GB2347690A - Alignment device for a jig-fed sewing machine - Google Patents

Abstract

A jig-fed sewing machine (10) has a sewing head (11), a support table (12) over which a jig (13) loaded with fabric can be fed to the sewing head (11), and a drive wheel (14) arranged to make driving engagement with a drive edge (15) of the jig (13) in order to advance the jig relative to the sewing head (11). The jig has a guide groove (16) which is engaged by a guide of the sewing head, and which guides the advancing movement of the jig, and a snubber (17) is also engageable with the jig edge (15) at a position spaced from the drive wheel (14) in order to assist the guidance and alignment of the jig during its advancing movement. Biasing means in the form of compression spring (18) applies a biasing force from the snubber (17) to the jig edge (15).

Description

ALIGNMENT DEVICE FOR A JIG-FED SEWING MACHINE This invention relates to an alignment device for a jig-fed sewing machine.

In the mass production of garments (or other stitched fabrics e. g. seat covers), using industrial-type sewing machines, it is known to use specially designed jigs, which are loaded with layers of fabric in predetermined arrangements, and then are fed to a sewing station at which the sewing head of the machine can operate to form required sewn seams through the fabric layers as the jig is advanced relative to the head.

The jig usually has a guide groove, which moves relative to a fixed guide at the sewing station, and which determines the direction of the sewn seam. The jig also is usually driven along a required path of advancing movement, by a drive wheel which makes frictional engagement with the outer periphery of the jig i. e. the outer jig edge.

The guide groove is usually spaced inwardly of the driven edge of the jig by a substantially constant distance, and therefore the groove and the edge extend parallel to each other and, for a typical garment, the required path of a sewn seam can include one or more straight line, and one or more curved portion, and therefore the orientation of the jig relative to the sewing head alters during a typical cycle of advancing movement of the jig. Also, the drive wheel usually makes engagement with the jig edge at a position substantially alongside the usual presser foot and the sewing needle, so that any adjustment in alignment of the jig (during its drive advancing movement) effectively comprises pivotal adjustment about the instantaneous point of engagement of the drive wheel with the drive edge of the jig.

Therefore, in order to control the pivotal adjustment of the jig, it is usual to arrange a so-called"snubber" forwardly of the drive wheel, and which also engages the jig edge and which therefore assists in adjusting the alignment of the jig so that the guide groove adjusts its alignment to the sewing head when necessary, in order to define a required seam pass.

However, in existing arrangements, the snubber usually is spring-loaded so as to apply a substantially constant biasing force to the jig edge, and while this can work reasonably well in most circumstance, there can be problems in practice owing to the fact that the flexibility of the jig (to transfer displacement of the jig edge) tends to vary lengthwise of the guide groove. Also, when the guide groove undergoes a substantial change in direction, the orientation of the jig has to change substantially relative to the sewing head, and maintenance of proper engagement of the drive wheel and the snubber with the jig edge can be a particular problem in this phase of the advancing cycle of movement.

Therefore, the application of a substantially constant transverse biasing force from the snubber to the jig edge can have the undesirable result of the jig becoming disengaged i. e. jumping out of its required alignment.

Thus, the constant biasing force may be required at certain positions along the driven edge of the jig (to ensure maintained correct alignment), but the force may be excessive at other regions, and particularly regions where the jig is more flexible, and which may have the undesired result of the jig becoming disengaged.

The present invention therefore seeks to provide improved engagement of the snubber with the jig edge, so as to reduce the risks of the jig becoming disengaged from the sewing head during a cycle of advancing movement of the jig.

According to the invention there is provided a jig-fed sewing machine having a sewing head, a support table over which a jig loaded with fabric can be fed to the sewing head, a drive wheel arranged to make driving engagement with a drive edge of the jig in order to advance the jig relative to the sewing head, a guide engageable in a guide groove of the jig in order to guide the advancing movement of the jig, and a snubber also engageable with the jig edge at a position spaced from the drive wheel in order to assist the guidance and alignment of the jig during its advancing movement; in which means is provided to apply a biasing force from the snubber to the jig edge, such force being variable as required according to the position of engagement along the length of the jig edge.

Thus, the invention provides a biasing force which can vary lengthwise of the jig edge as required, so that increased biasing force can be applied at any one region if necessary, and a smaller biasing force can be applied at another region (which will usually be a region at which the jig is more likely to become disengaged from the usual presser foot of the sewing machine).

The snubber may therefore have a biasing spring to apply a main biasing force, and an additional means to apply a controllable additional biasing force when required.

Conveniently, the additional means comprises a pressure cylinder, preferably a pneumatic cylinder, which is arranged in a controlled pressure circuit which is pre-programmed with pressure data corresponding to different parts of an advancing cycle of operation of the jig.

A preferred embodiment of alignment device according to the invention for a jig-fed sewing machine will now be described in detail, by way of example only, with reference to the accompanying perspective drawing.

Referring now to the drawing, there is shown in perspective illustration a jig-fed sewing machine designated generally by reference 10 and having a sewing head 11, a support table 12 over which a jig 13 loaded with fabric (not shown) can be fed to the sewing head 11, and a drive wheel 14 arranged to make driving engagement with a drive edge 15 of the jig 13 in order to advance the jig relative to the sewing head 11.

The jig has a guide groove 16 which is engaged by a guide of the sewing head, in known manner, and which guides the advancing movement of the jig during a cycle of operation. A snubber 17 is also engageable with the jig edge 15, at a position spaced from the drive wheel 14, in order to assist the guidance and alignment of the jig during its advancing movement. The sewing head, via the presser foot and sewing needle, engage in the guide groove 16, and the advancing movement of the jig 13, under guidance, causes a sewn seam to be formed through the fabric layers along a predetermined seam path.

The snubber 17 has biasing means to apply a biasing force to it, and which is then transferred to the jig edge 15, and the main biasing means takes the form of a compression spring 18, which can apply a substantially constant main biasing force. However, to provide a biasing force from the snubber to the jig edge which can be varied, as required, according to the position of engagement along the length of the jug edge, an additional means is provided which provides a controllable additional biasing force when required. The additional means comprises a pressure cylinder 19, preferably a pneumatic cylinder, which is arranged in a controlled pressure circuit which is preprogrammed with pressure data corresponding to different parts of an advancing cycle of operation of the jig.

Therefore, when an additional biasing force is required, the cylinder 19 is energised, so that the spring force is augmented by the additional force, at positions along the driving edge 15 where this additional force is required. On the other hand, at regions along the driving edge 15 where a lesser biasing force is required, e. g. at more flexible regions of the jig and/or particularly at regions of the jig where the guide groove 16 undergoes a major change in direction (transition from one straight run to another), the cylinder 19 is not energised, and reliance is put only on the biasing force provided by the compression spring 18.

The sewing machine 10 also has photocell 20 which monitors spaced apart monitor strips (not shown) provided on the jig 13, to provide further control in the operation of the cycle, in known manner. The drive wheel 14 is mounted on the end of a drive wheel arm 21, controlled by an actuator arm 22, which applies the drive wheel 14 into driving engagement with the driven edge 15 of the jig. A damper 23 may also be coupled with the spring and pneumatic pressure biasing arrangement provided for snubber 17.

Therefore, the improved jig alignment mechanism disclosed herein has the following main functions: 1. Primary function-to improve the quality of the stitch-line and the trimmed edge of a jacket forepart.

Ideally, when a jig travels along a straight edge, the jig orientation should be at a normal to the axis of the sewing head. However, usually this is not the case with existing known arrangements, and the jig will travel at an angle to the normal. In extreme cases, the resulting sewn seam will appear slightly stepped, and the cut edge slightly jagged.

The design details disclosed herein, in the embodiment of the invention, have the following main features: (a) The reactive force produced by the snubber unit 17 on the edge of the jig can be increased. However, care has to be exercised, because the application of too great a reactive force from the snubber, close to the usual throat plate"D"piece, may cause the jig outer track to be pushed over the"D". The jig may then become damaged by the sewing machine. The jig is particularly vulnerable to this at certain parts of the sew cycle.

Therefore, to allow the reactive force of the snubber to be altered during the sew cycle, the pneumatic cylinder 19 is provided, which can apply additional biasing force to the snubber 17, when required only, and be disengaged at the points where the jig is vulnerable to being pushed over the "D".

(b) The embodiment of the invention also provides a sprung block mounted on the table surface.

(c) A further advantage arising out of this improved embodiment is that, when a"step-back trimming device"is added to the sewing machine, there is obtained a slightly increased step-back margin.

The preferred application of the invention is in the manufacture of garments. However, it should be understood that the invention has general application to the stitching of fabrics together e. g. for making car seat covers.

Claims (5)

1. A jig-fed sewing machine having a sewing head, a support table over which a jig loaded with fabric can be fed to the sewing head, a drive wheel arranged to make driving engagement with a drive edge of the jig in order to advance the jig relative to the sewing head, a guide engageable in a guide groove of the jig in order to guide the advancing movement of the jig, and a snubber also engageable with the jig edge at a position spaced from the drive wheel in order to assist the guidance and alignment of the jig during its advancing movement; in which means is provided to apply a biasing force from the snubber to the jig edge, such force being variable as required according to the position of engagement along the length of the jig edge.

2. A jig fed sewing machine according to claim 1, in which the snubber has a biasing spring to apply a main biasing force, and an additional means to apply a controllable additional biasing force when required.

3. A jig fed sewing machine according to claim 2, in which said additional means comprises a pressure cylinder which is arranged in a controlled pressure circuit which is pre-programmed with pressure data corresponding to different parts of an advancing cycle of operation of the jig.

4. A jig fed sewing machine according to claim 3, in which the pressure cylinder is a pneumatic cylinder.

5. A jig fed sewing machine according to claim 1 and substantially as hereinbefore described with reference to, and as shown in the accompanying drawing.