The present disclosure generally relates to paving machines, and more specifically to a screed assembly for a paving machine.
When constructing roads, bridges, parking lots and other such surfaces, paving machines may be used to deposit, spread and compact paving material, such as asphalt, on a base surface, ground surface, thereby creating a flat, consistent surface over which vehicles will travel. A paving machine generally includes a tractor portion having a chassis and a hopper for storing the paving material, an auger that distributes the paving material on a base surface and a screed assembly that levels and compacts the paving material, ideally leaving a mat of uniform depth and smoothness. The screed assembly is typically rear-mounted on the paving machine behind the hopper, the chassis and the auger relative to the direction of travel. Further, the screed assembly is typically drawn behind the paving machine by a pair of pivotally mounted tow arms.
Among other things, the screed assembly may include a main screed and one or more extension screeds. The extension screeds are laterally extendable from the main screed to adjust for varying base surface widths. In addition, the main screed and the extension screeds may each include bottom-facing screed plates that facilitate the compacting and leveling of the paving material on the base surface. Screeds typically pave with a slight nose up angle of attack in the paving direction for optimal screed paving performance of floatability, stability, screed plate wear, and pre-compaction. To get the main screed and any extensions screeds in this optimal nose up angle of attack, a process called nulling the screed is used.
U.S. Pat. No. 5,356,238 discloses a screed with an actuator for adjusting screed angle to achieve a nulling position through inputs provided at the operator station. Sensors are provided to monitor the current angle or position of the screed.
While effective, there remains a need for improved screed assemblies for work machines used in high wear applications, such as paving.
In accordance with one aspect of the present disclosure, a screed assembly is disclosed. The screed assembly has a screed frame that includes a main screed. Attached to the main screed is a drop arm that is used to attach the screed assembly to a work machine. An actuator device of the screed assembly adjusts the main screed from a neutral position to a nulled position by rotating the main screed around an axis of the pivot pin. The screed assembly further has a controller that determines if the main screed is in the neutral position and adjust the main screed to the nulled position by sending a null adjustment signal to the actuator device, and the actuator device rotating the main screed from the neutral position to the nulled position in response to the null adjustment signal.
In accordance with another aspect of the present disclosure, a work machine is disclosed. The work machine has a tractor portion that includes a frame, a traction system which supports the frame and is used to move the traction portion along a paving reference, and the frame supports an operation station. The work machine further includes a screed assembly, which has a screed frame that includes a main screed. Attached to the main screed is a drop arm that is used to attach the screed assembly to the work machine. An actuator device of the screed assembly adjusts the angle of attack of the main screed from a neutral position to a nulled position by rotating the main screed around an axis of the pivot pin. The screed assembly further has a controller that determines if the main screed is in the neutral position and adjust the main screed to the nulled position by sending a null adjustment signal to the actuator device, and the actuator device rotating the main screed from the neutral position to the nulled position in response to the null adjustment signal.
In accordance with a further aspect of the present disclosure, a method of automatedly nulling a screed is disclosed. The method includes attaching a main screed of a screed frame to a work machine with a drop arm, with the drop arm attached to the main screed by a drop arm pivot pin. After the main screed is attached, a controller of determines if the main screed is in a neutral position and sends a null adjustment signal to an actuator device. The actuator device adjust the main screed from the neutral position to a nulled position by rotating the main screed around an axis of the drop arm pivot pin in response to the null adjustment signal.
These and other aspects and features of the present disclosure will be more readily understood when read in conjunction with the accompanying drawings.
Referring to
The work machine 2 generally includes a tractor portion 4 which propels the work machine 2 and supports an operator control station 6, an asphalt conveyor system 7, and the screed assembly 1. The tractor portion 4 propels the work machine 2 at a steady rate along the paving reference 3 and includes a frame 8, an engine 9 supported by the frame 8, and ground engaging elements 10 supporting the frame 8 and driven by the engine 9. The ground engaging devices 10 may be tracks as shown, or any other similar device such as wheels.
The operator control station 6 may be configured to provide operator control over the work machine 2. The operator control station 6 may include one or more operator seats 11. In one embodiment, the operator control station 6 may be mounted to the frame 8 proximal to the rear of the tractor portion 4.
The asphalt conveyor system 7 is configured to transfer hot asphalt material or other paving material from a truck (not shown) in front of the work machine 2, through the tractor portion 4, and to the paving reference 3 at the rear of the work machine 2. A hopper 12 may be positioned at the front of the work machine 2 and may contain the paving material that is to be formed into a mat on the paving reference 3. The paving material may be dumped into the hopper 12 from trucks (not shown) that deliver the paving material to a worksite. The work machine 2 may also include one or more conveyors (not shown) at the bottom of the hopper 12. The conveyors transport the paving material from the hopper 12 to the rear of the tractor portion 4. The work machine 2 may further include one or more augers (not shown) or other material feed components instead of or in addition to the conveyors. The augers distribute the paving material in front of the screed assembly 1 positioned at the rear end of the tractor portion 4. As the work machine travels forward, the paving material is evenly spread and compacted by the screed assembly 1.
The screed assembly 1 may be pivotably attached to the tractor portion 4 by a drop arm 14 on each side of the frame 8 and towed behind the tractor portion 4 to spread and compact the paving material into a layer or mat of desired thickness, width and uniformity. The drop arms 14 are pivotally connected to each side of the frame 8 such that the relative position and orientation of the screed assembly 1 relative to the frame 14 and to the surface being paved, the paving reference 3, may be adjusted by raising or lowering the drop arms 14 via tow arm actuators 15. The tow arm actuators 15 may be any suitable actuators, such as, for example, the hydraulic cylinders depicted.
The screed assembly 1 may also be connected to the tractor portion 4 by a lifting assembly 16. The lifting assembly 16 is configured to move the screed assembly 1 between a lowered position (shown in
The lifting assembly 15 may include a plurality of lift cylinders or other actuators (not shown) connected to the top of the screed assembly 1. In some embodiments, the lift cylinders may also provide further control over the paving process by applying additional downward force to the screed assembly 1.
The screed assembly 1 may be a compilation of components that cooperate to shape, level, and compact an asphalt mixture delivered from the hopper onto a base surface and may have any of a number of configurations known in the industry.
As best shown in
Referring back to
The drop arms 14 are rotatably attached to the main screed 19 by a drop arm pivot pin 28 on both sides of the main screed 19. Once the screed assembly is fixedly attached to the tractor portion 4 of the work machine 2, the drop arm pivot pins 28 allows the main screed 19, screed frame 18, and any extension screeds, such as the left hand and right hand extension screeds 20, 21, to rotate, relative to the tractor portion 4, around an axis A of rotation. To control this rotation, the screed assembly 1 includes threaded thickness screws 30 that are attached to the drop arm 14 at threaded thickness screw receivers 31 and attached to the screed frame 18 at a threaded thickness screw attachment point 32. A threaded thickness screw handle 34 is turned by an operator of the work machine 2 in order to extend and retract the threaded end 35 of the threaded thickness screws 30 into the threaded thickness screw receivers 31. This extending and retracting of the threaded thickness screws 30 rotates the main screed 19, screed frame 18, and any extension screeds, such as the left hand and right hand extension screeds 20, 21 around the axis A of rotation.
To set up the screed assembly 1 for a paving process, the left hand and right hand extender plates 20, 21 are first raised about 6 millimeters, or between 3-9 millimeters, above the main screed plate 26. The primary screed is floated on the starting paving reference 3, thereby supporting the entire screed assembly 1 weight on the paving reference 3. When the screed assembly 1 weight is supported on the paving reference, the main screed and the left hand and right hand extension screeds 20, 21, are considered in a neutral position. A neutral position, in another exemplary embodiment, includes any pre-determined height of the main screed 19, or the left hand and right hand extension screeds 20, 21, above the paving reference or engaged with the paving reference.
After the primary screed 19, or the left hand and right hand extension screeds 20, 21, are in the neutral position, a nulling process occurs. In one exemplary process, the nulling process first includes pulling the tractor portion 4 forward slightly until any loose slack in all the screed pin joints, such as the drop arm pivot pin 28, has been removed. In the nulling process an operator of the work machine 2 actuates both the threaded thickness screw handles 34, in which the turning of the threaded thickness screw handles 34 actuates the right hand and left hand threaded thickness screws, such as threaded thickness screw 30, rotating the main screed 19, screed frame 18, and any extension screeds, such as the left hand and right hand extension screeds 20, 21 around the axis A of rotation as described above. This actuation is continued until there is no tension felt in each of the left hand and right hand threaded thickness screws, such as threaded thickness screw 30. When the left hand and right hand extension screeds 20, 21 have no tension, the screed is considered in a nulled position. As best shown in
After the primary screed 19, or the left hand and right hand extension screeds 20, 21, if included (hereinafter referred to as the screeds 19, 20, 21), are in the nulled position, the screed assembly is in a loose state. The loose state includes any slope/slack in all pin joints of the screed apparatus, including and any slope, slack, or looseness in the drop arm pivot pin 28, between the threaded thickness screws and their attachment points 32, the threaded thickness screw receivers 31 and the drop arms 14, or any of the hydraulic actuators or the lifting assembly of screed assembly 1. To remove this looseness, slope, slack, the operator of the work machine 2 further actuates the threaded thickness screw handles 34 in the same direction as during the nulling process, in which actuates the threaded thickness screws 30, until tension is felt in the threaded thickness screws 30. This actuation, in one exemplary embodiment, cause the screeds 19, 20, 21 to further rotate in the direction of rotation used in the nulling process, resulting in an increased nosed up angle of attack. This increase in nose up angle of attack is smaller than the increase of angle of attack of the nulling process, and may be 0.001-1 millimeters, 1-2 millimeters, 2-3 millimeters, depending on how much looseness, slope, or slack exist in the screed assembly 1. This increase in nose up angle of attack, after the screeds 19, 20, 21 are in the nulled position, applies a pre-tension to the screed assembly and places the screed assembly into a rigid state. The rigid state being after the pre-tension is applied to the screed assembly 1 that was previously in the nulled position.
The screed assembly 1 of the work machine 2 may also include additional components and systems, such as, for example, tamper devices, leveling arms, vibrators, heating elements and walkways (not shown), as are known to those skilled in the art.
Turning to
In one exemplary embodiment, prior to sending the null adjustment signal 70, the controller 68 determines the screeds 19, 20, 21 are in the neutral position from the grade control sensor 61, or any height measurement sensors (not shown). After the screed assembly 1 is attached to the work machine 2, the grade control sensor 61 measures the position, or the height, of the screeds 19, 20, 21, with respect to the paving reference 3, and sends a grade control measurement 69 to the controller 68, the controller 68 utilizing the measurement 69 to determine if the screeds 19, 20, 21 are in the neutral position. Further, in one exemplary embodiment, the work machine 2 may include the operator control 56 that receives the input 54 from the operator of the work machine 2. Once the input 54 is received, a screed assembly nulling signal 72 is sent to the controller 68 prior to the controller determining if the screeds 19, 20, 21 are in the neutral position. In a further exemplary embodiment, the controller is automated to determine if the screeds 19, 20, 21 are in the neutral position after the screed assembly 1 is attached to the work machine 2 without receiving the screed assembly nulling signal 72.
In one exemplary embodiment, the screed assembly 1 includes the tension measurement system 58, that is located on the screed assembly 1. The tension measurement system 58 takes a measurement, after the screed assembly 1 is in the nulled position, to determine a tension state of the screed assembly 1. The tension state can be the loose state or the rigid state, as described above. In one exemplary embodiment, embodiment, the tension measurement system 58 takes a tension measurement 73, the tension measurement 73 being a measurement of all the pin joints in the screed assembly 1, and sends the tension measurement 73 to the controller 68. After receiving the tension measurement 73, the controller 68 sends the rigid state adjustment signal 71 to the actuator device 40, wirelessly or through a physical connection, and the actuator device 40 places the screed assembly 1 into the rigid state.
As discussed above, the actuator device may be the linear actuator 42. In that embodiment, after the screeds 19, 20, 21 are in the nulled position, the controller 68 sends a pre-determined rigid state adjustment signal to the actuator device 40 prior to the actuator device 40 placing the screed assembly into the rigid state. The pre-determined rigid state adjustment signal 74 is a pre-determined amount of turns the electric motor 46 extends or retracts the rod 44, or turns the rod 44, to place the screed assembly 1 into the rigid state. The amount to extend or retract rod 44 is pre-determined by the size of the components that make up the screed assembly 1.
In a further embodiment, the electric motor 45 includes the torque measurement sensor 64. After the screeds 19, 20, 21 are in the neutral position, the torque measurement sensor 64 senses and measures the amount of torque in the electric motor 46, or the amount of torque the electric motor is placing on the rod 44. The torque measurement sensor 64 sends a torque measurement 76, or continuously measures and sends the measurements to the controller 68, and the controller 68 utilizes the torque measurement to determine that the screeds 19, 20, 21 are in the nulled position and stops the linear actuator 42 from further rotating the screeds 19, 20, 21 once the screeds 19, 20, 21 are in the nulled position, thus placing the screed assembly 1 into the nulled position. Further, after the screeds 19, 20, 21 are in the nulled position, the torque measurement sensor 64 takes a second measurement, or continuously measures, and sends a second torque measurement 77 to the controller 68. The controller 68 utilizes the second torque measurement 77 to determine the tension state of the screed assembly 1 prior to the controller sending the rigid state adjustment signal 71 to the actuator device 40 to place the screed assembly 1 in the rigid state.
Instead of, or in addition to, the torque measurement sensor 64, the electric motor includes a current draw sensor 66 to measure a current draw of the electric motor. After the screed assembly 1 is in the neutral position, the current draw sensor 66 takes, or continuously takes, the measurement and sends a current draw measurement 78 to the controller 68, and the controller 68 utilizing the current draw measurement 78 to determine the screeds 19, 20, 21 are in the nulled position based on the measured current draw. Further, after the screed assembly 1 is in the nulled positioned, the current draw sensor 66 may take, or continuously take further measurements, of the current draw of the electric motor 46, and send a second current draw measurement 79 to the controller 68. The controller utilizing the second current draw measurement 79 to determine the tension state of the screed assembly 1, and the controller sending the rigid state adjustment signal 71 to the actuator device 40.
Also discussed above, the actuator device may be the hydraulic actuator 50. The hydraulic actuator 50, in one exemplary embodiment, includes the hydraulic pressure sensor 60. In the neutral position, the hydraulic pressure sensor takes a measurement of, or continuously measures, the hydraulic pressure in the hydraulic actuator 50, and sends a hydraulic pressure measurement 80 to the controller 68. The controller 68 utilizes the hydraulic pressure measurement 80 to determine that the screed assembly 1 is in the nulled position, and stops the actuator device from rotating screeds 19, 20, 21 once the nulled position is achieved. Once in the nulled position, the hydraulic pressure sensor may further take a measurement of, or continuously measure, the hydraulic pressure in the hydraulic actuator 50 and send a second hydraulic pressure measurement 81 to the controller 68. The controller utilizing the second hydraulic pressure to determine a tension state of the screed assembly 1 and send the rigid state adjustment signal 71 to the actuator device 40 place the screed assembly 1 in the rigid state.
Instead of, or in addition to, the hydraulic pressure sensor 60, the hydraulic actuator 50 includes the position sensor 62. In the nulled position, the position sensor 62 takes a measurement of, or continuously measures, the position of the hydraulic actuator 50, such as a measurement of a hydraulic rod to its cylinder, for example, and sends a position measurement 83 to the controller 68. The controller 68 utilizes the position measurement 83 to determine the tension state of the screed assembly 1, and sends the rigid state adjustment signal 71 to the actuator device 40 to place the screed assembly in the rigid state.
In general, the teachings of the present disclosure may find applicability in many industries including, but not limited to, asphalt paving machines. More specifically, the teachings of the present disclosure may find applicability in any industry using screed assemblies in a paving operation, such as, but not limit to, paving, construction, excavating, and the like.
In accordance with the scope of the present disclosure, in one such operation it is desirable to automate the nulling of a screed assembly and application of pre-tension to place the screed assembly in a rigid state. The present disclosure provides a method for automatedly nulling a screed.
Turning now to
While the preceding text sets forth a detailed description of numerous different embodiments, it should be understood that the legal scope of protection is defined by the words of the claims set forth at the end of this patent. The detailed description is to be construed as exemplary only and does not describe every possible embodiment since describing every possible embodiment would be impractical, if not impossible. Numerous alternative embodiments could be implemented, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims defining the scope of protection.
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