US3888404A

US3888404A - Safety for fastener driving tool

Info

Publication number: US3888404A
Application number: US397021A
Authority: US
Inventors: Howard B Ramspeck; Raymond F Novak
Original assignee: Duo Fast Corp
Current assignee: Duo Fast Corp
Priority date: 1973-09-13
Filing date: 1973-09-13
Publication date: 1975-06-10
Anticipated expiration: 1992-06-10

Abstract

A fastener driving or applying tool includes a fluid actuated cycle valve for controlling a main valve to move through an automatic sequence of opening and closing movements to operate a piston actuated fastener driving blade through power and return strokes. In two embodiments, the degree of bias applied to the cycle valve is varied to provide a single cycle of power and return strokes (single cycle tool) or a series of such cycles (multifire tool). The tool includes a trigger or firing control and a safety control, and a fluid actuated piston prevents movement of the cycle valve unless the safety control is actuated prior to the firing control.

Description

United States Patent Ramspeck et al.

[ June 10, 1975 SAFETY FOR FASTENER DRIVING TOOL Primary Examiner-Granville Y. Custer, Jr. [75] lnvemors' 23:31: :kgz jfz gzgngfig Anomey, Agent, or Firm-Mason, Kolehmainen,

both of m Rathburn & Wyss [73] Assignee: Duo-Fast Corporation, Franklin [57] ABSTRACT Park' A fastener driving or applying tool includes a fluid ac- [22] Filed: Sept. 13, 1973 tuated cycle valve for controlling a main valve to move through an automatic sequence of opening and [21] Appl' 397,021 closing movements to operate a piston actuated fastener driving blade through power and return strokes. 52 US. Cl 227/8; 227/130 In two embodiments. the degree of bias pp to the s [1 Int. Cl. B250 1/04 cycle valve is varied to Provide a Single cycle of Power [581 Field at Search 227/7, 8, 130; 91/356 and return Strokes g cycle 1001) or a series of such cycles (multifire tool). The tool includes a trigger [56] References Cited or firing control and a safety control, and a fluid actu- UNITED STATES PATENTS ated piston prevents movement of the cycle valve un- I less the safety control is actuated prior to the firing 3,278JO3 l/l966 .lullfs et al 227/l30 control 3.638.532 2/l972 227/l30 X 3,685,396 8/ I972 Obergfcll 227/130 X 14 Claims, 9 Drawing Figures l ll 1 62 l;

ll 2 l: F

' ll 4 ?4 Q; e

fiA"? 3O I Q F6--% E l 46 l "l 4? 64* i 65-? SAFETY FOR FASTENER DRIVING TOOL This invention relates to a fastener applying tool and. more particularly, to such a tool with automatic stroke sequences and a new and improved safety therefor.

A safety standard that is becoming increasingly applicable to power actuated fastener driving tools including pneumatic nailers and staplers is one requiring the tool to be disposed against the workpiece before the operation ofa firing control, such as a trigger. US. Pat. Nos. 3,677,456 and 3,677,457 disclose two arrangements for inhibiting operation of fastener driving tools when a trigger control is operated prior to a safety control. The arrangements shown in these two patents are ones in which a main valve assembly controlling the supply of pressurized fluid to and the exhaust of fluid from the drive cylinder is opened and closed directly by the trigger control and the safety control. However, there are a number of nailers and staplers using cycle valves to provide automatic opening and closing sequences of the main valve, and it would be desirable to provide a safety-bcfore-trigger safety control for this type of tool.

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

Another object is to provide a fastener applying tool of the type including a cycle valve which includes means for preventing operation of the tool unless a workpiece engaging safety is actuated prior to a firing control.

A further object is to provide a new and improved safety for automatic main valve sequence fastener driving tools, which safety includes a fluid actuated piston for inhibiting initiation of a sequence of operations of the main valve.

A further object is to provide a safety for a fastener driving tool using a cycle valve in which a movable fluid actuated piston mechanically blocks movement of the cycle valve when a safety control and a firing control are operated in an improper sequence.

In accordance with these and many other objects, an embodiment of the present invention comprises a fastener driving tool including a main cylinder containing a drive piston for actuating a fastener driving blade. A main valve is operable to opened and closed positions to supply pressurized fluid to and exhaust fluid from the main cylinder, respectively. The movement of the main valve to its opened and closed positions to provide power and return strokes of the fastener driving blade is controlled by a fluid actuated cycle valve having two magnitudes of fluid bias applied thereto so as to obtain either single cycle or multifire operation. A pneumatic piston disposed in a position in which it can be moved into an abutting mechanical relationship with the cycle valve is selectively controlled by a workpiece engaging safety and a firing or trigger control to mechanically block movement of the cycle valve whenever the firing control is actuated prior to the safety. In the multifire embodiment, the locking piston also includes valve means for selectively applying the bias necessary for multifire operation only after it has been determined that the safety control has been actuated prior to the trigger or firing control.

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. I is an elevational view in partial section illustrating the fastener driving tool embodying the present invention;

FIG. 2 is a schematic diagram of the pneumatic control circuit used in the tool shown in FIG. I to provide single cycle operation;

FIG. 3 is a schematic diagram illustrating the fluid controls used in the tool shown in FIG. I to obtain multifire operation;

FIG. 4 is an enlarged sectional view taken along line 4-4 in FIG. 1 illustrating a multiflre control valve assembly shown in normal position;

FIG. 5 is a sectional view taken along line 5-5 in FIG. 4 illustrating a combined safety and trigger or firing control;

FIG. 6 is a sectional view taken along line 6-6 in FIG. 4 illustrating a cycle valve and sequence control piston included in the control valve assembly;

FIG. 7 is a fragmentary sectional view similar to FIG. 4 illustrating the control valve assembly after the operation of the safety control and prior to the operation of the firing control during a proper sequence of operation;

FIG. 8 is a fragmentary sectional view similar to FIG. 4 illustrating the control valve assembly on an improper operating sequence in which the firing control has been actuated prior to the safety control; and

FIG. 9 is a fragmentary sectional view similar to FIG. 6 illustrating a portion of a cycle valve for attaining sin gle cycle operation in the manner shown achematically in FIG. 2 of the drawings.

Referring now more specifically to FIG. I of the drawings, therein is illustrated a fastener driving tool which is indicated generally as 20 and which embodies the present invention. The fastener driving tool 20 includes a housing 22 having a forward or head portion 22A defining a chamber 24 continuously supplied with pressurized fluid such as compressed air from a reservoir defined by a hollow rearwardly extending handle portion 228 of the housing 22. A drive cylinder 26 disposed in the chamber 24 slidably receives a drive piston 28 to which the upper end of a fastener driving blade or element 30 is connected. The lower end of the driver blade 30 is slidably received within a drive track 32 formed in a nosepiece structure 34 forming a part of the housing 22. A conventional magazine assembly indicated generally as 36 supplies successive staples 38 from a strip thereof to the drive track 32 below the lower end of the driver blade 30.

A main valve assembly 40 in a normal closed condition connects the upper end of the interior of the cylinder 26 to the atmosphere and can be moved to an open position to supply pressurized fluid to the cylinder 26 to move the piston 28 and connected driver blade 30 through a power stroke. The main valve assembly 40 is automatically moved through this cycle of operation by a cycle valve in a control valve assembly indicated generally as 42. The control valve assembly 42 is controlled by a conventional workpiece engaging mechanism indicated generally as 44 and a firing control or manual trigger 46. The control valve assembly 42 is arranged so that the main valve 40 cannot be moved to an open position if the trigger 46 is actuated prior to operation of the safety mechanism 44 by placing the nosepiece structure 34 against a workpiece.

The construction of the tool 20 can be of any of the types well known in the art and can, for example. be

constructed as shown and described in detail in US. Pat. No. 3.638.532. In general. the combined main and exhaust valve assembly 40 is normally held in a closed position by a plurality of compression springs 50 and pressurized air admitted to an annular chamber 52 over a passageway 54 by the control valve assembly 42, the chamber 52 being formed in a closure cap 56 for the tool 20. With the main valve assembly 40 in its normal position. communication between the pressurized fluid in the chamber 24 and the upper interior of the cylinder 26 is closed off. and this upper interior is connected to the atmosphere over a system of passageways including a plurality of passageways 58 formed in the closure cap 56. When the control valve assembly 42 is actuated by the manual trigger 46 and the workpiece engaging assembly 44, the chamber 52 is vented to the atmosphere over the passageway 54 by the control valve assembly 42. and the main valve assembly 40 moves upwardly to close the connection to atmosphere above the upper interior of chamber 26 and to place the upper interior of the cylinder 26 in communication with the pressurized fluid in the chamber 24. This drives the piston 28 downwardly through a power stroke during which the lower end of the fastener driving blade 30 engages a staple 38 disposed in the drive track 32 and drives this staple into a workpiece.

When the piston 28 reaches the lower end of its power or drive stroke determined by engagement with a resilient bumper 60, pressurized fluid from the interior of the cylinder 26 flows through one or more openings 62 in the piston 28 and through one or more ports 64 to be collected within a fluid return chamber 66. This pressurized fluid is also supplied as a control signal to the control valve assembly 42.

When the control valve assembly 42 initiates a return stroke of the piston 28, pressurized fluid is again supplied over the passageway 54 to the chamber 52. This pneumatic bias coupled with the bias provided by the springs 50 moves the main valve 40 downwardly so that it again seats on the upper end of the cylinder 26 to close off communication with the pressurized fluid in the chamber 24. In this position the main valve assembly 40 also opens the exhaust passages 58 so that the interior of the cylinder 26 above the piston 28 is con nected to the atmosphere. At this time pressurized fluid enters the interior of the cylinder 26 below the piston 28 through one or a number of ports 68. This compressed air forces the piston 28 upwardly to the normal position shown in FIG. 1. The piston is retained in this position by an O-ring 70 on the piston which rests on a shoulder formed in the upper end of the cylinder 26. The air below the piston 28 leaks to the atmosphere around the lower end of the driver blade 30 and through the drive track 32 so that at the conclusion of the return stroke of the piston. both the lower end of the interior of the cylinder 26 and the air return chamber 66 are placed substantially at atmospheric pressure.

The workpiece engaging assembly or means 44 which is actuated when the tool 20 is placed adjacent a workpiece can be of any suitable well known construction. such as that shown in US. Pat. No. 365,049, In general, the assembly 44 includes a linkage or mechanism 72 mounted on the housing 22 and the nosepiece struc ture 34 and resiliently biased to a position in which a workpiece engaging portion 72A of the mechanism projects downwardly below the lower end of the nosepiece structure 34. An upper portion 728 of the mechanism 72 is coupled by a lost motion arrangement to the lower end of a safety valve stem 74 forming apart of the control valve assembly 42. The illustrated lost motion coupling includes a pair of spaced enlargements or collars 748 on the valve stem 74. When the tool 20 is placed adjacent the workpiece, the lower end portion 72A engages the workpiece and moves the mechanism 72 upwardly. The upper portion 728, after taking up the lost motion between the spaced collars 74B, engages the upper collar 748 to move the valve stem 74 upwardly. When the tool 20 is moved away from the workpiece, the resilient biasing means 75 moves the linkage 72 downwardly so that after lost motion is taken up. the portion 72B engages the lower collar 748 to move the valve stem 74 to the normal position shown in FIG. 1.

Referring now more specifically to FIG. 3 of the drawings. therein is illustrated in schematic form the control valve assembly 42 for operating the tool 20 as an autofire tool in which the piston 28 will repeatedly cycle through power and return strokes within the cylinder 26 so long as the work engaging assembly 44 and the trigger 46 remain operated. The control valve assembly 42 is such that the workpiece engaging assem bly 44 must be actuated to shift the safety valve stem 74 before the trigger 46 is operated in order to enable the control valve assembly 42 to produce operation of the tool 20. As illustrated in the schematic diagram, in the normal condition of the tool 20, the main valve assembly 40 connects the upper interior of the cylinder 26 to the atmosphere. In this normal condition, a continuous pneumatic bias applied to a piston portion 40A tending to open the main valve 40 is overcome by the pneumatic bias applied to a greater area piston portion 408 by a cycle valve 76. In the physical embodiment of FIG. 1, the piston portion 40B includes the larger, upper area of the annular valve disposed in the chamber 52, and the piston portion 40A includes the smaller. lower area exposed to the fluid pressure in the chamber 24.

In the normal condition of the tool 20, a valve 78 controlled by the safety stem 74 normally supplies pressurized fluid to a piston 80 which is mechanically coupled to the cycle valve 76 as indicated in dashed line to hold the cycle valve 76 in the illustrated position in which pressurized fluid is supplied to the piston portion 408 of the main valve assembly 40. The bias applied by the piston 80 overcomes the bias applied in an opposite direction by a piston portion 76A on the cycle valve which is normally connected to pressurized fluid through a valve assembly 82 controlled jointly by the trigger 46 and the workpiece engaging assembly 44. A second piston portion 768 on the cycle valve 76 providing a biasing force similarly directed to the piston portion 76A is used to effect autofire operation. A greater area piston portion 76C is provided for biasing the cycle valve 76 in an opposite direction. The piston portion 768 is normally connected to the atmosphere through the ports 64 at the lower end of the cylinder 26 through a valve 84 controlled by the piston 80. A passage to the piston portion 76C is normally blocked at a valve 86 controlled by the piston 80.

Assuming that the tool 20 is to be placed in operation to provide autoflre operation in the correct sequence, the workpiece engaging assembly 44 is first actuated to move the valve stem 74 upwardly so that the valve 78 first shifts to its alternate position. In this position. the

piston 80 is connected to the atmosphere. and the bias applied to the piston portion 76A through the valve 82 is effective to shift the cycle valve 76 to its alternate position. This movement of the cycle valve 76 mechanically moves the piston 80 to its released position in which the state of the

valves

84 and 86 controlled thereby are shifted. When the valve 84 is shifted, pressurized fluid applied to the autofire piston portion 768 to provide the bias necessary to effect cyclic autofire operation of the cycle valve 76. The operation of the valve 86 connects the piston portion 76C to the port 64 to receive fluid pressure when the piston 28 reaches the end of its power stroke. The bias applied to the

piston portions

76A and 76B holds the cycle valve 76 in its alternate position so that the piston portion 403 on the main valve assembly 40 is connected through the cycle valve 76 to the valve 82 controlled by the safety stem 74 and the trigger 46.

When the trigger 46 is operated after the actuation of the workpiece engaging assembly 44 in the desired sequence, the valve 82 is shifted to its alternate setting and the piston portion 40B on the main valve assembly 40 is connected to the atmosphere. This permits the continuous bias applied to the piston portion 40A of the main valve 40 to open the main valve assembly and supply compressed air to the upper interior of the cylinder 26 while closing off the connection to the atmosphere. This moves the piston 28 downwardly through a power stroke during which a stable 38 is driven into a workpiece.

When the piston 28 reaches the bottom of its power stroke, pressurized fluid supplied by the main valve assembly 40 enters the port 64 in the lower end of the drive cylinder 26 (FIGS. 1 and 3) and is supplied to the piston portion 76C. The greater area piston portion 76C provides a biasing force greater than that supplied by the piston portion 76B, the portion 76A now being connected to the atmosphere through the operated valve 82. Thus, the piston portion 76C shifts the cycle valve 76 to the setting shown in FIG. 3 in which pressurized fluid is again applied to the piston portion 408. This closes the main valve by shifting the main valve assembly 40 to the position illustrated in FIG. 3. In this position, the upper interior of the cylinder 26 is connected to the atmosphere, and the piston 28 is moved through a return stroke in the manner described above.

When the piston 28 has been returned to its normal position, the pressurized air in the lower end of the cylinder 26 leaks to the atmosphere in the manner described above, and thus pressurized fluid from the piston portion 76C on the cycle valve 76 leaks to the atmosphere through the port 64. When this pressure is decreased sufficiently, the bias applied to the piston portion 76B shifts the cycle valve 76 to its alternate position so that the piston portion 408 is again connected to the atmosphere through the cycle valve 76 and the operated valve 82. This opens the main valve 40 by shifting the valve assembly 40 to its alternate position, and another power stroke of the piston 28 is initiated. This operation continues until such time as the trigger 46 and the workpiece engaging assembly 44 are released. When these elements are released, the

valves

78 and 82 return to the position shown in FIG. 3. When the valve 78 is released, the pneumatic bias is again applied to the piston 80, and this piston forces the cycle valve 76 to its illustrated state in which pressurized fluid is again applied to the piston portion 403 to hold the main valve assembly 40 in its closed state. In addition, when the piston is shifted, the valve 84 is moved to its illustrated position in which the piston portion 768 is connected to the atmosphere through the port 64. This removes the autofire bias from the piston portion 768 of the cycle valve 76. When the valve 82 is released, bias is reapplied to the piston portion 76A of the cycle valve, and pressurized fluid is applied to the connection of the valve 82 to the cycle valve 76 so that the piston portion 40B cannot be connected to the atmosphere until such time as the valve 82 is operated.

The control valve assembly 42 is such that the autofire operation of the tool 20 described above cannot be initiated whenever the trigger 46 is actuated to shift the valve 82 to its alternate state prior to the operation of the valve 78 to its alternate state by actuation of the workpiece engaging assembly 44. More specifically, when the valve 82 is actuated first to its alternate state, this valve connects the piston portion 76A to the atmosphere so that the only bias applied to the cycle valve 76 tending to shift it to its alternate state is removed. Accordingly, when and if the workpiece engaging assembly 74 is thereafter operated to shift the valve 78 to its alternate state, the piston portion 80 is again con nected to the atmosphere. However, since this piston portion is moved as described above through mechanical engagement with the cycle valve 76 and since no bias is now applied by either of the

piston portions

76A or 768 to the cycle valve, the cycle valve 76 remains in the setting illustrated in FIG. 3, and pressurized fluid remains applied to the piston portion 408 of the main valve assembly 40 so that this valve cannot be moved to its open condition. Accordingly, the valve 82 must be released to its setting shown in FIG. 3 to reapply a bias to the piston portion 76A followed by operation of the valve 78 by the workpiece engaging assembly 44 before autofire operation of the tool 20 can be initi ated.

The mechanical construction and implementation of the valving shown in FIG. 3 is illustrated in FIGS. 4-8 of the drawings. The mechanical construction of the control valve assembly 42 can be of any suitable type and can, for example, be of the general nature disclosed and described in US. Pat. No. 3,685,396. In general, the control valve assembly 42 is carried in a valve housing 88 as an integral subassembly which can be secured to a wall of the head portion 22A of the housing 22 by suitable fasteners such as machine bolts or screws 90. Passages in the valve housing 88 communicating with the various control components are coupled to ports terminating related passageways formed in the housing 22. A mechanical arrangement other than those described below can be devised for carrying out the control functions described above with reference to FIG. 3 of the drawings.

FIGS. 4-6 of the drawings illustrate the control valve assembly 42 in its normal position. The housing 88 includes a bore 92 (FIGS. 4 and 5) open at its opposite end to the atmosphere and in which is slidably mounted the safety valve stem 74. The normal position of the valve stem 74 is set by engagement of a locating washer 94 by a shoulder formed on the valve stem 74. The valve stem 74 in cooperation with the bore 92 defines the valve 78 and also carries and forms a part of the valve 82.

To pro. ide the valve 78, the valve stem 74 carries a pair of spaced O-

rings

96 and 98 between which termi nates a passageway 100 communicating with pressurized fluid in the chamber 24 so that the area between the O-

rings

96 and 98 within the bore 92 is continuously supplied with pressurized fluid. This fluid normally passes through a passageway 102 (FIG. 4) to the lower end of a second valve bore 104 in the housing 88 in which is slidably mounted the bias piston 80. The pressurized fluid supplied over the passageway 102 normally biases the piston 80 to the position shown in FIG. 4 in which it is set by engagement of the piston with a sleeve 106 disposed within the bore 104. In this position, a projection 80A engages the lower end of an elongated piston member 108 forming a part of the cycle valve 76 to hold the cycle valve 76 in the normal position illustrated in FIG. 3 of the drawings.

When the valve stem 74 is moved upwardly to effect the functional actuation of the valve 78 shown in FIG. 3, the valve stem 74 is moved to the position shown in FIG. 7 in which the lower O-ring 96 is disposed above the point in the bore 92 at which the passageway terminates. This connects the passageway 102 and thus the lower end of the bore 104 beneath the piston 80 to the atmosphere through the bore 92 inasmuch as the interface between the washer 94 and the cylindrical portion of the valve stem 74 is not sealed. In this manner, the valve 78 shown in FIG. 3 is provided by the passageway 100, the O-ring 96, and the port terminating the passageway 102 within the bore 92.

To provide the valve 82 (FIG. 3) operated by conjoint actuation of the workpiece engaging assembly 44 and the trigger 46, there is provided a recess 110 in the upper end of the valve stem 74 in which is movably mounted a valve member 112. The chamber or recess 110 is supplied with pressurized fluid at its lower end from the passageway 100 by an opening 114 (FIG. 4) passing through the valve stem 74 to the chamber or recess 110. Pressurized fluid supplied to the chamber 110 biases the valve element 112 upwardly so that an enlargement 112A thereon seats on an O-ring 116 carried on the valve stem 74, thereby sealing off communication between the chamber 110 and the atmosphere. In the normal condition of the valve 82, the pressurized fluid within the chamber 110 passes through an opening 118 in the valve stem 74 and a portion of the bore 92 sealed by a further O-ring 120 carried on the valve stem 74 and a passageway 122 to be supplied to the cycle valve 76 through an opening in a sleeve 124 dis posed in the upper end of the bore 104.

To operate the valve 82 to its alternate setting from that illustrated schematically in FIG. 3, both the trigger 46 and the workpiece engaging assembly 44 must be operated. When the workpiece engaging assembly 44 is operated. the valve stem 74 is moved upwardly to the position shown in FIG. 7. If the trigger 46 is then pivoted in a counterclockwise direction (FIG. the trigger 46 engages the outer end of the valve element 112 and moves it downwardly so that the enlarged portion 112A moves out of engagement with the O-ring 116. This connects the chamber 110 to the atmosphere through the open upper end of the bore 92. This movement of the valve element 112 also moves an O-ring 126 carried on its lower end into engagement with a tapered or sloping wall surface on the valve stem 74 providing a valve seat and closes off communication between the passageway 114 and the passageway 118.

This terminates the supply of pressurized fluid from the passageway to the passageway 122. Thus, the cycle valve 76 is connected to the atmosphere over the passageway 122 and the operated valve 82.

The cycle valve 76 (FIGS. 4 and 6) includes the piston member 108 and adjacent portions of the

sleeves

106 and 124 and the bore 104. The portion of the bore 104 intermediate the sleeves I06 and 124 is connected over the passageway 54m the chamber 52 (FIG. 1) in which is disposed the large surface piston portion 408 (FIG. 3) of the main valve assembly 40. In the normal position of the piston member 108 to which it is biased by the piston 80, an O-ring 128 on the piston member 108 is out of engagement with the upper end of the sleeve 106 so that the passageway 54 is in communication with pressurized fluid supplied by the chamber 24 through a passageway 130. The passageway 54 is held out of communication with the passageway 122 to which pressurized fluid is supplied by the valve 82 in its normal condition by an O-ring 132 which is carried on the piston 108 and which is seated on the lower end of the sleeve 124. When the cycle valve 76 is moved to the alternate position shown in FIG. 7, the O-ring 128 seats on the upper end of the sleeve 106 to close off communication between the passageways S4 and 130., and the O-ring 132 moves out of engagement at the lower end of the sleeve 124 to connect the passageway 54 to the passageway 122 controlled by the valve 82.

To relate various portions of the piston 108 to the piston portions 76A, 76B. and 76C of the cycle valve 76 referred to in the description of FIG. 3, the lower end of the piston 108 provides the piston portion 76C and is so designated. The uppermost portion of the piston 108 which is disposed within a reduced diameter portion 104A of the bore provides the piston portion 76B. The next lowest portion of the piston 108 which is of a slightly larger diameter than the piston portion 76B provides the piston portion 76A which is selectively supplied with a biasing pressure over the passageway 122.

The valves 84 and 86 (FIG. 3) that are selectively opened and closed by the piston 80 are provided by three O-

rings

134, 136, and 138 carried on the piston 80 and movable within the lower end of the valve bore 104. The upper O-ring 134 normally closes off communication between the piston portion 76C on the piston 108 (FIGS. 3 and 6) and a passageway (FIG. 6) extending from the bore 104 to the air return chamber 66. Thus, the passageway 140 normally does not provide communication between the piston portion 76C and the port 64 in the cylinder 26. When the piston 80 drops to its displaced position (FIG. 7 the passageway 140 is placed in communication with the piston portion 76C within the lower end of the sleeve 106. Thus, the O-ring 134 on the piston 80 provides the valve 86 shown schematically in FIG. 3.

The O-

rings

134 and 136 in the normal position of the piston 80 also place the passageway 140 in communication with a passageway 142 (FIG. 6) extending at the upper end of the reduced diameter portion 104A of the valve bore 104. Accordingly, the valve bore 104A is normally placed in communication with the atmosphere over the

passageways

140 and 142, the air return chamber 66, and the ports 64. The O-ring 136 normally closes off communication between the passageway 142 and a passageway 144 directly supplied with pressurized fluid from the chamber 24.

When the piston 80 is displaced to its lower position (FIG. 7), the O-ring I34 closes off communication between the passageways I40 and 142, and the Oring 136 places the passageway 142 in communication with the passageway 144. Thus, pressurized fluid from the chamber 24 is now supplied to the piston portion 768 in the valve bore 104A to provide an autofire bias to the cycle valve 76. Thus, the O-

rings

134 and 136 and the cooperating structures including the passageways I30, 144, and 142 provide the valve 84 shown schematically in FIG. 3.

When the tool is to be operated in its proper sequence, this tool is placed against a workpiece so that the valve stem 74 is moved upwardly from the normal position shown in FIG. 4 to the actuated position shown in FIG. 7. As the O-ring 96 passes the termination of the passageway 102, compressed air normally holding the piston 80 in the position shown in FIG. 4 is vented to the atmosphere through the lower portion of the valve bore 92. Since compressed air is continuously supplied from the passageway 100 through the openings I14 and 118 and the passageway 122 to the piston portion 76A on the piston 108, the piston 108 moves downwardly from the position shown in FIG. 4 to the position shown in FIG. 7. In moving to this position, the O-ring 128 engages the adjacent portion of the sleeve 106 to close off communication between the passageway 54 and the pressurized fluid inlet passage 130. Since the O-ring 132 has moved out of engagement with the adjacent end of the sleeve 124, the passageway 54 extending to the main valve assembly 40 is now connected to the passageway 122 and receives pressurized fluid supplied from the passageway 100.

Further, when the piston 80 moves downwardly from the position shown in FIG. 4 to the position shown in FIG. 7, the O-ring 134 places the passageway 140 in communication with the open lower end of the sleeve 106 so that pressurized fluid subsequently accumulated in the return chamber 66 through the ports 64 can pass over the passageway 140 to the piston portion 76C. The O-ring 134 also closes off communication between the

passageways

140 and 142 and places the passageway ]42 in communication with pressurized fluid supplied from the passageway 144 so that an autofire bias is forwarded over the passageway 142 to the piston portion 768 on the piston 108.

Thus, following the actuation of the work engaging assembly 44 to shift the safety valve stem 74 to the position shown in FIG. 7, the components of the control valve assembly 42 are moved to the position shown in FIG. 7.

With the components in this position, actuating the trigger 46 to the position shown in dot and dash outline in FIG. 5 moves the trigger portion 46 shown in FIG. 7 downwardly against the upper end of the valve element 112 to move it down so that the O-ring 126 seats on the adjacent portion of the valve stem 74 to close off communication between the passageway 122 and the passageway 100. This removes the source of closing fluid bias for the large piston portion 408 of the main valve assembly 40. This downward movement of the valve element 112 moves the enlarged portion 112A out of engagement with the O-ring 116 so that the passageway 122 is connected to the atmosphere. This discharges the pressurized fluid from the large area piston portion 408 and permits the main valve 40 to be opened by the small area biasing portion 40A continuously supplied with fluid from the chamber 24. Accord ingly, the main valve 40 is opened to initiate a power stroke of the piston 28 in the driver blade 30 in the manner described above. At the end of this power stroke, pressurized fluid from the interior of the cylinder 26 passes through the ports 64 to be accumulated within the chamber 66 and then passes over the passageway 140.

This fluid accumulates in the area in the bore 104 above the O-ring 134 on the piston and acts on the piston portion 76C of the piston 108. Since the effective area of the piston portion 76C is greater than the effective area of the piston portion 768, the pressure supplied through the passageway I40 moves the piston I08 upwardly to the normal position shown in FIG. 4. In doing so, the O-ring 132 seats on the sleeve 124 and the O-ring 128 moves out of engagement with the sleeve 106. This connects the passageway 54 to the pressurized fluid supplied through the passageway 130, and the pressurized fluid thus supplied to the passageway 54 acts on the large area piston portion 408 of the main valve assembly 40 to move this valve assembly to its closed condition. This initiates a return stroke of the piston 28 in the manner described above.

Incident to this return stroke, pressurized fluid collected in the return chamber 66 is dissipated to the atmosphere through the

ports

64 and 68, and the bias applied to the piston portion 76B on the piston 108 exceeds the bias applied to the piston portion 76C thereon. This moves the piston 108 back to the position shown in FIG. 7, and pressurized fluid is exhausted from the chamber 52 (FIG. 1) in the main valve assembly 40 so that the main valve assembly 40 again opens to initiate a second cycle of operation of the tool 20. This cyclic operation continues under the control of the bias applied to the

piston portions

768 and 76C so long as the trigger 46 remains depressed or actuated, and the workpiece engaging assembly 44 is operated.

Whenever these two assemblies or either one of these assemblies is released, the valve element 112 is moved upwardly by the pneumatic bias supplied through the passageway so that the enlarged portion 112A seats on the O-ring 116 and the ()-ring 126 moves out of engagement with the adjacent portion of the valve stem 74. This returns pressurized fluid to the passageway 122 for holding the main valve 40 closed in the manner described above. Further, when the safety mechanism 44 is released, the O-ring 96 moves below the port terminating passageway 102 (FIG. 4). At this time, pressurized fluid from the passageway 100 flows over the passageway 102 and into the lower end of the valve bore 104. This moves the piston 80 upwardly to bias and hold the piston 108 in the normal position shown in FIG. 4. In addition, the bias applied over the passageway 142 (FIG. 6) to the autoflre piston portion 76B is discharged to atmosphere over the passageway 140, and the supply of biasing fluid previously available from the passageway 144 is intercepted by the O-ring 136. In addition, the O-ring 134 cuts off the piston portion 76C on the piston 108 from communication with the signal passageway 140. The tool 20 can be placed in multifire operation in the manner described above by first actuating the workpiece engaging assembly 44 followed by the actuation of the manual trigger or firing control 46.

Assuming, however, that an attempt is made to operate the tool 20 in an improper sequence, the trigger 46 is first actuated fully to the position shown in dot and dash outline in FIG. 5. This moves the trigger 46 to the position shown in section in FIG. 8. If the tool is then moved toward the workpiece, the safety valve stem 74 begins to move upwardly. However, when the valve stem 74 reaches the position shown in FIG. 8, the prior full actuation of the trigger 46 causes the valve element 112 in the valve assembly 82 to move down wardly to the position shown in FIG. 8 at a time prior to movement of the O-ring 96 above the port terminat' ing the passageway [02. When the valve element 112 moves down, the O-ring 126 again interrupts the con nection between the passageway 122 and the source of pressurized fluid provided by the passageway [00. This movement of the valve element 112 also moves the enlarged portion 112A thereon out of engagement with the O-ring H6 so that the passageway [22 is connected to the atmosphere. This discharges pressurized fluid acting on the piston portion 76A of the piston 108 in the cycle valve 76 and removes the only bias tending to move the piston 108 downwardly as viewed in FIG. 8.

Accordingly, if the tool 20 is thereafter placed against the workpiece so that the safety valve stem 74 becomes sufficiently elevated to move the O-ring 96 above the port terminating the passage 102, pressurized fluid acting on the lower surface of the piston 80 within the valve chamber 104 is again discharged to the atmosphere through the open lower end of the valve bore 92. However, the piston 80 is held in the position shown in FIG. 8 by the resilient O-

rings

134, 136, and 138 inasmuch as there are no pneumatic biases acting on either the piston 80 or the piston 108 in the cycle valve assembly 76. Since the piston 108 remains in the position shown in FIG. 8, the passageway 54 leading to the main valve assembly 40 remains connected to the pressurized fluid supplied through the passageway 130 because the O-ring H8 is not seated on the upper end of the sleeve 106. The passageway 54 cannot be connected to the atmosphere because the O-ring 132 remains seated on the sleeve 124. Thus, a cycle of operation of the tool cannot be initiated at this time.

If the manual trigger 46 is released so that the fluid pressure supplied through the passageway 100 can again restore the valve 82 including the valve element 112 to the normal position shown in FIGS. 4 and 7, the passageway 122 is again pressurized, and the piston portion 76A can provide a downwardly directed force shifting both the piston 80 and the piston 108 to the lower position shown in FIG. 7. This permits the initiation of multiflrc operation.

Accordingly, the control valve assembly 42 includes means for preventing initiation of autofire operation of the tool 20 unless this tool is first placed against the workpiece to actuate the assembly 44 followed by manual actuation of the trigger 46. The piston 80 holds the piston 108 in the cycle valve assembly 76 in its normal position when the valve 82 controlled by the trigger 46 in the assembly 44 is operated prior to the valve 78 controlled by the workpiece engaging assembly 44. When the trigger 46 is first operated, the bias for moving the cycle valve 76 normally applied to the piston portion 76A is removed which means that the control piston 80 remains in its elevated position and that the valve means 84 and 86 (FIG. 3) remain in their normal settings so that an autofire bias cannot be applied to the piston portion 768 and so that the passage 140 supplying a fluid pressure signal to the piston portion 76C cannot be opened.

The control valve assembly 42 can also be provided in a modified form 42A to provide single cycle operation rather than multifire operation. In single cycle operation, the drive piston 28 moves through one power and return cycle and remains in this position even though the trigger 46 and the workpiece engaging assembly 44 remain actuated until such time as at least one of these components is released and reoperated. This modified control assembly 42A (FIG. 2) also insures that the tool 20 cannot be operated through even the single cycle of operation unless the workpiece engaging assembly 44 is actuated prior to the manual trigger 46.

The only mechanical modification required in the control valve assembly 42 to provide the single cycle control valve assembly 42A is illustrated in FIG. 9 of the drawings. More specifically, the passageway 142 normally connecting the reduced diameter portion 104A of the valve bore for the cycle valve 76 is plugged or not provided. and the upper end of the reduced diameter portion 104A is vented to the atmosphere through a passageway 150. Thus, the piston portion 768 on the piston 108 for the cycle valve assembly 76 cannot be supplied with the pneumatic bias required for multifire operation. ln other respects, the single cycle control valve assembly 42A is identical to the control valve assembly 42.

A schematic diagram of the control valve assembly 42A for providing single cycle operation is illustrated in FIG. 2 of the drawings. in this schematic diagram the valve 84 has been omitted as well as the piston portion 768 inasmuch as these components perform no useful function. The valves and controlling mechanism shown schematically in FIG. 2 are realized by the same mechanical structures described above with the modifications shown in FIG. 9.

Assuming that the tool 20 is to be operated in a proper sequence, this tool is placed against a workpiece, and the valve stem 74 moves upwardly to first actuate the valve 78. When the valve 78 is actuated to its alternate setting, compressed air is vented from the control piston 80. The bias supplied by the valve 82 for the piston portion 76A moves the cycle valve 76 to its alternate setting, and in doing so forces the piston downwardly within the valve bore 104 to the position shown in FIG. 7. This actuates the valve 86 so that the piston portion 76C is placed in communication with the ports 64 over the passageway and the air return chamber 66. When the cycle valve 76 moves to its alternate setting, the piston portion 408 on the main valve assembly 40 is coupled to the valve 82.

When the valve 82 is next actuated by fully depressing the trigger 46, the piston portion 408 is connected to the atmosphere, and the piston portion 40A is effective to shift the main valve assembly 40 to its alternate setting so that compressed air is supplied to the upper interior of the cylinder 26. This moves the piston 28 and the driver blade 30 through a power stroke during which a stable 38 is driven. When the piston 28 reaches the end of its power stroke, pressurized fluid from the upper interior of the cylinder 26 is forwarded through the ports 64 and the actuated valve 86 to the piston portion 76C. This bias immediately shifts the cycle valve 76 to its normal position illustrated in FIG. 2 inasmuch as the prior actuation of the valve 82 removes all bias from the piston portion 76A. When the cycle valve 76 returns to this setting, pressurized fluid is again applied to the piston portion 408 of the main valve assembly 40, and this valve assembly moves to its illustrated closed setting in which the upper interior of the cylinder 26 is connected to the atmosphere. This permits the return of the piston 28 to its normal position as described above.

The control valve assembly 42A remains in this position with the cycle valve 76 in the position illustrated in FIG. 2 holding the main valve assembly 40 closed inasmuch as no bias is applied to the cycle valve 76 to permit its return to an operated position when the air acting on the piston portion 76C is dissipated to the atmosphere through the ports 64 in the manner described above. The frictional engagement of the O-rings on the piston 108 (FIG. 3) in the cycle valve assembly 76 retains the piston in the position shown in FIG. 4 in the absence of a bias. When the trigger 46 is released and the workpiece engaging assembly 44 is released, the

valves

78 and 82 return to the normal settings iilustrated in FIG. 2. This restores the piston 80 to a position biasing or blocking the piston 108 of the cycle valve assembly 76 in its normal position. This movement of the piston 80 also opens the valve 86 so that the piston portion 76C on the cycle valve 76 is no longer connected to the port 64. The reapplieation of bias from the valve 82 to the piston portion 76A is not effective to shift the cycle valve 76 inasmuch as the bias provided thereby is less than the bias afforded by the control piston 80.

If an attempt is made to initiate a single cycle operation of the tool 20 by first operating the trigger 46 followed by the operation of the workpiece engaging assembly 44, the valve 82 is first operated to remove the bias from the piston portion 76A, and the valve 78 is thereafter operated to remove the pneumatic bias from the control piston 80. As set forth above, the resilience of the O-rings on the pistons 80 and I08 prevents movement of these pistons from the normal position shown in FIG. 4 because no pneumatic biases are effective on any of these pistons. This means that the cycle valve 76 cannot be moved from its normal position shown schematically in FIG. 2 in which it supplies a continuous connection of pressurized fluid to the large piston portion 408 of the main valve assembly 40. This means that the main valve assembly 40 cannot be operated from its normal and illustrated closed state in which the upper interior of the cylinder 26 is connected to the atmosphere. Accordingly, a single cycle operation of the tool 20 cannot be initiated if the workpiece engaging assembly 44 is not actuated prior to the operation of the manual trigger 46. By releasing and reoperating the trigger 46, a single cycle operation of the tool 20 can be initiated.

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 that will fall within the spirit and scope of the principles of the present invention.

We claim:

1. A tool for driving fasteners into a workpiece comprising a powered fastener driving assembly including a driver element actuated by a drive piston movable within a cylinder,

a fluid controlled main valve means opened to supply pressurized fluid to and closed to exhaust fluid from the cylinder,

a fluid controlled cycle valve coupled to the main valve means and movable to alternate positions to control opening and closing of the main valve means,

a first control means coupled to the cycle valve including a valve controlled by independently operable manual means and safety means actuated by placing the tool adjacent the workpiece for moving the cycle valve to a position effecting opening of the main valve means only when both of the manual means and the safety means are actuated.

and a second control means coupled to the cycle valve and responsive to the operation of at least one of the manual means and safety means for preventing movement of the cycle valve when the manual means is operated prior to the safety means.

2. A tool for driving fasteners into a workpiece comprising a powered fastener driving assembly including a driver element actuated by a drive piston movable within a cylinder,

a fluid controlled cycle valve coupled to the main valve means and movable to alternate positions to control opening and closing of the main valve means, said cycle valve including at least one fluid responsive surface for moving the cycle valve to one of said alternate positions,

a first control means coupled to the cycle valve including independently operable manual means and safety means actuated by placing the tool adjacent the workpiece for moving the cycle valve to a position effecting opening of the main valve means only when both of the manual means and the safety means are actuated,

and a second control means coupled to said fluid responsive surface on the cycle valve for preventing movement of the cycle valve by preventing the supply of fluid to the fluid responsive surface when the manual means is operated prior to the safety means.

3. A tool for driving fasteners into a workpiece comprising a powered fastener driving assembly including a driver element actuated by a drive piston movable within a cylinder,

a fluid controlled cycle valve coupled to the main valve means and movable to alternate positions to control opening and closing of the main valve means. said cycle valve being movable to a position effecting closing of the main valve means under the control of fluid supplied to the cylinder,

a first control means coupled to the cycle valve including independently operable manual means and safety means actuated by placing the tool adjacent the workpiece for moving the cycle valve to a position effecting opening of the main valve means only when both of the manual means and the safety means are actuated.

and a second control means coupled to the cycle valve and to the first control means for preventing movement of the cycle valve after the manual means and the safety means are operated when the manual means is operated prior to the safety means.

4. The tool set forth in claim 3 in which the second control means includes a fluid actuated piston mechanically coupled to the cycle valve and biasing the cycle valve against movement to a position effecting opening of the main valve means.

5. A tool for driving fasteners into a workpiece comprising a powered fastener driving assembly including a driver element actuated by a drive piston movable within a cylinder,

a fluid controlled main valve means for selectively supplying pressurized fluid to and exhausting fluid from the cylinder,

a cycle valve coupled to the main valve means and movable to alternate positions to control opening and closing of the main valve means,

a first control means coupled to the cycle valve including manual means and safety means actuated by placing the tool adjacent the workpiece for moving the cycle valve to said main valve opening control position when both of the manual means and the safety means are actuated,

a second control means coupled to the cycle valve and to the cylinder for moving the cycle valve to, said main valve closing control position,

a fluid actuated control piston coupled to the cycle valve for controlling its movement,

and means coupling the control piston to the first control means and controlling the control piston to prevent movement of the cycle valve to said opening control position when the manual means is actuated prior to the safety means.

6. The tool set forth in claim 5 including means mounting the control piston for movement into and out of engagement with the cycle valve.

7. The tool set forth in claim 6 in which the first control means includes means for applying a biasing force to the control piston to hold the control piston in engagement with the cycle valve to prevent movement of the cycle valve when the manual means is actuated prior to the safety means, said first control means rendering said biasing means ineffective when the safety means is actuated.

8. A tool for driving fasteners into a workpiece comprising a powered fastener driving assembly including a driver clement actuated by a drive piston movable within a cylinder through power and return strokes,

a fluid controlled main valve means that is opened to supply pressurized fluid to and that is closed to exhaust fluid from the cylinder,

a cycle valve coupled to the main valve means and movable between a first position to control opening of the main valve means and a second position to control closing of the main valve means,

a first control means coupled to the cycle valve in cluding manual means and safety means actuated by placing the tool adjacent the workpiece for moving the cycle valve to its first position when both of the manual means and the safety means are actuated,

a second control means coupled to the cycle valve and to the cylinder for moving the cycle valve to its second position when the piston has moved through its power stroke,

a fluid actuated control piston normally preventing movement of the cycle valve to its first position, means coupling the control piston to the first control means,

and release means in the first control means for controlling movement of the control piston to permit movement of the cycle valve to said one first posi tion only when the safety means is actuated prior to the manual means.

9. The tool set forth in claim 8 in which the release means includes valve means controlled by the safety means for selectively supplying an exhaust connection and pressurized fluid to the fluid actuated control pistonv 10. A tool for driving fasteners into a workpiece comprising a powered fastener driving assembly including a driver element actuated by a drive piston movable within a cylinder,

a cycle valve coupled to the main valve means and cyclically movable to alternate positions to control opening and closing of the main valve means,

a first control means coupled to the cycle valve including independently operable manual means and safety means actuated by placing the tool adjacent the workpiece for initiating cyclic movement of the cycle valve between its alternate positions when both of the manual means and the safety means are actuated,

and a second control means coupled to the cycle valve and the first control means for preventing cyclic movement of the cycle valve after the safety means and manual means are operated whenever the manual means is operated prior to the safety means.

11. The tool set forth in claim 10 in which the second control means includes a fluid actuated bias valve for applying a fluid bias to the cycle valve,

and the first control means includes valve means for selectively connecting the bias valve to pressurized fluid and an exhaust.

12. A multiflre tool for driving a series of fasteners into a workpiece comprising a powered fastener driving assembly including a driver element actuated by a drive piston movable within a cylinder,

at fluid operated cycle valve coupled to the main valve means and movable to alternate positions to control opening and closing of the main valve means,

bias valve means for applying a fluid bias to the cycle valve means to move the cycle valve means to one of its alternate positions,

means coupled to the cycle valve and to the cylinder for applying a fluid bias to the cycle valve means to move the cycle valve to the other of its alternate positions,

and control means including manual means and safety means actuated by placing the tool adjacent the workpiece for initiating movement of the cycle valve when both of the manual means and the safety means are actuated. said control means including means operating the bias valve means to apply a fluid bias to the cycle valve means only when the safety means is actuated prior to the manual means.

13. A tool for driving fasteners into a workpiece comprising a powered fastener driving assembly including a driver element actuated by a drive piston movable within a drive cylinder,

a cycle valve coupled to the main valve means and movable to alternate positions to control opening and closing of the main valve means, said cycle valve including a valve cylinder and a valve piston movable therein for controlling the connection of exhaust and pressurized fluid to the main valve means a piston means movable within the valve cylinder between a position biasing the valve piston and a position spaced from the valve piston.

first passage means placing the valve cylinder in communication with the drive cylinder at a point located between the piston means and the valve piston for applying a fluid bias from the drive cylinder to the valve piston,

second passage means communicating with the valve cylinder at a point spaced from the valve piston to apply a fluid bias to the piston means only,

and valve means controlling the application of fluid pressure to the second passage means.

14. A tool for driving fasteners into a workpiece comprising a powered fastener driving assembly including a driver clement actuated by a drive piston movable within a cylinder,

main assembly means opened to supply pressurized fluid to and closed to exhaust fluid from the cylindcr.

cycle means coupled to the main assembly means and movable to alternate positions to control opening and closing of the main assembly means,

a first control means coupled to the cycle means including means controlled by independently operable manual means and safety means actuated by placing the tool adjacent the workpiece for moving the cycle means to a position effecting opening of the main assembly means only when both of the manual means and the safety means are actuated,

and a second control means coupled to the cycle means and responsive to the operation of at least one of the manual means and safety means for preventing movement of the cycle means when the manual means is operated prior to the safety

Claims

1. A tool for driving fasteners into a workpiece comprising a powered fastener driving assembly including a driver element actuated by a drive piston movable within a cylinder, a fluid controlled main valve means opened to supply pressurized fluid to and closed to exhaust fluid from the cylinder, a fluid controlled cycle valve coupled to the main valve means and movable to alternate positions to control opening and closing of the main valve means, a first control means coupled to the cycle valve including a valve controlled by independently operable manual means and safety means actuated by placing the tool adjacent the workpiece for moving the cycle valve to a position effecting opening of the main valve means only when both of the manual means and the safety means are actuated, and a second control means coupled to the cycle valve and responsive to the operation of at least one of the manual means and safety means for preventing movement of the cycle valve when the manual means is operated prior to the safety means.

2. A tool for driving fasteners into a workpiece comprising a powered fastener driving assembly including a driver element actuated by a drive piston movable within a cylinder, a fluid controlled main valve means opened to supply pressurized fluid to and closed to exhaust fluid from the cylinder, a fluid controlled cycle valve coupled to the main valve means and movable to alternate positions to control opening and closing of the main valve means, said cycle valve including at least one fluid responsive surface for moving the cycle valve to one of said alternate positions, a first control means coupled to the cycle valve including independently operable manual means and safety means actuated by placing the tool adjacent the workpiece for moving the cycle valve to a position effecting opening of the main valve means only when both of the manual means and the safety means are actuated, and a second control means coupled to said fluid responsive surface on the cycle valve for preventing movement of the cycle valve by preventing the supply of fluid to the fluid responsive surface when the manual means is operated prior to the safety means.

3. A tool for driving fasteners into a workpiece comprising a powered fastener driving assembly including a driver element actuated by a drive piston movable within a cylinder, a fluid controlled main valve means opened to supply pressurized fluid to and closed to exhaust fluid from the cylinder, a fluid controlled cycle valve coupled to the main valve means and movable to alternate positions to control opening and closing of the main valve means, said cycle valve being movable to a position effecting closing of the main valve means under the control of fluid supplied to the cylinder, a first control means coupled to the cycle valve including independently operable manual means and safety means actuated by placing the tool adjacent the workpiece for moving the cycle valve to a position effecting opening of the main valve means only when both of the manual means and the safety means are actuated, and a second control means coupled to the cycle valve and to the first control means for preventing movement of the cycle valve after the manual means and the safety means are operated when the manual means is operated prior to the safety means.

5. A tool for driving fasteners into a workpiece comprising a powered fastener driving assembly including a driver element actuated by a drive piston movable within a cylinder, a fluid controlled main valve means for selectively supplying pressurized fluid to and exhausting fluid from the cylinder, a cycle valve coupled to the main valve means and movable to alternate positions to control opening and closing of the main valve means, a first control means coupled to the cycle valve including manual means and safety means actuated by placing the tool adjacent the workpiece for moving the cycle valve to said main valve opening control position when both of the manual means and the safety means are actuated, a second control means coupled to the cycle valve and to the cylinder for moving the cycle valve to, said main valve closing control position, a fluid actuated control piston coupled to the cycle valve for controlling its movement, and means coupling the control piston to the first control means and controlling the control piston to prevent movement of the cycle valve to said opening control position when the manual means is actuated prior to the safety means.

8. A tool for driving fasteners into a workpiece comprising a powered fastener driving assembly including a driver element actuated by a drive piston movable within a cylinder through power and return strokes, a fluid controlled main valve means that is opened to supply pressurized fluid to and that is closed to exhaust fluid from the cylinder, a cycle valve coupled to the main valve means and movable between a first position to control opening of the main valve means and a second position to control closing of the main valve means, a first control means coupled to the cycle valve including manual means and safety means actuated by placing the tool adjacent the workpiece for moving the cycle valve to its first position when both of the manual means and the safety means are actuated, a second control means coupled to the cycle valve and to the cylinder for moving the cycle valve to its second position when the piston has moved through its power stroke, a fluid actuated control piston normally preventing movement of the cycle valve to its first position, means coupling the control piston to the first control means, and release means in the first control means for controlling movement of the control piston to permit movement of the cycle valve to said one first position only when the safety means is actuated prior to the manual means.

9. The tool set forth in claim 8 in which the release means includes valve means controlled by the safety means for selectively supplying an exhaust connection and pressurized fluid to the fluid actuated control piston.

10. A tool for driving fasteners into a workpiece comprising a powered fastener driving assembly including a driver element actuated by a drive piston movable within a cylinder, a fluid controlled main valve means for selectively supplying pressurized fluid to and exhausting fluid from the cylinder, a cycle valve coupled to the main valve means and cyclically movable to alternate positions to control opening and closing of the main valve means, a first control means coupled to the cycle valve including independently operable manual means and safety means actuated by placing the tool adjacent the workpiece for initiating cyclic movement of the cycle valve between its alternate positions when both of the manual means and the safety means are actuated, and a second control means coupled to the cycle valve and the first control means for preventing cyclic movement of the cycle valve after the safety means and manual means are operated whenever the manual means is operated prior to the safety means.

11. The tool set forth in claim 10 in which the second control means includes a fluid actuated bias valve for applying a fluid bias to the cycle valve, and the first control means includes valve means for selectively connecting the bias valve to pressurized fluid and an exhaust.

12. A multifire tool for driving a series of fasteners into a workpiece comprising a powered fastener driving assembly including a driver element actuated by a drive piston movable within a cylinder, a fluid controlled main valve means for selectively supplying pressurized fluid to and exhausting fluid from the cylinder, a fluid operated cycle valve coupled to the main valve means and movable to alternate positions to control opening and closing of the main valve means, bias valve means for applying a fluid bias to the cycle valve means to move the cycle valve means to one of its alternate positions, means coupled to the cycle valve and to the cylinder for applying a fluid bias to the cycle valve means to move the cycle valve to the other of its alternate positions, and control means including manual means and safety means actuated by placing the tool adjacent the workpiece for initiating movement of the cycle valve when both of the manual means and the safety means are actuated, said control means including means operating the bias valve means to apply a fluid bias to the cycle valVe means only when the safety means is actuated prior to the manual means.

13. A tool for driving fasteners into a workpiece comprising a powered fastener driving assembly including a driver element actuated by a drive piston movable within a drive cylinder, a fluid controlled main valve means for selectively supplying pressurized fluid to and exhausting fluid from the cylinder, a cycle valve coupled to the main valve means and movable to alternate positions to control opening and closing of the main valve means, said cycle valve including a valve cylinder and a valve piston movable therein for controlling the connection of exhaust and pressurized fluid to the main valve means, a piston means movable within the valve cylinder between a position biasing the valve piston and a position spaced from the valve piston, first passage means placing the valve cylinder in communication with the drive cylinder at a point located between the piston means and the valve piston for applying a fluid bias from the drive cylinder to the valve piston, second passage means communicating with the valve cylinder at a point spaced from the valve piston to apply a fluid bias to the piston means only, and valve means controlling the application of fluid pressure to the second passage means.

14. A tool for driving fasteners into a workpiece comprising a powered fastener driving assembly including a driver element actuated by a drive piston movable within a cylinder, main assembly means opened to supply pressurized fluid to and closed to exhaust fluid from the cylinder, cycle means coupled to the main assembly means and movable to alternate positions to control opening and closing of the main assembly means, a first control means coupled to the cycle means including means controlled by independently operable manual means and safety means actuated by placing the tool adjacent the workpiece for moving the cycle means to a position effecting opening of the main assembly means only when both of the manual means and the safety means are actuated, and a second control means coupled to the cycle means and responsive to the operation of at least one of the manual means and safety means for preventing movement of the cycle means when the manual means is operated prior to the safety means.