Abstract:
A method for producing impacts from rotary motion, the method including: inputting the rotary motion to an input shaft, converting the rotary motion to a linear motion; storing potential energy in one or more elastic elements resulting from the linear motion; and releasing the stored potential energy when the stored potential energy reaches a predetermined level to accelerate an impact mass to produce the impact.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    The present disclosure relates generally to chisels, and more particularly to chisel or hammer head attachments for portable electrical drills, portable electrical screw drivers, drill presses, and the like with changeable chisel tools or the like. 
         [0003]    2. Prior Art 
         [0004]    Chisels are used for breaking bricks or concrete blocks or the like; for roughing concrete or bricks; for driving rods into the ground; for scaling, chipping or chiseling; for caulking, tuck pointing, and removing old mortar; for light demolition; for cutting slots between holes; for removing scale, rust, and weld splatter; for digging in hard clay, packed dirt, or gravel; for cutting asphalt or hard ground; for removing tile and other various debris from floors; and the like. Manual chisels are very easy to use and is usually one of the most common tools that both professional and casual users. Electrically driven chisel units on the other hand are relatively large and expensive and are used mainly by professional users who routinely require the tool for their work. 
         [0005]    In current electrically operated chisel units, the rotary motion of an electrical motor is used to provide a reciprocating motion of a hammer via a mechanism such as a crank shaft type or the like. The generated reciprocating motion is then used to drive a hammer mass to impact an anvil to which the chisel head is attached and is generally provided with sliding guides and relatively soft return springs. The hammer impact will then drive the chisel head forward to impact the intended surface and return quickly to or close to its rest position via the return spring before it is impacted again. In certain electric chisels the hammer mass is attached to the reciprocating mechanism via a spring to reduce the transmission of the impact shock load during hammer to anvil and the chisel impact to the operator. 
         [0006]    In general, the relative size, weight and cost of such electrically driven chisel units makes them unattractive to very casual users or professional users who may rarely need the device, particularly if they have to carry it from job to job, particularly for light chiseling work. 
         [0007]    A need therefore exists for relatively light weight, small and inexpensive electrically driven chisels, particularly for use by casual users and for professional users who may rarely need the device, particularly if they have to carry their tools from job to job or the like. 
         [0008]    It is the object is to provide a method and related device designs for the development of highly effective chisel head attachment units, hereinafter referred to as “chisel head attachment units”, that are relatively small and lightweight and inexpensive that can be readily attached and/or directly driven by commonly used portable electrical drill units and electrical screw drivers. 
         [0009]    It is also the object to provide methods and related device designs for the development of chisel head attachment units in which the driving electrically driven drill units or electrical screw drives would input mechanical energy into the units which is stored in potential energy storage spring(s) and are then released after the level of stored potential energy has reached a prescribed level, a “hammer” against which the potential energy storage spring element(s) are preloaded (in one or combination of compression, tension, bending and/or torsion) is released. As a result, at least a portion of the potential energy stored in the potential energy storage spring element(s) is transferred to kinetic energy of the hammer element. The hammer element would in turn impact at least one translating or rotating chisel head, thereby providing it with a forward momentum for impacting the intended target surface. 
         [0010]    It is another object to provide methods and related device designs for the development of chisel head attachment units in which the prescribed level of generated impact force, i.e., the aforementioned prescribed level of potential energy stored in the device potential energy storage spring element(s), is readily adjustable by the user and is essentially independent of the type and power of the electrically drivel drill unit or electrically driven screw driver unit that is used to drive the present chisel head attachment units. 
       SUMMARY 
       [0011]    Accordingly, methods and related device designs are provided for the development of chisel head attachment units for electrically driven drills and electrically driven screw drivers with the capability of providing the means of adjusting the generated impact force levels to a desired level with a certain range. 
         [0012]    The electrically driven drills and screw drivers may be of portable type that is driven by the AC power outlet or be driven by rechargeable batteries. The chisel head attachment unit may be similarly attached to the drill head of a drill press to provide the described chisel impacting action. 
         [0013]    The disclosed chisel head attachment unit is comprised of: a body within which the device mechanisms are housed. The chisel head attachment unit body can be provided with a handle, such as a folding type, that the user hold with one hand to counter the rotational torque transmitted to the unit body as is described later in this disclosure and also for positioning the chisel at the desired positioning with respect to the surface to be impacted and for guiding over the desired path over the target surface. Alternatively, the chisel head attachment unit body may be provided properly formed surfaces to allow the user to directly hold the unit body in one hand. The latter design is particularly suitable for relatively small chisel head attachment units. 
         [0014]    The driving electrical drill or screw driver chuck is then engaged to the head chisel attachment unit input drive, which can be formed with a hexagonal or similar cross-section for ease of being secure held to the drill or screw driver chuck. Commonly used hex-head adapters may also be used on electric screw drivers for quick engagement to and disengagement from the present chisel head attachment units. 
         [0015]    The rotation of the chisel head attachment unit input drive is transmitted to a (potential energy storage) spring system preloading mechanism directly or via a speed reducing gearing to amplify the level of input torque. The input torque amplification mechanism would provide the means of achieving higher levels of force/torque for preloading the potential energy storage spring element(s), thereby to store larger amounts of potential energy in the spring elements(s). As a result, higher levels of chisel impact forces can be achieved. The speed reducing gearing is particularly necessary for chisel head attachment units that are required to provide high levels of chisel impact forces. 
         [0016]    As the potential energy storage spring elements are preloaded, the spring system force/torque is directed to press on a hammer mass, which is prevented from moving in response to the applied force/torque via a provided stop element. Then as the input drive of the chisel head attachment unit is rotated a prescribed amount, thereby preloading and storing a prescribed amount of potential energy in the spring elements, the aforementioned hammer mass stop is pulled away, thereby allowing a portion such as a very larger portion of the potential energy stored in the spring elements to be transferred to the hammer mass as kinetic energy. The hammer mass element is then accelerated towards an anvil and impact the anvil and causes it to travel forward within a provided guide (or rotate for rotary type of chisel head attachment units). The chisel end (which can be separate chisel ends used for one or more of the aforementioned tasks) are directly and fixedly attached to the opposite end of the anvil element and together with the anvil element is provided with a forward momentum for impacting the intended target surface. The anvil element is also provided with a relatively light spring to bring it back to or towards its pre-impact rest position following each hammer impact. 
         [0017]    The amount of chisel head attachment unit input drive rotation that causes the aforementioned hammer mass stop to be pulled back and release the hammer mass is adjusted by manually positioning the “stop engagement end” that is provided in the chisel head attachment mechanism. 
         [0018]    It is appreciated by those skilled in the art that similar but in general smaller levels of chisel impact can be achieved by using input torque amplification other than gearings, for example by using a cam or a linkage type mechanism. 
         [0019]    It is also appreciated by those skilled in the art that in certain applications, for example for roughing a concrete or other similar surface, only relatively low levels of chisel impact levels are required. For such applications, the torque amplification mechanisms such as gearing, cams or linkage mechanism type mechanisms are not required. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    These and other features, aspects, and advantages of the apparatus will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
           [0021]      FIG. 1  illustrates the schematic overall view of a chisel head attachment unit and a typical portable electric drill or screw driver and their engagement mechanism. 
           [0022]      FIG. 2  illustrates the schematic of the basic impact generating mechanism of one embodiment of the chisel head attachment unit. 
           [0023]      FIG. 3  illustrates the schematic of an alternative embodiment of the basic impact generating mechanism of the chisel head attachment unit of  FIG. 2 . 
           [0024]      FIG. 4  illustrates one method of adjusting the level of impact force between the chisel head attachment unit hammer and anvil. 
           [0025]      FIG. 5  illustrates an alternative methods of adjusting the level of impact force between the chisel head attachment unit hammer and anvil. 
           [0026]      FIG. 6  illustrates the schematic of one embodiment of the input drive to impact cam motion transmission component of the chisel head attachment unit of  FIG. 1 . 
           [0027]      FIG. 7  illustrates the method of using a tensile springs for mechanical potential energy storage in the embodiments of  FIGS. 2 and 3  instead of compressive spring. 
           [0028]      FIG. 8A  illustrates the schematic of the cross-sectional view of the basic impact generating mechanism of a second embodiment of the chisel head attachment unit. 
           [0029]      FIG. 8B  illustrates the schematic of the frontal view of the basic impact generating mechanism of a second embodiment of the chisel head attachment unit. 
           [0030]      FIG. 9  illustrates the schematic of a “chisel head unit” embodiment with integrated electric driving electric motor. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    The overall view of a chisel head attachment unit  30  and an electric drill or screw driver  31  (hereinafter referred to only as the electric drill) driving it is shown in the schematic of  FIG. 1 . The electric drill  31  may be battery powered or powered by a line voltage and is illustrated schematically herein with the shape shown in  FIG. 1 . An input drive shaft  32  of the chisel head attachment unit  30  is engaged by a chuck  33  of the electric drill  31 . The input drive shaft  32  of the chisel head attachment unit  30  can be provided with a hexagonal or other similar cross-sectional area geometry for better torque transmission from the chuck  33  to the input drive shaft  32 . The chisel head attachment unit  30  is also provided with at least one handle  34  for the user to hold with one hand to guide and direct the chisel end  35  against the intended impacting surface  36  as the chisel end  35  travels downward in the direction of the arrow  37 . The handle can be configured for both hands (while a second person operates the electric drill  31  or configured for other parts of the body, such as the knees. The chisel head attachment unit  30  can be provided with a chuck  38  to accept different types of chisel ends  35 . 
         [0032]    The basic operation of the mechanisms of the first embodiment of the chisel head attachment unit  30  is herein described via the overall schematic of  FIG. 2 . In  FIG. 2  and for the sake of clarity, the main elements of the impact generating portion of the chisel head attachment unit  30  is shown alone without the aforementioned device input drive and the speed reducing gearing (if any) and its motion transmission elements for driving the impact generating mechanism. The latter mechanisms will be described later in this disclosure. 
         [0033]    The chuck  33  of the electrical drill or screw driver  31 ,  FIG. 1 , is attached to the input drive shaft of the chisel head attachment unit  30 , either directly or through a gearing or the like motion transmission unit (usually for speed reduction purposes) as was previously described. The output of the gearing or the like motion transmission unit (not shown) is then used to rotate at least one cam  10  in the direction of the arrow  11 . The at least one cam  10  is attached to a disc  25  which is rotated continuously by the output of the reduction gearing or the like motion transmission unit of the chisel head attachment unit  30 . 
         [0034]    As the cam  10  is moved in the direction of the arrow  11 , its inclined cam profile surface  28  will force the hammer end  12  upward, thereby compressing the potential energy storage spring  13  between the structure  14  of the housing of the chisel head attachment unit  30  and the shoulder  22  provided on the hammer  15 . The hammer  15  itself can travel in the guide  21  which is provided in the structure  14  of the chisel head attachment unit  30 . Then when the tip  20  of the cam  10  passes the end  12  of the hammer  15 , the hammer  15  is released and the potential energy stored in the spring  13  accelerates the hammer  15  down and causes the tip  12  of the hammer  15  to impact the surface  23  of the anvil  16 , thereby imparting downward momentum to the chisel  24  element, thereby allowing the user to impact the chisel head  17  against the desired object surface. After each impact, the lightly preloaded compressive spring  18  causes the chisel  24  to be pulled back and ready for the next impact by the hammer  15 . In one embodiment, the chisel head  17  is attached to the chisel element  24  via a chuck  26  so that the chisel heads  17  can be quickly changed. 
         [0035]    It is appreciated by those skilled in the art that by adjusting the amount of preload in the potential energy storage spring  13 , the level of stored potential energy at the time of hammer  15  release is varied. In general, this can be the method of adjusting the level of impact between the hammer  15  and the surface  23  of the anvil  16 . Alternatively, the level of impact between the hammer  15  and the surface  23  of the anvil  16  may also be adjusted by raising or lowering the anvil  16  relative to the hammer  15 , noting that by reducing the distance, the level of momentum with which the hammer  15  impacts the surface  23  of the anvil  16  is reduced. 
         [0036]    It is appreciated by those skilled in the art that as the tip  12  of the hammer  15  passes the tip  20  of the cam  10 , the hammer  15  begins to be pushed down by the force of the compressively loaded potential energy storage spring  13 . The tip  12  of the hammer is desired to have close to a spherical surface (such as with significantly larger diameter as shown in the schematic of  FIG. 2 ) for proper concentration of impact force on the surface  23  of the anvil  16 . As a result, the hammer  15  is not suddenly released as the lowest point on the tip  12  passes the sharp point  20  of the cam  10  and would still rub against the tip  20  of the cam until the entire stem  27  of the hammer  15  has passed the tip  20  of the cam  10 . 
         [0037]    To ensure that the hammer  15  is released suddenly with minimal rubbing against the surface of the cam  10  around the tip  20 , the alternative engagement and release arrangement shown schematically in  FIG. 3  can be used. In this alternative embodiment shown schematically in  FIG. 3 , the tip  12  of the hammer  15  is no longer used to preload the potential storage spring  13  as was shown for the embodiment of  FIG. 2 . In the alternative embodiment of  FIG. 3 , the preloading of the potential storage spring  13  is achieved instead by providing the end of the hammer  15  with an (such as integral) element  39  which is provided with an inclined surface  40  which matches and rides against the inclined surface  28  of the cam  10  as the disc  25  rotates and cause the cam to travel in the direction of the arrow  11 . In this embodiment, the tip  12  of the hammer  15  is positioned beyond (in front as shown in the schematic of  FIG. 3 ) the side of the cam  10 . Then as the cam  10  travels in the direction of the arrow  11 , the potential energy storage spring  13  of the chisel head attachment unit  30 ,  FIG. 1 , is continuously preloaded until the tip  41  of the element  39  reaches the tip  20  of the cam  10 . At which time the element  39  and thereby the hammer  15  is suddenly released. The hammer  15  is then accelerated downwards towards the surface  23  of the anvil  16 . The tip  12  of the hammer  15  will then impact the surface  23  of the anvil  16  as was described previously for the embodiment of  FIG. 12 , thereby imparting downward momentum to the chisel element  24 , thereby allowing the user to impact the chisel head  17  against the desired object surface. After each impact, the lightly preloaded compressive spring  18  will similarly cause the chisel element  24  to be pulled back and ready for the next impact by the hammer  15 . 
         [0038]    It is appreciated by those skilled in the art that for a given compressive deformation of the mechanical potential energy storage spring  13  provided by the rotation of the cam  10 ,  FIGS. 2 and 3 , the amount of mechanical potential energy stored in the spring  13  is increased by having the spring  13  be initially preloaded in compression. Such preloading is also highly desirable so that the hammer mass  15  is accelerated downwards towards the anvil  16  during at all times during its downward motion. 
         [0039]    As was previously indicated, in different embodiments of the chisel head unit attachment  30 ,  FIG. 1 , the level of impact force between the hammer mass  15  and the anvil  16 ,  FIGS. 2 and 3 , can be adjusted by varying the distance between the tip  12  of the hammer  15  and the surface  23  of the anvil and/or by varying the amount of preload in the potential energy storage spring  13  to vary the velocity of the tip  12  of the hammer  15  at the time of impact with the surface  23  of the anvil  16 . 
         [0040]    The anvil and chisel portion of the chisel head attachment unit embodiments of  FIGS. 2 and 3  (indicated by the numeral  42  in  FIG. 3 ) is redrawn in  FIG. 4 . To varying the distance between the tip  12  of the hammer  15  and the surface  23  of the anvil  16 , the chisel element  24  is provided with an adjustment “nut” type element  44  which rides on the provided thread, which can be a fine thread, over the stem of the chisel element  24 , between the chisel holder  26  and the housing structure  14  of the chisel head attachment unit  30 . Then by rotating the adjustment element  44 , the distance  33  and thereby the distance between the tip  12  of the hammer  15  and the surface  23  of the anvil  16  ( FIGS. 2 and 3 ) is varied. The adjustment element  44  can be provided with position holding means (not shown) such as spring loaded engagement balls or teeth that are commonly used in adjustable devices such as torque wrenches and the like, which can have high and low marking and grading, to prevent the adjustment element  44  to turn and vary the impact level as the chisel head attachment unit  30  is being operated. 
         [0041]    Alternatively, by varying the level of preload of the potential energy storage spring  13 , the total mechanical potential energy stored in the spring  13  is varied, thereby the level of acceleration that the spring  13  imparts on the hammer mass  16  and the level of momentum with which the hammer mass  16  impacts the anvil  16  is varied. For example, by increasing the level of potential energy storage spring  13  preload (compressive preload for the case of the embodiments of  FIGS. 2 and 3 ), the total mechanical potential energy stored in the spring  13  as the hammer mass  15  is released as previously described due to the rotation of the cam  10  in the direction of the arrow  11 , since it is accelerated by a larger spring  13  force while traveling the same distance before impacting the anvil  16 , therefore its velocity and thereby momentum at the time said impact is increased. The opposite effect is obviously achieved by reducing the level of preload on the potential energy storage spring  13 . 
         [0042]    It is appreciated by those skilled in the art that numerous methods known in the art may be used to provide to the user the means to manually adjust the level of preloading of the potential energy storage spring  13 ,  FIGS. 2 and 3 , an example of which is shown in the schematic of  FIG. 5 . In  FIG. 5 , the hammer and potential energy storage spring  13  portion of the chisel head attachment unit embodiments of  FIGS. 2 and 3  (indicated by the numeral  45  in  FIG. 3 ) is redrawn. Two elements  46  and  47  are then provided between the chisel head attachment unit housing structure  14  and the spring  13 . The element  47  can be provided with a hole through which the stem of the hammer mass  15  is passed. The element  46  can be provided with a slot, which allows it to be moved back and forth in the direction of the arrow  48 . The two elements  46  and  47  are provided with mating inclined surfaces shown in  FIG. 5  so that by moving the element  46  to the left (right) the level of preloading of the potential energy storage spring  13  is increased (decreased). It is noted that since the end element  39  of the hammer mass  15  is held against the surface of the cam  10 , while varying the preloading of the spring  13  does not cause the hammer mass upward or downward motion. The adjustment element  46  can be provided with position holding means either against the housing structure  14  or the element  47  (not shown), such as by the use of spring loaded engagement balls or teeth which are commonly used in adjustable devices such as torque wrenches and the like, which can have high and low marking and grading, to prevent the adjustment element  46  to displace and vary the preloading level of the spring  13  as the chisel head attachment unit  30  is being operated. 
         [0043]    One embodiment of the input drive to impact cam motion transmission component of the chisel head attachment unit  30 ,  FIG. 1 , is shown schematically in  FIG. 6 . In the present embodiment of the chisel head attachment unit  30 , the chuck of the aforementioned electric drill or electric screw driver is attached to the input drive  52 ,  FIG. 6 , of the chisel head attachment unit  30 . The input drive  52  can be of hexagonal shape for easy and secure attachment to the electric drill or electric screw driver chuck, such as via a hex adaptor (not shown) for ease of engagement and disengagement. The input drive  52  is the end of the input shaft  51  which is free to rotate inside bearings  53  provided in the housing structure  14  of the chisel head attachment unit  30 . A gear element  50  is fixedly attached to the input shaft  51 , which upon rotation of the input shaft  51  by the driving electric drill or electric screw driver  31 ,  FIG. 1 . The gear  50  is engaged with the gear  54 , which is also mounted on a shaft  55 , which can freely rotate in bearings  56  provided in the housing structure  14  of the chisel head attachment unit  30 . The gear  54  is in turn engaged with the gear  57 , which is also mounted on a shaft  58 , which can freely rotate in bearings  59  provided in the housing structure  14  of the chisel head attachment unit  30 . 
         [0044]    The aforementioned cam  61  (element  10  in  FIGS. 2 and 3 ) which is used to store mechanical potential energy in the energy storage spring (element  13  in  FIGS. 2 and 3 ) is fixedly attached to the gear  57  directly or via an intermediate (disc like) element  60 . In  FIG. 6  the cam surface  62  ( 28  in  FIGS. 2 and 3 ) is shown to be the surface over which the mating elements of the hammer mass  16  (surface  40  in the embodiment of  FIG. 3  and the tip  12  in the embodiment of  FIG. 2 ). 
         [0045]    It is appreciated by those skilled in the art that as can be observed in the schematic of  FIG. 7  for the cam  61  to push upward the aforementioned mating elements of the hammer mass  16  (surface  40  in the embodiment of  FIG. 3  and the tip  12  in the embodiment of  FIG. 2 ), the attaching gear  57  must be rotating in the clockwise direction as indicated by the arrow  67 . This means that the input drive shaft  51  must also be rotated in the clockwise direction as shown by the arrow  68  in  FIG. 7 . In the schematic of  FIG. 7 , this is the case since the idler gear  54  reverses the direction of rotation of the input gear  50 . The ratio of the number of teeth on the gear  50  to that of the number of teeth on the gear  57  indicates the reduction ration between the two gears. In general and as can be observed in the schematic of  FIG. 7 , the provision of the idler gear  54  allows the gears  50  and  57  to be provided with enough distance to facilitate the provision of relatively larger diameter cam  61  and disc  60 , particularly for accommodating multiple cams  61 . However, in an alternative embodiment, particularly when the speed reduction is not necessary or it is even desired to increase the input speed (for example when using electrical screw drivers as input drives), the idler gear  54  may be eliminated, in which case the input shaft  51  has to be driven in the counterclockwise direction, i.e., opposite to the direction of the arrow  68 . In fact, in certain applications, the shaft  58  itself may be the input drive, and the (hex) head  52  may be located on the extended top portion of the shaft  58  and be driven directly by the electrical drill or electrical screw driver  31 . 
         [0046]    It is also appreciated by those skilled in the art that for the sake of simplicity, only one cam  61  is shown in the schematic of  FIG. 7 , even though multiple such cams may also be provided. In certain applications, one may also choose to use multiple cams with multiple profiles. 
         [0047]    In the embodiments of  FIGS. 2 and 3  and also in  FIG. 5 , the mechanical potential energy storage spring  13  are shown to be a (which can be preloaded) compressive spring. It is, however, appreciated by those skilled in the art that torsion and tensile (which can also preloaded in torsion and tension) springs may also be configured to be used instead. The mechanical energy storage and hammer assembly of such an embodiment is shown in the schematic of  FIG. 7  (all other components shown in the schematic of  FIG. 7  are identical to those of  FIG. 5 ). As can be seen in  FIG. 7 , the mechanical potential energy storage spring  13  ( FIGS. 2 and 3 ) is replaced with at least one tensile (which can be preloaded in tension) spring  63 , which is attached to the housing structure  14  of the chisel head attachment unit  30 ,  FIG. 1 , on one end  65  and to the relatively rigid element  64  on the other end  66  as shown in  FIG. 7 . The relatively rigid element  64  is fixedly attached to the indicated end (or thereabout) of the hammer mass  15 . 
         [0048]    The basic operation of the mechanisms of the second embodiment of the chisel head attachment unit  30  is described via the overall schematic of  FIGS. 8A and 8B . In  FIGS. 8A and 8B , for the sake of clarity, the main elements of the input drive and the hammer and potential energy storage spring portion of the chisel head attachment unit  30  are shown. The anvil and chisel end assembly of the device is considered to be as was described for the previous embodiments shown in the schematics of  FIGS. 2-5 . 
         [0049]    In the embodiment of  FIGS. 8A and 8B , the input drive  70 , which can be hexagonal in cross-section is provided for attachment to the chuck  33  of the driving electrical drill or electrical screw driver  31 ,  FIG. 1 . The input drive shaft  71 , which is free rotate in the bearing  72  provided in the housing structure  14  of the chisel head attachment unit  30 ,  FIG. 1 , is fixedly attached to the housing  73  of the hammer mass  74 . The rotation of the input drive  70  shown by the arrow  75  by the driving electrical drill or electrical screw driver  31 ,  FIG. 1 , would therefore rotate the housing  73 . The housing  73  is provided with an internal helical groove  76  along a portion of its inner body up to the opening section  78  on a section of housing  73 . It is noted that in the cross-sectional view of  FIG. 8A  the (square) cross-sectional view of the internal helical groove  76 , which are indicated by the numeral  76 . The same helical internal groove in the frontal view of the  FIG. 8B  is shown with dashed lines and is indicated by the numeral  77 . It is also noted that in the frontal view of  FIG. 8B , the open section  78  of the tubular lower section of the housing  73  is shown, where the upper end  79 ,  FIG. 8B , of the helical groove  77  is shown to end. The surface  80  of the open section  78  at the upper end  79  of the groove  77  is shown to be nearly vertical, and can be slightly angled outward on from the vertical towards the bottom portion as can be seen in  FIG. 8B . 
         [0050]    The hammer mass  74  is positioned inside the opening  83  inside the housing  73  on one end and is free to slide up and down without rotation in the guide  82  provided in the housing structure  14  of the chisel head attachment unit  30 ,  FIG. 1 . The lower portion of the hammer mass  74  that runs inside the guide  72  can be square or is provided with splines or the like (not shown) to prevent it from rotating while traveling vertically in the guide  82  as shown in  FIGS. 8A and 8B . The hammer mass  74  is also provided with the element  81 , which engages the helical groove  77  as can be seen in the cross-sectional view  FIG. 8A , in which the engaging element  81  is shown in the lower exposed end of the grove  76 . 
         [0051]    Then as the input drive  70  is rotated clockwise in the direction of the arrow  75 , the element  81  is forced to travel (slide) up the helical groove  77 , thereby forcing the hammer mass  74  to slide up inside the opening  83  of the housing  73 . As a result, the mechanical potential energy storage compressive spring  84  provided in the opening  83  of the housing  73  is compressed, thereby storing mechanical potential energy. The potential energy storage spring  84  can be initially preloaded to allow larger amount of mechanical potential energy to be stored in the spring. Then as the element  81  reaches the surface  80  of the open section  78  and passes the edge  85  of the opening  79  of the helical groove  77 , the element  81  is released, thereby allowing the preloaded compressive potential energy storage spring  84  to accelerate the hammer mass  74  downwards, and force the tip  86  of the hammer mass  74  to impact the surface  23  of the anvil  16 ,  FIGS. 2 and 3 , thereby imparting downward momentum to the chisel  24  element, thereby allowing the user to impact the chisel head  17  against the desired object surface as was previously described. 
         [0052]    Then following each hammer mass  74  release, impact with the anvil and its return to its initial position, the continued rotation of the housing  73  by the electrical drill or the screw driver will bring the lower opening end  76  of the helical grove (which can be wide enough and is essentially at the level of the lower surface  87  of the housing  73 ,  FIG. 8A ) to re-engage the element  81  of the hammer mass  74 , and start another cycle of potential energy storage spring  84  compression and hammer mass  74  release. The process will continue until the electrical drill or the electric screw driver  31 ,  FIG. 1 , is turned off. 
         [0053]    It is appreciated by those skilled in the art that in an alternative embodiment, the chisel chuck  26  and the chisel end  17  ( FIGS. 2 and 3 ) may be directly attached to the end  86  of the hammer mass  74 ,  FIGS. 8A and 8B . Then the aforementioned momentum of the hammer mass  74  as it is accelerated downwards by the preloaded potential energy storage spring  84  following its release can be used to impact the chisel end  17  against the intended surface. 
         [0054]    In the above embodiments, an external device such as an electrical drill or electric screw driver ( 31  in  FIG. 1 ) or drill press is used to drive the input drive of the chisel head attachment units. In an alternative embodiment shown in the schematic of  FIG. 9  the driving electric motor is integrated with the chisel head attachment unit to form an all-in-one electrically driven chisel  90 . In such an all-in-one electrically driven chisel  90 , the drive shaft  91  of the device electric motor  94  is attached to the input drive  32  of the previously described “chisel head attachment” unit  30 . The electrical chisel  90  may be provided with a housing  92  to which the drive motor  94  is held fixed, for example by peripheral elements  93  that prevents its rotation relative to the housing  92 . However, in one embodiment the housing  92  and the housing  14  of the chisel head portion,  FIGS. 2 and 3 , are integral, and in fact the entire unit  90  is designed as an integral unit to minimize the number of components and complexity. 
         [0055]    The electric motor  94  may be powered by external power via a wire through an outlet (not shown) or via a battery pack  95 . 
         [0056]    It is also appreciated by those skilled in the art that in the all-in-one electric chisel embodiment  90  of  FIG. 9 , the user may or may not prefer to use the handle  34  and may also choose to hold the entire unit body in one hand. For this reason, the handle  34  may be totally eliminated or be supplied as an attachment, particularly for smaller chisel  90  units in which the chisel body is relatively small and easy to hold in one hand and that the motor torque is relatively low for the user hand to resist. 
         [0057]    While there has been shown and described what is considered to be preferred embodiments, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.