CONCRETE SCREEDING MACHINE WITH ELEVATION CONTROL OVER CONTOURED SUPPORT SURFACE

Description

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the filing benefits of U.S. provisional application Ser. No. 63/730,983, filed Dec. 12, 2024, which is hereby incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to an apparatus and method for screeding freshly poured concrete that has been placed over a support surface.

BACKGROUND OF THE INVENTION

Screeding devices or machines are used to level and smooth uncured concrete to a desired grade. Known screeding machines typically include a screed head, which includes a vibrating member and a grade setting device, such as a plow and/or an auger device. Such screeding machines are used to smooth and screed concrete placed over a horizontal support surface, such as a floor of a building or structure.

SUMMARY OF THE INVENTION

A screeding machine is operable to screed concrete that is placed at a support surface. The screeding machine includes a base unit (such as a wheeled base unit that is driven along the support surface during the screeding pass) and a screed head assembly that is raisable and lowerable relative to the base unit via elevation cylinders or actuators. The screed head assembly may include a plow and a vibrating member that floats on the concrete surface behind the plow during a screeding pass of the screeding machine. The base unit includes a laser sensor that senses a laser plane generated by a laser plane generator at the worksite. A control system is operable to control the screed head to adjust elevation of the screed head assembly or to adjust the plow relative to the vibrating member to establish the grade of the uncured concrete responsive at least in part to (i) sensing of the laser plane by the laser sensor at the base unit and (ii) a target thickness of the concrete at the support surface. The screed head includes first and second sensors disposed at opposite end regions of the screed head for sensing the laser plane by the laser sensor. The control system may operate to adjust the actuators based the first and second sensors sensing the laser plane and based on adjustment of a target sensing region or setpoint of the first and second sensors, with the adjustment of the target sensing region or setpoint being based on the sensing of the laser plane by the laser sensor at the base unit and the target thickness of the concrete at the support surface. In other words, the elevation of the laser plane as perceived by the laser sensor at the base unit may be used to adjust the setpoint or target point (i.e., the point or region where the laser plane is supposed to be received) of the sensors disposed at opposite end regions of the screed head, which will result in an adjustment to the elevation of the screed head assembly via the actuators. The setpoints of the laser sensors at the screed head are thus adjusted or determined based at least in part on where the laser plane is sensed by the laser sensor at the base unit and the target thickness of the screeded concrete at the support surface.

Optionally, a sonic tracer may be disposed at a first end region of the screed head assembly for sensing a screeded concrete surface adjacent to concrete being screeded during the current screeding pass of the screeding machine. The control system is operable to control the first actuator to adjust elevation of the first end region of the screed head assembly responsive to the sonic tracer. The control system may control the second actuator at the opposite second region of the screed head assembly to adjust elevation of the second end region of the screed head assembly based at least in part on (i) sensing of the laser plane by the laser sensor at the base unit, (ii) an angle determined by an angle sensor disposed at the base unit, and (iii) a target thickness of the concrete at the support surface. Optionally, the control system may control the second actuator to adjust elevation of the second end region of the screed head assembly based at least in part on (i) an angle determined by the angle sensor disposed at the base unit, and (ii) a target thickness of the concrete at the support surface.

These and other objects, advantages, purposes and features of the present invention will become apparent upon review of the following specification in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a concrete screeding machine;

FIG. 2 is a side elevation of the concrete screeding machine of FIG. 1, shown with the machine at a support surface;

FIG. 3 is a perspective view of a concrete screeding machine having a sonic tracer and angle sensors for screeding concrete at an angled surface; and

FIG. 4 is an end elevation of the screed head of the concrete screeding machine of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings and the illustrative embodiments depicted therein, a concrete screeding machine 10 includes a base unit 12 with a support mechanism 14 at an end of the base unit for supporting a screed head or screed head assembly 16 at an outer end thereof (FIGS. 1 and 2). The base unit 12 is movable or drivable to a targeted area at a support surface with uncured concrete placed thereat and then moved or driven along a screeding path while the screed head 16 screeds the uncured concrete. The screed head 16 is supported at the support mechanism 14 via a pair of actuators 17 that raise and lower and adjust the screed head 16 and/or actuators that adjust the plow or grade establishing member relative to the vibrating member of the screed head 16. The screed head 16 includes a pair of sensors 18 (such as laser receivers) that sense a laser plane generated by a laser plane generator 19 at or near the support surface. The base unit 12 includes a third sensor 20 that is operable to sense the laser plane generated by the laser plane generator 19 at or near the support surface. In other words, the sensors 18, 20 capture or generate sensor data based on detecting or not detecting the laser plane generated by the laser plane generator 19. The screeding machine 10, when screeding uncured concrete along the support surface, is operable to control or adjust elevation of the screed head 16 based in part on the sensor 20 at the base unit 12 or chassis of the machine 10, as discussed below.

In the illustrated embodiment, the base unit 12 comprises an articulating wheeled base unit 12 having a forward portion 12a (that leads the machine 10 when operating in the screeding direction) and a rearward portion 12b (that trails the forward portion 12a during the screeding pass and that supports the screed head 16). The screed head 16 is mounted at the trailing end of the rearward portion 12b so that the screed head 16 follows the base unit 12 during the screeding pass. Each portion of the base unit 12 includes at least one wheel or track or other means for moving or driving the base unit 12 along the placed concrete and the support surface. For example, each portion may have a pair of wheels or tracks, so that the base unit 12 comprises four wheels or tracks, with at least some of the wheels being rotatably drivable and steerable to maneuver the base unit 12 and the screed head 16 to an appropriate screeding position relative to the concrete to be screeded and to maneuver the base unit 12 and the screed head 16 along the screed path.

The forward portion 12a of the base unit 12 includes the laser sensor 20 that is mounted on a rod that extends vertically from the base unit 12. As shown in FIG. 2, the rod and sensor 20 may be mounted at a rearward end of the forward portion 12a of the base unit 12, such as generally above the pivot joint that pivotally joins the forward portion 12a to the rearward portion 12b. As the base unit 12 is maneuvered along the support surface or deck, the sensor 20 senses the laser plane generated by the laser plane generator 19 to determine the distance “S” between the sensor and the subgrade or deck or support surface (FIG. 2).

The screed head 16 includes a grade setting device 22 (such as a strike off plow, but could optionally include a vibrating plow and/or auger) and a vibrating member 24. The controller of the screeding machine 10 individually controls the actuators 17 of the screed head 16 to raise and lower the plow 22 responsive to signals generated by sensors of the machine 10, such as, for example, responsive to signals generated by laser receivers 18, which sense the laser reference plane generated at the work site, or such as, for example, 3D target/sonic tracers or any suitable sensor or sensing system that operates to generate an output indicative of the grade or angle or location of the screed head 16 at the concrete. Optionally, the screed head 16 may include adjustable plow wings 26 that are adjustably positioned at the grade establishing member or plow 22 and that are adjustable along the grade establishing member 22. The plow wings 26 function to limit excess concrete that is pushed by the grade establishing member 22 from flowing around the ends of the plow, and may utilize aspects of the wings and machines described in U.S. Pat. No. 11,965,345, which is hereby incorporated herein by reference in its entirety.

The actuators 17 are pivotally mounted at one end at brackets at the rearward portion 12b of the base unit 12 and at the other end at the screed head assembly 16. Thus, independent extension and retraction of the actuators 17 (and optionally in conjunction with extension and retraction of a third actuator 28) will adjust the screed head elevation and tilt or angle relative to the base unit 12 (and thus relative to the laser sensor 20 at the base unit 12).

Placing and screeding concrete on elevated decks is typically done at structures that include cambered I-beams covered by corrugated steel panels that support the concrete until it is cured to add to the structural integrity. Pre-cambered I-beams deflect variably based on the load induced by concrete, people, and tools used to screed and finish the concrete. Therefore, the concrete thickness will vary if screeding the surface is done responsive to a laser sensor at the screed head 16 that is following a planar laser beam or plane as is typically done on non-elevated slabs. Typically, decks are intended to be screeded to a set thickness to meet a fire rating.

The third laser receiver 20 is mounted to the chassis or base unit 12, such as at the forward portion 12a of the base unit 12 of the laser screed machine 10, and tracks the elevation of the base unit 12 as the machine 10 moves across the deck in reference to the datum of the level laser beam. The changes in the base unit's elevation are correlated to the deflection of the deck or support surface. Based on the determined deflection of the deck, a programming shift can be applied to the setpoint in the laser receivers 18 controlling the height settings on the screed head 16.

The third sensor or receiver 20 is mounted to the chassis or base unit 12 at or around the middle of the machine 10 to measure the deflection changes of the deck due to the load of concrete. As the machine 10 screeds the concrete, the middle receiver 20 measures the deck deflection and the machine's software uses that data to offset the laser receivers 18 at the screed head 16 in order to maintain the height of the screed head 16 at a consistent height above the corrugated deck.

When the screeding machine 10 is positioned at a start or starting location of a screeding pass or path, the screeding machine 10 is moved along the concrete while the screed head 16 operates to establish a desired grade of the concrete surface and smooth or finish or screed the concrete. The control system of the machine 10, based in part on sensing by the laser receiver 20 at the center of the machine chassis 12, plots the subgrade dimension “S” as the machine 10 travels over the deck or subgrade. The dimension “S” data is then filtered into a signal “S” that has a smaller standard deviation. For example, because the wheels of the machine 10 may encounter uneven structure (e.g., corrugation, rebar, etc.), the system may average the determined dimension S over a period of time or distance traveled and use the averaged dimension for adjusting control of the screed head 16. The screed head 16 is then controlled to a dimension G, which is a function of “S{circumflex over ( )}” and the desired pour thickness “T”: G(x)=S{circumflex over ( )}−T+C, where C denotes one or more offset parameters.

The screed head 16 is thus controlled in a manner that accommodates for changes or fluctuations or curvature in the subgrade or deck as the machine 10 moves along the deck during a screeding pass. The sensor 20 at the base unit 12 senses the height of the sensor 20 relative to the subgrade and then adjusts control of the screed head 16 so the screed head 16 is controlled based on the height of the sensors 18 (as determined by the sensors sensing the laser plane) and based on the subgrade dimension S (determined via the sensor 20 at the base unit 12) and based on the desired or target thickness T of the concrete and based on one or more offset parameters. In other words, the system adjusts the setpoint or target point of the sensor 18 (i.e., the point or region where the laser plane is supposed to be received at the laser receiver or sensor 18 during a screeding pass) responsive to the determined subgrade dimension S and the target thickness T. The setpoints of the laser sensors 18 at the screed head 16 are thus adjusted or determined based at least in part on where the laser plane is sensed by the laser sensor 20 at the base unit 12 and the target thickness of the screeded concrete at the support surface.

Optionally, a screeding machine may be operable to screed concrete placed at a contoured or three-dimensional surface using a sonic tracer for sensing previously screeded concrete to set the elevation of one side of the screed head. For example, and with reference to FIGS. 3 and 4, a screeding machine 110 includes a base unit 112 with a support mechanism at an end of the base unit 112 for supporting a screed head or assembly 116 at a rearward end of the base unit 112. The base unit 112 is movable or drivable to a targeted area at a support surface with uncured concrete placed thereat and then moved or driven along a screeding path while the screed head 116 screeds the uncured concrete. The screed head 116 is supported at the support mechanism 114 via a pair of cylinders or actuators that raise and lower the screed head 116 responsive to sensors 118 (such as laser receivers). The sensors 118 are operable to sense a laser plane generated by a laser plane generator 119 at or near the support surface. The base unit 112 includes a third sensor 120 that is operable to sense the laser plane generated by the laser plane generator 119 at or near the support surface, and includes an angle sensor 122 for sensing an angle or tilt of the base unit or chassis 112. The screed head 116 includes a head angle sensor 124 for sensing an angle or tilt of the screed head 116, and includes a sonic tracer 126 at one or both ends of the screed head 116 for sensing the previously-screeded concrete surface as the screed machine 110 moves along a subsequent or adjacent screeding pass.

As the screeding machine 110 traverses over the three-dimensional or contoured or non-level surface, the concrete is screeded to a uniform thickness resulting in a final grade that is an offset of the subgrade contour. As the machine 110 travels along the deck and concrete during a screeding pass, the control system, based on sensing by the sensors mounted on the machine chassis, plots changes in machine position and orientation. The control system, based on the chassis-mounted laser receiver 120, plots the machine elevation (dimension Z), from which the changes in subgrade elevation can be derived, and the control system, based on the chassis-mounted angle sensor 122, plots the machine angle with respect to true level (around axis X and Y), which matches the slope of the subgrade. In other words, based on the laser receiver 120 sensing movement of the base unit 112 relative to the laser plane and/or based on the angle sensor 122 sensing movement of the base unit 112 relative to the subgrade, the control system maps elevation, slope and/or contour of the subgrade. This mapped elevation, slope and/or contour may then be used to adjust the elevation, pitch and/or roll of the screed head 116 during screed passes.

During a screeding pass, the elevation on the one side of the screed head 116 (the side that moves along the previously-screeded concrete, such as the left side in FIGS. 3 and 4) is controlled based on the sonic tracer 126 sensing the previously-screeded concrete and the control system reading and controlling the screed head 116 in relation to the finished surface of the previous pass. The opposite side of the screed head 116 (e.g., the right side in FIGS. 3 and 4) may be controlled responsive to sensing by the head-mounted angle sensor 124 and/or the laser receiver 118, and the system controls the elevation, pitch, and roll of the screed head 116 in relation to a mathematical function of subgrade-dependent data. This is the data that is collected by the angle sensor 122 and laser receiver 120 mounted on the machine chassis 112. Put another way, the control system controls the elevation, pitch, and roll of the screed head 116 based on the mapped elevation, slope and/or contour of the subgrade and one or both of the angle of the screed head 116 sensed by the angle sensor 124 and the elevation of the screed head 116 relative to the laser plane sensed by the laser receiver 118.

The elevation on the left side of the screed head 116 is controlled responsive to the sonic tracer 126, both at the start of and throughout the entire screeding pass, by referencing the finished concrete grade of the previous screeding pass. The right side of the screed head 116 can be controlled responsive to the laser sensor or receiver 118 on the right side of the screed head 116, and/or responsive to the angle sensor 124 on the screed head 116, and/or responsive to the laser sensor 120 at the base unit 112 (e.g., the mapped contour of the subgrade). When controlling via the head-mounted laser sensor or receiver 118, the receiver 118 is used to hold the screed head 116 at a calculated distance below the level laser beam. The function for this calculated distance is:

ER ⁡ ( S ) = S - T - [ ( L / 2 ) * sin ⁡ ( Θ ) ] ,

where ER is the Elevation-Right (right side of the screed head), S is the vertical distance from the laser beam to the subgrade as reported by the chassis elevation receiver 120, O is the angle reported by the chassis angle sensor 122 (which may be positive or negative depending on the surface slope), T is the desired concrete thickness, and L is the length (or width) of the screed head 116 (i.e., the dimension of the screed head 116 from one end to the other).

Optionally, the laser receivers mounted on the screed head 116 and on the base unit 112 may be positioned on telescopic masts driven by respective actuators with position feedback. This allows the receivers to be shifted vertically to keep the laser beam within the receiver window while still tracking the intended dimension as the machine 110 moves along a sloped surface. In other words, the masts supporting the receivers on the screed head 116 and base unit 112 of the screeding machine 110 may extend or retract to position the respective sensors or receivers at a height that is able to sense the laser plane. The system may extend or retract one mast in this manner and may extend the other mast a corresponding amount and may track the extension/retraction amount.

When controlling the right side of the screed head 116 (the end or side opposite the sonic tracer 126) via the angle sensor 124, the control system, based in part on the angle sensor 124 at the screed head, operates to control the screed head 116 to an angle that matches the angle of the subgrade as reported by the angle sensor 122 on the chassis 112. In other words, the control system will adjust the right-side actuator so that the angle output by the angle sensor 124 at the screed head 116 corresponds to the angle output by the angle sensor 122 at the base unit 112. The subgrade-dependent signals collected by the laser receiver 120 and the angle sensor 122 mounted on the chassis 112 are subject to signal filtering to decrease or reduce the standard deviation of the data.

According to an aspect of the disclosure, a screeding machine for screeding uncured concrete at a support surface includes a base unit and a screed head assembly supported at the base unit. The screed head assembly includes a grade establishing member and a vibrating member. The screed head assembly includes first and second sensors at respective ends of the screed head assembly and actuators operable to adjust a height of the respective ends of the grade establishing member of the screed head assembly responsive to the respective first and second sensors sensing a laser plane. The base unit includes a third sensor that senses the laser plane. A control system is operable, during a screeding pass of the screeding machine, to control the actuators to adjust elevation of the grade establishing member of the screed head assembly to establish the grade of the uncured concrete responsive at least in part to sensing of the laser plane by the third sensor and a target thickness of the concrete at the support surface. This aspect may include one or more of the following optional features.

In some implementations, the control system operates the actuators to adjust elevation of the screed head assembly so that the first and second sensors on the screed head assembly sense the laser plane at a setpoint. The setpoint is determined based at least in part on an elevation that the third sensor disposed at the base unit senses the laser plane. In some examples, the control system operates to adjust the actuators based on a height dimension determined responsive to sensor data captured via the third sensor and filtering or averaging of the sensor data to reduce the standard deviation in the sensor data. In some aspects, the base unit of the screeding machine includes a wheeled base unit that is driven along the support surface during the screeding pass. In some implementations, the actuators include a respective actuator disposed at a respective side of the screed head assembly. Each actuator is responsive at least in part to the respective first sensor or second sensor.

In some examples, the base unit includes a forward portion and a rearward portion. The forward portion is disposed in front of the rearward portion as the screeding machine travels in a screeding direction during the screeding pass. The screed head assembly is disposed at the rearward portion. In further examples, the third sensor is disposed at a pivot joint that pivotally connects the forward portion and the rearward portion. In other further examples, the third sensor is disposed at the forward portion.

According to another aspect of the disclosure, a screeding machine for screeding uncured concrete at a support surface includes a base unit and a screed head assembly supported at the base unit. The screed head assembly includes a grade establishing member and a vibrating member. The screed head assembly includes first and second actuators operable to adjust a height of respective end regions of the grade establishing member of the screed head assembly, and a sonic tracer at a first end region of the screed head assembly for sensing a screeded concrete surface adjacent to concrete being screeded during a screeding pass of the screeding machine. The base unit includes a laser sensor that senses a laser plane and an angle sensor. A control system is operable to control the first actuator to adjust elevation of the first end region of the grade establishing member of the screed head assembly responsive to the sonic tracer. The control system is operable to control the second actuator to adjust elevation of a second end region of the grade establishing member of the screed head assembly based at least in part on sensing of the laser plane by the laser sensor disposed at the base unit, an angle determined by the angle sensor disposed at the base unit, and a target thickness of the concrete at the support surface. This aspect may include one or more of the following optional features.

In some implementations, the control system is operable to control the second actuator to adjust elevation of the second end region of the grade establishing member of the screed head assembly based on a length of the screed head assembly. In some examples, the control system is operable to control the second actuator to adjust elevation of the second end region of the grade establishing member of the screed head assembly based in part on a head-mounted angle sensor disposed at the screed head assembly. In further examples, the control system is operable to control the second actuator to adjust elevation of the second end region of the grade establishing member of the screed head assembly so that an angle of the grade establishing member of the screed head assembly detected by the head-mounted angle sensor corresponds to the angle determined by the angle sensor disposed at the base unit.

In some aspects, the control system is operable to control the second actuator to adjust elevation of the second end region of the grade establishing member of the screed head assembly based in part on a laser sensor disposed at the second end region of the screed head assembly and sensing the laser plane. In further aspects, the laser sensor disposed at the second end region of the screed head assembly is mounted on an extendable and retractable mast. The control system extends or retracts the mast to position the laser sensor for sensing the laser plane.

In some implementations, the laser sensor at the base unit is mounted on an extendable and retractable mast. The control system extends or retracts the mast to position the laser sensor for sensing the laser plane. In some examples, the base unit of the screeding machine comprises a wheeled base unit that is driven along the support surface during the screeding pass.

In some aspects, the base unit includes a forward portion and a rearward portion. The forward portion is disposed in front of the rearward portion as the screeding machine travels in a screeding direction during the screeding pass. The screed head assembly is disposed at the rearward portion. In further aspects, the laser sensor is disposed at a pivot joint that pivotally connects the forward portion and the rearward portion. In other further aspects, the laser sensor is disposed at the forward portion.

According to yet another aspect of the disclosure, a screeding machine for screeding uncured concrete at a support surface includes a base unit and a screed head assembly supported at the base unit. The screed head assembly includes a grade establishing member and a vibrating member. The screed head assembly includes first and second actuators operable to adjust a height of respective end regions of the grade establishing member of the screed head assembly, and a sonic tracer at a first end region of the screed head assembly for sensing a screeded concrete surface adjacent to concrete being screeded during a screeding pass of the screeding machine. The base unit includes an angle sensor. A control system is operable to control the first actuator to adjust elevation of the first end region of the grade establishing member of the screed head assembly responsive to the sonic tracer. The control system is operable to control the second actuator to adjust elevation of a second end region of the grade establishing member of the screed head assembly based at least in part on an angle determined by the angle sensor disposed at the base unit, and a target thickness of the concrete at the support surface. This aspect may include one or more of the following optional features.

In some implementations the control system is operable to control the second actuator to adjust elevation of the second end region of the grade establishing member of the screed head assembly based on a length of the screed head assembly. In some examples, the control system is operable to control the second actuator to adjust elevation of the second end region of the grade establishing member of the screed head assembly based on sensing of a laser plane by a laser sensor disposed at the base unit. In further examples, the laser sensor disposed at the base unit is mounted on an extendable and retractable mast. The control system extends or retracts the mast to position the laser sensor for sensing the laser plane. In other further examples, the control system is operable to control the second actuator to adjust elevation of the second end region of the grade establishing member of the screed head assembly further based on another laser sensor disposed at the second end region of the screed head assembly and sensing the laser plane.

In some implementations, the control system is operable to control the second actuator to adjust elevation of the second end region of the grade establishing member of the screed head assembly based in part on an angle sensor disposed at the screed head assembly. In further implementations, the control system determines contour of the concrete at the support surface based at least in part on the angle determined by the angle sensor disposed at the base unit. The control system controls the second actuator based on the determined contour and an angle of the screed head assembly determined by the angle sensor disposed at the screed head assembly.

In some examples, the control system is operable to control the second actuator to adjust elevation of the second end region of the grade establishing member of the screed head assembly based in part on a laser sensor disposed at the second end region of the screed head assembly and sensing a laser plane. In further examples, the laser sensor disposed at the second end region of the screed head assembly is mounted on an extendable and retractable mast. The control system extends or retracts the mast to position the laser sensor for sensing the laser plane.

In some aspects, the base unit of the screeding machine comprises a wheeled base unit that is driven along the support surface during the screeding pass. In some implementations, the base unit comprises a forward portion and a rearward portion. The forward portion is disposed in front of the rearward portion as the screeding machine travels in a screeding direction during the screeding pass. The screed head assembly is disposed at the rearward portion.

The screeding machine comprises a pressurized hydraulic fluid system powered by an engine at the base unit that drives the hydraulic system to generate pressurized fluid for controlling the elevation actuators or cylinders and for controlling the extension and retraction of the lateral actuator and for controlling operation of the vibrating member and for driving and steering of the wheels of the base unit. The screeding machine and the screed head or assembly may utilize aspects of the screeding machines and screed heads described in U.S. Pat. Nos. 4,655,633; 4,930,935; 6,227,761; 6,976,805; 7,044,681; 7,121,762; 7,175,363; 7,195,423; 7,396,186; 7,850,396; 8,038,366; 9,835,610; 10,190,268 and/or 10,895,045, and/or U.S. Publication Nos. US-2023-0258005; US-2022-0316154; US-2010-0196096 and/or US-2007-0116520, which are all hereby incorporated herein by reference in their entireties.

The screeding machine may be controlled by an operator (that may sit or stand at the base unit or may walk next to the base unit) or may be remote controlled via a remote controller (whereby an operator may be located at a location remote from the placed uncured concrete that is being screeded by the screeding machine). The base unit may comprise a two or three or four (or more) wheeled device and may comprise an articulating frame (with two wheels at one portion and at least one wheel at the other portion). The screed head may comprise a six foot head or may comprise a smaller or larger head depending on the particular application of the screeding machine. The elevation cylinders include masts for the laser receivers, and the masts may comprise longer masts (e.g., 8 foot masts or 10 foot masts or longer) for use on large line jobsites.

Changes and modifications to the specifically described embodiments can be carried out without departing from the principles of the present invention, which is intended to be limited only by the scope of the appended claims as interpreted according to the principles of patent law.