Sewing – Special machines – Pattern controlled or programmed
Reexamination Certificate
2000-10-13
2002-03-12
Nerbun, Peter (Department: 3741)
Sewing
Special machines
Pattern controlled or programmed
C112S220000, C112S239000, C112S323000, C112S470180
Reexamination Certificate
active
06354233
ABSTRACT:
The present invention pertains to a sewing or embroidery machine.
Prior-art sewing machines have, in general, a hook cooperating with a thread-carrying needle as well as a feed device with a drive for the feed element and a holding-down means with a presser foot for the fabric being sewn.
During the sewing operation, the fabric being sewn is usually held between the feed element and the presser foot, which lies on the fabric being sewn in a non-positive manner. The feed element, which is usually driven in a positive-locking manner and is provided with teeth on its top side, moves forward out of the area of the needle plate during the feed phase proper and presses the fabric to be sewn against the presser foot and it pushes the presser foot upward. The feed element now performs an essentially elliptical movement, and the feed movement proper takes place in the direction of the longitudinal axis of the ellipse and the lifting movement in the direction of the minor axis of the ellipse.
If these movements are brought about by means of mechanical gears, cam or control lever mechanisms are usually used for this purpose, and the stitch length can be changed by displacing the articulation points in the case of control lever mechanisms and either by changing the effective eccentricity of the cam or by changing the oblique position of the corresponding crank in the case of cam mechanisms. Thus, while the stitch length can be changed during sewing by actuating a manual button or another actuating means, the lifting movement of the feeder can be changed by an intervention performed by means of tools only when the machine has been stopped.
It has become known from DE 29 03 031 in connection with pattern-forming zigzag sewing machines that the feeder can be moved by means of an impulse motor via linkages and lever mechanisms in order to thus bring about a change in the length of the corresponding sewing pattern by changing the stitch length. To make it possible to change the width of the sewing pattern during sewing as well, the drive generating the transverse movement of the needle bar also has an impulse motor, by means of which the overstitch width of the needle movement can be changed.
Even though it is thus known that both the overstitch width of the needle movement and the stitch length can be changed during sewing, also changing the amount of the vertical movement of the feed element during sewing has not become known since.
In prior-art sewing machines, the feed element strikes the presser foot in a rapid sequence during sewing, and the force with which the spring presses down the presser foot is selected to be relatively strong in order to prevent the presser foot from being lifted off from the fabric being sewn.
However, a temporary separation of the presser foot from the fabric being sewn cannot always be prevented even in the case of a relatively strong pressing force of the presser foot, which is on the order of magnitude of more than 6 kg, especially at high speeds of sewing, at which the forcibly driven feed element strikes the underside of the presser foot in a correspondingly rapid sequence and the presser foot is set to vibrate. This results, on the one hand, in a non-uniform feed of the fabric being sewn and, on the other hand, in an adverse effect on the quality of sewing due to the resulting non-uniform tapering of the stitch.
DE 36 36 548 A1 describes a sewing machine in which the presser foot for the fabric being sewn can be raised by means of a servo coil. The pressing force of the presser foot on the fabric being sewn can be set by means of another servo coil. Furthermore, the stitch length can be preset here manually and can be reduced by means of a servo magnet.
The values of the pressing force of the presser foot, which are read into a memory via a potentiometer, can be compared with preset values during the operation of the sewing machine, so that the pressing force of the presser foot on the fabric being sewn can be changed correspondingly. A dependence of the pressing force of the presser foot on the movement characteristic of the feed element is not intended here and is not achieved, either.
The basic object of the present invention is to provide a feed means for sewing machines of this class, which makes it possible, while guaranteeing a corresponding synchronization of the horizontal and vertical movements of the feed elements, to vary these [movements] independently from one another during sewing even at high speeds of rotation.
This object is accomplished in a sewing machine of this class by the feed means for driving the feed element having a linear drive with two drivable elements (rotors), wherein one rotor is movable in the horizontal direction and the other rotor in the vertical direction, and that a control means with a control circuit for the horizontal movements as well as with a control circuit for the vertical movements of the feed element is associated with the feed means, wherein both control circuits are subordinated to a main control means, which has a data processing means and receives its synchronization impulses from an encoder as a function of the particular instantaneous position of the needle or hook, and to which the actual values of the horizontal and/or vertical movements of the feed element can be alternatingly sent.
This offers the possibility of changing both the amount and the phase position of the vertical movement of the feed element independently from both the amount and the phase position of its horizontal movement and of affecting the amount of the vertical movement of the feed element independently from its horizontal movement such that a sufficient flux of force is guaranteed between the fabric being sewn and the feed element, on the one hand, and, on the other hand, it is not necessary to select a needlessly strong contact pressure of the presser foot. It is, of course, also possible to vary the phase position of the vertical movement and/or the phase position of the horizontal movement of the feed element within limits preset by the requirements of stitch formation in relation to the phase position of the movement of the needle and/or hook.
While the intervention with the movement characteristic of the feed element is performed exclusively to change the stitch length in the prior art, intervention in the characteristic of the vertical and/or horizontal movement of the feed element is possible according to the present invention at any time due to the main control means (even while the stitch length is maintained) during each and every stitch formation operation In order to always perform the entire phase of stitch formation while maintaining optimal conditions.
All the mechanical components, such as shafts and gear trains, which are needed in prior-art sewing machines to move the feed element and to change its movement, may be eliminated due to the present invention, and so are, in particular, the electromechanical auxiliary units which are known in sewing machines with automatically adjustable stitch length and sewing direction as well. The stitch length and the sewing direction can be changed at full sewing speed.
Another object of the present invention is to provide feed and holding-down means for a sewing machine of this class, which make it possible to affect the cooperation of the presser foot with the feed element such that the pressing force of the presser foot can be adjusted during the sewing operation to the particular instantaneous velocity and the instantaneous vertical force of the feed element.
This object is accomplished in sewing machines of this class by the cooperation of the feed element with the presser foot being able to be regulated by a main control means having a data processing means and acting on both a control means for the drive of the feed element and on a control means for the drive of the presser foot such that the pressing force of the presser foot follows the instantaneous movement of the feed element, wherein the main control means receives its synchronization from an encoder
G.M. Pfaff Aktiengesellschaft In Insolvenz
McGlew and Tutle, P.C.
Nerbun Peter
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