U.S. patent application number 15/677613 was filed with the patent office on 2017-12-21 for crop machine with an electronically controlled hydraulic cylinder flotation system.
The applicant listed for this patent is MacDon Industries Ltd.. Invention is credited to James Thomas Dunn, Graham Michael Leverick, Russell George Lyons, Bruce Robert Shearer.
Application Number | 20170359955 15/677613 |
Document ID | / |
Family ID | 59077945 |
Filed Date | 2017-12-21 |
United States Patent
Application |
20170359955 |
Kind Code |
A1 |
Dunn; James Thomas ; et
al. |
December 21, 2017 |
Crop Machine with an Electronically Controlled Hydraulic Cylinder
Flotation System
Abstract
In a crop harvesting machine there is provided a pair of
hydraulic float cylinders for a header relative to a vehicle, where
a float pressure to the cylinders is directly controlled by an
electronic control supplying a variable control signal to a PPRR
valve arrangement to maintain the float pressure at a predetermined
value. At the set pressure a predetermined lifting force is
provided to the header. A position sensor is used to generate an
indication of movement and/or acceleration. The electronic control
is arranged, in response to changes in the sensor signal, to
temporarily change the control signal to vary the lifting force and
thus change the dynamic response of the hydraulic float cylinder.
In order to reduce static friction so that the system can react
quickly, an arrangement is provided for causing relative
reciprocating movement in an alternating wave pattern between the
piston and cylinder.
Inventors: |
Dunn; James Thomas;
(Winnipeg, CA) ; Leverick; Graham Michael;
(Winnipeg, CA) ; Lyons; Russell George; (Winnipeg,
CA) ; Shearer; Bruce Robert; (Winnipeg, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MacDon Industries Ltd. |
Winnipeg |
|
CA |
|
|
Family ID: |
59077945 |
Appl. No.: |
15/677613 |
Filed: |
August 15, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15188468 |
Jun 21, 2016 |
|
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15677613 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A01D 41/141 20130101;
F15B 2211/426 20130101; F15B 2211/526 20130101; A01B 63/10
20130101; F15B 13/0401 20130101; F15B 11/08 20130101; A01D 41/127
20130101; F15B 13/044 20130101; A01B 63/008 20130101 |
International
Class: |
A01D 41/127 20060101
A01D041/127; F15B 11/08 20060101 F15B011/08; F15B 13/044 20060101
F15B013/044; A01B 63/00 20060101 A01B063/00; F15B 13/04 20060101
F15B013/04; A01B 63/10 20060101 A01B063/10 |
Claims
1. A crop machine comprising: a support vehicle for running over
ground; a crop component including a crop engaging system and at
least one ground engaging component for providing a supporting
force from the ground; a support apparatus for supporting the crop
component from the vehicle for upward and downward floating
movement of the crop component so that a proportion of a supporting
force is supplied by a lifting force from the support apparatus and
a remaining portion is supplied by the ground engaging component;
the support apparatus including at least one hydraulic float
cylinder having a piston movable in the cylinder arranged such that
movement of the piston relative to the cylinder causes said lifting
force to be applied to the crop component; a first hydraulic
circuit containing a hydraulic fluid for applying a pressure to a
first side of the piston in the cylinder in a direction to lift the
crop component; the first hydraulic circuit being providing a
pressure greater than that necessary to lift the crop component
from the ground; a second hydraulic circuit containing a hydraulic
fluid for applying a pressure to a second side of the piston in the
cylinder in a direction to lower the crop component; a valve
component in the second circuit for controlling the pressure of
said hydraulic fluid to said second side; and an electronic control
system for supplying a control signal to the valve component so as
to vary the hydraulic pressure in said second circuit so as to vary
the lifting force.
2. The crop machine according to claim 1 wherein there is provided
a sensor arranged to provide a sensor signal to said electronic
control system in response to movement of the crop engaging
assembly in said upward and downward floating movement of the crop
engaging assembly, said electronic control system being arranged in
response to said sensor signal to temporarily change the control
signal to temporarily change the lifting force.
3. The crop machine according to claim 2 wherein said electronic
control system is arranged subsequently in response to said sensor
signal to revert to a set value.
4. The crop machine according to claim 2 wherein said electronic
control system is arranged in response to changes in said sensor
signal to temporarily change the control signal to vary the lifting
force and thus change the response of the hydraulic float cylinder
in response to detected movement of the crop engaging assembly.
5. The crop machine according to claim 2 wherein said electronic
control system and said sensor are arranged in response to said
signal to generate a value indicative of acceleration of the crop
engaging assembly in said upward and downward floating movement of
the crop engaging assembly.
6. The crop machine according to claim 2 wherein said electronic
control system and said sensor are arranged upon detection of
acceleration or movement in said upward floating movement to change
the control signal to increase the lifting force to assist the
acceleration in said upward floating movement.
7. The crop machine according to claim 6 wherein said electronic
control system and said sensor are arranged upon detection of an
end of acceleration in said upward floating movement to change the
control signal to decrease the lifting force to dampen said upward
movement.
8. The crop machine according to claim 2 wherein said electronic
control system and said sensor are arranged to change the control
signal to decrease the lifting force to a value less than said set
value.
9. The crop machine according to claim 2 wherein said electronic
control system and said sensor are arranged upon detection of
acceleration or movement in said downward floating movement to
change the control signal to decrease the lifting force to assist
the acceleration in said downward floating movement.
10. The crop machine according to claim 9 wherein said electronic
control system and said sensor are arranged upon detection of an
end of said acceleration in said downward floating movement to
change the control signal to increase the lifting force to dampen
said downward movement.
11. The crop machine according to claim 2 wherein said sensor
comprises a position sensor for generating as said sensor signal a
position signal indicative of a position of the cylinder in said
movement and wherein the electronic control system is arranged to
calculate from the position signal a velocity and acceleration of
the crop engaging assembly.
12. The crop machine according to claim 1 wherein said electronic
control system is arranged to operate the electronic control system
in dependence on an operating state of the crop engaging
assembly.
13. The crop machine according to claim 1 wherein said electronic
control system is arranged to provide a plurality of preset
flotation system dynamics.
14. The crop machine according to claim 1 wherein said electronic
control system is responsive to a ground speed signal to modify the
changes in the control signal.
15. The crop machine according to claim 1 wherein the electronic
control system includes an arrangement for causing relative
reciprocating movement in an alternating wave pattern between said
one component of said at least one float cylinder and said another
component of said at least one float cylinder.
16. The crop machine according to claim 15 wherein said relative
reciprocating movement is provided by an alternating wave pattern
signal applied by said electronic control system to said valve
arrangement to change said predetermined pressure in dependence on
a value of the signal.
17. The crop machine according to claim 15 wherein said alternating
wave pattern has an amplitude sufficient to cause the seals to
break free from static frictional engagement with the component so
as to maintain movement between the components at said cylinder
seals to reduce static friction.
18. The crop machine according to claim 15 wherein said alternating
wave pattern has a frequency in the range 5 to 15 Hz.
19. The crop machine according to claim 15 wherein said cylinder
seals comprise annular seals between a peripheral surface of a
piston head and an inside cylindrical surface of a cylinder.
20. The crop machine according to claim 15 wherein the alternating
wave pattern is halted when the cylinder is used in a lifting or
lowering state.
Description
[0001] This application is a divisional application of application
Ser. No. 15/188,468 filed Jun. 21, 2016.
[0002] This invention relates to crop machine with an
electronically controlled hydraulic cylinder flotation system of
the header on support tractor. In particular the arrangement
provides firstly a construction in which the effect of static
friction provided by cylinder seals is significantly reduced so as
to reduce resistance to motion of the cylinder in the floating
action. Secondly the arrangement herein provides a dynamic control
system which modifies the forces applied by the cylinder in
response to movement of the header relative to the tractor. The
present invention can be used in many different engaging systems
such as hay tools, rakes, pickups, etc but is particularly
applicable both for swathers or windrowers where the header is
carried on a swather tractor and for combine harvesters where the
header is carried by a combine adapter connected to the feeder
house. If used for cutting crop for harvesting, the header can use
different cutting systems including sickle bars and rotary mowers
or like cutting arrangements.
BACKGROUND INFORMATION
[0003] Most windrowers on the market all have some type of
hydraulic header flotation. These types of flotation systems
suspend the header from the windrower so that there remains a small
percentage of the header mass supported by the ground. The
advantages to these types of hydraulic float systems include the
ability to easily adjust to a wide range of header weights/types,
full adjustability of flotation system from the cab, few moving
parts, compact, has built in dampening effects and is well received
in the market.
[0004] However, due to internal friction of the cylinder seals of
the flotation cylinders, these systems typically have poor ground
following capabilities unless the mass supported by the ground is
significant, in the order of 15% of the header mass. With this
level of ground pressure (mass of header carried by the ground),
wear on the ground contacting components is significant. Also, when
hitting an obstacle, a higher ground pressure is undesirable.
[0005] In the traditional hydraulic float systems, the header float
cylinders are each connected to a respective accumulator, pressure
sensor and pressure control valve. The pressure control valves are
in turn connected to a hydraulic pressure source such as a load
sense pump. The controller receives input signals from the pressure
sensors and makes adjustments to the pressure control valves to
maintain a known pressure in the accumulator/cylinder circuit. The
accumulator/cylinder system acts much like a spring so that when
the header hits an obstacle and needs to go over the obstacle, the
accumulator supplies pressure and flow to the cylinder to aid the
movement of the header. When the header needs to go down into a
ditch or low spot, the float cylinder drives oil back into the
accumulator.
[0006] MacDon has traditionally maintained a coil spring flotation
system that does not have the same friction limitations and
typically has better ground following capabilities. A typical
MacDon spring flotation system can achieve ground pressure in the
order of 10% of the header mass while still having acceptable
ground following capabilities. The spring flotation systems are
currently used on MacDon windrowers and combine adapters.
[0007] Header flotation systems typically use a fluid circuit
including an accumulator, hydraulic cylinders, and control valves
to perform the flotation function. The vehicles may have a single
hydraulic cylinder, or one on each side of the header, to perform
both a lift and flotation function, or they may have separate
hydraulic cylinders for the lift and flotation functions with the
capability of independently adjusting the flotation force for each
side of the header. Typically the operator selects the desired
flotation setting by actuating rocker switches; wherein one switch
position reduces header contact force with the ground, and another
position increases header contact force with the ground. Once the
flotation setting is selected, the control valves will return to
this preset flotation condition whenever the flotation mode is
selected, regardless of subsequent header lift and lower
operations.
[0008] One aspect of the operator selected flotation setting is
that it determines how quickly the header returns in a controlled
acceleration or controlled "fall" to its terrain contact position
after rising in response to contact with an elevated feature of the
terrain. If the header falls too slowly, regions of the field may
not be cut at the desired height. If the header falls too rapidly,
however, the header may impact or ride roughly over the ground,
thereby resulting in undesirably harsh or jarring ride
characteristics. It is also possible that the header could impact
the ground in some conditions, such as uneven terrain, with
sufficient force to result in damage to the header and/or the crop.
Typically, an operator's flotation setting will be a function, at
least in part, on the ground speed of the vehicle. As a general
rule, when traveling over a field of uneven terrain at a relatively
low speed, terrain following can be achieved at slower header
accelerations, compared to a higher speed. Thus, for travel at
lower speeds, an operator would likely use a flotation setting to
allow the header to fall more slowly than that selected for a
higher speed.
SUMMARY OF THE INVENTION
[0009] According to a first aspect of the invention there is
provided a crop machine comprising:
[0010] a support vehicle for running over ground to be
harvested;
[0011] a crop component including a crop engaging system and at
least one ground engaging component for providing a supporting
force from the ground;
[0012] a support apparatus for supporting the crop harvesting
component from the vehicle for upward and downward floating
movement of the crop harvesting component so that a part of a
supporting force is supplied by the support apparatus and a part
supplied by the ground engaging component;
[0013] the support apparatus including at least one hydraulic float
cylinder arranged such that application of a hydraulic fluid under
hydraulic pressure to said at least one float cylinder causes a
lifting force to be applied to the crop harvesting component by
movement of said at least one float cylinder which lifting force is
proportional to said hydraulic pressure;
[0014] said at least one float cylinder comprising cylinder seals
over which one component of said at least one float cylinder slides
relative to another component of said at least one float
cylinder;
[0015] a source of hydraulic fluid for supply of the hydraulic
fluid to said at least one float cylinder at a pressure greater
than said hydraulic pressure;
[0016] a return for said hydraulic fluid;
[0017] a valve arrangement for controlling a flow of and pressure
of said hydraulic fluid from said source to said at least one float
cylinder;
[0018] the valve arrangement being connected to said at least one
float cylinder such flow of fluid into and out of said at least one
float cylinder is controlled by the valve arrangement at said
hydraulic pressure controlled by the valve arrangement;
[0019] an electronic control system for supplying a control signal
to the valve component to change said predetermined pressure in
dependence on a value of the signal;
[0020] said valve arrangement comprising: [0021] a first connection
to said source; [0022] a second connection to said at least one
float cylinder [0023] a third connection for discharge of said
hydraulic fluid to said return; [0024] and a valve component
operable to control flow of hydraulic fluid from said source to
said at least one float cylinder and flow of hydraulic fluid from
said at least one float cylinder to said return so as to maintain
said hydraulic pressure in said at least one float cylinder at a
predetermined pressure set in dependence upon said control signal
from said control system;
[0025] and an arrangement for causing relative reciprocating
movement in an alternating wave pattern between said one component
of said at least one float cylinder and said another component of
said at least one float cylinder.
[0026] The objective is that preferably the alternating wave
pattern has an amplitude sufficient to cause the seals to break
free from static frictional engagement with the component so as to
maintain movement between the components at said cylinder seals to
reduce static friction. The amplitude necessary to achieve this can
vary in accordance with pressures in the cylinder and weight of the
header and can be readily determined by a person skilled in the
art. The seal or seals concerned are typically those at the
cylinder wall at the piston head and/or the cylinder head at the
piston rod. In some cases cylinders can be used where there is no
seal at the rod. Other constructions can also of course be
provided. The action in which the seal breaks free from the other
component may need actual movement of the seal along the surface or
may need only a flexing of that seal so that its surface breaks
away from contact with a fixed portion of the surface of the
component. In any event it can be determined that the amount of
force required to cause movement of the components in response to a
control signal can drop to a figure as much as of the order of 10%
of the normal value where the alternating signal is not
applied.
[0027] Preferably the alternating wave pattern has a frequency in
the range 5 to 15 Hz
[0028] Preferably the relative reciprocating movement is provided
by an alternating wave pattern signal applied by said electronic
control system said valve arrangement to change said predetermined
pressure in dependence on a value of the signal. However the
movement can be obtained by changes in the pressure of the fluid
applied to the cylinder applied to the fluid by a component
different from the valve. Various sources for the changes in the
pressure can be obtained including mechanical components. Also
other components on the header which generate a fluid pressure can
be used to provide an alternating fluid pressure.
[0029] The pattern can typically be sinusoidal but other shapes can
also be used.
[0030] In order to avoid interference with the operation of the
cylinder to control float, preferably the alternating wave pattern
has a frequency in the range XXX. Where the valve is of the type
which uses a spool to alternate between input and output flows,
this frequency is significantly different from the typical range of
frequency of the movement of the spool.
[0031] As the alternating wave pattern is used at a situation where
the header may remain stationary for a period of time such as
during a floating action where no ground changes occur, the
alternating wave pattern can be halted when the cylinder is used in
a lifting or lowering state at which time the cylinder is of course
continually moving. This avoids the necessity for calculations to
extract the waveform from the sensing systems when the waveform is
not required.
[0032] According to a second aspect of the invention there is
provided a crop machine comprising:
[0033] a support vehicle for running over ground;
[0034] a crop engaging component including a crop cutter system and
at least one ground engaging component for providing a supporting
force from the ground;
[0035] a support apparatus for supporting the crop harvesting
component from the vehicle for upward and downward floating
movement of the crop harvesting component so that a predetermined
proportion of a supporting force is supplied by the support
apparatus and a remaining portion is supplied by the ground
engaging component;
[0036] the support apparatus including at least one hydraulic float
cylinder arranged such that application of a hydraulic fluid under
hydraulic pressure to said at least one float cylinder causes a
lifting force to be applied to the crop harvesting component by
movement of said at least one float cylinder which lifting force is
proportional to said hydraulic pressure;
[0037] a source of hydraulic fluid for supply of the hydraulic
fluid to said at least one float cylinder at a pressure greater
than said hydraulic pressure;
[0038] a return for said hydraulic fluid;
[0039] a valve arrangement for controlling a flow of and pressure
of said hydraulic pressure from said source to said at least one
float cylinder;
[0040] the valve arrangement being connected to said at least one
float cylinder such flow of fluid into and out of said at least one
float cylinder is controlled by the valve arrangement at said
hydraulic pressure controlled by the valve arrangement;
[0041] an electronic control system for supplying a control signal
to the valve component to change said predetermined pressure in
dependence on a value of the signal;
[0042] said valve arrangement comprising: [0043] a first connection
to said source; [0044] a second connection to said at least one
float cylinder [0045] a third connection for discharge of said
hydraulic fluid to said return; [0046] and a valve component
operable to control flow of hydraulic fluid from said source to
said at least one float cylinder and flow of hydraulic fluid from
said at least one float cylinder to said return so as to maintain
said hydraulic pressure in said at least one float cylinder at a
predetermined pressure set in dependence upon said control signal
from said control system;
[0047] a sensor arranged to provide a sensor signal to said
electronic control system in response to movement of the crop
harvesting component in said upward and downward floating movement
of the crop harvesting component;
[0048] said electronic control system being arranged to provide a
set value of said control signal to provide said lifting force at a
set value to maintain said predetermined proportion of said
supporting force;
[0049] said electronic control system being arranged in response to
said sensor signal to temporarily change the control signal to
temporarily change the lifting force.
[0050] Preferably the electronic control system is arranged
subsequent to the temporary change, in response to said sensor
signal, to revert to the set value. In this way, preferably, the
electronic control system is arranged in response to changes in
said sensor signal to temporarily change the control signal to vary
the lifting force and thus change the response of the hydraulic
float cylinder in response to detected movement of the crop
harvesting component.
[0051] For example the electronic control system is arranged upon
detection of an end of the acceleration in said upward floating
movement to change the control signal to decrease the lifting force
to dampen the upward movement.
[0052] In this way the control system can be used to increase the
lifting force dynamically during the time that the header is being
lifted by contact with the ground or another obstacle so as to
improve the response to forces from ground contact. In addition as
soon as the ground contact is removed thus halting any further
acceleration, the lifting force can be significantly reduced so
that the weight of the header is re-applied in the downward
direction thus damping any further upward floating movement. This
avoids or reduces the situation where the header is lifted by
ground force or engagement with an obstacle and then remains lifted
for an extended period of time thus interfering with the cutting of
the crop while the header remains raised.
[0053] It will be appreciated that the dynamic control of the
lifting forces depending upon the movement of the header can be
used both in a ground flotation mode and also when cutting at a set
raised height. In the latter condition, float action is typically
provided in order to float the header over any obstacles, even
though the main cutting action is at the raised position from the
ground. Also in some cases such as ditches and mounds the ground
height may vary sufficiently that the header engages the ground
even though nominally set at a height above the ground. In all of
these cases, therefore, the dynamic control of the lifting forces
increases the available force to lift the header over the change in
height of the ground or over the obstacle. At the same time the
lifting action is halted or reduced when the obstacle is cleared so
as to reduce the time that the header remains elevated above the
required condition.
[0054] In a situation where the header is at a raised cutting
height, the downward forces can also be dynamically controlled to
most effectively return the header to the required cutting height.
Thus the downward forces may be increased at the beginning of the
downward movement and may be reduced toward the end of the downward
movement to bring the header more smoothly back to its required
height.
[0055] In order to provide the best damping force, preferably the
electronic control system is arranged to change the control signal
to decrease the lifting force to a value less than said set value.
The header will therefore accelerate downwardly in view of this
reduced lifting force until the header reaches the ground whereupon
the downward acceleration is halted and the control system
reapplies the set value.
[0056] In a symmetrical manner, preferably the electronic control
system is arranged upon detection of acceleration in the downward
floating movement to change the control signal to decrease the
lifting force to assist the acceleration in said downward floating
movement. That is, when the header has been riding on the ground
with no float required, and when a dip in the ground requires that
the header fall to the lower ground level, the lifting force can be
rapidly decreased so as to assist the downward movement of the
header using the weight from the header. Also the electronic
control system can be arranged upon detection of an end of said
acceleration in said downward floating movement, that is the header
has re-engaged with the ground, to change the control signal to
increase the lifting force to dampen said downward movement.
[0057] Preferably the sensor comprises a position sensor for
generating a position signal indicative of a position of the
cylinder in its movement and the electronic control system is
arranged to calculate from the position signal a velocity and
acceleration of the crop harvesting component. However other sensor
arrangements may be provided including for example a specific
acceleration detection device and a specific relative movement
detection device, all of which senses are now readily available in
effective and inexpensive form due to their wide usage in other
areas.
[0058] Preferably the electronic control system is therefore
arranged to achieve a comprehensively adjustable spring rate for
the dynamics of the flotation system.
[0059] Preferably the electronic control system is therefore
arranged to achieve comprehensively adjustable damping for the
dynamics of the flotation system.
[0060] In this invention, the electronic control system can be
arranged to achieve comprehensively adjustable flotation system
dynamics based on operating state of the implement including but
not limited to implement height, ground speed and changes in
terrain (incline angle, etc)
[0061] in additional preferably the electronic control system can
be arranged to allow for the operator to select from preset
flotation system dynamics which can be tailored to different field
conditions and implements.
[0062] In order to take advantage of the benefits of a hydraulic
flotation system, the arrangement herein provides a system that
reduces the effect of the friction in the flotation system to
provide excellent ground following capabilities. This system may be
applied to windrowers and combine adapters or any other
agricultural implement that is floating suspended from carrier (hay
tools, rakes, pickups, etc). The system can be used when floating a
header that is cutting on the ground as well as a header that is
cutting at a height above ground level. While the system is
particularly applicable to the main header float at the front of
the tractor, the same construction can also be used for the wing
float on a flex draper header of the type shown in U.S. Pat. No.
5,005,343 (Patterson) issued 9 Apr. 1991, the disclosure of which
is incorporated herein by reference.
[0063] The system herein comprises one or more float cylinders that
are used to suspend the header from the carrier. At (or near) each
cylinder is an electronically controlled proportional pressure
reducing relieving (PPRR) valve that controls the pressure at that
cylinder. The valve is controlled by an electronic controller that
takes pressure (or force) and position/velocity/acceleration
feedback from the float system and varies the pressure in the
cylinder to obtain prescribed float characteristics. A hydraulic
pressure and flow is supplied to the valve from a source, that
could be an accumulator charged to more than the maximum pressure
demanded by the float system, a drive circuit that has a minimum
pressure that is more than the maximum pressure demanded by the
float system, or some other hydraulic source. However the pressure
from the valve is applied directly and immediately to the cylinder
without the presence of an accumulator in the circuit which would
otherwise dampen the action of the pressure on the cylinder.
[0064] That is while most systems have an accumulator hydraulically
connected directly to the cylinder in float mode, the present
arrangement uses an electronically controlled PPRR valve directly
between the pressure source and the float cylinder. This allows the
system to have very precise, instantaneous control of the float
cylinder pressure so that it can adjust the pressure based on
instantaneous changes of the float system. The accumulator systems
are far less precise/responsive since a change of hydraulic
pressure, when commanded, is split between cylinder movement and
accumulator charge).
[0065] Each float cylinder has a respective position sensor,
pressure sensor and pressure reducing relieving valve. The valve is
then coupled to a pressure source. The controller receives input
from the sensors and controls each PPRR valve independently based
on these input signals. The signal from the position sensor may be
directly linked to the cylinder or may be linked to some other
float link(s) that indicate header position. This signal can be
used to calculate in the electronic control system velocity and
acceleration of the header as well as header position in the float
range. The PPRR valves directly control the cylinders with no
accumulator between the valve and the cylinder. This is the
simplest representation of the system.
[0066] In another improvement of the invention that adds an
accumulator, pressure sensor and control valve to enhance the
response of the float system. The controller receives an input
signal from the pressure sensor and controls the valve to maintain
a pressure range in the accumulator that is some value higher
(200-250 psi for example) than the maximum pressure demanded at
pressure sensors. This maximum pressure is dependent on header
weight and can be determined via calibration using conventional
methods where the lifting force is increased gradually until the
header just lifts from the ground and by adding a predetermined
value to that detected value, or by stored values based on header
ID for each header size and type.
[0067] With this method, the accumulator can supply instantaneous
flow to the PRR valves likely more quickly than the load sense pump
can respond to the demand of flow.
[0068] Note that this type of float system may also be used to
float the wings on a flex header. Using a cylinder to react the
weight of the wing near the wing pivot and controlling that
cylinder with the proposed system.
[0069] In addition to the above, the electronic control algorithms
include a method of controlling the output to the proportional PRR
valve controlling the cylinder pressure, to encourage the header to
follow the ground more effectively.
[0070] Part of the electronic control that we use involves applying
an oscillating control signal to the PPRR valve that supplies float
pressure to the cylinder. This creates a varying pressure in the
cylinder that causes the cylinder to oscillate slightly. In doing
so, the cylinder is always in motion and this reduces the friction
effect of the cylinder seals. This oscillation of the pressure also
helps to compensate for the hysteresis or dead band of the
proportional pressure reducing/relieving valve. This type of valve
includes a spool oscillating back and forth between input and
output fluid positions to maintain the pressure at a position
determined by the signal to the solenoid of the valve where the
position of the spool is controlled by a pilot connection to the
output pressure line. Typically the pilot connection is internal to
the valve itself and does not require a duct to the output line or
to the controlled cylinder. This type of valve has a dead band
between where it relieves pressure and where it reduces
pressure.
[0071] A further feature of the system is that the system provides
a programmable spring rate or float decay that can be customized to
a variety of float requirements such as cutting height, ground
speed, soil conditions etc. This spring rate can instantaneously
and continually be adjusted based on sensor inputs from the float
system, operator or other systems such as radar, sonar or laser
detection of obstacles and ground contours.
[0072] A further feature of the system includes the ability to have
adjustable dampening of the float system, again based on float
requirements or situations.
[0073] Another feature involves the increase or decrease of float
cylinder pressure based on float position and direction of
movement. For example, this allows us to decrease the float
pressure if the header is detected to be moving down (while cutting
through a ditch for example) so that the header will follow the
ground as the ground drops away. A similar adjustment can be made
to increase the float pressure if the header is detected to be
moving up over a mound.
[0074] Another feature involves the increase or decrease of float
cylinder pressure based on header velocity and/or acceleration.
[0075] Other features of the invention provide:
[0076] -a- Oscillating float pressure to reduce effects of
proportional PRR valve hysteresis as well as system (mechanical)
and cylinder seal friction.
[0077] -b- Sensing change in float position/last travel
direction/velocity (this can be done with sensors measuring
cylinder length, float link position etc) and then
decreasing/increasing float pressure to make the header fall faster
or raise faster.
[0078] -c- Different float characteristic settings based on ground
condition, ground speed, crop, cutting on/off the ground.
[0079] -d- Programmed spring rate.
[0080] Feedback from a pressure sensor may not necessarily be
required as the system may be able to just use the output to the
PWM valve. For example, the valve output pressure can be correlated
to valve electronic input so technically, if we send the valve a
known signal, we can know what output pressure the valve is set to.
However typically the pressure sensor may be required due to
changes in valve characteristics due to temperature changes, wear,
vibration etc which may be too large to make this viable.
[0081] The signal from the pressure sensor can be used as a feed
back to confirm that the valve is indeed outputting the required
output pressure as set by the control signal. Thus it may be
possible to provide an arrangement in which the feedback is used
only periodically to check the output value so that the signal from
the pressure sensor is not directly and repeatedly used by the
control system. That is, periodically the output pressure can be
checked and a correction factor used in subsequent calculations by
the control system, if it is found that the measured output
pressure does not match the intended value as set by the control
device.
[0082] As an alternative, an arrangement can be made to work where
the system knows the position of the header in the float range
(from the position sensors) and can use this knowledge to make
changes to the float pressure to find an optimum value that places
the header with a minimal ground force based on velocity and
acceleration calculations.
[0083] While the alternating wave movement is preferably provided
by a wave form in the signal from the control device, it also
possible to use an alternative method in which a mechanical version
of dithering such as a piston/crank arrangement that oscillates the
float pressure. For example in a sickle cutter the system could use
the pulsing of the knife drive circuit as well.
[0084] Various methods of obtaining float supply pressure can be
used including drive circuit pressure, drive circuit pressure with
an accumulator and check valves, closed loop load sense pump.
[0085] Calibration is typically carried out by the conventional
method in which the system is operated to increase float pressure
until header just leaves the ground and then use the system to
increase/decrease float pressure to get optimum ground contact
pressure. Other calibration methods can of course be used, many of
which are known to persons skilled in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0086] Embodiments of the invention will now be described in
conjunction with the accompanying drawings in which:
[0087] FIG. 1 is a side view of a vehicle having a header and a
header flotation system in accordance with the present invention.
In this embodiment, the vehicle is a windrower.
[0088] FIG. 2 is a schematic illustration of a simple arrangement
of the control system according to the present invention for use in
the header of FIG. 1.
[0089] FIG. 3 is a schematic illustration of a second arrangement
of the control system according to the present invention for use in
the header of FIG. 1 which includes an accumulator as a part of the
fluid source to ensure sufficient and immediate fluid flow to
satisfy the PPRR valves.
[0090] FIG. 4 is a schematic illustration of a third arrangement of
the control system according to the present invention for use in
the header of FIG. 1 arranged to capture energy of header
floating.
[0091] FIG. 5 is a flowchart showing the operation of the
system.
DETAILED DESCRIPTION
[0092] FIG. 1 shows the present invention utilized in connection
with the self-propelled windrower 100, however, it will be
appreciated that the principles of the present invention are not
limited to a self-propelled windrower, or to any specific type of
harvesting machine having a header. The figure shows windrower 100,
which comprises a tractor 102 and a header 104. The header 104 is
pivotally attached to the front end of the frame or chassis 106 of
windrower 100 such that it can move up and down with respect to
chassis 106.
[0093] Such attachment of the header 104 to the frame 106 is
achieved through a pair of lower arms 108 (only the left one being
shown, the right one being in the same position and in mirror
configuration on the right side of the vehicle) pivoted at one end
to the frame 106 and at the other end to the header 104 as well as
through a central upper link 110.
[0094] The link 110 may take the form of a single or double
hydraulic cylinder 112 whose extension and retraction is controlled
by the operator to remotely control the angle of the sickle bar 114
on the lower front of the header 104.
[0095] A single lift/flotation cylinder 116 is shown
interconnecting the lower arm 108 to the frame 106. Cylinder 116
supports each side of the header, i.e., each side of the header is
supported by its own lift/flotation cylinder 116. Again, only the
left side lift/flotation cylinder 116 is shown. The right side
lift/flotation cylinder 118 is identically constructed, configured,
and arranged as left side lift/flotation cylinder 116 and is
interconnected in the identical manner to the header and the frame
but is configured in mirror image form to that of the left side of
the vehicle.
[0096] A position sensor 120 is coupled to and between frame 106
and bell crank 122 and is configured to sense the position of the
cylinder. This can be done at the cylinder or at another location
such as at the relative position of bell crank 122 with respect to
frame 106. The position sensor shown here is a potentiometer
providing a signal which varies when the header moves up and down
(has a vertical component of translation) with respect to frame
106. In this sense, the position sensor is also a height sensor
which detects the height of the header from the tractor. The
particular arrangement of position sensor 120 with respect to frame
106 and with respect to bell crank 122 can be varied depending on
the space available, the type transducer desired, and the
resolution of the sensor.
[0097] The arrangement therefore provides a crop machine, typically
a crop harvesting machine, comprising the support vehicle 102 for
running over ground to be harvested and a crop component, typically
a harvesting header 104, including a crop engaging system 114 and
at least one ground engaging component or skid plate 128 for
providing a supporting force from the ground. The support apparatus
110, 106, 116 and 108 acts to support the crop harvesting header
from the vehicle for upward and downward floating movement of the
crop harvesting header so that a part of a supporting force is
supplied by the support apparatus and a part supplied by the ground
engaging component 128.
[0098] The support apparatus includes at least one and typically
two hydraulic float cylinders 116 and 117 arranged such that
application of a hydraulic fluid under hydraulic pressure to the
float cylinders 116 and 117 causes a lifting force to be applied to
the crop harvesting header by movement of the float cylinder which
lifting force is proportional to the hydraulic pressure applied to
the cylinder.
[0099] The float cylinders include cylinder seals 116A over which
the piston component slides relative to the cylinder component of
the float cylinder. The circuit 10 applying pressure to the
cylinders includes a source 12 of hydraulic fluid for supply of the
hydraulic fluid to the float cylinder at a pressure greater than a
required hydraulic pressure. The source 12 includes a pump 16 and a
drain 14 providing a return for the hydraulic fluid.
[0100] The circuit includes two separate sections for supplying
fluid under pressure to the respective cylinders 116 and 117,
including for each a respective valve arrangement 18, 20 for
controlling a flow of and pressure of the hydraulic pressure from
the source to the respective cylinders.
[0101] As explained previously, the valves are of the PPRR type
which include a spool 21 which can slide back and forth within the
valve to connect inlet and outlet ports 22, 23 to the line 24 to
the respective cylinder. The spool is driven by a solenoid 25 so as
to position the solenoid at a required location to generate a
required pressure depending upon a signal to the solenoid provided
by a controller 28 on a control line 29. The spool is also
controlled by pilot pressure on line 30 and 31 connected
respectively to the inlet and outlet to the valve. Such valves are
commercially available from many different suppliers and are known
as proportional pressure reducing/relieving valves. These act to
maintain the pressure within the cylinder as it supplied along the
line 24 at a predetermined value set by the signal on the line 29
from the control system by repeatedly supplying and discharging
fluid relative to the cylinder through the ports 22 and 23.
[0102] The control signal to the valves is the generated and
controlled by and electronic control system in order to change the
predetermined pressure in the respective cylinder in dependence on
a value of the applied signal.
[0103] Thus the valve arrangement includes a first connection 33 to
the source 12 and a second connection 34 to the return together
with the outlet 24 to the cylinder.
[0104] The valve component operates to control flow of hydraulic
fluid from the source to the float cylinder and flow of hydraulic
fluid from the float cylinder to the return so as to maintain the
hydraulic pressure in the float cylinder at a predetermined
pressure set in dependence upon the control signal from the control
system.
[0105] The control system 28 includes a subcomponent 35 which acts
to generate an alternating wave signal so as to provide an
arrangement for causing relative reciprocating movement in an
alternating wave pattern between the piston component of the float
cylinder and the cylinder component of the float cylinder so as to
maintain movement between the components at the cylinder seals. 122
to reduce the effect of static friction.
[0106] That is the relative reciprocating movement is provided by
the alternating wave pattern signal applied by the electronic
control system to the valve arrangement to change the predetermined
pressure in dependence on a value of the alternating wave
signal.
[0107] The subcomponent 35 is controlled by the control system 28
so that the alternating wave pattern is applied only when the
cylinder is in float mode and not when the cylinder is used in a
lifting or lowering state.
[0108] The circuit further includes pressure sensors 40 and 41
which detect the pressure in the fluid supply lines to the
cylinders to provide a signal which is communicated to the control
system 28. As the valves are arranged to provide the pressure
output in response to the control signal supplied, the measurement
of the pressure output is not theoretically required. However in
view of temperature and other changes which may occur, it is
desirable to check the output pressure to ensure that it does not
drift over time and the is maintained at the required pressure as
determined by the control signal. The feedback check provided by
the pressure sensors can be carried out periodically and is not
part of the control system operation to generate the output
signals.
[0109] The position sensors 120 and 121 which detect the position
of the cylinders provide a signal which is supplied back to the
control system 28. The system may run using only input from the
position sensors since the control system 28 can calculate from
changes in the signal from the position sensors both the velocity
and acceleration of the cylinder and therefore of the header. A
suitable algorithm to make such calculations is of course
well-known to persons skilled in this art. However in addition to
the position sensors or as an alternative thereto, the system may
include an accelerometer 42 mounted on the header at one or more
suitable locations to provide an output indicative of relative
movement of the header and acceleration of the header.
[0110] The circuit can further include an operator input 45 which
allows the operator to input various parameters as necessary for
controlling the control system 28. The control system also includes
input lines responsive to various parameters of the operating
header including for example a ground speed indicator 46 and a crop
condition indicator 47. These are shown only schematically as
persons skilled in the art can determine suitable input parameters.
A further input line can be provided from a prediction system 48
which can use ground height and crop height sensors to detect in
advance and the intended height of the cutting action. The signal
can be used to predict obstacles or required changes in cutting
height so that the control system can generate suitable signals to
raise or lower the cylinders 116, 117 to a required position.
[0111] The electronic control system is arranged to provide dynamic
control of the lift force applied by the cylinders to the header.
Thus, in response to any movement of the header detected by the
position sensors or by other accelerometer and relative movement
type sensors, the control system can change the pressure applied to
the cylinders by the control valves so as to increase or decrease
the lifting force from the preset float condition to change the
movement of the header.
[0112] In this way, for example, upon detection of acceleration in
the upward floating movement the control system can act to change
the control signal to increase the lifting force to assist the
acceleration in the upward floating movement.
[0113] Furthermore the electronic control system can act upon
detection of an end of the upward acceleration in the upward
floating movement to change the control signal to decrease the
lifting force to dampen the upward movement.
[0114] These two dynamic actions can be used for example on
impacting an obstacle or on rapid rise in the ground level to
rapidly accelerate the header upwardly to clear the ground and then
to halt the upward movement by a damping action to cause the header
to float back downwardly as quickly as possible. To force the
header downwardly more quickly, the electronic control system can
act to change the control signal to decrease the lifting force to a
value less than the set float value.
[0115] Symmetrically, the electronic control system can act upon
detection of acceleration in the downward floating movement to
change the control signal to decrease the lifting force to assist
the acceleration in the downward floating movement and upon
detection of an end of the acceleration in the downward floating
movement to change the control signal to increase the lifting force
to dampen the downward movement.
[0116] In FIG. 3 is shown an arrangement in which there is provided
on additional accumulator 60 which has a pressure sensor 61 and a
supply valve 62. This accumulator can be used to provide or to
ensure sufficient fluid flow to the inlet of the valves 18 and 20
to meet the requirements for rapid flow of fluid into the cylinders
if required. In this way, if the pressure source 16 which comprises
a pump has insufficient flow rate at startup, the flow can be
provided by the accumulator.
[0117] In FIG. 4 is shown on optional hydraulic schematic to
capture energy of header floating can also be used.
[0118] In this version of the invention, the cylinders 116 and 117
are inverted relative to that shown in FIGS. 2 and 3. Also the
pressure supplied to the cylinders from the valves 18 and 20 is
opposed by pressure from a supply 201 including an accumulator 200
at a constant pressure so that lift force is generated by a
difference in pressure from the valves 18 and 20 relative to that
of the supply 201. In other words, the lifting action is provided
by the pressure from the source 201 and this is opposed by the
pressure supplied by the valves 18 and 20 to decrease the lifting
force to a value determined by the valves 18, 20 under control of
the control system 28. In order therefore to increase the lifting
force, the pressure in the cylinders supplied by the valves 18, 20
is reduced, and vice versa.
[0119] That is there is an additional accumulator 200 that supplies
float energy to the float cylinders that is above what is normally
required to float the header. The PPRR valves 18, 20 are controlled
to add down force to the cylinders 116, 117 to make the header
float down to the ground. The control system for the PPRR valves is
similar to the arrangement described above but with this system,
the flow and/or pressure required to adjust the float are
lower.
[0120] Also with this system, the system is capturing the energy
from the header floating down, into the accumulator 200 using an
intervening shut-off valve 203. A pressure sensor 202 and control
valve 204 are used in conjunction with the controller 28 to control
the pressure in this accumulator system.
[0121] As set forth above, this is maintained at a constant value,
which can be set at different values depending on various operating
parameters, and the variations in the lifting force are applied by
the valves 18, 20 on the upper side of the piston to apply a
variation in the pressure opposing the constant upward force on the
lower side of the piston.
[0122] Thus the float cylinders can be used in either orientation,
and are shown inverted in this embodiment. It can be appreciated
that the float cylinders could be used in a pull configuration
rather than a push configuration as well. In all FIGS. 2, 3 and 4,
the header weight is in the downward direction. That is the
variations in the pressure supplied by the valves can be used in a
number of different orientations to change the lift force generated
by the cylinders.
[0123] The sensors to collect information about the dynamic state
of the implement can include a linear potentiometer which measures
the extension of the hydraulic cylinder and a pressure transducer
providing feedback of the supplied pressure. In other
interpretations, the force transmitted to the implement through the
hydraulic cylinder could be monitored with a force transducer or
the height of the implement from the ground could be measured
either directly or indirectly.
[0124] In addition, instead of calculating velocity and
acceleration from the position sensor, movement sensors and
accelerometers can be used to provide direct signals proportional
to these values.
[0125] The arrangement could be used to achieve a comprehensively
adjustable spring rate for the dynamics of the flotation system of
the implement
[0126] The arrangement could be used to achieve comprehensively
adjustable damping for the dynamics of the flotation system of the
implement The arrangement could be used to achieve comprehensively
adjustable flotation system dynamics based on operating state of
the implement including but not limited to implement height, ground
speed and changes in terrain (incline angle, etc)
[0127] The arrangement could allow for the operator to select from
pre-set flotation system dynamics which can be tailored to
different field conditions and implements.
[0128] While existing float systems can achieve acceptable ground
forces when the header is stationary, because the applied force is
generally independent of the header's state of motion, the header
will still dynamically respond based on its mass, not the set point
of the float system. For example, the float system could be set
such that the ground force is 500 lbs, however, in order for the
header to accelerate upwards or downwards, an additional input of
force is required. Based on Newton's second law (F=ma), this
additional force will generate an acceleration in the header which
is inversely proportional to the header's mass. Therefore, while
the header may be statically light (i.e., light when it is
stationary), in order for it to actually move up and down to follow
the ground, its dynamics will still be governed by its mass and
higher ground forces will be required to actually lift the header.
An implication of this arrangement is that the lower the static
ground force is set, the slower the header is able to fall. This is
because the maximum input force into the float system to make the
header fall is equal to the floated weight of the header.
Therefore, the smaller the floated weight of the header, the
smaller the resulting acceleration. The existence of friction
within the system will also factor into how light the float system
is able to be. Friction creates an asymmetry between the required
ground force when lifting and lowering the header. This leads to
higher ground force when lifting and slower movement when lowering.
This also creates a limit to how light the static ground force can
be set as the floated weight must be larger than the friction in
the system in order for the header to actually be able to fall
after being lifted.
[0129] The float system of the present invention allows these
limitations to be reduced because the force applied by the float
system can be controlled based on the header's state of motion.
Based on the sensor feedback collected, the controller can actually
add more force to the system when the header is being lifted in
order to help it lift more quickly with less ground force.
Additionally, when the header starts to fall, the controller can
decrease the applied force so that it falls more quickly. By being
able to adjust the force provided by the float system based on the
header's state of motion, the dynamics of the header can be altered
so that it is no longer governed solely by the mass of the header.
This can allow a heavy header to not only have acceptable ground
force when stationary, but also lift and lower as though it
actually has less mass. This also circumvents the limitation that
the minimum downwards acceleration is tied to the floated weight of
the header, allowing the float system's stationary ground force to
also be lower than could be achieved with a conventional float
system.
[0130] It is desirable to provide mechanical improvements such as
reduced system friction, a smaller dead band in the hydraulic valve
and reducing hydraulic restriction for flow traveling into and out
of the cylinder since these will reduce the amount of intervention
required by the controller to produce favourable dynamics.
Improving the quality of the feedback signals to reduce the effects
of noise (both mechanical and electrical) provides the controller
with more reliable data from which to make control decisions.
[0131] The intention of a float system is to reduce the ground
force of a header in order to reduce wear and improve ground
following capabilities. To date, all float systems are based on a
static balance of the implement. In other words, a force is applied
such that it lifts a portion of the header's weight so that the
ground force is lower. Provided the header is not moving up or down
throughout its float range, this system is effective at reducing
ground force. For example, if a header weighs 7000 lbs and the
float system is set to carry 6800 lbs, then only 200 lbs needs to
be reacted by the ground. However, considering only the static
state of the system neglects two important factors; friction and
inertia.
[0132] In a friction-less system, the ground force is the same
whether the header is being lifted or lowered (assuming this is
done very slowly). However, when friction is introduced in the
system, the ground force is no longer the same when lifting and
lowering. In fact, the difference between the ground force when
lifting and lowering is equal to twice the friction in the system.
As a result of friction, there is a minimum ground force which can
be achieved. If this minimum threshold is exceeded, the header will
no longer fall under its own influence after it is lifted as the
floated weight of the header is not sufficient to overcome
friction. While minimizing the friction in the system can help to
reduce this effect, it will still represent a limitation of the
system.
[0133] Another important short-coming of basing a float system on
the static balance of the header is that the dynamics of the header
will still be governed by the header's weight when it is in motion.
Based on Newton's second law:
a header = F float + F ground m header - g ##EQU00001##
[0134] Thus a 7000 lbs header (with no friction), set to 200 lbs
static ground force can only achieve a maximum downwards
acceleration of 0.03 g. It also requires 900 lbs of ground force to
accelerate the header upwards at 0.1 g. While the static ground
force can be set reasonably light, the lighter this becomes, the
slower the header is capable of falling after being lifted. Also,
the slope of the line (and consequently the ground force required
to produce a given acceleration) remains tied to the mass of the
header, not to the set point of the float system. As a result of
this limitation, the header will still respond dynamically like it
is 7000 lbs; all the float system is able to change is the static
ground force of the system. When the effect of friction is combined
with this limitation, it is unsurprising that there are limitations
to how light an existing float system can get before its ground
following capabilities are compromised.
[0135] In order to try and improve the dynamic response of the
float system, the float system needs to not only change the static
ground force, but also how much ground force is required to lift
and lower the header. The hydraulic float system described herein
achieves this is by introducing feedback regarding the dynamic
state of the system into the float control system. While a wide
number of different measurements can be used to infer information
regarding the dynamic state of the system (such as force, hydraulic
pressure or other kinetic measurements), as described herein, the
extension of the float cylinder is measured with a potentiometer
and this signal can be differentiated numerically to determine the
full kinematic state of the system.
[0136] In order to alter the dynamics of the header using the float
system, the input force from the float system cannot remain
constant, but instead must vary with respect to the dynamic state
(velocity and acceleration) of the header. The goal of the control
algorithm is to not only reduce the static ground force when the
header is stationary, but also to reduce the amount of force
required to lift the header and to allow the header to fall more
quickly (as though it were a lighter header). Such a system allows
for lower ground force as well as better ground following
capabilities. A dynamically changing force applied by the float
system can reduce the impact of friction within the system.
[0137] The target pressure calculated by the position, velocity and
acceleration state of the cylinder is generated by using a simple
PID controller. This PID intermittently looks at the difference
between the target pressure and the measured pressure and then
adjusts the output to try and minimize the error. The PID
controller can be supplemented with an open-loop lookup table. The
ability to robustly and reliably maintain the cylinder pressure at
the target pressure facilitates the development of a responsive and
stable cylinder response.
[0138] Dithering is superimposed on the output to the PWM valve in
attempt to reduce the amount of hysteresis in the system. Dithering
is the intentional addition of "noise" into the signal. In this
setup, sinusoidal dithering waves were used. It should be noted
that while the output of the controller can be sinusoidal, the
achieved pressure fluctuation is not necessarily perfectly
sinusoidal due to the ability of the hydraulics to replicate the
input signal. This dithering signal was calculated and simply added
to the output of the PID controller to obtain the total output to
the valve.
[0139] There are three parameters which can be controlled to change
the nature of the dithering; the wave's amplitude, period and shape
(sinusoidal, square, triangular, etc.). A variety of different
parameters can be used to try and reduce hysteresis and improve the
response of the system.
[0140] Relatively effective dithering can be achieved with a
dithering wave period of only 80-100 msec and an amplitude of only
2% of the overall operable PWM duty cycle range although both a
longer period and higher amplitude dithering wave can be necessary
to achieve a similar result.
[0141] The period of the dithering wave appears to be bounded on
the low end by the responsiveness of the PRR valve as well as the
ability to deliver the flow required to move the cylinder. Above
this lower limit, the effect of the dithering wave is more directly
related to the power input of each half waveform. Consequently, a
higher amplitude waveform is necessary at shorter dithering
periods, while a lower amplitude waveform can be used with a longer
dithering wave period. By maintaining a dithering magnitude of 7%
and varying the dithering period at short dithering periods of
<150 msec were not particularly effective. Dithering periods of
200-250 msec are effective, whereas if the dithering period is
increased further, the header can noticeably shake. This shaking
could be reduced by lowering the amplitude of the waveform so that
the power of each half waveform is lower. However, it is best to
keep the dithering period as low as possible in order to help
improve the reaction time of the system, so the shortest dithering
period which is effective should be selected.
[0142] Any required motion will only be aided by half of the
dithering waveform and hindered by the other half of it. It is
helpful to interpret the dithering wave as the controller
consecutively checking to see if the header wants to lift, and then
checking if it wants to lower. The amount of power in the dithering
half-wave required to perform these checks will relate to both the
friction in the system as well as the responsiveness of the
hydraulics. It is helpful to disable dithering when in a lifting or
lowering state as half of the dithering wave will be acting against
the intended motion.
[0143] Pressure, position, velocity and acceleration inputs into
the control structure are calculated as follows. As discussed
previously, the cylinder is kept in constant motion by having the
pressure in the cylinder always varying slightly by having a
sinusoidal wave applied to the valve output (referred to as
dithering). This can make it more difficult to determine the
pressure and position of the cylinder as this adds a substantial
amount of noise. As a result, filtering and averaging techniques
are used to try and distinguish the bulk movement of the system
while ignoring the motion caused by dithering. These techniques can
retain more responsiveness by using the properties of the dithering
wave instead of simply filtering more aggressively.
[0144] Since dithering creates variation in both the pressure in
the cylinder as well as the position, both of these values are
averaged over a single dithering wave period in order to try and
reduce the influence that dithering has on their calculation. A
shorter dithering period is therefore desirable to help improve
responsiveness of this calculation.
[0145] Since the velocity and acceleration terms are based on a
difference calculation, these are performed differently than the
position and pressure terms; instead of looking at only a single
dithering period, these calculations look at the last two dithering
periods. The position (or velocity) is then compared at equivalent
locations within the dithering wave. This allows for the
calculation to be sensitive to changes in position which are lower
in magnitude than those created by the dithering wave. Again, the
calculation is averaged over a single dithering period. The
velocity is calculated by looking at how much the position has
changed between comparable locations in the dithering waveform. In
order for a hydraulic float system to produce adequate ground
following capabilities, it is desirable for it to mimic the
response of a spring. In order to simulate a spring-like effect,
the extension of the cylinder is used to vary the cylinder
pressure. In this setup, a simple linear spring rate was added. The
spring rate is introduced by creating a linear function which
determines the target pressure based on the measured cylinder
extension. This made the required input force get higher as the
wing was lifted higher. The below equation shows the most recent
spring rate used to alter the header's dynamics:
P target = P [ psi ] - ( 0.26 [ psi mm ] * y [ mm ] )
##EQU00002##
[0146] Based on the current spring-based system, it is believed
that having the header get heavier as it gets lifted is beneficial.
This has the effect of biasing the header so that it naturally
wants to fall. However, provided that the target pressure at a
given height leads to a non-zero ground force, the header should
always want to fall. If terrain leads to extended periods of time
spent with the header either raised or lowered, these periods of
time occur with ground force which is either lighter or heavier
than the set point. Provided the spring rate is not set
particularly aggressively, this is likely not an issue, however,
there may be value to having a more even header response throughout
its range of motion to avoid it either being too light and wanting
to lift off when too heavy and inclined to push when too light.
[0147] In one arrangement, the header's set point pressure can
follow around a moving average of the header's position. This is an
effective way to implement a spring rate without sacrificing header
pressure performance when spending extended periods of time away
from its normal position. Such an arrangement makes the header
initially want to return to its last position (by either getting
heavier when lifted or lighter when lowered), but have it adapt to
a change in position if it is maintained for a period of time.
[0148] In addition to having the dynamics of the header change with
respect to the header's position through the use of a spring rate,
the header's potentiometer signal is also used to change the target
pressure with respect to velocity and acceleration. As described
previously, both the velocity and acceleration terms were
calculated in a way as to try and minimize the detection of
movement caused by dithering so as to only focus on the header's
bulk movement
[0149] The velocity term relates to the damping of the system.
However, since the header already had an over-damped response, this
term is used to try and reduce the damping of the system by
reinforcing the motion of the header. This term has some
similarities to lift and lower assist pressures except instead of
adding a constant pressure to the target, the effect varies with
the magnitude of the header's velocity. It should be noted that
this term would have the effect of tending to de-stabilize the
header. It is helpful to create a nonlinear velocity-based function
which restricts smaller velocities and reinforces larger
velocities. It would also likely be beneficial to make this term
saturate at a maximum value to ensure this effect does not reduce
the require ground force to lift the header below zero (which would
cause the header to continue to accelerate upwards until it reached
full raise.
P target = P [ psi ] - ( 6.0 [ psi mm / s ] * y . [ mm s ] )
##EQU00003##
[0150] The acceleration term relates to the inertia of the system.
By reinforcing accelerations, the controller is able to reduce the
effective inertia of the header to help it to react to input forces
as though it weighed less. However, in practice, taking a numerical
second derivative of a sensor input is inherently noisy, so the
ability to implement this is limited. That said, there is still
value to incorporating a term which ties target pressure directly
to the acceleration of the header to some extent. While initially a
single constant is used, this term can be split into two
parameters; one to control the impact of positive accelerations and
one to control the impact of negative accelerations.
P target = P [ psi ] - ( 0.4 [ psi mm / s 2 ] * y [ mm s 2 ] ) for
y .gtoreq. 0 ##EQU00004## P target = P [ psi ] + ( 0.06 [ psi mm /
s 2 ] * y [ mm s 2 ] ) for y < 0 ##EQU00004.2##
[0151] Positive accelerations relate to when ground force is
increased and the header starts to lift, or when the header impacts
the ground after falling. In order to help the header stick after
it lands on the ground, positive accelerations were used to
decrease the target pressure of the controller somewhat. This makes
the header heavier momentarily when it contacts the ground to help
stop it from bouncing up again. This does also have the effect of
make the header somewhat heavier when you first try to lift it.
However, since the acceleration of the header impacting the ground
is notably larger than the acceleration input when lifting the
header, the effect is more noticeable in the case of an impact.
[0152] Negative accelerations relate to when the header slows down
while lifting and begins to fall. In order to help stop the header
from hanging up, negative accelerations are also used to decrease
the target pressure of the header, making it momentarily heavier
and therefore less likely to hang up. If you begin to slow down the
rate at which you lift the header, it starts to get heavier.
[0153] It is possible to develop nonlinear equations which use the
position, velocity and acceleration states of motion (as well as
other variables such as ground speed, cut height, etc.) to
extensively customize the dynamic response of the system.
[0154] Translating the control structure's target pressure into the
output float force of the system quickly and accurately is
important for optimizing the system response. While the closed loop
PID structure is quite effective at replicating the target
pressure, more advanced control techniques can help to further
improve this response. The inclusion of an open loop lookup table
and downgrading the PID controller to a correction factor can be
used. It is possible to reduce the impact of valve lag by providing
momentary overshoots in the current output to the solenoid to help
it change directions more quickly.
[0155] Reliably and robustly measuring the position, velocity and
acceleration of the cylinder is required for responsively
controlling the float dynamics without introducing instability. It
is desirable that these calculations provide a clean signal with as
little lag as possible. In the current configuration, all
calculations are tied to the dithering period, regardless of
whether dithering is actually active. It may be beneficial to move
towards two distinct calculations; one when dithering is active and
one when it is not. This may help to allow for higher
responsiveness is situations where noise caused by dithering does
not need to be accounted for.
[0156] The hydraulic float system described herein provides a float
system which is more responsive, with improved ground following
capabilities and a lower ground force. The system is based on using
an electronic controller and feedback from sensors in order to
decide what pressure should be supplied to the hydraulic float
cylinder. This pressure is then supplied by using a proportional
pressure reducing/relieving valve based on the output signal from
the controller. The resultant system allows for a highly
customizable hydraulic pressure (and consequently force) provided
by the float system. This allows for the float system to adjust the
force provided by the float system in order to reduce the effects
of friction in the system as well as to fundamentally alter the
dynamics of how the header moves.
* * * * *