CA1295361C - Anti-lockup drive mechanism for a position controlled linear actuator - Google Patents

Abstract

Abstract of the Disclosure A linear actuator is provided with an electric motor rotating a drive pinion gear in mesh with an intermediate gearing arrangement which in turn is in mesh with a main drive gear for rotating a drive screw journalled within a main body housing.
Rotation of the drive screw causes longitudinal advancement of a drive nut axially advancing an extension rod bearing to move an output load connected to an opposite end of the extension rod.
The intermediate gearing arrangement includes a lost motion mechanism allowing the drive pinion to complete approximately one revolution before imparting rotative torque to the drive screw allowing the drive motor to develop an operating torque to prevent lockup of the actuator. The lost motion mechanism includes a pair of arcuate slots formed in a first intermediate gear in contact with the drive pinion and a pair of dowel projections projecting from a second intermediate gear into the slots. The second intermediate gear is connected to the drive screw. Upon actuation of the drive motor, the first intermediate gear rotates through a predetermined angular interval until the dowel projections move from one extreme position in the associated slot to the opposite extreme position at which time an abrupt force is imparted to the second intermediate gear to rotate the drive screw.

Description

12~3~1 The present invention relates to a linear actuator which is provided with a first level of position control and a second level of position and overload control and, more particularly, to an improved drive mechanism having an anti-lockup feature for transferring rotary force from an electric motor to axially move a connected extension rod of the linear actuator to move a load.
Linear actuators are typically utilized in situations where a thrust force is used for applying linear motion. Examples of the utilization of such thrust force is in the operation of lever arms, cranks, slides and valve levers in industrial equipment. Such actuators are utilized for alternately moving objects between predetermined positional limits. The actuators can be utilized for moving the movable member between positions within such predetermined limits by the utilization of appropriate feedback means.
According to the present invention a linear actuator comprises, a housing; a drive screw rotatably supported within said housing; a drive nut in threaded engagement with said drive screw; a body tube assembly connected to said housing and positioned about said drive screw, said body tube assembly containing reaction force surfaces for preventing rotation of said drive nut; an extendible member having a load connecting member on its free end and having the opposite end thereof connected to a drive nut, said extendible member adapted for axial movement so as to extend out of said body,tube; drive means including an electric drive motor containing windings for rotating said drive screw; said drive means including intermediate gearing means for transmitting rotative torque output from said electric drive motor to rotate said drive screw, said intermediate gearing means including a lost motion arrangement means for delaying rotation of said drive screw for a predetermined interval during which a drive pinion of said electric drive motor rotates through a predetermined angular interval, said lost motion arrangement means enabling said drive pinion to attain a .'~, ~
~1`'~ , ~

~ 5361 rotational speed approaching a predetermined operating speed before imparting rotative torque to drive said drive screw through the intermediate gearing means, said lost motion arrangement preventing lockup of the electric motor and over-heating of the motor windings tending to occur when an output load is connected to the load connecting member, wherein said intermediate gearing means includes a first intermediate gear and a second intermediate gear both mounted intermediate the electric motor and the drive screw, said first intermediate gear in contact with a drive pinion and said second intermediate gear connected to transmit rotative force to the drive screw, said lost motion arrangement mear.s being formed between said first and second intermediate gears to enable initial rotation of said first intermediate gear under the driving force of the drive pinion before imparting rotative force to the second intermediate gear and thereby the drive screw.
Embodiments of the invention will now be described with reference to the accompanying drawings in which:
Figure 1 is a cross-sectional view of the preferred embodiment of the linear actuator according to my prior design set forth in the aforesaid United states Patent 4,712,441;
Figure 2 is a partial cross-sectional view of the anti-lockup drive mechanism according to the present invention when employed in the linear actuator of Figure 1;
Figure 3 is an enlarged cross-sectional view of the anti-lockup feature of Figure 2 removed from the linear actuator; and Figure 4 is an end view taken along the line 4-4 of Figure 3 depicting the lost motion mechanism in the intermediate gear anti-lockup assembly.
Figure 1 is a cross-sectional view of a preferred embodiment of the linear actuator described in my above-identified copending U.S. patent application, wherein the linear 12~3~

actuator 10 includes a body housing 12 formed with an upper compartment 14, an intermediate motor casing opening 16, and a body tube opening 18 at the lower end thereof. The upper compartment 14 is closed by a cover plate 20 which is sealed to the body housing 12 by a cover gasket 22. A gear compartment face plate 24 is provided for sealing the drive gear mechanism 26 within the body housing 12. A face plate gasket 28 is provided for this purpose. Suitable socket head screws are provided to secure the cover plate 20 and face plate 24 to the body housing 12.
The internal operation of the linear actuator 10 is shown in Figure 1, wherein electric drive motor 44 which is retained within motor casing 46 provides rotary power to a drive pinion gear 48 which in turn transmits power through an intermediate gear 50 to the main drive gear 52 which is journalled to the end of the drive screw 54 by a Woodruff key 56. Rotation of drive screw 54 moves the drive nut 58 axially within the body tube 60. The body tube assembly 62 is formed by the external body tube 60 which is fitted into opening 18 and housing 12, the internal drive screw 54, the drive nut 58 and an extension rod 64 affixed to the outer side of drive nut 50 so as to extend beyond the end cap 70 of the body tube assembly 62.
The drive nut 58 is secured against rotation by reaction surfaces such as described in my United States Patent 4,712,441 dated December 15, 1987, inventor William F.
Abraham, assignee Brunswick Valve and Control Inc., entitled "Position Controlled Linear Actuator" which are formed internally within body tube 60. Drive nut 58 may be a square-sided nut as disclosed in U.S. Patent 4,712,441 and drive screw 54 is shown coaxially centred within the extension rod 64.
Extension rod 64 is thus axially extendible beyond the end cap 70 of the body tube assembly 62. This extension rod 64 is secured at the outer end of the body tube assembly 62 by an ~.;
l~

2953~

~nd ¢~p 70 which is ~o~e~ from a non-~errous metal which then ac~s as a bushing a~d a seal.
The driven end of drlve ~rew 5~ is æupported ~y 8 pair of ang~lar con~a~ bea~ings 72 ~nd 7~ which are supported within a b~a~ing op~ning wi~hin body hou~lng 12. A main gear spacer 78 i~ provlded betwe~n the main d~lv~ gear ~2 and the two bearings 72 and 74. The ~ain drive ge~r l~ secur~d to th~ ~nd o the driv~ sc~ew 54 by a ~l~x nut B0. The intermed$a~ gea~ 50 i~ retai~d on a dowel pin Y2 whiah is ~ournalleq ~etween ~earings 84 and 86. Thls lntermediat~ ~ear 50 has an out~ teeth set ~B fo~ contactlng the d~iv~3 plnlon g~ar 48 and an inner set ~0 ~or ~ontaat wlth the main drive g~a~ ~2.
~he ~otor drlve ~h~ft 32 connected~o a ~otor core 93 i~ supported by a if ron~ bearing gq withln body h~using 12 and at 15 the outer end by a bearlng 96 which 1~ xetained in the motor c~slng 4~. The motor s~ato~ ga is secured wlthin moto~ ca~ing 46 and i~ provided wlth a thermal sensing elemeAt 100 whiah together wlth th~ switoh 102 ~orm~ an ove~load controller m~an~ 103 shown ~ohemat~aally. Th~ thermal ~n~ing elem~nt 100 csn i~dir~ctly co~trol the ~wltch 102 a~ ~hown. Al~o, the ~her~al ~eA~lng element 100 and swi~ch 102 can pre~erably be combined into a ~inglo b~-m~talllc swit~h su~h as di~clo~ed in u.s. Patent No.

3, 219, ~56 ~o ~unwiddle~

Motor ~asing 4~ aled wlthin opening 1~ and housing Z5 12 by an o-~iny.
A oapaoitor ~ub-assembly 104 læ provided wlthin compa~tment 14 ln orde~ to provlde for chsng~ of pha~ between the wlndlngs ln motor 44 to effec~ ~he ln~tant rever~al of direction of rota~ion. Motor ~4 ~ preferably a single phase 30 motor and is ~onne~;:t~d to the capacitor sub~assembly by, a 53~1 connection terminal 106 as shown. The drive pinion gear, intermediate gear and the main gear then comprise the drive means of the linear actuator.
During operation of the axial movement of extension rod 64 between the terminal stroke limits, the electric drive motor 44 is utilized to provide rotational power through the drive gear mechanism 26 so that rotational power is delivered to drive screw 54. A limit switch assembly (not shown) described in detail in my U.S.
Patent 4,712,441 can be set so that power to the electric drive motor 44 is interrupied just prior to the drive nut 58 reaching either of the two terminal positions which limit its stroke. In the event that the limit switches fail, the drive nut 58 will come into contact with either the back stop 108 or the front stop 110. Mating back stop reaction shoulder portion 112 is provided on drive nut 58 to provide a complementary abutment to the reaction shoulder 114 on the back stop 108. Back stop 108 is secured to the inner end of drive screw 54 by a set screw 116 which rests in a mounting slot 118. A similar reaction shoulder 120 is provided for front stop 110 for co-action with a mating reaction shoulder portion 122 secured to the front face of drive nut 58. Both the back stop 108 and the front stop 110 are secured to and rotate with the drive screw 54. A retaining flex nut 124 is provided for retaining front stop 110.
The abutment shoulders 114 and 120 and the shoulder portions 112 and 122 on the drive nut 58 thus function to restrain the movement of drive nut 58 relative to drive screw 54 so that the actuator stroke mechanism which is provided by the body tube assembly 62 is not jammed at the ends of the extension rod stroke when the power to the drive motor 44 has not been interrupted by the limit switch assembly. In such an event, as .

53 ~1 ~ J

illustrated in Figu~e l, the driv~ nu~ 5~ will come into a~utment contsct with the back etop 108 with ~ ~a~y g~p 126 remaining batween ~he abutment shoulde~ exten~ion 112 and t~e bsck stop 108. Contin~ed op~rat~on o~ d~ive motor 44 will cause the ~tatox coil~ ga to h~at up beyond th~ p~edetermined temperature whioh i~
~en~ed by ~h~3 the~mal elem~n'c 100. The overload c:ont~olle~ means 103 then operat~s to disengage th~ elsctric powe~ supply to motor 44.
In the event th~t the ~ nsion rod 64 ls prevented from mov~ment durlng th~ axia~ movement of drive nu~ 5~, ~his ~ame ov~rhe~ting of th~ mo~o~ 8tator winding will occur whl~h wlll then re~ulk ln the ~leatria power being interrupted fr~m the drive motor 44~ Th~, the overloa~ con~ol me~ns 103 funations ~oth at the te~mi,nal limi~s o~ the axial movement of ext~ns~ on rod G4 as well as within tho~e limit~ in the event o~ an ove~load thrust oondition.
~he ext~nsion rod 64 i~ fitted with a load ~onneator 125 whi~ has lnternal ~hreads 127 ~or oonneatin~ wlth the load ~no~ ~hown). A clevi~ bra~k~t 128 ~not ~hown ~n F~gu~ 1) on the oppo~ite end o~ ~h~ liflear ~ctustor p~ovide~ a plvotal ~onneotion ~o a reaotion ~upport surf~ae. The clevis ~r~cket ls secured to ~he gear compartm~nt ~ace plate 24 by so~ke~ head c~p ~crews 13~
and 132 wh~h ~e balanced by a corresponding cap æcrew pair (not shown ) .
~1~ear qctuator~ ~uch a~ th~ type described above usually lnclude the ele~ri~ moto~ ~hi~h is ~onne~ted to the d~ive screw throush a drive means which u~illæe~ either ~ ~ear t~aln or a drive belt. In the case of a drive me~hani~m in ~he form of a g~r ~raln, and wlth referenoe to my a~tuator des~ibed ~ove, th~ d~ive pinion gear 4B is mounted upon an ou~pu~ sh~ft S

2~ 5 3&~

of drive motor 4~. The intermediate gear 50 which inolud~ ~
lar~er diamet~r gear 51 pre~ ked on~o a hub portion 50R
~hereo~ ~n~lude~ th~ ou~r ~ee~h ~et 8~ in direct mesh with drive pln~on gea~ 4B. ~n tu~n, the teeth o in~e~ ia~e ~ear S0 are 5. in di~ect mesh wlt~ ma~n d~iv~ ~ear S~ for impa~ting axial movement to dr~v~ nut 5a and ther~aby extens~on rod 64.
One problem pre~ent in my a~oresa~d lin~ar aatuator and ln other linear actuator~ having a d~ive ~echani~m in ~he ~orm of a gea~ traln i~ tha~ upOn in~tially actu~tlns the drive motor 44 to longitudlnally a~van~e the d~lve nut 58 throu~h th~ ge~r train 4~,50,52 there ls 2 tendency ~or th~ d~ive ~e¢h~ni~ to ~o~kupll ~lnc~ the motor drlve ~ha~ 92 has not a~t~i~ed a speed approa~hing operatlng speed and therefo~ ~ay. not havs developed sufficlent torque~to ove~ome the lnertla o~ the driven system, i.e., the gea~ t~aln 4~,50,52, drive screw 54, drlve nut 58, exten~ion rod 64 and an ou~pu~ load, if any, ~onnecte~ to and driven by th~ linear a~tuator. Frequentl~ lockup" occurs when the linear aatuator conne~:ted to ~n output load (e.g., a hopper aon~a ~ nlng ~ine m~t~rial ) ~ 9 idle i~or any length oi~ tl~e . Loaku~
20 may ~lso o~ in ~he event that op~r~tion o~ the linea~ a~l:uator ~top~ at a tlm~ when the d~ive nu~ i9 ~t an extreme end of stroke po~itlon undsr which the drlvQ nut tends to wedge t~Pith r~pe~t to th~ driva sarew 54. :)4viou~1y, one disadvantage of the lo~kup is th~ inablllty o tho llnea~ actu~t~ tc) pe~c)rm it~ intended 25 ~un~tion re~ult~ ny in down time and los~ of production until the pro~lem has b~en ~o~e~ted.

Summary o~ th~ Inven~ion I~ ls a~co~dlngly one ob~e~t o~ ~h~ present inv~ntion to provld~ a lin~ar a~tuator wi~h a ~ombinatlon of improyqd 2~ ~ 3~

eatu~es whi~h include an anti-lockup m~hanl-~m in ~he drive ~ear train p~ovldlng a llmlted amo~nt of los~ motion in the gear tr~in to ~nable th~ drive moto~ to approa~h and possi~ly attaln full ~eed. As a result, ~h~ tia of the d~iv~a motor rotor 5p~odu~Qs an lmpa~t or a ~hammer blow~ ~f~e~ to the gear t~ain Ov~Omin~ the tendency of the drive mechanlsm o~ driven part o~
the ~ystem to ~ock~
Another ob~eot of the invention i~ to provide a linear ~atuator wlth an anti-lo~kup gear ~ra~n easily ln~o~porated into 10the linear actuator o~ my prlor design and with the addition of only a minim21 numb~r of ~arts and which antl-lockup f~ature is lndep~nd~ntly ~un~tlona~ o~ the other improvement ~eatures o~ my pr~or de~i~n such as the features o~ a f~rst,.l~vel of pos1 tional control and a seo~nd level of posltlon and overload oontro~ in my 15prio~ design~
S~ill anothe~ obJect is to p~ovido an anti-~ockup feature cap~bl~ of u~ in other types o~ ea~ a~tuators lnc~rporating ~ drive nleohani~m havlng a gear traln to p~vent ~v~rheating of th~ eleotric m~tor ~nd motor windln~ thereof 20above a pred~t~rmln~d tamp~r~tu~ whioh may re~ult during ~amming or loakup of ~he ~qtu~t~r ~troke mechani~m.
YQt ~nother ob~eat i5 to prov~d~ an anti-loakup featuxe ca~able of rellable operation in ~ugged and ho~tll~ envi~onments.
Th~ above~noted obJeatives are achleved by construc~ion 25o~ a lin~ar.actuator in accordance with the presen~ invention.
The aatuator 1~ f~med wi~h a compact body hou~ing which prov~de~
for the ~ p~anc~ o~ an electrlc motor housing and ~ body tube a~sembly withln which ~h~ drive screw and drive nut are con~ained. The axes of the ele~tric moto~ and the drlve screw 30ar~ arranged in pa~allel on the same ~de of the body housing.

i 5 3~

Xn order to uti~lze a low cost single ph~se reversible moto~, a ~apa~itor sub-~ssembly and housing ~here~o~ may also be p~ovided in an l~t~-fit~ing relation~hlp with the main ~ctuator body hou~ing.
The roto~ of th~ el~3ctric motor rotat~a~ a drive pinion ~ear which ~shes w~th an intermediate ~peed r~du~tion gear which in ~urn is in mesh with a ~ain d~ive ye~r whi~h ls key~d to one end of the drive sorew. The d~ive s~rew is ~ournalled within the msin body hou~ing by a pair o~ an~ular contact bearin~s and at the ou~r end of the body tube sss~mbl5~ by a non-f2rrous ~crew guide bea~ing, ~otational motlon ~rom the ~lectrlc motor is tran~ml~t~d through the drlve pinion ~ea~, in~rm~dia~e g~r a~d the main gea~ to the drive screw. Th~ drive pinion g~ar, interm~di~te seari2nd the maln gear th~n ¢omp~i~e the drive means o~ the ll~r ~tuator.
In aaaordanc~ with the present inv~ntion, the ~nti~
lockup ~eature ~ompri~es a pair of intQrm~diate gear~ mounted on a dowel pin supported in be~rings. A flrst intermedi~te gea~ in me~h with th~ drive pinlon g~ar lna~ud~ at les~t on~ srcuste 810'C ln which is r~ceiv~d ~ aow~l pln ~laving on~ ~n~ ~ightly ~itt~d within a hol~ ~or~od in th~ se~ond lnte~mediat~ y~a~. ~he se40nd ln~rmediate gear ln~l~de~ tee~h ln me~h wlth the ma~n drlve ~e~r, Upon initia~ a~tuat~on o ~he dr~ve mo~o~, ~h~ i~t lntermedia~e g~a~ 1~ rotated by the drive pihion ge~ th~ough an angul~ $nte~val during whi~h time the dowel pin travels ~hrough the 5~0t without impar~ing driYing movement to the seoond intermedi~te gear ln mesh with the main drlve gear. ThiS
arrangemen~ allo~ the motor dr1ve sha~ ~o develop an output speed approaahin~ ol~erating ~peed. As the rotor outpu~ sha~t 12~53~

approaches the operating speed, the dowel pin of the second intermediate gear engages the opposite end of the arcuate slot in the rotating first intermediate gear imparting a sudden torque to the second intermediate gear transmitted to the output load through the main drive gear, drive screw, drive nut and extension rod. The lost motion between the first and second intermediate gears thus enables the drive motor to reach a speed approaching full operating speed to produce an impact "hammer blow"
transmitted to the main drive gear through the second intermediate gear to ensure reliable start-up of the linear actuator with or without an output load.
Preferably, a pair of arcuate slots are formed in the first intermediate gear in diametrically opposing position on opposite sides of the support dowel pin carrying the first and second intermediate gears. The angular extent of each slot is to some degree dependent on the gear ratio between the first intermediate gear and the drive pinion in mesh therewith. In the preferred embodiment, such gear ratio is approximately 4:1 in which case each slot subtends an angular interval of approximately 90 degrees. Thus, the motor output shaft and drive pinion thereon completes one full revolution before the first intermediate gear actuates the second intermediate gear and during which time the output shaft approaches full speed operation.

"

~29~361 Figure 2 is a partial cross-sectional illustration of linear actuator 150 incorporating the anti-lockup feature of the present invention. Linear actuator 150, apart from the improved anti-lockup intermediate gear train assembly 155 of my new design, otherwise corr~sponds to linear actuator 10 (Figure 1) disclosed in the aforesaid United States Patent 4,712,441. Identical reference numerals are employed in Figures 1 and 2 to denote elements common to both embodiments.
Anti-lockup gear train assembly 155 comprises a first intermediate gear 157 and a second intermediate gear 159 mounted on dowel pin 82 journalled between bearing 84 and 86. The first intermediate gear 157 is spaced from bearing 84 with spacer 160 and has gear teeth 157a for contacting the drive pinion gear 48. The second intermediate year 159 has gear teeth 159a for contact with the main drive gear 52. A pair of dowel pins 162 are press-fitted or otherwise fixed within blind holes 164 formed parallel to each other within second gear 159 on opposite sides of dowel ~:

29536~

pin a2~ ~h~ ~r~a ~nd~ 16~. of dow~l pin~ 1~2 pro~e~ ~rom the right-hand sid~ ~Figure 3) of ~e~ond ge~ g g~ner~lly perpendlcul~r ~o th~ pl~ne o~ th~ ond g~ar whe~ th~y ar~
resp~ctively received wl~h ar~uate ~lots 165 formed in fi~st gear . 157 in diametri~lly oppo~lng ~ela~n ~bout dowe~ pin 8~. The diameters o~ dow~l plns 152 ~t ~ee ends 162a thexeof 18 sllgh~y le~ th~ ~he radial width of ~aoh s~ot 16~ to p~ovide a loo it therewlth. ThQ dowel pins 162 are fu~th~ dlmensioned so tha~ ~ree ends 16~a pro~ect well within the slots ~i.e., preerab~y at least h~lf the thickness o~ ~h~ slo~ ~s ~ea~ured between the parall~1 end ~aces o~ gear 1~7) without pro~ecting outw~dly from the B10~ tow~ds bearing`84.
U~on aatuatlng d~ive motor 44 t~ operate linear octuato~ lS~, th~ motlve forc~ transmit~ed ~hrough ou~put shaf~
lS ~2 drive~ pinlon 48 t~ lmpart rotational moven~nt to first ~n~rmediate gear 157. Initially, the first int~rmediate ~ear 157 is ln the po~ition general~ y depicted in ~igu~e 4 with dowel ~ins 162 ~ositioned mo~e or less against diametrically oppo~ed ends o~ ~lots 16~. ~owev~r, rota~on ~ g~r 157 in th~ ~unter .aloclcwlse dir~t~ on o~ Figure~ 4 caus0~ t~l~ dowel pins 162 to travel th~ough the ~lots by vl~tue of the rot~ry movement of the slo~8 ~ormed in the flrst intermediate~ gear. During this intorv~ t wil~ be appre~iated that drive motor 44 i~ only powerlng driv~ plnion 48 and ~he ln~e~mediatc gear 1S7 and therefore e~counters mlnimal inertla as th~ moto~ ou~put ~aft ro~a~es 'co opera~lng spe~d a~ which time dowel plns 1~ abu~
against ~hs opposi~e diame~rlcally opposed end~ ~f ar¢uats slots 1~5. When this occurs, drive motor 44 ha~ developed sufficien~
torqu~ to abruptly transm~t motiYe force ~o se~ond intermedlate ge~r 15~ po~ering main drlve gear 52, drive scr~w S4, drive nu~

i, ,1 ~ ~9 5 5~ and ~xten~ion rod 5~ to overcome the inertial r~ anc~ o~
these driven pa~s ~ dri~e thq ou~put l~ad. I~ th~ m~n~e~, the 103t motion arran~ment pro~i~e~ by arcuat~ slo~s 16~ and dowel pin~ 162 1~ ~ea~s 157,159 respectively allow ~rive motor 44 to develop opora~ing to~ue t~ re~ia~ly oper~t~ linear a~tu~tor 150 by eliminati ng the tenden~y of ~he driven parts to lockup with or without an output loa~ eor3ne~ed ~h~!re~o.
~ he angular extent of ea~h 310t 165 in the clrcumferen~ial dirqot~on of gear 157 is somewhat depen~ent upon LO the gear ra'cio betweerl d~lve plnion 48 and first intermediate gear 157. To explain, it requlres approximately one revolution of output ~ha~ nd ther~by drive J?inion 4 ~plus or minu~
25% ) for the ou~p-~t ~;h~ft to reach operatiny ~pe~d and ths~eby d~velop suf~ nt anti-~oakup tor~ue, Therefo~ is L5 preferabl~s to design the arauate interval o~ ea~h ~lot 1~$ so that drive pinion 48 ~ompl~e~ one r~volution before dowel pins 162 t~avel from on~ end of ~heir asso¢l~ted slot to the opposite end. In on~ ~ommerci~l embodim~n~ o~ linea~ a~tuato~ 15G, the gear ratio is pr~f~a~ly ab~ut 1:4, meanin~ that slots 165 ~hould 20 be formed to subtend an angular interv~l of approximately gO
degree~ ~or sach ~lo~. In the event the gear ratio changes as b~tw~an di~ferent ~omme~c:ial ~mbodiments of lirle~r aetuato~ 150, it i~ pre~e~abl~ to deslgn slots 1~5 in the m~nner deso~ ed above so that pinion 43 compl~3t~ one ~volu~ion be~o~e dowel 25 p~ns 1~2 t~qvel i'rom one end o~ thei~ as~ooi.~t~d sJ~o~ to th~
opposite end.
It will b~ appr~iated that the for~e imp~c~ ~cting upon second lnt~mediate gear 15~ as dowel~ 162 ~ach th~
op~?osite end o~ their assoclated ~lot~ 1~5 i9 to some d~gree 30 dependen~ upon th~ radial posltion o tha ~310t:5 relativ~ t~o the 1~

2~ 5 361 central lon~i~udin~l axi8 o$ dowel pin ~2 upon whiah gears 157,l5g ~re mounted. In o~her wo~d~, by lo~atln~ ~lots 1~5 at a greater radlal d~stanee ro~ dowel p~n ~, the ~ora~ or ~hammer blow" imp~t transmitt~d from gear 157 to the ge~r 159 is ~reater . than i~ slots 16~ wer~ lo~ed close~ to dowel pin 82. In oth~r words, by loc~tlng thq s~ot# 165 ~t ~ greater ~adial looation than th~t di~clo~ed in Figure ~, it would not be neces~ary for ~lot~ 165 ~o have an ar~uate qxtent dependent upon th~ gear ~atio; i.e., the ~ame impact ~ox¢e ob~ained with the arrangement o ~lots depicted ~n ~ig~r~ 4 ~n al~o be obtained by ~ ocatin~
the ~lots at a radially ~reate~ po~ition th~n the ~igure 4 lo~ation and, lf deslred, ~orming the ~lots to have an arauate extent less than 50 degree~. In commercial.praatice o~ linear ac~uator 150, ho~ever, it is often dlfflault to relocate slots lS 1~5 from the F$gu~e ~ position due to the smaller diam~ter o~
~e~ond lntermcd~a~ gear l5g whl¢h typia~lly msy have a root diameter of a.~ inch~s ~one lnch out~ide diameter) whereas dowel p~n 82 ha~ a t~plcal diameter ~ 3/8 inches. It ls preferred, howeve~, to maint~in slots l~ ~nd thereby dowel pln~ 1~2 midw~y betw~en th~ ou~er periph~ry o~ dowel pin 82 Qnd the root di~meter of s~cond ~.nterme~iate gear 15~.
Althou~h the present in~en~ion may be pra~ic~d with onl~ on~ ~lot 165 ~ceivln~ e end 162a oP ~ne dowel pin 162, ~h~ p~ovislon of two slots 15 preferred to provide better forcs di~ribution to prevent shearing of the dow~l pin~ 162.
The in~ention may be embodied in other specific for~s without dep~rting from the splrit or e~sentia~ char2cteristi~s thereof. For example, lt i~ possibl~ ~o for~ arcuate slot~ 165 in ~e~ond intermediate gear lss and to p~es~ fit dowels 162 in~o holes formed in first gear 1~7 with ~ree ends 162a pro~e~ting ~ . .

12953~1 lnto the ~econd g~ar. ~he p~e8en~ embodim~nts are ther~fore to be co~side~ed in all resp~cts a~ illu~t~tive ~nd not ~s restric~ , the 6aope of the invention being i~dicated by th~
appended claims rathe~ than by the foregoing description, ~nd all changes whloh come withln the meaning and ~ange of e~uivalency of tho claim~ are the~efore intended ~o be ~-mbraced ~herein.

Claims (15)

1. A linear actuator comprising:

a housing;

a drive screw rotatably supported within said housing;

a drive nut in threaded engagement with said drive screw;

a body tube assembly connected to said housing and positioned about said drive screw, said body tube assembly containing reaction force surfaces for preventing rotation of said drive nut;

an extendible member having a load connecting member on its free end and having the opposite end thereof connected to said drive nut, said extendible member adapted for axial movement so as to extend out of said body tube;

drive means including an electric drive motor containing windings for rotating said drive screw; said drive means including intermediate gearing means for transmitting rotative torque output from said electric drive motor to rotate said drive screw, said intermediate gearing means including a lost motion arrangement means for delaying rotation of said drive screw for a predetermined interval during which a drive pinion of said electric drive motor rotates through a predetermined angular interval, said lost motion arrangement means enabling said drive pinion to attain a rotational speed approaching a predetermined operating speed before imparting rotative torque to drive said drive screw through the intermediate gearing means, said lost motion arrangement preventing lockup of the electric motor and over-heating of the motor windings tending to occur when an output load is connected to the load connecting member, wherein said intermediate gearing means includes a first intermediate gear and a second intermediate gear both mounted intermediate the electric motor and the drive screw, said first intermediate gear in contact with a drive pinion and said second intermediate gear connected to transmit rotative force to the drive screw, said lost motion arrangement means being formed between said first and second intermediate gears to enable initial rotation of said first intermediate gear under the driving force of the drive pinion before imparting rotative force to the second intermediate gear and thereby the drive screw.

2. The linear actuator of claim 1, wherein said lost motion arrangement means includes at least one arcuate slot formed in one of the first and second intermediate gears and a dowel projection received in the other of said first and second intermediate gears and having a free end extending into the slot, whereby rotation of said first intermediate gear under the driving force of the drive pinion causes the dowel projection to travel through the slot before contacting the opposite end of the slot for imparting a sudden rotative force to the second intermediate gear and thereby the drive screw.

3. The linear actuator of claim 2, further including a pair of arcuate slots formed in diametrically opposing location to each other on opposite sides of the dowel projection and a said dowel projection being received in each slot.

4. The linear actuator of claim 3, wherein each arcuate slot subtends an angular interval approximately equal to the gear ratio of the drive pinion to the first intermediate gear multiplied by 360 degrees.

5. The linear actuator of claim 3, wherein the arcuate extent of each slot is sufficient to enable the drive pinion to complete approximately .75 - 1.25 revolutions before the dowel projection travels from one end of the slot to the opposite end of the slot.

6. The linear actuator of claim 3, wherein each dowel projection has a central longitudinal axis extending substantially parallel to the central axis of the second intermediate gear, the longitudinal axis of the dowel projection being formed approximately midway between the root diameter of the second intermediate gear and the longitudinal axis of the dowel projection supporting said first and second intermediate gears.

7. The linear actuator of claim 3, wherein said dowel projections are force-fitted into diametrically opposed blind holes formed in the second intermediate gear.

8. The linear actuator of claim 7, wherein each dowel projection projects into its associated slot at least approximately half the thickness of the first intermediate gear.

9. The linear actuator of claim 3, wherein opposite ends of each slot are rounded and have a diametral extent slightly greater than the diameter of the associated dowel projection to prevent wedging of said dowel within said opposite ends.

10. A linear actuator comprising:
a housing;
a drive screw rotatably supported within said housing;
a drive nut in threaded engagement with said drive screw;
a body tube assembly connected to said housing and positioned about said drive screw, said body tube assembly containing reaction surfaces for preventing rotation of said drive nut;
an extendible member having a load connecting member on its free end and having the opposite end thereof connected to said drive nut, said extendible member adapted for axial movement so as to extend out of said body tube;
drive means including motor means for rotating said drive screw, said drive means including intermediate gearing means for transmitting rotative torque output from said motor means to rotate said drive screw, said intermediate gearing means including a gear train having a lost motion arrangement means therein for delaying rotation of said drive screw for a predetermined interval during which a drive pinion means of said motor means rotates through a predetermined angular interval, said lost motion arrangement means enabling said drive pinion means to attain a rotational speed approaching a predetermined operating speed for imparting rotating torque to drive said drive screw through the intermediate gearing means.

11. A linear actuator comprising:
a housing;
a drive screw rotatably supported within said housing;
a drive nut in threaded engagement with said drive screw;
a body tube assembly connected to said housing and positioned about said drive screw;
an extendible member having a load connecting member on its free end and having the opposite end thereof connected to the drive nut, said extendible member adapted for axial movement so as to extend out of said body tube;
drive means including motor means for rotating said drive screw, said drive means including intermediate gearing means for transmitting rotative torque output from said motor means to rotate said drive screw, said intermediate gearing means including a gear train having a lost motion arrangement means therein for delaying rotation of said drive screw for a predetermined interval during which interval said motor means increases its torque output.

12. An actuator comprising:
a housing;
a drive screw rotatably supported within said housing;
an extendible member having a load connecting member on its free end and having the opposite end thereof connected to the drive screw, said extendible member adapted for axial movement so as to extend out of said housing upon rotation of the drive screw;
drive means including motor means for rotating said drive screw, said drive means including gearing means for transmitting rotative torque output from said motor means to rotate said drive screw, said gearing means including a gear train having a lost motion arrangement means therein for delaying rotation of said drive screw for a predetermined interval during which interval said motor means increases its torque output.

13. A linear actuator comprising:
a housing;
a drive screw rotatably supported within said housing;
a drive nut in threaded engagement with said drive screw:
a body tube assembly connected to said housing and positioned about said drive screw, said body tube assembly containing reaction surfaces for preventing rotation of said drive nut;
an extendible member having a load connecting member on its free end and having the opposite end thereof connected to said drive nut, said extendible member adapted for axial movement so as to extend out of said body tube;
drive means including motor means for rotating said drive screw, said drive means including intermediate gearing means for transmitting rotative torque output from said motor means to rotate said drive screw, said intermediate gearing means including a lost motion arrangement means for delaying rotation of said drive screw for a predetermined interval during which a drive pinion means of said motor means rotates through a predetermined angular interval, said lost motion arrangement means enabling said drive pinion means to attain a rotational speed approaching a predetermined operating speed for imparting rotating torque to drive said drive screw through the intermediate gearing means, wherein said intermediate gearing means includes a first intermediate gear and a second intermediate gear both mounted intermediate the electric motor and the drive screw, said first intermediate gear in contact with a drive pinion and said second intermediate gear connected to transmit rotative force to the drive screw, said lost motion arrangement means being formed between said first and second intermediate gears to enable initial rotation of said first intermediate gear under the driving force of the drive pinion before imparting rotative force to the second intermediate gear and thereby the drive screw.

14. A linear actuator comprising:
a housing;
a drive screw rotatably supported within said housing;
a drive nut in threaded engagement with said drive screw;
a body tube assembly connected to said housing and positioned about said drive screw;
an extendible member having a load connecting member on its free end and having the opposite end thereof connected to the drive nut, said extendible member adapted for axial movement so as to extend out of said body tube;
drive means including motor means for rotating said drive screw, said drive means including intermediate gearing means for transmitting rotative torque output from said motor means to rotate said drive screw, said intermediate gearing means including a lost motion arrangement means for delaying rotation of said drive screw for a predetermined interval during which interval said motor means increases its torque output, wherein said intermediate gearing means includes a first intermediate gear and a second intermediate gear both mounted intermediate the electric motor and the drive screw, said first intermediate gear in contact with a drive pinion and said second intermediate gear connected to transmit rotative force to the drive screw, said lost motion arrangement means being formed between said first and second intermediate gears to enable initial rotation of said first intermediate gear under the driving force of the drive pinion before imparting rotative force to the second intermediate gear and thereby the drive screw.

15. An actuator comprising:
a housing;
a drive screw rotatably supported within said housing;
an extendible member having a load connecting member on its free end and having the opposite end thereof connected to the drive screw, said extendible member adapted for axial movement so as to extend out of said housing upon rotation of the drive screw;
drive means including motor means for rotating said drive screw, said drive means including gearing means for transmitting rotative torque output from said motor means to rotate said drive screw, said gearing means including a lost motion arrangement means for delaying rotation of said drive screw for a predetermined interval during which interval said motor means increases its torque output, wherein said intermediate gearing means includes a first intermediate gear and a second intermediate gear both mounted intermediate the electric motor and the drive screw, said first intermediate gear in contact with a drive pinion and said second intermediate gear connected to transmit rotative force to the drive screw, said lost motion arrangement means being formed between said first and second intermediate gears to enable initial rotation of said first intermediate gear under the driving force of the drive pinion before imparting rotative force to the second intermediate gear and thereby the drive screw.