Power plants – Pressure fluid source and motor – With control means for structure storing work driving energy
Reexamination Certificate
1998-09-15
2001-08-14
Lopez, F. Daniel (Department: 3745)
Power plants
Pressure fluid source and motor
With control means for structure storing work driving energy
C091S169000, C092S052000, C248S162100, C267S118000
Reexamination Certificate
active
06272853
ABSTRACT:
The invention relates to a hydraulic lifting-lowering-system for a working table, a couch or lying furniture or another heavy object, the height level of which it is frequently desired to adjust or change, and said system comprising a predetermined amount of hydraulic fluid, a hydraulic fluid accumulator, the fluid pressure of which on the hydraulic fluid side is adjustable, a single acting hydraulic cylinder with two end caps, a piston pressure chamber and a piston rod which via a piston rod sealing ring extends sealingly out through the one end cap of the cylinder.
Within the fields of chiropractics and physiotherapy it has lately been recommended to use such systems for avoiding overloading damages in the neck, the back and the shoulders, partly by avoiding heavy liftings and partly by changing the working position frequently and having the possibility to change freely between a sitting and standing position.
From DE-A- 30 21 559 is known such system in connection with a height adjustable hospital bed for reducing heavy liftings for the nursing personnel. This known system has a.o. the disadvantage that hand or foot activated pumping work should be done by all lifting operations for the bed.
From U.S. Pat. No. 4,037,811 is known a support for an instrument, whereby an instrument is balanced by a single acting hydraulic cylinder being connected to a hydraulic accumulator. One of the disadvantages by this arrangement is that the cylinder should have an expensive telescopic column
11
,
15
of triangular cross section for guiding its rectilinear movement, whereby one telescopic part
11
is provided with a spring loaded pressure shoe
50
pressing the part
15
against the wall sides
52
of the part
11
, cf. column 2, line
58
to column 3, line 4, said guiding system provides a mechanical friction which can be overcome by the gear transmission
25
-
28
by rotation of a crank handle.
Said disadvantages can be avoided by a hydraulic system according to the present invention, which is special by the combination that the hydraulic cylinder is of the plunger piston type and that the cylinder wall of the hydraulic cylinder is slidably and telescopically mounted in a cylindric guiding tube surrounding the piston rod in its entire length and being rigidly secured to the one end of the piston rod via a cross plate or similar construction part. Thus, beyond that the force of pressure applied at the end of the hydraulic cylinder at a given accumulator size is only changing a little over a relatively long stroke length, a very simple and stable and reliable system without handle is achieved. It has turned out that e.g. a working table being supported by such system, the operating pressure of which is pre-adjusted in accordance with the weight and load of the working table of e.g. 25 kg, and the stroke length of which is predetermined according to the desired height regulation range of the working table of e.g. 400 mm, only required a force corresponding to the force of the weight of about 200 g (1,96 N) vertically towards the table plate to change the height level of the table arbitrarily within the mentioned 400 mm.
This corresponds to a very little pressure change in the piston pressure chamber, namely 0.8%, such that the accumulator can be so selected that its operative pressure is altered 0.8-10% at the most, or even better: 1.0-2.5% at the most, during the relative stroke of the plunger piston rod from one to its other operative position of its predetermined stroke length, which stroke is relative to the hydraulic cylinder.
Preferably, the end caps of the hydraulic cylinder are connected via an inner telescopic tube carried telescopically in the cylindric guiding tube serving as an outer telescopic tube, which together with the plunger piston rod has been secured coaxially in a mounting block, and the outer telescopic tube via a slide bushing externally upon the inner telescopic tube at that end cap, through which the piston rod extends, together with a slide bushing in the outer end of the outer telescopic tube is adapted to guide the inner telescopic tube when it is displaced in the outer telescopic tube. An advantage connected thereto is that even though the operating pressure is rather high, typically 40-150 bar, a rugged and stable guiding can be achieved at low friction of the telescopic construction.
The plunger piston rod advantageously may comprise a longitudinal bore forming a part of the pressure fluid connection between the piston pressure chamber and the hydraulic fluid side of the accumulator.
The hydraulic fluid accumulator may e.g. be of the kind with a pressure fluid tight membrane separating the hydraulic fluid from a gaseous fluid serving as pneumatic spring. This permits the system to obtain very low friction losses in the accumulator and thus permits low manoeuvering forces for a user who desires to change said height adjustment. A possible adjustability of the gas pressure permits a change of the force of the supporting ability of the hydraulic cylinder.
The accumulator may also be of the spring type whereby a compression spring exerts a force on a piston in an accumulator cylinder. Thus is achieved an economic embodiment of the accumulator, and if the spring pressure is adjustable, a simple adjustment of the hydraulic pressure in the activator circuit is obtained by just tightening or slackening the compression spring.
An embodiment, by which the hydraulic fluid accumulator is of the spring type, and a compression spring exerts a force against a piston in an accumulator cylinder, is characterized in that the wall of the accumulator cylinder is formed by that part of the plunger cylinder wall which is situated between a stop ring and one end cap, whereby the piston is arranged also in the hydraulic cylinder and is fluid proof sealed and displaceable on the plunger piston rod between said stop ring on said piston rod and said end cap into which the piston rod is displaceably arranged.
Here the spring is thus fully built-in in the hydraulic cylinder, whereby a small outer diameter for the lifting-lowering-unit can be achieved at the expense of the fact that the spring should be dimensioned with the free length and spring characteristic demanded for the relevant and thus economical lifting-lowering-unit.
REFERENCES:
patent: 3168278 (1965-02-01), Ogden
patent: 3436048 (1969-04-01), Greer
patent: 3486417 (1969-12-01), Di Vita et al.
patent: 3825244 (1974-07-01), Bauer
patent: 3861740 (1975-01-01), Tajima et al.
patent: 3865341 (1975-02-01), Fortnam et al.
patent: 4415135 (1983-11-01), French
Antonelli Terry Stout & Kraus LLP
Lopez F. Daniel
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