Machine For Automatically Driving Threaded Fasteners

Abstract

Vacuum is established within a rubber sleeve telescoped over a screwdriver and holds a threaded screw in driving engagement with the screwdriver as the latter is rotated and advanced by a power driven spindle to drive the screw into a workpiece. If the screwdriver is advanced without the screw being held in the sleeve, the resulting absence of vacuum is detected and is used to produce a signal causing retraction of the screwdriver short of the workpiece. Each time the screwdriver is retracted, a blast of air is shot through the sleeve to eject any screw that may have been improperly retained in and retracted with the sleeve. In another embodiment, the vacuum is established within a wrench-type socket carried on the end of the spindle.

Description

BACKGROUND OF THE INVENTION

This invention relates to a machine for automatically driving threaded fasteners and, more particularly, to a machine of the type which includes a fastener driver carried on and projecting from the end of a power rotated and power reciprocated spindle. As the spindle is advanced through a forward stroke, a fastener is delivered to the machine and is held in driving engagement with the driver as the latter advances and rotates to thread the fastener to a workpiece. Thereafter, the spindle and the driver are retracted through a return stroke preparatory to the delivery of the next fastener to the machine. Machines of this general type are shown in Dixon U.S. Pat. No. 2,989,996 and Dixon U.S. Pat. No. 3,279,045.

SUMMARY OF THE INVENTION

The primary aim of the present invention is to hold the fastener in engagement with the driver of a machine of the above character in a new, improved and relatively inexpensive manner which insures positive and reliable retention of the fastener, which allows the fastener to be held for a longer period of time during threading of the fastener to the workpiece, and which enables automatic control of the advance of the spindle according to whether a fastener has been properly delivered to and held by the machine. A more detailed object is to achieve the foregoing by using vacuum to hold the fastener in driving engagement with the driver and by controlling the application and release of the vacuum in a novel manner.

The invention also resides in the novel provision of a resiliently yieldable sleeve telescoped over a driver in the form of a screwdriver and adapted to seal against the fastener to enable vacuum to build up within the sleeve to hold the fastener in engagement with the screwdriver. This aspect of the invention is further characterized by the unique mounting of the sleeve permitting the application of vacuum to the sleeve while enabling a standard commercially available screwdriver to be used in the machine with only minor structural modifications.

A further object of the invention is to detect the presence and absence of a buildup of vacuum within a sleeve on the end of the spindle and to retract the spindle short of its full forward stroke when the vacuum buildup is absent, thus indicating that a fastener has not been delivered to or held in the sleeve. Still another object is to override the vacuum during the return stroke of the spindle and to pneumatically eject from the sleeve any fastener that may have been retained in and retracted with the sleeve.

Other objects and advantages of the invention will become apparent from the following detailed description when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a new and improved fastener driving machine embodying the novel features of the present invention.

FIG. 2 is a perspective view of an exemplary fastener adapted to be driven by the machine.

FIG. 3 is perspective view of a different type of fastener adapted to be driven by the machine.

FIG. 4 is a perspective view of still another type of fastener adapted to be driven by the machine.

FIG. 5 is an enlarged fragmentary cross section taken substantially along the line 5-5 of FIG. 1.

FIG. 6 is an enlarged fragmentary cross section taken substantially along the line 6-6 of FIG. 1.

FIG. 7 is a fragmentary front elevation of the machine shown in FIG. 1, parts being broken away and shown in section.

FIG. 8 is an enlarged view of parts shown in FIG. 6, certain elements being broken away and shown in section.

FIG. 9 is a cross section taken substantially along the line 9-9 of FIG. 8.

FIG. 10 is an enlarged cross section taken substantially along the line 10-10 of FIG. 8.

FIG. 11 is an enlarged cross section taken substantially along the line 11-11 of FIG. 8.

FIG. 12 is a fragmentary view of parts illustrated in FIG. 8 and showing a driver and sleeve operating on the type of fastener shown in FIG. 2.

FIG. 13 is a view similar to FIG. 12 but showing a modified driver and sleeve operating on the type of fastener shown in FIG. 3.

FIG. 14 is a view similar to FIG. 12 but showing still another type of driver operating on the fastener shown in FIG. 4.

FIG. 15 is an enlarged fragmentary cross section taken substantially along the line 15-15 of FIG. 6.

FIG. 16 is a diagram schematically showing pneumatic and electrical circuits for controlling operation of the machine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in the drawings for purposes of illustration, the invention is embodied in a machine 20 operable automatically to drive threaded fasteners 21 into successive workpieces 23 (FIG. 7) delivered to an assembly station, only one fastener and one workpiece being shown herein. Suitable feeding mechanism (not shown) delivers the workpieces to the machine one at a time to receive the fasteners.

While the fasteners 21 could be a threaded bolt or nut with a driving portion or head of any selected size and shape, the exemplary fastener shown in FIG. 2 is a threaded machine screw having a cylindrical head 24 formed with a Phillips-type socket 25. The screw 21 is adapted to be threaded into a hole 26 in the workpiece 23 by a driving tool which herein is in the form of a screwdriver 27 (FIG. 8) whose working end is formed with a Phillips-type tip 29 sized to telescope into the socket to turn and drive the screw. The screwdriver is a standard commercially available type made of hardened steel and includes a coupler 30 threaded into the lower end of an elongated upright driving spindle 31, a shank 33 projecting from the spindle and formed with the tip 29, and an annular collar 34 encircling the shank and abutting the end of the spindle.

The spindle 31 is journaled for rotation and guided for up and down reciprocation on a supporting bracket 35 (FIG. 1) projecting laterally from an upright standard 36. As the spindle is rotated and advanced downwardly, a screw 21 initially stored in a hopper 37 is pushed along a track 39 by a transfer device 40 and is delivered to and held between a pair of initially closed pivoted jaws 41, the screw being held in the jaws below the tip 29 of the screwdriver 27 as shown in FIG. 6. With continued downward advancement of the spindle, the tip seats in the socket 25 and begins rotating the screw, the jaws open, and the screw is threaded downwardly into the hole 26 in the workpiece 23 (see FIG. 7). Thereafter, the spindle is retracted upwardly through a return stroke, and another screw is delivered to the jaws preparatory to the next downward stroke of the spindle. The machine cycles quite rapidly and is capable of driving up to 60 screws per minute.

To advance and retract the spindle 31, a reciprocating pneumatic actuator 43 (FIG. 6) is supported on the bracket 35 and includes a piston 44 which is slidable up and down within a cylinder 45 in response to the admission of pressurized air alternately into opposite ends of the cylinder. The spindle extends through and is journaled rotatably in both the piston and a quill-like rod 46 anchored to the lower face of the piston and projecting downwardly out of the lower end of the cylinder. The spindle is prevented from sliding axially within the piston and the rod and thus is advanced and retracted when the piston is reciprocated downwardly and upwardly.

Rotation of the spindle 31 is effected by rotary air motor 47 FIGS. 1 and 7) which is coupled to the upper end of the spindle to reciprocate with the latter. The motor is supported on the upper end of a sleeve 49 which rotatably receives and reciprocates with the spindle and which is formed with a laterally projecting arm 50 carrying a cylinder 51. The latter is telescoped over spaced spools 53 slidable on an upright rod 54 and urged away from one another and against snaprings 55 on the rod by a compression spring 56 encircling the rod between the spools. As shown most clearly in FIG. 7, the rod is guided for up and down sliding by the bracket 35 and carries at its lower end an arm 57 which rotatably and slidably receives the spindle. The jaws 41 are pivoted on the arm 57 as indicated at 59 and normally are urged toward their closed positions by a spring 59a (FIG. 1).

The operation of the machine 20 as described thus far is disclosed in detail in the aforementioned Dixon U. S. Pat. No. 2,989,996 to which reference may be had for a specific step-by-step explanation of the operational sequence. In brief, the jaws 41 initially are closed and are positioned at a level to receive a screw 21 delivered from the track 39. In the initial position of the jaws, the arm 57 engages the lower end of the bracket 35, the upper spool 53 is held downwardly within the cylinder 51 by the upper snapring 55, and the lower spool 53 is spaced upwardly from the lower snapring 55 and engages the lower end of the cylinder. As the piston rod 46 is extended with a screw held between the closed jaws, the spindle 31 and the cylinder 51 move downwardly in unison relative to the rod 54 until the screwdriver 27 engages the screw and the upper end of the cylinder engages the upper spool 53. The cylinder 51 then forces the rod 54 and the jaws to advance downwardly in unison with the spindle until an adjustable stop 60 (FIG. 7) on the upper end of the rod engages the bracket 35 to prevent further downward movement of the rod and the jaws with the latter positioned just above the workpiece 23. Thereafter, the spindle continues to shift downwardly relative to the jaws and causes the screwdriver to rotate the screw, the upper spool 53 sliding downwardly on the stopped rod 54 and compressing the spring 56 to allow downward movement of the spindle relative to the rod. As the spindle advances relative to the jaws, a cam 61 carried on the spindle engages and spreads the jaws apart (see FIG. 7) to free the screw for continued downward movement toward and threading into the workpiece.

After the screw 21 has been driven, the piston rod 46 is retracted to shift the spindle 31 upwardly, the jaws 41 springing closed as an incident to retraction of the cam 61. During the upward stroke of the spindle, the upper spool 53 engages the upper snapring 55 to shift the rod 54 upwardly and thereby retract the jaws to the level of the track 39. Another screw then is delivered to the jaws preparatory to the next downward stroke of the spindle.

Advantageously, the screw 21 is held in positive driving engagement with the screwdriver 27 by a vacuum force at least from the time the jaws 41 open until the time the screw is threaded well into the workpiece 23. As a result, there is less danger of losing the screw during this interval and, in addition, the screw may be positively held even while being threaded into particularly shaped holes or workpieces having narrow clearances which obstruct the jaws and prevent the jaws themselves from holding the screw during the initial threading thereof.

In the present instance, the vacuum is established within a sleeve 65 (FIG. 8) telescoped over the screwdriver 27 and communicating with a vacuum pump VP (FIG. 16) operable to suck air upwardly through the sleeve. In accordance with one aspect of the invention, the sleeve is made of resiliently flexible material such as rubber so as to seal against the head 24 of the screw 21 to enable a holding vacuum to build up in the sleeve. As shown most clearly in FIG. 8, the sleeve is coaxial with the screwdriver and includes a cylindrical lower end projecting downwardly approximately one-sixteenth of an inch beyond the tip 29 of the screwdriver and having a relaxed internal diameter which is just slightly smaller than the diameter of the head of the screw.

As the spindle 31 is initially advanced downwardly, the sleeve 65 telescopes over the head 24 of the screw 21 and flexes outwardly as shown in FIG. 12 while the screw is being held stationary in the jaws 41 and just before the screwdriver tip 29 seats in the socket 23. The rubber lightly grips and seals around the head thus sealing off the lower end of the sleeve so that the pump VP exhausts the air in the sleeve and causes a vacuum to build up within the sleeve to draw the screw upwardly and to hold the screw in snug engagement with the screwdriver. Because the sleeve is resiliently flexible and is sized to contract around the head, a good seal always is established between the sleeve and the head even though the latter may be undersized or slightly out of round.

When the jaws 41 open, the vacuum within the sleeve 65 continues to hold the screw 21 as the screwdriver 27 advances the screw on downwardly past the jaws to thread the screw into the hole 26 in the workpiece 23. Thus, the screw is held positively and in an upright position during the critical period when the screw just starts threading into the hole and, indeed, is held until completely tightened. As a result, there is little danger of the screw being thrown from the machine 20 or of being cross-threaded into the workpiece. The machine thus is more reliable and trouble-free in service use.

The secure holding of the screw 21 effected by the vacuum within the sleeve 65 is particularly advantageous when the hole 26 is formed alongside a stepped shoulder 66 on the workpiece 23 as shown in FIG. 7, when the hole is formed with a counterrecess as indicated at 67, or when some other obstruction interferes with and restricts downward movement of the jaws 41. The shoulder 66 limits the level to which the jaws may be advanced downwardly to hold the screw but, with the screw being held in the sleeve by vacuum, the sleeve may advance downwardly immediately alongside the shoulder to hold the screw until the latter is threaded. In certain instances, the sleeve may advance below the upper surface of the workpiece and directly into the counterrecess 67 so as to provide positive holding of the screw while the latter begins threading into the main hole 26 and until the screw is snugly seated.

The invention also contemplates applying the vacuum to the sleeve 65 in a manner that permits use of the standard commercially available screwdriver 27 in the machine 20 without need of substantially modifying the screwdriver. Herein, the vacuum pump VP communicates with the sleeve through an axially extending bore 69 (FIG. 8) formed in the spindle 31. As shown in FIG. 8, the upper end portion of an enlarged metal sleeve 70 is telescoped over the spindle and abuts a snapring 71 on the spindle. The inner wall of the sleeve is recessed as indicated at 73 to form an annular chamber around the spindle, the chamber communicating with the bore through a radially extending hole 74 formed in the spindle. The upper end of the chamber 73 is sealed relative to the spindle by a rubber O-ring 75 which advantageously is compressed between opposed circumferential grooves 76 formed in the outer surface of the spindle and the inner wall of the sleeve 70. The O-ring thus acts as a detent and serves to hold the sleeve 70 on the spindle.

Near its lower end, the metal sleeve 70 is formed with a rigid sleevelike tube 77 (FIG. 8) of reduced diameter which is telescoped into the rubber sleeve 65 and over the screwdriver shank 33, the tube being somewhat larger in diameter than the shank to leave an axially extending air passage between the two. The rubber sleeve may be bonded to the tube but preferably is held releasably thereon by virtue of the resilient rubber being contracted around the tube. Just above the tube, the sleeve 70 is formed with a cylindrical recess 79 (FIG. 8) which is sized to receive the annular flange 34 on the screwdriver shank. The wall of the wall of the recess 79 extends around and fits tightly against the outer wall of the flange to keep the sleeves 65 an 70 precisely centered on the axis of the spindle 31.

Fluid communication between the rubber sleeve 65 and the chamber 73 in the upper sleeve 70 is established simply by grinding two diametrically opposite flats 80 (FIGS. 8 and 10) on the outer wall of the annular flange 34 thereby to define two air passages disposed between the walls of the flange and the recess 79 and leading from the chamber to the tube 77 into communication with the sleeve 65. Accordingly, only a simple and easily performed modification need be made to the standard screwdriver 27 to adapt it for use with the vacuum-equipped machine 20.

To establish communication between the vacuum pump VP and the bore 69 in the spindle 31, a cylindrical manifold collar 81 FIGS. 6, 8 and 15) is telescoped over both the spindle and the piston rod 46 and is mounted to reciprocate with the rod while remaining rotationally stationary. As shown most clearly in FIG. 8, a flexible line 83 communicating with the vacuum pump is connected into the collar and communicates with the bore 69 through a radial hole 84 in the spindle. The collar is sealed to the spindle by O-rings 85 which enable rotation of the spindle within the collar while preventing the leakage of air along the spindle.

To advantage, the manifold collar 81 is mounted for limited lateral floating relative to the piston rod 46 to avoid binding of the collar against the spindle 31 or leakage of air past the O-rings 85 in the event the bores 86 and 87 (FIG. 6) extending through the collar are not precisely concentric with one another and with the rod and the spindle. For this purpose, the collar is fastened to the piston rod by screws 89 (FIGS. 6 and 15) which are threaded into holes in the collar but which extend loosely into oversized holes 90 in the rod. With this arrangement, the collar may float or tilt slightly on the rod and assume a position allowing free rotation of the spindle without permitting any air leakage past the O-rings.

In accordance with another aspect of the invention, the buildup of vacuum within the sleeve 65 is detected during the downward stroke of the spindle 31 and, if the screw 21 fails to enter or remain in the sleeve to cause the vacuum to build up, the spindle is automatically retracted short of its full downward stroke to prevent the screwdriver 27 from striking the workpiece 23 without a screw and causing damage to the screwdriver, the sleeve, the workpiece or all three. Thus, advantage is taken of the vacuum to make the machine 20 fail-safe in case a screw is not properly advanced with the screwdriver toward the workpiece.

To explain the foregoing more clearly, reference is made to FIG. 16 which is a diagram of electrical and pneumatic circuits for controlling the machine 20, the electrical circuit including lines L.sub.1 and L.sub.2 connected across a conventional power source. Initially and during a normal cycle of operation, a start switch ST is closed momentarily, as for example by a workpiece 23 moving into position beneath the screwdriver 27, and serves to energize a solenoid SOL-A which admits air from an air pressure source AP into the upper end of the cylinder 45 to advance the spindle 31 downwardly. When the screwdriver 27 advances downwardly to the track 39 and a screw 21 properly enters the sleeve 65, vacuum builds up within the sleeve to cause the actuator 95 of a vacuum-responsive switch VS to shift the switch from a position making its contact A to a position making its contact B. With advance of the screwdriver just below the track, an operating rod 96 (FIGS. 1 and 16) carried on the spindle closes a checkpoint switch CP which sets a timer TR. Then, as the screw is threaded into the workpiece and tightened to the proper degree, a switch TQ (FIG. 16) closes and energizes a solenoid SOL-R through the closed checkpoint switch CP to shift the valve V-1 to a position admitting air into the lower end of the cylinder 45 to retract the spindle preparatory to another cycle, the switch TQ being responsive to the torque on the spindle. If the screw strips the threads in the workpiece and fails to tighten to cause closure of the torque switch TQ, the timer TR times out and closes its contacts TR-1 to energize the retract solenoid SOL-R through contact B of the vacuum switch VS thereby to prevent the screwdriver from remaining at the bottom of its downward stroke and simply spinning the screw. As the spindle retracts and pulls the screwdriver upwardly from the screw, the vacuum within the sleeve 65 and the line 83 is broken to enable a spring 99 (FIG. 16) to return the vacuum switch VS to its normal position making its contact A. In addition, the checkpoint switch CP is opened to reset the timer TR and open the contacts TR-1.

In the event that a screw 21 is not delivered to the jaws 41 and picked up in the sleeve 65 during the downward stroke of the spindle 31, the vacuum fails to build up in the sleeve as the screwdriver 27 advances past the track 39 and thus the spring 99 holds the vacuum switch VS in a position in which the switch continues to make its contact A. Accordingly, as soon as the spindle advances sufficiently far for the operating rod 96 to close the checkpoint switch CP, the retract solenoid SOL-R is energized through the checkpoint switch and the contact A of the vacuum switch. As a result, the spindle is retracted well short of its full downward stroke and before the screwdriver strikes the workpiece 23. Thus, the workpiece will not be marred or damaged by the screwdriver and, in addition, the screwdriver and the sleeve will not be chewed up or damaged as a result of spinning against the workpiece without a screw.

If for some reason the screw 21 is initially picked up in the sleeve 65 but then subsequently lost after closure of the checkpoint switch CP, the vacuum in the sleeve 65 will be broken to cause the vacuum switch VS to remake its contact A and cause retraction of the spindle 31. Accordingly, the machine 20 is fail-safe in that the spindle is always retracted unless a screw continuously advances ahead of the screwdriver 27 toward the workpiece 23.

The invention further contemplates ejecting the screw 21 automatically from the sleeve 65 during retraction of the spindle 31 in the event the screw fails to thread into the workpiece 23 and starts to return upwardly with the sleeve. For this purpose, the air pressure source AP is adapted to be connected to the sleeve during the return stroke of the spindle and overrides the vacuum pump VP to force a downwardly directed blast of air through the sleeve to blow out the screw.

As shown in FIG. 16, the air pressure source AP communicates with the sleeve 65 through the line 83 under the control of a valve V-2 which is adapted to be actuated by a solenoid SOL-P. As air is admitted into the lower end of the cylinder 45 to retract the spindle 31, a pressure-responsive switch PS communicating with the cylinder is closed to energize the solenoid SOL-P and shift the valve V-2 to a position establishing communication between the pressure source AP and the sleeve 65. As a result, a jet of air is directed downwardly through the sleeve to eject any screw that may have been retained therein and to clear the sleeve so as to prevent jamming of the machine 20 during the next downward stroke of the sleeve. While the sleeve could be cleared in some instances simply by cutting off the vacuum, the use of the positive pressure created by the pressure source AP is more reliable and also eliminates the need of employing valves in the vacuum line 83.

The machine 20 can be adapted to drive fasteners other than the type of screw 21 shown in FIG. 2. For example, by replacing the screwdriver 27 with a screwdriver 27' (FIG. 13) having a bladelike tip 29', a screw 21' (FIG. 3) with a rounded head 24' and a straight slot 25' may be driven, the sleeve 65 surrounding the screwdriver 27' being adapted to seal against the sides of the head 24' and against the upper surface of a washer 100 formed integrally with the head. Instead of a screwdriver, the machine may be equipped with a wrench-type driving sleeve or socket 105 (FIG. 14) which is sized to telescope over and drivingly engage the polygonal-shaped head 24" of a screw 21" (FIG. 4). The socket may be threaded into the end of the spindle 31 and is formed with a hole 106 which communicates with the bore 69 in the spindle to enable a holding vacuum to be created in the socket.

From the foregoing, it will be apparent that the present invention brings to the art a more reliable and trouble-free way of holding a fastener in engagement with the driver of an automatic fastener driver machine and facilitates use of the machine in conjunction with workpieces having difficult-to-reach holes. In addition to positively holding the fasteners, the vacuum enables automatic control of the machine to prevent malfunctions which otherwise would interfere with optimum operation of the machine.

Claims

We claim:

1. In a machine for automatically driving a threaded fastener having a head of a selected size and shape, the combination of, a support, a power rotated and power reciprocated spindle mounted on said support, a screwdriver carried on one end of said spindle and having a shank projecting from the spindle, an annular collar encircling said shank and abutting the end of the spindle, said screwdriver having a working end operable to engage the head of the fastener to drive the latter, a sleeve coaxial with and projecting from the working end of said screwdriver and located to telescope over the fastener head during advancement of said spindle, said sleeve being made of resiliently yieldable material and being sized and shaped to seal around the fastener head as an incident to such telescoping, a second sleeve of relatively rigid material having one end portion telescoped over and fastened to said spindle, said second sleeve having a second end portion telescoped into said resilient sleeve and over said screwdriver and terminating short of the working end thereof, said second sleeve having a cylindrical intermediate portion located between said end portions and encircling and engaging said collar to keep said sleeves centered on the axis of said spindle, angularly spaced air passages located between the outer surface of said collar and the inner surface of said intermediate portion for establishing fluid communication between the end portions of said second sleeve, and means communicating with said one end portion of said second sleeve and operable to establish a vacuum within the resilient sleeve for drawing and holding the fastener in engagement with said screwdriver.

2. A machine as defined in claim 1 in which said air passages are defined by angularly spaced flats on the outer surface of said collar.

3. A machine as defined in claim 1 in which said first sleeve is contracted around the second end portion of said second sleeve and is held thereon by virtue of the resiliency of the material of the first sleeve.

4. In a machine for automatically driving a threaded fastener having a head of a selected size and shape, the combination of, a support, a power rotated and power reciprocated spindle mounted on said support, a screwdriver carried on one end of said spindle and having a shank projecting from said spindle, an annular collar encircling said shank and abutting the end of the spindle, said screwdriver having a working end operable to engage the head of the fastener to drive the latter, a sleeve coaxial with and projecting from the working end of said screwdriver and located to telescope over the fastener head during advancement of said spindle, said sleeve being made of resiliently yieldable material and being sized and shaped to seal around the fastener head as an incident to such telescoping, a second sleeve of relatively rigid material telescoped over and projecting from said spindle and carrying said resilient sleeve, said rigid sleeve having a cylindrical portion encircling and engaging said collar to keep said sleeves centered on the axis of the spindle, an air passage located between the outer surface of said collar and the inner surface of said cylindrical portion and leading from said rigid sleeve to said resilient sleeve to establish fluid communication between the two, and means communicating with said rigid sleeve and operable by way of said air passage to establish a vacuum within the resilient sleeve for drawing and holding the fastener in engagement with said screwdriver.

5. A machine as defined in claim 4 in which the outer surface of said spindle and the inner surface of said rigid sleeve are formed with opposing circumferential grooves, and further including an O-ring of resiliently yieldable material seated in said grooves and compressed between said surfaces to hold said rigid sleeve on the spindle while establishing an airtight seal between the rigid sleeve and the spindle.

6. A machine as defined in claim 4 in which said spindle is formed with an axially extending bore communicating with said rigid sleeve, a nonrotatable and reciprocable quill rotatably receiving said spindle, a manifold collar telescoped over said spindle and said quill and establishing communication between said vacuum means and said bore, and means mounting said manifold collar on said quill for reciprocation with the latter while allowing limited lateral floating of the collar relative to said quill.

7. In a machine for automatically driving a threaded fastener, the combination of, a support, a power rotated spindle mounted on said support for reciprocation through forward and return strokes, means on said support for advancing and retracting said spindle through said forward and return strokes, a driver carried on one end of said spindle and having a working end operable to engage the fastener to drive the latter, a sleeve coaxial with the working end of said driver and sized to telescope over the fastener at a predetermined point during the advance stroke of said spindle, a vacuum source communicating with said sleeve and operable to create a buildup of vacuum within the sleeve when the latter is telescoped over the fastener thereby to hold the fastener in engagement with the working end of said driver, and means for detecting the absence of a buildup of vacuum within the sleeve after the latter has advanced past said predetermined point and operable in response to such detection to cause automatic retraction of the spindle through said return stroke before the spindle completes a full forward stroke.

8. A machine as defined in claim 8 further including means for disabling said vacuum source during the return stroke of said spindle.

9. A machine as defined in claim 7 further including a source of pressure fluid adapted to be connected into communication with said sleeve and operable when connected to override said vacuum source and to create a positive pressure in the sleeve, and means operable automatically as an incident to retraction of said spindle through said return stroke to connect said pressure source to said sleeve whereby any fastener retained in and retracted with the sleeve is ejected therefrom by said positive pressure.

10. In a machine for automatically driving a threaded fastener, the combination of, a support, a power rotated spindle mounted on said support for reciprocation through forward and return strokes, a sleeve projecting from one end of said spindle and having an open end sized to telescope over the fastener during the forward stroke of the spindle, a vacuum source communicating with said sleeve and operable to draw air through the sleeve from the open end thereof and to create a buildup of vacuum within the sleeve when the sleeve is telescoped over the fastener thereby to hold the fastener in the sleeve, and means for retracting said spindle short of its full forward stroke in response to detecting an absence of a buildup of vacuum in said sleeve after the spindle has advanced a predetermined distance through said forward stroke.

11. A machine as defined in claim 10 in which said sleeve is a wrench-type socket shaped to telescope over and drivingly rotate said fastener.

12. A machine as defined in claim 10 further including a screwdriver projecting from the end of said spindle and telescoped into said sleeve.