BE1031201B1 - Scissor lift with assistance - Google Patents

Abstract

The invention relates to a lifting device using a scissor mechanism comprising an assist mechanism for starting the lifting process. The assist mechanism includes an offset system that allows the assist mechanism and scissor arm to be driven by a single axle.

Description

1 BE2022/6091

Scissor lift with assistance

The invention relates to the field of scissor lifts, in particular compact scissor lifts for lifting large loads per surface.

Scissor lifts are well known for selectively raising or lowering objects for easier loading/unloading. For example, in the printing field, scissor lifts are used inside "stacking units" to facilitate the stacking of sheets of paper or booklets. The scissor lift platform is initially inserted into the stacker and receives the sheets that have been processed in neighboring connected units (printer, folder, die-cutter, etc.). The scissor lift platform starts in the high position (to be close to the paper exit) and slowly lowers as paper accumulates on the stack. Once fully loaded, the scissor lift is removed from the stacker, and an operator must pick up the stack. For ergonomic reasons, the platform is raised to facilitate this operation. Once emptied, the scissor platform is reinserted into the stacker and a new cycle is started. The vertical movement of the platform is achieved using a scissor arm mechanism.

When it comes to the general principle of scissor lifts, they comprise two or more elongated members connected together at or near their midpoint (like scissors) at a pivot point. In general,

2 BE2022/6091 two parallel sets are arranged for greater stability. In a low position, the elongated elements are close to a parallel horizontal position, while in a high position, the elongated elements are close to a parallel vertical position. The upper end of the elongated members supports the elevator platform while the lower end of at least one elongated member is connected to a motor configured to horizontally move said end of the elongated member. The motor generally drives a horizontal lead screw which imparts horizontal movement to a crosspiece (or transverse beam) connected to the lower ends of one of the elongated elements. The ends of the elongated elements can thus be brought closer to each other, which has the effect of lifting the platform, or moved away from one another, which has the effect of lowering the platform. shape.

Each elongated element can be extended by another series of elongated elements also connected in the middle to increase the vertical movement of the platform without increasing the bulk of the elevator. Indeed, such scissor platforms must be compact to fit into the stacker. The stacker being an element of a chain of elements along which the paper circulates, it is not possible to modify its configuration.

Paper is heavy, and these scissor lifts must be able to lift heavy loads per unit area.

The mechanism of such a lift is based on the transformation of a horizontal force into a vertical force. The highest force is required at the start of the upward movement. This initiation stage is difficult. This is why the elevator

3 BE2022/6091 is never completely collapsed and a minimum angle of 8° is generally maintained.

Elevators have been developed where the mechanism is divided into two phases, a lifting phase, to assist the initiation phase, and a translation phase to complete the upward movement.

Document US 9,310,753 explains the principle of such lifting mechanisms. To assist the initial phase of the upward movement of the elevator, a spring assistance assembly is arranged to exert, when the platform is in its low position, a traction tension dui is transmitted to an arm equipped with a roller which pushes the platform upwards. Alternatively, instead of a spring, the assist arm may be driven (pushed instead of pulled by the spring) by the front of a sliding carriage which exerts force on the assist arm, up 'at a point where the rear of the sliding carriage contacts the end of the elongated member and pulls it forward to drive the remaining upward movement of the elevator. This assistance mechanism is generally effective for angles between 8° and 21°.

US2003/0075657A1 discloses a scissor lift with a lead screw (and actuator) connected to a carriage with rollers which are arranged to roll on a ramp while contacting a cam surface mounted on a first arm of the scissors during the initial phase of the elevation movement, thus communicating an upward movement to said arm. The carriage also supports a rod to provide horizontal movement to the second arm of the scissors. A shift mechanism (sliding linkage) on the carriage

4 BE2022/6091 allows the rollers to move first, until reaching a stop which allows the carriage to then act on the rod or crosspiece.

In this device, the cart is rather bulky and takes up a significant amount of space at the base of the system. The position of the cams, close to the pivot points of the arms, results in an ineffective "leverage effect". Furthermore, for a high load, the forces exerted on such mechanisms are very significant and the multiplicity of parts leads to a multiplication of the weak points of potential failure.

The applicant therefore found it necessary to manufacture more robust mechanisms which can be very compact while allowing the lifting of heavy loads.

Solution of the invention

To this end, the invention relates to a lifting device comprising a base and a platform placed on a scissor mechanism comprising a first arm with a movable lower end and a second arm pivotally mounted on the base, the two arms being connected together around their central point by a pivot and describing an angle a with the base, and in which the platform is movable from a low position to a high position under the action of an actuator arranged to actuate means passing through the lower end of the first arm through a nozzle having a section larger than said means, thus allowing said means to slide inside said nozzle, said means being pivotally connected to one end of a mechanism with wedge or wedge having:

> BE2022/6091 - a corner arm (or a corner pivot linkage) arranged in a plane parallel to the scissor arms, - a two-wheeled roller mounted at the other end of the arm, - a lower cam arranged on the base on the path of one of the wheels, and - an upper cam arranged on the second arm of the scissor lift, in the plane of the other wheel and substantially facing the lower cam, so that the wheels can contact both cams simultaneously.

Preferably, the means passing through the lower end of the first arm can for example be a transverse beam arranged perpendicular to the plane of the scissor arms, said beam being movable horizontally perpendicular to its axis. The actuator drives the movement of the moving means. For example, the actuator drives horizontal movement of the cross beam. The beam is not necessarily long. It may be part of another element, such as a projection from a lead screw.

Preferably, the length of the corner arm is at least 50% less than the length of the scissor arms. Preferably, the length of the corner arm represents less than 35% of the length of the scissor arms, preferably less than 30%. This allows leverage to be optimized.

The fact that the nozzle of the movable scissor arm has a section greater than the section of the transverse beams makes it possible to create an offset between the actuation of the corner arm and the actuation of the scissor arm at the start of the upward movement, thus creating a lifting assistance mechanism.

6 BE2022/6091

The nozzle can have any suitable shape, and can for example be circular, or a groove in which the transverse beam can slide.

Such a groove can for example be a few millimeters to a few centimeters longer than the section of the bar, and is typically calculated to obtain the desired offset.

At the start of an upward movement of the elevator, the scissor arms are close to a horizontal position (typically between 5 and 10° from horizontal), the crossbar is in contact with the nozzle towards the end of the scissor arm, the roller of the corner arm rests on the base. Under the action of the actuator, the crossbar moves horizontally in order to impart movement to the jamming mechanism: one wheel of the roller rolls on the lower cam which causes a thrust of the other wheel on the upper cam to give a vertical upward movement to the second arm. During this time, the crossbar moves inside the nozzle without inducing a translation effect on the scissor arm.

Since the length of the wedge arm is less than half the length of the scissor arms, the cams are positioned near the end of the scissor arms, allowing powerful leverage to lift the scissors and platform. shape.

When the roller wheel reaches the top of the lower cam and, preferably simultaneously, the other roller wheel reaches the lower point of the upper cam, the crossbar has reached the opposite end of the nozzle and begins to transmit a translation movement

7 BE2022/6091 at the end of the scissor arm, thus ensuring the continuation of the upward movement of the platform.

The roller wheels are each free to rotate in either direction, depending on the upward or downward movement of the elevator. They can turn in opposite directions.

The lower cam has a substantially triangular profile with a cam base resting on the base of the lifting device, an ascending side arranged to support the rise of the rollers during the action of the wedge mechanism during the lifting phase and a descending side . One of the wheels rolls on the rising side of the cam during the initial phase of lifting.

The upward side of the lower cam can be linear. Preferably, a linear ascending side makes an angle B1 with the base (horizontal or rest side) of between 10 and 65°.

In an advantageous embodiment, the rising face of the lower cam has a concave curved profile, that is to say a non-linear profile following an order function of at least the 1st order. This means that the face rising makes an evolving (increasing) angle 81 with the base. This angle preferably starts between 1° and 20°, preferably between 5° and 15°.

This allows for a low upward angle at the start of the assist, to increase efficiency, and a higher angle later in the assist to keep the cam short enough.

Even more advantageously, the rising face of the lower cam has a hybrid profile comprising a concave curved section extended by a linear section.

This allows a gentler recoil of the roller when descending from

8 BE2022/6091 the elevator, and allows slightly longer assistance than with a solely curved profile.

The upper cam also has a downwardly facing substantially triangular profile, with a cam base resting on and alongside the second arm (attached to and parallel to that arm) of the lifter, a lower side arranged to enter in contact with the rollers during the action of the wedge mechanism during the lifting phase and a third side.

The down side of the upper cam can be linear.

Preferably, a linear side towards the bottom makes an angle 82 with the second arm (its rest side) of between 10 and 65°.

In an advantageous embodiment, the downward side of the upper cam has a concave curved profile or a slope, that is to say a non-linear profile following a function of at least 1% order. This means that the face down makes a scalable (increasing) angle B2 with the second arm. This angle preferably starts between 1° and 20°, preferably between 5° and 15°. This allows for a low rise angle at the start of the assist, to increase efficiency, and a higher angle later in the assist to keep the cam short enough.

Even more advantageously, the downward face of the upper cam has a hybrid profile comprising a concave curved section extended by a linear section.

This allows a gentler recoil of the roller when descending the elevator, and allows slightly longer assistance than with a purely curved profile.

9 BE2022/6091

The upper cams and the lower cams are arranged such that one of the roller wheels rolls on the down side of the upper cam, while the other roller wheel rolls on the up side of the lower cam. A forward force is applied by the wedge arm on the roller, which is converted to an upward force as the wheel rolls on the up side of the lower cam resulting in an upward force transferred to the up side. the bottom of the upper cam and, therefore, to the second arm of the elevator.

The scissor lift of the invention may be a single or multi-stage lift. This means that a scissor arm can comprise one or more segments, typically arranged in an accordion fashion. For example, the elevator is a double-decker elevator, where each arm has two segments pivotally connected at one end.

The platform may be any surface suitable for supporting weights. Depending on the type of weight, it can be a plate, a plate with openings, a grid or have any other shape.

Detailed description of the invention

The invention will be better understood with reference to the detailed description of several embodiments with reference to the drawings where:

Figure 1 is a schematic view of the basic principle of a scissor lifting mechanism as known to those skilled in the art;

Figure 2 is a schematic view of a lifting mechanism of the invention;

10 BE2022/6091

Figure 3 illustrates the equations relating to the shapes of the cams;

Figure 4 illustrates the dependence a of equation 24 with

Figure 4a: Left terms of equation 24 as a function of y obtained for Bi =B: =29°34' and for various values of œ, 4b: Measured evolution of y, as a function of x during the assistance phase; 4c: Left-hand terms of equation 24 as a function of vw obtained for Bi =BR. =55° and for the same different values of “,

Figure 5 is a side view of a lower cam with a linear ascending profile;

Figure 6 is a side view of an upper cam with a linear downward profile;

Figure 7 is a side view of a lower cam with a curved ascending profile;

Figure 8 is a side view of an upper cam with a downwardly curved profile;

Figure 9 is a side view of a scissor lift according to the invention,

Figure 10 is a detail of Figure 9;

Figure 11 is a perspective view of the detail of Figure 10;

Figure 12 is a side view of the same scissor lift as that of Figure 9, in the elevated position;

Figure 13 is a detail of Figure 12;

Figure 14 is a perspective view of the detail of Figure 13;

Figure 15 is a side view of the scissor lift of Figures 9 to 11, in the low position, without the corner arm;

Figure 16 is a side view of the scissor lift of Figures 12 to 114, in the high position, without the corner arm;

Figure 17 is a perspective representation of a nozzle suitable for the scissor lift of the invention;

11 BE2022/6091

Figure 18 is a schematic representation of the forces involved in a two-stage scissor lift of the invention.

Figure 19 is a side view of an upper cam with a downward curved profile similar to Figure 8 but ending in a linear section.

Referring to Figure 1, a lifting device 1 as known in the art comprises a base 11 and a platform 12 placed on a scissor mechanism 10 comprising a first arm 13 with a movable lower end A and a second arm 14 with one end B pivotally mounted on the base, the two arms being connected together about their central point by a pivot 15, and in which the platform 12 is movable from a low position to a high position under the action of an actuator, acting for example on a transverse beam (not shown) arranged perpendicular to the plane of the scissor arms.

Typically, two sets of scissor arms are arranged in parallel so that the ends A and B of the arms of the two sets form a rectangle on the base 11 of the lifting device. This also means that the upper end of the arms defines a rectangle to support platform 12.

The transverse beam is arranged to, when actuated, move the movable lower end A of the first arm towards or away from the end B of the second arm. For example, the transverse beam is coupled to a lead screw, arranged horizontally on the base of the lifting device, the screw being actuated by a motor.

12 BE2022/6091

The first arm 13 and the second arm 14 describe an angle a with the horizontal base 11. When the platform is completely lowered, the angle reached is omin, and when the platform is at its maximum height, the angle reached is omax. Both arms have a length of 2L. For example, L=165 mm and omin = 8°26'.

The weight Wa of the scissor lift 10 itself acts on its center of mass, while the load (for example a stack of paper with a weight W=46Kg) acts half at point 132 (upper end of the first arm sequence) and for the other half at point 142 (upper end of the second arm sequence).

The total soil reaction W+Wa acts half at point A and half at point B.

The static condition is obtained if an external force F is applied essentially horizontally to the pivot of the scissor arm at point A.

The static condition can be obtained by evaluating the forces acting on the first scissor arm 13 and requiring that the total moment induced by these forces around the pivot 15 be zero.

The three forces acting on the first scissor arm 13 are: -the reaction of the ground on point A, the component perpendicular to the arm 13 being cos(œ).(W+Wa)/2 and therefore the moment induced around the pivot 15 being L.cos (a). (W+Wa) /2; -the upper force W/2 acting on the upper point 132 which gives rise to a force having a component perpendicular to the arm 13 of cos(a).(W)/2 and therefore a moment around the pivot 15 being L. cos( a).(W)/2;

13 BE2022/6091 -the actuated force F whose component perpendicular to the arm 13 being sin(o).F inducing a moment around the pivot 15 in the opposite direction to -L.sin(a).F.

So :

L.cos (a). (W+Wa) /2 + L.cos(o).(W)/2 - L.sin(œ).F = 0 (eg. 1)

So: F = cot(u). (W+Wa)/2 + cost (a). (W) /2 (eq. 2)

The force required from the actuator clearly increases almost exponentially when oa is reduced, following a law in 1/tan(a)=cot(a).

In our particular example, the maximum force required on the unassisted actuator at 8°26' is 6475 N, which is very high and requires a very powerful actuator.

It should also be noted the value of the moment around the pivot 15 that the force created by the actuator must achieve to maintain static equilibrium. At 8°26', the component of the force F directed perpendicular to the lower left arm is F.sin(a) and the moment around pivot 15 at this lowest angle is

M =F.sin(Q).L = 950N x 0.165m = 156.7 Nm (eq. 3)

With reference to Figure 2, where the elements of Figure 1 are all present and designated by the same reference numbers, the lifting mechanism 20 further comprises a corner arm (or pivoting wedging connection) 21 arranged in a plane parallel to the arms 13 and 14 of the scissor arms and having a length less than half the length of the scissor arms, that is to say less than L. One end A' of the corner arm 21 is located near the lower end A of the first arm 13. A double-wheeled roller 22 is mounted on the other end O of the corner arm 21. The double-wheeled roller 22 here comprises a small wheel 221 and a large wheel

14 BE2022/6091 222 mounted parallel to each other on the same axis.

A lower cam 23 is arranged on the base of the lifting device, here on the path of the smaller roller wheel 221, and an upper cam 24, which is arranged on the second arm 14 of the scissor lift, in the plan of the largest roller wheel 222. The upper cam 24 and the lower cam 23 are arranged substantially opposite each other, which means that the two wheels of the roller 22 can come into contact simultaneously with the cams located in the same respective plane.

The end A' of the corner arm (or wedging pivot) and the end A of the first arm (first arm pivot) of the scissor mechanism are movable on the same horizontal plane, that is to say at the same height h, above base 11.

They are also both operated by the same transverse beam, thanks to a shift mechanism as will be explained in more detail below. An xy reference frame is shown in Figure 2. The coordinates of the wedge pivot A! and the arm pivot A, denoted (A'x;A'y) and (Ax;Ay) are therefore such that A'y = Ay.

We will also note A'x=m and Ax=x. During a lifting action, starting from the lowest configuration of the platform (o= 8°26'), the wedge pivot A! will start slightly further from B than the arm pivot A such that x>m but as it moves more quickly, A' will merge with A at the end of the assistance phase such that x=m, here for example when a=21°.

The corner arm A'O is essentially almost horizontal when the elevator is in its lowest position, but as A' moves along the x-axis, the corner A'O

15 BE2022/6091 tilts and forms an angle y with respect to the horizontal line AB. A single transverse axis is mechanically linked to the actuator and passes through point A'. During the assistance phase, the pivot of arm A is not actuated by the transverse axis (the pivot of arm A is however not static, the action of the wedge or wedging mechanism causes the lifting of the arms of scissors, thus increasing the angle a, which implies a horizontal movement of the pivot of the arm A).

When this assistance ceases (the assistance phase ends), the arm pivot A and the corner pivot A' are combined and the same transverse axis acts on the arm pivot

HAS.

A short transverse axis is installed at point O (for example with a bearing) and on this axis the first wheel 221 of radius rl is in contact with the lower cam 23 and the second wheel 222 of radius r2 is in contact with the upper cam 24. When the elevator rises, the contact of the two wheels with the two cams is effective during the assistance phase where the wheel 221 of radius rl turns clockwise while the wheel 222 of radius r2 rotates counterclockwise. The active parts of the lower and upper cams are essentially the sets of all points that will be in contact with their respective wheel. The shape of these active parts of the lower and upper cam can be linear or curved but for the illustration here, these active parts of the lower and upper cam are represented linear.

The lower linear cam 23 which rests on the base forms an angle B1 with the horizontal (along the x axis) which is fixed.

The set of all points describing this lower cam

16 BE2022/6091 can be expressed in the reference frame (x,y) so their coordinates are P=(Px;Py).

The upper linear cam 24 is installed on the second arm 14 of the scissor lift and has a fixed angle ß2 with respect to this line (the arm line). The angle of this upper cam with the ground is variable and amounts to B2+a. The position of the points Q of contact between the wheel 222 and the cam 24 in the reference frame (x, V) are 0=(0x;Qy) but to simplify, we will also use another reference frame (u, v) located on the pivot B and rotating with the elevator such that the axis u is always aligned with the second scissor arm 14. The coordinates Q in this other frame of reference (u,v) will be designated by Q= (Qu; Qv).

A simple matrix coordinate change operation can then be used to obtain the coordinates Q in the reference frame (u,v) from those of the reference frame (x,y):

Los] (61 +) (or. 4) where the change matrix by rotation from the reference frame (x,y) to the reference frame (u,v) is:

Rs [ne cosa | (ea. 5) and the change matrix by translation from the frame of reference (x,y) to the frame of reference (u,v) is:

You (eq. 6)

The length of the corner arm of the segment A'O being Im, the coordinates P and Q in the coordinate system (x,y) are therefore:

B,=m+Ly cozy + Tr, sin, (eq. 7)

PB, = hw + Ly siny — 7, cos B, (eq. 8)

Q, = M + Ly COS y + 1, sin(B2 + a) (eq. 9)

Qy = hw + Ly siny + 7 cos($2 + a) (eq. 10)

17 BE2022/6091

Eq. 7 and Eq. 8 are the two equations describing the shape of the lower cam.

To obtain the shape of the upper cam thus in the reference frame (u,v), the combination of equation 4, equation 9 and equation 10 gives:

Q, = cos a [m + Lw cozy + rz sin(B, + a) — 2L] — sin a [Lw sin y + r2 cos(B, + a) (eg. 11)

Q, = sin a [m + Lw cozy + r2 sin(B, + a) — 2L] + cosa [Ly sin y + r2 cos(B, + a)] (eg. 12)

The purpose of the wedge or wedging mechanism is to convert the available horizontal force into forces having a substantial vertical component. This happens when B1 and B2+a are close to 45°. However, other design constraints must be included, such as having a linear cam here as well as favoring faster movement of the point

A' relative to the movement of A.

The wedge or wedging mechanism described so far contains a particular degree of freedom which is the value of the angle y which varies at the same time as the variation of the angle a of the elevator. There is therefore a dependence y= Y (a). This increases the robustness of the system since any imperfection between the theoretical shape of the cams compared to the actual shape or any imperfect positioning of the different elements would simply result in a slightly different orientation y taken by the corner arm compared to that planned.

For example, the following settings can be chosen:

B1= p2=38°, r1=14mm, r2=12mm, hn =24mm, Lw =52mm and L=165mn,

18 BE2022/6091 to illustrate how to design the shapes of the cams following two different approaches.

Design the wedge or timing mechanism by selecting the cam profile, for example a linear bottom cam:

The first approach linearizes the lower cam 23 by selecting a particular law y=yl(a) which leads to such a linear characteristic.

The different actuation speeds of the pivot points A' and A will result from this linear characteristic and the exact shape of the nozzle in which the pivot of the first arm A moves must then be adapted to the particular movement resulting from these points.

The coordinates of point O in the (x,y) frame are given by:

O = [m + Ly cos y, ; hw + Ly Sin y, ] (eq. 13)

The equation of the line d2 parallel to the slope of the lower cam and passing through the point O is: da :=y—r, cosB, = (x +rysin B,) + b (eq. 14)

Where b is a constant.

Imposing that Oe d2 gives: (hw + Ly siny,) — 7, cosB, = x + Ly cozy, + r, sin B, + b (eq. 15)

By rewriting it for b, we obtain: b = Ly(sin y, — cos yi) — x + const. (eq. 16)

With the x coordinate measured along the travel of the actuator, the origin, as shown in Figure 1, being located at a distance of 2L from the lower right fixed pivot of the scissor lift, we obtain: x = 2L (1 - cos(a)) (eg. 17)

19 BE2022/6091

As x is a function of a according to equation 17, for b to also be a constant, it is necessary to impose a particular variation of vl with at: . 2L(1-cos a) sin y, — COS =————— + const. . 18 (siny, Yi) uw (eq)

Then, using the formula sin(a — b) = sin acosb — cosa sin b

1. 1 1

And re-writing (siny, — cozy,) = V2(5siny, — cozy, )where = is seen once as cos” and once in the form sin T An analytical expression for Y1 can be derived: . __ My _ 2L(1—cos a)

V2 sin (y, 7) =S + const. (eq. 19)

And so: y, = Asin 2090 + const. | +! (eq. 20)

W

The value of the constant can be calculated by indicating for example that y1=0 for a=8°26', which gives: _ sy [V2L(1—cosa) _ x y, = Asin| 200 0.7556] +1 (eq. 21a)

To be exact, the shape of the cam and the variation yl (a) dictate the variation m=m(oœ) but a good approximation is obtained by taking a linear dependence of m with to as for the example where the crosspiece making the connection with the pivot of the corner mechanism or wedging has a horizontal displacement of 3 mm more than the pivot of the lower arm of the scissor lift: a-21 m =x-3( ZZ) (eg. 21b)

Thus, if we choose the evolution of vl and m given by Eg. 21a and 21b, for B1= B2=38°, we can then deduce the shape of the lower cam and the upper cam using Eq. 7-8 and Eq. 11-12. Figure 3 illustrates these shapes, and in particular, Figure 3a represents the law y= vl (a) according to equation 20, Figure 3b illustrates the active form of the lower cam, Figure 3c illustrates the active form of the

20 BE2022/6091 upper cam in the mark (x,y) and Figure 3d illustrates the active shape of the upper cam in the mark (u,v).

The lower cam is here effectively = linear by construction given the evolution vl of equation 21a.

However, the top cam is not linear in the (u,v) coordinate system and could be machined directly with this particular shape or the linear approximation of it can also be used.

Figures 5 and 6 illustrate suitable profiles for a lower cam and an upper cam with a slope or linear active portion.

Design the wedge mechanism or wedging by selecting the offset between the scissor arm and the wedge arm.

The second approach presented will consist of selecting the law

Y=Y2(@x) which will lead to the desired movement speeds of points A' and A. If the resulting shape of the lower and upper cams is close to linearity, they will simply be linearized to facilitate the manufacturing of the parts while relying on the tolerance of the mechanism to a slight deviation in shape via the adaptation of the real value taken by y.

In this section, a particular dependence Y=Y2 (a) is selected so that the different positions and feed rates of the pivot points A' and A have a selected offset such as x = m + 3 at 8°26' . As A' moves faster than A, A' will merge with A at the end of the assist so that x=m at 21°.

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We will establish the relationship between m and x (or between m and ao, given equation 17 which links x to o). Two points of the mechanism must be established: first the point R shown in Figure 2 located at the intersection of the slope of the upper cam and the lower right arm 14 of the elevator, which has coordinates in the reference ( u,v) of:

R=[R,;0] (eq. 22)

Equation 22 indeed implies in a simple way that the point

R rotates around the pivot point B, which establishes the relationship with the scissor lift in a simple way since Ry, =0.

Then, the point Q which is expressed in the frame (u,v) in the form Q=(Qu;Qv), which makes the connection with the wedge or wedging mechanism thus requires the realization of equations 11 and 12.

The relationship between the wedge or wedging mechanism and the scissor lift can therefore be expressed simply by noting the relationship between these two points in the right triangle of angle 82 and vertex R and ©: an =tan$, (eq 23)

The relationship between m and a is then obtained by injecting equation 11 and equation 12 into equation 23:

To facilitate the resolution of equation 24, v2 is set to zero for the lowest a, which makes it possible to find the value of Ru useful for positioning the wedge or wedging mechanism relative to the elevator, although 'a certain adjustment can be introduced at the level of the cam fixings.

22 BE2022/6091

When looking for a linearized cam solution, one simply needs to find the two ends of the active sections of the cam.

A first prototype was built with the corner arm and cams corresponding to the model values: Bl = ß2 = 29°34" with some minor deviations during manufacturing as explained below: e For o=8°26', m=x-3, which, using equation 17, leads to x=3.565mm and m=0.565mm.

Y2 =0 is set to zero, which allows us to extract from equation 24 that R, =-321.8mm.

Equations 9-10 and 11-12 then give the first theoretical point for this lowest value for the two cams:

P, =59.5mm, P, =11.8mm, Qu =-268.5mm and Q, =-30.2mm.

The values used for manufacturing the parts were slightly different and where:

P, =61.2mm, P, =13mm, Qu =-268.5mm and OQ, =-30.2mn. e For a=21°, m=x, which, using equation 17, leads to m=x=21.9mm.

To find the value of v2 at a=21°, the left term of Eq. 24 is plotted against y2 in Figure 4a.

Sometimes there is no intersection with the y2 axis, such as for a=21°, so equation 24 is not fully satisfied. Due to the relative degree of freedom that angle v2 can take to accommodate a small deviation from the theoretical form, equilibrium is observed on our first prototype before the left-hand term of equation 24 actually reaches zero. For example, for o=11.4° the value of y2 measured in Fig 4c is 6.5° while Fig4a predicts around 10°.

23 BE2022/6091

The simplest way to find the second point to determine the shape of the two cams for the highest assistance value (o=21°) can therefore avoid solving equation 24 but rather simply fix a certain value of y2 at 21°.

By proceeding in this way, at ao=21°, for the first prototype a value of y2=26° then using equations 9-10 and 11-12 we theoretically obtain:

Px=75.6mm, Py=34.6mm, Qu=-246.2mm and Qv=-61.9mm.

The values actually used to make the parts were slightly different:

Px=77.3mm, Py=35.8mm, Qu=-248.5mm and Qv=-60.9mm.

Figures 5 and 6 illustrate the profiles respectively for a lower cam and an upper cam of this prototype.

In this example, for the lower cam between the start and end of the assistance, APx=77.3-61.2=16.1mm and APy=35.8-13=22.8mm. Likewise for the upper cam, AQu=20m and

AQv=30.7mm.

The actual tilt angle of the active part of this cam differs from the values B1 and ßß2 due to the movement of the complete mechanism (such as the corner pivot A' moving faster than the pivot of the first arm A of the elevator , thanks to the presence of a nozzle creating an enlarged opening around the pivot of the first arm A through which passes the beam causing the movement of the corner arm A').

But in addition to this, the wedge or wedging mechanism must maintain contact with the lift using the cams. In the verticals passing through the contact points of the wheels with their respective cam (located here for example at approximately 100mm from the crossing pivot of the lifting arms 15), the elevator moves substantially upwards.

24 BE2022/6091

The model above was described for a simple single-story elevator; however, it is common to have several floors, with the arms arranged in an articulated, accordion-like manner.

For example, in the case of a 2-story elevator, the height z=2+ (2L sina) and using L=100mm, we can deduce that from a=8°26' to a=21°, Az= 85mm. The evolution y of 26° only brings for Ly =52mm a contribution of Az=(Lw +18.4+3 mm): tan 26°= 36mm so the remaining Az=49mm must come from the cam itself (in this case Az=22.8mm for the lower cam and Az is approximately 26mm for the upper cam since

AQv=30.7mm). Likewise, for the lower cam Ax=16mm and for the upper cam Ax=20mm, which corresponds to real physical angles of 55° and 60° respectively.

As can be seen in Figure 4b, when 81=82=55°, there is then always an intersection with the v2 axis and therefore an exact solution for all values & listed up to 21°. Thus, following the above procedure, if too small angles for B1 and B2 are selected, the actual resulting angles for the slope of the linear cam would have to be significantly higher to maintain contact between the wedge or timing mechanism and the upper cam during the entire assistance phase, which proportionally would negatively impact the effective efficiency of the overall wedge mechanism. However, maintaining contact between the corner arm and the cams throughout the assistance phase is favored by large values of B1 and B2. This is the reason why, for the second prototype described below, in order to achieve greater assistance efficiency within drastic space constraints,

25 BE2022/6091 non-linear lower and upper cams have been implemented.

Nonlinear cams

A second prototype was manufactured with a wedge arm and cams where the linear active part of the cams was replaced by parabolas (second order equation). This means that the apparent angles B1 and ß2 are not constant during the assistance phase. The initial values of the angles Bl and ß2 of the cams are kept very low in order to maximize the effectiveness of the assistance for the lowest angles a while the cams have values B1 and

B2 greater at the end of the assistance to maintain contact between the corner arm and the riser. More precisely, taking as an example r, =14mm, r: =12mn, hu =24mm, Lg =52mm and L=165mn, the linear slope was first calculated to facilitate the design, choosing B = B > = 42°. Rather than having the wedge arm contact the slope of the cam at such a large angle for all lifting positions, the nozzle on the first arm (offset mechanism) has here been selected with a groove circular larger so that the pivot point of corner A' is located 13mm from the pivot of the first arm

A at o=8°26', then A' will merge with A at o=21°. The linear slope of the ascending side of the cams is thus replaced by a parabolic profile, starting with a very low angle B at a =8°26' which will increase to an angle B=42° at o=21°. e For o=8°26', m=x-13, which, using equation 17, leads to x=3.565mm and therefore m=-9.43mm. Note that a linear slope solution that could serve as a guide to obtaining the second order one is obtained here using Eg. 24 for Ru=-301.7mm.

26 BE2022/6091

We find the first point (Px1, Pyl) of the parabola of the lower cam by setting y2=0 at this angle a and choosing that the wheel of the corner arm is tangent to this parabola. So Pa =mtLu =42.57mm and Pu =hw - r1=10mm.

We find the first point (Qx1, Qyl) of the parabola of the upper cam by setting y2=0 at this angle a and choosing that the wheel of the corner arm is tangent to this parabola. Thus, Qu =m+Lw =42.57mm and On =hn +r2=36mm. Using equation 4, this point in the reference frame (u,v) has coordinates Qul=-286.1mm and Qvl=-30.3mm. e For o=21°, m=x=21.92mm. The second point (Po , Py ) of the lower cam parabola is given by Ps =m+Ly +rlsinB1=83.29mm and P,, =35.8mm (same height as the end point of the slope design linear).

The parabola for the lower cam therefore has an active part during the equation assistance: y=alx-Pa)?+Py1 where a= D= 0.0156 (Eq. 25)

The second point (Qu , Qu ) of the upper cam parabola is found by setting y2=26° at this angle a in a similar manner (this is also the end point of the linear slope design). So Qu =-244.1mm and Q,2 =-63.5mm.

The parabola of the upper cam being rotated by 8°43 relative to the u axis, the equation of its active part is more easily expressed in parametric coordinates. Indeed, by setting x(t)=t-0x1 and y(t)=-b(t-0x1)2+0y1, where b= 22% =0.012.

27 BE2022/6091

Using Eq.5 with o=-8°26', the parametric equations of the active part of the upper cam in the frame of reference (u,v) are then: u(t) = (t — Q,1) cos 8.43 + (b(t — Qx1)“ +Q,1)sin 8.43 (Eq. 26) v(t) = —(t— Q,1) sin 8.43 + (b(t — Q,1)* + Q,1) cos 8.43 (Eq. 27)

Figure 7 shows the shape of the lower cam and Figure 8 illustrates the profile of the upper cam manufactured for this second prototype.

With reference to Figures 9 to 16, the operational application of the wedge or wedging mechanism of the invention will be detailed, using the cams of the second prototype above by way of illustration.

A lifting device 101 as known in the art comprises a base 111 and a platform 112 placed above a scissor mechanism 110, here a two-stage mechanism, comprising a first arm 113 with a lower end movable 123 and a second arm 114 with one end 124 pivotally mounted on the base, the two arms having here for example a distance between their pivots of 21=330mm. The total length of arm 114 is for example 356 mm, while the total length of arm 113 is for example 366 mm (this arm being longer due to the presence of the nozzle). These arms are connected together around their central point by a pivot 115, and in which the platform 112 is movable from a low position (Figure 9) to a high position under the action of an actuator on a transverse beam 116 arranged perpendicular to the plane of the scissor arms.

The transverse beam 116 is arranged to, when actuated, move the movable lower end 123 of the first arm towards or away from the end 124 of the second

28 BE2022/6091 arm. For example, the transverse beam is coupled to a lead screw, arranged horizontally on the base of the lifting device, the screw being actuated by a motor.

The transverse beam 116 passes through the lower end 123 of the first arm 113 through a nozzle 125, which has a hole of elongated section allowing the transverse beam to slide in said nozzle. A suitable nozzle is for example illustrated in Figure 15.

The end of the transverse beam 116 is pivotally connected to one end 151 of a corner mechanism 150 comprising: - a corner arm 152 (or wedging pivot connection) arranged in a plane parallel to the arms 13 and 14 of the scissor arm and here having a total length of 83mm with a corresponding inter-axis distance A'O= 55 mm, or less than half the length of the scissor arms (L=165mm), - a roller with double wheels being mounted on the other end of the arm 152, with an external wheel 154 and an internal wheel 153, - a lower cam 155 being arranged on the base 111, on the path of the external roller wheel 154, and - an upper cam 156 being arranged on the second arm 114 of the scissor lift, in the plane of the internal wheel 153 of the roller. In the lowest lifting position, the upper cam and the lower cam are next to each other, so that the inner wheel 153 and the outer wheel 154 are in contact with their respective cams.

When the platform is in its lowest position, the transverse beam 116 passes through the bushing 125 of the lower end 123 of the first arm, near the left side of the bushing. To start lifting the platform-

29 BE2022/6091 shape, the transverse beam 116 is actuated to the right. At the start of the movement (assistance phase), the transverse beam 116 slides freely in the nozzle, without exerting any force on the first arm. For example, the nozzle here allows the transverse beam to travel 13 minutes between the two ends of the nozzle. When the beam reaches the second end of the nozzle on the right, it occupies the pivoting position A of the first arm. The transverse beam, however, applies a lateral force to the corner arm 152. The outer roller wheel 154 begins to roll on the lower cam 155 with a rising profile. The associated internal wheel 153 of the roller rolls on the upper cam 156, communicating to said upper cam an upward reaction force which causes the lifting of the second arm 114 (to which the upper cam is attached).

For an angle corresponding to Ao = 21° - 8°26' = 12°34' the pivot point of the corner arm (beam 116) will make a stroke which is here 13mm longer than the stroke of the pivot A of the first arm. The arc length inside the groove of the nozzle is therefore 13mm (as illustrated in Figure 17) and the corresponding circle which has such an arc length for an angle of Ao has a radius given by: Rbushing = 13mm / Ao = 59.3mm. The horizontal projection of this groove arc is Rbushing. sin(Ao) = 12.9 mm.

When the roller wheels have reached the top of the cams, the assistance phase is over, the advancing transverse beam has reached the pivot point A of the first arm 113 and will now apply a force directly to this arm, according to the principle classic scissor lift. The roller of the corner arm can then roll freely on the base 111.

30 BE2022/6091

During the descent phase of the platform 112, the transverse beam 116 controls the first arm 113 during the entire descent movement, with the exception of a first phase corresponding to the movement of the beam 116 inside the platform. the nozzle 125, from one side to the other. When low angles ao are reached, the roller of the wedge or wedge mechanism simply rolls on the cams in the opposite direction.

With reference to Figure 18, the forces involved for a two-stage scissor lift according to the invention will now be detailed.

The load W is divided into one half (W/2) applied to the point

E (under one end of the platform) and the other half at point F (under the other end of the platform). The weight of the scissor platform itself, Wa, acts on the center of mass of the platform. The total weight (W+Wa) causes a reaction on the ground directed upwards and distributed for one half, (W+Wa) /2, at point A! (pivot point of the wedge mechanism or wedging associated with the first arm of the scissor platform, at the end of the transverse driving beam) and for the other half at point B (pivot point of the second arm) of the platform. The elevator transmits a horizontal force FBy to the fixed pivot point

B, which causes a reaction of equal amplitude but opposite direction. The cylinder transmits a horizontal force to point A' denoted here Fscrew. D is the joint of the first two-stage arm, and G is the joint of the second two-stage arm. To list all the forces acting on the lower arms AD and BG, it is also shown that the upper lifting stage applies vertical forces W/2 at points D and

G, as well as horizontal forces which rise at Wcota.

The lower lifting stage induces opposite reactions

31 BE2022/6091 also in D and G, having the same amplitude but an opposite force.

The wheel of radius rl mounted on the transverse axis passing through the point O of the wedging roller exerts a force perpendicular to the lower cam at the point P, which is broken down into a horizontal part FPx and a vertical part FPy. The reaction of the lower cam on this wheel creates equal and opposite forces in direction. Likewise, the wheel of radius r2 mounted on the same transverse axis passing through the point O of the wedging roller exerts a force perpendicular to the cam greater than the point Q, which is broken down into a horizontal part FQx and a vertical part FQy with its equal and opposite reaction of the upper cam.

We consider all the reaction forces acting on the corner arm alone which is also in static equilibrium.

The sum of the horizontal forces acting on the corner being zero, YF =0 therefore:

Fscrew — Fpx — Fox = 0 and therefore Fox = Fscrew — Fpx (Eq. 26)

The sum of the vertical forces acting on the corner being zero, XF, =0 therefore: —Fpy + Foy = 0 and therefore Fpy = Foy (Eq. 27)

The geometry of the lower cam also gives: pu = tanßı and therefore Fp, = Fp,tanf, (Eq. 28)

And similarly, the geometry of the upper cam gives: > = tan(ß, + a) and therefore Fo, = Foytan(B,+a) (Eg. 29)

Combining equation 26 and equation 28 gives:

Fox = Fscrew — Fpy tan; (Eq. 30)

By combining equation 27 and equation 30, we obtain:

Fox = Fscrew — Foy tan B; (Eq. 31)

32 BE2022/6091

Finally, the combination of equation 29 and equation 31 allows us to solve FQy:

Foy = In (Eq. 32)

Now that FOy is known, FQx can be deduced using equation 31:

For andere (Eq. 33)

The total amplitude of FO being simply F= (Fox) + (Foy) we can obtain FO, , that is to say that the useful component of FO which is directed perpendicular to the lower arm

BG, and which is capable of inducing a moment around the pivot point of the elevator C. Since by geometry Fo, =Focosfz, we can write

Fo = ee IT + (Gan + a)? (Eq. 34)

For the first prototype (linear cam), with Bl=B2=29°34' and at the lowest position ao=8°26', equation 34 gives FO =0.82 Fscrew. The useful distance L at =8°26' for this prototype is measured at 96.1mm. We must obtain the same moment around point C of 156.7 Nm given by equation 3 for the case without assistance and with Fscrew=6475N. When the wedge mechanism of the invention is present, this moment rises to M=Fg;"

L; and is obtained with Fscrew=1992 N. Theoretical efficiency of the assistance at the lowest lifting position therefore allows a reduction in the actuator force of 69%.

In practice, some approximations having been made, the efficiency gain may be lower, depending on the importance of the difference between the real cam profiles and the theoretical model.

Indeed, there is a divergence, as already indicated, between the angles 81 and B2 used to generate the shape of the cams

33 BE2022/6091 and their actual physical angular dimensions. To deduce the real effectiveness of the corner assistance, the resulting real angular dimensions (those which ensure contact between the corner arm, the cams and the riser during the entire assistance phase) must be used. Thus, for the first prototype, it is necessary to use the physical slope of the lower cam (55°) and that of the upper cam (60°) as they were manufactured. Equation 34 then gives

FO. =0.34 Fscrew, Li at Q=8°26' is still 96.1mm but the moment of 156.7Nm is then obtained with Fscrew=4745N therefore a real assistance efficiency at the lowest lifting position gives a reduction in the actuation force of 27% for this first prototype with linear cams.

The lifting and lowering times were measured on the first prototype and are summarized in table 1:

MC

Table 1

The time required to lift the weight up is of course slightly longer than that required to lower it.

The first prototype with linear cams made it possible to lift weights of up to 36 kg.

It follows from equation 34 that to maximize FQ and therefore the effectiveness of the wedge mechanism assistance, B1 and B2 should ideally be as small as possible. However, if B1 and B2 are too small, the corner arm will not be able to

34 BE2022/6091 keep contact with the elevator and its upper arm 114 until o=21°. Therefore, a nonlinear cam was constructed for the second prototype, with the initial part of the cam having small Bl and ß2 values to increase the efficiency at low a value. The cam then evolves towards greater values B1 and B2 in order to always keep contact between the corner arm and the upper cam. Such cam profiles make it possible to achieve efficiencies close to the theoretical efficiency calculated above. As a result, suitable actuators, for example motors, may be much less powerful than those required to lift existing scissor lifts. This also results in significant energy savings.

To combine the properties of linear cams and curved cams, another prototype was made. Referring to Figure 19, an upper cam 180 has a downward slope which is a second order curve as illustrated in Figure 8 over part of its length (to the left of the sharp vertical line). The end of the slope (to the right of the sharp vertical line), however, is machined further to obtain a straight line.

A first beneficial effect observed is a more regular return movement of the roller wheels when the elevator descends, particularly when contact between the cams and the wheels is reestablished.

The lifting tests were carried out under the same conditions as those described previously. They further demonstrate a beneficial effect of such a profile on platform loading. Lifting and lowering times

35 BE2022/6091 of different loads with this hybrid profile for the upper cam are collected in table 2.

Wa W+Wa | elapsed time | break time

THERE

Table 2

The light machining of the upper cam allowed the system to lift total weights of up to 50 kg.

Such lifting devices can advantageously be used in a paper stacking machine, because the overall mechanism is very compact.

Claims (13)

36 BE2022/6091 Claims 1. Lifting device (1; 101) comprising a base (11; 111) and a platform (12; 112) placed on a scissor mechanism (20; 110) comprising a first arm (13; 113) with a movable lower end (A; 123) and a second arm (14; 114) pivotally mounted on the base (11; 111), the two arms being joined together around their central point by a pivot (15; 115) and describing an angle a with the base, and in which the platform is movable from a low position to a high position under the action of an actuator arranged to actuate means (16; 116) passing through the lower end ( A) of the first arm (13; 113) through a nozzle (125) having an opening with a larger section than said means, thus allowing said means to slide inside said nozzle, said means being pivotally connected to a end (A') of a wedge mechanism (150) having: - a wedge arm (21; 152) arranged in a plane parallel to the arms (13, 14; 113, 114) scissor arms, - a double-wheeled roller (22; 153, 154) being mounted on the other end (O0) of the arm, - a lower cam (23; 155) arranged on the base (11 ; 111) on the trajectory of one of the wheels of the roller (221; 154), and - an upper cam (24; 156) arranged on the second arm (14; 114) of the scissor lift, in the plane of the other wheel (222; 153) and substantially facing the lower cam (23; 155) so that the roller can come into contact with both cams simultaneously. 2. A scissor lift according to claim 1, wherein the means passing through the lower end (A) of the first arm (13) is a transverse beam arranged 37 BE2022/6091 perpendicular to the plane of the scissor arms, said beam being movable horizontally perpendicular to its axis. 3. A scissor lift according to one of claims 1 or 2, wherein the length of the corner arm (21) is at least 50% less than the length of the scissor arms. 4. A scissor lift according to one of the preceding claims, wherein the two wheels (221, 222) of the double-wheeled roller (22) are parallel. 5. A scissor lift according to one of the preceding claims, wherein the two wheels (221, 222) of the double-wheeled roller (22) have a different diameter. 6. A scissor lift according to one of the preceding claims, wherein the lower cam (23) and/or the upper cam (24) has, at least in part, a linear active slope. 7. A scissor lift according to claim 6, wherein the linear active slope of the lower cam and/or the upper cam has an angle of between 10° and 65° with the base of the cam. 8. A scissor lift according to one of the preceding claims, wherein the lower cam (23) and/or the upper cam (24) has, at least in part, a concave curved active slope. 9. A scissor lift according to claim 8, wherein the concave curved active slope follows a function of at least first order. 10. A scissor lift according to one of the preceding claims, wherein the linear active slope of the lower cam and/or the upper cam comprises a concave curved segment at the lower angles extended by a linear segment. 11. A scissor lift according to one of the preceding claims, wherein the nozzle (125) is a groove. 12. A scissor lift according to one of the preceding claims wherein the first arm and the second arm comprise one or more segments. 13. A paper stacker comprising the scissor lift of any one of claims 1 to 12.