Safety Assembly For Fastener Driving Tool

Abstract

A safety mechanism particularly suited for smaller fastener driving or applying tools includes a mechanical latch carried on the nosepiece structure of the tool with a part of the latch disposed within the drive track immediately below the end of the driver blade. The latch is coupled to a workpiece engaging member which retracts the latch to permit driver blade movement when the tool is placed adjacent a workpiece. If the tool is operated before being placed against a workpiece, the driver blade engages and locks the latch in latching position so that it cannot be retracted or released by thereafter placing the tool against the workpiece. The illustrated embodiments include both positive and indirect cam type couplings between the latch and the workpiece engaging member as well as pivoting and sliding latches.

Description

The present invention relates to a fastener driving or applying tool and, more particularly, to a new and improved safety assembly for a fastener applying tool.

Safety assemblies for insuring that pneumatic and other power operated fastener driving or applying tools cannot be operated without being placed adjacent a workpiece are well known. Some of these assemblies use a floating fulcrum or other linkage to disable actuation of a single control valve until the tool is placed adjacent the workpiece and a manual trigger is actuated. Other assemblies use a plurality of control valves individually actuated by the manual trigger and the workpiece engaging member.

However, the size of and the space required for these assemblies are such that they are not particularly well suited for small tools such as those driving small or fine wire staples. In addition, these assemblies operate to restrain operation of the controls for the tools, and it is not easy to manufacture the same tool both with and without a safety assembly. This is of particular significance with respect to small tools because at present the requirements for a safety on a small staple or tacker vary considerably. In addition, in instances where this type of tool requires a safety, there is an increasing tendency for the safety to be such that it requires the tool to be placed against a workpiece before the operation of the trigger.

Accordingly, one object of the present invention is to provide a new and improved fastener applying tool.

Another object is to provide a new and improved safety assembly particularly suited for small tools.

A further object is to provide a new and improved safety assembly requiring the tool to be placed against the workpiece before operation of the trigger or manual control in order to permit the tool to be actuated.

A further object is to provide a safety assembly that positively restrains driver movement and does not require modification of the standard controls for the power or drive controlling unit.

Another object is to provide a safety assembly including a latch mechanically movable between blade latching and blade released positions.

In accordance with these and many other objects, an embodiment of the invention comprises a pnuematically actuated tool for applying fasteners or driving staples having a power unit or piston-cylinder arrangement controlled by a manual valve for actuating a driver blade which drives fasteners or staples supplied to a drive track in a nosepiece within which the lower end of the driver blade is reciprocably mounted. The safety assembly includes a mechanical latch normally disposed in the drive track in a position interposed between the lower end of the driver blade and the next staple or fastener to be applied. The mechanical latch is coupled to a workpiece engaging member projecting below the opening from the drive track through which fasteners are discharged by the fastener driving blade. When the tool is placed against a workpiece with the discharging opening in proximity to the workpiece, the workpiece engaging member is moved and is effective through a coupling to the mechanical latch to retract this latch to a released or ineffective position. When the usual manual control such as a trigger is then actuated to control the power unit to move the driver blade downwardly, the blade is free to move within the drive track to engage and set a staple.

On the other hand, if the trigger or manual control is actuated before placing the nose piece structure of the tool against a workpiece, the latch remains in its latching position interposed between the lower end of the driver blade and the fastener to be driven. The force applied to the blade by the operation of the tool causes the blade to bear against the mechanical latch and bias it to a position in which it cannot be retracted. Thus, placing the tool against a workpiece following the actuation of the trigger is not effective to retract the mechanical latch, and the blade cannot move through its usual power stroke, and the tool can only be operated by releasing the manual control, placing the tool against the workpiece, and thereafter reoperating the manual control.

In the various embodiments of the invention, the latch is mounted for sliding rectilinear or pivoted movement, and the coupling between the workpiece engaging member and the latch is both positive and indirect. Using the positive coupling, the workpiece engaging member cannot be depressed if the tool is operated prior to placing the nosepiece against a workpiece. With the indirect coupling, the workpiece engaging member can be depressed or actuated following operation of the tool, but his movement of the workpiece engaging member is not effective to release the latch.

Many other objects and advantages of the present invention will become apparent from considering the following detailed description in conjunction with the drawings in which:

FIG. 1 is a side elevational view in partial section illustrating a first embodiment of the safety assembly shown in a latching or normal position;

FIG. 2 is a fragmentary end elevational view, slightly enlarged, taken in the direction of line 2--2 in FIG. 1;

FIG. 3 is a fragmentary side elevational view, slightly enlarged, showing the safety assembly of FIGS. 1 and 2 in a released position;

FIG. 4 is a fragmentary end elevational view taken along line 4--4 in FIG. 3;

FIG. 5 is a fragmentary side sectional view of a second embodiment of the invention shown in a latching position;

FIG. 6 is a fragmentary side elevational view similar to FIG. 5 illustrating the safety assembly in an actuated or released position;

FIG. 7 is a fragmentary side sectional view illustrating a third embodiment of the safety assembly shown in its normal or latching position;

FIG. 8 is a fragmentary end elevational view taken in one direction of line 8--8 in FIG. 7; and

FIG. 9 is a sectional view similar to FIG. 7 illustrating the safety assembly in a released or actuated position.

Referring now more specifically to FIG. 1 of the drawings, therein is illustrated a fastener driving tool indicated generally as 10 having a safety assembly which is indicated generally as 12 and which embodies the present invention. The tool 10 includes a housing 14 containing a pneumatically actuated piston-cylinder power unit (not shown) for reciprocating a connected driver blade 16, the lower end of which is slidably mounted within a drive track 18 formed in a nosepiece structure 20. A magazine assembly indicated generally as 22 disposed between the nosepiece structure 20 and the lower end of a handle portion 14A of the housing feeds successive fasteners to be applied, such as staples 24 from a strip thereof, into the drive track 18.

When the tool 10 is to be operated, the lower end of the nosepiece structure 20 is placed adjacent a workpiece to actuate the safety assembly 12. If a manual or trigger actuated control assembly indicated generally as 26 is then operated, the power unit drives the blade 16 downwardly within the drive track 18 to engage and set the staple 24 supplied to the drive track 18 by the magazine assembly 22. If, on the other hand, the trigger actuated control assembly 26 is first actuated prior to placing the nosepiece 20 adjacent a workpiece, the safety assembly 12 remains in a latch condition, and the driver blade 16 is not free to move.

The tool 10 can be of any suitable well known construction and, for example, can comprise a fastener driving tool of the type shown in U.S. Pat. No. 3,673,922. In a tool of this construction, the actuation of the control unit 26 supplies pressurized air to the piston-cylinder arrangement so that the driver blade 16 is driven downwardly through a power stroke. When the control unit 26 is released, the blade 16 is retracted. Alternatively, the control included in the tool 10 could be such as to automatically restore the blade 16 to its normal position while the control unit 26 remains operated. The magazine assembly 22 can also be one of those well known in the art and can, for example, comprise the magazine assembly shown in U.S. Pat. No. 3,437,250. Such a magazine includes resilient biasing means for forcing a strip of staples 24 to the left (FIG. 1) so that the end staple 24 is always disposed within the drive track 18 beneath the lower end of the driver blade 16 when this blade is in its normal or retracted position.

The safety assembly 12 is mounted on the workpiece structure 20 adjacent the front of the tool 10. The assembly 12 includes a mechanical latch member 28 with a projecting or finger portion 28A. The finger portion 28A is interposed between the lower end of the blade 16 and the crown of the staple 24 in the drive track 18 when the latch member 28 is in its latching position. The latch member 28 is provided with access to the drive track 18 through an opening 30 formed in a front wall 20A of the nosepiece structure. Engagement of the edge surfaces of the latch member 28 with the adjacent wall surfaces of the housing 14 and the nosepiece structure 20 mounts the latch for reciprocating rectilinear movement from left to right and from right to left as shown in FIG. 1.

To provide means for controlling the position of the mechanical latch 28 in dependence on the position of the tool 10 relative to a workpiece, there is provided a workpiece engaging member or element 32 which is disposed against the flat outer surface of the front wall 20A within a centrally disposed recess formed in the inner surface of a cover plate 34. The plate 34 is secured to the front wall 20A of the nosepiece structure 20 by any suitable means such as a plurality of machine screws or bolts 36. The upper end of the retaining plate 34 is provided with a centrally disposed opening in which is received the outer portion of the mechanical latch 28 and an outward projection 32A on the workpiece engaging member 32. The projection 32A extends generally parallel to and in a side-by-side relation with the latch member 28.

To provide means for shifting the position of the mechanical latch 28 in dependence on the position of the workpiece engaging member 32, there is provided a cam follower pin 38 secured to a side wall of the projecting portion 32A on the workpiece engaging member 32. The outer or free end of the cam follower pin 38 is disposed within an upwardly and inwardly inclined closed slot 40. The slot 40 provides a cam surface, and the pin 38 provides a bearing surface bearing against the cam surface defined by the slot 40. In the normal position of the safety assembly 12 in which the latch member 28 is in its latching position with the projecting portion 28A inserted into the drive track 18 beneath the lower end of the driver blade 16, the pin 38 occupies the position within the slot 40 shown in FIGS. 1 and 2 of the drawings. This normal position is established by a compression spring 42 disposed within a centrally formed slot 44 in the workpiece engaging member 32 and interposed between the part of the member 32 defining the lower end of the slot 44 and a pin or projection 34A formed integral with or secured to the retaining plate 34 and normally disposed within the upper end of the slot 44. This compression spring 42 biases the workpiece engaging member 32 to its lowermost position determined by engagement of the upper end of the slot with the projection 34A. In this position, the lower end of the workpiece engaging member 32 projects beyond the lower end of the drive track 18 and more specifically below a fastener discharging opening 18A therein.

When the tool 10 is to be operated in its proper sequence, the lower end of the nosepiece structure 20 containing the opening 18A is pressed against or immediately adjacent a workpiece 46 including, for example, a layer of material 46A to be attached to a base member 46B. When the tool is moved to this position (FIG. 3), the workpiece engaging member 32 is moved upwardly against the bias of the compression spring 42 so that the pin 38 moves upwardly within the slot 40. During relative movement between the pin 38 and the slot 40, the mechanical latch 28 is displaced to the left from the position shown in FIG. 1 to the position shown in FIG. 3 so that the projecting portion 28A on the latch member 28 is withdrawn from the drive track 18 to a position disposed to the side of lower end of the driver blade 16. During this movement, the compression spring 42 is compressed between the material defining the lower end of the slot 44 and the pin or projection 34A on the retaining plate 34 (FIG. 4).

If the manual control 26 is then actuated, the power unit moves the driver blade 16 downwardly so that it engages the crown of the staple 24 in the drive track 18 and moves this staple downwardly through the discharge opening 18A. Further movement of the driver blade 16 drives the staple 24 through the parts 46A and 46B of the workpiece 46. When the driver blade 16 is retracted, the magazine assembly 22 feeds the next staple 24 into the drive track as soon as the lower end of the blade 16 clears the next staple 24 supplied by the magazine 22. If the tool 10 is maintained in constant engagement with the workpiece, as by sliding the tool 10 along the workpiece 46, the trigger or manual control unit 26 can be reoperated to drive additional staples.

However, when the tool 10 is lifted out of engagement with the workpiece 46, the compression spring 42 biases the workpiece engaging member 32 downwardly from the position shown in FIGS. 3 and 4 to the position shown in FIGS. 1 and 2. During this movement, the bearing surface on the pin 38 slides along the cam surface defined by the slot 40 and shifts the mechanical latch 28 to the right from the position shown in FIG. 3 to the position shown in FIG. 1 so that the projecting portion 28A on this latch is interposed between the staple 24 in the drive track 18 and the lower end of the driver blade 16.

If an attempt is now made to operate the tool 10 by actuating the control unit 26, the driver blade attempts to move downwardly, and its lower end bears against the projecting portion 28A on the latch 28. This clamps the mechanical latch 28 against the adjacent surfaces of the housing 14 and the front wall 20A of the nosepiece to hold it in position as well as arresting downward movement of the driver blade 16. Since the lower end of the driver blade 16 is positioned in immediate proximity to the projecting portion 28A, the blade 16 does not attain any appreciable amount of energy, and the mechanical latch 28 is not injured. In this manner, operation of the tool 10 to drive a staple 24 into the workpiece 46 is inhibited whenever the control 26 is operated prior to placing the nosepiece structure 20 against or adjacent the workpiece 46.

The pin 38 and the slot 40 in the mechanical latch 28 provide a positive coupling between the latch 28 and the workpiece engaging member 32. Thus, if the latch 28 is held in its latching position by the biasing force applied by the lower end of the actuated blade 16, the workpiece engaging member 32 cannot be displaced from the normal position shown in FIGS. 1 and 2. In other words, with the mechanical latch 28 held in the position shown in FIG. 1 by engagement with the lower end of the blade 16, any attempts to force the member 32 upwardly by placing the tool against the workpiece are ineffective because the forces that can be developed tending to move the mechanical latch 28 to the left (FIG. 1) by applying upwardly directed force to the lower end of the member 32 are not sufficient to overcome the retaining or clamping force applied to the projection 28A by the driver blade 16. Thus, the tool 10 cannot be made to operate after the control 26 has been operated by forcing the workpiece engaging member 32 against the workpiece 46. When the tool 26 is released and the pneumatic bias removed from the drive system for the driver blade 16, the mechanical latch 28 is released and can be shifted from its latching position shown in FIG. 1 to the released position shown in FIG. 3.

Referring now more specifically to FIGS. 5 and 6 of the drawings, therein is illustrated another embodiment of the safety assembly which is indicated generally as 50. The safety assembly 50 can be used w ith the tool 10 and is shown in the drawings in conjunction with such a tool. However, in FIGS. 5 and 6, the front wall of the nosepiece structure 20 is designated as 52 rather than as 20A as in the embodiment shown in FIGS. 1-4 because of slight structural differences. The safety assembly 50 is mounted on the front wall 52A and provides means for positively retaining or latching the driver blade 16 in its normal or retracted position whenever the tool 10 is operated by the actuation of the control unit 26 prior to placing the discharging opening 18A adjacent the workpiece 46.

To provide means for normally latching or retaining the driver blade 16 in its normal or retracted position, a generally U-shaped mechanical latch 54 with an L-shaped upper portion is provided. The front wall 52 includes a smaller lower opening 56 in which the lower leg of the latch 54 is disposed and a larger upper opening 58 communicating with the drive track through which an upper leg of the latch 54 extends so as to be disposed beneath the lower end of the driver blade 16 in the normal or latching position of the latch member 54. A compression spring 60 disposed in an outwardly facing recess in the front wall 52 engages the bight portion of the U-shaped latch 54 to provide a bias directed to the left in FIG. 5.

To provide means for shifting the position of the latch 54 in dependence on placing the tool 10 against a workpiece 46, there is provided an elongated closed wire loop forming a workpiece engaging member 62. A lower bight or transverse portion 62A of the workpiece engaging member 62 is normally disposed beneath the discharge opening 18A from the drive track in the nosepiece structure 20. A compression spring 64 interposed between the housing 14 and an upper transverse or bight portion 62B on the workpiece engaging member 62 biases the portion 62B into engagement with the area forming the junction of the leg and bight portions of the latch 54. The parts of the assembly 50 are retained in position adjacent the front wall 52 of the nosepiece structure 20 by a generally U-shaped cover plate 66 which is secured to the nosepiece structure 20.

The compression spring 64 is stronger than the compression spring 60, and thus the compression spring 64 acting on the top bight portion 62B of the workpiece engaging member 62 overcomes the bias of the spring 60 and forces the end of the upper leg of the latch 54 to the normal position within the drive track 18 disposed beneath the lower end of the driver blade 16 as shown in FIG. 5. When the tool 10 is moved against the workpiece 46 (FIG. 6), the lower bight portion 62A engages the workpiece 46, and the workpiece engaging member 62 is moved upwardly against the bias of the compression spring 64. The bight portion 62B provides a bearing surface bearing against a cam surface provided by the arcuate junction of the leg and bight portions of the latch 54. Thus, as the bight portion 62B moves upwardly, the compression spring 60 is effective to pivot or displace the mechanical latch 54 to the left to the position shown in FIG. 6 so that the outer free end of the upper leg of the latch 54 is moved from beneath the lower end of the driver blade 16. Thus, when the manual control 26 is operated, the driver blade 16 is free to move downwardly and drive the staple 24 within the drive track 18 into the workpiece 46, as shown in FIG. 6. So long as the tool 10 is held against the workpiece 46, the manual control 26 can be repeatedly operated to produce repeated power strokes of the tool during which successive staples 24 are driven.

When the tool 10 is moved away from the workpiece and the driver blade 16 is retracted to its normal position, the compression spring 64 moves the workpiece engaging member 62 downwardly so that the bearing surface provided by the bight portion 62B cams against the arcuate cam surface on the latch 54. This cams the upper leg of the latch 54 into the drive track 18 so that it outer free end is disposed beneath the lower end of the blade 16. This displacement takes place against the bias of the spring 60. The tool 10 must now be placed against the workpiece 46 and the workpiece engaging member 62 elevated before the driver blade 16 can be moved through another fastener driving stroke.

If the manual control 26 is operated with the safety assembly 50 in the position shown in FIG. 5, the initial downward movement of the driver blade 16 produced thereby forces the lower end of this blade against the free end of the upper leg of the mechanical latch 54 and forces this latch into contact with the cover plate 66 and portions of the front wall 56 to lock this latch in the latching position shown in FIG. 5. If the tool 10 is thereafter placed against the workpiece 46, the workpiece engaging member 62 can be moved upwardly against the bias of the compression spring 64 because of the indirect coupling between the member 62 and the mechanical latch 54. However, the biasing force applied to the mechanical latch 54 by the blade 16 exceeds the resilient bias afforded by the spring 60, and the latch 54 remains in its latching position. It is necessary to release the manual control 26 to remove the driving force of the driver blade 16 before the spring 60 is effective to retract the latch 54 to its released position. Reoperation of the manual control 26 at this time permits the driver blade to move through a fastener driving stroke.

A third embodiment of a safety assembly which is indicated generally as 70 is illustrated in FIGS. 7-9 of the drawings. The safety assembly 70 is also adapted for use with a fastener driving tool similar to the fastener driving tool 10 including the power unit for reciprocating the driver blade 16 and the magazine assembly 22 for supplying successive staples or fasteners 24 to the drive track 18 in the nosepiece 20. In the safety assembly 70 the front wall of the nosepiece structure 20 is of a different configuration from the front walls 20A and 52 of the safety assemblies 20 and 50, respectively, and the front wall of the nosepiece structure 20 in the safety assembly 70 is designated as 72.

To provide means for preventing movement of the driver blade 16 out of its normal position whenever the manual control 26 for the tool 10 is operated prior to placing the discharge opening 18A against the workpiece 46, a generally L-shaped mechanical latch 74 is provided having an upper leg 74A which extends through an opening 76 in the front wall 72 so that the outer free end of the leg 74 is disposed within the drive track 18 immediately beneath the lower end of the driver blade 16 and above the crown of the staple 24 supplied to the drive track 18 by the magazine 22. The lower end of the other leg of the mechanical latch 74 is bifurcated or provided with a notch and rests on a locating pin 78. One end of the pin 78 is staked or otherwise secured to the front wall 72. A collar 78A is provided on the pin 78 to aid in locating the latch 74 and to permit a limited degree of pivotal movement of the latch about its point of engagement with the pin 78. The outer end of the locating pin 78 is received within an opening formed in a closure plate 80 which is secured to the front wall 72 by a plurality of suitable fastening means such as machine bolts or screws 82. The front wall of the retaining plate or housing 80 is spaced from the grooved surface of the front wall 72 to define a cavity for receiving the moving components of the safety assembly 70.

To provide means for controlling movement of the mechanical latch 74 between its latching position (FIG. 7) and its released position (FIG. 9), a workpiece engaging member 84 is provided. The workpiece engaging member 84 includes a somewhat thicker lower end portion 84A, the lower surface of which is adapted to be placed in engagement with the workpiece 46. This portion 84A is slidably mounted within a groove or channel 86 formed in the lower end of the front wall 72 of the nosepiece structure 20. A central portion of the member 84 is provided with a longitudinally extending opening 88 which at its lower end receives a compression spring 90, the lower end of which bears against the member 84 and the upper end of which bears against a shoulder 72A terminating the upper end of the groove 86. The compression spring 90 normally biases the workpiece engaging member 84 to the normal position shown in FIGS. 7 and 8 in which the lower end of the portion 84A projects beyond the discharge opening 18A from the drive track 18.

To provide means for controlling the position of the mechanical latch 74, a transverse upper portion 84B of the workpiece engaging member 84 which also terminates the central opening 88 includes an inwardly and upwardly inclined cam surface 92 against which bears a bearing surface formed at the junction of the two legs of the mechanical latch 74. A flat spring 94 disposed within an opening or recess 96 in the front wall 72 engages the longer leg of the latch 74 and continuously biases the bearing surface on the latch 74 against the cam surface 92. The compression spring 90 provides a greater biasing force than the spring 94 so that in the normal position of the assembly 70 (FIGS. 7 and 8) the free end of the leg 74A of the latch 74 is disposed beneath the lower end of the driver blade 16.

When the tool 10 is moved against the workpiece 46 (FIG. 9), the end portion 84A of the workpiece engaging member 84 engages the workpiece 46 and is moved upwardly against the bias of the spring 90. During this movement the cam surface 92 moves upwardly, and the flat spring 94 pivots the latch 74 in a counterclockwise direction about the pivot defined by the pin 78 from the position shown in FIG. 7 to the position shown in FIG. 9. This retracts the leg 74A of the latch 74 from the drive track 18 and permits the driver blade 16 to move downwardly through a power or fastener driving stroke when the manual control 26 is actuated. The tool 10 can be operated one or more times so long as the workpiece engaging member 84 is maintained in engagement with the workpiece 46 and is held in its upper or actuated position.

When the tool 10 is removed from the workpiece 46, the compression spring 90 moves the workpiece engaging member 84 downwardly so that the cam surface 92 acting on the bearing surface formed on the latch 74 pivots this latch in a clockwise direction from the position shown in FIG. 9 to the position shown in FIG. 7 against the bias of the flat spring 94. This moves the leg 74A of the latch beneath the retracted driver blade 16. Any operation of the manual control 26 and thus of the tool 10 with the assembly 70 in the position shown in FIG. 7 moves the driver blade 16 into engagement with the leg 74A to prevent downward movement of the blade 16 through a fastener driving stroke.

The biasing force applied to the latch leg 74A by the driver blade 16 under these conditions is such that the latch 74 is locked in its latching position. Since the safety assembly 70 includes an indirect coupling between the workpiece engaging member 84 and the latch 74, the workpiece engaging member 84 will be elevated to its actuated position shown in FIG. 9 by placing the operated tool 10 against the workpiece 46. However, the biasing force applied by the blade 16 to the latch leg 74A exceeds the bias of the flat spring 94, and the mechanical latch 74 remains in its latching position even though the workpiece engaging member 84 is actuated to its elevated position. The tool 10 can be operated only by releasing the manual control 26 and thereafter operating this control with the tool 10 in a position against the workpiece 46.

Although the present invention has been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art which will fall within the spirit and scope of the principles of this invention.

Claims

What is claimed and desired to be secured by Letters Patent of the United

1. In combination with a power driven blade for driving fasteners into a workpiece,

a drive track structure defining a drive track in which a fastener engaging portion of the blade is movable and from a lower end portion of which a fastener driven by the blade is discharged,

a mechanical latch movable into and out of the drive track and normally in a latching position latching the blade to prevent movement thereof,

a workpiece engaging means movably mounted adjacent the lower end portion of the drive track and movable from a normal position to an actuated position when the drive track structure is disposed adjacent a workpiece,

and release means coupled between the mechanical latch and the workpiece engaging means for controlling movement of the mechanical latch relative to the drive track to a released position in which the blade is free to move through the drive track and discharge a fastener when the workpiece engaging means is moved from its normal position to its actuated position.

2. The combination set forth in claim 1 in which

the mechanical latch includes a blade engaging portion extending transverse to the drive track and underlying the fastener engaging portion of the blade in close proximity thereto when the mechanical latch is in its

3. The combination set forth in claim 1 in which

the release means includes resilient means biasing the mechanical latch to its released position and cam means moved by the workpiece engaging means and coupled to the mechanical latch for controlling movement of the

4. The combination set forth in claim 3 including

additional resilient means biasing the cam means to move the cam means to

5. The combination set forth in claim 1 in which

the release means includes structure on the workpiece engaging means and the mechanical latch defining sliding cam engagement surfaces for controlling movement of the latch between its latching and released

6. The combination set forth in claim 5 in which

the mechanical latch includes a cam surface,

and the workpiece engaging means includes a surface bearing on the cam

7. The combination set forth in claim 6 in which

the cam surface on the mechanical latch is defined by an elongated slot,

and the surface bearing on the cam surface includes a pin carried on the

8. The combination set forth in claim 5 in which

the workpiece engaging means includes a cam surface,

and the mechanical latch includes a surface bearing on the cam surface on

9. The combination set forth in claim 1 in which

the workpiece engaging means includes a member slidably mounted on the drive track structure and having an opening therein closed at one end by a transverse portion,

the mechanical latch is disposed within said opening,

and the release means includes a cam surface and a bearing surface engaging the cam surface, one of the cam and bearing surfaces being formed on the latch and the other of the cam and bearing surfaces being formed on said

10. The combination set forth in claim 9 in which

the mechanical latch includes a generally L-shaped portion with one leg latching the blade and the junction of the said one leg and the other leg

11. The combination set forth in claim 1 including

means mounting the mechanical latch for generally rectilinear movement

12. The combination set forth in claim 1 including

means mounting the mechanical latch for generally pivotal movement between

13. A tool operated by a power unit for applying fasteners to a workpiece comprising

a nosepiece structure defining a drive track into which fasteners are fed at a given point and from which fasteners are discharged through an opening,

a fastener applying element movable by said power unit in said drive track between a retracted and an operated position to apply fasteners to the workpiece through the opening,

a mechanical latch movable between a latching position latching the fastener applying element against movement to its operated position and a released position permitting movement of the fastener applying element to its operated position,

workpiece engaging means movable from a normal position to an actuated position when the opening from the drive track is placed adjacent the workpiece,

release means coupled between the latch and the workpiece engaging means for moving the latch from its latching position to its released position when the workpiece engaging means is moved to its actuated position,

and control means operable to control the power unit to move the fastener applying element toward its operated position, said fastener applying element being free to move to its operated position when the latch is moved to its released position prior to operation of the control means, said fastener applying element applying a biasing force to the latch to hold it in its latching position when the control means is operated prior

14. The tool set forth in claim 13 in which

the release means includes resilient means applying a given biasing force to the latch biasing the latch toward its released position and said given biasing force is less than the biasing force applied to the latch by the

15. The tool set forth in claim 13 in which

the release means includes structure providing a positive coupling between the latch and the workpiece engaging means to prevent movement of the workpiece engaging means from its normal position when the latch is held

16. The tool set forth in claim 13 in which

the release means includes structure providing an indirect coupling between the latch and the workpiece engaging means to permit movement of the workpiece engaging means to its actuated position when the latch is held

17. The tool set forth in claim 13 in which

the latch includes an L-shaped portion with one leg movable into and out of the drive track,

means are provided including the other leg of the L-shaped portion for mounting the latch for pivotal movement relative to the nosepiece structure,

and resilient means are provided acting on the latch for biasing the latch

18. The tool set forth in claim 17 in which

the release means includes a cam surface and a bearing surface bearing on the cam surface for coupling the latch to the workpiece engaging means, one of said surfaces being formed on the workpiece engaging means and the other surface being formed on the latch.