GB1289990A - - Google Patents

Abstract

1289990 Sewing machine FARAH MFG CO Inc 8 Dec 1969 [30 Jan 1969] 59871/69 Heading D1G In a sewing machine an upper thread break detector comprises a switch controlled by the unbroken thread to repetitively open and close the switch, ducting means responsive to the repetitive operation to energise a relay, and means, operable when the thread breaks, the switch remains closed and the relay is deenergised, to signal that a break has occurred and/or stop the sewing machine, the switch being connected with a voltage source in a high impedance circuit so that fouling of the switch contacts by contaminents, which raise the contact resistance, can be tolerated. The switch is formed by a fixed contact 9 and the check spring 8 which is pulled away from contact 9 at each stitching cycle by the action of the take up lever. Operation. Relay 16 is energised when the sewing machine motor clutch is engaged to start the machine, the relay energising the circuit of lamp 17. The upper thread engages a loop 10 on the check spring 8 to open the switch contacts during stitch forming, the transistor 13 then being ON to charge capacitor 18 and switch transistor 14 ON and energise relay 15 to open the circuit of lamp 17. During the on-off action of the switch during normal stitching capacitor 18 maintains transistor 14 in this ON condition. On breakage of the upper thread the switch remains closed, capacitor 18 discharges and transistor 14 is turned OFF to de-energise relay 15 and complete the warning lamp circuit. The specification describes the values of the components of the circuit and states that a switch contact resistance of several thousands ohms, due to contaminants such as lint, may be tolerated. U solenoid valve may replace the lamp and then controls a pneumatic cylinder operating a brake and clutch.