the reed and thus the light beam of the photoelectric detecting scheme crosses the warp line as shedded so that the warp line detected signal at that timing triggers the delay circuit more specifically the output of the photoelectric device 10 obtainable when the light beam between the light source 9 and the photoelectric device 10 crosses the upper side warp line when the warp is most shedded is withdrawn as the upper side warp line detected signal and is applied to the delay circuit 13 in lieu of the opening signal of the above described timing switch 12 the delay circuit 13 is triggered by the above described upper side warp line detected signal and provides an output pulse which falls at the predetermined rotational angle 80 u00b0 or 90 u00b0 of the crank shaft 6 while the subsequent delay circuit 14 is triggered in response to the fall of the pulse output whereby the system operates in substantially the same manner as described in conjunction with the foregoing embodiment according to the last described embodiment no mechanical timing switch is necessary resulting in simplicity of structure of the system fig7 is a block diagram of another embodiment of the present invention the major portion of the fig7 embodiment is substantially the same as the fig3 embodiment therefore only a different portion of the fig7 embodiment will be described in the following the timing pulse obtainable.