Abstract: A cover which covers outer peripheries of fastening screws are disposed on an outer periphery of a hammer case. A stopper which detachably positions and fixes the cover to the outer periphery of the hammer case is disposed.

Abstract: A powered hammer includes a housing, a tool holder coupled to the housing and configured to hold a tool, a motor within the housing, a piston slideably mounted within the housing, a drive mechanism that converts rotary output of the motor into a reciprocating motion of the piston, a ram slideably mounted forward of the piston and that is reciprocatingly driven by the piston, and a beat piece support mounted in the housing forward of the ram. A beat piece is slideably supported by the beat piece support. The beat piece is repetitively struck by the ram and that in turn repetitively strikes an end of a tool when the tool is held in the tool holder to transfer the momentum of the ram to a tool. The beat piece support includes a seal that is slidingly engaged by the beat piece. The seal includes an absorbent material.

Abstract: It is an object of the invention to provide an improvement in ease of operation of a driving mode switching mechanism in a hammer drill. According to the invention, a representative hammer drill includes a driving mode switching mechanism which has an operating part, a first switching member and a second switching member. The operating part can be turned to at least three rotating positions in its circumferential direction, while the operating part can be turned 360° on the rotation axis in the both directions. Thus, the user can select the desired driving mode in the shortest turning distance without passing though an unnecessary driving mode position. Therefore, ease of operation in mode change can be enhanced.

Abstract: In a driving tool, a diameter of an intermediate member is enlarged to increase a mass of the intermediate member and an outside diameter of a cylinder at a position where the intermediate member is internally provided is enlarged in accordance with the enlarged diameter of the intermediate member. Further, in the driving tool, a bearing thickness of a ball bearing is reduced correspondingly to a dimension of the enlarged outside diameter of the cylinder and a washer is provided at a part where the ball bearing abuts on the cylinder in the forward and backward moving direction thereof.

Abstract: The invention provides a power tool which includes a tool bit, a first operating mechanism that linearly drives the tool bit and thereby causes the tool bit to perform a predetermined operation, and a dynamic vibration reducer 151 that reduces vibration in the operation of the tool bit. The dynamic vibration reducer includes a weight 153 that can linearly move under the action of biasing forces of a plurality of biasing springs 157 acting upon the weight 153 toward each other. The weight 153 is driven by a second operating mechanism 116 that mechanically excites at least one of the elastic elements, via the elastic element.

Abstract: It is an object of the invention to provide a technique which is effective in improving the durability of an angular positioning device of a tool bit and in reducing weight of a tool body in an impact tool. A representative impact tool includes a tool body, a lubricant sealed in the housing space, a driving mechanism, a tool holder, an angular positioning device disposed on a tip end side of the tool body and serves to fix a position of the tool bit around the axis with respect to the tool body. The angular positioning device includes first and second locking members. The first locking member is disposed between the tool body and the tool holder. The second locking member is disposed opposite to the first locking member. One end of the first locking member in the axial direction of the tool bit extends into the housing space of the tool body and is connected to the tool body within the housing space.

Abstract: The invention is based on a power hand tool, in particular a hammer drill and/or hammer chisel, with a percussion unit (10), which comprises a tumble bearing unit (12) with a tumble body (14) and also a piston (16). It is proposed that the power hand tool comprises at least two bearing locations (18, 20; 22, 24) arranged in parallel in the force of flux, by means of which the tumble body (14) is coupled to the piston (16).

Abstract: It is an object of the invention to provide a technique for further improving the vibration reducing performance in an impact tool. A representative impact tool includes a tool body, a cylinder housed within the tool body, a dynamic vibration reducer having a weight that linearly moves under a biasing force of an elastic element, wherein the dynamic vibration reducer reduces vibration of the tool body during hammering operation by the movement of the weight in the axial direction of the tool bit, and a mechanical vibration mechanism that actively drives the weight by applying external force other than vibration of the tool body to the weight via the elastic element. The weight and the elastic element are disposed on the axis of the tool bit and between an inner wall surface of the tool body and an outer wall surface of the cylinder in such a manner as to cover at least part of the outer wall surface of the cylinder in the circumferential direction.

Abstract: A hammer drill includes a body, a motor; a centre of gravity, and a hammer mechanism driven by the motor in reciprocating movement along a hammer axis at a first distance from the centre of gravity. A counter mass is mounted within the body for sliding movement along a slide axis at a second further distance from the centre of gravity. A biasing member biases the counter mass to a mid-position along the slide axis. The biasing means may be a leaf spring or a helical spring. The counter mass may be slideably supported on rods and may be able to twist about a number of axes.

Abstract: A hammer drill with rolling contact at the contact surfaces for transmission of axial force between a drive shaft and wave race. By using roller bearings, line contact is obtained. The area of contact is thus close to zero as opposed to a relatively large area in engagement systems using toothed surfaces. Use of point or line contact reduces heat generation and reduces energy loss due to friction.

Abstract: Self drilling anchors and related methods and apparatus. In one embodiment an apparatus comprises a drill bit, a hammer mechanism for hammering the drill bit in a first direction and in a second direction, and a selection mechanism for controlling whether, at a given point in time, the drill bit is hammered in the first or second direction.

Abstract: A preferred embodiment of a rotary tool reciprocating motion conversion attachment for a rotary power hand tool is described which is configured to be attached to a nose portion of the hand tool housing. The attachment has a rotary drive train in a housing that is connectable to the output shaft of the hand tool, the drive train driving a barrel cam having an exterior cam groove. A cam follower rides in the cam groove and produces reciprocating motion, with the cam follower being part of a cam follower assembly to which an implement holder is attached. The preferred embodiment has a cam groove configuration which causes the implement holder to move slower during a cutting stroke and faster during a return stroke, thereby tending to optimize the operation of the cutting implement. The preferred embodiment also includes a planetary gear set for reducing the rotational speed of the hand tool output shaft to reduce the speed of reciprocation of the attachment.

Abstract: A hand-held power tool includes a percussion mechanism (3) arranged in the tool housing (2), and a motor (4) for driving the percussion mechanism and connected therewith by a gear unit (5), with the percussion mechanism including an eccentric (6) a piston (7), and a connection rod (21; 41) connecting the eccentric with the driving piston (7) and having a first part (22; 42) connectable with the eccentric (6), a second part (23; 43) connectable with the drive piston (7) and telescopically displaceable relative to the first part (22; 42), and a spring for damping vibrations occurring during operation of the power tool and arranged between the first (22; 42) and second (23; 43) parts.

Abstract: An automatic reduction-ratio changing apparatus comprises a planetary gear mechanism including a sun gear, planet gears, and an internal gear. When a load, which exceeds a predetermined torque, is applied to the internal gear, a pawl of a lock lever is engaged with a ratchet section of a housing to stop the rotation of the internal gear and lock the internal gear. When a displaceable member of an actuator is displaced from an outward route to a homeward route, the rotation of a motor is reversed, and an input shaft and a cam are rotated in a reverse direction to release from the locked state. Accordingly, the speed reduction ratio, which is transmitted from an output shaft to the actuator, is automatically switched.

Abstract: A power tool (10) with a housing (12) which accommodates a driven shaft (32) for holding a material-removing tool (40) and which sets the driven shaft into rotary oscillating motion capable of being produced by an eccentric (22) rotating around an axis extending at a right angle to the driven shaft (32), the eccentric engaging in a connecting element coupled with the driven shaft (32), is usable in a more diverse manner because the rotary oscillating motion of the driven shaft (32) and, therefore, the tool (40), is adjustable with a certain travel and is therefore adaptable to special applications.

Abstract: A cover which covers outer peripheries of fastening screws are disposed on an outer periphery of a hammer case. A stopper which detachably positions and fixes the cover to the outer periphery of the hammer case is disposed.

Abstract: Power tools of the type under consideration include hammer drills, for example, which are electric or battery powered and includes two modes of operation: a rotation mode and a rotation-hammer mode. A manually operable selector lever enables the hammer drill to be selectively operated in one of the two modes by disengaging and engaging a hammer mechanism. In rotation-hammer mode, the drive shaft of the hammer drill rotates a tool element about a rotational axis and oscillates the tool element along a rotational axis. An attachment mountable within the chuck of a hammer drill prevents a tool element from rotating when the hammer drill is operating in rotation-hammer mode. The hammer drill attachment transfers hammer action, but not rotation, to the tool element. The hammer drill attachment enables dual function power tools to be operated in a hammer only mode to perform a function, for example, chiseling.

Abstract: An apparatus for providing percussion action in a rotary power tool having a rotary output shaft, the apparatus comprising at least one moveable mass adapted to have a component of movement parallel to the axis of the rotary output shaft to cause impacts to be applied to a working member of the tool; and a device for intermittently converting rotary movement of the rotary output shaft into movement of at least one the moveable mass to cause the impacts to be applied to the working member.

Abstract: An electrically powered hammer comprising a hammer housing (10,15) with a hollow cylindrical spindle (4) mounted within it and an air cushion hammering mechanism mounted within the spindle for generating repeated impacts on a tool or bit of the hammer which hammering mechanism includes a piston (24). A rotatingly driven intermediate shaft (6) is rotatably mounted in the housing and a wobble drive arrangement (12, 16, 18, 20) reciprocatingly drives the piston (24). The wobble drive arrangement includes a wobble sleeve (12) rotatably mounted on the intermediate shaft (6) and a wobble bearing (14, 16, 18) on the wobble sleeve. A support bearing (46, 42) for the intermediate shaft is mounted on the wobble sleeve forwardly of the wobble bearing assembly. The support bearing (46, 42) comprises a bearing ring (46) and the bearing ring is formed with a peripheral flange which can be fixed to a housing part (10) of the hammer housing (10,15).

Abstract: An impact tool enables a front cover part to be easily attached to and detached from a housing body, with a device having a simplified structure. The front cover part has an annular fastening portion clamped to the outer peripheral surface of a front edge portion of the housing body, a cylindrical portion extending from the front end of the housing to the region of the fastening portion, and a connecting portion connecting together the cylindrical portion and the fastening portion. The fastening portion is split at a circumferential part thereof to form a pair of circumferentially opposing tongue-shaped portions. A clamping device is provided between the tongue-shaped portions, which is movable between a clamping position where it pulls the tongue-shaped portions toward each other and an unclamping position where the tongue-shaped portions are released from being pulled toward each other.

Abstract: The invention is based on a hand power tool, in particular a drill- and/or chipping hammer, comprising a striking mechanism (10) that has a drivable pot-type piston (12) with at least one idle opening (14). It is proposed that the idle opening (14) is capable of being closed via a controllable, separate closing element (16).

Abstract: An electrical tool includes a housing having inlet (7) and outlet (8) openings, a brushless electric motor (2) and an inverted rectifier (3) both arranged in the housing (9) between inlet (7) and outlet (8) openings in an air stream (5) of an air volume (6), and a link condensator (10) located in the housing (9) in the air stream (5), with the inverted rectifier (3) being arranged, in the air flow direction, downstream of the link condensator (10) and upstream of the electric motor (2).

Abstract: An electrical tool includes a housing having inlet (7) and outlet (8) openings, a brushless electric motor (2) and an inverted rectifier (3) both arranged in the housing (9) between inlet (7) and outlet (8) openings in an air stream (5) of an air volume (6), and a link condensator (10) located in the housing (9) in the air stream (5), with the inverted rectifier (3) being arranged, in the air flow direction, downstream of the link condensator (10) and upstream of the electric motor (2).

Abstract: A driving tool includes a block and an impactor received in a front and a rear chambers of a handle, a driving shank attached to the block, and a plunger engaged between the block and the impactor. The impactor includes a cavity formed in one end for selectively receiving the tip of the plunger and for impacting onto the plunger and the block and the driving shank when the tip of the plunger is aligned with and engaged into the cavity of the impactor. The block has a guide device for guiding the block and the driving shank to rotate relative to the handle.

Abstract: Disclosed and taught is a novel drive mechanism for a cyclic operating tool employing an energized flywheel to provide the necessary energy to perform a working cycle. The drive mechanism disclosed is particularly useful in hand tool applications such as a hand held nailing machine. The flywheel may be energized by a corded or battery powered motor. The herein disclosed mechanism teaches a novel pair of ball ramp cam plates wherein a first pair of ball ramps cause an initial engagement of a clutch with the energized flywheel whereupon rotation of the clutch causes activation of a second pair of ball ramps which affect compression of a spring which acts to increase the pressure applied to the clutch thereby assuring a slip free engagement between the clutch and he flywheel throughout the working cycle of the drive mechanism.

Abstract: In a conventional impact generator, a grease receives centrifugal force by the rotation of a rotary member, thereby keeping away from surfaces of the rotary member and a weight. Consequently, insufficient lubrication is caused between the weight and a member (for example, a tappet and the like) which comes in contact with the weight. An impact generator D comprises an impregnating member 60 capable of impregnating the grease. The impregnating member 60 is extended from a vicinity of an inner peripheral wall surface 59 of a chamber E1 for accommodating a rotary member 10 and a weight 30 to a position where the impregnating member 60 comes in contact with the weight 30 performing a circular motion.

Abstract: A split tool tamper having a motor, a frame, a single tool shaft, and a tamping tool. The motor is coupled to the frame and the tool shaft is coupled to the motor. The tool shaft is further coupled to a single tamping tool.

Abstract: A mechanical hammer for sculptors, comprising a body (1) suitable for being handled, a striking element (5) that slidingly engages in the body (1); a tool (6) releasably engaging with a first end of said striking element (5) accessible from the exterior of the body (1); a rotating element (10) that pivotally engages in the body (1) having a first end connected to rotating drive means located at the exterior of the body (1); cooperating means provided at the second end of the striking element (5) and of the rotating element (10), both inside the body (1), for transforming the rotating motion of the rotating element (10) into a reciprocating motion of the striking element (5) under to load through the tool (6).

Abstract: A rotary impacting apparatus is provided that includes a housing, a rotor rotatable about an axis, a main reciprocative implement and an impact member. The impact member is arranged to exert an impacting force on the main reciprocative implement when the main receprocative implement is advanced relative to the axis. The rotor is supported by the housing via needle bearings.

Abstract: A portable apparatus for driving a post into the ground is provided in an embodiment. The apparatus has a base removably attachable to the post as well as a hammer module tethered to the base to permit vertically reciprocating motion of the module relative to the base and post. The apparatus may be motor driven with rotating, eccentrically mounted cams providing the mechanism for creating a hammering force through reciprocating motion. The hammer module has a face which imparts the hammering force to the top of the post. A method for using such an apparatus is provided in a further embodiment.

Abstract: An electric tool including a hammer mechanism (9), a drive motor (11) for driving the hammer mechanism (9), a gear (10) for connecting the drive motor (11) with the hammer mechanism (9), a ventilator wheel (7) provided in an end region of the drive motor (11) remote from the gear (10) and connected with an exhaust opening (8), and separate air channels (3,4) having each a suction opening (5,6) and ending at a side of the wheel (7) adjacent to the drive motor (11), with one of the air channels (3) being associated at least with the gear (10), and another of the air channels (4) being associated at least with the drive motor (11).

Abstract: A hand-held pneumatic impact tool and method of controlling the same for use in fine hand working operations includes a handpiece, a foot-operated flow control valve and a hand operated flow control needle valve. The handpiece includes a housing having a cavity and annular shoulder accommodating a stepped piston dividing the cavity into three chambers. The design provides a means to oscillate a piston without delivering impacts and to oscillate the piston with varying amounts of impact energy.

Abstract: A power tool has a drive mechanism with an output shaft which performs an intermittent rotary motion. The output shaft drives, via an overrunning clutch, a tool drive shaft to drive a tool, which thus performs a quasi-continuous rotary motion that, as the load on the machine increases, transitions increasingly into a discontinuous rotary motion. The power tool can advantageously be used as a hand-held power tool for screwing, drilling, sawing, sanding, and the like, a high output torque with a low reaction torque being achievable as a result of the intermittent drive mechanism.

Abstract: A hammer mechanism (14) for a rotary drill (10) comprises a hollow piston (18), a drive (15,26) for effecting reciprocating motion of the piston (18) towards and away from an end portion (35) of a rotatable output spindle (13) of the drill (10) and a ram (21) adapted to slidably locate in a hollow portion of the piston (18). In use, reciprocating movement of the piston (18) is transferred to the ram (21) and the ram (21) periodically strikes the end portion (35) of the output spindle (13), thereby providing the hammer action of the drill. The hammer mechanism (14) also comprises a plurality of guide pins (27,28) fixed in position relative to a housing portion (11) of the drill (10), the piston (18) being provided with a plurality of guide cylinders (23,24) each one of which is adapted to cooperate with a corresponding one of the guide pins (27,27) so as to guide the reciprocating motion of the piston (18).

Abstract: An airflow regulation arrangement for regulating the impact of the strikes delivered from a striking member (6) to an intermediate member (10) and a bit, thus reducing the vibration, and also for regulating the impact of recoils of the striking member (6) is disclosed for use in an electrical hammer (1). The airflow regulation arrangement comprises an air inlet (14) provided in an air chamber (5) in a cylinder (3) of the electrical hammer (1), exhaust ports (15) provided in a second air chamber (9), and air passages (16) in communication with the air inlet (14) and the exhaust ports (15). The air passages (16) are connected to choke passages (17), the cross sectional area of which is one fifth to one sixth of that of the air passages (16).

Abstract: A rapping hammer system adapted for periodically rapping and cleaning tubes of a heat exchanger unit to remove undesired deposits from outside the tubes. A plurality of rapping hammers are each pivotably attached to a radial arm extending outwardly from and spaced apart along a rotatable shaft. A spring device is attached to each radial arm and arranged to contact the rapping hammer with sufficient force so as to substantially restrain repeated striking movements of the rapping hammer against an impact stem of the heat exchange unit following an initial impact of the hammer. A method is also disclosed for operating the rapping hammer system for periodically rapping and cleaning the outside surface of heat exchanger tubes such as boiler tubes of accumulated ash and soot deposits.

Abstract: An apparatus is provided for delimbing tree limbs of a felled tree including housing structure constructed and arranged to be movable to a tree processing location. Support and feeding structure is constructed and arranged with respect to the housing structure to support a stem portion of the tree while a limb thereof is severed and to move the stem portion progressively through the housing structure. Blade structure is mounted on the housing structure and is constructed and arranged to move into engagement with a limb. Impact hammer structure is operatively coupled to the blade structure such that successive impacts generated by the impact hammer structure on the blade structure move the blade structure progressively thorough a limb.

Abstract: A hammer drill has a three-part hammering sleeve. A hardened tool socket is attached to a guide tube made of unhardened steel by an axial connection. For connection to the driving gearwheel, the guide tube furthermore carries a latching ring fixed on the guide tube by three rollers which make possible good torque transmission. This construction has the advantage that it is no longer necessary to harden the entire hammering sleeve but only the tool socket and the latching ring. The guide tube can be composed of soft steel. The connections and ensure large-area transmission of force, wear on the soft guide tube caused by conventional connection techniques thereby being avoided.

Abstract: In a ram boring machine that has a striking piston reciprocating in a tubular housing and a striking tip that may be formed as a chisel and projects from the housing, connection of the striking tip to the housing by means of a bayonet joint makes installation and removal or replacement of the striking piston or a worn chisel possible in a simple manner.

Abstract: The hydraulic jackhammer is provided with a rotor turbine which is driven by a liquid stream in order to activate the tup for driving against a jumper rod. After passing by the turbine rotor, the liquid stream is mixed with air and passed through a nozzle into a guide channel under pressure in order to cool the casing. Some of the liquid-air mixture is passed through the hollow jumper rod for spraying onto a jumper bit and sprayed onto the rock being drilled.

Abstract: The yam device has a plurality of guides and a striking mass which is movable so as to be displaceable thereat by means of a hydraulic cylinder, wherein the hydraulic cylinder is arranged with its longitudinal axis outside the path of the center of gravity of the striking mass. The striking mass can comprise a first elastomeric and/or plastic component and a second heavy metal component. Three guides which can be parallel to the movement path of the center of gravity are provided for the guidance of the striking mass, the striking mass is preferably constructed so as to be guided at its respective end areas. The ram device and the striking mass preferably have a symmetry plane defined by the axis of the hydraulic cylinder and the movement path of the center of gravity and the guides located out of the symmetry plane are arranged in two planes which are at an angle of 120.degree. or less relative to each other and symmetrically disposed on each side of the symmetry axis.

Abstract: This invention relates to a device for driving a drilling or percussion tool having a spindle that rotates with respect to a housing. One end of the spindle is adapted to fasten to a tool piece and the other end is connected to an osciliating percussion body movable in the housing by means of a guideway. A drive shaft rotates the tool spindle into rotation or actuates the percussion body via a transmission that is provided with means for converting the rotary motion of the drive shaft into an oscillatory motion of a drive member. The drive member is connected to the percussion body through an elastic member having a non-linear spring characteristic.

Abstract: An improved pneumatic impact imparting tool includes a follower which is slidably accommodated in a recess formed on the inner end part of a rotor in a pneumatic motor. The follower is formed with a projection for moving a ball around a cam face as it is rotated together with the rotor. When the ball reaches the peak of the cam face, the follower is displaced in the axial direction and enters a recess formed on the inner end part of an anvil and collides therein against stoppers formed in the recess. Thus, rotational movement of the rotor is transmitted to the anvil in the form of intermittent turning movement of the latter.

Abstract: A rotary hammer has a hammer body with an electric motor section which comprises a receiving section for receiving transmission mechanisms in a frame which serves as a shell barrel. A driving electric motor is installed in the shell barrel. The body also has a vibration and transmission mechanism section in which the transmission mechanisms including the motion conversion transmission mechanism and the vibrating mechanism are held by a bracket removably connected to the frame. In addition, the hammer body has a tool holding section in which the tool holding member for concomitantly rotatably holding the tool is rotatably supported by a bracket removably connected to the frame. The three sections are so arranged that they can be assembled and disassembled individually as separate component units.

Abstract: An extractor for removing worm elements which are fastened for rotation on the worm shaft of a worm extruder wherein a frame formed of longitudinal and cross members has a locking device in one of the cross members for holding the worm elements and an opposed, displaceable, pneumatic piston-cylinder unit on another cross member. The piston-cylinder unit has a pressure piston which is extendable axially towards the worm shaft. Between the worm shaft and the piston-cylinder unit is a slide which is displaceable longitudinally and can be engaged by the piston of the piston-cylinder unit. The slide carries an impact device which is pneumatically actuatable and includes an impact shaft for engaging the worm shaft. The locking device includes two clamp jaws which are axially aligned with the impact shaft and the piston and engage the worm profile with an inner profile surface of identical type.

Abstract: An angular attachment to a rotary and percussive power machine, such as a hammer drill, includes a rotary power input tubular member driven by a rotary part of the power machine, a tubular power output supported for rotation at an angle relative to the axis of rotation of the power input member and including a holder for a rotary and percussive work tool. The tubular power input and output members are interconnected by an intermediate power transmission. A device for transmitting impacts from the percussive part of the power machine includes two guiding channels arranged in alignment with central bores of the tubular power input and output members and each enclosing at least one impact deviating element. The impact deviating elements are in sliding engagement with each other and with a corresponding coupling member arranged in respective contact bores of the power input and output members.

Abstract: The present invention relates to a new and improved piezoelectric high voltage impact mechanism including a hollow housing means having groove means with two portions and a shoulder portion at their juncture, provided on its inner surface, an actuator means having two projections slidably received in the upper portion of the groove means, a hammer means with two lug members movably received in the lower portion of the groove means and an actuating spring means torsionally connecting the actuator means and the hammer means so that the hammer is held on the shoulder in the housing as actuation is initiated. Energy is stored in the spring during actuation and the actuator pushes the hammer off the shoulder, initiating an impact in a straight-line avoiding unnecessary dispersal of energy and ensuring a stable high voltage pulse.

Abstract: A device for driving a drilling and/or impacting tool including a shaft journalled in a housing so as to be rotatable, if necessary. One end of the shaft is connectable with the tool whereas the other end is accessible for an oscillatory impact body movable in the housing by a guide, a rotatable driving shaft setting and a transmission. The transmission includes a device for converting the rotary movement of the driving shaft into an oscillatory movement of a driving element which is connected through an elastic member with the impact body.

Abstract: A device for driving a drilling and/or impacting tool including a shaft journalled in a housing so as to be rotatable, if necessary. One end of the shaft is connectable with the tool whereas the other end is accessible for an oscillatory impact body movable in the housing by a guide, a rotatable driving shaft setting and a transmission. The transmission includes a device for converting the rotary movement of the driving shaft into an oscillatory movement of a driving element which is connected through an elastic member with the impact body.

Abstract: This invention relates to a device for driving a drilling or precussion tool having a spindle that rotates with respect to a housing. One end of the spindle is adapted to fasten to a tool piece and the other end is connected to an oscillating percussion body movable in the housing by means of a guideway. A drive shaft rotates the tool spindle into rotation or actuates the percussion body via a transmission that is provided with means for converting the rotary motion of the drive shaft into an oscillatory motion of a drive member. The drive member is connected to the precussion body through an elastic member having a non-linear spring characteristic.