Patent ID: 6863007

Claim:
A method for determining the lower thread supply on the lower thread bobbin ( 29 ) of a sewing machine ( 1 ) having a light transmitter ( 51 ) and a light receiver ( 53 ), comprising directing a light beam bundle ( 57 ) from the light transmitter ( 51 ) through slits ( 49 ′, 49 ″) in a hook base ( 27 ) and through peripheral openings ( 45 ′, 45 ″) situated in a hook body ( 17 ), tangential to a bobbin core ( 43 ) and to a thread packing, through a packing space ( 47 ) between flanges ( 35 , 39 ); receiving at least one of the light beams ( 57 x ) by a light receiver ( 53 ); forwarding a received signal to a machine control unit for the calculation of a spool packing diameter (D); and acquiring a momentary angle of rotation (alpha) of the hook body ( 17 ) and/or a time (t) when one of the light beams ( 57 x ) is registered by the light receiver ( 53 ).