CA1039001A - Electric fastener driving tool - Google Patents

Abstract

ELECTRIC FASTENER DRIVING TOOL

Abstract of the Disclosure An electric fastener driving tool includes a vane carried by the armature and movable in a cylinder in response to movement of the armature in drive and return strokes.
Movement of the vane in the cylinder during the return stroke displaces air through a restricted path thus preventing undesirable rebound. The vane is unloaded during the drive stroke by a check valve controlling flow through a bypass passage extending through the vane. The air path includes a portion surrounding the armature winding to cool the winding with air moved through the path by the vane.

Description

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The present invention relates to electrically operated ~astener driving tools and in particular to the prevention of undesirable armature rebound.
Electric fastener driving tools of the type to which the present invention relates commonly include an armature carry-; ing a driver blade and propelled through a drive stroke upon energization of a winding. A spring typically is provided for returning the armature to its original position in a return stroke following the drive stroke, Fasteners are supplied to the drive path of the driver blade prior to the drive stroke and are driven through the drive path and into a workpiece by ~he driver blade. Tools of this type are disclosed in United States patents No. 3,172,121 - Doyle et al and No. 3,209,180 - Doyle.
One of the problems encountered with fastener driving tools of this character is that of ar~ature rebound, When the resistance encountered by the armature in a drive stroke is relatively small, for example when short fasteners are driven, the armature rebound may be excessive. This rebound cannot only cauæe damage to the tool, but also can cause a second rebound at the end of the return stroke wherein the driver can ~' return part way through a drive stroke and drive another fastener part way along the drive trac~. When this occurs, the next energization of the winding can result in a jamming of the . .
fa~teners in the drive track due to the presenc~ of ~wo fasteners in the track at the ~ame time.
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; In the two above identified United States patents . .
Yj there are disclosed arrangements capable of limiting armature ~ rebound. In these arrangements a vane i8 carried by the armature - and moves in a cylindrical air chamber in the tool housing. The ~ 30 cylindrical chamber is part of an air path extending to the ., . . ' :

_ t _ , vicinity of electrical components requiring cooling. As the armature moves through drive and return strokes~ the vane displaces air in the path and causes cooling air to flow. Due to the restricted nature of the air path, the vane also has a damping effect slowing rebound of the armature.
An unfortunate difficulty encountered with these known vane and cylinder arrangements is that damping takes place not only during the -rebound stroke but also during the drive stroke. The loss of driving power in structures developed heretofore has been so severe that such known arrangements have not been entirely satisfactory.
Among the important objects of the present invention are to provide an improved electrically operated fastener driYing tool; to provide a tool wherein undesirable armature rebound is prevented; to prevent such undesir-able rebound without substantially diminishing the force of the drive stroke;
and to provide an improved tool overcoming the disadvantages, including those discussed above, of known electric fastener driving tools.
In brief, in accordance with the above and other objects of the ~ -~
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present invention, there is provided an electrically operated fastener driving tool comprising a housing, an annular winding within said housing having a central axial opening, an armature slidably mounted in said opening, .,.~ ~ 20 nose means defining a drive path, a driver carried by said armature and movable in a drive stroke in said drive path upon energization of said wind-- ing, means for introducing fasteners into said drive path, biasing means for moving said armature and said driver in a return stroke following said .~
drive stroke, a cylindrical chamber in said housing, said armature including a portion disposed in said chamber for movement parallel with the chamber axis during said drive and return strokes, an air path through said housing including said chamber and first and second opening means communicating between opposite ends of said chamber and the exterior of said housing, an air resistance vane carried by said armature portion within said chamber, .. , ~,, . ~ . .

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and a check valve supported on said vane and operated by air in said air path for unloading said vane during drive stroke movement of said armature.

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~n accordance with an important feature of the ~nven- ;
tion, an air displacement me~ber i~ carried by the armature within the chamber so that the displacement of air during the return stroke damp~ movement of the àrmature and prevents ~, 5 undesirable rebound The air displacement member i~ unloaded or bypassed during the drive ~troke so that re~istance to 7 movement during the drive stroke i~ minimized, Preferably, a ~ , bypass passage extends through the air displacement member and .3~ ~ is controlled by means of a check valve ~upported on the air 10 displacement member The present invention together with the above and other objects and advantage~ will be best under~tood from the following d-tail~d description of the embodiment of the invention illustrat-ed in the drawings, wherein ,~ ~15 ~ FIG 1 is a part~al sectloDal view of~an elec~ric fastener driving tool constructed in accordance with the present invention PIG 2 ~ a view similar to FIG 1 illustrating the tool in the midst of a drive strokei and ~ ~
20~ FIG 3 is a~perspeetive :view partly broken away-of a portion of the~tool of FIG 1 ~ ~ -,,~ a~ing refer-nce now~to th- drawings there is illus- -tr-ted~an~ otrically~operated faJténer driving-tool designated a~a~whole by~the reference numer~l 10 and constructed in , 25~ ' accordance~w~th the prinoiple~ of the pre~ent invention In gen l~the tool 10 include~-a~hou~ing 12 having a forward or ; ;~ ; he~d portion 14 and a handle portion 16, only a small fra$ment ~, ~ of ~hdoh~i~ illustrated in FIGS 1 and 2 Within the head p~rtion 14 are upportod a olonoid w~nd~ng 18 and ~n armature '~ 30 20 Upon enorgization of windlng 18, ~rmature 20 is accelerated . ,~ .

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to move a driver blade 22 through a drive track 24 thereby to drive a fastener supplied to the drive track 24 from a magazine 26.
In accordance with the present invention, the tool 10 is provided with an improved rebound controlling structure generally designated as 30. As described in detail below, the struc~ure 30 performs important functions in the operation of the tool 10 including the prevention of unde-cirable armature rebound following a drive stroke while avoiding undesirable 10 loss of power during ~he drive stroke. In the illustrated embodiment of the invention, the structure 30 also provides ~ cooling of the winding 18 and, i~ desired, other electrical - components.
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Proceeding now to a more detailed description of the ~ 15 structure and operation of the tool 10, the head portion 14 is genexally cylindrical in shape and includes a main body member 32 the upper end of which i8 closed by a cap member 34 held in ;-~
place by cap screws 36. The lower end of body 32 i provided ~- with an opening 38 within which is received a nose assembly 40 . 20 defining the drive track 24. A passage 42 in the nose assembly :
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' 40 communicates with the drive track 24 and provides a path for ; the escape o~ air propPlled into the drive track during downward ;~, acceleration of the armature 20.
In order to cushion impacts of the armature 20 as it s 25 reaches its lowermost or drive position and its uppermost or .."~i 1 return position, a pair of resilient bumpers 44 and 46 are provided. Bumper 44 is received in a complementary recess at the upper end of the nose aQsembly 40, while bumper 46 i9 , :~
c~rr~ed by the cap member 34.
Magazine 26 may be of any conventional type and serves . . - . , ~
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10~9001 . to advance fasteners from a supply of fasteners into the drive - track. The fastener width is interrelated with the width of the dr~ve track to the end that only a single fastener is presented to the driver blade 22 within the drive track 24 prior to each `~ 5 drive stroke of the blade.
The lower portion of the head portion 14 defines a cavity ~8 for receiving the solenoid winding 18. The winding 18 is wound in conventional fashion upon a bobbin structure includ-- ing an ~nner sleeve 50 and an outer casing 52. A pair of electrical conductors 54 and 56 ara interconnected with the ~i winding 18 in the usual ~ashion for periodically energizins the 5 ` winding, and it should be understood that in accordance with , known prac~ice a suitable trigger operated switch and power i supply circui~ry may be disposed within the handle portion 16 , of~the housing 12.
Winding 18 is held securely in place within cavity 48 by means of a snap ring 58. A spider member 60 retained below . ~ .
the snap ring 58 captures the winding casing 52 against a support shoulder 62 ~efined at the lower end of the body member 32.
'-..,d Armature 20 is formed of magnetic ma~erial and is cylindrical in shape ~o as to slide freely through a central ~ axial opening 64 defined within winding 18 by the inner sleeve 50. Preferably armature 20 may be partly hollow in order to concentrate the msjority of its mass within the winding 18

2~ th OE eby to provide efficient ~agnetic accelexation of the armature during a ~rive stroke. The driver blade 22 is-captured within a recess in the lower end of the armature 20 by means of ,~, d a retaining pin 66. As will read~ly be understood by those skilled in the art, the shape of the driver blade 22 is chosen to ~ 30 complement that o the drive track 24 and the partlcular type of i~ fastener to be driven by the tool lO.
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n order to return the armature 20 and dri~er blade 22 to its return or normal position following each drive stroke, a biasing spring 68 is provided. In the illustrated arrangement, spring 68 comprises a coil spring held in compression between the snap ring 58 and a qpring retainer 69 carried near the . uppermost end of the armature 20.
.. In many respects the tool 10 may be similar in struc-ture and operation to electrically operated fastener driving tools known in the past such as those d~sclosed in the above identified United States patents No. 3,172,121 and No. 3,209,180. .
Reference may be had to those patents for a description of portions of the tool 10 beyond those necessary for an understand~
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~ ing of the present invention. . -~
.:~ In order to prevent undesirable rebound of the ~ ~ :
,? . ~ :-!~ 15 armature 20, and to permit an unimpeded drive stroke, the tool .` ~ 10 is provided in accordance with the present invention with the : novel structure.30. Proceeding now to a description of the . structure~30, with reference to FIGS. 1 and 2 it can ~e.As~en -that the head portion 14 of the housing 12 is provided with a . ` ~ 20 cylindrical chamber 70 disposed above and coaxial with the cavity 48 and winding 18. Armature 20 includes an upper end portion 72 disposed in chamber 70j which end portion moves .~.
~xially between upper and lower positions as the armature 20 ~ and driver blade 22 move in drive and return strokes.
.~ 25 In accordance with the invention, an air displacement . . . ~ .
~ member in ~he form of a vane 74 is carried at the end 72 of the i~ armature 20 and cooperates with the chamber 70 to provide.for damping or slowing of the rebound motion of the armature 20.
~ A check valve generally designated as 76 unload~ or bypasseQ
-~ 30 the vane 74 during each drive stroke to the end that the force ~;
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1(S39001 or power generated in the drive stroke is not decreased by the structure 30.
An air path is defined through the housing 12, and in part is formed by the cylindrical chamber 70. M~re specifically, an opening or port 78 is formed in cap member 34 at the upper ; end of the cylindrical chamber 70. The opposite end of chamber 70 communicates through the spider member 60 with a number of openings or ports 80 formed in the side wall of body member 32 adjacent ~he lower end of winding 18. Air flows between the cylindrical chamber 70 and the ports 80 along a segment of the air path designated as 82 and defined by a clearance between the inner wall of the winding cavity 48 and the outer wall of the winding casing 52, Due to the provision of air path segment 82, displaced air intimately envelopes and thus cools winding 18.
, 15 If desired, structure 30 may al~o serve to provide a :i flow of cooling air adjacent other electrical components mounted in handle portion 16 of the housing 12. For this purpose, there .~ - is provided an opening or port 84 extending from the lower end of the cylindrical chamber 70 to the interior of the handle 16 wherein may be mounted an electrical switch, power supply and the like.
Vane 74 is in the form of a ~lat ~heet of functionally `
~igid material such as plastic or the like and has an outer ~ circumference substantially equal to the inner diameter of :-~ 25 chamber 70. The vane 74 is held in place between the spring ;. xetainer 69 and a retention bushing 86 mounted at the end 72 of :~ armature 20. Due to a relatively close fit between the outer edge of the vane 74 and the wall of the chamber 70, the vane is , capable of acting as a piston within the chamber 70 by displacing air upon movement axially through the chamber.
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1~39001 In order to unload or bypass the vane 74 during a drive stroke, the check valve 76 includes a valve member in the form of a sheet or layer of flexible material 88 such as rubber or the like overlying the upper face of the vane and held in position between the vane and the retention bushing 66. As can be seen in FIG. 3, the valve member 88 is sufficiently large in diameter to overlie a number of bypass passages or openings 90 formed at spaced positions around the vane 74. The material of valve member 88 is chosen to be sufficiently flexible so that 10 the openings 90 are uncovered by air pressure during downward ~ ~
motion of the vane 74 and are covered or closed during upward , ~, ' motion of the vane 74.
In the operation of the structure 30 and tool 10, in the normal condition armature 20 is held by the biasing spring 68 1~ in its uppermost position against the bumper 46. When winding 18 is energized, the armature 20 is subjected to a magnetic field and is abruptly propelled downwardly in a drive stroke ~, during which the drives blade 22 picks up a fastener in the drive track 24 and drives the fastener into a workpiece.
~^ 20 ~dvantageously, the structure 30 does not impede movement of the armature in a drive s~xoke. More specifically, "~ ,as the vane 74 mDves downwardly within the chamber 70, the check ~,, valve 76 opens as illustrated in ~IG. 2 due to deflection of the ,~ ~lexible valve member 88. Air flows freely through the bypass ., ,; 25 openings 90 thus unloading or disabling the vane 74. Because ~,~ the structure 30 provides little resistance to movement of the ,'~, armature 20, a powerful and unimpeded drive stroke results.
~- At the end of the drive stroke, the lower end of `::
armature 20 strikes the bumper 44. Under some conditions, the ~' 30 resistance encountered by the driver blad~ 22 may be relatively :

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small, as for example when a short fastener is dr~ven or when the workpiece material exhibits relatively little resistance.
Under such circumstance~, at the end of the drive stroke not only is the biasing spring 68 fully compressed, but also bumper 44 may be substantially compressed. As a result, a substantial force in the upward direction may be applied to armature 20 by ~, the bumper 44 and spring 68 resulting in a tendency for a power-ful rebound. In the absence of a rebound control such as provided by the structure 30, the rebound may be so great that the arma-; 10 ture is propelled forcefully against the upper bumper 46 from `~ which it once again rebounds in a downward direction. This can reault in partial driving of the next fastener from the magazine assembly 26 so that ppon the next energization of winding 18, , a jam of fasteners in the drive track 24 occurs. This forceful upward rebound may also result in damage to the cap member 34 ~;~ and/or the cap screws 36.
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The problem of excessive rebound is overcome by the ~ structure 30 of the present invention. More specifically, ,~ durinq upward movement during a return stroke of the armature 20, the check valve 76 is closed by movement of the valve member 88 against the surface of the vane 74. ~he openings or bypass passages 90 are closed and thq flow of air therethrough is prevented. As a result, the vane 74 encounters substantial resistance as it displaces air along the air path through the head 14. The amount of resistance can be controlled through dimensioning the air path and specifically through properly di~ensioning the port 78 and/or the ports 80. In the illustrated ~i ~rrangement si~ce the~e ports each have effective areas substan-tially smaller than the cross ~ectional area of the chamber 70, ~; 30 motion of the armature 20 ~n a return stroke i~ substantially . ~ .
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damped or snubbed and excessive rebounds are positively and reliably prevented.
Only minimal air is displaced in the air path during a drive stroke due to opening of the check valve 76. In a S return stroke the situation is different because the check valve 76 is closed. Thus, during each return stroke a substantial volume of air is exhausted fxom the housing 10 through the upper port 78 and a similar volume of air is drawn into the housing through the lower ports 80, the path segment 82, and, if desired, the port 84. This air flows intimately around ~he . ~inding 18, and, if desired, other electrical components and ~-p~oduces a de~irable cooling effect.
While the invention has been described with reference to details of the illustrated embodiment, such details are not , 15 intended to limit the scope of the in~ention as defined-in the following claims.

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Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An electrically operated fastener driving tool comprising a housing, an annular winding within said housing having a central axial opening, an armature slidably mounted in said opening, nose means defining a drive path, a driver carried by said armature and movable in a drive stroke in said drive path upon energization of said winding, means for introducing fasteners into said drive path, biasing means for moving said armature and said driver in a return stroke following said drive stroke, a cylindrical chamber in said housing, said armature including a portion disposed in said chamber for movement parallel with the chamber axis during said drive and return strokes, an air path through said housing including said chamber and first and second opening means communicating between opposite ends of said chamber and the exterior of said housing, an air resistance vane carried by said armature portion within said chamber, and a check valve supported on said vane and operated by air in said air path for unloading said vane during drive stroke movement of said armature.

2. The tool of claim 1, said vane comprising a rigid planar member substantially the size of the chamber, aperture means in said vane, and said check valve con-trolling flow through said aperture means.

3. The tool of claim 2, said check valve com-prising a flexible valve member overlying said aperture means.

4. The tool of claim 1, said air path further comprising a portion of said path surrounding said winding.

5. The tool of claim 1, at least one of said first and second opening means having an effective cross sectional area substantially smaller than the cross sectional area of said chamber.

6. An electrically operated fastener driving tool as claimed in claim 3, said aperture means comprising a plurality of holes in said vane in a generally circular array surrounding said armature, said valve member comprising a sheet of flexible material having a shape corresponding to that of the vane and overlying said array of holes.

7. An electrically operated fastener driving tool as claimed in claim 6 further comprising a retention bushing fixed to said armature portion, said biasing means comprising a spring, a spring retainer surrounding said armature portion adjacent said bushing, said spring being held in compression against said spring retainer, and said vane and said valve member being sandwiched between said retention bushing and said spring retainer.