GB821858A - Improvements in regulating devices for tuning vibratable mechanical systems, especially material-testing apparatus - Google Patents

Abstract

821,858. Automatic control systems for mechanical vibrators. LOSENHAUSENWERK DUSSELDORFER MASCHINENBAU A.G. July 19, 1956 [Sept. 16, 1955], No. 22350/56. Class 38 (4). In a mechanical vibrator, e.g. for testing materials, the vibrating mass produces a measuring voltage which is in phase with the vibration of the mass, and the phase of the measuring voltage is compared with the phase of the sine wave voltage producing the vibrations, and the natural frequency of the mechanical system is altered in dependence upon the phase difference between the two voltages. In this way, when the frequency of the exciting voltage is changed the mechanical resonance of the system is correspondingly changed. As shown, a vibrating table is mounted by means of a disc 2 between two annular air pads 3, 4, which are held in an annular frame 5, the air pads being connected together by tubes 31. The table is excited in known manner from a sine wave generator 6 via an amplifier 7. A device 9, fixed to the vibrating table, produces a measuring voltage which is in phase with the vibrations of the table and is fed to a phasecomparing device 10 which is also supplied with the exciting voltage. There is normally a phase difference of 90 degrees between the two voltages when the system is in resonance, variations from this value producing a positive or negative voltage which via amplifier 11 and servomotor 12 controls a rotary valve 13. The valve 13 controls a passage 14 open to the atmosphere, a passage 15 communicating with the air pads, and a passage 16 connected to a compressed-air pipe, the air pads being connected to the pressure pipe 16 or with the atmosphere via 14 according to whether the servomotor is actuated by a positive or a negative voltage.