US2627943A

US2627943A - Lifting mechanism

Info

Publication number: US2627943A
Application number: US258791A
Authority: US
Inventors: Jr Russell Hastings
Original assignee: SHEPARD CO LEWIS
Current assignee: LEWIS-SHEPARD Co; SHEPARD CO LEWIS
Priority date: 1951-11-29
Filing date: 1951-11-29
Publication date: 1953-02-10
Anticipated expiration: 1970-02-10

Description

Feb. 10, 1953 R. HASTINGS, JR 2,627,943

LIFTING MECHANISM Filed Nov. 29, 1951 4 Shee ts-Sheet 1 IN VEN TOR.

X J MAzT,

BY 6 YW Q K,

4 77'0ENEYS Feb. 10, 1953 R. HASTINGS, JR 2,627,943

- LIFTING MECHANISM Filed NOV. 29, 1951 4 Sheets-Sheet 2 I INVENTOR. [I I, FIG. 5. BY

Feb. 10, 1953 R. HASTINGS, JR 2,627,943

LIFTING MECHANISM Filed Nov. 29, 1951 4 Sheets-Sheet 3 1 Mimi? m a In e-// X INVENTOR. mu M7} BY )1 6 7w 7 014;

4TTOP/VfYS Feb. 10, 1.953 R. HASTINGS, JR 2,627,943

LIFTING MECHANISM Filed Nov. 29, 1951 4 Sheets-Sheet 4 FIG. 8.

Patented Feb. 10, 1953 UNITED STATES PATENT OFFICE LIFTING MECHANISM Russell Hastings, Jr., Wellesley Hills, Mass., as-

signor to Lewis-Shepard Company, Watertown, Mass, a corporation of Massachusetts ApplicationNovember 29, 1951, Serial No. 258,791

13Claims. 1

This invention relates to improvements in an existing type of lifting mechanism occasionally employed in the construction of industrial lift trucks, stackers and like devices for elevating, stowing, transporting and otherwise handling merchandise and various articles of manufacture and parts thereof. In the type of mechanism referred to, the merchandise or other articles to be elevated are picked up by or deposited in a load-carriage vertically movable on an upright which is itself vertically movable on a stationary upright secured to the base of the mechanism and generally referred to as a mast. The lifting means in existing mechanisms of this type generally comprises a single hydraulic ram, a pair of chains each attached to the load-carriage at one end and at the other end to the plunger of the ram, and a number of idlers or sprockets around which each chain is successively passed in such manner that, when the ram is actuated, the load-carriage is first raised to the top of the movable upright at three times the speed at'which the ram plunger moves, and then the movable upright itself, together with said carriage, is elevated at the same relative speed along the mast.

As mechanism of this type has been constructed heretofore, its operation has not been wholly satisfactory because of a lack of smoothness in the movement of the load-carriage; instead of being smooth and even the movement would be jerky. This irregular movement is in effect a vibratory motion with a slow vibration rate of about two or three cycles per second. It may be initiated by any minute irregularity in the guideways of the uprights sufficient to cause a very slight increase of friction .between the operating parts; and it also may be initiated in either chain by the action of that chain in passing over an idler or sprocket, and once startedmay become more intense because of the combined effect of the elasticity in a long lifting chain and the variable friction in the operating members.

The object of the present improvements is to provide mechanism of the type aforesaidwhich, in operation, will be substantially free of these irregularities, to the end that the movement of the load-carriage continuously from its loading position to its discharging position and viceversa may be smooth and regular.

In practising my invention, I employ chains having articulate links rather than any other form of cable for reasons which it is not necessary to explain here. Hence, though in describing and illustrating my improvements I specifically refer to the use of chains as such, I do not wish to be understood as excluding the otheriforms of cables.

As shown in'the 'accompanying-drawings, mechanism of the type aforesaid. and containing my improvements is incorporated in an industrial lift truck whereof Fig. l is a perspective view showing the load-carriage raised to the top of the inner frame. Fig. 2 isa-front elevation; Figs..:3, i and '5 are elevations on a plane indicated-by-the line "lli inFig. 2, Fig. 3 showing the carriage in its leading position, Fig. 4 showing the carriage raised to the top of the inner frame, and Fig. 5 showing, the carriage and inner frame raised on the mast; Figs. 6, 7 and 8' are explanatory :d-iagrams; and Fig. 9 is a detail view on a larger scale showing the. ram plunger and its associated parts.

The mast ID which, as shown here, comprises a pair of upright channel bars firmly braced together to form a frame-like structure, is secured to a base H which, in case the mechanism is mounted on a truck, as here, maybe the truckbody. The channels of the mast face each other so as to provide guides for an inner frame or upright 52 which may likewise be composed of channel bars with their channels facing each other. This inner frame is fitted to the mast so as to be movable longitudinally thereof. The load-carriage !3 which, as here shown, is of the conventional forked-type customarily used in industrial lift trucks, stackers :and other related mechanisms, is fitted to the inner frame-so as to be movable longitudinally thereof while guided by the channels of that frame. To reduce. :friction, the parts guided by the-channelsmay vhe provided with the customaryrollers .(not: shown).

Each chain of the pair ['5 is of equal length and operatively connectedat one :endto the loadcarriage, thence passed successively around four idlers or sprockets and operatively attached at its other end to a crosshead 116 mounted on the plunger ll of a ram the cylinder 18 of which is secured to the base ll. Thev four :idlers for one of the chains and the four for the-otherchai-n together comprise four pairs of sprockets the respective pairs of which are denoted byt'he numerals I9, 20, 2! and 22, and both sprockets of any pair are identical in structure and dimensions. The pair iii is journaled on and near the top of the inner frame [2, the pair 2 0 on and near the bottom of that frame, the pair 2 l in bearing supports it depending from the crosshead I6, and the pair 22 in bearing supports '23 attached to the base H by anchor rods 14. The four sprockets over which one of the chains is looped lie in a single plane, the four over which the other chain is looped lie in a plane parallel to the first, and each chain runs, as shown, from the end thereof which is operatively attached to the load-carriage to and over one of the sprockets l9, thence in succession to and around one of each of the sprockets of the respective pairs 29, 2| and 22, and thence to the crosshead (6 to which its other end, as already stated, is attached.

I have observed that a contributing cause of the irregularities in the operation of the prior mechanisms of this type is the fact that all the runs of the chains did not lie parallel each to each and to the plunger of the ram; for I have found that by selecting idlers or sprockets having such relative dimensions that all the runs of the chains will be disposed in parallel relation to the plunger, said contributing cause may be removed. To this end, therefore, I use sprockets for the first, second and third pairs, i9, 26 and 2| respectively, having such relative pitch diameters that the pitch diameter of a sprocket of the second pair 20 plus the pitch diameter of a sprocket of the third pair 2| will be less than the pitch diameter of a sprocket of the first pair 19; and I make the pitch diameter of each sprocket of the fourth pair 22 less than the pitch diameter of each sprocket of the third pair 2|; in addition I secure the crosshead [6 to the ram plunger I! in such position relative-thereto, and attach the dead ends of the chains at such points 24 on the bearing supports I6 secured to the crosshead, that the distance (Figs. 4 and 9) from the longitudinal central line 25 of the ram to a line connectin the points 24 will be equal to (Zr-R) where r is the radius of a sprocket of the fourth pair 22, and R the radius of a sprocket of the third pair 2|. When the sprockets have these relative dimensions and the crosshead is mounted on the plunger in the position just defined, all the runs of the chains will lie parallel to each other and to the plunger of the ram and the mechanism will be more evenly balanced than hitherto. This arrangement, as I have found, will conduce to the smoothness of operation of the mechanism, provided the size of each of the idlers or sprockets is such that the pitch line of each is equal to an even number of pitch lengths of the chains; for unless this condition obtains, the chordal action of the chains, when pa sing over an idler r sprocket, will tend to develop a vibratory motion since the distance from the center or pitch line of the chain to the center line of the sprocket is continually changing. To

illustrate this chordal action, and how I prevent it from developing an irregularity in the movement of the chains, reference may be had to the diagrams of Figs. 6, 7 and 8. In these three diagrams, for the sake of illustration, the size of the sprocket S there shown is reduced to a pitch line of only four chain pitch lengths (a pitch length on the scale of these diagrams being the distance between the pitch points marked 23 and 30). These diagrams show that if the two lengths of the chain which depend from each side of the sprocket S are parallel and if the pitch line of that sprocket is equal to the sum of an even number or chain pitches, a uniform linear motion of one end of the chain will produce an equal and constant linear motion of the other end of the chain because the moment arm or distance from the center of the chain depending from one side of the sprocket to the center of the sprocket will at all times be equal to the corresponding moment arm at the other side of the sprocket. For example, as shown in Fig. 7, when the sprocket has rotated 22 /2 from the point P in Fig. 6, the effective moment arm at each side of the sprocket will have been reduced from the original distance B (Fig. 6) to a new distance .92R (Fig. '7) both of these equal moment arms giving a balanced condition. Again, when the rotation has progressed to (Fig. 8) the corresponding moment arms will become .71R on each side of the sprocket. In the example just referred to the two runs of the chain from the sprocket S are parallel and the pitch line of the sprocket is equal to an even number of pitches of the chain. With both of these conditions met, a uniform linear motion is provided when the chain passes over a sprocket.

As each successive pitch point first reaches and is engaged by a sprocket or idler, the corresponding pin of the chain starts to rotate through a few degrees, and this rotation continues until the next pitch point engages the sprocket or idler. Inasmuch as starting friction is greater than running friction, this tends to impart a slight jerk to the chains. Such jerk, because it is very slight, is inconsequential by itself, but if the chains are arranged so that a jerk occurs simultaneously in both chains, it is more likely to initiate a vibratory motion in the entire suspension especially if the frequency of these jerks is harmonically related to the natural period of vibration of the entire suspension, whereby a succession of slight jerks may develop into a substantial vibration. To prevent such jerks from occurring simultaneously in both chains, I make the connecting link 3! (Fig. 2) in which one of the chains terminates and through which that chain is operatively attached to the load-carriage, longer, by one-half a chain pitch, than the connecting link 32 by which the other chain is operatively attached to the load-carriage; and the lengths of the connecting links 33 and 34 (Fig. 2) by which the other ends of the chains are operatively attached to the crosshead 16, also differ by one-half a chain pitch. In this way each chain, so to speak, takes turn with respect to the engagement of its links with the respective sprockets or idlers over which they operate, and thus insures that the successive jerks of one chain will alternate with those of the other.

In addition, I provide an equalizer bar 21 which is interposed between the chains and the load carriage and to which the latter is pivoted at 23.

This bar not only insures that the tension on each chain will always be the same and centralizes the liftin force on the carriage, but also reduces, by its lever action, the magnitude of the jerks from each chain.

In practice I may fix the respective sizes of the sprockets as follows: I first determine the pitch line length, in terms of an even number of chain pitches, of the smallest size sprocket it is practicable to use. Assuming that for mechanism of a given capacity the pitch line length of the smallest size sprocket suitable for use is equal to fourteen chain pitch lengths, I use a sprocket of that size for the sprockets 22 and preferably also for the sprockets 20. Then for the sprockets 2! I use sprockets having a pitch line length equal to eighteen chain pitch lengths; and for the sprockets I9 I use sprockets having a pitch line length of thirty-six chain pitch lengths. In a case where the respective sizes of the sprockets are determined in this manner and the

sprockets

22 and 20 are of equa1 size and that size taken arena-43 5 as a unit or base, the size of the sprockets 2| will be greater than the sprockets 22 and the sprockets l9 twice the size of the sprockets 2|. But of course other relative sprocket sizes may be adopted in practising my improvements.

By the diagrams of Figures 6, '7 and 8 where, as shown, the chains depending from a sprocket or idler are parallel and the pitch line of the sprocket is equal to an even number of chain pitches, I have shown why under these conditions the mechanism will be evenly balanced. Referring again to those diagrams, it will be noted that at the pitch points of each depending chain the latter is tangent to the pitch circumference of the sprocket r idler at the same instant, as shown in Fig. 6. In the more general case, where the depending chains are not parallel, it will be obvious that the mechanism will also be evenly balanced provided that the relation between the pitch diameter of the sprocket or idler and the chain pitch is such that each dependent end of the chain will be tangent at its pitch points to the pitch circumference of the sprocket or idler at the same instant.

In operation: when the ram is actuated the load-carriage will be raised from its loading position (Fig. 3) to the top of the inner frame (Fig. 4) at three times the speed with which the plunger moves, while the inner frame will remain stationary. When the carriage reaches the top of the inner frame, its movement on the inner frame will be checked by the upper crossmember of the inner frame; then, as the plunger continues its upward movement, the inner frame together with the carriage will move up the mast (Fig. 5) without any break in the continuity of the movement of the carriage, or its speed, from its loading. position to its discharging position wherever the latter may be. The reason why the inner frame will remain stationary while the carriage is being raised to the top of the inner frame is that the load on the ram when the inner frame moves is greater by the weight of that frame than when the ram lifts the carriage alone. Heretofore, in mechanisms of this type it has invariablybeen necessary to provide means to latch the inner frame to the mast during the lifting of the carriage to the top of the inner frame, since the latter, but for the latch, would frequently, if not always, begin its movement prematurely. Since this is due either :to poorly balanced conditions within prior mechanisms of this type, or to the development therein of one or more of the irregularities pointed out above, or to both these causes, the utility of my improvements which remove these causes will be appreciated. Nevertheless the use of my improvements together with such latching means, should that be considered desirable for any reason, would still be within the scope of my invention.

In illustrating and describing the type of mechanism in which my improvements are to be incorporated, I have shown and described the ram as having its cylinder [8 secured to the base H. In such case the movable member of the ram will be its plunger l1. But since it is not unusual, in hydraulic lifting mechanism, to mount the ram so that its cylinder will be the movable member and its plunger the stationary member, I wish it understood that my improvements are applicable to mechanism of the type referred to irrespective of how the ram is mounted therein. I also wish it understood that while I prefer for practical reasons to use chains of articulate links 6 rather than other forms of cables in practising my improvements, I do not consider thatthe substitution of other forms of cables for the chains as such, removes the mechanism from the scope of my invention.

I claim-as my invention:

1. In a lifting mechanism of the type described which comprises a mast secured to the base of said mechanism, an upright fitted to and mmable longitudinally of the mast, a load-carriage fitted to and movable longitudinally of said .upright, a ram the stationary member of which .is secured to said base, a pair of equidiameter idlers journaled on and near the top of said upright, a second pair of equidiameter idlers 'journaled on and near the bottom of said upright, a third pair of equidiameter idlers journaled on the movable member of the ram, a fourth pair of equidi-ameter idlers the journal supports of. which are attached to said base, a pair of cables of equal length each of which is operatively-connected at one end to the load carriage, thence passed successively to and around an idler of the first, second, third and fourth pairs respectively and thence to the movable member of the ram to which 'its other end is operatively connected, the improvement in the aforesaid mechanism which consists in this, namely, that the sum of the pitch diameters of an idler of the second pair and an idler of the third pair is less than the pitch diameter of an idler of the first pair, that the pitch diameter of an idler of the fourth pair is less than the pitch diameter of an idler of the third pair, and that the distance between the longitudinal center line of the ram and .a line connecting the points where the cables are at,- tached to the ram is equal to two-thirds of the difference between the diameter of an idler of the fourth pair and the radius of an idler of the third pair.

2. The improvement defined in claim 1 wherein the movable member of the ram is its plunger and the stationary member is its cylinder, and wherein said cylinder is secured to the base of said mechanism and the cables operatively connected to said plunger.

3. The improvement defined in claim 1 wherein an equalizer bar is interposed between the cables and the load-carriage and to which the load-carriage is pivotally connected.

The improvement defined in claim 1 wherein the pitch diameters of each of the idlers. of the second and fourth pairs are equal, the pitch diameter of each idler of the third pair twosevenths greater than the pitch diameter of .an idler of the fourth pair, and the pitch diameter of each idler of the first pair twice the pitch diameter of an idler of the third pair.

5. In a lifting mechanism of the type described which comprises a mast secured to the base of said mechanism, an upright fitted to and movable longitudinally of the mast, a load-carriage fitted to and movable longitudinally of said upright, a ram the stationary member of which is secured to said base, a pair of equidiameter idlers journaled on and near the top of said upright, a second pair of equidiameter idlers journaled on and near the bottom of said upright, a third pair of equidiameter idlers journaled on the movable member of the ram, a fourth pair of equidiameter idlers the journal supports of which are attached to said base, a pair of cables of equal length each of which is operatively connected at one end to the load-carriage, thence passed successively to and around an idler of the first, second,

third and fourth pairs respectively and thence to the movable member of the ram to which its other end is operatively connected; the improvement in the aforesaid mechanism which consists in this, namely, that the pair of cables comprises two chains each of articulate links and having the same pitch, and that the pitch circumference of each idler is approximately equal to the sum of an even number of pitch lengths of the said chains.

6. The improvement defined in claim wherein an equalizer bar is interposed between the chains and the load-carriage and to which said carriage is pivotally connected.

7. The improvement defined in claim 5 wherein the diameters of each of the idlers of the second and fourth pairs are equal, the pitch diameter of each idler of the third pair two-sevenths greater than the pitch diameter of an idler of the fourth pair, and the pitch diameter of each idler of the first pair twice the pitch diameter of an idler of the third pair.

8. In a lifting mechanism of the type described which comprises a mast secured to the base of said mechanism, an upright fitted to and movable longitudinally of the mast, a load-carriage fitted to and movable longitudinally of said upright, a ram the stationary member of which is secured to said base, a pair of equidiameter idlers journaled on and near the top of said upright, a second pair of equidiameter idlers journaled on and near the bottom of said upright, a third pair of equidiameter idlers journaled on the movable member of the ram, a fourth pair of equidiameter idlers the journal supports of which are attached to said base, a pair of cables of equal length each of which is operatively connected at one end to the load-carriage, thence passed successively to and around an idler of the first, second, third and fourth pairs respectively and thence to the movable member of the ram to which its other end is operatively connected; the improvement in the aforesaid mechanism which consists in this, namely, that the pair of cables comprises two chains each of articulate links and having the same pitch and terminating in connecting links for operatively connecting the respective chains to the loadcarriage at one end and to the movable member of the ram at the other end, the lengths of the connecting links adjacent to the load-carriage differing from each other by one-half achain pitch, and the lengths of the connecting links adjacent to the movable member of the ram also differing from each other by one-half a chain pitch.

., 9. The improvement defined in claim 5 wherein each chain terminates in connecting links for operatively connecting the respective chains to the load-carriage at one end and to the movable member of the ram at the other end, the lengths of the connecting links adjacent to the loadcarriage diifering from each other by one-half a chain pitch, and the lengths of the connecting links adjacent to the movable member of the ram also differing from each other by one-half a chain pitch.

10. The improvement defined in claim 8 wherein an equalizer bar is interposed between the chains and the load-carriage and to which said carriage is pivotally connected.

11. In a lifting mechanism of the type described which comprises a mast secured to the base of said mechanism, an upright fitted to and movable longitudinally of the mast, a load-carriage fitted to and movable longitudinally of said upright, a ram the stationary member of which is secured to said base, a pair of equidiameter idlers journaled on and near the top of said upright, a second pair of equidiameter idlers journaled on and near the bottom of said upright, a third pair of equidiameter idlers journaled on the movable member of the ram, a fourth pair of equidiameter idlers the journal supports of which are attached to said base, a pair of cables of equal length each of which is operatively connected at one end to the load-carriage, thence passed successively to and around an idler of the first, second, third and fourth pairs respectively and thence to the movable member of the ram to which its other end is operatively connected; the improvement in the aforesaid mechanism which consists in this, namely, that the pair of cables comprise two chains each of articulate links and having the same pitch and the relation between the pitch diameter of each idler and the chain pitch being such that each end of the chain depending from an idler will be tangent to the pitch circumference of the idler at both pitch points at the same instant.

12. In a lifting mechanism of the type described which comprises a mast secured to the base of said mechanism, an upright fitted to and movable longitudinally of the mast, a load-carriage fitted to and movable longitudinally of said upright, a ram the stationary member of which is secured to said base, a pair of equidiameter idlers journaled on and near the top of said upright, a second pair of equidiameter idlers journaled on and near the bottom of said upright, a third pair of equidiameter idlers journaled on the movable member of the ram, a fourth pair of equidiameter idlers the journal supports of which are attached to said base, a pair of cables of equal length each of which is operatively connected at one end to the load-carriage, thence passed successively to and around an idler of the first, second, third and fourth pairsrespectively and thence to the movable member of the ram to which its other end is opertaively connected; the improvement in the aforesaid mechanism which consists in this, namely, that the pair of cables comprises two chains each of articulate links and having the same pitch and so disposed that the links of one chain are in staggered relation to the links of the other chain.

13. The improvement defined in claim 5 wherein the chains are so disposed that the links of one chain are in staggered relation to the links of the other chain.

' RUSSELL HASTINGS, J R.

No references cited.