Abstract:
In an aspect of the invention a ripping mechanism for a vehicle is provided which includes a support frame, a ripping member, a vibrator mechanism, a pressure sensor, and a control system. The control system is configured to determine when the ripping member is engaged with hard material using the pressure sensor. When the ripping member is engaged with hard material, the control system is configured to permit operation of the vibrator mechanism. In some embodiments, the control system may further be configured to automatically start the vibrator mechanism when it detects that the ripping member is engaged with hard material. When the ripping member is not engaged with hard material, the control system is configured to deactivate the vibrator mechanism. In some embodiments, deactivation of the vibrator mechanism means that the control system turns off the vibrator mechanism. In some other embodiments, deactivation of the vibrator mechanism means that the control system prevents operation of the vibrator mechanism. In yet other embodiments deactivation of the vibrator mechanism may entail both turning off the vibrator mechanism and preventing operation of the vibrator mechanism. In yet other embodiments, the control system may include a switch that permits a vehicle operator to select which of these aforementioned actions the control system takes when determining that the ripping member is not engaged with hard material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/275,972, filed Oct. 18, 2011, entitled “Vibratory Ripper Having Pressure Sensor For Selectively Controlling Activation Of Vibration Mechanism”, which is a continuation-in-part of U.S. patent application Ser. No. 12/906,850, filed Oct. 18, 2010, entitled “Vibratory Ripper”, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to plowing, trenching and ripping machines and more particularly to rippers that are used for ripping hard materials, such as rock, concrete and the like. 
       BACKGROUND OF THE INVENTION 
       [0003]    Plowing, trenching and ripping machines are well known for digging trenches or various depths and through various types of material. In certain situations, such as when trying to form a trench through rock, concrete or the like, such machines can encounter some difficulty. It has been proposed in the past to use vibration to assist with such machinery. However, while the use of a vibrator mechanism may assist with this operation, it can cause additional stress on the machine itself. It is desirable to find ways of reducing the stresses incurred by the machines as a result of the use of vibrator mechanisms. 
       SUMMARY OF THE INVENTION 
       [0004]    Generally speaking, the invention is directed to a ripping mechanism for a vehicle. The ripping mechanism includes a support frame, a ripping member and an impact mechanism which is configured to reciprocate the ripping member forwardly and rearwardly. The impact mechanism is preferably a vibrator mechanism. 
         [0005]    According to one aspect of the invention, the ripping mechanism has a longitudinal axis, is mountable to the vehicle and is movable between a raised position and a lowered position. The ripping member has an engagement head that is configured for plowing a groove in the ground and that is pivotally supported on the support frame about a ripping member pivot axis that is positioned such that pivoting of the ripping member displaces the engagement head longitudinally. The impact mechanism is preferably a vibrator mechanism. The vibrator mechanism is connected to the ripping member wherein activation of the vibrator mechanism causes reciprocating pivoting movement of the ripping member. 
         [0006]    According to another aspect of the invention a ripping mechanism for a vehicle is provided which includes a support frame, a ripping member, a tilt adjustment cylinder, a vibrator mechanism, a pressure sensor, and a control system. The support frame has a longitudinal axis and including a main frame portion that is mountable to a vehicle and a ripping member frame portion that is pivotably connected relative to the main frame portion. The ripping member is pivotally mounted to the ripping member frame portion about a laterally oriented ripping member pivot axis. The ripping member has an engagement head that is configured for plowing a groove in the ground. The tilt adjustment cylinder is connected between the main frame portion and the ripping member frame portion and is adjustable in length for orienting the ripping member frame portion in a selected orientation to control the angle of attack of the engagement head. The vibrator mechanism is operatively connected to the ripping member. Activation of the vibrator mechanism causes reciprocating movement of the engagement head at least partially longitudinally when the ripping member frame portion is in the selected orientation. The control system includes a pressure sensor fluidically connected to the tilt adjustment cylinder for determining hydraulic pressure supporting the ripping member frame portion. The control system is configured to deactivate the vibrator mechanism based at least in part on the pressure sensed by the pressure sensor. 
         [0007]    According to another aspect of the invention a ripping mechanism for a vehicle is provided which includes a support frame, a ripping member, a tilt adjustment cylinder, a vibrator mechanism, a pressure sensor, and a control system. The ripping member has an engagement head that is configured for plowing a groove in the ground. The ripping member is positionable in a selected working position and working orientation by adjustment of the support frame. The ripping member is movable relative to the support frame to cause reciprocating movement of the engagement head at least partially longitudinally. The tilt adjustment cylinder is operable to orient the ripping member in the selected orientation. The vibrator mechanism is operatively connected to the ripping member and is activatable to cause reciprocating movement of the engagement head at least partially longitudinally. The control system includes a pressure sensor fluidically connected to the tilt adjustment cylinder for determining hydraulic pressure supporting the ripping member frame portion. The control system is configured to deactivate the vibrator mechanism based at least in part on the pressure sensed by the pressure sensor. 
         [0008]    According to another aspect of the invention a ripping mechanism for a vehicle is provided which includes a support frame, a ripping member, a vibrator mechanism, and a control system. The control system is configured to determine when the ripping member is engaged with hard material using the pressure sensor. When the ripping member is engaged with hard material, the control system is configured to permit operation of the vibrator mechanism. In some embodiments, the control system may further be configured to automatically start the vibrator mechanism when it detects that the ripping member is engaged with hard material. When the ripping member is not engaged with hard material, the control system is configured to deactivate the vibrator mechanism. In some embodiments, deactivation of the vibrator mechanism means that the control system turns off the vibrator mechanism. In some other embodiments, deactivation of the vibrator mechanism means that the control system prevents operation of the vibrator mechanism. In yet other embodiments deactivation of the vibrator mechanism may entail both turning off the vibrator mechanism and preventing operation of the vibrator mechanism. In yet other embodiments, the control system may include a switch that permits a vehicle operator to select which of these aforementioned actions the control system takes when determining that the ripping member is not engaged with hard material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present invention will now be described by way of example only with reference to the attached drawings, in which: 
           [0010]      FIG. 1  is a perspective view of a vehicle with a ripping mechanism in accordance with an embodiment of the invention; 
           [0011]      FIG. 2   a  is a perspective view of the ripping mechanism shown in  FIG. 1 ; 
           [0012]      FIG. 2   b  is a side view the ripping mechanism shown in  FIG. 1 ; and 
           [0013]      FIG. 2   c  is a top view of the ripping mechanism shown in  FIG. 1 . 
           [0014]      FIG. 3   a  is a side view of a ripping mechanism according to a second embodiment of the present invention; 
           [0015]      FIG. 3   b  is top view of the ripping mechanism shown in  FIG. 3   a;    
           [0016]      FIG. 4  is a simplified schematic diagram showing a portion of a hydraulic system and a control system utilized by the ripping mechanism shown in  FIG. 3   a;    
           [0017]      FIG. 5  is a magnified elevation view of a vibrator mechanism that is part of the ripping mechanism shown in  FIG. 1 ; and 
           [0018]      FIG. 6  is a simplified schematic diagram showing the portion of the hydraulic system and the control system shown in  FIG. 4 , and further including accumulators as part of the hydraulic system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Reference is made to  FIG. 1 , which shows for a vehicle  10  with a ripping mechanism  12  in accordance with an embodiment of the present invention. The vehicle  10  may be any type of vehicle, such as, for example, a bulldozer, an excavator, a tractor, a trencher, a pipelayer, a brush tractor or a utility plow. 
         [0020]    The ripping mechanism  12  includes a support frame  14 , a ripping member  16  and a vibrator mechanism  18 . In the exemplary embodiment shown in  FIGS. 2   a  and  2   b , the support frame  14  has a longitudinal axis shown at  19 . 
         [0021]    The support frame  14  is mountable to the vehicle  10  and is movable between a raised position ( FIG. 2   b ) and a lowered position.  FIG. 1  shows the support frame  14  in a partially lowered position. 
         [0022]    The support frame  14  includes a main frame portion  20  and a ripping member frame portion  22  that is movably supported on the main frame portion  20 . The main frame portion  20  has a pivot connector  24  at its front end (shown at  26 ) for pivotally connecting to the vehicle  10  about a main frame portion pivot axis  28 . At least one height adjustment cylinder  30  is provided and is pivotally connectable to the vehicle at a first end  32  and is pivotally connectable at a second end  34  to the main frame portion  20 . In this exemplary embodiment, there are two adjustment cylinders  30  (as shown in  FIG. 2   a ). The adjustment cylinders  30  are preferably hydraulic cylinders and may be connected to a source of pressurized hydraulic fluid from the vehicle  10 . The height adjustment cylinders  30  are positioned such that changing the amount of extension of the height adjustment cylinders  30  pivots the main frame portion  20  about the main frame portion pivot axis  28  thereby changing the angle of the main frame portion  20  relative to the vehicle  10 . Because of the position of the ripping member frame portion  22  relative to the main frame portion pivot axis  28 , (ie. because the ripping member frame portion  22  is horizontally offset from the pivot axis  28 ), extending or retracting the cylinders  30  causes a change in height of the ripping member frame portion  22  relative to the vehicle  10 . 
         [0023]    In the exemplary embodiment shown, the ripping member frame portion  22  is pivotally connected to the main frame portion  20  about a ripping member frame pivot axis  35 . At least one tilt adjustment cylinder  36  is provided and is pivotally connectable at a first end  38  to the vehicle  10  and is pivotally connectable at a second end  40  to the ripping member frame portion  22 . In this exemplary embodiment, there are two adjustment cylinders  36  (as shown in  FIG. 2   c ). The adjustment cylinders  36  are preferably hydraulic cylinders and may be connected to a source of pressurized hydraulic fluid from the vehicle  10 . The tilt adjustment cylinders  36  are positioned such that changing the amount of extension of the tilt adjustment cylinders  36  pivots the ripping member frame portion  22  about the ripping member frame pivot axis  35 . 
         [0024]    In the embodiment shown, extending and retracting the height adjustment cylinders  30  causes the ripping member frame portion  22  to pivot relative to the main frame portion  20  unless the tilt adjustment cylinders  36  are simultaneously extended or retracted along with the cylinders  30 . It is alternatively possible however, for the tilt adjustment cylinders  36  to connect at their first ends  38  to the main frame portion  20  and not to the vehicle  10 , in which case, extending and retracting the height adjustment cylinders  30  would not cause the ripping member frame portion  22  to pivot relative to the main frame portion  20 . 
         [0025]    The ripping member  16  has a ripping member body  44 , a trench wall forming member  46  and an engagement head  48 , both of which are removably mountable to the ripping member body  44  via threaded fasteners so that they can be removed and replaced when worn. The engagement head  48  is configured for plowing a groove in the ground and has a selected shape, particularly at its leading edge, to facilitate breaking up rock, concrete and other hard materials via repeated impact. The engagement head is preferably replaceable to facilitate repair in the event of wear. The ripping member body  44  (and therefore, the ripping member  16 ) is pivotally supported on the ripping member frame portion  22  about a ripping member pivot axis  50 , which extends laterally so that pivoting of the ripping member  24  changes the angle of attack of the engagement head  48 . 
         [0026]    At least one aft limit member  52  and at least one forward limit member  54  are provided on the ripping member frame portion  22 , and are positioned to limit the forward and aftward movement of the ripping member  16  about the ripping member pivot axis  50 . The aft and forward limit members  52  and  54  are preferably made from a resilient material such as neoprene. 
         [0027]    The vibrator mechanism  18  is connected to the ripping member  16  and in the embodiment shown is mounted solely and directly to the ripping member body  44 . Activation of the vibrator mechanism  18  causes reciprocating pivoting movement of the ripping member  16  about the ripping member pivot axis  50  between the forward and aft limit members  54  and  52 . It can be seen from the figures that the pivot axis  50  is vertically closer to the bottom of the ripping member  16 , where the engagement head  48  is located, than the top of the ripping member  16 , where the vibrator mechanism  18  is located. This provides leverage to amplify the torque provided by the vibrator  18  about the pivot axis  50 , which advantageously increases the force applied in the longitudinal direction by the engagement head  48 . 
         [0028]    The vibrator mechanism  18  may have any suitable structure. In a preferred embodiment shown in  FIG. 5 , the vibrator mechanism  18  includes a motor  90  that has an output shaft  91  oriented along a laterally directed axis, which drives one or more eccentrically weighted rotating members  92 . In the embodiment shown in  FIG. 5 , two rotating members  92  are driven by the motor  90 . The two rotating members  92  are geared together and arranged so that they counter-rotate, and so that their eccentrically weighted portions shown at  93   a  and  93   b,  are on the front side (shown at  94   a ) at the same time and on the rear side (shown at  94   b ) at the same time so that their effect is additive. However, when the first weighted portion  93   a  is at the top of its rotation, the second weighted portion  93   b  is at the bottom of its rotation and vice versa, so that their effects are canceled by one another. As a result of this arrangement, the eccentrically mounted weights  92  generate essentially no vertical vibration force and essentially no laterally directed vibration force, but significant longitudinally directed force, so as to generate longitudinal vibration on the ripping member  16 . The motor  90  may be a hydraulic motor and may thus be connected to a hydraulic power source from the vehicle  10 . Alternatively the motor  90  could be an electric motor, or any other suitable kind of motor. 
         [0029]    It will be noted that, while the angle of attack of the engagement head  52  is adjustable, the movement of the engagement head  52  is substantially longitudinal due to its position being substantially directly vertically offset from the ripping member pivot axis  50  when the ripper mechanism  12  is in a lowered position suitable for ripping. While this is advantageous, it is not necessary, and it is possible for the engagement head  52  to move in a direction that is largely longitudinal but that has a significant vertical component. 
         [0030]      FIGS. 3   a  and  3   b  show another embodiment of a ripping mechanism  112 , which includes a support frame  114 , a ripping member  116  and a vibrator mechanism  118 . In the exemplary embodiment shown in  FIGS. 2   a  and  2   b , the support frame  14  has a longitudinal axis shown at  19 . 
         [0031]    The support frame  114  is mountable to the vehicle (not shown) and is movable between a raised position and a lowered position shown in  FIG. 3   a . The support frame  114  has a longitudinal axis  119 . The support frame  114  includes a main frame portion  120  and a ripping member frame portion  122  that is movably supported on the main frame portion  120 . 
         [0032]    The main frame portion  120  includes a mounting plate  124 , a longitudinally oriented lower carriage portion  126 , and longitudinally oriented upper arm portions  128 . 
         [0033]    The mounting plate  124  includes mounting features  130 ,  132  for mounting the support frame  114  to the vehicle as a modular unit, including all adjustment cylinders as will be discussed in greater detail below. These mounting features will vary depending on the vehicle to which the support frame  114  is mounted. 
         [0034]    The longitudinally oriented lower carriage portion  126  is pivotally connected at one end thereof via pivot joint  134  to the mounting plate  124 . The longitudinally oriented lower carriage portion  126  is pivotally connected at the opposite end thereof via pivot joint  136  to the ripping member frame portion  122 . The lower carriage portion  126  can be formed as a box, or more preferably utilizing two substantially parallel longitudinally extending rails. 
         [0035]    At least one and preferably two height adjustment cylinders  140  as seen best in  FIG. 3   b  are connected between the mounting plate  124  and the longitudinally oriented lower carriage portion  126 . In the illustrated embodiment the height adjustment cylinder housings shown at  143  are pivotally connected to ears  142  on the mounting plate  124  and the pistons or extensible portions shown at  144  of the height adjustment cylinders  140  are pivotally connected to an isolation mount  146  pivotally mounted to the lower carriage portion  126 . 
         [0036]    Each longitudinally oriented upper arm portion  128  is pivotally connected at one end thereof via pivot joint  137  to the mounting plate  124 . The opposite end of each upper arm portion  128  is connected to a tilt adjustment cylinder  152 , with the piston or extensible portion  154  thereof being pivotally connected to the ripping member frame portion  122  via pivot joint  156 . 
         [0037]    The ripping member  116  has a ripping member body  160 , a trench wall forming member  162  and an engagement head  164 , both of which are removably mountable to the ripping member body  160  via threaded fasteners so that they can be removed and replaced when worn. The engagement head  164  has a selected shape particularly at its leading edge to facilitate breaking up rock, concrete and other hard materials via repeated impact. The ripping member body  160  (and therefore, the ripping member  116 ) is pivotally supported on the ripping member frame portion  122  about a laterally extending ripping member reciprocating axis  166  analogous to the ripping member pivot axis  50  described in connection with other embodiments. 
         [0038]    At least one aft limit member  172  and at least one forward limit member  174  are provided on the ripping member frame portion  122 , and are positioned to limit the forward and aftward movement of the ripping member  116  about the ripping member reciprocating axis  166 . The aft and forward limit members  172  and  174  are preferably made from a resilient material such as neoprene. 
         [0039]    The vibrator mechanism  118  is connected to the ripping member  116  and in the embodiment shown is mounted solely and directly to the ripping member body  160 . Activation of the vibrator mechanism  118  causes reciprocating pivoting movement of the ripping member  116  about the ripping member reciprocating axis  166  between the forward and aft limit members  174  and  172 . 
         [0040]    The vibrator mechanism  118  may be similar to the vibrator mechanism  18 . 
         [0041]    It will thus be seen from the foregoing that the support frame  114  is designed as two parallel four-bar linkages. Extension and retraction of the height adjustment cylinders  140  will cause the lower carriage portion  126  to pivot about a lateral axis disposed at pivot joint  134 , which in turn cause the upper arm portions  128  to pivot about a lateral axis defined by pivot joint  150 . As the ripping member frame portion  122  is connected to the lower carriage portion  126  and upper arm portions  128 , actuation of the height adjustment cylinders  140  will raise and lower a working position of the ripping member frame portion  122  relative to the ground. In addition, extension and retraction of the tilt adjustment cylinders  152  will cause the ripping member frame portion  122  to pivot about a lateral axis defined by the lower pivot joint  136 . As the ripping member frame portion  122  pivots, it will cause a change a change in working orientation and in the angle of the ripping member body  160  relative to the ground, consequently changing the angle of attack of the engagement head  168 . 
         [0042]    It will be noted that, while the angle of attack of the engagement head  164  is adjustable, for at least some angles of attack its position is substantially directly vertically offset from the ripping member reciprocating axis  166  when the ripper mechanism  112  is in a lowered position suitable for ripping. As a result, the movement of the engagement head  164  is substantially longitudinal in such situations. Furthermore, because the vibratory forces generated by the vibrator mechanism  118  is largely longitudinally directed, relatively little vertical vibratory force and vibratory motion may be imparted to the ripping member  116  and to the engagement head  164  more particularly. While this is advantageous, it is not necessary, and it is possible for the engagement head  164  to move in a direction that is largely longitudinal but that has a significant vertical component. 
         [0043]    The hydraulic flow diagram for the lift and tilt adjustment cylinders  140  and  152  is shown in  FIG. 4 . As can be seen the height adjustment cylinders  140  both connect to a height adjustment cylinder control valve  200  via a first height adjustment cylinder hydraulic line  202  and a second height adjustment cylinder hydraulic line  204 . When the control valve  200  is in the position shown in  FIG. 4 , the height adjustment cylinders  140  are maintained in a particular selected position. When the control valve  140  is moved one way or the other from the position shown in  FIG. 4 , the height adjustment cylinders  140  either extend or retract to raise or lower the ripping member  116 . As can also be seen, the tilt adjustment cylinders  152  both connect to a tilt adjustment cylinder control valve  206  via a first a first tilt adjustment cylinder hydraulic line  208  and a second tilt adjustment cylinder hydraulic line  210 . When the control valve  206  is in the position shown in  FIG. 4 , the tilt adjustment cylinders  152  are maintained in a particular selected position. When the control valve  206  is moved one way or the other from the position shown in  FIG. 4 , the tilt adjustment cylinders  152  either extend or retract to change the orientation of the ripping member  116  in one rotational direction or the other. 
         [0044]    During operation of the ripping mechanism, the vibrator mechanism  18  or  118  transmits a great deal of vibrational energy to the ripping member  16  or  116 . When the ripping member  16  is in the ground with the engagement head  48  or  164  engaged with relatively hard material, the vibrational energy is at least partially absorbed by the ground, which reduces any deleterious effect it has on the components of the ripping mechanism  12  or  112  and of the vehicle  10  itself. However, if the engagement head is lifted out of its trench the vibrational energy generated by the vibrator mechanism  18  or  118  can induce a great deal of stress on the ripping mechanism  12  or  112  and the vehicle  10 , which could cause increased wear and potentially premature failure of one or more components thereof. The same problem can occur if the engagement head  48  or  164  remains in the trench but encounters soft soil, or becomes spaced from the front end of the trench, which can occur, for example, if the vehicle  10  backs up or if the adjustment cylinders  30 ,  36 ,  130  or  136  are adjusted to adjust the height or orientation of the ripping member  16  or  116 . 
         [0045]    In order to prevent inadvertent stressing of the ripping mechanism  12  or  112  and the vehicle  10 , a pressure sensor  180  shown in  FIG. 4  is connected to the first tilt adjustment cylinder hydraulic line  208  and thus reads the pressure in the line  208  that is used to support the ripping member  116  in any particular selected orientation. When the vibrator mechanism  118  is on, the pressure in the hydraulic line  208  varies over a range of pressures as the engagement head reciprocates back and forth. This range of pressures depends on several factors such as how aggressively the vehicle  10  is being driven forward to urge the engagement head  48 ,  164  into engagement with the front end of the trench, and the hardness of the material at the front end of the trench. When the engagement head is engaged with hard material, the hard material exerts a relatively strong resistance to the impacts from the engagement head  48 ,  164  and thus exerts a strong reactionary force on the engagement head  48 ,  164 . This in turn urges the ripping member frame portion  22  to urge the tilt adjustment cylinder pistons shown at  214  to retract (in the embodiment shown in  FIG. 3   a ). This increases the pressure in line  208 , and decreases the pressure in line  210 , as compared to a scenario where the engagement head  48 ,  164  was not engaged with any material, or was engaged with relatively soft material (e.g. loose earth) that offered little resistance to its impacts. Thus the peak pressure read by the pressure sensor  180  during engagement with hard material would be higher than the peak pressure read by the pressure sensor  180  during engagement with soft material or no material. 
         [0046]    As a result of this difference in peak pressures in the two situations (i.e. engaged with hard material or engaged with soft material/no material), a controller shown at  182 , which receives signals from the pressure sensor  180 , can determine whether the engagement head  48 ,  164  is engaged with hard material or not. In the embodiment shown, where the pressure sensor  180  senses the pressure on line  208 , a peak pressure reading in a pressure range that is above a selected upper threshold would indicate that the engagement head  48 ,  164  is engaged with hard material and a peak pressure reading that is lower than a selected lower threshold would indicate that the engagement head  48 ,  164  is engaged with soft material or no material. It will be noted that if the pressure sensor were on line  210  a low peak pressure reading would indicate to the controller  182  that engagement head  48 ,  164  was engaged with hard material and a high peak pressure reading would indicate that the engagement head  48 ,  164  was engaged with soft material or no material. 
         [0047]    If the pressure read from the sensor  180  indicates engagement with soft material or no material, then the controller  182  may be programmed to automatically deactivate the vibrator mechanism  118 . For the purposes of this disclosure, deactivation of the vibrator mechanism  18 ,  118  refers to turning off the vibrator mechanism  18 ,  118  when it is on, and/or preventing the vibrator mechanism  18 ,  118  from being able to be turned on if it is off. If the pressure read from the sensor  180  indicates engagement with hard material, then the controller  182  may be programmed to respond in any of several ways. For example, the controller  182  may be programmed to automatically turn on the vibrator mechanism  18 ,  118 . Alternatively, the controller  182  may be programmed to permit the turning on of the vibrator mechanism  18 ,  118  in the event that the vehicle operator tries to do so. As used herein, the term “altering an operational state” of the vibrator mechanism  18 ,  118  encompasses deactivating, activating and/or permitting activation of the vibrator mechanism  18 ,  118 . In some embodiments, the vehicle  10  may include a switch that would permit the vehicle operator to choose between an ‘automatic’ mode in which the vibrator mechanism  18 ,  118  is automatically turned on when the pressure reading is sufficiently high, and a ‘manual’ mode in which the vibrator mechanism  18 ,  118  indicates to the vehicle operator that the vibrator mechanism  18 ,  118  can be turned on when the pressure reading is sufficiently high. It will be understood that when the vibrator mechanism is off, the pressure signal from the pressure sensor  180  may not cycle between two readings since the engagement head  48 ,  164  is not being reciprocated. 
         [0048]    The upper and lower threshold pressures that are used by the controller  182  to determine whether to deactivate the vibrator mechanism  18 ,  118  may be different pressures, or alternatively, they may be the same pressure. In embodiments, wherein they are different pressures, the control logic may incorporate a hysteresis loop to prevent unwarranted rapid powering on and off of the vibrator mechanism. The control logic may also employ a timer to ensure a minimum power on or power off time so as to prohibit excessive switching frequencies. In an alternative embodiment of the control logic, a pressure sensor  180  may be employed on each of the lines  208  and  210 , with the difference in pressure readings being used as the basis for controlling the operability of the vibrator  18 ,  118 . 
         [0049]    The controller  182  and the pressure sensor  180  together make up a control system. The term ‘control system’ is intended to be interpreted broadly, however. In a more complex embodiment, the control system may be a system with a controller with a microprocessor and digital memory and a pressure sensor that sends electrical signals to the microprocessor for use in determining the pressure. Alternatively, the control system could, in a simpler embodiment, be a simple electric circuit that is closed or opened based on the pressure sensed by pressure sensor  180 . In yet another alternative embodiment the control system could be a hydraulic circuit that is closed or opened based on the pressure sensed by pressure sensor  180 . 
         [0050]    In one example, the pressure sensor  180  may be provided in the form of a pressure switch, such as a pressure switch having part number PSW-198 sold by Omega Engineering, Inc. of Stamford, Conn., USA which opens or closes a circuit based on the sensed pressure. In some embodiments, the opening or closing of the circuit may be sensed by controller  180  in order to determine what action to take. In other embodiments, the controller  182  may be omitted entirely and the opening or closing of the circuit may directly control whether the vibrator mechanism  18 ,  118  is operable or not. 
         [0051]    In  FIG. 4 , the pressure sensor  180  is shown as being connected to the line  208 . It is alternatively possible for the pressure sensor  180  to be connected to a tilt adjustment cylinder  36  or  152  itself. 
         [0052]    Reference is made to  FIG. 6 , which shows an alternative hydraulic layout, in which at least a first accumulator  250  and optionally a second accumulator  252  are connected to the lines  208  and  210 , respectively. With certain types of tilt adjustment cylinders  36  or  152 , the seal between the piston and bore of the cylinder can be extremely fluid tight. Especially when coupled with a valve  206  that provides essentially no leakage, fluid pressure trapped in the lines  208  and  210  can serve to function as a rigid fluid lock, allowing virtually no movement of the piston to take place. The expected increase in pressure can be less than anticipated in these cases, as the vibration of the vibrator  18 ,  118  is transferred directly to the vehicle or frame through the cylinders  36 ,  152 . By installing the accumulator  250  and optionally  252  in the circuit, a small compressible volume is provided in the lines  208 ,  210  that allows the expected pressure fluctuation to occur. This improves the reliability of the operation of the control system. 
         [0053]    While the above description constitutes a plurality of embodiments of the present invention, it will be appreciated that the present invention is susceptible to further modification and change without departing from the fair meaning of the accompanying claims.