Note: Descriptions are shown in the official language in which they were submitted.
- 2170088
Descr;ption
GR~PPT~ CONTROT
Te~hn;c~l F;el~
This invention relates generally to a
control system that automatically controls the
operation of a grapple and, more particularly, to a
control system that automatically controls the
operation of a grapple using hydraulic fluid pressure
feedback.
Backgrollnd Art
The present invention is particularly suited
for use on a grapple skidder. A grapple skidder is
primarily used to retrieve fallen logs. The grapple
includes a pair of tongs that closes in order to grasp
the logs. Today's skidders only provide for manual
control over the grapple. Thus, when the operator
desires to close the tongs, he simply positions a
control handle to a detent position. Responsively, a
hydraulic pump supplies high fluid pressure to a pair
of hydraulic cylinders that actuate to close the
tongs. However, while the control handle remains in
the detent position, the hydraulic pump continuously
operates in a high pressure mode, which draws valuable
engine horsepower.
The present invention is directed to
overcoming one or more of the problems as set forth
above.
D;sclosure of the Invention
In one aspect of the present invention, an
apparatus for automatically controlling a work element
of an earth working machine is disclosed. The work
~170088
element includes a grapple having a pair of tongs,
where the tong pair is controllably actuated by a
hydraulic cylinder. An electrohydraulic valve
controllably actuates the hydraulic cylinder in
response to a command signal. A sensor senses the
fluid pressure in the hydraulic cylinder and
responsively produces a pressure signal. A controller
receives the pressure signal, compares the pressure
signal magnitude to a pressure setpoint, and delivers
a command signal to the electrohydraulic valve to
automatically actuate the tong pair.
Brief Description of the Drawings
For a better understanding of the present
invention, reference may be made to the accompanying
drawings in which:
Fig. 1 is a diagrammatic view of a work
implement of an earth working machine;
Fig. 2 is a block diagram of an
electrohydraulic control system of the earth working
machine;
Fig. 3 is a flowchart of the program control
of an automatic control of the work implement; and
Fig. 4 is a flowchart of the program control
of an adapting algorithm associated with the automatic
control of Fig. 3.
Best Mo~e for ~Arry;ng Ollt the Tnvent;on
Referring now to the drawings, Fig. 1
illustrates a planar view of a work implement 100 of
an earth working machine 105. For example, the
illustrated work implement 100 is referred to as a
grapple 110, while the illustrated earth working
machine is referred to as a log skidder. The grapple
110 includes a pair of tongs 115 that are used to
21700~8
grasp fallen logs. The tong pair 115 is controllably
actuated by linearly extendable hydraulic cylinders
120, while the grapple 110 is controllably rotated by
a hydraulic motor 125.
Referring now to Fig. 2, a block diagram of
an electrohydraulic system 200 associated with the
present invention is shown. An operator control
device 205 provides for manual operation of the
grapple 110. For example, the operator control device
205 may include a joystick control lever with a
plurality of switches that provides for clockwise and
counter-clockwise rotation of the grapple 110, and
tong open, close and hold functions. The operator
control device 205 produces control signals that are
received by a controller 210. The controller 210 is a
microprocessor based system. The controller 210
receives the control signals and produces command
signals that are received by electrohydraulic control
valves 215,220. Electrohydraulic control valves 215
control the flow of hydraulic fluid to extend or
retract the hydraulic cylinders 120, while
electrohydraulic control valves 220 control the flow
of hydraulic fluid to rotate motor 125 clockwise or
counter-clockwise. Both electrohydraulic control
valves 215,220 are solenoid actuated. A pump 222
supplies pressurized hydraulic fluid to the control
valves 215,220. Preferably, the pump 222 is of the
load sensing type, which includes a load sensor (not
shown) for sensing the hydraulic load associated with
the system via the electrohydraulic control valves
215,220.
Advantageously, the grapple may be
automatically operated. For example, the retraction
of the hydraulic cylinders 120 may be controlled
automatically with little operator input to control
2170088
the closing of the tong pair. Accordingly, a pressure
sensor 225 is provided to sense the hydraulic fluid
pressure in the hydraulic cylinder that closes the
tong pair. A corresponding pressure signal is
produced by the pressure sensor 225 and is delivered
to the controller 210. Thus, the tong pair 115 may
automatically be closed in order to capture logs based
on the force produced by the tong pair 115.
Reference is now made to Fig. 3, which
illustrates a flowchart of an auto control for closing
the tong pair 115. The program depicted on the
flowchart is adapted to be utilized by any suitable
microprocessor system.
First, at decision block 305, the program
control determines the status of a three position,
rocker switch, which indicates the manual operation of
the tong pair 115. For example, the manual switch is
positional from a spring biased, neutral position (an
Uoff" position) to two extreme positions (an Uopen''
position and a Uclosen position). If the switch is
positioned at the "open" position for a predetermined
amount of time, the control then proceeds to block 310
where the controller 210 produces the required command
signals to open the tong pair 115 and a flag
~initialized" is set to Ufalsen. If, however, the
switch is positioned at a "close" position for a
predetermined amount of time, then the program control
proceeds to block 320 where the controller 210
produces the required command signals to close the
tong pair and the flag ~initialized" is set to "false".
However, if the switch is positioned to the
~close" position for a period of time less than the
predetermined period of time, then the control
proceeds to decision block 325 to determine if the
operator is initiating the auto close portion of the
~17008~
control by referencing the position of an auto switch.
If the auto switch position is at the "off" position,
then the tong pair is held at the present position and
the flag "initialized" is set to ~false" <330>.
However, if the auto switch is positioned at the "on"
position, then the auto close portion of the control
is initiated. First, the hydraulic cylinder fluid
pressure is read at block 335. The program control
then determines if a pair of pressure setpoints ("turn-
off" and ~turn-on") have been initialized <340>. If
not, the program control enters a setpoint subroutine
<345>, which will be explained in greater detail with
reference to Fig. 4.
Assuming that the pressure setpoint pair is
initialized, the program control proceeds to decision
block 350, where the control determines if the fluid
pressure is greater than an upper pressure setpoint,
"turn-off~. If so, the controller 210 holds the tong
pair 115 at the present position by de-energizing the
solenoids associated with the tong control valve
<355>.
However, if the result of decision block 350
is negative, then the program control continues to
decision block 360 to determine if the fluid pressure
is less than a lower pressure setpoint, uturn-on". If
so, the controller 210 delivers the required command
signal to actuate the appropriate tong control valve
215 in order to close the tong pair <365>.
Note, while the program is initiating the
auto close portion of the control, blocks 335-365 will
continuously be updated. Accordingly, the tong
control valve will automatically be commanded to close
until the fluid pressure reaches the upper pressure
setpoint, Uturn-off''. However, once the fluid pressure
reaches the upper pressure setpoint, then the control
2170088
will de-energize the tong control valve solenoids.
Thus, the control maintains sufficient pressure on the
tong pair to minimize the possibility of dropping
logs, while additionally minimizing the hydraulic pump
load on the engine.
The control drops out of the auto close
portion of the control by the positioning of the
manual switch to the ~open~ or Uclose" positions for the
required amount of time, or the positioning of the
auto switch to the UOffn position.
Additionally, an auto open portion of the
control may be initiated by the positioning of the
manual switch to the "open~ position for a period of
time less than the predetermined period of time.
Although the auto open portion of the control is not
shown with reference to a flowchart, its function may
be easily understood. For example, the auto open
portion of the control will cause the tong pair to
open until the fluid pressure reaches a predetermined
pressure level, at which time, the tong pair is held
to its present position.
Reference is now made to Fig. 4, to discuss
the setpoint subroutine. The purpose of the setpoint
subroutine is to adapt the pressure setpoint pair to
the maximum pressure of the electrohydraulic system in
order to be responsive to fluid pressure changes due
to model differences of the control valves, changing
hydraulic temperatures, and wear of the
electrohydraulic system.
As shown by block 410, the pressure setpoint
pair, "turn-off" and ~turn-on", and the variable
Umaxpress'' are set to predetermined initial values.
However, the pressure setpoint pair and Umaxpress" will -
be subsequently modified.
~170088
For example, if the flag Utong_close'' is set
to Uonn <405> and the fluid pressure is greater than
~maxpress~ <415>, then Umaxpress~ is set equal to the
present fluid pressure <420>. If the fluid pressure
is greater than the upper pressure setpoint, "turn-
offn, then amaxpress" is set to the pressure associated
with the upper pressure setpoint, "turn-off" <430>.
Moreover, the upper pressure setpoint, Uturn-off'', is
set to a predetermined percentage of Umaxpress" <435>;
and the lower pressure setpoint, ~turn-on", is set to
the pressure associated with "turn-off~ minus a
predetermined hysteresis value <440>. Additionally, a
flag UinitializedN is set to ~true" <445>.
Adverting back to decision block 415, if the
fluid pressure is less than "maxpress~ yet greater than
the lower pressure setpoint <450>, then the pressure
setpoint pair will be adapted as shown by blocks 435
and 440.
Thus, once the hydraulic system is unable to
produce a hydraulic fluid pressure at the pressure
limit defined by ~maxpress~, the control adapts the
pressure setpoint pair based on the maximum pressure
that the hydraulic system can produce.
Tndustr;~l A~ c~hil;ty
The present invention overcomes the problem
of running the hydraulic pump continuously in a high
pressure mode (while the tongs are closed) because the
auto close portion of the control only actuates the
control valves when pressure is required to close the
tongs. For example, due to the load sensing
properties of the pump, the pump runs in a high
pressure mode when a load is demanded, e.g., when the
control valves are actuated. Thus, the present
invention monitors the hydraulic fluid pressure in the
00~8
tong cylinders, and only actuates the tong control
valves when the fluid pressure falls below a
predetermined value. Consequently, the pump only runs
in a high pressure mode when high pressure is needed;
thereby, saving valuable engine horsepower and
improving fuel efficiency.
While the present invention has been
particularly shown and described with reference to the
preferred embodiment above, it will be understood by
those skilled in the art that various additional
embodiments may be contemplated without departing from
the spirit and scope of the present invention.
