Device for conveying articles to be sewed

Abstract

The invention relates to a device for conveying articles to be sewed, which is provided for a sewing device or sewing machine. Said device comprises at least one material advancing device for advancing the article to be sewed in the advancing direction of the material with an advancing speed defined by the speed of the machine and by the stitch length. The device also comprises at least one material conveying supplementary device which, in the form of a pressing means, subjects the upper material layer of the article to be sewed to a pressing force. The material conveying supplementary device rotates with a rotational speed, is arranged behind the material advancing device in the advancing direction of the material and can be proportionally driven with regard to the speed of the machine and to the stitch length. At least one device can increase the pressing force, which is exerted by the device onto the upper material layer of the article to be conveyed, with an increasing speed of the machine and/or in addition to the proportional increase with increasing speed of the machine, can further increase the rotational speed of the material conveying supplementary device.

Description

[0001] This invention relates to a device intended for a sewing means or sewing machine for transport of sewn material, having

[0002] at least one feeder means for advancing the sewn material in the feed direction with an advance rate which is determined by the machine rpm and by the stitch length and

[0003] at least one auxiliary material transport means which acts on the upper layer of the sewn material in the form of a pressure means with a pressure force, which rotates with a peripheral speed, and which is located in the material feed direction behind the feeder means and can be driven in proportion to the machine rpm and to the stitch length.

[0004] Here the auxiliary material transport means (compare to the prior art in this respect for example publication U.S. Pat. No. 4,182,251) is used to compensate for the offset between the upper layer and the lower layer of the sewn material which is to be worked with the sewing means (the concept of "sewing means" below also includes sewing machines, this invention relating both to sewing means and also sewing machines).

[0005] This offset occurs according to experience when the lower material layer is entrained by interference by the teeth of the feeder means while the upper material layer is entrained simply by the friction between the upper material layer and the lower material layer.

[0006] In order to allow this friction to take effect, the sewn material during stitch formation and sewn material transport is held down with a so-called pressure means so that the upper material layer and the lower material layer are compressed between the pressure means and the feeder means and are transported by the feeder means in the material feed direction.

[0007] During this transport phase, at this point between the upper layer of the sewn material to be transported and the pressure means, frictional forces arise which can cause an offset in the transport length between the upper material layer and the lower material layer. This is exceptionally undesirable since the offset effect which adversely affects the results of sewing occurs at low rpm of the main shaft of the sewing means and moreover at low advance rates; the offset effect becomes greater, the higher the rpm and the feed rates.

[0008] The reason for this is the manner of operation of the feeder means which at the start of the transport phase moves up, i.e. in the direction of the pressure means so that the teeth of the feeder means can fit into the lower layer of the sewn material. During this time the sewn material pushes the pressure means--to a certain extent forces it--up so that the pressure on the material layers increases due to the inertial mass of the pressure means.

[0009] The feeder means executes a somewhat elliptical motion: While the pressure means is moved somewhat farther to the top, the feeder means begins to push the material layers in the material advance direction. During this transport phase the pressure of the pressure means decreases dramatically until the spring force brakes the motion of the pressure means which is pointed upward, i.e. away from the feeder means and the pressure means presses again on the sewn material.

[0010] In the extreme case it can even happen that the pressure means loses contact with the sewn material for a short time due to its vertical, upward motion and in this way the frictional connection between the upper material layer and the lower material layer is cancelled. This known and extremely undesirable phenomenon emerges the more dramatically, the higher the rpm of the main shaft of the sewing means and thus the advance rates, so that the offset between the upper material layer and the lower material layer becomes greater and greater with the sewing speed which is a measure of the advance rate.

[0011] At the end of the transport phase the feeder means moves down, i.e. in the direction away from the pressure means so that the pressure of the pressure means again briefly decreases. The latter phase however has no significant effect on the offset between the upper material layer and the lower material layer.

[0012] In order to compensate for the offset effect, the auxiliary material transport means engages the upper material layer. Here material transport solely with the auxiliary material transport means would cause so-called "negative offset", i.e. leading of the upper material layer relative to the lower material layer.

[0013] With correct adjustment of the peripheral speed of the auxiliary material transport means to the machine rpm and to the set stitch length it should be possible to produce a sewn section without offset.

[0014] Thus, a material transport device for a sewing machine is known (compare DE 29 36 697 C2) in which a pressure mechanism is assigned to the driven material transport roll and is used on the one hand to adjust the gap between the material support surface and the material transport roll (roller) so that the material transport roll cannot make direct contact with the material support layer, and which on the other hand enables adjustment of a pretensioning force with which the material transport roll presses the workpiece against the material support surface; in any case this adjusted pretensioning force remains unchanged during the end of sewing.

[0015] Furthermore, a device for transport of sewn material is known (compare DE 29 27 869 C2) in which the auxiliary material transport means in forward transport should execute a somewhat greater amount of transport (amount of advance) than the feeder means so that the sewn material during advance in the feed direction is kept permanently under tension. When sewing the upper material layer and the lower material layer this is intended to prevent "slip folding", i.e. in other words, formation of an offset; in any case the set ratio between the amount of transport of the feeder means and the material transport roll of the auxiliary material transport means during the sewing process remains constant regardless of the respective sewing machine rpm.

[0016] But it has been found that the offset between the upper material layer and the lower material layer is dependent on the rpm of the main shaft of the sewing means, i.e. on the so-called machine rpm, so that with this conventional device under changing conditions, such as for example at variable rpm of the main shaft of the sewing means and moreover at a variable advance rate, satisfactory and completely uniform sewing results cannot be achieved.

[0017] Proceeding from the above described disadvantages and deficiencies, the object of this invention is to make a generic device for transport of sewn material such that even with an offset between the upper material layer and the lower material layer which varies as a result of changing condition (such as for example at variable rpm of the main shaft of the sewing means and moreover at variable advance rate) convincing, especially completely uniform sewing results can always be achieved.

[0018] This object is achieved by a device for transport of sewn material as claimed in the preamble of the main claim, in which according to the teaching of this invention by at least one means

[0019] the pressure force which is exerted by the auxiliary material transport means on the upper layer of the sewn material to be transported can be increased with increasing machine rpm and/or

[0020] the peripheral speed of the auxiliary material transport means can be further increased in addition to the proportional increase with increasing machine rpm.

[0021] Thus, surprisingly the fact that the machine rpm and/or the stitch length and moreover the advance rate have an effect on the manner of operation and function of the auxiliary material transport means is taken into account. The pressure force which is exerted by the auxiliary material transport means on the upper layer of the sewn material to be transported can be increased by at least one means with increasing machine rpm. In this way it is possible to take into account the fact that the offset between the upper material layer and the lower material layer increases with increasing machine rpm so that the auxiliary material transport means must develop an increasingly greater tensile stress in the upper material layer.

[0022] Alternatively or in addition thereto, according to the teaching of this invention the peripheral speed of the auxiliary material transport means in addition to the proportional increase can be increased even more with increasing machine rpm. In this way it is possible to take into account the fact that the offset between the upper material layer and the lower material layer grows with increasing machine rpm so that the auxiliary material transport means must also develop increasingly greater tensile stress in the upper material layer.

[0023] In order to be able to choose the pressure force of the auxiliary material transport means and/or the peripheral speed of the auxiliary material transport means depending on the machine rpm, there is at least one means which can be made for example as at least one actuator.

[0024] According to preferred embodiments which can be executed independently of one another or in conjunction with one another, it is provided that

[0025] the pressure force and/or the peripheral speed can be additionally adapted to the composition of the sewn material which is to be transported, preferably by the means; and/or

[0026] the pressure force F.sub.p is given by the equation

F.sub.p=F.sub.0+R.times.n

[0027] in which

[0028] F.sub.0 is a constant force;

[0029] R is the coefficient of friction with a magnitude which is determined by the friction ratios between the auxiliary material transport means and the upper material layer; and

[0030] n is the machine rpm; and/or

[0031] the rpm of the means is a measure of the peripheral speed of the auxiliary material transport means or is equal to the peripheral speed of the auxiliary material transport means; and/or

[0032] the rpm n.sub.p of the means is given by the equation

n.sub.p=k.times.n.times.L,

[0033] in which

[0034] k is a matching factor;

[0035] n is the machine rpm;

[0036] L is the stitch length

[0037] and/or

[0038] the auxiliary material transport means operates in low rpm ranges (N.sub.p<500/min) of the means in an intermittent mode; and/or

[0039] the on and off times of the means are determined by the angular positions of the main shaft of the sewing means or sewing machine; and/or

[0040] the auxiliary material transport means in high rpm ranges (n.sub.p>500/min) of the means operates in a continuous mode; and/or

[0041] the transport path of the auxiliary material transport means per stitching process is greater, especially slightly greater, than the advance path of the feeder means; and/or

[0042] the pressure force of the auxiliary material transport means and/or the rpm of the means can be electronically controlled; and/or

[0043] there is at least one electronic control means for controlling the pressure force of the auxiliary material transport means and/or the rpm of the means; and/or

[0044] the machine rpm can be determined in the electronic control means; and/or

[0045] the electronic control means receives information about the stitch length by input by means of one control panel; and/or

[0046] the electronic control means receives information about the composition of the sewn material to be transported by input by means of at least one control panel; and/or

[0047] the means has at least one linear motor which is preferably operated with direct current; and/or

[0048] the linear motor has at least one stator element which is made as a housing; and/or

[0049] in the stator element a least one rotor element made as a drive rod is supported; and/or

[0050] the stator element is located on the back of the housing head of the sewing means or sewing machine; and/or

[0051] the means has

[0052] at least one drive motor which is operated preferably with direct current,

[0053] at least one gear located between the drive motor and the auxiliary material transport means and

[0054] at least one transfer element located between the gear and the auxiliary material transport means for transfer of motion to the auxiliary material transport means;

[0055] and/or

[0056] the matching factor k is given by the formula

k=k.sub.1.times.k.sub.2.times.k.sub.3,

[0057] k.sub.1 being the parameter for the diameter of the auxiliary material transport means, for the constant of the linear motor and for the stepping-down of the gear;

[0058] k.sub.2 being a measure for the functional dependency of the offset between the upper material layer and the lower material layer on the machine rpm; and

[0059] k.sub.3 being the parameter for the composition of the sewn material to be transported;

[0060] and/or

[0061] the means has a carrier element which is connected to the rotor element and to which the drive motor, the gear and the transfer element are attached; and/or

[0062] the carrier element is supported locked; and/or

[0063] the carrier element is supported locked by means of a guide rod; and/or

[0064] the carrier element is pretensioned by at least one elastic, low-mass coupling element; and/or

[0065] the coupling element has at least one helical spring; and/or

[0066] the auxiliary material transport means is made as at least one rotating roller, especially as at least one rotating delivery roller; and/or

[0067] the means is made as at least one actuator.

[0068] In particular the following can be explained on the preferred embodiments which can be provided independently of one another or linked to one another;

[0069] According to one inventive development of this device, the pressure force and/or the peripheral speed, preferably by the means, can be additionally matched to the composition of the sewn material to be transported. In this way it is possible to take into account the fact that the offset between the upper material layer and the lower material layer is determined not only by the machine rpm, but also by the composition of the sewn material to be transported and accordingly especially by the friction ratios between the lower material layer and the upper material layer and especially by the friction ratios between the upper material layer and the pressure means.

[0070] The essential aspect of this invention is moreover that when the upper material layer and the lower material layer are sewn together an offset caused by nonuniform presser forces and by the resulting nonuniform advance conditions, i.e. the lag of the upper material layer, can be compensated by providing an individually adaptable auxiliary material transport means which acts on the upper material layer, in addition to the conventional feeder means.

[0071] In this way the upper material layer is placed slightly under tensile stress, and the amount of tensile stress in a manner important to the invention can be influenced by the amount of the pressure force of the auxiliary material transport means by the possibility of a low pressure force causing preferably premature slippage of the auxiliary material transport means and thus low tensile stress in the upper material layer; correspondingly a higher pressure force can cause later slippage of the auxiliary material transport means and thus a higher tensile stress in the upper material layer.

[0072] Here the tensile stress during brief phases of low presser force results in that the upper material layer is slightly pulled ahead relative to the lower material layer and thus the otherwise occurring offset is balanced.

[0073] With reference to manner of operation and the function of this invention for transport of sewn material it can be considered that the offset between the upper material layer and the lower material layer forms essentially at the start of each transport phase, since in this interval the pressure of the pressure means decreases greatly as a result of the manner of operation and the function of the feeder means. For this reason the auxiliary material transport means acquires special importance since with the force which is adjustable according to the teaching of the invention and with which the auxiliary material transport means presses against the material layers, stretching in the material layers is influenced:

[0074] Thus, at the start of the transport phase in which as a result of the decreasing pressure of the pressure means a material offset forms between the upper material layer and the lower material layer, this stretching pulls the upper material layer relative to the lower material layer in the material feed direction and thus equalizes the offset of the upper material layer which is due otherwise to the reduced pressure of the pressure means. Thus, assuming correct adjustment of the parameters, a longer seam can be achieved between the upper material layer and the lower material layer.

[0075] Feasibly, the quantitative amount F.sub.p of the pressure force can be reproduced by the formula F.sub.p=F.sub.0+R.times.n, F.sub.0 being a constant force, R the coefficient of friction with a magnitude which is determined by friction ratios between the auxiliary material transport means and the upper material layer, and n the machine rpm.

[0076] The formula F.sub.p=F.sub.0+R.times.n moreover shows that the pressure force--in addition to a constant portion which is independent of the coefficient of friction and of the machine rpm--can be increased feasibly essentially linearly with the coefficient of friction between the auxiliary material transport means and the upper material layer and/or essentially linearly with the machine rpm.

[0077] Depending on the respective technical circumstances, the rpm of the means can be a measure for the peripheral speed of the auxiliary material transport means or for example with direct stepping-up or with direct stepping-down--equal to the peripheral speed of the auxiliary material transport means.

[0078] Here the rpm n.sub.p of the means can be advantageously given by the formula n.sub.p=k.times.n.times.L, k being an adaptation factor, n the machine rpm and L the stitch length.

[0079] It is moreover apparent from the formula n.sub.p=k.times.n.times.L that the rpm of the means and accordingly the peripheral speed of the auxiliary material transport means--in addition to an adaptation factor which is specified below--can feasibly be increased essentially linearly with the machine rpm and/or essentially linearly with the stitch length.

[0080] The adaptation factor k is feasibly given by the formula k=k.sub.1.times.k.sub.2.times.k.sub.3, k.sub.1 being the parameter for the diameter of the auxiliary material transport means, for the constant of the linear motor (compare below) and for the stepping-down of the gear (see below), k.sub.2 being the measure of the functional dependency of the offset between the upper material layer and the lower material layer on the machine rpm, and k.sub.3 being the parameter for the composition of the sewn material to be transported.

[0081] The formula k=k.sub.1.times.k.sub.2.times.k.sub.3 moreover shows that the rpm of the means and accordingly the peripheral speed of the auxiliary material transport means are dependent on the technical circumstances and prerequisites of the means and of the auxiliary material transport means (--->factor k.sub.1), on the function of the offset between the upper material layer and the lower material layer over the machine rpm (--->factor k.sub.2) and on the composition of the sewn material to be transported (--->factor k.sub.3).

[0082] According to one feasible embodiment of this invention, the auxiliary material transport means in low rpm ranges n.sub.p<500/min of the means operates in the intermittent mode. In other words, this means that the drive motor of the means is turned on in the transport phase and is turned off in the non-transport phase. Here the on and off times of the means are advantageously determined by the angular position of the main shaft of the sewing means or sewing machine.

[0083] According to one preferred embodiment of this invention, above rpm n.sub.p on the order of roughly 500/min switching to continuous drive takes place, i.e. the auxiliary material transport means can be operated in the continuous mode in high rpm ranges n.sub.p>500/min. But in this connection it must be considered that in the rpm ranges n.sub.p above roughly 500/min intermittent motion by mass inertia and by the elastic behavior of the drive members gradually slows down anyway to quasicontinuous motion.

[0084] In this connection it is important that the stretching of the material layers is dependent on the friction ratios between the auxiliary material transport means and the (composition) of the upper material layer. In this respect stretching in the sewn material can also be influenced with the adjustable force with which the auxiliary material transport means is pressed against the sewn material.

[0085] In one feasible development of this invention the transport path of the auxiliary material transport means per stitching process is greater, especially slightly greater, than the advance path of the feeder means. This technical measure also ensures that the sewn material when advancing in the material feed direction is always kept under tension; when sewing the upper material layer and the lower material layer this always results in formation of offset being prevented.

[0086] The above explained embodiments, features and advantages of the auxiliary material transport means become very effective when the auxiliary material transport means according to one feasible development of this invention is made as at least one rotating roller, especially as at least one rotating delivery roller.

[0087] According to one especially inventive development of this invention for transport of sewn material, the pressure force of the auxiliary material transport means and/or the rpm of the means (-->peripheral speed of the auxiliary material transport means) can be electronically controlled. To do this there can be at least one electronic control means for controlling the pressure force of the auxiliary material transport means and/or the rpm of the means (-->peripheral speed of the auxiliary material transport means).

[0088] Since at this point the pressure force of the auxiliary material transport means and/or the rpm of the means (-->peripheral speed of the auxiliary material transport means) can depend among others on the machine rpm, the machine rpm according to one feasible embodiment of this invention can be determined in the electronic control means so that at any time it is possible to match the pressure force of the auxiliary material transport means and/or the rpm of the means (-->peripheral speed of the auxiliary material transport means) to the machine rpm.

[0089] Furthermore, the peripheral speed of the auxiliary material transport means can be determined not only by the machine rpm, but among others also by the stitch length. Since this stitch length in a sewing means is generally set mechanically, the stitch length is generally not known to the electronic control means. Last but not least, for this reason the electronic control means can acquire information about the stitch length feasibly by input by means of at least one control panel. The setpoint for the rpm of the drive motor of the means and thus its rpm can be inventively determined then by at least one computational algorithm.

[0090] Furthermore, the pressure force of the auxiliary material transport means can be determined not only by the machine rpm, but among others also by the friction force acting between the auxiliary material transport means and the upper layer of the sewn material. Since this friction force in a sewing means is generally dependent on the composition of the sewn material to be transported, the friction force is generally not known to the electronic control means. Last but not least, for this reason the electronic control means can acquire information about the composition of the sewn material to be transported feasibly by input by means of at least one control panel. The setpoint for the pressure force of the auxiliary material transport means can be inventively determined then by at least one computational algorithm.

[0091] When the means advantageously has at least one linear motor which is operated preferably with direct current, and which essentially has at least one stator element which is made as a housing in which feasibly at least one rotor element made as a drive rod is supported, and/or if the means advantageously has at least one drive motor which is operated preferably with direct current, the pressure force of the auxiliary material transport means and/or the rpm of the means (-->peripheral speed of the auxiliary material transport means) can be controlled by at least one (current) regulator.

[0092] Here the invention exploits the fact that in a linear motor the pressure force imparted by it and/or in a drive motor the rpm or peripheral speed imparted by it is directly proportional to the current supplied to the linear motor or drive motor, in any case essentially so. For this reason, the linear motor current or the drive motor current is electronically controlled and accordingly the desired pressure of the auxiliary material transport means and/or the desired rpm of the means (-->peripheral speed of the auxiliary material transport means) is accomplished.

[0093] Here it can be of inventive importance that the force of the linear motor need not be measured. Feasibly the auxiliary material transport means should be made such that it can be lifted off the upper layer of the sewn material, for example in order to be able to take the sewn material away from the sewing means. This can also be effected by means of the linear motor, and it should be noted that the linear motor in this connection need not perform any positioning function. With respect to the embodiments, the features and the advantages of the linear motor reference is made in the full scope to the type of motor, as is described in German patent application DE 199 45 443.4 or in the international patent application WO 00/18997.

[0094] In this connection, according to one especially inventive development of this device for transport of sewn material, both the initial value and also the part of the pressure force which is dependent on the advance speed can be suitably parameterized and for example can be matched to the respective sewing conditions via at least one control panel.

[0095] According to one especially inventive development of this invention the means has

[0096] at least one stator element (compare above) which is made as a housing and which can be connected to at least one holding plate (solidly) and/or which can be located on the back of the housing head of the sewing means,

[0097] at least one rotor element made as a drive rod (compare above),

[0098] at least one drive motor operated preferably with direct current (compare above),

[0099] at least one gear located between the drive motor and the auxiliary material transport means and

[0100] at least one transfer element located between the gear and the auxiliary material transport means for transfer of motion to the auxiliary material transport means.

[0101] The means can have at least one carrier element which is supported preferably locked, which is connected to the rotor element, and on which the drive motor, the gear and the transfer element are mounted (the locked support of the carrier element can be accomplished for example by means of at least one guide rod).

[0102] Furthermore, one embodiment is recommended in which the carrier element is pretensioned by means of at least one elastic, low-mass coupling element, preferably by means of at least one helical spring. With respect to the embodiments, features and advantages of the coupling element reference is made in the full scope to the German patent application DE 199 45 443.4 or to the international patent application WO 00/18997, especially with respect to the power-saving manner of operation which is associated with the coupling element.

[0103] Other embodiments, features and advantages of this invention are described below in the drawings using FIGS. 1 to 5 by which the embodiment of the device for transport of sewn material as claimed in the invention is illustrated in exemplary form.

[0104] FIG. 1 shows one embodiment of a device for transport of sewn material as claimed in the invention in a side cross section;

[0105] FIG. 2 shows a diagram of the force F of the pressure means as a function of the angle of rotation .phi. of the main shaft of the sewing means;

[0106] FIG. 3 shows a first embodiment of the means from the device for transport of sewn material from FIG. 1 in a cross section;

[0107] FIG. 4 shows a schematic of the interaction between the control mechanism and electronic control means of the sewing means; and

[0108] FIG. 5 shows a diagram of the pressure force F.sub.p of the auxiliary material transport means as a function of the machine rpm n.

[0109] Identical reference numbers relate to elements or features which are made identical or similar in FIGS. 1 to 5.

[0110] In the drawings a device for transport of sewn material intended for a sewing means 10 or sewing machine 10 (compare FIG. 4) is shown which has a feeder means 1 which is countersunk in the stitch plate 7 (compare FIG. 1) for advancing the sewn material in the material feed direction D (compare FIG. 1: arrow). Furthermore, the sewing means 10 (hereinafter the concept of "sewing means" also comprises sewing machines, this invention relating both to sewing means and also to sewing machines) has an auxiliary material transport means 2 which rotates with a peripheral speed U.sub.p and which acts on the upper layer 8 of the sewn material with a pressure force F.sub.p and which is located in the material feed direction D behind the feeder means 1.

[0111] Here the auxiliary material transport means 2 is used to compensate for the offset between the upper layer 8 and the lower layer 9 of the sewn material to be worked with the sewing means 10. This offset occurs when the lower material layer 9 is entrained by the teeth of the feeder means 1 by force, while the upper material layer 8 is entrained only by the friction between the upper material layer 8 and the lower material layer 9.

[0112] In order to allow this friction to take effect, during stitch formation and transport of the sewn material with the pressure means 9 the sewn material is held down so that the upper material layer 8 and the lower material layer 9 are compressed between the pressure means 6 and the feeder means 1 and transported by the feeder means 1 in the material feed direction D.

[0113] During this transport phase (compare FIG. 2), between the upper layer 8 of the sewn material to be transported and the pressure means 6 friction forces occur which can cause an offset in the transport length between the upper material layer 8 and the lower material layer 9. This offset effect occurs at low machine rpm n of the main shaft of the sewing means 10 (compare FIG. 4) and moreover at low advance speeds; the offset effect becomes stronger, the higher the machine rpm n and the advance speeds become.

[0114] The reason for this is the manner of operation of the feeder means 1 which moves up at the start of the transport phase (compare FIG. 2, angular position .phi..sub.a), i.e. in the direction of the pressure means 6, so that the teeth of the feeder means 1 can fit into the lower layer 9 of the sewn material. During this time the sewn material pushes the pressure means 6--to a certain extent forces it--up (compare FIG. 1: arrow A) so that the pressure on the material layers 8, 9 increases due to the inertial mass of the pressure means 6.

[0115] The feeder means 1 executes a somewhat elliptical motion: While the pressure means 6 is being moved somewhat farther to the top, the feeder means 1 begins to push the material layers 8, 9 in the material advance direction D. During this transport phase the force F of the pressure means 6 decreases dramatically (compare FIG. 2: dramatic drop of the force F exerted by the pressure means 6 as a function of the angle .phi. of rotation of the main shaft of the sewing means 10) until the spring force brakes the motion of the pressure means 6 which is pointed upward, i.e. away from the feeder means 1, and the pressure means 6 presses again on the sewn material.

[0116] In the extreme case it can even happen that the pressure means 6 loses contact with the sewn material for a short time due to its vertical, upward motion and in this way the frictional connection between the upper material layer 8 and the lower material layer 9 is cancelled. This phenomenon emerges the more dramatically, the higher the rpm n of the main shaft of the sewing means 10 and thus the advance rates, so that the offset between the upper material layer 8 and the lower material layer 9 becomes greater and greater with the sewing speed which is a measure of the advance rate.

[0117] At the end of the transport phase (compare FIG. 2: angular position .phi..sub.e) the feeder means 1 moves down, i.e. in the direction away from the pressure means 6 so that the pressure of the pressure means 6 again briefly decreases. The latter phase however has no significant effect on the offset between the upper material layer 8 and the lower material layer 9.

[0118] In order to compensate for the offset effect, the auxiliary material transport means 2 engages the upper material layer 8 (compare FIG. 1). Here material transport solely with the auxiliary material transport means 2 would cause so-called "negative offset", i.e. leading of the upper material layer 8 relative to the lower material layer 9.

[0119] With correct adjustment of the peripheral speed U.sub.p (compare FIG. 1) of the auxiliary material transport means 2 to the machine rpm n (compare FIGS. 4 and 5) and to the set stitch length L, it should be possible to produce a sewn section without offset. Here the device for transport of sewn material according to the embodiment of FIGS. 1 to 5 is made such that even with an offset between the upper material layer 8 and the lower material layer 9 which varies as a result of changing conditions (such as for example at variable machine rpm n of the main shaft of the sewing means 10 and moreover at variable advance rate) convincing, especially completely uniform sewing results can always be achieved.

[0120] To do this, the pressure force F.sub.p which is exerted by the auxiliary material transport means 2 which is made in the form of a rotating delivery roller on the upper layer 8 of the sewn material to be transported and/or the peripheral speed U.sub.p can be matched to the advance rate by the means 3 (compare FIG. 3). Thus, in this embodiment of FIGS. 1 to 5 the pressure force F.sub.p which is exerted by the auxiliary material transport means 2 on the upper layer 8 of the sewn material to be transported can be increased by the means 3 with increasing machine rpm n and/or the peripheral speed U.sub.p of the auxiliary material transport means 2 can be increased even further in addition to the proportional increase with increasing machine rpm n.

[0121] Thus, the fact that the machine rpm n and/or the stitch length L and moreover the advance rate have an effect on the manner of operation and function of the auxiliary material transport means 2 is taken into account. The pressure force F.sub.p which is exerted by the auxiliary material transport means 2 on the upper layer 8 of the sewn material to be transported can be increased by the means 3 with increasing machine rpm n (compare FIG. 5). In this way it is possible to take into account the fact that the offset between the upper material layer 8 and the lower material layer 9 increases with increasing machine rpm n so that the auxiliary material transport means 2 must develop an increasingly greater tensile stress in the upper material layer 8.

[0122] Alternatively or in addition thereto, the peripheral speed U.sub.p of the auxiliary material transport means 2 in addition to the proportional increase can be increased even more with increasing machine rpm n. In this way it is possible to take into account the fact that the offset between the upper material layer 8 and the lower material layer 9 grows with increasing machine rpm n so that the auxiliary material transport means 2 must also develop increasingly greater tensile stress in the upper material layer 8.

[0123] In order to be able to choose the pressure force F.sub.p of the auxiliary material transport means 2 and/or the peripheral speed U.sub.p of the auxiliary material transport means 2 depending on the machine rpm n, there is at least one means 3 which can be made as an actuator in the example shown in FIG. 3.

[0124] In the explained embodiment the pressure force F.sub.p and/or the peripheral speed U.sub.p can be adapted by the means 3 in addition to the composition of the sewn material which is to be transported. In this way it is possible to take into account the fact that the offset between the upper material layer 8 and the lower material layer 9 is determined not only by the machine rpm n, but also by the composition of the sewn material to be transported and accordingly especially by the friction ratios between the lower material layer 9 and the upper material layer 8 and especially by the friction ratios between the upper material layer 8 and the pressure means 6.

[0125] The essential aspect of this invention is moreover that when the upper material layer 8 and the lower material layer 9 are sewn together an offset caused by nonuniform presser forces F--as shown in FIG. 2--and by the resulting nonuniform advance conditions, i.e. the lag of the upper material layer 8, can be compensated by providing an individually adaptable auxiliary material transport means 2 which acts on the upper material layer 8, in addition to the conventional feeder means 1.

[0126] In this way the upper material layer 8 is placed slightly under tensile stress (compare FIG. 1), and the amount of tensile stress can be influenced by the amount of the pressure force F.sub.p of the auxiliary material transport means 2 by the low pressure force F.sub.p causing low tensile stress in the upper material layer 8 and for this reason premature slippage of the auxiliary material transport means 2; correspondingly a higher pressure force F.sub.p can cause a higher tensile stress in the upper material layer 8 and for this reason later slippage of the auxiliary material transport means 2.

[0127] Here the tensile stress during brief phases of low presser force F (compare FIG. 2) results in that the upper material layer 8 is slightly pulled ahead relative to the lower material layer 9 and thus the otherwise occurring offset is balanced.

[0128] With reference to manner of operation and the function of the device for transport of sewn material exemplified using FIGS. 1 to 5, it can be considered that the offset between the upper material layer 8 and the lower material layer 9 forms essentially at the start of each transport phase (compare FIG. 2: angular position .phi..sub.a), since in this interval the pressure of the pressure means 6 decreases greatly as a result of the manner of operation and the function of the feeder means 1. For this reason the auxiliary material transport means 2 acquires special importance since with the adjustable force F.sub.p (compare FIG. 5) with which the auxiliary material transport 2 means presses against the material layers 8, 9, stretching in the material layers 8, 9 is influenced:

[0129] Thus, at the start of the transport phase (compare FIG. 2: angular position .phi..sub.a) in which as a result of the decreasing pressure of the pressure means 6 a material offset forms between the upper material layer 8 and the lower material layer 9, this stretching pulls the upper material layer 8 relative to the lower material layer 9 in the material feed direction D (compare FIG. 1) and thus equalizes the offset of the upper material layer 8 which is due otherwise to the reduced pressure of the pressure means 6. Thus, assuming correct adjustment of the parameters, a longer seam can be achieved between the upper material layer 8 and the lower material layer 9.

[0130] The auxiliary material transport means 2 in low rpm ranges n.sub.p<500 min.sup.-1 of the means 3 operates in the intermittent mode. This means in other words that the drive motor 33 (compare FIG. 3) of the means 3 is turned on in the transport phase (compare FIG. 2: angular positions .phi..sub.a<.phi.<.phi..sub.e) and is turned off on the non-transport phase (compare FIG. 2: angular positions 0<.phi.<.phi..sub.a and angular positions .phi..sub.e<.phi.<2- .PI.). Here the on and off times of the means 3 are advantageously determined by the angular position .phi. of the main shaft of the sewing means 10 (compare FIG. 2).

[0131] Above rpm n.sub.p on the order of roughly 500 min.sup.-1 switching to continuous drive takes place, i.e. the auxiliary material transport means 2 operates in the continuous mode in high rpm ranges n.sub.p>500 min.sup.-1 of the means 3. But in this connection it must be considered that in the rpm ranges n.sub.p above roughly 500 min.sup.-1 intermittent motion by mass inertia and by the elastic behavior of the drive members gradually slows down anyway to quasicontinuous motion.

[0132] In this connection the stretching of the material layers 8, 9 is dependent on the fiction ratios between the auxiliary material transport means 2 and the (composition) of the upper material layer 8. In this respect stretching in the sewn material can also be influenced with the adjustable force F.sub.p with which the auxiliary material transport means 2 is pressed against the sewn material.

[0133] The transport path of the auxiliary material transport means 2 per stitching process is slightly greater than the advance path of the feeder means 1. This technical measure also ensures that the sewn material when advancing in the material feed direction D is always kept under tension; when sewing the upper material layer 8 and the lower material layer 9 this always results in formation of offset being prevented.

[0134] The pressure force F.sub.p of the auxiliary material transport means 2 and/or the rpm n.sub.p of the means 3 (-->peripheral speed U.sub.p of the auxiliary material transport means 2) can be electronically controlled. To do this there can be at least one electronic control means 4a, 4b (compare FIG. 4) for controlling the pressure force F.sub.p of the auxiliary material transport means 2 and/or the rpm n.sub.p of the means 3 (-->peripheral speed U.sub.p of the auxiliary material transport means 2).

[0135] Since at this point the pressure force F.sub.p of the auxiliary material transport means 2 and/or the rpm n.sub.p of the means 3 (-->peripheral speed U.sub.p of the auxiliary material transport means 2) can depend among others on the machine rpm n, the machine rpm n can be determined in the electronic control means 4a, 4b (compare FIG. 4) so that at any time it is possible to match the pressure force F.sub.p of the auxiliary material transport means 2 and/or the rpm n.sub.p of the means 3 (-->peripheral speed U.sub.p of the auxiliary material transport means 2) to the machine rpm n.

[0136] Furthermore, the peripheral speed U.sub.p of the auxiliary material transport means 2 can be determined not only by the machine rpm n, but among others also by the stitch length L. Since this stitch length L in a sewing means 10 is generally set mechanically, the stitch length L is generally not known to the electronic control means 4a, 4b. Last but not least, for this reason the electronic control means 4a can acquire information about the stitch length L by input by means of one control panel 5 (compare FIG. 4). The setpoint n.sub.set (compare FIG. 4) for the rpm n.sub.Motor of the drive motor 33 of the means 3 and thus its rpm n.sub.p is determined then by at least one computational algorithm RA 1 (compare FIG. 4).

[0137] Since at this point the means 3 has a drive motor 33 which is operated with direct current (compare FIGS. 3 and 4), the rpm n.sub.p of the means 3 (-->peripheral speed U.sub.p of the auxiliary material transport means 2) can be controlled by the (current) regulator (4a) (compare FIG. 4). Here the embodiment shown in FIGS. 1 to 5 exploits the fact that in the drive motor 33 the rpm n.sub.p imparted by it is directly proportional to the current supplied to the drive motor 33, in any case essentially so. For this reason the drive motor rpm D.sub.motor (compare FIG. 4) is electronically monitored and accordingly the desired rpm n.sub.p of the means 3 (-->desired peripheral speed U.sub.p of the auxiliary material transport means 2) is accomplished.

[0138] Furthermore, the pressure force F.sub.p of the auxiliary material transport means 2 can be determined not only by the machine rpm n, but among others also by the friction force acting between the auxiliary material transport means 2 and the upper layer 8 of the sewn material. Since this friction force is dependent on the composition of the sewn material to be transported, the friction force is generally not known to the electronic control means 4a, 4b. Last but not least, for this reason the electronic control means 4b acquires information about the composition of the sewn material to be transported by input by means of at least one control panel 5 (compare FIG. 4). The setpoint F.sub.set (compare FIG. 4) for the pressure force F.sub.p of the auxiliary material transport means 2 can be determined then by a computational algorithm RA II (compare FIG. 4).

[0139] Since at this point the means 3 has a linear motor 30 which is operated with direct current (compare FIGS. 3 and 4), the pressure force F.sub.p of the auxiliary material transport means 2 is controlled by the (current) regulator 4b (compare FIG. 4). Here the embodiment shown in FIGS. 1 to 5 exploits the fact that in a linear motor 30 the pressure force F.sub.p imparted by it is directly proportional to the current supplied to the linear motor 30 (compare FIG. 4: I.sub.Motor), in any case essentially so. For this reason, the linear motor current I.sub.Motor is electronically monitored and accordingly the desired pressure of the auxiliary material transport means 2 is accomplished.

[0140] Here the force of the linear motor 30 need not be measured. The auxiliary material transport means 2 is made such that it can be lifted off the upper layer 8 of the sewn material, for example in order to be able to take the sewn material away from the sewing means 10. This can also be effected by means of the linear motor 30, and it should be noted that the linear motor 30 in this connection need not perform any positioning function. With respect to the embodiments, the features and the advantages of the linear motor 30 reference is made in the full scope to the type of motor, as is described in German patent application DE 199 45 443.4 or in the international patent application WO 00/18997.

[0141] In this connection, both the initial value F.sub.0 and also the part F.sub.p>F.sub.0 of the pressure force F.sub.p (compare FIG. 5) which is dependent on the advance speed can be suitably parameterized and for example can be matched to the respective sewing conditions via the control panel (5) (compare FIG. 4).

[0142] Thus the quantitative amount of the pressure force F.sub.p can be reproduced by the formula F.sub.p=F.sub.0+R.times.n (compare FIG. 5), F.sub.0 being a constant initial value (compare FIG. 5), R being the coefficient of friction which in FIG. 5 appears as the slope of the plotted line, with a magnitude which is determined by friction ratios between the auxiliary material transport means 2 and the upper material layer 8, and n being the machine rpm (compare FIGS. 4 and 5).

[0143] The formula F.sub.p=F.sub.0+R.times.n plotted graphically by FIG. 5 moreover shows that the pressure force F.sub.p--in addition to a constant portion F.sub.0 which is independent of the coefficient of friction R and of the machine rpm n--can be increased essentially linearly with the coefficient of friction R between the auxiliary material transport means 2 and the upper material layer 8 and essentially linearly with the machine rpm n.

[0144] As already explained, depending on the technical circumstances, the rpm n.sub.p of the means 3 is equal to the peripheral speed U.sub.p of the auxiliary material transport means 2. Here the rpm n.sub.p of the means 3 is given by the formula n.sub.p=k.times.n.times.L, k being an adaptation factor, n the machine rpm and L the stitch length.

[0145] It is moreover apparent from the formula n.sub.p=k.times.n.times.L that the rpm n.sub.p of the means and accordingly the peripheral speed U.sub.p of the auxiliary material transport means 2--in addition to an adaptation factor k which is specified below--can be increased essentially linearly with the machine rpm n and/or essentially linearly with the stitch length L.

[0146] The adaptation factor k is in turn given by the formula k=k.sub.1.times.k.sub.2.times.k.sub.3, k.sub.1 being the parameter for the diameter of the auxiliary material transport means 2, for the constant of the linear motor 30 and for the stepping-down of the gear 34, k.sub.2 being the measure of the functional dependency of the offset between the upper material layer 8 and the lower material layer 9 on the machine rpm n, and k.sub.3 being the parameter for the composition of the sewn material to be transported.

[0147] The formula k=k.sub.1.times.k.sub.2.times.k.sub.3 moreover shows that the rpm n.sub.p of the means 3 and accordingly the peripheral speed U.sub.p of the auxiliary material transport means 2 are dependent on the technical circumstances and prerequisites of the means 3 and of the auxiliary material transport means 2 (--->factor k.sub.1), on the function of the offset between the upper material layer 8 and the lower material layer 9 over the machine rpm n (--->factor k.sub.2), and on the composition of the sewn material to be transported (--->factor k.sub.3).

[0148] It is apparent from the explanations above that the means 3 within the framework of the embodiment illustrated using FIGS. 1 to 5 plays an important role. Here its linear motor 30 has a stator element 31 which is made as a housing, which is securely connected to a holding plate (not shown in FIGS. 1 to 5 for the sake of clarity), and which is located on the back of the housing head of the sewing means 10. A rotor element 32 made as a drive rod is supported in the stator element 31.

[0149] The means 3 furthermore has a drive motor 33 which is operated with direct current, a gear 34 located between the drive motor 33 and the auxiliary material transport means 2, and a transfer element 35 located between the gear 34 and the auxiliary material transport means 2 for transfer of motion to the auxiliary material transport means 2.

[0150] The means 3 here has a carrier element 36 which is supported locked, which is connected to the rotor element 32, and on which the drive motor 33, the gear 34 and the transfer element 35 are mounted. The locked support of the carrier element 36 is accomplished by means of a guide rod 37.

[0151] Furthermore, the carrier element 36 is pretensioned by means of an elastic, low-mass coupling element 38 in the form of a helical spring. With respect to the embodiments, features and advantages of the coupling element 38 reference is made in the full scope to the German patent application DE 199 45 443.4 or to the international patent application WO 00/18997, especially with respect to the power-saving manner of operation which is associated with the coupling element 38.

Claims

1. Device intended for a sewing means (10) or sewing machine (10) for transport of sewn material, having at least one feeder means (1) for advancing the sewn material in the material feed direction (D) with an advance rate which is determined by the machine rpm (n) and by the stitch length (L) and at least one auxiliary material transport means (2) which acts on the upper layer (8) of the sewn material in the form of a pressure means with a pressure force (F.sub.p), which rotates with a peripheral speed (U.sub.p), and which is located in the material feed direction (d) behind the feeder means (1) and can be driven in proportion to the machine rpm (n) and to the stitch length (L), characterized in that by at least one means (3) the pressure force (F.sub.p) which is exerted by the auxiliary material transport means (2) on the upper layer (8) of the sewn material to be transported can be increased with increasing machine rpm (n) and/or the peripheral speed (U.sub.p) of the auxiliary material transport means (2) can be further increased in addition to the proportional increase with increasing machine rpm (n).

2. Device as claimed in claim 1, wherein the pressure force (F.sub.p) and/or the peripheral speed (U.sub.p) can be adapted preferably by the means 3 in addition to the composition of the sewn material which is to be transported.

3. Device as claimed in claim 1 or 2, wherein the pressure force (F.sub.p) is given by the equationF.sub.p=F.sub.0+R.times.nin which F.sub.0 is a constant force; R is the coefficient of friction with a magnitude which is determined by the friction ratios between the auxiliary material transport means (2) and the upper material layer (8); and n is the machine rpm.

4. Device as claimed in at least one of claims 1 to 3, wherein the rpm (n.sub.p) of the means (3) is a measure of the peripheral speed (U.sub.p) of the auxiliary material transport means (2) or is equal to the peripheral speed (U.sub.p) of the auxiliary material transport means (2), the rpm (n.sub.p) of the means (3) being given by the equationn.sub.p=k.times.n.times.L,in which k is a matching factor; n is the machine rpm; L is the stitch length

5. Device as claimed in at least one of claims 1 to 4, wherein the auxiliary material transport means (2) in low rpm ranges (n.sub.p<500 min.sup.-1) of the means (3) operates in the intermittent mode, the on and off times of the means (3) being preferably determined by the angular position (.phi.) of the main shaft of the sewing means (10) or sewing machine (10).

6. Device as claimed in at least one of claims 1 to 5, wherein the auxiliary material transport means (2) in high rpm ranges (n.sub.p>500 min.sup.-1) of the means (3) operates in a continuous mode.

7. Device as claimed in at least one of claims 1 to 6, wherein the transport path of the auxiliary material transport means (2) per stitching process is greater, especially slightly greater, than the advance path of the feeder means (1).

8. Device as claimed in at least one of claims 1 to 7, wherein there is at least one electronic control means (4a and 4b) for controlling the pressure force (F.sub.p) of the auxiliary material transport means (2) and/or the rpm (np) of the means (3), in which especially the machine rpm (n) can be determined and/or, which receives especially information about the stitch length (L) by input by means of at least one control panel (5) or which receives especially information about the composition of the sewn material to be transported by input by means of at least one control panel (5).

9. Device as claimed in at least one of claims 1 to 8, wherein the means (3) has at least one linear motor (30) which is operated preferably with direct current, and which preferably has at least one stator element (31) which is made as a housing and in which preferably at least one rotor element (32) made as a drive rod is supported.

10. Device as claimed in claim 4 and as claimed in claim 9, wherein the matching factor (k) is given by the formulak=k.sub.1.times.k.sub.2.times.- k.sub.3,k.sub.1 being the parameter for the diameter of the auxiliary material transport means (2), for the constant of the linear motor (30) and for the stepping-down of the gear (34); k.sub.2 being a measure for the functional dependency of the offset between the upper material layer (8) and the lower material layer (9) on the machine rpm (n); and k.sub.3 being the parameter for the composition of the sewn material to be transported.

11. Device as claimed in claim 9 and as claimed in claim 10, wherein the means (3) has at least one carrier element (36) which is connected to the rotor element (32), to which the drive motor (33), the gear (34) and the transfer element (35) are attached; and/or which is preferably supported locked by means of at least one guide rod (37).

12. Device as claimed in claim 11, wherein the carrier element (36) is pretensioned by at least one elastic, low-mass coupling element (38), especially by means of at least one helical spring.