Abstract:
A steerable mine detonation apparatus is adapted to be pushed by a steered vehicle. The apparatus comprises a frame and at least two spaced apart ground engaging members adapted to support the apparatus and adapted to exert a force on mines in the apparatus&#39; path of sufficient to cause detonation thereof. At least one ground engaging member is steerable, and at least one steerable ground engaging member is attached to the frame so as to pivot with respect thereto about a substantially vertical axis and is connected to a steering linkage, the apparatus further comprising a steering mechanism operatively connected to the steering linkage and, in use, to the pushing vehicle. An actuator adapted to vary the configuration of the steering mechanism, is controlled to provide that, in use, the turning radius of at least a part of the innermost ground engaging member is less than or equal to the turning radius of the innermost wheel of the pushing vehicle, and the turning radius of at least a part of the outermost ground engaging member is greater than or equal to the turning radius of the outermost wheel of the pushing vehicle.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to mine detonating apparatus. The invention relates particularly, but not exclusively, to mine detonating apparatus for use with vehicles that are fitted with wheels that are steered. 
       BACKGROUND OF THE INVENTION 
       [0002]    In regions of conflict it is often necessary for wheeled vehicles to use roads, tracks and other terrain that may have been mined or laid with other improvised explosive devices (IEDs). 
         [0003]    Mines and IEDs can be fitted with a variety of different types of fuses however they are often fitted with fuses that are designed to detonate as a result of the wheel of the vehicle passing over them, such IEDs possibly including both pressure and time delay fuses. In the remainder of this document the terms mine and IED are used interchangeably and collectively, i.e. an IED may be a mine and a mine may be an IED. 
         [0004]    By detonating as a result of the wheel passing over them, mines explode so as to inflict the maximum damage to the vehicle, wheel and the associated steering mechanism. 
         [0005]    Relatively small amounts of explosive can easily disable a vehicle. 
         [0006]    A mine clearing apparatus intended for use with armoured personnel carriers (APCs) is described in U.S. Pat. No. 6,915,728. In this invention a pair of rollers is pushed in front of the APC in front of the tracks and a further set of rollers is towed behind the APC. 
         [0007]    The position of the rollers in front of the vehicle is adjusted to partially follow the path of the vehicle by a signal resulting from the position of a further roller set mounted behind the vehicle. 
         [0008]    The invention disclosed here is for a mine roller system that can be attached to a host vehicle or is part of the host vehicle and is pushed ahead of the host vehicle so that the path of the wheels of the host vehicle follow within the path followed by the mine roller system as it goes round a corner as well as in a straight line. 
         [0009]    Mine roller systems that have been designed for use with wheeled vehicles are generally characterised as follows: 
         [0010]    They comprise a frame attached to the front of the host vehicle. The frame is fitted with a number of IED detonating wheels designed to apply a downwards force on the ground in front of the vehicle to simulate the effect of a vehicle passing over them thus activating pressure influenced and other fuses that may be used with the IEDs before the vehicle passes over them. 
         [0011]    The IED detonating wheels are usually spring loaded to allow them to lift up over local obstacles and down into local hollows and still apply a force on the ground. The wheels are grouped into banks that are pivotably mounted onto a frame in such a way as to allow them to caster relative to the frame. They sometimes have a steering mechanism that moves the position of the supporting frame off which the wheels are castered. 
         [0012]    It is apparent that known equipments do not sweep the path of the vehicle very well as the host vehicle goes around a bend in the road. 
         [0013]    It is therefore an aim of the invention to overcome or at least alleviate the problem identified above. 
       SUMMARY OF THE INVENTION 
       [0014]    According to one aspect of the invention there is provided an apparatus as specified in Claim  1 . 
         [0015]    The apparatus may comprise at least two spaced apart steerable ground engaging members, and preferably two spaced apart steerable ground engaging members. Two spaced apart steerable ground engaging members may be set up to tow in, which assists in the apparatus following a path. 
         [0016]    The actuator may be a fluid operated ram, a fluid operated motor, an electrically operated ram, or an electrically operated motor. A fluid operated ram could be actuated hydraulically or pneumatically. In the case where a motor is used rather than a ram, power transmission apparatus may be provided. 
         [0017]    Preferably, the steering mechanism includes a feedback system adapted to measure deviation of the apparatus from the path, generate a feedback signal and to adjust the steering linkage according to the feedback signal to return the apparatus to said path. This provides the advantage that during use, when the apparatus is subject for forces that cause movement thereof to one side, the steering mechanism adjusts the steering linkage and hence the steering angle of the steerable ground engaging members to bring the apparatus back to the desired path, for example after a collision with a stone, or whilst traversing a slope. The apparatus therefore would not run off path for more than a brief period. 
         [0018]    The feedback signal may be generated mechanically, electronically, electrically or hydraulically. 
         [0019]    The steering mechanism may further comprise at least one member arranged to pivot about a substantially vertical axis. 
         [0020]    Advantageously, the steering mechanism comprises first and second members each arranged to rotate about substantially vertical axes, wherein the actuator is adapted to adjust the relative position of the first member with respect to the second. 
         [0021]    The first and second members may be mounted to rotate about the same substantially vertical axis independently of each other. 
         [0022]    Preferably, one of the first and second members is operatively connected to the steering linkage, and the other of the first and second members may be operatively connected to the pushing vehicle. 
         [0023]    In one embodiment, the steering mechanism comprises a linkage, the linkage including a tie member pivotably attached at one of its ends to one of the first and second members and operatively attached to the steering system at its other end. The linkage may further include a tie member pivotably attached at one of its ends to the other of the first and second members at its other end to a pushing vehicle. 
         [0024]    Preferably, the steering linkage includes a connector mounted on the frame and operatively connected to the or each steerable ground engaging member, and the steering mechanism. Operative connection of the connector to the steerable ground engaging members may be achieved by the use of track rods, and/or the fluid actuators. Operative connection of the connector to the steering mechanism is advantageously by means of a tie rod. 
         [0025]    At least one ground engaging member may be adapted to follow the path of the apparatus set by the at least one steerable ground engaging member. 
         [0026]    The apparatus may further including a steering lock providing locked and unlocked configurations of the or each steerable ground engaging members. The steering lock may include at least one element movable between a locked configuration in which said element engages with a part of the steerable ground engaging member and an unlocked configuration in which the said element is disengaged from the steerable ground engaging member. 
         [0027]    Preferably, the actuator is provided with a neutral setting in which the actuator configuration changes according to passive forces exerted thereon. This allows the apparatus to be moved when the steerable ground engaging members are locked. For example, where the actuator is hydraulic, the hydraulic circuit powering the actuator is provided with valves that permit a float setting to be selected, in which the actuator is free to extend or retract. 
         [0028]    Preferably, the ground engaging members are mounted to pivot about a substantially horizontal axis. 
         [0029]    Each steerable ground engaging member may include a plurality of individual ground engaging elements, each element preferably being mounted to move independently in a substantially vertical plane. 
         [0030]    Another aspect of the invention provides the combination of a pushing vehicle and connect thereto a steerable mine detonation apparatus adapted to be pushed by a steered vehicle, the apparatus comprising a frame, at least two spaced apart ground engaging members adapted to support the apparatus and adapted to exert a force on mines in the path thereof sufficient to cause detonation thereof, wherein at least one ground engaging member is steerable, and wherein the at least one steerable ground engaging member is attached to the frame so as to pivot with respect thereto about a substantially vertical axis and is connected to a steering linkage, the apparatus further comprising a steering mechanism operatively connected to the steering linkage and including an actuator adapted to vary the configuration of the steering mechanism, and a control means including a controller configured to receive an input signal related to the turning radius of a pushing vehicle and to generate an actuator control signal related to the input signal, and to control the actuator according to the actuator control signal, wherein the so controlled actuator configures the steering mechanism to adjust the steering linkage such that the at least one steerable ground engaging member is positioned to follow a path which provides that, in use, the turning radius of at least a part of the innermost ground engaging member is less than or equal to the a turning radius of the innermost wheel of the pushing vehicle, and the turning radius of at least a part of the outermost ground engaging member is greater than or equal to the a turning radius of the outermost wheel of the pushing vehicle. 
         [0031]    As mentioned above, in clearing mines and IEDs, it is particularly important that the mine rollers should cover the path that the wheels of the pushing vehicle will traverse. The invention accomplishes this. Further, the invention provides an apparatus configured such that it returns to the required path automatically after being subjected to a force causing deviation of the apparatus from the path. Still further, the apparatus of the invention provides for the mine rollers to be spaced from the pushing vehicle by a significantly greater distance than is the case mine rollers of the prior art. This means that in the event of a mine being detonated, the risk of the pushing vehicle being damaged is much reduced, the maximum pressure of the explosion diminishes with the cube of the distance from source of the explosion, and hence increasing the distance between the rollers and the pushing vehicle has a marked effect on the likelihood of the vehicle being damaged by an explosion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    The Drawings illustrate preferred embodiments of the invention, and are by way of example only. 
           [0033]      FIG. 1  is a plan view of a known mine clearance roller. 
           [0034]      FIG. 2  is a plan view of a device according to a first embodiment of the invention on a straight heading. 
           [0035]      FIG. 3  is a side view of the device illustrated in  FIG. 2 . 
           [0036]      FIG. 4  is a plan view of the device illustrated in  FIGS. 2 and 3  unhitched from the pushing vehicle. 
           [0037]      FIG. 5  is a side view of the device illustrated in  FIG. 4 . 
           [0038]      FIG. 6  is a plan view of the device illustrated in  FIGS. 4 and 5  locked for reversing. 
           [0039]      FIGS. 7 to 12  illustrate the combination of the device and the pushing vehicle executing a turn where: 
           [0040]      FIG. 7  is a plan view of the device travelling on a straight path just prior to commencing a turn to the left; 
           [0041]      FIG. 8  is a plan view of the device illustrated in  FIG. 7  with the steering wheels of the pushing vehicle turned to the left to an angle of approximately 10 degrees to commence the turn; 
           [0042]      FIG. 9  is a plan view of the device established on a turn with the pushing vehicle&#39;s steering wheels set at a steering angle of approximately 10 degrees; 
           [0043]      FIG. 10  is a plan view of the device moving on to a smaller turning radius with the steering wheels of the pushing vehicle turned to the left to an angle of approximately 20 degrees; 
           [0044]      FIG. 11  is a plan view of the device established on a turn with the pushing vehicle&#39;s steering wheels set at a steering angle of approximately 20 degrees; and 
           [0045]      FIG. 12  is a plan view of the device established on a turn with the pushing vehicle&#39;s steering wheels set at a steering angle of approximately 40 degrees. 
           [0046]      FIG. 13  is a schematic representation of parts of the alignment linkage of the first embodiment of the invention. 
           [0047]      FIG. 14  is a side view of a ground engaging wheel of the device. 
           [0048]      FIG. 15  is a front view of the device. 
           [0049]      FIG. 16  is a plan view of a device according to another embodiment of the invention on a straight heading 
           [0050]      FIG. 17  is a plan view of the device illustrated in  FIG. 17  executing a turn. 
           [0051]      FIG. 18  is a plan view of the device following a deviation thereof from a desired path. 
       
    
    
     DETAILED DESCRIPTION OF THE PRIOR ART EMBODIMENT 
       [0052]    The sketch in  FIG. 1  shows one possible arrangement of a known system. The sketch shows the plan view of a vehicle fitted with three roller sets at its front travelling around a bend from right to left. 
         [0053]    In  FIG. 1 , about one third of the path followed by the vehicle would not be swept by the rollers. This is a concern because seeing the operational capabilities of existing equipment, the enemy can simply plant their IEDs on the bends in the road and easily defeat an existing roller system. 
         [0054]    If the framework is steered using a mechanism that reacts these forces against the host vehicle, the forces required to steer tend to induce loads much higher than intended on the front wheels and steering mechanism of the host vehicle. This is likely to result in increased wear and premature failure of the steering mechanism of the host vehicle. 
         [0055]    It is also apparent that the spring loaded wheels that are intended to detonate mines and other IEDs are sometimes very close to the body of the host vehicle. 
         [0056]    It is well known that the effectiveness of an explosive blast reduces with increased distance. With the detonating wheels so close to the vehicle the detonation created by them usually causes substantial damage to the vehicle and puts the crew of the vehicle at increased risk. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0057]    The present invention serves to overcome some of the limitations of existing inventions. 
         [0058]    The mine roller system disclosed here is pushed ahead of the host vehicle in such a way that the path of the wheels of the host vehicle automatically follows more closely within the path covered by the mine roller system as it goes round a corner as well as in a straight line. It is possible, particularly in a tight turn, that during the period between the steering wheels of the pushing vehicle being turned and the mine roller system reacting, the path taken by the wheels of the pushing vehicle may not be covered completely. This may be overcome by the provision of a manual override system to steer the mine roller system in advance of the steering wheels of the pushing vehicle for example. 
         [0059]    The mechanism invented induces small additional loads on the steering mechanism of the host vehicle thus reducing the likelihood of excessive wear and premature failure of the host vehicle systems. 
         [0060]    The mine rollers are pushed ahead of the host vehicle a substantial distance away from the front of the vehicle thereby reducing the risk of injury to the crew of the host vehicle and damage to the vehicle. 
         [0061]    In the following description we describe the use of the equipment with a four wheel drive truck (however, the fact that the truck has four wheel drive is not relevant). 
         [0062]    We envisage that it will be practical to adjust the weight of the mine roller system if required depending on the vehicles with which the system is being used. 
         [0063]    The steering mechanisms invented are shown diagrammatically in  FIGS. 2 to 18 : 
         [0064]    Notice the substantial “stand off” distance achieved between the wheel sets of the mine roller system and the front of the pushing vehicle. 
         [0065]    Referring particularly to  FIGS. 16 and 17 , in these drawings the wheeled host vehicle, is shown in plan view, with the mine roller system (MRS) fitted in front of it. The arrangement comprises the frame ( 4 ) connected to the vehicle ( 10 ) along the centre line. The frame can conveniently be mounted onto the NATO pintle usually found on the front of military vehicles. Mine roller sets ( 1 ), ( 2 ), and ( 3 ) are pivotally attached to the frame ( 4 ), so that they can caster about substantially vertical axes. Roller set ( 3 ) is further pivotally attached to the frame ( 4 ) by an intermediate bracket ( 11 ). 
         [0066]    In operation, the linkage system, schematically indicated by elements ( 5 ), ( 6 ), ( 7 ) and ( 8 ) serves to automatically steer the roller sets ( 1 ) and ( 2 ) to keep them on a path in front of the vehicle. If the roller becomes out of line or the host vehicle makes minor steering adjustments, the linkage geometry is such that it will serve to maintain the roller sets ( 1 ) and ( 2 ) in front of the vehicle. Roller set ( 3 ) is free to caster 360 degrees. The roller set is not steered, it simply follows the path taken by the roller sets ( 1 ) and ( 2 ). 
         [0067]      FIG. 17  shows a plan view of the mine roller system pushed by the vehicle, travelling around a bend. 
         [0068]    Note how the front roller sets are steered closely along the path that the wheels of the host vehicle follow. 
         [0069]    This is made possible by the geometry chosen for the linkage. The angle that the frame of the mine roller system needs to take is indicated as “A” in  FIG. 17 . Notice how the roller sets are in line with the frame. This is made possible by adjusting the length of linkage member ( 5 ). 
         [0070]    The required length for linkage member ( 5 ) is determined by measuring the turning circle being negotiated. This is done electronically by use of a simple linear transducer or some other measuring device connected to the vehicle&#39;s steering mechanism. The measuring device may measure any parameter of the vehicle&#39;s steering mechanism from which the vehicle&#39;s turning circle may be calculated. From this electronic measurement, the programmable logic controller (PLC) programme calculates the required angle “A” according to an algorithm (which is not disclosed herein, the algorithm being within the knowledge of the person skilled in the art) and the required length of linkage member ( 5 ). 
         [0071]    When negotiating a bend of a particular turning circle, the mine rollers are automatically steered on the required path. In the same way as when the required steering angle “A” is zero ie when travelling in a straight line, small deviations in steering angle of the host vehicle are compensated for by automatic tracking of the steering mechanism. If the mine rollers become out of line, the linkage automatically adjusts to compensate and steer the roller set into line. 
         [0072]    In practice the linkage member ( 5 ) is a hydraulic cylinder. The extension i.e. the position of this is accurately controlled by use of an integral linear transducer and electronic closed loop feedback system. 
         [0073]    The hydraulic cylinder ( 5 ) is only actuated when the turning circle changes. At constant turning circles and in a straight line the cylinder doesn&#39;t extend or retract. The steering is automatically maintained in the correct position by the mechanism. This is important because it means that the minimum amount of power is used and the auxiliary hydraulic power pack required remains small and can be powered from the host vehicle inter-vehicle starting socket. It also means that it is not necessary to constantly correct for small steering misalignments this is achieved automatically with no hydraulic power consumption. 
         [0074]    As the wheels of the host vehicle are steered, the turning radius that will be created is calculated from measurements received from a transducer fitted to the steering mechanism of the vehicle. The PLC is programmed to calculate the angle “A” that the frame is required to adopt to ensure that the host vehicle will follow the roller sets. The control circuitry then serves to actuate the hydraulic cylinder so as to rotate the link  5   a.  This causes the wheelsets to steer so as to bring the framework to the appropriate angle. 
         [0075]    Referring now to  FIGS. 2 to 6 , there is shown another embodiment of the invention. Where parts of the embodiment now described correspond to parts of the device described with reference to  FIGS. 16 and 17 , like reference numerals are used. 
         [0076]    Referring first to  FIGS. 2 to 6 , the mine roller apparatus  20  comprises a frame  4 , which includes an A frame formed by structural members  22 ,  23 , formed for example from tubular steel. A push bar  21  extends from the apex of the A-frame and terminates in a hook  21   a,  which attaches to a pintle  9  of the pushing vehicle. Frame  4  supports a shaft  25 , which is hollow in the illustrated example, and which extends in a substantially perpendicular direction to the longitudinal axis of the apparatus  20 . Two elements of the mine roller steering mechanism are mounted on the shaft  25 . The first is an elongate member  24  which includes a bracket  26  attached to the end of the member  24  proximate the A frame through which the shaft  25  passes. A bracket  27  is attached to the elongate member  24  towards the free end thereof. One end of a rod  28  is pivotally connected to the bracket  27 , the other end of the rod being pivotally connected to the pushing vehicle  10  by means of a pivot attachment  29 . The rod  28  forms part of a feedback system. The elongate member  24  mounts another bracket  30  to which one end of an extensible actuator  31 , in the form of a hydraulic ram in the present example, is attached. The other end of the actuator  31  is attached to a bracket  26  by a pivot attachment  32 , which may comprise a pin passing through holes in the bracket  26  and end of the actuator  31 . The bracket  26  is also pivotally mounted on the shaft  25 , that is it may rotate about the shaft  25 . The actuator  31  serves to change the angle of the member  24  relative to the bracket  26 . A tie rod  36  extends between and is pivotally attached to the bracket  26  at pivot attachment  33  and a plate  35  of a roller steering linkage. The plate  35  is pivotably attached to a bracket  58 , which is attached to the frame  23  by a bracket  59 . The shaft  25 , elongate member  24  and bracket  26  are illustrated in detail in  FIG. 13 . 
         [0077]    The apparatus includes a steering angle sensor for sensing the steering angle of the steering wheels (the front wheels) of the pushing vehicle  10 . Of course the steering angle of the steering wheels need not be measured directly. Any measuring device connected to the pushing vehicle&#39;s steering mechanism, and arranged to measure a parameter of the vehicle&#39;s steering mechanism from which the vehicle&#39;s turning circle may be calculated may be used. The PLC runs an algorithm that calculates the length at which actuator  31  must be set to move the roller sets  1 ,  2  to a position in which the roller sets pass over the track of the inner most wheel of the pushing vehicle (this corresponds approximately to the calculation of the length of the actuator  5  to provide angle A described with reference to  FIGS. 2 and 3 ). 
         [0078]    In this example the rod  28  is of fixed length. Hence, the rod  28 , the push bar  21  the elongate member  24  and the part of the front of the pushing vehicle  10  extending between the pintle  9  and the pivot attachment  29  form a parallelogram linkage. 
         [0079]    The movement of the mine clearance apparatus will now be described with reference to  FIGS. 7 to 9  and  10  to  12 . In  FIG. 7  the pushing vehicle  10  is just about to commence a turn to the left. In  FIG. 8  the pushing vehicle  10  has turned the front wheels  10   a,    10   a   1  to the left. As the wheels of vehicle are being steered to the left, the steering angle sensor detects the angle through which the front wheels have been turned (10 degrees in this case) and the PLC calculates the require length of actuator  31  to position the mine clearance apparatus  20  in relation to the pushing vehicle  10  such that the path followed by at least a part of the roller set  2  (the inner roller set when turning to the left) passes over the path that the unsteered inner wheel of the pushing vehicle (in the example the left hand rear wheel) will follow when executing the turn. 
         [0080]    Hence, when the actuator  31  is retracted to the length required by PLC, the plate  35  is caused to rotate anti-clockwise. The roller sets  1 ,  2  are connected to the plate  35  by track rods  7 ,  8 , and hence turning the plate  35  anti-clockwise in turn turns the roller sets  1 ,  2  anti-clockwise. 
         [0081]    With the roller sets  1 ,  2  set in the position illustrated in  FIG. 8  the mine clearance apparatus  20  tracks across to the left towards the desired position as the apparatus is pushed forwards. As the apparatus  20  moves from the position illustrated in  FIG. 8  to the position shown in  FIG. 9 , the change in shape of the above-mentioned parallelogram causes the plate  26  and hence the plate  35  to turn clockwise until the position illustrated in  FIG. 8  is reached where the assumed steering angle of roller sets  1 ,  2  corresponds to that which is required to keep the apparatus  20  on the turning radius that ensures that the path traversed by at least a part of the inner roller set  2  covers the path traversed by the left rear wheel  10   b  of the vehicle  10 , and the path traversed by at least a part of the outer roller set  1  covers the path traversed by the right front wheel  10   a ′ of the pushing vehicle  10 . 
         [0082]    In  FIG. 10  the driver of the pushing vehicle has turned to wheels  10   a,    10   a   1  to increase the turning angle to 20 degrees, this increase in steering angle occurring as the vehicle moves forwards. Again, the PLC determines the required length of actuator  31  and causes the length thereof to be changed. The roller sets  1 ,  2  are turned anti-clockwise and the apparatus tracks across to the left to assume to position illustrated in  FIG. 11 , in which the path traversed by the wheels of the pushing vehicle are covered by the rollers  1 ,  2 . 
         [0083]    In  FIG. 12 , the driver of the pushing vehicle  10  has increased the steering angle to 40 degrees, the change in steering angle resulting in the length of the actuator decreasing to provide the required angle A. The apparatus tracks across to the left. 
         [0084]    In each of the Figures referred to above, a roller set  3  is illustrated. The roller set  3  is situated between roller sets  1  and  2 , and is not steering in the same manner as roller sets  1  and  2 . Roller set  3  is attached to the structural member  23  by means of a pivot linkage  60  comprising a towing eye  62  extending from a draw bar of the roller set  3 , a clevis hitch  64  and a pin  6  configured to pass through aligned holes in the towing eye  62  and clevis hitch  64  (see  FIG. 5  in particular). 
         [0085]    In the Figures the outer roller sets  1 ,  2  are steerable and the centre roller set  3  is unsteered, but follows the steered path because it is connected to the apparatus as described above. It may be envisaged that the centre roller set may be steered as well as the outer roller sets. Further, it may be envisaged that the centre roller may be steered and the outer rollers unsteered, but connected to the apparatus in a manner that provides for them to be able to follow the path determined by the steered centre wheel set, for example using the method of attachment to the structural member  23  as described above in relation to roller set  3 . 
         [0086]    In addition to providing for the roller sets  1 ,  2  to clear the path of the inner most wheel of the pushing vehicle, the linkage arrangement of the apparatus and its geometry provide that the apparatus will always come to an equilibrium position corresponding to the steering angle and hence desired path of the pushing vehicle and will return to the desired path after any deviation therefrom, i.e. the linkage arrangement provides a feedback system. This feature is now described with reference to  FIGS. 2 and 18 . Referring to  FIG. 2 , if for example, one of the rollers were to hit a large stone and the apparatus  20  were thrown across to the right to the position illustrated in  FIG. 18 , without the driver of the pushing vehicle  10  making any corrective steering input, the apparatus  20  would be caused to return to the set steered path because the deviation of the apparatus to the right would cause the shape of the parallelogram to change causing the elongate member  24  to rotate anti-clockwise about shaft  25 , which due to the fixed length of actuator  31  causes the bracket  26  to rotate anti-clockwise about shaft  25 , which due to the action of the tie rod  36  causes the plate  35  to also rotate anti-clockwise, which in turn causes the roller sets  1  and  2  to take up a position to steer the apparatus  20  to the left. As the apparatus  20  returns to the desired path the parallelogram returns to the correct shape for the desired path and the combination of the apparatus and pushing vehicle return to a steady state. In this example the feedback signal representing the deviation of the apparatus from the desired angle A, is provided by the mechanical linkage, in particular, the mechanical link attaching the steering mechanism to the vehicle provided by rod  28 . However, the feed back system need not be wholly mechanical arrangement. For example, the link  28  could be replace with a linear actuator, one end being connected to the elongate member  24  and the other to a fixed part of the apparatus, for example the push bar  21 . A transducer may be provided to generate an electronic signal representative of the actual angle A, which may be compared with the calculated angle A. The controller may be programmed to generate a signal which is used to adjust the length the actuator and hence increase the steering angle of the roller sets  1 ,  2  to bring the apparatus back such that the angle A is the calculated angle A. Such an electronic feed back arrangement would operate on a continuous loop and adjust the length of the actuator as the apparatus returned to the desired path, or upon the return of the apparatus to the calculated angle A. Electronic communication between the pushing vehicle  10  and the apparatus may be by wire or wireless. 
         [0087]    An alternative electronic feedback signal could utilise the actuator  31 . In such an arrangement, the link  28  would be removed, and the actuator would extend between a fixed object and the bracket  26 , for example the position of member  24  may fixed. The required length of actuator  31  to provide the required angle “A” would be calculated as described above. If the apparatus were to hit an object resulting in a deviation to the right, the actual angle A would not correspond to the required angle A. This difference may be used to calculate a new length of actuator  31  to adjust the steering angle of the roller sets  1 ,  2  to bring the apparatus back to the path as described in the preceding paragraph. 
         [0088]    A feature of the apparatus  20  is that whilst it is inherently stable whilst being pushed forward, it is inherently unstable when the pushing vehicle is reversed. It would be undesirable for reversing the combination of the pushing vehicle  10  and apparatus  20  to be difficult. To alleviate the problem of inherent instability when reversing, the apparatus  20  includes reversing locks  40 , which in the illustrated example are operable remotely from the cab of the pushing vehicle  10 . Referring specifically to  FIGS. 4 and 6 , each reversing lock  40  comprises a swing arm  41 , one end of which is pivotally connected to a bracket  42  mounted on the structural member  23 . An actuator  44 , in the form of a hydraulic ram in the illustrated example, is pivotally attached to the other end of the swing arm  41 , and to bracket  45  which is mounted on the structural member  23 . The reversing lock also includes a stop  46 . 
         [0089]    In  FIG. 6 , both roller sets  1 ,  2  are locked. In the locked state, it can be seen that the actuator  44  is extended and the swing arm  41  is in engagement with the stop  46  which is attached to the roller mount, and similarly, swing arm  41   a  is in engagement with its corresponding stop. Hence, rotation of the roller sets  1 ,  2  about their substantially vertical axes is prevented. 
         [0090]    In  FIG. 4 , the steering locks  40  associated with the roller sets  1  and  2  are shown in its unlocked state. In this state the roller set  2  may rotate about its substantially vertical axis, the range of rotation to the left being limited by the engagement of the stop  46  with the surface  41 ′ of the swing arm  41 . Roller set  1  may rotate about its substantially vertical axis in a counter clockwise direction to an amount limited by the engagement stop  46  with the surface  41 ′ of the swing arm  41 . 
         [0091]    With the steering lock in the locked configuration, pivotal movement between the pushing vehicle  10  and the apparatus  20  must be provided for in order for the combination to execute a turn. This could be achieved in a number of ways. For example, the rod  28  may be detached, or the tie rod  36  may be detached. However, both of these methods would require a person to walk from the pushing vehicle  10  to the apparatus  20 . Given that there is potential for unexploded IED&#39;s to be present, it is highly desirable that the operator should remain in the vehicle. Hence, the preferred means of providing for pivotal movement between the pushing vehicle  10  and the apparatus  20  is to provide the valve controlling the length of actuator  31  with a float setting, and a control means in the cab of the vehicle  10  to allow the valve to be switched to float mode. With the actuator in float mode the elongate member  24  is free to pivot about shaft  25  and hence the vehicle  10  may pivot with respect to the apparatus  20 . 
         [0092]    The roller set  3  is simply lifted clear of the ground during reversing, for example by means of a winch or hydraulic ram. 
         [0093]    Referring now to  FIG. 14 , each roller  56  of the roller sets  1  to  3  is mounted to pivot about a substantially horizontal axis, and a biasing means  57  (such as a gas spring, coil spring or hydraulic ram and accumulator) is provided to ensure that each individual roller  56  follows the surface over which it traverses. 
         [0094]    Referring now to  FIGS. 14 and 15 , each roller set  1 ,  2  is mounted on pivot mount  50 , the pivot axis of which lies in a substantially horizontal plane about a pin  52 . Further, the wheel is  56  is mounted on a bracket  55  which is in turn pivotaly mounted on a bracket  54  by means of a pin or the like, the bracket  54  being connected to a plate which is mounted on the pin  52 . A biasing means, such as a gas spring (or coil spring, or a hydraulic ram and accumulator or any other suitable biasing means)  57  extends between the bracket  55  and the plate  53 . Such a mounting provides for the roller sets  1 ,  2 ,  3  to follow ground undulations and mitigates against IED&#39;s being missed simply because they lie in a hollow between the extreme edges of the roller sets  1  to  3 . Regarding the roller set  3 , roll movement of the roller set may be accommodated by a pivot mount extending rearward from the drawbar  61  substantially along the axis of the drawbar, or alternatively, the hitching of the drawbar  61  to the frame may include a ball hitch or a ball link. 
         [0095]    Ballast weights  51  may be provided to ensure that there is adequate weight on the wheels  56  of rollers  1  to  3 . 
         [0096]    The extension of the ram  31  is preferably not abrupt. Advantageously, the steering angle of the vehicle is sensed at small time intervals so that the change the length of the ram  31  occurs gradually so that in practice the cylinder moves and wheelsets start to turn as the vehicle starts to turn. 
         [0097]    While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.