AU561735B2 - A loop-taker mechanism in a sewing machine - Google Patents

Description

A loop-taker mechanism in a sewing machine ^•

The present invention relates to a loop-taker mechanism in a sewing machine including an arrangement for facilitating the guiding of the upper thread loop around a bobbin and a bobbin case journalled in a rotating hook.

In a generally used design of a loop-taker mechanism with a rotating hook member friction forces in the journalling surfaces develop a torque on the bobbin case. The torque is counteracted by a holder arm preventing the bobbin case from rotating in the machine. As the upper thread loop has to pass between the holder arm and the bobbin case an essential force is required in the upper thread for guiding the loop around the bobbin case. A general solution for decreasing this force is the arrangement of a movable arm which temporarily swings back the bobbin case so that a fissure is formed between the holder arm and the bobbin case at the moment when the upper thread passes. Such an arm is space demanding and raises the cost of the mechanism. Moreover, it will require an accurate adjustment. The present invention presents a solution for achieving an open way for the thread through the mechanism without using any price raising, complicating members. Instead, according to the invention two magnets are used which are positioned opposed to each other, one being fastened in the bobbin case and one in an especially designed bobbin case bracket, which bracket replaces the holder arm used in the former designs. The improved properties of the arrangement here referred to will according to the invention appear, when the arrangement is carried out in accordance with the characterizing clause of Claim 1.

An embodiment of a loop-taker mechanism according to the invention provided with a hook rotating in a horizontal plane beneath the needle of the sewing machine will be described in the following with reference to the accompanying drawing in which Fig. 1 shows a vertical cross section A-A through such a loop-taker mechanism, Fig. 2 is a horizontal projection of the mechanism and Fig. 3 is a partial cross section B-B showing a bobbin, a bobbin case and a bobbin case bracket. A hook 1 (Figs. 1 and 2) is provided with a toothed wheel 2 which by means of a driving belt or shaft makes the hook rotate in the direction of the arrow (Fig. 2) around a fixed shaft 3 positioned in the body 4 of the machine. A bobbin case 5 and a bobbin 6 are journalled in a cavity 7 of the hook. The bobbin case is retained in the hook by means of a pin 8 and a bobbin case bracket 9 fixed on the body 4 at a distance to the bobbin case 5 such that the upper thread 10 when caught by a hook tip 11 can be guided by the latter around the bobbin case in a manner known per se. The bobbin case bracket 9 being at a distance 12 from the bobbin case, is in the shown embodiment provided with two lugs 13, 14 keeping the bobbin case in the proper vertical position and with another lug 16 keeping the bobbin case laterally. The lugs are located on the bracket so that the upper thread loop passes a fissure 15 when guided around the bobbin case. The bobbin case is also provided with a magnet 17 and the bracket with a magnet 18 with equal poles (N-N) of the magnets facing each other, as shown in Fig. 3.

When the thread loop is guided around the bobbin case the friction force on the thread in the journallϊng surfaces of the cavity 7, due to the masses of the bobbin case and the bobbin and also the friction of the thread loop when passing the top surface of the bobbin case will reduce the distance 12 so that that the pulling force in the thread must increase in order to make the thread run in the fissures between the bracket and the bobbin case when leaving the hook tip 11 at a point 19 (Fig. 2). The two magnet poles N, N repel each other and counteract the reduction of the distance 12 so that the force in the thread need not be increased to any essential degree.

The described embodiment is an example of a realization of the invention. Of course, modifications are possible without departing from the inventive idea. The invention can thus be applied to other types of loop-taker mechanisms than the shown one and the disposition of the magnets 17, 18 can also be varied. For example one magnet can be a horse shoe magnet and the other magnet be positioned with opposed poles between the poles of the horse shoe magnet so that the thread can be pulled through the U-shaped fissure between the two magnets.

Claims

Claims 1. A loop-taker mechanism in a sewing machine including a rotating hook member and a bobbin case with an under thread bobbin journalled therein and a bobbin case bracket fixedly secured to the machine body, character¬ ized in that the bobbin case bracket (9) has a cavity (7) in which the bobbin case (5) is located and retained by protrusions above the cavity, such as lugs (13,14,16), that one of two magnet poles (17, 18) repelling each other is located on the bobbin case bracket at a portion of the cavity which is free from said protrusions, and that the other pole is located on the bobbin case, whereby this one is subject to a force directed to a portion of said cavity located below such protrusion.

2. A loop-taker mechanism according to Claim 1, characterized in that the bobbin case bracket (9) is countersunk in a recessed portion of the hook member (1).

3. A loop-taker mechanism according to Claim 1, characterized in that the magnet poles (17,18) are countersunk in the bracket (9) and the bobbin case (5), respectively, and develop a force perpendicular to the axis of the bobbin (6).

4. A loop-taker mechanism according to Claim 1, characterized in that a fissure (15) for guiding a thread between the bobbin case (5) and the bracket (9) is kept open by the force, even when the thread due to the movement of the hook member (1) presses the bobbin case in the direction to the bracket.