DE3907240A1 - Transport device for sewing machines - Google Patents

Abstract

According to the invention, by means of a force sensor which is known per se, for example a piezoceramic element, the momentary presser foot force is determined during the sewing work, the measured value is compared in an evaluation circuit with 2 adjustable control variables, and, depending on the result of the comparison, an actuator, for example a pneumatic pressure transducer influenced by a direct-current motor, is activated. The presser foot force is regulated via a working cylinder by means of a change in pressure. <IMAGE>

Description

The invention relates to a transport device for sewing machines according to the preamble of claim 1.

With conventional sewing machines, the material is transported through the corresponding movement of the transporter together play with a spring-loaded presser. The metabolism can be adjusted by hand so that in Ab dependence of the sewing material characteristics and the intended maximum Speed the material is always clamped securely.

The presser by its mass, the spring of the presser to generate the pre-tension, the elasticity of the material and the feed dog on the one hand and the elasticity of the sewing good and the throat plate on the other hand form vibratory Systems with at least two natural frequencies, which are ver tical movement of the feed dog to be vibrated. The consequence of these vibrations is a fluctuating force between presser and feed dog or throat plate, whose Amplitudes further above or below the statically preset Metabolism.

The static material presser force to be set by hand must be set so high that the minima of the force amplitudes always result in a value F _min <0 in accordance with the characteristics of the sewing material and the maximum speed provided.

The consequence of such a presser force setting for a sewing machine speed of n = 10,000 min ^{-1 which} is common today is that when the sewing machine speed is reduced in the meantime, the high presser force still acts, which can lead to fabric damage. If, on the other hand, one set the presser force for a lower speed, the sewing material would "float" when the sewing machine speed was increased, which would mean a disturbance in the transport of the sewing material.

In US-PS 25 41 888 and DE-OS 31 18 726 are now facilities described that a speed-dependent pusher device point. Mechanical, pneumatic and hydraulic Speed controller suggested. The speed-dependent presser foot Force adjustment is only one side of the requirement. As already mentioned, the different characters also required a different presser foot force.

For example, a soft, elastic material requires less presser foot powers as a hard poplin fabric. This fact is confirmed by the statements in the invention descriptions mentioned in not considered in any way.

The invention has for its object a device for Control of the transport, especially the presser foot force, in sewing to create machines that are independent of the characteristics of the Sewing material and the current sewing machine speed set the minimum value of the presser foot force constant. According to the invention, this object is achieved with a transport device solved according to claim 1 by the characterizing features. By the momentary push button becomes a force transducer known per se foot force determined during the sewing process, the measured value in one Evaluation circuit compared with two adjustable manipulated variables and depending on the result of the comparison, an actuator, e.g. B. a pneumatic influenced by a DC motor Pressure converter, activated. A change in pressure will cause a Working cylinder regulated the presser foot force.

The invention is based on an exemplary embodiment, he to be refined. In the drawings shows

Fig. 1 side view of an embodiment of an overlock sewing machine,

Fig. 2 Block diagram of the Auswertesteuerung,

Fig. 3 representation of the force curve between the presser foot and the feed dog.

The sewing material 1 is clamped between the presser foot 2 and the feed dog 3 in the transport phase. The foot pressure required for this is realized by a pneumatically actuated piston 5 , the piston rod 6 of which is connected to the presser foot via the presser foot holder 4 (see FIG. 1). A force transducer 7 is installed in the presser foot sole 2 and determines the instantaneous force between the presser foot and the feed dog or between the presser foot and the throat plate during sewing. In an amplifier 9 , the signal from the force transducer 7 is amplified so far that it can control two comparators 10 and 11 , in which it is compared with the voltages U _{r 1} and U _{r 2} . The voltages U _{r 1} and U _{r 2} correspond to the preselectable minimum forces F ₁ and F ₂ between presser foot and material (see FIG. 3). In Fig. 3 three different states of the force curve between the presser foot and the feed dog are shown.

If the momentary presser foot force falls below the minimum force F ₁ ( FIG. 3c), the flip-flops 12 and 13 are set, the output signal of which is received by the handwheel transmitter 14 in two further flip-flops 15 and 16 , upon which the flip-flops 12 and 13 are deleted. The output signals of the flip-flops 15 and 16 are combined in two AND circuits 17 and 18 to form the signals which switch an electric motor 19 in clockwise or counter-clockwise rotation.

The electric motor 19 is in turn connected to a pressure transducer 20 , so that the air pressure set can be changed, in this case increased. The pressure transducer 20 is connected via the air line 23 to the working cylinder 8 , the force of which is increased.

If the force F ₂ ( FIG. _{3 a} ) is not undershot between two signals from the handwheel transmitter 14 , then none of the tilting stages 12 and 13 is set, so that there is no transfer to the stages 15 and 16 . At the output of the AND circuit 17 now appears the signal which switches the electric motor 19 in the direction of rotation, which causes a pressure decrease at the output of the pressure transducer 20 . If the force F _{2 is} undershot between two signals of the handwheel transmitter 14 and the force F _{1 is} not undershot ( FIG. 3b), the flip-flop 13 is set. When the signal from handwheel encoder 14 arrives, there is no switching signal at the outputs of AND circuits 17 and 18 after transfer to flip-flop 16 . This corresponds to the standstill of the electric motor 19 and thus no change in the contact pressure, since this has already reached the optimal value.

The stage 21 has a monostable behavior and causes a short L pulse to reset the flip-flops 12 and 13 at every transition from H to L of the handwheel encoder.

22 is a circuit which detects the rotating movement of the sewing machine. When the machine is at a standstill, the tilt stages 15 and 16 are set such that the electric motor 19 comes to a standstill. This ensures that no unwanted Druckver position occurs. During the rotating movement of the sewing machine, an H signal at the output of 22 ensures that the flip-flops 15 and 16 can work freely.

The purpose of the invention is thus achieved.  

List of the reference numerals used

1 sewing material
2 presser foot
3 feed dogs
4 presser foot holders
5 pistons
6 piston rod
7 power transmitters
8 working cylinders
9 amplifiers
10 comparator
11 comparator
12 flip-flop
13 flip-flop
14 handwheel encoder
15 flip-flop
16 flip-flop
17 AND circuits
18 AND circuits
19 electric motor
20 pressure transducers
21 level
22 circuit
23 air duct

Claims (3)

1. Transport device for sewing machines, consisting of a presser foot and its holder, one on the presser foot we kende press device, a throat plate and one or more feed dogs, characterized in that in the presser foot ( 2 ) or in the presser foot holder ( 4 ) or on the Stitch plate or a force measuring device ( 7 ) is provided on the feed dog ( 3 ) or on the feed dog carrier, which emits an electrical signal that corresponds to the force between the feed dog ( 7 ) and presser foot ( 2 ) or between the throat plate and presser foot ( 2 ) , and that this force transducer ( 7 ) is connected to an evaluation circuit which contains two comparators ( 10; 11 ) in which the incoming signal is compared with the target variables U _{r 1} and U _{r 2} and that the evaluation circuit with an actuator ( 19 ) connected is. 2. Device according to claim 1, characterized in that the Force transducer from one or more piezoceramic ele ment exists. 3. Apparatus according to claim 1, characterized in that a pneumatic pressure transducer ( 20 ) via a working cylinder ( 8 ) with the presser foot holder ( 4 ) is connected.