WO1988000170A1

WO1988000170A1 - Lifting mechanism

Info

Publication number: WO1988000170A1
Application number: PCT/SE1987/000312
Authority: WO
Inventors: Per-Olof Sehlstedt
Original assignee: Sehlstedt Per Olof
Priority date: 1986-07-04
Filing date: 1987-07-01
Publication date: 1988-01-14
Also published as: SE8602983L; DK85988A; SE8602983D0; SE456342B; DK85988D0

Abstract

A lifting mechanism of the kind which includes two scissor arms (4, 6) hingedly connected to each other and in which the lifting movement takes place in two steps, i.e. a first step where the lifting is accomplished in that rollers (21a, 21b) rotatably connected to a transverse shaft (19) are rolling up along oblique surfaces (23) of one of the scissor arms (4) whereas the lifting movement in a second step is accomplished in that said shaft (19) directly transmits power to one of the scissor arms (6) and where the shaft extends through an oblong hole (20) in said scissor arm (6). According to the invention one of the scissor arms consists of a U-shaped beam (6) having the web portion thereof directed upwardly and said oblong holes (20) being provided in the downwardly directed flanges of the U-shaped beam. The shaft (19) extends through a sliding block (18) displaceable in the U-shaped beam said sliding block at the end of the first lifting movement coming into contact with a stop (22) provided in the U-shaped beam and owing to the fact that the diameter of the shaft (19) is somewhat inferior to the width of the oblong hole contact between the shaft and the wall portions surrounding the hole (20) in the U-shaped beam is prevented.

Description

Lifting mechanism

The present invention refers to a lifting mechanism and more specifically to a device of such character which includes at least two pairs of scissor arms pivotally connected to each other by means of a joint or a shaft and provided to cooperate in raising or lowering a table or the like in relation to an underlying base portion by means of at least one longitudinally extensible power transmission device, for example, a hydraulic cylinder, the two scissor ends extending backwards from the joint being fixedly but hingedly connected to the table and the base portion, respectively whereas the opposite ends of the arms are movable, for example by rollers, along the base portion and whereas a shaft extending transversely of the direction of action of the power transmission device is connected to said power transmission device, said shaft extending through an oblong hole in one of the scissor arms and being provided to cooperate by means of rollers or the like with a slideway which preferably is connected to the other one of the scissor arms so as to accomplish by means of the rollers rolling along the slideway and on displacement of the shaft from a position in which the scissor arms are in one plane that at least one of the scissor arms is swung to a position in which a substantial moment arm has been established between the shaft and the joint between the scissor arms.

A lifting mechanism of the kind referred to is disclosed in SE 83.04655-7. The mechanism in question functions well but has some serious disadvantages. One of these is that the transverse shaft transmits the power to one of the scissor arms by sliding against the upper surface limiting the oblong hole in one of the scissor arms. This is disadvantageous since the shaft like the scissor arm in question is made from steel and further since the contact surface between the arm and said upper surface is limited which also gives high surface pressures. A further drawback is that the lifting table disclosed in said patent publication although it may be made low has to be relatively wide.

The primary object of the present invention has been to create a lifting mechanism which does not have said disadvantages and which further may be manufactured at relatively low costs and in a rugged shape. In order to achieve this and further objects the invention has the characteristics of the claims.

The accompanying drawing illustrates an exemplary embodiment of the invention.

Fig. 1 is a schematical side view of a lifting table made according to the invention whereas

Fig. 2 is a perspective partial view of the mechanism in a folded position.

The lifting table illustrated in the drawing includes a base portion generally designated as 1. Said base portion has upwardly directed bearing brackets 2 for a horizontal shaft 3 about which is pivotally mounted a first scissor arm 4 which as will become clear from the following description comprises two parallel upended rails which preferably by means of spacing means (not shown) are kept at a predetermined distance from each other. This first scissor arm is by means of a shaft 5 pivotally connected to a second scissor arm 6, which consists of a channel beam located upside down. Adjacent to one free end thereof this scissor arm 6 has a sliding block 8 which as appears from fig. 1 is intended to slide along a planar surface of the base portion. In the opposite end thereof the scissor arm 6 is hingedly connected to a lifting plate generally designated 10 about a shaft 9. The first scissor arm 4 has near to the free end thereof a sliding block 12 which is pivotall y mounted about a shaft 11 and is provided to slide along a planar under side of the lifting plate 10.

A hydraulic cylinder generally designated as 13 has the piston rod 15 thereof hingedly connected to the scissor arm 5 preferably about the same shaft 3, about which the scissor arm 4 is pivotally mounted.

The plunger 15 of the hydraulic unit is connected to a yoke 16 (see also fig. 2) the mutually parallel flanges of which have bearing holes 17 which are in register with a through bearing hole in a parallelepipedic sliding block 18 preferably made from a material with good friction and tensile properties. Extending through said bearing holes is a shaft 19, which extends through oblong holes 20 provided in the flanges of the second scissor arm. Said holes are of a width which somewhat exceeds the diameter of the shaft 19.

In the ends projecting from said oblong holes the shaft 19 rotatably supports rollers 21a,21b for a purpose to be described. Said second scissor arm 6 further has a stop 22 for limiting the sliding motion of the sliding block.

The rollers supported by the shaft 19 are intended to roll up on slideways when the shaft is displaced transversely of the length direction thereof and said slideways are in the illustrated embodiment constituted by oblique surfaces 23 of elements connected to the upended rails of said first scissor arm 4.

In the inactive lower position of the scissor arms they take the position shown in fig. 2. The scissor arms then are substantially parallel with the first scissor arm 4 embracing the second scissor arm 6.

Upon activating the hydraulic cylinder the plunger rod 15 thereof will displace the yoke 16 in a direction towards the stop 22 causing the sliding block 18 connected to the yoke and having the upper surface thereof in contact with the under side of the web portion of the channel beam 6 to be displaced along said under side. Since the width of the oblong hole 20 somewhat exceeds the diameter of the shaft 19 and since the sliding block is permanently guided in the second scissor arm the shaft 19 will not touch any part of the second scissor arm which means that there is no friction between this one and the shaft.

When the rollers 21a,21b are rolling up on the oblique surfaces the second arm 6 is swung upwardly. At the same time the first scissor arm 4 will of course be swung upwardly since it is connected to the second scissor arm via the shaft 5.

When the rollers 21a,21b are to reach the top point of the oblique surfaces 23 the sliding block 18 will abut the stop 22. Owing to the just mentioned pivoting movements there has then been established a sub stantial moment arm between the shaft 19 and the shaft 5 which interconnects the two arms 4 and 6. The continued lifting motion thereafter occurs by the aid of this moment arm as the power the hydraulic cylinder is directly transferred to the scissor arm 6, i.e. about the shaft 19 which latter as a consequence of the abutment of the sliding block 18 against the stop 22 will be stationary and consequently also to the scissor arm 4.

Claims

1. Lifting mechanism of the kind which includes at least two scissor arms (4,6) interconnected by means of a joint or shaft and provided to cooperate in raising or lowering a table (10) or the like in relation to an underlying base portion (1) by means of at least one longitudinally extensible power transmission device, for instance a hydraulic cylinder, the two scissor ends extending backwards from the joint being fixedly but hingedly connected to the table and the base portion, respectively whereas the opposite ends of the arms are movable, for example by rollers, along the base portion or the table and whereas a shaft (19) extending transversely of the direction of action of the power transmission device is connected to said power transmission device, said shaft extending through an oblong hole (20) in one of the scissor arms (6) and being provided to cooperate by means of rollers (21a,21b) or the like with a an oblique slideway (23) which preferably is connected to the other one (4) of the scissor arms so as to accomplish by means of the rollers rolling along the slideway and a displace ment of the shaft (19) from an initial position in which the scissor arms (4,6) are in one common plane that at least one of the scissor arms is swung to a position in which a substantial moment arm has been established between the shaft (19) and the joint (5) between the scisso arms (4,6), c h a r a c t e r i z e d in that the scissor arms consist of an inner arm (6) in the shape of an inverted U-profile and an outer arm (4) which in a folded position encloses the inner arm along two long sides, that the shaft (19) extending through the oblong hole pivotally supports a yoke (16) connected to the power transmission device said yoke also pivotally supporting a sliding block (18) which is provided to transmit the power from the power transmission device to the inner arm by sliding with one surface thereof along the inner side of the web portion of the U-shaped profile and which is so dimensione that the shaft (19) will pass through the oblong holes (20) -the width of which somewhat exceeds the diameter of the shaft- without touching the walls of the inner arm (6) which limit the oblong holes and that the inner arm (6) has a stop (22) against which the sliding block (18) abuts when the rollers (21a,21b) supported by the shaft (19) by having rolled up on the- slideway (23) have caused that said substantial moment arm has been established between the shaft (19) and the joint (5) between the scissor arms such that the continued lifting movement is accomplished by a direct transmission from the power transmission device to the inner arm via the sliding block (18) and the stop (22).

2. Lifting mechanism according to claim T, c h a r a c t e r i z e d in that the sliding block (18) has a preferably parallelepipedical shape, is made from a material with good sliding properties and is inserted between mutually parallel flanges of the yoke (16) which latter has a through bore, which is concentric with the corresponding hole in said flanges and serves to support the shaft (19) which in the ends thereof rotatably supports the rollers (21a, 21b) which are intended to cooperate with the slideway (23).