Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Thomas Bernhard Andersson
An apparatus for setting the position of a device
provided with a plurality of adjusting hydraulic cylinders
The present invention relates to an apparatus for setting
S the position of a device provided with a plurality of adjusting
hydraulic cylinders by simultaneously supplying to the various
cylinders quantities of hydraulic medium corresponding to the
desired setting of said device.
In order to allow the level of a working table or the like
/~ to be adjusted, the legs of the table or the frame structure
thereof are made telescopically raisable and lowerable. Previous-
ly, the adjustment has normally been done mechanically. It has
also been pro~osed, however, to effect this adjustment hydrauli-
cally. Then a hydraulic cylinder arrangement has been assigned
to each leg which is to be adjusted ver~cally. In order ~or the
table top to move in a parallel movement, it is necessary for
all hydraulic cylinders to be supplied with the same amount of
oil, assuming that they have the same area. Since it is possible
that the various legs may carry different loads, it is not poss-
O ible to supply the hydraulic cylinders from a conventional hy-
draulic pump with branch lines. In accordance with an earlier
proposal, there has been arranged instead a multivlicity of se-
parate hydraulic pumps, each in the form of a hydraulic cylinder
with an associated piston rod in side by side relationship. In
~5 this arrangement, the piston rods must be displaced exactly
uniformly in order to obtain the same output flow from each cy-
linder. If, however, the loads acting on the cylinders which
respective piston pumps are to supply vary greatly, ~roblems
can arise in this type of arrangement as a result of uneven load-
3~ iny, since the force with which the piston rods of the differenthydraulic pumps must be actuated will also vary greatly.
A main object of the present invention is to eliminate among
: other things the above mentioned drawbacks of prior art
equipment and to obtain an apparatus for setting the position of
~- a device provided with a plurality of adjusting hydraulic
cylinders which output the desired quantity of hydraulic medium
to each cylinder irrespective of the pressure in the respective~
cylinder and which eliminates problems resulting from unev
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loading. In addition to its application to tables, the invention
can also be applied to all kinds of objects arranged to be ad-
justed by means of at least two hydraulic cylinders.
In accordance with the invention there is provided a height
adjustable table for use as a data terminal or the like,
comprising a plurality of supporting legs and a table top, a
plurality of height adjusting hydraulic cylinders, one said
cylinder being provided in each said leg, and means for
simultaneously supplying to the various cylinders quantities of
hydraulic medium corresponding to the desired setting of said
table, said hydraulic cylinders each communicating with a
respective displacement chamber of a single hydraulic pump
loeated on said table top, said pump being common to all said
hydraulic cylinders and comprising a pump cylinder and a piston
rod axially displaceable therein, wherein the piston rod is
stepped to form a plurality of annular, coneentrical piston
surfaces and the inner diameter of the pump cylinder is stepped
in a eorresponding manner to the piston rod, such that there is
formed in front of each piston surface a displacement chamber,
said chambers being simultaneously mutually sealed at the
beginning of a working stroke of the pump, and being maintained
in mutually sealed relationship during said working stroke,
whereby equal quantities of hydraulic medium are supplied to
each said hydraulic cylinder, thereby maintaining the table
level regardless of any unevenness of load thereon.
By the French patent specifications 1,235,486 and 1,575,806,
hydraulie eylinders are previously known, the piston rods of whieh
are provided with a plurality of piston means. However, the struc-
ture of the prior art devices are relatively complicated and
among other things they have to be made in several sections.
Thus, both the manufacturing and the mounting of hydraulic cy-
linders having that type of piston means are relatively time
consuming and cost demanding. Further, a great number of sealing
surfaces and sealing means are required. The risk of leakages
is increased with each sealing surface.
The above problems are solved by the present invention
according to which the piston rod is stepped to form a plurality
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of annular, concentrical piston surfaces,and the inner diameter
of the cylinder is stepped in a corresponding manner to the
piston rod, such that there is formed in front of each piston
surface a displacement chamber, said chambers being mutually
sealed during a working stroke of the pump.
Both the piston rod with piston means and the surrounding
cylinder can readily be manufactured in one pi~ce by simple
machining techniques.
By gi~ing the piston means the same area, part-flows of
exactly the same magnitude can be obtained from each chamber.
Alternatively the flows can be adjusted in the desired manner
relative to one another by varying said areas.
It is preferred that a sealing element surrounds the
piston rod behind each step and in that the inner surface of
the cyl;nder is provided with means leaking hydraulic medium
between adjacent chambers when the piston rod is pulled back.
This facilitates filling of the pump with hydraulic medium.
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So that the invention will be more readily understood
and optional features thereof made apparent, an exemplary em-
bodiment thereof will now be described with reference to the
accompanying schematic drawing, in ~hich Figure 1 is a longi-
S tudinal sectional view through a hydraulic pump used in an appa-
ratus according to the invention, and Figure 2 illustrates one
manner of application of an apparatus according to the invention.
The hydraulic pump illustrated-in Figure 1 is of the ois-
ton type and is generally identified by the reference 1. The pump
/0 comprises a plurality of piston means, which have the form of
step surfaces or shoulders 2 located on a common central body 3,
serving as a piston rod. The piston rod 3 provided with said
shoulders is arranged in a correspondingly steoped cylinder
housing 4, such that in the illustrated position of the piston
rod in Figure 1 there is formed between the piston rod 3 and the
cylinder 4 before each shoulder 2 serving as piston means a
peripherally extending chamber 5. Arranged behind each piston
means 2 is a sealing element 6 in the form of an O-ring, said
sealing element being located in a peripheral groove in the
a O piston rod 3 and being in sealing contact with the wall of the
cylinder 4. Each chamber 5 is provided with a separate connecting
channel 7, through which hydraulic oil can be oumped out or
supplied.
In the illustrated embodiment, the piston rod 3 is arranged
~5 to be operated by means of a spindle 8 which is provided with a
pin 10 which can be screwed into a hole 9 in the oiston rod 3.
The spindle can be turned by means of a knob 11 or like element,
this turning movement being converted into an axial displacement
of the piston rod 3 as a result of the screw engagement between
3 the pin 10 and the hole 9. The references 12 and 13 identify
bearing means for taking up radial and axial forces respectively.
The aforedescribed hydraulic pump has the same effect as
four separate pumps, as respective piston means 2 discharge an
individual flow of oil from the associated chamber 5 through re-
3 S soective connection 7. Before oil can be discharged, however,it is obvious that the pump must be filled with oil, which can
be effected in different ways. For example, lines coupled to the
connection 7 can be immersed in a container filled with oil and
oil drawn into the chambers of the pump as the piston rod 3 is
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withdrawn, or separate filling passages can be arranged for this
purpose. Preferably the inner surface of the cylinder 4 is pro-
vided with means, e.g. grooves, leaking hydraulic medium between
adjacent chambers 5 when the piston rod 3 is pulled back for
S filling purposes. In one embodiment the piston rod 3 can be
arranged to be drawn back a further distance than illustrated
resulting in that the respective O-ring 6 passes the inclined
first portion of each step and full communication between said
chambers 5 in the filling position.
/0 If all the piston means 2 have the same area, orecisely
equal quantities of oil can be discharged through respective
connections 7, irrespective of any counterpressure in the lines.
If a higher pressure prevails in one line than in the others,
this higher pressure will not cause the corresponding piston
/5 means to drag, since all piston means are rigidly connected to
the same piston rod 3. All forces which occur will also be cen-
tralized to the common piston rod 3, and hence no problems will
manifest themselves as a result of uneven loading or the like.
A hydraulic pumo constructed in the aforedescribed manner is
o e~tremely compact and simple to use and to manufacture.
Figure 2 illustrates a manner of application of a hy-
draulic pump constructed in accordance with the embodiment
illustrated in Figure 1. In the Figure 2 embodiment, the hydrau-
lic pump 1 is mounted on a vertically adjustable data-terminal
table. Each of the legs of the table is in the form of two -tele-
scooically arranged sections 1~, 15, which can be displaced
relative to one another by means of a hydraulic cylinder 16
arranged in respective leg. Each hydraulic cylinder communicates,
through a line 17, with an associated chamber 5 in the hydrau-
3 o lic pump 1, which pump can be arranged in a readily accessibleplace. By rotating the operating knob 11, the table top can be
moved in a parallel pattern of movement vertically, i.e. it can
both be raised and lowered, depending upon the direction in
which the knob 11 is turned, An uneven load on the table top
will not affect its setting in the horizontal plane.
The hydraulic pump illustrated in Figure 1 can be used,
however, in many other ccnnections, where it is desired to dis-
pense equal or given volumes to different lines. Thus, in this
latter case the piston means 2 shall not have the same area, but
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their area can be ada~ted in dependence upon the quantities of
oil which are required in respective lines. A common feature,
however, is that the discharge quantities of oil can be establish-
ed substantially precisely, since they are solely dependent upon
S respec-tive piston surfaces.
The aforedescribed hydraulic ~ump can be modified in
several respects within the scope of the accompanying claims.
Thus, the piston rod can be oPerated in a desired manner and,
for example, may be motor driven. Further, any number of piston
/~ means may be provided.
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