Abstract: A method of controlling a motor-driven let-off motion in a loom including a system for controlling a let-off motion motor includes the steps of sampling a variation of warp tension during each revolution of a main shaft of the loom, effecting at least proportional and integral control modes on the average of sampled values, adding a proportional and integral output to a basic speed signal at a prescribed ratio, and applying a sum signal to the system for controlling the let-off motion motor.

Abstract: For ideal stoppage of loom rotation at a constant crank angle, initiation of braking action on loom rotation is always automatically and properly timed on the basis of initial stop lag angle representative of the current braking function so that the resultant actual stop angle should match the preselected stop crank angle and, more preferably, the initial stop lag angle is renewed to cover gradual deterioration in the braking function.

Abstract: The amplitude of a signal (original waveform) produced by weft sensors is relativized, and the signal waveform is analyzed in various aspects based on multiple parameters to discriminate a weft yarn and a jet of fluid accurately. More specifically, a discriminating function is calculated beforehand from a signal indicative of the weft yarn and jet of fluid under normal weft insertion conditions, and a signal produced in actual detection operation is compared with the discriminating function to determine whether the weft yarn is present or not. The discriminating function can be obtained by extracting feature parameters from a signal generated by the weft sensors, and relativizing the feature parameters with respect to the original signal waveform to find a reference quantity. The feature parameters include the original waveform per se, a differentiated value thereof, an integrated value thereof, frequencies in certain frequency ranges, and sampling averages of the above parameters.

Abstract: Jet looms have feelers for detecting whether a weft yarn has been properly inserted through a warp shed at an end of the warp shed.Air jet looms have photoelectric feelers the sensitivity of which becomes lowered with time due to dust or fly waste attached to the feelers in operation. Water jet looms incorporate electrode feelers with insulation therebetween tending to be deteriorated due to water applied, and hence the sensitivity of such feelers is also reduced with time.An apparatus according to the present invention increases the gain of a variable-gain amplifier for amplifying an output signal from the feeler as the level of the output signal is lowered, so that the amplified signal is maintained at a suitable level.