Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DEPT~ LIMIT CONTROL SYSTEM FOR AGRICULTURAL IMPLEMENTS
BACK5ROUND OF THE IN~ENTION
Field of the Invention
This invention relates to a control system for an
agricultural implement and more particularly to a control
system which is readily adjustable and which facilitates
accurate control of the positioning and movement of a work-
ing element while being economically manufacturable and
relatively simple and straightforward in construction and
operation. The control system can be readily applied to
existing implements of various designs or can be incor-
porated during manufacture.
Description of the Prior Art
In agricultural implements such as plows, harrows
and the like, the plow bottoms, discs or other working
elements must be controllably movable upwardly or downwardly
during operation to adjust for varying soil conditions and
must be movable to a fully raised position for travel or to
clear an obstacle. Hydraulic systems are generally used and
in a typical system, a manually adjustable valve controls
flow of a fluid to and from a hydraulic cylinder which
operates a rockshaft arranged to control the vertical posi-
tion of discs or plow bottoms. The hydraulic cylinder maybe double-acting or may be single-acting with the force of
gravity being relied upon to effect downward movement of the
workins implement.
Systems have been proposed which rely on mechan-
ical stops. These systems cannot be ad~usted during opera-
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tion. The operatox must dismount, predict some incrementalchange in depth, then make a mechanical change which may
require tools.
Systems have also been proposed using, in place of
5 the manually operated valve, an electrically operated valve
controlled from a command potentiometer operated by the
operator.
Systems using a manually operated valve are, in
general, very rugged and highly reliable while being rela-
10 tively inexpensive to manufacture, but they have limita-
tions. For example, when a plow bottom is raised to clear
an obstacle or at the end of a row, it requires considerable
care and expertise to rapidly return the plow bottom to the
optimum plowing level. Electrically controlled systems are
15 more easily controlled and might provide greater flexibility
but those heretofore proposed have been relatively expensive
and have other disadvantages, including increased power
consumption and no "limp-home" or manual override and back-
up provisions.
SUMMARY OF THE INVENTION
This invention was evolved with the general
object of overcoming disadvantages and shortcomings of prior
art arrangements and of providing a system which is readily
adjustable and which facilitates accurate control of the
movement and positioning of a working element of an agri-
cultural implement while being relatively simple in con-
struction and operation and economically manufacturable.
In accordance with this invention, a secondary
control is applied to a hydraulic system which raises and
lowers a working element of an agricultural implement and
which is controlled from a main raise-lower control manually
adjustable by an operator. The secondary control includes
electrically opexated valve means for connection to the
hydraulic system, a limit control means for establishing a
manually set limit on lowering movement of the working
element and an electrical system for controlling the valve
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means from the limit control means to limit lowering move-
ment of the working element in accordance with the manually
set limit. With this comparatively simple arrangement, the
hydraulic system can be operated in normal fashion from the
main raise-lower control but the operator can set whatever
limit is desired on the lowering movement by setting the
secondary control. In operating a disc harrow, for example,
he can use the main control in determining the optimum depth
for existing soil conditions and he may then set the secon-
dary control to operate at that depth. Then when encounter-
ing an obstacle or at the end of a row, he can use the main
control to lift the harrow and thereafter use it for lower-
ing until the limit position is reached and then continue
operation at the optimum depth. Thus a "memory" operation
is obtained and accurate, reliable and efficient control is
facilitated.
The electr cal system includes transducers for develop-
ing signals corresponding to the manually set limit and to the
vertical position of the working element and a comparator means
20 for comparing such signals to control the secondary valve means.
The transducers in a preferred embodiment are potentiometers
operating as voltage dividers to develop analog signals which
are compared by a high gain differential amplifier. Preferably,
positive feedback means are provided for producing a bi-stable
25 h~steretic switchin~ operation and a high degree of stability and
reliability in operation.
With the electrical control, the depth control
means can be readily in~talled in proximity to the o~era-
tor's station of a tractor and in proximity to the main
.30 raise-lower control, facilitating adjustment whenever
desired and permitting adjustment during movement of the
implement. Indicator means may be associated with the depth
control means, permitting use thereof as a monitor to in-
dicate when a desired depth has been reached as well as an
35 indication of actual depth.
In accordance with a specific feature, the secon-
dary electrically operated valve means is connected in
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series with a main valve of the hydraulic system which is
coupled between a pump and at least one working cylinder
coupled mechanically to the working element. The hydraulic
system may thus be of a standard highly reliable type such
; as one usiny a manually adjustable spool valve and the
arrangement can be readily installed on an existing imple-
ment or can be readily incorporated during manufactur~ of an
implement without change in its basic design.
In accordance with specific featu~es, the secon-
-O dary valve is located between the main valve and the workins
cylinder or cylinders and preferably it is located close to
the wor~ing cylinder or cylinders and on the "drop side" to
increase accuracy of control especially when a master-slave
cylinder arrangement is used, and also to provide additional
resistance against "leak-down" of an implement dur~ng opera-
tion.
This invention contemplates other objects, fea-
tures and advantages which will become more fully apparent
from the following detailed description taken in conjunction
O with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
.
FIGURE 1 is a perspective view illustrating a
depth control arrangement according to the invention, shown
applied to a trail behind self-supported disc harrow imple-
ment;
FIGURE 2 is a view illustrating diagrammaticallythe hydraulic system o the implement and the coupling of
the depth control arrangement thereto; and
FIGURE 3 is a circuit diagram of an electrical
,0 system of the depth control arrangement of the invention.
DESCRIPTION OF A PREFERRED EMBODIME NT
Reference numeral 10 generally designates a depth
monitoring and control system constructed in accordance with
- the principles of this invention and shown diagrammatically
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as applied to a trail behind disc harrow implement generally
designated 11 which is drawn by a tractor generally desig-
nated 12 and which includes working elements in the form of
discs 13. It will be understood that the invention may be
applied in controlling the position of working elements of
other types of agricultural implements and may be used, for
example, in controlling the position of the bottoms of
plows, the headers of combines, the buckets of loaders, and
backhoes, the blades of scrapers, etc.
A hydraulic system is used for raising and lower-
ing the discs, controlled by a lift control valve 14 located
in the operator's cab of the tractor 12 and operated by a
control lever lS.
In accordance with the invention, depth control
means are provided, including a unlt 16 located in the cab
of the tractsr and including an adjustment knob 18 for
establishing a manually set limit on lowering movement of
the discs 13. In a typical operation, the operator, through
operation of the control lever lS, determines the optimum
level for the discs 13 according to prevailing soil condi-
tions with the knob 18 being positioned to set the corres-
ponding limit on lowering movement. Then, whenever an
obstruction or hazard is encountered or when turning at the
end of a row, the lever 15 is operated to raise the discs
13. After the obstruction or hazard is cleared or after the
turn is completed, the lever 15 is again operated to lower
the discs until the set limit is reached, the discs 13 being
then positioned and thereafter maintained at the optimum
depth as previously set by the operator. No readjustment is
necessary~
It is noted that a graduated scale 19 (Figure 3)
is located adjacent the knob 18 so that the setting for any
particular condition of operation may be noted and there-
after the knob 18 may be positioned at the same setting
whenever desired.
In the illustrated disc harrow implement generally
designated 11, the discs 13 are carried from a frame struc-
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ture 20 supported ~rom a pair of inner support wheels 21 and
2? and a pair of outer support wheels 23 and 24. The inner
wheels 21 and 22 are supported on axles of arms which are
secured to a rockshaft 26 actuated ky a pair of hydraulic
5 cylinders 27 and 28. The outer wheels 23 and 24 are sup-
ported in a similar manner from shafts actuated by a palr of
hydraulic cyllnders 29 and 30. As best seen in Figure 2 in
conjunction with Figure l the frame structure 20 and thereby
the discs 13 are raised by supplying fluid under pressure
10 through lines 31 and 32 to the cylinders 27 and 28 from
which fluid is supplied through lines 33 and 34 to cylinders
29 and 30. Fluid flows from cylinders 29 and 30 through
lines 35 and 36 to reservoir 40 when cylinders 29 and 30 are
being filled.
To lower the discs 13, the operation is reversed
with fluid flowing through lines 35 and 36 to cylinders 29
and 30, with fluid flowing from cylinders 29 and 30 through
lines 33 and 34 to cylinders 27 and 28 and with fluid flow-
ing from cylinders 27 and 28 through lines 31 and 32 eventu-
ally to the reservoir 40.
Figure 2 shows a pump 39 that has an inlet con~
nected to the reservoir 40, the outlet of pump 39 and the
reservoir 40 being connected through lines 41 and 42 re-
spectively to the lift control valve 14. Lift control valve
14 is connected through a line 43 to lines 31 and 32 and
through a line 44 to lines 35 and 36.
In the system of this invention, a secondary valve
45 is provided which is operated by a solenoid 46 and which
is preferably located on the implement generally designated
11 close to the cylinders 27 and 28. The manner of flow
through valve 45 is indicated diagrammatically in Figure 2.
When solenoid 46 is deenergized, fluid may flow in either
direction as indicated by double ended arrow 47. r~en
solenoid 46 is energized, a check valve 48 is operative,
permitting flow from line 43 to lines 31 and 32 for raising
of the discs 13 but blocking flow in the reverse direction
to prevent lowering of the discs 13.
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The liEt control valve 14 has -three positions. In
a neutral position, fluid flows in a recirculating path from
line 41 to line 42, as indicated by arrow 50 with fluid flow
to or from lines 43 and 44 being blocked, as indicated by
lines 51 and 52. In a "raise" position, fluid flows from
line 41 to line 43 and from line 44 to line 42 is indicated
by arrows 53 and 54. In a "lower" position, fluid flows
from line 41 to line 44 and from line 43 to line 42 as
indicated by crossed arrows 55 and 56.
In Figure 3 it can be seen that the operating
solenoid 46 for the valve 45 is connected to terminals 57
and 58, terminal 57 being connected through a fuse 59 to a
positive supply terminal 60 of the tractor electrical system
and also connected through a protective diode 61 to ground.
Terminal 58 is connected to the collector of a transistor
62, the emitter of which is connected to ground. A protec-
tive diode 63 and an indicator lamp 64 are connected between
terminals 57 and 58, in parallel with the solenoid 46. Lamp
64 is preferably positioned in the unit 16 adjacent the
adjustment knob 18 within view of the operator, signalling
to him that the pre-set optimum depth has been reached.
The base of the transistor 62 is connected through
a resistor 65 to the output of an operational amplifier 66
which has a plus input connected to the movable contact of a
potentiometer 68 which is connected between ground and an
output line 69 of a regulated voltage supply 70 connected to
` the terminal 57. The potentiometer 68 forms a depth or
level sensing transducer, the movable contact thereof being
mechanically connected to the rockshaft 26 in a manner such
as to move toward the grounded end of the resistance element
and away from the supply end thereof in response to rotation
of the rockshaft 26 in a direction to raise the frame struc-
ture 20 and discs 13.
The minus input of the operational amplifier 66 is
connected through a resistor 72 to the terminal 58 and is
also connected through a resistor 73 to the movable contact
of a potentiometer 74 which has end terminals connected
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through fixed resistors 75 and 76 to ground and to the
regulated voltage supply line 69. Potentiometer 74 forms a
depth limit control transducer, its movable contact being
mechanically connected to knob 18.
In operation, when the control lever 15 (Figure 2)
of valve 14 is moved to a "raise" position, fluid flows from
the pump outlet through line 41 and through passage 53 of
valve 14, thence through line 43 and through passage 47
through valve 45 and thence through lines 31 and 32 to
10 cylinders 27 and 28. Fluid flows from cylinders 27 and 28
to cylinders 29 and 30 through lines 33 and 3A and return -
flow is from cylinders 29 and 30 and through lines 35 and
36, through line 44, through a path through valve 14 as
represented by passage 54 and thence through line 42 to the
15 reservoir 40.
When the control lever 15 of valve 14 is moved to
a "lower" position, fluid flows from the outlet of pump 39
through line 41, thence through the path through control
valve 14 as represented by passage 55 and through line 44
20 and lines 35 and 36 to cylinders 29 and 30. Fluid flows
through lines 33 and 34 from cylinders 29 and 30 to cylin-
ders 27 and 28 respectively and return flow is from cylin-
ders 27 and 28 through lines 31 and 32, through the passage
47 of valve 45 and through line 43, the passage 54 through
25 valve 14 and through line 42 to reservoir 40.
When the discs 13 (Figure l) are fully raised, the
movable contact of the depth sensing potentiometer 68
(Figure 3) is at a limit of its movement toward the grounded
end of the resistance element thereof and the voltage
30 applied to the plus input of the amplifier 66 is at a
minimum. As the discs 13 are lowered, the voltage applied
to the plus input of amplifier 66 increases and at a certain
position, determined by the setting of the potentiometer 74,
the voltage applied to the plus input is more positive than
3~ that applied to the minus input. The amplifier 66 then
- produces a positive output vol-age which is applied to the
base of transistor 62 which then conducts heavily to ener-
gize the solenoid 46 and operate the valve 45.
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When valve 45 is so operated, flow from cylinders
27 and 28 (Figure 2) and through lines 31 and 32 is blocked
by the check valve 48 and with flow from cylinders 27 and 2
being blocked, flow from cylinders 29 and 30 and through
5 lines 33 and 34 is also blocked. Thus downward movement of
the discs 13 is limited, the limit position being determined
by the setting o~ the potentiometer 74, adjustable through
the adjustment knob 18. When the limit is reached, the
control lever 15 may be released to allow the valve 14 to be
10 operated to its neutral position ~y suitable spring means
associated with the valve.
It is noted that the potential of the collector of
transistor 62 and terminal 58 is substantially equal to the
potential of terminal 57 when transistor 62 is non-conduc-
tive and drops to close to ground potential when transistor62 conducts heavily. Through the resistor 72, which pro-
vides positive feedback, the potential of the minus input of
amplifier 66 is shifted in a negative direction from a value
slightly above to a va~ue slightly below the potential of
the contact of potentiometer 74. Thus, once the plus input
of amplifier 66 becomes only very slightly more positive
than its minus input, the positive feedbac~ insures that it
will rapidly become much more positive to cause the ampli-
fier to produce a positive output with a high degree of
stability. Similarly, the amplifier is rapidly cut off when
the plus input becomes only very slightly more nega~ive than
the minus input and the circuit has a bi-sta~le operation,
hysteretic operation~ This feature is lmportant in avoiding
oscillatory operations which t~e system may have a tendency
to produce such as hydraulic "bouncing" caused by the accu-
mulator effect of flexible hydraulic lines, or electric
signal fluctuations.
It will be understood that modifications and
variations may be effected without departing from the spirit
and scope of the novel concepts of this invention.
