Abstract:
An early warning system for a tractor operator engaged in towing or pushing an aircraft includes two ultrasonic sensors that are used to create a detection area in which the aircraft should be present when the steering angle is well within a safe range. When one of the detectors fails to detect the presence of the aircraft, then the operator is alerted, before over steering can occur, in order that corrective action can be undertaken. Accordingly, complex distance-measuring algorithms can be avoided as can the requirement that an aircraft fuselage have a specially modified detection region.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to an aircraft tractor and, more particularly to a turn-out sensor for such a tractor.  
       BACKGROUND OF THE INVENTION  
       [0002]     It is often desirable to tow or push an aircraft at an airport rather than use the aircraft&#39;s engines for propulsion. For example, during an aircraft tow or pushback operation, a tractor attaches to the aircraft&#39;s landing gear and provides the propulsion power to move the aircraft. There are two general types of aircraft towing in practice—towbar and towbarless tractors. With towbar-type towing, a long slender bar is used between the tractor and the nose landing gear of the aircraft. With towbarless-type towing, a towbar is not needed; instead, the nose gear is picked up by the tractor during operation.  
         [0003]     An important factor when towing or pushing an aircraft using either type of towing method involves the “aircraft steering angle”. The aircraft steering angle is the angle between the wheel of the nose landing gear and the longitudinal axis of the aircraft. Regardless of the direction of the deviation, the steering angle is usually referred to in an absolute sense (e.g., 70E) rather than as signed values (e.g., −55E). Because it is possible, with either type of tractor, to steer the nose landing gear beyond its mechanical limits (known as “over-steer”), an indicator of such a condition would be useful. If a maximum aircraft steering angle is being exceeded, then damage to the aircraft and tractor is possible.  
         [0004]     Past attempts at alerting tractor operators to over-steer conditions have focused on detecting when a maximum steering angle has be reached. At such a point, damage may already be occurring to either the tractor or the aircraft or it may be too late for the operator to react and correct the situation. Still other attempts at addressing this problem have included an over-torque sensor on the tractor that mechanically detects that the maximum over-steer condition has been met. Typically, the over-torque sensor can control the drive motor of the tractor so as to disengage it if needed or trip an alarm that alerts an operator. Other attempts have included, for example, measuring multiple distances from the tractor and the two sides of the aircraft in order to calculate the steering angle. Similar attempts have included parallel beams emitted from the tractor and a pair of detectors for determining when one of the beams is interrupted by an aircraft because of over-steering. Other attempts have required special markings, or targets, be affixed to the side of the aircraft along with the use of a collimated light source such as a laser. Such a system requires modifying an aircraft and relies on a particularly narrow angle of incidence with the target to ensure proper reflection.  
         [0005]     Whatever the merits of these prior techniques, there remains an unmet need for a simple, efficient and reliable system and method to provide advanced warning of over-steering during aircraft towing and pushing operations.  
       SUMMARY OF THE INVENTION  
       [0006]     Accordingly, embodiments of the present invention provide an early warning to a tractor operator engaged in towing or pushing an aircraft. In one embodiment, two detectors are used to create a detection area in which the aircraft should be present when the steering angle is well within a safe range. When one of the detectors fails to detect the presence of the aircraft, then the operator is alerted, before over steering can occur, in order that corrective action can be undertaken. In particular, these detectors minimize false positives, are simple to operate, and perform reliably in a wide range of weather conditions and lighting environments. Furthermore, these embodiments do not require performing complex algorithms, using collimated energy sources, nor modifying the fuselage of an aircraft. In other embodiments, only one detector is used.  
         [0007]     One aspect of the present invention relates to a oversteer avoidance system for an aircraft tractor that utilizes two uncollimated energy transmitters and receivers, such as ultrasonic detectors. The ultrasonic detectors are positioned on the tractor such that when the tractor is engaged with the aircraft, one ultrasonic detector is located on each side of the aircraft&#39;s fuselage. Each ultrasonic sensor includes a coverage area in which a target within that area will result in a reflection signal being returned to the sensor. The sensors are positioned such that both sensors will detect the presence of the aircraft within their respective coverage areas when the aircraft steering angle is within a safe range. However, when a predetermined steering angle is exceeded, one of the sensors will not receive a reflected signal and, therefore, will activate an alarm. This predetermined angle can be less than the maximum possible oversteer angle so that the operator is warned of the potential condition early enough to easily take corrective action. In response to the warning alarm, the operator can reduce the steering angle so as to avoid over-steer or, alternatively, more closely monitor the towing activity with the awareness that over-steering may occur. Other embodiments of the present invention contemplate utilizing a single sensor that is able to detect the presence of a region near the nose of the aircraft when the steering angle is within a permitted range but detects its absence when the over steering angle exceeds a threshold angle.  
         [0008]     Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  illustrates a front view of a tow tractor and aircraft showing the cone-shaped sensing area of a pair of ultrasonic sensors.  
         [0010]      FIG. 2  illustrates a perspective view of the arrangement of  FIG. 1 .  
         [0011]      FIG. 3  illustrates a perspective view of a tow tractor and aircraft when the steering angle has caused the aircraft to leave the sensing area of one of the ultrasonic sensors.  
         [0012]      FIG. 4  illustrates a schematic view of pertinent circuitry within a tow tractor that includes an early warning over steering system in accordance with embodiments of the present invention.  
         [0013]      FIG. 5  illustrates a flowchart of an exemplary method of warning of over steering condition in accordance with an embodiment of the present invention.  
         [0014]      FIG. 6  illustrates an alternative embodiment in which a single sensor is used to provide warning of an over steering condition.  
     
    
     DETAILED DESCRIPTION  
       [0015]     The operation and selection of ultrasonic sensors are well understood by a skilled artisan in this field. However, as a brief background, such a sensor emits ultrasonic waves in a cone-shaped pattern. When the ultrasonic waves encounter a reflective target, some energy is reflected to the sensor and subsequently detected. Ultrasonic sensors, in particular, receive reflected energy over a wide range of incidence angles between the sensor and the target. An ultrasonic sensor typically has a detection window such that targets less than a minimum distance away are not detected and returns from targets farther than a maximum distance are ignored. Some parameters that characterize an ultrasonic sensor include its range, its operating frequency, and its beam angle. In response to the detection of a target within the sensing area, the sensor will output a signal, typically an electrical pulse, that is received, and processed, by other circuitry that responds appropriately to the pulse.  
         [0016]      FIG. 1  illustrates a front view of a towbarless tractor  102  engaged with an aircraft  104  in a straight-ahead towing position. The towbarless tractor  102  is depicted transparently, so as not to obscure the location and view of the ultrasonic sensors  106 ,  108 . These sensors are located substantially near the rear of the tractor  102  and on each side of the tractor  102 . Looking from the front of the tractor  102  (and the aircraft  104 ), the ultrasonic sensor  106  is on the left side of the tractor  102  and the other sensor  108  is on the right side of the tractor  102 .  
         [0017]     As shown, the sensors  106 ,  108  are located nearly at the edge of their respective sides of the tractor  102 . Additionally, the sensors  106 ,  108  are located to the rear of the tractor  102  so that they are behind the front landing gear of the aircraft  104  when the tractor  102  has engaged the aircraft.  
         [0018]     Each ultrasonic sensor emits a conical, or substantially conical, area of ultrasonic waves. The cone  101  from the sensor  106  has a major axis  110  and the cone  103  from the sensor  108  has a major axis  112 . The angle  120 , 122  each major axis  110 ,  112  forms with a horizontal plane are selected so that the aircraft  104  intersects both cones  101 ,  103  of ultrasonic waves when the aircraft  104  is turned-out less than its over-steer angle. From the perspective view of  FIG. 2 , the major axes  110 ,  112  also form an angle  128  with a vertical plane, as well.  
         [0019]     As shown in  FIGS. 1 and 2 , the orientation of the cones  101 ,  103  of ultrasonic waves are symmetrically arranged on the tractor  102 . In other words, each sensor  106 ,  108  is located the same distance from the front of the tractor  102 ; each sensor  106 ,  108  is located the same distance from the center of the tractor  104 ; the angle  120  and  122  are the same; and each cone  101 ,  103  forms the same angle  128 . These angles  120 ,  122 , and  128  are selected so that the aircraft  104  intersects both cones  101 ,  103  when the tractor  102  and aircraft  104  form a steering angle between  0  degrees and a predetermined maximum angle, such as one that is less than an over-steer angle.  
         [0020]     The angles  120 ,  122  and  128  depend on a number of factors such as, for example, the range of sensors  106 , 108 ; the height of the aircraft fuselage  104  above the tractor  102 ; the beam angle of the sensors  106 ,  108 ; and the selected range of steering angles within which the aircraft  104  should intersect the cones  101 ,  103 .  
         [0021]     The maximum steering angle, or over-steer condition, varies for different type of aircraft but typically ranges from between approximately 55E-90E for most commercial passenger jets. Because the tractor  102  can be utilized with a variety of different aircraft, the sensors  106 ,  108  should be selected and positioned for responding to a wide range of conditions. For example,  45 E can be selected as the maximum steering angle in which the aircraft  104  will intersect both cones  101 ,  103 . If that angle is exceeded, the aircraft will not be detected by one of the sensors  106 ,  108 .  
         [0022]     With this maximum angle selected, and prior knowledge that for most passenger jets, the aircraft  104  is about 0.25-4 meters above the tractor  102 , the sensors  106 ,  108  and their orientation can be identified. While many ultrasonic sensors are manufactured that have a range of around 0.25-4 meters and a beam angle between 5-20 E, one exemplary ultrasonic sensor useful in this application is manufactured by Pepprl+Fuchs® as model UB4000-30GM-E4-V15. This model has a beam angle of around 10E and operates at a frequency of approximately 85 kHz. With these operational attributes, the angles  120 ,  122  are selected to be substantially 27.5E and the angle  128  is substantially 15E. These specific values are given by way of example only. One of ordinary skill would recognize that a different maximum steering angle or a different ultrasonic sensor could be used by adjusting the angles  120 ,  122  and  128 . Additionally, the sensors  106 ,  108  do not necessarily have to be arranged symmetrically as depicted in these figures. Various arrangements can be designed as long as their detection areas are aligned to provide the appropriate over-steer warning.  
         [0023]     When an operator tows, or pushes, the aircraft  104  with the tractor  102 , the steering angle may increase. As the steering angle increases, the fuselage of the aircraft  104  will drift right or left of the back or the tractor  102 . If the aircraft  104  drifts enough, then it will no longer be within the sensing area of one of the cones  101 ,  103 .  FIG. 3  illustrates when the aircraft is being steered at an angle that causes it to exit the sensing cone  101 . As viewed in  FIG. 3  from the front of the tractor  102 , a significant portion of the fuselage of the aircraft  104  is to the left of the tractor  102 ; a condition for which corrective action may be warranted. When the sensor  106  determines that the aircraft  104  is no longer detected within its sensing area  101 , the sensor  106  can activate an alarm signal to alert the operator. In response the operator can reduce the steering angle to a safe range, or more carefully monitor the situation with the awareness that the over-steer angle is imminently approaching.  
         [0024]      FIG. 4  illustrates a schematic view of relevant portions of the tractor  102 . In actuality, the tractor  102  is a complex system of circuits and assemblies that allow an operator to easily move large aircraft. However, as implementation of this conventional functionality is well understood by one of ordinary skill, those details are omitted from  FIG. 4  so as not to obscure the principles of the present invention.  
         [0025]     In general, the tractor  102  includes a control system  402  that is typically a microprocessor-based, or micro controller-based, control system. This system  402 , monitors operation of the various parts of the tractor and provides an interface for the operator by which the tractor  102  can be controlled. As explained earlier, ultrasonic sensors  106 ,  108  are physically located on the tractor  102 . In addition to this mechanical connection with the tractor  102 , the sensors  106 ,  108  also communicate with the control system  402  over channels  406 ,  408 . These channels can be wireless, or wired; additionally, they can be redundant or have other safety features to identify if communications are lost or other errors or signal degradation exist in the circuitry.  
         [0026]     The sensors  106 ,  108  are connected with the tractor control systems  402  so that they can be selectively operated during towing operations of the tractor  102 . As such, the sensors can be disabled when the tractor  102  is not pushing or towing an aircraft. Additionally, when activated, the sensors  106 ,  108  communicate to the control system  402  whether the presence of the aircraft  104  is being detected within their respective sensing areas  101 ,  103 . As would be appreciated by a skilled artisan, interrupt-driven as well as polling-based interface methods can, be used when the sensors  106 ,  108  communicate with the control system  402 .  
         [0027]     When the control system  402 , determines that one of the sensors  106 , 108  does not detect the aircraft  102 , then the control system  402  can activate an alarm  404 . The alarm will typically be located within the cab of the tractor  102  but can be placed in any location where it is noticeable by the operator. Furthermore, the alarm  404 , can be audible, visual, or both and can vary in tone or frequency based on whether the steering condition persists or worsens. It is anticipated that once becoming aware of the alarm  404 , the operator will steer the aircraft  104  such that both sensors  106 ,  108  once again detect the aircraft  102 . Once this happens, the control system  402  can deactivate the alarm  404 .  
         [0028]     Referring now to  FIG. 5 , this figure depicts a flowchart of one exemplary algorithm that the tractor control system  402  can implement to avoid over-steer conditions. According to this flowchart, the oversteer avoidance system is activated in step  502 . Once this occurs, the sensors  106 ,  108  are active and emit sensing cones  101 ,  103 , respectively. Next, in step  504 , one of the sensors  106 ,  108  determines whether or not it detects the presence of the aircraft  104  in its sensing area. Concurrently, in step  506 , the other of the sensors  106 ,  108  similarly determines if it detects the presence of the aircraft  104  in its sensing area. Both of these monitoring determinations are then used, in step  508 , to determine if one of the sensors  106 ,  108  failed to detect the presence of the aircraft  104 . If both sensors  106 ,  108  detected the aircraft: 1104 , then the alarm can be de-activated (or remain un-activated), in step  512 , and monitoring can continue with steps  504  and  506 . However, if one of the sensors  106 ,  108  failed to detect the aircraft  104 , then the alarm is activated (or continues to be activated), in step  510 , and monitoring continues with step  504  and  506 . In response to the state of the alarm  404 , the operator can adjust the towing (or pushing) operation of the aircraft  104 .  
         [0029]     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited by the terms of the appended claims and their equivalents. For example, the ultrasonic sensor arrangement described herein can be retrofitted to an existing tractor in addition to being originally installed equipment. Additionally, detectors and sensors other than ultrasonic sensors can be utilized as well. These other types of sensors can include uncollimated light transmitters and receivers as well as sound-wave transmitters and receivers operating at lower frequencies. By using uncollimated sources of electromagnetic energy, the reflection of energy back to the receiver on the tractor can occur for a wide variety of aircraft fuselage shapes, fuselage materials, energy incidence angles, and aircraft steering angles.  
         [0030]      FIG. 6  illustrates one alternative embodiment in which a single ultrasonic, or other uncollimated energy, sensor is used to provide a warning of an over steering condition. In general, in the two-sensor embodiment described earlier, each sensor focuses energy on a respective section of the fuselage that moves in relation to the tractor  102  based on the steering angle. This area of the fuselage is selected so that it is within a sensor&#39;s detection region when the over steering angle is below a threshold and is outside of the sensor&#39;s detection region when the over steering angle exceeds a threshold. A similar area of the fuselage may be selected and used in conjunction with a single sensor as well. While the specific placement of the single sensor depends on a number of factors, such as, for example, the height of the fuselage and the beam angle of the sensor, the sensor is placed so that it detects a region of the fuselage whose movement is indicative of the steering angle.  
         [0031]     In  FIG. 6 , a sensor  604  is placed on a platform  602  of the tractor  102 . The sensor  604  is placed along the centerline of the tractor  102  so that it aligns with the nose landing gear  608  of the aircraft  104 . As shown in  FIG. 6 , the sensor  604  is located a particular distance  606  in front of the nose landing gear  608 . The platform  602  advantageously allows the sensor to be moved in a horizontal plane. As the tractor  102  ages while in use, the alignment of the tires and other components may change so that the sensor  604  is no longer aligned with the landing gear  608  and at the desired distance  606 . Accordingly, the platform  602  permits adjustment of the location of the sensor  604  using any of a variety of methods known to one of ordinary skill in the art.  
         [0032]     Other, alternative embodiments, contemplate the platform  602  being adjustable in the vertical plane as well so as to effect a change in the height of the sensor  604 . Also, to accommodate aircraft of different sizes, the platform  602  may allow an operator of the tractor to adjust the position of the sensor  604  in order to selectively change the distance  606  of the sensor  604  from the nose landing gear  608 .  
         [0033]     In accordance with one embodiment of the present invention, the sensor  604  is an ultrasonic sensor having a beam angle of approximately 40° to 55° and located ahead of the nose landing gear  608  by a distance  606  of approximately six to eight feet. With such a placement of the sensor  604 , it will be located about 12 to 18 feet below the nose region of a typical commercial-sized jet aircraft. The sensor  604  is advantageously oriented so that its cone of energy  610  is directed substantially straight-upwards in the vertical direction.  
         [0034]     When the steering angle between the aircraft  104  and the tractor  102  is below a maximum steering angle (e.g., 45°, or 50°), then some portion  612  of the fuselage is located above the sensor  604  within its detection region. However, when the maximum steering angle is exceeded, the entire portion  612  of the fuselage moves so that it no longer “covers” the sensor  604  and, thus, the sensor  604  no longer detects the aircraft  104 . When the sensor  604  no longer detects the aircraft  104 , then the operator of the tractor  102  is warned of the possible over steering condition.  
         [0035]     In addition to the above specific embodiment, the present invention contemplates within its scope using a single sensor arrangement to provide over steering warnings for a number of different aircrafts. Thus, in each such case, the fuselage size, shape and height as well as the particular over steering angle for that aircraft, would be considered when selecting the sensor&#39;s beam angle and location on the tractor. These considerations would be used to determine the sensor&#39;s location so that it will detect a region of the aircraft&#39;s nose when the steering angle is within a permitted range and not detect that region when a maximum steering angle is exceeded.  
         [0036]     In another embodiment, the sensor  604  and the two sensors  106  and  108  may be utilized in conjunction with one another to provide a total of three different sensors that may trigger the over steering alarm condition. Thus, embodiments of the present invention contemplate using one, two, and even more than two sensors to detect the presence or absence of the fuselage from appropriate detections regions so as to provide an alarm indicative of an over-steering condition.