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FIELD OF THE INVENTION 
     The present invention pertains to the field of roller screeds and more particularly pertains to powered roller screeds for screeding cementitious material. 
     BACKGROUND OF THE RELATED ART 
     Concrete structures are formed by pouring a cementitious material, such as cement and aggregate (referred to herein as concrete) 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, or support, 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. A board, long enough to span the forms, is laid on top of each form and thereafter pulled down the length of the forms by workers at each end of the board. This 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 supports 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 areas surrounded by obstacles and are more difficult to transport than the smaller screed described above. Also, in the event the screed becomes mis-aligned with the forms, the screed must be manually re-aligned, such as by holding back a leading end of the screed so that the trailing end can catch up. 
     Accordingly, there is a need in the industry to provide a powered screed that can be easily operated, even in areas that are constrained by nearby obstacles, and conveniently transported and set up for use. 
     SUMMARY OF THE INVENTION 
     The present invention provides a frameless roller screed having a drive tube to assist the screed operators to move the screed along forms over freshly poured concrete. The present invention has no form-spanning supporting structure or frame, thereby providing a lightweight, maneuverable, and easily transported screed. In addition, by providing handles, arranged as levers, in combination with a single drive tube and strike tube, the handles can be easily manipulated to control the effect of the drive tube for easy operation. 
     Preferably, hydraulic motors drive the strike tube and the drive tube. The strike tube is the leading edge of the screed as the screed is powered along the forms and by rotating the strike tube the advantages of a rotary screed are achieved—i.e., a better surface on the concrete. The drive tube is powered to provide mechanical assistance to push excess concrete forward as the screed moves along the forms. By providing motive power to the screed of the present invention, the screed operators can concentrate on achieving a high-quality finish on the concrete. 
     Preferably, the present invention screed is maneuvered by handles located on opposite ends of the screed and arranged as levers. The handles are pivotally mounted to frame elements so that the handles may be pivoted to provide greater screed maneuverability. For example, the handles may be pivoted outward allowing the screed to be driven up to obstacles such as a vertical wall at the end of a concrete pad. 
     Further, 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. Accordingly, 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. 
     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. Preferably, at least one of the plates includes an anti-skew box structure that prevents the tubes from skewing relative to one another and relative to the plates. 
     Accordingly, the present invention provides a frameless, powered roller screed having motive force to drive the screed along forms and assist in the difficult task of screeding heavy concrete. In addition, the present invention provides handles that can lever the drive tube to provide substantial control over the motive force generated by the drive tube. Also, the handles are provided with pivotal connections to connecting plates for greater screed maneuverability. And, by providing no frame elements that extend across the forms, the screed of the present invention is relatively easier to transport and setup as compared to prior art screeds having drive tubes. 
    
    
     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 the roller screed of the present invention wherein the screed tubes are shown in broken view to represent indefinite lengths. 
     FIG. 3 is a top plan view of an alternative embodiment of the roller screed of the present invention wherein the screed tubes are shown in broken view to represent indefinite lengths. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As stated, a conventional method of making a concrete pad is to pour concrete onto a surface and 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 . The concrete is spread so that it covers the floor surface and contacts the forms  12 . It is then necessary to screed a top, or exposed, surface of the concrete. 
     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 drive tube  18 . The strike tube  16  and drive tube  18  are supported by plates comprising 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) for powering the screed. In operation, hydraulic power is used 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 . Accordingly, the strike tube  16  slips on the forms  12  as the screed proceeds 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 . Additionally finishing of the surface may also be necessary. 
     As stated, the screed  14  includes the drive tube  18  and strike tube  16 . In a preferred embodiment, each tube extends across the forms  12  and each is supported at one end by the idler element plate  22  and at another end by the drive element plate  20 . Hydraulic motors  34  and  36  are coupled to the drive element plate and receive hydraulic power via the hydraulic hoses  30  to provide rotation to the strike tube and drive tube. 
     The strike tube and drive tube are rotatably mounted on the respective plates by thrust bearings  38   a - 38   f . Each thrust bearing is fixedly coupled to one of the plates  22 ,  20 . 
     The screed  14  of the present invention includes no supporting structure or framework to support the span of the screed across the forms  12 . Accordingly, only the drive tube  18  and strike tube  16  span the forms  12 . By providing a power driven screed have a minimal support structure, the screed of the present invention is more portable and maneuverable than a screed having a form-spanning framework. 
     Preferably, the control handle  24  is pivotally mounted to the screed  14 . In the preferred embodiment, the control handle  24  includes a bushing  40  that is rotatably coupled to a pin  42   a  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  44  is substantially aligned with the longitudinal direction of the strike tube  16 , the strike tube can be driven very close to a vertical wall. 
     And, similarly, the second handle  28  includes a bushing  46  that is rotatably mounted on a pin  42   b  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 turn the controls on the control mechanism  26  to provide hydraulic power to the hydraulic motors  34  and  36 , which in turn will rotate the drive tube  18  and the strike tube  16 , respectively. 
     Preferably, 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 further 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. 
     This method of controlling the screed further permits the two operators to coordinate the screed motion. If one end of the screed lags behind the other end, one operator may raise or lower a particular end of the screed to increase or decrease its forward progress. Thus, each operator has significant control of the motive force of the operator&#39;s respective end independently of the hydraulic control device. 
     The Tubes 
     Preferably, the strike tube  16  and drive tube  18  are similar. 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 are sealed by a round disc  48  that is fixedly attached, such as by welding, to the tubes so as to close off an interior of the tubes. The disc  48  further supports a tube axle  50  that extends axially outward from each end of each tube  16 ,  18 . 
     Preferably, the tubes are connected to the plates  20 ,  22  by the thrust bearings  38   a - 38   f  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, 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, the motors are mounted on a motor plate  49  that is spaced-apart from the drive plate  22 . This arrangement permits space to make connections between the axles, splined shafts, and the motors. 
     In order to prevent skewing, or 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 with an anti-skew box member  60 . With reference to the box member coupled to the drive plate  20 , a preferred embodiment of the box member  60  includes a flange plate  62  arranged approximately 90 degrees to the plate  20 . The box member  60  further includes a return plate  66  arranged substantially parallel to the plate  20  and approximately 90 degrees to the flange plate  62 . A bottom plate  68  is connected to the drive plate  20 , the flange plate  62 , and the return plate  66  to provide additional rigidity to the box member structure. Additionally, further plates or cross-members may be provided for additional rigidity, such as across the opening from a distal end of the return plate  66  to the drive plate  20 . 
     The anti-skew boxes  60  provide connection of the strike tube to the plates  20  at two spaced-apart locations that are rigidly connected. Accordingly, the relationship of the plates to the strike tube axle is substantially more secure than would be a single point connection between the plates and the strike tube axles. Accordingly, the anti-skew box maintains the drive plate  20  at an orientation substantially orthogonal to the strike tube axle  50  and assists in maintaining the parallel orientation of the drive tube and strike tube. 
     In alternative embodiments, an anti-skew box member  60  may be located on the strike tube only, the drive tube only, or a combination of the strike tube and the drive tube. 
     Drive Mechanism and Power Supply 
     Preferably, the present invention is coupled to a hydraulic power supply (not shown) via hydraulic hoses  30 . In the present embodiment, the screed has hydraulic supply line  30   a  and a hydraulic return line  38   c . The hydraulic supply line  30   a  is coupled to the control device  26  and connected to a manifold (not shown) wherein the supply line is divided into two supply lines  30   a ′ that extend down the handle to the hydraulic motors  34  and  36 . Hydraulic fluid returns to the control device through return lines  30   c′.    
     The control device  26  is further provided with valve means to control, or regulate, the flow of hydraulic fluid to the respective hydraulic motors  34 ,  36  so that the control device can control the speed of rotation of each tube  16 ,  18  individually. By providing individual control, the control device is able to set a rotational speed and direction for the strike tube  16  and thereafter regulate the rotational speed and direction of the drive tube  18  so as to set a desired direction and speed for moving the screed along the forms  12  to screed the concrete  10 . 
     Alternately, the control device may be arranged to switch the function of the strike tube and the drive tube so that the screed may be driven in a first direction and then driven in an opposite direction. For example, in the configuration as shown in FIG. 1, the screed device moves in the direction of motion  32  until the screed reaches an end of the forms  70 , at which time the handles may be pivoted about respective pins  42   a ,  42   b  and the control device operated so that the leading tube becomes the strike tube and the trailing tube is the drive tube and the direction of travel is reversed. 
     Additionally, by providing additional controls to the control device  26  the direction of rotation of the strike tube  16  may be controlled so as to rotate in the same direction as the drive tube  18 , but a higher rate of rotation, on a final pass over the concrete so as to provide a skim coat. 
     Preferably, the drive tubes include a non-slip surface, such as a wear-resistant, elastomeric material that has a relatively high coefficient of friction with the forms. A suitable material is a high wear synthetic rubber, such as is used on road tires. 
     In yet another configuration, four hydraulic hoses  30  may be provided from two hydraulic power supplies to the control device  26  wherein two hoses are hydraulic supply lines and two hoses are hydraulic return lines. This four-hose embodiment may provide less complicated connections and fittings at the control device. 
     Additional Alternative Embodiments 
     In the embodiment of FIGS. 1 and 2, the drive tube  18  is shown configured substantially similar to the strike tube  16 . Alternatively, the drive tube may be configured in a split arrangement as shown in FIG.  3 . In a split-arrangement drive tube, separate drive tube portions  18   a  and  18   b  are separately supported by frame element extensions  20   a  and  22   a . The drive tube portions have a length sufficient to extend away from the frame elements  20 ,  22  and rest on the respective forms  12 . In the configuration shown, both drive tube portions  18   a  and  18   b  are powered. Drive tube portion  18   a  is powered by hydraulic motor  34  as in the embodiments described above. Drive tube portion  18   b  is powered by an additional hydraulic motor  35 . Drive portion  18   a  is provided to properly balance the screed on the forms and prevent an unstable structure. 
     In the embodiments of FIGS. 1-3, the hydraulic motors are shown mounted outboard of the frame element  20 . Alternatively, the hydraulic motors  34  and  36  may be mounted above ends the tubes  16 ,  18  and provide motive power to the tubes by gear, belt, or chain connection to sprockets mounted on the tube axles  50 . 
     In FIG. 1 the control mechanism  26  is generically represented as including two control knobs. Alternatively, the control mechanism  26  may take many different forms, such as including dead man switches coupled to the handle extensions  72  that protrude outboard from the control handle  24 . 
     In yet another embodiment, the screed may be operated by one person. In this embodiment, the second handle is oriented 180° from the direction of screed motion, that is, the second handle is oriented so that it is pointing backward and extends over the drive tube. A weight  74  is attached to the second handle thus urging the handle downward toward the screed so that the drive tube applies more pressure to the form. Preferably, the weight is approximately 40 lbs. (88 Kg.) and is located approximately 10 to 12 inches (25 to 50 cm) away from the idler plate along the handle. 
     The screed is then operated by a single operator who controls the screed from the control handle  24 . By setting the hydraulic power controls at the control device the screed is set in motion. Thereafter, the operator can easily control the screed by raising and lowering (i.e., moving away from or toward the form) the handle so as to control the amount of motive force the drive tube imparts to the screed. 
     SUMMARY 
     This patent specification sets forth a detailed description of a preferred embodiment of the invention as known to the inventors 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. To include all such information would unduly confuse the description of the preferred embodiments and would not serve to provide further information to persons skilled in the art of this 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.

Summary:
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. No framework or other supporting structure extends between ends of the screed thereby making the screed more portable than comparable screeds having a structure that supports the roller tubes and extends the length of the screed. Handles are pivotally coupled to plates at each end of the screed to maneuver and control the screed during operation. Because the handles are pivotally mounted, they can be pivoted outward to permit the screed to maneuver close to obstacles located near the pad. Additionally, the combination of the handles, strike tube, and drive tube permit the handles to be used as levers to control the effective motive power of the drive tube, thereby providing substantial control to the screed operators.