Trapper of sewing machine

Abstract

The invention provides a thread tension device of a sewing machine controlling a wide range of thread tension while dispensing with a resistor with a large allowable current value. This thread tension device is provided with: a thread tension appliance (93) generating a tensile force to a sewing thread of a sewing machine; an actuator (19) becoming a drive source of the tensile force generation; a control means (50) outputting a control signal according to a target tensile force; and a driving circuit (20) driving the actuator by energizing a drive current according to the control signal. Thedrive circuit is provided with: detecting means (44, 45) connected to the actuator, detecting the drive current and capable of changing over a detection resistance value; and a resistor changeover means (35) changing over the detection resistance value by the target tensile force. When the target tensile force is larger than the prescribed value, the drive circuit detects the drive current at a small detection resistance value and controls the drive current.

Description

Technical field [0001] The present invention relates to a thread clamping device of a sewing machine having a driving source for adjusting the tension applied to the sewing thread. Background technique [0002] Conventionally, the following thread clamping devices are known, which have: a tension disc or a rotary tension type thread tensioner that applies tension to the sewing thread; and a voice coil motor (voice coil motor) that serves as a drive source for generating the tension. motor); and a control mechanism that controls the tension of the voice coil motor according to the increase or decrease in the amount of output current (for example, refer to Patent Document 1). [0003] The control mechanism of the thread clamping device shown in the above-mentioned document 1 has: a CPU that performs predetermined control according to a control program; a D / A converter that performs analog conversion on a control signal of the CPU; and a drive circuit that performs a The control sign...

AI Technical Summary

Problems solved by technology

[0008] Therefore, there is a disadvantage that a resistance element with a large allowable power is required as the resistance element, and resistance heat generation is also increased.

[0009] On the other hand, if a resistance element with a small resistance value is used to limit heat generation, a voltage drop will occur in a low-tension region, such as when an AC servo motor is used for driving the upper shaft of a sewing machine, or a switching power supply is used for power supply. In a noisy environment, it is difficult to perform correct control

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