Laboratory Jack

Abstract

A platform jack apparatus of the type using scissors-type mechanisms. The platform or load support is carried on the scissors mechanisms and means are provided for selectively actuating the scissors mechanisms to raise and lower the platform. The actuating means comprises a rotatably driven screw rod carrying nut members thereon. Connecting bars or links extend from the nut members to the lower ends of the scissors mechanisms so that rotation of the screw rod produces vertical movement of the platform. The relationship between the screw rod, the connecting links, and the scissors mechanisms is such that for any one load, the force input required is substantially constant throughout the platform's range of movement.

Description

The present invention is directed toward the art of lifting devices and, more particularly, to an improved platform-type jack.

The invention is especially suited for use as a laboratory jack for raising and lowering laboratory equipment and will be described with particular reference thereto; however, it should be appreciated that the invention is capable of broader application and could be used in many environments.

Relatively small size platform jacks are often used in laboratories for vertical positioning of laboratory equipment. Normally, the jacks have included a horizontal platform supported from a base by a pair of lazy-tong or scissors-type mechanisms. One or more drive screws were connected with the links of the mechanisms and arranged so that by rotating the screws the links were pulled together or pushed apart to raise and lower the platform. Generally, the pair of scissors mechanisms were positioned in parallel planes and spacer rods extended between the joints of the two mechanisms. The manually actuated drive screws passed through threaded openings in a horizontally aligned pair of the spacer rods. By turning the screws, the spacer rods were moved to drive the scissors' link mechanisms.

As can be appreciated, with the described relationship between the drive screws and the scissors mechanisms, the force required to rotate the rods varied depending upon the position of the scissors mechanisms. That is, for any one load on the platform, the rotational force varied as the elevation of the platform was changed. To further explain, when the platform was in its lowest position, the links of the scissors mechanisms were approaching parallelism with the drive screws. Consequently, a relatively large force was required to rotate the screws. On the other hand, as the platform was raised, the angle between the drive screws and the links increased. Thus, the force required was reduced.

The high force requirements present when the scissors mechanisms were in their contracted or platform-lowered position had the effect of substantially reducing the usefulness of these jacks. Additionally, for the same reason, if it were desired to actuate the drive screws with a motor, the motor had to be sized to meet the high force requirements at the platform-lowered position. Consequently, the motor was oversized throughout the major portion of the useful lifting length of the jack.

The present invention overcomes the noted problems. According to the invention there is provided a platform jack including at least one scissors mechanism having diagonally crossed links arranged to raise and lower the platform. The scissors mechanism is actuated by an improved drive linkage including at least one drive link member lying in a plane generally perpendicular to the plane of the crossed links. The drive link member is drivingly connected at one end to an end of one of the crossed links and its opposite end is pivotally connected to a drive nut carried on a rotatable drive screw extending in the plane of the link.

The described drive arrangement, as will hereafter more fully be explained, results in a substantially uniform drive force for the entire path of lifting movement. Consequently, if the unit is manually actuated, a weaker person can operate it successfully. Similarly, if the mechanism is to be provided with a motor, the motor can be of smaller size than that required by prior mechanisms.

Accordingly, a primary object of the invention is the provision of a scissors jack having a drive mechanism in which the input force required is substantially uniform throughout the entire extent of its elevational movement.

Another object of the invention is the provision of a jack of the type described which is particularly suited for motorized, remote-control operation.

A further object of the invention is the provision of a platform jack drive mechanism which is especially suited for small size jacks for use in laboratories and the like, but which can equally well be used in large jacks.

A still further object is the provision of a jack of the type referred to which is simple to construct and operate, as well as being rugged and reliable.

These and other objects and advantages will become apparent from the following description when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a pictorial view of a jack formed in accordance with a preferred embodiment of the invention;

FIG. 2 is a plan view of the jack shown in FIG. 1 with portions broken away to more clearly show the actuating linkage;

FIG. 3 is an end view of the jack shown in FIG. 1 with portions of the right-hand side broken away to show the scissors mechanism; and,

FIG. 4 is a cross-sectional view taken on line 4--4 of FIG. 3.

Referring more particularly to FIG. 1, the overall arrangement of the preferred embodiment of the jack is shown as including a horizontally extending base 10 and a support plate or a platform 12 which is supported above the base 10 by a scissors or lazy-tong-type mechanism 14. The scissors mechanism 14 is actuated to selectively raise or lower the platform 12 by a drive linkage mechanism 16. Preferably the drive linkage is driven by a reversible electric motor 18.

The details of base 10 form no part of the present invention. The base could have a variety of different constructions but is shown in the subject embodiment as comprised of a generally rectangular metal plate 20 which is of a size sufficient to carry both the link mechanism 14 and the motor 18. In the embodiment under consideration the plate 20, as well as the other main structural parts of the jack, are formed from aluminum so that the jack is relatively lightweight to permit it to be easily moved about the laboratory.

The platform 12 is shown as being defined by a rectangular metal plate 22. Obviously however, the support or platform portion of the jack could be of many shapes and configurations depending upon the intended use for the jack. As shown, the plate 22 is carried by a pair of angle members 24,26 which extends horizontally across the width of the plate 22. The angle members 24,26 are connected to the undersurface of the plate 22 in any convenient manner, such as, for example, through the use of machine screws 28. As shown, the machine screws 28 are received in recessed openings in the plate 22 so as to provide a smooth support surface.

As can be seen in FIGS. 1-4, similar angle members 30,32 extend transversely across the base plate 20. Although they could obviously be arranged differently and be of a different size, the angles 30,32 are shown as being substantially identical in size to the angles 24,26. Additionally, the angles 30,32 are spaced apart a distance corresponding to the spacing of the angles 24,26. Also, the angles 30,32 are connected to the base plate 20 by the use of flathead machine screws 34.

Extending between the base plate 20 and the top plate or platform 22 is a relatively conventional lazy-tong or scissors-type assemblies 14. In the embodiment shown, the mechanism 14 includes two scissors link mechanisms 36,38 which are positioned in spaced, parallel planes and extend between the opposed angle members 24,30 and 26,32 respectively. The mechanisms 36,38 are substantially identical in construction and each include four equal length links. The mechanism 36 is shown as comprised of four links 39-42 whereas the mechanism 38 is comprised of four substantially identical links 43-46. The links 39,40 and 43,44 are respectively diagonally crisscrossed and interconnected at their intersection by a spacer or tie bar 48. The links are pivotally connected to each other and the spacer bar 48 by machine screws 50 passing through openings in the links and into threaded openings in the ends of the bar. The links 41,42 and 45,46 are similarly crossed and interconnected at their midpoints by a spacer or tie bar 52. Bar 52 is pivotally connected to the links by machine screws 54 which extend through openings formed in the links and into threaded openings in the ends of the bar 52.

Connected between the upper ends of links 39,43 and the lower ends of links 42,46 is a tie bar 58. Bar 58 is pivotally connected by shoulder bolts 60 which pass through the openings in the ends of the links. The bolts 60 have accurately ground shoulders which act as pivots for the links. Similarly, the upper ends of links 40,44 and the lower ends of links 41,45 are interconnected by a spacer bar 62 connected at its ends to the links with shoulder bolts 64. Additionally, spring washers 66,68 are provided with the shoulder bolts 60,64. These washers maintain a constant lateral force or tension on the links and the heads of the shoulder bolts to minimize any sidewise movement of the links which would tend to decrease stability.

In the embodiment under consideration, the link mechanism 14 is connected at its lower end to the vertically extending legs of the angle plates 30,32. As shown, each of the plates 30,32 are provided with pairs of elongated grooves or guide slots 70,72. The guide slots extend horizontally and parallel to the base plate 20. Connected between the lower ends of the links 40 and 44 is a hexagonal bar member 74. As best shown in FIG. 2, the bar member 74 is provided at its ends with guides in the form of roller bearings 76,78 and the links. The lower ends of the opposite links 39,43 are similarly arranged and interconnected by a hexagonal bar 80 which is also provided with roller bearings 82 that are identical in arrangement to the previously mentioned rollers 76,78.

At the upper end of the mechanism 14 is similarly arranged and includes two hexagonal bars 90,92 (see FIG. 3) extending between the ends of links 42,46 and 41,45, respectively. These bars are also provided with roller bearings connected to their outer ends by machine screws and received in horizontal slots 94 and 96 formed in the downwardly extending legs of the angle plates 24,26.

The arrangement thus far described is relatively conventional and, as can be appreciated, by actuating a pair of the connector bars, for example, bars 58 and 62 toward and away from one another the elevation of the platform 12 can be varied. In the past, the usual actuating mechanism has included one or more screw rods passing horizontally between two of the tie members, for example, screw rods passing through threaded openings the tie members 74,80. By rotating the screws the mechanism could be raised and lowered.

One of the primary drawbacks of this particular type of prior mechanism was that when the mechanism is in its lowermost position (i.e., with the platform down) the links of the scissors mechanism are nearly horizontal. Consequently, when it is desired to elevate the platform from this lowermost position, the parts are in a relationship wherein extremely high forces must be applied to the horizontal drive screws to produce an elevating movement of the platform. That is, the mechanism is nearly at a dead center position. However, as the mechanism approaches its fully elevated position the force required becomes substantially less since the scissors links are approaching vertical alignment. Thus, throughout the full extension of the mechanism the force required to lift any particular weight varies substantially. This has been a distinct drawback with this particular type of jack mechanism. Additionally, it has made it extremely difficult to convert to power operation since the motors provided had to be strong enough to actuate the mechanism at the lowermost position wherein an extremely high force was not required throughout the major portion of the actuation.

The subject invention overcomes the prior problems and provides an actuating mechanism which permits a substantially constant force to raise or move the platform throughout the full range of extension. Although, according to the invention, the mechanism could have a variety of specific designs and layouts, the preferred embodiment is as best shown in FIGS. 1 and 2. In particular, the mechanism includes a first drive screw member 100 which lies in a plane perpendicular to the plane of the mechanisms 36,38. Screw member 100 extends between the upwardly extending legs of the angles 30,32, respectively. Additionally, an intermediate support 104 is provided with a bearing 106 and positioned centrally of the rod 100. The support 104 is merely a section of angle member which is connected to the lower plate by a pair of machine screws 108.

Carried on the screw rod 100 are a pair of drive nut members 110 and 112 (See FIGS. 1 and 4). Extending laterally from the drive nut members are pairs of drive links 114 pivotally connected at their inner ends to the outer portions of the drive nuts 110. The outer ends of the links 114 are received in elongated grooves or slots 120 formed in the drive bars 74,80. Pivot pins 122 extend downwardly through the bars 74,80 to pivotally connect the bars 114 thereto. The bars 116 are similarly connected to the drive nut 112 and extend to slots 130 formed in the bars 74,80. Pivot pins 132 extend downwardly to pivotally connect the bars 116 to the respective bars 74,80.

At the upper end of the scissors assembly 14 there is provided a guide assembly 131. The assembly 131 can best be understood from FIGS. 2-4. The assembly functions to constrain the upper ends of the links of the scissors assembly to have equal and opposite relative movement with reference to the centerline of the platform 12. In particularly, the assembly includes a central guide rod 133 which extends between the angle members 24 and 26. The rod 133 is supported centrally by an angle member 135. Slidably mounted on the rod are guide blocks 137. The blocks 137 are each connected to the bars 90,92 by pairs of links 139. As can be seen from FIG. 2, the links 139 are pivotally connected in the same manner as previously mentioned links 114.

Referring again to the drive screw 100 it will be appreciated that opposite ends of the drive screw 100 are threaded oppositely (e.g., the right-hand end as viewed in FIG. 2 is threaded with a right-hand thread whereas the left-hand end has a left-hand thread). Accordingly, rotation of the screw 100 causes the drive nuts 110,112 to be simultaneously moved toward and away from one another. Consequently, the links 114,116 are moved to cause the bars 74,80 to move toward and away from one another to cause extension and retraction of the scissors mechanism 14.

The operation and advantages of the drive mechanism can best be understood by reference to FIG. 2. Assume that the mechanism is in the retracted or platform-lowered position. At this time the drive nut 110 is in the position shown dotted and identified with the reference numeral 110'. The links of the respective scissors mechanism 36,38 are in the position where they extend nearly horizontally. Consequently, as previously mentioned, the force which must be applied to move the links toward one another to elevate the platform 12 is at a maximum. Referring again to the location of the drive nut 110 shown dotted in FIG. 2, it will be seen that at this time the links 114 are generally somewhat in alignment and, consequently, the component of force acting in the direction perpendicular to the direction of movement of the drive nut is at a maximum. As the nut 110 is moved toward the solid line position, the noted force component is reduced because of the changing angular relationship between the links 114 and 116. Simultaneously however, the links of the scissors mechanisms 36,38 are moving to a more vertical position such as shown in FIG. 1. Thus, the mechanical advantage of scissors mechanism is increasing so that the actuating force required to extend the scissors mechanism is reducing. The result is that the drive mechanism and the scissors mechanism are complementary and the platform can be moved throughout its entire range of movement with a relatively constant force input to the screw 100.

It would be possible to use one or any odd number of drive link assemblies; however it is much preferable to use an even number such as shown. This is because by the use of an even number the forces applied to the hexagonal bars can be equally distributed. Note that the components of force applied by the drive links are exactly equal. The components which act perpendicular to the bars 74 and 80 are additive. Those that act perpendicular to the bars are equal and opposite, thereby preventing lateral loads on the roller bearings or twisting of the bearings in the guide grooves or slots.

Although the drive screw 100 could be manually rotated it is preferable to provide a reversible electric motor 18 carried on the base plate 20 and provided with a housing 19. As best shown in FIG. 2, the motor 18 has its output shaft 150 connected to a reduced-diameter end portion 152 of the drive shaft 100 by a conventional coupling 154. The motor is supplied with current through a cord 156. Shown carried on the front face of housing 19 is the usually off-on switch 158 and a reversing switch 160.

Many additional types of controls or features can be provided with the jack assembly. For example limit switches can be arranged for actuation by the drive nuts at the opposite ends of travel to automatically stop the motor when the jack is in its fully extended or fully lowered positions. Likewise, extension control cables can be added so that the unit can be controlled from a remote hand-held or foot-actuated switch.

Claims

Having thus described my invention, I claim:

1. A load-lifting jack comprising a base, a load supporting platform;

means supporting said platform on said base for movement toward and away from said base;

said supporting means including at least one pair of first and second diagonally crossed links with one end of each of said links operatively supported on said base and the other end of each of said links operatively connected to said platform whereby movement of the base-supported ends of said links toward each other causes movement of said platform away from said base;

a pair of toggle links defining a toggle linkage means supported on said base with one end of one of said toggle links being connected to one of said crossed links and one end of the other of said toggle links being connected to the other of said crossed links;

means interconnecting the other ends of said toggle links;

actuating means connected to said connected ends of said toggle links for moving said toggle links toward and away from each other;

said toggle linkage means being so arranged that said toggle links move toward a collapsed condition when said platform moves away from said base.

2. The jack of claim 1 wherein said toggle links lie in a plane generally perpendicular to the plane of said crossed links.

3. The jack of claim 2 wherein said actuating means comprises a rotatable drive screw, and said interconnecting means includes a drive nut carried on the drive screw and movable therealong.

4. The jack of claim 3 and further including reversible motor means for rotating said drive screw.

5. The jack of claim 1 wherein said supporting means for said platform further includes a second pair of first and second diagonally crossed links operatively connected to said base and said platform, and

a second pair of toggle links defining a second toggle linkage means operatively connected to said second pair of crossed links for moving the ends of said crossed links toward and away from each other;

said second toggle linkage means being arranged such that the ends of said second pair of crossed links move toward each other as said toggle linkage means is collapsed.