Patent Publication Number: US-2005117973-A1

Title: Method and system for preparing a trench and laying pipe in a trench

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/505,322 filed Sep. 23, 2003, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION  
      The present subject matter relates to pipe laying systems, and more particularly to a system for laying pipe in a trench, including excavating and backfilling the trench, and more particularly to a system truly operable by an operator outside of the trench.  
     BACKGROUND OF THE INVENTION  
      Many prior art patents refer to laying pipe in a trench. “Pipe laying” is often used to refer to the operation of joining a new pipe section to a pipe in the ground. Laying pipe below ground level is referred to as laying pipe below grade. However, that is just one of a number of steps that must be performed to provide an underground pipe. Pipe laying in the present context also includes other steps that are necessary between the step of initial excavation of a trench before pipe is laid below grade and the step of backfilling the trench after pipe is laid.  
      In order to provide a pipe below grade, a number of basic procedures are commonly necessary. First a trench is cut, and a bed, generally of gravel, is prepared and graded for the pipe to be laid in. The pipe is then laid in the trench, and opposed ends of successive pipe segments are prepared for joining. Certain types of pipe require lubrication to be applied to at least one of the opposed ends for proper joining. Once the lubrication is applied to the end, the pipe is lowered into the trench and inserted into the opposed end of the end of the successive pipe section in the trench. Normally, the outside diameter of the new pipe section is received in an inner diameter of the pipe in the trench. In order to be able to receive a pipe section of the same diameter as the pipe in the trench, the pipe end receiving the pipe needs to have an increased diameter. This is accomplished by providing each pipe section with a bell shape of increased diameter at one end. If rocks or dirt are present on the inner diameter of the pipe, the new pipe section will not be properly received. Preparation includes removing interfering particles from the inner diameter of the existing pipe. A layer of gravel of at least a preselected depth is deposited over the pipe. Finally, the trench must be backfilled.  
      Specific requirements for providing pipes below grade are generally mandated by local construction codes. While these codes may vary, they have several basic principles in common. The general objectives to be met in laying pipe are articulated in a publication known in the industry as the “Green Book.” This is the  Standard Specifications for Public Works Construction,  2000  Edition ; BNi Building News; Anaheim, Calif. Well-known standards are prescribed in this publication. For example, section 306-1.2 describes installation of pipe. Section 306-1.2.1 relates to bedding; section 306-1.2.3 relates to field joining of clay pipe; and section 306-1.3.2 relates to mechanically compacted backfill. Many techniques have been brought to bear in providing graded trenches and in joining pipes within trenches. Shortcomings in the prior art in each of these areas are examined separately.  
      A first area of concern is safety. One form of trench is cut having vertical walls. Working in open trenches is dangerous. Trench walls present a danger of cave-in. Uncharted or otherwise unaccounted for power lines can be encountered by workers in a trench. Placing construction personnel in the trench invokes a variety of safety requirements which greatly increase complexity and expense in construction. Safety regulations include a requirement to shore trench walls. There is a great deal of literature in the art regarding constructing retaining walls to prevent their collapse around construction personnel. Shoring of trench walls is both time consuming and expensive. Even when all safety requirements are faithfully followed, danger to construction personnel still exists, and worker injuries still occur. It is desirable to keep workers out of the trenches.  
      Prior patents disclose methods and means for joining pipe in trenches without construction personnel being present in the trench. U.S. Pat. No. 5,795,101 is entitled Pipe Laying Robot Apparatus and Method for Installing Pipe. Joining of a pipe section to a pipe in a trench by a workman outside of the trench is illustrated. U.S. Pat. No. 3,561,615 shows a pipe manipulating structure that can move a pipe section resting on blocks into a receiving end of a pipe. In-trench operator intervention will be required to set the blocks. This prior art does not disclose how to join the pipes under a number of foreseeable conditions without in-trench intervention by an operator. These conditions are not discussed in the prior patents.  
      For example, one such condition is presence of debris such as dirt and rocks on the inner diameter of a receiving pipe. If dirt and rocks are between that inner diameter and the outer diameter of an inserted pipe, there may be a failure in creating a seal between the pipe section and the pipe end. The removal of dirt, gravel and rocks prior to insertion of a pipe section into the pipe has customarily been performed by workers in trenches. Also, this prior art assumes that no adjustment is necessary to the grading. However, sections of pipe that are inserted often do not have uniform diameter. As discussed above, one end of a pipe may include an increased outer diameter bell section for receiving an end of the next pipe. In order to keep the majority of the pipe, i.e. the cylindrical portion with a smaller outer diameter, at grade, it may be necessary to scoop out a recess in the gravel pipe bed to receive the bell section. Since in-trench operator intervention will be required, use of the prior art devices will not avoid the need to shore trenches.  
      Another area of condition to consider is for the way in which the bed is graded. Grading trenches is very important in order to provide proper drainage. While water supply pipes inherently include a source of pressure to force water through pipes, drainage pipes do not have a continuous source of pressure behind them such as, for example, gravity as provided from a water tower. If grading is not provided within close tolerances, once water stops flowing through a drainage pipe, areas of standing water will be provided. In the case of sewage drainage, standing water can produce methane gas. Methane is highly explosive, and methane in the line presents a great danger. A grading tolerance within fractions of an inch is required.  
      One recent advance in grading is the provision of a self-propelled vehicle in the trench which uses automated sensors to provide the proper grade. U.S. Pat. No. 6,781,683 discloses a laser guidance system that can be used to guide earth-moving equipment. U.S. Pat. No. 5,631,658 discloses a remote control bulldozer. Vehicles are guided by a global positioning system (GPS). However, this prior art does not address a solution to particular problems of working in a trench. A base unit sits at grade level outside of the trench and transmits to an antenna on the vehicle within the trench. The line of sight from the base unit to the vehicle antenna may be blocked unless the vehicle carries an antenna on a vertical extension which may project near or above grade level. However, the vertical extension may contact utility lines or other obstacles. It is highly desirable to provide an arrangement for transmitting signals to an in-trench vehicle which does not create the danger of collision of an antenna with obstacles.  
      A material-pushing blade is mounted to a front end of the earthmover to forward ends of first and second pivot arms. Normally, two hydraulic actuators are required for each pivot arm to determine the height and the angle of the blade. This construction is more expensive and requires a more complicated control signal scheme than a system in which a single actuator could be used for each pivot arm.  
      Another shortcoming of the prior art is the manner in which pipe is covered after it is laid. Specifications generally require a contractor to be able to demonstrate that the pipe has been covered to at least a preselected depth with a bed material such as gravel. It is common practice to cover the pipe with extra gravel so that the contractor can assure a contracting authority that specifications have been met. It is not unusual for contractors to use 20% more fill than theoretically required in order to meet specifications since there is not a reliable way to otherwise document compliance with specifications. A nominal price for such fill material is $12 per ton. A contractor could expend hundreds of thousands of dollars in a year for extra fill.  
      Prior devices have limitations in sizes of pipes they can handle and types of pipe sections. It is preferable to be able to handle a small diameter pipe, for example, four inches, as well as the traditional drainage pipe. It is also desirable to have the ability to manipulate fittings such as wyes for lateral connections. It is also desirable to provide the capability to control the apparatus without having an operator tethered to a control box.  
     SUMMARY OF THE INVENTION  
      Briefly stated, in accordance with the present invention there are provided a system for laying a pipe in a trench and a method. The system includes a subsystem comprising a pipe laying device and a subsystem comprising a pipe bed grading device. Grading is done on pipe bed material in a trench by a remotely controlled earth-moving machine included in a first subsystem. Pipe is laid by remote control by an operator or operators outside of the trench using a second subsystem. Preparation and pipe treatment steps are also controlled from outside the trench. The pipe is covered with a cover material, e.g. gravel, which may be provided from a conveyor carried on a truck over the trench. The first subsystem is used to grade the pipe covering layer.  
      In the first subsystem, a remotely controlled earthmover is remotely guided, as by an infrared laser. Remote signals control positioning of a material-pushing blade. The blade is mounted to a front end of each of first and second independently pivoted arms. Each arm pivots about a point adjacent a rear end of the earthmover. The blade is linked to the earthmover and mounted to the pivot arms in a manner to enable a single hydraulic actuator for each pivot arm to determine height and tilt of the blade.  
      In the second subsystem, a pipe joining system, which may be remotely operated, comprises a transport assembly and a first gripper unit supported to the transport assembly. A second gripper unit is also supported to the transport assembly and is coaxially aligned with and axially movable with respect to said first gripper unit. Each gripper unit is selectively engageable or disengageable from a workpiece, e.g. a pipe section. The transport assembly is coupled by a coupling unit to a movable support unit. The coupling unit includes roll, pitch and yaw adjusters to define the spatial orientation of the transport unit. An axial translator moves the second gripper unit with respect to the first gripper unit.  
      In further forms, the pipe joining system comprises means for treating pipe ends.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention may be further understood by reference to the following description taken in connection with the following drawings.  
       FIG. 1  is a perspective view of a machine excavating a trench;  
       FIG. 2  is a composite elevation, partially in cross section illustrating methods and systems utilized in accordance with embodiments of the present invention;  
       FIG. 3  is a plan view of the site of  FIG. 2  and including some of the apparatus included in  FIG. 2 ;  
       FIG. 4  is a cross sectional elevation of a pipe installed in a trench;  
       FIG. 5  is an elevation of a pipe laying apparatus comprising a subsystem of an embodiment of the invention;  
       FIG. 6  is an elevation of a pipe manipulator suspended from a boom;  
       FIGS. 7 and 8  are opposite side elevations of the apparatus of  FIG. 6 ;  
       FIGS. 9 and 10  are partial detailed front and side elevations of the apparatus of  FIG. 6  further illustrating a pipe cleaning and treatment unit;  
       FIG. 11  illustrates an alternative embodiment of an air or liquid line in a pipe cleaning and treatment unit;  
       FIG. 12  is a plan view of a control unit for commanding control circuits within subsystems;  
       FIG. 13  is a block diagram of a control system comprising the control unit of  FIG. 12  and the pipe laying apparatus of  FIG. 5 ;  
       FIGS. 14, 15  and  16  are respectively an exterior side elevation, plan view and a front elevation of a remote controlled grader;  
       FIG. 17  is a partial detailed side elevation of the grading apparatus viewed from an interior side; and  
       FIG. 18  is a plan view of a grader control unit. 
    
    
     DETAILED DESCRIPTION  
       FIG. 1  is a perspective view of an excavator  1  having an excavator bucket  2  to remove earth  5  in order to dig a trench  6  below grade, i.e. surface level,  7 . The trench  6  has a floor  8  and opposite side walls  9  and  10 . In an application in which a 8-inch pipe will be laid, a nominal width for the trench  6  is 24 inches. The excavator  1  may straddle the trench  6  and move from time to time along a centerline  12  of the trench  6 . Generally, municipal sewer specifications will dictate that the trench  6  must be substantially straight. In this case, centerline  12  is a horizontal axis. Movement parallel to the centerline  12  will be referred to as axial movement. An overview of the pipe laying procedure that follows excavation of the trench  6  is described with respect to  FIG. 2 . After the pipe laying procedure, the excavator  1  will move earth  5  to backfill remaining open portions of the trench  6 .  
       FIG. 2  is a composite illustration of a trench  6  in cross section in which apparatus used at different times in the process of laying a pipe are illustrated together.  FIG. 3  is a plan view of the site of  FIG. 2  with some of the apparatus of FIG.  2  shown in use.  FIG. 4  is a cross sectional illustration of a pipe that has been laid below grade. The same reference numerals are used to denote corresponding components. As seen in  FIG. 2 , a truck  14  carries a load of bed material  16  and a conveyor  18 . The bed material is selected to comply with specifications for the particular task. A common form of bed material  16  is aggregate. The conveyer  18  may dispense the bed material  16  into the trench  6  as the truck  14  travels over the trench  6 . The bed material rests on the trench floor  8  to form a pipe bed  20 . The pipe bed  20  has a top  22  which is initially uneven. Since a level support must be provided for pipe to be laid, the pipe bed  20  must be graded so that the top  22  is substantially planar.  
      In order to grade the pipe bed  20 , in accordance with an embodiment of the present invention, a grading subsystem  30  is provided. The grading subsystem includes a guidance beacon  32 . In a preferred form, the guidance beacon  32  is an infrared laser providing a guidance beam. The guidance beacon  32  is mounted within the trench  6 . An earthmover  34  comprises a miniature bulldozer having a blade  36  for leveling the pipe bed  20 . A laser detector  38  is supported to the earthmover  34  at a height to detect the guidance beam. An operator  40  located above grade may use a remote control unit  42  to control the earthmover  34 .  
      After grading is completed, pipe is laid. A pipe  50  is illustrated in the trench  6  located on the bed  20 . In the present description, “pipe” refers to a conduit located below grade. The pipe  50  comprises pipe sections  51  which are successively installed to a current end  52  of the pipe  50 . Once the pipe section  51  is installed, it becomes part of the pipe  50 , and its free end becomes the current end  52  of the pipe  50 . In one preferred form, each pipe section  51  comprises a cylindrical body  54  at a first end and a bell  55  at a second, opposite end. The cylindrical body  54  comprises the conduit defined by the pipe  50 . The bell  55  has an inner diameter approximating the outer diameter of the cylindrical body  54 . The current end  52  of the pipe  50  comprises a bell  55 . In assembling the pipe  50 , the second end of successive pipe section  51  are inserted in the bell  55  at the current end  52 . A recess  58  may be formed in the bed  20  to accommodate the greater diameter of each bell  55 .  
      A second, pipe laying subsystem  60  is provided for handling and installing pipe sections  51 . The pipe laying subsystem  60  is also illustrated in and described with respect to  FIG. 5 , which is an elevation enlarged with respect to  FIG. 2 . The pipe laying subsystem  60  comprises a tractor  62  which travels to successive positions along the length of the trench  6 . Preferably, the tractor  62  will be to the side of the trench  6 . The tractor  62  includes a rotatable turret  64  supporting an articulated boom  65  having a tiltable section  66  supporting a suspended section  68 . The suspended section  68  may be generally maintained in a vertical orientation. The suspended section  68  supports a pipe handler  70  that includes a coupling unit  72 , transport assembly  74  and a pipe treatment unit  76 . The treatment performed by the pipe treatment unit  76  may comprise cleaning dirt from an inner diameter of the bell  55 . Pressurized fluid, for example, may be used for cleaning. A preferred fluid is air. Additionally, pressurized lubricant may be dispensed.  
      The tractor  62  includes a hydraulic system  78  providing motion control through a plurality of hydraulic lines  80  coupled to various components within the pipe handler  70 . Input signals may be provided to the hydraulic system  78  from a control circuit  82 . The control circuit  82  may be operated by an operator  86  using a control unit  88 . The control unit  88  may comprise a remote control unit communicating with the control circuit  82  by radio frequency signals. Alternatively, the control unit  88  could be wired to the control circuit  82 . The operator  40  and the operator  86  could be the same person. In many applications, however, they may be separate operators  40  and  86  performing their respective functions at different locations at the same time.  
      The operator  86  aligns the pipe handler with a pipe section  51  above grade. Then the operator  86  controls the motion of the pipe handler  70  to move the pipe section  51  into the trench  6  and in axial alignment with the pipe  50 . The pipe handler  60  grips the pipe  50  as further described below to maintain the axial alignment. The pipe treatment unit  76  may be operated, and then the pipe handler  70  is operated to slide an end of the pipe section  51  into the bell  55  of the pipe  50 . The current pipe section  51  becomes part of the pipe  50 . The pipe handler  70  is released from the pipe  50 , and a next pipe section  51  may be added to the pipe  50  in the same manner.  
       FIG. 4  illustrates a completed installation. After the pipe  50  is laid, it must be covered with a cover layer  94  if local codes provide that requirement. The cover layer  94  may be aggregate. The cover layer  94  may be deposited from the conveyor  18  carried by the truck  14 . The particular material used for the cover layer  94  will generally be dictated by applicable regulations or specifications. However, specifications will also generally have a requirement for a minimum depth of the cover layer  94  above the top of the pipe  50 . Contractors must be able to demonstrate that this specification has been met. Common practice in the art has been to use excess amounts of material to assure that this minimum is met.  
      In accordance with an embodiment of the present invention, the grading subsystem  30  may again be used, this time to grade the cover layer  94 . The guidance beacon  32  is set to a known height. The detector  38  can detect its height relative to the guiding beacon  32  within a preselected tolerance. The level of the upper surface of the cover layer is a fixed distance from the detector  38 . The depth of the cover layer  94  is determined by subtracting the height of the pipe  50  from the height of the cover layer  94 . A contractor can thus document compliance with specifications for the depth of the cover layer  94 . Consequently, the contractor can avoid the expense of having to use extra fill. After the cover layer  94  is formed, the excavator  1  ( FIG. 1 ) is used to deposit a backfill layer  96  to fill the trench to grade  7 . Generally, compaction apparatus (not shown) is used on the backfill layer  96  to avoid future subsidence. These operations yield a pipe  50  installed below grade  7 .  
       FIGS. 6-8  are partial detailed views of the pipe laying subsystem  60 .  FIG. 6  is an elevation of the pipe manipulator  70  suspended from the boom section  68 . For simplicity in the drawing, the hydraulic lines  82  are partially broken away.  FIGS. 7 and 8  are opposite side elevations of the apparatus of  FIG. 6 . Roll, pitch and yaw of the transport assembly  74  are determined by controlled movement of the coupling unit  72 . The coupling unit  72  comprises a main plate  114 . A shaft  110  is journaled in the main plate  114  and coupled for rotation by a hydraulic motor  112 . The hydraulic motor  112  is supported on the main plate  114 . The transport assembly  74  is coupled to the shaft  110  by a plate  116 . The operator  86  ( FIG. 2 ) controls operation of the hydraulic motor  112  to determine yaw of the transport assembly  74 .  
      Roll and pitch of the transport assembly  74  are determined by the roll and pitch of the main plate  114 . The main plate  114  is pivoted with respect to the boom section  68  in a first degree of freedom, in this case pitch, by a first pivot  120  mounted in the plate  114 . The main plate  114  is pivoted in a second degree of freedom by a pivot  122  supported from the boom section  68 . A hydraulic cylinder  126  is secured between a link coupling  118  on the main plate  114  and a link coupling  125  at the pivot  120 . The hydraulic cylinder  126  is hydraulically connected to one of the hydraulic lines  80 . When hydraulic cylinder is extended or retracted, the main plate  114  pivots about the pivot  122 .  
      Rotation in a second degree of freedom, roll, is powered by a hydraulic cylinder  127  hydraulically coupled to one of the hydraulic lines  80 . The operator  86  controls extension of the hydraulic cylinder  127  to determine pitch of the manipulator  70 . A hydraulic cylinder  127  is connected at an upper end to a link coupling  128  mounted on the boom section  68 . A lower end of the hydraulic cylinder  127  is connected to a link coupling  129  on an arm  130  ( FIGS. 6 and 7 ) extending from the pivot  122 . The main plate  114  rotates about the pivot  120  as the hydraulic cylinder  127  extends or retracts.  
      The pipe transport  74  comprises a track housing  132  supported to the plate  116 . While the track housing  132  need not comprise a particular shape, it is conveniently a generally rectangular housing. Suspended from the track housing  132  are first and second clamp units  134  and  136 . In one preferred form, the clamp unit  134  is fixed to the track housing  132 , and the clamp unit  136  is movable with respect to the clamp unit  134 . The direction of movement is preferably in a line toward or away from the clamp unit  134  along an axis  133  of the track housing  132 , and is referred herein as the axial direction. Movement is provided by coupling the clamp unit  136  to a hydraulic actuator  131  which extends in the axial direction in the track housing  132 . The hydraulic actuator  131  comprises an axial translator.  
      Referring to  FIGS. 6 and 7  taken together, the clamp unit  134  is supported to the track housing  132  by a frame  138 . Supported to the frame  138  are first and second pivot axes  142  and  144 , preferably parallel to the axis  133 . A pair of pivot arms  145  and  146  are suspended from the pivot axis  142 . A pair of pivot arms  147  and  148  is suspended from the pivot axis  144 . The pivot arm  148  is behind the pivot arm  146  in  FIG. 6  and behind the pivot arm  147  in  FIG. 7 . Hydraulically actuated levers  151  and  152  operate the pivot arms  145  and  146 . Hydraulically actuated levers  153  and  154  operate the pivot arms  147  and  148 . A first axially extending engaging pad  160  is connected between the pivot arms  145  and  146 . A second axially extending engaging pad  162  is connected between the pivot arms  147  and  148 . In one embodiment of the invention, engaging pads  160  and  162  to substantially match the outer diameter of pipe section  51  ( FIG. 2 ). When the levers  151  and  152  and the levers  153  and  154  operate, the engaging pads  160  and  162  move toward each other. In this manner, a pipe section  51  may be gripped on command.  
      With reference to  FIGS. 6 and 8 , the clamp unit  136  is supported to the track housing  132  by a frame  139 . The frame  139  supports a first pivot axis  180  and a second pivot axis  182  extending in the axial direction. Axially spaced pivot arms  184  and  186  are mounted to the pivot axis  180 . Axially spaced pivot arms  188  and  190  are mounted to the pivot axis  182 . The pivot arm  188  is located behind the pivot arm  184  in  FIG. 6  and is behind the pivot arm  190  in  FIG. 8 . The pivot arms  184  and  186  are operated by levers  194  and  195 . The pivot arms  188  and  190  are operated by levers  192  and  193 . An axially extending engaging pad  196  is supported to the pivot arms  184  and  186 . An axially extending engaging pad  198  is supported to the pivot arms  188  and  190 . Each of the pivot arms described above is removable from its respective pivot axis. Differently sized pivot arms may be substituted. Differently sized engaging pads may be substituted. The engaging pads may be made of rubber. However, the engaging pads need not necessarily be resilient. In this matter, different sizes of pipe may be accommodated by the pipe handler  70 .  
      It is preferred that the engaging pads  196  and  198  are significantly elongated with respect to corresponding components in the gripper unit  134 . The gripper unit  134  is used to fix the pipe handler  70  with respect to a pipe  50  in the trench  6  and needs only grip the pipe  50  adjacent the end  52 . The elongated gripper unit  136  lifts a pipe section  51  from a source of supply and carries the pipe section  51  into the trench  6 . In one preferred form, it is preferred to grip the pipe section along a majority of its length. The gripper unit  136  will need to support weight in addition to moving the pipe section  51  axially.  
      Various tools may be coupled to the track housing  132  in place of or in addition to the gripper units  134  and  136  and operated as well by the control unit  88 . The tools may comprise devices for treating the pipe  50 .  FIG. 9  illustrates a preferred form of the pipe treatment unit  76  of  FIG. 2 . The pipe treatment unit  76  cleans debris from an interface at the pipe joint between the pipe  50  and pipe section  51  and can lubricate the interface as well without the need to send an operator onto the trench  6 .  
       FIG. 9  is a partial detailed view of  FIG. 6  illustrating the pipe treatment unit  76 ,  FIG. 10  is a side view of  FIG. 9 , and  FIG. 11  illustrates a further embodiment. The pipe treatment unit  76  comprises a housing  220  containing a reciprocating drive unit  224 . The drive unit  224  comprises means for moving a treatment carriage  226  in treating engagement, i.e., moving treatment means into a position in which a desired treatment is performed. In the present embodiment, treatment comprises dispensing fluid. In one preferred form, treatment means are moved to a treatment position, and the treatment carriage  226  is stationary while treatment is performed. First, pressurized air is blown inside the bell  55  of pipe end  52 . Additionally, a lubricating liquid may be sprayed inside the bell  55 . The drive unit  224  may comprise, for example, a hydraulic motor coupled to one of the hydraulic lines  80  or a piston and cylinder unit. Alternatively, the drive unit  224  may comprise a hydraulic actuator operated by electric current. A 12-volt supply is conveniently employed in the field. The pipe treatment unit  76  is mounted for motion in a treatment path. In the present embodiment, the treatment path comprises a line segment parallel to and axially spaced from a diameter of the end  52 . In the present embodiment, the motion is vertically down and then up. Motion in other directions could be provided. Depending on the structure of the treatment means, motion may be unnecessary.  
      In the embodiment of  FIGS. 9 and 10 , the treatment carriage  226  carries an air line  228  including a conduit  230  terminating in a nozzle  232 . Also mounted to the treatment carriage  226  is a liquid line  234  including a conduit  236  terminating in a nozzle  238 . The air line  228  is coupled to a source of compressed air that could, for example, be located on the tractor  62 . A valve located at the compressed air source or at the treatment carriage  226  may be operated by the control unit  88 . Similarly, the liquid line  234  is coupled to a tank which may be at the tractor  62 . The tank contains lubricating liquid. One form of lubricating liquid that may be used is soapy water. The treatment carriage  226  has a normal position in which the nozzles  232  and  238  are out of the path between the pipe  50  and a current pipe section  51 . After the pipe section  51  is moved into axial alignment with the pipe  50 , or at a different time if desired, the drive unit  224  is activated The nozzles  232  and  238  are moved to the treatment position. In a first treatment operation, the air line  228  is actuated. Dirt and gravel are blown out of the bell  55 . In a second treatment operation, the liquid line  234  is actuated, and lubricating liquid covers and inner diameter of the bell  55 . In other embodiments, treatment may be performed while the treatment carriage  226  is in motion. It is also possible to provide a single pass in which an air treatment is provided when the treatment carriage  226  moves down and a liquid treatment when the treatment carriage  226  moves up.  
       FIG. 11  is a partial detailed view of  FIG. 9  illustrating an alternative form of conduit  250  that could be included in the air line  228 , liquid line  234  or both. The conduit  250  has a T-section  252  having first and second opposite ends terminating at  256  and  258  respectively. The conduit  250  may be used to treat the pipe  50  and the pipe section  51  at the same time.  
       FIG. 12  is a plan view of the control unit  88 . A first safety switch  272  is provided for enabling or disabling the control unit  88  in order to prevent accidental movements. A second safety switch  274  is provided to selectively enable or disable the subsystem  60 . An on-off switch  276  determines the status of the link, e.g., radio transmitter, included in the control unit  88 . A first control section  280  is provided to control the tractor  62 . Multiposition switches  282  and  284  included in the first control section  280  may comprise joysticks controls including joysticks  283  and  285  respectively. To describe joystick positions, the 12 o&#39;clock position is referred to as up, the 6 o&#39;clock position is referred to as down, the 9 o&#39;clock position is referred to as left and the 3 o&#39;clock position is referred to as right. Movement of a joystick to a position intermediate the above-described positions combines components of the commands corresponding to the positions between which the joystick is placed. The description of the functions of the switches in the embodiment of  FIG. 12  serve as direction for construction of one of several alternative forms of the control circuit of  FIG. 13 .  
      The switch  282  controls motion of the tractor  62 . Motion of the joystick  283  up or down commands motion forward or backward respectively. Left or right motion steers left or right respectively. The joystick  285  is movable up and down to control raising and lowering of the tiltable section  66  of the boom  64 . Left and right movement of the joystick  285  controls pivoting of the suspended section  68  with respect to the tiltable section  66 . Additionally, the switch  284  may be rotated to operate the hydraulic cylinder  127  ( FIG. 6 ) to tilt the transport assembly  74  with respect to the tractor  62 .  
      At the left of  FIG. 12 , a joystick control  290  includes a joystick  291 . The joystick  291  is movable up and down to operate the hydraulic cylinder  126  to control pitch of the transport assembly  74 . Left and right movement of the joystick  291  controls rotation of the boom  64  with respect to the tractor  62 . Rotation of the switch  290  operates the hydraulic motor  112  to rotate the pipe handler  72 .  
      Rocker switches  300 ,  302 ,  304 ,  306  and  308  are provided to control handling of pipe sections  51  and treatment of the pipe joint prior to joining a pipe section  51  to the pipe  50 . Each rocker switch is spring biased to a central, off position, and may be tilted about a central axis in a first or a second direction, referred to here as up and down, in order to close a first or a second pair of contacts. The rocker switch  300  is pressed up to actuate the piston drive  131  to move the clamp unit  136  toward the clamp unit  134 , and is pressed down to actuate the piston drive  131  to move the clamp unit  135  away from the clamp unit  134 . The rocker switch  302  is movable down or up to move the clamp unit  134  to an open or closed position. Similarly, the rocker switch  304  is movable down or up to move the clamp unit  136  to an open or closed position.  
      In order to provide for treatment, the rocker switch  306  is movable down or up to select treatment with air or lubricant respectively. The rocker switch  308  is movable down to move the treatment carriage  226  ( FIG. 10 ) down and up to move the treatment carriage  226  up. Alternatively, the rocker switch  308  may be connected to initiate one cycle of down and up motion of the treatment carriage  226  by depressing the switch once in either direction.  
      Many other arrangements may be provided to embody the control unit  88 . Use of joysticks may be desirable since many operators  86  may have developed facility with joysticks in the course of playing video games. However, many other embodiments are possible. For example, the surface of the control unit  88  could comprise a touchscreen display of a tractor  82 , boom  64  and pipe handler  74 . Switches in the display may be embedded at the location of illustrated components so that the operator  86  may command movement by touching images on the screen of components to be controlled. Many different assignments of function to a particular type of switch may be made.  
       FIG. 13  is a generalized block diagram of a control unit  88 . The control unit  88  may be embodied in analog or digital circuitry. Transmission from the control unit  88  to the control circuit  82  at the tractor  62  may be via radio frequency, infrared or other links. Various forms of modulation, multiplexing and use of plural channels are known in the art to provide intelligence indicative of the various functions to be commanded. In the control circuit  88  an input stage  320  contains user-operated devices  326  which respond to the operator  86 . The user-operated devices  326  may comprise the above-described switches. A voice link could also be included. Each user-operated device  326  is coupled to a sensor device  328  in a sensor stage  330 . Each sensor device  328  reacts to action by the operator  86  on a user-operated device  326  by generating a voltage in an analog embodiment or a count in a digital embodiment. The sensor devices  328  provide intelligence to modulation stage  334 , which imposes sensed intelligence signal on transmitted signals from a transmitter  338 . In one preferred embodiment, the control unit  88  utilizes pulse width modulation.  
       FIGS. 14, 15  and  16  are a side elevation, plan view and a front perspective view of the earthmover  34 . The earthmover  34  is a miniature bulldozer in one embodiment having a chassis  390  supporting a gasoline engine  394 . The chassis  390  also supports a housing  398  which may contain a control circuit  400  that receives commands from the control unit  42  ( FIG. 2 ). The housing  398  may also contain a hydraulic system  402 . The hydraulic system  402  is coupled to supply hydraulic power via a controlled manifold  403  to components further described below in order to respond to commands from the control circuit  400 . For simplicity in illustration, hydraulic lines are not shown. However, the hydraulic lines are embodied in a conventional manner. The control circuit  400  may be coupled to an operator interface box  404 , which may contain a receiver to respond to signals from the control unit  42 . The interface box  404  may be mounted on the engine  394 . A display  405  in the interface box  404  may be tilted with respect to a horizontal plane so that it is visible to an operator  40  ( FIG. 2 ) above grade.  
      The gasoline engine  394  supplies power to a hydraulic pump to drive a hydraulic motor indicated at  420  to drive a sprocket  416  on each lateral side at the rear of the earth mover  34 , e.g., the right and left sides in  FIG. 16 . The laterally opposed sprockets  416  are independently driven. Rollers  406  support laterally opposite track units  410  and  412 . In the present embodiment, each of the track units  410  and  412  comprises a pair of tracks  414 . Alternatively, single tracks  414  may be utilized. The track unit  410  loops around the sprocket  416  and an idler  415  at a rear and a forward and rear ends of a track arm  418 . The track arm  418  is pivoted to the chassis  390  on a pivot axle  423 . A laterally opposed, track arm  428 , which is effectively a mirror image of the track arm  418  in  FIG. 17  is similarly mounted to support the track unit  412 . The track arms  418  and  428  can rotate independently. Consequently the earthmover  34  can stay level as inclines vary under the track units  410  and  412 .  
      The laser detector  38  is mounted on a post  430  supported on a platform  434  projecting from the rear of the blade  36 . In this manner, the inclination of the laser detector  38  with respect to the beacon  32  ( FIG. 2 ) is indicative of the angle of the blade  36  with respect to a vertical axis. The post  430  is of a sufficient height so that the structure of the earthmover  34  will not block transmissions from the guidance beacon  32  ( FIG. 2 ). If it is desired to avoid contact with items outside the trench  6 , the post  30  should not project above grade from the trench  6 .  
      A ball joint support  439  is supported to the chassis  390 . A stabilizer rod assembly  441  has an A-shaped contour having first and second legs coupled to pivots  440   a  and  440   b  at the rear of the blade  36 . The stabilizer rod assembly  441  comprises threaded rods which may be set to adjust the pitch of the blade  36 . Additional pivot mounts  442  and  444  are connected to the rear side (facing the chassis  390 ) of the blade  36 . The pivot mounts  442  and  444  are connected to forward ends of push rods  446  and  448  respectively. The push rods  446  and  448  are pivoted to the chassis  390  at pivot points  450  and  452  respectively. In accordance with an aspect of one embodiment of the present invention, this arrangement allows for push rods  446  and  448  that are proportionally longer than in prior art arrangements. The extended length provides for minimizing error in the commanded position of the blade  36 . As seen in  FIG. 17 , the pivot point  452  is on an axis  456 . Preferably, the push rods  446  and  448  are laterally inward of the track units  410  and  412  respectively.  
      In accordance with a further aspect of one embodiment of the present invention, the vertical position of the blade  36  is adjustable by first and second hydraulic arms  460  and  462 . Lower ends of the first and second hydraulic arms  460  and  462  are pivotally secured to the push rods  446  and  448  respectively. A support for each of the upper ends of the first and second hydraulic arms  460  and  462  is provided. Posts  464  and  466  are provided, each secured to a side of a front end of the chassis  390 . A retaining pin  468  passes through a mounting bracket  470  at an upper end of the hydraulic arm  460 . Similarly, a retaining pin  470  passes through a mounting bracket  472  at an upper end of the hydraulic arm  462 . When the first and second hydraulic arms  460  and  462  are operated, the height of the blade  36  is adjusted.  
      A blade slope sensor  480  is mounted to the top of the blade  36  to sense pitch, or side-to-side tilting, of the blade  36 . The blade slope sensor  480  may be hard wired or coupled by a radio or optical link to the control system  400 .  
       FIG. 18  is a plan view of the control unit  42 . The conventions used to describe switch positions with respect to  FIG. 12  are used here. A three position switch  492  controls gasoline engine  394 . The three positions are off, on and start. A switch  494  has an on position and an off position to select the state of the laser detector  38 . First and second joystick switches  496  and  498  in the current example are provided to control the track units  412  and  410  respectively. The switch  496  or  498  is moved to the up position to command forward motion, and is moved to the down position to select reverse motion. Steering is accomplished by selecting opposite directions of motion for the respective track units  410  and  412 . First and second blade control switches  502  and  504  command actuation of the hydraulic arms  460  and  462  respectively. In this manner, the blade  36  is raised or lowered. In the present illustration, the switches  502  and  504  are incorporated in the joystick switches  496  and  498  respectively. The switch  502  includes a trigger switch  506  which can be grasped by a finger of and operator and a button switch  507  which can conveniently be accessed by a thumb of an operator. Similarly, the switch  504  comprises a trigger switch  508  and a button switch  509 . The trigger switches  506  and  508  command motion in a first direction. The button switches  507  and  509  command motion in an opposite direction. In an alternative form, the switches  502  and  504  may comprise rocker switches with a center, neutral position and up and down positions. The up position selects raising of the respective side of the blade  36  and the down position selects lowering of the blade  36 . Prior art control systems maintain travel of the earthmover  34  in a substantially straight line when no steering commands are provided. The control unit  42  may be embodied in the same manner as illustrated in  FIG. 12  with respect to the control unit  88 .  
      Embodiments of the present invention provide for reliable laying of pipe below grade while avoiding the need to expose workers to the dangers of being in a trench. One subsystem grades the trench and another subsystem connects pipe sections to the below grade pipe. The present subject matter being thus described, it will be apparent that the same may be modified or varied in many ways. Such modifications and variations are not to be regarded as a departure from the spirit and scope of the present subject matter, and all such modifications are intended to be included within the scope of the following claims.