US2341014A - Feed mechanism - Google Patents

Description

Feb. 8, 1944. w. BLAIR 2,341,014

` FEED MECHANISM Filed Sept. 2, 1941 3 Sheets-Sheet l Zmventor Hkz/7597"4 /aj-r W. BLAIR FEEDv MECHANISM Feb. 8, 1944.

3 Sheets-Sheet 2 Filed Sept. 2, 1941 W. BLAIR FEED MEC'HANISM Filed Sept Feb. 8, 1944.

. 2, 1941 3 Sheets-Sheet 3 InU vhf Patented Feb. 8, 1944 UNITED STATES PATENT OFFICE FEED MECHANISM Walter Blair, Detroit, Mich. Application September 2, 1941, Serial No. 409,183

12 Claims.

This invention relates, in general, to feed mechanisms and, in particular, to the type thereof adapted for feeding or handling fastener elements. c

One ofthe objects of the present invention isr to provide a new and improved feeding or handling device for fastener elements, such as the bolts illustrated herein, which is simple, compact and inexpensive in construction and automatic, accurate and efcient in operation.

Another object is to provide a new and improved arrangement and combination of the working parts of a feeding or handling device for fastener elements so that, in the event the parts become subjected to undue stresses, there x will occur neither breakage nor damage of any sort.

Another object is to provide a new and improved feeding or handling device for fastener elements wherein the possibility of jamming has beeneliminated, together with the usually accompanying dangers and disadvantages.

Another object is to provide a new and improved fastener feeder or handler having a plurality of spaced stations of control for the fasteners which cooperate with one another in manners and to advantages heretofore unknown in devices of a similar type.

Other objects and advantages of the invention will become readily apparent from a reference to the following specification taken in conjunction with the accompanying drawings of which there are three (3) sheets and wherein:

Figure 1 is a side elevational view of my feeding device with parts broken away and in section to illustrate more clearly some of the details of construction thereat;

Figure 2 is a plan view of the device shown in Figure l, this View also having parts broken away for a similar reason;

Figures 3, 4 and 5 lare sectional views taken along the lines 3 3, 4 4 and 5 5, respectively, in Figure 1;

Figure 6 is a sectional view taken along the line 6 6 in Figure 2 but shows the escapement mechanism in the position therefor opposite that shown in Figure 1 and said Figure 2;

Figure 7 is a sectional view taken along the line I 'I in Figure 6;

Figure S is a view similar to Figures 1 and 6 but shows the escapement mechanism in a position intermediate those shown in said Figures 1 and 6; and

Figure 9 is a view similar to Figure 1 but shows a slightly modified construction.

As shown in the drawings, the device includes a base IFJ to which is fixed and from which eX- tends a pair of transversely spaced uprights It and I2, these uprights rigidly carrying a forward wall I3 and this wall rigidly carrying, at one vmay pass bodily freely therethrough.

side thereof, a forwardly extending head, generally indicated at I4.

Head I4 comprises, substantially, a relatively thick plate I5 the upper end of which preferably slants downwardly in a forward direction and the front end of which is formed in a general manner to provide an integral, downwardly extending section or portion I6, the rear end of said plate providing the location at which said head is carried by or, if desired, integrally formed with wall I3.' Head I4 is to provide. among other things, the means by which fastener elements, such as bolts I'I, are to be guided from one selected location to another, and, for this reason, the aforementioned, vdownwardly slanting upper end of plate yI5 is formed along its length with a slotted guideway I 8 and the aforementioned portion or section I6 of said plate is formed along its length with a bored guideway 9 the upper end of which communicates with the front end of said guideway I8. The size of guideway I8 is such that elements I'I 'may ride freely therealong with the heads thereof seated upon the upper surface of-plate I5, whereas the 'size of guideway I9 is such that said elements It goes without saying that the slanting nature of the upper end of head I4 is in anticipation of the reliance upon gravity for the motivation of elements I'I relatively to said head, and it is clear that said upper end could be level in case any other force were to be used to move said elements.

It is to be noted that the front upper corner portion of head I4 is raised, as at 2D, slightly above the general level thereat. Otherwise, the momentum of elements I'I leaving passageway I8 would carry them forwardly so that their heads would tend to catch on to the upper surface of plate I5 and oppose free entrance of said elements into passageway I 9. This provision. incidentally, is quite advantageous whether gravity or any other force is employed.

I propose, for reasons soon to be outlined, to provide several stations of control in the pathway to be followed by elements I1 from their source to their point of distribution, and one of these stations is represented by an escapement mechanism, generally indicated at 2|. Mechanism 2|, as will be understood shortly, is employed in conjunction with elements I1 to enable them to be advanced individually along their path of travel, and to this end it is comprised of a pair of detents 22 and 23 which are spaced apart a distance not much greater than the shank diameter of one of said elements and are to be found operable for alternate protraction into and retraction out of guideway I8 through a slot 24 provided therefor in plate I5 and communieating with said guideway. It can be seen, therefore, that simultaneous residence of detent 22 within guideway I8 and detent 23 without said guideway, in the one and alternately recurring instances, and simultaneous residence of said detent 22 without said guideway and said detent 23 within said guideway, in the next and alternately recurring instances, can be and are effective for performing the desired act of individually advancing said elements, the presence of the force of gravity, or its equivalent, of course, being presumed.

Detents 22 and 23 are integrated with'or xed to the upper ends of a pair of carriers or arms 25 and 26 so as to be movable therewith, rand the lower ends of these arms are pivotally secured, as at 21, to a boss 28 formed on the adjacent side face of plate I and extending laterally therefrom between said arms. The two units 22-25 Aand 23-23 are normally biased toward plate l5 about the axis of pivot means 21 under the influence of the two . sections 29 and 30 of a spring which lis xed intermediate said sections to boss 28 above said means, which implies that the normal position for each of said detents is the position of residence within guideway I8, the .position effective for opposing advancement of elements I1 along said guideway.

However, as has been statedbefore, the intention is to have one of the two detents extend into and out of the path of travel of the .fastener elements while the other one is extending out of andinto said path. To 'this end, an oscillatable, T-shaped actuator 3l is employed, it being pivotally connected, as at 32, to boss 28 below spring 29-30 and the under side .of its two legs being formed with rounded portions or cams 33 and 34 operable for drivingly engaging laterally extending step portions or followers 35 and 36 liormed on the lower ends of detent carriers and 26. It can be seen, therefore, that movement of actuator 3l-33--34 in one of the two possible directions about the axis of pivot 32 causes posi-` tive movement of unit 22-25--35 away from plate I5 about the axis of pivot 21 in opposition to the pressure of spring section 29 and simultaneously permits spring section to move unit 23--23--36 toward said plate about said axis of said pivot 21, whereas movement of said actuator 31--33-34 in the other of said two possible directions about said axis of said pivot 32 causes positive movement of said unit 23--26-36 away from said plate about said axis of said pivot 21 in opposition to the pressure of said spring section 3i! and simultaneously permits said spring section 29 to move said unit 22-25-35 toward said plate about said axis of said pivot 21. Incidentally, Figure l shows detent '22 in guideway i8 and detent 23 out of said guideway due to actuator 3I-33-34 being in one of the above mentioned positions therefor, while Figure 6 shows said detent 22 out of said guideway and said detent 23 in said guideway due to said actuator being in its other position.

The lower end of actuator 3 I-33--34 is slotted, as at 31, to receive a driving pin 38 through the agency of which said actuator is oscillated about the axis oi its pivot '32, said pin being formed on and intermediate the ends of a reciprocable rod 39. The front or driven end of rod 39 is freely carried within a bore 40 provided therefor in portion i6 of plate I5 and communicating with guideway I9 in said portion, whereby said rod end serves as a detent for controlling in the vicinity thereoi` advancement therebeyond of the elements I1 advanced by mechanism 2l, for it is clear that prctractlon of said rod establishes an obstruction in the path of said elements and retraction of said rod removes said obstruction. It is anticipated that the lower end of guideway i9 is to be communicated with a power driver (not shown) for the elements I1 (note the optionally disclosed magazine or tube 4I which would be ordinarily provided between said guideway and said driver), and the detent-forming rod 39 is to be found extremely useful in preventing jamming of said elements at either side of said rod.

It is proposed to employ, between the control stations represented by mechanism 2| and rod 39, another control station to be represented by a detent 42 carried integrally on the upper end of a plate spring 43, this spring being anchored at its lower end to the 'front face of the downwardlyextending portion 'IS of plate I5 and said detent 42 being rearwardly directed and adapted, responsive to movement of said spring, for being projected .into and out of the pathway for elements I1 through an aperture 44 provided therefor .in head Iii at approximately the meeting point of the guideways I8 and I9 formed therein.

, Spring i3 is such Athat the normal position of detent 42 is that of residence 'within the path- Way followed by elements I1 after leaving station 2| and before arriving at station 39, and this position is naturally maintained except during the application of a pressure upon said spring which'is sufcient to overcome the pressure of the latter and cause said detent to be driven from said pathway. rIhis detent-retracting pressure is shown in Figure 1 as being established responsive to a driving contact being set up between actuator 3I and one end of a rod 45 which is slidably carried within a boss 46 formed on head portion I6 and has 'its other end drivingly connected to and intermediate the anchored and detent-forming ends of spring 43, such as by means of a pin 46'; on the other hand, as shown in Figure 9, it may be desired to establish this detent-retracting pressure in response to the setting up of a driving contact between the free endof rod39 and the inner end of a pin 41 which is carried by spring 43 in alignment with said rod and an aperture 48 in head portion I6.

`As shown in Figure l, detent 22 is in its protracted position, detent 23 is in its retracted position land detent 42 is in its protracted position, all because detent 3S is in its retracted position. These simultaneously existing conditions indicate that `detent 22 is, for the time being, obstructing forward travel of the elements i1 residing therebehind, that detent 23 has permitted the element I1 previously passed on thereto to pass forwardly therebeyond, that detent i2 is obstructing forward travel therebeyond of said last mentioned element, and that detent 39 has permitted the element .I1 ahead of said last mentioned element to pass therebeyond into the magazine 4 I. These conditions also exist in Figure 9.

As shown in Figure 6, detent 22 is in its retracted position, detent 23 is in its protracted position and detent 42 is in its retracted position` all because detent 3S is in its protracted position. This means, with reference to the conditions existing in Figure l, that the element I1 which had been detained immediately behind the now retracted detent 22 has passed on to the now protracted detent 23, and that the element t1 which had been detained in its travel by the now retracted'detent 42 has passed on to the now protracted detent 39.

The conditions set forth in the two next preceding paragraphs are those which occur during normal operation of the apparatus, that is, during absence of any undue stresses to which the moving parts might be subjected. However, a condition is illustrated in Figure 8 which might and will arise if, for any reason, magazine 4i becomes so full that detent 39 can not follow its normal course of movement. In this showing, it will be rnoted that actuator 3| has been stopped substantially midway between its two extreme positions by the shank of the element Il' in the way of detent 39, this meaning that further advancement of said element is prevented and that detents Z2 and 23 are free to be simultaneously protracted into guidewayl l under the influence of their springs 29 and 30 to prevent advancement at this time of any element past either of said detents 222 and 23. It is also to be noted that the length of rod i5 is such that, when the condition being discussed at present will have arisen, contact between said rod and actuator 3l will not by then have taken place (it being clear that such contact is not existent except when said actuator is much nearer the limit position toward which it is approaching when the assumed condition will have arisen), this meaning that detent t2 will be in its protracted position and thereby capable of preventing accentuation of said condition then existing at detent 39.

In view of the desirability of meeting and overcoming the situation shown in Figure 8 without resulting damage to the parts involved, I provideI a drive for rod 39 and actuator 3l which may and does continue in operation after said rod and actuator have come to a standstill due to said situation. This drive includes a piston rod or plunger de which is pivotally connected (for reasons soon to appear) at one of its ends, as at 50, to the outer end of rod 39 and bo-dily received within a cylinder-forming member 5l. Plunger it@ and member 5l are made adaptable for unitary movement and for reciprocation relatively `one to the other by the use of a play connection in its outermost position (see Figure l) with respect to the cylinder in member 5l, but it may give slightly (see Figure 6) as actuator 3l approaches the end of its clockwise stroke, thereby permitting said member to move slightly forwardly relative to said plunger, and it gives far more (see Figure 8) when rod 39 strikes the shank of an element l? during its protractile stroke. It goes without saying, of course, that slots 53 extend suiciently behind pin 52 to prevent engagement between said pin and the rear walls of said slots at least until member 5l has reached the end of its protractile stroke for, otherwise, said member, plunger fit and rod 39 would be urged to protract unitarily and thus make breakage or damage inevitable if the condition of Figrue S were then in existence.

Reciprocation of member 5l is eiectuated by the rotation of a crank 55, the throw of which is readily ascertainable by a comparison of Fighas been said, pivotally interconnected, for, otherwise, this interconnection might be rigid. The support for shaft 56 comprises the two forwardly extending arms 53 of a bifurcated bracket 59, in which said shaft is .iournalled at positions intermediate its ends, said bracket being fixed to the front face of a plate Si! which is, in turn, xed to uprights l'l and I2 below wall i3. Shaft 56, in addition to carrying and rotating crank 55, also carries and is rotated responsive to the rotation of a driving means, such as a pulley El.

Pulley 6I can be driven in any well known manner, but I desire, for the purpose of illustration, to associate the driving thereof with the driving vof the means by which I intend to feed guideway I8 automatically with elements Il. For this reason, the discussion of the driving of pulley 6l will be held in abeyance temporarily.

Secured to base member ill in rearward alignment with upright l2 is another upright 52, and these two uprights, which are parallel and vertical, have their opposing faces grooved along their lengths to provide guide channels 53 and (it in which a feeder plate 55 is disposed for vguided movement upwardly and downwardly relatively to said uprights and, incidentally, to head M. As is shown best in Figure 3, plates l 5 and 65 are arranged in longitudinal alignment with each other and, as is shown best in Figure G, in substantial end-to-end relationship with each other. Also, as is shown best in Figure 6, the upper end of plate declines forwardly preferably at a sharper a gle than does the upper end of plate I 5. |All these features, in addition to the one which embodies the provision in the upper surface of plate $5 of a slotted guideway running similarly as the slotted guideway it in the upper surface of plate I5, indicate that, when said plate 65 is raised along channels @i3 and 64 so that the front end of its upper surface is level with or even slightly above the rear end of the upper surface of said plate I5, said guideways @t and 8 provide a continuous pathway for the shanks of any elements il which said plate E5 might then be carrying and said upper surfaces of said plates 65 and i5 provide a slanting, continuous seat or runway for the heads of said elements. This raised condition of feeder plate F55 is shown in Figure 6.

When feeder plate 65 is in its lowered position, as can be seen best in either Figure 1 or Figure 3 and as is distinguished from the position thereof shown in Figure 6, guideway 66 in its upper end is preferably self-chargeable with kthe stems or shanks of fastener elements il which are stored within a hopper dened at its front by wall E3, at its rear by a wall 5l secured to and extending between upright 62 and another upright 68 anchored to base member Ill behind upright li and laterally of said upright 62, at one of its sides by a wall Bil secured to and extending between said uprights l2 and 52, at the other of its sides by a wall 'lll secured to and extending between said uprights H and 63, and at its bottom by a wall 'H which slants downwardly toward said wall I3 as well as down` wardly toward said wall 6B.

lt will be noted that the vertical path of travel for feeder plate E5 is immediately adjacent the inner face of hopper wall 69 toward which hopper wall 'H slants downwardly in one of its two directions (the other of which is toward wall I 3), and, in View of the lowermost position for said plate being that, see Figure 3, whereat the upper end of said plate is at the level or slightly below the lower end of said wall 1l, it can readily be seen that guideway 66 is free to receive (and sort as well) the shanks of some of the elements Il within the hopper, whereupon upward movement of said plate to its uppermost position, see Figure 6, will enable said shanks to be in position to be discharged from said guideway into guideway I8 of head I4, the wall surface of said plate adjacent said end of said Wall 'H the while serving itself as a hopper wall in place of the corresponding portion of said wall 69.

In the driving of feeder plates 65 along its vertical guideways 63 and 64, it has been found advantageous to provide a dwell in the movement thereof occurring at the upper end of its stroke so that the elements Il being carried thereby will have sumcient time during which to displace themselves into the guideway I8 in head i4 before said plate commences its downward stroke. To attain this end, I provide a shaft l?. which is rotatable about an axis transverse with respect to plate 65, and this shaft has an arm F3 mounted at one of its ends thereon for rotation therewith, the other end of said arm carrying a pin 'M which is drivingly received within a slot 75-16-11 formed in a base plate I8 anchored to and extending across the lower end of said plate 65. As shown in Figure 6, the two end portions of the slot formed in base plate 'I8 are those indicated at 'I6 and TI and the portion therebetween is the one indicated at 15, this central portion 'I5 being formed arcuately with a radius of curvature equal to the radial distance between the axes of shaft 12 and pin M, so that the aforementioned dwell might be and clearly is realized, and said end portions 'l and ll, which are merely horizontal continuations of said portion 15, clearly serving as the driven means for plate 65. It goes without saying, of course, that the horizontal spacing between the outer ends of slot portion T6 and Tl should be no less than twice the aforementioned radial distance, for, otherwise, there would be an attempt on the part of pin 14 to force plate 65 forwardly or rearwardly during assumption by arm 'i3 of a horizontal position.

Shaft l2 may be driven in any well known manner, except that consideration should be given to the quantity of the elements il needed in the guideway I8 behind the mechanism 2i. In other words, the speed with which the device employed at the discharge end of magazine M disposes of the fastener elements fed thereto is more or less the factor which determines how fast shaft 12 should be driven, and, because this rate of disposal is usually quite low, I propose using a standard drive with a reduction system between it and said shaft, for, otherwise, upward dispositioning of plates 65 at too frequent intervals would yield little or no benefit. The drive consists of a mo-tor 19 which is of any well known construction and design and anchored to base member I6, its shaft driving a belt 80 which in turn drives a pulley 8l carried by and at the side of a support 32 also anchored to said base member and serving at the same timev as the supporting means for the feeder plate actuating shaft 12. The shaft of pulley 8| carries a relatively small diameter pinion 83, which is part of my speed reduction system, and the aforementioned feeder plate actuating shaft 12 carries a relatively large diameter gear 84, which is another part of said system, in driven mesh with said pinion. It is clearly seen, then, that operaifi tion of motor 19 eiectuates rotation of arm 13 which, in turn, causes feeder plate 65 to move upwardly and downwardly at the rate determined by the pinion-gear ratio.

Provision of motor 19 for the driving of feeder plate 65 may also, if desired, meet the demand for the driving of unit 39-48-5I through the agency of crank 55, this crank, its shaft 56 and the pulley 6l thereon being unitarily driven by means of a belt 85 which interconnects said pulley and a driving pulley 86 carried on shaft 'i2 along with the gear 84 and the arm 13.

Although the invention has been described with some detail it is to be understood that such description is for the purpose of illustration only and is not to be taken as being definitive of the limits of the inventive idea. The right is reserved to make such changes in the details of construction and arrangement of parts as will fall within the purview of the attached claims.

What I claim is:

l. In a handling device for fastener elements, means defining a pathway for travel of the elements therealong, means operable for controlling advance of the elements beyond a predetermined location in said pathway, other means operable for controlling advance of the elements beyond another prdetermined location in said pathway, means operatively interconnecting said secondand third-named means for alternate control thereof, and means controlled 'by the operation of the interconnecting means for controlling advance of the elements beyond predetermined location in said pathway intermediate said rstand second-named locations.

2. In a device for handling fastener elements, means defining a pathway for travel of the fastener elements therealong, driving means movable in opposite directions, a plunger movable in opposite directions responsive to movement of said driving means projecting into said pathway, an escapement mechanism operable responsive to movement of said plunger in one of said directions therefor for effectuating advance of the elements and to movement of said plunger in the other of said directions therefor for terminating said advance, means operable responsive to said movement of said plunger in said one direction for limiting said advance and to said movement of said plunger in said other direction for efectuating extension of said advance, and a detent interposed between said plunger and escapement mechanism for controlling travel of the elements following said extension of said advance.

3. In a device of the character described, means providing a guideway for supporting therewithin a series of fastener elements, an escapement mechanism operable for effectuating individual advancement of the elements along said guideway, a plunger operable for actuating said escapement mechanism, and an oscillatable lever interconnecting said escapement mechanism and plunger and yieldable responsive to the subjection of said escapement mechanism to a stress sufficient to terminate the operation thereof for permitting continued operation thereafter of said plunger.

4. In a device of the character described, means providing a guideway for supporting therewithin a series of fastener elements, an escapement mechanism operable for controlling the advancement of the elements along said guideway, an oscillatable lever actuatable for operating said escapement mechanism, a reciprocating member including a pair of sections one of which is connected to said oscillatable lever for actuating same, and spring means interconnecting said sections and yieldable responsive to the subjection of said one section to a stress sufficient to terminate the driving thereof for permitting continued driving thereafter of the other of said sections.

5. In a device of the character described, means providing a guideway for supporting therewithin a series of fastener elements, an escapement mechanism operable for controlling the advancement of the elements along said guideway, an oscillatable lever actuatable for operating said escapement mechanism, a reciprocating member having a pair of telescoped sections one of which is connected to said oscillatable lever for actuating same, said one section constituting a detent movable into and out of said guideway for controlling further advancement of the elements advanced responsive to the operation of said escapement mechanism and spring means interconnecting said sections and yieldable responsive to the subjection of said detent to a stress suicient to restrict the movement thereof for permitting continued driving thereafter of the other of said sections.

6. In a device of the character described, means providing a guideway for supporting therewithin a series of fastener elements, escapement mechanism operable for controlling the advancement of the elements along said guideway, an oscillatable lever actuatable for operating said escapement mechanism, a reciprocating member having a pair of sections one of which is connected to said oscillatable lever for actuating same, said one section constituting a detent movable into and out of said guideway for controlling further advancement of the elements advanced responsive to the operation of said escapement mechanism, means interconnesting said sections and yieldable responsive to the subjection of said detent to a stress sufficient to restrict the movement thereof for permitting continued driving thereafter of the other of said sections, and a second detent operable responsive to the driving of said one section for movement into and out of said guideway to control advancement of the elements advanced responsive to the operation of said escapement mechanism and to be advanced by said sectional movable detent.

7. In a device for handling fastener elements, an inclined guide way terminating in a vertical chute, an escapement mechanism operable in the guide way for advancing the fastener elements one by one to the chute, a reciprocating detent movable into and out of said chute, an oscillatable lever interconnecting said detent and escapement mechanism, and a detent interposed at the juncture of said guide way and chute adapted to be operated 4by the oscillatable lever.

8. In a device for handling fastener elements, an inclined guide way terminating in a vertical chute, an escapement mechanism in the guide Way for advancing the fastener elements one by one, a reciprocating plunger detent adapted to project into and out of the vertical chute, an oscillatable lever interconnecting the escapement mechanism and the plunger detent for alternate operation thereof, and a detent interposed at the juncture of the guide way and chute operated by the oscillatable lever to intercept said fastener elements and prevent the jam-ming thereof in the chute.

9. In a handling device for fastener elements, means defining a pathway for travel of the elements therealong, an intermittent feed mechanism operable for eecting individual advancement of the elements along said pathway, an escapement mechanism for initially arresting and advancing said elements along said pathway comprising a pair of detents spaced from each other adapted to alternately project into the pathway, a detent adjacent the exit of said pathway for finally arresting and allowing the advance of said elements and means interconnecting said last named detent and escapement mechanism whereby the escapement mechanism will be operated in timed relationship to the operation of said last mentioned detent.

10. In a device for handling fastener elements, means defining a pathway for travel of the fastener elements therealong, a reciprocable driving member movable in opposite directions, a reciprocable driven element resiliently connecting the driving member likewise movable in opposite directions responsive to the reciprocation of said driving member, said driven element being adapted to project into said pathway and alternately arrest and allow the advance of the elements therefrom, and an escapement mechanism ahead of said driven element comprising a pair of spaced detents operable responsive to the movement of the driving member and driven element for controlling the travel of the elements following the advance thereof from said driven element.l

11. In a device of the character described, means providing a guideway for supporting and feeding therewithin a series of fastener elements therealong, a pair of detents supported for movement into and out of the path followed by the elements, spring means normally urging said detents nto said path, a pair of projections formed on each of said detents and responsive to the driving thereof for urging said detents out of said path in opposition to said spring means, oscillatable driving means cocperable first with one of said projections and then with the other of said projections for urging said detents alternately out of said path, and a detent stop adjacent the outlet of said guideway operable in timed relation to said oscillatable driving means for movement into and out of said guideway in advance of the forward detent of said pair.

12. In a device of the character described, means providing a guideway for supporting and feeding therewithin a series of fastener elements, a pair of detents supported for movement into and out of the path followed by the elements, spring means normally urging said detents into said path, projections formed on each of said de.. tents, an oscillatable lever for urging said detents out of said path in opposition to said spring means, said oscillatable lever being cooperable first with one of said projections and then with the other of said projections for urging said detents alternately out of said path, a third detent operable in timed relation to said oscillatable lever for movement into and out of said path ahead of the forward detent of said pair, and a fourth detent operable in timed relation to said third-named detent for alternate movement into and out of said path between said pair of detents and said third-named detent.

WALTER BLAIR.

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