U.S. patent application number 10/255033 was filed with the patent office on 2004-03-25 for apparatus for controlling bounce of hydraulically powered equipment.
Invention is credited to Pfaff, Joseph L., Stephenson, Dwight B., Tabor, Keith A..
Application Number | 20040055455 10/255033 |
Document ID | / |
Family ID | 31946506 |
Filed Date | 2004-03-25 |
United States Patent
Application |
20040055455 |
Kind Code |
A1 |
Tabor, Keith A. ; et
al. |
March 25, 2004 |
APPARATUS FOR CONTROLLING BOUNCE OF HYDRAULICALLY POWERED
EQUIPMENT
Abstract
When a swinging boom driven by a hydraulic cylinder stops,
inertia causes continued motion of the boom which increases
pressure in a chamber of the hydraulic cylinder. Eventually that
pressure reaches a level which causes the boom to reverse
direction. Then pressure in an opposite cylinder chamber increases
until reaching a level that causes the boom movement to reverse
again. This oscillation continues until the motion is dampened by
other forces acting on the boom. As a result, an operator has
difficulty in properly positioning the boom. To reduce this
oscillating effect, a sensor detects when the cylinder chamber
pressure increases above a given magnitude and then a determination
is made when the rate of change of that pressure is less than a
defined threshold. Upon that occurrence, a control value is opened
to relieve the pressure in that cylinder chamber.
Inventors: |
Tabor, Keith A.; (Richfield,
WI) ; Pfaff, Joseph L.; (Wauwatosa, WI) ;
Stephenson, Dwight B.; (Delafield, WI) |
Correspondence
Address: |
QUARLES & BRADY LLP
411 E. WISCONSIN AVENUE
SUITE 2040
MILWAUKEE
WI
53202-4497
US
|
Family ID: |
31946506 |
Appl. No.: |
10/255033 |
Filed: |
September 25, 2002 |
Current U.S.
Class: |
91/433 |
Current CPC
Class: |
F15B 2211/3111 20130101;
F15B 2211/5154 20130101; F15B 2211/31576 20130101; F15B 2211/6313
20130101; F15B 2211/7053 20130101; F15B 2211/528 20130101; F15B
2211/50527 20130101; E02F 9/2228 20130101; F15B 21/008 20130101;
E02F 9/2207 20130101; F15B 2211/6309 20130101; F15B 2211/30575
20130101; F15B 2211/3144 20130101; F15B 2211/327 20130101; F15B
2211/8613 20130101; F15B 2211/6346 20130101; F15B 11/006 20130101;
F15B 2211/55 20130101 |
Class at
Publication: |
091/433 |
International
Class: |
F15B 011/10 |
Claims
What is claimed is:
1. A method for controlling movement of a member that is driven by
a hydraulic actuator connected to a valve assembly through which
fluid flows, the method comprising: receiving a command designating
that movement of the member in a given direction is to stop;
sensing a parameter which varies with movement of the member;
employing the parameter to determine when movement of the member
has slowed to a defined speed and in response thereto producing an
indication; and in response to the indication and to receiving the
command, relieving pressure in the hydraulic actuator.
2. The method as recited in claim 1 wherein: sensing a parameter
comprises sensing pressure occurring in the hydraulic actuator; and
employing the parameter comprises determining a rate at which the
pressure changes and producing the indication when the rate is less
than a defined threshold.
3. The method as recited in claim 1 wherein employing the parameter
comprises determining a rate at which the parameter changes and
producing the indication when the rate has a defined value.
4. The method as recited in claim 1 wherein relieving pressure in
the hydraulic actuator comprises opening a control valve.
5. The method as recited in claim 1 wherein relieving pressure in
the hydraulic actuator is further in response to the pressure in
the hydraulic actuator being greater than a threshold value.
6. The method as recited in claim 1 further comprising: determining
whether a pressure relief valve connected to the hydraulic actuator
is closed; and wherein relieving pressure in the hydraulic actuator
occurs in response to the hydraulic actuator being closed.
7. The method as recited in claim 6 wherein determining whether the
pressure relief valve is closed is based on comparing pressure in
the hydraulic actuator to a defined pressure level.
8. The method as recited in claim 6 further comprising when the
pressure relief valve is determined not to be closed, opening a
valve in the valve assembly.
9. The method as recited in claim 1 further comprising: determining
whether a pressure relief valve connected to the hydraulic actuator
is open after receiving the command; after determining that the
pressure relief valve is open, detecting closure of the pressure
relief valve; and upon detecting closure of the pressure relief
valve, opening a control valve that relieves pressure remaining in
the hydraulic actuator.
10. The method as recited in claim 9 wherein detecting closure of
the pressure relief valve comprises detecting when pressure in the
hydraulic actuator decreases below a given level.
11. A method for controlling movement of a member that is driven by
a hydraulic actuator having a first chamber and a second chamber,
the method comprising: receiving a command designating that
movement of the member in a given direction is to stop; sensing
pressure in the first chamber; determining a rate at which the
pressure in the first chamber changes; and after receiving the
command, relieving pressure in the first chamber in response to the
rate of change of the pressure being less than a defined
threshold.
12. The method as recited in claim 11 wherein relieving pressure in
the first chamber occurs only after pressure in the first chamber
exceeded a defined threshold.
13. The method as recited in claim 11 wherein relieving pressure
comprises, for a given period of time, opening a control valve
connected to the first chamber.
14. The method as recited in claim 11 further comprising relieving
pressure in the second chamber in response to receiving the
command.
15. The method as recited in claim 14 wherein relieving pressure in
the second chamber comprises opening a control valve for a defined
period of time.
16. A method for controlling movement of a member that is driven by
a hydraulic actuator having a first chamber and a second chamber,
the method comprising: receiving a command designating that
movement of the member in a given direction is to stop; sensing
pressure in the first chamber; determining whether a pressure
relief valve connected to the first chamber is open or closed; and
after receiving the command: (a) if the pressure relief valve is
open, determining when the pressure relief valve closes and
thereafter relieving pressure remaining in the first chamber, and
(b) if the pressure relief valve is closed, determining a rate of
change of the pressure in the first chamber, and relieving that
pressure in response to the rate of change being less than a
defined threshold.
17. The method as recited in claim 16 further comprising relieving
pressure in the second chamber in response to receiving the
command.
18. The method as recited in claim 17 wherein relieving pressure in
the first chamber comprises opening a first control valve, and
relieving pressure in the second chamber comprises opening a second
control valve.
19. The method as recited in claim 16 wherein determining whether
the pressure relief valve is open comprises determining whether the
pressure in the first chamber is greater than a given pressure
level.
20. The method as recited in claim 16 wherein determining when the
pressure relief valve closes comprises detecting when pressure
within the first chamber decreases below a given pressure
level.
21. The method as recited in claim 16 wherein determining when the
pressure relief valve closes comprises detecting when pressure in
the first chamber decreases and pressure in the second chamber
increases.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to hydraulically powered
equipment, such as off-road construction and agricultural vehicles,
and more particularly to apparatus for reducing bounce when a
hydraulically driven member on the equipment is stopped
suddenly.
[0005] 2. Description of the Related Art
[0006] With reference to FIG. 1, a backhoe 10 is a common type of
earth moving equipment that has a bucket 12 attached to the end of
an arm 14 which in turn is coupled by a boom 15 to the frame of a
tractor 18. A joint 16 enables the bucket, arm, and boom assembly
17 to pivot left and right with respect to the rear end of the
tractor. A hydraulic cylinder 19 is attached on one side of the
tractor 18 to the boom 15 and provides the drive force for the
pivoting motion. For larger backhoes, a pair of hydraulic cylinders
are attached on opposite sides of the tractor 18 to pivot the boom.
Hydraulic fluid is supplied to the cylinder 19 through valves that
are manipulated by the backhoe operator. This movement of the boom
15 is referred to as "swing" or "slew".
[0007] As the boom swings, pressurized fluid is introduced into one
chamber of the cylinder 19, referred to as the "driving chamber",
and fluid is exhausted from the other cylinder chamber, referred to
as the "exhausting chamber". When the operator suddenly stops the
boom swing, inertia causes the motion of the backhoe assembly 17 to
continue in the direction of the swing. The amount of inertia is a
function of the mass of the backhoe assembly 17 and any material
carried in the bucket 12. This continued movement after the control
valves have been shut compresses the hydraulic fluid in the
previous exhausting chamber of the cylinder 19 and may produce a
void, or cavitation, in the previous driving cylinder chamber. Anti
cavitation valves typically are provided in the hydraulic system to
overcome this latter problem.
[0008] Eventually the backhoe assembly 17 stops and starts moving
in the opposite swing direction due to the relatively high pressure
created in the previous exhausting chamber. This subsequent
movement produces a reversal of the pressure conditions, wherein
the previous driving chamber of the boom swing cylinder 19 becomes
pressurized. As a result, the backhoe assembly 17 swing oscillates
until inherent dampening provided by other forces eventually brings
the assembly to a stop. This phenomenon is known either as "swing
bounce" or "swing wag" and increases the time required to properly
position the boom 15, thereby adversely affecting equipment
productivity.
[0009] Various approaches have been utilized to minimize the swing
bounce. For example, U.S. Pat. No. 4,757,685 employs a separate
relief valve for each hydraulic line connected to the swing
cylinder, which valves vent fluid to a tank line when excessive
pressure occurs in that cylinder. Additional fluid is supplied from
the supply line through makeup valves to minimize voids in the
cylinder as the swing stops.
[0010] U.S. Pat. No. 5,025,626 describes a cushioned swing circuit
which also has relief and make-up valves connected to the hydraulic
lines for the boom swing cylinder. This circuit also incorporates a
cushion valve which in an open position provides a fluid path
between the cylinder hydraulic lines. That path includes a flow
restriction orifice. The cushion valve is resiliently biased into
the shut position by a spring and a mechanism opens the cushion
valve for a predetermined time period when the pressure
differential between the cylinder chambers exceeds a given
threshold.
[0011] Both of the previous circuits required a number of
relatively complex valves. Therefore, it is desirable to provide a
more simplified mechanism for reducing swing bounce.
SUMMARY OF THE INVENTION
[0012] A hydraulic system includes a control valve assembly, which
selectively couples a pump and a tank to a hydraulic actuator that
drives a member on a machine. The system has a device which
produces a command designating desired movement of the load. A
sensor detects pressure in the hydraulic actuator.
[0013] A method is provided to reduce bounce of the member when it
stops. A command is received from the device designating that
movement of the member in a given direction is to stop. The signal
from the sensor is employed to determine the rate at which the
pressure in the hydraulic actuator changes. When the rate of change
of the pressure is less than a defined threshold after receiving
the command, pressure in the hydraulic actuator is relieved. For
example the pressure is relieved by opening a control valve that is
connected to the hydraulic actuator.
[0014] In one application, the present bounce reduction method is
used on a machine in which the member is driven by a cylinder that
has first and second chambers. It is a well-known practice that
this type of installation includes first and second pressure relief
valves that are respectively connected to the first and second
cylinder chambers. Thus upon receiving the command, pressure in the
second chamber is relieved by opening an associated control valve.
Then a determination is made whether the first pressure relief
valve is open due to excessive pressure in the first chamber. If
the first pressure relief valve is found to be open, the bounce
reduction method waits for that valve to close, and thereafter
opens another control valve that relieves pressure remaining in the
first chamber. Otherwise if the first pressure relief valve is
found to be closed, the rate of pressure change in the first
chamber is determined, and pressure in the first chamber is
relieved by opening the other control valve when the rate of
pressure change is less than a defined threshold.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a side view of a backhoe incorporating the present
invention;
[0016] FIG. 2 is a schematic diagram of a hydraulic circuit for the
swing function of the backhoe boom;
[0017] FIG. 3 is a block diagram of the microcomputer controller in
FIG. 2;
[0018] FIG. 4 is a state diagram depicting operation of a swing
bounce reduction routine that is executed by the controller;
[0019] FIG. 5A graphically depicts pressure changes in a chamber of
the hydraulic cylinder that swings the backhoe assembly; and
[0020] FIG. 5B is a graph of the slope of the changing pressure in
FIG. 5A.
DETAILED DESCRIPTION OF THE INVENTION
[0021] With reference to FIG. 2, a hydraulic circuit 20 for the
backhoe 10 has a pump 22 which forces fluid from a tank 24 into a
supply line 26. A conventional system pressure relief valve 28
opens in the event that the pump pressure exceeds a given safety
threshold, thereby relieving that pressurized fluid to the tank 24
via the tank return line 29.
[0022] The supply line 26 and tank return line 29 are connected to
a plurality of functions on the backhoe tractor 10. The hydraulic
circuit for the boom swing function is shown in detail in FIG. 2. A
valve assembly 30 of four solenoid operated, directional control
valves 31-34 selectively couples the supply line 26 and tank return
line 29 to a pair of actuator conduits 35 and 36 which lead to
ports of a hydraulic actuator, such as a cylinder 19, that swings
the boom 15. Specifically, the supply line 26 is connected by the
first directional control valve 31 to the first actuator conduit 35
and by the second directional control valve 32 to the second
actuator conduit 36. The tank return line 29 is coupled by the
third directional control valve 33 to the first actuator conduit 35
and by the fourth directional control valve 34 to the second
actuator conduit 36. For example, the valve described in U.S. Pat.
No. 6,328,275 may be used in valve assembly 30. However, other
types of valves may be utilized to implement the present inventive
concept. The four directional control valves 31-34 are illustrated
in the closed, or shut, position in which the actuator conduits 35
and 36 are disconnected from the pump and tank return lines 26 and
29. The first and second actuator conduits 35 and 36 also are
designated by the letters A and B, respectively and the pressures
in the actuator conduits (and the associated cylinder chamber) are
designated Pa and Pb.
[0023] In the exemplary hydraulic circuit 20, the first actuator
conduit 35 is connected to the head chamber 42 of the boom cylinder
19 and the second actuator conduit 36 is connected to the
cylinder's rod chamber 40. Depending upon which specific ones of
the four directional control valves 31-34 are activated, hydraulic
fluid from the pump 22 is sent to one of the actuator conduits 35
or 36 and the other actuator conduit 36 or 35 is connected to the
tank return line 29. Thus by opening either a combination of the
first and fourth directional control valve 31 and 34 or the second
and third directional control valves 32 and 33, the cylinder 19 is
driven to extend or retract its piston rod 44 and thus move the
backhoe boom 15 right or left. Although the present invention is
being described in terms of operating a hydraulic cylinder, it
should be understood that the novel concepts can be used with other
types of hydraulic actuators, such as a hydraulic motor with a
rotating shaft.
[0024] A first pressure relief valve 37 is connected to the first
actuator conduit 35 to relieve excessive high pressure that may
occur in the head chamber 42. Similarly, a second pressure relief
valve 39 is connected to the second actuator conduit 36. These
pressure relief valves 37 and 39 have a conventional design and are
set to open at a significantly high pressure threshold. However, if
a very heavy load is being carried in the bucket 12 when the boom
15 stops swinging, the pressure in a cylinder chamber due to the
inertial load may exceed that threshold causing the associated
pressure relief valve to open, as will be described. A pressure
relief valve 37 or 39 opens when the pressure Pa or Pb in the
respective actuator conduit 35 or 36 exceeds the pressure in the
return line 29 plus a relief threshold, determined by force from a
valve spring.
[0025] Pressure sensors are provided throughout the hydraulic
circuit 20. Specifically, a first sensor 46 measures pressure in
the supply line 26 and a second sensor 47 is located in the tank
return line 29. Third and fourth pressure sensors 48 and 49 are
provided in the first and second actuator conduits 35 and 36,
respectively, and produce electrical signals indicating the
pressure within the cylinder chambers 42 and 40 to which those
actuator conduits are connected. The electrical signals from the
four pressure sensors 46-49 are applied to inputs of an electronic
controller 50. The controller 50 also receives input signals from
an operator input device, such as a joystick 52. As will be
described, the controller 50 responds to these input signals by
producing output signals which activate the solenoids of the four
directional control valves 31-34 to operate the swing function of
the backhoe assembly 17.
[0026] Referring to FIG. 3, the controller 50 incorporates a
microcomputer 54 which is connected by a set of buses 55 to a
memory 56 in which the programs and data for execution by the
microcomputer are stored. The set of buses 55 also connect input
circuits 57 and output circuits 58 to the microcomputer 54. Each
input circuit 57 for the pressure sensors 46-49 includes a first
order, low-pass filter which attenuates frequencies above 100 Hz.
This filtering removes any noise that might be present on the
pressure sensor signals applied to the controller 50. The output
circuits 58 provide signals to devices that indicate the status of
the hydraulic system 20 to the backhoe operator. A set of valve
drivers 59 controls the application of electricity to the solenoid
coils in the four directional control valves 31-34. As will be
described, the controller 50 executes software which implements a
control algorithm for swinging the backhoe boom 15.
[0027] When the backhoe operator activates the joystick 52 to swing
the boom 15 to the right or left, the signal generated by the
joystick causes the controller 50 to begin executing a boom swing
software routine that is stored in the memory 56. This routine
controls selected ones of the four directional control valves 31-34
necessary to produce the indicated movement of the boom. On each
execution pass through the control software for the backhoe 10,
another routine is executed which detects when the boom swing is
stopping and takes action to counter any significant bounce that
may occur.
[0028] With reference to FIG. 2 and the state diagram of FIG. 4,
the swing bounce reduction routine 60 commences at State 62 at
which the routine remains when the boom is not swinging. In this
State 62, the controller periodically tests to determine whether
the boom is moving and if so, in which direction. To do so, the
controller 50 examines the velocity command produced from the
joystick signal. In the exemplary hydraulic system 20, a velocity
command that is greater than zero indicates that the piston rod 44
is being extended from the cylinder 19, whereas a negative velocity
command indicates that the piston rod is retracting into the
cylinder. Assume initially that the velocity command is greater
than zero, in which case a transition occurs from the Direction
Test State 62 to the Swing Commanded State 64.
[0029] The operation of the swing bounce reduction routine 60
remains in this swing commanded State 64 until the operator
manipulates the joystick 52 to indicate the boom is either stop or
move in the opposite direction. That indication from the operator
produces a new velocity command from the joystick which is either
zero or a negative value in this situation. That change in the
velocity command is detected at State 64 and produces a transition
to State 66. If the velocity command now is zero, the routine for
controlling the valve assembly 30 will close all four directional
control valves 31-34.
[0030] The valve closure causes pressure within the rod chamber 40,
from which fluid was previously being exhausted, to build up as the
rod continues to extend from the cylinder due to the inertia load
of the backhoe assembly 17. In addition, a significant pressure
remains momentarily in the head chamber 42, which aids continued
extension of the piston rod 44. Therefore upon entry into State 66,
the swing bounce reduction routine 60 causes the third directional
control valve 33 to open so that the pressure is relieved from the
head chamber 42 to the tank return line 29. This initial pressure
relief ensures that the pressure within the head chamber does not
contribute to the continued motion of the backhoe assembly 17.
[0031] While the swing bounce reduction routine 60 is in State 66,
the controller 50 periodically compares the absolute value of the
velocity command to a velocity threshold. When the velocity command
exceeds that threshold, the operator is again commanding motion of
the backhoe assembly 17 in either direction. In that case, boom
swing bounce is not a concern and a transition is made back to the
Direction Test State 62 where the direction of the operator
commanded boom motion is determined. This transition to State 62
also occurs when the operation remains in State 66 for more than
500 milliseconds. After remaining in State 66 for 180 milliseconds,
the controller 50 Begins comparing the pressure level Pb in the rod
chamber 40 to a first threshold level (THRESHOLD 1) to determine
whether the pressure within the previous exhausting cylinder
chamber has build up to a significant level indicating that a
bounce is likely to occur when the boom motion stops. The 180
millisecond delay prevents a pressure aberrations, which can occur
momentarily when a directional control valve closes, from producing
a state transition. Therefore, after the 180 milliseconds delay, if
the pressure Pb within the rod chamber 40 exceeds the first
pressure threshold a transition occurs to State 68.
[0032] At State 68 the controller 50 determines when to initiate a
pressure relief operation to prevent rebounding of the backhoe
assembly 17. In order to understand how the present swing bounce
reduction routine 60 make that determination, reference is made to
FIG. 5A which graphically depicts pressure change within the rod
chamber 40 following closure of the valves when the piston rod 44
is being extended. Initially that pressure rises until the motion
of the boom 15 stops at time Ti, after which the pressure Pb
decreases as the boom moves in the opposite direction. The swing
bounce reduction routine 60 makes one of two transitions from State
68 depending on whether the pressure rises to a level that causes
the second pressure relief valve 39 to open. That event is
indicated by pressure Pb in the second actuator conduit 36
exceeding the valve's constant relief threshold plus the pressure
Pr in the return line 29, as represented by the input signal from
sensor 47.
[0033] While the second pressure relief valve 39 remains closed,
the swing bounce reduction routine 60 at State 68 uses the rate of
change of the pressure Pb to determine when to open the fourth
direction control valve 34 to relieve that pressure and prevent
rebound of the backhoe assembly 17. If that control valve is opened
too soon, sufficient pressure will not build up in the rod chamber
40 to significantly slow the piston rod 44 and the attached backhoe
assembly 17. In that situation, inertia may cause the boom assembly
17 to continue swinging until striking a stop at one end of the
pivot joint 16. Conversely, if the valve is not opened soon enough,
the pressure will not be relieved in time to prevent rebound of the
piston and bounce of the backhoe assembly 17. The rate of change of
the pressure Pb in the second actuator conduit 36 is employed as an
indicator of when the backhoe assembly 17 has slowed enough that
the pressure can be relieved in time to prevent boom bounce. The
rate of change corresponds to the slope of the pressure curve in
FIG. 5A and is given mathematically by the derivative of the
pressure which is plotted on the graph of FIG. 5B.
[0034] Thus, the controller 50 employs the input signal from
pressure sensor 49 at State 68 to determine the derivative (dPb/dt)
of the pressure Pb in the second actuator conduit 36. The
derivative value is checked to determine whether it is less than a
second threshold (THRESHOLD2), indicated by a dotted line, which
occurs as the rate of pressure change decreases just prior to the
point 67 of maximum pressure. This condition indicates that the
hydraulic actuator and the boom assembly attached thereto have
slowed a given amount. When this condition exists while the second
pressure relief valve 39 is closed (i.e. pressure Pb is less than
the relief threshold plus the return line pressure Pr), a
transition is made from State 68 to State 70.
[0035] The preferred embodiment of the swing bounce reduction
routine 60 employs the rate of pressure change to determine when
the hydraulic actuator and the boom assembly have slowed to a point
at which action to reduce bounce can be taken. However, other
methods for making that determination can be used instead, For
example, a sensor can provide a signal indicating the swing
position of the boom and the rate of position change used to
determine when to implement bounce reduction. A velocity sensor or
an accelerometer alternatively could be employed to detect when
motion of the hydraulic actuator or the boom assembly has slowed to
the point at which bounce reduction can be implemented.
[0036] At State 70, the controller 50 opens the fourth directional
control valve 34 to relieve the pressure in the rod chamber 40 of
cylinder 19 to the tank 24 via the return line 29. This prevents
the pressure which has previously built up by the continued
extension of the piston rod 44 from causing the piston rod to
bounce back in the opposite direction. The fourth directional
control valve 34 remains open for a fixed period of time (e.g. 40
milliseconds) after which the control valve is closed and a
transition returns the swing bounce reduction routine to the
Direction Test State 62.
[0037] However, if a determination is made at State 68 that the
second pressure relief valve 39 has opened, i.e. pressure Pb
exceeds that valve's relief threshold plus the pressure Pr within
the tank return line 29, a transition occurs to State 72. Because
opening of the second pressure relief valve 39 provides a path
which relieves pressure from the rod chamber 40, the swing bounce
reduction routine 60 remains in State 72 until a closure of the
second pressure relief valve 39 is detected. That closure is
indicated by a the pressure Pb within the second actuator conduit
36 decreasing below the relief threshold plus the pressure in the
tank return line 29, or by a pressure drop in the second actuator
conduit 36 accompanied by a pressure increase in the first actuator
conduit 35 as transpires when the piston rod 44 rebounds and moves
in the opposite direction. When either of these conditions occurs,
the swing bounce reduction routine 60 makes a transition from State
72 to State 74.
[0038] The controller 50 in State 74 opens the fourth directional
control valve 34 to relieve any residual pressure within the rod
chamber 40 for a predefined period (e.g. 30 milliseconds) after
which the fourth directional control valve is closed. This action
relieves the pressure within the cylinder 19 due to the inertial
motion of the backhoe assembly 17 thereby preventing rebound of the
piston and bounce of the backhoe boom 15. The swing bounce
reduction routine 60 remains in State 74 for a total of 500
milliseconds after which a transition occurs back to the Direction
Test State 62.
[0039] While in State 62, when the operator desires that the boom
15 swing in the opposite direction, as indicated by the joystick 52
producing a negative velocity command, a transition is made to
State 76. State 76 is the reciprocal of State 74 and operation of
the anti-bounce routine is similar thereto with the understanding
that the boom 15 is moving in the opposite direction. Therefore,
when the velocity command is zero or greater, as occurs when the
operator intends to stop the boom or reverse its direction, another
transition occurs to State 74. Because in this mode of operation
the piston rod 44 is retracting into the cylinder 19, pressurized
fluid from the pump 22 was previously applied to the rod chamber
40. Therefore at State 74, the fourth direction control valve is
opened by the controller 50 to relieve that pressure Pb so that it
does not contribute to the continued motion of the boom 15.
Operation at this time is similar to that which occurred at State
66 when motion in the opposite direction was stopping. Therefore,
under similar transition conditions, if the operator's movement of
the joystick produces a new velocity command or 500 milliseconds
have elapsed, a transition occurs back to the Direction Test State
62. Otherwise, the swing bounce reduction routine 60 eventually
makes a transition to State 78.
[0040] In State 78, if the first pressure relief valve 37 is not
detected as opened, the anti-bounce routine enters State 80 where
the pressure in the head chamber is relieved by opening the third
directional control valve 33. Thereafter, the operation returns to
the Direction Test State 62. Otherwise, when the pressure Pa in the
head chamber 42 is great enough to open the first pressure relief
valve 37, a transition occurs to State 82 where the operation
remains until the relief valve closure is detected. At that time,
operation moves into State 66 where residual pressure within the
head chamber 42 is relieved by opening the third direction control
valve 33 for a predefined period before transitioning back to the
Direction Test State 62.
[0041] The foregoing description was primarily directed to a
preferred embodiment of the invention. Although some attention was
given to various alternatives within the scope of the invention, it
is anticipated that one skilled in the art will likely realize
additional alternatives that are now apparent from disclosure of
that embodiment. For example, although the invention has been
described in the context of reducing swing bounce of a backhoe
assembly, the novel technique can be applied to other types of
motion by a variety of machine members. Accordingly, the scope of
the invention should be determined from the following claims and
not limited by the above description.
* * * * *