Abstract:
A control system for use with an asphalt paving machine receives inputs from an operator interface for inputting a desired tamping frequency or a desired tamping rate (tamps/ft) and a speed sensor that produces a signal indicative of the speed of the asphalt paver. The control system includes an automatic mode and when in automatic mode the system modifies the tamping frequency to better achieve a desired number of tamps per foot traveled irrespective of speed.

Description:
TECHNICAL FIELD  
         [0001]    The present invention generally relates to asphalt paving machines, and more particularly to a control for a tamping mechanism on an asphalt paving machine.  
         BACKGROUND  
         [0002]    Asphalt paving machines are used to spread asphalt relatively evenly over a desired surface. These machines are regularly used in the construction of roads, parking lots and other areas where a smooth durable surface is required for cars, trucks and other vehicles to travel. An asphalt paving machine generally includes a hopper for receiving asphalt material from a truck and a conveyor system for transferring the asphalt from the hopper for discharge on the roadbed. Screw augers spread the asphalt transversely across the road bed in front of a floating screed, which is connected to the paving machine by pivoting tow arms or draft arms. The screed smoothes and somewhat compacts the asphalt material and ideally leaves a roadbed of uniform depth and smoothness. The screed is sometimes equipped with an eccentric bar that rotates and thereby causes the screed to vibrate, which assists with the compaction. Although the screed compacts the asphalt material to some degree, it is often desirable to exert greater compaction force on the asphalt. To do so, some screeds include a tamping mechanism which often includes a tamping bar, located in front of the screed, relative to the direction of travel of the paving machine, and transversely to the direction of travel. The tamping bar moves up and down, striking the asphalt on each downward stroke thereby imparting increased compaction force on the asphalt. The speed with which the tamping bar moves upward and downward is generally controlled by an operator input device such as a control knob.  
           [0003]    It is desirable to have the asphalt on the roadbed compacted uniformly so that the density of the roadbed is consistent from one place to another. Prior art tamping systems control only the frequency of the up and down motion of the tamping bar thereby causing the screed to tamp at a fixed rate. If the asphalt paving machine is moving at a constant speed the tamping bar will strike the asphalt the same number of times per unit distance traveled. Because the tamping bar strikes the asphalt the same number of times for every foot traveled, it is more likely to produce a uniformly dense roadbed. However, if the operator changes the speed of the asphalt paving machine the number of times the tamping bar strikes the asphalt per foot traveled will change, thereby increasing the likelihood that the density of the roadbed will be inconsistent.  
           [0004]    It would be preferable to have an automatic tamping control that would deliver a uniform number compaction strokes for each unit distance traveled, irrespective of the speed of the asphalt paving machine.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention includes a control system for use with a tamping mechanism on an asphalt paver. The control system preferably includes an electronic control module that is connected with an operator input device for inputting a desired tamping frequency. The electronic control module is also connected to a speed sensor that produces a signal indicative of the speed of the asphalt paver. The electronic control module controls the speed of the tamping mechanism as a function of the operator input and the asphalt paver speed.  
           [0006]    These and other advantages of the present invention will be apparent upon reading the detailed description in connection with the drawings and appended claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The drawings are provided to assist in the understanding of the present invention and represent a preferred embodiment of practicing the invention. Other embodiments could be created that will fall within the scope of the present invention as defined by the appended claims.  
         [0008]    [0008]FIG. 1 is a side view of an asphalt paving machine;  
         [0009]    [0009]FIG. 2 is a side view of a screed including a tamping mechanism associated with the asphalt paving machine of FIG. 1;  
         [0010]    [0010]FIG. 3 is a block diagram of a control system of preferred embodiment of the present invention; and  
         [0011]    [0011]FIG. 4 is a flowchart of preferred software control of the control system of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0012]    A preferred embodiment of the best mode of practicing the present invention is described herein. Referring first to FIG. 1, a typical form of track-laying, floating screed asphalt paver  30  is shown. In accordance with well known practice, the paver is provided with push rollers  31  at the front, for engaging and pushing forwardly on the wheels of a truck loaded with asphalt paving material. The paving material is arranged to be discharged progressively from the truck into a hopper  32  at the front of the paver. Conveyor means (not shown) controllably transport the paving material to the rear of the paver and deposit it in a mass  33  on the prepared paving bed  34 . Screw augers  35  distribute the paving material laterally in front of a screed, generally designated by the numeral  36 . The screed is towed behind the paver and connected thereto by a pair of elongated, forwardly extending tow bars  37  connected at their front ends to the chassis of the paver. In accordance with known practice, by controlling the elevation of the tow points  38  and the angle of attack of the bottom surface of the screed  36 , a level, uniform paving mat  39  is laid behind the paver as it advances forwardly.  
         [0013]    Referring now to FIG. 2, a screed  36  of the type used in connection with the asphalt paver  30  is shown. The screed  36  comprises a baseplate  100  which is configured to float on paving material  33  laid upon a prepared paving bed  34  and to “smooth” or level and compact the paving material on the base surface, such as for example a roadway or roadbed. The base plate  100  is connected, preferably by means of a carrier  105 , to a vibrating shaft  110  coupled to a vibratory drive (not depicted). As is known to those skilled in the art, the vibratory shaft  110  generally includes weights placed eccentrically so that when the vibratory drive rotates the vibrating shaft  110 , the shaft  110  causes the screed  36  to vibrate. The vibrating screed  36  to some degree improves compaction and quality of the asphalt mat being laid on the prepared paving bed  34 .  
         [0014]    The screed also includes a tamping mechanism  111  which includes a tamping bar  115  arranged in front of the baseplate  100  and extending generally transversely to the paving direction over substantially the entire width of the baseplate  100 . The tamping bar  115  is configured to be driven so as to move alternately in upward and downward directions (i.e., generally toward and away from the base surface). Preferably, the tamping bar  115  is driven by an eccentric drive  120  and is configured to be adjustably displaceable by the amount of an adjustable stroke of the eccentric drive  120 . A speed sensor  290  is preferably located adjacent the eccentric drive and produces a speed signal on an electrical connector  300  that is an input to an electronic control module  210 , described in more detail below with reference to FIGS. 3 and 4. Further, the tamping bar  115  has a lead-in slope  125  located at the front edge of the bar  115 . The angle of the lead-in slope  125  is preferably between 30 degrees and 70 degrees, so as to ensure an optimum feed of the paving material.  
         [0015]    The screed  36  has preferably includes a front wall  130  disposed proximal to the screw auger  35  (shown in FIG. 1), the screw auger  35  functioning to spread paving material falling off the end of a conveyor mounted on the paver  30  The front wall  130  includes a lower guide portion  135  which is preferably inclined relative to the tamping bar  115  and which terminates adjacent to the bar  115 , such that the guide portion  135  directs paving material from the auger  35  to the tamping bar  115 . The angle of inclination of the guide portion  135  preferably corresponds approximately to the angle of the lead-in slope  125  of the tamper bar  115 .  
         [0016]    Referring now to FIG. 3, a block diagram of a preferred embodiment of an electronic control system  200  for use with the tamping mechanism  111  is shown. The electronic control system preferably includes an electronic control module (“ECM”)  210  connected with the various system components shown. A tamper bar mode selector  230  is connected with the ECM  210 . In the drawing, the tamper bar mode selector is shown as a three position toggle switch  240 . Those skilled in the art will recognize that other devices, including rotary switches, depressible button switches and the like could readily and easily be substituted for the three position switch. As described in more detail below with reference to FIG. 4, the mode selector  230  preferably includes three positions corresponding to an off mode, a manual mode and an automatic mode. The operator of the asphalt paving machine preferably places the mode selector  230  in a position corresponding to the desired mode. The mode selector then produces a mode signal on electrical connectors  250  indicative of the selected mode.  
         [0017]    A tamper bar desired speed input  260  is connected with the ECM  210  by connector  270 . Although this input is described herein as a desired speed input, it also controls the desired number of tamps per unit distance when the system is in the automatic mode. As shown in the drawing, the tamper bar desired speed selector is shown as a rotary dial  280 . Preferably there are markings on the dial indicating to the operator a general desired tamping bar rotational velocity (when in manual mode) or a desired number of tamps per foot (when in automatic mode). The operator of the asphalt paving machine moves the dial to a position corresponding to the desired rotational speed of the tamping bar or number of tamps per foot and the rotary dial  280  produces a signal on connector  270  indicative of the desired tamping bar speed or tamps per foot.  
         [0018]    A tamping bar speed sensor  290  is associated with the eccentric drive  120  of the tamping mechanism  111  and produces a tamping bar speed signal on connector  300  indicative of the rotational velocity of the eccentric drive  120 . Preferably, the tamping bar speed sensor is a passive sensor, such as a magneto restrictive type sensor. However, other types of speed sensors can be used without deviating from the scope of the present invention.  
         [0019]    The ECM  210  produces a tamper bar control signal  310  to control the rotational speed of the shaft eccentric drive  120 . As shown in the drawing, the tamper bar control signal  310  is received by a solenoid  320  connected with a hydraulic pump  330  associated with the hydraulic motor  125 . The tamper bar control signal  310  controls the flow of hydraulic fluid through conduits  340 , 350  and thereby controls the rotational speed of the hydraulic motor  125  and eccentric drive  120  of the tamper bar. Although the preferred embodiment shows the use of a hydraulic pump  330  and motor  125  to control the rotational speed of the eccentric drive  120 , other power sources could readily and easily be substituted for the hydraulic motor without deviating from the scope of the present invention. For example, in some applications it might be preferable to replace the hydraulic motor with an electric motor and controllably power the motor with electric power through associated power circuitry.  
         [0020]    Also connected with the ECM  210  is a asphalt paving machine speed sensor  360  that produces a signal on connector  370  indicative of the speed that the asphalt paving machine is travelling. The speed sensor is preferably associated with a driveline on the asphalt paving machine, which connects the engine to the tracks, or other ground engaging device. The speed sensor produces a signal indicative of the speed of the track, or other ground engaging device, which can be readily converted by the ECM  210  to ground speed. Any of a variety of well known speed sensors could be used in connection with the present invention.  
         [0021]    Referring now to FIG. 4, a block diagram of a preferred embodiment of the software control associated with the ECM  210  of the present invention is shown. Software control begins in block  400  and passes to block  410 .  
         [0022]    In block  410  the ECM  210  reads the signal on connectors  250  and determines whether the operator has placed the tamper bar mode selector  230  in the position corresponding to off mode. If the mode selected is the off mode then software control returns to block  400 . Otherwise, program control continues to block  420 .  
         [0023]    In block  420 , software control determines whether the operator has placed the tamper bar mode selector  230  in the position corresponding to manual mode. If the mode selected is the manual mode then software control passes to block  430 . Otherwise, software control passes to block  440 .  
         [0024]    In block  430 , the ECM  210  reads the desired tamping speed signal on connector  270  produced by the tamping bar desired speed input  260 . Program control then passes to block  470 . In block  470 , the ECM produces a tamper bar control signal as a function of the desired connector  270 . In a preferred embodiment of the invention the speed of the tamper bar shaft  122  is controlled open loop. However, as will be apparent to those skilled in the art, the ECM  210  could readily and easily use the electrical connector  300  as feedback to implement a closed loop tamper bar speed control. From block  470  program control returns to block  400 .  
         [0025]    Returning to block  420 , as described above if the position of the mode selector  230  does not correspond to the manual position, then software control passes to block  440  and the control system is in automatic mode.  
         [0026]    Software control passes from block  440  to block  450 .  
         [0027]    In block  450 , the ECM  210  reads the signal on connector  270 , which in the automatic mode corresponds to a desired number of tamps per foot (or other unit distance) that the asphalt paving machine travels. Program control then passes to block  460  where the ECM determines a corresponding desired tamping speed. To do this, the ECM preferably reads the asphalt paving machine speed signal on connector  370  and calculates the desired tamping bar speed. In a preferred embodiment, the control system of the present invention uses two asphalt paving speed sensors  360  and averages the signals of those two sensors. Program control then passes to  470 .  
         [0028]    As described above, in block  470 , the ECM produces a tamper bar control signal as a function of the desired connector  270 . In a preferred embodiment of the invention the speed of the tamper bar shaft  122  is controlled open loop. However, as will be apparent to those skilled in the art, the control could readily and easily use the electrical connector  300  as feedback to implement a closed loop tamper bar speed control. From block  470  program control returns to block  400 .  
       INDUSTRIAL APPLICABILITY  
       [0029]    The control described in the present application permits the operator of the asphalt paving machine to select between three modes of tamping: an off mode; a manual mode; and an automatic mode. In the off mode, the screed will not tamp the asphalt material. In the manual mode the operator can select a desired tamping speed which produces a desired tamping rate (i.e., a desired number of tamps per unit time). In the automatic mode the operator can select a desired number of tamps per unit distance. In the automatic mode the control will automatically adjust the tamping speed as a function of the speed that the asphalt paving machine is moving. This will allow the operator to better achieve consistent compaction from the tamper bar with minimum operator action.