Abstract:
A compaction machine such as a vibration trench roller has a supplemental receiver such as an eye located generally centrally of the machine and within a common reception zone of another receiver on the machine. The eye can receive a signal that is blocked from impinging upon the machine&#39;s other receiver(s), preventing the machine from shutting down when it passes beneath an obstruction and negating the need for the operator to reposition himself or herself to reestablish communications with the machine. The supplemental receiver may be positioned so as to maximize the operating range of the controller while reducing or avoiding false signals that otherwise could occur due to signal reflection. This positioning may include providing shielding around the supplemental receiver that creates a geometric umbrella of reception capability that forms a protection zone beneath it. Signals transmitted from within the protection zone cannot impinge on the supplemental receiver.

Description:
CROSS REFERENCE TO A RELATED APPLICATION 
       [0001]    This application claims priority under 35 USC §1.119(e) to earlier U.S. Provisional Patent Application Ser. No. 62/076,809, filed Nov. 7, 2014 and entitled REMOTE CONTROLLED COMPACTION MACHINE, the contents of which are incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to remote controlled compaction machines such as trench rollers and, more particularly, relates to a compaction machine with improved remote control capabilities and to a method of operating such a machine. 
         [0004]    2. Discussion of the Related Art 
         [0005]    Compaction machines are used in a variety of ground compaction and ground leveling applications. Most compaction machines have supports in the form of plates or rollers that rest on the surface to be compacted, and most of these supports are excited to vibrate so as to compact and level a worked surface. These machines are commonly referred to as “vibratory compactors.” 
         [0006]    A common vibratory compactor, and one to which the invention is well-suited, is a vibratory trench roller. The typical vibratory trench roller includes a chassis supported on the surface to be compacted by front and rear rotating drum assemblies. Each drum assembly supports a respective subframe of the chassis. In the case of an articulated trench roller, the subframes are coupled to one another by a pivot connection. Each of the drum assemblies may include a stationary axle housing and a drum that is mounted on the axle housing and that is driven to rotate by a dedicated hydraulic motor. Hydraulic motors are typically supplied with pressurized hydraulic fluid from a pump which may be powered by an engine mounted on one of the subframes. 
         [0007]    Each drum may be excited to vibrate by a dedicated exciter assembly that is located within the associated subframe and is powered by a motor connected to a pump. Each exciter assembly typically comprises one or more eccentric masses mounted on a rotatable shaft positioned within the subframe. Rotation of the eccentric shaft imparts vibrations to the subframe and to the remainder of the drum assembly. The entire machine may be configured to be as narrow as possible so as to permit the machine to fit within a trench whose floor is to be compacted. Machine widths of less than 3 feet (1 meter) are common. Vibratory trench rollers of this basic type are disclosed, e.g., in U.S. Pat. No. 4.732,507 to Artzberger; U.S. Pat. No. 4,793,735 to Paukert; U.S. Pat. No. 5,082,396 to Polacek; U.S. Pat. No. 7,059,802 to Geier et al.; and U.S. Pat. No. 8,585.317 to Sina, the entireties of which are hereby expressly incorporated by reference thereto. 
         [0008]    Vibratory trench rollers often are controlled remotely using a transmitter on a remote controller that transmits infrared (IR) or other signals to the trench roller on a line-of-sight basis. The control signal is generated by manipulation of a joystick and/or other controls on the remote controller and controls operation of the machine. The IR signal is received by a receiver in the form of a photodetector or “eye” on the machine. causing the machine to stop or start travel in the desired direction (forward or reverse) and/or to control the machine&#39;s exciter assemblies. Two a signals may be transmitted simultaneously, namely, a relatively high-intensity control signal having a range of on the order of 50-65 feet (15-20 meters) and a relatively low intensity safety signal having a range of about 6.6 feet (2 meters). The safety signal is generated whenever the remote controller is active and causes the machine to cease moving upon receipt of the safety signal. The machine thus stops moving if the operator is located in a “safety zone” that is typically within about 6.6 feet (2 meters) of to the machine. 
         [0009]    Trench rollers often are used in trenches having reinforced side walls. For example, referring to  FIG. 1 , a vibratory trench roller or “machine”  10  may he used to compact the floor  14  of a trench  12 . The reinforcement or “trench shoring” often takes the form of vertical reinforcing sheets or walls  16  located along each side wall of the trench  12  and a number of spaced cross supports  18  extending laterally between the side walls near the top edge  20  of the trench  12 . The machine  10  typically is controlled by an operator stationed above the trench  12  via a hand-held remote controller  22 . The remote controller  22  transmits an IR signal  24  that propagates in an expanding arc until it impinges on the machine  10 , where it is detected by one of two eyes  26  and  28  located on opposite ends of the machine  10 . Each eye  26  or  28  faces to the rear or front of the machine  10  and often cannot receive signals from an operator standing beyond the opposite end of the machine. Thus, each eye  26  or  28  can be considered to be associated with its own dedicated “reception zone.” This means that, under many operating conditions, only one eye  26  or  28  can receive signals  24  from the remote controller  22  at any given time. 
         [0010]    Being located between the remote controller  22  and the machine  10 , the cross supports  18  can block a portion of the signals  24 , creating a “dead zone” formed by a “shadow” located downstream of the cross support  18  in the direction of IR signal propagation. The dead zone is bordered by the line  30  in  FIG. 1 . The machine  10  shuts down when the operative eye (rear eye  28  in the illustrated example) is positioned in the dead zone and experiences loss of signal, requiring the operator to reposition the remote controller  22  to a location in which signal receipt by the eye  28  can be reestablished. The need to reposition can be irksome to the operator, particularly if he or she is positioned on another machine, such as an excavator, and either has to move the machine or climb down off from it to reposition the remote controller  22 . 
         [0011]    The need therefore has arisen to provide a remote-control-operated vibratory trench roller or other compaction machine that does not experience loss of signal when the machine passes beneath or behind an obstruction such as a cross support of a shored trench. 
         [0012]    The need additionally has arisen to provide a method of operating such a compaction machine. 
       SUMMARY OF THE INVENTION 
       [0013]    In accordance with an aspect of the invention, a compaction machine such as a vibratory trench roller is provided with a supplemental receiver such as a photo detector located generally centrally of the machine. It may be located within a common reception zone of another receiver on the machine. The supplemental receiver can receive a signal from a remote controller that is blocked from impinging upon the machine&#39;s other receiver(s), preventing the machine from shutting down when it passes beneath or behind an obstruction such as cross-support of a trench shoring system. The supplemental receiver thus negates the need for the operator to reposition himself or herself to reestablish communications with the machine. 
         [0014]    In a possible implementation, the machine includes a mobile chassis, a compaction device on which the mobile chassis is mounted and which compacts the surface on which the machine is supported, and first and second receivers configured to simultaneously receive a line of sight-based signal from the same remote controller, whereby one of the receivers will continue to receive the signal if a signal path to the other receiver is blocked by an obstruction. 
         [0015]    The first receiver of this configuration may be supported on the chassis in the vicinity of a first longitudinal end of the machine, and the second receiver may be supported on the chassis in the vicinity of a longitudinal center of the machine. A third receiver may be supported on the chassis in the vicinity of a second longitudinal end of the machine opposite the first longitudinal end. The second receiver is located in a first common reception zone with the first receiver and in a second common reception zone with the third receiver. 
         [0016]    The supplemental receiver may be positioned so as to maximize the operating range of the remote controller while reducing or avoiding the receipt of false activation signals that otherwise could occur due to signal reflection off from, for example, an operator located in the vicinity of the machine. This positioning may include providing shielding around the supplemental receiver that creates a geometric umbrella of reception capability that forms a protection zone beneath it. Signals transmitted from within the protection zone cannot impinge on the receiver. 
         [0017]    For example, the shielding may comprise a recess in a portion of the hood in which the second receiver is mounted and/or a shield that is located laterally between the second receiver and an edge of the recess and that extends above a base of the recess 
         [0018]    Also provided is a method of operating a compaction machine that includes simultaneously transmitting a control signal from a remote controller to first and second spaced receivers in a common reception zone on a compaction machine such that, if the transmission of the control signal to one of the receivers is blocked, by an obstruction, the control signal is still received by the other receiver. 
         [0019]    The first and second receivers may be located in the vicinity of a front end of the machine and a central portion of the machine, respectively, and the compaction machine may further comprise a third receiver located in the vicinity of a second end of the machine. In this case, the transmitting step causes the signal to impinge either the first and second receivers in a first reception zone or the second and third receivers in a second reception zone in the absence of the presence of an obstruction. 
         [0020]    An additional step may comprise blocking receipt of control signals to the second receiver that are located in a protection zone located beneath a geometric umbrella of reception capability extending around the second receiver. 
         [0021]    These and other features and advantages of the invention will become apparent to those skilled in the art from the following detailed description and the accompanying drawings. It should he understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    Preferred exemplary embodiments of the invention are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which: 
           [0023]      FIG. 1  is a somewhat schematic sectional side elevation view of a trench in which a prior art vibratory trench roller is positioned, and is appropriately labeled “PRIOR ART”; 
           [0024]      FIG. 2  is an isometric view of a vibratory trench roller constructed in accordance with an embodiment of the invention; 
           [0025]      FIG. 3  is a top plan view of the trench roller of  FIG. 2 ; 
           [0026]      FIG. 4  is a somewhat schematic sectional side elevation view of a trench with the trench roller of  FIGS. 2 and 3  positioned therein; 
           [0027]      FIG. 5  is a front elevation view of the trench roller of  FIGS. 2-4 , shown in with control signals reflecting to and from an operator; 
           [0028]      FIG. 6  is an isometric view of a hood of the trench roller of  FIGS. 2-5 ; 
           [0029]      FIG. 7  is an enlarged fragmentary isometric view of a portion of the hood of  FIG. 6 ; 
           [0030]      FIG. 8  is an enlarged fragmentary side elevation view of a portion of the hood of  FIG. 6 ; 
           [0031]      FIG. 9  is a top plan view of the hood of  FIGS. 6-8 , showing an umbrella beneath which a protection zone is formed; and 
           [0032]      FIG. 10  is an isometric view corresponding to  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    Referring now to the drawings, and initially to  FIGS. 2 and 3 , an exemplary compaction machine  50  is illustrated that is constructed in accordance with an embodiment of the present invention. The machine  50  of this embodiment is a vibratory trench roller  50 . The vibratory trench roller  50  comprises a self-propelled machine supported on the ground via a front rotating drum assembly  52  and a rear rotating drum assembly  54 . It is typically used to compact the bottom of trenches prior to laying pipelines or the like and/or to compact recently-filled trenches. The machine  50  comprises an articulated chassis  56  having front and rear subframes  58  and  60 , respectively. The front and rear subframes  58  and  60  are connected to one another via a pivot connection  62  and are supported on the ground via the front and rear drum assemblies  52  and  54 , respectively. The chassis  56  may have a narrow width, such as about  20  inches (50 cm) wide, to permit the machine  10  to be used to compact the bottom of relatively narrow trenches for laying pipeline and the like. The front subframe  58  may support an engine (not shown) accessible via a ventilated hood  64 . The rear subframe  60  may support a control system for the machine  50  as well as an enclosed storage compartment accessible via a pivotable cover  66  on a rear hood  68 . As is generally understood in the art, each of the front and rear drum assemblies  52  and  54  may be excited to vibrate by a dedicated exciter assembly (not shown) that is powered by a drive system. Each exciter assembly typically comprises one or more eccentric masses (not shown) mounted on a rotatable shaft(s) (not shown) positioned within an axle housing. Rotation of each eccentric mass imparts vibrations to the associated axle housing and, in turn, to the remainder of the drum assembly. In this way, the front and rear rotating drum assemblies  52  and  54  are operable to compact the ground. 
         [0034]    Still referring to  FIGS. 2 and 3 , first and second receivers  70  and  72  or “eyes” are located at the front and rear ends of the machine  50 , respectively, typically near the edges of the front and rear hoods  64  and  68 . Each eye  70  and  72  also is mounted on or near a longitudinal centerline  76  of the machine  50 . In addition, and pursuant to an embodiment of the invention, a supplemental third eye  74  is provided at a location designed to be within a common reception zone with either of the eyes  70  or  72 . A “reception zone”, in this context, should be understood to mean a volume occupied by a given IR signal being transmitted from a given location as described below. The eye  74  is located in a first common reception zone with eye  70  and a second common reception zone with eye  72 . 
         [0035]    Each of the eyes  70 ,  72 , and  74  of the illustrated embodiment is an IR photodetector. Each of the eyes  70 ,  72 , and  74  includes a receiver and related circuitry forming a module that is mounted in an opening in the respective hood  64  or  68  and that is covered by a protective transparent cover bolted to the hood  64  or  68 . One such cover is shown at  75  in in the exploded view of  FIG. 7 . However, as discussed below, each eye  70 ,  72 , and  74  could be configured to detect signals in other spectrums in addition to or instead of signals transmitted in the IR spectrum. 
         [0036]    Electronics of the machine  50  receive signals from the eyes  70 ,  72 , and  74  to start and stop the machine  50 , to control propulsion and steering of the machine  50  in a desired (forward or reverse) direction, and to control the machine&#39;s exciter assemblies. 
         [0037]    Preferably, the third or supplemental eye  74  is located on top of the machine  50  and generally laterally centrally of the machine  50 , and most preferably at or adjacent the longitudinal centerline  76  of the machine  50 , so as to be generally equally accessible from both sides of the machine  50 . The eye  74  also is positioned generally longitudinally centrally of the machine  50  so as to be within about ⅓ of the machine&#39;s length from its lateral centerline  78  and possibly generally equidistant from each of the eyes  70  and  72 . In a machine that is 8 feet (2.43 m) long, the third eye  74  preferably is located within 1.5 feet (0.3 m), and more preferably within 1 foot inches (0.30 m) of the lateral centerline of the machine  50 . As a result, the effective reception zone is of generally equal size for the combination of the first and third eyes  70  and  74  and for the combination of the second and third eyes  72  and  74 . In the present case, the third eye  74  is located on the rear portion of the front subframe  58  on top of the hood  64 . Preferred positioning of the third eye  74  on the hood  64  is discussed below. 
         [0038]    The operational benefits of the third eye  74  can be appreciated with reference to  FIG. 4 . The roller  50  is shown as being used to compact the floor  14  of the trench  12  described above in conjunction with  FIG. 1 . The trench  12 , which may be 6-12 feet (1.8-3.6 meters) deep or even deeper, is shored with vertical reinforcing walls located along each side wall of the trench  12  and a number of spaced cross supports  18  extending laterally between the side walls  16 , typically near the top  20  of the trench  12 . The reinforcing walls  16  and cross supports  18  may be formed by a “trench box” as is well known in the industry. 
         [0039]    The machine  50  is controlled by an operator stationed above the trench  12  via a hand-held remote controller  22  that transmits an IR signal  24 . The remote controller  22  can be actuated to control some or all operating parameter of the machine. For example, it can be used to start and stop the engine. It also can be used to control the FORWARD/REVERSE direction of machine travel and to steer the machine  50 , possibly using joysticks on the remote controller  22 . Remote controller  22  also can be used to control the machine&#39;s vibrations as generated by the exciters, including at least an “ON/OFF” control and possibly including controlling vibration intensity as well such as via a “HIGH/LOW” control. The IR signal  24  can be set to one of several different control channels in order to allow multiple machines to operate in the same area without interference from one another. This function can be controlled, for example, by a channel selection switch on the remote controller  22 . The remote controller  22  performs these functions by transmitting an IR. signal  24  that propagates from the remote controller  22  in an expanding arc until it impinges on the machine  50 . The signal  24  is received by one or more of the eyes  70 ,  72 , and  74  on the machine  50 , transmitted to the machine&#39;s circuitry, and decoded to execute the commands transmitted by the remote controller  22 . 
         [0040]    In the position shown, the front eye  70  is outside of the second “reception zone” of the remote controller  22  because it, is not within the arc of the IR signal  24 . In addition, rear eye  72  is in a “dead zone” consisting of the “shadow” located downstream of one of the cross supports  18  in the direction of IR signal propagation. The dead zone is bordered by the line  30  in  FIG. 4 . However, even through transmission to the eye  72  is blocked by the obstruction  18 , the machine  50  nevertheless continues to be controlled because the signal  24  is still received by the third eye  74 , which is positioned in a common reception zone with the eye  72 . But for the presence of the third eye  74 , the machine  50  would have shut down due to loss of signal, and the operator would have to reposition himself or herself so that the eye  72  is outside of the dead zone in order to resume machine operation. 
         [0041]    It should be mentioned that the third eye  74  also is in a common reception zone with the first eye  70  so that an operator positioned in front of and above the machine  50  could continue to operate the machine  50  even if signal transmission to the first eye  70  was blocked by a cross support  18  or other obstruction. 
         [0042]    Referring now to  FIG. 5 , the remote controller  22  may be configured to transmit two separate IR signals simultaneously. The first signal  80  is a relatively high-intensity control signal  80  having a range of on the order of 50-65 feet (15-20 meters). This signal is often called a “far field” signal. The second signal  82  is a relatively low-intensity safety signal  82  having a range of about 6.6 feet (2 meters). This signal often is called a “near field” signal. The safety or near field signal  82  may be generated whenever the remote controller  22  is active and causes the machine  50  to cease moving and vibrating upon machine receipt of the safety signal  82  via one or more of the eyes  70 ,  72 , and  74 . The machine  50  thus stops moving and vibrating if an operator  84  is located in a “safety zone” of about a 2 meter radius from the machine  50 . 
         [0043]    As can be seen by the arrows representing the signals  80  and  82  in  FIG. 5 , both signals  80  and  82  can be reflected off the machine  50 . The near filed signal  82  is too weak to reflect back to the operator  84  unless the operator is positioned very near the machine  50 , well within the 2 meter safety zone. However, when the operator  84  is located in this safety zone, the much stronger far field signal  80  may reflect off the machine  50 , to the head or shoulders of the operator  84 , and back to the machine  50 . If the supplemental or third eye  74  is not shielded from this reflected signal, the reflected signal may impinge on the eye  74 , causing the machine  50  to move despite the fact that the operator is located within the safety zone. 
         [0044]    Referring now to  FIGS. 6 and 7 , the desired shielding is achieved in the present embodiment by recessing the third eye  74  within an upper surface  90  of the hood  64  and by providing additional shielding adjacent the eye  74 . The resultant geometry produces a protection zone that prevents signals that are transmitted from beneath a desired height within the 2 meter safety zone from impinging on the eye  74 . This shielding is sufficient to reduce or avoid transmission of a reflected far field signal in the safety zone to the eye  72  without unacceptably reducing the effective operational range of the remote controller  22 , especially from in front of and behind the machine  50 . 
         [0045]    Turning now to  FIG. 6 , the eye  74  of this embodiment is mounted in a recess  92  in the rear end portion of the upper surface  90  of the hood  64 . The recess  92  extends longitudinally of the hood  64  from a rear edge  94  toward approximately the center of the hood  64  and is laterally centered on the hood  64 . Recess  92  is bordered at its lateral edges by generally longitudinally extending right and left sidewalls  96  and  98  and at its front edge by a front wall  99 . The depth, length, and width of the recess  92 , as determined by the length, height, and spacing between the sidewalls  96  and  98  and the location of the front wall  99 , depend largely on aesthetics, so long as the recess  92  is wide enough and deep enough to form an incident angle from the eye  74  to the upper edge of the front wall  99  and each sidewall  96  and  98  of the recess that is shallow enough to achieve the protective effects discussed below. 
         [0046]    Referring to  FIGS. 7 and 8 , in which a protective IR transparent covering over the eye  74  has been removed, the eye  74  is mounted in a pocket  100  that is formed in the bottom of the recess  92  and that is bordered by a peripheral wall  102 . The pocket  100  is stepped in this embodiment so as to receive the eye  74  in a deeper central portion thereof. The pocket  100  is circular but could be other shapes as well. First and second arcuate side shields  104  and  106  are positioned laterally between the eye  74  and the peripheral wall  102  of the pocket  100 , and thus laterally between the eye  74  and the respective sidewalls  96  and  98  of the recess  92 . Each shield  104  and  106  extends at least generally vertically 1) from a base located within the outer edge of the central, deeper portion of the pocket  100  2) to an upper edge  110 ,  112  thereof. The purpose of these shields  104  and  106  is to block IR radiation being transmitted toward the eye  74  below a relatively shallow angle that may be generated when the signal is reflected off from an operator standing near the machine  50  as opposed to being transmitted directly by the remote controller  22  from a safe distance above the machine  50 . A protection zone of expanding height, below which the eye  74  cannot receive a control signal, thus extends completely around the machine  50 . 
         [0047]    The volume of the protection zone, as well as the radius, arc length, height, and inclination of each of the shields  104  and  106  and area and depth of the pocket  100 , are largely application specific. They also are a matter of designer preference in recognition of the fact that any signal blockage comes at the cost of a reduction of operational range. That reduction comes in the form of being unable to transmit signals to the eye  74  from within the protection zone. The shields  104  and  106  thus need not, and preferable do not, completely encircle the eye  74 . instead, they leave gaps in front of and behind the eye to reduce the magnitude of the angle in front of and behind the machine  50 , thus facilitating control of the machine  50  by an operator stationed in or near a trench in front of or behind the machine  50 . Referring again to  FIG. 4 , a steeper angle, indicated by line  130 , undesirably limits the minimum distance that the operator can be from the machine  50  while holding the remote controller  22  at a given reference height “H” (indicated by line  134 , with the reference height being measured from the top 20 of the trench  12  simply for convenience) and still achieve line of sight for control of the machine  50  via the eye  74 . A shallower angle, indicated by line  132 , increases this minimum distance. Compare points D 1  and D 2  on line  134  in  FIG. 4 . Of course, the machine  50  also can be controlled if the IR signal impinges one of the other eyes  70  or  72 . 
         [0048]    Toward these ends, each shield  104  and  106  extends through an effective arc, i.e., an arc length in which the shield extends to a height providing shielding beyond that provided by other components of the machine, of less than 180°, and more typically through an arc length of about 60° to 100° °. As with other design considerations, the height and shape of each shield  104 ,  106 , as well as its distance from the eye  74 , is designed to produce a protection zone of desired configurations as described immediately below and are largely determined by overall machine geometry and designer preference. 
         [0049]    One possible configuration of the protection zone as determined by the dimensions, shape, and positioning of the recess  92 , the pocket  100 , and the shields  104  and  106  collectively forming the shielding, can be appreciated with reference to  FIGS. 9 and 10 , which show a geometric “umbrella”  120  formed by an infinite number of lines  122  extending around the eye  74 . Nineteen such lines  122  are shown in  FIGS. 9 and 10 , spaced at 10 degree increments to form eighteen segments the angle of each of which relative to the horizontal is designated in  FIG. 10 . Signals transmitted in the protection zone beneath the umbrella  120 . whether transmitted directly or by reflection, cannot impinge on the eye  74 . The umbrella  120  of this embodiment is symmetrical about the longitudinal centerline  76  of the machine  50 , so only half of the umbrella  120  is illustrated, it being understood that that the other half is a mirror image of the illustrated half. Each line  122  of the umbrella  120  extends from the eye  74  to an obstruction that blocks IR light from below that line from impinging on the eye  74 . The obstruction may, for example, comprise the top edge  110  or  112  of one of the shields  104  or  106  or a top edge  114  of the pocket wall  102 . The angle of each line  122  relative to the horizontal depends on the height of the corresponding obstruction and the horizontal distance from that obstruction to the eye  74 . Thus, if the obstruction is formed by the top edge  110  of the central portion of the shield  104 , the angle is determined by the horizontal and vertical distances between the eye  74  and the upper edge  110  of the central portion of the shield  104 . 
         [0050]    Under typical operating conditions, the remote controller  22  is held at arm&#39;s length and about chest height. 
         [0051]    When the operator  84  is in this position and is located within the trench  12 , the mere fact that that the eye  74  is recessed within the pocket  100  prevents signals from reaching the eye  74  because the remote controller  22  is beneath the height of the machine  50 . As discussed above in conjunction with  FIG. 5 , when the operator  84  approaches the machine  50 , the far field IR signals can reflect off the side of the machine  50  at an upward angle, then reflect off the operator&#39;s upper body or head, and then impinge on top of the machine  50 . However, the shields  104  and  106  prevent the signal from reaching the eye  74  in this situation and, thus, present undesired machine propulsion. 
         [0052]    Referring again to  FIGS. 9 and 10 , the angles of the lines  122  were developed specifically for the illustrated vibratory trench roller  50  and are based on the height and width of the roller  50  and other aspects of roller geometry. The actual angles of the lines  122  relative to the horizontal illustrated roller  50  are designated in  FIG. 10 . The lines that extend at 22.5°, for instance, cover an area of 7 radial segments of 10° each, or 70°. The next 10° segment on each end of this segment of the umbrella  120  start to taper down slightly to 19°, and thereafter essentially drops off completely. The angle of the lines  122  extending directly over the front and rear ends of the machine  50  ideally should be zero or even of a negative slope. However, because the upper surface  90  of the hood  64  of this particular machine  50  is sloped, the inventors could only achieve a 7° angle toward the rear and a 3° angle toward the front. The deviations of these values from the ideal are insignificant to the design. The most important part of the design from an operator safety standpoint is the 90° of coverage in the middle portion of the umbrella  120  or, stated another way, in an arc extending 45° from either side of a line  78  that laterally bisects the umbrella  120 . The resultant configuration obtains good protection to the sides of the machine  50  by providing relatively steep umbrella angles but, as discussed above in connection with  FIG. 4 , maximizes the operational range in front of and from the rear of the machine where the operator is most likely to be positioned during operation. 
         [0053]    It must be emphasized that the shape of the geometric umbrella  120  and thus of the safety zone beneath it is highly dependent on the machine design. If the machine  50  were to be longer in length than the illustrated 8.0 feet (2.43 m), it may be desirable to enlarge the size of the protection zone to accommodate the longer machine. As another example, if the machine were lower to the ground than illustrated, this angle would need to be steeper to provide the same level of operator protection. 
         [0054]    The ideal shape of the geometric umbrella  120  also is dependent on the the reflectivity of the particular signals being transmitted from the controller  22 . More reflective signals would counsel for a more aggressive design providing a larger protection zone. 
         [0055]    Although the best mode contemplated by the inventors of carrying out the present invention is disclosed above, practice of the above invention is not limited thereto. It will be manifest that various additions, modifications and rearrangements of the features of the present invention may be made without deviating from the spirit and the scope of the underlying inventive concept. 
         [0056]    For example, while the invention has been described in conjunction with a two-axle articulated trench roller, it is to be understood that the invention may be applicable to other remote-controlled rollers having more or fewer than two axles such as to skid steer rollers. It is also applicable to remote controlled compaction machines other than rollers, such as vibratory plate compactors. In addition, while the machine  50  is described as having three receivers, it is to be understood that the invention is applicable to machines having more or less than three receivers, so long as at least one of the receivers offers at least some the redundancy features of the eye  74  described herein so as to assure continued machine operation if the transmission of the control signal to another receiver is blocked by an obstruction. In addition, the concepts described herein are applicable to line of sight remote control systems other than IR based control systems. For instance, it is conceivable that the control signals could be in the UV, visible, microwave, or radio spectrum rather than the IR spectrum.