein the adjustment signal comprises a signal having first characteristics when the net physical quality is greater than a first predetermined value and having second characteristics when the net physical quality is less than a second predetermined value, the first and second predetermined values defining the predetermined range .

27. The apparatus (10) of claim 24 wherein the pump system (18) is operable to pressurize the fluid to a relatively low pressure as a function of receiving the adjustment signal having first characteristics and is operable to pressurize the fluid to a relatively high pressure as a function of receiving the adjustment signal having second characteristics .

28. The apparatus (10) of claim 27 wherein the actuator is operable to lower the work implement as a function of receiving the pressurized fluid having the relatively low pressure and operable to raise the work implement as a function of receiving the pressurized fluid having the relatively high pressure .

29. The apparatus (10) of claim 24 wherein the first sensor comprises a pressure sensor (12) , the first physical quality comprise a pressure, and the pressure sensor (12) is operable to measure a hydraulic pressure within the hydraulic cylinder (30) , and to generate a pressure signal as a function of the measured hydraulic pressure, and the force signal comprises the pressure signal.

30. The apparatus (10) of claim 24, further comprising an input device coupled with the controller (16) , the input device operable to allow data to be input to the controller (16), the controller (16) operable to determine the predetermined range as a function of the data.

31. The apparatus (10) of claim 24 wherein the work implement comprises a bucket (52) .

32. The apparatus (10) of claim 24 wherein the operating machine comprises a loader (100) .

33. The apparatus of claim 24, further comprising : a second sensor (14) coupled with the hydraulic cylinder (30) to monitor a second physical quality exerted on the hydraulic cylinder (30) , the second physical quality comprising a physical quality exerted by a hydraulic system (18) of the operating machine on the hydraulic cylinder (30), and the second sensor (14) is operable to transmit a second signal as a function of the second physical quality exerted on the hydraulic cylinder (30) ; and the controller (16) is coupled with the second sensor (14) to receive the second signal, and the net physical quality is a function of the first signal and the second signal .

34. The apparatus (10) of claim 33 wherein the net physical quality comprises the first signal minus the second signal .

35. A method for controlling the position of a work implement on an operating machine, the operating machine having a hydraulic cylinder (30) coupled with the work implement, the hydraulic cylinder (30) operable to move the work implement, comprising: determining a first physical quality exerted on the hydraulic cylinder (30) ; comparing the first physical quality to a predetermined range; and adjusting the position of the work implement in response to the first physical quality being outside of the predetermined range.

36. The method of claim 35 wherein adjusting a position of the work implement comprises: lowering the work implement when the first physical quality is above the predetermined range; and raising the work implement when the first physical quality is below the predetermined range.

37. The method of claim 35 wherein the first physical quality comprises a pressure of a hydraulic fluid within the hydraulic cylinder (30) , and determining the first physical quality comprises measuring the pressure of the hydraulic fluid.

38. The method of claim 35 wherein the first physical quality comprises a pressure of a hydraulic fluid within the hydraulic cylinder (30) multiplied by an area, and determining the first physical quality comprises measuring the pressure of the hydraulic fluid.

39. The method of claim 38 wherein the measuring the first physical quality further comprises multiplying the pressure by the area.

40. The method of claim 35, further comprising setting the predetermined range.

41. The method of claim 40 wherein setting the predetermined range comprises inputting a datum indicative of a desired predetermined range.

42. The method of claim 40 wherein setting the predetermined range comprises: placing the work implement in a baseline position,- and measuring a baseline physical quality on the hydraulic cylinder (30) , the predetermined range corresponding to the baseline physical quality.

43. A method for controlling the position of a work implement on an operating machine (100) , the operating machine (100) having a hydraulic cylinder (30) coupled with the work implement and operable to move the work implement, comprising: determining a first physical quality exerted on the hydraulic cylinder (30) ; determining a second physical quality exerted on the hydraulic cylinder (30) ; determining a net physical quality as a function of the first and second physical qualities; determining if the net physical quality is within a predetermined range; and adjusting the position of the work implement if the net physical quality is not within a predetermined range.

44. The method of claim 43 wherein determining the net physical quality comprises subtracting the second physical quality from the first physical quality.

45. The method of claim 43 wherein adjusting the position of the work implement comprises : lowering the work implement when the net physical quality is above the predetermined range; and raising the work implement when the net physical quality is below the predetermined range.

46. The method of claim 43 wherein: the physical quality force comprises a pressure of a hydraulic fluid within a first area (32) of the hydraulic cylinder (30) and determining the first physical quality comprises measuring the pressure of the hydraulic fluid within the first area (32) and multiplying the pressure by a first area (32) ; and the second physical quality comprises a pressure of a hydraulic fluid within a second area (34) of the hydraulic cylinder (30) , and determining the second physical quality comprises measuring the pressure of the hydraulic fluid within the second area (34) and multiplying the pressure by a second area (34) .

47. The method of claim 43, further comprising setting the predetermined range.

48. The method of claim 47 wherein setting the predetermined range comprises inputting a datum indicative of a desired predetermined range.

49. The method of claim 47 wherein setting the predetermined range comprises: placing the work implement in a baseline position; and measuring a baseline force on the hydraulic cylinder (30) , the predetermined range corresponding to the baseline force.