A method is provided for contactless optical detection of yarn at a workstation of a textile machine in which the yarn moves in a sensing slot between a source of radiation and an optical sensor having at least one row of radiation sensitive elements, whereby shading of the individual radiation sensitive elements by yarn moving through the sensing slot is monitored and a state of the yarn is evaluated on a basis of the monitoring. The method monitors and evaluates a position of the yarn in the sensing slot or a time course of the position of the yarn in the sensing slot. A change is detected in the position or in the time course of the position of the yarn in the sensing slot corresponding to a yarn break before an end of the yarn break passes through the sensing slot. When the yarn break is sensed, a stop signal is generated for the workstation.

A method is provided for contactless optical detection of yarn at a workstation of a textile machine. The yarn moves in a sensing slot between a radiation source and an optical sensor having at least one row of radiation sensitive elements. Shading of the individual radiation sensitive elements by yarn moving through the slot is monitored and a state of the yarn is evaluated based on the monitoring, which includes monitoring and evaluating a position of the yarn in the sensing slot or a time course of the position of the yarn in the sensing slot. A change is detected in the position or in the time course corresponding to a yarn break before an end of the yarn break passes through the sensing slot. When the yarn break is sensed, a stop signal is generated for the workstation.

In order to optically sense a yarn moved in the longitudinal direction of the yarn, a yarn sensor has a light source, a detector and a light guiding element. The yarn sensor is based on the effect of frustrated total internal reflection (FTIR). Because of the FTIR effect, scattered light exiting the light guiding element in the contact region between the yarn and an outer surface of the light guiding element is detected by means of the detector, in which case sensing of the yarn lying against the outer surface is enabled. Alternatively, the reduced intensity in the totally internally reflected beam is then sensed by the detector. The intensity in the totally internally reflected beam is reduced mainly by the scattered light coupled out of the light guiding element.

In order to optically sense a yarn moved in the longitudinal direction of the yarn, a yarn sensor has a light source, a detector and a light guiding element. The yarn sensor is based on the effect of frustrated total internal reflection (FTIR). Because of the FTIR effect, scattered light exiting the light guiding element in the contact region between the yarn and an outer surface of the light guiding element is detected by means of the detector, in which case sensing of the yarn lying against the outer surface is enabled. Alternatively, the reduced intensity in the totally internally reflected beam is then sensed by the detector. The intensity in the totally internally reflected beam is reduced mainly by the scattered light coupled out of the light guiding element.