Elevator – industrial lift truck – or stationary lift for vehicle – Having specific load support drive-means or its control – Includes scissored supporting levers in drive-means
Reexamination Certificate
2001-07-09
2004-01-06
Kramer, Dean J. (Department: 3652)
Elevator, industrial lift truck, or stationary lift for vehicle
Having specific load support drive-means or its control
Includes scissored supporting levers in drive-means
C187S211000, C108S145000, C182S141000
Reexamination Certificate
active
06672430
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a device and method for adjusting a force applied to a movable element such as a platform.
Scissors-type linkages are used in many devices and machines for providing movable characteristics, e.g. in lifting devices such as liftable platforms. The scissors-type linkage allows for lifting a platform into an upper, open or extended position starting from a lower, close or retracted position in which the platform can come very close to a base or the floor or can even contact one of those.
A movable element such as a liftable platform which is connected, e.g. to a base, a floor, an operation deck or the frame of a machine such as a printing machine, can be moved, e.g. raised, by the operator himself, by a driving device such as a motor or by the assistance of an energy-recycling mechanism or device.
The force which is applied to the movable element has to be adjusted based on the weight of the movable element, the weight of the scissors-type linkage and perhaps on the weight of a load or an operator in the case where the scissors-type linkage is used to lift or hold goods or operators. If no additional loads are present, the force only has to compensate or exceed the gravitational and frictional forces of the mechanism itself.
It is advantageous to use an energy-recycling device such as a gas spring for moving or raising the element. The energy which becomes free when the element is moved in its lower position can then be stored in the energy-recycling device, e.g. in the compression of a gas in the gas spring, and can be used to assist the movement into the upper position.
U.S. Pat. No. 4,712,653, which is incorporated by reference herein, discloses an energy-recycling scissors lift including a platform, a base and a pair of scissors linkages, each having a pair of first and second scissors legs. A bridge structure connects each of the second legs together. A sealed gas cylinder, attached to the base and the bridge structure, moves the platform to an extended position above the base. Energy is stored in the sealed gas cylinder as the platform descends to a retracted position and a compensation device is attached to the scissors lift to compensate for the overforce caused by the sealed gas cylinder.
A weight adjustment mechanism is used which includes means for adjusting the forcing-point radius, i.e the radius of the mounting point of the sealed air cylinder to the bridge structure with regard to the mounting point of the scissors legs at the base, to compensate for and dissipate an amount of overforce imparted by the sealed gas cylinder. Therefore, the weight adjustment mechanism can be used to fine tune a sufficient force that maintains the platform in its extended position, resulting in a scissors lift which can be easily started down to its retracted position. The weight adjustment mechanism can also adjust the upward force needed to start the platform towards its extended position.
The above-referenced patent has the disadvantage that the force applied to the platform in its retracted position can not be adjusted independently from the force applied to the platform in its extended position and vice versa.
FIG. 1
shows a prior art device
1
for lifting a platform
2
. The device
1
comprises a scissors-type linkage
4
, which includes a first scissors leg
6
and a second scissors leg
8
which are connected at a pivot point
10
. A second pair of scissors legs in addition connects the platform
2
and a base
16
but it is not shown for purposes of clarity.
FIG. 1
shows the scissors-type linkage
4
in a closed position or closed mode. The first scissors leg
6
is mounted with one end to the platform
2
at a mounting point
12
whereas the other end is movingly supported by a roll
14
. The second scissors leg
8
is mounted with one end to the base
16
at a mounting point
18
whereas the other end is movingly supported by a roll
20
. The device
1
further comprises a gas spring
22
having a cylinder
24
and a piston rod
26
. The gas spring
22
is mounted with one end to the scissor type linkage
4
at a first mounting point
28
and with the other end at a second mounting point
30
to a mounting plate
32
of the base
16
.
The gas spring
22
applies a force
34
to the platform
2
which assists the lifting of the platform
2
. If an operator grips the platform at a handle
36
and pulls or pushes the platform up, he only has to apply an additional force to the platform so that the sum of the force applied by the gas spring
22
and the force applied by himself exceeds the gravitational force on the platform
2
and lifting device
1
.
FIG. 2
shows the prior art device
1
for lifting the platform
2
, in which the platform
2
is in an upper position and the scissors-type linkage
4
is in an open position or open mode. The gas spring
22
applies a force
134
to the platform
2
which maintains the platform
2
in the upper position, i.e. the force
134
must be equal to or can be greater than the gravitational force on the platform and the lifting device
1
. Advantageously the force
134
exceeds the gravitational force only minimal.
As can be seen from
FIGS. 1 and 2
the second mounting point
30
of the gas spring
22
does not move because it is fixed at the mounting plate
32
of the base
16
. Therefore, the force
134
is smaller than the force
34
as indicated by the respective length of the arrows
34
and
134
. The force applied to the scissors-type linkage
4
and subsequently to the platform
2
by the gas spring
22
depends on the angle between the piston rod
26
and the first scissors leg
6
and it depends on the compression of the gas spring.
Both positions of the platform
2
, the upper shown in FIG.
2
and the lower position shown in
FIG. 1
, can be fixed by the use of a fixing element such as a pin.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and device for adjusting a first force applied to a movable element in a first position so that a second force applied to the movable element remains constant.
It is a further alternate or additional object of the present invention to provide a method and device for independently adjusting a first and a second force applied to a movable element such as a platform.
The terms “first force”, “second force”, “third force” and “fourth force” in this application are used herein solely to distinguish the forces from one another, and are not meant to have any other specific meaning.
The present invention provides a method for adjusting a first force applied to a movable element in a first position of the movable element by a force applying device, the force applying device applying a second force to the movable element in a second position of the movable element, comprising the steps of:
connecting the movable element and a base element with a scissors-type linkage;
mounting the force applying device to the scissors-type linkage at a first mounting point;
mounting the force applying device to the base element at a second mounting point;
moving at least one of the first and the second mounting points along a constant force curve, so that the second force remains constant as the first force is adjusted.
The terms “first mounting point”, “second mounting point”, “third mounting point” and “fourth mounting point” in this application are used herein solely to distinguish the mounting point from one another, and are not meant to have any other specific meaning.
The method according to the invention advantageously allows for compensating for force applying device wear or deviations in strength as it is supplied by the manufacturer, e.g. gas spring wear or deviation. Further, the method according to the invention allows the operators to easily adjust the required force, e.g. a lifting force, to their own liking, preference or need.
According to the invention the method may further comprise the steps of:
providing a further force applying device, the further force applying device applying a
Boucher Ronald Henry
Hebert Raymond Alphonse
Chin Paul T.
Davidson Davidson & Kappel LLC
Heidelberger Druckmaschinen AG
Kramer Dean J.
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