A SIGNAL ARRANGEMENT IN A SEWING MACHINE

Abstract: A signal arrangement for the purpose of supplying a signal as a pre-warning to the operator of a sewing machine when the bobbin thread is about to run out. A bobbin (19) in a case (13) is inserted in the loop taker (10) having an opening (22) for a radially directed light beam from a light source (24). A side thereof are sensors (29, 30) receiving reflected light from surfaces (34, 35) on the bobbin body when this is free from thread. When the bobbin contains a plurality of thread layers the light will hit the thread and no reflection occurs. After the thread is consumed the surfaces are uncovered and the reflex which then occurs releases the signals in the sensors. A friction clutch (31) between the loop taker and the bobbin is provided to rotate the bobbin together with the loop taker. Several reflexes give pulses in the sensors arranged in a special order owing to the fact that the light source, the reflectors and the sensors are positioned in a predetermined sequence. The special order of the pulses are by way of an electronic signal expressing that the thread is out.

Description: r- A signal arrangement in a sewing machine \ The present invention relates to an arrangement for supplying a signal pre-warning the operator of a sewing machine of the fact that the thread on a bobbin is about to run out. Arrangements for immediate detection of the thread content of a bobbin are 5 known in which several principles based on several kinds of signals have been used. Mechanical devices, such as lever arms, sensing the thread content and putting a sound source into action when a predetermined minimum is reached have, however, the drawback of bad accuracy and of making the change of the bobbin difficult. By the introduction of an optic detection by means of a photoelectric 10 cell, mechanical components can be omitted, but the accuracy is still bad. Therefore, it is considered necessary to develop this system by making use of distinct points of measuring etc. whereby the accuracy is improved. By the present invention a signal arrangement is presented which is provided with a light source and a light sensor directed to a reflecting surface on the 15 bobbin body which reflects the light when the bobbin is nearly empty. A reflex is then received by the sensor which gives a signal to an electronic unit from which a warning signal is passed to the operator. At this moment there is still thread on the bobbin but if the sewing proceeds so that the thread goes out pulses of reflected light will occur in a predetermined order in dependence on the positions 20 of the source and the sensor, respectively, which pulses by the electronic unit release another signal by which (for example) the sewing is stopped. The advantage of such an arrangement is achieved therein that the sewing can proceed until the thread has in practice run out. Moreover, the drawbacks of mechanical detection arrangements as mentioned in the foregoing are eliminated. 25 With the intention that these properties shall be obtained the object of the invention shall be carried out in accordance with the characteristics of Claim 1. An example of an embodiment of the invention will be described in the following with reference to the accompanying drawing, which shows in Fig. 1 a vertical projection of a shuttle mechanism of a sewing machine, in Fig. 2 the 30 same mechanism in a cross section at the arrows π - π of Fig. 1, in Fig. 3 an exploded sketch of the shuttle mechanism, in Fig. 4 the same projection as in Fig. 1 but with the bobbin in another position and in Fig. 5 a block diagram of a decoder. The Figures show the whole shuttle mechanism including the signal arrange¬ ment according to the invention. The mechanism comprises a loop taker 10 on a carrier 11 having a horizontally journalled shaft 12 so that a bobbin case 13 is inserted into the loop taker from the side and is retained there by a releasable latch 14 engaged in an annular groove 15 on a bobbin shaft 16. The bobbin case can be released from the shaft and removed by rotating the latch about a pin 17. Arranged in the bobbin case is an exit 18 for thread from a bobbin 19 located in the case. At the exit a leaf spring 20 projects under which the thread is pressed against the surface of the case and is thus tensioned. The bobbin is inserted in the case in such a manner that it rotates in the direction of the arrow 21 when the thread is pulled out therefrom. In its wall the case has an opening 22 extending about half the way around the periphery of the case so that the bobbin is visible through the opening. The entire mechanism is assembled under a loop taker cover 23 which by means of screws is secured to a bearing bracket in the sewing machine body. The design of the signal arrangement of this embodiment is shown in Figs. 1, 3 and 4. In a plan perpendicular to the bobbin shaft 16 electronic components are entered, each one into its hole in the loop taker cover 23 and directed to the bobbin shaft. One component is a lamp (LED or the like) 24, the light beam of which is shown by arrows 25 in Figs. 1 and 4. The beam passes through the opening 22 and a fissure 26 in the loop taker towards the central portion 27 of the bobbin 19. This portion has a plurality of plane surfaces of a reflecting material which reflects the light along the arrows 28 through the fissure and the opening against someone of the other components which are phototransistors 29, 30 connected by output v/ires to a decoder. 3etween the loop taker and the bobbin a ring 31 of an elastic material is disposed which presses against the bobbin and tends to rotate it in the direction of rotation of the loop taker according to the arrow 32. By rotation through a small angle in this direction the light is reflected according to the arrows 33 (Fig. 4) and after another small rotation the surface 34 leaves the light beam and no light is reflected. If the rotation of the bobbin continues the surface 35 enters into the beam and light is reflected to the phototransistors according to Figs. 1 and 4, respectively. When there is thread on the bobbin in several layers and the bobbin is inserted as shown in Fig. 2 it rotates in the direction opposite to the loop taker when thread is pulled out, in doing this the end surface of the bobbin slips against the ring 31. The light beam from the lamp hits the wound thread but is not reflected. When less than one layer of the thread remains the surfaces 34, 35 are uncovered and hit by the light beam which is reflected. Depending on the direction of rotation (arrow 21) the transistor 30 is first hit and then the transistor 29. The direction of rotation is thus expressed by the sequence of the electric pulses from the transistors. As soon as the thread has run out the bobbin 5 is let free and starts rotating in the direction of rotation of the loop taker (arrow 32). The sequence of the electric pulses will then be inverted in relation to the former. The signals mentioned in the foregoing relating to the pre-warning and the ending of the thread, respectively, will now be explained with the said inversion of 10 the pulse sequence as a condition. The pre-warning signal occurs when less than one layer of thread remains at a rotation according to the arrow 21. A stop signal occurs when the thread comes off the bobbin, which then reverses. The two signals here referred to can be generated in a decoder 36. The latter can for instance be constituted by a TTL - (transistor - transistor-logic) standard circuit 15 No. CD 4515B (Fig. 5). The two inputs 37, 38 of the wires from the transistors 29, 30 receive pulses in a positive or a negative sequence - assuming that positive is the sequence when the bobbin rotates according to the arrow 21 and negative when in the opposite direction. At the positive pulse sequence the decoder supplies a voltage on the output 39. As said in the foregoing, the pulses first occur 20 during the rotation of the bobbin according to the arrow 21, when the thread is about to run out, and then during the rotation of the bobbin according to the arrow 32, when the thread has come off the bobbin, which then follows the rotation of the loop taker. During the positive sequence (signal 39) a pre-warning is given, e.g. a lamp is lit, and during the negative sequence (signal 40) the 25 machine stops. The system now described can be simplified and adapted for only pre- warning when the thread is about to run out, i.e. when the bobbin body appears under the thread winding and causes reflections. Such a simple system constitutes the substantial idea of the invention and is defined in the following claims. _- SUBSTITUTE SHEET

Claims: Claims 1. A signal arrangement in a sewing machine for sensing and indicating the thread content on a bobbin by means of a light source and at least one sensor supplying a signal when illuminated, characterized in that the light source (24) and the sensor (29,30) are directed to the central portion (27) of the bobbin which is provided with at least one reflector (34,35) which is uncovered when the thread on the bobbin (19) is about to run out. 2. A signal arrangement according to Claim 1, characterized in that two sensors (29,30) are positioned next to one another in the tangential direction of the bobbin and that the reflex from the reflector hits the respective sensor in different moments in an order which is dependent on the direction of rotation of the bobbin. 3. A signal arrangement according to Claim 2, cha racterized in that the signals from the sensors are supplied to a decoder (36) which on one of two output wires (39,40) gives a signal for the one or the other direction of rotation of the bobbin. 4. A signal arrangement according to Claim 1, cha racterized in that the bobbin is connected by means of a friction clutch (31) to a drive member (10) included in the machine and rotating in., the direction for winding thread on the bobbin, which clutch is adjusted for slippage between the bobbin and the drive member when thread is unwound from the bobbin. 5. A signal arrangement according to Claim 4, characterized in that the bobbin is driven by the stitch-forming elements of the machine in the unwinding direction when thread is unwound, but by the friction clutch in the direction for winding when the thread content is out. 6. A signal arrangement according to Claim 5, characterized in that the friction clutch is constituted of a ring (31) of an elastic material positioned between the bobbin and a loop taker (10) included in the stitch-forming elements. 7. A signal arrangement according to Claim 6, characterized in that the light source and the sensors are positioned in a loop-taker cover (23) included in the stitch-forming elements. 8. A signal arrangement according to Claim 1, characterized in that the said reflector is made of plane mirror surfaces on the central portion of the bobbin or of prismatic bodies formed in the bobbin material. OMPI

Inventors: LINDH PER AKE LENNART, SKOGWARD KENNETH OSCAR EMANUEL
Applicants: HUSQVARNA AB, LINDH PER AKE LENNART, SKOGWARD KENNETH OSCAR EMANUEL
Application year: 1982
Main classification: D05B59
IPC codes: D05B59