DD270327A1 - TRANSPORT DEVICE FOR SEWING MACHINES - Google Patents

Abstract

The invention relates to a device for controlling the transport device to Naehmaschinen. According to the invention is determined by a known force transducer, such as a piezoceramic element, the current Drueckerfusskraft during the sewing process, the measured value in an evaluation circuit with 2 adjustable Stellgrößen compared and depending on the result of the comparison, an actuator, for. B. is influenced by a DC motor pneumatic pressure transducer is activated. By a pressure change over a working cylinder the Drueckerfusskraft is regulated. Fig. 1

Description

For this 3 pages drawings

Field of application of the invention The invention relates to a device for controlling the transport devices on sewing machines. Characteristic of the known state of the art In conventional sewing machines, the material is transported by the corresponding movement of the conveyor

in interaction with a spring-loaded presser foot. The material pressing force can be adjusted by hand in such a way that depending on the Nähgutcharakteristik and the intended maximum speed, the fabric is always securely clamped.

The fabric presser by its mass, the spring of the fabric presser to produce the biasing force, the elasticity of the sewing material

and the transporter on the one hand and the elasticity of the sewing material and the needle plate on the other hand form vibratory

Systems with at least two natural frequencies, which are excited by the vertical movement of the conveyor to vibrate

become. The result of these oscillations is a fluctuating force between the presser foot and the feed dog or

Throat plate whose amplitudes are further above or below the static preset material pressing force. The manually set static material pressing force must be determined according to the characteristics of the sewing material and the

provided maximum speed are set so high that the mentioned minimums of the force amplitudes always a

Value F _m i _n > 0. The result of such a Stoffdrückerrafinzstellung for today customary sewing machine speed of η = 10000 min ' ¹ is

that, when the sewing machine speed is lowered in the meantime, the high fabric pressing force still acts, which can lead to a Storf damage. If, on the other hand, one were to adjust the material-pressing force for a lower speed, then when sewing machine speed is increased, the sewing material "floats", which means a disturbance in the material to be transported.

In US-PS 2541888 and DE-OS 3118726 devices are now described, which is a speed-dependent Have trigger device. It proposes mechanical, pneumatic and hydraulic speed controllers. The

Speed-dependent presser foot force adjustment is only one side of the requirement.

As already mentioned, the different characteristics of the material also require a different presser foot force. For example, a soft, elastic material requires a lower pommel foot than a hard poplin material. This fact is going through

the statements in the aforementioned invention descriptions in any way taken into account.

Object of the invention

The aim of the invention is to provide a device for controlling the transport, especially the presser force, in sewing machines, which ensures a perfect seam quality.

Explanation of the essence of the invention

The invention has the object to provide a presser foot device for sewing machines, which keeps a preset minimum value of the presser foot force independent of the characteristic of the sewing material and the current sewing machine speed.

According to the invention the object is achieved in that determined by a known force transducer, such as a piezoceramic element, the instantaneous presser foot force during the sewing process, the measured value in an evaluation circuit with 2 adjustable control variables compared and depending on the result of the comparison, an actuator, for. B. influenced by a DC motor. ' pneumatic pressure transducer, is activated. By a pressure change is controlled by a working cylinder, the pusher force. The force transducer can optionally be arranged in a presser foot, a presser foot holder, on the throat plate or on the feed dog or on the feed dog carrier.

embodiment

The invention will be explained in more detail with reference to an embodiment. In the accompanying drawings show:

Fig. 1: side view of an embodiment of an overlock sewing machine Fiy.2: Block diagram of the evaluation control Fig. 3: Representation of the force curve between presser foot and feed dog

The fabric 1 is clamped between the srf press 2 and the feed dog 3 in the transport phase. The presser foot force required for this purpose is realized by a pneumatically actuated piston 5, whose piston rod 6 communicates with the presser foot via the presser foot holder 4 (see FIG. 1). In the Nähfußsohle 2 a Kraftmeßgeber 7 is installed, which determines the instantaneous force between presser foot and feed dog or between presser foot and stitch plate during sewing. In an amplifier 9, the signal of 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 ₁ ) and U _t2 Dit. Voltages U _r) -nd U _r2 correspond to the preselectable minimum forces Ft or F ₂ between presser foot and sewing material (see FIG. 3).

In Figure 3, three different states of the force curve between presser foot and feed dog are shown. If the instantaneous presser foot force undershoots the minimum force F ₁ (FIG. 3 c), the flip-flops 12 and 13 are set, the output signal of which is accepted by the handwheel transmitter 14 upon arrival of a signal in two further flip-flops 15 and 16, whereupon the flip-flops 1? and 13 are deleted. The output signals of the flip-flops 15 and 16 are knotted in two AND circuits 17 and 18 to the signals vei, which switch an electric motor 19 in the right or left rotation. The electric motor 19 in turn is connected to a pressure transducer 20, thereby changing the set air pressure, in this case increasing. The pressure transducer 20 is connected via the air line 23 with the working cylinder 8 in connection whose power is increased.

If the force F ₂ (FIG. 3 a) is not undershot between two signals of the handwheel transmitter 14, then none of the flip-flops 12 and 13 are set, so that no takeover takes place in stages 15 and 16. The signal now appears at the output of the AND circuit 17 , which switches the electric motor 19 in the direction of rotation, wnlche at the output of the pressure transducer 20 causes a decrease in pressure. If the force F _{2 is} undershot between two signals of the handwheel transmitter 14 and the force Fi does not fall below it (FIG. 3 b), then the flip-flop 13 is set. Upon arrival of the signal from the handwheel 14 after switching to the flip-flop 16 is no switching signal to the outputs of the AND circuits 17 and 18. That corresponds to standstill of the electric motor 19 and thus no change in the contact pressure, since this already reaches the optimum value Has. The stage 21 has monostable behavior and causes a short L-pulse to reset the flip-flops 12 and 13 at each transition from H to L of the handwheel transmitter.

22 is a circuit which detects the rotary motion of the sewing machine. When the machine is stopped, the flip-flops 15 and 16 are set so that the E motor 19 comes to a standstill. This ensures that no unwanted pressure adjustment occurs. During the rotating movement of the sewing machine, a Η signal at the output of 22 ensures that the flip-flops 15 and 16 can operate unhindered

 Thus, the purpose of the invention is achieved.

Claims (3)

1. Transport device for sewing machines, consisting of a presser foot and its holder, acting on the presser foot pushing device, a throat plate and one or more transporters, characterized in that in the presser foot (2) or in the presser foot holder (4) or on the throat plate or on the feed dog (3) or on the feed dog carrier a force measuring device (7) is provided which emits an electrical signal corresponding to the force between the feed dog (7) and presser foot (2) or between needle plate and presser foot (2), and this force measuring transducer (7) is connected to an evaluation circuit which contains two comparators (10, 11) in which the incoming signal is compared with the nominal values Un and U _r2 and in that the evaluation circuit is connected to an actuator (19). 2. Apparatus according to claim 1, characterized in that the force transducer consists of one or more piezokoramischen elements. 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.