EP1394310A2 - Method for determining the underthread supply and sewing machine with monitoring of the underthread supply - Google Patents

Abstract

A light beam (57a, 57b) is projected from a light source (51) through apertures (49', 49) in the bobbin carrier (27) and hook body (17) on to a receiver (53). The angle of rotation of the hook body (17) when light is detected by passing both the aperture edge and the surface of the thread package is used to calculate the package diameter. An Independent claim is also included for a sewing machine with this method of underthread sensing, the receiver (53) being connected to the machine control. Alternative methods involve measuring the position on the receiver where the initial or final light ray is detected, measuring the duration of light reception, or measuring the amount of light received. The corresponding receivers detect the position or the amount of light received.

Description

The invention relates to a method for determination of the bobbin thread and a sewing machine with a Bobbin thread monitoring according to the generic term of Claims 1 and 4.

When sewing and embroidering with a sewing machine as is well known, two threads, the upper thread and the lower thread, looped together. The upper one, called the needle thread, is placed on or next to the sewing machine Supplied coil, the size of which is essentially freely selectable is. The second thread, called the bobbin thread, is on one Coil wound, which is rotatable inside the mounted and drivable gripper of the sewing machine is inserted and is freely rotatable there. By the size of the gripper consequently becomes the maximum size the bobbin. The spooled The bobbin thread quantity or the bobbin thread supply is in each Fall in relation to the upper thread supply on the outside of the machine housing arranged coil many times smaller and therefore has to be replenished or more often be replaced. In addition, the bobbin is at Sewing is not visible from the outside as it is inside of the gripper housing, which is arranged in the forearm is. For this reason, the monitoring of the current Bobbin thread supply and bobbin thread withdrawal during the Sewing difficult. To make matters worse, often when sewing smaller pieces of material through the Operator a partially already filled Bobbin is wound with another thread, because there is no empty coil left. That other Thread is not with the one already on the spool connected. After consuming this outer thread no seam can be generated anymore, although on the spool core for example 50% or 70% of another thread is wound up.

Measuring devices are already from the prior art known to try the end or the Remaining amount of the bobbin thread can be rotated in the looper held bobbin and determine the Stop the sewing machine before the end of the bobbin thread from Upper thread is pulled out through the material and especially before other stitches are sewn on the underside of the fabric therefore not from a bobbin thread being held.

GB-A 2 296 721 describes a device for detection the amount of remaining thread on a bobbin one Known sewing machine. A ray of light from one Light transmitter essentially tangential through the annulus between the two coil flanges and the spool sent through to a light receiver. These are in Gripper housing and in the coil housing diagonally holes placed opposite, through which the Rays of light are sent through. The rays of light are passed very close to the mandrel, so that End of thread supply can be determined as soon as the Rays of light can penetrate this area. Is the The bobbin is still filled with thread, so the receiver cannot Light signal can be received. A second sensor detects the movements of the gripper, so clearly it can be seen whether the thread supply has now been used up or whether only the gripper is stationary. With one Device can only the thread supply shortly before complete emptying of the coil can be detected.

From US-A 4,825,789 a further device for detecting the thread end on a bobbin of a sewing machine is disclosed. In this device too, a light beam is directed tangentially from the light transmitter over the coil mandrel to a light receiver. As long as there is thread supply on the bobbin, the light beam cannot reach the light receiver. Only shortly before the end of the thread can these sensors transmit a signal to the operator of the machine, which indicates the end of the thread in the bobbin.
With both known devices, only the end of the thread or the point in time before the end of the thread is reached can be recognized. Thread breaks or a determination of the thread quantity currently present and thus the point in time at which the thread end is reached cannot be recognized with the known devices.

The object of the present invention is to provide a method for determining the bobbin thread supply and a sewing machine with a bobbin thread monitoring system, with which the current thread quantity on the bobbin can be determined at any time.
Another task is to calculate the time at which the lower thread ends on the lower thread spool from the amount of thread consumed per unit of time.

These tasks are solved by a method for determining the bobbin thread supply and a sewing machine with a bobbin thread monitoring system in accordance with the features of claims 1 and 4.
Further advantageous embodiments of the invention are given in the dependent claims.

With one radially spaced from the gripper body Light source can be tangential to the axis of rotation of the coil or beams of light directed by the gripper Gripper body through on a photosensitive element sent and there the time of arrival of the first Light beam with the current angle of rotation of the gripper compared and thus exactly the diameter of the current one Thread supply can be determined on the bobbin. With the same device, namely the light source and one photosensitive element that is finite Length, the location where the Beam of light along with knowing the current one Angle of rotation of the gripper compared and thus the Diameter of the thread supply can be determined. Further can with the same arrangement by measuring the Length of time during which a light beam strikes the photosensitive element drops, the coil diameter and so that the thread supply can be determined. Of course the possible measurement parameters could also be combined to determine the thread supply to to increase the measuring accuracy. The accuracy can neither due to small fluff, dust, abrasion or other influences be significantly affected. It can also inexpensive elements (a light emitting diode and a photosensitive element) can be used. Along with a continuous measurement of the mean Coil speed with suitable means and the time Diameter decrease and bobbin thread consumption per stitch, regardless of the thickness of the thread, the Be calculated at the end of the latter.

Figur 1

eine Seitenansicht einer schematisch dargestellten Nähmaschine mit im Bereich des Greifers aufgeschnittenem Freiarm einer Freiarmnähmaschine,

Figur 2

eine Ansicht eines Greifers in Achsrichtung,

Figur 3

eine Ansicht des Greifers in Figur 2 in Seitenansicht (teilweise aufgeschnitten),

Figur 4

ein Querschnitt längs Linie IV-IV in Figur 3,

Figur 5a

eine schematische Darstellung eines umlaufenden Greifers mit darin angeordneter Spule, mit annähernd maximaler Fadenmenge, wobei die vordere Kante der Ausnehmung den Beginn einer Messung darstellt,

Figur 5b

eine schematische Darstellung eines umlaufenden Greifers mit darin angeordneter Spule, mit halber Packung,

Figur 5c

eine schematische Darstellung eines umlaufenden Greifers mit darin angeordneter Spule, Spule leer,

Figur 6a

eine schematische Darstellung eines umlaufenden Greifers mit darin angeordneter Spule, mit annähernd maximaler Fadenmenge, wobei die hintere Kante der Ausnehmung den Beginn der Messung darstellt,

Figur 6b

eine schematische Darstellung eines umlaufenden Greifers mit darin angeordneter Spule mit halber Packung,

Figur 6c

eine schematische Darstellung eines umlaufenden Greifers mit darin angeordneter Spule, Spule leer.

The invention is explained in more detail on the basis of illustrated exemplary embodiments. Show it

Figure 1

1 shows a side view of a schematically illustrated sewing machine with a free arm of a free arm sewing machine cut open in the region of the hook,

Figure 2

a view of a gripper in the axial direction,

Figure 3

2 shows a side view (partially cut away) of the gripper in FIG. 2,

Figure 4

3 shows a cross section along line IV-IV in FIG. 3,

Figure 5a

1 shows a schematic illustration of a rotating hook with a bobbin arranged therein, with an approximately maximum amount of thread, the front edge of the recess representing the start of a measurement,

Figure 5b

1 shows a schematic representation of a rotating gripper with a coil arranged therein, with half a pack,

Figure 5c

1 shows a schematic representation of a rotating gripper with a coil arranged therein, coil empty,

Figure 6a

1 shows a schematic representation of a rotating hook with a bobbin arranged therein, with an approximately maximum amount of thread, the rear edge of the recess representing the start of the measurement,

Figure 6b

1 shows a schematic illustration of a rotating gripper with a coil with half a package arranged therein,

Figure 6c

is a schematic representation of a rotating gripper with a coil arranged therein, coil empty.

The purely schematically shown in the example in Figure 1 Free-arm sewing machine 1 comprises a base 3, one Upper arm 5, a lower or free arm 7 and the three Parts connecting machine housing 9. In the upper arm 5 a needle bar 11 and the presser foot bar 13 attached. In the forearm 7 is schematically in the cut area indicated by a circle of the grippers 15. The Details of the gripper 15 are shown in FIGS. 2 to 4 shown enlarged.

The gripper 15 described in the example also includes other elements a gripper body 17 which on a Drive shaft 19 sits and through a pinion 21 in Drive connection to the main shaft of the Sewing machine drive stands (main shaft not shown). It doesn't matter whether the gripper is one rotating acts firmly on the drive shaft attached, or around an oscillating one that is loose in the Gripper driver inserted and consequently not firmly on the Drive shaft 19 is arranged.

A thread guard or is seated peripherally on the hook body 17 -baffle plate 23 with a driver tip 25. Inside of the gripper body 17 is on the front end of the Drive shaft 19 a coil carrier 27 for receiving a Bobbin case 28 for a bobbin - short bobbin 29 - freely rotatable. The bobbin case 28 is by means of a closure 31 at the front end 33 one in Coil carrier 27 fastened coaxially to the drive shaft 19 Wave stub 20 held. In Figure 2 is of the Coil 29 only a small section of the front Flange 35 visible. In flange 35 are annular arranged openings 37 embedded. The rear flange 39 of the coil 29 is visible in Figure 3. There is the front flange 35 covered by the bobbin case 28. The apex 41 of the coil core 43 is also there Coil 29 partially visible. The latter two Elements are visible because in the gripper body 17 Recesses 45 'and 45 "and 27 slots in the coil carrier 49 ', 49 "are attached, which have a tangential Only allow a view through the gripper 15.

In order to enable the view, ie the passage of light rays 57 of a peripherally arranged light source 51, the coil capsule 28 is also surrounded peripherally by a jacket only over an arc of approximately 180 degrees.
A look through the gripper 15 is possible in each case when the two recesses 45 ', 45 "on the gripper body 17 and the slots 49', 49" on the coil carrier 27 and the omitted part in the jacket of the coil capsule 28 are in register. Since the bobbin 27 is stationary with respect to the sewing machine housing 9 when sewing, the view through the recess 45 'on the hook body 17 becomes possible if the two opposite recesses 45', 45 "and slots 49 ', 49" above the axis of rotation A of the drive shaft 19 lie (as shown in Figure 4).

The cross-section of the possible once per gripper rotation View-through depends on what has been determined constructively Geometry of the gripper 15 and the dimensions of the Recesses 45 ', 45 "and slots 49', 49" only from current pack diameter D of the on the coil 29 in annular packing area 47 wound thread from. The full cross-section is at full pack smallest (see FIG. 5a); largest with empty pack (see Figure 5c). The lower limit of each See-through cross section in the fixed recess 45 "is through the apex 41 of the coil pack or Given coil core 43; the top by the respective location the front edge 61 of the recess in the direction of rotation P 45 ".

The angle of rotation position of the gripper 15, at which the beam passage or passage per revolution is detected, can be used directly as a measure for the calculation of the current coil diameter D. The measuring method is now explained in more detail:
At a radial distance from the periphery of the gripper 15, the light source 51 and on the other side of the gripper 15, that is to say essentially diagonally opposite, is a light receiver 53 with a reception area extending at least over a length a ₀ -a ₃ (vertical line 5), which is able to receive the beams 57a-57b of the beam 57 emitted by the light source 51. The light beams 57a-57b penetrate both the two recesses 45 ', 45 "in the gripper body 17 and the slots 49', 49" in the coil carrier 27 when they temporarily overlap. The recesses 45 ', 45 "and the slots 49', 49" are therefore covered once per complete revolution of the gripper body 17 or once during a cycle 'with oscillating grippers 15. In FIG. 4, which represents a cross section through the gripper 15, the geometric position of the recesses 45 ', 45 "and the slots 49', 49" is clearly shown. Furthermore, the light rays 57a, 57b emanating from the light source 51 and delimiting the beam 57 at the top and bottom can be seen, which fall through the gripper 15 onto the light receiver 53. The light beam 57a represents a tangent between the light source 51 and the bobbin core 59. The light beam 57b is also a tangent, specifically a tangent to the packing of a full bobbin, the diameter of which approximately corresponds to the diameter of the flanges of the lower thread bobbin 29. The two light beams 57a, 57b in FIG. 4 and also in FIG. 5c consequently represent the two extreme values of the beam 57.
A CCD element, a photodiode or phototransistor or another light-sensitive element can be used as the light receiver 53

In the examples shown, the light emitted by the light source 51 reaches the light receiver 53 as a diverging beam 57 through the gripper 15 as soon as the front edge 61 of the recess 45 "in the direction of rotation P clears the passage of light rays. The light beam 57x, determined by the thread pack is the first one that can be detected by the light receiver 53.
5a to 5c, the gripper body 17 rotates counterclockwise, ie in the direction of the arrow P. The "first" light beam is designated 57x. If the coil 29 is empty, the first light beam 57x corresponds to the light beam 57 a and reaches the light receiver 53 at the point a ₃ (cf. FIGS. 4 and 5c). However, if the bobbin 29 is completely filled with thread, the majority of the packing space 47 is not transparent to light. The first light beam 57x can consequently only pass further upwards and strikes the light receiver 53 at point a ₁ (cf. also FIG. 5a). FIG. 5b shows the situation with a coil 29 half full. Here, the first light beam 57x hits point a ₂ , which lies between the two extremes a ₁ and a ₃ . As an alternative to a diverging light beam, a light beam with parallel rays can also be used.

The following are four possibilities of the device, determine the diameter D of the thread pack, demonstrated. The current position of the leading edge 61 of the Recess 45 "is known in Example 2 provided. Their position is from the rotational position of the Main shaft of the sewing machine 1 can be calculated.

Example 1 (location)

The light receiver 53 recognizes the location a ₁ to a _{3 of} the impingement of the first light beam 57x, which strikes the light receiver 53 as soon as the front edge 61 of the recess 45 "allows the light beam 57x to pass through. Knowledge of the location (a ₁ to a ₃ ) the impingement of the first light beam 57x on the light receiver 53 enables the pack diameter D to be calculated directly because there is a direct geometric connection (FIGS. 5a-5c). Alternatively, the location of the last light beam could be detected before the rear edge 62 on the Recess 45 "begins to close the light cone (Figures 6a-6c).

Example 2 (time)

The time t _{1 of} the light beam 57x upon impact is recorded and compared with the angle of rotation alpha of the front edge 61 on the gripper body 17. The diameter D of the packing can also be calculated from these two parameters (FIGS. 5a-5c; FIGS. 6a-6c).

Example 3 (exposure time)

The times t _x to t _{o of} the incidence of the first light beam 57a until the last light disappears on the receiver 53, ie the duration of illumination. Together with the known speed n of the gripper 15 and the size of the recess 45 ″, the diameter D of the coil package can also be calculated (width of the light cone in FIGS. 6a-6c).

Example 4 (amount of light)

Instead of the time period t _x - t _o as described in Example 3, the amount of light or light energy (mW) which strikes the receiver 53 can be recorded and used to calculate the diameter D. The accuracy of this measurement is, however, less than that in Example 3, since errors are inevitable due to, for example, fusing and aging of the light source 51 (area of the light cone in FIGS. 6a-6c).

The above-mentioned examples for recording data for calculating the pack diameter D can also be combined in order to be able to increase the accuracy.
The four possible measurement types not only determine the instantaneous diameter D, but also the decrease in diameter D resulting per unit of time and thus also the consumption of thread and the point in time at which the thread on the bobbin 29 is completely used up.

The continuous measurement of the diameter D of the Coil pack 47 thus enables the current Thread consumption regardless of the thickness of the thread determine. In this case, as an additional parameter the average speed n of the coil 29 is required. For the Known means are available for detecting the speed n of the coil to disposal.

Knowing the thread consumption can further regulate the thread tension of the upper thread can be used. If the thread consumption per stitch is greater than that known theoretical value resulting from the stitch type and the stitch length and the thickness of the material to be sewn the upper thread tension is too great and it becomes the lower thread pulled too deep into the material. By loosening the Upper thread tension can pull the lower thread into the Material to be brought to the desired size. Is analog too little bobbin thread consumption compared to theoretical value an indication that the upper thread tension is too low and must therefore be increased.

To determine the speed n of the bobbin 29 can the known means, such as in the DE-A-4 116 638 are used. A reliable measurement of the speed n of the bobbin 29 can also be used with a device such as that in CH Patent Application No. 00893/02 of May 30, 2002 is disclosed will be achieved. With the one disclosed there Measuring method or device, the speed n Bobbin 29 can be reliably detected at any time, in particular, the bobbin 29 can come to a standstill be recognized immediately. Even when shocks let the sewing machine vibrate the bobbin 29, what can be misinterpreted as "non-standstill". This allows a thread break or the end of one on an already existing thread wound thread the lower thread bobbin 29 and the sewing machine stop before the bobbin thread leaves the stitch plate can. Another advantage of speed measurement is that the direction of rotation of the coil 29 can be recognized. On Signal is emitted when the coil is inserted incorrectly.

Claims (5)

Method for determining the bobbin of thread on the bobbin (29) of a sewing machine (1) with a light transmitter (51) and a light receiver (53), a light beam (57) from the light transmitter (51) through slots (49) made in the bobbin holder (27) ', 49 ") and through in the gripper body (17) arranged peripheral recesses (45', 45") tangential to the bobbin core (43) and the thread pack through the packing space (47) between the flanges (35, 39) and at least one the light beams (57x) are received by the light receiver (53) and the received signal for calculating the coil package diameter (D) is forwarded to the machine control, characterized in that the instantaneous angle of rotation (alpha) of the gripper body (17) and / or the point in time (t ) is detected when a light beam (57 _x ) is registered by the light receiver (53). A method according to claim 1, characterized in that the location (ax) of the first and / or last light beam (57x) on the light receiver (53) is detected. A method according to claim 1, characterized in that the duration of the light reception and / or the amount of light is detected during a gripper revolution that strikes the light receiver (53). Sewing machine with a bobbin thread monitoring device, comprising a hook (15) with a hook body (17), a bobbin holder (27) arranged in the hook body (17) and a freely rotatable bobbin (29) arranged in the bobbin holder (27) in a bobbin case (28) ), a light transmitter (51) and a light receiver (53), slots (49 ', 49 ") and recesses (45', 45") being provided in the periphery of the gripper body (17) and in the jacket of the coil carrier (27) , which allow a tangential passage of light rays (57) from the light source (51) to the light receiver (53) through the packing space (47) on the coil (29), characterized in that a CCD element, a light receiver (53) A photocell or a phototransistor is used, which light receiver (53) registers the location of the impact of the first and / or last light beam (57) on the light receiver (53) and is connected to the machine control. Sewing machine according to claim 4, characterized in that the light receiver (53) comprises means which detect the amount of light received and / or exposure time.

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