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BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a tool for removal of a chisel from a chisel holder, having an actuating member, which has a push-off section, wherein the actuating member can be displaced along a displacement direction. 
     2. Discussion of Related Art 
     A tool is known from PCT Reference WO 97/23710 wherein a pin-shaped push-off section is connected to a handle by a hinged connector. The tool is employed for the removal of a chisel inserted into a receiving bore of a chisel holder. The receiving bore is embodied as a through-bore, so that a chisel shank of the inserted chisel is accessible from the rear. A security element is drawn up on the end of the chisel shank, which is held in a groove of the receiving bore and thus maintains the chisel in the chisel holder. If the chisel is to be replaced, for example after reaching a wear limit, the push-off section is pushed through the rear opening into the receiving bore and is brought into contact with the free end of the chisel shank. 
     Then the handle can be pivoted until it rests against a support section. It is then possible to adjust the handle in the hinged connector with respect to the push-off section. The leverage thus created is introduced into the chisel via the push-off section so that the hold provided by the security element is released. Once the chisel is removed and the tool taken out, a fresh, unworn chisel can be placed against the receiving bore and driven in by a hammer. Changing a chisel by the known arrangement requires great force and, in case of tight space conditions, cannot be performed without danger. 
     Further removal arrangements are known from German Patent Reference DE 30 26 930 A1. These require a plunger, which is mounted in the area for the receiving bore of the chisel. The plunger can be linearly displaced against the shank end of the chisel, so that the chisel can be moved out of the receiving bore. Hydraulic systems or mechanical lever systems are employed for driving the plunger. These known tools require a lot of structural space, which cannot always be provided. Also, fine particles of the removed material enter the receiving bore designed as a blind bore during the operational use and cannot leave it again. They then impair the function of the removal arrangement and the free rotatability of the chisel in the insert. 
     Tools are known, which propose the insertion into or removal of a chisel from a chisel head. For example, German Patent Reference DE 43 23 669 C1, German Patent Reference DE 84 03 441 U1, U.S. Pat. No. 6,526,641 B1 and German Patent Reference DE 32 23 761 C2 show claw retractors that engage a circumferential groove in the chisel head with adjustable claws. For removal, the claws can then be adjusted in the longitudinal direction of the chisel. These known tools always require a shaped surface on the chisel head, behind which they can extend when pulling out the chisel. If this shaped surface is worn out because of heavy wear on the chisel, or if the chisel head is broken off, the tools are useless. 
     SUMMARY OF THE INVENTION 
     It is one object of this invention to provide a tool of the type mentioned above but which considerably simplifies the replacement of the chisel. 
     This object is attained if the actuating member can be shifted by an actuating unit, the actuating unit has a draw-in section spaced apart from the push-off section and arranged transversely with respect to the displacement direction of the actuating unit, and the actuating member can be power-operated bidirectionally in the displacement direction by the actuating unit. 
     While the push-off section is used for chisel removal, the chisel can be brought into the mounting position by the draw-in section. This becomes possible by the actuating unit, which shifts the actuating member bidirectionally, and therefore into the mounting and the removal direction. The actuating member can be power-operated by the actuating unit, for example by an electric or a hydraulic drive mechanism, so that the work of replacing the chisel is considerably more easy for the user. Thus, the tool in accordance with this invention can perform mounting, as well as removal work. 
     In accordance with this invention, the actuating member can have a receiving section between the push-off section and the draw-in section, which is accessible transversely to the displacement direction of the actuating member. With a matched body contour, the chisel can be easily inserted into the receiving section. The body contour can have a circumferential groove at the shank of the chisel, for example, which the actuating member engages. 
     If the extension of the receiving section transversely to the feed direction is less than or equal to the maximal cross section of the actuating member in this direction, then the receiving section does not extend past the actuating member transversely to the feed direction. It is thus possible to achieve a compact construction. This has advantages, for example, if the chisel is to be mounted or removed through a receiving bore, in which the chisel is maintained. 
     For providing large mounting forces, and in particular also large removal forces, in one embodiment of this invention, the actuating unit has a hydraulic unit with a hydraulic cylinder, on which a piston can be displaced, and the actuating member is connected with the piston via a piston rod. In this case, the hydraulic unit can have a reversing unit, which makes possible a force to act bidirectionally on the piston. 
     For a tool which is easy to manipulate, in one embodiment of this invention, the hydraulic unit is connected to an electric motor, the electric motor is connected to a battery, and the hydraulic unit, the electric motor and the battery can be combined in a manually operable structural unit. In that case, the tool can be operated independently of an external energy supply and can be easily handled. 
     Mounting and removal can be dependably performed, if there is a positive connection between the chisel and the actuating member. Thus, with this invention, the actuating unit has two support faces oriented in opposite directions, which are directed in the displacement direction of the actuating member. 
     For achieving a fixed and positionally-stable association of the mounting tools during mounting, as well as removal, the actuating unit has two support elements, which are arranged spaced apart from each other in the displacement direction. With these support elements the tool can then be supported on counter-faces of the chisel holder, and the like, which are especially thus provided. 
     It should be possible to place the actuating member into a defined initial position for easy operation. In one embodiment of this invention, the actuating unit has an alignment section on which the actuating member is aligned in its retracted or extended end position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This invention is explained in greater detail in view of an exemplary embodiment represented in the drawings, wherein: 
         FIG. 1  shows a tool unit arranged on a cutting roller tube in a lateral view and in section; 
         FIG. 2  shows a representation in accordance with  FIG. 1 , in a top view; 
         FIG. 3  shows the tool unit in accordance with  FIGS. 1 and 2  with a tool, and at the end of the removal movement, the removal position, in an enlarged detailed view and in section; 
         FIG. 4  shows the representation in accordance with  FIG. 3  at the end of the mounting movement, the mounting position; and 
         FIG. 5  shows the arrangement in accordance with  FIG. 4 , in a top view. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As  FIG. 1  shows, a tool unit is attached, in particular welded, to the roller surface  11  of a cutting roller tube  10  of a rock-cutting machine, for example a surface mining machine, a road-cutting machine, or the like. 
     Customarily, a plurality of the tool unit represented is used and is arranged at even spacing from each other. 
     The tool unit comprises a base element  20  which, with a concave contact section, is placed on the roller surface  11  and welded on it. The base element  20  has a tool receptacle  21 , into which a chisel  30 , in particular a round shank chisel, is inserted. In the customary way, the chisel  30  has a chisel head and an adjoining chisel shank  33 . As shown in  FIG. 3 , the chisel  30  has a clamping sleeve  35  in the area of or near its chisel shank  33 . The clamping sleeve  35  enters and engages a circumferential groove  34  of the chisel shank  33  with holding elements  36 . It is thus freely rotatable, but is held fixed against being released in the axial direction. 
     In the tool embodiment in accordance with  FIGS. 3 to 5 , in the mounted state the chisel head is supported on a support face of a chisel holder  40 , with the interposition of a wear-protection disk  31 . On its end facing away from the chisel head, the chisel shank  33  has an end piece, which is not covered over by the clamping sleeve  35 . This end piece forms a collar  37 , with a diameter less than the diameter of the remaining shank area. The collar  37  has a circumferential groove  38 . A cylindrical support element  39  adjoins the groove  38 . 
     The chisel holder  40  has a chamfering extending around the chisel receiver  42 , which is used as a centering receptacle  41  and delimits the insertion opening  43  for the chisel  30 . The chisel holder  40  can be inserted into a chisel holder receptacle  23  of the base element  20  and can be fixedly connected with the base element  20 , for example welded to it such as shown by weld seams  46  in  FIG. 4 . In case of wear, it is possible to cut the weld seams  46  open and to exchange the chisel holder  40  for a fresh, not worn, one. In one embodiment of the tool, the base element  20  and the chisel holder  40  are combined into a one-piece structural unit, such as shown in  FIG. 1 . 
     As  FIGS. 3 and 4  and  FIG. 1  further show, the base element  20  and the chisel holder  40  form a pocket-shaped, laterally open bulge  45 , open toward the top in accordance with  FIG. 1 . 
     A tool can be introduced into the bulge  45  and can be used for mounting, as well as the removal of the chisel  30 . 
     The tool has an actuating unit  60  surrounding a cylinder-shaped interior chamber  63 . A piston  66  is linearly conducted between two end positions in the interior chamber  63 . The piston  55  is sealed against the cylinder wall delimiting the interior chamber by an O-ring. A piston rod  67  is connected to the piston  66  and is conducted out of the interior chamber  63  through a closure insert  68 . The closure insert  68  is sealingly inserted into the open side of the actuating unit  60 . The piston rod  67  is also sealed against the closure insert  68 , so that a pressure-proof interior chamber  63  results. On its free end, facing away from the piston  66 , the piston rod  67  has an actuating member  70 . The actuating member  70  is fastened to it by a dowel pin  72  pushed through the bore  71  of the actuating member  70 . The actuating member  70  has a draw-in section  73  and a push-off section  74  spaced apart from each other, so that a claw results. The spacing is selected so that the chisel  30  can be inserted into the claw so that the draw-in section  73  engages the groove  38 . 
     On its rear end, the actuating unit  60  has a support element  61  formed by a widened contour. 
     A flat support face  62  at the end closes off the actuating unit  60  in the rear, while a support face  69  is arranged on the opposite front side. The support face  69  is formed by a front support element  69 . 1 , which has a lateral cutout  69 . 2 . 
     A handle  50  with a battery-operated hydraulic unit  51  is connected to a handle holder  65  of the actuating unit  60 . Because the electrical current supply is integrated into the handle  50 , an easily manipulated tool results. 
     The hydraulic unit  51  is connected via hydraulic lines  64 . 1  and  64 . 2  with the interior chamber  63 . The interior chamber  63  and the hydraulic unit  51  are filled with a fluid, in particular a hydraulic fluid. 
     Referring to  FIG. 4 , the process for removing the chisel  30  from the chisel receiver  42  of the chisel holder  40  will be described. The tool is inserted into the bulge  45 . In the process, the tool is centered with the support elements  61  and  69 . 1  on counter-faces of the base element  20  and of the chisel holder  40 , so that it can be aligned. The support element  61  and the actuating member  70  aid the inserting movement, wherein the support element  61  acts against the cylindrical support element  39  of the chisel  30 . The support elements  61  and  69 . 1  guide the tool perpendicularly with respect to the inserting movement, such as shown in  FIG. 5 . 
     When inserting the tool into the bulge  45 , a cutout  69 . 2  in the support element  69 . 1  makes access to the chisel  30  possible, and the draw-in section  73  engages the groove  38  of the chisel  30 . In this mounting position, it is possible to activate the hydraulic unit  51 . During this, hydraulic fluid is conveyed through the hydraulic line  64 . 2 , and the piston  66  is axially displaced in the direction toward the chisel  30 . The flat push-off section  74  is simultaneously placed against the free end of the chisel  30 . The chisel  30  is pushed out of the receiving bore  42  against the frictional force exerted by the clamping sleeve  35 . During this process, the actuating unit  80  is supported by its support face  62  on the corresponding counter-face of the base element  20 , as shown in  FIG. 3 . The front-side support face  69  is then released, which is shown by the spacing area having a dimension of 3 mm. The push-out movement of the piston  66  is limited at the closure insert  68 . 
     The actuating member  70  is extended out of the chisel receiver  42  sufficiently far, so that the chisel is released and can be removed. 
     The process for mounting a chisel  30  will be described. 
     Proceeding from the position of the tool shown in  FIG. 3 , it is possible to insert the support section  39  of a chisel  30  into the groove area of the actuating member  70  formed between the draw-in section  73  and the push-off section  74 . The positioning indicated in  FIG. 3  results. The hydraulic unit  51  can be reversed by a switching arrangement  52 , so that the hydraulic fluid is conveyed via the hydraulic line  64 . 1  into the interior chamber  63  and is pumped out of it through the hydraulic line  64 . 2 . Thus, the piston  66  is displaced from left to right in the drawing plane of  FIG. 3 , until it reaches the end position shown in  FIG. 4 . During this, the chisel  30  is drawn into the chisel receiver  42  by the draw-in section  73  engaging the support element  39 . To make mounting easier, the free end of the chisel  30 , as well as the clamping sleeve  45 , are threaded into the centering receptacle  41 . In the process, the circumference of the longitudinally-slit clamping sleeve  35  is compressed and is drawn under friction along the interior wall defining the chisel receiver  42  until it reaches the end position shown in  FIG. 4 . During the draw-in, the support element  69 . 1  of the actuating unit  60  is supported on the contact face  44  of the chisel holder  40 , while the support section  22  is released. In the mounted state, the wear-protection disk  31  of the chisel  30  engages the centering receptacle  41  with a centering insert  32 . 
     Once the chisel  30  is drawn in, the tool can be lifted out of the tool receptacle  21 . To prevent the actuating member  70  from becoming twisted in relation to the actuating unit  60 , in the position shown in  FIG. 5 , the actuating member  70  is aligned secure against turning in the circumferential direction against a stop, the alignment section  69 . 3 , of the actuating unit  60 . 
     German Patent Reference 10 2007 030 640.9, the priority document corresponding to this invention, and its teachings are incorporated, by reference, into this specification.

Summary:
A tool for mounting a chisel on a chisel holder, having an actuating member, which has a push-off section, wherein the actuating member can be displaced along a displacement direction. It is possible to simplify changing the chisel if the actuating member can be shifted by an actuating unit. The actuating unit has a draw-in section, which is spaced apart from the push-off section and is arranged transversely with respect to the displacement direction of the actuating member. The actuating member can be power-operated bidirectionally in the displacement direction by the actuating unit.