Arrangement in a sewing machine

Abstract: A measuring arrangement for measuring the real fabric feeding in a sewing machine consists of a wheel (18) which is rotated by the fabric without slip and is located on a special presser foot (12). There is a potentiometer (22) and a sliding contact (23) which gives a measuring quantity representing the rotation of the wheel when feeding voltage to the potentiometer and rotating the wheel. The measuring quantity is transferred to a computer unit in the sewing machine being able to calculate the feeding of the fabric positively or negatively. Such an arrangement will particularly be useful when it is desired to sew a buttonhole totally automatically.

Description: The present invention relates to an arrangement in a sewing machine for measuring the distance of feeding of the working material in forward and reverse directions, comprising a gauge wheel actuated by a resilient means to engage the working material in order to be rotated by the movement thereof. An arrangement for measuring a length can consist of a converter which makes an angle of a linear magnitude e.g. a number of revolutions in a rotatable sensor which follows a linear feeding of a material. In order to obtain a good accuracy the rotation of the sensor must follow the feed piece exactly and the angle measuring be carried out by creating a measuring quantity which carefully represents the angle. The invention relates to an improvement of hitherto known converters of a linear movement of a determined size to a thereof determined angle which is converted in electronic circuits from an analogous measuring quantity into a digital number. As a result of such a conversion the measured magnitude can be used in a control system including a processing of data for making operations on a working material. In the present case the arrangement is used in an electronic sewing machine for controlling the stitch forming components in forming a special fancy seam. In this application the requirement for a high accuracy is great; the measuring arrangement shall be sensitive for very small displacements of the working material. It is also important that the arrangement separates and assigns the right sign to the displacements in the forward and the backward directions respectively. It is known from FR 2,521,605 to utilize a sensor providing a signal corresponding to the movement of the fabric, and a control means receiving the signal in order to stop the machine after a predetermined distance of movement. This patent also proposes to sense the speed of the fabric and to integrate the speed signal in order to determine the distance of movement. DE 30 273 20 discloses an arrangement comprising a frame which is movable with the fabric and has a gear drive mechanism for transferring the movement to a rheostat in order to sense the distance of movement of the fabric. The object of the present invention is to provide an arrangement of the kind mentioned in the introduction which as compared to the previously known arrangements is more compact and less complicated to manufacture and also more reliable in operation. This has been obtained by an arrangement which is generally characterized by a sensor made integral with the gauge wheel and comprising a rheostat connected to a voltage source for producing a voltage proportional to the amount of rotation of the gauge wheel. An embodiment of the arrangement according to the invention will be described in the following with reference to the accompanying drawings which show in: Fig. 1 a vertical projection of a presser foot of a sewing machine provided with embodiment of the arrangement. Fig. 2 a horizontal projection of the same presser foot with a cross section of the arrangement. Fig. 3 a vertical projection of the arrangement. Fig. 4 a wiring diagram of the electronic circuits connected to the arrangement. Fig. 5 a buttonhole sewn by means of these circuits. The presser foot is detachably located on a bar 10 and is in the usual way displaceable between an upper resting position and a lower working position. The attachment in the lower end of the bar is a snap-on attachment 11 from which the foot can be easily detached and exchanged for another one. The foot shown is a buttonhole foot 12 combined with a measuring arrangement 13. The sewing machine is assumed to be an electronic computerized sewing machine with a program for sewing of buttonholes. The design of the arrangement is shown in Fig. 1 and 2. The body is provided with two halves 14, 15 united by means of shafts 16, 17. The one, 16, also serves as a shaft for a wheel 18, with a toothed periphery which projects into an opening 20 between the two halves 14, 15. On the inside of one of them, 14, a circular disk 21 is supporting a resistance surface 22 concentrical with the wheel, and constituting a part of a potentiometer. A sliding contact 23 of it is positioned on the wheel so that different settings are effected on the potentiometer when the wheel rotates. From the resistance 22 and the contact 23 electric wires come into a cable 24 which ends with a plug 25 fitting into a corresponding socket on the sewing machine. Fig. 2 shows that the presser foot and the measuring arrangement are united by means of a shaft 17 being at one end attached to the presser foot and constituting a pivot for the measuring arrangement in a vertical plane. A screw spring 26 is concentrically placed on the shaft 17 between the measuring arrangement and the presser foot and has attachment points 27, 28 on the arrangement as well as on the foot. The purpose of the spring is to press the wheel in the direction towards the stitch plate of the machine i.e. towards a working material guided through the sewing place while the wheel is easily rotating on its shaft 16 and follows the movement of the material forwards as well as backwards. In order to limit the turning capacity of the spring a couple of pins 29, 30 are located on the body half next to the presser foot and hit it from below as well as from above. Thus they constitute a stop for the movement of the arrangement in the vertical plane. A further spring 31 is provided in this half 15 near to the wheel 18 which is influenced by this spring to rotate into a starting position so that the sliding contact 23 goes to an end position on the resistance 22. The function of the measuring arrangement according to the foregoing is hereinafter described together with a system for automatic sewing of buttonholes with an electronic sewing machine. The system is illustrated as a block diagram in Fig. 4 which also includes an arrangement 32 for measuring a button of a size to fit the buttonhole. The arrangement 32 includes a potentiometer 33 which supplies a voltage corresponding to the size of the button on a wire to an analogue/digital converter 34 in which the voltage is encoded and applied to a comparator 35. The above mentioned measuring arrangement provides a voltage which successively increases the longer the wheel 18 rotates. This voltage is gradually encoded in a second analogue/digital converter 36 and set to zero when the wheel 18 is reaching its initial position. The code from the converter is first applied to the comparator 35 and then on a wire 37 to an AND-circuit. A start contact 38 supplies a start signal to a counter 39 when a buttonhole is to be sewn and adjusts it to zero. The buttonhole sewing then starts with a space A in the reverse direction (Fig. 5). This is indicated by a signal on a wire 40 from the counter. During the sewing the wheel 18 rotates in contact with the fabric and the converter 36 provides an increasing digital code to the comparator. When this code coincides with the code recorded in the comparator from the converter 34 a puls is released from the comparator which together with a signal on the wire 40 in an AND-circuit 41 to an OR-gate 42 releases a counting pulse to the counter 39. The output signal of the latter then changes from the wire 40 to a second output 43 which means zero-rated feeding and bar stiches B. In order to make the machine sew a certain number of such stitches a special control circuit is provided with an armshaft detector 44, a stitch counter 45, a second comparator 46 and a memory 47 on which a predetermined binary number is recorded and transferred to the comparator 46. When the stitch counter outputs the same number (number of stitches) as the recorded number the comparator applies a signal to a wire 48 which together with the signal on the wire 43 in an AND-circuit 49 via the OR-gate 42 releases a counting pulse to the counter 39. As a result the output signal of the counter 39 changes from the wire 43 to a third output 50. This controls forward feeding of the fabric and sewing the space stitches C. During the forward feeding the wheel 18 rotates in the opposite direction to that one mentioned before and the converter 36 supplies a decreasing digital code to the comparator 35. When this count has reached 0 a signal is supplied on an output 51 which together with the signal on the wire 50 in an AND-circuit 52 via the OR-gate 42 releases a counting pulse to the counter 39. This output signal of the counter changes from the wire 50 to a fourth output 53 which controls zero-rated feeding and bar stitches D. After the number of stitches stored in the memory 47 are sewn another signal from the gate 42 triggers the counter 39 to the next output 54 controlling a stop of the machine. When the next buttonhole is to be sewn the contact 38 is actuated again. A system according to Fig. 4 can be included into an ordinary microprocessor used in electronic sewing machines. Such a microprocessor is then provided with analogue inputs for the measuring quantities arising on the potentiometers 33 and 22, 23. The part of the system related to automatic buttonholes is separately recorded in the computer with the moments in principle stated here. When using the computer in such a way it is possible to utilize the measuring arrangement for long seams. Then the wheel rotates several revolutions and the signal from the potentiometer thus will be a saw tooth voltage. The arrangement described is an example how to realize the invention. It will be apparent that variations in producing the measuring quantity may exist e.g. a variable capacitor or a coil instead of a potentiometer.

Claims: Arrangement in a sewing machine for measuring the distance of feeding of the working material in forward and reverse directions, comprising a gauge wheel (18) actuated by a resilient means (26) to engage the working material in order to be rotated by the movement thereof, characterized by a sensor (22, 23) made integral with the gauge wheel and comprising a rheostat connected to a voltage source for producing a voltage proportional to the amount of rotation of the gauge wheel. Arrangement according to claim 1, characterized in that the gauge wheel (18) is arranged in a housing (14, 15) and that the rheostat comprises a circular resistance means (22) provided in the housing, said gauge wheel having a resilient contact means (23) in sliding engagement with said resistance means.

Inventors: FRIMAN BERTIL AKE HARRY, FRIMAN, BERTIL AKE HARRY
Applicants: HUSQVARNA AB, HUSQVARNA AKTIEBOLAG
Application year: 1989
Main classification: D05B3
IPC codes: D05B3, D05B27