Patent ID: 7069869

Claim:
A thread tension regulating apparatus for an over-lock sewing machine, comprising: a batch conversion device including (i) thread tension regulation cams, fixed on a dial cam shaft, for setting thread tension pressure adapted to a stitching method, (ii) swing pieces exhibiting a swinging motion according to a set lift of said thread tension regulation cams, respectively, (iii) spring bearings provided on a dial tension shaft so as to exhibit a swinging motion via engagement with ends of said swing pieces, respectively, and (iv) thread tension discs for forming set thread tension pressures, respectively, under spring forces supported by said spring bearings, respectively; fine adjustment devices for finely adjusting, via respective adjusting knobs, the set thread tension pressures formed by said thread tension discs; a home position returning member; a first interlock device for displacing said home position returning member in a first direction in response to rotation of a respective one of the adjusting knobs from a home position in a pressurizing direction; and a second interlock device for displacing said home position returning member in the first direction in response to rotation of the respective one of the adjusting knobs from a home position in a depressurizing direction, wherein (i) said first interlock device includes a first interlock obviating device for causing said second interlock device to take a non-operating condition when said first interlock device operates, and (ii) said second interlock device includes a second interlock obviating device for causing said first interlock device to take a non-operating condition when said second interlock device operates.