Abstract:
The invention relates to a current collector  1  for a device  2  that can be displaced with and against the driving direction F along a conductor line  5 , comprising a current collector cart  8  for the guided displacement along a guide element  9  of the conductor line  5 , and an energy transmission system. The invention solves the problem of providing a current collector and an energy transmission system, which enable an energy-conserving, contact-reliable and damage-free displacement of the current collector along a conductor line and a simple connection of the current collector to the conductor line, in that at least one first lever assembly  12 L between the current collector cart  8  and displaceable device  2  is provided with a first drive lever arm  13 L, the first end of which can be connected in a rotatable manner to the displaceable device  2  and the second end of which is connected in a rotatable manner to a second end of at least one first tension lever arm  14 L, the first end thereof being connected in a rotatable manner to a current collector cart, wherein a first adjustment drive  15 L is provided in order to be able to move the current collector cart  8  between a retracted position on the displaceable device  2  and an extended position away from the displaceable device  2 , and wherein a first locking device  16; 18 L;  15 L is provided, in order to lock the first drive lever arm  13 L when displacing the displaceable device  2  in the driving direction F in a predetermined extended position.

Description:
FIELD OF THE INVENTION 
     The invention pertains to a current collector and to an energy transmission system. 
     BACKGROUND OF THE INVENTION 
     Known energy transmission systems in the form of conductor line systems of the type known, for example, from DE 196 47 336 A1 feature devices that can be displaced on a conductor line, e.g., cable roller assemblies or transport suspension gears of an overhead conveyor. These devices frequently carry electrical loads such as driving motors for displacing the displaceable devices on the conductor line. In order to supply these electrical loads, current collectors with one or more sliding contacts are usually provided on one or more of the displaceable devices and can be inserted into corresponding voltage-carrying and current-carrying longitudinal line branches of the conductor line. In this case, the current collectors are rigidly connected to the displaceable devices and only the contacting of the sliding contacts with the line branches is realized in a movable fashion. Conductor lines of this type are normally used in manufacturing facilities that are accommodated in enclosed buildings. However, other types of conductor lines such as conductor rail systems or overhead contact systems known from railways may also be used for this purpose. 
     There is an increasing trend to also utilize conductor line systems in other systems with displaceable devices in order to supply electrical loads on the devices, for example, in cranes for loading containers or in RTG crane systems. In these systems, the loads arranged on the cranes are usually supplied via long lines that are wound onto and unwound from cable drums mounted on the cranes during a displacement. One example of such a cable drum arrangement is described in DE 44 29 268 A1. In order to displace the crane, the supply line is wound onto and unwound from the cable drum arranged on the crane in accordance with the movement of the loading crane. This known technique has the disadvantage that the line being wound and unwound needs to be placed on the ground without introducing significant tensile forces into the line. In addition, the line may become tangled while it is being wound or unwound such that the crane can no longer be displaced. In crane systems of this type with RTG cranes (Rubber Tired Gantry), the RTG cranes that are equipped with rubber tires and with a travel drive in the form of an internal combustion engine can be freely displaced in all directions. In the normal loading mode, the RTG cranes are positioned in longitudinal lanes between container loading berths and sort and load the containers in these loading berths. In order to quickly relocate containers in a full loading berth, RTG cranes are frequently pulled from currently empty or only slightly filled loading berths and driven to the full loading berth by means of the internal combustion engine. The electrical connection of the RTG cranes needs to be disconnected at the empty loading berth and reconnected at the full loading berth in a complicated, hazardous, and time-consuming fashion. In addition, the displacement of the RTG cranes by means of internal combustion engines is harmful to the environment and is becoming more and more expensive due to rising fuel prices, such that electric drives should be provided for movement within longitudinal lanes while the internal combustion engines should be used only for the free travel between the longitudinal lanes. 
     It would therefore be desirable, particularly in the field of crane systems, to supply the electrical loads on the crane with electric energy via a conductor line. However, since cranes of this type consist of very large systems that are typically used outdoors and therefore subjected to unfavorable ambient conditions, movements of the crane need to be decoupled as well as possible from movements of a current collector trolley that is connected to the crane and can be displaced on the conductor line. 
     One approach for this decoupling can be found in the field of rail-bound electric vehicles such as, for example, electric locomotives, in which one-leg pantographs or pantograph-type current collectors mounted on the roof of the locomotive usually can press a pantograph slipper against an overhead line. With respect to the supply of the vehicles with electric energy, it is particularly important that the pantograph slipper permanently contact the overhead line and this contact also be reliably maintained during motion-induced vibrations. The current collectors are therefore realized in such a way that a pressing mechanism reliably presses the pantograph slipper in the direction of the overhead line. This means that a force is continuously exerted in the direction of the overhead line. 
     One application of such pantograph-type current collectors in cranes is disclosed in DE 739 960 A. In this case, a double-link current collector is provided with a base plate, on which a skate is arranged by means of a double-link assembly with upper and lower link pairs in order to be guided along a conductor rail. The two lower links are connected to one another by means of a parallel motion such that their upper hinge points always carry out uniform motions, wherein the pressing force for the skate is generated by a tension spring that is arranged essentially parallel to the skate the between the upper links. An adjustment drive for retracting and extending the skate is not provided in this case. 
     Such a solution is very disadvantageous for conductor line current collector trolleys that are guided along a conductor line on a guide. In this case, a force needs to be continuously exerted transverse to the traveling direction, i.e., transverse to the longitudinal direction of the conductor line, such that the energy consumption increases. In addition, the constant pressing forces exerted transverse to the traveling direction leads to increased friction between the current collector trolley and the conductor line such that the energy consumption is additionally increased. Consequently, the displacement of the current collector trolley along the conductor line requires a significantly higher expenditure of force and energy. Since the current collector trolley is continuously pressed against the conductor line transverse to the traveling direction, the sensitive contacting between the sliding contacts and the longitudinal branches of the conductor line may become damaged. If the displaceable devices should be additionally displaced between several conductor lines at different locations as it is the case, e.g., with RTG cranes, damage may occur due to the protruding pantograph. 
     SUMMARY OF THE INVENTION 
     The present invention therefore is based on the objective of eliminating the above-described disadvantages and making available a current collector, as well as an energy transmission system, that allows an energy-saving, reliably contacting and non-damaging displacement of the current collector along a conductor line, as well as a simple connection of the current collector to the conductor line. Only low lateral forces should occur between the current collector and the conductor line, in particular, during the displacement of the current collector on the conductor line. 
     According to the invention, this objective is attained with a current collector having the characteristics of claim  1 , as well as an energy transmission system having the characteristics of claim  13 . Other embodiments of the invention are disclosed in the dependent claims. 
     According to the invention, the initially mentioned current collector, as well as the initially mentioned energy transmission system, is characterized by the at least one first lever assembly that is arranged between the current collector trolley and the displaceable device and features a first drive lever arm, the first end of which can be rotatably connected to the displaceable device and the second end of which is rotatably connected to a second end of at least one first tension lever arm, the second end of which is rotatably connected to the current collector trolley, wherein a first adjustment drive is provided in order to move the current collector trolley between a retracted position on the displaceable device and an extended position away from the displaceable device, and wherein a first locking device is provided in order to lock the first drive lever arm in a predetermined extended position when the displaceable device is displaced in the traveling direction. Due to this measure, the current collector trolley is advantageously pulled by the displaceable device via the first tension lever arm and only low lateral forces act upon the current collector trolley and the conductor line, i.e., transverse to the traveling direction. The first drive lever arm is advantageously locked as steep as possible, i.e., as far as possible transverse to the traveling direction, such that the angle between the first tension lever arm and the traveling direction becomes as small as possible. The inventive current collector and energy transmission system also allow a reliable connection with the conductor line if the displaceable device is not displaced exactly parallel to the guide element, but rather with variations. Alternatively, the first adjustment drive may also be arranged between the displaceable device and the first tension lever arm in order to lock the first tension lever arm at its distance from the displaceable device. 
     In an advantageous embodiment of the invention, a second lever assembly is provided that features a second drive lever arm, the first end of which can be rotatably connected to the displaceable device and the second end of which is rotatably connected to a second end of at least one second tension lever arm, the first end of which is rotatably connected to the current collector trolley, wherein the first lever assembly and the second lever assembly are arranged relative to one another in a pantograph arrangement. Due to this measure, the current collector trolley can be easily guided during the retraction and extension. 
     If a second locking device is provided in an advantageous additional development of this embodiment in order to lock the second drive lever arm in a predetermined extended position when the device is displaced opposite to the traveling direction, the current collector trolley can be pulled by the first tension lever arm during the displacement in the traveling direction and by the second tension lever arm during the displacement opposite to the traveling direction. In comparison with the preceding embodiment that features only the first locking device and in which the current collector trolley is pushed during the displacement opposite to the traveling direction, this provides the advantage that possible tilting of the current collector part can be avoided when it is pushed opposite to the traveling direction. It is also advantageous to lock the second drive lever arm as steep as possible in this case, i.e., as far as possible transverse to the traveling direction, such that the angle between the second tension lever arm and the traveling direction becomes as small as possible. 
     A second adjustment drive between the displaceable device and the second drive lever arm makes it possible to realize the retraction and extension of the current collector trolley in an exact and, in particular, symmetrically controlled fashion. The second adjustment drive may alternatively also be arranged between the displaceable device and the second tension lever arm in order to lock the second tension lever arm at its distance from the displaceable device. Alternatively, the first adjustment drive also may be advantageously arranged between the first drive lever arm and the second drive lever arm. 
     In an embodiment of the invention that is advantageous with respect to the operational technology, the first and/or the second adjustment drive may consist of a pneumatic cylinder and/or hydraulic cylinder. In this embodiment, the pneumatic and/or hydraulic cylinders may be realized in the form of a first and/or a second locking device such that a simple design of the locking device is achieved. 
     In another embodiment of the invention, a first flexible drawgear element, for example, in the form of a cable, a band, a chain, or the like is provided as a first locking device and is arranged on the displaceable device and on the first drive lever arm, wherein this first drawgear element is tensioned when the first drive lever arm is extended and the current collector is displaced in the traveling direction such that it pulls the current collector trolley. The drawgear element transmits only tensile forces, but no compressive forces. In an advantageous additional development of this embodiment, a second flexible drawgear element is provided as a second locking device and is arranged on the displaceable device and on the second drive lever arm, wherein this second drawgear element is tensioned when the second drive lever arm is extended and the current collector is displaced opposite to the traveling direction such that it pulls the current collector trolley. This embodiment, as well as the embodiment of the invention described hereafter, has the advantage that the adjustment drives can be switched off and therefore require no energy during the displacement of the displaceable device. 
     In another embodiment of the invention, a first and/or second locking device in the form of a first limit stop arranged on the first drive lever arm and a second limit stop arranged on the second drive lever arm may be provided, wherein the limit stop or the limit stops contact the displaceable device once the predetermined extended position of the respective drive lever arm is reached. This embodiment can be easily realized and makes it possible to easily lock the drive lever arm or drive lever arms. 
     The inventive energy transmission system is advantageously operated in such a way that the current collector trolley is initially extended transverse to the traveling direction from an idle position on the displaceable device toward the guide element of the conductor line by means of the adjustment drive or the adjustment drives, wherein the displaceable device is subsequently displaced in the traveling direction until the locking device locks the first drive lever arm in a predetermined extended position, and wherein the adjustment drive or the adjustment drives are then switched off. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantageous embodiments and practical additional developments of the invention are described in greater detail below with reference to preferred exemplary embodiments that are illustrated in the attached drawings. In these drawings: 
         FIG. 1  shows a schematic top view of a first embodiment of an inventive energy transmission system with an inventive current collector in an idle position; 
         FIG. 2  shows the illustration of  FIG. 1  with the current collector in an extended position; 
         FIG. 3  shows the illustration of  FIGS. 1 and 2  after the start-up of the displaceable load; 
         FIG. 4  shows the illustration of  FIGS. 1-3  during the displacement of the displaceable load; 
         FIG. 5  shows a schematic top view of a second embodiment of an inventive energy transmission system with an inventive current collector in an idle position; 
         FIG. 6  shows the illustration of  FIG. 5  with the current collector in an extended position; 
         FIG. 7  shows the illustration of  FIGS. 5 and 6  after the start-up of the displaceable load; 
         FIG. 8  shows the illustration of  FIGS. 5-7  during the displacement of the displaceable load; 
         FIG. 9  shows a schematic top view of a third embodiment of an inventive energy transmission system with an inventive current collector in an idle position; 
         FIG. 10  shows the illustration of  FIG. 9  with the current collector in an extended position; 
         FIG. 11  shows the illustration of  FIGS. 9 and 10  after the start-up of the displaceable load; 
         FIG. 12  shows the illustration of  FIGS. 9-11  during the displacement of the displaceable load; 
         FIG. 13  shows a schematic top view of a fourth embodiment of an inventive energy transmission system with an inventive current collector in an idle position; 
         FIG. 14  shows the illustration of  FIG. 13  with the current collector in an extended position; 
         FIG. 15  shows the illustration of  FIGS. 13 and 14  after the start-up of the displaceable load, and 
         FIG. 16  shows the illustration of  FIGS. 13-15  during the displacement of the displaceable load. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a schematic top view of a first embodiment of an inventive energy transmission system with an inventive current collector  1  in an idle position. 
     The current collector  1  is mounted on a traveling pedestal of a crane  2  that can be displaced on the ground  3  in—and opposite to—a traveling direction F by means of an electric travel drive. In the drawings, the crane  2  is displaced on the ground  3  on graphically indicated rubber tires  4 . The crane  2  may consist of a container-loading crane or an RTG crane. 
     A generally known conductor line  5  is provided in order to supply the crane  2  with electric energy via the current collector  1 . The conductor line  5  features a plurality of voltage-carrying or current-carrying line branches  6  that are merely indicated in  FIGS. 1-4 . In  FIGS. 3 and 4 , sliding contacts  7  of a current collector trolley  8  of the current collector  1  engage into the line branches  6  from above in order to supply the crane with electric energy. One example for such an energy transmission by means of a conductor line is disclosed in DE 196 47 336 A1, to which the present application hereby refers with respect to the design of the electric contacting between the line branches  6  and the sliding contacts  7 . 
     According to  FIGS. 3 and 4 , the current collector trolley  8  is guided laterally, i.e., transverse to the traveling direction F of the current collector trolley  8 , in the traveling mode on a guide element that is realized in the form of a guide rail  9  and arranged along the conductor line  5 , namely by means of guide rollers  10 . For this purpose, the guide rollers  10  feature outer guide rollers  10   a  and inner guide rollers  10   b  that encompass the guide rail  9  in the operational position ( FIGS. 3 and 4 ). However, another suitable guide element may be provided instead of the guide rail  9  and the guide rollers  10  on the current collector trolley  8  may be replaced with other suitable guide means for laterally guiding the current collector trolley  8  along the conductor line  5 . 
     Instead of the conductor lines described in the present exemplary embodiments, it would also be possible to use other types of corresponding energy transmission systems such as, for example, generally known conductor rail systems or current collectors that are guided on power lines. In the present context, it is essential that the current collector trolley  8  be guided along the energy transmission system on a guide element. 
     Since the crane  2  not only features the electric travel drive, but also a travel drive in the form of an internal combustion engine, e.g., a diesel engine, the crane  2  can also move in the parking position illustrated in  FIGS. 1 and 2  without connecting the current collector  1  to the electric conductor line  5 . Instead of providing an internal combustion engine for traveling without a connection to the conductor line  5 , it may also be advantageous to provide a buffer battery for the electric travel drive in order to bridge this short traveling distance. 
     A pantograph arrangement  11  with a first lever assembly  12 L on the left side in  FIG. 1  and a second lever assembly  12 R on the right side in  FIG. 1  is provided in order to displace the current collector trolley  8  from the retracted position illustrated in  FIG. 1  into the extended position illustrated in  FIG. 2 . In the following description, the letter “L” added to the reference symbols refers to the left, first lever assembly  12 L, and the letter “R” refers to the right, second lever assembly  12 R. 
     The first lever assembly  12 L features a first drive lever arm  13 L that is rotatably coupled to the crane  2  with a first end. The first drive lever arm  13 L is rotatably connected to a second end of a first tension lever arm  14 L with its other second end. The other first end of the first tension lever arm  14 L is rotatably coupled to the left region of the current collector trolley  8 . In this case, the first lever assembly  12 L is realized in such a way that the first ends of the first drive lever arm  13 L and the first tension lever arm  14 L lie, with respect to the traveling direction F, behind and to the right of the connected second ends of the first drive lever arm  13 L and the first tension lever arm  14 L in the parking or idle position illustrated in  FIG. 1 . 
     The second lever assembly  12 R is essentially realized symmetric to the first lever assembly  12 L and features a second drive lever arm  13 R that is rotatably coupled to the crane  2  with a first end. The second drive lever arm  13 R is rotatably connected to a second end of the second tension lever arm  14 R with its other second end. The other second end of the second tension lever arm  14 R is rotatably coupled to the right region of the current collector trolley  8 . In this case, the second lever assembly  12 L is realized in such a way that the first ends of the second drive lever arm  13 L and the second tension lever arm  14 L lie, with respect to the traveling direction F, in front and to the left of the connected second ends of the second drive lever arm  13 L and the second tension lever arm  14 L in the parking or idle position illustrated in  FIG. 1 . 
     The first drive lever arm  13 L can be moved back and forth between the positions illustrated in  FIGS. 1 and 2  about its rotary connection with the crane  2  by means of a first adjustment drive  15 L that consists of a controllable pneumatic cylinder in this case. Likewise, the second drive lever arm  13 R can be moved back and forth between the positions illustrated in  FIGS. 1 and 2  about its rotary connection with the crane  2  by means of a second adjustment drive  15 L that is also realized in the form of a controllable pneumatic cylinder. 
     Instead of being coupled to the crane  2 , the first and the second drive lever arm  13 L and  13 R and/or the adjustment drives  15 L,  15 R may also be rotatably coupled to a base element that, in turn, is mounted on the crane  2 . 
     In the exemplary embodiments illustrated in  FIGS. 1-16 , the rotational axes of the rotary connections respectively extend perpendicular to the plane of projection and the ground such that the motion of the lever arms and the pneumatic cylinders takes place parallel to the plane of projection. This is advantageous with respect to the manufacturing and operational technology, but the motions may also take place in other planes as long as a clear and defined positioning of the current collector trolley  8  on the guide rail  9  of the conductor line  5  and a reliable contacting of the sliding contacts  7  in the line branches  6  are ensured. 
     In order to minimize the lateral forces acting upon the conductor line  5  and the guide rail  9  when the crane  2  travels in the traveling direction F, a locking device for the first drive lever arm  13 L in the form of a cable  16  is mounted between the front end of the crane  2  with respect to the traveling direction F which is situated on the left side in  FIG. 1  and the second end of the first drive lever arm  13 L. The function of this cable  16  is described in greater detail below with reference to  FIGS. 1-4 . 
     In  FIG. 1 , the crane  2  and the current collector  1  are in an idle or parking position without an electric connection to the conductor line  5 . In this position, the crane  2  is displaced with the internal combustion engine only and the pneumatic cylinders  15 L,  15 R are operated with compressed air generated by the internal combustion engine or compressed air from a reservoir. An electronic and/or electric control arranged on the crane can be operated with a buffer battery. 
     When the crane  2  needs to be put into operation from the idle position illustrated in  FIG. 1  and displaced along the rail arrangement  3 , the two pneumatic cylinders  15 L,  15 R are initially extended such that the second ends of the drive lever arms  13 L,  13 R are moved toward one another. Due to the pantograph principle, the second ends of the first tension lever arms  14 L,  14 R are also moved toward one another such that their first ends are extended in the direction of a stationary stopping face  17  that essentially extends parallel to the conductor line  5  and the guide rail  9  transverse to the traveling direction F. Consequently, the current collector trolley  8  is also moved toward the stopping face  17  until the outer guide rollers  10   a  come in contact with this stopping face. The current collector  1  is now in the extended position illustrated in  FIG. 2 . The cable  16  is not yet tensioned. 
     Subsequently, the crane  2  travels toward the conductor line  5  in the traveling direction F by means of the internal combustion engine such that the left guide rollers  10   a ,  10   b  encompass the guide rail  9  as illustrated in  FIG. 7 . Subsequently, the connection to the line branches  6  is also produced by means of the sliding contacts  7  such that the electric travel drive can now be supplied via the conductor line. In order to save as much energy as possible, the pneumatic cylinders  15 L and  15 R are depressurized during the start of the movement toward the left from the position illustrated in  FIG. 2  such that no pressing force presses the current collector trolley  8  against the stopping face  17  and only low friction-related lateral forces act in the direction of the conductor line  5 . 
     Alternatively, it may be advantageous to act upon the pneumatic cylinders  15 L,  15 R with pressure until at least the front guide rollers  10   a ,  10   b  on the left side in  FIG. 1  encompass the guide rail  9 . In the safest alternative, the pneumatic cylinders  15 L,  15 R are acted upon with pressure until the right guide rollers  10   a ,  10   b  in  FIG. 1  also encompass the guide rail  9 . 
     Due to the depressurized pneumatic cylinders  15 L,  15 R, the frictional forces, in particular, between the guide rollers  10   a  and the stopping face  17  and the inertia of the current collector  1 , the pantograph arrangement  11  initially buckles toward the right, opposite to the traveling direction F when the movement starts as illustrated in  FIG. 3 . However, an additional, complete buckling of the pantograph arrangement  11  is prevented due to the fact that the cable  16  is now tensioned. The first drive lever arm  13 L is locked in its position illustrated in  FIG. 3  and prevented from turning additionally in the clockwise direction due to the forces, particularly frictional forces, that act opposite to the traveling direction F, as well as the tensioned cable  16 . The forces exerted upon the current collector trolley  8  by the traveling crane  2  are now transmitted to the current collector trolley  8  via the first tension lever arm  14 L such that the pantograph arrangement  11  remains in this position during the further displacement ( FIG. 4 ). 
     In order to maintain lateral forces acting upon the current collector  8  transverse to the traveling direction F as low as possible, it is therefore advantageous if the angle α according to  FIG. 3  between the first tension lever arm  14 L and the guide rail  9  or a straight line extending parallel thereto through the rotary joint between the current collector trolley  8  and the first tension lever arm  14 L is as small as possible. The first tension lever arm  14 L therefore primarily serves as a drawgear element in order to pull the current collector trolley  8  that is guided laterally and therefore in the transverse direction by the guide rollers  10   a ,  10   b  and the guide rail  9  in the traveling direction. This means that essentially only tensile forces are transmitted to the current collector trolley  8  while lateral forces in the direction away from the crane  2  or toward the crane are minimized. This represents a significant advantage over conventional pantograph-type current collectors because, among other things, the connection between the line branches  6  and the sliding contacts  7  is sensitive to transverse loads. Consequently, transverse loads of this type that could, for example, cause the sliding contacts  7  to break off or lead to faulty contacting of the sliding contacts  7  in the line branches  6  are prevented. 
     In order to correspondingly minimize the lateral forces exerted upon the conductor line  5  and the guide rail  9  when the crane  2  travels opposite to the traveling direction F, another locking device for the second drive lever arm  13 L in the form of a cable may be mounted between the right end of the crane  2  in  FIG. 1  that represents the rear end with respect to the traveling direction F and the second end of the second drive lever arm  13 R. The function of this right cable corresponds to the above-described function of the left cable  16 , however, when the crane  2  travels opposite to the traveling direction F. 
       FIGS. 5-8  show a schematic top view of a second embodiment of an inventive energy transmission system with an inventive current collector  8  [sic], wherein this second embodiment essentially can be distinguished from the embodiment illustrated in  FIGS. 1-4  by the design of the locking device. In the following description, identical components are therefore identified by the same reference symbols and the essential differences are described. 
     In the exemplary embodiment illustrated in  FIG. 5 , a limit stop  18 L in the form of an arm with the shape of a ring segment is provided on the first end of the first drive lever arm  13 L that is coupled to the crane  2 . When the crane  2  starts to move in the traveling direction F while the pneumatic cylinder  15 L is depressurized, the limit stop  18 L contacts the crane  2  at the angle of the rotational movement of the first drive lever arm  13 L shown in  FIG. 7 , i.e., it defines the position of the first drive lever arm  13 L. This once again results in the adjustment of the desired angle α between the guide rail  9  and the first tension lever arm  14 L that also primarily serves as a means for transmitting tension in this case. 
     Accordingly, a second, right limit stop  18 R may also be provided for traveling opposite to the traveling direction F. The limit stop may also be realized with a design different from that of the arm-shaped limit stops  18 L,  18 R, for example, in the form of a limit stop element between the crane  2  and the lower end of the first and the second drive lever arm  13 L,  13 R as indicated in a dotted fashion in  FIG. 7 . 
     This inventive embodiment of the current collector and the energy transmission system also makes it possible to depressurize the pneumatic cylinders  15 L,  15 R after the guide rollers  10   a ,  10   b  are threaded into the guide rail  9  such that additional energy does not have to be constantly generated during the displacement. The current collector trolley is primarily pulled along the guide rail  9  such that the occurring lateral forces can be minimized. 
     The alternative embodiment of the invention illustrated in  FIGS. 9-12  once again can essentially be distinguished from the embodiments illustrated in  FIGS. 1-8  by the design of the locking device. 
     In the embodiment of the invention illustrated in  FIGS. 9-12 , the locking device is realized in that the pneumatic cylinder  15 L of the first drive lever arm  13 L with respect to the traveling direction F is locked in the position illustrated in  FIG. 11 . In contrast, the second pneumatic cylinder  15 R that represents the rear pneumatic cylinder with respect to the traveling direction is depressurized such that the front first drive lever arm  13 L also remains stationary in this case and the left first tension lever arm  14 L essentially transmits tensile forces to the current collector trolley  8 . This current collector trolley also is essentially pulled along the guide rail  9  in this case while hardly any lateral forces are exerted thereupon. Vice versa, the second pneumatic cylinder  15 R is locked in a corresponding position while the first pneumatic cylinder  15 L is depressurized when the crane  2  travels opposite to the traveling direction F. 
     The embodiment of the invention illustrated in  FIGS. 13-16  can be distinguished from the embodiment according to  FIGS. 1-4  in that only the left first lever assembly  12 L is provided in this case and the right second lever assembly  12 R illustrated in  FIGS. 1-4  is eliminated. In this case, the function also corresponds to the function of the embodiment according to  FIGS. 1-4 , wherein the lever assembly  12 L is in this case realized with an additional holding device such that the current collector trolley  8  can be moved transverse to the traveling direction F between the retracted position illustrated in  FIG. 13  and the extended position illustrated in  FIG. 16  essentially parallel to the guide rail  9 . Holding devices of this type are already known from the prior art. In this embodiment, the locking device may also be realized in the form of a cable  16 , a limit stop according to  FIGS. 5-8 , or the pneumatic cylinder  15 L according to  FIGS. 9-12 . 
     In another alternative embodiment of the invention, only an adjustment drive arranged between the current collector trolley  8  and the crane  2  may be provided instead of the pneumatic cylinder  15 L or the two pneumatic cylinders  15 L,  15 R. This adjustment drive ensures the retraction and extension of the current collector trolley  8  and is depressurized when the extended position of the current collector trolley  8  on the stopping face  17  is reached such that one of the above-described locking devices once again locks the first or the second drive lever arm  13 L,  13 R depending on whether the crane  2  travels in—or opposite to—the traveling direction F. 
     The different types of locking devices described above may also be combined with one another such that, for example, a cable  16  is provided on the first lever assembly  12 L and a limit stop  18 R is provided on the second lever assembly  12 R.