Method for controlling bounce of a work implement

A method is provided for controlling the bounce of a work implement attached to a machine having an electro-hydraulic system. The method comprises the steps of sensing the operating pressure in an actuator arrangement connected between the frame of the machine and the work implement, monitoring an upper and a lower operating pressure level in the actuator arrangement to establish a threshold pressure level and altering the pressure level in the actuator arrangement in the event the threshold level is exceeded to re-establish the threshold pressure level. Once the original threshold level is attained, the system is reset. This effectively eliminates the bounce of the work implement at the initial onset of the bounce and resets the system to react to future bounces.

TECHNICAL FIELD 
This invention relates generally to the control of a work implement 
attached to a machine and more particularly to eliminating the bouncing of 
a work implement during use. 
BACKGROUND ART 
In many machines, such as motorgraders, when the blade or work implement is 
being used to grade a road surface, the machine may begin to lope or 
bounce. This results in the road surface being scalloped or rough 
resulting in the need to rework the road surface a second or more times. 
This is generally attributed to the fact that the actuators are locked in 
position and cannot move up or down. In known machines, it is generally 
the practice for the operator to raise the blade, change the blade angle 
or reduce the machine speed once he detects the bounce. However, by the 
time the operator detects the bounce, a large area has already been 
affected. It is desirable to detect and provide corrective measures at the 
initial onset of the bounce. 
The subject invention is directed to overcoming one or more of the problems 
as set forth above. 
DISCLOSURE OF THE INVENTION 
In one aspect of the present invention, a method is provided for 
controlling the bounce of a work implement attached to a machine having an 
electro-hydraulic system. The electro-hydraulic system includes a 
microprocessor, an actuator arrangement connected between the machine and 
the work implement, a source of pressurized fluid that receives fluid from 
a reservoir, an electro-hydraulic directional control valve disposed 
between the source of pressurized fluid and the actuator, and a control 
lever electrically connected to the microprocessor and operative to 
control movement of the electro-hydraulic directional control valve. The 
method includes the steps of detecting the initiation of a bounce and 
altering the pressure level in the actuator arrangement to eliminate the 
bounce. 
The present invention provides a method that automatically controls the 
bounce in a work implement at the initial onset of the bounce by altering 
the pressure within the actuator to maintain a minimum threshold peak to 
peak pressure level thus controlling the operating force therein.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring to FIG. 1 of the drawings, a front portion of a machine, such as 
a motorgrader 10, is illustrated. The front portion of the motorgrader 10 
includes a frame 12, a pair of steerable front wheels 14 connected to the 
frame 12, a single work member, such as a blade 16, and an actuator 
arrangement 17, such as first and second actuators 18,20, connected 
between the frame 12 and the blade 16. Each of the first and second 
actuators 18,20 has a head end 22 and a rod end 23. It is recognized that 
the use of the term actuator arrangement used herein could mean one, two 
or more actuators even though two are illustrated and described. 
Referring to FIG. 2, an electro-hydraulic system 24 is schematically 
illustrated for controlling the blade 16. The electro-hydraulic system 24 
includes a source of pressurized fluid, such as a variable displacement 
pump 26, which receives fluid from a reservoir 28 and delivers the 
pressurized fluid to an actuator arrangement 17, such as the respective 
first and second actuators 18,20, through an electro-hydraulic directional 
control valve arrangement 29, such as respective first and second 
electro-hydraulic directional control valves 30,32. Each of the first and 
second electro-hydraulic directional control valves 30,32 is movable from 
a closed, neutral (N) position toward first and second operative positions 
(R,L) and a float (F) position in a well known manner responsive to 
receipt of an electrical signal from a microprocessor 36. 
The first electro-hydraulic directional control valve 30 is connected to 
respective head and rod ends 22,23 of the first actuator 18 by conduits 
38,40. The second electro-hydraulic directional control valve 32 is 
connected to respective head and rod ends 22,23 of the second actuator 20 
by conduits 42,44. A first variable pressure relief valve 46 is connected 
through a first shuttle valve 48 to the conduits 38,40 and the relief 
settings thereof is controlled in response to a first electrical signal 
received from the microprocessor 36. A second variable pressure relief 
valve 52 is connected through a second shuttle valve 50 to the conduits 
42,44 and the relief settings thereof is controlled in response to a 
second electrical signal received from the microprocessor 36. Each of the 
first and second shuttle valves 48,52 is operative to direct the highest 
pressure signal, in a well known manner, from the associated conduits 
38,40 and 42,44 to the respective variable relief valves 46,50. Each of 
the first and second variable relief valves 46,50 is connected to the 
reservoir 28 in a conventional manner. 
A first pressure sensor 56 is connected to the head end 22 of the first 
actuator 18 and an electrical signal representative of the pressure 
therein is delivered to the microprocessor 36. A second pressure 57 is 
connected to the rod end 23 of the first actuator 18 and an electrical 
signal representative of the pressure therein is delivered to the 
microprocessor 36. A third pressure sensor 58 is connected to the head end 
22 of the second actuator 20 and an electrical signal representative of 
the pressure therein is delivered to the microprocessor 36. A fourth 
pressure sensor is connected to the rod end 23 of the second actuator 20 
and an electrical signal representative of the pressure therein is 
delivered to the microprocessor 36. 
The electrical signals from the microprocessor 36 that activate the 
respective first and second electro-hydraulic directional control valves 
30,32 are generated in response to movement of a control lever mechanism 
59, such as respective control levers 60,62, that is electrically 
connected to the microprocessor 36. It is recognized that both of the 
first and second electro-hydraulic directional control valves 30,32 could 
be controlled by one control lever without departing from the essence of 
the subject invention. Movement of the respective control levers 60,62 is 
initiated by a machine operator between the respective neutral (N), raise 
(R), lower (L), and float (F) positions. The degree of movement of the 
respective control levers 60,62 in a given direction is electrically 
transmitted to the microprocessor 36 and determines the magnitude of the 
electrical signal being delivered from the microprocessor 36 to the 
respective first and second electro-hydraulic directional control valves 
30,32. As noted above, the respective first and second electro-hydraulic 
directional control valves 30,32 are moved in proportion to the electrical 
signal received from the microprocessor 36. 
Each of the control levers 60,62 has a switch 64 mounted thereon and 
electrically connected to the microprocessor 36. Depressing either of the 
switches 64 and moving the associated control lever 60/62 conditions the 
microprocessor 36 to simultaneously send the same electrical signal, that 
represents movement of the one control lever 60/62, to both of the first 
and second electro-hydraulic directional control valves 30,32. 
Consequently, movement of only one of the control lever 60/62 results in 
both actuators 18,20 moving together and at the same rate of speed. The 
same results occur if the other of the switches 64 is depressed and the 
associated lever 60/62 is moved. If both of the switches 64 are depressed 
at the same time, the control levers 60,62 operate independent of each 
other to individually control the respective actuators 18,20 in a typical 
manner. 
A variable force control 66 is provided and is electrically connected to 
the microprocessor 36. The variable force control 66 includes first and 
second pressure selector knobs 68,70. Each of the first and second 
pressure selector knobs 68,70 is movable from an "OFF" position towards an 
"UP" position or a "DOWN" position. The magnitude of the pressure setting 
is increased by moving the respective selector knobs 68,70 from the "OFF" 
position towards the "UP" or "DOWN" positions. In order to utilize the 
variable force control 66 solely for bounce control, a single on/off 
switch could be provided to condition the electro-hydraulic system for 
bounce control. 
It is recognized that various forms of the electro-hydraulic system could 
be utilized without departing from the essence of the invention. For 
example, even though sensing of the pressures in the head and rod ends 
22,23 of the first and second actuators 18,20 are illustrated and 
described, it is recognized that sensing the extended position of the 
respective actuators 18,20 could be utilized. Likewise even though 
different pressure selector knobs 68,70 are illustrated, the subject 
electro-hydraulic system 24 could use only one pressure selector knob to 
control the force being subjected to the blade 16 by the actuators 18,20. 
Industrial Applicability. 
In the operation of the machine 10 shown in FIG. 1 and the 
electro-hydraulic system 24 illustrated in FIG. 2, the operator makes an 
input to both of the control levers 60,62 in the same direction in order 
to move the blade 16. If the operator moves both of the control levers 
60,62 towards the "R" or raise position, electrical signals proportional 
to the degree of movement of the respective control levers 60,62 are 
directed to the microprocessor 36. The received signals from the 
respective control levers 60,62 are processed to identify the magnitude of 
the signal and direction of lever movement. Respective electrical signals 
proportional to the received signals from the first and second levers 
60,62 are delivered to the respective electro-hydraulic directional 
control valves 30, 32 to proportionally move the respective directional 
valves 30,32 thus directing pressurized fluid from the pump 26 to the rod 
ends 23 of the respective actuators 18,20 to raise the blade 16. In order 
to lower the blade 16, the operator moves the respective control levers 
60,62 towards the "L" or lower position. Electrical signals representative 
of the position of the respective control levers 60,62 are directed to the 
microprocessor 36 and the microprocessor 36 directs proportional signals 
to the respective electro-hydraulic directional control valves 30,32 which 
directs pressurized fluid to the head ends 22 of the actuators 18,20 to 
lower the blade 16. As is well known, the blade 16 can be placed in a 
"float" position by moving the respective control levers 60,62 to the "F" 
or float position. In the float position, the head and rod ends 22,23 of 
the respective actuators 18,20 are interconnected to each other and to the 
reservoir 28. In this position, the blade 16 is permitted to slide or 
float along the top of the work surface without having any down force, 
other than the weight and associated components of the blade 16, being 
applied thereto. 
From those skilled in the art, it is recognized that one side of the blade 
16 can be raised higher or lower than the other side by moving only one of 
the control levers 60,62 or by moving one of the control levers 60,62 more 
or less than the movement of the other one of the control levers 60,62. 
Naturally this depends on the operation being performed by the machine. 
As described above, raising or lowering of the blade 16 requires movement 
of both of the control levers 60,62 at the same time. As is well known, 
movement of both of the control levers 60,62 at the same time requires the 
operator to use both hands. In the subject arrangement, movement of one 
the control levers 60,62 can result in both of the actuators 18,20 moving 
at the same time and at the same rate. In order to move both actuators 
18,20 at the same time, the operator merely depresses one of the switches 
64 on one of the control levers 60/62. For example, when the operator 
depresses the switch 64 on the control lever 60, an electrical signal is 
directed to the microprocessor 36 to condition the microprocessor 36 so 
that on subsequent movement of the control lever 60 simultaneous signals 
are directed to both of the electro-hydraulic directional control valves 
30,32. These simultaneous signals are proportional to the movement of the 
one control lever 60. Likewise, if the operator depresses the other switch 
64 on the second control lever 62, simultaneous signals, that are 
proportional to the movement of the second control lever 62, are directed 
to both of the electro-hydraulic directional control valves 30,32. This 
allows the operator to use only one hand to raise or lower the blade 16 
thus freeing the other hand for other operations such as steering the 
machine, shifting the gears of the transmission, etc. 
In the event both of the switches 64 are depressed at the same time and 
both of the levers 60,62 are moved at the same time, the microprocessor 36 
functions to send only individual signals to the respective 
electro-hydraulic directional control valves 30,32. 
In order to provide a constant force on the blade 16 in a downward or 
upward direction, the variable force control 66 is used. The operator 
moves the respective selector knobs 68,70 to a desired position which 
relates to a pressure operating level. As noted above, this operating 
pressure level can be varied from a minimum pressure level to a maximum 
pressure level. It is recognized that one selector knob 68/70 could be 
placed in a different position than the other in order for more force to 
be applied to one side of the blade 16 as compared to the other side 
thereof. Once the operator moves the respective selector knobs 68,70 to 
their desired positions, the selected positions are electrically 
transmitted to the microprocessor 36. The microprocessor 36 transmits an 
electrical signal to the first and second electro-hydraulic directional 
control valves 30,32 in order to direct pressurized fluid from the 
variable pump 26 through the respective first and second electro-hydraulic 
directional control valves 30,32 to the head ends 22 of the first and 
second actuators 18,20. The blade 16 is moved downwardly into contact with 
the work surface at a rate of speed as determined by the electrical signal 
being delivered to the first and second electro-hydraulic directional 
control valves 30,32 from the microprocessor 36. Simultaneously an 
electrical signal is transmitted from the microprocessor 36 to each of the 
variable pressure relief valves 46,50 thus setting their effective 
operating pressure. The setting of the variable pressure relief valves 
46,50 is proportional to the respective settings of the selector knobs 
68,70. The position of the selector knob 68 relates to the setting of the 
first variable pressure relief valve 46 and the position of the selector 
knob 70 relates to the setting of the second variable pressure relief 
valve 50. 
Since the weight of the blade 16 and other associated structure may produce 
a force against the work surface higher than desired, the operator may set 
the respective selector knobs 68,70 at a position towards "UP". In this 
instance, the pressurized fluid from the variable pump 26 is directed to 
the rod end 23 of the respective actuators 18,20 to urge the actuators 
18,20 upwardly. However, the pressure level is maintained at a level low 
enough not to lift the blade 16 from the work surface but large enough to 
subtract from the force of the total weight of the blade 16 and its 
associated components acting on the work surface. As noted above, the 
pressure setting of the first and second variable pressure relief valves 
46,50 are set according to the selected position of the respective 
selector knobs 68,70. 
Movement of either of the control levers 60,62 interrupts the variable 
force control 66. In order to restart the variable force control 66, the 
respective selector knobs 68,70 must be returned to their "OFF" positions 
and if desired moved back to a desired constant force position. 
During a normal blading operation with the blade in a fixed position and 
the actuators 18,20 locked in the fixed position, and the machine 
encounters a bump or hard area the work element or blade 26 may start s to 
bounce or lope. When the bounce starts, the pressure level in the 
respective actuators 18,20 varies. As noted above, during any blading 
operation, the first, second, third and fourth pressure sensors 56,58 are 
continuously sensing the pressures in the respective head and rod ends 
22,23 of each of the actuators 18,20 and delivering an electrical signal 
representative of the sensed pressures therein to the microprocessor 36. 
In one embodiment, the microprocessor 36 is continually monitoring the 
peak to peak pressure levels therein and comparing the peak to peak 
pressures to a predetermined threshold level. The predetermined threshold 
level can be determined in several ways. For example, peak to peak 
pressures in only the head ends 22 of each actuator 18,20 could be sensed 
and their respective electrical signals delivered to the microprocessor 36 
or peak to peak pressures in only the rod ends 23 of each actuator 18,20 
could be sensed and their respective electrical signals delivered to the 
microprocessor 36. Furthermore, the peak to peak pressures of the 
difference in pressure between the head and rod ends 22,23 of each of the 
actuators 18,20 could be determined by the microprocessor 36 and used as 
the threshold pressure level. Each of the above noted ways of determining 
the threshold pressure level could be utilized without departing from the 
essence of the invention. 
If the predetermined threshold level is exceeded, as would occur if the 
blade 56 starts to bounce, the variable force control 66 is automatically 
adjusted or turned on to a predetermined level or to a position equal to 
the average of the threshold pressure level. As noted above, this adjusts 
the position, if needed, of the first and second electro-hydraulic 
directional control valves 30,32 and sets the first and second variable 
relief valves 46,50 to a predetermined level or to the average of the 
threshold pressure level. Once the variable force control is turned on to 
control the bounce, the actuators are allowed to move up or down in a 
controlled manner. The variable force control 66 is active for a 
predetermined period of time or until the peak to peak pressures are 
within the threshold pressure level. Preferably, the variable force 
control 66 is not turned off until a second smaller predetermined 
threshold pressure level is attained. Once the bounce has been eliminated 
and the variable force control 66 has been turned off, the actuators 18,20 
are once again locked since the first and second electro-hydraulic 
directional control valves 30,32 have been returned to their centered, 
flow blocking position. At the same time the first and second variable 
relief valves 46,50 are set to their maximum pressure levels to 
effectively prevent flow to the reservoir 28. It is recognized that an 
electrically controlled blocking valve could be placed in the lines 
between the respective shuttle valves 48,52 and the variable relief valves 
46,50 in order to block the flow therethrough instead of setting the 
variable relief valves 46,50 to their maximum positions. 
The bounce of the blade 26 is effectively eliminated by sensing and 
controlling the peak to peak pressures within the respective actuators 
18,20. Furthermore, by sensing the above normal threshold pressure level 
early, the bounce can be eliminated at substantially the same time that it 
starts thus eliminating any scalloping or roughness to the work surface. 
In another embodiment, the microprocessor 36 applies the Goertzel algorithm 
to detect the bounce. The output of the Goertzel algorithm is compared 
with a predetermined threshold level. If the output exceeds the 
predetermined threshold level then the bounce is detected and the variable 
force control 66 is turned on to eliminate the bounce. 
Thus the method for controlling the bounce of a work implement attached to 
a machine having an electro-hydraulic system includes the steps of 
detecting the initiation of a bounce between the work element and the work 
surface and altering the pressure in the actuator arrangement disposed 
between the frame and the work implement to eliminate the bounce. The step 
of detecting the initiation of the bounce includes the steps of 
continuously monitoring the operating pressure level in the actuator 
arrangement and delivering electrical signals representative thereof to a 
microprocessor. The microprocessor establishes a predetermined threshold 
pressure level based on the sensed peak to peak pressures. The step of 
altering the pressure level in the actuator arrangement includes the steps 
of establishing a predetermined pressure level in the actuator arrangement 
by connecting a variable pressure relief valve to the actuator arrangement 
and controlling the setting thereof to establish a pressure level therein 
that is equivalent to the average of the peak to peak pressure in the 
threshold pressure level. The method further includes the step of turning 
off or resetting the system once the bounce has been eliminated and/or the 
initial threshold pressure level has been reestablished. 
In view of the foregoing, it is readily apparent that the subject method 
for controlling the bounce of a work implement attached to a machine 
effectively eliminates the bounce of the work implement or blade 
substantially at the same time that it starts. The subject method 
substantially eliminates any unwanted up and down movement of the blade 
relative to the work surface by continuously monitoring the pressure in 
the actuators 18,20 and controlling the variations of the pressures 
therein within a predetermined threshold level. 
Other aspects, objects and advantages of the invention can be obtained from 
a study of the drawings, the disclosure and the appended claims.