Abstract:
The driving device  1,  in accordance with the invention, has a ram  3,  which, driven by compressed air, drives in the fastener  2.  A pump device  5  produces the compressed air. The pump device  5  has a pump cylinder  23,  a pump piston  22,  and an annular magnet arrangement  28, 46  around the pump cylinder  23.  The pump piston  22  can move in the pump cylinder  23,  along an axis  11.  An axial closure  25  of the pump cylinder  23  closes off, with the pump piston  22,  a pump volume  27  within the pump cylinder  23.  The annular magnet arrangement  28, 46  has a magnetic coil  28,  which encloses the pump cylinder  23  and which overlaps, along the axis  11,  at least in part, with the magnetizable closure  25  and, in part, with the magnetizable pump piston  22.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention under consideration concerns a driving device for the driving of fasteners, such as nails, rivets, pins, braces, clamps, or other, preferably, pin-like fastening elements. Furthermore, the invention concerns a controlling method for a driving device. 
       BRIEF SUMMARY OF THE INVENTION 
       [0002]    The driving device, in accordance with the invention, has a ram, which drives in the fastener, driven by compressed air. A pump device produces the compressed air. The pump device has a pump cylinder, a pump piston, and an annular magnet arrangement around the pump cylinder. The pump piston can move in the pump cylinder, along an axis. An axial closure of the pump cylinder closes off, with the pump piston, a pump volume within the pump cylinder. The annular magnet arrangement has a magnetic coil, which encloses the pump cylinder and which, along the axis, overlaps, at least in part, with the magnetizable closure, and in part, with the magnetizable pump piston. 
         [0003]    The pump cylinder, with its half side closed by the closure, forms, together with the pump piston, a linear piston stroke pump. The drive of the piston stroke pump is carried out by the magnetic coil, which can draw the magnetizable pump piston into the center of the magnetic coil and thereby can compress the air in the pump volume. 
         [0004]    The arrangement of the closure within the magnet arrangement, preferably, within the magnetic coil, has proved to be efficient for the compression of the air. The necessary force for the compression of the air rises more or less inversely to the diminishing distance between the pump piston and the closure. As a result of the arrangement of the magnetizable closure within the magnet arrangement, the force exerted by the magnetic coil on the pump piston is also increased more or less inversely to the distance between the closure and the pump piston. The energy can be transferred optimally by the magnetic coil onto the volume work of the pump volume via the entire movement of the pump piston. 
         [0005]    The closure and the pump piston are preferably formed from a soft magnetic material. As soon as the magnetic coil is not energized, the closure and the pump piston are largely unpolarized and are depolarized by the surrounding stray fields. Without the magnetic coil, the closure and the pump piston are not attracted to each other. 
         [0006]    One development provides for the closure to overlap with at least 10% of the magnet arrangement, preferably, the magnetic coil, along the axis. The pump piston preferably overlaps, in each position, for at least 10% with the magnet arrangement, preferably, the magnetic coil, along the axis. 
         [0007]    One development provides for a pressure chamber to have intermediate storage for the compressed air produced by the pump device. The pump device does not drive the ram directly. A volume of the pressure chamber is dimensioned to hold an air quantity for one driving operation or for fewer than five driving operations. An air quantity held by the pump volume is advantageously less than the air quantity provided for one driving operation. The pump piston requires several strokes, until an air quantity needed for the driving operation is made available. 
         [0008]    One development provides for the ram to be rigidly connected with a driving piston, the driving piston to close off a working volume within a hollow guide cylinder, and for it to be possible to feed the compressed air into the working volume. The compressed air, which is produced by the pump device and held, in the interim, in the pressure chamber, accelerates the driving piston in the guide cylinder. The ram is carried along by the driving piston and drives in the nail or another fastening means. 
         [0009]    A controlling method for the driving device has the following steps: generation of the compressed air, in that a current pulse is fed into a magnetic coil, and the magnetic field produced moves a magnetizable pump piston within the magnetic coil in a pump cylinder, and acceleration of a ram with the compressed air onto a fastener arranged in the driving direction. The driving device converts electrical energy into a magnetic field, into a compression of air, and subsequently, into the kinetic energy of the ram. The conversion of the energy from the magnetic field into compression is particularly efficient using the pump piston, conducted within the magnetic coil. 
         [0010]    A development provides fir a pressure chamber to be loaded with the compressed air and, as a response to an actuation of an operating element by the user, for the ram to be accelerated with the compressed air from the pressure chamber. The loading of the pressure chamber is carried out by energizing the magnetic coil with a sequence of current pulses for the multiple back and forth movement of the pump piston. One single stroke to make available the air quantity for the driving operation has the obvious advantage that the additional pressure chamber and an intermediate storage of the compressed air are omitted. The driving device is lighter and has fewer loss channels. The multiple stroke has nevertheless proved to be more efficient, since the pump device works in an especially efficient manner, in particular with a short stroke, and thus the disadvantages of the additional pressure chamber are more than compensated for. 
         [0011]    An amplitude and/or a duration of the current pulses can increase within one sequence. The pump device does more volume work, in particular by attaining a higher pressure, with increasing air quantity in the pressure chamber per stroke, so as to further load the pressure chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0012]    The following description explains the invention with the aid of the exemplary embodiments and figures. The figures show the following: 
           [0013]      FIG. 1 , a driving device 
           [0014]      FIG. 2 , a pump device of the driving device 
           [0015]      FIG. 3 , a succession of switching sequences 
           [0016]      FIG. 4 , a section of the driving device 
       
    
    
       [0017]    The same or functionally similar elements are shown with the same reference symbols in the figures, unless otherwise indicated. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0018]      FIG. 1  shows an exemplary driving device  1  for nails  2  or similar pin-like fastening elements. The driving device  1  has a compressed air-driven ram  3 , which drives the nail  2  into a workpiece. The compressed air for one driving operation is kept in the pressure chamber  4 . A pump device  5  in the driving device  1  loads the pressure chamber  4  with an air quantity sufficient for the driving operation and to the needed pressure level. 
         [0019]    The components of the driving device  1  that are essential for the functionality are located within a housing  6 , in particular, the ram  3 , the pressure chamber  4 , and the pump device  5 . The user can conduct the driving device  1  with a handle  7  and can hold it while driving the nails  2 . The handle  7  is not detachably connected with a housing  6  of the driving device  1 , but it is rigidly connected or with dampening elements. The driving device  1  is primarily supplied with electrical energy, for example, by means of a battery packet  8 , which can be affixed, in a nondetachable or preferably in a detachable manner, to the handle  7  or the housing  6 , by the user. A triggering switch  9  is on or near the handle  7 ; it triggers a driving operation upon actuation by the user. Preferably, in addition to the actuation of the triggering switch  9 , there is also the release of a safety mechanism, for example, by pressing the driving device to a wall. 
         [0020]    The ram  3  has an impact head  10 , which is adapted, in its form, to the nails  2  used. The impact head  10  has typically, approximately, the same diameter as a head of the nails  2 . The impact head  10  is conducted along a work axis  11  within a nail guide  12 . The nail  2  is placed, for the driving operation, into an essentially tubular nail holder  12 . The placing of the nail can be done manually by the user, semiautomatically or automatically, by a feeder. The impact head  10  strikes the nail  2  within the nail guide  12  and drives the nail  2  in the driving direction  13 , along the work axis  11  from the nail guide  12 , perhaps into a workpiece. 
         [0021]    On its back end, turned away from the nail, the ram  3  is provided with a driving piston  14 . The driving piston  14  preferably has an essentially larger diameter than the impact head  10 , so as to drive the ram  3  efficiently with the compressed air. 
         [0022]    The driving piston  14  is inserted into a guide cylinder  15 , closed on half its side. The driving piston  14  lies, all-round, on the inner jacket surface  16  of the guide cylinder  15 , pressure-tight, and is conducted by the jacket surface along the work axis  11 . An end of the guide cylinder  15 , turned away from the nail  2 , is closed by a bottom  17 . The driving piston  14  thus closes off a pneumatic work volume  18  in the driving direction  13  within the guide cylinder  15 . 
         [0023]    The pressure chamber  4  is connected with the work volume  18  via a controllable supply line  19 . The supplying through the supply line  19  is preferably carried out via an opening in the bottom  17 . The supply line  19  comprises a switchable valve  20 , which is opened as a response to an actuation of the triggering switch  9 . 
         [0024]    The pressure chamber  4  has a sufficient volume, so as to store an air quantity for preferably precisely one driving operation. The volume is, for example, in the range of 100 cm 3  to 300 cm 3 . With a fully loaded pressure chamber  4  for one driving operation, the pressure is between 7 bar and 10 bar. The pressure chamber  4  is surrounded with a thermally insulating jacket  21 , which, for example, a wall of the pressure chamber  4  lines on the inside or is placed on the outside surface. The jacket  21  is, for example, made of a plastic, preferably, of a foamed plastic. 
         [0025]    The pump device  5  ( FIG. 2 ) fills the pressure chamber  4  with air, until the air quantity needed for the driving operation and/or the pressure needed for the driving operation are attained. The pump device  5  has a linearly moved pump piston  22 . In the embodiment shown, the pump piston  22  is conducted along the work axis  11 ; the pump piston  22 , however, can also be conducted along another axis  11 . The pump piston  22  moves within a hollow pump cylinder  23 . The cross section of the pump piston  22  and the inside cross section of the pump cylinder  23  fit exactly, so as to guarantee a pressure-tight closure. Sealing rings on the pump piston  22  can reconcile tolerances in production. Opposite a front surface  24  of the pump piston  22 , the pump cylinder  23  is closed by a stationary closure  25 . The front surface  24  of the pump piston  22  and the front surface  26  of the closure  25 , facing it, enclose air in a pump volume  27 . 
         [0026]    The pump piston  22  is moved by a magnetic coil  28  along the axis  11 . The magnetic coil  28  is located around the pump cylinder  23 ; preferably, the magnetic coil  28  is coaxial to the axis  11  of the pump cylinder  23 . The drive is based on reluctance forces which act on the pump piston  22 . The pump piston  22  is made of a magnetic, preferably, ferromagnetic material. The magnetic field produced by the magnetic coil  28  in the pump cylinder  23  pulls the pump piston  22  into the pump cylinder  23 . 
         [0027]    The pump piston  22  is made of a soft magnetic material, whose coercive field strength is less than 1000 A/m. A weak external magnetic field can already change or cancel an existing polarization in the pump piston  22 . The magnetic polarization impressed by the magnetic coil  28  therefore essentially remains contained in the pump piston  22  only for the duration of the field applied by the magnetic coil  28 . The pump piston  22  is, for example, made of ferromagnetic steel, preferably, a soft-annealed steel. 
         [0028]    The closure  25  is made of a soft magnetic material, for example, the same material as the pump piston  22 . The magnetic field produced by the magnetic coil  28  is introduced by the closure  25  into the pump cylinder  23 . The magnetic field fins between the front surface  24  of the pump piston  22  and the front surface  26  of the closure  25 , parallel to the axis  11 . The closure  25  projects along the axis  11  into the magnetic coil  28 . A front end section  29  of the magnetic coil  28  thus overlaps with the closure  25 . The front end section  29  assumes at least 10% of the magnetic coil  28 . A length  30  of the front end section  29  preferably is between 10% and 30% of the length  31  of the magnetic coil  28 . The pump piston  22  never comes out completely from the magnetic coil  28 . In the basic position of the pump piston  22 —that is, in its position moved out the furthest from the pump cylinder  23 —the pump piston  22  overlaps with a back end section  32  of the magnetic coil  28 . The back end section  32  has a length  33  of at least 10% of the length  31  of the magnetic coil  28 , preferably, up to 20% of the length  31  of the magnetic coil  28 . The pump volume  27  is completely within the magnetic coil  28 , with a length  34  of at most 80% of the magnetic coil  28 . 
         [0029]    The pump volume  27  is clearly smaller than the volume of the pressure chamber  4 . For example, the pump volume  27  contains less than 20%, preferably, between 5% and 10% of the air quantity needed for a driving operation. The efficiency of the pump device  5  rises greatly, in a nonlinear manner, with increasing approximation of the pump piston  22  to the closure  25 . The efficiency of the total system of the driving device  1  is increased by the small pump volume  27 , instead of a pump volume in the order of magnitude of the pressure chamber  4 , in spite of the additional expense of making available the pressure chamber  4  and the losses resulting from the pressure chamber  4 . 
         [0030]    The pump device  5  is controlled by a control device  35 . The control device  35  loads the pressure chamber  4  upon the start of the operation or after a driving operation. The loading is carried out by a sequence  36  of current pulses  37 , which are fed into the magnetic coil  28  ( FIG. 3 ). With each of the current pulses  37 , the pump piston  22  is drawn from its basic position into the magnetic coil  28  and compresses the air in the pump volume  27 . A large part of the compressed air flows into the pressure chamber  4 . A spring  39  and/or an additional magnetic coil  40  can draw out the pump piston  22  from the pump cylinder  23  into the basic position. The pump volume  27  is ventilated before the next current pulse  37 . For example, the pump piston  22  releases a ventilating channel  41 , as soon as the pump piston  22  is moved back to the basic position. Preferably, the ventilating channel  41  is opened, as soon as the pump piston  22  begins its backward movement. A position sensor can determine whether the pump piston  22  has reached the basic position. 
         [0031]    The sequence  36  preferably comprises at least 5 current pulses  37 , preferably, at most 30 current pulses  37 . The pressure chamber  4  is completely pumped by the pump device  5 , corresponding to 5 to 30 strokes. The introduction of energy of the current pulses  37  increases during the sequence  36 ; preferably, the duration  42  of the current pulses  37  is increased; alternatively or additionally, the amplitude  43  of the current pulses  37  can be increased. The duration  42  and the current strength/amplitude  43  can be definitively prespecified. The current pulses  37  are coordinated in such a way that the pump piston  22  is drawn from its basic position to the closure  25 , preferably without touching the closure  25  at the end. The force exerted by the magnetic coil  40  on the pump piston  22  rises with the selected buildup during its movement to the closure  25 . The characteristic curve of this increase is similar to the characteristic curve of the increase of the counterforce being built up by the compressed air. The current strength  43  can be maintained constant during a current pulse  37 . 
         [0032]    The closure  25  is provided with an outlet valve  44 , for example, a nonreturn valve. The outlet valve  44  preferably opens as soon as the pressure in the pump volume  27  exceeds the pressure in the pressure chamber  4 . The pump device  5  increases the pressure within the pump volume only slightly above the pressure in the pressure chamber  4 , so as to shift the air quantity from the pump volume  27  into the pressure chamber  4 . The thermal losses appearing during the compression can be kept small in this way. The outlet valve  44  closes as soon as the pump piston  22  moves back to the basic position. 
         [0033]    The user can actuate the triggering switch  9 , so as to trigger the driving operation. The control device  35  preferably first tests whether the pressure chamber  4  is loaded. If the pressure chamber  4  is not loaded, for example, after a long inactivity of the driving device  1 , the control device  35  loads the pressure chamber  4 . The pressure chamber  4  is loaded with the complete sequence  36  of the current pulses  37 . The control device  35  shortens the sequence  36 , if the pressure chamber  4  is partially loaded. For example, the control device  35  determines, by means of a pressure sensor, the pressure in the pressure chamber  4 . For each pressure, a notation is made in a control table as to how many of the first current pulses  37  of the sequence  36  are to be skipped—that is, with which of the current pulses  37  of the sequence  36 , one is to begin. If the pressure chamber  4  is loaded, the control device  35  opens the controllable valve  20 . The air quantity under pressure in the pressure chamber  4  accelerates, by means of the driving piston  14 , the ram  3 . After the driving operation, the driving piston  14  is retrieved—for example, by means of a pump, a spring, a motor, the user—and the switchable valve  20  is closed. The work volume  18  is preferably ventilated for the retrieval of the driving piston  14 . The control device  35  loads the pressure chamber  4  by means of the sequence  36  of current pulses  37 . 
         [0034]    The magnetic coil  28  is preferably surrounded by a magnet yoke  46 . The magnet yoke  46  covers, with a ring  47  in each case, the two front sides  48  of the magnetic coil  28 . The magnet yoke  46  extends, in a radial direction, to the pump piston  22  or the closure  25 . Ribs  49  of the magnet yoke  46 , running parallel to the axis  11 , connect the two rings  47 . The magnet yoke  46  is, for example, formed from individual plates of a ferromagnetic steel. 
         [0035]    The pump piston  22  has a shell-like structure consisting of an outer shell  50  and a core  51 . The radially outermost shell  50  is made of a ferromagnetic material. The magnetic field is conducted within the outer shell  50 . A wall thickness of the outer shell  50  is in the range between 5% and 25% of the diameter of the pump piston  22 . A core  51  of the pump piston  22  can be hollow or it can be filled with a nonmetal material, for example, plastic. The front surface  26  is preferably a plate of steel, so that it is not deformed during the compression. Alternatively, the pump piston  22  can be a massive cylinder made of a ferromagnetic material, for example, steel. 
         [0036]      FIG. 4  shows a development of the guide cylinder  15  for the driving piston  14  and the pressure chamber  4 . The pressure chamber  4  is permanently open to the work volume  18  in the guide cylinder  15 . The driving piston  14  forms the switchable valve  20  and prevents the air in the pressure chamber  4  from flowing out, until a driving operation is triggered. A blocking mechanism  52 , for example, a ratchet element, holds the driving piston  14  in its basic position. The blocking mechanism  52  can be released by the control device  35 , whereupon the driving piston  14 , acted on by pressure, is accelerated in the driving direction  13 .