FIELD OF THE INVENTION 
     The present invention relates generally to agricultural round balers for forming round bales of cut crop material and twine wrapping systems that automatically wrap the formed bales with twine before expelling them onto a field for subsequent handling. More particularly, the invention relates to improvements in the bale wrapping system by providing four twine dispensing arms that result in a decrease in the amount of time it takes to wrap a formed bale with twine. 
     BACKGROUND OF THE INVENTION 
     Typical round balers (also referred to simply as a “baler”), such as disclosed in U.S. Pat. No. 6,209,450 to Naaktgeboren et al., are agricultural machines that pick up a cut crop material from the ground and form it into a compacted round bale in a bale forming chamber. When the bale has been sufficiently compacted to a desired density or a desired size depending on the baler construction, bale density or bale size sensors, as appropriate, send signals to a controller that subsequently sends a signal to an operator&#39;s panel to stop forward motion of the baler so that a bale wrapping operation can be performed, wherein the formed bale is wrapped with netting or twine to produce a completed wrapped bale. 
     Typically, the wrapping operation is performed by a bale wrapping mechanism controlled by a bale wrapping algorithm preprogrammed into a controller (i.e., microprocessor) that is part of the baler. In the prior art baler of the present assignee, the bale wrapping mechanism has two twine wrapping tubes/arms, wherein each tube/arm dispenses a single strand of twine. When a wrap cycle is initiated, the twine tubes/arms are moved arcuately to an extended or insert position with an end of each respective twine strand dangling from the end of the corresponding twine tube/arm; optionally, a pusher mechanism, often referred to as a “duckbill,” is actuated to move the dangling twine ends toward the formed bale so that the ends of the twine strands are adjacent to the bale near its lengthwise middle. Subsequently, the dangling strands are caught by the cut crop material of the rotating bale as it rotates in the bale forming chamber so that the twine is pulled from the twine tubes/arms and wraps around the bale as the bale continues to rotate. As twine is pulled from the twine tubes/arms and wraps about the rotating bale, the twine tubes/arms are moved from the middle to the ends of the bale so that twine wraps all along the length of the bale. At the end of a wrap cycle, a tying operation is performed as is generally known. Before the completed wrapped bale is expelled from the baler, the twine strands must be cut, then the baler tailgate opens and the completed wrapped bale is expelled from the baler to the ground. 
     However, there are two problems with the assignee&#39;s prior bale wrapping apparatus having two twine tubes/arms. First, during the wrapping operation, each twine tube/arm is moved across a portion of the width of the rotating surface of the bale in a prescribed fashion to control the position of the twine on the bale to provide a secure wrap, then at least two wraps are required with the tubes/arms stationary at the beginning and the end of the wrapping cycle in order to effectively tie the bale securely. The problem with this system is that it takes an excessive amount of time to wrap a bale. Second, when applying twine to the bale, the two twine tubes/arms move to a starting position to insert twine into the bale forming chamber, then the tubes/arms gradually move back to a home position to finish wrapping the bale. As twine is applied to the bale, tension must be applied to the twine to ensure that the bale is tied securely. While twine tension helps in securing the bale, it is detrimental to starting the twine wrapping cycle. For this reason, it would be advantageous to have a mechanism that places low tension on the twine as it starts to wrap on the bale, then increases tension on the twine after the twine has started wrapping about the bale. 
     The present invention endeavors to provide a round baler with an improved bale wrapping apparatus with four twine tubes on two twine dispensing arms to facilitate the rapid wrapping of a formed bale. Furthermore, the present invention will provide structure that provides low tension in the twine at the beginning of a wrap cycle and that provides greater tension in the twine once the wrap cycle had progressed. 
     Accordingly, one object of the present invention is to overcome the disadvantages of the assignee&#39;s prior bale wrapping apparatuses having two twine tubes/arms (i.e., one twine tube per arm). 
     Another object of the present invention is to provide a bale wrapping apparatus that achieves the wrapping and tying of a formed bale in less time than the prior devices, thereby shortening the time to complete a bale wrapping cycle by 40-50%. 
     Another object of the present invention is to provide a bale wrapping apparatus that automatically adjusts the tension in the twine so that there is low tension in the twine at the beginning of a wrap cycle and higher tension in the twine after the beginning of a wrap cycle. 
     Another object of the present invention is to provide a bale wrapping apparatus that keeps four twine strands more evenly spaced across the surface of a bale during a bale wrapping operation. 
     Another object of the present invention is to provide a bale wrapping apparatus that is practical and cost effective to manufacture. 
     Another object of the present invention is to provide a bale wrapping apparatus that is both durable and reliable, and easy to maintain. 
     SUMMARY OF THE INVENTION 
     In accordance with the above objectives, a first preferred embodiment of the present invention provides a round baler comprising: (a) a housing; (b) a bale chamber defined in part by walls of the housing and having an opening for receiving a cut crop material; (c) a bale forming apparatus defining at least a portion of the bale chamber, configured to form a rotating bale of cut crop material in the chamber, and disposed inside the housing; (d) a bale wrapping apparatus disposed near the bale chamber to wrap a rotating bale formed in the chamber: (e) four twine supply rolls rotatingly connected to the housing and defining four twine strands; (f) four twine dispensing tubes, wherein each dispensing tube presents a corresponding one of the four twine strands so that an end of each strand dangles from the corresponding tube, each tube being movable between (1) a home position and (2) a twine insert position, wherein each twine strand end dangles adjacent to a position of a bale rotating in the chamber when the four dispensing tubes are in the twine insert position; and (g) two twine tensioning members disposed so that each twine tensioning member receives two of the four twine strands, wherein each twine tensioning member has a receiving portion through which the two strands are threaded, wherein each twine tensioning member is positioned to provide slack tension on the ends of the respective two strands when the four dispensing tubes are in the twine insert position, and wherein each twine tensioning member is positioned to increase wrapping tension on the respective two strands after the respective two strands have started to wrap the rotating bale. 
     In accordance with a second preferred embodiment of the present invention, the first preferred embodiment is further modified so that each twine tensioning member has two holes formed therein to provide the receiving portion and wherein each hole receives threaded therethrough one of the respective two strands. 
     In accordance with a third preferred embodiment of the present invention, the first preferred embodiment is further modified so that each twine dispensing tube is provided by a tube or a ring through which a respective one of the four strands is threaded therethrough. 
     In accordance with a fourth preferred embodiment of the present invention, the first preferred embodiment is further modified so that each twine dispensing tube is movable along an arcuate path between the home position and the twine insert position. 
     In accordance with a fifth preferred embodiment of the present invention, the first preferred embodiment is further modified so that the bale wrapping apparatus further comprises two arm members, each arm member being connected to a respective two of the four twine dispensing tubes. 
     In accordance with a sixth preferred embodiment of the present invention, the first preferred embodiment is further modified so that each arm member includes two hollow portions through which a respective one of the four twine strands passes. 
     In accordance with a seventh preferred embodiment of the present invention, the fifth preferred embodiment is further modified so that the bale wrapping apparatus further comprises a twine arm pivotally connected at one end to a cam member connected to each arm member and pivotally connected at the other end to a base mount. 
     In accordance with an eighth preferred embodiment of the present invention, the seventh preferred embodiment is further modified so that each twine tensioning member is provided by a portion of the base mount. 
     In accordance with a ninth preferred embodiment of the present invention, the seventh preferred embodiment is further modified so that each twine arm is provided by two link members, each link member being pivotally connected at one end to a respective cam member and pivotally connected at the other end to the base mount. 
     In accordance with a tenth preferred embodiment of the present invention, the ninth preferred embodiment is further modified so that each link member has a hollow portion and one of the four twine strands is threaded through the hollow portion of each link member. 
     In accordance with an eleventh preferred embodiment of the present invention, the first preferred embodiment is further modified so that each twine dispensing tube is movable to a cutting position, and wherein each twine tensioning member provides additional tension to each of the respective two strands when the four twine dispensing tubes are in the cutting position. 
     Further objects, features and advantages of the present invention will become apparent from the Detailed Description of Preferred Embodiments, which follows, when considered together with the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cutaway side elevational view of a round baler in accordance with the present invention. 
     FIG. 2 schematically illustrates a plan view of the twine wrapping apparatus and the twine cutting mechanism with the twine arms in the first position. 
     FIG. 3 schematically illustrates a plan view of the twine wrapping apparatus and the twine cutting mechanism with the twine arms in the cutting position. 
     FIG. 4 schematically illustrates a plan view of the twine wrapping apparatus and the twine cutting mechanism with the twine arms in the home position. 
     FIG. 5 schematically illustrates the increased tension in one of the twine strands exerted by the rotating bale when the twine arms are in the first position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the invention will now be described with reference to the Figures in which like parts are indicated by like reference numerals. The apparatus of the present invention as shown in FIG. 1 is a round baler  10  including a main frame or housing  11  and a bale forming chamber  22  formed inside of housing/frame  11 , wherein the bale forming chamber is illustrated as a fixed bale forming chamber for forming a geometrical package out of cut crop material  16 . The geometrical package of cut crop material formed in the bale forming chamber  22  is known as a “bale.” The bale is formed by a chain conveyer  24 , also referred to as an “apron,” that surrounds and defines a portion of the chamber  22 . Apron  24  serves to rotate the cut crop material in the bale forming chamber  22  by using slats  33  of the apron  24  that engage and rotate the cut crop material, thereby moving the cut crop material about the bale forming chamber  22  to form the bale  52  as described in U.S. Pat. No. 6,164,050, which is incorporated herein by reference in its entirety. Preferably, the bale produced in the bale forming chamber  22  has a cylindrical shape; however, one skilled in the art would appreciate that the present invention can be practiced on balers that produce other bale shapes and can be practiced by round balers having a variable bale forming chamber. 
     Main frame  11  includes a main support beam  13  on which a pair of wheels  21  (only one shown) is rotatably affixed. A tongue  23  extends from a front portion of frame  11  to provide a conventional hitch connection for connecting to a tractor  12  or other work vehicle. Frame  11  also includes a pair of sidewalls  25  (only one shown) between which the bale forming chamber  22  extends. A pair of stub shafts  27  (only one shown) pivotally connect tailgate  28  to main frame  11 . Tailgate  28  pivotally rotates about the stub shafts  27  from the closed position shown in FIG. 1 to an open position as is conventionally known so that a completed wrapped bale can be discharged to the ground for subsequent handling. Tailgate  28  includes a pair of tailgate sidewalls  29  (only one shown) that are coextensive with sidewalls  25 . 
     Baler  10  includes a pick-up assembly  14  for picking up a cut crop material  16 , such as straw, hay, and the like, from a field and delivering it to a moving conveyer  18 , which feeds the cut crop material into the bale forming chamber  22  while the baler moves across a field. Although FIG. 1 illustrates conveyer  18  as a feeder rotor, one skilled in the art would recognize that a stuffer mechanism, such as disclosed in U.S. Pat. No. 5,595,055 to Horchler, Jr., et al., which is incorporated herein by reference in its entirety, could be used in place of the feeder rotor without departing from the scope of the present invention. The pickup assembly  14  has tines  57  and a pair of wheels  19  (only one shown), and operates in a known manner. 
     The bale forming chamber  22  is defined by the coextensive sidewalls  25  and  29 , apron  24 , rotating floor roll  20 , and rotating stripper roll  26 . A rotating bale  52  is formed within the bale forming chamber  22  when cut crop material is fed into the chamber by the pickup assembly  14  as is known. When the bale  52  reaches a predetermined size such as occurs in variable size chambers, or in the alternative when the bale  52  reaches a predetermined density such as occurs in fixed size chambers, appropriate size or density sensors respectively indicate that the bale is ready to be wrapped. Subsequently, the baler  10  stops its forward motion while a bale wrapping operation is performed by a bale wrapping assembly  30 . 
     Bale wrapping assembly  30  is disposed within housing/frame  11  so as to be adjacent to the bale forming chamber  22  and serves to wrap wrapping material, such as net, twine or plastic sheet, around the bale  52  formed within the bale forming chamber. The bale wrapping assembly  30  illustrated in FIG. 1 includes a twine wrapping apparatus  32  and may optionally include a net wrapping apparatus (not shown) as is, for example, disclosed in U.S. Pat. No. 6,209,450. The twine wrapping apparatus  32  dispenses four twine strands  72   a ,  72   b ,  72   c ,  72   d  as shown in FIGS. 1-4 that are stored on at least four twine balls  70  (only one shown), and the net wrapping apparatus dispenses netting or plastic sheets that is stored on a roll. When the bale  52  is completely formed, the operator of the baler  10  operates the bale wrapping assembly to dispense either twine or netting/plastic sheeting in a known manner. Balers that have a bale wrapping assembly that includes only a twine wrapping apparatus  32  will only dispense twine. 
     Twine wrapping apparatus  32  includes two pivotally mounted twine dispensing arms  34  and  35  upon which are mounted two twine tubes  47  each. As shown in FIGS. 2,  3  and  4 , the twine wrapping apparatus  32  has a base mount  38  connected to frame  11 . Twine arms  34  and  35  are pivotally mounted on base mount  38  so that each twine arm can pivot between a “first position” (also referred to as the “twine insert position”) shown in FIG. 2 at the start of a twine wrapping cycle as will be described later to a “cutting position” as shown in FIG.  3 . Between twine wrapping cycles, the twine arms  34 ,  35  are stored in a “home position” as shown in FIG.  4 . Twine arms  34 ,  35  are driven to move by a twine wrap actuator (not shown), which is powered by a twine wrap actuator drive motor such as disclosed in U.S. Pat. No. 6,209,450 B1 to Naaktgeboren et al, incorporated herein by reference in its entirety. Gears  62  transmit power from the twine wrap actuator to pivot the twine arms  34 ,  35  in a controlled manner such as would be directed by an on board computer or microprocessor. 
     Twine arm  34  includes two link members  39 ,  40  that are pivotally connected at one end to the base mount  38  and pivotally connected at another end to cam member  41 . Twine arm  35  includes two link members  42 ,  43  that are pivotally connected at one end to base mount  38  and pivotally connected at another end to cam member  44 . Each cam member  41  and  44  is connected to an arm member  46  that has two twine tubes  47  for dispensing one twine strand each. Thus, each twine arm  34 ,  35  in accordance with the present invention includes two individual twine arms  47  connected in pairs, wherein each twine arm dispenses a single strand of twine. A parallel linkage ensures that the four twine tubes  47  are always maintained perpendicular to the cylinder axis of the cylindrical bale  52  as evident from FIGS. 2-5. The parallel linkage is formed by link members  39 ,  40 ,  42 ,  43  and the cam members  41 ,  42  so that the two twine arms  34  and  35  connected to the base mount  38  provide this parallel linkage that keeps respectively paired twine dispensing tubes  47  evenly spaced and perpendicular to a bale axis BA (see FIG. 5) as the twine arms move across a surface of the bale during a twine wrapping operation. One skilled in the art would appreciate from FIG. 5 that bale axis BA is the cylindrical axis about which cylindrical bale  52  rotates once the bale is formed. Consequently, the twine in each twine tube pair remains evenly spaced across the surface of the bale during the twine wrapping operation. The result of these features is that the twine wrapping apparatus keeps all four twine strands properly and more evenly spaced across the surface of the bale during the twine wrapping operation. 
     Baler  10  is provided with four twine balls  70  (only one shown) and each twine ball provides one of the twine strands  72   a ,  72   b ,  72   c , and  72   d . Each twine strand  72   a ,  72   b ,  72   c , and  72   d is threaded through a respective hole  75  in a twine tensioning member  60  of the base mount  38  and through a respective one of the link members  39 ,  40 ,  42 ,  43  because each link member  39 ,  40 ,  42 ,  43  is a hollow tube with openings  76 ,  77  through which a twine strand may pass. Arm members  46  include two tubular hollow portions  49  through which a twine strand may pass. Each twine tube  47  is preferably a hollow tube that is contiguous with one of the tubular hollow portions  49  of the arm members  46  so that a twine strand may pass through a respective contiguous hollow tube portion  49  and corresponding twine tube  47 . Alternately, hollow portions  49  could be grooves or indentations in arm members  46  and each twine tube  47  is a hollow tube or ring that is constructed to be contiguous with the hollow portions  49 , or to be not contiguous with the hollow portions  49 . In one preferred embodiment of the invention, each arm member  46  includes two twine tubes  47  as described above but the hollow portions  49  have been omitted. 
     During baler operation, the formation of a bale  52  is achieved in the conventional manner while baler  10  moves along a field of cut crop material picking up the cut crop material with pick-up assembly  14 , and delivers the cut crop material using conveyer  18  to move the cut crop material through bale chamber inlet  48  defined by floor roll  20  and stripper roll  26 . When the bale  52  has reached a certain size or density, depending upon whether baler  10  is a variable chamber baler or a fixed chamber baler, size or density sensors (as appropriate) are activated and signal the operator or an on board computer that the bale  52  is ready for the bale wrapping operation. Upon initiation of the bale wrapping operation, the twine arms  34 ,  35  move from the home position shown in FIG. 4 to the first position shown in FIGS. 2 and 5 (see also phantom lines in FIG.  4 ). In the first position, the ends of twine strands  72   a ,  72   b ,  72   c , and  72   d  dangle into inlet  48  where they get caught and carried by the rotating bale  52 . In this manner, the twine strands  72   a ,  72   b ,  72   c , and  72   d  wrap around bale  52  and secure the cut crop material as the bale rotates. During a predetermined sufficient number of wrappings, twine arms  34 ,  35  pivot from the first position back to the cutting position shown in FIG. 3 so that twine is wrapped around both the center and the peripheral portions of bale  52 . When the twine arms  34 ,  35  reach the cutting position, there is tension in each of the twine strands  72   a ,  72   b ,  72   c , and  72   d  and a cutting procedure takes place to cut each of the twine strands  72   a ,  72   b ,  72   c , and  72   d  simultaneously. The bale wrapping operation concludes with the cutting of the twine strands, then the twine arms  34 ,  35  return to the home position, and the completed wrapped bale is discharged to the ground when tailgate  28  opens. 
     The present invention, being a four twine tube round baler twine system, provides four twine strands  72   a ,  72   b ,  72   c , and  72   d  simultaneously for wrapping the bale  52 , which decreases the number of revolutions the bale must undergo before completing the bale wrapping cycle. Decreasing the number of bale revolutions required during the bale wrapping cycle plainly decreases the amount of time needed to complete the wrapping cycle. However, the twine wrapping apparatus  32  also provides automatic adjustment of the tension in the twine strands  72   a ,  72   b ,  72   c , and  72   d  during the bale wrapping operation so that there is low tension in the ends of twine strands  72   a ,  72   b ,  72   c , and  72   d  at the beginning of the wrap cycle and a higher tension in the twine after the beginning of the wrap cycle. As shown in FIG. 4, the ends of twine strands  72   a ,  72   b ,  72   c , and  72   d  are dangling from twine tubes  47  and have no tension on them when the twine arms  34 ,  35  are in the home position. Likewise, the remainder of each twine strand  72   a ,  72   b ,  72   c , and  72   d  has a relatively low tension therein when the twine arms  34 ,  35  are in the home position. 
     FIG. 2 shows the twine strands  72   a ,  72   b ,  72   c , and  72   d  with the twine arms  34 ,  35  in the first position just as each twine strand is being caught by the rotating bale. For the initial moments when the twine arms  34 ,  35  are in the first position, the end of each twine strand  72   a ,  72   b ,  72   c , and  72   d  is dangling and experiences no significant tension (also referred to as “slack tension”). Consequently, the remainder of each twine strand  72   a ,  72   b ,  72   c , and  72   d  has a relatively low tension, or slack tension, therein when the twine arms  34 ,  35  initially reach the first position. However, as the end of each twine strand  72   a ,  72   b ,  72   c , and  72   d  is caught and carried by the periphery of the rotating bale  52 , each twine strand experiences more tension. FIG. 5 demonstrates this increased tension in the twine as the periphery of bale  52  catches the twine. For simplicity&#39;s sake, only twine arm  34  and twine strand  72   b are illustrated. As shown by comparing FIGS. 2,  4  and  5 , it is clear that twine strands  72   a ,  72   b ,  72   c , and  72   d  experience low tension at the beginning of a twine wrapping cycle (i.e., twine arms  34 ,  35  have just arrived in the first position) and then experience a higher amount of tension when the periphery of the rotating bale  52  catches and pulls each strand after the beginning of the twine wrapping cycle. The automatic increase in the tension in the twine strands  72   a ,  72   b ,  72   c , and  72   d  is provided by the friction that occurs in the system due to the twine configuration shown in FIGS. 2-4 and due to the friction in the two holes  75  of each twine tensioning member  60 . Although twine tensioning members  60  have been shown to have two holes  75  for receiving two of the twine strands  72   a ,  72   b ,  72   c , and  72   d , each twine tensioning member could be constructed with some other suitable receiving portion such as a groove without departing from the scope of the present invention. 
     FIG. 3 shows the twine arms  34  and  35  located in a maximally retracted position, being the cutting position, which generates additional tension in each twine strand  72   a ,  72   b ,  72   c , and  72   d  at the end of the wrapping cycle. The twine configuration shown in FIG. 3, wherein each twine strand  72   a ,  72   b ,  72   c , and  72   d , respectively, is threaded through a hole  75  in one of the two twine tensioning members  60  of base mount  38  and through hollow link members  39 ,  40 ,  42 , and  43 , creates enough friction in the twine strands so that each twine strand  72   a ,  72   b ,  72   c , and  72   d  experiences additional tension when the twine arms are in the cutting position. This additional twine tension facilitates the cutting of the twine strands by twine cutting mechanism  80 . Twine cutting mechanism  80  includes shear bars  82  mounted to frame  11  and knife assemblies  84  disposed on a rotatable elongated bar  86  so that each twine strand is cut by one of the knife assemblies when it rotates to engage a respective one of the shear bars during a twine cutting operation. 
     While the present invention has been described with reference to certain preferred embodiments, one of ordinary skill in the art will recognize that additions, dcletions, substitutions, modifications and improvements can be made while remaining within the spirit and scope of the present invention as defined by the appended claims.
A round baler including a housing; a bale chamber; bale forming apparatus; and bale wrapping apparatus including: four twine supply rolls defining four twine strands; four twine dispensing tubes, each tube presenting one of the strands so that each strand dangles from the corresponding tube, each tube movable between home and twine insert positions, wherein each strand dangles adjacent to a bale rotating in the chamber when the tubes are in the insert position; and two twine tensioning members disposed so that each tensioning member receives two strands, wherein each tensioning member has a receiving portion through which two strands are threaded, wherein each tensioning member is positioned to provide slack tension on two respective strands when the tubes are in the insert position, and wherein each tensioning member is positioned to increase wrapping tension on the two strands after the two respective strands have started to wrap the bale.