Abstract:
A crane trolley, especially a single-rail trolley with a short overall height, with a traveling mechanism frame ( 2 ) having a hoisting mechanism ( 1 ), which can travel by running wheels ( 3, 3   a ) on a rail, especially a lower flange ( 4   a ) of an essentially horizontal beam ( 4 ), wherein at least one running wheel ( 3   a ) can be driven, and a friction roller ( 10 ) interacting with the driven running wheel ( 3   a ) is arranged on the underside ( 4   b ) of the rail. In order to create a crane trolley that guarantees a reliable reduction in the slippage of the driven running wheel ( 3   a ) with a simple design, a pair of friction rollers ( 10 ) is provided, which may be positioned against the underside ( 4   b ) of the rail by adjusting the spacing from each other via a common pressing mechanism.

Description:
BACKGROUND OF THE INVENTION 
   The invention concerns a crane trolley, particularly one with a short overall height. The invention is particularly useful with a single-rail trolley having a running gear frame having a hoisting mechanism, which can travel by running wheels on a rail. The invention is illustrated with a crane trolley having a lower flange of an essentially horizontally situated beam, with at least one running wheel being driven, and on the underside of the rail is arranged a friction roller interacting with the driven running wheel. 
   In crane trolleys with short overall height, in order to accomplish a compact and space-saving construction, the hoisting mechanism is arranged at the side, next to the beam carrying the rail, so that the actual load lifting tackle—the load hook—can be lifted as high as possible underneath the beam. This arrangement of the hoisting mechanism next to the beam produces an off-center position of the center of gravity of the running gear frame relative to the center of the beam. Due to this off-center shifting of the center of gravity, there is a risk when operating without a payload that the running wheels arranged on the rail, especially the lower flange of a beam, will lift up relative to the hoisting mechanism. 
   Such lifting should be avoided in order to prevent damage to the crane trolley and/or beam and avoid a slippage of the driven running wheels. 
   Various solutions are known from practice for solving this problem. One variant is to arrange a counterweight on the side of the running gear frame opposite the hoisting mechanism, so as displace the center of gravity back to the middle of the beam. A counterweight, on the one hand, takes up additional space, and on the other hand the proper weight of the crane trolley and the load on the beam is needlessly increased. 
   Generic crane trolleys are known from DE 42 09 565 C2 and EP 0 620 179 B1, in which a friction roller interacting with at least one driven running wheel is arranged on the underside of the lower flange. This likewise driven friction roller can be forced by a spring mechanism against the underside of the lower flange, in order to increase the traction of the driven running wheel. 
   These designs used in familiar driven friction rollers are often cumbersome and take up space, due to the drive unit of the friction roller. Furthermore, the wear behavior of the interacting driven running wheels and friction rollers is normally different, so that the rolling radii change in different ways, which again results in additional slippage of the less loaded wheel. 
   U.S. Pat. No. 3,212,455 discloses a single-rail crane trolley in which a friction roller can be adjusted on the underside of the traveling rail opposite a running wheel in order to prevent an undesirable tilting. By adjusting a screw, the friction roller can be swiveled in order to adjust the distance between the particular running roller and itself to prevent a tilting depending on the traveling rail. 
   SUMMARY OF THE INVENTION 
   The invention provides a crane trolley of the aforementioned kind, which ensures a reliable reduction of the slippage of the driven running wheel with a simple construction. 
   The solution to this problem is characterized, according to an aspect of the invention, in that a pair of friction rollers is provided, which can be adjusted on the underside of the traveling rail by adjusting the distance from each other with a common pressure mechanism. 
   Due to configuring the friction roller for increasing the traction as a non-driven friction roller pair, it is possible to make the friction roller design especially light and compact and thus space-saving, since a drive unit for the friction rollers has been eliminated. 
   In order to make sure that the friction roller pair ensures operation of the driven running wheel regardless of the direction of travel of the trolley, the two friction rollers of each pair of friction rollers may be arranged symmetrically to the axis of rotation of the particular running wheel underneath the running wheel, so that the two friction rollers of a pair of friction rollers always have the same radial load and ensure a uniform pressing of the running wheel against the lower flange of the beam, acting as the traveling rail. 
   According to one practical embodiment of the invention, it is proposed that each pair of friction rollers can be secured to the running gear frame by a support rod linkage, which preferably comprises two double-arm levers swiveling about a common axis, with a friction roller rotationally mounted at one free end of each lever. This scissors-like design of the support rod linkage is not only especially easy to produce, but also it is very flexible in use, since the distance between the two friction rollers of the pair can be adjusted relative to each other, so that the design can also be used regardless of the thickness of the rail, especially the thickness of the lower flange, and be adapted to it. 
   According to one embodiment of the invention, the other two free ends of the levers of the support rod linkage are joined together via a spring-loaded pressing mechanism, by which the position of the friction rollers of the pair and their pressing force against the underside of the rail, especially the lower flange, can be adjusted. 
   The pressing mechanism consists preferably of a screw joining together the two free ends of the levers and a pressure spring that can be placed on the screw and tightened by a nut. Besides the especially simple and economical design of this mechanism, it offers the possibility of adjusting the friction rollers continuously in broad limits and varying the pressing force by choice of the spring length and characteristics. 
   Furthermore, it is proposed that the support rod linkage of each pair of friction rollers can be fastened on a cross arm arranged on the running gear frame transverse to the direction of travel. Since the cross arms are preferably cross arms that join together the parts of the running gear frame arranged to the right and left of the beam, the installation of the support rod linkage carrying the pair of friction rollers requires no additional structural parts that would not be necessary if the pair of friction rollers were not installed. 
   According to a first embodiment of the invention, the positioning of the support rod linkage on the cross arm is done by a spacing tube which can be placed on the cross arm. 
   In a second embodiment of the invention, the support rod linkage is positioned precisely on the cross arm by a set collar which can be secured to the cross arm, for example, by means of a threaded pin or a stud screw. 
   Finally, it is proposed that a pair of non-driven friction rollers may be arranged underneath all running wheels, which are arranged in a row with the at least one driven running wheel in the direction of travel. 
   Further features and benefits of the invention are described by means of the enclosed drawings, which show two sample embodiments of the invented crane trolley only as examples. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front view of a crane trolley, according to the invention; 
       FIG. 2  is a top view of the crane trolley of  FIG. 1 , with the beam removed to reveal additional details thereof; 
       FIG. 3  is a sectional view along line III—III of  FIG. 1 ; 
       FIG. 4  is a perspective side view of a support rod linkage with pair of friction rollers; 
       FIG. 5  is the same view as  FIG. 1 , showing a first embodiment for the positioning of the support rod linkage; and 
       FIG. 6  is an enlarged view of a portion of  FIG. 5 , but representing a second embodiment for the positioning of the support rod linkage. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to the drawings and the illustrative embodiments depicted therein, a crane trolley represented in front view and top view in  FIGS. 1 and 2  basically consists of a running mechanism frame  2 , containing a hoisting mechanism  1 , which can travel by four running wheels  3 ,  3   a  along a traveling rail, configured as a lower flange  4   a , of an essentially horizontally positioned I-beam  4 , wherein one running wheel  3   a  is driven by a traveling mechanism  5 . As an alternative to driving only one running wheel  3   a , several running wheels can also be driven by the one traveling mechanism  5  or separate mechanisms for each. The crane trolley can also be used in connection with other beams, such as box girders, as long as the traveling rail has a cross section having opposite traveling surfaces for the running wheels  3 ,  3   a  and the friction rollers  10  to be described hereafter. 
   In order to be able to lift a load hook  6  via a cable pulley block  7  by means of the hoisting mechanism  1  as high as possible underneath the beam  4 , the traveling mechanism frame  2  of the illustrated single-rail trolley has an especially low overall height. This low overall height is achieved in that the traveling mechanism frame  2  is formed from two frame pieces  2   a  and  2   b , which are arranged on either side next to the beam  4 . The two frame pieces  2   a  and  2   b  of the traveling mechanism frame  2  are joined rigidly together via cross arms  8  running transverse to the direction of travel of the trolley. The hoisting unit, consisting of a cable drum  1   a  of the hoisting mechanism  1  and a reeving part  9 , which contains for example a cable end fastening, is arranged so that the load hook  6  guided on the cable pulley block  7  is positioned perpendicular beneath the vertical axis of the beam  4 , in order to minimize strain on the beam  4 . 
   Besides the represented use of a cable pulley block  7 , it is of course also possible to operate the hoisting mechanism  1  with a chain pulley block. 
   The arrangement of the traveling mechanism frame  2  at the side next to the beam  4  produces a position of the center of gravity of the traveling mechanism frame  2  that is shifted off-center—relative to the middle of the beam  4 —toward the frame piece  2   a  containing the hoisting mechanism  1 . This displacement of the center of gravity can have the effect that, when the trolley is operating without payload, the running wheels  3  arranged opposite the hoisting mechanism  1  and especially the driven running wheel  3   a  will lift up and/or slip. 
   In order to prevent such a lifting or slippage, especially for the driven running wheel  3   a , in the embodiment depicted there is arranged beneath the driven running wheel  3   a  a pair of friction rollers, consisting of two friction rollers  10 , interacting with the driven running wheel  3   a  and resting against the underside  4   b  of the traveling rail, fashioned as a lower flange  4   a . The construction and the mode of operation of the pair of friction rollers shall be explained more closely hereafter by  FIGS. 3 and 4 . 
   In order to stabilize the straight running of the trolley, four guide rollers  11  are furthermore mounted in the vicinity of the running wheels  3 ,  3   a , able to turn about the vertical on the frame pieces  2   a  and  2   b  of the traveling mechanism frame  2 , which thrust against the outer flanks  4   c  of the lower flange  4   a  of the beam  4 , as can be seen in  FIG. 1 . 
   The cross section representation of  FIG. 3  and the perspective view of  FIG. 4  show the layout of the pair of friction rollers as well as its positioning on the trolley. As can be seen from the figures, the pair of friction rollers can be secured via a support rod linkage  12  on the traveling mechanism frame  2 , consisting of two double-arm levers  14  that can swivel about a common axis  13 . The two friction rollers  10  of the pair are each mounted so that they can rotate at one free end of either lever  14  of the scissors-like linkage  12 . 
   In order to secure the linkage  12  on the traveling mechanism frame  2 , the levers  14  have a borehole  15  in the region of the swivel axis  13 , by which the linkage  12  can be pivoted on one of the cross arms  8 , which join the two frame pieces  2   a  and  2   b  together. In the embodiment depicted, the linkage  12  is mounted on the front cross arm  8  in  FIG. 2  and positioned, as can be seen from  FIGS. 2 and 3 , so that it is arranged centrally beneath the driven running wheel  3   a , and the two friction rollers  10  of the pair are arranged symmetrically to the axis of rotation  3   b  of the traveling wheel  3   a.    
   The positioning of the linkage  12  on the cross arm  8  is an especially advantageous design, since no additional structural parts are required for the mounting of the linkage  12  that would not be necessary if the linkage  12  were omitted. 
   In order to bring the friction rollers  10  of the pair to bear against the underside  4   b  of the lower flange  4   a  and in this way also press the driven running wheel  3   a  by its running surface against the lower flange  4   a , the free ends of the lever  14  placed opposite the friction rollers  10  are joined together by an adjusting mechanism, such as a pressing mechanism  16 . Activating this pressing mechanism  16  brings about a mutual swiveling of the levers  14  relative to each other and thus an adjusting of the spacing between the friction rollers  10 . 
   In the embodiment depicted in  FIGS. 3 and 4 , the pressing mechanism  16  consists of a screw  16   a  that joins together the two free ends of the lever  14 , a helical compression spring  16   b  that can be placed on the screw  16   a , and a nut  16   c  that can be screwed onto the screw  16   a  and is used to compress and release the spring  16   b.    
     FIGS. 5 and 6  show two variants of how the support rod linkage  12  can be positioned exactly underneath the driven running wheel  4   a  on the cross arm  8 . In the first embodiment shown in  FIG. 5 , the positioning of the linkage  12  occurs by a spacer tube  17  which can be placed on the cross arm  8 , thrusting against the frame piece  2   a  at one end and against the levers  14  of the linkage  12  at the other end. 
   According to the second embodiment depicted in  FIG. 6 , the support rod linkage  12  is positioned by a set collar  18  that can be placed on the cross arm  8  and bears against the linkage  12 , and the set collar  18  can be locked on the cross arm  8  by a threaded pin  18   a , for example, or a stud screw  18   a . 
   With the help of the spacer tube  17  or the set collar  18 , the position of the support rod linkage  12  can be chosen freely according to the width B of the lower flange  4   a  of the beam  4 , but it will preferably be adjusted so that the friction rollers  10  are arranged centrally beneath the driven running wheel  3   a.    
   Besides using only one pair of friction rollers that is arranged exclusively beneath the driven running wheel  3   a , it is also possible, of course, to arrange pairs of friction rollers beneath several running wheels  3 , especially beneath all running wheels  3  on the part of the lower flange  4   a  of the beam  4  that lies opposite the frame piece  2   a  containing the hoisting mechanism  1 , since these running wheels  3  have the greatest danger of lifting off and/or slipping because of the shifting of the center of gravity. 
   The adjustment of the friction rollers  10  of the pair using the pressing mechanism  16  is done as follows: 
   The friction rollers  10  bearing against the underside  4   b  of the lower flange  4   a  counteract the tendency of individual running wheels  3 ,  3   a  to lift off from the lower flange when operating without a payload, due to the shifting of the center of gravity of the traveling mechanism frame  2 . 
   Depending on the mass of the trolley itself and the width B of the lower flange  4   a  of the beam  4 , the compression spring  16   b  of the pressing mechanism  16  will be more or less loaded. By turning the nut  16   c  on the screw  16   a , the compression spring  16   b  is further shortened until the driven running wheel  3   a  arranged above the support rod linkage  12  makes contact by its running surface with the lower flange  4   a  of the beam  4 . This is the zero position of the radial load of the driven running wheel  3   a.    
   Now, in order to produce a radial load on the driven running wheel  3   a  that is sufficient to propel the trolley without a payload and thus avoid a slippage, the compression spring  16   b  is further tightened until the driven running wheel  3   a  no longer slips upon acceleration of the traveling mechanism  5 . In this position, the compression spring  16   b  of the pressing mechanism  16  still has sufficient distance from the maximum stress position to avoid a slippage by further tightening, even when the running surface of the lower flange  4   a  is wet or oily. 
   The length and characteristic of the compression spring  16   b  can be chosen so that the support rod linkage  12  and thus the pair of friction rollers can be adjusted to conventional flange thicknesses. 
   The above-specified crane trolley is distinguished in that the arrangement of the friction rollers is very compact, space-saving, and easily installed. 
   Furthermore, in combination with a frequency-regulated traveling mechanism  5 , the run-up torque and thus the starting acceleration can be regulated and limited to a justifiable extent, which can considerably reduce the size of the radial load on the driven running wheel  3   a  as compared to solutions without frequency converter. 
   Changes and modifications in the specifically described embodiments can be carried out without departing from the principles of the invention which is intended to be limited only by the scope of the appended claims, as interpreted according to the principles of patent law including the doctrine of equivalents.