Sewing machine with reference speed correction by dimensional ratio between motor- and armshaft-pulleys.

摘要

A sewing machine comprises a multiplier for multiplying an operator-controlled variable reference speed value by a multiplying factor, a tachogenerator for generating speed-related pulses at a rate proportional to the speed of rotation of a motor pulley and an angular position detector for generating a position pulse in response to a predetermined position of an armshaft pulley which is coupled by a belt to the motor pulley. A ratio detector is provided for counting the speed-related pulses present during the interval between successive ones of the position pulse to generate a count as a representation of the diameter of the armshaft pulley and deriving a ratio value between the count and a value representative of the diameter of the motor pulley. The ratio value is applied to the multiplier as the multiplying factor to alter the reference speed value. A speed control circuit is responsive to the speed-related pulse for deriving an actual motor speed value and controls the speed of the motor in accordance with a difference between the actual motor speed value and the altered reference speed value.