Abstract:
A powered rotary screed provides a powered strike tube that rotates to provide a finish to wet concrete during screeding and a drive tube that provides motive power to the screed to assist with the difficult task of removing excess concrete from a poured pad, or other horizontal concrete surface. The drive tube is split to provide two separate portions that can be independently controlled for easy control of the screed as the screed works concrete. The drive tube portions are elongate cylinders that are axially aligned and rotatable relative to one another. Separate motors drive respective drive tube portions and can be individually controlled to prevent skewing of the screed.

Description:
This application is a continuation-in-part of U.S. patent application Ser. No. 09/304,616, filed May 3, 1999, now U.S. Pat. No. 6,350,083. 
    
    
     FIELD OF THE INVENTION 
     The present invention pertains to the field of powered roller screeds used to screed cementitious material. 
     BACKGROUND OF THE RELATED ART 
     Concrete structures are formed by pouring a cementitious material, such as cement and aggregate (comprising concrete slurry) into a form, or other container, and permitting the material to cure under proper conditions. In the case of a. concrete pad, such as a floor, foundation, or roadway, concrete is poured onto a ground, or support, surface and contained by forms connected to, and rising above, the ground surface. The forms are longitudinal members arranged along a border of a desired location for the concrete pad to contain the viscous concrete and provide a guide for the concrete&#39;s thickness and to level the top surface of the concrete. 
     After concrete is poured between forms, it is spread evenly between the forms. A screed is then used to remove excess concrete and level the top surface of the concrete so it is even with the forms. Often, several passes of a screed over the concrete is necessary to achieve the desired surface. Precision is required to conform to building codes and to perform quality work. 
     A very primitive screed, which is still useful on small jobs, is a simple straight edge such as a straight board. The board, chosen long enough to span the forms, is laid on top of each form and thereafter worked side-to-side and pulled down the length of the forms by workers at each end of the board. This process pushes forward excess concrete: excess concrete is concrete that is higher than the top surface of the forms. While quite suitable for small jobs, such a screed is impractical on large jobs because of the work required to move the excess concrete. 
     A more practical screed for larger jobs is disclosed in Mitchell, U.S. Pat. No. 4,142,816. Mitchell discloses a powered screed having a hydraulic motor to spin a tubular member while the screed is pulled along the forms by two workers, one each located on either side of the forms. As with most rotary screeds, the tubular member spins in a direction opposite a direction of travel of the screed. By spinning the tube, this screed provides a good surface to the concrete. However, substantial work is required to pull the screed along the forms. The hydraulic motor, spinning the tube, does not assist to propel the screed forward and the heavy concrete that builds up in front of the screed requires a large amount of force to move. In addition, workers located at each end of the Mitchell screed must keep the screed tube substantially perpendicular to the forms—frequently this is a difficult task because of uneven amounts of concrete from side-to-side and unequal strengths of the workers. 
     Larger, powered screeds are suitable for large, high-volume jobs. U.S. Pat. No. 5,456,549 discloses a powered rotary screed having a modular frame that spans across concrete-retaining forms to support a strike tube and drive tubes. The frame provides rigidity and support so that the screed can span large distances between forms. The strike tube rotates opposite the direction of screed travel to screed the concrete and the drive tubes provide motive force to propel the screed.. While very useful for large jobs, and jobs that are not constrained by space limitations, these larger screeds are difficult to use in close quarters and are more difficult to transport. 
     Accordingly, there is a need in the industry to provide a powered screed that can be easily controlled during use, and conveniently transported and set up for use. 
     SUMMARY OF THE INVENTION 
     The present invention provides a frameless roller screed having two tubes: a strike tube and a drive tube. The strike tube is located at a leading edge of the screed and is made to rotate so as to oppose the direction of motion of the screed. The strike tube contacts rough laid concrete to level the concrete to the height of the forms and finish the surface of the concrete. The rotational motion of the. screed tube provides a better quality finish to the concrete surface than can be achieved with a non-rotating strike tube or a strike tube that rotates in the direction of travel. 
     In preferred embodiments, the drive tube of the present invention is a split drive tube having independently controlled portions that provide superior control of the screed during operation. The drive tube is split into first and second drive tube portions that are separately controlled by the operator so that left and right ends of the screed may be independently driven to adjust for misalignment that may occur as the screed moves along the forms. Oftentimes, uneven concrete will present uneven resistance to the screed and impede the forward progress of the screed on one side, thereby misaligning the screed on the forms. The split drive tube of the present invention permits the operator to adjust the motive power at one end of the screed relative to the other end so as to compensate for such misalignment. 
     In preferred embodiments, the first and second drive tube portions are cylindrical and the two portions are axially aligned and coupled. The drive tube portions are coupled so as rotate independently of each other and each portion is separately driven to permit separate control of the respective portions. 
     Preferably, hydraulic motors drive the strike tube and the drive tube. The strike tube is powered by a single motor for control of the rotational speed and direction of rotation of the strike tube. 
     The drive tube is powered by two motors. One motor controls each one of the respective two drive portions, thus allowing separate control of the first and second drive portions as to rotational speed and direction of rotation. 
     In addition, the screed includes handles located on opposite ends of the screed that are arranged as levers to assist with control of the screed. The handles are coupled to the screed such that an operator can push a distal end of the handle downward, or raise the distal end upward, to lever the drive tube about the strike tube. Pushing down on the handle tends to lift the drive tube off of the forms so that forward motion of the screed may be easily, and quickly, halted. Alternatively, lifting the handles places more of the screed&#39;s weight on the drive tube and increases the drive tube&#39;s pressure on the forms so that the drive tube can provide more motive force without slipping. 
     Using the handles as the primary means to control the screed during operation requires trained operators at each end of the screed. However, by providing the drive tube as a split drive tube, as disclosed in the present invention, allows one person control and operation of the screed. 
     The roller tubes of the present invention are coupled together by plates located on distal ends of the screed. The screed has no frame that extends substantially over the concrete, or spans the forms. 
     Accordingly, the present invention provides a frameless, powered rotary screed having a split drive tube with separately controllable ends that permit the screed operator to control the screed&#39;s motive force at, each end separately to adjust for uneven concrete and prevent skewing of the screed on the forms. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a preferred embodiment of a power driven roller screed of the present invention including an environment of screed forms supporting the roller screed and cementitious material located between the forms. The screed tubes are shown in broken view to represent indefinite lengths. 
     FIG. 2 is a top plan view of a preferred embodiment of a drive end of the roller screed showing the motors and their respective connections to the strike and drive tubes. 
     FIG. 3 is an end-view elevation of the roller screed drive end of FIG.  2 . 
     FIG. 4 is a cross-section, side-view elevation of the roller screed drive end of FIG.  2 . 
     FIG. 5 is a schematic diagram of a preferred embodiment of a hydraulic system for the split drive tube screed of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As stated, a conventional method of making a concrete pad, or floor, is to pour concrete onto a surface between concrete forms. With respect to FIG. 1, viscous concrete  10  is poured onto a floor, or ground surface, between two spaced-apart, longitudinal forms  12   a  and  12   b  (collectively, forms  12 ). The concrete is spread so that it covers the floor surface and contacts the forms  12 . It is then necessary to screed a top surface of the concrete as an initial finishing step. 
     A preferred embodiment of a screed  14  of the present embodiment is shown located atop the forms  12  and includes a strike tube  16  and split drive tube  18 . The strike tube  16  and drive tube  18  are coupled by end plates: a drive element plate  20  and idler element plate  22 . Attached to the drive element plate  20  is a control handle  24  having a control mechanism  26  mounted thereon. Attached to the idler element plate  22  is a second handle  28 . 
     Hydraulic hoses, shown collectively at  30 , provide hydraulic pressure from a hydraulic source (not shown) to rotate the strike tube  16  and drive tube  18 . The strike tube  16  is the leading-edge of the screed at the point of contact with the concrete as the screed proceeds along the forms  12 . The drive tube  18  frictionally engages the forms and is hydraulically powered to move the screed along the forms and is the trailing edge of the screed. In the arrangement of FIG. 1, the screed will travel in the direction indicated by arrow  32 . 
     In general, the control mechanism  26  is operated to control hydraulic power to the strike tube  16  and drive tube  18 . Preferably, the rotation speed of the strike tube  16  will be fast relative to the rotation speed of the drive tube  18 . In addition, the drive tube and strike tube will rotate in different directions. Thus, the strike tube will be driven to rotate such that a top of the strike tube is moving opposite the direction of travel and a top of the drive tube  16  is moving in the direction of travel  32 . Further, in preferred embodiments, the strike tube has a smooth surface and the drive tube has a non-slip surface where the drive tube. rests atop the forms  12 . Accordingly, the strike tube  16  slips on the forms  12  and the drive tube frictional engages the forms  12  to drive the screed along the forms. 
     The relatively high rotational speed of the strike tube, and its reverse rotation direction, provides a finish surface to the concrete  10 . Additional finishing of the surface may also be necessary. 
     Preferably, the control handle  24  is pivotally mounted to the screed  14 . In the preferred embodiment, the control handle  24  includes a bushing  34  that is rotatably coupled to a pin  36  that is fixedly attached to the drive element plate  20 . The control handle may be rotated outboard of the screed in order to make the screed more maneuverable in tight situations. For example, by rotating the control handle outboard  90  degrees from the orientation shown in FIG. 1 so that the longitudinal handle extension  38  is substantially aligned with the longitudinal direction of the strike tube  16 , the strike tube can be driven very close to a vertical wall. 
     Similarly, the second handle  28  includes a bushing  34  that is rotatably mounted on a pin  36  that is fixedly attached to the idler element plate  22  so that the second handle  28  may be rotated relative to the idler element plate so as to maneuver the screed. 
     In operation, an operator will grab the control handle  24  and operate the controls on the control mechanism  26 . A second worker will grab the second handle  28 . Subsequently an operator will use the control mechanism  26  to provide hydraulic power to hydraulic motors  62 ,  78 , and  88 , which in turn will rotate the drive tube  18  and the strike tube  16 . 
     Controls are provided to control the direction of rotation, and the speed of rotation, of each tube individually. As stated, preferably, the strike tube  16  is controlled so as to spin at relatively high rotational speed and opposed to the direction of travel. In contrast, the drive tube  18  is operated to propel, or drive, the screed  14  in the direction of travel  32  at a rate of speed approximately equal to a walking pace. Thus, an operator is located at each handle and the controls are operated to spin the strike tube and rotate the drive tube to move the screed so that freshly poured concrete in front of the screed  14  is screeded level with the forms  12 . It may be desirable to make additional passes over the concrete to achieve the desired finish. 
     The screed may be controlled during operation by raising and lowering the handles. When the operators raise the distal end of the handles, the screed pivots about the strike tube and more weight is placed on the drive tube thereby allowing the drive tube to obtain a better grip on the forms and provide more motive force to the screed. Alternatively, pushing down on the distal end of the handles pivots the screed about the strike tube and raises the drive tube off the forms thereby reducing the pressure of the drive tube on the form and the ability of the drive tube to push the screed forward. The operators can fine tune control of the screed by varying degrees of raising and lowering the distal ends of the handles. 
     The split drive tube  18  of the present invention further assists in controlling the screed during operation and enables operation of the screed by a single operator. Rotatably-coupled, axially-aligned drive tube portions can be independently controlled to control the speed and power applied to each respective drive tube portion. Thus, a drive tube end that encounters more resistance to forward motion can be driven with greater power to overcome a tendency of the screed to become skewed. If the screed becomes skewed, the drive tube portion at the end that is lagging behind can be made to rotate more quickly so as to cause the lagging end to catch up to the advanced end. Conversely, the advanced end may be slowed, or temporarily stopped, to allow the lagging end to catch up. 
     The Tubes 
     Preferably, the strike tube  16  and drive tube  18  are similar in dimensional characteristics. Each tube is approximately six inches in diameter and fabricated of a structural metal such as steel or aluminum. Oftentimes it is desirable to have heavy tubes, making steel, or iron, a preferred material. The ends of each tube, and tube portions, are sealed so as to close off an interior of the tubes. 
     Preferably, the tubes are connected to the plates  20 ,  22  by thrust bearings  40  that are bolted to the plates  20 ,  22 . Where the tubes connect to a hydraulic motor,, a shaft having a splined portion and a threaded portion (not shown) is provided wherein the splined portion passes through the bearing and plate and connects to a coupler  42 , which in turn connects to the hydraulic motor. This method of connection is know in the art and taught in U.S. Pat. No. 5,456,549. 
     As shown, hydraulic motors  62 ,  78 , and  88  are mounted on a motor plate  44  that is space-apart from the drive element plate  22 . This arrangement permits space to make connections between drive and strike tube axles  80 ,  90 , splined shafts, couplers  42 , and the motors  78 ,  88 . 
     In order to prevent misalignment of the tubes relative to the plates  20 ,  22 , and relative to each other, at least one plate, and preferably both plates, are provided as an anti-skew box  46 . With reference to the box member  46  of the drive element plate  20 , a preferred embodiment of the box member  46  includes plates  48  and flanges  50  arranged as a box-like parallelogram. The box member  46  further includes a bottom plate  52  to provide additional rigidity to the box member  46 . Additionally, further plates or cross-members may be provided as desired for additional rigidity. 
     The anti-skew boxes  46  provide connection of the strike and drive tubes to the plates  48  at two spaced-apart locations that are rigidly connected. Accordingly, the relationship of the plates to the tubes&#39; axles is substantially more rigid than would be a single point connection between the plates and the tubes&#39; axles. Accordingly, the anti-skew box maintains the drive plate  20  at an orientation substantially orthogonal to the strike and drive tubes  16 ,  18  and assists in maintaining a parallel orientation of the drive tube and strike tube. 
     The drive tube is split into a first portion  58  and a second portion  60 . The portions are cylindrical, axially aligned, and arranged so that each portion is at opposite ends of the screed  14 . Thus, each drive tube portion  58 ,  60  setsatop the opposite sides of the forms  12   b  and  12   a,  respectively as shown in FIG.  1 . 
     The second portion  60  includes first and second cylinders  60   a  and  60   b  that are fixedly coupled together. The cylinder  60   a  is a drive cylinder and preferably includes a non-slip outer surface to assist in gripping the forms  12  to propel the screed. The drive cylinder  60   a  is rotatably coupled to the idler plate  22 . Bolted to the drive cylinder  60   a  is the cylinder  60   b  that serves as a spacer cylinder. The spacer cylinder  60   b  has a length that is selected to adjust the overall length of the screed to the form width and so that the combined length of the first and second cylinders  60   a  and  60   b  and the first drive tube portion  58  is substantially equal to a length of the strike tube  16 . 
     The first drive tube portion  58  is also a drive cylinder, similar to the first cylinder  60   a.  In particular, the first drive tube portion includes a non-slip outer surface to grip the forms  12  to assist with propelling the screed. 
     The first drive tube portion  58  is belt driven by a hydraulic motor  62  that is mounted directly on the drive element plate  20 . The first portion motor  62  drives a first belt gear  64  that is coupled to a second belt gear  68  by a belt  66 . The second belt gear  68  is fixedly coupled a block  70  that is rotatably mounted to the drive element plate  20  by a ball bearing assembly  72  that is coupled to a circular flange  74  that is welded to the plate  20 . The block  70  is fixedly coupled to the first drive tube portion  58  at an end thereof. The first drive tube portion  58  is further supported by a bushing  76  located within the tube. 
     Accordingly, when hydraulic power is supplied to the motor  62 , the motor turns the belt  66  which turns the block  70  and thus turns the first drive tube portion  58 . The hydraulic motor  62  may be controlled to drive the first drive tube portion in either a first direction of rotation or a second, opposite, direction of rotation. The hydraulic motor  62  is provided with an adjustment in the form of a arcuate slot  77  cut in the drive element plate  20  to permit the motor to be rotated about mounting bolt  80  to tighten the belt. 
     The second drive tube portion  60  is driven by a hydraulic motor  78  that is coupled to the motor plate  44 . Coupler  42  couples the motor  78  to a shaft  80  that passes through a thrust bearing  40 . The shaft continues through, but not contacting, the second belt gear  68  and connects to an inner tube  82 , that is located within the first drive tube portion  58 , by a block coupler  84 . The inner tube  82  proceeds within the first drive tube portion  58  to a stepped block  86  that bolts to spacer cylinder  60   b  of the second drive tube portion  60 . The combination of the stepped block  86 , inner tube  82 , and block coupler  84  rotate freely within the first drive tube portion  58  and ride within bushing  76 . 
     Thus, motor  62  may be operated to rotate the first drive tube portion  58  and the motor  78  may be operated to rotate the second drive tube portion  60 . The motors may be arranged so as to operate independently or cooperatively. In independent operation the motors each have separate controls and are independently controlled as desired. In cooperative arrangement, the motors share hydraulic (or electric) power and a single control determines relative power as between the motors to change the relative speed of rotation of the two drive tube portions  58 ,  60 . Other arrangements are within the scope of the invention. A preferred arrangement for operation of the motors is disclosed below. 
     The strike tube  16  is driven by a hydraulic motor  88  attached to the motor plate  44 . A coupler  42  couples the motor  88  to an axle  90  of the strike tube  16 . The axle  90  passes through a thrust bearing  40 , the drive element plate  20 , and couples to the strike tube  16 . Preferably, the strike tube  16  is independently operated. In general,the strike tube will run at a constant rate of rotation and is controlled only to stop the strike tube, or reverse direction of rotation. 
     Drive Mechanism and Power Supply 
     With reference to the schematic diagram of FIG. 5, a preferred embodiment of a hydraulic system for control of the three motors  62 ,  78 , and  88 , and hence the tubes  16 ,  18 , is described. A hydraulic oil reservoir  100  provides hydraulic fluid to a pump  102  via hydraulic line  104 . From the pump, hydraulic fluid is directed to a selector valve  106  that controls the hydraulic flow to the screed via a disconnect  108 . A relief valve  110  is located between the pump  102  and the selector valve  106  to shunt overpressure fluid from the high pressure side of the pump. 
     At the screed, the hydraulic fluid flow is split at a flow divider  112  into two paths; one to a hydraulic motor  114  that drives the strike tube  16  and one path that flows to hydraulic motors  116  and  118  that drive the split drive tube  18 . In preferred embodiments, the divider is set to create a theoretical flow of approximately 7.78 gallons per minute to the strike tube motor  114  and 2.50 gallons per minute to the drive tube motors  116  and  118 . These flows are sufficient to rotate the strike tube at a rate up to 400 revolutions per minute and the drive tube at a rate up to 40 revolutions per minute. 
     The actual flow to the strike tube motor  114  is controlled by a directional control valve  120  that includes a flow control valve, represented at  122 . The control valve  120  has three positions for forward rotation, no rotation, and backward rotation. The flow control  122  is internal to the directional control valve  120  and is controlled by the same lever  124  as the directional control valve  120 . 
     The hydraulic flow to the drive tube motors  116  and  118  proceeds from the flow divider  112  to a flow control valve  126  and then to a first directional control valve  128 . From the first control valve  128 , the hydraulic fluid flows to the first drive tube motor  116 , then to a second directional control valve  130 , and then to the second drive tube motor  118 . The first and second control valves  128 , 130  each have three positions for driving a respective motor forward or backward, and a neutral position that does not drive the motor. The valves  128 ,  130  are shown set at the neutral position in FIG.  5 . The flow control valve  126  controls the speed of the motors, and hence the rate of rotation of the drive tube portions  58 ,  60 . Because the motors  116 ,  118  are connected in series, both motors are driven at the same rotational speed. However, each motor may be individually controlled as to its direction of rotation, or placed in neutral. 
     The flow valves  122 ,  126  are pressure compensated valves. The hydraulic fluid leaves the screed via disconnect  132 , through a filter  134 , and to the reservoir  100 . 
     Additional Alternative Embodiments 
     In the embodiment of FIGS. 1-5, the drive tube  18  includes the first drive tube portion  58  and the second drive tube portion  60  that has the first cylinder  60   a  and the spacer cylinder  60   b.  Alternatively, the second drive tube portion may be a unitary cylinder that extends from the first drive tube portion to the idler plate  22 . 
     In the configurations shown and described above, separate motors  62 ,  78  control the first and second drive tube portions, respectively. In alternative embodiments, the first and second drive tube portions  58 ,  60  may be driven by a single motor, and a clutch, or other variable drive mechanism or power transfer device, may be used to permit separate control of power to the respective portions  58 ,  60 . 
     In the embodiments of FIGS. 1-4, the hydraulic motors  78  and  88  are mounted outboard of the drive element plate  20 . Alternatively, the hydraulic motors  62 ,  78  and  88  may be mounted above ends of the tubes  16 ,  18  and provide motive power to the tubes by gear, belt, or chain connection to sprockets mounted on the tube axles  80 ,  90 . 
     In FIG. 1 the control mechanism  26  is generically represented as including four control levers. Alternatively, the control mechanism  26  may take many different forms, such as including dead man switches, or knobs, or other control means. 
     The hydraulic flow schematic of FIG. 5 provides a preferred embodiment. However, alternative embodiments of routing the hydraulic power to the motors is also within the scope of the invention. The drive tube motors  116 ,  118  may be arranged in parallel and provided with separate flow control valves so that each drive tube motor may be separately controlled as to rotational speed. Alternatively, one drive tube motor may be used to drive both drive tube portions  58 ,  60 , wherein a clutch, or other variable power transfer device, is used to control the power provided to the respective drive tube portions so as to permit individual control of the drive tube portions. 
     Summary 
     This patent specification sets forth a detailed description of a preferred embodiment of the invention as known to the inventor at the time the underlying patent application was filed. Also disclosed are such alternative embodiments, known at the time of filing, that readily occur to the inventors. No attempt is made to describe all possible embodiments, modes of operation, designs, steps or means for making and using the invention. 
     Where necessary, the specification describes the invention and states certain arrangements of parts, materials, shapes, steps, and means for making and using the invention. However, the invention may be made and used with alternative arrangements, materials, and sizes. Thus, it is intended that the scope of the invention shall only be limited by the language of the claims and the law of the land as pertains to valid patents.