the utility vehicle 10 , illustrated in fig1 is an agricultural combine . the combine is supported on front driven and rear steerable wheels 12 and 14 , respectively , and is provided with an operator &# 39 ; s cab 16 from which it is controlled by an operator . the present invention could also be used on other utility vehicles , such as , self propelled forage harvesters , self - propelled large balers and tractors having ground engaging implements or seeding machines . a grain tank 18 is located behind the operator &# 39 ; s cab 16 . the grain tank 18 is used for temporarily storing clean grain until it is transferred to a grain cart or truck by unloading auger 20 . the grain tank 18 is supported on a frame 22 formed by two side sheets . the harvested crop is separated into its large and small components within the side sheets . the crop is first harvested by a harvesting assembly 64 ( see fig2 ) and from the harvesting assembly 64 the harvested crop is directed to a feeder house 38 . the feeder house 38 is an upwardly sloping conveyor which conveys the harvested crop past a stone trap 40 to a threshing assembly . the threshing assembly comprises a threshing cylinder 24 with associated concave 26 and a beater 28 . the threshed crop material is transferred to a separation assembly comprising straw walkers 30 which expand the threshed crop mat to release grain trapped in this mat . clean grain and chaff falling from the concave 26 and the straw walkers 30 is directed to a grain pan 32 . crop material other than grain is expelled over the rear of the straw walkers 30 and out of the combine . the grain pan 32 directs the clean grain and chaff to a cleaning assembly which comprises sieves 34 and a cleaning fan 36 . the cleaning fan 36 blows the chaff out the rear of the combine , whereas the clean grain falls downwardly and is collected on the floor of the combine . the clean grain is transferred upwardly by a clean grain elevator to the grain tank 18 . the roof of the operator &# 39 ; s cab 16 is provided with a first position sensor 42 . the first position sensor is an antenna for the reception of gps signals . although this sensor is located on the roof of the operator &# 39 ; s cab 16 , it may be located at any position on the combine where it would receive a good gps signal . the front of the operator &# 39 ; s cab 16 is provided with a second position sensor 44 . the second position sensor 44 has a transmitter for emitting laser radiation which reaches the ground approximately 10 meters ahead of the vehicle 10 . the laser radiation is reflected back from the ground or crop to the sensor 44 which is also provided with a receiver for receiving this reflected radiation . the distance to the reflection point from the sensor 44 is determined by the propagation time of the laser radiation to be received by the receiver . the second position sensor 44 is pivoted about an approximately vertical axis , in order to scan a region transverse to the direction of forward movement of the vehicle 10 . the signal of the receiver makes it possible to establish the angle between the forward operating direction and the position of the boundary of standing crop . such position sensors 44 are known and are described , for example , in u . s . pat . nos . 6 , 095 , 254 , and 6 , 101 , 795 , whose disclosures are incorporated herein by reference . there is a possibility of using a laser distance sensor in which the transmitter and receiver are not rotated , but a mirror rotating step - by - step or continuously is used to scan the visible region . it can scan an angular region of up to 180 °. such sensors are available from sick a . g ., d - 72796 , reute , under the designation lms . the first position sensor 42 and the second position sensor 44 communicate over a bus with a controller 46 having a memory 48 . the controller 46 supplies a steering signal to a steering controller 50 . the steering controller 50 is used for controlling the steering angle of the rear steerable wheels 14 . [ 0021 ] fig2 shows a plan view of the utility vehicle 10 during an agricultural harvesting operation . the harvesting assembly 64 is a harvesting platform , that cuts the plants ( cereal crop ) from the field . numerical designator 68 characterizes the boundary of operation between the previously harvested proportion of the field and the plants 62 that are still to be harvested . this boundary of operation in this application is known as a crop edge . the angular region covered by the scanning sensor 44 is scanning region 66 . it can be seen that the right portion of the scanning region 66 overlaps the boundary of operation 68 . furthermore , it can be seen that a time delay exists between the measurement of the position of the boundary of operation 68 and the point in time at which the vehicle 10 reaches the measurement point . this time delay must be considered in the providing a steering signal to the steering controller 50 . [ 0022 ] fig3 is a flow chart illustrating the operation of the controller 46 . after the start in step 100 , step 102 follows in which the first position signal of the first position sensor 42 is received . the position signal transmitted by the position sensor 42 from the satellite antenna may exhibit differing degrees of accuracy depending on external conditions . position sensor 42 may have a limited view of the sky and may not receive a sufficiently large number of gps satellites or in the case dgps may not receive the correction signals . obstacles located in the vicinity of the utility vehicle such as buildings or trees create errors in the propagation time that can also reduce the accuracy . therefore the first position sensor transmits signal quality information about the quality or the accuracy of the first position signal , that is derived from the number of gps satellites received at that time and the amplitude ( field strength ) of the signals received by the first position sensor 42 . the first singal quality information transmitted to the controller 46 is therefore a measure of the accuracy or reliability of the first position signal . in the following step 104 , the controller 46 receives a second position signal from the second position sensor 44 . the second position signal contains distance information as well as the angle between the longitudinal centerline of the utility vehicle 10 and the crop edge at that time . optical sensors for the recognizing crop edges of a windrow or standing crop may operate with less accuracy in dusty conditions , in fog , with lodged grain crop , and in very thin crop stands . in addition these sensor may have difficulty in finding the crop edge when operating around sharp curves , upon entry into a crop stand , upon reaching the end of the field , and for when several edges are encountered . in these cases the second position signal would not be as accurate and precise influencing the steering negatively . for this reason the controller 46 is supplied with a second signal quality information that is derived from the size of the change in the signal at the crop edge received by the receiver of the second position sensor 44 . the greater the change in the signal from the crop edge , the more precise the measurement of the angle will be by which the crop edge is located . in step 106 , the actual position of the utility vehicle 10 is calculated from the first position signal and the second position signal . the second position signal contains information about the position of the utility vehicle 10 relative to the crop edge , whose accuracy is in the centimeter range . since the harvesting operation normally is performed along parallel tracks with an offset that is specific to the harvesting assembly , the crop edge can be calculated from previous crossings of the field , in which the position of the utility vehicle 10 was stored in memory 48 . on the basis of the position previously calculated of the crop edge and the position of the utility vehicle 10 relative to it , the second position signal can be utilized to improve the accuracy of the first position signal . the position of the utility vehicle 10 is determined by considering the direction and the velocity of the vehicle 10 as well as the distance required by the vehicle 10 to cover the time delayed location sensed by the second position sensor 44 . in this way the first position signal from the first position sensor 42 is compared with the time delayed second position signal of the second position sensor 44 . the controller 46 considered both position signals and the quality information associated with both position signals . the better the quality of one of the signals relative to the other signal , the more strongly it is considered and weighted in calculating the actual position of the utility vehicle 10 . in the next step 108 , the controller 46 evaluates the accuracy of the second position signal to determine if it is greater than a threshold value stored in memory 48 , that corresponds to an accuracy of a few centimeters . if the accuracy is sufficient , step 110 follows , in which a steering signal is generated , based on the second position signal , and is transmitted to the steering controller 50 . the steering signal is selected by the controller 46 on the basis of the second position signal or the position calculated in step 106 in such a way that the utility vehicle 10 is guided in a manner known in itself along the crop edge . the target path information stored in memory 48 corresponds to the intended path along the crop edge where , however , no map is stored in memory , but only the desired transverse distance between the longitudinal centerline of the utility vehicle 10 and the crop edge . in step 112 the controller 46 orders that the position information calculated in step 106 be stored in memory 48 . step 112 is again followed by step 102 . if step 108 concludes that the accuracy of the second position signal is not adequate , step 114 follows , in which the position signal as was calculated in step 106 , whose accuracy can be improved in case the accuracy of the second position signal is inadequate or independent thereof can be improved by local sensors for the movement of the utility vehicle 10 , the steering angles and acceleration and possibly the inclination of the slope , and generates a steering signal from the path previously covered by the utility vehicle 10 that was recorded in the memory arrangement 48 , and supplies this to the steering controller 50 . since the operation on the field is normally performed in parallel paths with an offset depending on the width of the crop recovery arrangement , the path of the utility vehicle 10 can be predicted on the basis of the position calculated in step 106 ( as was recorded ). the method of the designation of the target path ( for example , by a map , on the basis of the boundary of the operation or the previous path ) may also be provided as input by the operator , in addition to the automatic selection . step 114 is followed by step 112 . 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 .
an automatic steering system is provided with a first position sensor for generating a first position signal and a second position sensor for generating a second position signal . both position signals are communicated to a controller having a memory . the controller is also supplied signal quality information about the quality of the position signals . the controller evaluates the position signals based on the signal quality information and weights the position signals accordingly to calculate the position of the vehicle and select the vehicle &# 39 ; s target path . the target path is selected from several target paths and is the best that corresponds to the position of the vehicle . the controller then generates a steering signal that is communicated to a steering controller for steering the vehicle .