DRIVF, ASSEMBLY WITH OVBKKJDE MECHANISM

CROSS-REFERENCE TO RELATED APPLICATION This application claims the benefit of U.S. Provisional Application No. 60/756,338, filed January 4, 2006, the disclosure of which is hereby expressly incorporated by reference.

BACKGROUND

Persons with mobility impairments ofiea depend on a wheelchair or walking aid to facilitate mobility, As a result they are frequently subjected to physical barriers and obstacles such as stairs and curbs. Current ADA legislation requires that these physical barriers be removed, and as a result, ramps have been designed to address this need.

However, ramps can be very long &&d difficult to climb, Further, depending on the elevation change and available space, ramps may be impractical- One solution is a

^■ wheelchair lift, Wheelchair lifts for commercial buildings and private residences must be designed and tested to me$t the requirements of the- ASME Code: AI 8.1 ₅ SAFETY

STANDARD fOR PLATFORM UFTS AND STAIRWAY CHAIRIiFTS,

The wheelchair lift may Include certain aetuatable components that act as protective barriers or supports; however, those components must meet certain force requirements defined. In the ASMB Code. Wheelchair lifts typically incorporate an overload assembly having a control system that utilizes contact switches to sense obstructions encountered by the component. Upon sensing an obstruction, the control system typically either shuts down ihe actuator, effectively stopping the component or limits ihQ force of the actuator by a curøsM limit or pressure regulator. The overload assembly may be either active or passive. An active overload assembly uses powered controls to achieve force limits, and a passive type uses regulators to limit forces (such as hydraulic relief valves). AH active assembly does not easily allow manual override, and passive systems can overheat,

Ii is desked to have a reliable overload assembly that limits the force the actuator imposes on the actuatable component without damaging the assembly or the obstruction. SUMMARY

A drive assembly for a wheelchair lift is provided. The drive assembly includes an actuating assembly in communication with a component of the wheelchair lift The actuating assembly is configured to selectively apply a driving force to move the

component between at least first and second positions. The drive assembly also includes an overload assembly coupled to the actuating assembly- The overload, assembly is configured to redirect application, of the driving force from die component to the overload assembly when a force applied to the component exceeds a predetermined limit, 5 This summary is provided to introduce a selection of concepts in a simplified form that are further described below in. the Detailed Description. This summary is not intended to identify key .features of the claimed subject matter, nor is ii intended Co be used as an aid in determining the scope of the claimed subject matter.

DESCRIPTION OF THE DRAWINGS

10 The foregoing aspects and many of the attendant advantages of this invention will become better understood by reference to the following detailed description, when taken iα conjunction with the accompanying drawings, wherein:

FIGURE 1 is an isomeric view of a typical wheelchair lift assembly having a drive assembly constructed m accordance with the present disclosure;

1.5 FIGURE 2 is an isometric view of a drive assembly for a wheelchair Mi constructed in. accordance with one embodiment of the present disclosure;

FIGURE 3 is a side cross-sectional view o.f the drive assembly of FIGURE 2.. taken substantially through Section 3-3;

FIGURE 4 is a top planar view of the drive assembly of FIGURE 2 in a first 0 overload position;

FIGURE 5 is an isometric view of the drive assembly of FIGURE 2 coupled to an arm guard;

FIGURE 6 is an isometric view of the drive assembly of FIGURE 2 coupled to a handrail assembly: 5 FIGURE ? is a cross-sectional view of the lift assembly of FIGURE I token substantially through Section 7-7, wherein, the drive assembly of FIGURE 2 is coupled to a barrier gate;

FIGURE 8 is an isometric view of a drive assembly for a wheelchair lift constructed in accordance with an alternate embodiment of the present disclosure; 0 FIGURE 9A is a front planar view of the drive assembly of FIGURE 8 in a first overload position;

FIGURE 9B is a front planar view of the drive assembly of FIGURE Z m a second overload position;

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FI ⁽ KiRE 10 Is an Isometric view of a drive assembly for a wheelchair lift constructed In accordance with another embodiment of the present disclosure; and

FIGURE 11 is a side plaaar view of a drive assembly for a wheelchair lift constructed m accordance with still yet another embodiment of the present disclosure.

DETAILED DESCRIPTION OF TEB EMBODIMENTS

A drive assembly 100 suitable tor use with a well-known wheelchair lift A may be best understood by referring to FIGURES 1- 4, One such wheelchair lift is disclosed, in. US Patent No. 6,601 ,677 _* entitled Cωtvertibh lift Mechanism Having a Number of Retractable Stairs with a Lift Platform Positioned Thereunder, the disclosure of which is hereby expressly incorporated by reference. Although one- type of wheelchair lift is illustrated it should be apparent that the scope of the present disclosure is not intended to he so limited.

The wheelchair lift assembly A includes several actuatable components, such as an arm guard B, ramp barrier C ₅ barrier gate D, and handrail extension E. The drive assembly 100 constructed in accordance with one embodiment of the present disclosure includes & frame or base 112 _f an overload assembly 102,. and an actuating assembly 1.04, The overload assembly 102 includes a bearing assembly, or linear slide 114, coupled to the base 112.

Referring to FIGURES 2 and 3. the linear slide- .1.14.includes a slide rail 116 and a slide bearing assembly 118. The siϊde rail 116 is fixedly coupled to the base 112 in any suitable manner. The slide rail 116 is C-shapcd m cross section to define a receiving channel 127. A longitudinal groove 122 is formed m the bottom of the rail. 116 and along the length of the slide rail 116, and a longitudinal notch 124 is formed therewuhrø.

The reeeivisg ehaatiel 12? of the slide rail 116 sHdabiy receives at least a portion of the slide bearing assembly 11 S. The slide bearing assembly 1.18 includes a bearing plate 128, an intermediate plate 130, aad a mounting plate 132. The bearing piale 128 Is sized and shaped to tit within the receiving channel 127. The bottom of the ^' bearing plate 128 includes a longitudinal protrusion 136 that is slidably received within the longitudinal groove 122, and the longitudinal protrusion 136 includes a recess that slidably receives the notch 124,

The .mounting plate 132 is positioned above the bearing plate 128 and ihe intermediate plate 130 is disposed therebetween. The mounting plate 132, intermediate

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plate 130, and bearing plate 128 are coupled together in any well known manner. In the alternative, the mounting plate 132, mteπaediate plate 130, mid beating plate 128 may be formed as one piece, A carriage 14:2 Is coupled to the mourning pfate .132 in substaaliaUy the center of the mounting plate. As shown Iu FIGURE 2 ₅ the bearing plate ,12S _> intermediate plate 130, and mounting plate 132 ate substantially the same length and are- all shorter in length than, the slide rail 116 such that the plates 12S ₅ . 130, and 132 may slmultaoeoαsly be translated, along the slide rail 116 in either linear direction _*

Referring back to FIGURE- 2, the overbad assembly 102 further includes at least one override mechanism that helps limit the effects of the drivirxg force delivered to the actuatable component Preferably, the assembly 102 includes two opposing pairs of gas springs 144, or a first pair of gas springs 145 and a second pair of gas springs 147, Each gas spring 144 is disposed between a mounting device 154 located, at a comer of the base 1.12 and the carnage 142. Although a gas spring is suitable for use as an override mechanism, other types of mechanisms could be used. Examples include, but are not limited to, a pneumatic dampener, a slip clutch, a release valve, or the like.

Each gas spring 144 includes a gas cylinder 156 and a rod 158. A piston (rsot shown) is coupled to the end of the rod )SZ, and inert gas stored within the cylinder 156 is compressible by the piston. The gas springs 144 may be any off-the-shelf gas spring with the required preset load, which is determined by the force of the compressed gas ors the piston. Gas springs with differing preset loads or with adjustable preset loads are also wiihm the scope of the present disclosure. Moreover, each gas spring 144 has a predetermined stroke length, aαd a predetermined spring rate. Although each gas spring 144 may have different stroke lengths and spring rates, it h preferred that the gas spriags 144 of both pairs of gas springs 145 and 147 have substantially equal stroke lengths aad spring rates. It should be appreciated by one skilled in the art that other types of springs, such as coil compression springs or extension springs, may also be used, but gas springs .144 are preferable.

The cylinder ends of the gas springs 1.44 are coupl&d to the mounting devices 154 h\ any suitable manner. The gas springs 144 are suspended above the base 112 and linear slide 114 by a support bracket 160 and tie 162. The bracket 160 is fixedly coupled to the base 112 and extends upwardly therefrom to contact the gas cylinder 156, A suitable tie 162 is used to secure the cylinder 156 to the bracket .160, The ends of the rods 15% are receivable within recesses (not shown) formed in the carriage 142. The rod ends of the

second pair of gas springs HS engage one side of the carriage 142, and the rod ends of the first pair of gas springs 147 engage the other side of ifte carriage 142.

Each gas spring 144 has the appropriate preset load (or is adjustable) so that fee rod 158 is in a fully extended position. Accordingly, when ali four gas springs .144 are simultaneously coupled to the carriage .142 through the rod tip e«ds, they maintain the position of the carriage 142 (and therefore the linear slide 1.14) in a mid or neutral position. If the preset load on any gas spring 144 is overcome, the gas spring 1.44 will compress, In other the rod I5S will retract within the cylinder 156 so that the piston further compresses the inert air. In effect, the load on the gas spring 1.44 will. increase slightly. Thus, if a force exerted on the carnage 142 exceeds the preset load of a pair of gas springs 145 or 147, the pair of gas springs 144 will compress accordingly. Because the rods 15S are originally in a fully extended, preset load condition, the opposing pair of gas springs 144 come out of contact with the carriage 142 and are supported by the mounting device 154 and the bracket 160. Still referring to FIGURE 2, the actuating assembly 104 Includes a suitable actuator 146 for selectively applying a driving force to move the actuatabte component The actuator 146 is preferably a linear actuator having an actuator cylinder 168 coupled to an actuator base- 170, and a push rod 174 sHdably received within the actuator cylinder 168, The stroke length of the push, rod 174 is equal to or less than the stroke length of the gas springs 144, The linear actuator 146 is driven by a motor 166 aαd includes limit switches (not shown) that shut the actuator 146 off In the fully extended and fully retracted positions, The actuator base 170 is mounted to the linear slide 114 through the carriage 142. The linear actuator 146 is preferably pivotally mounted to the carriage 142 such that the linear actuator 146 is rotafable about an axis transverse to the longitudinal axis of the actuator cylinder 1.68. or axis Y.

The actuating assembly 104 further includes a suitable gear system, 1mkage _; sprocket assembly, or other suitable assembly for transmitting the mechanical, power of the actuator 146 to the actuatabie component. As shown in. FIGURE 2. the push rod .174 is coupled to a gear system 148 having first and second gears 150 and 152. The end of the push rod 174 is operably coupled to the first gear 150, which drives the second gear 152 to rotate the drive shaft 178. The drive shaft 178 in turn reciprocates the actuafabk component between at least first and second positions. The end of the push rod 174 is preferably pivotally coxφled to one end of a pair of gear driving levers 176,

which are in turn fixedly coupled to the first gear 150. As tlie push rod 174 extends and retracts to drive the first gear 150, the gear driving levers 1.76 allow the push rod 174 to pivot about axis Y.

As can best be seen by referring to FIOLJRE 4, the overload assembly 102 limits the driving force of the actuator 146 on the actuatable component by redirecting application of the driving force from the component to the overload assembly 102 when the component encounters an. obstruction. In other words, movement of the component is redirected to the overload assembly 102. When the push rod 174 is retracting within the cylinder 168 to move the component, the force from the obstruction causes the component to cease or slow its movement, thereby preventing or slowing the rotation of the gear shaft 178, the gear system 14$, and the push rod 174. The actuator 1.46 continues to retract; however, application of the driving force is redirected and instead pulls the cylinder 168 toward the gear system 14S along the push rod 174. As a result, the carriage 142 is also pulled towards the gear system 148 and applies a force on the rods 158 of the first gas springs 145. Thus, the application of the driving force is redirected to move the gas springs 145 instead of the component ϊf the force exceeds the preset load in the first gas springs 145. tJie first, gas springs 145 compress and the carriage 142 and actuator cylinder 168 slide with the mounting plate 132 towards the pair of compressed .springs 145. The second pair of gas springs 147 come out of contact with the carriage J 42. As the gas springs 145 continue to compress, the driving force on the component is limited by the spring force governed by the spring rate. However, the actuator 146 does not turn off until the push rod 174 is fully retracted and a limit switch (not shown) causes it to shut down. Since ihe gas spring stroke length is equal to αr greater than the stroke length of the linear actuator 146, the linear actuator 146 will stop retracting before the first gas springs 145 fully compress. Thus, damage to the linear actuator 146 is minimized, such as damage from stall torque, high electric current during .stall condition, and back-driving during niarmal operation.

The same is true if the push rod 174 is extending to move the component and the component encounters an obstruction (not showa), causing the push rod 174 to cease or slow its translation. The actuator 146 continues to extend; however _* the cylinder 168 is instead pushed away from the gear system 148 along the push rod 174. As a result, the carnage 142 is also pushed away from the gear system 148 and applies & force on the rods 158 of the second gas springs 147.

Once the redirected force exceeds the? preset load in the second gas springs 147, the second gas springs 147 compress &nά the carriage 142 and actuator cylinder 168 slide with the mounting plate 132 towards the compressed pair of second springs 147. The first pair of ga<s springs 1.45 comes out of contact with the carnage 142. As the second pair of gas springs 145 continue to compress, the driving force on the component is limited by the spring force governed by the spring rate. The limit switch causes fee actuator 146 to shut off when the push rod 174 is fully extended.

The overload assembly 102 allows selective manual override any time fee actuafable component is "unlocked," Le. not appropriate for use as a guard, handrail _> etc. If unlocked, the actuatabte component can be moved .manually by applying a force to the component The force is increased ualii the resultant net .force against the gas springs 144 (either the first or second pair of gas springs 145 or 147, depending on the direction of the force) exceeds the preset load. Once the force exceeds the preset load is the springs 144, the gas springs 144 compress and the carriage 142 and actuator 146 slide with the mounting plate .132 towards the pair of compressed springs 144. The opposing pair of gas sprmgs 144 comes out of contact with the carnage 142, The force that can be exerted on the aetuatable component is limited by the spring rate of the gas springs 144. Moteover, the .manual .movement of the aetuatable component is limited to the stroke length of the gas springs 144. Now referring to FIGURE 5, the drive assembly 100 is shown, in combination with an arm guard B. The drive shaft 178 of the drive assembly 100 is coupled to the arm guard B to reciprocate or move the arm guard B between at least first and second directions, or between at least an extended and collapsed position. A connecting link 182 is operably coupled, to the ami guard B at one end such that the connecting link 182 is reciprocated by the drive assembly 100 along with the arm guard B- The connecting link 182 is driven in a generally vertical direction by the arm guard B through a cam assembly, a linkage, a gear system, or other suitable assembly. The connecting link comprises a counterweight 186 and a turnbuekle 188,, with the counterweight 186 operably coupled to the arm guard B and the turabαckie IM prvotally coupled to one mm ofa bell crank 184.

A ramp barrier C (shown in FIGURE I) is pivotally coupled to the other arm of the bell crank ϊ84 through, a ifakage, cam assembly, gear system, or other suitable assembly such that the bell αaak 1.84 transmits the moliαα of the connecting link 182 to

the ramp barrier C, Accordingly, tlie arm guard B arid mmp barrier C are simultaneously reciprocated by the drive assembly 100 between extended and collapsed positions.. Moreover, the counterweight balances the loads between the ana guard B and ramp barrier C. However, it should be appreciated that the- arm guard B and/or ramp battier C may instead be constructed of lighter materials such that a counterweight would be unnecessary.

To lower the ami guard B, the motor 166 drives the actuator 146 to retract the push rod 174 thereby rotating the first gear 150 clockwise. The first gear ISO drives the second gear 152 in a counterclockwise direction, which in turn drives the drive shaft 178 counterclockwise to lower the ami guard B, As the arm guard B is being lowered, trie connecting fink 182 is driven in a generally upward direction, and the bell crank 184 is rotated m a counterclockwise direction to lower the rtratp barrier C.

If the arm guard B or. ramp barrier C encounters an obstruction as they are being lowered, the first gear 150. second gear 152 _f and push rod 174 slow in movement The cylinder 168 and carriage 142 are pulled toward the gear system 148 and the first pair of springs 145 compress, As a result, the application of the driving force of the actuator 146 is redirected to the first pair of springs 145, and damage to the obstruction and the actuator is prevented. The actuator 146 shuts off when it is fully retracted.

To raise the arm gtiard B and ramp barrier C, the push rod 174 is extended to rotate the Erst, gem- 150 counterclockwise, and to rotate the second gear 152 and drive axle clockwise. The connecting link 182 is driven in a generally downward direction, rotating the bell crank 184 clockwise to raise the ramp barrier C If the arm guard B or ramp barrier C encounters an obstruction as they are being raised,, the push rod 174 slows or stops, and the cylinder 168 slides sway from the gear system 148 along the push rod 174. The cylinder 168 pushes the carriage 142 aαd causes the second pair of gas springs 14? to compress. The linear actuator 146 will shut off when it is fully extended. It may also be appreciated Oiat the arm guard B and ramp barrier C can be operated independently by separate drive assemblies 100 with no connecting link 382.

Referring to FIGURE 6, fee drive assembly 100 is shown in combination with a handrail assembly E in the lowered position. The drive shaft 178 of the drive assembly 100 Is coupled to the handrail assembly E to reciprocate the handrail assembly E between a .raised and lowered position. Art optional gas spring 190 is

pivotaJly coupled to the drive shaft .178 through a yoke or link 192. The gas spring 190 counterbalances the handrail assembly B and reduces the load on the drive assembly 1 (K).

To raise the handrail assembly E, the actuator 146 retracts the pushrød 174 and drives the first gear 150 in a clockwise direction _* The first gear 150 drives the second gear 352 and the drive axle 17§ in a counterclockwise direction, thereby raising the handrail assembly E, If the handrail assembly E encounters an obstruction as it k being raised, the push rod 174 slows in translation. The cylinder 168 and carriage 142 are pulkd toward the gear system .14S and the first pair of springs 145 compress. As a result application of the driving force of the actuator 146 is redirected to the first pair of springs .145, and damage to the- obstruction and the actuator is prevented Hie actuator 14(> shots off when it JS fully retracted-

To lower the handrail assembly E, the push rod 174 is extended to rotate the first gear 150 counterclockwise- and to rotate the second gear 152 and drive axle 178 clockwise to raise the handrail assembly H. If the handrail assembly E encounters an obstruction as it is being lowered, the push tod 174 slows or stops, and the- cylinder 16S slides away from the gear system 148 along the push rod 174, The cylinder 168 -pushes the carriage 142 and causes the second pair of gas springs 147 to compress. The linear actuator 146 will shut off when If is fully extended.

Now referring to FIGlJRFi 7, the drive assembly 100 is shown in combination with a barrier gate D, The drive assembly 100 is rnoomed in any suitable manner beneath the barrier gate D such that the drive axle 178 drives the batϊier gate D between first and second directions, i.e. between open and closed.

To close the barrier gate D, the posh, rod 174 is extended to rotate- the first gear .130 counterclockwise aact to rotate the second gear 152 and drive axle 178 clockwise- to move the barrier gate D toward the wheelchair lift assembly A, If the barrier gate D encounters an obstruction as it. is being closed, the push rod 174 slows or stops, and the cylinder 168 slides away trorn the gear system 148 along the push rod 174, The cylinder 168 pushes the carriage 142 and causes the second pair of gas springs 14? to compress. The linear actuator 146 will shut off when it k fully extended, To open the barrier gate D ₅ the actuator 146 retracts the push, rod 174 and drives the first gear 150 m a clockwise direction. The first gear- ϊ50 drives the second gea? 152 and the drive axle 178 m a counterclockwise direction, thereby opening the barrier gate D. If the barrier gate D eacoimters an obstruction as it is being opened, the push

rod 174 slows in translation. The cylinder 168 and. carriage .142 are pulled toward the gear system 148 and the Bret pair of springs 1,45 compress. As a result, the driving movement of the actuator 146 is redirected to the first pair of springs 145., and damage io the obstruction and the actuator is prevented. The actuator 146 shuts off when it is fully retracted.

FIGURE 8 depicts an alternate embodiment of the drive assembly 200, with the materials, operation, and uses of the drive assembly 200 illustrated in conjunction "with the above described components. Although the above drive assembly 100 is described in great detail and shewn m combination with the actuatable components B-H, the drive assembly 200 is the preferred embodiment The drive assembly 200 includes an overload assembly 202 having a gas spring housing 212 with a middle gas spring 247 and two lateral gas springs 245 disposed therewithm. The gas spring housing 212 may be any suitable shape such that it provides the appropriate compression surfaces for the gas springs 245 and 24?. The cylinder end of the middle gas spring 247 protrudes through an opening in the gas spring housing 212 and is mounted to a mounting portion 253 of art actuator base 270. The rod end of the middle gas spring 247 is coupled to a compression bar 254 disposed, within the bottom of the gas spring housing 212. The rod ends of the lateral gas springs 245 are coupled to the compression bar 254. and the cylinder ends of the lateral gas springs 245 are coupled m compression to an upper housing edge 213 of the gas spring housing 212 opposite the compression bar 254.

The drive assembly 200 includes a motor 266 and a linear actuator 246 secured to the actuator base 270, and the push rod 274 of the linear actuator 246 is opera biy coupled to a gear system or linkage (not shown) of the actuatabie component. The drive assembly 200 may be pivotally coupled to the wheelchair lift assembly A via a pivotal attachment 215 extending outwardly from the bottom surface of the housing 212.

Similar to the overload assembly 102 ₅ the overload assembly 202 protects the actuator and obstruction when an actuatable component engages am obstruction. As best seen by referring to FIGURE 9A _S when the push, rod 274 Is .retracting to move the actoatabie component and the actuatable component encounters an obstruction, the obstruction causes the gear system (not shown) and push rod 274 to slow or stop. The actuator 246 contimies to retract; however, application of the driving force is redirected and the cylinder 26S is instead polled toward the gear system along the push rod 274. As a result, the actuator cylinder 268 _f actuator base 270, the middle gas spring 247, and the

compression bar 254 are simultaneously pulled upward, and the compression bar 254 exerts a force on the rods of the lateral gas springs 245. Once the force exceeds the preset load of 1 ^' h.e lateral gas springs 245, the lateral gas springs 245 compress against the housing edge 213. As the lateral gas springs 245 continue to compress _* fee driving force of the linear actuator 246 on the component is limited by the spring rale of the lateral gas springs 245. Moreover, the linear actuator 246 shuts off when it is fully retracted _*

Referring to FIGURE 9B, if the push rod 274 is extending to move the actuatahle component and the component encounters an abstraction _* the push rod 274 slows or stops. The actuator 246 continues to extend, &nά the cylinder of the middle gas spring 247 is pushed away from the gear system along the push rod 274. As a result, application of the driving lbrec is redirected to the rod of the middle gas spring 247, Once the force exceeds the preset load in the middle gas spring 247, the middle gas spang 247 compresses against the compression bar 254, As the middle gas spring 247 compresses, the- driving force of the actuator 246 on the component is limited by the characteristic of the middle gas spring 247. ^' The linear actuator 246 shuts off when the actuator Is fully extended.

Now referrirjg to FIGURE 10, another embodiment of the drive assembly 300 includes- an overload assembly 302 having a frame defined by a first plate 306 and a second plate 308 that are both preferably U-shaped but may be any suitable shape. First and second housing members 396 and 398 are coupled to the exterior of the first and second plates 306 and 308 for receiving and retaining the cylinder ends of gas springs 344, The first and second plates 306 and 308 are coupled, together by first and second rods 310 and 311. First and second sleeve bearings 312 and 313 are slidably received on the first and second rods 310 and 311 and are interconnected by a stidable support.332 to cooperatively form a linear slide 314, The overload assembly 302 further includes a carriage 342 mounted on the slidable support 332. A linear actuator (not shown) may be pivotaϊly coupled to the slidabfc support 332 at pin hole 399 with a pin or other fastener,

A plurality of gas springs 344 are disposed between the first and second housing members 396 and 398 and the carriage 342. A iϊrsi pair of preloaded gas springs 345 are in compression contact wife the carriage 342 at the rod ends of the gas springs 345 a&d are received within the first housing member 396 at the cylinder ends of the gas springs 345. A second pair of preloaded gas springs 347 opposing the first pair are in

compression COB lad. with the carriage 342 at the rod ends of the gas springs 347 and are received within the second housing member 398 at the cylinder ends of the gas springs 347,

The overload assembly 302 operates in a simitar fashion to the overload. 5 assembly 102» ϊn other words, when an actuatable component encounters an obstruction while the component is being actuated, application of the driving force is redirected to one pair of gas springs 345 or 34? that will compress after the preset load is exceeded to allow the actuator to continue extending or retracting, The actuator eylkidet and carriage 342 will slide with the sleeve bearings 312 when the springs 345 or 347

10 compress. The actuator is allowed to fully extend or retract before the limit switch shuts the actuator off. Thus, damage to the actuator or obstruction is prevented.

FIGURE 1 1 depicts still yet another embodiment of the drive assembly 400. The drive assembly 400 includes an overbad assembly 402 having & frame deiϊned by two longitudinal base xoάs 412 spaced apart in a parallel relationship and coupled together at

1.5 their ends by end blocks 454. A linear slide 414 is siidabty disposed between the longitudinal base rods 412. A carriage 442 is coupled to one side of the linear slide 414, aα<! an actuator mounting piece 470 is coupled to the other ήάa of the linear slide 4.14. The actuating assembly 404 includes a linear actuator 446 coupled to the actuator mounting piece 470 at one end. ami coupled to the actuatable component at the other end. 0 First and second preloaded gas springs 445 and 447 oppose one another with the cylinder ends being coupled to the end blocks 454 and the rod ends in compression contact with the carriage 442 to maiataia the carriage 442 and linear actuator 446 m a neutral position.

The overload assembly 402 operates in. a similar fashion to the overload assembly 102, In other words, when an. actuatable component (such, as art arm. guard) 5 encounters an obstruction while the component is being actuated, one gas spring 445 or 447 will compress after the preset load is exceeded to redirect application of the driving force and allow the actuator 446 to continue extending or retracting. The actuator cylinder 468 and carriage 442 will slide with the linear slide 414 when a spring 444 compresses. The actuator 446 is allowed to fully extend or retract before the limit switch 0 shuts the actuator off. Thus, damage to the actuator or obstruction Is prevented.

While the preferred embodiment of the invention has been illustrated and described. If will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.