Abstract:
An electric machine tool for tools which operate by percussion, the electric machine tool having a machine housing; a rotatingly drivable work spindle seated in the machine housing; a tool receiver provided for receiving a tool and driven by the work spindle; a mechanical striking mechanism having a beater accelerated in an axial direction and actuating a shaft of the tool in the axial direction by blows; a driver unit which derives an acceleration of the beater from rotational movement, the driver unit having an axially displaceably arranged scanning member which rotates synchronously with the work spindle; two circular-shaped curved paths which guide the scanning member and are fixed in the housing, said circular-shaped curved paths having elevations and depressions, each of the elevations pointing in an axial direction of the work spindle in a direction of the scanning member.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an electric machine tool for tools which operate by rotation and/or percussion, such as a drill and/or riveting hammer or impact drilling machine. 
     In connection with a known drill and/or riveting hammer of this type (DE 41 21 279 A1), the drive unit comprises an eccentric seated on a gear shaft, which drives the work spindle via a gear wheel and, via a needle bearing, receives a coupling sleeve having an opening, as well as an elastically yielding driver member, which is seated, tiltable around an axis oriented transversely in relation to the gear shaft, in the machine housing. The driver member has a lever extending away from the axis toward the coupling sleeve, which engages the opening in the latter, and a two-legged hoop extending away from the axis, which is closed on its free end in a loop-like manner and is hinged with play between two collars formed on the beater. The beater is received with displacement play in the hollowly embodied drive spindle, wherein an inserted O-ring acts as a damper on the beater and prevents it from being displaced on its own. A header or a riveting bolt has been inserted between the tool shaft and the beater. 
     During operation, the driver member is driven via the eccentric in a back-and-forth movement, wherein only the vertical excursions of the eccentric are transmitted to the lever, while the transverse movements of the anchor sleeve do not reach the lever because of the opening, which is widened in this direction. Accordingly, the driver member performs a back-and-forth movement around its axis. At the moment of the impact of the beater on the header, and therefore on the tool, the driver member is at dead center on the tool side. Following the strong impact, the beater is reflected and flies backward toward the hoop of the driver member, which also moves backward. When the striking mechanism is well adjusted, the front collar touches the hoop of the driver member only slightly, or not at all. After passage through dead center on the motor side, the driver member again comes into contact with the front collar of the beater. Because of the kinetic energy of the beater, the hoop is bent backward in the process. Thus, the energy still stemming from the recoil of the beater is transferred to the elastic driver member and stored therein as spring energy. In the subsequent forward movement of the hoop, the latter accelerates the beater in the direction toward the tool, both because of the forward movement of the driver member and because of the backward springing hoop, wherein as a rule the beater attains higher velocities than the driving hoop. This leads to the separation of the beater from the driver member. The beater then flies freely over a defined distance, until another impact on the header and the tool takes place. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an electric machine tool which avoids the disadvantages of the prior art. 
     In keeping with these objects in the inventive electric machine tool the driver unit has a scanning member which rotates synchronously with the work spindle, is axially displaceably arranged, and is guided with axial plate between two circular-shaped curved paths, which are arranged fixed against relative twisting in respect to the work spindle and have elevations and depressions pointing in the axial direction of the work spindle. 
     The electric machine tool has the advantage, that because of the mechanical striking mechanism constructed in accordance with the invention it is possible to omit a gear shaft and therefore to achieve greater spindle rpm. By means of the selection of the axial elevations and depressions provided on the curved paths, a corresponding number of beats per spindle revolution is achieved. By means of the striking mechanism in accordance with the invention it is possible to produce an electric machine tool with the emphasis on small tool diameters in a very cost-efficient manner, wherein the lubrication outlay is very small. 
     In accordance with a preferred embodiment of the invention, the elevations and depressions of the curved paths, which extend parallel with the axial direction of the work spindle, are constituted by several periods of a sine-like curve, wherein the two curved paths extend parallel with or offset from each other. Three or five periods of a sine curve per curved path are preferred. 
     In accordance with an advantageous embodiment of the invention, the spring-loaded actuators are designed as contact springs, which can be simply and cost-effectively manufactured and installed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be explained in greater detail in the following description by means of exemplary embodiments represented in the drawings. Shown in a partially schematic representation are in: 
     FIG. 1, in a partial view a longitudinal section of a drill hammer for selective drilling or impact drilling, 
     FIG. 2, in a partial view a section along the line II—II in FIG. 1, 
     FIG. 3, in a partial view a developed view of two curved paths in the striking mechanism of the drill hammer in FIG. 1, 
     FIGS. 4 to  7  in respectively partial views a modified striking mechanism in accordance with further exemplary embodiments. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The drilling hammer, represented in a partial view in longitudinal section in FIG. 1 as an exemplary embodiment of a general, preferably manually guided electric machine tool with a tool, which operates rotatingly and/or by impact, has a housing  10  and a sleeve-shaped work spindle  11 , also called a spindle sleeve, which is seated rotatingly and axially displaceably in the housing  10 , as well as an electric motor, not represented here, for the rotary drive of the work spindle  11 . A tool receiver  12  is formed on the front end of the work spindle  11 , in which a shaft  13  of a tool is received, fixed against relative rotation and limitedly axially displaceable. The drive spindle  11  is caused to rotate by means of a gear wheel  14 , which is seated, fixed against relative rotation, on the spindle end of the work spindle facing away from the tool receiver  12  and meshes with a drive pinion  14  formed on the shaft end of a driveshaft  15  seated in the housing  10 . The driveshaft  15  is connected by means of a gear, not represented here, with the power take-off shaft of the electric motor, or it itself constitutes the power take-off shaft. 
     A mechanical striking mechanism  16  is provided for the impact drilling operation, which has a beater  18 , which is accelerated in its axial direction and impacts via a striking pin or header  17  on the shaft  13  of the tool held in the tool receiver  12 , as well as a driver unit  20 , which derives the acceleration of the beater  18  from a rotary movement of the work spindle  11 . The beater  18  and the header  17  are received with play and axially displaceably in the sleeve-shaped drive spindle  11 . The displacement movement of the header  17  is limited in the direction toward the beater  18  by a snap ring  19  inserted into the work spindle  11 , and in the direction toward the tool receiver  12  by the front end of the shaft  13 . 
     The driver unit  20  comprises a scanning member  21 , which rotates synchronously with the work spindle  11 , is arranged axially displaceable, and is guided with axial play between two parallel ring-shaped curved paths  22 ,  23 , which are arranged coaxially with the work spindle  11  in a manner fixed against relative twisting in the housing  10 , as well as two spring-loaded actuators, which are operative in the displacement path of the beater  18 , act in opposite directions from each other and can be directly or indirectly tensed by the scanning member  21 , wherein the spring-loaded actuators are preferably embodied as contact springs  24 ,  25 . A developed view of the curved paths  22 ,  23  is represented in a partial view in FIG. 3, wherein the arrow  28  in FIG. 3 lies in the axial direction of the work spindle  11  and points toward the tool receiver  12 . As can be clearly seen, the curved paths  22  have elevations  221 , or respectively  231 , and depressions  222 , or respectively  223 , which point in the axial direction of the work spindle  11 . In the case of the example, the elevations  221 , or respectively  231 , and depressions  222 , or respectively  223 , are represented by a sine curve, wherein several periods of a sine curve are present over the circumference of the curved paths  22 ,  23 . Three or five periods are preferably provided, so that therefore three, or respectively five, elevations  221 , or respectively  231 , and three, or respectively five depressions  222 , or respectively  223 , are present on each curved path  22  or  23 . The number of the elevations and depressions, which are co-linear in the axial direction, depends on the desired number of impacts on the shaft  13  of the tool during one revolution of the work spindle  11 . 
     The curved paths  22  and  23  are respectively formed on a cam disk  26 , or respectively  27 . The cam disk  26  is rigidly fixed in the housing  10 . The cam disk  27  is displaceably guided on preferably three bolts  29 , arranged on a graduated circle which is coaxial with the work spindle  11 , and are offset in respect to each other by a circumferential angle of 120°. The bolts  29  are clamped in place in the machine housing  10  and each receives a contact spring  30 , which is supported between the two cam disks  26 ,  27 . By the action of the contact springs  30 , the cam disk  27  rests against an axial bearing  33 , which is axially non-displaceably fixed in place on the work spindle  11  by means of two disks  31 ,  33 . The displacement mobility of the cam disk  27  is used for switching the striking mechanism  16  on or off. If the operator of the drill hammer pushes the tool clamped in the tool receiver  12  against a work surface, the tool is displaced into the tool receiver  12  over a limited displacement distance. The displacement movement of the tool is transferred by the shaft  13  to the header  17  which, via the snap ring  19 , displaces the work spindle  11 , which is seated in the housing  10  by means of a sliding bearing  34  and a roller bearing  35 , sufficiently far so that the cam disk  27  touches a limit stop  36  formed on the housing  10 . In this operating position represented in FIG. 1, the striking mechanism  16  is switched on and the scanning member  21  is conducted between the two curved paths  22 ,  23  on the cam disks  26 ,  27 . If the tool is lifted off the work surface, the contact springs  30  push the cam disk  27  toward the left in FIG. 1, wherein the cam disk  27  pushes the work spindle  11  back again via the axial bearing  33 . In the process the distance between the two curved paths  22 ,  23  is increased far enough, so that the scanning member  21  freely turns between the two curved paths  22 ,  23  without coming into contact with them. The striking mechanism  16  is turned off. 
     The striking mechanism  16  must be completely shut off for drilling operations. To this end, a manually operated shut-off member  37  in the form of a locking handle, which can be rotated by 180° and into which a set pin  38  has been eccentrically placed, is arranged on the machine housing  10 . By turning the shut-off member  37  by 180°, the set pin  38  pivots into the displacement path of the cam disk  27  and is placed immediately in front of the cam disk  27  in the base position of the cam disk  27  which the latter assumes under the restoring force of the contact springs  30  when the tool is not in operation. A displacement movement of the cam disk  27  is blocked by means of this, the striking mechanism  16  is turned off and the drill hammer operates as a drill with the tool only turning. 
     In the exemplary embodiment of the driver unit  20  represented in FIG. 1, the scanning member  21  is seated with play with an annular element  39  on the beater  18  and extends with a scanning finger  40 , which projects radially from the annular element  39 , through an axial slit  41  in the spindle sleeve  11  as far as the curved paths  22 ,  23  on the two cam disks  26 ,  27 . The scanning finger  40  is also indicated in the developed view of the curved tracks  22 ,  23  in FIG.  3 . The two contact springs  24 ,  25  of the driver unit  20  have been pushed on the beater  18  and are supported on the one side on the front faces of the annular element  39 , which face away from each other in the axial direction, and on the other side on radial shoulders  42 ,  43  formed on the beater  18 . 
     During the operation of the striking mechanism  16 , with each elevation  221  the curved path  22  accelerates the beater  18  in the direction toward the header  17 , where it impacts on the header  17  and through it exerts a blow on the front of the shaft  13  of the tool. When the cam disk  27  rests against the limit stop  36  on the housing  10 , the parallel distance of the two curved paths  22 ,  23 , and the contact springs  24 ,  25  are matched to each other in such a way that the scanning finger  40  of the scanning member  20  is uncoupled to a large extent from the curved paths  22 ,  23  when the beater  18  impacts on the header  17 . After the impact on the header  17 , the beater  18  is reflected and flies backward in the direction toward the depression  222  of the curved path  22 . When the striking mechanism is well adjusted, the scanning finger  40  touches the depression  232  of the curved path  23  only slightly or not at all. It can possibly be necessary to offset the curved paths  22 ,  23  in respect to each other in the circumferential direction for adjusting the striking mechanism. After passing through the dead center of the curved path  22  at the lowest point of the depression  222 , the scanning finger  40  again touches the curved path  22 . Because of the kinetic energy of the beater  18 , the beater  18  is displaced against the contact spring  25  in the direction toward the scanning member  21  and is cocked by this, so that the kinetic energy of the beater  18  is converted into spring tension. Thereafter the beater  18  is accelerated in the forward direction by this energy and the following elevation  221  of the curved path  22 , and the described process is repeated. 
     In the modified driver unit  20 , which is represented in FIG. 4 in a partial view, the scanning member  21  is constituted by the abutting spring ends  241  and  251 , which are radially bent outward. A separate component with an annular element  39  and a scanning finger  40  is omitted. After assembly, the two spring ends  241 ,  251 , which are firmly connected with each other, project through the axial slit  41  in the spindle sleeve or drive spindle  11  and are guided between the two curved paths  22 ,  23  on the cam disks  26 ,  27  in the same way as described. 
     By means of a sketch drawn in FIG. 5 it is indicated that the two adjoining spring ends can also be connected in one piece with each other. In that case the two contact springs  24 ,  25  constitute a one-piece contact spring  44  with a radially projecting spring bend  441 , which passes through the axial slit  41  in the spindle sleeve or drive spindle  11  and is guided between the curved paths  22 ,  23  as the scanning member  21 . 
     The driver unit  20 , represented in a partial view in longitudinal section in FIG. 6 has been modified in respect to the above described driver unit  20  to the extent that the contact springs  24 ,  25  are arranged outside of the spindle sleeve or drive spindle  11 . The scanning member  21  has two slide rings  45 ,  46 , which are seated with play on the spindle sleeve  11  and on each of which a radially projecting hollow scanning protrusion  45   a,    46   a  is formed as one piece with them. A connecting pin  47 , which has been conducted through the insertion slit  41  in the spindle sleeve  11  and is anchored on the beater  18 , projects into the scanning protrusions  45   a,    46   a,  which can be displaced in relation to each other. Axial holding slits  45   b,    46   b  are located in the scanning protrusions  45   a,    46   a,  through which the connecting pin  47  extends. The connecting pin  47  is placed, fixed against relative rotation, in the scanning protrusions  45   a,    46   a,  but can be displaced in the axial direction by means of the slide rings  45 ,  46 . The contact springs  24 ,  25  arranged in the interior of the scanning cams  45 ,  46  are supported on the one side on the inner wall of the scanning cams  45 ,  46 , and on the other side on the connecting pin  47 . The slide rings  45 ,  46  are acted upon by the tension force of the contact springs  24 ,  25 , in a way so they are pushed apart, so that the connecting pin  47  comes to rest against the brackets  45   c,    46   c  on the scanning protrusions  45   a,    46   a.  The arrangement of the cam disks  26 ,  27  is made as in FIG. 1, so that the scanning cams  45 ,  46  are guided between the two cam paths  22 ,  23 . 
     In the modified driver unit  20  represented in a partial view in longitudinal section in FIG. 7, the cam disk  26  carrying the curved track  21  is also designed to be axially displaceable and is guided on the bolts  29  in an axially displaceable manner. Transversely to its axial direction, the cam disk  27  is divided into a disk element  271  carrying the curved track  23  and a disk element  271  supported on the axial bearing  33  fixed in place on the spindle sleeve or drive spindle  11 . The scanning member  21  is rigidly connected with the beater  18  and projects through the axial section  41  in the spindle sleeve  11  and again is guided between the two curved paths  22 ,  23 . The two contact springs  24 ,  25  coaxially surround the spindle sleeve  11 , while the contact spring  24  is supported between the housing  10  and the cam disk  26 , and the contact spring  25  between the two disk elements  271  and  272  of the cam disk  27 . 
     The functioning of the modified driver unit  20  in accordance with FIGS. 6 and 7 is the same as that of the driver unit  20  in FIG. 1, so that in this respect reference is made to the description there.