Abstract:
A bale wrapper is provided that comprises a rotating arm holding a film dispenser. The arm rotates around an axis thereby wrapping the film from the film dispenser around the bale. Rotation of the arm is stopped when a sensing arrangement mounted ahead of the arm senses an obstacle. The arm is driven with a first speed sufficiently slow to prevent any risk of injury and the arm and the film dispenser from being damaged by hitting an obstacle detected by the sensing arrangement when an obstacle sensor observing a sensitive range in the environment of the bale wrapper detects an obstacle. The arm rotates at a second speed faster than the first speed when the obstacle sensor detects no obstacle.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a bale wrapper having at least one arm holding a film dispenser, and a drive arrangement for rotating the arm around an axis in a direction of rotation and thereby wrapping the film from the film dispenser around a bale. A sensing arrangement is mounted in the direction of rotation ahead of the arm and is arranged to stop rotation of the arm when the sensing arrangement senses an obstacle. The drive arrangement is operable to drive the arm with a first speed sufficiently slow to prevent the arm and the film dispenser from getting damaged by hitting an obstacle detected by the sensing arrangement. The invention further relates to a corresponding method for wrapping a bale. 
     BACKGROUND OF THE INVENTION 
     Bale wrappers are used in agriculture to wrap bales with films of impervious material such as plastic, to envelop the baled material in an airtight manner for the process of ensilage of fodder. The plastic is wrapped by rotating the bale around its horizontal axis, while either the bale, as disclosed in GB 2 159 489 A, or an arm carrying the wrapping material, as disclosed in EP 0 829 197 A and EP 1 186 225 A, is rotated simultaneously around a vertical axis. Such wrappers are typically mounted on a common frame with a baler as disclosed in EP 1 186 225 A or embodied as independent machines connected to a tractor for transporting either the wrapper to the respective bales lying on a field or the bales to the wrapper as disclosed in EP 0 829 197 A and GB 2 159 489 A. 
     In order to prevent accidents, wrappers with rotating arms are usually protected by mechanical sensing arrangements in the form of light secondary arms running ahead of the main arms holding the film dispensers. Once one of the secondary arms comes in contact with an obstacle, it tilts back and activates a braking mechanism that stops the main arms before they hit the obstacle. This safety system is however only reliable within a certain speed range and thus limits the rotational speed of the arms and the working speed of the entire wrapper. When the wrapper is used in combination with a baler, the time required for wrapping the bale is, however, critical for the throughput of the combination. 
     It has been proposed to provide a self-propelled, unmanned autonomous wrapper with safety devices for avoiding accidents (DE 196 08 014 A). The safety devices comprise mechanical sensing rods and infrared sensors for detecting organisms and engines based upon the generated heat. If, for example, the wrapper comes closer than 20 m to a tractor/baler combination operating on the same field, detected by means of positioning systems, the wrapper is automatically switched off, until this distance is exceeded again. It should however be mentioned that presence sensors like those proposed in DE 196 08 014 A suffer from the disadvantage that they detect all kind of obstacles such as bales lying in the field, trees or fences, and thus often lead to unintended interruptions of work. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a bale wrapper that is capable of wrapping the bale with a sufficient high speed, but assures an appropriate level of safety. 
     Accordingly a bale wrapper is provided that comprises one, two, three or more arms. The arms each holding a film dispenser and being connected to a drive arrangement such that they can rotate around an axis in a direction of rotation and thereby wrap the film from the dispenser around a bale to be wrapped. A sensing arrangement is mounted in the direction of rotation ahead of the arm and stops the rotation of the arm once the sensing arrangement interacts with an obstacle. Further, at least one obstacle sensor is provided that observes a sensitive zone in the environment of the bale wrapper. The obstacle sensor is connected to the drive arrangement. In the event that the obstacle sensor detects an obstacle within the sensitive zone, the arm is driven with a first speed. The first speed is sufficiently slow such that the sensing arrangement is working in the intended manner. Thus, once an obstacle is encountered by the sensing arrangement, no risk of injury will occur and the arm and the film dispenser will not be damaged by hitting the obstacle. Preferably, the first speed is slow enough that the arm and the film dispenser will not touch the obstacle at all. The arm is driven with a second speed faster than the first speed when the obstacle sensor detects no obstacle. 
     Thus, the wrapper will work with a relatively high speed of the arms as long as the obstacle sensor detects no obstacle in the environment of the bale wrapper. On the other hand, if the obstacle sensor detects an obstacle, the speed is reduced to the first speed allowing the sensing arrangement to stop the arm without any damage to the arm and ribbon dispenser and harm to the obstacle if necessary. The present invention hence decreases the wrapping time without negatively influencing safety. 
     The obstacle sensor can be a distance sensor, in particular a microwave sensor and/or radar sensor and/or ultrasonic sensor and/or a scanning laser sensor. The obstacle sensor can also be an infrared sensor. In another embodiment or additionally to the distance sensor, the obstacle sensor comprises a two or three dimensional camera and an image processing system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the invention will be described below with reference to the accompanying drawings wherein: 
         FIG. 1  is a lateral view of a bale wrapper; 
         FIG. 2  is a top view of the bale wrapper of  FIG. 1 ; and, 
         FIG. 3  is a flow diagram according to which the controller in  FIG. 2  works. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference now to the drawings it can be seen that  FIG. 1  shows a side view of a bale wrapper  10  that is provided as a part of a baler/wrapper combination  12 . The latter comprises a frame  14  supported on wheels  15 . The frame  14  supports a baler  16  with a rear door  18  and the bale wrapper  10 . In operation the baler/wrapper combination  12  is pulled behind a tractor (not shown) by a tongue as described in detail in EP 1 186 225 A, the contents of which are incorporated herein by reference. It should be mentioned that the present invention is not restricted to a baler/wrapper combination  12 , because the bale wrapper  10  could be provided as an independent machine, coupled directly to a tractor for driving the bale wrapper  10  to the bales lying on a field, or transporting the bales to the bale wrapper  10 . The bale wrapper  10  could also be a self-propelled unit, manned or unmanned. 
     A bale  22  produced in the baler  16  is transported by a movable table  24  from the baler  16  to a wrapping position in the bale wrapper  10 . During the wrapping operation, the bale  22 ′ to be wrapped is thus lying on the table  24  that comprises a belt  26  surrounding two rollers  28 . Above the table  24 , two opposite arms  30  having orthogonal vertical and horizontal sections surround the bale  22 ′. Each vertical section of the arms  30  supports a film dispenser  32 . The inner ends of the horizontal sections of the arms  30  are connected to a drive arrangement  34  operable to rotate the arms  30  around a vertical axis. The drive arrangement  34  is connected to the frame  14  by a support frame  38  and comprises a hydraulic motor coupled to the hydraulic-system of the tractor. During operation, the drive arrangement  34  (or a separate hydraulic motor) is also driving the rollers  28 , such that the bale  22 ′ is rotating around its horizontal center axis, while the arms  30  rotate around the bale  22 ′ and film is unwound from the film dispensers  32  and wrapped around the bale  22 ′. Film holders  36  press the film against the bale  22 ′ during the start of the wrapping operation and cut it off after the wrapping process. The speeds of the arms  30  and of the rollers  28  can, but need not be, synchronized to obtain a desired positioning of the film  52  on the bale  22 ′. 
     A top view of the baler/wrapper combination  12  is shown in  FIG. 2 . Here it can be seen that the arms  30  and the film dispensers  32  are protected by a sensing arrangement comprising horizontal bars  40  and vertical rods  42  mounted to the outer ends of the bars  40  and extending downward to the height of the table  24 . The bars  40  and rods  42  are mounted ahead of the arms  30  with respect to the direction of rotation of the latter, which is, in  FIG. 2 , in the clockwise direction. The bars  40  are mounted pivotally around the vertical axis to the adjacent arms  30  and spring-biased into the shown rest position. Sensors  44  detect the angular position of the bars  40  with respect to the arms  30 . The sensors  44  comprise a potentiometer or inductive switch or a magnetic sensor and a magnet or any other suitable device for detecting the angular position of the bar  40  with respect to the adjacent arm  30 . The sensors  44  are connected by wires (preferably a bus), or via a wireless connection, to a controller  46  that controls the speed of the drive arrangement  34 . It should be noted that the mechanical sensing arrangement with bars  40 , rods  42  and sensors  44  shown can be replaced with a contactless sensing arrangement, which could for example comprise a light barrier or a laser distance measuring device looking downward from a position ahead of the arm  30  to detect the presence of obstacles. 
     Additional obstacle sensors  48  are mounted to the frame  14  at both sides of the bale wrapper  10  and at its rear. The obstacle sensors  48  have overlapping sensitive ranges  50  that extend to a distance lying in the order of 1 to 10 m from the wrapper  10 . The sensitive ranges  50  of the obstacle sensors  48  cover the entire area through which an obstacle, like a human being, could approach the bale wrapper  10 . The obstacle sensors  48  can make use of any suitable technology, for example microwaves, radar, ultrasound, or infrared light, or could comprise a scanning laser sensor detecting the time of flight. The obstacle sensors  48  could also comprise a camera and an image processing system. The obstacle sensors  48  are connected to the controller  46 . The controller  46  is also suited to control the baling operation (e. g. opening and closing of the door  18  and positioning the table  24  between a forward loading position and a rear baling position). 
       FIG. 3  illustrates the logic employed by the controller  46 . After a bale  22  is built in the baler  16 , it is wrapped with a net or twine, and then the door  18  opens. The table  24  is then brought to a forward loading position, in which it receives the bale  22 , which is in turn unloaded from the baler  16  by gravity or action of rollers or belts or chains surround the baling chamber or by a separate feeding means and reaches the table  24 . The table  24  with the bale  22  is then slid into the wrapping position as shown in  FIGS. 1 and 2 . Door  18  is then closed and the baling operation resumes. At the same time, the wrapping process starts (step  100 ), in which the controller  46  controls the drive arrangement  34  to rotate the arms  30  around the vertical axis and the rollers  28  and thus the table  24  to rotate around the horizontal axis. Thus, the bale  22 ′ rotates around its horizontal center axis and the arms  30  with the film dispensers rotate around the vertical axis, such that film  52  is unwound from the film dispensers and wrapped around the bale  22 ′. 
     The speed of the arms  30  and of the rollers  28  controlled by controller  46  depends on the signals from the sensors  42  and from the obstacle sensors  48 . If in step  102 , the sensors  42  indicate that at least one sensing arrangement has left its rest position, possibly due to the fact that an obstacle was touched, the controller  46  instructs the drive arrangement  34  to stop the arms  30  and the rollers  28  (step  104 ). This can be performed by stopping the hydraulic flow through the hydraulic motor of the drive arrangement by controlling a suitable valve, or by rotating a swash plate of the hydraulic motor of the drive arrangement into a stop position, and if necessary, by activating an additional brake. Thus, once an obstacle like a human being or an animal or a branch of a tree for example, comes into the circumference covered by the arms  30  and the film dispensers  32 , their rotation is immediately stopped, such that damage to the film dispensers  32  and harm to the obstacle are avoided. 
     If the sensors  42  indicate that the sensing arrangement does not detect an obstacle, since bars  40  and rods  42  are in their rest position, the speed of the drive arrangement  34  commanded by the controller  46  depends on the signals from the obstacle sensors  48  (step  106 ). If the obstacle sensors  48  indicate that an obstacle is within one of their sensitive ranges  50 , the controller  46  instructs the driving arrangement  34  to rotate the arms  30  and the rollers  28  with a first speed (step  108 ). This first speed is the highest possible speed that allows stopping the arms  30  from rotating when the sensors  42  should indicate that the rods  42  have touched an obstacle, without any risk of harm to a human being or damage of the film dispensers  32  (or even without any contact to the obstacle). Thus, it is assured that the sensing arrangement can stop the arms  30  as intended, since an obstacle is present in one or more of the sensitive ranges  50 , and there is hence a risk that stopping the arms  30  might be necessary. 
     On the other hand, if the obstacle sensors  48  indicate that there is no obstacle within the sensitive ranges  50 , the controller  46  controls the drive arrangement  34  to drive the rollers  28  and the arms  30  with a second speed, which is faster than the first speed (step  110 ). In a preferred embodiment, the second speed is twice the first speed. Thus, as long as there is no risk of a collision with an obstacle, the arms  30  rotate with a higher speed, that would not allow halting the arms  30  by the sensing arrangement without damage or contract (but that does not negatively influence the safety, since such a collision is not possible according to the signals from the obstacle sensors  48 ). The second speed allows a fast wrapping of the bale  22 ′. After steps  108  and  110 , step  102  follows again. 
     Finally, when the bale  22 ′ is entirely wrapped, the film  52  is separated from the supply on the film dispensers  32  by means of the film holders  36  and the bale  22 ′ is released to the ground, by tilting the table  24  to the rear. 
     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.