GB2085935A - Sewing machine with a transversely mobile feed dog - Google Patents

Abstract

A sewing machine incorporates a feed dog arranged to move transversely and includes a support shaft (16) for said dog (15), said shaft being arranged to move axially against the action of elastic means (80); a decoder unit (20, 25) arranged to receive control signals from a processing unit and to assume three working positions corresponding to the resumed position of said dog (15) and a linkage (23, 17, 40) which converts each said working position into a corresponding angular swing of an arm (57) extending radially from a shaft (42) axially coupled to said shaft (16). In operation the shaft (16) is positioned irrespective of any slack in the various linkages and the dog (15) is movable transversely providing wider than normal movement for forming an embroidery pattern. <IMAGE>

Description

SPECIFICATION Sewing machine with a transversely mobile feed dog This invention relates to a sewing machine with a transversely mobile feed dog. In particular, the invention relates to a sewing machine in which in addition to mechanisms which control the transverse movement of the needle bar and the movement of the dog which conveys the fabric forwards and/or backwards, there is provided a mechanism which enables the transverse movement of the dog to be controlled. In such machines, the dog is therefore actually subjected to two types of movement, of which the first takes place in a longitudinal vertical direction and provides for conveying the fabric in the feed and/or return direction, while the second takes place in a transverse direction and enables said fabric to be conveyed to the left or to the right relative to said feed direction.

At present, the mechanisms used for controlling the transverse movement of the dog are substantially constituted by a feeler which is urged by elastic means to cooperate frontally with a cam, and which by means of a linkage converts the cam contour variations into transverse movements of the dog.

Although the aforesaid known mechanisms are widely used in certain of the sewing machines at present available, they have certain drawbacks. For example, different cams have to be used in order to obtain different transverse movement cycles for the dog, so that it is necessary for the operator to intervene each time in order to mount the required cam. Moreover, the transverse movements of the fabric are always limited to the radius of action of the cam, and it is therefore not possible for the machine to carry out embroidery work which extends in a transverse direction beyond a certain maximum limit. Finally, these mechanisms are of low precision and are particularly complicated. The object of the present invention is to provide a sewing machine which is free from the aforesaid drawbacks of sewing machines of known type.

The aforesaid object is attained according to the present invention by a sewing machine of the type comprising a feed dog arranged to move transversely, characterised by comprising a support shaft for said dog, said support shaft being arranged to move axially against the action of elastic means; a decoder unit arranged to receive control signals from a processing unit and to assume three working positions according to whether said dog is to be caused to undergo a transverse increment towards the right, a transverse increment towards the left or no transverse increment; and a linkage which converts each said working position into a corresponding angular swing of an arm extending radially from a shaft coupled axially to said support shaft for said dog, said arm carrying a roller rotatable about its axis and slidable on a surface of a profiled element connected to a fixed part of said machine.

The present invention will be more apparent from the description of a preferred embodiment given hereinafter by way of non-limiting example with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a sewing machine according to the present invention; Figures 2, 3, 4 and 5 are views of certain details of the machine of Fig. 1; and Figure 6 shows the pattern of the vertical movements "v" (Fig. 6a) and transverse movements "t" (Fig. 6b) of the feed dog of the sewing machine of Fig. 1.

In Fig. 1, the reference numeral 10 indicates overall a sewing machine comprising a base 11 and a support column 12, from which there extends an arm 1 3 which supports a needle 1 4. The machine 10 comprises a feed dog 1 5 which is carried at one end of a shaft 16, the other end of which is connected to the exit of a drive unit 1 7 illustrated in detail in Figs. 2, 3 and 4. The machine 10 also comprises a decoder unit 20 of known type, which in particular comprises two bars 21, 22, each of which can respectively assume a rest position or a working position such as to be either partly retained inside the unit 20 or urged to the outside of it as can be better seen in Fig. 2.The unit 20 is substantially a decoder of electromechanical type which receives an electric signal from a processing unit (not shown) and converts said signal into a corresponding movement of the bars 21 and/or 22, so that it is possible to obtain different cycles consisting of different combinations of the aforesaid movements according to the contents of the programme memorised in the processing unit.

Between the bars 21 and 22 and the control inlet of the drive unit 1 7 there is disposed a motion transmission linkage 23, which is described hereinafter with reference to Fig. 2.

In detail, the linkage 23 is constituted by a pair of rocker arms 25, 26, the first of which has its opposing ends slidably engaged in slots 27, 28 disposed at the ends of each said bar 21, 22. The rocker arm 26 is mounted rotatable about a support pin 30, and has one end connected to a central pin 29 of the rocker arm 25 and its other end connected to a pin 32 carried by a first end of a bar 31.

This latter has its other end pivoted to the end of a U-shaped arm 33 extending radially from a cylindrical member 34 which is mounted rotatable about a pin 35 supported by a wall 36 (see Fig. 3) of the frame of the machine 10. From the cylindrical member 34 there extends an appendix 38, of which a forkshaped end engages a corresponding appen dix 39 extending radially from a slide 40 substantially constituted by a tubular member 41 which slides axially on a shaft 42.

The surface of the tubular member 41 comprises three radial notches 44, each of which is arranged for snap-engagement by a resilient bar 45 fixed at one end to a support wall 46 (see Fig. 3). An arm 48 extends radially from the member 40, and has one end shaped in the form of a circumferential arc and indicated by 49, and arranged to cooperate with three cams 51, 52, 53 respectively, keyed on to a shaft 50 which is connected to a drive in a manner not illustrated.

In particular, the cam 52 is substantially constituted by a circular dise mounted in an axial position on the shaft 50, while the cams 51 and 53 are mounted on opposite sides of the cam 52, and relative to the circular contour of the cam 52 they each comprise a tooth which has the same angular extension in each case and projects outwards, and is followed by a cavity which extends below the profile of the cam 52, and vice versa, so that during a 360 rotation of the shaft 50, the end of the arm of the slide 40 either firstly encounters the tooth and then the cavity if the arm 48 is positioned on the cam 53, or firstly encounters the cavity and then the tooth if the arm 48 is positioned on the cam 51.

From the tubular member 41 of the slide 40 there extends an apendix 55 bent at 90 and comprising at its end a fork portion 56 which engages a shaft 57 disposed radially and coupled angularly to the shaft 42. At the end distant from the shaft 42, the shaft 57 carries a roller 58 which is rotatable about its axis and is retained on the shaft 57 by means of a nut and locking nut 59, 60 which are screwed on to a threaded end 61 of the shaft 57. Said end 61 is fixed to a support 62 by means of a cylindrical spring 63 which, by way of the shaft 57, acts substantially in such a manner as to always keep the arm 48 of the slide 40 urged into contact with the surface of one of said cams 51, 52, 53.Finally, the roller 58 cooperates with the surface of a cone frustum portion 65 disposed at one end of a cylinder 66 which is screwed into a support wall 67 of the frame (not shown) of the machine 10.

With particular reference to Figs. 2 and 4, the shaft 42 comprises at its ends two pins 69 and 70 respectively, the first of which is rotatable in a bore in a support wall 71, and the second of which cooperates frontally with a ball 72 and is contained, together with said ball, in a circular seat in a support member 73. This latter is angularly connected by a screw 74 to the shaft 1 6 which is supported at its ends by walls 75, 76 forming part of the frame of said sewing machine 10.In known manner, by means af a crank mechanism 78 the shaft 1 6 supports the feed dog 15, which is supported by a shaft 79 forming part of said crank mechanism and mounted rotatable about its axis. to the shaft 79 there is connected a strong resilient lamina 77 mounted radially to the shaft 79 and having an end resting on the lower surface of the base 11 in order to impress on the shaft 79 a twisting moment which prevents the dog 1 5 from rising arbitrarily from its rest position.

With particular reference to Figs. 2, 4 and 5, a leaf spring 80 is mounted on the outer surface of the wall 76 by means of screws 81 and a plate 82. The end of the leaf spring 80 cooperates frontally with the end portion of the shaft 16 so as to urge this latter axially in the direction of the wall 75 and, with particular reference to Fig. 2, so as to urge the shaft 42 axially such that the roller 58 is always kept in contact with the facing cone frustum portion 65.

In Figs. 2, 4 and 5 the reference numeral 84 indicates a mechanism arranged to control the cyclic raising of the dog 1 5 during the course of one sewing cycle. The mechanism 84 comprises substantially a shaft 85 which at a first end carries a radial arm 86 cooperating with the lower surface of the dog 15, and at its opposite end carries a radial arm 89 on which there is mounted a pin 90 which supports a roller 91 in a rotatable and axially slidable manner. This latter rests on a cam element 96 keyed on to the shaft 50, and is kept urged against said shaft by the force which the resilient lamina 77 exerts on the shaft 85 (connected to the roller by the arm 89) by way of the shaft 79 and dog 15, which rests on the arm 86 also extending from the shaft 85.The element 96 is substantially constituted (see Fig. 4) by a cam portion 97 and a portion 98, these portions facing each other.

With particular reference to Fig. 2, as stated the roller 91 is mounted slidably along the pin 90, and its position along said pin can be chosen by means of a manually operable bar 100 comprising a fork end 101 engaged with the roller 91. At the end distant from the end 101, the bar 100 comprises a rectangular notch 102 arranged to engage an aperture 1 03 in the support wall 71 of said machine against the action of a return spring 1 05.

That part of the bar 100 comprising the notch 102 is accessible to the operator, and under normal operating conditions of the machine 10 is in the position shown in Fig. 2 corresponding to the positioning of the roller 91 on rhe cam 97. In a different working position, the notch 102 is engaged with the aperture 103, so that the roller 91 moves axially along the pin 90 and is brought into contact with the surface of said disc 98.

The operation of the sewing machine - 1 0 is described hereinafter with particular reference initially to Fig. 2.

As stated, the bars 21 and 22 of the decoder unit 20 can assume a first or a second working position. Fig. 2 shows a working position in which the bar 21 is retracted and the bar 22 is urged to the outside so that the pin 29 of the rocker arm 25 is in an intermediate position between two limiting positions which it can assume according to whether both the bars 21, 22 are retracted, or are urged outwards respectively.

The position assumed by the pin 39 of the rocker arm 25 in Fig. 2 is such that, by way of the rocker arm 26, the bar 31, the arm 33 and the appendix 38 of the member 34, the slide 40 becomes positioned such that the arm 48 of this latter rests on the intermediate cam 52 of the cam assembly 51, 52, 53 (see also Fig. 4). As the cam 52 is constituted substantially by an axial cylinder, the rotation of the shaft 50 does not cause any angular movement of the slide 40, so that the roller 58 carried by the shaft 57 remains at rest and consequently the shaft 42 also remains at rest. Under such conditions, the shaft 1 6 receives no axial thrust from the shaft 42, and consequently is kept in its rest position by said leaf spring 80.The sewing machine 90 consequently carries out the usual sewing cycle, with the raising movements of the dog 1 5 being controlled by the shaft 85 by way of the cam 97 and synchronised with the movements of the needle 14, so that the fabric is moved substantially forwards or backwards according to the rotary motion transmitted to the shaft 1 6 by a feed mechanism, not shown but of known type.

It will now be assumed that both the bars 21 and 22 of the decoder unit 20 are retracted. Consequently (see Fig. 2) the pin 29 of the rocker arm 25 is moved upwards and the bar 31 is therefore moved downwards by means of the rocker arm 26. Thus, the member 34 rotates clockwise and causes the slide 40 to move such that the arm 48 of this latter rests on the surface of the cam 51.

With reference to Fig. 3, assuming that the shaft 50 rotates in an anti-clockwise direction, the cam 51 initially causes an anti-clockwise movement of the slide 40 about its axis (shaft 42), followed by a clockwise movement until it reaches a position opposite the aforesaid maximum position, and finally an anticlockwise movement to return to its initial position. The angular swings of the slide 42 about its axis cause the shaft 57 to make a corresponding movement by way of the fork portion 56, and thus induce the roller 58 to slide on the facing surface of the cone frustum portion 65 at the end of the cylinder 66.

In the example now considered (see Fig. 3) the roller 58 is firstly urged towards the largest diameter zone of the portion 65, then moves until it reaches the zone of smallest cross-section, and finally returns to the intermediate zone of the portion 65. As the roller 58 is mounted rotatable about the shaft 57 and this latter is fixed to the shaft 42, the movements of the roller 58 lead to an axial movement of the shaft 42, this movement being transmitted to the shaft 1 6 which controls the movements of the dog 1 5.

In the example now described, the shaft 1 6 is caused to move against the action of the leaf spring 80 firstly in such a manner as to increment its axial position in an outward direction, then to re-enter as far as the outer surface of the wall 76, and finally to return to an intermediate rest position. The pattern of the axial movements of the shaft 1 6 and thus of the transverse movements (t) of the dog 1 5 is illustrated in the first part of Fig. 6b, during the course of a complete sewing cycle which is considered to extend through 360 . Fig. 6a correspondingly shows the vertical movement (v) of the dog 1 5 controlled by the shaft 85.

By comparing the two graphs, it can be seen that the dog 1 5 firstly moves from left to right Fig. 2) before it is raised. Subsequently, in the intermediate zone in which it is raised, it is also compelled to move from right to left.

Finally, when it is again lowered, it returns to its initial position so that the transverse increment is zero. Such a movement pattern for the dog 1 5 causes the fabric resting on it to make a transverse increment, in Fig. 2, from right to left through a predetermined distance, or, in Fig. 1, from left to right. In conclusion, with reference to Fig. 1, during one cycle the dog 1 5 causes the fabric to move towards the right through an incremental unit of predetermined value, in the example under consideration.

An exactly opposite behaviour with a transverse increment of the fabric towards the left occurs when both the bars 21 and 22 of the decoder unit 20 are urged outwards. In this case, the arm 48 of the slide 40 is caused to slide on the cam 53, and consequently the roller 58 is firstly moved towards the zone of smallest cross-section of the cone frustum portion 65, then it makes a complete stroke from this zone to the zone of greatest crosssection, and finally returns to the intermediate zone. The shaft 1 6 is now urged in the opposite direction to the preceding, and changes its axial position as indicated in the second part of Fig. 6b, so that it moves firstly towards the left while the dog is still lowered, then totally towards the right while the dog is raised, and then returns to its initial position while the dog is lowered.In this case, the dog 1 5 causes the fabric to make a movement from left to right in Fig. 2, or with reference to Fig. 1 a transverse increment towards the left of a predetermined value for each sewing cycle.

Finally, with reference to Figs. 4 and 5, it can be seen that the choice of axial position of the roller 91 along the pin 90. determines whether the fabric is to be fed by the dog 1 5 or not. In this respect, the fabric moves only when the dog is raised, and this happens only when the roller 91 slides on the cam 97. The operator can cause the roller 91 to slide on the disc 98 by operating the lever 100, such that the notch 102 engages with the slot 103. In this case, the dog 50 is no longer compelled to rise by the arm 86, and consequently is no longer able to drag the fabric From an examination of the characteristics of the machine 10 according to the present invention, it can be seen that it attains the aforesaid objects.

Firstly, the described mechanism acts with high precision in that any slack occurring along the linkage connecting the bars 21 and 22 to the shaft 1 6 has no influence on the positioning accuracy of the shaft 1 6. This is because the axial movements of the shaft 1 6 depend on the movements of the shaft 42 and, as stated, on the angular position of said shaft which is determined only by the position of the roller 58 on the surface of the cone frustum portion 65. In addition, by means of a single mechanism (roller 58 and portion 65) it is possible to control transverse movements of the dog 1 5 both towards the left and towards the right without any limitation, it being necessary only to repeat a transverse movement of the dog 1 5 in the same direction for a required number of cycles in order to obtain fabric movements which are unobtainable with devices known at the present time.

Manual control is no longer required if cams are to be replaced, because all movements are controlled by the decoder unit 20 which, as stated, is controlled by a processing unit in a completely automatic manner.

Finally, it is apparent that modifications can be made to the machine 1 0 heretofore described without leaving the scope of the inventive idea.

Claims (6)

1. A sewing machine (10) of the type comprising a feed dog (15) arranged to move transversely, characterised by comprising a support shaft (16) for said dog (15), said support shaft being arranged to move axially against the action of elastic means (80); a decoder unit (10, 25) arranged to receive control signals from a processing unit and to assume three working positions according to whether said dog (15) is to be caused to undergo a transverse increment towards the right, a transverse increment towards the left or no transverse increment; and a linkage (23, 17, 40) which converts each said working position into corresponding angular swing of an arm (57) extending radially from a shaft (42) coupled axially to said support shaft (16) for said dog (15); said arm (57) carrying a roller (58) rotatable about its axis and slidable on a surface of a profiled element (65) connected to a fixed part of said machine (10).

2. A sewing machine as claimed in claim 1, characterised in that said decoder unit (20, 25) comprises a decoder element (20) of electromechanical type arranged to receive electrical control signals as input, and to provide an output which causes two bars (21, 22) to be positioned in a first or in a second position; and a rocker arm (25) comprising end portions connected to respective end portions of said bars (21, 22), said rocker arm comprising a pin (29) in a central position which is arranged to assume a first, a second or a third working position of said three working positions according to whether said bars (21, 22) are both positioned in said first working position, or whether one is positioned in the first and the other is positioned in the second working position or vice versa, or whether both are positioned in said second working position respectively.

3. A sewing machine as claimed in claim 1 or 2, characterised in that said linkage (23, 17, 40) comprises substantially at least one slide (40j slidable axially relative to said shaft (42); and a drive unit (1 7) for said slide (40) controlled by said decoder unit (20, 25) and arranged to position a first arm (48) of said slide (40) in one of said three working positions, for each of which said arm (48) is urged to cooperate with a corresponding surface of a respective first, second or third cam (51, 52, 53).

4. A machine as claimed in claim 3, characterised in that said slide (40) comprises a second arm (55), of which one end (56) is coupled to said arm (57) extending radially from said shaft (42), and causes said arm (57) to swing about said shaft (42) in accordance with the contour of said first, second or third cam (51, 52, 53).

5. A machine as claimed in any one of the preceding claims, characterised in that said profiled element (65) is of cone frustum shape, and said roller 58 is arranged to slide, during one sewing cycle, respectively from a zone of intermediate cross-section to a zone of smallest cross-section to then pass to a zone of greatest cross-section and return to said zone of intermediate cross-section, or vice versa, or remain always in said intermediate zone, with consequent transmission of an axial movement to said shaft (42) by way of said arm (57);said shaft (42) finally transmitting said axial movement to said dog (15) by way of the relative support shaft (16).

6. A sewing machine with a transversely mobile feed dog, substantially as described with reference to the accompanying drawings.