Motors: expansible chamber type – Cyclically operable – Working member controlled motive fluid for distributor motor
Reexamination Certificate
1999-10-01
2001-08-14
Nguyen, Hoang (Department: 3748)
Motors: expansible chamber type
Cyclically operable
Working member controlled motive fluid for distributor motor
C091S308000, C091S314000
Reexamination Certificate
active
06272968
ABSTRACT:
The invention relates to a control system of a pneumatic oscillation cylinder by means of which the cylinder carries out linear motion and the length and speed of whose oscillation motion are easily adjusted.
Previously known is a control system of a pneumatic oscillation cylinder by means of which a paper machine scraper is moved and where the pneumatic cylinder to-and-from motion is produced by means of a reversing valve connected to the pneumatic line. The reversing valve is controlled by means of pressure difference obtained from the system. In this known design the air stream that leaves the piston-pushed cylinder is slightly choked in order to get overpressure into the outlet line. When the piston and the piston rod arrive at a wanted reversing point, the rod or an additional part fixed to it hits an obstruction and the piston motion stops. Almost immediately this causes reduction of overpressure from the outlet line. Reduction of overpressure is utilised for moving the piston of the pneumatic valve so that reversing takes place. Same procedure is applied in both piston-reversing points. In the most simplified case the piston hits the cylinder ends, whereby neither external obstructions nor stoppers are needed. Neither can the oscillation length then be adjusted,.
In the praxis the solution has turned out quite inconvenient, since the pressure difference controlling the reversing valve changes at once when, for instance, the oscillation speed is changed in adjusting the working pressure. On the other hand, if striving to adjust the speed of motion in keeping the working pressure unchanged, a corresponding situation, where the pressure difference changes, is also achieved. The adjustment will also become complicated, since many chokers that effect one another must be adjusted.
In the above design the working pressure must all the time remain on a level corresponding approximately to the adjustment or higher, otherwise the cylinder motion stops, since there will then be no pressure difference necessary for the reversing valve.
In known solutions the weakness is the delay occurring also in the reversing points, which is due to the not-fast-enough drop of overpressure on the piston outlet side when the piston stops, since overpressure is discharged through an adjustable choke valve. A further disadvantage is that the piston hits the cylinder end or the piston rod hits an obstruction, which may cause a swing of the scraper and thus a scraping error.
By means of a control system as per this invention easy control, fast and jerk-free passing of the reversing points is achieved as well as a system not sensitive to working pressure variations. In conducting the streams of discharge pressure air into the box around the device an overpressure state in the box is produced and the equipment made applicable to severe conditions, in connection with a paper machine, for instance. The invention is characterized in what is presented in the patent claims.
REFERENCES:
patent: 2884860 (1959-05-01), Ellis et al.
patent: 3651642 (1972-03-01), Bauch et al.
patent: 4680930 (1987-07-01), Dollison
patent: 1 500 537 (1969-06-01), None
patent: 1 450 878 (1969-07-01), None
patent: 1 904 811 (1969-09-01), None
Larson & Taylor PLC
Nguyen Hoang
Polarteknik PMC Oy AB
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