GB2283025A - Sewing machine - Google Patents

Abstract

The needle (24) of a sewing machine is driven, e.g. by a crank (40), in the fore and aft direction to advance a workpiece while in engagement therewith, and a press-foot (30) is driven, e.g. by a slider (45), in the lateral direction to move the workpiece sidewards when the sewing needle (24) is disengaged therefrom to produce zig-zag stitching. Both drives may be taken from a common motor (37) and shaft (36) or separate cam or stepping motor drives may be provided to allow more complex stitch patterns with intermittent zig-zag. The needle feed throw may be adjusted. The press-foot drive may be disengaged manually. <IMAGE>

Description

SEWING MACHINE The present invention relates to a sewing machine and in particular to a sewing machine capable of sewing both straight and zig-zag chain stitches.

According to the invention, there is provided a sewing machine which comprises a body having an upper part and a lower part providing therebetween a sewing region through which a piece of article to be sewn is to pass on a sewing platform including a needle hole provided by the lower body part, a sewing mechanism supported by the upper body part and including a sewing needle assembly and a press-foot assembly extending down onto the platform for performing sewing operation, and a drive mechanism provided within the body for driving the sewing mechanism to perform sewing operation during which a sewing needle of the sewing needle assembly is driven to advance a said piece of article while in engagement therewith and a press-foot of the press-foot assembly is driven to move a said piece of article sidewards when the sewing needle is disengaged from a said piece of article.

Preferably, the press-foot assembly is pivotably mounted for sideward pivotal movement in order to effect the saig sideward movement of a said piece of article.

Advantageously, the underside of the press-foot is provided with engaging means arranged to engage during sewing operation a said piece of article relatively more strongly sidewards than in the advancing direction of a said piece of article.

It is preferred that the engaging means is in the form of ribs extending in the advancing direction of a said piece of article.

Preferably, the press-foot is pivotably connected to the rest of the press-foot assembly for sideward pivotal movement relative thereto.

In a preferred embodiment, the drive mechanism includes cam means for driving the press-foot assembly to effect the said sideward movement of a said piece of article.

More preferably, the cam means comprises a rotatable cam and a sliding cam follower co-acting between the cam and the press-foot assembly.

In a specific construction, the rotatable cam comprises a co-axial collar providing around its rim a camming profile against which the cam follower slidably engages.

The sewing machine may further include first manually operable means arranged to move the cam and the cam follower apart in order to disable the camming action therebetween.

In a preferred embodiment, the drive mechanism includes crank means for driving the sewing needle assembly to effect the said advancement of a said piece of article.

The sewing machine may further include second manually operable means arranged to displace the crank means in order to change the magnitude of the driven movement of the sewing needle assembly advancing a said piece of article.

In a specific arrangement, the sewing needle assembly and the press-foot assembly are mechanically coupled together, and the drive mechanism includes a single electric motor driving both the sewing needle assembly and the press-foot assembly.

In a modified embodiment, the drive mechanism comprises a microprocessor-based control circuit and two stepper motors controlled by the control circuit to drive the sewing needle assembly and the press-foot assembly, respectively.

The sewing machine as outlined above may further include a self-synchronised hook provided directly underneath the needle hole of the sewing platform for co-operation with the sewing needle to perform a chain stitching operation.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a front view of an embodiment of a sewing machine in accordance with the invention; Figure 2 is a front perspective view of an internal operating mechanism of the sewing machine of Figure 1; Figure 3 is a rear perspective view of a sewing mechanism of the operating mechanism of Figure 2; Figure 4 is a front perspective view of a drive mechanism of the operating mechanism of Figure 2; Figure 5 is a three-dimensional schematic diagram illustrating the general operation principle of the operating mechanism of Figure 2; Figure 6 illustrates the operation and construction of a press-foot of the sewing mechanism of Figure 3;; Figure 7 is a schematic diagram corresponding to Figure 5, illustrating the operation principle of the operating mechanism of Figure 2, in a cam control system; Figure 8 is a schematic diagram corresponding to Figure 5, illustrating the operation principle of the operating mechanism of Figure 2, in a microprocessor-controlled stepper motor system; Figures 9A to 9E show five types of chain stitches which the sewing machine of Figure 1 or a modified sewing machine of the present invention can make; Figure 10 is a front perspective view of an internal operating mechanism of a slightly modified embodiment of the sewing machine of Figure 1; Figure 11 is a rear perspective view of a sewing mechanism of the operating mechanism of Figure 10; Figure 12 is a front perspective view of a drive mechanism of the operating mechanism of Figure 10;; Figures 13A to 13C illustrate the co-operation between the sewing mechanism of Figure 11 and the drive mechanism of Figure 12 to change stitch length; and Figures 14A and 14B illustrate the co-operation between the sewing mechanism of Figure 11 and the drive mechanism of Figure 12 to change stitch pattern.

Referring firstly to Figures 1 to 4 of the drawings, there is shown a sewing machine 10 embodying the invention, which sewing machine 10 includes a body 11 formed by a base 12 and a sewing head 13 sitting on the base 12. The base 12 provides a sewing platform 14 in which a needle hole 15 is formed. The sewing head 13 overlies the platform 14 to form therebetween a sewing region. A stitch pattern selector 16, a stitch length selector 17 and a stitch tension knob 18 are provided on the front side of the sewing head 13. The sewing machine 10 has an internal operating mechanism within the sewing head 13 as shown in Figure 2, which is formed by a sewing mechanism 19 (Figure 3) and a drive mechanism 20 (Figure 4). The sewing mechanism 19 is provided generally above the sewing platform 14, and the drive mechanism 20 is provided generally within the opposite end of the sewing head 13.

The sewing mechanism 19 is formed by a box-like casing 21 holding a needle assembly 22 and a press-foot assembly 23, both of which extend vertically through the casing 21. The needle assembly 22 is formed by a sewing needle 24, a needle trunk 25 holding the needle 24, and an integral cross-bar 26 on the needle trunk 25. The cross-bar 26 is exposed on the side of the casing 21 facing the drive mechanism 20, and has a co-extending groove 27 which is closed at its rear end 28. The forward end of the crossbar 26 projects through the front wall of the casing 21 to act as a thread lever 29 (see also Figure 1). The needle trunk 25 is vertically slidably journalled through the top and bottom walls of the casing 21, and is pivotable backwards and forwards about the top casing wall.The needle trunk 25 extends vertically when it is in its forward-most pivotal rest position, and is resiliently biassed to this vertical rest position by an internal spring (not shown) urging the needle trunk 25 forwards.

The press-foot assembly 23 is formed by a press-foot 30 and a trunk 31 holding the press-foot 30. The press-foot trunk 31 is vertically slidably journalled through the top and bottom walls of the casing 21, and is pivotable sideways about the bottom casing wall. The press-foot trunk 31 is resiliently biassed with the press-foot 30 in its left-most position by an elbow spring 34 provided on the rear wall of the casing 21, as shown in Figure 3. The uppermost end of the press-foot trunk 31 has a rearwardly projecting stud 35, against which the elbow spring 34 acts. The trunk 31 is pivotable about the bottom wall of the casing 21 in order to bring the press-foot 30 into a central position with the trunk 31 extending vertically and eventually into a right-most position, as illustrated in Figure 6.

The press-foot assembly 23 includes a compression coil spring 32 disposed on the trunk 31 within the casing 21 for resiliently biassing the whole assembly 23 downwards so as to urge the press-foot 30 against the sewing platform 14.

The press-foot 30 is pivotably mounted at the bottom end of the trunk 31 for sideward pivotal movement such that the press-foot 30 will remain in co-planar flat contact with the sewing platform 14 irrespective of the sideward pivotal position of the press-foot trunk 31, as illustrated in Figure 6. The press-foot assembly 23 further includes an inverted generally L-shaped lever 33, exposed on the rear side of the casing 21 (see Figure 3) for lifting up the press-foot 30 from the sewing platform 14. The lever 33 is pivotably mounted and has its inner end engaging the pressfoot trunk 31 for moving the trunk 31 upwards against the action of the coil spring 32 when the lever 33 is flipped up.

The drive mechanism 20 is formed by a driving shaft 36 and an electric motor 37 in drive engagement with the right end of the shaft 36 via a gear train 38. A hand-wheel 39 is provided at the right end of the shaft 36 for manual rotation of the shaft 36. A radially extending crank arm 40 is provided at the left end of the shaft 36, said crank arm 40 carrying an axially extending crank stud 41 which slidably engages within the groove 27 of the cross-bar 26 of the needle assembly 22 for driving the assembly 22.

At an intermediate position, the driving shaft 36 carries a gear wheel 42. The drive mechanism 20 includes a gear wheel 43 having on its left side an integral co-axial collar 44 which has a specially designed rim profile to act as a rotatable cam. The gear wheel 43 is in drive engagement with the gear wheel 42 such that rotation of the driving shaft 36 will cause simultaneous rotation of the cam collar 44. The drive mechanism 20 further includes a slider 45 which has its right end 45A abutting axially the rim of the cam collar 44 and has its left end 45B abutting the stud 35 on the press-foot trunk 31. The slider 45 is resiliently biased against the cam collar 44 under the action of the elbow spring 34 urging the press-foot trunk stud 35, thereby acting as a cam follower to the cam collar 44.With this arrangement, rotation of the cam collar 44 will cause sliding movement of the slider 45 which in turn will cause sideward pivotal movement of the press-foot trunk 31, thereby resulting in controlled lateral movement or side-kicking action of the press-foot 30. The extent of such a side-kicking action (corresponding to the "zig-zag width" referred to below) is adjustable by changing the axial position of the assembly of gear wheel 43 and cam collar 44 and/or the length of the slider 45 if, for example, the slider 45 is formed by two sections slidably secured together.

Referring more specifically to the profile of the rim of the cam collar 44, it has two distinctive high and low flat segments 46A and 46B and a pair of sloping segments 46C therebetween, as best shown in Figure 3. When the slider end 45A engages each of these two flat segments 46A and 46B while the cam collar 44 is rotating, the slider 45 will not slide and hence the press-foot 30 will not move sideways.

However, when the slider end 45A engages the sloping segments 46C while the cam collar 44 is rotating, the slider 45 will be slid thereby resulting in sideward movement of the press-foot 30 in opposite directions. The press-foot 30 will move to the right when the slider end 45A moves up one sloping segment 46C and will return to the left when the slider end 45A moves down the opposite sloping segment 46C. During a complete turn of rotation of the cam collar 44, the press-foot 30 moves to the rightmost position, stays in this position for a certain period of time depending on the arc length of the flat segment 46A, returns to the rest left-most position, and finally stays in this position for another certain period of time depending on the arc length of the flat segment 4613.

Turning now to the operation of the needle assembly 22.

Upon rotation of the driving shaft 36 and hence the crank arm 40 and stud 41, the needle trunk 31 and hence the sewing needle 24 will be pivoted backwards when the crank stud 41 reaches and thereby engages the closed end 28 of the groove 27 of the cross-bar 26. When the crank stud 41 reaches its rearmost position and starts to return, the needle 24 will return forwards under the action of the internal biassing spring (not shown) until the crank stud 41 leaves or disengages from the groove closed end 28, after which the needle 24 will stay in the rest forwardmost position until the crank stud 41 comes round to again engage the groove closed end 28. This completes a rotation cycle of the driving shaft 36 and correspondingly a cyclic back-kicking action of the sewing needle 24.The extent of such a back-kicking action (corresponding to the "stitch length" referred to below) is adjustable by changing the relative position of the closed end 28 along the cross-bar groove 27.

In a different construction, the crank drive provided by the crank arm 40 and crank stud 41 and the grooved crossbar 26 may be replaced by a cam drive for driving the sewing needle assembly 22, said cam drive incorporating a specially profiled cam to effect relatively more complicate sewing needle motion than simple cyclic motion.

During each back-kicking action, the sewing needle 24 will also move downwards and upwards, extending into and out of the needle hole 15 of the sewing platform 14, under the cranking action of the crank stud 41 engaging opposite sides of the cross-bar groove 27.

Directly underneath the sewing platform 14 and the needle hole 15, a self-synchronised hook (not shown) is pivotably supported within the base 12. The hook is resiliently biassed and arranged to be pivoted by the sewing needle 24 through direct engagement therewith upon entrance of the sewing needle 24 through the needle hole 15. The hook serves to retain through a hooking action a loop of thread brought into by the needle 24 and prepare the retained thread loop for the next entrance of the needle 24. When the needle 24 next comes, it will pass through the previously retained thread loop with a second thread loop while at the same time the first thread loop is released from the hook. The second thread loop is eventually retained by the hook upon retrieval of the needle 24. This completes one stitch of chain stitching operation.

When the sewing needle 24 is performing stitching operation underneath the needle hole 15, it is necessarily engaging the pieces of article being sewn placed on the sewing platform 14. Upon retrieval of the needle 24 while still engaging the pieces of article and from the moment when the crank stud 41 engages the groove closed end 28, the needle 24 kicks back momentarily as described above, thereby advancing the pieces of article for one stitch length.

The operation of the sewing mechanism 19 and in particular the sewing needle assembly 22 and the self-synchronised hook and the operation of the drive mechanism 20 are more fully described in co-pending UK Patent Application No.

9213316.4.

When the sewing needle 24 has completely retrieved from the needle hole 15 and the pieces of article, the press-foot assembly 23 is arranged to perform a side-kicking action, thereby moving the pieces of article gripped underneath to one side.

As shown in Figure 6, the underside of the press-foot 30 has on each side thereof four parallel ribs 47 which are provided to grip the pieces of article underneath relatively more strongly in the lateral direction (for ensuring the side-kicking movement of the pieces of article) than in the back-to-front direction (for permitting advancement of the pieces of article during the back-kicking action of the needle 24).

As shown in Figure 4, the gear wheel 43 is necessarily larger than the gear wheel 42 because the side-kicking action cannot take place during the occurrence of a backkicking action but between back-kicking actions, in that the back-kicking action effects stepwise advancement of the pieces of article being sewn and is therefore necessarily continual. As a first condition, it is necessary for the larger gear wheel 43 to have an integral number (two or more) times of teeth compared with the smaller gear wheel 42 in order to ensure that the operations of the needle assembly 22 and the press-foot assembly 23 are in step.As a second condition, when the press-foot assembly 23 is in side-kicking operation, the side-kicking action must be controlled to take place when the sewing needle 24 is not in engagement with the pieces of article being sewn, as the needle 24 will hinder any sideward movement of the pieces of article. The operations of the needle assembly 22 and the press-foot assembly 23 are synchronised when these two conditions are satisfied.

The co-operation between the needle assembly 22 and press foot assembly 23 of the sewing mechanism 19 and the drive mechanism 20 is schematically illustrated in Figure 5. In this diagram, X represents the lateral direction of movement effected by the press-foot 30, Y represents the back-to-front direction of movement effected by the sewing needle 24, and Z represents the up-and-down direction of movement of the sewing needle 24. The Y and Z directions of movement are inherently coupled together. Cylinders X, Y and Z represent the movement driving force in the three directions, which is provided by the single drive mechanism 20. The box X represents the control effected by the cam collar 44 upon the X direction of movement. The box Y represents the control on the Y and Z directions of movement, which is effected by the crank arm 40 and stud 41 and the grooved cross-bar 26.

Figure 9A shows straight train stitching effected by the sewing machine 10 when only the needle assembly 22 is in (back-kicking) operation. The side-kicking operation of the press-foot assembly 23 can be disabled by immobilising the slider 45 and/or the cam collar 44. Figure 9B shows simple zig-zag train stitching effected when both the needle assembly 22 and the press-foot assembly 23 are in back-kicking/side-kicking operation. In order to make these simple zig-zag train stitching, the gear ratio of the gear wheel 43 to the gear wheel 42 must be two-to-one.

Figure 9C shows a train stitching having regular but only occasional zig-zaps, which is effected with a said gear ratio more than two-to-one.

In the embodiment of sewing machine described above, the stitch length and the zig-zag width must be preset before operation and will subsequently remain constant. More complicate stitching patterns, for example as shown in Figure 9D with varying stitch length and as shown in Figure 9E with varying zig-zag width, can only be effected by modified sewing machines of the same invention. Such modified sewing machines have two synchronised cam systems for controlling the operations of the needle assembly and the press-foot assembly, respectively, as illustrated in Figure 7. These cam control systems may be replaced by a microprocessor-based control circuit and two stepper motors controlled by the control circuit to drive the sewing needle assembly and the press-foot assembly, respectively, for more sophisticated and/or versatile stitch pattern designs, as illustrated in Figure 8.

Reference is now made to Figures 10 to 14 of the drawings, showing therein a slightly modified sewing machine 50 embodying the invention, with corresponding parts designated by the same reference numerals compared with the sewing machine 10. In this sewing machine 50, the driving shaft 36 is engaged, at a position about one-third of its length from the crank arm 40, by a hinged bracket 51. The bracket 51 engages the driving shaft 36 from the front side thereof, acting against the internal spring (not shown) urging the needle trunk 25 forwards. The bracket 51 is hinged at its bottom end by an integral hinge pin 51A and is held in position at its top end 51B by a slide button 52 (which is equivalent to the stitch length selector 17 of the sewing machine 10). The slide button 53 has a rear profile 53 which extends relatively further back at its left end 53A than at its right end 53B.

In a first situation where the right end 53B of the slide button 52 engages the upper end 51B of the hinged bracket 51 (as illustrated in Figure 13B), the driving shaft 36 and hence the crank arm 40 and stud 41 are permitted to come forwards to a greater extent than in a second situation where the slide button left end 53A engages the bracket upper end 51B (as shown in Figure 13A). Consequently, as illustrated in Figure 13C, the needle trunk 25 will be pivoted backwards by the crank stud 41 to an extent Ds in the first situation relatively smaller than the corresponding extent DL in the second situation. It is to be understood that the bracket 51, in co-operation with the slide button 52, serves to displace the driving shaft 36 in order to alter the position at which the rotational drive is applied to the needle assembly 22. With the provision of the bracket 51 and the slide button 52, the length of the stitches to be sewn by the sewing machine 50 can be selected.

In this sewing machine 50, the slider 45 has an integral leg 54 which extends longitudinally with respect to the slider body from behind the right slider end 45A. A slide button 55 (which is equivalent to the stitch pattern selector 16 of the sewing machine 10) is provided in the path of movement of a free end 54A of the slider leg 54.

When the slide button 55 is in the rightmost position as shown in Figure 14A, it is isolated from the slider leg free end 54A, thereby permitting the slider 45 to be slid left-and-right by the cam collar 44 to effect zig-zag stitching. When the slide button 55 is in the leftmost position as shown in Figure 14B, it abuts with the slider leg free end 54A and pushes the whole slider 45 to the left and thus out of engagement from the cam collar 44. In this situation, the cam collar 44 is no longer acting upon the slider 45, and consequently the slider 45 will not pivot the press-foot assembly 23 sideways during operation of the needle assembly 22 which can therefore only perform straight line stitching.

The invention has been given by way of example only, and various modifications of and/or alterations to the described embodiments may be made by persons skilled in the art without departing from the scope of the invention as specified in the appended claims.

Claims (15)

1. A sewing machine which comprises a body having an upper part and a lower part providing therebetween a sewing region through which a piece of article to be sewn is to pass on a sewing platform including a needle hole provided by the lower body part, a sewing mechanism supported by the upper body part and including a sewing needle assembly and a press-foot assembly extending down onto the platform for performing sewing operation, and a drive mechanism provided within the body for driving the sewing mechanism to perform sewing operation during which a sewing needle of the sewing needle assembly is driven to advance a said piece of article while in engagement therewith and a press-foot of the press-foot assembly is driven to move a said piece of article sidewards when the sewing needle is disengaged from a said piece of article.

2. A sewing machine as claimed in claim 1, wherein the press-foot assembly is pivotably mounted for sideward pivotal movement in order to effect the said sideward movement of a said piece of article.

3. A sewing machine as claimed in claim 1 or claim 2, wherein the underside of the press-foot is provided with engaging means arranged to engage during sewing operation a said piece of article relatively more strongly sidewards than in the advancing direction of a said piece of article.

4. A sewing machine as claimed in claim 3, wherein the engaging means is in the form of ribs extending in the advancing direction of a said piece of article.

5. A sewing machine as claimed in any one of claims 1 to 4, wherein the press-foot is pivotably connected to the rest of the press-foot assembly for sideward pivotal movement relative thereto.

6. A sewing machine as claimed in any one of the preceding claims, wherein the drive mechanism includes cam means for driving the press-foot assembly to effect the said sideward movement of a said piece of article.

7. A sewing machine as claimed in claim 6, wherein the cam means comprises a rotatable cam and a sliding cam follower co-acting between the cam and the press-foot assembly.

8. A sewing machine as claimed in claim 7, wherein the rotatable cam comprises a co-axial collar providing around its rim a camming profile against which the cam follower slidably engages.

9. A sewing machine as claimed in claim 7 or claim 8, further including first manually operable means arranged to move the cam and the cam follower apart in order to disable the camming action therebetween.

10. A sewing machine as claimed in any one of the preceding claims, wherein the drive mechanism includes crank means for driving the sewing needle assembly to effect the said advancement of a said piece of article.

11. A sewing machine as claimed in claim 10, further including second manually operable means arranged to displace the crank means in order to change the magnitude of the driven movement of the sewing needle assembly advancing a said piece of article.

12. A sewing machine as claimed in any one of the preceding claims, wherein the sewing needle assembly and the press-foot assembly are mechanically coupled together, and the drive mechanism includes a single electric motor driving both the sewing needle assembly and the press-foot assembly.

13. A sewing machine as claimed in any one of claims 1 to 5, wherein the drive mechanism comprises a microprocessorbased control circuit and two stepper motors controlled by the control circuit to drive the sewing needle assembly and the press-foot assembly, respectively.

14. A sewing machine as claimed in any one of the preceding claims, further including a self-synchronised hook provided directly underneath the needle hole of the sewing platform for co-operation with the sewing needle to perform a chain stitching operation.

15. A sewing machine substantially as hereinbefore described with reference to Figures 1 to 9 or Figures 10 to 14 of the accompanying drawings.