GB2081033A - Sewing Machine - Google Patents

Abstract

A sewing machine which includes an electric motor having a stator winding in which a switch is provided in the stator winding circuit for varying the torque output of the motor, the switch in one position enabling normal torque to be produced by the motor for sewing purposes and in another position shunting out part of the stator winding so as to produce increased torque from the motor for sewing heavier material. <IMAGE>

Description

SPECIFICATION An Improved Sewing Machine Prior Art Ordinary household sewing machines are driven by an electric motor having a stator with a stator winding. The impedance of this stator winding is such as to enable the motor to develop sufficient torque to sew most materials. However, it is sometimes desirable to sew thicker materials or materials which, because of their nature, the needle finds difficult to penetrate. Leather is one such material. Increased torque is necessary from the motor in order effectively to sew such material.

With ordinary sewing machines, the output of the motor under normal operating conditions is less than 90 watts and its starting torque is about 0.8 to 1.5 kg cm. The operating torque is from 0.45 to 0.6 kg cm. When sewing thicker materials or, for example, leather, the required load is above 1 20 watts and, therefore, the normal torque developed by the motor is insufficient. It is possible, of course, to compensate for this by using a larger motor but this means that the sewing machine is operating inefficiently for most of its working time. It also means that the cost of the sewing machine is increased and it consumes more power.

It is the main object of this invention to provide a sewing machine in which materials of different thickness and/or consistency may be sewn expeditiously.

Statement of Invention According to the present invention there is provided a sewing machine, including an electric motor having a stator winding, characterised in that the impedance of the stator winding circuit is adjustable to vary the torque generated by the motor. Preferably, the stator winding circuit includes two windings in series and a switch is provided for shunting out one of said windings to produce increased torque from the motor.

Brief Description of Drawing The Figure of the drawing is a circuit diagram for a sewingmachine constructed in accordance with the invention.

Detailed Description of Preferred Embodiment Referring now to the drawing, a sewing machine has an electric motor with a rotor g and a stator h and a starting capacitor f. The stator h has two windings a and b in series connected to a plug i.

Connected between the two windings a and b is a switch having three terminals c, d and e. The winding a is connected to terminal c and the winding b is connected to terminal e. Terminal d is connected by the wirejdirectly to the stator.

The switch has a moveable arm k.

During normal operation of the sewing machine, when sewing material such as cloth of normal thickness, the arm kwill connect terminals c and e which means windings a and b will be in series and the motor will generate sufficient torque for the sewing process. It may well be that the motor develops 1/20th of a horsepower in this mode.

If the sewing machine is then to sew material of greater thickness or higher consistency, then the arm k is moved so that the terminals c and d are connected which has the effect of shunting out the winding b from the motor winding circuit whereby the only impedance in the stator winding circuit will be the winding a. This has the effect of permitting more current to flow through the winding a and have developing more torque in the motor. This additional torque may develop about 1/10th of a horsepower.

The invention applies equally to motors which operate on any known voltage source, for example, 110 or 240 volts.

Claims

1. A sewing machine, including an electric motor having a stator winding, characterised in that the impedance of the stator winding circuit is adjustable to vary the torque generated by the motor.

2. A sewing machine as claimed in Claim 1, in which the stator winding circuit includes two windings in series and in which a switch is provided for shunting out one of said windings to generate increased torque from the motor.

3. A sewing machine having a stator winding circuit substantially as herein described with reference to the accompanying circuit diagram.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION An Improved Sewing Machine Prior Art Ordinary household sewing machines are driven by an electric motor having a stator with a stator winding. The impedance of this stator winding is such as to enable the motor to develop sufficient torque to sew most materials. However, it is sometimes desirable to sew thicker materials or materials which, because of their nature, the needle finds difficult to penetrate. Leather is one such material. Increased torque is necessary from the motor in order effectively to sew such material. With ordinary sewing machines, the output of the motor under normal operating conditions is less than 90 watts and its starting torque is about 0.8 to 1.5 kg cm. The operating torque is from 0.45 to 0.6 kg cm. When sewing thicker materials or, for example, leather, the required load is above 1 20 watts and, therefore, the normal torque developed by the motor is insufficient. It is possible, of course, to compensate for this by using a larger motor but this means that the sewing machine is operating inefficiently for most of its working time. It also means that the cost of the sewing machine is increased and it consumes more power. It is the main object of this invention to provide a sewing machine in which materials of different thickness and/or consistency may be sewn expeditiously. Statement of Invention According to the present invention there is provided a sewing machine, including an electric motor having a stator winding, characterised in that the impedance of the stator winding circuit is adjustable to vary the torque generated by the motor. Preferably, the stator winding circuit includes two windings in series and a switch is provided for shunting out one of said windings to produce increased torque from the motor. Brief Description of Drawing The Figure of the drawing is a circuit diagram for a sewingmachine constructed in accordance with the invention. Detailed Description of Preferred Embodiment Referring now to the drawing, a sewing machine has an electric motor with a rotor g and a stator h and a starting capacitor f. The stator h has two windings a and b in series connected to a plug i. Connected between the two windings a and b is a switch having three terminals c, d and e. The winding a is connected to terminal c and the winding b is connected to terminal e. Terminal d is connected by the wirejdirectly to the stator. The switch has a moveable arm k. During normal operation of the sewing machine, when sewing material such as cloth of normal thickness, the arm kwill connect terminals c and e which means windings a and b will be in series and the motor will generate sufficient torque for the sewing process. It may well be that the motor develops 1/20th of a horsepower in this mode. If the sewing machine is then to sew material of greater thickness or higher consistency, then the arm k is moved so that the terminals c and d are connected which has the effect of shunting out the winding b from the motor winding circuit whereby the only impedance in the stator winding circuit will be the winding a. This has the effect of permitting more current to flow through the winding a and have developing more torque in the motor. This additional torque may develop about 1/10th of a horsepower. The invention applies equally to motors which operate on any known voltage source, for example, 110 or 240 volts. Claims

1. A sewing machine, including an electric motor having a stator winding, characterised in that the impedance of the stator winding circuit is adjustable to vary the torque generated by the motor.

2. A sewing machine as claimed in Claim 1, in which the stator winding circuit includes two windings in series and in which a switch is provided for shunting out one of said windings to generate increased torque from the motor.

3. A sewing machine having a stator winding circuit substantially as herein described with reference to the accompanying circuit diagram.