| 摘要 |
<p>A device determines the true feed transmitted by a feed device of an industrial sewing machine to the sewn material. The number of threads passing in front of a sensor is counted and the feed is derived from the predetermined thread density. In order to obtain a thread count of maximum precision irrespective of the orientation of the sewn material, a rotating slit diaphragm (7) with at least one parallel-edged radial slit (8) is arranged in front of the photoelectric cell (10) of the sensor. Preferably, a second, stationary slit diaphragm (5) whose angular position can nevertheless be varied comprises a slit (6) which opens over a certain angular range. The rotary slit diaphragm (7) has a larger number of slits (8). The required rotational speed of the rotary slit diaphragm (7) can therefore be reduced. To prevent errors due to the pattern of the fabric, the device can function in the relatively long infrared wavelength range.</p> |
