Abstract:
An in-ground lawn cutting device is disclosed that uses a rotating cord to trim and mulch grass much faster than conventional means. A spool rotates at high speed and extends a weighted cord that cuts grass within a circle. The spool height can be slowly lowered to mulch grass as it cuts. When finished, the cord is retracted and the spool can be lowered at least partly below grade. The device can detect the height of surrounding vegetation and/or the presence of nearby obstructions through reflection or transmission between devices of LASER or other light. The device can issue an audible and/or visual alarm when an obstruction is detected, and/or immediately before and during the cutting. In some embodiments the device can be tilted, the cutting cord can be adjusted in length, and/or a controller is included. The controller can be wireless, hand-held, and/or controlled by a hand-held wireless remote.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention generally relates to landscaping maintenance, and more specifically to lawn mowing. 
       BACKGROUND OF THE INVENTION 
       [0002]    Lawns are very common in landscaping, and are highly prevalent in areas surrounding homes, apartment buildings, highway medians, sports fields, golf courses, and other landscaping venues. Lawns can include many types of grasses and other vegetation, and most lawns need to be periodically trimmed so as to maintain them at a uniform height, thereby maintaining both their attractiveness and their ease and comfort of use. 
         [0003]    A profound amount of manual labor is expended each year trimming lawns and dealing with the resultant clippings. Many lawns need to be trimmed every one to two weeks, depending on the type or types of vegetation included. So-called “self propelled” lawn mowers and riding lawn mowers make the task less arduous by reducing the physical effort required of the operator. However, the required operator time is not reduced by these approaches. “Mulching” lawn mowers produce clippings that are sufficiently fine so that they quickly sink below the surface of the cut lawn and rapidly decompose. However, the time required to mow the lawn remains unchanged. Very large lawn mowers allow lawns to be trimmed more quickly, and therefore require less operator time, but they are very costly and require significant storage space, making them practical only for professional lawn cutting services. 
         [0004]    Robotic lawn mowers have been proposed, which are essentially self-propelled lawn mowers that are guided by a computer and some sort of position determining system. However, these devices do not decrease the time required to trim a lawn, and are not widely used due to the practical difficulties associated with their programming, customization to a given lawn environment, and maintenance. 
       SUMMARY OF THE INVENTION 
       [0005]    An in-ground lawn cutting device is claimed that uses a weighted cutting cord extended from a rotating spool to automatically trim and mulch surrounding vegetation in a small fraction of the time required by conventional means. 
         [0006]    The in-ground lawn cutting device includes a housing that can be buried at least partly below grade, a rotatable spool that can be positioned at an elevation above grade when the housing is buried at least partly below grade, a rotation motor located in the housing and attached to the rotatable spool, the rotation motor being able to cause the rotatable spool to rotate, and a cutting cord with a weight attached to a distal end of the cord, the weighted distal end being extendable from the rotatable spool while the rotatable spool is rotating, thereby sweeping the cutting cord over a substantially disk-shaped area and trimming the height of vegetation located within the area. 
         [0007]    In preferred embodiments, the in-ground lawn cutting device also includes a cutting height apparatus that is able to increase and decrease the elevation of the rotatable spool. In some of these embodiments, the rotatable spool can be positioned at least partly below grade when the rotatable spool is not rotating, and in some of these embodiments the elevation above grade can be slowly decreased while the rotatable spool is rotating and the cutting cord is extended, so as to cut surrounding vegetation into small segments as the height of the surrounding vegetation is reduced. In some of these embodiments the cutting height apparatus is a cutting height motor that is able to vertically reposition the rotation motor, thereby also vertically repositioning the rotatable spool. 
         [0008]    In some preferred embodiments the in-ground lawn cutting device also includes an optical stage that contains a light source and a light detector that are able to detect the height of surrounding vegetation and/or the presence of nearby obstructions. In some of these embodiments the optical stage is located above and fixed to the rotating spool, and in some of these embodiments the light source is a LASER. In other of these embodiments the light detector is able to detect light transmitted by the light source and reflected from surrounding vegetation and/or obstructions near the in-ground lawn cutting device. And in still other of these preferred embodiments the light detector is able to detect light transmitted by other in-ground lawn cutting devices when the light is not intercepted by surrounding vegetation or obstructions near the in-ground lawn cutting device. 
         [0009]    In various preferred embodiments the in-ground lawn cutting device includes a tilt apparatus that is able to tilt the plane of the disk-shaped area swept out by the lawn cutting device, and in some of these preferred embodiments the tilt apparatus is able to tilt the rotation axis of the rotation motor and the rotatable spool in relation to the housing. 
         [0010]    In preferred embodiments the in-ground cutting device includes an alarm stage that is able to transmit at least one of an audibly detectable alarm signal and a visually detectable alarm signal to persons and animals near the in-ground cutting device. In some of these embodiments the alarm stage transmits an alarm during a time interval immediately prior to extension of the cutting cord, and in some of these embodiments the alarm stage transmits an alarm whenever the cutting cord is extended. In still other of these embodiments where the in-ground cutting device also includes an optical stage that is able to detect the presence of nearby obstructions, the alarm stage transmits an alarm when an obstruction is detected. 
         [0011]    In some preferred embodiments the length of the cutting cord is adjustable, so as to adjust the radius of the substantially disk-shaped area over which the cutting cord is swept. 
         [0012]    In various preferred embodiments the in-ground cutting device also includes a controller that is able to initiate periodic determinations of vegetation height surrounding an in-ground cutting device, initiate detection of obstructions near an in-ground cutting device, issue an alarm when an obstruction is detected within a cutting area, initiate cutting of vegetation according to periodic time intervals and/or a maximum vegetation height, control a plurality of in-ground cutting devices, and when an obstruction is detected, provide identifying information regarding the cutting device that is closest to the obstruction. Some of these embodiments also include a hand-held remote control that can control at least some functions of the controller, and in some of these embodiments the controller is wireless and/or hand-held. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention will be more fully understood by reference to the detailed description, in conjunction with the following figures, wherein: 
           [0014]      FIG. 1A  is a sectional view of a preferred embodiment showing the spool positioned above grade and the cutting cord extended; 
           [0015]      FIG. 1B  is a sectional view of the embodiment of  FIG. 1A  at right angles to the sectional view of  FIG. 1A ; 
           [0016]      FIG. 1C  is a sectional view of the embodiment of  FIG. 1A  with the cutting cord not extended and the spool positioned partly below grade; 
           [0017]      FIG. 2  is a functional diagram showing how a plurality of cutting devices can be positioned in the ground so as to cut a lawn within a rectangular area; 
           [0018]      FIG. 3  is a sectional view of the embodiment of  FIG. 1A , illustrating optical detection of a nearby obstruction; 
           [0019]      FIG. 4  is a sectional close-up view of a combined optical and alarm stage from a preferred embodiment; 
           [0020]      FIG. 5  is a functional diagram showing transmission of light from one cutting device to a plurality of nearby cutting devices, so as to detect the height of vegetation between the devices; and 
           [0021]      FIG. 6  is a perspective view of a cutting device controller from a preferred embodiment. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0022]    With reference to  FIG. 1 , the cutting device includes a housing  100  that is buried in the ground, mostly or entirely below grade  102 . In preferred embodiments the housing  100  is between 8 inches and two feet in length, and between 4 and 5 inches in diameter. A rotatable spool  104  is extendable from the housing  100  to an elevation above grade  102 , and a rotation motor  106  located in the housing  100  and attached to the rotatable spool  104  is able to cause the rotatable spool to rotate very rapidly. In the embodiment of  FIG. 1A , the rotation motor  106  is connected to the spool  104  by a shaft  108  that is coaxial with the rotation motor  106  and the spool  104 . 
         [0023]    A cutting cord  110  with a weight  112  attached to its distal end can be extended from the rotatable spool  104  while the rotatable spool  104  is rotating, so as to sweep the cutting cord  110  over a substantially disk-shaped area surrounding the housing and thereby trim the height of any grass or other cuttable vegetation  114  located within the area. In preferred embodiments, the cutting cord  110  is a thin braded metal line, approximately 0.030 mm in thickness, that extends itself by centrifugal force to a preset length. 
         [0024]    In the embodiment of  FIG. 1A , the cutting device includes a cutting height apparatus  116  that is able to raise and lower the elevation of the rotating spool  104 . In this embodiment, the cutting height apparatus  116  is a motor that controls the height of a threaded shaft  118  connected to the base of the rotation motor  106 , thereby lifting and lowering the rotation motor  106 , the connecting shaft  108 , and the rotatable spool  104 . In various embodiments, the maximum height to which the spool  104  can be raised is between  16  inches and  24  inches. 
         [0025]    In this embodiment the cutting height apparatus  116 , the threaded shaft  118  and the rotation motor  106  are all contained inside of an inner housing  120  with a curved, toothed bottom  122  that mates with a tilting gear  124  located below the inner housing  120 . The tilting gear can  124  move the base  122  of the inner housing  120  back and forth, causing the entire assembly contained inside of the inner housing  120  to tilt, and thereby causing the substantially disk-shaped cutting area of the cutting cord to tilt. This feature can be used to compensate for an imperfectly vertical installation, shifting of the ground after installation, or a sloping grade. In some preferred embodiments the inner housing  120  and associated toothed bottom  122  and tilting gear  124  can be rotated about the vertical axis by an arbitrary angle, thereby allowing the inner housing  120  to be tilted in any desired direction. 
         [0026]    The preferred embodiment of  FIG. 1A  also include a module  126  mounted above the spool  104  that contains a light source, a light detector, and a speaker that can emit an audible alarm signal  126 . In this embodiment, the alarm signal is active whenever the cutting cord  110  is extended. A set of power cables  130  bring power to the unit and carry it on to other units, and a set of signal cables  132  convey signals between the cutting devices and between the cutting device and a control unit. In preferred embodiments, these cables  130 ,  132  can be installed by a pipe-laying machine. 
         [0027]      FIG. 2B  is a sectional view of the embodiment of  FIG. 1A  through a section taken at  90  degrees to the section of  FIG. 1A . In  FIG. 1B  the pivots  134  that support the inner housing  120  can be seen, as well as the tilting motor  138  that can rotate the tilting gear  124  so as to tilt the inner housing  120 .  FIG. 2C  is a sectional view of the embodiment of  FIG. 1A  through the same section as  FIG. 1A , but with the cutting cord  110  not extended (i.e. retracted into the spool  104 ), and with the spool  104  lowered so as to be partly below grade. The alarm is no longer sounding because the cutting operation is finished and the cutting cord  110  has been retracted into the spool  104 . 
         [0028]      FIG. 2  is a functional diagram that illustrates a plurality of cutting devices  100  arranged within a rectangular lawn  200  so as to cut the grass of the lawn  200  using as few cutting devices as possible. Most of the cutting devices  100  are arranged in a classic “hexagonal” pattern that creates a repeated pattern of hexagons with each hexagon including a cutting device  100  at each vertex and one in the center. The size of the hexagons is determined by the diameter of the circular cutting area  202  of each cutting device  100 . In preferred embodiments the circular area cut by a single cutting device can be varied from 5 inches to 25 feet. Near the boundaries of the lawn  200 , the locations  204  and cutting circle diameters  206  of some of the cutting devices are altered so as to minimize projection of the cutting circles  202 ,  206  beyond the lawn  200 . While  FIG. 2  illustrates the principles underlying placement of the cutting devices within a lawn, in practice the cutting devices would be placed slightly closer to each other to ensure overlap of the cutting circles at all points. In some embodiments the rotation of the cutting cords  110  is synchronized and/or the heights of the spools  104  are varied so as to avoid collisions between the cutting cords. 
         [0029]    As was mentioned above, the preferred embodiment of  FIG. 1A  includes a module  126  mounted above the spool  104  that contains a light source and a light detector. In  FIG. 3 , the module  126  is shown emitting a LASER beam  300  that strikes an obstruction  302  (shown in the drawing as a shoe). Scattered light  304  from the object  302  is detected by the module  126 , causing the system to abort the cutting operation. 
         [0030]      FIG. 4  presents a close-up cutaway of the module  126  mounted in  FIG. 1A  above the spool  104 . A LASER  400  light source emits a beam of light  300  through the transparent cover of the module  126 . The LASER light  300  strikes an obstruction ( 302  in  FIG. 3 ), and some of the light  304  is reflected back to the module  126  and enters a filter  402  that excludes light from sources other than the LASER  400 . The light then enters a light detector  404  which generates a signal that is transmitted to a controller, causing the lawn cutting cycle to be aborted. A sound generating device  406  is also located inside of the module  126 . When the obstruction is detected, the sound generating device  406  generates sound  408 , which is reflected off of the top of the spool and is easily heard by an operator who can then quickly locate which cutting device  100  has sensed the object, and can therefore quickly locate and remove the object from the cutting zone. During an active lawn cutting cycle, the all of the sound emitting devices  406  in a plurality of cutting devices  100  emit sound, so as to warn anyone in the area that the lawn cutting system is active. 
         [0031]    In some preferred embodiments, the height of the grass is detected by cutting devices  100  using reflected light, as described above. In other preferred embodiments, light emitted by one cutting device  100  is detected by neighboring devices  100 , providing a method that is more sensitive to very small objects such as blades of grass.  FIG. 5  presents a functional diagram of the embodiment of  FIG. 2 , where the cutting cords  110  are not extended and one of the cutting devices  100  is transmitting light to its nearest neighbors. As is illustrated in the figure, when the cutting devices  100  are arranged in a “hexagonal” pattern each cutting device  100  can obtain up to six grass height measurements using this method, but obstructions  302  that do not lie between cutting devices  100  cannot be detected in this way. 
         [0032]      FIG. 6  illustrates a controller  600  used in a preferred embodiment to control a plurality of cutting devices  100 . The controller  600  includes a display that indicates the most recently measured height of the grass  602  and the interval at which the height is measured  604 . These parameters, as well as other parameters, can be varied either by pushing on “up” and “down” arrows  606 , so as to increase or decrease the values, or numbers can be directly entered via a numeric keypad  608 . Additional buttons are provided that temporarily display parameters and allow them to be set. The height to which the grass is to be cut  610  can be selected, and a time interval  612  (such as bi-weekly) and/or a maximum grass height  614  can be selected as criteria for initiating a cutting cycle. The frequency with which the height of the grass is to be checked  616  can also be set, as well as the tilt angle of the cutting device  618 . If desired, a cutting cycle can also be manually initiated  620 . 
         [0033]    In this preferred embodiment, when a cutting cycle is initiated a loud, shrill, audible warning signal is emitted from the cutting devices before cutting begins, so as to warn people in the area and frighten away any animals or birds. The audible warning signal is continued throughout the cutting process. After the warning signal has sounded for approximately  10  seconds, the spools on the cutting devices are raised to a few inches above the grass level and the optical modules are rotated by  3600  to check the cutting zones for any remaining obstructions  302 , such as people, pets, toys, birds, rocks, and such like. If an obstruction  302  is detected, cutting is aborted, a “zone block” error light  622  is illuminated on the controller  600 , and a display  624  on the controller  600  indicates in which cutting zone the obstruction  302  was detected. When the obstruction  302  has been removed the zone block status is reset  626 . 
         [0034]    Once the cutting zones are determined to be free of obstructions  302 , rotation of the spools  104  begins, and the cutting cords  110  are extended. The spools  104  are then slowly lowered, cutting the grass  114  into very short segments, typically less than 1/16 inch in length, that quickly settle into the grass and decompose. When the cutting cords  110  reaches the specified “cut-to” height  610 , the rotation of the spools  104  is stopped, the cutting cords  110  are retracted into the spools  104 , and the spools  104  are lowered at least partly below grade  102 . 
         [0035]    In the embodiment of  FIG. 6 , the controller  600  communicates with the cutting devices  100  through in-ground communication cables  132 . In some embodiments, most or all of the functions of the control panel  600  are also available on a wireless, hand-held remote control. And in some preferred embodiments, communication with the cutting devices is wireless  100 , and/or the cutting devices  100  are controlled by a fixed controller  600 , a hand-held remote, or both. 
         [0036]    Other modifications and implementations will occur to those skilled in the art without departing from the spirit and the scope of the invention as claimed. Accordingly, the above description is not intended to limit the invention except as indicated in the following claims.