CONTROL ARRANGEMENT OF FEEDING IN A SEWING MACHINE

Abstract: The present invention has enabled a more comfortable way of using a sewing machine by introducing a new control which is aimed at setting a comfortable cloth feeding speed.

Description: The present invention relates to an arrangement of a sewing speed control in a sewing machine with setting means for i.a. r.p.m. and stitch length. In sewing machines with a simple control of stitch length and r.p.m. the operator has a possibility to set maximum values on these controls and finds then that the cloth feeding speed on the stitch plate will be unconveniently high, making it difficult to guide the working material ahead with a desirable accuracy. By setting a great stitch length the operator must then control the r.p.m. by the foot control so that a comfortable cloth feeding speed can be achieved. However, it may be difficult to adjust and keep an optimal r.p.m. by means of the foot control at several stitch lengths. In electronic sewing machines feeding is effected by means of a stepping motor which requires special solutions of the problem to keep a limited, predetermined feeding speed. A special arrangement of this kind is previously described in a Patent Specification US-A- 4 559 887. The problem has been solved by the invention from a new point of view which involves a presetting of a comfortable cloth feeding speed and after that a limiting of the maximum r.p.m. of the sewing machine so that the predetermined speed of the cloth is not exceeded at a full adjustment of the speed control of the sewing machine. In this new point of view the maximum r.p.m. (r) of the sewing machine is a function of the cloth feeding speed (v) and the stitch length (s) according to the formula r = v s Since the speed of the cloth v is limited and predetermined (constant), the maximum r.p.m. will thus decrease at an increase of the stitch length s. A device for achieving these properties is defined in the characteristics of Claim 1. A couple of embodiments according to the invention will be described in the following with reference to the accompanying drawing which shows in Fig. 1 a stitch length control mechanically connected to a current control, Fig. 2 several controls connected to a computer with control means for driving a motor. The stitch length control is schematically shown in Fig. 1 in a part of a sewing machine body 10 with bearings 11, 12 of a rod 13 with a finger grip 14 and an inclined guiding surface 15. The rod can be displaced in longitudinal direction, whereby a dial 16 points on a scale 17 on the body showing the stitch length at the adjusted position. The adjustment (displacement) is transferred by movement transferring means to a guide (not shown) by which several feeding lengths of the feeder are adjusted. The current control of the driving motor 18 is here positioned in close connection to the guiding surface 15, and a pin 19 is in engagement with the surface during certain positions of the stitch length control. The current to the motor is adjusted on a variable resistor 20, the r.p.m. of the motor increasing when a movable contact 21 is moved upwards on the resistor. The pin and the contact are joined to follow one another up and down on the resistor. When the pin abuts the surface 15, the contact cannot move any longer upwards on the resistor and the r.p.m. not even be further increased. Thus, the device serves as an r.p.m. limiter, whereby the restriction of r.p.m. is greater the bigger stitch length the machine carries out. An electronic embodiment of the arrangement is shown in Fig. 2. For the reason of completeness a speed of cloth control 22 is shown in the form of a potentiometer by which the feeding speed thus can be adjusted separately. In a conventional way of electronic sewing machines there are also a stitch length control 23 and a motor speed control 24 in connection with a microcomputer 25. A control circuit 26 in this one supplies a control signal to a driving circuit 27 of the driving motor 18. A counting operation is carried out in the computer in accordance with the formula in the foregoing: r ≦ v s where v is a value adjusted on the control 22. The sign ≦ is added in order to show that the machine can be driven slower (by means of the speed control 24) than the maximum value admitted by the adjustments. If the adjustments are changed, the computer calculates a new value of r which is stored and serves as a reference for a highest value of the control signal supplied to the driving circuit, there controlling a current to the motor corresponding to an equivalent value of r. Of course, calculating circuits for these operations may also be disposed in machines lacking the microcomputer. The speed of cloth control has the highest adjustable value which in case of a great stitch length limit the r.p.m. This restriction protects the included electronic feeding components against overload and has therefore enabled the use of such components.

Claims: 1. Arrangement of a speed control in a sewing machine provided with a control for setting stitch length (s) and controllable means for the r.p.m. (r) of a driving motor (18), characterized by a separate control means (27) for a feeding speed (v) of cloth on the stitch plate, comprising means responsible to the stitch length (s) and the feeding speed (v) for limiting the r.p.m. (r) of the motor in accordance with the formula: r ≦ v s and calculating means for determining a maximum current value for the r.p.m. control (24) of the motor in accordance with said formula and prohibiting exceeding thereof. 2. Arrangement according to claim 1, characterized in that the calculating means is part of a microcomputor (25) in the sewing machine. 3. Arrangement according to claim 1, characterized in that the control for cloth feeding speed is manually adjustable by a knob or the like on the sewing machine .

Inventors: SKOGWARD, KENNETH OSCAR EMANUEL
Applicants: HUSQVARNA AKTIEBOLAG
Application year: 1987
Main classification: D05B19
IPC codes: D05B69, G05B9