Motors: expansible chamber type – With correlated control of motive fluid and locking means – Sequential operation of locking means and motive fluid control
Patent
1995-06-05
1998-04-07
Denion, Thomas E.
Motors: expansible chamber type
With correlated control of motive fluid and locking means
Sequential operation of locking means and motive fluid control
91 45, 92 8, 92 28, F15B 1526
Patent
active
057351872
DESCRIPTION:
BRIEF SUMMARY
The present invention generally relates to a pneumatical piston-cylinder unit of the type which is commonly sued in many industrial fields for actuating various machine parts or objects by a predetermined force. For this purpose it is many times possible to chose between electrical, pneumatical or hydraulical actuation means. Pneumatical and hydraulical actuation menas are usually utilized in cases where compressed or hydraulic power is available.
A hydraulic piston-cylinder unit is advantageous in several respects over pneumatical piston-cylinder units, in the following referred to as "air cylinders". Since, however, air cylinders usually have a substantially lower purchase cost, are simplier to manage and install, can be formed with less dimensions, are formed so that there is no need to bother about managing hydraulic oil, which sometimes causes problems, etc., pneumatical cylinders are in many cases chosen instead of hydraulic cylinders.
"Air cylinders", however, suffer from some disadvantages in air cylinders a piston operates between the two ends of the cylinder, which ends thereby define the piston stroke. If it should be desired to change said piston stroke this has usually been made by means of external magnetos, mechanical stop means and similar means. Such means necessarily make use of external cables, conduits, mechanical stop means etc. which often are considered as obstacles and which may cause problems and operation errors.
Another limitation of air cylinders is that the piston usually "creeps" when the compressed air is cut off depending on the compressability of the air, said creeping may follow in the former direction of power, or in the opposite direction in case the cylinder is acted on by an outer counter power, whereby the air cylinder "creeps" or becomes more or less resiliently compressed. The same problem appears in case the compressed air unintentionally drops out depending on operation troubles or for any other reason. It is therefore not possible to block the piston exactly in the position it takes when the air was cut off or dropped out.
It is also difficult or impossible to, more or less exactly, control the moving speed of the air piston, since the speed is depending on the air pressure and on the counter pressure, respectively, that the piston is subjected to. Further, the air piston generally starts moving hesitatingly and with a successively increased movement. The only possibility of controlling the maximum speed of the air piston is, in most cases, to reduce the air pressure, but in such case the piston, or course, also gets a correspondingly reduced actuation power.
It may also be a problem that the air piston normally always has a maximum speed in the very moment that the piston is to be stopped at the end of its stroke.
The basis of the invention therefore has been the idea of combining a conventional air cylinder with a hydraulic unit, which position the piston takes when the air pressure is cut off or drops out, piston, need of changing the air pressure and without changing the actuation power for the air piston, narrow tolerances.
It is known in the art to utilize hydraulic means in combination with air cylinders in various connections. Thus, SE-A 363.664, as an example, discloses an air cylinder, in which a hydraulic system is utilized, in which a liquid dampens the moving speed of the air piston following a controllable choking of the flow passageway of the hydraulic fluid, like in a so called hydraulic shock absorber. The same function is obtained in the U.S. Pat. Nos. 2,664,859 and 3,302,533 and in the German publication DE-A 1.625.651.
All said known apparatus, however, only provide a damping, in some cases a controllably strong damping, of the moving speed of the piston or of the movement of the air piston just preceding the stopping thereof, but none of said publications discloses an apparatus in which the piston can be effectively stopped and can be positively kept exactly in the position that the piston takes when the air pressure is being cut off or drops
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Denion Thomas E.
Pos-Line Aktiebolag
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