US 3929176 A
A screw is blown through a flexible tube and into the jaws of a transfer mechanism which is associated with a hand-held screw driving gun. Thereafter, the jaws are advanced to deliver the screw into telescoping relation with a retractible tubular finder which surrounds the driving bit of the gun, the jaws holding the screw during initial driving of the screw and then returning to receive another screw from the tube. The machine includes unique means for (a) placing the screw into and blowing the screw through the tube, (b) advancing and returning the jaws along different paths to enable the jaws to place the screw in the finder while holding and maintaining control over the screw during initial driving, (c) momentarily retracting the finder during advance of the jaws to enable the screw to be telescoped with the finder, (d) automatically controlling the advance and return of the jaws in response to extension and retraction of the finder, and (e) controlling opening and closing of the jaws to enable the jaws to tightly grip the screw during its delivery while still holding the screw during initial driving.
Description (OCR text may contain errors)
' nied States Patent [1 1 Dixon 51 Dec. 30, 1975 MACHINE FOR AUTOMATICALLY DRIVING THREADED FASTENERS  Inventor: Paul H. Dixon, Belvidere, Ill.
 Assignee: Babette Dixon, Trustee, Belvidere,
22 Filed: 0a. 25, 1974 21 Appl. No.: 517,920
Primary ExaminerAl Lawrence Smith Assistant Examiner-Gary L. Smith Attorney, Agent, or Firm-Wolfe, Hubbard, Leydig, Voit & Osann, Ltd.
57 ABSTRACT A screw is blown through a flexible tube and into the jaws of a transfer mechanism which is associated with a hand-held screw driving gun. Thereafter, the jaws are advanced to deliver the screw into telescoping re lation with a retractible tubular finder which surrounds the driving bit of the gun, the jaws holding the screw during initial driving of the screw and then returning to receive another screw from the tube. The machine includes unique means for (a) placing the screw into and blowing the screw through the tube, (b) advancing and returning the jaws along different paths to enable the jaws to place the screw in the finder while holding and maintaining control over the screw during initial driving, (c) momentarily retracting the finder during advance of the jaws to enable the screw to be telescoped with the finder, (d) automatically controlling the advance and return of the jaws in response to extension and retraction of the finder, and (e) controlling opening and closing of the jaws to enable the jaws to tightly grip the screw during its delivery while still holding the screw during initial driving.
22 Claims, 26 Drawing Figures US, Patent Dec. 30, 1975 Sheet10f13 3,929,176
U.S. Patant Dec. 30, 1975 Sheet20f13 3,929,176
US. Patent Dec.30, 1975 Sheet30f13 3,929,176
Sheet 5 of 13 Dec. 30, 1975 LIL US. Patent US. Patent Dec. 30, 1975 Sheet60f13 3,929,176
US. atem Dec.30,1975 Sheet70f13 3929,76
US Pawn Dec.30, 1975 SheetSof 13 3,929,176
I 4 f E: alga-2i; I fiw fl IS I US. Patent Dec.3(), 1975 Sheet90f 13 $929,176
US. Patant Dec. 30, 1975 Sheet 10 0f13 3,929,176
US. Patent Dec. 30, 1975 Sheet110f13 3,929,176
.atnt Dec. 30, 1975 Sheet 12 of 13 3,929,176
US. Patent Dec.30, 1975 Sheet 13 of 13 3,929,176
(Z V w'w MACHINE FOR AUTOMATICALLY DRIVING THREADED FASTENERS BACKGROUND OF THE INVENTION This invention relates generally to a machine for automatically driving threaded fasteners such as screws into a workpiece. More particularly, the invention relates to a machine of the type which includes a driving gun with a power-rotated screwdriver, a finder associated with the driver, and mechanism for transferring screws one at a time from a pick-up station to a delivery station where the screw is placed in the finder preparatory to being driven. The finder of such a machine keeps the screw in alinement with the driver and enables the driver to move into driving engagement with the head of the screw.
Automatic machines of the foregoing type are disclosed in my US. Pat. Nos. 3,279,045 and 3,675,302. In these machines, the driving gun is mounted on a supporting bracket and is automatically reciprocated toward and away from the workpiece to effect driving of the screws. In another type of automatic machine, the driving gun is held in the hand of the operator and is manually moved toward and away from the workpiece in order to drive the screw. A very widely used hand-held gun is of the semi-automatic type in which the screws are not fed automatically to the finder but instead are manually started into the workpiece and then are driven home by the power-rotated driver. Such a gun includes a comparatively simple tubular finder which is telescoped over the driver and which is urged to and normally disposed in an extended position so as to telescope over the head of the screw. During driving of the screw, the screw head presses against the finder and moves the latter to a retracted position along the driver. When the driver is released from the driven screw, the finder automatically returns to its extended position preparatory to telescoping over the next screw.
- SUMMARY OF THE INVENTION One of the aims of the present invention is to provide a new and improved automatic fastener driving machine which is particularly adapted for hand-held operation and which is simpler in construction and more trouble-free in operation than prior automatic handheld machines.
Another object is to provide an automatic machine having a hand-held gun which is adapted to drive relatively short screws at comparatively high speeds.
An important object is to provide an automatic fastener driving machine which may utilize the relatively inexpensive semiautomatic driving gun that is presently available, the machine being capable of delivering each screw rapidly to and holding the screw precisely in the comparatively simple tubular finder of such a gun and being capable of driving the screw after the finder has been retracted through only a very short stroke.
A more detailed object of the invention is to provide an automatic fastener driving machine in which a normal retract-extend motion of the finder is used to control the movement of the mechanism for transferring the screws from the pick-up station to the finder.
Another object is to utilize the motion of the transfer mechanism to first retract the finder and enable the screw being delivered to be placed in line with the 2 finder, and then to re-extend the finder into telescoping relation with the newly delivered screw.
The invention further resides in the novel construc tion, mounting and movement of the transfer mechanism'to enable the mechanism to place the screw in line with the finder, to hold the screw in a stable position in the finder during initial driving of the screw, and then to retract clear of the finder and the screw before obstructing further driving of the screw.
Still another object is to" provide a novel transfer mechanism having a pair of opposed jaws which are uniquely controlled to tightly grip, loosely hold and then completely release the screw at appropriate times during the machine cycle.
Another object of the invention is to provide a unique unit for receiving the: screws from a remote supply and for delivering the screws rapidly to the pickup station adjacent the driving gun, such delivery being effected by blowing the screws through a flexible tube which extends between the unit and the gun.
A related object is to blow the screws through the delivery tube while keeping the screws properly oriented even though the screws may be of such small size as to tumble within the tube.
The invention also resides in. the provision of a novel shuttling cartridge which is adapted to carry a small screw through the tube to keep the screw properly oriented, the cartridge discharging the screw at the pick-up station and then traveling reversely through the tube to receive the next screw from the main supply.
These and other objects and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a new and improved automatic fastener driving machine incorporating the unique features of the present. invention.
FIG. 2 is a fragmentary side elevation of the driving gun and parts of the transfer mechanism and showing the gun and the transfer mechanism as positioned pre paratory to the start of the cycle.
FIG. 3 is a side elevation of parts of the transfer mechanism.
FIG. 4 is a fragmentary cross-section taken substantially along the line 44 of FIG. 2.
FIG. 5 is an enlarged fragmentary cross-section taken substantially along the line 5-5 of FIG. 2.
FIG. 6 is a fragmentary cross-section taken substantially along the line 6-6 of FIG. 5 but showing parts as positioned during initial contact of the screw with the workpiece.
FIG. 7 is a fragmentary cross-section taken substantially along the line 77 of FIG. 6.
FIG. 8 is a fragmentary cross-section taken substantially along the line 88 of FIG. 6.
FIG. 9 is a fragmentary cross-section taken along the line 9-9 of FIG. 5 but showing parts in still further moved positions just after initial driving of the screw.
FIG. 10 is a rear elevation of parts shown inFIG. 9.
FIG. 11 is a view somewhat similar to FIG. 2 but on an enlarged scale and showing the parts as the transfer mechanism returns to the pick-up station to receive a new screw.
FIG. 12 is an enlarged rear elevation of parts shown in FIG. 11.
FIG. 13 is an enlarged side elevation of parts shown in FIG. 11 but showing the parts located in the pick-up station and receiving a new screw.
FIG. 14 is a rear elevation of parts shown in FIG. 13.
FIG. 15 is an enlarged side elevation of parts which appear in FIG. 2, the parts being shown in a moved position.
FIG. 16 is a view similar to FIG. 11 but showing the parts during initial advance of the new screw from the pick-up station.
FIG. 17 is an enlarged rear elevation of parts shown in FIG. 16.
FIGS. 18 and 19 are views generally similar to FIG. 6 but showing successive positions of the parts during the final advance of the new screw from the pick-up station.
FIG. 20 is an enlarged elevational view of parts of the screw feeding and delivery unit shown in FIG. 1.
FIG. 21 is a view similar to FIG. 20 but shows certain parts in moved positions.
FIG. 22 is an enlarged fragmentary cross-section taken substantially along the line 2222 of FIG. 20.
FIG. 23 is an enlarged fragmentary cross-section taken substantially along the line 2323 of FIG. 21.
FIG. 24 is a view generally similar to FIG. 23 but illustrates a modified feeding and delivery unit in which the screw is carried through the tube by a cartridge.
FIG. 25 is a perspective view of the cartridge.
FIG. 26 is a view which shows the cartridge and the screw arriving at the pick-up station for delivery of the screw into the jaws of the transfer mechanism.
GENERAL ORGANIZATION OF THE MACHINE As shown in the drawings for purposes of illustration, the invention is embodied in a machine 30 for automatically driving threaded fasteners such as screws 31 into holes in a workpiece 33 which herein is held in a horizontal plane by a suitable fixture 34. The machine includes a driving gun 35 which, in this instance, may be held in the hand of the' machine operator and maneuvered to any selected position over the workpiece, the gun being manually moved downwardly to drive the screw'and then returned upwardly out of engagement with the screw. If the workpiece is disposed in other than a horizontal plane, the operator may turn the gun at right angles to the workpiece and then drive the screws by moving the gun toward and away from the workpiece. It should be recognized, however, that certain principles of the invention are applicable to a machine having a driving gun mounted on a supporting bracket and adapted to be reciprocated automatically by a power actuator. Machines of this type are disclosed in my aforementioned patents.
The driving gun 35 of the machine 30 is one of those popular guns which are presently made available to the market in different models by several manufacturers and which conventionally have been used extensively to drive screws in a semi-automatic operation. That is, guns similar to the gun 35 have been widely used to drive the screws home after the operator has first started the screws into the workpiece with his fingers. In general, the gun 35 is of the so-called push-to-start type and includes an elongated barrel 36 which houses a rotary air motor (not shown) adapted to rotate a driver such as a screwdriver bit 38 (FIGS. 6 and 7) having a flat blade 39 sized to fit into the slotted heads of the screws 31. The bit is telescoped into and projects downwardly out of the barrel 36 and its lower end portion is telescoped into a tubular sleeve or finder 40 which holds the head of the screw in alinement with the blade while the blade seeks and moves into driving engagement with the screw head.
Except for the provision of a ring 41 (FIG. 7) whose purpose will be explained subsequently, the finder 40 is identical to the finders presently being used on conventional semi-automatic guns. As shown in FIG. 7, the finder is telescoped slidably into the lower end portion of the barrel 36 and over the lower end portion of the driver bit 38 and is keyed against rotation by a set screw 43 threaded into the barrel and extending into a slot 44 in the upper end portion of the finder. A coil spring 45 is telescoped into the barrel and is compressed against the upper end of the finder so as to urge the finder downwardly to a normal extended position (see FIG. 2) relative to the blade 39 of the bit 38. When the finder is in its extended position, its lower end portion projects downwardly beyond the blade and is adapted to telescope over the head of the screw 31 to hold the screw in a driving position in line with the bit. The lower end of the finder is formed with a counterbore 46 (FIG. 7) whose side wall closely encircles the screw head and whose top wall or roof defines a downwardly facing shoulder adapted to seat against the upper side of the screw head. Accordingly, the counterbore captivates the screw head against radial and upward movement relative to the finder and helps keep the head in axial alinement with the bit 38 so that the blade 39 may telescope into the slot in the head.
Driving of the screw 31 is effected by moving the gun 35 downwardly while the screw head is telescoped into the counterbore 46 of the finder 40. When the screw is first pressed against and stopped by the workpiece 33, the screw head bears against the roof of the counterbore and momentarily stops downward movement of the finder. With continued downward movement of the gun, the barrel 36 and the driver bit 38 move downwardly relative to the stopped finder and thus the latter assumes an upwardly retracted position (FIG. 6) with respect to the bit and exposes the end of the blade 39. As the finder approaches its retracted position, the blade contacts the screw head and results in the application of upward pressure on the bit 38. Such pressure causes opening of an air valve (not shown) to effect the delivery of pressurized air to the rotary motor of the gun 35 through a line 47 (FIG. 1) leading to the motor. The bit thus begins rotating and moves into driving engagement with the screw so as to thread the latter into the workpiece. During driving of the screw, the barrel 36, the bit 38 and the finder 40 all move downwardly in unison with the screw until the screw is driven to its final home position in the workpiece. The gun 35 then is lifted upwardly away from the screw and, as an incident thereto, the rotary motor is stopped automatically and the finder 40 is returned to its normal position (FIG. 2) by the spring 45.
THE INVENTION IN GENERAL In one of the important aspects, the present invention contemplates the utilization of a conventional driving gun 35 of the above character in a machine 30 having delivery and holding action of the transfer mechanism, the screws may be automatically placed in the conventional but difficult-to-load finder 40 and are-maintained under extremely stable control during the critical period of initial threading.
THE TRANSFER MECHANISM More specifically, the transfer mechanism 50 is mounted within a main support or housing 51 which herein is defined in part by a pair ofvertically extending and horizontally spaced side plates 53 and 54 lorier members 76 (FIGS. 3, a and whose rear sides are joined by an integral strap 77. Each carrier member is formed with a downwardly projecting lower leg 79 (FIG. 9) and with an upwardly and outwardly curved upper leg 80. Formed on the upper end portion of the lower leg of each carrier member is a tubular knuckle cated at the rear side of the gun 35. Cradles 55 and 56 (FIG. 2) on the front of the housing 51 serve to support the upper portion and mid-portion, respectively, of the gun barrel 36 while the lower portion of the barrel is secured to the housing by means to be described subsequently. An elastic band 57 isstretched around the upper portion of the barrel and is anchored to the upper cradle 55 to press the barreltightly into the cradle. Axial movement of the barrel is restricted by a washer 59 which is fitted into a circumferentially extending groove 60 in the barrel and which is anchored to a vertically extending screw 61. The latter is threaded into the upper cradle and may be adjusted vertically to bring the washer into alinement with the grooves of different models of semi-automatic guns.
The transfer mechanism 50 includes a holder which herein is formed by a pair of opposed jaws 63 adapted to receive a screw 31 at a pick-up station 64 (FIG. 13) and then move downwardly and forwardly to a delivery station 65 (FIGS. 2 and 18) to place the screw in its driving position in telescoping relation with the finder 40. In addition to moving between the pick-up and delivery stations, the jaws are mounted to swing between closed and open positions (FIGS. 14 and 10), in which the jaws hold and release the screw shank. The screw is delivered to the jaws while the jaws are disposed in the pick-up station 64 and are in their closed positions (see FIGS. 13 and 14). For this purpose, a flexible plastic tube 66 extends into the housing 51 and has its lower or delivery end 67 located in the pick-up station 64. Just after the jaws have been returned upwardly and rearwardly to the pickup station, a screw is blown shank-first through the tube by pressurized air and moves between and is held by the jaws for subsequent transfer to the delivery station 65. Insertion of the screws into and blowing of the screws through the tube is effected by a feeding and delivery unit 70 (FIG. 1 and FIGS. to 23) which will be described subsequently.
In this instance, each jaw 63 includes a generally upright arm 71 (FIGS. 9 and 10) whose lower end is formed with an upper quarter-tubular boss 73 and a lower semi-tubular finger 74 of reduced diameter, the boss and the finger being joined by a downwardly tapering half-cone 75. When the jaws are closed and are positioned in the delivery station 65 as shown in FIG. 5, the bosses 73 loosely embrace the rear side. of the finder 40, the screw head rests against the innersurfaces of the halflcones 75, and the fingers 74 encircle and hold the screw shank.
81 which is sandwiched between similar knuckles 83 on the upper end of the adjacent jaw 63. A pin 84 is telescoped through each set of alined knuckles and mounts the jaw to swing laterally between its open and closed positions on the associated carrier member.
As shown in FIGS. 3, 9 and 17, a roller follower 85 is journaled intermediate the ends of the upper leg of each carrier member 76 while a similar follower 86 is journaled at the lower end of each lower leg 79. The upper and lower followers and 86 are adapted to ride within upper and lower cam tracks 87 and 88 (FIGS. 16 and 17), respectively, which are defined by slots formed in the inner sides of the side plates 53 and 54 of the housing 5l','the lower set of cam tracks being offset downwardly and forwardly from the upper set. The followers and the tracks coact the one another to guide the carrier members 76 and the jaws 63 as the latter are moved back and forth between the pick-up from the pick-up station 64 to the delivery station 65 and as the jaws return upwardly and rearwardly from the delivery station to the pick-up station. The lower cam tracks 88, however, are shaped to cause the lower followers 86 to travel along different paths during the advance and return of the jaws, such different paths beingfollowed for an important purpose to be explained subsequently.
As shown in FIG. 9, each lower cam track 88 includes an upper, downwardly extendingportion whose width corresponds generally to the diameter of the associated follower '86 so that the follower will travel along the same path both when moving downwardly and upwardly in the upper portion. Below the upper portion, each lower cam track 88 widens out to a dimension significantly greater than the diameter of the follower 86 and includes a lower edge which extends first downwardly and forwardly at a rather steep slope and then progresses forwardly in a direction extending substantially radially of the finder 40. The radially extending portion of the lower edge of the lower cam track 88 is indicated by the reference numeral 90 in FIGS. 9 and 13 and is located adjacent the lower end of the track. When the jaws 63 are advanced downwardly To mount the jaws 63 to move between the pick-up carriage is of one-piece'construction and is formed by two horizontally spaced and vertically extending carand forwardly to the delivery station 65, each lower 'follower86 rides along the lower edge of the associated lower track 88. During the return of the jaws to the pick-up station 64, each lower follower 86 travels along the upper edge of its lower track 88. Herein, the upper edge includes a vertical portion 91 (FIGS. 9 and 13) which is located adjacent the lower end 'of the track 88 and which extends axially of the finder 40. The vertical portion 91 mergeswith a generally upwardly and rearwardly extending portion which, in turn, leads to the 7 upper portion of the track.
In order to move the jaws 63back and forth between the pick-up and. delivery stations 64 and 65, an air cylinder 93 (FIGS. 1, 2 and 4) is secured to the upper end of the housing 51 and includes an elongated rod 94 which is adapted to be reciprocated downwardly and upwardly when pressurized air isadmitted. into the upper and lower ends of the cylinder through lines 95 (FIG. 2). The lower end of the rod is connected to a block 96 which is guided for up and down movement by slots 97 (FIG. 4) formed in the inner sides of the side plates 53 and 54 of the housing 51. Downwardly and forwardly curved links 99 are pivotally connected at their upper ends to the block as indicated at 100 and are pivotally connected at their lower ends at 101 to the upper ends of the upper legs 80 of the carrier members 76. Thus, downward advance of the rod 94 causes the carrier members 76 and the jaws 63 to move downwardly and forwardly to the delivery station 65 while upward retraction of the rod returns the jaws upwardly and rearwardly to the pick-up station 64. During the advance of the jaws, the rod 94 acts through the curved links 99 and the curved legs 80 of the carrier members 76 to apply to the carrier members a counterclockwise force which tends to rock the carrier members counterclockwise about the upper followers 85 so as to keep the lower followers 86 pressed against the lower edges of the lower cam tracks 88. Conversely, the rod 94 applies a clockwise force to the carrier members as the jaws are returned and thus the jaws are rocked clockwise about their upper followers to cause the lower followers 86 to travel along the upper edges of the lower cam tracks 88.
RETRACTING TI-IE FINDER TO PLACE THE SCREW The jaws 63 begin moving downwardly and forwardly from the pick-up station 64 with the new screw 31 immediately after the previous screw has been driven and the gun 35 has been lifted upwardly to enable the finder 40 to return to its normal extended position relative to the blade 39. One of the important features of the invention is that movement of the jaws 63 from the pick-up station 64 to the delivery station 65 causes the extended finder 40 to momentarily move upwardly to its retracted position to enable the screw 31 to be moved past the finder and placed in its driving position beneath and in line with the finder. Thereafter, the finder is moved downwardly to its extended position and automatically telescopes downwardly over the head of the newly delivered screw.
Momentary retraction of the finder 40 is effected through the provision of a linkage 103 (FIG. 6) which is connected to the finder 40 and which herein is adapted to be actuated by one of the lower followers 86 as the carrier members 76 shift downwardly and outwardly to move the jaws 63 to the delivery'station 65. Part of the linkage 103 is formed by the aforementioned ring 41 on the finder 40, the ring being telescoped over and anchored rigidly to the finder. Underlying the ring is an inwardly projecting horizontal finger 104 (FIGS. 6 and 7) which is formed on the lower end of a vertically extending link or lift bar 105. The latter is guided for free up and down sliding in a hole 106 in a bracket 107 which is anchored to the side plates 53 and 54 of the housing 51 and which includes a semicircular cradle or strap 109 for anchoring the lower end portion of the gun barrel 36 to the housing.
The upper end of the lift bar is formed with an outwardly projecting horizontal finger 110 (FIGS. 6 and 7) which coacts with a member such as a bellcrank lever 111 having a generally horizontal arm 113 disposed in underlying relation with the finger 110 and normally resting against a stop 114 on the upper end of the bracket 107. A connection between the finger 110 and the bellcrank 111 is established by a screw 115 threaded into the finger and bearing against a ball 116 carried by the bellcrank arm 113.
As shown in FIG. 6, the bellcrank 113 is located on the outer side of the side plate 53 and is mounted to a pivot about a horizontal pin 117 connected to the side plate. The bellcrank includes a generally vertical arm 119 whose inner side rigidly supports a lug 120 (FIGS. 18 and 19) which extends into the housing 51 through an opening 121 formed through the side plate 53. The lug is disposed in the path traveled by the adjacent lower follower 86 when the jaws 63 are advanced downwardly and forwardly from the pick-up station 64 to the delivery station 65.
During the final portion of such advance, the lower followers 86 ride along the generally radially extending portions 90 of the lower cam tracks 88 and cause the jaws 63 to move the screw 31 generally radially toward the finder 40. Upon entering the radial portion 90, the follower 86 adjacent the side plate 53 engages the rear side of the lug 120 and then passes under the lug so as to rock the bellcrank 111 clockwise (see FIG. 18), the follower thus acting as a cam. As an incident to such rocking, the ball 116 acts through the screw 115 to raise the lift bar 105 upwardly in the hole 106 and cause the lower finger 104 to bear against and lift the ring 41. As a result, the finder 40 is raised to its retracted position against the bias of the spring 45 and is shifted clear of the advancing screw 31 so that the latter can make its final radial approach to its driving position beneath the finder. As the screw reaches such position, the lower follower 86 moves into the end of the lower cam track 88 and passes from beneath the lug 120 to free the bellcrank 111 for counterclockwise rocking. Accordingly, the spring 45 is able to expand and thus snaps the finder 40 back downwardly to its extended position (see FIG. 19) to cause the end portion of the finder to telescope downwardly over and seat against the screw head while the jaws 63 continue to hold the screw shank. Thus, the momentary retraction of the finder during delivery of the screw enables the screw to be placed beneath the finder while the subsequent extension of the finder enables the finder to telescope over the screw head.
CONTROLLING THE RETURN AND ADVANCE OF THE TRANSFER MECIYIANISM Further in accordance with the invention, the normal retract-extend motion undertaken by the finder 40 just before and after driving of the screw 31 is used to advantage to initiate back and forth movement of the jaws 63 between the pick-up and delivery stations 64 and 65. Herein, this is achieved by using the ball 116 as a valve which switches between open and closed states or positions to cause the creation of pneumatic signals for controlling the flow of air through the lines 95 and to the ends of the cylinder 93.
As shown in FIG. 6, the ball 116 is located within a hole 121 formed within and opening out of the upper side of the upper arm 113 of the bellcrank 111. The hole 121 is adapted to communicate with a horizontal 9 passage 123 which is formed in the arm 113 and which communicates with a flexible line 124 by way of a fitting 125. A flow of pressurized air is directed continuously into the line 124.
When the finder 40 is in its normal extended position preparatory to a screw 31 being driven, the ring 41 bears downwardly against the lower flange 104 of the lift bar 105 as shown in FIG. 2 and in phantom in FIG. 6. Thus, the screw 115 on the upper finger 110 presses downwardly against the valve ball 116 to seat the ball against the bottom of the hole 121. The ball thus closes off the passage 123 to prevent any air from escaping out of the line 124.
As the screw 31 is initially pressed against the workpiece 33, the finder 40 retracts with its normal motion and pulls the ring 41 upwardly from the lower finger 104 of the lift bar 105 (see FIG. 6). Accordingly, the lift bar no longer is captivated against upward movement and no longer presses against the valve ball 116. Thus, the pressure within the passage 123 forces the ball and the lift bar upwardly and unseats the ball to allow air to escape out of the line 124 through the hole 121. The flow of air through the line results in actuation of a control valve (not shown) which dumps pressure from the upper end of the cylinder 93 and admits pressurized air into the lower end of the cylinder. Accordingly, the rod 94 is retracted and begins shifting the jaws 63 upwardly and rearwardly toward the pickup station 64 immediately upon retraction of the finder. The lower end of the cylinder remains pressurized as long as the finder is in its retracted position and thus the jaws are moved to and held in the pickup station during driving of the screw. As the jaws reach the pick-up station, a probe 126 (see FIGS. 11 and 15) on the block 96 telescopes into and closes off a line 127 which extends into the housing 51 and which also receives a flow of pressurized air. Closure of the end of the line 127 by the probe 126 produces a pneumatic signal which is routed to the feeding and delivery unit 70 to cause another screw 31 to be blown through the tube 66 and into the fingers 74 of the jaws 63 (see FIG. 13).
When the screw 31 being driven has been completely tightened, the gun 35 is lifted away from the screw to enable the finder 40 to spring downwardly to its normal extended position. During the final part of such movement, the ring 41 once again bears against the lower finger 104 (FIGS. 6 and 7) of the lift bar 105 to cause the screw 115 on the upper finger 110 to press the ball 116 downwardly to its closed position in the hole 121. The flow of air through the line 124 thus is interrupted so as to produce a signal causing the cylinder control valve to de-pressurize the lower end of the cylinder 93 and to admit pressurized air into the upper end of the cylinder. Accordingly, the rod 94 is extended to advance the jaws 63 downwardly and forwardly toward the delivery station 65 in order to place a new screw 31 in the finder 40. The upper end of the cylinder remains pressurized to keep the jaws in the delivery station and in holding relation with the screw shank until the screw is pressed against the workpiece 33 to once again effect retraction of the finder and opening of the valve ball 116.
It will be apparent from the foregoing that the normal retraction undertaken by the finder 40 as the screw 31 is first pressed against the workpiece 33 is utilized to initiate return of the jaws 63 to the pick-up station 64 while the subsequent extension of the finder after com- 10 pletion of the driving operation is used to initiate advance of the jaws to the delivery station 65. lmportantly, however, the momentary retraction and subse quent extension undertaken by the finder during delivery of the screw does not change the position of the valve ball 116 and thus the advance of the jaws 63 toward the delivery station is not interrupted by such extension and retraction. As the follower 86 engages the lug 120 to rock the bellcrank 111 clockwise and momentarily retract the finder 40, the valve ball 116 presses upwardly against the screw 115 in the upper finger of the lift bar 105 (see FIG. 18). Thus, the ball 116, the screw and the lift bar 105 all move upwardly in unison with the finder 40 and, since the ball and screw are in pressing engagement, the ball remains in a closed position in the hole 121 to prevent the escape of air from the line 124. Similarly, the ball 116, the screw 115 and the lift bar 105 all move downwardly in unison when the follower 86 moves from beneath the lug 120 to enable the spring 45 to extend the finder 40. The ball thus remains seated in the hole 121 as the finder is returned to its extended position. When the finder is subsequently retracted, however, by pressing against the screw 31, the ring 41 simply moves upwardly away from the lower finger 104 of the lift bar 105. This enables the air pressure in the line 124 to act through the ball 116 and move the lift bar 105 upwardly a short distance relative: to the stationary bellcrank 111 so that the ball may open the hole 121 and permit air to bleed from the line. Accordingly, the ring 41 and the lower finger 104 of the lift bar 105 constitute a lost-motion connection which enables the valve ball 116 to remain closed whenever the finder is retracted by the bellcrank 111 and the lift bar but which enables the bellcrank to remain stationary and the ball to open whenever the finder is retracted as a result of the screw 31 being pressed against the workpiece.
OPENING AND CLOSING THE JAWS In keeping with another feature of the invention, the jaws 63 of the transfer mechanism 50 are biased to and are held in their closed positionsin a unique manner which enables the jaws to tightly grip and maintain precise control over the screws 31 during the advance of the screw toward the delivery station 65, to continue to confine and control the screw during initial driving while permitting turning of the screw, and to easily release the screw and move axially along the finder 40 upon being initially returned from the delivery station. Such action is produced by using spring pressure to keep the jaws closed as they are advanced toward the delivery station and by releasing the spring pressure and mechanically clamping the jaws during their final approach into the delivery station.
More specifically, the spring pressure is applied to the jaws 63 by a so-called horseshoe spring 129 (FIGS. 9, 10 and 12) which comprises a. substantially U-shaped strip of spring metal adapted to move into and out of straddling relation with the jaws to apply and release the pressure. The spring 129 is positioned with its legs 130 located generally on the outboard sides of the jaws and with its bridge 131 backed by a tang 133 formed integrally with and depending from the connecting strap 77 of the carrier members 76.
As shown in FIGS. 9 and 14, two links 134 are pivotally connected by pins 135 to the lower legs 79 of the carrier members 76 and are pivotally connected by pins 136 to the ends of the legs 130 of the spring 129, the
1 1 links being located between the side plates 53 and 54 and the outboard sides of the spring legs. The spring legs 130 receive the pins 136 with a slip-fit and thus are capable of sliding laterally on the pins and toward and away from the links 134.
The links 134 mount the spring 129 pivotally on the carrier members 76 to swing downwardly between an apply position (FIG. 13) in which the spring is operably connected to the jaws 63 and a release position (FIG. 9) in which the spring is disconnected from the jaws. To effect swinging of the spring between such positions, supplementary plates 137 (FIGS. 5 and 6) are bolted to the outer sides of the side plates 53 and 54 adjacent the lower end portions thereof and each includes a bottom lip 139 which underlies the lower edge of the adjacent side plate. For the most part, the inboard edge of each lip 137 is coplanar with the inner side of the adjacent side plate. The upper end of each lip, however, is formed with a lug 140 (see FIGS. 5, 6 and 9) which extends inwardly from the side plate and whose beveled lower edge defines a stop surface 141. In addition, an inwardly extending abutment 143 is formed on the lower end of each lip and includes a beveled upper edge which defines a stop surface 144.
When the jaws 63 are in the pick-up station 64, the spring 129 is located in its apply position shown in FIG. 13 and its legs 130 are in tight engagement with raised flats 145 on the outboard sides of the jaws 63 (see FIG. 14). The raised flats 145 are wedged rather tightly between the spring legs 130 and thus the legs are pressed against the links 134 which, in turn, are pressed against the inboard sides of the side plates 53 and 54. Accordingly, the spring 129 is loaded and exerts inward pressure on the jaws 63 to bias the fingers 74 thereof into the closed position in which the fingers contact one another and define a tubular chuck for receiving the shank of the screw 31. As the screw is blown through the tube 66 and into the jaws (see FIGS. 13 and 14), its shank moves between the fingers and separates the fingers just slightly, the shank thus being tightly gripped by the spring-loaded fingers.
As the jaws 63 are advanced from the pick-up station 64 to the delivery station 65, the spring pressure is maintained on the jaws except during the final approach of the jaws into the delivery station. Thus, the fingers 74 tightly grip the shank of the screw 31 and provide good control of the screw during its rapid advance toward the delivery station. Because of the tight grip, such good control is maintained even if the gun 35 is in an inclined or horizontal position.
During the final approach of the screw 31 into the delivery station 65, the lower ends of the links 134 engage and are stopped by the stop surfaces 144 of the abutments 143 on the lips 139 (see FIG. 19). Such stopping causes the links and the spring 129 to pivot counterclockwise about the pins 135 as the jaws 63 continue their advance, the spring thus being moved to its release position with respect to the jaws. With the spring 129 stopped and with continued advance of the jaws, the raised flats 145 on the jaws move out from between the spring legs 130 and thus the spring is disconnected from the jaws and is no longer effective to urge the jaws to their closed position. Just before the raised flats 145 move out from between the spring, however, they move between and are mechanically clamped by the inboard sides 146 of the abutments 143 on the lower ends of the lips 139 (see FIG. 5). Hence, the abutments keep the jaws in their closed position 12 while the screw 31 makes its final approach to the delivery station 65 and is placed in the finder 40. The fingers 74 thus confine the screw shank and hold the screw in the finder until such time as the operator starts to drive the screw.
When the operator presses the screw 31 against the workpiece 33 and the finder 40 retracts to initiate return of the jaws 63 out of the delivery station 65, the lower followers 86 move upwardly along the axial portions 91 of the lower cam tracks 88 and cause the jaw fingers 74 to move upwardly or axially along the screw shank. The fingers do not grip the screw shank quite so tightly when the jaws 63 are clamped by the abutments 143 as when the jaws are held closed by the spring 129. Accordingly, the fingers may slide upwardly along the shank and the screw may rotate within the fingers as the fingers initially retract and as the blade 39 begins driving the screw. The upwardly retracting fingers 74 continue to confine the shank as the first one or two threads of the screw are driven into the workpiece and thus the fingers maintain control over the screw until it is started and is capable of being controlled solely by the finder 40.
As the fingers 74 begin moving upwardly along the shank of the screw 31, the raised flats 145 on the jaws 63 begin moving upwardly from between the abutments 143 (see FIG. 9). As soon as the flats clear the abutments, the jaws are no longer clamped and, since the spring 129 is still in its release position, the jaws are free to swing to their open position and release the fingers 74 from the screw (see FIG. 10). Such swinging occurs as the half cones first cam against the end of the finder 40. Once open, the jaws 63 remain in their open position as the fingers 74 first retract upwardly along the finder and then are pulled rearwardly away from the finder along a path substantially as indicated by the line 147 in FIG. 11.
The jaws 63 stay open until they make their final approach back into the pick-up station 64. As this time, the ends of the links 134 engage the stop surfaces 141 on the lugs to cause the spring 129 to pivot downwardly to and stop in its apply position as the jaws complete their final movement (see FIG. 13). During such movement, carn surfaces 149 (FIGS. 9 and 13) on the ends of the raised flats 145 engage the spring legs 130 and close the jaws 63 while simultaneously spreading the legs so that the flats may move between the legs and place the jaws under spring pressure. Accordingly, the spring is operably re-connected to the jaws as the jaws complete their final movement into the pick-up station 64.
A SUMMARY OF OPERATION OF THE GUN AND THE TRANSFER MECHANISM With the exception of the feeding and delivery unit 70, all of the basic elements of the machine 30 have now been described. The following summary of operation has been presented in order to explain an overall cycle of the machine. At the beginning of each cycle, the jaws 63 are clamped closed in the delivery station 65 by the inboard sides 146 of the abutments 143 and hold a screw 31 in telescoping relation with the finder 40 (see FIGS. 2 and 5). As the first step in the cycle, the operator manipulates the gun 35 to press the screw against the workpiece 33. As the gun then is moved downwardly, the finder begins retracting as shown in FIGS. 6 and 7. Just as the finder reaches its retracted position, the blade 39 presses against the screw head