Air auto shut-off

An automatic shutoff mechanism is designed for a pneumatic tool having an air motor, a pressurized airflow path to the motor and a torquing mechanism driven by the motor. The shutoff mechanism includes a valve member moveable between open and closed positions relative to the airflow path and biased to the open position. A trip apparatus is responsive to application of a predetermined torque for moving the valve member to a trip position disposed in the airflow path sufficiently to expose the valve member to the pressurized airflow for driving the valve member from the trip position to the closed position. Mechanical and electromechanical embodiments are disclosed.

BACKGROUND

This application relates to pneumatic tools and, in particular, to control mechanisms therefore. The application relates specifically to shutoff mechanisms for disconnecting a pneumatic motor from a supply of pressurized pneumatic fluid.

Pneumatically operated tools of varying types are known, including a wide variety of pneumatically-operated hand tools. Many such tools are designed for torque application to a workpiece and may include devices such as screw or nut driving tools, impact wrenches and the like. Such tools are typically provided with a trigger valve mechanism to manually control the flow of pressurized pneumatic fluid, typically air, to an air motor. Some pneumatic tools are also provided with automatic shutoff mechanisms, responsive to a particular event or condition, such as the application of a predetermined torque level. Such prior shutoff arrangements have typically been rather complex, bulky, expensive, relative slow acting and/or difficult to adjust.

SUMMARY

There is disclosed herein an improved technique for automatic shutoff of a pneumatic tool.

The technique includes use of a valve member biased to a normal open position and a trip apparatus responsive to application of a predetermined torque by the tool for moving the valve member into the pressurized airflow path a distance sufficient that the airflow itself will then drive the valve member to a closed position, shutting off airflow to the motor.

In a mechanical embodiment of the shutoff mechanism, the trip assembly includes an inertia member coaxial with the motor rotor shaft and a helical coupling between the inertia member and the rotor shaft such that they rotate together at constant velocity, but that upon rapid deceleration of the rotor shaft the inertia member moves rotatably and axially relative to the rotor shaft to a position spaced from the valve member a distance inversely proportional to the torque applied by the tool, the trip assembly moving the inertia member into engagement with the valve member upon application of the predetermined torque.

Where the pneumatic tool is an impact tool, in one mechanical embodiment of the shutoff mechanism the inertia member is biased to a home position spaced a maximum distance from the valve member and, in response to each impact, moves toward the valve member a distance proportional to the torque applied and then back to the home position.

In another embodiment, the trip assembly includes a clutch mechanism responsive to movement of the inertia member from its home position for preventing its return to the home position until the valve has been tripped, and preventing premature tripping upon transition from free run down of a fastener to initial torque resistance.

In another embodiment, the shutoff mechanism is electromechanically operated, the valve member being a solenoid actuated in response to a torque sensing device.

There is also a disclosed method for automatically shutting off a pneumatic torque-applying tool when a predetermined torque is reached by disposing a valve member adjacent to the pressured airflow path upstream of the motor and, when the predetermined torque is reached, moving the valve member from its open position to a trip position disposed in the airflow path and spaced from the open position a distance such that the valve member is exposed to a pressured air load which drives it to the closed position.

DETAILED DESCRIPTION

Referring toFIG. 1, there is illustrated a pneumatic torquing tool10in the nature of an impact tool, having a housing11with an elongated, generally cylindrical barrel portion12and a depending handle portion13cooperating to define a known pistol grip configuration. The distal end of the handle portion13is adapted to be coupled to a source of pressurized pneumatic fluid, such as air, in a known manner, the airflow to the motor being controlled by a known trigger valve assembly14. Mounted in the barrel portion12of the housing11is a known air motor15having a cylinder16surrounding a rotor17provided with a plurality of circumferentially spaced and radially extending vanes, the front and rear ends of the motor15being respectively closed by front and rear end plates18and19, again all in a known manner. Coupled to the forward or output end of the rotor17is an output mechanism20, which, in the illustrated embodiment, includes a torquing mechanism in the nature of a known impact mechanism21, which may be of the double dog type. The output mechanism20also includes an output member22which is connected to the impact mechanism21and is adapted for coupling to a suitable drive tool, such as a socket, for coupling to an associated fastener or other work piece to which torque is to be applied, again all in a known manner. The rear end of the rotor17defines a stub shaft23journaled in a bearing24. The tool10may also be provided with a reversing valve assembly25, again of a known construction, for cooperation with the trigger valve assembly14to control the direction of rotation of the air motor15. In operation, the valve assemblies14and25channel the input pressurized airflow through passageways to the rear of the housing11, where the airflow enters the air motor15, exiting at the forward end thereof. The passages permit the pressured air stream to enter the rear of the air motor15at different locations, depending upon the condition of the reversing valve assembly25, as will be explained more fully below.

Referring now also toFIGS. 2-9, the pneumatic tool10is provided at its rear end with an automatic shutoff mechanism, generally designated by the numeral30(FIGS. 1 and 2) for automatically shutting off the air motor15upon the occurrence of a predetermined event, such as the development of a predetermined reactive force on the tool which, in the embodiment ofFIGS. 1-9, corresponds to the application of a predetermined torque to the associated work piece. The shutoff mechanism30includes a valve plate31having a front face32and a rear face33(see FIGS.5-7), with an inlet port34extending therethrough between the two faces. Formed in the rear face33and communicating with the port34is a generally Y-shaped groove35, the arms of which partially encircle a central cylindrical bore36formed through the plate31and provided at the rear face33with a first relatively deep counterbore37and a larger-diameter shallow counter bore37a. The bore36is also provided with a counterbore37bin the front face32(FIG.7). Formed through the plate31adjacent to its upper end is an arcuate port38. Formed in the front face32of the valve plate31is a generally question mark-shaped groove39, which partially encircles the central bore36for reversing the direction of the air motor15.

The shutoff mechanism30also includes a valve seat40(FIG. 8) which is in the nature of a relatively thin plate having a front face41which is disposed in use against the rear face33of the valve plate31substantially congruent therewith (see FIGS.2and3). Formed through the valve seat40are a pair of diametrically opposed, concentric arcuate apertures43. Formed in the front face41, respectively radially inwardly and outwardly of the arcuate apertures43, are concentric circular grooves for receiving O-ring seals44(see FIG.3). Also formed in the front face41is a generally Y-shaped groove45which is disposed so as to be matingly congruent with the Y-shaped groove35in the valve plate31for cooperation therewith to define a channel providing communication between the inlet port34and the arcuate apertures43. Formed through the valve seat40is a circular central bore46concentrically inside the inner O-ring seal44. Formed through the valve seat40adjacent to the upper end thereof is an arcuate aperture48disposed for registry with the port38in the valve plate31.

The shutoff mechanism30also includes an end plate50which has a front face51(seeFIG. 9) disposed in use against the rear face of the valve seat40substantially congruent therewith (see FIGS.2and3). Formed in the front face51is an arcuate groove53which forms a nearly complete circle and terminates in radially outwardly extending legs54. The groove53is positioned for registry in use with the arcuate apertures43in the valve seat40, with the ends of the legs54being in registry with the arcuate aperture48in the valve seat40. A central bore56is formed through the end plate50inside the arcuate groove53coaxially therewith for registry with the central bore46of the valve seat40, the bore56being provided in the front face51with a shallow counterbore57. An end cap58is disposed in use against the rear face of the end plate50substantially congruent therewith, and has a central bore59formed therethrough in registry with the central bore56of the end plate50. In use, the front face32of the valve plate31is disposed against the rear end plate19of the air motor15, being preferably spaced therefrom by a suitable gasket58a(FIGS.2and3). The valve plate31, valve seat40, end plate50and end cap58are secured together and to the motor15by suitable fasteners59a(one shown in FIG.1).

Referring in particular toFIGS. 1-4, the shutoff mechanism30also includes a hollow cylindrical plug insert60having an internally threaded bore61therethrough provided at the forward end thereof with a counterbore62. Projecting radially outwardly from the front end of the plug insert60is an annular flange63. In use, the plug insert60is received through the central bores56and59in the end plate50and in the end cap58, with the flange63seated in the counterbore57. A slotted adjusting screw65is threadedly engaged in the plug insert60and is provided with a radially outwardly projecting annular flange66having a circumferential groove67therein for receiving an O-ring seal68circumferentially sealing the forward end of the adjusting screw65against the counterbore62of the plug insert60. Alternatively, the screw could have a lever that seats in circumferentially spaced detent recesses to facilitate manual adjustment and ensure repeatability of settings.

The shutoff mechanism30also includes a shaft extension70having a coupling end71with flats formed thereon and mateably receivable in the stub shaft23of the motor rotor17for rotation therein. Just rearwardly of coupling end71is a radially outwardly projecting annular flange73which is disposed in the central bore36of the valve plate31and is encircled by a lip seal74. Formed in the outer surface of the shaft extension70rearwardly of the flange73are a plurality of circumferentially spaced helical grooves75, which may be three in number, in each of which is seated a corresponding ball76. The shaft extension70is coaxially encircled by an annular actuation member in the form of an inertia ring80, which has plural helical grooves81formed in the inner surface thereof, respectively cooperating with the grooves75in the shaft extension70for forming helical tracks for the balls76and confining the balls therein. Provided on the rear face of the inertia ring80is an annular thrust bearing82, which is engaged with an annular end flange83of a cylindrical thrust washer84. The rear end of the cylindrical thrust washer84is counterbored to define an annular shoulder85, against which is seated one end of a helical compression adjustment spring86, the other end of which is seated against the flange66of the adjustment screw65(see FIG.2).

The cylindrical thrust washer84extends through the center of an annular valve member in the nature of a disc valve87, which seats in the counterbore37aof the valve plate31. The disc valve87has a annular counterbore88formed in the rear face thereof, in which is seated one end of a helical compression reset spring89, the rear end of which is seated against the flange63of the plug insert60(see FIG.2). It will be appreciated that the disc valve87is resiliently retained by the reset spring89in a normal open position seated in the valve plate counterbore37a. This spring force also retains the plug insert60seated in the end plate counterbore57. Also, the thrust washer84and the inertia ring80are biased forwardly to a normal rest or home position, shown in the drawings, by the adjustment spring86with a force which can be varied by the adjustment screw65.

In operation of the air motor15in a forward or fastener-tightening direction, when the trigger valve assembly14is actuated, pressurized airflow will pass upwardly through the handle portion13of the housing, through the open trigger valve assembly14, and then rearwardly through the inlet port34of the valve plate31to the rear face thereof, and then upwardly through the channel formed by the Y-shaped grooves35and45, as indicated by the arrows inFIG. 2, then rearwardly through the arcuate apertures43in the valve seat40to the arcuate groove53and the end plate50, to the ends of the legs54, and then back forwardly through the arcuate aperture48in the valve seat40and the port38in the valve plate31to the rotor17of the air motor. Thus, it can be seen that this pressurized airflow path passes rearwardly of the disc valve87, which is seated in its normally open position. The air pressure may serve to assist the reset spring89in urging the disc valve87to its seated open position in the counterbore88.

As is well known, when a fastener is being run in, there will initially be negligible torque and the motor rotor17, shaft extension70and inertia ring80will all rotate together. As torque builds up, the impact mechanism21will begin imparting impulses or impacts to the work piece. With each such impact, the rotor17and shaft extension70will momentarily stop. However, the inertia ring80, which is not fixed to the shaft extension70, will try to continue rotating. The continued rotation of the inertia ring80relative to the shaft extension70will cause the inertia ring80to move axially rearwardly by operation of the helical ball-and-groove coupling to the shaft extension70, thereby driving the thrust washer84axially rearwardly against the urging of the adjustment spring86. The extent of the axial movement will be proportional to the amount of torque applied. Immediately after the rotor17and the shaft extension70resume rotation, the thrust washer84and inertia ring80will be returned forwardly to their home positions under the urging of the adjustment spring86.

Typically, each successive impact will exert a slightly higher torque than the preceding one. Thus, with each impact of the impact mechanism21, the inertia ring80will move axially a slightly greater distance rearwardly, returning each time to its home position between impacts. Eventually, when a predetermined torque level is reached, corresponding with the adjustment setting of the adjustment screw65, the inertia ring80will move rearwardly a sufficient distance that the end flange84of the thrust washer84will engage the front face of the disc valve87, unseating it and pushing it rearwardly from its normal open position a slight distance into the pressurized airflow. This will expose the front face of the disc valve87to the pressurized airflow, the pressure of which will then slam the disc valve87rearwardly the rest of the way to a closed position, sealed against the O-rings44of the valve seat40, thereby shutting off airflow through the arcuate apertures48in the valve seat40, blocking airflow to the air motor15and shutting it off. It will be appreciated that the O-rings44could be located on the disc valve87instead of on the valve seat40(see FIG.2). As soon as the operator releases the trigger valve assembly14, the pressurized airflow from the source will be shut off, relieving the air pressure on the disc valve87, and permitting it to return to its normal open position under the urging of the reset spring89.

Thus, automatic shutoff of the tool10is accomplished at a predetermined torque level preventing over torquing of the work piece. It is significant that the disc valve87need be moved only a very small distance from its normal open position, typically in the range of from about 0.01 inch to about 0.02 inch, to permit the pressurized airflow to take over and drive the disc valve87to its closed position, thereby using the pressurized airflow to perform most of the work in overcoming the force exerted by the reset spring89and effecting a very rapid shutoff. The shutoff mechanism is easily adjusted to vary the shutoff torque, is very compact, with all parts located at the rear of the air motor, and is relatively inexpensive.

If the reversing valve assembly25is actuated to operate the air motor15in a reverse or fastener-loosening direction, the pressurized airflow path will be different, bypassing the shutoff mechanism30, which is not needed, since there will be no torque limit to be concerned with. Thus, in this case, the airflow will be directed so that, at the front face32of the valve plate31, it will not enter the inlet port34, but will rather enter the reverse groove39, which channels it directly to a reverse-direction inlet port in the motor rear end plate19without going past the disc valve87.

Referring now also toFIGS. 11-13, there is illustrated another embodiment of automatic shutoff mechanism, generally designated by the numeral90, which utilizes substantially the same valve plate31, valve seat40, end plate50and end cap58described above in connection with the automatic shutoff mechanism30ofFIGS. 1-10, and creates the same airflow paths. The same plug insert60and adjusting screw65are also used. The shutoff mechanism90utilizes a global shaft extension91which differs somewhat from the shaft extension70, described above. The shaft extension91has plural helical grooves92formed in the outer surface thereof for respectively receiving balls93. However, in this case, each of the helical grooves92has a sloping base or root94, which is inclined so that the forwardmost end of the groove is further from the rotational axis than the rearwardmost end thereof, as can best be seen in FIG.11. The shaft extension91has a reduced-diameter rearward end95, provided at its distal end with a plurality of radially outwardly projecting spokes96, which may be three in number, and cooperate to define a slotted annular ring provided with a circumferential groove97in its outer surface, in which are seated a washer98and retaining ring99.

The shutoff mechanism90includes an inertia ring100which coaxially encircles the shaft extension91and has plural helical grooves101formed on the inner surface thereof for cooperation with the grooves92in the shaft extension91to form helical tracks for the balls93. Mounted at the rear end of the inertia ring100is a thrust bearing102which engages the forward end of a thrust washer103, which has at its rearward end a reduced-diameter cylindrical portion which is axially slotted to define a plurality of equiangularly spaced fingers104, the inner surfaces of which are counterbored to define a part-annular shoulder105.

The forward end of the adjustment spring86seats against the shoulder105on the fingers104of the inertia ring100. The shutoff mechanism90also includes a disc valve106, which is similar to the disc valve87described above and again seats in a normal open position in the counterbore37aof the valve plate41. However, the disc valve106is provided with a counterbore107and with a plurality of equiangularly spaced arcuate apertures108therethrough, shaped and dimensioned for respectively receiving therethrough the fingers104of the inertia ring100. The disc valve106is retained in its open position by the reset spring89in the same manner as was described above with respect to the disc valve87.

Disposed coaxially within the inertia ring100is a cylindrical reset sleeve110which has a main body111disposed in use coaxially between the helically grooved portions of the shaft extensions91and the inertia ring100, the main body111having plural circumferentially extending slots112therein for respectively receiving the balls93therethrough. The main body111is integral at its rearward end with a radially inwardly extending annular shoulder113, which is in turn integral at its radially inner end with a rearwardly projecting, reduced-diameter end portion114which has a plurality of equiangularly spaced axial slots115formed therein defining fingers116, the outer surfaces of which are grooved adjacent to their distal ends for receiving therein a washer117and a retaining ring118. When assembled, the radial spokes96of the shaft extension91will respectively project radially outwardly through the slots115of the reset sleeve110, but remain inside the fingers104of the inertia ring100, as can best be seen inFIG. 11. Ahelical compression reset spring119encircles the reset sleeve fingers116, having one end thereof seated against the washer117and the other end thereof seated against the shoulder113, for resiliently urging the reset sleeve110forwardly against the shoulder95aof the shaft extension91.

The operation of the shutoff mechanism90is similar to that of the shutoff mechanism30, described above. However, in this case, with each impact of the impact mechanism21, when the inertia ring100moves axially rearwardly relative to the shaft extension91, it will not return to its normal home position before the next impact. Rather, the reset sleeve110cooperates with the sloping helical grooves92in the shaft extension91to operate as a clutch to prevent return of the inertia ring100between impacts. More specifically, it can be seen that the reset spring119continuously urges the reset sleeve100and, thereby, the balls93, forwardly, continuously tending to wedge the balls93between the radially converging helical grooves92and101. Thus, in response to an impact, the inertia ring100is permitted to move rearwardly through the helical groove-and-ball coupling action described above, but is prevented from returning forwardly to its home position by its wedging action of the balls. Thus, there is a step-wise or additive movement of the inertia ring100rearwardly until, when the predetermined torque is reached, the thrust washer103engages and unseats the disc valve106, which is slammed to its closed position by the pressurized airflow stream in the manner described above. As the disc valve106moves to its closed position, it engages the washer117on the reset sleeve fingers116, pulling the reset sleeve110and, thereby, the balls93, rearwardly, releasing the clutch wedging action and permitting the inertia ring100to return to its home position under the urging of the adjustment spring86. The disc valve106will be reset after release of the trigger valve assembly14, in the same manner as described above.

Referring now toFIGS. 14 and 15, there is illustrated another embodiment of automatic shutoff mechanism, generally designated by the numeral120. Many of the parts of the shutoff mechanism120are the same as were used in the shutoff mechanisms30and90, described above, and common parts in those several embodiments bear the same reference numerals. The shutoff mechanism120utilizes a modified end plate121, which is similar to the end plate50, described above, except that it has a rear face122in which is formed a rectangular circuit board recess123and an aperture124through the end plate121for circuit leads. The rear face122of the end plate121is covered, in use, by an end cap125(FIG.14), which has therein a display window126for viewing a display which may form a part of a circuit board mounted in the recess123.

The shutoff mechanism120includes a trip assembly129, which includes a shaft extension70A which is substantially the same as the shaft extension70, described above, except that its helical grooves75A are disposed adjacent to its distal end rather than adjacent to the flange73. An inertia ring130encircles the shaft extension70A and has helical grooves131on its inner surface which cooperate with the grooves75A on the shaft extension70A to perform helical tracks for balls76A, in the manner described above, except that the helices are curved in the opposite direction. The inertia ring130has a radially inwardly extending annular end flange132at its forward end and has formed axially in the front surface thereof an annular groove133. Encircling the shaft extension70A adjacent to the flange73is an annular thrust washer134which is channel-shaped in transverse section and is secured to the valve plate31as by screws135(one shown). The thrust washer134seats a thrust bearing136. A helical reset spring137has one end thereof seated against the thrust washer134and the other end thereof seated in the groove133of the inertia ring130for resiliently urging the inertia ring130rearwardly. A suitable magnetic sensor138is seated in a radial cavity139in the valve plate31immediately above the inertia ring130.

A disc valve140is seated in the counterbore37aof the valve plate31so that it is spaced a slight distance rearwardly of the inertia ring130in its normal home position illustrated in the drawings. Formed in the rear face of the disc valve140is an annular spring groove141in which is seated one end of a helical reset spring142, the rear end of which is seated in a counterbore143in the end plate121for resiliently urging the disc valve140to its normal open position. Disposed in the central bore of the end plate121is a solenoid145, which has a forwardly extending plunger or shaft146which extends through a central opening in the disc valve140and is connected to a suitable retainer on the front side of the disc valve140. A circuit board147is seated in the circuit board recess123of the end plate121and is electrically connected to the solenoid145and to the sensor138by suitable leads (not shown). It will be appreciated that the circuit board147may include a suitable display which is visible through the display window126in the end cap125, and may also be provided with suitable input devices, such as a push buttons or the like, which may extend through suitable apertures (not shown) in the end cap125.

In operation, the inertia ring130will move axially back and forth in response to impacts delivered by the impact mechanism21, in much the same way as was described above in connection with the shutoff mechanism30, except that in this case the inertia ring130will move forwardly when the rotor extension70A stops and will return rearwardly to its home position. These movements will be sensed by the sensor138, which will output an electrical signal having a value proportional to the axial extent of the movement, which signal will be compared by a microprocessor or other suitable circuitry on the circuit board147, with a preset signal level corresponding to a predetermined torque value, which may be input by the user through the input means described above. When the predetermined torque level is reached, the circuit board147will output a signal to the solenoid145, which will actuate to pull the disc valve140a slight distance rearwardly into the air stream, causing it to slam to a closed position in the manner described above.

Referring now toFIG. 16, there is illustrated a trip assembly, generally designated by the numeral150, which may be substituted for the trip assembly129in the shutoff mechanism120of FIG.14. The trip assembly150has a modified shaft extension151provided at its end with a an axial bore152which receives the shaft146of the solenoid145and its associated coupler. Integral with the shaft extension151at its rear end is a radially outwardly extending annular end wall153which terminates at its radially outer edge in a forwardly projecting cylindrical flange154. Encircling the shaft extension151is an annular bobbin sensor155, which is a field sensor, which may be a magnetoelastic sensor of the type sold by Magna-Lastic Devices, Inc., or other contactless stress measuring device. The sensor155has an annular, radially outwardly extending flange at its forward end which is secured, as by fasteners156, to the valve plate31. The forward end of the cylindrical flange154of the shaft extension151may slightly overlap the bobbin sensor155. The region of shaft extension151within the bobbin sensor155is specifically magnetized so that it can generate an electromagnetic field signal which can be sensed by the sensor155in a non-contact manner. The sensor155detects changes of torque through the magnetization and outputs a signal which is interpreted by the electronics on the circuit board147for measuring the amount of force reflected from the impact mechanism21, which results in torsional stresses in the shaft extension155proportional to the torque applied and sensed by the sensor155. The signal generated by the sensor155is proportional to the torque applied and is compared by the electronics on the circuit147to a predetermined reference torque level and, when they match, the solenoid145is actuated in the manner described above. If desired, the achieved torque value could then be displayed on the display of the circuit board147and the solenoid145is then deactivated, permitting the disc valve140to be returned to its normally opened position by the spring142when the trigger valve assembly14is released. A method of producing a circular magnetized, non-contact torque sensor of the type just described is disclosed in U.S. Pat. No. 5,887,335.

While, in the illustrated embodiments, the pneumatic tool10is a hand tool, it will be appreciated that the automatic shutoff principles disclosed herein would be applicable to other types of pneumatic devices. Also, while the illustrated embodiments are utilized in a torque-applying tool, it will be appreciated that the automatic shutoff principles disclosed herein, particularly those in the electromagnetic embodiments ofFIGS. 14-16, could be used in pneumatic tools delivering other types of forces to a work piece, such as pneumatic hammers, chisels and the like. Also, while the illustrated embodiments have been shown as utilized in a torquing tool of the impact type, it will be appreciated that certain of the automatic shutoff principles herein could be utilized with other types of non-impact torquing tools.

From the foregoing, it can be seen that there has been provided an improved automatic shutoff mechanism for a pneumatic tool which is relatively simple, compact, inexpensive, fast-acting and easy to adjust.