US2211474A

US2211474A - Lifting platform

Info

Publication number: US2211474A
Application number: US272087A
Authority: US
Inventors: Muller Willy
Original assignee: ELWA ELEKTRO AG
Current assignee: ELWA ELEKTRO AG; ELWA-ELEKTRO AG
Priority date: 1938-07-31
Filing date: 1939-05-06
Publication date: 1940-08-13
Anticipated expiration: 1957-08-13
Also published as: NL52135C; DE751012C; FR855121A; CH211997A

Description

Aug. 13, 1940. w. MULLER LIFTING PLATFORM Filed May 6, 1939 5 Sheets-Sheet 1 Aug. 13, 1940. w, MULLER LIFTING PLATFORM Filed May 6, 1959 5 Sheets-Sheet 2 Aug. 13, 1940. w. MULLER 2,211,474

LIFTING PLATFORM Filed May 6, 1939 5 Sheets-Sheet 3 Aug. 13, 1940. w MULLER 2,211,474

LIFTING PLATFORM Filed May 6, 1939 5 Sheets-Sheet 4 Aug. 13, 1940. w. MULLER LIFTING PLATFORM Filed May 6, 1939 5 Sheets-Sheet 5 1 wS RQ AI. M

Patented Aug. 13, 1940 UNITED STATES PATENT OFFlCE A 2,211,414 LIFTING PLATFORM Application May 6, 1939, Serial No. 272,087 In Germany July 30, 1938 7 Claims.

The invention relates to low, transportable lifting platforms or hoists intended especially for hoisting power-driven vehicles and having a jacking frame in the form of an articulated parallelogram, wherein the supporting frame is connected to the foundation frame by means of swinging supports, and the erecting from the folded position is effected by means of rollers which are driven in between the swinging supports and inclined tracks located upon the foundatlon frame, in the manner of wedges.

In the known lifting platforms of this kind the inclined track consists of a straight path inclined to about to degrees, the highest point of which lies at a higher level than the highest point of the platform in the folded position. The initial erecting movement is effected by means of the said inclined track as the effect of a force is extremely unfavourable at the beginning of the lifting motion, that is to say especially in the lower half of the lifting range of the platform namely, on and immediately after passing above the said track. During the further raising of the supporting frame, a piston rod provided for the erecting and the spindle of the roller articulated to the said piston rod, enter a groove made in the swinging support, so that from that moment on the further movement of the supporting platform is effected along an arc of a circle the centre of which is the stationary centre of rotation of the swinging support. Owing to this arrangement the greatest force must be applied at the commencement of the raising operation, the said force diminishing as the roller approaches the highest point of the inclined track, and then suddenly increasing again to maximum value as the roller is lifted off the inclined track, and-finally diminishing greatly up to the end of the inclined track, and finally diminishing greatly up to the end of the lifting movement. The ratio of the peak forces to the mean value is thus considerably greater than unity and in addition rather unfavourable. All the parts of the lifting platform must be dimensioned according to the peak forces, and the driving requires a hydraulic jack which considerably decreases the transportability of the lifting platform. Furthermore, as the piston rod acting upon the roller must have the same swinging motion as the supporting platform at the outer end of the swinging support which is articulated to the supporting frame, 1. e. along an arc whose radius is the length of the swinging support, it must be made pivotable together with the hydraulic device or the cylinder thereof.

In order to produce a more satisfactory ratio of forces, that is to say to flatten the power peak occurring when the roller is lifted from the inclined track, it has also been proposed in such an arrangement to allow the inclined track to rise at about degrees and to join to the upper end thereof a lever controlled by the swinging support by means of connecting rods and forming an extension of the inclined track. This foldable arrangement of the extension of the inclined track is intended to keep the height of the lifting platform in the folded down position as low as possible.

In another similar known lifting platform commonly known as Woods cradle for which a hydraulic drive must also be provided, the ratio of forces is still more unsatisfactory than in the platform hereinbefore described, as it is provided with an inclined track in the form of a straight line which has a gentle slope with respect to the centre of the rotation of the swinging support, and is located below the foundation frame and co-operates during the raising of the .swinging support by means of the roller with the curved track arranged upon the swinging support, the said curved track having its maximum height, 1. e. its maximum distance from the central axis or line connecting the points of articulation of the swinging support, near the centre of rotation located on a level with the foundation frame, and flattening in the direction of the points of articulation of the swinging support to the supporting frame.

The force to be exerted for the raising movement in this form of lifting device increases from the commencement to the end of the pivoting movement of the swinging support approximately along a straight line, that is to say the ratio of the power peak to the mean value is considerably greater than unity.

As the entire pulling or pushing mechanism must be dimensioned in proportion to the peak forces, a diagram line which is as far as possible horizontal, contrary to the diagrams of forces of the known lifting trucks, is decisive and desirable for the manufacture of a light lifting platform.

The lifting platform hereinbefore mentioned and having the Woods cradle requires anchoring in the ground, or it will be too high, and this is detrimental to transportability.

The aim of the invention is to produce a transportable variable, light lifting platform having a low height which can be driven direct by means of an electro-motor thus avoiding hydraulicgears, and affording unobstructed accessibility to the lower parts of the raised vehicle by keeping the space enclosed by the supporting and foundation frames clear of driving mechanisms.

The invention ensures this and is characterised in that the inclined tracks are each in the form of a gradually ascending guide track having substantially the shape of a cissoid or extended cycloid which commences at a distance of about two-thirds of the length of the swinging support from the center of rotation thereof, and reaches its maximum height near the vertical line drawn through the centre of rotation of the swinging support, the said maximum height only slightly exceeding the height of the foundation frame, so that the point of contact of the roller with the swinging support continuously approaches the pivotal point of the said support in such a manner that therequired effort is approximately constant over the whole lifting range, i. e. the ratio of the maximum force to the mean value approximates to unity.

In this manner easy transportability, due to a reduction in weight, and minimum height can be combined without diificulty when the roller traverses its whole path along such a guide track,

the latter being, for the purpose of obtaining the optimum value, as far as possible increased in height towards its end without however thereby increasing the overall height of the platform. According to the invention this is possible by employing two parallel curved tracks arranged on opposite sides of the swinging support so that the latter can pass down between them to some extent when in the folded position.

In order to obtain the optimum value and a curve of the ratio of force and distance, extending as far as possible in a straight and approximately horizontal line, the guide track is given, at its commencement, a steep cycloidal ascending gradient, and towards its end beyond the maximum height a slightly descending gradient, so that the point of attack of the roller in the initial position approaches nearer to the centre of rotation of the swinging support compared with, for example, an extended cycloid, thus reducing the length of the lever arm and increasing the force.

The constructional form of the lifting platform or hoist according to the invention is preferably attained by causing the draw spindle which is driven by an eleotromotor and arranged horizontally between the curved tracks below the swinging support, to act upon the axle which connects the two rollers running upon the curved tracks, by means of a push rod attached to the end of the draw spindle, the said axle carrying rollers which run upon the swinging support, and being preferably connected by means of a pull-rod to the axle of a second pair of rollers which at the same time run upon curved tracks for the purpose of raising and lowering the second swinging support on the same side of the platform.

The articulating of the push rod which is formed of two parallel struts to the end of the spindle may be suitably effected by means of a link fork or the like, which on both sides of an auxiliary roller running upon the foundation frame acts upon the axle of the said roller, the said axle connecting the stays of the push rod.

In this manner the push rod is allowed to work at a satisfactory angle, the draw spindle driven by the electromotor remaining in a horizontal position, so that the arrangement eliminates a swinging device which would make the drive more expensive and so that the spindle can be mounted in the simplest possible manner.

Finally it must be mentioned that the rollers may have a relatively large diameter, which in combination with a relatively large width ensures a low surface load.

The drawings illustrate one constructional form of a lifting platform according to the invention shown diagrammatically by way of example and the curve of forces is shown by means of a working diagram compared with the working diagrams of other known lifting platforms.

Figure 1 illustrates a side view of the lifting platform,

Figure 2 Figure 1,

Figure 3 is a side elevation of the lifting device partly broken away and to a larger scale and showing in dotted lines various stages of lifting.

Figure 4 is a fragmentary top plan view according to Figure 3.

Figure 5 is a side view of a portion of the lifting platform. and shows the supporting rollers and the varying ratios of forces for different positions on the guide curve, and shows the resolution of the lifting forces in each of said positions,

Figure 6 is a diagram showing the lifting force in each of the six positions of the supporting rollers illustrated in Figure 5,

Figures 7 and 8 illustrate in the same manner the varying ratios of forces for different positions of the supporting rollers in a known lifting plat form having an inclined surface for guiding the roller up to a height somewhat above the greatest height of the folded platform.

Figures 9 and 10 are similar to Figures 7 and 8 respectively, but relate to a lifting platform having an inclined surface more extended and steeper than that shown in Figure 7.

Figures 11 and 12 illustrate a force diagram for another known lifting platform having a Woods cradle and Figure 13 illustrates a modification of the curved track according to the invention.

Referring to the drawings I is the foundation frame of the transportable lifting platform or hoist and 2 the supporting frame by means of which a vehicle or the like is to be raised. The supporting frame or platform 2 is connected to the foundation frame i by means of swinging

supports

3, 3 in the manner of an articulated parallelogram or parallel motion linkage with pivoting points at 4. 5 are inclined runways or flaps by means of which the vehicle can be run on to the supporting frame when the platform is folded, one of these inclined runways being firmly attached to and raised together with the supporting frame, as indicated in dotted lines in Figure 1. In the folded condition the platform is approximately 30 cm. high.

The lifting mechanism for erecting the frame 2 by means of the swinging supports 3, 3' consists of curved tracks 6 attached to the foundation frame i, the said tracks having gradually ascending guide surfaces 1 (Figures 3 and 13), approximatelyof the shape of a cissoid or extended cyicloid, which for the purpose of obtaining maximum lifting value while approaching the centre of rotation of the swinging support 3 may be in the form of a steep cycloid at the commencement and after reaching maximum height descend slightly toward the end, as shown in Figure 13 in comparison with Figures 3 and 5. The curved is a top plan view according to tracks 8 are each arranged on both sides of the swinging supports (Figure 4) so that in the folded position of the lifting platform the swinging supports lie between the said curved tracks 8, the highest point of the said curved track not exceeding the height of the supporting frame when the lifting platform is folded down. The curved track 8 extends over a length of approximately two thirds of the length of the swinging support. Rollers 8 co-operate with the curved tracks and are mounted on a common shaft 8 (Figure 4) two further rollers it being mounted between the rollers 8 on the same shaft, the swinging supports being supported by the rollers It. When lifting the supporting frame 2 the rollers 8 rotate in one direction and the rollers ill in the opposite direction. The rollers 8 and Ill may possess a relatively large diameter as the swinging support 3 moves between the curved tracks 6; in this manner a low height is obtained for the lifting platform in the folded down position. On the shaft 9 there are located in addition, outside of the rollers l8, two parallel members ii forming the push rod for the rollers ill, the opposite end of these members il being connected together by means of a pin l2, carrying an auxiliary roller 53, running on the foundation frame i. The push rod H is coupled to the horizontal draw spindle I! by means of a link fork or the like it acting upon the pin i2, the draw spindle being in suitable manner movable in longitudinal direction and adapted to be driven at it by means of a chain wheel directly from an electromotor or the like. On the shaft 9 there are further mounted pull rods ll leading to the lifting device for the swinging support 3' and these may carry rollers 8 at their ends similar to the arrangement shown in Figure 4; the pull rods I! may however alternatively be articulated to the swinging supports 3', so that the latter work in known manner as drag supports. It is however preferable to arrange for a lifting device having curved tracks 6 and rollers 8, I0 also for the swinging support 3'.-

Figure 5 shows six different positions of the roller 8 on the guiding curve 1 and shows further the corresponding positions of the swinging support 3. The investigations by graphic method show in the polygons of forces or triangles of forces on the upper end of the swinging support, the resolution of the vertical force (exerted by the weight of the vehicle on the platform of the hoist) into a component in the direction of the swinging support and into a component, which acts vertically thereto on the end of the swinging support and which produces a moment on the swinging support (see numbers 7.5, 12, 15, 17, 19, 20, which show the augmentation of the said moment by the lowering of the platform 2 in the ratio to the vertical force, which latter remains the same).

- The said vertical force reacts against the said roller in the ratio of the whole distance of the swinging support to the distance of theroller from the turning point of the swinging support. This force resulting from this latter ratio, resolves into a component, which acts radially to the curvature of the guide I, and into a component in the direction of the push rod I I. This latter force again resolves into a small component on the auxiliary roller l3 in the direction vertically to the base frame I and into the tension force acting along the draw spindle ii.

The numbers 1-6, shown in Fig. 5 in a smaller scale parallel to the base frame i, show the different corresponding positions of the turning axis of the auxiliary roller l3 according to the shown different positions of the roller 8 on the guiding track I and acting to the swinging support 8. Near the rollers are shown the polygons or triangles of forces pertinent to the positions 1-6, and in which some components are indicated with 22, 21 and 3|, which appear in corresponding work diagram of Fig. 6.

As may be seen from Figure 6 the effort required for lifting the supporting frame is approximately constant over the entire lifting range. The mean value of this effort is indicated by a dotted horizontal line. The peak of the force still further approaches this mean value when the guide curve 1 is given the form illustrated in Figure 13 as a modification of the form shown in Figure 5, and wherein the track after reaching a maximum value descends slightly toward the rear end; by making the guide track 1 somewhat steeper at the beginning and moving it slightly towards the centre of rotation 4, the effort required for the commencement of the lifting is also brought nearer to the mean value.

In the diagram of Figure 12 the mean value is also indicated by a horizontal dotted line, and the great difference in the power curve of the lifting platform according to the invention can be easily seen when comparing it with the power peak and the force to be exerted at the beginning of the lifting movement. The ratios shown in the diagrams in Figures 8 and 9 are somewhat more satisfactory than in Figure 12, but also in these the value is not nearly so satisfactory as in Figure 6.

In Figure 9 the inclined surface is illustrated for simplicitys sake in a manner similar to that of Figure '7, but it incorporates the known extension in the form of a lever described in the description, at the top of the inclined surface as in Figure 7.

I claim:

1. A lifting platform comprising a foundation frame, a supporting frame, swinging supports for said latter frame forming a parallel motion linkage between said frames, pushing rollers acting against said swinging supports to elevate said supporting frame from folded position close to said foundation frame to elevated position, and means for guiding said pushing rollers along gradually ascending substantially cissoid paths during their lifting movement.

2. A lifting platform comprising a foundation frame, a supporting frame, swinging supports between said frames forming a parallel motion linkage, and permitting movement of said supporting frame from folded position close to said foundation frame to elevated position, inclined tracks fixed with respect to said foundation frame, and having gradually ascending guide surfaces respectively substantially in the shape of cissoids, and roller means acting as wedges between said swinging supports and said guide surfaces and movable into position to elevate said supporting frame.

3. A lifting platform for power driven vehicles comprising a foundation frame, a supporting frame, swinging supports between said frames forming a parallel motion linkage permitting movement of said supporting frame from folded position close to said foundation frame to elevated position, inclined tracks secured to said foundation frame, and having gradually ascending guide surfaces respectively substantially in the shape of cissoids, roller means acting as wedges between said swinging supports and said guide surfaces, and movable into position to elevate said supporting frame, said guide surfaces commencing at a distance of approximately twothirds of the length of said swinging supports from the center of rotation thereof, and reaching a maximum height near the vertical plane of said center, said maximum height exceeding the height of said foundation frame only slightly, whereby the points of contact between said roller means and said swinging supports continuously approach said center and the required lifting effort is approximately constant over substantially the whole lifting range.

4. A lifting platform as claimed in claim 3 characterized in that said guide surfaces each ascends steeply at its commencement substantially in the form of a cycloid, said commencement being brought closer to said center of rotation, and said guide surfaces after reaching their highest point descending slightly towards their ends.

5. A transportable lifting platform adapted especially for power driven vehicles comprising a foundation frame, a supporting frame, swinging supports between said frames forming a parallel motion linkage, and permitting movement of said supporting frame from folded position close to said foundation frame to elevated position, a pair of inclined tracks fixed to said foundation frame and disposed on opposite sides of each of said swinging supports to permit said supports to pass down between said tracks to some extent when in folded position, each of said tracks having a gradually ascending guide surface substantially in the shape of a cissold, and roller means acting as wedges between said swinging supports and said guiding surfaces and movable into position to elevate said suppo frame- 6. In a transportable lifting platform intended especially for power driven vehicles, the combinatlon comprising a foundation frame, a supporting frame, a pair of swinging supports between said frames near each end thereof forming a parallel motion linkage, and permitting movement of said supporting frame from folded position close to said foundation to elevated position, a pair of inclined tracks fixed to said foundation frame near each end of said latter frame, and 1 each having a gradually ascending guide surface substantially in the shape of a cissoid, a draw spindle arranged substantially horizontally between said tracks below said swinging supports, a shaft mounted transversely with respect to said 1 spindle, a pair of rollers on said shaft riding on one of said pair of tracks respectively, a push rod connecting the free end of said draw spindle and said shaft, one or more rollers on said shaft riding in engagement with one of said swinging sup- 2 ports, whereby said first mentioned rollers and said last mentioned rollers rotate in opposite directions during elevating movement of said supporting frame, a second shaft mounted transversely with respect to said spindle, roller means 2 on said latter shaft riding over the other pair of tracks respectively and in engagement with the other pair of swinging supports, and a pull rod extending between and connected to said shafts.

7. The combination as claimed in claim 6 3 characterized in that the articulation between said draw spindle and said push rod includes a fork extension on said draw spindle, a pin conmeeting saidfork and said push rod, and an auxiliary roller supported on said pin and riding over 3 said foundation frame.

WILLY MULLER.