fig1 shows a side view of an agricultural tractor 10 in the form of a tractor and a implement 12 , coupled by way of a draw bar 14 to a suspension coupling 28 of the tractor 10 , in the form of a round baler with a variable size baling chamber . the tractor 10 is built on a frame 18 , which is supported on steerable front wheels 20 and drivable rear wheels 22 and carries a cab in which there is a work station for the operator 26 . the implement 12 comprises a carriage 32 that is supported on the ground via steerable wheels 34 , a processing element 36 in the form of a crop collector 38 to collect crops lying on the ground in a windrow 40 , and a conveyer 42 that conveys the crops taken up by the crop collector 38 into a container 46 in the form of a baling chamber 44 . the baling chamber 44 is limited in a manner that is in fact known by baling elements ( not depicted ) in the form of belts . a completed bale can be ejected through a back door that can pivot upwards , and deposited on the field . the mechanical drive of the driven elements of the implement 12 is carried out by the tractor 10 via a universal joint shaft 30 , although a drive with electric motors would also be conceivable , which are supplied with electrical energy by the tractor 10 . in total , three sensors 50 are distributed over the width of the container 46 ; they are used to detect the diameter of the bale and / or to detect the tension of the baling elements , which likewise contain information on the distribution of the crops over the width of the container 46 . the sensors 50 are connected to a control device 52 , which is located on board the implement 12 , but which could also be located on board the tractor 10 . the control device 52 is connected via a valve arrangement 56 to a first actuator 54 in the form of a hydraulic cylinder , which is articulated on one end on the draw bar 14 and on the other end on the carriage 32 . the control device is connected , moreover , via the valve arrangement 56 to a second actuator 58 in the form of a hydraulic cylinder , which is coupled to a rod 60 to swivel the wheels 34 of the implement 12 around the vertical axis . by way of feedback sensors 70 , 72 , the control implement 52 gives information regarding the actual angles of the draw bar 14 and the wheels 34 . a detection device 62 in the form of a camera is placed on the front side of the tractor 10 ; it detects the windrow 40 optically and is connected to an image processing system , which emits a steering signal to a steering control 64 of the tractor , which in turn adjusts the steerable front wheels 20 of the tractor via a suitable actuator ( not depicted ) in such a manner that the longitudinal middle axis of the tractor 10 is conducted at least approximately on a theoretical line 66 , which corresponds to the longitudinal axis of the windrow 40 . in another embodiment , data regarding the position of the windrow are stored in the steering control 64 and a position - determining device 68 ( for example , in the form of a gps antenna ) transmits to the steering control 64 up - to - date position information , which is used together with the stored data regarding the position of the windrow by the steering control 64 to control the actuator for the steerable front wheels 20 . both variants mentioned in this paragraph can also be combined ( see ep 1 266 553 a2 ). the steering control 64 continuously transmits to the control device 52 data regarding the lateral position of the theoretical line 66 relative to the longitudinal middle axis of the tractor 10 and the corresponding time of the detection and / or the corresponding position in the forward direction , and is , to this end , connected to the control device 52 via a bus . in the light of the foregoing , the mode of operation of the control device 52 shown in fig3 is produced . after the start in step 100 , step 102 follows , in which the expected position of the theoretical line 66 relative to the middle line of the implement 12 after traversing a stretch of the length x ( of , for example , 1 m ) is determined on the processing element 36 . thus , the expected lateral offset of the windrow 40 relative to the longitudinal middle plane of the implement 12 is determined on a site lying approximately the distance x in front of the implement 12 . this position can be determined with the aid of the signals by the steering control 64 and the distance traversed until the attaining of the elapsed time or the distance traversed from the implement 12 ( between the detection by the detection device 62 and the reaching of the site ). the lateral movement of the implement can be derived from the signals of the feedback sensors 70 , 72 and / or another feedback sensor ( not depicted ) located between the draw bar 14 and the coupling 28 , and / or an individual position - determining device 74 is allocated to the implement 12 , or for the purpose , a kinematic model ( see wo 2008 / 005159 a2 ) is used for the combination of the tractor 10 and the implement 12 . in the following step 104 , the lateral distribution of the crops in the container 46 is detected by the sensors 50 . then step 106 follows , in which the theoretical positions for the actuators 54 and 58 are calculated . they are determined in such a way that , on the one hand , the processing element 36 is still orthogonal to the theoretical line 66 even after the traversing of the distance x ; on the other hand , however , the distribution of the crops in the container corresponds to the filling strategy , which can , for example , imply that first the left half of the bale is built up to a diameter of 10 % of the desired bale size , then the right half is built up to a diameter of 20 % of the desired bale size , then , in turn , the left half of the bale is built up to a diameter of 30 %, etc . in this respect , one can additionally refer to the state of the art according to ep 1 634 491 a1 and ep 1 813 146 a2 , whose disclosures are incorporated in the documentation under consideration by reference . in step 106 , then , signals for the valve arrangement 56 are determined and transmitted , which are based on the result of step 104 and the initial values of the sensors 70 , 72 with regard to the up - to - date positions of the actuators 54 and 58 . step 102 follows , in turn . it should be noted that other refinements would also be possible . thus , the tractor 10 and / or the implement 12 could be equipped with an inclination sensor ( not depicted ) for the detection of the side inclination of the ground , whose signals are supplied to the control device 52 . the control device 52 can then steer the implement 12 upwards on the slope , so as to compensate for slippage . the signals of the inclination sensor can also be used in order to place the implement 12 parallel to the slope before automatically ejecting a bale and thus preventing it from rolling down the slope . 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 .
provided is a combination of a tractor and a implement drawn by the tractor by way of a draw bar , supported on the ground by wheels , the implement having a processing element interacting with a field . a controller is connected to a first actuator disposed for adjusting the angle between the draw bar and the implement , and to a second actuator disposed for adjusting the angle of the wheels of the implement about the vertical axis . the controller can be operated for actuating the two actuators in such a manner that the longitudinal axis of the processing element is always oriented at least nearly orthogonal to a target line .