Motors: expansible chamber type – With motive fluid valve – For double-acting motor
Reexamination Certificate
1999-07-13
2001-03-20
Ryznic, John E. (Department: 3745)
Motors: expansible chamber type
With motive fluid valve
For double-acting motor
C091S41700A
Reexamination Certificate
active
06202536
ABSTRACT:
This invention relates to pneumatic actuators and, more particularly, to a reciprocatory actuator of the kind comprising a cylinder which defines two cylinder chambers separated by a piston which is reciprocable in the cylinder.
When operation of such actuators, also referred to as linear motors, is commenced, starting from an idle condition of the actuator with both cylinder chambers at zero pressure, a first or start stroke of the piston is initiated by admitting the operating fluid, i.e. air or other gaseous fluid, under pressure into one of the cylinder chambers. The piston then tends to move at excessive speed, because its movement is not impeded by a back pressure in the other cylinder chamber. A back pressure will be present to prevent the piston from overspeeding or moving at such excessive speed only after the first stroke of the piston has been completed.
To prevent such overspeeding of the piston it has been common practice to initiate the operation of the actuator at a reduced pressure of the operating fluid and raise the pressure to the normal working pressure only after completion of one or more operating cycles.
Operating the actuator in this manner is disadvantageous in several ways. For example, the initial stroke or strokes are normally ineffective, and initial operation of the actuator at a reduced pressure may be impracticable if a force corresponding to the normal operating pressure is required from the actuator during the first stroke. Moreover, a pressure regulator is required for changing the initial reduced operating pressure to the normal operating pressure, and it may be difficult to change the back pressure as desired to adapt it to changes in the load to be driven by the actuator.
In accordance with a first aspect of the present invention there is provided a method of operating a pneumatic reciprocatory actuator of the kind comprising a cylinder which defines a forward-motion chamber and a return-motion chamber, and a piston which is reciprocable in the cylinder and separates the forward-motion chamber and the return-motion chamber, in which a start stroke of the piston in a direction expanding the forward-motion chamber is initiated by admission of a gaseous operating fluid from an inlet port into the forward-motion chamber with both said chambers initially at substantially zero pressure, characterised by also admitting the operating fluid from the inlet port into the return-motion chamber during the start stroke until a back pressure of a predetermined magnitude has been produced in the return-motion chamber, and then closing the return-motion chamber, whereby the return-motion chamber will form a cushioning chamber for cushioning the movement of the piston and thereby preventing piston overspeeding during the start stroke.
In accordance-with a second aspect there is provided a pneumatic actuator comprising a cylinder having an inlet port for operating fluid and defining a forward-motion chamber and a return-motion chamber, a piston which is reciprocable in the cylinder and separates the forward-motion chamber and the return-motion chamber, and a valve device controlling flow of operating fluid into and out of the forward-motion chamber through a first fluid passage extending between the inlet port and the forward-motion chamber, characterised in-that the valve device includes a pressure control valve unit which is disposed in a second flow passage extending between the inlet port and the return-motion chamber and openable in response to the application to the inlet port of a predetermined first pressure to pass operating fluid from the inlet port to the return-motion chamber and closable in response to pressurisation of the return-motion chamber by a predetermined second pressure lower than the first pressure to block flow of operating fluid from the return-motion chamber.
Preferred embodiments of the method and the actuator according to the invention include features set forth in the dependent claims.
The invention is applicable to actuators for various uses, such as actuators for use in reciprocating work machines or machines for opening and closing doors, actuators for use as pneumatic springs, pneumatic shock absorbers, etc.
In accordance with the invention, overspeeding of the piston during the first or start stroke is effectively avoided even if the full operating pressure is immediately applied to the forward-motion chamber.
In accordance with the invention, the back pressure to be produced in the return-motion chamber can also be adjusted rapidly and by simple means to suit different loads such that a lower back pressure is produced for lighter loads and vice versa. If desired, the adjustment can be effected during operation of the actuator, e.g. automatically under control by a load-sensing device connected to an adjusting mechanism.
REFERENCES:
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patent: 2593412 (1952-04-01), Chadwick et al.
patent: 2932283 (1960-04-01), Jeffery
patent: 2986124 (1961-05-01), Allemann
patent: 3012541 (1961-12-01), Meulendyk et al.
patent: 3068849 (1962-12-01), Thorner
patent: 4314502 (1982-02-01), Brinkel et al.
patent: 4367673 (1983-01-01), Krueck et al.
patent: 74116 (1987-08-01), None
Larson & Taylor PLC
Pos-Line AB
Ryznic John E.
LandOfFree
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