CA1037407A

CA1037407A - Conveyor stop mechanism

Info

Publication number: CA1037407A
Application number: CA244,050A
Authority: CA
Inventors: Bernard J. Allor (Jr.)
Original assignee: Taylor and Gaskin Inc
Current assignee: Taylor and Gaskin Inc
Priority date: 1975-04-04
Filing date: 1976-01-22
Publication date: 1978-08-29
Also published as: JPS51118280A; IT1056934B; DE2612933C2; GB1494171A; DE2612933A1; FR2306113A1; BR7600549A; US3995561A; FR2306113B1; JPS554049B2

Abstract

CONVEYOR STOP MECHANISM

ABSTRACT

A power and free conveyor has a stop lug on the carrier body adapted to abut a stop member movable into the path of the carrier along the conveyor track to arrest movement of the carrier, the stop member serving to disengage the driving dog from the power chain prior to abutting the stop lug. The stop lug is spaced rearwardly of the driving dog a distance exceeding rebound of the carrier whereby accidental re-engage-ment of the driving dog with the power chain is avoided. The stop log is positioned to engage the power chain pusher lug on a decline in the conveyor system should the hold back dog fail to do so, thereby preventing a runaway.

Description

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. ~037~7 :., , I FIELD OF INVENTION
;" ~his invention relates to power 4nd ~ree conveyors .l whexein a plurality of carrier9 are propclled along a main ,'~ track by depending pusher lugs on a superjacent conveyor .. . ..
~1 ~ . chain engaging upstanding pusher dogs o~ the carriers. The '"1~"' ~ . ,.1; ' carriers comprise wheeled trolleys having depending hooks or the like for suspending the loads to be transported.
An~accumulating lever projecting forwardly-of the carriers ls~raised when~ a following trolley overtakes a preceding~
10 ~ trolley, causing the assooiated pusher dog to be lowered out~of driven~engagement with~the pusher lug. A hold-back~
dog~spaced rearwardly of the pusher dog is intended to engage the~pusher lug to prevent runaway of the carrier on downgrades~.
A stop lug on the carrier is adapted to engage a stop member positioned along the main track and selectively movable into and out of the path of the pusher dog to depress the same out o~ engagement with the pusher lug. This invention r,elates 18 to improvement9 in the a~ove described mechan~sm.

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LCKGROUl~D OF THE INVENTIO~
' A power and free conveyor of the type above described ~' - ,:
is ~hown in U. S. Patent 3,503,3~7. A problem has been found ' ;
' to exist durlng stopping of the carriers in that when a carrier '-' is suddenly arrested by engagement of the stop member with '' ' :~ I
' the stop lug on the carrier body, the carrier tends to rebound ' back away rom the stop member and this rebound is sometimes '' sufficient to allow the pusher dog to be released by the stop ::.:i: . ~ 1 :
member, whereby the'next depending pusher lug on the conveyor ' 10 chain will re-engage the pusher dog once more, propelling 'l the carrier forward and into engagement with the stop member. ~`~
' Thus, a serious bump-and-release-bump-and-releaae sequence ¦~
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d' ~ may be initiated which is potentially damaging to the entire 1-~
''~'~ conveyor syste~ AS it can caus~ breakage o~ lugs, dogs, stoQs, l~ etc. necessitating shUtdoWn o the conveyor system.
''~', Another prior art Patent 3,437,054 provides a hold-back ;
dog spaced rearwardly of the pusher dog which is intended to engage the stop member and arrest movement of the carrier.
However, this structure re~uires that the main track and the conveyor chain track~be spaced ~ertically farther apart at the 6top~stations to avoid engagement of the pusher lug with~
the;hold-back dog.
;In'Patent 3j434,431 the hold-back dog is pivoted on ~ ~ ~ :~
the~carrler.~ I have found this unreliable and noisy during accumulatlon and on~downgrades, respectively. ¦
Accordingly I have discovered that both the'rebound proble~ raised by Patent 3,503,337 and the problems of the structure shown in Patents 3,937,054 and 3,43~,431 may be ¦
` obviated. My solution is partiaularly~ though not exclusively,

2-~37~07 . appropriate for use with power and free carriers wherein the . hold-back dog is enslaved to the pusher dog such that when the latter is depressed by the stop member or otherwise, the hold-back dog is also depressed. ~:
; SUMMARY OF THE INVENTION
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:~ In one particular aspect the present invention provides in :

. a conveyor s~.stem, the combination comprising: a main track, a .... . .
plurality of carriers movable along said main track, a conveyor track, a conveyor movable along said conveyor track, each of said .:
-.; 10 carriers having a body and a depressable pusher dog with a forwardly "; , .
: facing inclined caminy surface,said conveyor having a pusher lug .. adapted to engage behind said pusher dog to propel the carriers along the main track, a hold back dog pivotally mounted on each carrier spaced rearwardly ~rom the pusher dog A distance suEiEicient .. ` to allow forward plvoting oiE the hold bac]c dog with a pusher lug disposed between the pusher and hold back dogs, means for pivoting .,.
the hold back dog forwardly to an inoperative position upon depres~
sion of the pusher dog, a stop member mounted along said conveyor and adapted to be moved into and out of position for engaging and overriding the forwardly facing inclined caming surface of the pusher dog to depress the dog out of engagement with the pusher lug and cause the dog to pass under the stop member, each carrier body having a stop lug spaced rearwardly from the pusher and hold back dogs to engage said stop member, said stop member having a dimension ~.;
.. ~ measured longitudinally of the main track exceeding the distance between the pusher dog and the stop lug whereby the stop member will engage the stop lug while continuing to hold the pusher dog depress-I ed, and said stop lug being spaced rearwardly Erom the pusher dog : a distance exceeding rebound of the carrier upon the stop member i.i ~L
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engaging the stop lug. ;
As a result of this construction the likelihood of carriers :~
rebounding sufficiently to effect accidental re-engagement with the power chain is substantially reduced, the likelihood of a ;
:. runaway on a downgrade is also substantially reduced if not com-pletely eliminated, and the cost of construction is not increased despite obtaining these desirable results. .`~.
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~,~ ~" ', . ' f-'~ . ' . . ;' ' ~ 7~07 BRIEF DESCRIPTION OF TEE DRAWINGS
Figs. 1, 2 and 3 are side elevations, partially in section, through a power and free stop station showing the relationship of the various parts of a typi~al carrier and - stop member embodying the invention and illustrating the ... .
sequence of movements;
Fig. 4 is a view similar to Fig. 2 taken substantially on the line 4-4 of Fig. 6;
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~ Fig. 5 illustrates a power and free conveyor embodying `;~ 10 my invention showing a carrier just prior to and during move-~ ment through a downgrade;
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Fig. 6 is a plan view of a stop positioned along the main conveyor track for arresting movement of a carrier; and Fig. 7 is a side elevation partly in section of the : .,i ~ stop shown in Fig. 6.
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, BRIEF DESCRIPTIOl7 OF PREFERRED EMBODIM~NT
, In the drawing9 a powe~ and free conveyor i9 shown having a main conveyor track 10 comprising opposed inwardly ,... . .
opening C-shaped channels 12 and 14 tsee Fig. 7) upon which is mounted a carrier 16 supported in the channels by four ; 1 trolley wheels, two of which are shown at 18 and 20. Lateral guide rollers 22 and 24 engage the peripheral edges of the lower flanges;channels 12 and 14.
Each carrier comprises a body 26 upon which the wheels 18-29~ are mounted.~ In~aadition, the body is provlaea~wlth a depenaing hook or other~devi~ce 28 for suspending the load L~to be conveyed. In lieu of a~hook~per se, a load carrying bar~ m Q ~be~provided which is connected to the trolley as by ;
the element~28 and extends rearwardly, or to the right as ~ 30 viewed in Fig. 1, to be connected to a trailing trolley similar ', ' 1 , ~
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to the arrangement shown in my Canadian Patent No. 942,223 ;
~ issued February 19, 1974. In normal practice there will be - a plurality of carriers or trolleys 16 functioning in a powerand free conveyor system, and each adapted to carry, either , ~; itself or in combination with a trailing trolley, an~article A or load to be conveyed. In the drawing~, ~nly one trolley ~ is shown, but it is to be understood by those skilled in the '.': .:.
i art that more than one such trolley is intended. ~J~e~ .
Each trolley or carrier is provided with a~drivin~
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dog 30 having a forwardly facing inclined surface 32 rearwardly J f terminating in a generally horizontal surface 34. At the rear edge of surace 34 there is a vertiaally extending pusher lug engaging face 36 adapted to be engaged by a depending pusher lug 38 on a power conveyor chain 40 suspended by rollers .. . .
; '~ and suitable brackets 42 rom a aonveyor chain track 44 arranged super~aaent th~ main track lO. Re~erence to my aieorementioned Canadian Patent No. 942,223 illu9trates the general arrangement !
of and support or the power chain and its depending pusher lugs. Normally the power chaln 40 is provided with a succession `
¦~ ( 20 of pusher lugs 38 spaced at predetermined distances along 1 .
'~; the chain and each adapted to engage, selectively, with the pusher dog 32 at its face 36 to propel the carrler along the main track lO.
The pusher;dog 30 is supported in the carrier body ~
6 for vertical shiftable ~ovement between positions of engage-ment and disengagement with the pusher lugs 38.- In a preferred embodiment shown in Figs. l,~3 and 5, the pusher dog 30 is pivotally connected at 46, at its lower end, to a forwaraly ;~ -; projecting pivotally supported actuating arm 48. When the 30 forward end o~ actuating arm 48 engages a suitably disposed rearward projection on a preceding trolley, tho arm i9 elevated ~, ~:j: , .
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",',, in a fashion well understood in the art,and thereby causes 'f~ the pusher dog 30 to be lowered out of engagement with the ,;'i pusher lug 38 thereby disengaging the carrier from the power ''` chain.
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''','' In the embodiment of the invention shown herein, there ;: .
t',~ is also a hold-back dog 50 pivotally mounted at 52 on the . . - . .
',~' carrier body and counterweighted at 54 so that the dog normally ' assumes the position shown in Figs. 1, ~ and S. The dog ~ has a orwardly directed face 56 adapted to engage the trailing ;;~ 10 face 58 of the pusher lug 38 to prevent the trolley ~rom : overrunning the lug. Such a condition may occur during a , ~:
"' downgrade or,decline section of the conveyor shown at the left~
in Fig. 5.
, In,the construction shown herein this hold-back dog is provided with a forwardly extendlng ~inger 60, see Fig. S, ," which underlies a rearwardly projecting and cooperating ~inger ." ~
~, , 62 on the pusher dog whereby upon lowering o~ the pusher dog the hold-back dog will be similarly lowered and such is shewn ,, I
in Fig. 4 wherein the hold-back dog has been pivoted counter-,,! 1 20 clockwise a distance such that it projects above the carrier ,~ ,;
less than does the pusher dog.
The carrier is also optionally but preferably provided with anti - rebound mechanism in the form of wheel abutments 64 on the front trolley wheels 18 which are selectively engaged by~a~pawl 66 piv~otally mounted at 6a on the carrier body.
;;, A~laterally pro~ecting pin 70 on the pusher dog engages beneath the~pawl 66 and holds lt out of contact with the abutments u ~ 54 when~the pusher dog 30 is in its operative engaged position wlth the pusher ,lug 38 but when the pusher dog is lowered ', out oP engagement with the pusher lug, the pin 70 descends .-~!
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and allows the pawl 66 to engage the abutments to dampen ;~ rebound movement of the trolley upon it suddenly being axrested during it5 forward travel. The construction ~: and arrangement of this anti-rebound mechanism-is more fully disclosed in my aforementioned Canadian Patent No. 942,223.
On occasion I have found that during movement of the j carriers through a downgrade, as shown in Fig. 5, the hold-back ; dog 50 fails to engage the pusher lug 38 resulting in a runaway condition. To avoid this I have provided a secondary hold-back means comprising a pair of upstanding stop lugs 72 and 74 intri- ~ ~
gal with the carrier body 26 and having forwardly directed faces ~;
76 ~or engaging the trailing side of the pusher lug ~8. As these ~, ~econdary lugs are immovably fixed on the carrier body, th~
will providc a positive engagement with the pu9her lug durlng ;` a downgrade in the aonveyor system.
Normally the main tracks l0 and th~ chain conveyor track are spaced apart such that the lower end of the pusher . lug 38 will be spaced above the upper end of the seconaary lugs 72 and 74 as shown in Figs. 1-4. ~owever, in the area ~ ;
i 20 of a downgrade or decline in ths conveyor system the main track and conveyor chai~ track are spaced slightly closer together so ;that the~lower end of the pusher lug 38 will extend below~
the~upper end of the secondary lugs 72 and 74 whereby the same may~be~engaged in~ the event of a failure of the hold-back dog 50 to~ engage the~pusher lug. This capability is illustrated ~ t' ~'~
in Fig. 5 ; In addition to serving as a secondary hold-back, the ! :;
lugs 72 and 74 perform a further important ~unction now to ; ; be described and ia this regard and in the claims appended hereto are referred to as stop lugs rather than secondary hold-back lugs. It is conventional in power and free systems , . l . .
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; to provide some means for arresting forward movement of the carriers at preselected points during their travel through ~ ~ the conveyor sy-tem. These points are referred to herein ... .
~, as stop stations. In the disclosed embodiment the stop station A ~inc~ a stop member in the form of a hori~ontally dis-. posed blade 78 shown in various figs. o~ the drawings. This stop member is supported for rectilinear motion across the path of travel of the carriers. The blade is supported on the top of a box-like structure 80 which i9 welded as at 82 to the side of the main track 10. Within the box is disposed : .
a fluid pressure cylinder 84 which is`rigidly secured to an ` upper wall 86 of the box by bolts 88. The bolts pass through sp~cer elements overlying the top wall 86, whlch spacer elements ;; support a retainer plate 90 in spaced re ation above the top wall 86 to provide a guideway for the blade 78. ln addition, the spacer elements overlie opposite sld~ edges 92 and 94 .
o~ the blade to guide it in it~ rectilinear motlon. The pis~on ~; rod 96 is connected at 98 to a depending flange 100 welded to the bIade 78 and reinforced by webb elements 102. Upon pressurization of the cylinder at one or the other of its ends, the blade is shifted between positions extending across the main~track as shown in Figs. 6 and 7 to a position re-tracted out of the path of travel of a carrier on the track.
When the blade 78 is extended as shown in Figs. 6 s~ and 7~, iS ls;in a position;to engage the inclined caming face or~surface~ 32 o~ the pusher dog 30 to cam the dog downwardIy out of engagement~with the pusher lug 38. In Pig. 1 the ~
blade is shown ~ust as it contacts the caming surface 32 of ~ the pusher dog while in Fig. 2 the carrier has shifted further il; 30 forward to cause the blade to depress the pusher dog and the 8- ~
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blade now o~erlies the upper surface 34 of the dog holding it in the depressed condition. At the same time the up- ~ 11 stream edge 104 of the stop member is shown as abutting the forwardly directed face 76 of the stop lugs 72 and 74 arrest-ing forward motion of the carrier. Upon retraction of a stop `
member out of the path of the stop lugs, the pusher dog is permitted to rise by virtue o~ the gravity action of the actu-~ ating arm 48 positioning the dog for engagement with the next ;:~ pusher lug on the conveyor chain 40 for further movement of I
, 10 the carrier along the track 10. ~¦
It will be noted from Fig. 6 that the stop mechanism j is secured to the track 10 so that the rectilinear motion of `; the stop member is oblique to the direction o~ travel of the ¦
carrlers indicated by arrow A. It will al80 be noted that ~`
;i the upstream edge 104 or 9~0pping edge o~ the ~top memher ¦ , i9 at an angle to the direction o~ rect~linear mokion of , ' the stop member so that edge 104 is perpendicular to the .
direction of carrier travel and will abut both of the stop ;
lugs 72 and 74 on the carrier. A9 a result o~ this inclined , 1~ 20 cr oblique arrangement o the stop mechanism and movément of the stop member, upon~retraction of the stop member from ; ~ the position shown in Fig. 6 to a non-blocking position, the ~ i `
movement~of ~hé stop member 78 wlll be an immediate breaXaway ~i}~t ~ o~ contac$~wlth the-stop lugs 72 and 74. The importance of this~is that if a number o~ carriers have accumulated behind the one being helld by the stop mechanism, there may be sub-~ stantial forces urging the stop lugs 72 and 74 against the 'J,i~ stop member. By the immediate brea~away action af~orded by ~ the obligue arrangement above described, retraction of the i" :~
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stop member can be effected more easily as it will not be * necessary to drag the surface 104 across the faces 76 of the stop lugs.
An important f,-ature of the construction is that it ::
prevents rebounding of the carrier and accidental re-engagement of the pusher lug 38 with the pusher dog 3,0. I have discovered that with prior art arrangements, when the carrier stops engage a stop member which has been positioned across the path of carrier movement to abut them and ,at the same time depress . , .
the pusher dog to disengage it from the pusher lug, particu-larly as shown in U. S. Patent 3,503,337, the sudden arresting of forward movement o f the carrier will cause a bounceback -~' oS the carrier in the opposite direction from its normal travel and such bounceback is sometimes suffioient to cause the pusher ' dog to move out from under the 9top m~mber allowing th~ dog to rise and when the next pusher lug on the power chain comes along it engages the pusher dog immediately accelerating the 'l carrier and then ~Ust a3 suddenly the stop member will again ~il aepress the pusher dog and effect a disengagement. The result 'l ( 2~ is a severe bump-and-release-bump-and-release sequence which ~ tends to destroy the system. ~y ànalysis has led me to the ;' ',~ conclusion that this is caused by the magnitude of the forward ;energy of the load suspended from the carrier at the time of~impact of the stop lugs with the stop member. It i5 the ~ 1 reactionary~force ca~used~by the~forward energy that caoses ;~
the~trolley~or carrier to rebound.~ Since the reactionary ~t ~ force;is~dirèctly proportional to the magnitude of the forward energy, lf the magnitude of the forward energy can be de,creasea before~impact of the~stop member with the stopping luqs, then the rebound problem can be reduced. I have found that by ~:

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constructing the trolley and stop member as shown herein and ~ove described, the magnitude of the forward energy of the load can be decreased sufficiently before impact of the stop :~
lugs with the stop member so that the reactionary force iS
substantially reduced. 1 :
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force can be greatly dissipated if the anti-rebound abutments ,.i. ' . ~ `;
; on the trolley wheels are allowed to react with the pawl 66 :
so that the wheels are locked during all or at least a portion of the rebounding motion of the carrier. Without the abutment ` and pawl arrangement, the free rolling frictional force during rebounding, such as would be present in the construction shown ; in Patent 3,503,337 is only about one to one and one-half percent of rolling friction force when the t~olley iq rebound-' ing. On the other hand, if the pawl and abutment engagcment ,;1 is permitted to ocaur 90 that sliding friction o~ the trolley wheels on the main track ocaurs, there is a thirty percent ~ sliding friction force to overcome or tend to offset the ;
;,;, reactionary force during rebounding.
,~ ; 20 By positioning the stop lugs 12 and ~4 rearwardly s~ of the pusher dog, the distance that the carrier must move following~disengagement of the pusher dog from the pusher lug~provldes~for~a decrease in the magnitude of the forward 1; energy of~the load prior to the stop member a`outting the stop -~
lugs~because~during this time the carrier is not powered by the~drive chain. ~Consequently, when the stop member engages ;
the otop lugs~there wlll be a reduction ln the magnitude of the;forward moving load forces and consequently a reduction in the reactionary force~ At the same time( positioning the ; 30 ~top lugs rearwardly o~ the pushex dog will allow the pawl :

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66 to engage the abutments 64 of the trolley wheels so that - during rebounding the wheels will be positively locked and . ., ; - will be forced to slide in the main track. The friction created by these sliding wheels will also serve to reduce the reactionary force.
In addition, by positioning the stop lugs rearwardly :
of the pusher dog, the carrier must rebound a subs~antial , , distance before the pusher dog is allowed to rise sufficiently - to re-engage the pusher lug. Referring to Figs. 1-3, in Fig, lo 1 the carrier is shown moving along the mlin track 10 under .,;. . ..
;~ , the influence of the pusher lug 38 and the stop member 78 .. . . .
;'; has ~ust contacted the sloping face 32 o~ the pusher dog.
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the carrier continues to move the stop blade will cause , the pusher dog to be depressed and at a c~rtain point on the ~, inclined face 32 the stop member will have depressed the dog sufficiently to disengage ib from the pusher lug 38. ~he distance between this point o~ disengagemenb and the forward ~ faces 76 of the stop lugs is referred to as dimension D shown ,,,~ ( in Figs. 1 and 3. As the carrier continues to move it must ~! 20 move the distance equal to dimension D before the stop member :.. !:, , engages the stop lugs. During this time the carrier will begin to~sl;ow~down as a result of rolling friction and the ;i ~ sliding friction of the stop member across the inclined face ;32 and the upper face~34~o~ the pusher dog. When the stop member engages the stop lugs, the load L will swing forward -`-~
J~ as shown~in~Fig. 2 and the reactionary force is thereupon lnitiated. In order for the carrier to rebound sufficiently to re-engage the pusher dog with the pusher lug, it must be rebound by;the dimension D as sbown in ~ig. 3. Before it ;

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can rebound this far the reactionary force will be dissipated ~in many cases. With the provision of the pawl 66 and abut- - ;
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ment 64, however, the forward trolley wheels 18 will be locked ; against reverse rotation and will create a slidin~ Priction between the wheels and the track resisting the rebounding motion. When the trolley comes to a stop during rebounding, ., . ,,;, .
the load will then swing rearwardly as showr,f in Fig. 3 tending to shift the trolley in the opposite direction. In order for the pawl and abutment arrangement to be effective, it ~
0 i5 necessary to provide sufficient traveI during rebounding ~ ~-; motion such as that provided by dimension D.
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The width of the stop member measured along the center ~ line o the carrier travel and shown at W in Fig. 6 must be i;~ suPficient to bridge between the pusher dog and the stop lugs.
~; I have ~'ound that iP the stop lugs 72 and 7~ are posltioned rearwardly of the rear Pace 36 oP the pusher dog a distance approximately twice the thickness T o the pUsher lug, satis- ;
.~ ;; .!,~, factory operation can be obtained, though it is apparent this , distance aan be greater, particularly if the pawl and abutment ( 20 arrangement on the trolley wheels are not utilized and a "~ greater bounceback lS ~to be expected.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a conveyor system, the combination comprising:
a main track, a plurality of carriers movable along said main track, a conveyor track, a conveyor movable along said conveyor track, each of said carriers having a body and a depressable pusher dog with a forwardly facing inclined caming surface, said conveyor having a pusher lug adapted to engage behind said pusher dog to propel the carriers along the main track, a hold back dog pivotally mounted on each carrier spaced rearwardly from the pusher dog a distance sufficient to allow for-ward pivoting of the hold back dog with a pusher lug disposed be-tween the pusher and hold back dogs, means for pivoting the hold back dog forwardly to an inoperative position upon depression of the pusher dog, a stop member mounted along said conveyor and adapted to be moved into and out of position for engaging and overriding the forwardly facing inclined caming surface of the pusher dog to de-press the dog out of engagement with the pusher lug and cause the dog to pass under the stop member, each carrier body having a stop lug spaced rearwardly from the pusher and hold back dogs to engage said stop member, said stop member having a dimension measured longitudinally of the main track exceeding the distance between the pusher dog and the stop lug whereby the stop member will engage the stop lug while continuing to hold the pusher dog depressed, and said stop lug being spaced rearwardly from the pusher dog a distance exceeding rebound of the carrier upon the stop member engaging the stop lug.

2. The invention defined in claim 1 characterized in that each of said carriers has trolley wheels engaging the main track, at least one of said wheels having anti-rebound means for locking the wheel against reverse movements, and said stop lug being spaced rearwardly from the pusher dog a distance sufficient to allow said anti-rebound means to become operative to lock said trolley wheel.

3. The invention defined by claim 1 characterized in that said stop member is mounted for rectilinear movement across the path of travel of the carriers with the direction of movement being inclined to the direction of movement of the carriers, said stop member having an edge disposed perpendicularly to the direction of movement of the carriers, and said inclined positioning of the mem-ber in combination with the perpendicular edge being operable to cause a quick breakaway of such edge of the stop member from a carrier when the stop member is retracted.

4. The invention defined by claim 1 characterized in that a pair of said stop lugs is provided disposed on opposite sides of the carrier body from said pusher dog.

5. The invention defined by claim l characterized in that said stop lug projects above the carrier a height exceeding that of the hold-back dog when the same is in its inoperative position.

6. The invention defined by claim 1 characterized in that said main track and said conveyor track are closer together through-out downgrades in the conveyor system whereby said stop lug extends into a position overlapping the pusher lug to prevent accidental runaways in downgrades.