GB2168085A - Apparatus for automatically adjusting the stitch pitch of a sewing machine - Google Patents

Abstract

A stopping apparatus for a sewing machine allows the last stitching point to be positioned at a predetermined point. During stitching, when a photo sensor detects the end of the workpiece, an electronically controlled apparatus adjusts the stitch pitch by detecting the deviation between the needle hole and the last stitch point. A disc with slits circumferentially on its furace is pivoted along a main shaft (2) of a sewing machine; thus the deviation is signalled. The signal causes a stepping motor (18) to rotate and thus a cam (17) pivoted along a main shaft of this stepping motor is also rotated. At the last stitch or two or three stitches before the last, a solenoid (16) acts to pull a feed adjuster lever until it contacts with said cam, thus the stitch pitch is adjusted. The number of stitches needed to finish the stitching after the photo sensor has detected the end of workpiece is operated through a CPU system. Thus, when the counter has counted said number, the machine stops automatically. <IMAGE>

Description

SPECIFICATION Apparatus for automatically adjusting the stitch pitch of a sewing machine The invention relates to an automatic stitch pitch adjuster for a sewing machine which allows needle points to be positioned and stopped accurately at predetermined points, and more particularly to adjust automatically the stitch pitch to terminate the needle points at the predetermined points.

In Fig. 1 of the accompanying drawings there is illustrated by way of example one mode of providing a predetermined stitch line at the inner side of a workpiece. Thus for stitching along a collar portion there is selected a stitch line AB, BC, CD, at a distance "a" from the edge of the workpiece.

In such a case, each stitch line length is predetermined for each collar portion, thereby, to perform a stitching operation as disclosed in Japanese patent publication 53-38646.

According to this invention, two kinds of stitching are arranged. Each stitch pitch is different but the total stitch line length is equal, and these two stitchings which are previously set are mixed to perform the required stitch with the last needle point positioned to the predetermined point.

Since the second stitch pitch which is selected for adjusting the stitching is previously set, when the first needle point is not positioned constantly or when the elasticity of the workpiece is different, the needle points are not positioned at the predetermined points.

For instance, if the second stitch pitch was 1 mm, and the deviation caused by the elasticity of the workpiece was 0.5 mm, it is difficult to adjust the stitch pitch within less than 1 mm by changing the number of stitches and the quality of the stitched article is lowered.

Besides, in actual stitching, to set the first needle point accurately for each workpiece and where bulky workpieces are to be stitched, labour efficiency will be reduced and the cost will be raised.

This invention purports to improve such defects.

The invention allows the stitching to be stopped accurately and automatically at the predetermined point by detecting the required stitch line length and calculating the required number of stitches to complete the stitching up to the margin line.

Based on that number of stitches and the stitch line length, the revised number of stitches and the stitch pitch are calculated, and the sewing machine is adjusted automatically to feed the said stitch pitch, thus stitching with said stitch pitch and said revised number of stitches are terminated at the predetermined point.

A preferred embodiment of the invention is hereafter described in detail with reference to the accompanying drawings, in which: Figure 1, already mentioned, illustrates a known mode of stitching a collar with margin "a"; Figure 2 is a diagramatic view of the present invention; Figure 3 illustrates how to adjust the stitch pitch by use of a motor and a solenoid; Figure 4 illustrates the formation of a stitch line when, the present apparatus is employed.

Figure 5 is a flow chart of the present invention; Figure 6 is a block diagram of the present invention; Figure 7 is a block diagram of how to calculate P,/p.

Referring to Fig. 2, there is shown a conventional dog feeding mechanism 1 which is located under a bed and performs an appeardisappear motion at the surface of a throat plate, feeding at four steps. Also shown is a main shaft 2, and a conventional feed adjuster 3 connected to the main shaft 2 by a crank rod and which transmits a horizontal component of motion as a horizontal feed. An adjustment screw 4 is rotatable from the outside of the sewing machine, to advance or retract its end which engages a conventional adjusting cam 5. This cam 5 is thereby rotatable about its centre point. A rocking shaft 6 is fixed to the back end of the adjusting cam and a connecting rod 7 is connected to the rocking shaft 6 and adjusts the stitch pitch by changing the horizontal component of motion at the feed adjuster 3 in relation to the position of the cam 5.

Reffering also to Fig. 3, there is shown a feed lever 9 having fixed at one portion a horizontally projecting pin 9a. A spring 8 is provided at the end of the feed lever 9 and has its other end fixed to the machine frame; thus the lever is normally urged to move upwards.

A shaft 10 sustains a support section of the feed lever 9 which has an opening and in this opening, the shaft is inserted with clearance; the shaft is thus an adjusting shaft rotatably set against the machine frame.

A rocking lever 11 is fixed to the adjusting shaft 10 and projects horizontally to the bottom of the pin 9a of the lever 9.

When the lever 9 is rotated downwards, the pin 9a presses the rocking arm 11 and consequently the adjusting shaft 10 rotates counterclockwise.

The end of the adjusting shaft 10 is connected to the rocking shaft 6 by a connecting rod 12 and, depending on the rotation angle of the adjusting shaft 10, the feed is reduced or reversed.

Also shown is an L-shaped lever with its angle portion rotatably supported by the adjusting shaft 10 (Fig. 3).

At the free end of the L-shaped lever 13, an action pin 13a is fixed so as to project over the rocking arm 11.

A connecting arm 14 rotatably supports one end of the L-shaped lever 13.

An L-shaped operation lever 15 has its middle portion rotatably supported by the machine frame and its end connected rotatably to another end of the connecting arm 14.

Another end of the L-shaped operation lever is supported by an actuator 16a of a solenoid 16.

Up and down motion of the actuator 1 6a causes the connection between the L-shaped operation lever 15 and the connecting arm 14 to move to right and left.

A cam body 17 with one end surface forming a cam 1 7a is fixed to a stepping motor shaft 18.

The thickness between the circumference of the cam 17a and the other end of the cam body differs according to each circumferential position.

The projecting end of the connecting arm 14 is formed as a contactor 14a and this contactor 14a faces the surface of the cam 17a. Thereby, the distance between the contactor 14a and the surface of the cam 17a differs according to the rotation angle of the cam 17a.

Accordingly, the connecting arm 14 contacts the surface of the cam 1 7a when it moves to the right side.

Since the contact position differs depending upon the rotation of the surface of the cam 17a the moved distance of the contractor 14a also differs, and this moved distance causes the rocking arm 11 to rotate downward through an action pin 13a of the L-shaped lever and to reduce stitch pitch.

In short, the moved distance of the connecting rod 14 is defined by the rotation angle of the cam body 1 7 which is relatively rotated by a stepping motor 18, and by energising the solenoid 16, the reduced stitch pitch in response to the moved distance of connecting rod is obtained.

A potentiometer 19 is connected by linkage to the free end of the rocking arm 11, and the rotation of the rocking arm 11 is converted to an electric signal.

When the solenoid 16 is not energised, the potentiometer 19 detects the designated stitch pitch by the adjusting screw 4.

When the solenoid 16 is energised, the potentiometer 19 detects the designated stitch pitch by the stepping motor 5.

Referring to Fig. 6, a workpiece end sensor 20 (not shown on Fig. 2) is located in a frontal direction (opposite direction of feeding) in relation to the needle hole.

The workpiece end sensor 20 detects the end of the workpiece, and is located at a predetermined distance from the needle hole.

The workpiece end sensor consists of a projector 20a which is located at its upper side and a photo sensor which is located at its lower side.

Any type of workpiece end sensor is applicable provided that its function is the same, although its configuration may differ.

Referring to Fig. 6, there is shown a pulse generator 21 adjacent the main shaft.

A disc with slits is pivoted along the main shaft and as the main shaft rotates, the slits pass load at responding position is converted to a pulse signal.

There is a main shaft detector 22 and during one rotation of the main shaft the "L" level signal is emitted during the feeding process and an "H" level signal is emitted after the feeding process.

By use of the above described apparatus, the mode of terminating the stitching at the pre-set margin line accurately and the mode of automatically stopping the sewing machine will be explained together with its control circuit.

Referring to Fig. 4, one example of actual stitching according to this invention is explained.

Stitching starts from point X and stops at the margin line which is positioned 1 mm from the end of the workpiece and the stitch line is straight.

In this example, feeding (stitch pitch) per one needling is set 2 mm, and when stitching has proceeded up to 20 mm from the end of the workpiece, the workpiece-end-sensor 20 sends a detecting signal.

Thereby, the required stitch length after detecting the end of workpiece is (20-1 = 19) 19mm, and the required number of stitches is 19/2=9.5 stitches. If the workpiece is fed P, mm after detecting the end of workpiece, the required number of stitches is (9.5-P1/2) stiches.

For instance, if P,=0.4 mm as in Fig. 4, 9.5 -(P1/p)=9.5-(0.4/2)=9.3 (stitches).

So if 9 stitches are performed at the original pitch of 2 mm and the last stitch at 0.3 stitch, (2X0.3=0.6 mm stitch pitch), the stitching will be terminated at the margin line.

Referring to the Fig. 5 flow chart, and Fig. 6 block diagram, the above principle is further explained.

When the circuit is switched on, the pre-set stitch pitch adjusted by the adjusting screw 4 is detected by the potentiometer 19, and a determining circuit 23 operates the required number of stitches after the workpiece end sensor 20 detected end of the workpiece. Referring to the above example, the distance from the needle hole to the margin line is 19 mm, and the pitch is 2 mm. Thereby, the circuit 23 calculates 9.5 stitches (19T2=9.5).

As a next step, when the workpiece is started from the point X and fed until the end of the workpiece reaches 20 mm from the needle hole, the workpiece end sensor 20 detects the above positionings.

When the end of the workpiece is detected, the pulse generator 21 at the main shaft de tects the angular position of the main shaft.

Referring to this angle, the required stitch pitch P7 to perform the next stitch after the sensor detected, and ratio of unfinished stitch pitch to stitch pitch P (P,/p) are calculated.

In this example, p=2 mm, P1 =0.4 mm, then the unfinished pitch is -4=20%, as the sensor detected when the pitch performed 80%. Referring to Fig. 7 to detect the P,/p ratio, (refer to Fig. 4 for P1, P is the switch pitch) a main shaft detector 22 generates an "L" level signal during the feeding process and this signal is fed to the Gate 1.

The workpiece end sensor 20 is connected to the inverted intput of Gate 1 and to the input of Gate 2 and to output-enable-input of the table ROM (read only memory) 24.

The pulse train from a main shaft pulse generator 21 is fed into a phase counter 25 as a clock-signal through Gate 2.

The phase counter detects the phase position of the main shaft when the workpiece end sensor detected the end of workpiece.

When the workpiece is covering the workpiece-end-sensor 20 and the "H" level signal is being fed out, the pulse train from the main shaft pulse generator 21 is fed into a phase counter 25, and the counter counts up since the Gate 2 is opening.

Under such condition, if the workpiece end sensor 20 detected the end of the workpiece the output changes from "H" to "L".

Then the Gate 2 is closed and the pulse train is not fed to the phase counter 25, and the counter stops.

As the output from the workpiece end sensor 20 changes to "L", although the feeding process is finished and the main shaft detector outputs an "H" level signal, the phase counter 25 is not reset, and the phase at the time when- workpiece end sensor detected is maintained.

The relation between the phase of the main shaft and P1/p is not linear but curved and its curve is related to stitch pitch; thereby, to obtain the P,/p ratio from the main shaft phase, the table is required.

The phase value of the main shaft is fed to table ROM 24 as address, and the parameter of stitch pitch is fed in to address from the potentiometer through A/D converter and latch.

The parameter of the stitch pitch is latched when the workpiece end sensor 20 changes from "H" to "L".

Output from the workpiece-end-sensor 20 is fed into output-enable-input of table Row24, and when the sensor detects the end of the workpiece, the signal changes from "H" to "L" and the ratio P,p is fed out.

The operating machine 26 operates to minus P,/p from the said designated number of stitching and operates the number of stitches from the first stitches after the workpiece end sensor has detected until the sewing machine stops.

For instance, referring to the above described example, the designated number of stitches is 9.5 and P,/p is 0.2, (0.4T2=0.2) then 9.5-0.2=9.3 is operated.

This means that stitch work of 9 sttitches with 2 mm stitch pitch and one more stitch with stitch pitch of 2 mmX0.3=0.6 mm terminates at the pre-set position.

Thereby, decimal portion a (in this case 0.3) is fed into an operating machine 27 and applying the following formula the last pitch pl is fed out (pl=PXa).

In the above described example, the decimal portion is 0.3 and the stitch pitch is 2 mm; thereby, pl is 0.6 mm, (2 mmX0.3=0.6 mm). The stepping motor driver (STM) 28 receives the output of pl and rotates the stepping motor 18, and the cam 17 a positions to arrange a stitch pitch length of pl.

The operating machine 29 adds the number of stitches.

First stitching with the stitch pitch of P,/pX2 mm and last stitching with a stitch pitch corresponding to the decimal portion, (in this case 0.3) and stitchings with regular pitch, and in this example, total number of stitches is 11 (9+2=11), and this number 11 is set.

The reduction counter 30 starts counting the number of stitches when the workpiece end sensor acted, and in this example, 11 (number of stitches n') is reduced one by one per each stitch and when reduced to 1 (n'= 1), the stitching speed is slowed, and the solenoid signal 31 is generated. This signal draws the solenoid 16 (SOL) (ref. Fig. 3) via the solenoid driver 16f (Fig. 6).

The stepping motor 18 is already rotated to set the predetermined last pitch pl (0.6 mm), and thus the predetermined pitch is arranged.

When the solenoid 16 acts, the electric current to the stepping motor 18 is raised to strengthen the contact between the cam 1 7 and the contactor 14a.

When the sewing machine has performed the last stitch, n' counts 0 (n'=O) and 31a, solenoid driver 16f turns off and the stepping motor 18 reverts to original position.

As the solenoid 16 is de-energised, the actuator 16a drops by gravity, and the connecting arm 14 turns to its original position.

Thus, when the stitching starts again, it is at the original pitch of 2 mm.

After the solenoid driver 16f is turned off, the sewing maching stops at the needle-down position 32. If the mode is thread-cut mode 33, after cutting the thread, the sewing maching stops at the needle-up position 35.

In the above described example, the pulse motor is used to determine the required pitch, but the line or motor can also be used to set the stitch pitch in lieu of the pulse motor.

In the above described example, only the last pitch was adjusted but it is possible to adjust the last two or three stitch pitches. If the number of adjusted stitches is increased, the difference between the adjusted stitch pitch and the original stitch pitch is decreased; thereby more accurate cam positioning is achieved.

This invention allows adjustment of stitch pitch during stitching, after detecting the end of the workpiece and calculating the required number of stitches thereby, unlike adjusting of stitch pitch before stitching, the first needle point need not be accurately positioned, and stitching will be improved very much as the margin will be performed neatly with good appearance.

Claims (2)

1. A sewing machine having an automatic feeding apparatus for varying stitch pitch for a predetermined time in a sewing process, comprising; a feed dog for feeding a workpiece in synchronism with the rotation of a main drive shaft of the machine; a rotatable regulator connected with the feed dog to regulate the amount of feed of the dog in response to the rotated position; a connecting means movable within predetermined range and connected with said regulator and for varying gradually the amount of feed of said dog in response to movement of the connecting means in one direction; a first driving means for moving said connecting means to said direction; a setting means engageable with the connecting means on the path of movement of the connecting means and displaceable from the engagement position to said direction; a second driving means for displacing said setting means; a first circuit for operating a time of driving the first driving means; a second circuit for operating the displacement of the second driving means to regulate the amount of feed which ought to vary when the first driving means is operative; a third circuit for driving the first driving means at the time which operated by the first circuit and for driving the second driving means to displace the setting means to the position which was operated by the second circuit before said operating time.

2. A sewing machine having an automatic feeding apparatus for varying stitch pitch substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.