| 摘要 |
A sewing machine has a main drive shaft to which is drivingly coupled the output member of a coupling motor unit, the latter including an electric motor having a constantly rotating output shaft, a braking structure, and electrically controlled electromagnets for causing the output member to engage and become disengaged from the output shaft and the braking structure to increase and decrease the rpm of the main drive shaft of the machine. An rpm regulator has first and second inputs for receipt of a desired-rpm command signal and an actual-rpm feedback signal. The actual-rpm feedback signal is generated using a pole wheel rotating synchronously with the sewing-machine drive shaft and a plurality of pick-up transducers spaced along the pole-wheel periphery. During pole-wheel rotation, an A.C. voltage is induced in each such pick-up transducer. The spacing of the transducers relative to the spacing of the poles of the pole wheel is such that these induced voltages are phase-shifted relative to one another. Each transducer output voltage is applied to a respective rectifier. The rectified, pulsating output voltages from the plural rectifiers are algebraically summed, without the use of smoothing capacitors, to form a relatively smooth D.C. voltage which is suitable for use as the actual-rpm feedback signal of the system.
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