US2216058A - Automobile lift - Google Patents

Description

Sept. 24, 1940. E. B. THOMPSON 2,215,053

AUTOMOBILE LIFT Filed July 30, 1938 3 s t -s eet 1 Sept. 24, 1940. E. B. THOMPSON 2,216,058

' AUTOMOBILE LIFT Filed July 30, 1938. 3 Sheets-Sheet .2

llllllllllllll Sept. 24, 1940. E THOMPSON 2,216,058

AUTOMOBILE LIFT File y 5 1938 3 Sheets-Sheet s Patented Sept. 24,v 1940 i UNITED- STATES 2,216,058 7 AUTOMOBILE LIFT Elmer B. Thompson,

Des Moines, Iowa, assignor to Globe Hoist Company, Des Moincs, Iowa, a

corporation of Iowa Application July 30', 1938, Serial No. 222,227 15 Claims. (01. 254-89) Substantially all of the automobile liftsnow in use are of the so-called hydraulic type and employ an upright piston and cylinder which, when installed, projects to a considerable distance below the roadway or floor, and the cylinder is usually installed in solid concrete. If installed in a floor over a basement or room, the cylinder pro jects into the basement or room below and is, therefore, objectionable. If installed in rocky soil the installation is very expensive, and removal to a new location is also expensive.

The object of my invention is to provide a portable lift of such simple and inexpensive construction that it may be marketed competitively with hydraulic lifts, and at the same time may be quickly and easily installed by unskilled workmen upon any roadway. or floor Without occupying space below the floor. 7 o,

A further object is to provide a lift of this 20. class which, when thelift platform is in an elevated position, and if upon the breakage or fallwe of any part of the lift, the platform should start a rapid downward movement, the platform would be automatically locked and held after such rapid movement of only a few inches, so that no damage could result.

A further object is to provide a lift of this class in which in the event that any part of the platform during its normal downward movement 30 should engage any obstruction the motor will be automatically shut off and further downward movement prevented.

A further object is to provide means whereby in the event that any one of the corner posts should be substantially out of vertical alignment, to such an extent as to cause undue friction or wear on the working parts, the mechanism for raising and lowering the platform will be automatically locked and the motor shut off, thereby preventing further operation and avoiding undue friction, wear or breakage until the uprights are returned to and fixed in substantially upright positions.

A further object is to provide an improved and simplified manually operated safety lock for 45 holding the platform in its elevated position.

A further object is to provide simple and inexpensive means for automatically stopping the upward movement of the platform when it has reached its normally elevated position and in the 50 event that the motor continues to operate thereafter.

In the accompanying drawings Figure 1 shows a perspective view of my improved automobile lift, parts of the beams of the platform being broken away to show structural details;

Figure 2 shows an enlarged detail view, partly in vertical section, illustrating the gear mechanism between the motor shaft and the drive shaft in the adjacent transverse platform beam;

plate Figure 3 shows a transverse sectional view of same; t Figure 4 shows an inner face view, partly in section, of one ofthe corner upright posts and illustrating the gear mechanism and the automatic safety locking mechanism and the manually operated locking mechanism, taken on the line 4-4 of Figure 5;

Figure 5 shows a vertical sectional view of same taken on the line 5-5 of Figure 4;

Figure '6 shows a view somewhat similar to Fi ure 4 and illustrating the corner post at the corner where the electric motor is installed, and illustrating the switch mechanism for automatically shutting off the motor, and also illustrating in detail the rack bar and pinion for operating the switch;

Figure 7 shows an enlarged detail vertical sectional View of the safety lock escapement device taken on the line 1-1 of Figure 8;

Figure 8 shows a horizontal sectional view of one of the corner posts and illustrating the safety locking mechanism therein; and

Figure 9 shows a detail view illustrating the locking bar and the levers which support the clutch jaws and a portion of the platform, illustrating the manner in which the said levers are caused to grip the locking bar when the adjacent portion of the platform is tilted out of a horizontal position. i 7 My improved lift device comprises four upright corner posts, each of which is preferably independently fixed to the floor or roadway on which the lift is mounted. Each comprises a base It and an upright corner post II. This corner post is preferably made of plate metal and is rectangular in outline, and on its inner surface it is formed with a vertical slot I2, the edges of the metal adjacent the slot being bent inwardly at I3 toward the center of the post and then parallel with the adjacent side of the post, as shown at I4 in Figure 8. One of the corner posts adjacent the corner to which the electric motor is applied is formed with an additional slot I5 on the side opposite from the slot I2, as shown in Figure 3. At the top of each of the corner posts is a plate I6 firmly fixed in position.

The platform comprises two transverse beams I! and two longitudinal beams I8, all rigidly fixed together to form a substantially rigid platform. The transverse beams H, as shown in Figure 4, are hollow. Firmly fixed to each end of each of the transverse beams I! is an upright bracket I9. Fixed to. the outer surface of thebracket I9, as shown in Figure 5, is a block 20, and fixed to the outer surface of the block is a bearing plate 2|. Mounted in the'block 20 and the bearing plate 2| is a stationary shaft 22 extended outwardly and fixed in position by the set screw and .23. Rotatably mounted upon the'shaft 22 is a gear wheel 24, and fixed to this gear wheel is a toothed pinion 25. Extended longitudinally through the beam I! is a shaft 26 having fixed thereto a pinion 27 in mesh with the gear 24.

An electric motor 26 is mounted at one corner of the lift, and its shaft 29 extends downwardly through a casing 36 in which it is rotatably mounted, and a worm gear 3| is mounted at its lower end portion. This worm gear isin mesh with the large worm gear-32 rotatably mounted on the shaft 83 within the casing 30, as shown in Figures 2 and 3.

On this shaft 33 is a small pinion 34 mounted in the casing 38, and the pinion 34' is in mesh with thelarge gear 35 fixed to the adjacent shaft 86. This shaft 36' is, as shown in Figure 1, extended through the adjacent transverse beam H to the corner post [i opposite the one to which the motoris attached, and a beveled gear 31 is fixed to the shaft 36. 7 Within one of the longitudinalbeams 8 is a shaft 38 having at one end a beveled gear 39 in mesh with the beveled gear 37. This shaft 38 extends to the opposite one of the transverse platform beams l1 and is provided with a beveled pinion 38 in mesh with a beveled pinion 4|] on the shaft 26 within the other beam I.

J By this means it will be seen that on rotation of the motor both of the shafts 36 and 26 will be correspondingly rotated at a speed greatly reduced from that of the motor shaft, and they will all be rotated in unison. 'In Figure 6'I have shown at the top of the upright corner post adjacent the motor 28 an electric switch 4| of ordinary construction. This switchis arranged in the circuit of the motor 28, and when the switch is elevated the circuit is open, the switch being normally held in its lower position to close the circuit by means of the spring 42. I have not herein illustrated the wiring connections between the switch and the motor. These, however, are of the ordinary construction.-

For guiding the platform within the corner posts I have provided grooved guide rollers 43 mounted on the bolts 44 which are fixed to the bearing plates 2|, as shown in Figure 5. These grooved rollers enter and operate in the slots l2 in the corner posts, as shown in Figures 5 and .8.

' In each of the corner posts there is a rack bar, indicated by the numeral 45. This rack bar is formed with a series of openings 46 to receive the teeth 4'1 of the pinions 25, as shown in Figure 6. At the top portion of the rack bar there is arranged in line with the openings 46 a slot 48, shown in Figure 5. The rack bar extends upwardly through the top plate I6, as shown in Figure 6, and at its top is a collar 49 held in place by a set screw 58 and resting on the top plate l6. The lower end of the rack bar is free so that the rack bar is suspended on the top plate 5 and is free to move upwardly but not downwardly from its normal position. The upper end of the rack bar 45 is positioned directly below the switch 4| so that when the rack bar is slightly elevated above its normal position it will operate the switch'to open the circuit.

'With the construction heretofore described, and assuming that the motor is being operated to raise the platform it will be seen that the pinions Z5 at all four corners. of the platform will engage the rack bars 45, and since all the pinions 25 are operated at uniform speed, the platform will be elevatedequally at all corners, and when the pinions are elevated to their normal upward limit, the teeth 41 of the pinions 25 will enter the slots 48 and thereby prevent further upward movement of the platform even though the motor is operating, and when the downward movement is commenced the teeth 4'! will enter the openings 46 in the rack bar and move the platform downwardly in a horizontal position.

In the event that there should be a failure of any part of the mechanism, such, for instance, as a breakage of the shafts, which control the pinions 25, or breakage of one or more of the rack bars: 45, it is essential that further downward movement of the platform be immediately stopped and the platform locked in the elevated position in which said failure occurred. For this purpose I have provided the following mechanism:

Mounted in each of the corner posts is a looking bar 5| extended through the plate l6 and provided With a collar 52 held in place by a set screw 53, the lower end of the locking bar being free. This locking bar is, as illustrated in Figure 8, rectangular in outline with two relatively wide side edges and two relatively narrow edges, and it is smooth. Adjacent the locking bar 5| is an escapement bar 54. This escapement bar extends upwardly through the plate I6 and is provided with a collar 55 held in place by a set screw 56. The lower end of the escapement bar is free. This escapement bar, as shown in Figure 8, is substantially rectangular in outline and throughout its length it is formed with a series of uniform symmetrical alternately arranged curves 51, as shown in Figure 7.

Attached to and carried by the bracket I9 is a plate 58, and pivoted to this plate 58 are two levers 59. These levers are extended horizontally on opposite sides of the locking bar 5|, as shown in Figures 4 and 5, and their inner surfaces are smooth and in loose frictional engagement with the fiat sides of the locking bar 5|. Pivotally mounted between the outer ends of the levers 59 is a clutch jaw 60, shown in Figure 4. This clutch jaw is smooth on its surface adjacent the locking bar and in normal position is in loose frictional engagement with the said locking bar; and pivotally mounted between the levers 59 is a second clutch jaw 6|, smooth on its edge adjacent the locking bar and normally in loose frictional engagement therewith. Fixed to the clutch jaw 6| is a bracket 62, shown in Figure 6, and on this bracket is a rod 63 to which is pivoted a rectangular escapement frame 64 which extends upwardly and has pivotally mounted on its upper end an escapement shaft 65. This shaft has at one end a loop 66, as shown in Figure 8, and this loop encircles the escapement bar 54 and loosely fits it. On the other end of the escapement shaft 65 is a weight 61 extended transversely of the shaft. The parts of this escapement device are so proportioned relative to each other and to the curved portions in the escapement bar that during the normal up or down movement of the platform at the speed at which it is normally driven by the motor and reduced gearing mechanism, the curved portions of the escapement bar will engage the loop of the escapement shaft and cause it to rock and to thereby oscillate the weight 61, and this is done with a very slight amount of friction or loss of power. When, however, the platform commences to descend at a high rate of speed, such, for instance, as when such'failure on the part of the elevating mechanism occurs as would cause the platform to drop by gravity, then the. inertiaof the escapement weight would prevent it from oscillating in the manner in which it is normally oscillated by the escapement bar, and, hence, the escapement loop would be looked upon the escapement bar and would tend to remain in its elevated position. At this time the plate 58 connected to the platform, and the levers 59 connected to the plate 58 would remain stationary, and since the escapement frame is connected to the clutch jaw Bl, this clutch jaw would be held stationary, and when this has happened, the outer ends of the levers 59 would be moved downwardly and, hence, the clutch jaw 69 would be moved toward the adjacent edge of the locking bar 5| and they would jointly be moved toward the clutch jaw 6| into firmly gripping and locking contact therewith, and further descent of the elevator platform would be prevented.

The said levers 59 perform a somewhat similar locking function as follows:

It sometimes happens that, as illustrated in Figure 1, an obstruction, such, for instance, as a box, 68, is placed on the floor in the path of one of the platform beams, and during the normal descent of the platform and when the platform engages this obstruction it will, of course, prevent further downward movement of that part of the platform which engages the obstruction. The opposite corner of the platform, however, may continue to be moved downwardly, and this causes a tilting of the beam ll, as shown in Figure 1. In Figure 9 I have illlustrated the plate 58 attached to one corner of the platform in a slightly tilted position relative to the upright look bar, and since the levers 59 are carried by the plate and lie flat against the adjacent surfaces of the plate 58, the tilting of this plate 53 from the vertical position will tend to twist the levers 59 relative to the upright looking bar and thereby form a gripping engagement with the locking bar 5!, then as the platform moves a slight distance the levers thus held to the apparatus.

plied to the particular rack bar on the corner of the expense involved in so doing, but I have prevented, then the rack bars will, one after will bring the clutch jaws into locking engagement with the locking bar, thereby preventing further downward movement and avoiding injury When the locking bar is thus gripped and held by the levers 59, and the motor continues to operate, the adjacent rack bar 45 is moved upwardly. If it should happen that such upward movement of the rack bar is appost adjacent the motor, then, obviously, the switch mechanism 4| will at once be operated to open the circuit. I have not applied a switch device 4| to each of the corner posts on account found in practice that this is unnecessary because when the conditions occur as before described and as illustrated in Figure 1, and further downward movement of the platform is crating satisfactorily and efficiently. I have repeatedly placed a four ton truck on my lift, and when the motor is running in one direction, the lift and its weight are slowly elevated, and when the motor is reversed, they are slowly lowered.

Duringth'is time the escapement device oscillates in unison with the escapement bar and causes only a minimum of friction and wear. repeatedly demonstrated that under the above conditions and when some part of the mechanism is removed to permit the platform and its weight to drop, at the instant when the rapidly oscillated downward movement commences, the escapement weight, due to its inertia, will not operate in time with the movement ordinarily imparted to it by the escapement shaft, and, hence, the escapement loop will bind upon the escapement bar and lock the escapement device to the escapement bar, and the clutch jaws will engage the locking bar in such manner as to stop further downward movement of the platform within a very' few inches, and no injury to the apparatus occurs under such conditions. I have also demonstrated that even though the locking barand the clutch jaws were covered with oil, the binding force applied to these lock bars is suificient to cause the gripping jaws to lock in their position and prevent such further downward movement.

In practice it sometimes occurs, after a mechanic has been working on the under side of an automobile upon the platform, that articles are left beneath the platform, such, for instance, as the mechanics tool chest, and I have repeatedly demonstrated in actual practice that when this "occurs and the motor is still running in the direction for lowering the lift, and when the downward movement of any one corner of the lift is thereby stopped, the rack bar in the upright post adjacent the motor will be elevated to throw the switch when the corner of the platform under which the obstruction has been placed is held only a few inches. above the other corners of the platform, and that this tilting movement of the platform relative to the corner posts does not in any way injure the apparatus.

I have provided a manually operated platform locking device as follows: 10 indicates a locking bar loosely mounted in slots in the upright ll, said slots having one extension ll extended downwardly and into the path of the platform, and another extension 12 extended downwardly and out of the path of the platform; a spring 13 holds the locking bar downwardly. On the platform is a hook 14 with an inclined surface 15 above it to engage the bar 10 and move it upwardly and laterally in the slot 1!. When the bar 10 is in the slot extension H and the hook 14 engages'it from above, the platform is locked in its elevated position. i s

In the event that an operator is required to work beneath the platform when in its elevated position, then the operator may grasp the manually operated lock bar and move it to its inwardly extended position in the path of the safety hook, and then when the platform arrives at a lower position it is automatically locked and there held, and when it is desired to lower the platform, it is first raised by the motor to release the locking hook from the locking bar, and then the locking bar is manually moved to position out of the path of the locking hook.

My improved lift is portable and can be installed on a floor by unskilled workmen very quickly and easily and with a minimum. of expense and, as frequently happens, after it has been once installed it is desirable tomove it. to a new location. One of the reasons why it is easy to erect and install my improved lift is that if it should happen that during the installation the I have uprights were not in a substantially vertical position and the motor was started, then the levers 59 would exert their gripping action upon the locking rod and prevent the operation of the lift without any injury thereto, but, of course, when this occurs, the operator installing the elevator would be required to place all of the uprights in substantially vertical positions before it can be made to operate, but after it has been installed in such a manner that it will operate, I have found that the uprights will stay in substantially upright position without further attention by the operator and, obviously, this simple and inexpensive installation as compared with the installation of a hydraulic lift is an important factor.

Any of the ordinary escapement devices and operating bars may be used in my lift for actuating the clutch jaws.

I claim as my invention:

1. In a lift apparatus, the combination of an upright support, a platform mounted upon the support for vertical movement, power-operated mechanism for moving the platform up and down at relatively low speed, and meansfor automatically locking the platform against downward movement at relatively higher speeds, said means comprising an upright escapement bar, an escapement device carried by the platform and capable of being operated as an escapement by the escapement bar during the normal speed of travel of the platform and permitting the escapement device to move vertically relative to the escapement bar and also capable of becoming inoperative as an escapement when the speed of travel of the platform becomes excessive and under such conditions of becoming fixed to the escapement bar, an upright locking bar, a clutch jaw operatively associated with the locking bar, means carried by said platform and connected to said clutch jaw. for moving the clutch jaw toward and from the locking bar, and means for operatively connecting the escapement device to said clutch jaw for moving the clutchjaw into locking engagement with the locking bar when the said platform moves downwardly and the es capement device is held by the escapement bar against downward movement.

2. In a lift apparatus, the combination of an upright support, a platform mounted upon the support for vertical movement, power-operated mechanism for moving the platform up and down at relatively low speed, and means for automatically locking the platform against downward movement at relatively higher speeds, said means comprising an upright escapement bar, an escapement device carried by the platform and capable of being operated as an escapement by the escapement bar during the normal speed of travel of the platform and permitting the escapement device to move vertically relative to the escapement bar and also capable of becoming inoperative as an escapement when the speed of travel of the platform becomes excessive and under such conditions of becoming fixed to the escapement bar, an upright locking bar, a clutch jaw operatively associated with the locking bar, means carried by said platform and connected to said clutch jaw for moving the clutch jaw toward, and from the locking bar, and means for operatively connecting the escapement device to said clutch jaw for moving the clutch jaw into locking engagement with the locking bar when the said platform moves downwardly and the escapement device is held by the escapement bar against downward movement, said escapement bar being suspended from its upper end and free at its lower end.

3. In a lift apparatus, the combination of an upright support, a platform mounted upon the support for vertical movement, power-operated mechanism for moving the platform up and down at relatively low speed, and means for automatically locking the platform against downward movement at relatively higher speeds, said means comprising an upright escapement bar, an escapement device carried by the platform and capable of being operated as an escapement by the escapement bar during the normal speed of travel of the platform and permitting the escapement device to move vertically relative to the escapement bar and also: capable of becoming inoperative as an escapement when the speeed of travel of the platform becomes excessive and under such conditions of becoming fixed to the escapement bar, an upright locking bar, a clutch jaw operatively associated with the locking bar, means carried by said platform and connected to said clutch jaw for moving the clutch jaw toward and from the locking bar, and means for operatively connecting the escapement device to said clutch jaw for moving the clutch jaw into locking engagement with the locking bar when the said platform moves downwardly and the escapement device is held by the escapement bar against downward movement, said locking bar being suspended at its upper end and free at its lower end.

4. In a lift apparatus, the combination of an upright support, a platform mounted upon the support for vertical movement, power-operated mechanism for moving the platform up and down at relatively low speed, and means for automatically locking the platform against downward movement at relatively higher speeds, said means comprising an upright escapement bar, an escapement device carried by the platform and capable of being operated as an escapement by the escapement bar during the normal speed of travel of the platform and permitting the escapement device to move vertically relative to the escapement bar and also capable of becoming inoperative as an escapement when the speed of travel of the platform becomes excessive and under such conditions of becoming fixed to the escapement bar, an upright locking bar, two parallel levers pivoted at one end to the platform and arranged on opposite sides of the locking bar, a clutch jaw pivoted between the outer ends of said lever and adjacent one side of the locking bar, a second clutch jaw pivoted between said levers adjacent the opposite edges of the locking bar, said escapement device including a frame in which it is supported, and said frame being pivotally connected to the last mentioned clutch jaw.

5. In a lift apparatus, the combination of an upright support, a platform mounted upon the support for vertical movement, power-operated mechanism for moving the platform up and down at relatively low speed, and means for automatically locking the platform against downward movement at relatively higher speeds, said means comprising an upright escapement bar, an escapement device carried by the platform and capable of being operated as an escapement by the escapment bar during the normal speed of travel of the platform and permitting the escapement device to move vertically relative to the escapement bar and also capable of becoming inoperative as an escapement when the speed of travel of the platform becomes excessive and under such conditions of becoming fixed to the escapement bar, an upright locking bar, two parallellevers pivoted at one end to the platform and arrangedon opposite sides of the lockin bar, a clutch jaw pivoted between the outer ends: of said lever and adjacent one side of the lockin bar, a second clutch jaw pivoted between said levers adjacent the opposite edges of the lockin bar, said escapement device including a frame in which it is supported, and said frame being pivotally connected to the last mentioned clutch jaw, the adjacent faces of said levers being positioned so close tothe sides of said'locking bar that when the platform to which the levers are pivoted is tilted a substantial distance relativeto the locking bar in one direction, said levers will exert a clutching and locking action upon the locking bar.

6. In a lift of the class described, the combination of an upright support, a platform, an upright rack carried by the upright support and capable of independent vertical movement relative thereto, a pinion carried by the platform and. in mesh with the rack, a motor for rotating said pinion, said parts being so arranged and positioned that when downward movement of the platform is stopped while the motor continues to operate, the pinion will move the rack upwardly, and a switch device for starting and stopping the motor operatively connected to the rack for moving the switch device to inoperative position when the rack is moved upwardly.

7. In a lift device, the combination of an n right, a platform, a rack bar suspended atits upper end upon the upright support and capable of moving upwardly relative tothe support, an electric motor carried by the platform, a pinion operatively connected to the motor and in mesh with the rack, and an electric switch in the electric motor circuit positioned to be moved to open position when said rack is moved upwardly.

8. In a lift, the combination of four upright corner posts, a rack bar suspended at its upper end within each corner post, one of said rack bars being capable of upward movement relative to its post, a platform, an electric motor carried by the platform, a pinion in mesh with each of said rack bars, gearing mechanism connecting the motor with each of said pinions, and an electric switch in the motor circuit positioned to be operated upon. upward movement of said movable rack bar for opening the circuit and whereby when downward movement of the platform is stopped with the motor still running, the circuit will be broken and the motor stopped.

9. In a lift apparatus, the combination of four corner uprights, a platform between the uprights, an upright rack bar in each corner upright, a pinion carried by the platform at each corner thereof and in mesh with the adjacent rack bar, means for jointly rotating said pinions, a hook carried by the platform, 'a locking bar manually movable from position out of the path of the said hook to position in the path'thereof, and a spring applied to said locking bar for holding it in position to enter said hook when the latter approaches said bar from above.

10. In a lift apparatus, the combination of four corner uprights, a platform between the uprights an upright rack bar in each corner upright, a pinion carried by the platform at each corner thereof and in mesh with the adjacent rack bar, means for jointly rotating said pinions, a plate carried by the platform at one corner and formed with a notch and with a downwardly inclined surface above the notch, a locking bar near the top-of the upright adjacent said plate, the upright being formed with slots in which said looking bar is loosely mounted, said slots being formed with one extension inclined downwardly and toward the path of said hook, and also with another extension inclined downwardly away from the path of said hook, and a spring fixed to the looking bar and extended downwardly and fixed to the upright.

11. In a lift apparatus, the combination of an upright support, a platform movable vertically relative to the upright, an escapement device carried by the platform, means for operating the escapement device during normal vertical movee ments of the platform, an upright locking bar, a clutch jaw carried by the'platform to cooperate with the locking bar, and means for moving the clutch jaw into locking engagement with the locking bar, said means being actuated by said escapement device when the platform moves downwardly at a speed greater than normal.

12. In a lift apparatus, the combination of a support, a vertically movable platform on the support, an escapement device, means for operating it as an escapement during the vertical movements of the platform at normal speeds, a gripping device for holding the platform against vertical movement, and means actuated by said escapement when'the platform is moved at a speed greater than normal for moving the gripping device to position for stopping further downward movement of the platform.

13. In a lift apparatus, the combination of a support, a vertically movable platform on the support, an escapement device, a weight forming part of said escapement device and controlling sameby its inertia, means for operating it as an escapement during the vertical movements of the platform at normal speeds, a gripping device for holding the platform against vertical movement, and means actuated by said escapement when the platform is moved at a speed greater than normal for moving the gripping device to position for stopping furtherdo-wnward movement of the platform.

14. In a lift apparatus, the combination of an upright support, a platform vertically movable relative to the support, an upright rack bar suspended from the upper portion of the upright and free at its lower end, a pinion carried by the platform and in mesh with the rack bar, and means for operating the pinion, said parts being so shaped and arranged that when the pinion is rotating in a direction for moving the platform downwardly, and downward movement of the platform is prevented, the pinion will elevate the rack bar.

15. In a lift apparatus, the combination of an upright support, a platform vertically movable relative to the support, an upright locking bar, two levers on opposite sides of the locking bar and carried by the platform, a gripping jaw carried by said levers and capable of being moved by said levers into gripping engagement with the locking bar, said levers being so positioned that when the platform is tilted relative to the upright they will frictionally engage. the locking bar so that further movement of the platform will cause the levers to bring the clutch jaw into locking engagement with the locking bar.

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