Abstract:
A square baler having a baling chamber, a plunger reciprocable at one end of the baling chamber, a pre-compression chamber where charges of crop are amassed and pre-compressed by a rotor prior to transfer into the baling chamber. A transducer is provided for producing an electrical output signal indicative of the load on the rotor and a processing circuit is operative to estimate the rate of crop flow into the pre-compression chamber by analysing the output signal of the transducer over a complete filling and emptying cycle of the pre-compression chamber.

Description:
[0001]    This application is the US National Stage filing of International Application Serial No. PCT/EP2014/052531 filed on Feb. 10, 2014 which claims priority to Belgian Application BE2013/0099 filed Feb. 14, 2013, each of which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a square baler and is concerned with controlling the operation of the baler to produce well formed bales of uniform density. 
       BACKGROUND OF THE INVENTION 
       [0003]    In a square baler, crop is picked up from the ground by means of a rotary pickup having radially projecting tines. The crop picked up from the ground is advanced towards a rotor arranged at the lower end of an arcuate chute. The rotor serves to compress the crop into the arcuate chute, the latter acting as a pre-compression chamber. 
         [0004]    When a plunger reciprocating in a baling chamber of the baler is at the bottom dead centre position of its reciprocating cycle, a stuffer displaces the crop present in the pre-compression chamber into the baling chamber, the crop becoming a slice of the bale in the process of being formed. Once the bale in the baling chamber has reached a certain size, twine is wrapped around the bale and knotted to form a finished bale. The finished bale remains in the baling chamber while the next bale is being formed and is eventually discharged from the rear end of the baler. 
         [0005]    As square balers are well known and documented, it is believed that the above brief description will suffice for an understanding of the present invention. 
         [0006]    In order to produce well formed bales of uniform density, it is desirable to ensure that the density of the crop in the pre-compression chamber is at a desired level when a stuffer cycle is initiated. The stuffer cycle must of course be synchronised with the movement of the plunger of the baling chamber and can only take place at the end of a whole number of cycles of the plunger in the baling chamber. 
         [0007]    If, for example, a stuffer cycle is performed every three cycles of the plunger in the baling chamber, it would be undesirable for the crop density in the pre-compression chamber to reach the desired level either after two and half plunger cycles or three and half plunger cycles. In the former case, the crop density would be too great by the time the crop is transferred to the baling chamber. In the latter case, if a stuffer cycle is initiated by a pressure sensor in the pre-compression chamber, the stuffer cycle could be delayed by a complete plunger cycle. 
       OBJECT OF THE INVENTION 
       [0008]    It is therefore desirable to be able to estimate crop flow rate into the pre-compression chamber in order to be able to ensure that the crop density attains a desired level at the time that it is transferred into the baling chamber. 
       SUMMARY OF THE INVENTION 
       [0009]    According to the present invention, there is provided a square baler, comprising a baling chamber, a plunger reciprocable at one end of the baling chamber, a pre-compression chamber within which charges of crop are amassed and pre-compressed by a rotor prior to transfer into the baling chamber, and a pickup roller having radially projecting tines for picking up crop from the ground and advancing the crop to the rotor, characterised by a transducer for producing an electrical output signal indicative of the load on the rotor and a processing circuit operative to estimate the rate of crop flow into the chute by analysing the output signal of the transducer over a complete filling and emptying cycle of the pre-compression chamber. 
         [0010]    In the case of forage harvesters and combine harvesters, it has been previously proposed to use the load on various parts of the crop transport mechanism, to indicate the rate of flow. However, in such agricultural machines, the measured load does not undergo cyclic variation. By contrast, in a square baler, the load on the rotor varies during a complete filling and emptying cycle of the pre-compression chamber. At the commencement of a cycle, the pre-compression chamber is empty and little resistance is encountered in advancing the crop received from the pickup roller into it. Initially, the crop will not reach the opposite end of the chamber but will remain near the rotor. For more crop to be introduced into the pre-compression chamber, the crop already in the pre-compression chamber needs to be moved along towards the opposite end and this results in the rotor meeting progressively increased resistance. Once the pre-compression chamber is full, the rotor meets still further increased resistance as it attempts to compress the crop. Finally, on initiation of the stuffer cycle, the load on the rotor drops as the opening between the pre-compression chamber and the baling chamber is uncovered while the stuffer empties the pre-compression chamber by transferring its contents into the baling chamber. 
         [0011]    Despite the fluctuating nature of the output signal of the load measuring transducer, it has been found that by analysis of the waveform over a complete cycle, it is possible to estimate the crop flow rate entering the pre-compression chamber. 
         [0012]    A first parameter of the output signal that has been found to be related to the crop flow rate is the value of the peak load on the rotor. 
         [0013]    Though this value varies with the rate of crop flow, it does not allow for other drag forces acting on the rotor. For this reason, the difference between the maximum and minimum of the measured output signal has been found to be a more useful parameter. 
         [0014]    A further parameter that may be used is the average rate of increase of the measured load during the time that the pre-compression chamber is being filled. 
         [0015]    The rate at which crop is picked up will vary with the density of the crop on the ground and with the speed of travel of the baler. If the crop is sparse, then the baler can be moved faster to achieve the desired flow rate to reach the desired crop density in the pre-compression chamber just as the plunger of the baling chamber reaches it bottom dead centre position. The reading from the crop flow sensor may therefore be used to provide the operator with advice on when to increase or decrease the speed of the baler. 
         [0016]    In addition to using the crop flow rate to set a recommended baler speed, it may be used to vary the volume of the pre-compression chamber. The pre-compression chamber may have a movable wall to vary its volume and this provides a correction parameter that has a faster reaction time than the speed of the baler. If the crop flow rate is likely to result in excessive crop density in the pre-compression chamber, then its size may be increased relatively rapidly to ensure that a uniform crop density is admitted into the baling chamber in each cycle, even though the mass of the crop may vary between slices. 
         [0017]    In order to measure the load on the rotor, the load sensing transducer may be responsive to the tension in a chain driving the rotor. 
         [0018]    A sprocket may be mounted in engagement with a run of the drive chain and the transducer may serve to measure the force acting to displace the sprocket in a direction perpendicular with the run of the chain. 
         [0019]    Alternatively, the transducer may take the form of a torque measuring load cell mounted on the axle of the rotor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: 
           [0021]      FIG. 1  is a schematic representation of the moving parts of a square baler, 
           [0022]      FIG. 2  shows a transducer for measuring the tension in a chain driving the rotor, to determined the load on the rotor, 
           [0023]      FIG. 3  is a graph showing the variation in the output signal of the load sensing transducer during a filling and emptying cycle of the pre-compression chamber, and 
           [0024]      FIG. 4  is a schematic diagram of circuitry for analysing the output of the rotor load sending transducer in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0025]      FIG. 1  shows a flywheel  10  that is connected by an input shaft to the power takeoff shaft of a tractor (not shown). The flywheel drives a gearbox  12  that serves to rotate a crank arm  14  to cause reciprocating movement of a plunger  16 . The plunger  16  reciprocates within a baling chamber (not shown) to compress slices of crop that are introduced into the baling chamber by means of a pre-compression chamber  18 . The transfer of crop from the pre-compression chamber  18  to the baling chamber is effected by a stuffer mechanism  20 , also driven by the gearbox  12 , the end of a stuffer arm  22  following a kidney shaped path represented by a dotted line  24  in  FIG. 1 . As so far described, all the components are conventional and are operated in a conventional manner. 
         [0026]    The present invention is concerned only with ensuring that the crop amassed in the pre-compression chamber  18  has a desired density at the commencement of a stuffer cycle. In order to achieve this objective, it is necessary to measure the flow rate of crop into the pre-compression chamber  18 . 
         [0027]    The crop is introduced into the pre-compression chamber by a pickup roller  30  that has radially projecting tines. Crop picked up from the ground by the tines is advanced towards a powered rotor  32  that may serve as a chopper but the primary function of which is to compress the crop into the pre-compression chamber  18 . 
         [0028]    In order to measure the flow rate, a transducer is provided to determine the load on the rotor  32 . Such a transducer could take the form of a load cell built into the axis of the rotor  32  to measure the torque applied by its drive sprocket but to avoid modification to the axle it is possible to use a transducer as shown in  FIG. 2 . In  FIG. 2 , a transducer  40  is connected to a an idler sprocket  42  acting on a run of a chain  44  serving to transmit torque from a sprocket  46  driven by the gearbox  12  to a drive sprocket  48  of the rotor  32 . As the load on the rotor  32  increases, the tension in the chain  44  increases and applies a force in the direction of the arrow  50  which is measured by the transducer. The transducer may be a load cell or it may measure the compression spring (not shown) urging the idler sprocket  42  in a direction to maintain the tautness of the chain. 
         [0029]    During the course of a filling and emptying cycle of the pre-compression chamber  18 , the output signal of the transducer will vary in the manner shown schematically in  FIG. 3 . Essentially, the resistance to rotation of the rotor is at a minimum at the commencement of a cycle when filling begins, and increases to a maximum once the pre-compression chamber is full and its contents are being compressed. The resistance then drops as the pre-compression chamber is emptied by the stuffer  20  transferring its contents to the baling chamber while the plunger is near the bottom dead centre position of its stroke. 
         [0030]    In the present invention, the mean crop flow rate is determined from analysis of the waveform in  FIG. 3 . One of the parameters that varies with the flow rate is the maximum value. Assuming that a stuffer cycle occurs after a predetermined number of plunger cycles, then the density of the crop at the time of the transfer into the baling chamber will clearly depend on the crop flow and this affect the maximum load on the rotor. 
         [0031]    The maximum value will however also be affected by other loads acting on the rotor, for example friction and to eliminate the effect of such other factors on the estimated crop flow rate, it is preferred to rely on the difference between the minimum and maximum load on the rotor  32 . 
         [0032]    A parameter still more closely indicative of the crop flow rate is the average rate of increase in the load while the pre-compression chamber is being filled, that is to say the slope of the line designated  60  in  FIG. 3 . This gradient not only takes into account the difference between the minimum and maximum values of the resistive load on the rotor  32  but also the time it takes to fill the pre-compression chamber. It is possible for example to achieve the same difference and maximum load while actuating the stuffer mechanism once every three cycles of the plunger or once during every four cycle of the plunger. Clearly, however, the crop flow rate will be higher if it takes only three cycles of the plunger to fill the pre-compression chamber to the desired density. 
         [0033]    In  FIG. 4 , the output of the load cell  40  is supplied to a digital processor  70  that is suitably programmed and connected additionally to receive signals from a ground speed sensor  72  and gearbox speed sensor  74 . The gearbox speed signal is used to determined the duration of the reciprocation cycle of the plunger  16 . 
         [0034]    The time that it should take for the pre-compression chamber to be filled with crop up to a density within a desired range should coincide with a whole number multiple of the time it takes for the plunger  16  to perform a complete cycle of reciprocation. This is because a stuffer cycle can only be performed when the plunger  16  is at its bottom dead centre position, in which position the plunger  16  uncovers an opening that connects the pre-compression chamber  18  to the baling chamber. From a knowledge of the duration of the reciprocation cycle of the plunger  16 , the processor  70  can determine whether the crop pickup rate needs to be increased or decreased to achieve a crop density within a desired range at the correct time. 
         [0035]    The rate at which crop is picked up from the ground is of course dependent upon the speed at which the baler has driven over the ground. In an embodiment of the invention, the processor  70  can provide advice to the operator of the baler through a display screen  76  to increase or decrease the ground speed in order to improve the quality of the finished bales. 
         [0036]    Such speed control of the baler does not have a very rapid response, as the operator cannot be expected to accelerate or brake sharply to vary the crop density in the pre-compression chamber. It is therefore alternatively possible to vary the volume of the pre-compression chamber  18  to achieve slices of different thickness but of the desired density. It is known that the pre-compression chamber may have a movable wall and in the embodiment of the invention shown in  FIG. 4  such a movable wall is positioned by means of closed loop control circuit  78  to maintain a desired density, the volume of the pre-compression chamber being increased when the density is estimated to be too high and decreased when the predicted density is estimated to be too low.