Abstract:
A large rectangular baler includes pick-up and packer rotors, a pivotable stuffer, a plunger head, a knotter shaft and a needle yoke, and tension panels that are all driven hydraulically and independently controlled through electrically controlled valves that actuate the various hydraulic power devices used to power the various functions. An electronic control unit is coupled to each of the control valves and receives feedback signals from the controlled functions which are compared with values representing desired function results so as to further control the valves to attain the desired results. In addition to the feedback signals from the powered functions, signals from a bale length sensor and a ground speed sensor are also coupled to the electronic control unit for use in controlling the powered functions.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a large rectangular baler and, more specifically, relates to a drive and control system for such a baler. 
     BACKGROUND OF THE INVENTION 
     The power systems for large rectangular balers typically include mechanical drives including gear transmissions and shafts for transferring power from a power take-off of a tractor to drive the various functions of the baler such as the pick-up, pre-charge chamber packer, charge stuffer, plunger, needles and knotters. The speeds at which those of these functions that deal with the delivery of crop to the baling chamber are driven, with respect to each other, is pre-selected and designed into the baler by the selection of the gearing. This has the drawback that there is no way to easily adapt the operation of the baler to different crops or changing crop conditions as is desired for more efficient operation. For example, it might be desired to operate the pick-up and/or packer at a slower or faster speed, depending on whether the crop windrow is light or heavy or the crop itself is relatively dry and brittle or somewhat damp and tough, or depending upon the speed at which the baler is towed. This ability has the benefit of being able to handle the crop in a gentler manner which is especially helpful in reducing leaf loss when baling alfalfa, for example, and to reduce the possibilities of plugging the baler. 
     U.S. Pat. Nos. 6,161,368; 6,073,426 and 5,894,718 disclose various large rectangular baler control systems for mechanically driven balers which address crop feeding concerns, with the &#39;718 patent disclosing an embodiment including a planetary transmission with which an electric or hydraulic motor is associated so as to be able to change the drive speed and/or direction, however, this speed and/or direction change affects the entire drive system, which may not be desirable. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided an improved control system for a large rectangular baler. 
     An object of the invention is to provide a large rectangular baler control system including various drives constructed for being driven and controlled independently of one another for achieving operational efficiency of the baler. 
     A more specific object of the invention is to provide a large rectangular control system wherein the speed of the pick-up and/or packer arrangements can be varied at will without affecting the speed of operation of any other driven function. 
     Yet another object of the invention is to provide a large rectangular baler having independently controlled, hydraulic drive components for supplying power to all powered functions of the baler. 
     A more specific object of the invention is to use an electronic control unit capable of storing desired function values and for receiving feedback signals from controlled functions so that signals for operating control valves of the various hydraulic functions may continuously take into account the feedback signals for achieving the desired function value. 
    
    
     These and other objects of the invention will become apparent from a reading of the ensuing description together with the appended drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a somewhat schematic, left front perspective view of a large rectangular baler embodying the control system of the present invention. 
     FIG. 2 is a schematic, left side elevational view of the baler shown in FIG. 1, with the left side of the baling chamber being removed to reveal the relationship of the plunger head to the inlet located in the bottom of the baling chamber. 
     FIG. 3 is a right side elevational view of the feed duct, with parts in section, showing the pre-charge chamber and the packer and stuffer arrangements associated with it. 
     FIG. 4 is a schematic top plan view of the forward end of the baler showing the drive arrangement for the separate hydraulic pumps for supplying pressure fluid for driving the plunger head and auxiliary functions. 
     FIGS. 5 a  and  5   b  together show a schematic diagram of the electro-hydraulic control system of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIGS. 1 and 2, there is shown a large rectangular baler  10  including a main frame  12  supported on right- and left-hand sets of tandem wheels  14  for being towed over the ground by a tractor coupled to a forward end of a draft tongue  16 , which is fixed to a forward end of the frame  12 . A longitudinally extending baling chamber  18 , of rectangular or square cross-section, is supported centrally on the frame  12  at an elevation above the sets of wheels  14 . 
     A plunger head  20  is mounted in a forward section of the chamber  18  for being reciprocated through the action of a toggle linkage defined by a pair of transversely spaced first links  24  and a second link or crank arm  26 . The links  24  and  26  are pivotally coupled to each other at a pivotal connection  28 , with the pair of first links  24  being pivotally coupled to the plunger head  20  at respective pins  30 , and with the second link  26  being coupled to the frame  12 , as at a pin  32 . A hydraulic plunger head drive cylinder  34  is provided for toggling the links  24  and  26 , and for this purpose has a rod end coupled, as at a pin  36  to a location of the link  26  that is between the pivotal connections  32  and  28 , and has a rod end coupled to the frame  12 , as at pivot pin  38 . When the drive cylinder  34  is fully retracted, as shown in FIG. 2, the plunger head  20  is fully extended to the rear, with the pins  30  and  32  being located such that they lie along a longitudinal central axis of the baling chamber  18 . Extension of the cylinder  34  will cause the link  26  to be pivoted upwardly about the pin  32  resulting in the plunger head  20  being retracted to the extent that it uncovers a crop material inlet  40  extending entirely across a region located just in front of a stationary knife (not shown) provided across a forward end  42  of a bottom wall or floor  44  of the baling chamber  18 . 
     The baling chamber  18  includes a front section  46  of fixed cross section which is joined to a rear section  48 , of variable cross section, having opposite side panels  50  which are respectively mounted for swinging horizontally about vertical hinges (not shown) provided at their forward ends. Located at opposite sides of the baling chamber  18  are a pair of tension control cylinders  52 , each being coupled between upper and lower bell cranks  54  and  56 , respectively, having first legs respectively pivotally anchored to respective outer ends of upper and lower, transverse support members  58  and  60 , and having respective second legs pivotally coupled to the side panels  50 . Contraction of the cylinders  52  causes the side panels  50  to pivot towards each other to decrease the cross sectional area of the rear baling chamber section  48 , and thus, further restrict rearward movement of a formed bale  62  so as to increase the density of a forming bale  64 , and with extension of the cylinders  52  causing the side panels to pivot away from each other to increase the cross section of the chamber section  48  so as to cause the density of the forming bale  64  to decrease. 
     A twine tying arrangement  70  (omitted from FIG. 2) is provided for wrapping and tying multiple loops of twine about the completed bale  62  and includes a plurality of knotter drive gears  72 , here shown as being six in number, mounted at transversely spaced locations on a knotter shaft  74  that is rotatably mounted to the top of the baling chamber  18 . A needle yoke arrangement  76 , including opposite arms  78  joined by a cross tube  80 , is mounted for vertical pivotal movement about a horizontal transverse axis defined by pivotal connections  82  that connect respective ends of the arms  78  to opposite side locations of rear regions of the fixed front baling chamber section  46 . A plurality of curved, twine delivery needles  84 , equal in number to the knotter drive gears  72 , are respectively fixed to transversely spaced locations of the cross tube  80 . A crank arm  86  is provided at each of opposite ends of the knotter shaft  74 , and pivotally connected between each crank arm  86  and a plate  88  fixed to each needle yoke arm  78 , at a location close to the pivotal connection  82 , is a connecting rod  90 . 
     The knotter drive gears  72  and the needle yoke assembly  76  are both operated through the action of an extensible and retractable hydraulic knotter drive cylinder  92  (omitted from FIG. 2) connected between the frame  12  and one end of a length of roller chain  94 , that engages teeth of a sprocket (not visible) forming part of a one-way clutch  95  mounted to the shaft  74 , the other end of the chain  94  being fixed to one end of a coil extension spring  96  having its other end fixed to the frame  12 . The chain  94  drives the sprocket when the hydraulic cylinder  92  is retracted, this rotation being transferred to the shaft  74  by the one-way clutch  95  coupled between the sprocket and the shaft  74 . The rotation of the shaft  74  results in the needle yoke assembly  76  being swung vertically to deliver twine to knotters (not shown) coupled for being driven by the knotter drive gears  72  of the twine tying assembly  70 , the knotters each operating to tie a second knot to complete a twine loop about the bale just being completed, and to tie a first knot between twine ends of two strands of twine for being looped about the new bale being formed, all in one cycle of the needles. The one-way clutch  95  operates for permitting the extension spring  96  to unload and reset the hydraulic cylinder  92  for the next tying cycle without causing reverse rotation of the shaft  74  which already has the knotter gears  72  in position for the next tying cycle. 
     The bale tying cycle is initiated by a bale length sensor arrangement including a toothed metering wheel  98  (omitted from FIG. 2) mounted on a shaft  100  extending horizontally across and being rotatably mounted to the top of the baling chamber  18 . The metering wheel  98  has a toothed periphery which extends into the baling chamber  18  and is contacted by a forming bale so as to be rotated as the bale grows in length. In a manner explained more fully below, the rotation of the metering wheel is sensed and converted into a signal representing bale length, with a control signal being sent to initiate the tying cycle when the forming bale reaches a length corresponding to a desired bale length. 
     Referring now also to FIG. 3, there is shown a feed duct or chute  102  having an open forward end section  104 , disposed for receiving crop from a pick-up arrangement  106 , and being curved upwardly and rearwardly from the forward end section to a near vertical rear end located for delivering crop through the baling chamber inlet  40 . The pick-up arrangement  106  includes a rotary tine pick-up  107 , including a drive rotor or shaft, and a pair of stub augers  109  following the pick-up  107  for centering crop to the width of the baling chamber  18 . The duct  102  defines a pre-charge chamber  108  into which crop material delivered by the pick-up arrangement  106  is fed by a packer fork arrangement  110 . Upon the material being compressed to a pre-selected density within the pre-charge chamber  108 , a stuffer arrangement  112  engages a pre-compressed charge of crop material, sometimes called a flake or slice, and sweeps it from the pre-charge chamber  108  and into the baling chamber  18 , by way of the baling chamber inlet  40 . 
     The packer fork arrangement  110  includes a crank shaft  114  having opposite ends mounted for rotation in frame supports  116  and including a radially offset crank section  118  having a fork tine mounting tube  120  mounted to it for oscillating thereabout. Fixed at spaced locations along the tube  120  are a plurality of wedge-shaped packer tines  122 . Fixed to opposite ends of the tube  120  and projecting in a direction opposite from the tines  122  are arms  124  having their radially outer ends respectively coupled to first ends of a pair of guide or radius links  126  by pins  128 , with second ends of the radius links  126  being respectively pivotally anchored to the frame  12  by pivot pins  130 . A reversible hydraulic motor  132 , shown only in FIG. 5 b , is coupled for driving the shaft  114  in the clockwise direction, as considered in FIG. 3, during normal baling operation so that the packer tines  122  are caused to reach through respective slots  134 , provided in an upwardly and forwardly flared, upper forward wall section  136  of the duct  102 , and sweep crop material rearwardly into the open forward end section  104  of the duct  102 . 
     Provided for retaining crop material in the duct  102  until it has reached a predetermined degree of pre-compression, i.e., a predetermined density, is a retaining fork arrangement  138  including a horizontal, transverse shaft  140  having opposite ends rotatably mounted in a pair of brackets  142  fixed to a bottom wall  144  of the duct at a location spaced downwardly from a lip  146  extending the width of, and defining a rear end of, the bottom wall  144 . The fork arrangement  138  further includes a plurality of transversely spaced, hook-shaped retainer tines  148  fixed at transversely spaced locations along the shaft  140  and having upper, forwardly extending ends  150  located at a height greater than that of the duct lip  146 . The retainer tines  148  are pivoted with the shaft  140  between a retaining position, as shown, wherein the tine ends  150  extend over the lip  146  and into the end of the duct  102  so as to define an upper end of the pre-charge chamber  108 , and a release position (not shown), wherein the tine ends  150  are withdrawn from the duct  102  so as to permit the free discharge of the pre-compressed charge of crop material out of the duct  102  and through the baling chamber inlet  40 . A crank arm  152 , shown only in FIG. 5 b , is coupled to the shaft  140 , and coupled between the crank arm  152  and the frame  12  for selectively moving the tines  148  between their retaining and release positions is an extensible and retractable hydraulic tine cylinder  154 , also shown only in FIG. 5 b.    
     The retaining fork arrangement  138  operates in conjunction with a density sensor  160  including a hinged, spring-loaded, rectangular door  162  provided in, and extending across the width of, the bottom wall  144  of the duct  102  adjacent a forward end thereof in a location downstream from the area swept by the packer fork tines  122  of the packer assembly  110 . The tine ends  150  of the retaining fork arrangement  138  remain in their retaining position until the pressure of the compressed crop deflects the door  162  to an extent which corresponds to a condition when the pre-compressed charge of crop material reaches a pre-selected density. The density sensor  160  then sends a signal, in a manner described below, which actuates the tine cylinder  154  of the retaining fork arrangement  138  so that it is caused to be moved from its retaining position to its release position. The plunger head cylinder  34  is then in an extended condition wherein the plunger head  20  is retracted to a location forward of the baling chamber inlet  40 . The stuffer arrangement  112  is then operated to move the pre-compressed charge of crop material into the baling chamber  18 . 
     Specifically, the stuffer arrangement  112  includes a frame  164  located centrally above the duct  102  and fixed to a transverse pivot shaft  166  that is mounted for rotation in bearing holders  168  that are fixed to the frame  12  at transversely spaced locations, substantially vertically above the density sensor  160 . A guide tube  170  is fixed to the frame  164  and is oriented so as to be angled slightly rearward of vertical from top to bottom when the frame  164  is in an extreme forward position, as shown. For a purpose explained below, the interior of the guide tube  170  is splined, and mounted for reciprocation in the guide tube  170  is a support bar  172  having complementary splines formed thereabout along its length. A lower end of the support bar  172  is received between opposite legs of a transversely extending tine support  174 , that is in the form of a U-shaped channel, and is secured therein by spaced bolts  176  received in respective aligned sets of holes provided in the support bar  172  and the legs of the tine support  174 . Fixed, as by welding, at transversely spaced locations along the length of the web of the tine support  174  are a plurality of stuffer tines  178  that are wedge-shaped in profile and are arranged so that they taper to a point in a direction away from the tine support  174 . 
     A cross support  179 , which is generally C-shaped in cross section, is fixed to, and forms a joint between, a forward end of a rear upper wall section  182  of the duct  102 , that extends from the support  179  to the rear end of the duct  102 , and the rear end of the flared, upper forward wall section  136  of the duct  102 . The cross support  179  is located opposite from the door  162  in the lower duct wall  144 , and extending rearwardly in the upper rear wall section  182 , from a location adjacent the cross support  179 , are a plurality of transversely spaced, longitudinally extending slots  184  that are aligned with the stuffer tines  178  so as to permit them to extend into and sweep along the duct  102 . The splined coupling between the tube  170  and the support bar  172  keeps the support  174  oriented such that the tines  178  are maintained in alignment with the slots  184 . 
     An extensible and retractable hydraulic tine injector cylinder  186  is coupled between a pivot coupling  188 , carried by the frame  164 , and the stuffer tine support  174 , the cylinder  186  being retracted, with the tines  178  withdrawn from the pre-charge chamber  108 , when the stuffer arrangement  112  is in a forward, home or standby condition. Upon the crop material reaching the desired density within the chamber  108 , the cylinder  186  is caused to extend to move the tines  178  through the slots  184  and into the pre-charge chamber  108 , as shown in solid lines in FIG. 2, so as to engage the pre-compressed charge of crop material located there. An extensible and retractable stuffer or lift cylinder  180  is coupled between the main frame  12  and a central front location of the stuffer assembly frame  164 . The cylinder  180  is in a retracted condition, as shown in solid lines in FIG. 3, when the stuffer arrangement  112  is in its forward home or standby position. When the tine ends  150  of the retaining arrangement  138  are withdrawn from the end of the pre-charge chamber  108  and the injector cylinder  172  has been extended to place the tines  178  into the chamber  108 , the lift cylinder  180  is extended to cause the frame  164  to be rotated clockwise about the pivotal mounting  166 , as viewed in FIG. 3, so as to cause the tines  178  to be lifted and, thus, swept rearwardly through the pre-charge chamber  108  to eject the crop material located therein through the baling chamber inlet  40 . It is to be noted that the lower and upper rear wall sections  144  and  182  of the duct  102  are each located approximately at respective radius about the pivot shaft  166  so that the cross sectional dimension of the pre-charge chamber  108  remains approximately constant over the distance swept by the stuffer tines  178 . Once the lift cylinder  180  has completed its extension stroke, the injector cylinder  186  will be retracted to withdraw the tines  178  from the pre-charge chamber  108 , and then the lift cylinder  180  will be retracted to return the stuffer arrangement  112  to its initial, forward standby position. 
     Referring now also to FIG. 4, there is shown a power supply arrangement  190  for providing a supply of pressurized fluid for operating the various functions of the baler  10 . Specifically, a main power input shaft  192  is supported by longitudinally spaced bearings located in supports projecting upwardly from central locations of the tongue  16  such that the shaft  192  is located in a longitudinal center plane of the baler  10 . The forward end of the shaft  192  is coupled to the rear end of a telescopic drive shaft  194 , having a forward end adapted for being coupled to a power take-off shaft of a tractor  196 , schematically shown in FIG. 5 a , the engine of which serves as the source of power for the baler  10 . A power-splitting transmission  198  is coupled for transferring power from the main shaft  192  to a plunger pump drive shaft  2  and to an auxiliary function pump drive shaft  202 , visible only in FIG. 5 a . The transmission  198  includes a first belt pulley  204 , mounted for rotation with the main shaft  192 , a second belt pulley  206  mounted for rotation about the shaft  2  and a third pulley  208  fixed for rotation with the auxiliary function pump drive shaft  202 . A belt  210  is trained about the pulleys  204 ,  206  and  208 . The second pulley  206  is joined to an outer section of a combined friction and one-way clutch  212  having its inner section fixed for rotation with the shaft  2 . A reversible, variable displacement, plunger drive pump  214  is coupled to a rear end of the shaft  2 , and fixed to the shaft  2  at a location between the clutch  212  and the pump  214  is a flywheel  216  (omitted from FIG. 5 a ). A variable displacement, auxiliary function drive pump  218  is coupled to the rear end of the shaft  202 . 
     Accordingly, when the tractor power take-off is engaged, the main shaft  192  is driven and power is transferred from it to the shafts  2  and  202  by operation of the belt transmission  198 . Slippage may initially occur between the friction elements of the clutch  212  carried by the pulley  206  and those carried by the shaft  2  until the speed comes up to that determined by the main drive or power shaft  192 . The plunger drive pump  214  and the auxiliary function drive pump  218  will then be driven. If the tractor power take-off is disengaged, the shaft  192  will stop rotating. However, the stored energy in the flywheel  216  will cause the shaft  2  to continue rotating, but because the clutch  212  is a one-way clutch, this rotation will not be transferred to the auxiliary function drive shaft  202 . 
     Referring now to FIGS. 5 a  and  5   b , there is shown an electro-hydraulic control system  220  for all of the drive functions of the baler  10 , which are all hydraulic. The control system  220  features a computer configured as an implement control unit (ICU)  222 , which includes a non-volatile memory for storing various desired signal voltages sent to it by an operator control unit (not shown), which is located in the cab of the tractor  196 . The ICU  222  is coupled for retrieving sensed data or feedback from the various functions and compares this data to the stored data, with the information determined being used in the control of the functions, also as described below. 
     Specifically, considered in the order of the flow of crop through the baler  10 , a reversible hydraulic pick-up drive motor  230  is provided which is coupled for driving the tined rotor  207  and the centering stub augers  209  of the pick-up arrangement  106 . The drive motor  230  has a first port coupled, as by a conduit  232 , for receiving pressurized fluid selectively directed thereto by an electro-hydraulic, two-position, pick-up drive motor control valve  234 , having an input port coupled to a pressure supply conduit  236 , which is in turn coupled for receiving pressure fluid supplied by the auxiliary function drive pump  218 , the latter being coupled to a fluid reservoir  238 . A control terminal  240  of the control valve  234  is coupled to a control output port  242  of the ICU  222  by a conductor  244 . Upon receiving a control signal, the valve  234  will shift an amount corresponding to the control signal to connect a corresponding metered flow of pressurized fluid so as to cause the motor  230  to rotate at a desired speed and drive the pick-up arrangement  106  so as to deliver crop to the duct  102 . A speed feedback signal is provided by a pick-up speed sensor  246 , which is in the form of a well known magnetic pick-up associated with the tine rotor of the pick-up  207  so as to determine its rotational speed. This speed signal is coupled to a signal input terminal  248  by a conductor  250  and compared with an operator set target pick-up speed value stored in the ICU  222  and appropriate control signals are sent until the speed is that desired. 
     The crop delivered by the pick-up arrangement  106  is engaged and transported into the duct arrangement  102  by operation of the packer arrangement  110  which includes the reversible hydraulic drive motor  132  having opposite ports coupled to a spring centered, electro-hydraulic, packer motor control valve  254  by supply/return conduits  256  and  258 . The packer motor control valve  254  is a proportional valve which varies flow to and from the motor  252  to achieve a set target packer rotor speed, represented by a value that the operator has stored in the ICU  222  . The control valve  254  is connected to the fluid supply conduit  236  by a conduit  260  and to the reservoir  238  by a conduit  262 . A valve control terminal  264  of the valve  254  is coupled to an output terminal  266  of the ICU  222  by a conductor  268 . Normally, the sense of the control signal received at the control terminal  264  will cause the valve  254  to shift to the left so as to connect the pressure fluid supply conduit  236  to the motor  132  so as to cause it to rotate the packer rotor of shaft  114  clockwise, as viewed in FIG. 3. A packer rotor speed sensor  270 , in the form of a magnetic pick-up, is associated with the packer rotor so as to determine its rotational speed. A feedback signal representative of this speed is coupled to a signal input terminal  272  of the ICU  222  by a conductor  274  and is compared with the target packer rotor speed value stored in the ICU  222 . 
     The packer arrangement will continue delivering crop to the duct arrangement  102  until the pre-charge chamber density sensor  160 , which includes a pressure switch, is operated so as to send a “full” signal to a control input terminal  276  of the ICU  222  by a conductor  278 . The next operation required once the pre-charge chamber  108  is full is for the retainer fork arrangement  138  to be rotated so as to withdraw the tine ends  150  from the chamber. This is accomplished through extension of the tine control cylinder  154  by actuation of a solenoid-operated, spring centered, three-position, tine/fork cylinder control valve  280  having control input terminals  282  and  284 , respectively, at its opposite ends coupled to respective control output terminals  286  and  288  of the ICU  222  by respective conductors  290  and  292 . The control valve  280  is coupled to the pressure fluid supply conduit  236  by a conduit  294 . Concurrent with the extension of the tine control cylinder  154 , the fork injector cylinder  186  is caused to extend to move the fork tines  178  into the pre-charge chamber  108 , this movement coming about due to the fact that the fork injector cylinder  186  is coupled in series with the retainer tine control cylinder  154 . Specifically, a conduit  298  is coupled between the rod end of the cylinder  154  and the head end of the cylinder  186 , with the rod end of the latter being coupled to the control valve  280  by a conduit  3 . A retaining fork position sensor  302  is associated with the crank arm  152  and sends a signal representative of the retainer fork position to a control input terminal  304  of the ICU  222  by a conductor  306 , while a signal representative of the stuffer fork position is generated by a stuffer fork position sensor  308 , which is associated with the injector cylinder  186 , and sent to a control input terminal  310  of the ICU  222  by a conductor  312 . Thus, from these position feedback signals it is known when the retainer tine ends  150  are completely removed from, and when the stuffer fork tines  178  are completely injected into, the pre-charge chamber  108 . 
     With the retainer fork tines  148  withdrawn from, and the stuffer fork tines  178  extended into, the pre-charge chamber  108 , the next operation is for the stuffer fork arrangement  112  to be pivoted in order to lift the charge of material into the baling chamber  18 . This is done through extension of the stuffer or lift cylinder  180 , which is controlled by another proportional valve similar in construction to the packer motor control valve  254 . Specifically, provided is a spring centered, stuffer cylinder control valve  314  having a pair of supply/return ports coupled to the rod and head end of the stuffer cylinder  180  by a pair of conduits  316  and  318 , the valve  294  being coupled to the pressure supply conduit  236  and the reservoir  238 . A control terminal  320  at one end of the valve  314  is coupled for receiving a control signal from an output terminal  322  of the ICU  222  by a conductor  324 . Here the signal received would be of a sense for causing the control valve  314  to shift to the left, as viewed in FIG. 5 b , so that the stuffer cylinder  180  is extended. The position of the cylinder  180  is monitored by a position sensor  326  associated with either the stuffer cylinder  180  or the frame  164 , the sensor  326  generating a signal which is connected to an input terminal  328  of the ICU  222  by a conductor  310 . Accordingly, from this position feed back signal, it is known when the stuffer tines  178  reach the extreme upward movement of their travel shown in broken lines in FIG.  3 . 
     Once the flake or slice of crop material has been delivered to the baling chamber  18 , the plunger head  20 , which has been parked to the rear of the inlet  40 , is moved to the rear through operation of the plunger cylinder  34 . Fluid pressure for operating the plunger cylinder  34  is delivered by the reversible plunger drive pump  214 , which is shown coupled in a closed hydraulic system wherein it is dedicated for driving only the plunger cylinder  34 . Thus, the pump  214  has one port coupled to the rod end of the plunger cylinder  34  by a supply/return conduit  332  and the other port coupled to the head end of the plunger cylinder  34  by a supply/return conduit  334 . A charge pump  336 , that is also driven by the drive shaft  2 , is coupled to the reservoir  238  and operates for supplying make-up fluid to the closed system. Appropriate relief valves are provided for protecting the closed loop system. The plunger drive pump  214  includes a displacement control terminal  338  that is coupled to a control output terminal  340  of the ICU  222  by an electrical conductor  342 . According to the sense and magnitude of the signal received at the terminal  338 , the pump  214  will be driven either in a forward direction, wherein it supplies fluid to the head end of the cylinder  34  for causing its extension, a rearward direction, wherein it supplies fluid to the rod end of the cylinder  34  for causing its contraction, or for placing the pump  214  in a neutral condition wherein it supplies no fluid at all. The position of the plunger cylinder  34  is monitored by a position sensor  344  associated with either the cylinder  34  or the crank arm  26 . The sensor  344  creates a signal representative of the position and sends it to a control input terminal  346  of the ICU  222  by a conductor  348 . The ICU  222  will act to inhibit the sending of a control signal to actuate the stuffer cylinder  180  if the plunger head  20  is not properly positioned relative to the crop inlet  40 . Likewise, the ICU  222  will act to inhibit the sending of a control signal to actuate the knotter cylinder  92 , as described below, if the plunger head  20  is not in the correct position for permitting the needles  84  to swing upwardly through the baling chamber  18 . 
     It is noted, that instead of being coupled in a closed system as shown, the pump  214  could also be embodied in an open system wherein it delivers fluid to a proportional valve for controlling the flow of fluid to and from the plunger cylinder  34  so as to control its speed and direction of operation. 
     Movement of crop by the plunger head  20 , as the latter extends to compress a charge of crop material against the forming bale, will cause the latter to move to the rear resulting in rotation of the length sensing wheel  98 . A rotation sensor  350 , associated with the wheel  98  will send a signal to a control input terminal  352  of the ICU  222  by way of a conductor  334 . A value representing a desired bale target length is stored in the non-volatile memory of the ICU  122  and the signal from the length sensing wheel  98  is continuously updated and compared to the stored value. 
     Density of the compressed crop is monitored by using a force or load sensing arrangement  356  associated with the toggle linkage  24 ,  26  to sense the amount of force used in compressing the flake or slice against the forming bale, the force sensor  356  generating a signal representative of the force, this signal being sent to a control input terminal  358  of the ICU  222  by a conductor  360 . Stored in the non-volatile memory of the ICU  222  is a target force value representing the desired density and the signal received from the force sensor  356  is compared with the stored target value. 
     Also working to achieve a desired density are the pair of tension cylinders  52 . These cylinders  52  are coupled to a solenoid-operated tension control valve  362  by supply/return conduits  364  and  366 , which are respectively coupled to the head ends and rod ends of the cylinders  52 . The control valve  362  is connected to the pressure supply conduit  236  by a conduit  368 , and to the reservoir  238 . Extend and retract signal terminals  370  and  372  are respectively provided at the left- and right-hand ends of the valve  362  and are respectively coupled to control output terminals  374  and  376  of the ICU  222  by respective conductors  378  and  380 . The pressure developed in the cylinders  52  is monitored by a pressure sensor  382  which creates a representative electrical signal and sends it to a control input terminal  384  of the ICU  222  by a conductor  386 . 
     Assuming that the load sensor  356  sends a signal which is below the stored target value, a signal will be sent to the retract terminal  370  of the tension control valve  362 , causing the latter to shift to the left from the centered position shown so as to effect retraction of the cylinders  52  to cause the side panels  50  to pivot inwardly to further restrict the rearward movement of the bale of crop. Of course, a load sensor signal which is above the stored value will result in a signal being sent to the extend terminal  350  of the control valve  342  causing the latter to shift to the right so as to cause the cylinders  52  to extend and pivot the panels  50  outwardly to decrease the resistance to rearward movement of the bale. The amount of increase in the pressure signal received from the pressure sensor  382  may be used to prevent overshoot of the target value. 
     Once the forming bale has a length, as determined from an accumulation of the pulses produced by the sensor  350 , which equals a stored target bale length value, the needle yoke assembly  76  will be caused to deliver twine to the tying arrangement  70  by actuation of the needle and knotter drive cylinder  92 . For this purpose, knotter and needle control valve  388 , which is also a proportional valve, is respectively coupled to the rod and head ends of the cylinder  92  by supply/return conduits  390  and  392 , the control valve  388  also being connected to the pressure fluid supply conduit  236 , by a conduit  394 , and to the reservoir  238 . Control signals, for shifting the valve  388  from a normally centered position, are received by a control terminal  396  that is coupled to a control output terminal  398  of the ICU  222  by a conductor  4 . The speed and direction of operation of the cylinder  92  will be in accordance with the magnitude and sense of the signal received. In order for it to be known when the needle yoke assembly  76  is either in its standby position, shown in FIGS. 1 and 2, or at a tying position at its other extreme, a position sensor  402  is associated with the crank arm  86 . The sensor  402  creates a position signal that is connected to a control input terminal  404  of the ICU  222  by a conductor  406 . A tie monitoring sensor  408  is provided in conjunction with a slack twine arm (not shown), that is biased against a strand of twine extending between the twine source and the tying mechanism, with the sensor  408  acting in response to an abnormal lack of tension in the loop during the tying process to send a tie malfunction signal to a control input terminal  410  of the ICU  222  by a conductor  412 . 
     A baler ground speed sensor  414  is associated with one of the axles of the wheels  14  and acts to create a signal representative of the ground speed of the baler. This signal is sent to an input terminal  416  of the ICU  222  by way of a conductor  418 . The crop feeding functions especially may be affected by the ground speed so the operator may input a target ground speed for the baler and cause the towing tractor to be sped up or slowed down to achieve the target baler ground speed. Also, depending on the crop and crop conditions, the operator may place into the memory of the ICU  222  target values of pick-up and/or packer motor speeds based on a target baler ground speed. Then the ICU  222  will operate to maintain these target speeds during operation. Also, the ground speed signal may be used together with pick-up width and density information to determine the throughput of crop. 
     Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.