Abstract:
A crane grab head ( 100 ) comprising a pair of jaws ( 102;104 ), a power source for moving the jaws, and a connector ( 116 ) for connecting the grab head ( 100 ) to a crane, wherein each jaw ( 102;104 ) comprises at least one tooth ( 110 ) for engaging with an object. Each jaw ( 102;104 ) is driven by a respective hydraulic/pneumatic cylinder ( 108   a;   108   b) which is slideable linearly to move the jaws ( 102;104 ) between open and closed positions. The width of the grab measured between the extremities of the jaws ( 102;104 ) in the closed position is more than 1500 mm. The separation between a horizontal plane passing through the top of the uppermost cylinder ( 108   a;   108   b ) when the head ( 100 ) is held freely in normal use and a parallel plane passing through the lowermost edge of the lowermost tooth ( 110 ) is less than 250 mm.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed towards a crane grab head for picking up floor mats. 
       BACKGROUND OF THE INVENTION 
       [0002]    In situations where vehicular or pedestrian access is required on certain plots of land, for instance arable land, road or floor mats are often laid to act as a temporary surface to prevent damage to this underlying land. 
         [0003]    The floor mats used are generally modular and are usually inserted into position by the use of a crane. 
         [0004]    An example floor mat used is the DURA-BASE™ mat by Terrafirma Roadways. A perspective view of this mat is shown in  FIG. 1 . The mat is formed of two overlapping rectangular sections. Holes extend around the perimeter of the mat along the non-overlapping portions of the two sections. When two of these mats are placed next to each other, the mats overlap and the holes along the common edge of these two mats line up such that a temporary locking pin can be placed through the holes of both mats to secure the two mats together. 
         [0005]    Given their shape and size, handling and placing these mats into position has proved difficult. 
         [0006]    One method which has been used has chains which anchor to the four corners of the mat. The chains then connect to a crane arm which lifts the mat. The problem with this lifting method is that the chains are flexible making accurate manoeuvring and placing of the mat difficult. 
         [0007]    Alternatively, the mat has been placed onto a forklift. When in the correct position, the forklift operator angles the rails of the forklift downward causing the mat to slide off into position. The method is slow and can cause damage to the mats as they are positioned. 
         [0008]    An improved method for lifting these mats is a grab device from Terrafirma which allows mats, in particular DURA-BASE TM  mats, to be gripped, lifted, and placed into position. The present invention relates to improvements to this grab device. 
       SUMMARY OF THE INVENTION 
       [0009]    According to one aspect of the present invention, there is provided a crane grab head comprising a pair of jaws, a power source for moving the jaws, and a connector for connecting the grab head to a crane, wherein each jaw comprises at least one tooth for engaging with an object;
       wherein each jaw is driven by a respective hydraulic/pneumatic cylinder which is slideable linearly to move the jaws between open and closed positions;   wherein the width of the grab head measured between the extremities of the jaws in the closed position is more than 1500 mm; and   wherein the separation between a horizontal plane passing through the top of the uppermost cylinder when the head is held freely in normal use and a parallel plane passing through the lowermost edge of the lowermost tooth is less than 250 mm.       
 
         [0013]    The defined separation essentially represents the maximum height of the grab head excluding the connector. By minimising this separation, the bending moment applied to each tooth when the grab grips a mat is reduced. Reducing the bending moment reduces the chance of each tooth breaking during the gripping process, and thus increases the number of mats which can be positioned by the grab head before a tooth fails. This is of particular importance considering each tooth may be cyclically loaded between a gripping position and a non-gripping position hundreds of times a day. 
         [0014]    Also keeping the vertical separation to less than 250 mm allows the grab head to be more conveniently stowed when it is not in use. 
         [0015]    The teeth on both jaws may be level with one another. However, preferably the separation on one side is greater than the separation on the other. 
         [0016]    This may be achieved either by offsetting the cylinders for the two jaws, or by having the jaws and/or teeth on one side larger than the other. 
         [0017]    The offsetting of the teeth between the two jaws in the grab head means that teeth on one jaw are lower than those on the other. This allows the grab head to pick up objects which are not necessarily flat or which are stepped; for instance a DURA-BASE TM  mat, while still maintaining the resultant closing force on the jaws generally in line with the cylinders. 
         [0018]    The hydraulic/pneumatic cylinders may be arranged to pull together and push apart the pairs of jaws with equal force either way. This capability of the jaws to grip by either pulling and pushing means that the grab head can be used with much greater flexibility and allows the grab head to separate two mats by pulling them apart in a generally horizontal plane. Existing grab heads are not designed to do this and attempts to do so have resulted in premature breakage of the grab head. 
         [0019]    According to a second aspect of the present invention, there is provided a crane grab head comprising a pair of jaws, a power source for moving the jaws, and a connector for connecting the grab head to a crane, wherein each jaw comprises at least one tooth for engaging with an object;
       wherein each jaw is driven by a respective hydraulic/pneumatic cylinder which is slideable linearly to move the jaws between open and closed positions;   wherein the width of the grab head measure between the extremities of the jaws in the closed position is more than 1500 mm; and   wherein the tooth/teeth of the first jaw are spaced further beneath the cylinders when the head is held freely in normal use than are the tooth/teeth of the other jaw.       
 
         [0023]    As previously described, the offsetting of the teeth between the two jaws in the grab head allows it to pick up objects which are not necessarily flat or which are stepped; for instance a DURA-BASE™ mat, while still maintaining the resultant closing force on the jaws generally in line with the cylinders. 
         [0024]    At least one of the pair of jaws may comprise a visual indication which allows the pair of jaws to be distinguished from each other. The visual indication may be the fact that one jaw is coloured differently than the other jaw. 
         [0025]    According to a third aspect of the present invention, there is provided a crane grab head comprising a pair of jaws, a power source for moving the jaws, and a connector for connecting the grab head to a crane, wherein each jaw comprises at least one tooth for engaging with an object;
       wherein each jaw is driven by a respective hydraulic/pneumatic cylinder which is slideable linearly to move the jaws between open and closed positions;   wherein the width of the grab measured between the extremities of the jaws in the closed position is more than 1500 mm; and   wherein the pneumatic/hydraulic cylinders are arranged to pull together and push apart the pairs of jaws with equal force either way.       
 
         [0029]    The ability of the grab head to push apart the pairs of jaws allows it to separate two mats in a manner not possible with the prior art described above. 
         [0030]    Each jaw may comprise more than one tooth. By increasing the number of teeth present in the grab head, the pressure acting on each tooth by the power source is reduced. 
         [0031]    Each tooth preferably comprises a step which extends for less than  15  mm in the direction toward the other jaw, and which is configured to grip a complimentary shoulder of an object. 
         [0032]    The cylinders each may have a sold circular cross section. This cross section is preferable to the square cross section currently employed as it reduces the friction losses present in each cylinder. Reducing the friction in each cylinder contributes to the grab head having a low profile since the reduced friction allows the cross sectional width of each cylinder to be reduced. 
         [0033]    The grab head may be provided in conjunction with a jaw adaptor which is fastened to one of the jaws, wherein the jaw adaptor comprises at least one auxiliary tooth to take over the role of the tooth/teeth of the jaw to which the adaptor is fastened, such that the adaptor allows the separation between the auxiliary tooth/teeth and the tooth/teeth of the other jaw to be changed as compared to the separation between the tooth/teeth on the jaws without the adaptor in place. The grab head may be provided in conjunction with a floor element wherein the teeth are configured to grip the floor element. The floor element may be in particular a DURA-BASE™ mat. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    An example of an apparatus in accordance with the present invention will now be described with reference to the accompanying drawings, in which: 
           [0035]      FIG. 1A  shows a perspective view of a DURA-BASE™ floor mat; 
           [0036]      FIG. 1B  shows a plan view of the mat; 
           [0037]      FIG. 1C  shows a side view of the mat; 
           [0038]      FIG. 2A  shows a plan view of a crane head according to the present invention; 
           [0039]      FIGS. 2B and 2C  show perspective views of this crane head; 
           [0040]      FIG. 3  shows a detailed cross section view of the mat taken across the plane X-X from  FIG. 1B  when the crane head is grabbing the mat. 
           [0041]      FIGS. 4 and 5  each show a side view of a crane placing a gripped mat into position next to an already positioned mat. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0042]      FIGS. 1A-1C  show views of a floor mat  10 , or floor element, which the grab head of the present invention is designed to grip. The mat  10  is formed of a top and bottom sheet of material  11 ; 12  which overlap each other. 
         [0043]    Each mat  10  or sheet of material  11 ; 12  is formed of any appropriate material that can withstand the load of a vehicle passing over it. Preferably each mat can support a load weight of 40 tonnes/m 3 . The mat  10  has a density less than that of water so that it can float on water when loaded less than 250 kg. 
         [0044]    The two sheets  11 ; 12  of the mat  10  are slightly displaced horizontally and laterally from one another such that only the top sheet  11  is present along two neighbouring sides of the mat  10 , and only the bottom sheet  12  is present along the remaining two sides of the mat  10 . 
         [0045]    Where the two sheets  11 ; 12  do not overlap, a number of holes  13  extend through the projections of sheets  11 ; 12 . The cross section of each of these holes  13  is shown in  FIG. 3 . The distance between the holes may be fixed to a certain spacing so that the holes  13  form hole sets, for example A-A; B-B; and C-C as shown in  FIG. 1A . As will be described, these sets are the points where the grab head picks up the mat  10 . 
         [0046]    As shown in  FIG. 3 , a top and bottom ridge  14 ; 15  extends around the top and bottom edges of each hole  13 . 
         [0047]    To lift the mat  10 , the crane head  100  as shown in  FIG. 2  is used. The crane head  100  is formed of first and second jaws  102 ; 104  which connect to a central portion  106  via hydraulics or pneumatic actuation cylinders  108   a ; 108   b  and telescopic supports  109   a - d.  Each cylinder and support comprises a rod which slides between an open and closed position. The cylinders  108   a ; 108   b  are coplanar and are orientated parallel with each other. The supports  109   a - d  are also coplanar and are orientated parallel with each other. 
         [0048]    The first and second jaws  102 ; 104  each comprise two teeth  110 . Each tooth  110  extends downwardly from the jaw and terminates with a flange  112  which extends in the direction toward the other jaw. The extension of the flange towards the other jaw is preferably less than 15 mm in length, though is more preferably 12 mm. 
         [0049]    Although the teeth  110  on each jaw  102 ; 104  are shaped the same and have the same dimensions, the teeth  110  on the first jaw are located closer to the cylinders than are the teeth  110  on the second jaw. The difference in height between the two sets of teeth may be approximately 50 mm. To help the crane operator identify which jaw has the higher set of teeth, and thus identify which is the first jaw, the first jaw comprises a highly visible indication positioned at the top of the jaw. The indication may be in that the first jaw is a different colour to that of the second jaw. 
         [0050]    Each of the two jaws is connected to the central portion of the crane head by one of the two actuation cylinders  108   a ; 108   b  and two of the four supports  109   a - d.  Two of the supports  109   a ; 109   c  connect the central portion  106  to the first jaw  102 , whilst the remaining two supports  109   b ; 109   d  connect the central portion  106  to the second jaw  104 . To provide maximum support to the jaws whilst they are being moved, the two supports on each jaw are located on either side of the actuation cylinder for the jaw, which is more centrally located on the jaw. 
         [0051]    Each of the two actuation cylinders  108   a ; 108   b  operates in a telescopic fashion such that the distance between each jaw and the central portion can be varied. Each of the cylinders  108   a ; 108   b  may also be configured as a double acting ram  111  to allow either a pulling or pushing force to be applied. In this case, each cylinder  108   a ; 108   b  comprises a hydraulic/pneumatic port  113  on either side of the ram head  115  to allow it to move both ways. 
         [0052]    At the top of the central portion  106  is a servo-motor or stepper-motor  114  in combination with a pivot joint  116  which allows the grab head to be connected to the remaining part of the crane and also rotated and angled as needed. Electrical connections and pressure lines from the grab head also connect to the remaining part of the crane via the central portion  106 . 
         [0053]    An equaliser valve is used to distribute fluid pressure from a hydraulic/pneumatic pressure source on the crane to each of the cylinders  108   a ; 108   b  on the grab head. From the equaliser valve, any conventional hydraulic/pneumatic pressure system can be used to control operation of the double acting ram in each cylinder. 
         [0054]    The vertical separation between the bottom of the lowermost tooth/teeth of the grab head and the top of the cylinders is preferably as small as possible to ensure ease of stowage and minimise the bending moment exerted on each tooth when they are gripping an object. In the form shown in  FIG. 2 , the separation between a horizontal plane passing through the top of the uppermost cylinders when the head is held freely in normal use and a parallel plane passing through the lowermost edge of the lowermost tooth is less than 250 mm. 
         [0055]    Operation of the crane head is shown best with reference to  FIG. 1A  and  FIG. 3 . As previously described, the mat  10  comprises a series of hole sets A-A; B-B; and C-C. The separation between the holes in each sheet from these sets is the same. The separation and size of each hole in each set is also such to allow the two teeth from each jaw of the crane head to pass through all the holes in the set. 
         [0056]    Taking the example of the four holes indicated by hole set A-A, in use the crane operator initially orientates the crane head, via the stepper-motor  114  and the pivot joint  116 , and spaces the jaws, via the cylinders  108   a ; 108   b,  such that the teeth from the first jaw are positioned over the two holes from the hole set which are located on the top sheet  11  and the teeth from the second jaw are positioned over the remaining two holes from the hole set located on the bottom sheet  12 . 
         [0057]    The crane operator then lowers the crane head such that the teeth enter the holes A-A of the mat into the dotted position as shown in  FIG. 3 . In situations where the mat  10  is placed flat on the ground, the operator will know when the teeth are in the dotted position shown in  FIG. 3  since he will feel resistance in the movement controls of the crane due to the bottom of the teeth in the second jaw making contact with the ground. 
         [0058]    From this dotted position, the operator then moves the jaws together via the cylinders  108   a ; 108   b  such that the flange of each tooth overlaps the bottom ridge  15  of each hole  13  to grip and lift the mat as shown in  FIG. 4 . 
         [0059]    From the dotted position, the operator alternatively may move the jaws apart, rather than bring them together, such that the outer face of each tooth makes contact with the outer edge of each hole  13 . Moving the jaws outward provides an alternative way of gripping the mat. 
         [0060]    The crane operator then releases the teeth from engagement with the edges of the holes, using the cylinders, and returns the jaws to the dotted position shown in  FIG. 3 . From here, the crane operator then raises the crane head away from the newly positioned mat. 
         [0061]    The two mats can then be secured together by a locking pin or any other fastening means. 
         [0062]    The above process can then be repeated with a new mat as required. 
         [0063]    In some instances, it may be that the crane operator wishes to place a mat alongside an already positioned mat which has a top sheet, rather than a bottom sheet, sticking out. In this case, the crane operator must slide the bottom sheet of the new mat underneath the top sheet of the already positioned mat to allow the two mats to be connected. 
         [0064]    To slide the new mat underneath the already positioned mat, the operator first places the new mat next to the already placed mat as shown in  FIG. 5 . The operator then disconnects the second jaw from the mat, tilts the crane head from the new mat, and then expands the second jaw, which previously engaged with the pair of holes in the lower sheet of the new mat, such that it engages with the pair of holes in the upper sheet of the already placed mat. In this position, as the first and second jaws are each connected to a pair of holes in an upper sheet of a mat, the grab head may be slightly angled from the horizontal to compensate for the fact that the teeth of the second jaw are positioned slightly lower than the teeth from the first jaw. 
         [0065]    Once both the jaws are engaged with their holes in the upper sheets of the mats, the operator pulls the jaws together using the cylinders  108   a ; 108   b.  Since the weight of the crane is acting on the already placed mat, when the jaws are pulled together the new mat is the mat which moves. Thus the bottom sheet of the new mat slides underneath the top sheet from the already positioned mat and into a position for fastening. 
         [0066]    To separate the new mat from the already positioned mat after use, the previously described process is reversed as follows:
       i) the crane is positioned on the already placed mat as shown in  FIG. 5 . The grab head is then slightly angled from the horizontal such that the teeth from the second jaw are positioned in the holes of the upper sheet in the already placed mat and the teeth from the first jaw positioned in the holes of the upper sheet in the new mat;   ii) once both the jaws are engaged with their respective holes as in i), the operator then pushes the jaws apart using the cylinders  108   a ; 108   b  such that the outer face of the teeth in the first jaw make contact with the outer edge of each hole  13 . Since the weight of the crane is acting on the already placed mat, when the jaws are pushed apart the new mat slides laterally out from under the already placed mat (which remains stationary) into the position shown in  FIG. 5 ;   iii) once the new mat is in the position shown in  FIG. 5 , the new mat is then lifted as previously described (by re-engaging the flange of each tooth with the bottom ridge  15  of each hole  13 ).       
 
         [0070]    The ability to push two mats apart may be useful in situations other than the one described above if two mats are stuck together. 
         [0071]    Thus it will be appreciated that the outer side of each tooth can be used to separate two mats apart and the inner side of each tooth can be used to bring two mats together. However, only the inner side of each tooth, which comprises the flange which engages with the ridge in the mat, is used to lift the mat. 
         [0072]    Whenever a mat is gripped, it is preferable to use hole set A-A, rather than B-B or C-C. As the holes in A-A are the most centrally located on the mat, gripping the mat with these holes reduces the bending forces exerted on the teeth when the mat is lifted. 
         [0073]    In some embodiments of the grab head, one or both of the jaws may include a detachable adaptor. The adaptor includes a further tooth which is similar in shape to any of the other teeth previously described. The purpose of this auxiliary tooth is to take over the role of the teeth of the jaw to which the adaptor is fastened, such that the adaptor allows the separation between the auxiliary tooth and the teeth of the other jaw to be changed as compared to the separation between the teeth on the jaws without the adaptor in place.