| 摘要 |
1,234,903. Valves. ATLAS COPCO A.B. 20 Aug., 1969 [27 Aug., 1968], No. 41453/69. Heading F2V. [Also in Division G3] The speed of a fluid powered, hand held, grinding or drilling machine, e.g. for dentistry is kept constant by controlling the fluid pressure by a valve responsive to the difference between an actual speed signal and an adjustable reference signal. The control valve is preceded by a pressure reduction valve (Fig. 3, not shown). The actual speed signal is a D.C. voltage derived from an A.C. signal produced in a pick-up coil associated with magnetic inserts in the rotor of the machine and it is compared with the reference signal from a potentiometer in an integrating operational amplifier whose output is connected through a servo amplifier to the control valve. As shown, this comprises a coil 43 whose energization progressively causes an armature 45 to uncover a bleed orifice 41, against the pressure of a piston 46 connected to the inlet 38, but in an alternative arrangement (Fig. 7, not shown) the coil is disposed in an annular magnetic field and is mounted on a member which is movable axially to throttle the fluid supply.
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