Abstract:
An electric hand power tool with oscillating working movement, particularly translation movement, is made particularly compact and with low volume by an elastomeric module. The elastomeric module expands and/or contracts when electric voltage is applied, and is used as a drive for the hand power tool. The elastomeric module is coupled mechanically to a tool and is coupled electrically to a voltage source.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP 2009/058542 filed on Jul. 7, 2009. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is based on a hand power tool. 
     2. Description of the Prior Art 
     Very compact, small cordless hand power tools in the low to medium power class are known with a rotary working motion for drilling, screwdriving, milling, polishing, and sawing. 
     Less compact hand power tools of the medium power class have until now been designed with a translational working motion. They have rotating electric motors, which have the requisite power for the applications relevant to electric tools, such as sawing, sanding or scraping. Because of the gear that converts the rotary motion of the electric motor into a translational motion, the structural volume of these power tools is markedly greater than for hand power tools with a rotary working motion that make do without such a gear. Moreover, the hand power tools with a translational working motion lack the characteristic of a variably adjustable working stroke, which until now could be achieved only in a very complex way. 
     ADVANTAGES AND SUMMARY OF THE INVENTION 
     The advantage of the invention is that a hand power tool is provided with a drive which, for the working conditions practically required in hand power tools, makes a direct conversion of electrical energy into a translational motion possible, with the requisite adjustable stroke, frequency, power, and efficiency. 
     Because the drive employs dielectric elastomers, also called electroactive polymers, which expand and contract adjustably by up to 30% when voltage is applied, a reciprocating drive is feasible that works without the aforementioned gear that converts the rotary motion of an electric motor into a translational motion. 
     Because the drive is made from elastomers, not only its working frequency but its stroke and thus the deflections of the tool of the particular hand power tool are variously adjustable and programmable. 
     Because the drive in the form of a tube of dielectric elastomers is combined with a spring and virtually forms an “artificial muscle”, the drive forms a compact power takeoff module, and directly generates a reciprocating motion of the tool. 
     Because the drive in variants is provided with a variable thickness and winding of the elastomer, the stroke and the lifting forces can be adapted to the particular power required for the electric tool. 
     Because the drive is disposed multiple times in the opposite direction, a power takeoff rod can be driven electrically back and forth. 
     Because the drive has either a central power takeoff rod or a parallel-supported power takeoff rod that can be coupled with the drive, a small-volume special version, or an economical, larger-volume standard drive module, can be employed as needed. 
     Because the drive is used in conjunction with lithium-ion rechargeable batteries, the result is a very compact electric tool with reciprocating working motion for sawing, sanding, filing, scraping, and so forth. 
     Because the lifting rod of the saber saw is supported in pendulum fashion and is coupleable to a pendulum lifting mechanism, which imparts a pendulum motion, and in particular a pendulum motion moving forward in the working stroke, to the lifting rod during its reciprocating motion, the cutting power is better. 
     Because the lifting rod is supported in pendulum fashion and instead of being coupled to a pendulum lifting mechanism can be coupled to a further elastomer module, which drives the lifting rod in pendulum fashion during the reciprocating motion of the lifting rod, the pendulum stroke is reliably and variably controllable and programmable. 
     Because the lifting rod, on its upper end, has an oblong slot through which a pendulum shaft extends, about which the lifting rod is guided, in a manner capable of swinging like a pendulum in the advancement direction, the pendulum motion can be attained precisely and securely, attained at little effort or expense. 
     Because at least one pendulum roll is disposed for bracing on the sawblade spine for imparting the pendulum stroke, in particular in synchronism with the lifting motion of the lifting rod, the sawblade is guided especially securely in the workpiece engagement during the active pendulum stroke. 
     Because the pendulum roll is driven to move in pendulum fashion via its own drive, in particular via an elastomer module, the pendulum stroke can be regulated variably, independently of the sawing stroke of the lifting rod and adapted to that stroke. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in further detail below in terms of an exemplary embodiment, in conjunction with the associated drawings, in which: 
         FIG. 1  shows a longitudinal section through a saber saw of the invention without pendulum motion; 
         FIG. 2  shows a saber saw of  FIG. 1  with mechanical pendulum motion; and 
         FIG. 3  shows a saber saw of  FIG. 1  with electrical pendulum motion. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The cordless saber saw  10  shown in longitudinal section in  FIG. 1  has a housing  12  with a pistol grip  14 , which toward the bottom has an outward-protruding switch button  16  for switching a drive module  24  of the saber saw  10  on and off, and a rechargeable battery  18  on the inside, in particular a lithium-ion battery, for operating the drive module  24 . 
     The housing  12  is supported, positionably pivotably by at least 45° to either side for mitering cuts on a base plate  36  with a pivot joint  40  about a pivot axis  38 , which determines the advancement direction, for mitering cuts. The various pivoting positions of the housing  12  relative to the base plate  36  are releasably lockable by means of locking means  42  not further described. 
     The drive module  24  comprises a tubular elastomer module  23 , which contains a tube of dielectric elastomer. This module, together with a compression spring  26 , concentrically surrounds a lifting rod  22  and jointly with the spring  26  is braced axially on a piston  25 , which is coupled mechanically to the lifting rod  22  and in particular surrounds the lifting rod concentrically and nondisplaceably. 
     The elastomer module  23  is coupled electrically with the battery  18 , and an electronic unit  44 , which converts the voltage of the battery  18  to a high voltage and assigns it to the elastomer module  23 , is connected between the battery  18  and the elastomer module  23 . This electronic unit  44 , for instance after the actuation of the switch button  16 , contracts or expands with an adjustable stroke under high voltage—or after the high voltage is shut off and/or after short-circuiting of the elastomer, the elastomer module  23  expands counter to the force of the spring  26  with an adjustable stroke, or contracts again—depending on the type of elastomer—and in the process carries the piston  25  and thus the lifting rod  22  along with it with a variably adjustable stroke with rectilinear displacement. 
     When high voltage controlled via the electronic unit  44  or the like is applied, the elastomer module  23  works back and forth and jointly with the compression spring  26  of the lifting rod  22  imparts an oscillating lifting motion, which is suitable for reciprocating sawing work, to the saber saw  10 . 
     The lifting rod  22  is supported, displaceable up and down, in one upper and one lower lifting rod bearing  28  each. On its lower end, the lifting rod  22  has a retaining device  32 , known per se, for retaining a saber saw blade  34 , known per se, which can be used for sawing given a suitable lifting motion of the lifting rod  22 . 
     The elastomer module  23  is electrically connected via the switch button  16 , or short-circuitable by means of the switch button  16 , to the battery  18  and the following electronic unit  44 . The current supply can be made by means of arbitrary types of batteries, or for instance by means of a power cord. 
     The drive of the saber saw can also be represented with two contrarily disposed elastomer modules, which are connected in alternation to a voltage and thus realize the oscillating motion of the lifting rod without an intervening spring. 
     The compression spring  26 , depending on the type of elastomer, can also be designed as a tension spring. 
     The saber saw  100  shown in  FIG. 2  essentially matches the saber saw  10  of  FIG. 1  and differs from it only in terms of a pendulum lifting mechanism  46  associated with the lifting rod  221 . For that purpose, the lifting rod  221  is supported pivotably by its upper, lengthened end  21 , about a pendulum shaft  50  which is structurally connected to the housing and extends at the top transversely to the pivot axis  38 . For that purpose, the pendulum shaft  50  extends through an oblong slot  52  in the upper end  21  of the lifting rod  221 , so that the lifting rod, in its up-and-down motion is movable in pendulum fashion additionally in a plane defined by the advancement direction. To that end, the lifting rod bearings  28 , jointly with the lifting rod  221  and the drive module  24 , are supported drivably in pendulum fashion in the housing  12  by means of the pendulum lifting mechanism  46 , represented only by a symbol, so that the lifting rod  221  in the upward stroke moves in pendulum fashion in the advancement direction. 
     The saber saw  101  shown in  FIG. 3  differs from the saber saw  10  of  FIG. 1  only in terms of the pendulum drive of the lifting rod  221 . Instead of a pendulum lifting mechanism, there is a second elastomer module, in the form of a pendulum module  54 . It imparts a transverse motion with an adjustable stroke in the advancement direction counter to the pendulum spring  56  to the lower lifting rod bearing  28  in the upward stroke of the lifting rod  221 , so that in the downward stroke the reverse stroke is imparted to the lifting rod  221  by the pendulum spring  56 . To that end, the lifting rod  221  is supported pivotably by its upper, lengthened end  21  about the pendulum shaft  50 , structurally connected to the housing and extending at the top transversely to the pivot axis  38 , and for that purpose this pendulum shaft reaches through the oblong slot  52  in the upper end  21  of the lifting rod  221 . 
     Ideally, the saber saws  10 ,  100  and  101  have an adjustable stroke of approximately 1 to 10 mm, and the battery  18  is approximately 80 mm long, and the lifting rod with the integrated drive module  24  is approximately 100 mm long. As a result, with high power potential, the result is extremely compact dimensions of the saber saws. 
     Preferably, the saber saws  100  and  101  have a pendulum roll for bracing on the sawblade spine for transmitting an especially efficient pendulum stroke directly to the sawblade. 
     In further variants according to the invention of a saber saw, a conventionally driven saber saw, instead of a pendulum mechanism, has an elastomer drive module, or a saber saw with an elastomer drive module for driving the lifting rod has a piezoelectric drive for the pendulum motion of the lifting rod. 
     To generate reciprocating rotary motions of a power takeoff shaft for sanding and sawing, suitably disposed elastomer modules with the following lifting rod gears can also be employed to replace a conventional motor with an eccentric gear. 
     The use of the elastomer drive modules is also advantageous for driving a scraper or for generating the reciprocating motion of a rotary hammer power takeoff shaft for chiseling. 
     In a further, advantageous embodiment, a tool has high deflection frequencies at low amplitudes, and low deflection frequencies at high amplitudes—depending on the magnitude of the voltage applied and on the resultant stiffness of the elastomer. This kind of design allows the use of manifold working tools, such as sawblades, sanding attachments, chisels, and scraper inserts. 
     The foregoing relates to the preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.