Twine force sensing apparatus for use on a rectangular baler

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Patent issued

09/20/1994

Inventor(s):	Vansteelant, Marc G. Schoonheere, Marnix J.
Assignee	Ford New Holland, Inc. (New Holland, PA)
Application	No. 08/033,664 filed on 03/16/1993
Current US Class	100/4, 56/343, 100/18, 100/23, 100/43, 100/191
Field of search	100/4, 100/43, 100/179, 100/191, 100/192, 56/341, 56/343
International Classes:	B65B 5710, B65B 1326
Examiners
Primary	Gerrity Stephen F.
Attorney, agent or firm:	Seemar; Frank A. Miller; Larry W.
US patent references	3416824, 3851575, 4095520, 4196661, 4624180, 4765235, 4885991, 4930411, 4993317
Foreign patents	92200743.0 (03/16/1992, EP), 0223351 (04/30/1987, EP), 0286900 (09/30/1988, EP), 3640696 (05/31/1988, DE), 208748 (03/31/1984, DD)

A rectangular baler is disclosed comprising a bale case (6) into whichsuccessive charges of crop material are introduced; a plunger (7) disposedfor reciprocating movement in the bale case (6) to compact the chargeswhile advancing the compacted charges toward an exit opening in the balecase; and a knotter (8) for tying a flexible binding material, such astwine, in a form-stabilising manner around successive increments ofcompacted crop material while they advance in the bale case (6) to formbales. An elongated sensor (48), disposed on the knotter (8) in thetrajectory of the flexible material (49) projecting from a twine holder(32) towards a billhook (33), is operable to detect the tensile forcesoccurring in the binding material during bale formation and to producesignals, which are processed by a microprocessor (24) to, if foundnecessary, lower the density of the bales in order to avoid twine failure.
BACKGROUND OF THE INVENTION
The present invention relates to a sensing apparatus for detecting thetensile forces experienced in a strand of flexible binding material whilebeing wrapped and tied around a bale of crop material such as hay orstraw, for example.
In a conventional rectangular baler, as exemplified in U.S. Pat. No.3,416,824, hay, straw or similar crop material that has been previouslycut, windrowed or swathed, is picked up from the ground by a pick-up unitand fed in successive batches or charges into an elongated bale chamber intimed sequence with a reciprocating plunger. The plunger compresses thematerial into bales and, at the same time, gradually advances the balestowards the outlet of the bale chamber. As the bales reach a predeterminedlength as determined by a metering device, a knotter device is actuatedwhich wraps cord, twine or other flexible binding material around the baleand secures the ends of the binding material together.
In a typical rectangular baler the knotter device, commonly comprising twoor more knotters, is mounted on the bale chamber above a slot therein,each knotter comprising a twine holder from which twine extends toencircle a bale. During the baling operation, a leading strand of twine isheld by the twine holder and extends forwardly across a knot tying member,known in the art as a billhook, and a twine guiding member and then infront of the bale being formed. The twine guiding member supports thestrand so that it does not bear forcefully against the billhook. A needleis involved in completing the encirclement of twine around the bale and,when advancing, the needle lays a trailing strand across the twine guidingmember, the billhook and the twine holder. To initiate the formation of aknot by the billhook in the leading and trailing strands of twine, a twinefinger captures the strands and positively positions them against a heelof the billhook.
On completion of the operation of the knotter, the twine finger returns toits initial position. The tied knot is mechanically stripped from thebillhook by moving the twine guiding member thereacross; the membernormally embodying a knife operable to cut the twine from the twine supplyso that the tied bale is complete in itself. Finally, evacuation of thecompleted bale from the bale chamber is effected by starting the formationof a new bale in front of the completed one thereby forcing the latterrearwardly out of the baler.
The present day balers are expected to meet high demands regarding capacityof the baler, as well as density of the bales and reliability ofoperation. Under certain tough operating conditions, e.g. when baling dampsilage crop at a considerable density, the tying process mayintermittently fail. Failure occurs either because of breakage of thebinding material or because the binding material is pulled from the tyingmechanism. Both types of failure usually occur within a few plungerstrokes after a tying cycle. It is during this interval that the leadingstrand of the binding material encounters the greatest resistance tosliding between a completed bale and a new bale being formed as both arepushed toward the exit opening in the bale case. Also, at this stage ofthe bale formation, only little crop material is present between theplunger and the strand of twine at the leading end of the bale beingformed, meaning that the high acceleration forces of the plunger duringits compression stroke are not cushioned by the crop material but arealmost integrally transmitted to the binding material which thereby issubjected to elevated tensions, sometimes leading, as already mentioned,to the binding material being pulled out from the twine holder or tobreakage of the binding material in the vicinity either of the twineholder or the twine guiding member. These areas have been found to be themost critical for twine breakage as the binding material in these regionseventually might be slightly damaged by clasping the twine in the twineholder or by pulling the twine around the twine guiding member, wherebythe tensile strength of the twine may be reduced below a level sufficientto resist tensions experienced therein during bale formation.
In current large rectangular balers, bales commonly are wrapped withsynthetic twine, made of polypropylene and having a specific lengthbetween 130 and 150 m/kg with a corresponding tensile strength betweenrespectively 2900N and 2500N. Using twine with a specific length below 130m/kg, thus having a larger tensile strength, theoretically could lessentwine failure occurrence. However, such a twine is not currently availablein the field of agricultural application and moreover, even if it were,the use thereof could not be recommended as this would require allcomponents of a knotter mechanism to be redesigned and redimensionedcompletely, which would represent an enormous and expensive job having thecomplexity of a knotter mechanism in mind.
To at least alleviate the inherent problems of twine failure, thearrangement disclosed in DD-A-208,748 proposes to notify the operator atthe initiation of a tying cycle if a twine failure has occurred so thatoperation of the baler may be stopped before the bale is ejected. Duringnormal operation, a sensor arm, disposed in the path of travel of thebinding material and hence engaged thereby, is resiliently held in aposition away from an electrical switch. When the binding material breaks,the sensor arm is released and the electrical switch is actuated wherebythe operator is alerted to the twine failure. Although corrective actionthen can be taken while the broken bale is still in the bale chamber, itnevertheless will be appreciated that the foregoing inevitably leads todown time of the machine which is unacceptable.
SUMMARY OF THE INVENTION
It therefore is the objective of the present invention to overcome theaforedescribed disadvantages inherent to twine failure by detecting when atwine failure is likely to occur and to prevent it from happening.
According to the present invention, a rectangular baler is providedcomprising, a bale case into which successive charges of crop material areintroduced and having at least one wall portion which is movable generallylaterally thereof to vary the cross-sectional area of the bale case, aplunger disposed for reciprocating movement in the bale case to therebycompact the charges while advancing the compacted charges toward an exitopening therein, a knotter for tying a flexible binding material, such astwine, in a form-stabilising manner around successive increments ofcompacted crop material while they advance in the bale case to form balesof which the density at least partially is determined by the dimensions ofthe variable cross-sectional area, and a sensor for detecting the tensileforces occurring in the binding material during bale formation andproducing signals representative thereof.
More specifically, the sensor preferably comprises a rod-shaped elongatedbody, which is disposed in the trajectory of a leading strand of twineprojecting from a twine holder towards a billhook, whereby the tensileforces in the strand are partially transmitted to the sensor. Straingauges, attached to the sensor body, detect deflections of the sensorwhich correspond to the load imposed thereon and produce signalsproportional thereto, the signals being processed by a micro-processor fortaking the necessary steps to reduce the tension on the twine if foundimperative.
The foregoing and other objects, features and advantages of the inventionwill appear more fully hereinafter from a consideration of the detaileddescription which follows, in conjunction with the accompanying sheets ofdrawings wherein one principal embodiment of the invention is illustratedby way of example. It is to be expressly understood, however, that thedrawings are for illustrative purposes and are not to be construed asdefining the limits of the invention.

Having thus described the invention, what is claimed is:
1. In a rectangular baler comprising
a bale case (6) into which successive charges of crop material areintroduced and having at least one wall portion (14) which is generallylaterally thereof to vary the cross-section sectional area (18) of saidbale case (6),
plunger means (7) disposed for reciprocating movement in said bale case (6)to thereby compact said charges and advance such compacted charges towardan exit opening therein,
knotter means (8) for tying twine in a form-stabilizing manner aroundsuccessive increments of compacted crop material while they advance insaid bale case (6) to form bales of which the density at least partiallyis determined by the dimensions of said variable cross-sectional area(18),
sensor means (48) for detecting the tensile forces occurring in said twineduring bale formation and producing signals representative of said tensileforces,
control means coupled to said sensor means,
positioning means operatively associated with said wall portion,
said signals produced by said sensor means (48) are transmitted to saidcontrol means (24), which control means is operable to control saidpositioning means (16, 20) to move said at least one wall portion (14) tothereby vary said cross-sectional area (18) of said bale case (6) in amanner to control the density of the crop material compacted by saidplunger means (7), the improvement wherein
said control means (24) comprises a micro-processor (24) in which thevalues of the sensor signals are compared with a predetermined thresholdvalue entered into said micro-processor (24) through an operator panel(28); said micro-processor (24) being programmed in a manner such that,when the force values exceed said predetermined threshold value, saidpositioning means (16, 20) move said at least one wall portion (14) in adirection to enlarge said cross-sectional area (18) of said bale case (6)for correspondingly decreasing the bale density and thereby reducing saidtensile forces experienced in said twine.
2. A baler according to claim 1 wherein said predetermined threshold valueis proportional to the strength characteristics of said twine used duringthe baling operation.
3. In a rectangular baler comprising
a bale case (6) into which successive charges of crop material areintroduced and having at least one wall portion (14) which is movablegenerally laterally thereof to vary the cross-sectional area (18) of saidbale case (6),
plunger means (7) disposed for reciprocating movement in said bale case (6)to thereby compact said charges and advance such compacted charges towardan exit opening therein,
knotter means (8) for tying twine in a form-stabilizing manner aroundsuccessive increments of compacted crop material while they advance insaid bale case (6) to form bales of which the density at least partiallyis determined by the dimensions of said variable cross-sectional area(18),
sensor means (48) for detecting the tensile forces occurring in said twineduring bale formation and producing signals representative of said tensileforces, the improvement wherein said knotter means (8) comprises
at least one knotter (8) having a twine holder (32) operable to hold,during the baling operation, a leading strand of twine (30, 49);
a rotary billhook (33), which is disposed in a fixed position relative tosaid twine holder (32) during a substantial portion of a bale formingcycle during which a portion (49) of said leading strand of twine (30, 49)extends from said twine holder (32) towards and over said billhook (33);and
said sensor means (48) is mounted between said twine holder (32) and saidbillhook (33) in a manner such that said portion of twine (49) issupported thereby along its course from said twine holder (32) towardssaid billhook (33).
4. A baler according to claim 3 wherein said sensor means (48) comprises anelongated rod-shaped body (48), one end of which is releasably attached ina cantilevered fashion to a rigid extension (50) of said knotter (8) andthe other end of which supports said portion of twine (49).
5. A baler according to claim 4 further comprising strain gauges (52)operatively connected to said sensor body (48); the arrangement being suchthat the tensile forces experienced in said twine portion (49) are, atleast partially, transmitted to said sensor body (48) which, as a result,is deflected proportional therewith; said deflection being sensed by saidstrain gauges (52) which produce signals representative thereof.

DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic side elevational view of a rectangular balercomprising a knotter station on top of the bale chamber.
FIG. 2 is an enlarged side view of the knotter station incorporating asensor means.
FIG. 3 is a curtailed view of one knotter with certain parts removed, takenalong arrow V in FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to FIG. 1, the baler is basically conventional in that itcomprises a main frame 1 fitted with a pair of ground-engaging wheels 2and a tow bar 3, arranged to be attached to a tractor (not shown). Apick-up mechanism 4 picks up crop material from the ground and delivers itto a feed chamber 5 from where it is transferred to a bale case or chamber6 in which a bale of crop material is formed. A plunger 7 is reciprocablewithin the bale chamber 6 to act upon wads of crop material transferredfrom the feed chamber 5 into the bale chamber 6 and to compress these wadsinto a bale which, during formation, is moved progressively along the balechamber 6 from left to right as seen in FIG. 1. A completed bale is tiedwith twine or the like at a knotter station 8 and rearwardly dischargedfrom the machine.
The bale chamber 6 comprises a forward portion 10 with fixed dimensions anda rearward portion 12 of which the dimensions can be varied by means ofmovable top and side rails 14. A tension adjusting mechanism 16 isprovided for moving the rails 14 to thereby vary the cross-sectional areaof region 18 of the bale chamber 6 and as such controlling the density ofthe bales produced. The tension adjusting mechanism 16 includes ahydraulic cylinder unit 20 for moving the movable rails 14 and a currentcontrolled pressure valve 22 for controlling the hydraulic cylinder unit20. A micro-processor based control circuit 24 controls the operation ofthe baler and provides a pulse width modulated signal over lead 26 tocontrol valve 22. An operator's control and indicator panel 28 is providedso that an operator may observe indications of operating conditions invarious parts of the baler and may manually key in control data such asrelated to bale density for example. The construction of the bale chamber6 and the operation of the control circuit 24 as schematically shown inFIG. 1 are respectively described in more details in EP-B-0.152.970 andEP-B-0.223.351, to which reference is made.
Referring more specifically to FIGS. 1 and 2, the knotter station 8comprises a plurality of knotters which are transversely spaced on top ofthe bale chamber 6 and which all operate in the following identicalmanner. Arranging a strand of twine around a bale usually starts withclamping a leading end of the strand 30 in a twine holder 32 from where itprojects downwardly over a billhook 33 and a twine guiding member 34through the bale chamber 6. As the crop material is compressed andprogressively moved towards the exit of the bale case 6, the twine istaken along so that it extends along the top of the bale, down the leadingend thereof and beneath the lower surface of the bale. From there, thetwine extends through an eye in the forward end of a curved needle 35comprised in a pivotable needle assembly 36. A star wheel 38 isoperatively coupled to the knotter station 8 and monitors the bale lengthas a bale progressively is formed. When a bale has been formed to adesired extent, the tying operation is initiated by arcuately moving theneedle assembly 36 to project the forward ends of the needles 35 upwardlythrough the bale case 6 and into the region of the billhook 33 and thetwine holder 32 in order to carry a trailing strand of twine intoassociation with the leading strand of twine already clamped in the twineholder 32, whereafter both strands are knotted together by the billhook33. To free the knotted loop from the knotter 8, both strands are cut fromthe twine holder 32 by moving the twine guiding member 34, which supportsa knife 40, across the billhook 33 meanwhile stripping the knot therefrom.
It will be appreciated by a person skilled in the art that the cyclicmovement of the needle assembly 36 not only ensures the delivery of atrailing strand of twine to the twine holder 32 for tying a completed balebut moreover at the same time initiates the formation of a new bale byproviding the twine holder 32 with a new leading strand of twine.
As best seen in FIG. 2, all knotter components, such as the twine holder32, the billhook 33 and the twine guiding member 34, are incorporated in aknotter frame 42, which in turn is supported on the one hand by a knottershaft 44 and on the other hand by a support arm 46, rigidly connected tothe baler frame 1. The knotter shaft 44 furthermore is operative to driveall movable components of each knotter 8.
In the preferred embodiment of the present invention, a rod shaped sensor48 is provided intermediate the twine holder 32 and the billhook 33 in amanner such that the normally straight course of the leading twine portion49 therebetween becomes slightly upwardly angled as a result of saidportion 49 now supplementary being supported intermediate its course bythe sensor 48. As a knotter is inherently a relatively complicated andcompact arrangement, several functional limitations are to be taken intoaccount for positioning the sensor 48 properly in the confined space asproposed hereabove in order to avoid interference of operation between thesensor 48 and the twine holder 32, the billhook 33, the twine guidingmember 34 and the needle 35.
With particular reference to FIGS. 2 and 3, the sensor 48 is disposedgenerally horizontally and perpendicularly to the course of the leadingportion of twine 49, with the distal end of the sensor 48 supportingportion 49. The sensor 48 is provided with a threaded end for releasableconnection to a rigid arm 50 which forms a unitary structure with theknotter frame 42. Any deflection of the sensor 48 caused by a load imposedon the distal end thereof as a result of twine tension, is registered bystrain gauges 52, which are suitably disposed onto the sensor 48intermediate its ends and are operatively connected to the microprocessor24.
It will be clear that during the complete formation of a bale, exceptionmade of the actual tying cycle, the relative position of the twine holder32, the sensor 48 and the billhook 33 with respect to each other remainunchanged. In other words, whether a new bale only just has been started,whereby the leading strand of twine 30 extends nearly vertically, orwhether bale formation is reaching completion, whereby said strand 30 liesnearly horizontally, the enclosed angle .alpha. of the twine portion 49effected by the sensor 48 remains the same throughout the process offorming a bale. The foregoing thus implies that tensile forces of a givenvalue F in the twine portion 49 always result in a corresponding compoundforce of a given value F' acting on the sensor 48 in a predetermineddirection, being the bisector of the enclosed angle .alpha., irrespectiveof the stage of the bale formation.
Notwithstanding the foregoing, it nevertheless should be mentioned that theleading strand of twine 30 is also partially wrapped around the twineguiding member 34, to a degree dependent on the stage of the baleformation. Consequently, the more a bale under formation grows, the largerthe angle of enclosure of the leading strand 30 around the twine guidingmember 34 becomes, whereby a fraction of the tensile forces experienced inthe twine 30 is transformed in frictional forces. However, this fractionis virtually neglectable, the more that the influence thereof is minimalduring the first stage of the formation of a new bale; a stage which isconsidered to be the most critical for being confronted with twinefailure.
The value of the force F' on the sensor 48 is sensed by the strain gauges52 and translated in an electrical signal. In an ideal situation, there isa linear relationship between the electrical output of the strain gauges52 and the forces F' imposed on the sensor 48. In practice however, theremight be a slight deviation from the linear behaviour as a result of thenon-linear characteristics of the strain gauges 52 on the one hand and thecharacteristics of the binding material on the other hand. However,deviation electronically may be compensated.
Turning now to the actual operation of the sensor 48 during the formationof a bale, it will be appreciated from the foregoing that the value of theelectrical signals produced by the strain gauges 52 are proportional tothe tensile forces experienced in the twine portion 49, generated thereinas a result of resistance to sliding of the twine 30 between a completedbale and a new bale to be formed. These signals are compared in themicro-processor 24 with a preset threshold value, which is predeterminedin accordance with the characteristics of the binding material used. Aslong as the twines are subjected to loads which stay below thepredetermined acceptable level, bale density may be controlled by theelectronic bale density controller 24 such as disclosed in EP-B-0.223,351.However, if for one or other reason the binding material becomes tooheavily tensioned, thereby exceeding the preset value, priority is givento the output of the twine force sensor 48, in accordance to which themicro-processor 24 instructs the cylinder unit 20, through the pressurevalve 22, to immediately decrease the tension on the top and side rails 14of the bale chamber 6 in order to correspondingly decrease the tensileforces in the bale binding material so that twine failure is avoided.Twine overload most frequently may occur during the first plunger strokesin the formation of a new bale, as already mentioned, meaning that thetwine force sensor 48 usually only has to interfere with the normaloperation of the baler, more specifically in respect to the bale densitysetting, during this reduced stage of bale formation. In case the densitysettings of the baler would be so demanding that a continuous or at leasttoo frequent interference of the twine force sensor 48 would be required,then either the operator has to be warned through his indicator panel 28of the intolerable situation enabling him to manually change predetermineddensity settings or the normally operating bale density controller 24automatically may interfere to lower the density demands.
When bale formation approaches completion, twine forces usually are low.However, during the actual tying cycle, the leading and trailing strandsof twine are forcefully stripped from the sensor 48 due to the rotation ofthe billhook 33, imposing a considerable peak-load on the sensor 48,whereby a one-time signal is created which is representative for and canbe recognised as the completion of one bale and the initiating step in theformation of a subsequent one. It will be evident to a person skilled inthe art that, although the one-time peak-load may exceed the preset value,the density setting of the bale chamber 6 should not be modified as aresult thereof. Again, care thereof can be taken by the micro-processor24.
To facilitate the removal of the leading and trailing strands of twine fromthe sensor 48 during the tying cycle, the sensor 48 may be conicallyshaped or have a distal end which is slightly bent downwardly for bettercooperation with the billhook 33.
As an alternative, the cantilevered type sensor 48 may be replaced by aresiliently supported hingeable finger, movement of which can be measuredby a displacement transducer such as a linearly variable differentialtransformer (LVDT), which is well known in the art. Displacement of thehingeable finger is proportional to the load imposed thereon and thereforeis representative of the forces experienced in the twine.
Instead of employing the sensor 48 with the strain gauges 52, it also canbe proposed in another arrangement to provide the twine guiding member 34with strain gauges in order to detect deformations of member 34 as aresult of twine forces.
Considering further that the twine forces are transmitted to the twineholder 32 and hence to the knotter frame 42, the latter as a result aimsto rotate around the shaft 44 but is prevented from doing so by thesupport arm 46. In still another arrangement, a dynamometer may beprovided to measure the forces created in the support arm 46 which arealso representative of the twine forces. Eventually, deflections of thetwine holder 32 also can be used as a basis for determining twine forces.
While the preferred structure in which the principles of the presentinvention have been incorporated is shown and described above, it is to beunderstood that the invention is not to be limited to the particulardetails, as shown and described above, but that, in fact, widely differentmeans may be employed in the practice of the broader aspects of theinvention.