US3642039A

US3642039A - Power screwdriver

Info

Publication number: US3642039A
Application number: US829650A
Authority: US
Inventors: Harold Mcgee
Original assignee: Hill Rockford Co
Current assignee: Hill Rockford Co
Priority date: 1969-06-02
Filing date: 1969-06-02
Publication date: 1972-02-15
Anticipated expiration: 1989-02-15

Abstract

This screwdriver is driven pneumatically and has all pneumatic control means. The screw-gripping jaws operable pneumatically are separately controlled from the operation of the screwdriver to grip the screw first loosely as it is fed into place between the jaws, the jaws being thereafter closed for accurate positioning and guiding of the screw while the driving commences, the jaws finally opening wide as the screw is driven home. Pneumatic limit switches or valves control the operation of the screwdriver independently of the control of the screw-holding jaws, and a mechanically operable torque measuring gauge or clutch automatically shuts off pneumatic power to the screwdriver by switch or valve control when the screw is driven home or in the event of a jam due, for example, to cross-threading. There is an adjustability feature adapting the screwdriver to operation on different lengths of screws.

Description

United States Patent Feb. 15, 1972 McGee [54] POWER SCREWDRIVER [72] Inventor: Harold McGee, Rockford, Ill.

[73] Assignee: Hill-Rockiord Co., Rockford, Ill.

[22] Filed: June 2, 1969 [2]] Appl. No.: 829,650

[52] US. Cl ..144/32, 192/57, 81/524 [51] Int. Cl. ..B23p 19/06, B251) 33/08 [58] Field ofSearch ..144/32; 81/524, 52.5, 57; 192/56 [56] References Cited UNITED STATES PATENTS 2,880,770 4/1959 Ettinger 144/32 Primary Examiner-Donald R. Schran AttorneyAndrew F. Wintercom ABSTRACT This screwdriver is driven pneumatically and has all pneumatic control means. The screw-gripping jaws operable pneumatically are separately controlled from the operation of the screwdriver to grip the screw first loosely as it is fed into place between the jaws, the jaws being thereafter closed for accurate positioning and guiding of the screw while the driving commences, the jaws finally opening wide as the screw is driven home. Pneumatic limit switches or valves control the operation of the screwdriver independently of the control of the screw-holding jaws, and a mechanically operable torque measuring gauge or clutch automatically shuts off pneumatic power to the screwdriver by switch or valve control when the screw is driven home or in the event of a jam due, for example, to cross-threading. There is an adjustability feature adapting the screwdriver to operation on different lengths of screws.

PATENTEUFEBIS i912 3.642.039

' sum 1 0r 4 INVENTOR HAROLD MCGEE PAIENTEBFEB 15 L972 3. 642.039

SHEET 2 OF 4 INVENTOR HAROLD MCGEE Attornev PAIENTEDFEB 15 I972 SHEET 3 OF 4 HAROLD McGEE PATENTEDFEB 1 5 I972 SHEET 0F 4 PRESSURE SUPPLY FIGIO lacs v INVENTOR: HAROLD MCGEE RETURN Attornev POWER SCREWDRIVER This invention relates to a power screwdriver and is more particularly concerned with one that is driven pneumatically and has only pneumatic control means and embodies the following important features:

I. The screw to be applied is gripped by jaws operable by pneumatic pressure, and they are separately controlled from the operation of the screwdriver, the screw being first loosely held between the jaws when it is fed into place therebetween, and the jaws being thereafter closed and mechanicallylocked for more accurate positioning and guiding of the screw while the driving commences, the jaws finally opening wide when the screw is being driven home and there is, of course, no need for further guidance, the separately controlled jaws with their vertically reciprocable carrier sleeve being not limited to the present application but being useful generally as a parts placement assembly;

. Pneumatic limit switch or valve control of the operation of the screwdriver independently of the control of the screw-holding jaws;

3. A mechanically operable torque measuring gauge or clutch of unique design is incorporated in the screwdriver drive so that pneumatic power is automatically shut ofi' to the screwdriver by switch or valve control when the screw is driven home or in the event of a jam due, for example, to cross-threading, and

4. The adjustability feature for adaptability to different lengths of screws.

Other objects and advantages of my invention will be apparent in reading the following specification in which reference is made to the accompanying drawings, wherein:

FIG. 1 is a vertical section through a power screwdriver made in accordance with my invention, all of the parts being illustrated as positioned at the commencement of a cycle;

FIGS. 2, 3 and4 show the parts in three different positions illus rating one complete cycle, FIG. FIG. 2 being the returned position, ready for the commencement of a new cycle; FIG. 3 showing the intermediate screw engagement position, and FIG. 4 showing the screw-seating position, the torque-responsive clutch shown in FIG. I being omitted from the construction shown in these three figures;

F IG. 5 is an enlarged sectional detail illustrating the torqueresponsive clutch of FIG. I with the parts shown in drivetransmitting relationship;

FIG. 6 is a cross section on the line 6-6 of FIG. 5;

FIG. 7 is a sectional detail corresponding to a portion of FIG. 5, showing the parts in the power-off position following torque overload;

FIG. 8 is a section on the line 8-8 of FIG. 7;

FIG. 9 is a side view of a portion of FIG. 1, taken on the line 99 thereof; and

FIG. 10 is a pneumatic circuit diagram for the power screwdriver.

The same reference numerals are applied to corresponding parts throughout the views.

Referring to the drawings, and first mainly to FIG. 1, the frame 1 l of the screwdriver is vertically adjustable on a pair of laterally spaced vertical posts 12, as indicated at 13, and these posts are carried on a supporting base 14. A jaw carrier sleeve is slidable in a vertical hole 16 provided in the frame 11, and carries two threadedly

adjustable stops

17 and 18 on its opposite ends to limit downward and upward travel, respectively, each being suitably fitted with a setscrew 19 to maintain a given adjustment. A vertical slot 20 in one side of the sleeve has a dog 21 pivoted therein at its upper end, as at 22. The externally threaded ram 23, on which stop nut 24 is adjustable to limit downward travel of the ram by engagement on the sleeve 15, works inside sleeve 15 and is slidable in a bushing 25 pressfitted into the enlarged upper end portion 26 of the bore in sleeve 15. The ram 23 has a reduced elongated lower end portion 27 to the lower extremity of which a collar 28 is pinned, retaining behind it under preload a coiled compression spring 29 and its backup washer 30, the latter being slidable in the enlarged upper end portion 26 of the bore 31 while collar 28 is slidable in bore 31. The annular shoulder 32 intermediate the ends of ram 23 is so spaced that when the tapered lower end of collar 28 contacts the shoulder 33 on dog 21 to transmit downward movement to the sleeve 15, washer 30 is also engaged by shoulder 32 so that there will be no change in compression of the spring 29 and thus there is assurance that the sleeve 15 will not travel any faster downwardly than the ram. When the stop collar 17 engages the frame, as in FIG. 4, it positively limits downward travel of sleeve 15, and the dog 21 at that point locks the sleeve 15 while the ram moves on further downwardly in the screwdriving operation. Stop nut 24 is set to limit downward travel of the ram 23 so that the bit 39 cannot contact and damage a workpiece if there is no screw in place to be screwed in. As indicated at A in FIG. 1, the upper end of ram 23 threads into a fixed part of the main gear housing 34 to adjust the machine for different lengths of screws.

The main air cylinder C is bolted onto the upper end of frame 11 indicated. The hollow screwdriving rod 35, that operates inside the ram 23, has its reduced upper end portion connected with a gear 36 that is mounted in a ball bearing 36 in the gear housing 34 and serves to transmit power from the airoperated motor 37 through the gear train shown to the screwdriver bit 39 through an intermediate torque responsive ball clutch 40.

The main difference between the construction shown in FIG. I and that shown in FIGS.'2, 3 and 4 lies in this torque responsive ball clutch 40 and the hollow drive rod 35, both shown in FIG. 1, with the trip rod 41 reciprocable in rod for automatic shutoff of airdrive to the bit 39 by operation of switch or valve 42 when the three evenly spaced balls 43 in clutch move inwardly against the downwardly pressed larger central ball 44, raising it and rod 41 so that a ball 45 resting on the upper end of the rod 41 raises control lever 46 by pressure against the under side thereof intermediate its ends, against the resistance and mechanical advantage of spring 47 that presses the plunger 48 downwardly against the top of lever 46 near its outer end, keeping plunger 49 of switch or valve 42 depressed against its normal tendency to raise the lever 46. Lever 46 is pivoted at one end, as at 50, remote from plunger 48, and a fine adjustment as to torque measurement setting is possible by screw adjustment of the cap 51 relative to the sleeve 52 in which the spring 47 is housed along with plunger 48 in a fixed relationship to pivot for lever 46. On the other hand, the rod 35', shown in FIGS. 2-4, for transmitting drive to screwdriver bit 39, is adapted to transmit drive to the screwdriver bit until the drive motor37 stalls. a different means (not shown) being provided for its being shut off when that occurs.

A pair of opposed jaws 53 is carried on oscillatable fingers 54 pivoted intermediate their ends, as at 55, on opposite sides of housing 56, although the latter for convenience and purposes of better illustration, is shown in FIG. 2 to 4 as provided in the same plane with one of these fingers, instead of between and in a plane at right angles to a pair of these fingers, as shown in FIG. 1. Housing 56 is suitably secured to the reduced lower end portion 57 of jaw carrier sleeve 15, either by a threaded connection, as'shown in FIGS. 2 to 4, or by a clamp screw (not shown) in FIG. 1. Coiled compression springs 58 normally urge the lower ends of the fingers 54 inwardly toward each other to close the jaws 53, but a sleeve cam 59 that is slidable in housing 56 relative to the longitudinally spaced adjustable follower screws 60 and 61 provided on the fingers 54 on opposite sides of their pivots 55, serves to control the opening and closing of the jaws 53 and provide the locked condition of FIG. 3 when the cam 59 is centrally located relative to the screws 60 and 61. A piston 62 is reciprocable in a bore 63 in housing 56 parallel to the cam 59 and fingers 54, and is connected with the cam 59 by screw 64 to moveit up and down with the piston. When air is delivered to the upper end of the cylinder 63, the piston 62 is forced downwardly against a screw 65, compressing a spring-66 and,

of course, moving the cam 59 downwardly also to open the jaws 53 a controlled amount, determined by the adjustment of the screw 65. See FIG. 2. This is the situation when a screw S is fed from the feed chute 67 by a piston 68, shown in FIG. 1 as operable in a pneumatic cylinder 69, a gate 70 being automatically operated relative to the chute to place another screw in standby position on the lower end of the chute to be fed in between the jaws 53 prior to the commencement of the next cycle. When air is delivered to the lower end of cylinder 63, piston 62 is forced upwardly to the upper extreme position, causing the jaws 53 to be opened wide, as in FIG. 4, while the screw S is being driven home. When piston 62 is free to move in response to pressure of spring 66, as in FIG. 3, by reason of air pressure being released from both ends of cylinder 63, the screw S is mechanically locked between the jaws 53, and that is the situation during the starting of the screw into the work as in FIG. 3, where the screw S is about to be moved down and guided by the jaws into the work W in the middle ofa cycle.

Referring next to FIGS. to 8, which illustrate the torque measuring and responsive clutch 40 between the drive rod 35 and the screwdriver bit 39, the housing 71 for the clutch 40 is fixed to the lower end of the drive rod 35, as shown at 72, and has six identical arcuate recesses 73 provided therein, into any three alternate ones of which the three balls 43 are engaged to serve as drive keys under spring pressure exerted on the clutch control or trip rod 41 by spring 47 and pressure multiplication lever 46, the pressure being exerted on balls 43 evenly through the larger central ball 44. The balls 43 are guided for radial movement in three evenly spaced radial holes 74 provided in a drive plug 75 that is fixed to the threaded shank of the screwdriver bit 39, as shown at 76 in FIG. 5. Plug 75 has the upper end 77 of its axial bore enlarged for guidance of the larger central ball 44 in coaxial relationship to the clutch control or trip rod 41. A plurality of smaller antifriction bearing balls 78 operate in a circular raceway provided externally of the reduced upper end portion 79 of the plug 75, and, so long as the screwdriver bit 39 is being driven and there is dov..:ward'pressure from the drive rod 38 through the clutch housing 71 and drive balls 43 to plug 75, the bearing balls 78 perform no function, but as soon as the torque responsive clutch 40 releases, due to the inward thrust on the balls 43 being sufficient to overcome the downward thrust of the clutch control rod 41 on the central ball 44, the balls 78 work between the raceway on the end 79 of the plug 75 and a companion raceway 80 provided at the inner end of the bore 81 of the clutch housing 71, so that the housing 71 can turn freely relative to the screwdriver bit 39 and its drive plug 75, the balls 43 then remaining, as seen in FIG. 8, inside the circle of bore 81 on which lie the points 82 defined between the arcuate recesses 73. The engaged condition of the clutch is shown clearly in FIGS. 5 and 6, while the disengaged condition is clearly shown in FIGS. 7 and 8, the arrows in FIG. 7 clearly indicating the upward movement of the three balls 43, and how the upward movement of the central larger ball 44 causes upward movement of the clutch control rod 41 at the point of release of the clutch to operate the switch 42 and shut ofi the drive motor 37.

Thus far there has been mention made only of the one switch or valve 42 that is operated automatically upon a predetermined overload on the screwdriver bit 39 to prevent further torque being applied to the screw. There are three other limit switches or valves mounted on the frame 1 1, namely, switches or

valves

83, 84 and 89, as shown in FIG. 1. Switch or valve 83 is normally held depressed by the setscrew 85 on the spring depressed plate 86 when the ram 23 is in the elevated position, shown in FIG. 1, holding the stop collar 18 up against the plate 86. Switch or valve 84 is normally closed but arranged to be opened by downward engagement of setscrew 87 provided on plate 88 when the ram 23 reaches its lower limit position. The third limit switch or valve 89 is mounted in the upper end of the frame 11 alongside cylinder C and is held open when the gear housing 34 is in its upper extreme position, as shown in FIG. 1.

The operation of this screwdriver will now be described mainly by reference to FIG. 1, but also partly to FIGS. 2, 3 and 4, that construction being so closely related to that of FIG. 1. At the start of the cycle, a screw S is loosely disposed in the jaws 53 in aligned relation with the

screwdriver bit

39 or 39, and the

bit

39 or 39 is not rotating but is disposed nearby in retracted position relative to the screwhead as seen in FIGS. 1 and 2. The operator has workpieces at hand to be fastened together with screws and places such workpieces W on a table T with their holes I-I aligned with one another and with the shank of the screw S, and then depresses a foot switch F to cause piston 91 in the ram cylinder C to move the ram 23 downwardly along with its gear housing 34 and drive motor 37. Spring 29, being compressed to a predetermined preload between the collar 28 and washer 30, keeps the jaw carrier sleeve 15 elevated, holding limit switch or valve 83 depressed. Continued downward movement of ram 23 causes collar 28 to contact shoulder 33 of dog 21 which, being restricted in its swinging movement outwardly by an adjustable backup plate 92, serves to connect the jaw carrier sleeve 15 to move down with the ram until the stop collar 17 limits further movement, that being when dog 21 is pushed out of the way by collar 28 into place under plate 92. The latter is adjustable vertically relative to frame 11 by means of a screw 93 threaded in the frame and having its head 94 engageable selectively in any one of a plurality of vertically spaced notches 95 provided in the back of the plate 92. This adjustment and the adjustment of stop nut 17 are both taken care of at, the same time with the adjustment of ram 23 at A, these being to suit different lengths of screws S. A locknut 96 secures the screw 93 in its adjusted position. The further downward movement of the ram 23 carries the sleeve 15 with it, spring 29 under these conditions preventing the sleeve 15 from advancing any faster than the ram 23. Upon this downward movement of sleeve 15 with ram 23, limit switch or valve 83 is released starting the drive motor 37, so that the bit 39 can engage in the slot in screw S while still turning only slowly, thus avoiding damage to the screw slot. Continued downward movement of the ram 23 with sleeve 15 finally carries the dog 21 past the lower end of backup plate 92, at which point the dog 21 is swung outwardly by collar 28 so that shoulder 97 on the dog engages under plate 92 the same time that the stop nut 17 strikes plate 88 to operate limit switch or valve 84 and then stops. Operation of the limit switch or valve 84 causes pressure to be applied to the lower portion 98 of cylinder 63 causing the piston 62 to move upwardly and raise the cam 59 and open-the jaws 53 to release the screw S, which, by this time, has already been guided into the holes H in the workpieces W. Stop nut 24 limits downward movement of the ram 23 in the event there is no screw in the jaws 53, so that the bit 39 or 39' cannot reach the work and damage it. The ram 23 continues its downward movement relative to sleeve 15, driving the screw S home, whereupon the clutch 40 in FIG. 1 is immediately disengaged and switch 42 operated to shut off the motor 37. The construction of FIGS. 2 to 4 differs as previously stated in that the motor 37 stalls at this point and through its control means (not shown) has the air thereto immediately shut off. In either case the jaws 53 remain open due to friction of screws 61 on cam 59 while pressure is directed to the lower end of cylinder C to cause upward movement of ram 23, in the course of which the dog 21 is disengaged from the bottom of plate 92 when the collar-28 passes upwardly past the lower end of the dog 21, thus allowing the sleeve 15 to rise with the ram 23, releasing the switch or valve 84,- the operation of which exhausts the port 98. The jaws 53 remain open as the ram 23 continues upwardly, the plate 86 on the lower end of sleeve 15 at the limit of upward movement of this sleeve operating the switch or valve 83 to reset the relay for the motor 37 and timer. Ram 23 thereafter continues upwardly until finally screw operates switch or. valve 89 which (1) causes pressure to be supplied to port 99 of cylinder 63, moving piston 62 downwardly against the resistance of spring 66 to engage the stop screw 65, as in FIG. 2, in which position the jaws 53 are held open only enough for loading of another screw S; (2) admits pressure to the rear end of cylinder 69 so that piston 68 drops the standby screw into the partially opened jaws 53, and (3) exhausts port 98 of cylinder 63 and at the same time admits pressure to the forward end of cylinder 69 for return of piston 68, so that the gate mechanism 70 is operated to drop another screw to the standby position of the one shown at the lower end of chute 67 in FIG. 1, pressure to port 99 being released at this point also to permit piston 62 and cam 59 to rise to midposition by action of spring 66 so that the fingers 53 close on the screw by reason of the positioning of the annular shoulder 100 on cam 59 on dead center with respect to screws 60, as seen in Fit]. 3. 7

Referring to P16. 9 and the upper portion of FIG. 1, attention is called to the lockout latch 101, which is pivoted on the gear box 34 at 102 and is normally urged inwardly by a coiled compression spring 103 so as to engage its shoulder 104 under the outer end of the switch or valve control lever 46 when the clutch 40 is disengaged, and thus keep the air motor 37 inoperable until the ram 23 has returned to its upper extreme position for the start of a new cycle. Then a pin 105 projecting from the upper end of latch 101 rides on the conical bottom portion 106 of a cam 107 that is pinned to the vertical screw 108 mounted on and extending downwardly from the upper end of the frame 11, thereby releasing the control lever 46 and resetting it with switch 42 in the on position. Another latch 109 which is used only when operating with self-tapping sheet metal screws, where it is necessary that the screwdriver bit 39 be allowed to turn throughout the thread-cutting operation of the sheet metal screw, regardless of the greater resistance to turning, up until all the tapping is finished and the sheet metal screw is nearly driven home, at which time the latch 109 that is pivoted at 110, similarly as the other latch 101, is arranged to be kicked out of the way by its pin 111 engaging the conical upper face 112 ofa cam 1 13 that is threadedly adjustable with respect to the screw 108. Then the shoulder 114 on latch 109 is moved out of the way of control lever 46 allowing it to be raised by ball operation of the trip rod 41, as previously described, latch 101 at this point again being spring pressed into place to hold the control lever 46 in the power-off position by means of shoulder 104, until the ram 23 returns to its upper extreme position, when pin 105 riding on the conical surface 106 of cam 107 again releases the switch control rod 46 so that it is reset in the power-on position for the next cycle. Of course, when latch 109 is not used, an abutment, not shown, is provided for the right hand end of spring 103 to continue the spring operation of latch 101 as above described. With latch 109 removed, operation of clutch 40 is in response to a predetermined torque on bit 39 according to the setting of the adjusting nut 41.

The intake ports of

valves

83, 84, 89, 125 and 126 are all connected as seen in FIG. to the pressure supply line P. Valve 115 has one supply port connected to pressure line P and one connected to pressure regulator 129 to control speed of motor 37. Valve 116 has one supply port connected to pressure line P and one connected to a separate pressure regulator 130 to control pressure in the downward travel of piston 91 in cylinder C. Valve 117 has both intake ports connected through line 131 with pressure regulator 129.

in operation, the control circuit is designed to cause the piston 91 in cylinder C to come to a normal return position when pressurized. In this position, valve 115 is in its springpressed position connecting pressure line P to line 132 and the supply ports oflogic

valves

119 and 122. Pilot valve 89 is held open by ram 23, pressurizing line 133 to operate the pilot of valve 122 through check valve 120, valve 122 shifting to pressurize line 134, as a result of which pilot of valve 119 exhausts line 135. The control steps of a normal screwdriving cycle are as follows, starting with the above described condition:

I. Cycle start valve F is opened by foot pressure or by pilot means, applying pressure to line 136, shifting valve 116 to pressurize cylinder C for downward movement of piston 91 through line 137.

2. As the screwdriver ram 23 moves downwardly, pilot valve 89 is released, exhausting line 133. However, logic valve 122 remains in the shifted position as pilot pressure is maintained by check valve 120.

3. With continued downward travel of screwdriver ram 23 there is the mechanical connection with the jaw carrier sleeve 15 through dog 21, starting the sleeve 15 downwardly and releasing pilot valve 83 so as to pressurize line 139, logic valve 118,

pilot valves

128 and 42 through lines l40142, and pilot of valve 115, thus shift ing this valve and pressurizing line 143, starting the screwdriver drive motor 37 and exhausting line 132.

4. Logic valve 122 shifts to a normally closed position, which in turn exhausts line 134 allowing valve 119 to return to normally open position.

5. When the jaw carrier sleeve 15 reaches its lower limit position, stop nut 17 opens pilot valve 84 applying pressure to the bottom port 98 of the jaw control cylinder 63 opening the screw jaws 53, and at that point the screw S has already been started into the workpieces W.

6. Assuming the screw S is not a sheet metal screw the clutch 40 will automatically operate valve 42 when the screw has been driven home. This causes pilot valve 42 to shift, exhausting line 142 allowing valve to return to spring offset position, exhausting line 143, and stopping the air motor 37. Line 132 is also pressurized so that air flows through the normally open logic valve 119 to line 135. This shifts pilot valve 116 to start the piston 91 in cylinder C upwardly, and pressure is applied to the pilot of valve 123.

7. When the piston 91 in cylinder C returns to its uppermost position with the ram 23, valve 89 is contacted by the screw 90 and pilot valve 83 is released, leaving line 133 pressurized so that air flows through the logic valve 123 to line 144 to shift pilot valve 117 and advance the piston 68 in cylinder 69 for screw loading of jaws 53, while also pressurizing line 145 and jaw control cylinder 63 to insure having the jaws partially opened enough to admit a screw. Air continues to flow through valve 123 until pressure is exhausted from line 146.

8. Finally, valve is contacted by piston 68 in its advancing movement and pilot valve 117 is shifted to return the piston 68, the piston 68 finally operating pilot valve 126 to signal completion of a cycle, mechanical means at 70 causing dropping of a standby screw in readiness for the next cycle.

Assuming that for some reason a screw does not thread into the work, as by reason of no threads in it, pressure in line 139 fills the cavity 147 in the timer 124 causing shifting of the logic valve 118 to closed position, and causing exhausting of lines -142 so that pilot valve 115 shifts to its spring-pressed position, thus duplicating the return circuit as when the torque measuring clutch 40 is operated at the point of the screw in a normal operation being driven home.

lt is believed the foregoing description conveys a good understanding of the objects and advantages of my invention. While a preferred embodiment of the invention has been illustrated and described, this is only for the purpose of illustration, and it is to be understood that various modifications in structure will occur to a person skilled in this art.

lclaim:

1. In an automatic machine for driving a screw into a workpiece while it is disposed in alignment with the screwdriver bit, the combination of a frame, a jaw carrier sleeve mounted for endwise reciprocation in said frame, a hollow ram reciprocable endwise in said sleeve and having a screwdriver rod rotatable therein and reciprocable therewith, said rod carrying a screwdriver bit on its one end and having power-operable drive means drivingly connected therewith, screw-holding jaws mounted on said sleeve in operative relationship to said bit, stops at opposite ends of said sleeve positively limiting its endwise movement relative to said frame, spring means carried on said ram providing a spring-loaded lost-motion connection between said sleeve and said ram, latch means carried by said sleeve arranged to be operated by said ram at a predetermined point in the forward movement of said ram for positively connecting said ram and sleeve to move together through a predetermined travel until said latch means engages a part fixed relative to said frame to hold said sleeve against endwise movement while the ram and rod with bit continue endwise movement toward the work and relative to said jaws in driving a screw into a workpiece, said latch means being released in the return movement of said ram, means for transmitting reciprocatory movement to the ram and rod with bit, means for opening and closing the jaws in timed relation to the movement of said ram and rod with bit, and means for feeding screws one at a time to said jaws in timed relation to the movement of said ram and rod with bit.

2. A machine as set forth in claim 1 including a member carried by said frame adjustable in parallel relation to said jaw carrier sleeve serving as the part fixed relative to said frame to be engaged by said latch means to hold said sleeve while the ram and rod with bit continue movement toward the work and relative to said jaws in driving a screw into a workpiece.

3. A machine as set forth in claim 1 including switch means operable by one of said stops on said jaw carrier sleeve as it moves away from said frame in forward movement with said ram, said switch means controlling the poweroperable drive means connected with one end of said screwdriver rod to start the same.

4. A machine as set forth in claim 1 including switch means operable by one of said stops on said jaw carrier sleeve as it comes into engagement with said frame in forward movement with said ram, said switch means controlling the means for opening and closing the jaws so as to open the same after the screw has been started into a workpiece.

5. A machine as set forth in claim 1 including switch means operable in response to a predetermined resistance to turning of said screwdriver rod and bit in threading a screw into a workpiece controlling the power operable drive means connected with said screwdriver rod to stop said means.

6. A machine as set forth in claim 1 including switch means operable upon return of the ram to its starting position to set the screw-holding jaws in loading position and operate the screw-feeding means to feed a screw to said jaws,

7. A machine as set forth in claim 1 including switch means operable in response to a predetermined lapse of time from the arrival of said screwdriver rod and bit a workpiece to operate the switch means of claim 4 to stop the power-operable drive means in the event ofa faulty screw or a faulty workpiece.

8. A machine as set forth in claim 1 including switch means operable in response to a predetermined resistance to turning of said screwdriver rod and bit in threading a screw into a workpiece controlling the power-operable drive means connected with said screwdriver rod to stop said means, said machine further including lockout latch means to hold said switch means in off position until return of said screwdriver rod and bit to start position, and means to release said latch means and reset said switch means upon arrival of said screwdriver rod and bit at the start position.

9. A machine as set forth in claim 1 wherein the latch means comprises a dog pivoted on said jaw carrier sleeve and swingable outwardly by said ram in its forward movement to lockingly engage the part fixed relative to said frame and thereby lock said jaw carrier sleeve in forward position while said ram continues forward, said dog being released by said ram in its return position allowing return of said sleeve to its start position under action of said spring means.

10. A machine as set forth in claim 1 wherein the latch means comprises dog pivoted on said jaw carrier sleeve and swingable outwardly by said ram in its forward movement to lockingly engage the part fixed relative to said frame and thereby lock said jaw carrier sleeve in forward position while said ram continues forward, said dog being released by said ram in its return position allowing return of said sleeve to its start position under action of said spring means, said part fixed relative to said frame comprising a member adjustable in parallel relation to said sleeve to suit different lengths of screws and arranged to be engaged by said dog to hold said sleeve temporarily in its forward position.

11. A machine as set forth in claim 1 wherein the means for opening and closing the screw holding jaws provides three positions, namely, a partially open position for loading of a screw therebetween, a closed position for holding the screw firmly enough for guiding the same into a hole without interfering with its turning to thread into the hole, and a wide open position clear of the screw during its final threading.

12. A machine as set forth in claim 1 including switch means operable in response to a predetermined resistance to turning of said screwdriver rod and bit in threading a screw into a workpiece controlling the power operable drive means connected with said screwdriver rod to stop said means, said machine further including lockin latch means to hold said switch means in on position until substantially the end of forward movement of said screwdriver rod and bit, whereby to permit operating with screws that require harder driving, said switch means being free to operate then only when the screw is driven home.

13. A machine as set forth in claim 1 including switch means operable in response to a predetermined resistance to turning of said screwdriver rod and bit in threading a screw into a workpiece controlling the power-operable drive means connected with said screwdriver rod to stop said means, said machine further including lockin latch means to hold said switch means in on position until substantially the end of forward movement of said screwdriver rod and bit, whereby to permit operating with screws that require harder driving, said switch means being free to operate then only when the screw is driven home, and lockout latch means to hold said switch means in off position until return of said screwdriver rod and bit to start position, and means to release said last named latch means and reset said switch means upon arrival of said screwdriver rod and bit at the start position.

14. In an automatic machine for driving a screw into a workpiece while it is disposed in alignment with the screwdriver bit, the combination of a frame, a jaw carrier sleeve mounted for endwise reciprocation in said frame, a hollow ram reciprocable endwise in said sleeve and having a screwdriver rod rotatable therein and reciprocable therewith, said rod carrying a screwdriver bit on its one end and having power-operable drive means connected with its other end, screw-holding jaws mounted on said sleeve in operative relationship to said bit, stops at opposite ends of said sleeve positively limiting its endwise movement relative to said frame, spring means carried on said ram providing a spring-loaded lost-motion connection between said sleeve and said ram, means for transmitting reciprocatory movement to said ram and rod and bit, means for opening and closing the jaws in timed relation to the movement of said ram and rod with bit, switch means operable in timed relation to the movement of said ram to start the poweroperable drive means prior to said bit engaging the screw to be driven, and another switch means operable in response to a predetermined resistance to turning of said screwdriver rod and bit in threading a screw into a workpiece controlling said power-operable drive means to stop the same when the screw is driven home.

15. A machine as set forth in claim 14 including switch means operable in response to a predetermined lapse of time from the arrival of said screwdriver rod and bit at a workpiece to operate the last-named switch means to stop the power operable drive means in the event of a faulty screw or a faulty workpiece.

16. A machine as set forth in claim 14 including lockout latch means to hold said switch means in off position until return of said screwdriver rod and bit to start position, and means to release said latch means and reset said switch means upon arrival of said screwdriver rod and bit at the start position.

17. A machine as set forth in claim 14 including lockin latch means to hold said switch means in on position until substantially the end of forward movement of said screwdriver rod and bit, whereby to permit operating with screws that require harder driving, said switch means being free to operate then only when the screw is driven home.

18. A machine as set forth in claim 14 including lockin latch means to hold said switch means in on position until substantially the end of forward movement of said screwdriver rod and bit, whereby to permit operating with screws that require harder driving, said switch means being free to operate then only when the screw is driven home, and lockout latch means to hold said switch means in off position until return of said screwdriver rod and bit to start position, and means to release said last named latch means and reset said switch means upon arrival of said screwdriver rod and bit at the start position.

19. A machine as set forth in claim 1 including a trip rod extending through a center hole provided in said screwdriver rod, a clutch at one end of said trip rod responsive to a predetermined torque exerted on said screwdriver rod to disconnect the drive connection between said bit and screwdriver rod and give the trip rod endwise movement in a power off direction, and control means operable by said trip rod to stop the power-operable drive means connected with said screwdriver rod.

20. A machine as set forth in claim 1 including a trip rod extending through center hole provided in said screwdriver rod, a clutch including a plurality of circumferentially spaced drive balls serving as drive keys when spread radially outwardly relative to one end of said trip rod by a centrally located ball spring pressed by said trip rod in a drive on direction, said plurality of drive balls moving radially inwardly to a drive off position in response to a predetermined limit torque to shift said central ball and the trip rod with it to disconnect the drive connection between said bit and screwdriver rod, and control means operable by said trip rod to stop the power operable drive means connected with said screwdriver rod.

2 A machine as set forth in claim 1 including a trip rod extending through a center hole provided in said screwdriver rod, a clutch comprising a drive member and a driven member in concentric relationship, the central one of said members having radial openings provided therein communicating with an axial bore, the bore having a central ball reciprocable therein and bearing upon drive-transmitting balls reciprocable in said radial openings to spread the latter to drive positions projecting as drive keys from said radial openings, the other member having circumferentially arranged radial recesses provided therein to accommodate portions of said drive-trans mitting balls, and spring means applying pressure through said trip rod to said central ball to spread the drive-transmitting balls to drive position, whereby to declutch in response to more than a predetermined torque and cause the central ball to operate the trip rod to a power off position, and control means operable by said trip rod to stop the power-operable drive means connected with said screwdriver rod.

22. In an automatic machine of the character described, the combination of a frame, an elongated jaw carrier mounted for endwise reciprocation on said frame, article-holding jaws mounted on one end of said jaw carrier, stops at opposite ends of said jaw carrier positively limiting its endwise movement relative to said frame, means for transmitting reciprocatory movement to said jaw carrier means for opening and closing said jaws, and switch means operable by one of said stops on said jaw carrier as it moves relative to said frame, said switch means controlling the means for opening and closing said jaws so as to operate the same in timed relation to the movement of said jaw carrier.

23. A machine as set forth in claim 1 including means for adjusting the ram endwise with respect to the means for transmitting the reciprocatory movement to the ram and rod with bit to suit different lengths of screws.

24. A machine as set forth in claim 1 in which the stops at opposite ends of said sleeve are adjustable axially relative thereto. I

25. A machine as set forth in claim 1 including a stop nut adjustably threaded on the ram to limit downward travel of the ram relative to the jaw carrier sleeve.

26. A machine as set forth in claim 14, including means for adjusting the ram endwise with respect to the means for transmitting the reciprocatory movement to the ram and rod and bit to suit different lengths of screws.

27. A machine as set forth in claim 14 including a stop nut adjustably threaded on the ram to limit downward travel of the ram relative to the frame.

28. A machine as set forth in claim 22, including means for adjusting the elongated jaw carrier endwise with respect to the means for transmitting the reciprocatory movement to the jaw carrier to suit different lengths of articles.

Claims

1. In an automatic machine for driving a screw into a workpiece while it is disposed in alignment with the screwdriver bit, the combination of a frame, a jaw carrier sleeve mounted for endwise reciprocation in said frame, a hollow ram reciprocable endwise in said sleeve and having a screwdriver rod rotatable therein and reciprocable therewith, said rod carrying a screwdriver bit on its one end and having power-operable drive means drivingly connected therewith, screw-holding jaws mounted on said sleeve in operative relationship to said bit, stops at opposite ends of said sleeve positively limiting its endwise movement relative to said frame, spring means carried on said ram providing a springloaded lost-motion connection between said sleeve and said ram, latch means carried by said sleeve arranged to be operated by said ram at a predetermined point in the forward movement of said ram for positively connecting said ram and sleeve to move together through a predetermined travel until said latch means engages a part fixed relative to said frame to hold said sleeve against endwise movement while the ram and rod with bit continue endwise movement toward the work and relative to said jaws in driving a screw into a workpiece, said latch means being released in the return movement of said ram, means for transmitting reciprocatory movement to the ram and rod with bit, means for opening and closing the jaws in timed relation to the movement of said ram and rod with bit, and means for feeding screws one at a time to said jaws in timed relation to the movement of said ram and rod with bit.

3. A machine as set forth in claim 1 including switch means operable by one of said stops on said jaw carrier sleeve as it moves away from said frame in forward movement with said ram, said switch means controlling the power-operable drive means connected with one end of said screwdriver rod to start the same.

6. A machine as set forth in claim 1 including switch means operable upon return of the ram to its starting position to set the screw-holding jaws in loading position and operate the screw-feeding means to feed a screw to said jaws.

7. A machine as set forth in claim 1 including switch means operable in response to a predetermined lapse of time from the arrival of said screwdriver rod and bit a workpiece to operate the switch means of claim 4 to stop the power-operable drive means in the event of a faulty screw or a faulty workpiece.

14. In an automatic machine for driving a screw into a workpiece while it is disposed in alignment with the screwdriver bit, the combination of a frame, a jaw carrier sleeve mounted for endwise reciprocation in said frame, a hollow ram reciprocable endwise in said sleeve and having a screwdriver rod rotatable therein and reciprocable therewith, said rod carrying a screwdriver bit on its one end and having power-operable drive means connected with its other end, screw-holding jaws mounted on said sleeve in operative relationship to said bit, stops at opposite ends of said sleeve positively limiting its endwise movement relative to said frame, spring means carried on said ram providing a spring-loaded lost-motion connection between said sleeve and said ram, means for transmitting reciprocatory movement to said ram and rod and bit, means for opening and closing the jaws in timed relation to the movement of said ram and rod with bit, switch means operable in timed relation to the movement of said ram to start the power-operable drive means prior to said bit engaging the screw to be driven, and another switch means operable in response to a predetermined resistance to turning of said screwdriver rod and bit in threading a screw into a workpiece controlling said power-operable drive means to stop the same when the screw is driven home.

21. A machine as set forth in claim 1 including a trip rod extending through a center hole provided in said screwdriver rod, a clutch comprising a drive member and a driven member in concentric relationship, the central one of said members having radial openings provided therein communicating with an axial bore, the bore having a central ball reciprocable therein and bearing upon drive-transmitting balls reciprocable in said radial openings to spread the latter to drive positions projecting as drive keys from said radial openings, the other member having circumferentially arranged radial recesses provided therein to accommodate portions of said drive-transmitting balls, and spring means applying pressure through said trip rod to said central ball to spread the drive-transmitting balls to drive position, whereby to declutch in response to more than a predetermined torque and cause the central ball to operate the trip rod to a power off position, and control means operable by said trip rod to stop the power-operable drive means connected with said screwdriver rod.

24. A machine as set forth in claim 1 in which the stops at opposite ends of said sleeve are adjustable axially relative thereto.