Centering mechanism for a fastener driving device

A driving device for driving a fastener (2) includes a centering mechanism (9) for centering and guiding the fastener (2). The centering mechanism includes centering elements (10, 26, 36, 37) that are tiltably or slidably connected to a mounting body (3) to be movable in directions tangential to the fastener. The centering elements (10) have contact surfaces (19) for contacting the fastener (2) that are each substantially parallel to the direction of motion of the respective centering element (10). In this manner, the centering elements (10) cannot be deflected radially away from the fastener, and any forces applied laterally outwardly by the fastener against the contact surfaces (19) are rigidly received and resisted by the centering elements (10) and the mounting body (3) in which they are held.

FIELD OF THE INVENTION 
The invention relates to a driving device for driving screws, nails, 
rivets, pins and the like, which are generally called fasteners herein. 
The driving device includes a centering mechanism with centering elements 
that are laterally movable and elastically urged into contact with the 
fastener. 
BACKGROUND INFORMATION 
German Patent Publication 1,923,712 A1 describes a driving device for 
screws, having a centering mechanism for the screws including centering 
elements in the form of holding jaws tiltably arranged on a bearing or 
mounting body. The jaws have contact surfaces for holding the screws, and 
the contact surfaces extend perpendicularly or inclined at an angle 
relative to the respective plane of the tilting motion of the centering 
element. Centering mechanisms of that type, in which the contact surfaces 
of the centering jaws are perpendicular or inclined at an angle relative 
to the tilting plane of the centering jaws, are also known in driving 
devices for nails, pins and other fasteners. 
In the known centering mechanisms, the centering elements can yield, i.e. 
they can be deflected, away from the fastener when a lateral force acts on 
the fastener. As a result, the fastener is not securely held and guided 
while it is being screwed or impact driven. Thus, under certain 
circumstances, the fastener will be driven into the workpiece at an angle, 
which is especially undesirable in the construction of furniture and in 
other fine carpentry and cabinetry. 
OBJECTS OF THE INVENTION 
In view of the above it is the aim of the invention to achieve the 
following objects singly or in combination: 
to provide a fastener driving device having a centering mechanism for the 
fasteners, which is able to securely hold and guide the fasteners during 
the driving process; 
to provide a centering mechanism for such a driving device in which the 
centering elements cannot be deflected radially outwardly by a radially 
outward force applied by the fastener; 
to provide a centering mechanism for such a driving device in which the 
fastener contact surfaces of the centering elements extend substantially 
parallel to the plane of motion of the centering elements and especially 
extend perpendicularly to the respective tilting axis of the centering 
element; 
to provide a centering mechanism for such a driving device in which the 
centering elements remain in place to guide the fastener until the head of 
the fastener tiltingly deflects the centering elements away from the 
fastener; 
to provide radially inwardly protruding ribs on the centering elements of 
such a centering mechanism, which ribs engage the threading of a screw 
being driven so as to enforce an axial advance motion as the screw is 
being driven; 
to provide a centering mechanism that is applicable to stationary as well 
as handheld driving devices; and 
to provide a centering mechanism that can be radially adjusted to fasteners 
having different diameters. 
SUMMARY OF THE INVENTION 
The above objects have been achieved in a driving device having a centering 
mechanism according to the invention, including a mounting or bearing body 
connected to a motor housing and a centering mechanism for the fasteners 
connected to the bearing body. Centering elements of the centering 
mechanism are connected to the bearing body to be laterally movable 
relative to the fastener, while the centering elements are elastically 
urged into guiding and centering contact with the fastener. The respective 
contact surfaces of the centering elements that cooperate with the 
fastener are arranged to extend substantially parallel to the direction of 
motion of the respective centering element. More particularly, each 
centering element is tiltable about a tilting axis and the contact 
surfaces are substantially perpendicular to the tilting axes, or each 
centering element is slidable and the contact surfaces are substantially 
parallel to the direction of sliding. 
Due to the particular arrangement of the contact surfaces, all lateral 
forces that may affect the fastener are transmitted substantially 
perpendicularly to the contact surfaces of one or more of the centering 
elements and then rigidly transmitted to and taken up by the bearing of 
the respective centering element. 
It is impossible for the centering element to yield or be deflected away by 
the fastener during the driving process. Thus, the shaft of the fastener 
is securely held and guided straight into the workpiece. Thereby, it can 
always be ensured that the fastener is driven into the workpiece in the 
desired direction without any problems. The centering elements are only 
tilted away from the fastener once the head of the screw, which has a 
larger diameter than the screw shaft, presses the centering elements 
laterally apart, or when the impact driver head of a nail driver device 
pushes the centering elements laterally apart. 
The invention may especially advantageously be applied to screw driving 
devices in which the motor housing and the motor-driven screw driving bit 
are axially slidably arranged, against a spring bias, relative to a 
mounting body on which the centering elements are mounted. In such an 
embodiment, the mounting body can simultaneously serve as a contact foot 
or sole plate of the driving device. 
According to a further detail of the invention, the contact surfaces of the 
centering elements are provided with ribs that protrude radially inwardly 
from the contact surface and extend substantially perpendicularly to the 
driving direction. When a screw is being driven, the threads of the screw 
engage the ribs, so that the screw pulls itself axially through the 
centering mechanism, that is to say the screw pulls the mounting body 
against the spring arranged between the mounting body and the motor 
housing, so that the operator of the device need not apply the force 
necessary for compressing the spring. 
The above described feature is especially advantageous when gypsum 
wallboard, for example known as sheet-rock, is to be screwed onto wooden 
or steel studs and the like. Typically, the screws do not positively 
engage the wallboard, and the positive axial screwing advance of the screw 
only begins once the screw reaches the underlying workpiece made of wood 
or steel. If successive screws to be fed into the driving device are 
connected together by a plastic strip in the usual manner, then it can 
occur that the screw head comes into contact with the screw connector 
strip before the screw has been driven through the wallboard and 
positively engaged the wood or steel. In this case, the positive axial 
advance achieved by the screw engaging the ribs ensures that the screw is 
smoothly pulled out of the connector strip without requiring any extra 
force to be applied. 
In order that the centering elements are tilted out of the way by the screw 
head as described above, the centering elements include inclined ramp 
surfaces adapted to be contacted by the screw head. Preferably, the 
inclined ramp surfaces of two centering elements are arranged one before 
another in the driving direction so that the first centering element is 
tilted away before the second centering element. In this manner, the two 
centering elements can have mutually engaging or intertwining contact 
jaws, whereby the contact jaw of the first centering element is tilted 
away first and thereby releases the contact jaw of the second centering 
element, which is then tilted away. 
The invention can be applied to compressed air nailing devices, wherein the 
mounting body is rigidly attached to the motor housing, i.e. a 
cylinder-piston unit. Thus, only the impact driver rod is movable relative 
to the contact foot or shoe. 
It should be understood that the invention can be applied to stationary 
driving devices as well as handheld or portable driving devices.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BEST MODE 
OF THE INVENTION 
As shown in FIG. 1, a driving device includes a motor housing 1, which 
houses a motor (not shown) that drives a screw driving blade or bit 6 for 
driving a fastener 2, in this case a screw 2 for example, into a workpiece 
B. Alternatively, the driving bit may be an impact driver rod, a riveting 
head, or the like. A driving axis 6' extends axially through the bit 6, 
and optimally also through the fastener 2, and defines a driving direction 
in which the fastener 2 is driven. A bearing or mounting body 3 is axially 
slidably connected to the motor housing 1, and a spring 4 is interposed 
between the mounting body 3 and the housing 1 to bias the axial sliding 
motion of the mounting body 3 relative to the housing 1. The fastener 2 
comprises a shaft 7 and a head 8 that has a larger diameter than the shaft 
7. 
In order to hold and guide the fastener 2 before and during the driving 
process, the driving device according to the invention includes a 
centering mechanism 9, which comprises three identical centering elements 
10 which are each tiltably connected to the mounting body 3. In order to 
achieve the swinging or tilting connection of the centering elements 10, 
the mounting body 3 includes a mounting ring 11, which in turn comprises 
mounting blocks 12 as shown especially in FIG. 2. These mounting blocks 12 
have respective threaded holes 13 provided therein. A respective threaded 
bolt 14 is screwed into each threaded hole 13 and includes a protruding 
axis stud 15 on which a respective one of the centering elements 10 is 
mounted. An elastic ring spring or circular spring 16 encircles all three 
centering elements 10 and presses the centering elements generally 
inwardly toward the fastener 2. 
A respective leg 17 of each centering element 10 extends generally in the 
driving direction away from the end of the centering element 10 that is 
tiltably mounted on the respective protruding axis stud 15. A respective 
contact jaw 18 is arranged perpendicularly to the leg 17 at the free end 
thereof. Each contact jaw 18 includes a respective contact surface 19 that 
faces the fastener 2 and that is substantially perpendicular to the axis 
20--20 of the corresponding protruding stud 15 as shown especially in FIG. 
2. Thus, the contact surface 19 of each centering element 10 is 
substantially parallel to the plane of the tilting motion of the centering 
element 10 about the axis 20--20 of the protruding stud 15. As a result, 
any lateral or radial forces effective on the fastener 2 are transmitted 
into and firmly resisted by one or more of the centering elements 10, 
without yielding or deflecting in a radially outward direction relative to 
the fastener 2. 
Thus, the centering elements 10 are tiltable or swingable in planes 
parallel to the driving axis 6' and tangential to a circle centered on the 
driving axis 6', and the contact surfaces 19 are parallel to those tilting 
planes. Therefore, the centering elements 10 cannot yield radially away 
from the fastener 2, but instead can only tilt in directions tangential to 
the circumference of the fastener 2 and respectively about the 
corresponding axis 20--20 of the protruding axis stud 15. More 
particularly, the centering elements 10 will be urged to swing laterally 
away from the fastener 2 only when this is caused by the larger diameter 
head 8 of the fastener 2 as described next. 
As shown in FIG. 1, contact jaw 18 includes a jaw-spreading or 
tilt-actuating ramp surface 21, and the other centering elements include 
corresponding ramp surfaces, for causing a tilting motion of each 
centering element 10 when the fastener head 8 comes into contact with the 
ramp surfaces 21. The contact jaw 18 further includes a lead-in ramp 
surface 22, which facilitates feeding the fastener laterally into the 
proper position between the contact jaws 18, as shown especially in FIG. 2 
i.e. the lead-in ramp surfaces 22 guide a fastener 2 that is being fed 
laterally into the driving position and cause the respective centering 
element 10 to swing out of the way. 
FIG. 2 further shows that the threaded holes 13 that receive the threaded 
bolts 14 are arranged in the form of an equilateral triangle in the 
mounting ring 11. Correspondingly, the contact surfaces 19 of the three 
centering elements 10 also form an equilateral triangle to provide a 
symmetrical and stable guiding and holding of the fastener 2. Each 
threaded bolt 14 has a slot 23 to enable each bolt 14 to be turned with a 
screwdriver in order to adjust the position of the centering element 
perpendicularly relative to its tilting plane, that is to say, radially 
toward or away from the fastener 2, so as to adjust the space between the 
contact surfaces 19 to fit the diameter of the shaft 7 of different 
fasteners 2. 
FIGS. 3 and 4 show another example embodiment of the driving device 
according to the invention, in which a mounting body 24 is constructed to 
simultaneously serve as a contact foot which may be placed against the 
workpiece 5. As described above for the first example embodiment, a screw 
driving bit 6 serves to drive a fastener 2 such as a screw. Slots 25 are 
provided in the mounting body 24 to extend outwardly through the mounting 
body 24 in a pinwheel-like configuration as shown especially in FIG. 4. 
Three centering elements 26 are respectively slidably arranged in the 
three slots 25. A ring spring or circular spring 27 encircles the mounting 
body 24 at the area of the centering elements 26 so as to urge the 
centering elements 26 laterally inwardly, in directions corresponding to 
the pinwheel-shaped arrangement of the slots 25. 
Each centering element 26 has a contact surface 28 that extends 
substantially parallel to the plane of the sliding motion of the 
respective centering element 26. Thus, it is impossible for the centering 
elements 26 to yield or be deflected radially outwardly by a lateral force 
applied to the contact surface 28 by the fastener 2. When the larger head 
8 comes into contact with the centering elements 26, that is to say when 
the head 8 is driven through the space between the centering elements 26, 
the centering elements are pushed back against the tension of the circular 
spring 27 to allow the fastener head 8 to pass through. For this reason, 
each centering element 26 may include a ramp surface 26'. 
In order to accommodate different diameters of fasteners 2, it is possible 
to exchange the mounting body 24 with a different mounting body to provide 
a different spacing between the centering elements 26. 
FIGS. 5 to 7 show a third example embodiment of a fastener driving device 
according to the invention, wherein a mounting body 29 is slidably 
connected to a motor housing 31 under the effect of a biasing spring 30. A 
screw driving bit 6 is driven by a motor (not shown) to move axially 
together with the motor housing 31, but rotate freely relative thereto. 
The screw driving bit 6 drives a first screw 32', which is to secure a 
gypsum or sheet-rock panel 33 onto a workpiece 34 made of wood or steel 
and arranged behind the sheet-rock panel 33. The first screw 32' and a 
plurality of successive screws 32 are interconnected by a plastic 
connector belt or strip 35 in a generally known manner. As each screw is 
driven into the workpiece, it is pulled free from the connector strip 35. 
The apparatus according to this embodiment of the invention includes two 
centering elements 36 and 37 to hold and guide the screws 32'. Each 
centering element 36 and 37 is tiltably connected to the mounting body 29 
to tilt about a respective one of two mutually perpendicular tilting axes 
39--39 and 40--40, under the biasing effect of respective leg springs 38. 
The centering element 36 includes a contact jaw 41 having at least one 
contact surface 42, which is parallel to the tilting plane of centering 
element 36, as shown especially in FIG. 7. The centering element 37 
includes a contact jaw 43 having two opposite contact surfaces 44, which 
are parallel to the tilting plane of the centering element 37. 
As shown especially by FIGS. 5 and 6, the contact jaw 43 comprises ribs 45 
extending substantially perpendicularly to the driving direction and 
protruding radially inwardly from the contact surfaces 44. When the screw 
32' is being driven, the threads 46 of the screw 32' engage the ribs 45. 
In this manner, a positive axial feed advance is imposed on the rotating 
screw, which actively pulls itself axially through the space between the 
contact surfaces 44 and 42 because of the screw threads 46 engaging the 
ribs 45. As a result, on the one hand the mounting body 29 is pulled 
against the biasing effect of the spring 30 against the motor housing 31, 
and on the other hand the head 47 of the screw 32' is pulled free from the 
connector strip 35 once the head 47 reaches the strip 35. 
As shown in FIG. 7, the contact jaw 41 includes a pocket 50. The contact 
jaw 43 has a corresponding shape to be able to reach into or engage the 
pocket 50 of the contact jaw 41 in a resting state. The contact jaw 41 has 
a ramp surface 48 which causes the tilting motion of the contact jaw 41 
once the screw head 47 contacts the ramp surface 48. The contact jaw 43 
similarly includes a ramp surface 49. When viewed in the driving 
direction, the ramp surface 48 of the contact jaw 41 is arranged before 
the ramp surface 49 of the contact jaw 43. Thus, during the screw driving 
process, the screw head 47 first contacts the ramp surface 48 so as to 
tilt the contact jaw 41 laterally away from the screw 32', thereby 
releasing the contact jaw 43. Thereafter, the screw head 47 contacts the 
ramp surface 49 so as to tilt away the contact jaw 43. In this manner, the 
screw 32' is securely held and guided by the contact jaws 41 and 43 until 
the screw has reached the solid wood or steel of the workpiece 34. In this 
manner, the screw 32' is securely held against tipping in the sheet-rock 
panel 33, and the screw does not rely on a screwing grip in the sheet-rock 
material. 
Although the invention has been described with reference to specific 
example embodiments, it will be appreciated that it is intended to cover 
all modifications and equivalents within the scope of the appended claims.