AUTOMATIC DEVICE FOR DETACHING THE CAM FOLLOWERS IN A SEWING MACHINE

Abstract: Automatic device for detaching the cam followers in a sewing machine where a selector knob, when it is rotated, provides the detachment of the cam followers in the first stretch of rotation, and positions the desired cam in corres­ pondence of the cam follower in the second stretch of rotation. On the reduction collar of the selector knob two opposite grooves are made out, which engage pins transmit­ ting the translation movement to a shaft which operates a cam follower detaching lever.

Description: The present invention relates to a pattern cam selecting mechanism for a sewing machine. Sewing machines for the execution of ornamental sewings are known with which the operator, every time he chooses a new pattern, must operate a lever for disengaging the cam followers from the previously coupled cams and displace the cam stack or the cam follower so as to obtain the cam follower-cam coupling corresponding to the new selected pattern. If the operator forgets to disengage the cam followers and tries to displace the cam stack, persisting in this incorrect manipulation with a certain force, then the cam followers may be damaged if they are made out of thin sheet or the contours of the cams may be spoiled if they are made out of plastic material. In other sewing machines, for executing ornamental sewings, the cams are spaced in such a way that during their axial displacement they contact inclined walls of the cam followers, causing the radial displacement of said cam followers to enable the latter to overcome the differences in height existing between the contour in contact and the selected contour of the new cam. In this type of machine the number of patterns obtainable is limited because of the consistent defined distance between the contiguous cams; consequently, only a stack having a few cams can be provided in the machine. GB-A-938 417 discloses a pattern cam selecting mechanism in accordance with the preamble of the patent claim. In this known sewing machine the control handle is mounted on a shaft carrying a drum having a cam groove engaged by the end of a lever mounted on a hub slidably mounted on a shaft parallel to the cam shaft. A further lever is mounted on said hub engaging the cam stack for shifting the latter along the cam shaft. During movement of the cam stack the cam follower is disengaged from the cams by a linkage transmission mechanism comprising a plurality of elements. The invention has for its object to provide an improved pattern cam selecting mechanism of simple construction which is easy to manufacture and reliable in operation. This technical problem is solved by the characterizing features of the patent claim. Further features and advantages will become more readily apparent from the following description and from the enclosed drawings, in which: figure 1 is a front view of the sewing machine to which the device according to the present invention is applied; figure 2 shows in detail the device of Fig. 1 in its inoperative position; figure 3 shows in detail the device of Fig. 1 in its operative position; figure 4 shows a detail of the device of Fig. 2, and figure 5 is a detail of Fig. 3. With reference to figure 1, 10 denotes generally a sewing machine comprising a bed 11, a stand 12 extending upwordly from said bed 11, a bracket arm 13 and a head 14 which is mounted at an end of said arm 13 and from which the needle bar 15 extends. A vertical shaft 16 is coupled to the main shaft 17 of the sewing machine and rotated by the latter via a pair of gears 18. A bridge support 19 is freely mounted on the shaft 16 and a cam steack 20 is also mounted on said shaft within said support, free to follow the latter in its movements along the axis of said shaft but fixedly connected to said shaft in rotation about its own axis. The connection vertical shaft 16 - bridge support 19 - cam stack 20 is not described in detail as it is known in the art. The bridge support 19 provided for positioning the stack 20 has a rack 21 which is constantly engaged with a gear 22 mounted on a hollow shaft 26 enclosed in the automatic device 23 according to the present invention. Said device 23 (Figs. 2 and 3) comprises a selector knob 24 extending from the stand 12 and manipulated by the operator for selecting the cam corresponding to the desired pattern. Said knob has a reduced collar 41 on which two radially opposed grooves are formed, each comprising two inclined edges 45 and 46 forming a prostrate V and two edges 47 and 48 parallel to the axis of the selector knob 24 (Fig. 5). Said grooves 42 are engaged by pins 43 fixed to an element 33, in the shape of a prostrate U fixed in turn to a first bush 32. The free ends 35 of the prostrate U shaped element 33 are adapted to run in seats 36 in a toothed pulley 37 when the selector knob 24 is rotated. Said pulley 37 is fixedly connected to the hollow shaft 26 carrying tire gear 22. In the proximity of said gear 22 on the shaft 26 a disk 27 is mounted on which holes 28 are formed which ire circumferentially equidistant (Fig. 4) and the function of which will be explained hereinafter. A second bush 29 is inserted into the hollow shaft 26, the toothed pulley 37 and the hub 25 of the selector knob 24. Inside said second bush 29 a shaft 30 extends, an end of which is in contact with the ends of a screw 31, partially screwed onto the first bush 32, which is adapted to run in the second bush 29 as will be explained hereinafter. The axial adjustment of the screw 31 determines the position of the other end of the shaft 30 which projects from the second bush 29. To said other end of the shaft 30 there is Keyed, axially displaceable with said shaft, a bolt element 38 which engages the holes 28 of the disk 27 for locking the shaft 26 and consequently the knob 24 in a predetermined position. The end of the shaft 30 which projects from the bush 29 engages a cam follower disengaging lever 39 pivoted and free to oscillate at 40. When the operator desires to select a predetermined pattern he operates the selector knob 24 causing it to rotate clockwise or anticlockwise in order to displace the cam stack vertically until the cam for executing the selected pattern is positioned in correspondence with a cam follower 44 which transmits the transversal oscillations to the needle bar 15 in a manner known per se. In the first part of rotation of the knob 24 the pins 41 (Fig. 5) are pushed, in the case of clockwise rotation, along the inclined edge 45 of the groove 42 until they assume the position illustrated in figure 5. Said figure illustrates in dotted line the position in which the pins 43 would be on rotation of the knob 24 anticlockwise. The movement of the pins 43 causes a translation along the axis of the shaft 30 of the U-shaped element 33 and of the first bush 32 running in the second bush 29. As the screw 31 is fixed to the first bush 32, said screw 31 pushes the shaft 26 axially so that the bolt element 38 disengages from the holes 28 of the disk 27 and the end of said shaft 30 causes the cam follower disengaging lever 39 to rotate about the pin 40. By this rotation the lever 39 comes into contact with a lug 49 of the cam follower 44 and causes said cam follower 44 to disengage from the cam stack 20 rotating it about the axis 51. On further rotation of the knob 24 the edge 47 of the groove 42 comes in contact with the pins 43. This coupling causes the rotation of the element 33 of prostrate U-shape about the axis of the shaft 30; this rotation, via the free ends 35 of said element 33, the toothed pulley 37 and the hollow shaft 26, is transmitted to the gear 22 which is coupled to tie rack 21 of the bridge support 19. The rotation of the gear 22 causes an axial displacement of said bridge element 19 and consequently of the cam stack 20 as well until the desired cam is carried into coincidence with the cam follower 44. In known manner the toothed pulley 37, via a belt 52, displaces an indicator 53 (Fig. 1) which runs along a plate 54 in order to indicate which cam, corresponding to the pattern of said plate 54, is in correspondence with the cam follower 44. When the indicator 53 is positioned on the desired pattern the operator releases the selector knob 24. When this is done, the cam follower disengaging lever 39, under the action of a return spring 55, returns to its position illustrated in figure 2. This causes an axial displacement of the shaft 30 and as a consequence the pins 43 run along the inclined edge 47 until they reach the inoperative position and the bolt element 38 engages one of the holes 28 of the disk 27 so as to lock the cam stack 20 in the desired position. The return of the cam follower disengaging lever 39 frees the cam follower 44 which engages the cam corresponding to the desired pattern.

Claims: 1. A pattern cam selecting mechanism for a sewing machine comprising a shaft (16) coupled to the main shaft (17) of the machine, a support (19) freely mounted on said shaft (16) and a cam stack (20) also mounted on said shaft (16) within said support (19), free to follow the latter in its movements along the axis of said shaft (16) but fixedly connected to said shaft (16) in rotation about its own axis, wherein a selector knob (24), when it is rotated, causes the displacement of the support (19) of the cam stack (20) in the first part of the rotation occurring in the disengagement of the cam follower (44) and in the second part of the rotation the positioning of said stack (20) relatively to said cam follower (44), and wherein first means are provided for disengaging said cam follower and second means are provided for releasing, positioning and locking said cam stack (20) in correspondence with said cam follower (44), characterized in that said first means comprise a U-shaped element (33) connected to said knob (24) by means of pins (43), a first bush (32), fixed to said element (33), a screw partially screwed to said first bush (32) and having an end in contact with an end of a shaft adapted to run axially in a second bush (29), the other end of said shaft (30) being in contact with a cam follower disengaging lever (39) pivoted and free to oscillate about a pin (40), said lever (39) being in contact with a lug (49) of a cam follower (44), means being provided on said knob (24) for displacing said element (33) along the axis of said shaft in order to disengage the cam follower (44), a return spring (55) on said lever (39) being adapted to return said lever (39) and as a consequence said knob (24) to the inoperative position when said knob (24) is released, and that said U-shaped element (33) comprises radially opposite grooves (42) formed on a reduced collar (41) of said knob (24), each of said grooves (42) being formed by two inclined edges (45, 46) forming a V along which said pins (43) run during the first part of the rotation of said knob (24), and that said second means comprises a bolt element (38) engaging holes (26) formed on a disk (27) fixed to a hollow shaft (26), said hollow shaft (26) having a gear (22) engaged with a rack (21) of said support (19) carrying said cam stack (20), said bolt element (38) being disposed at the end of said shaft (30) in contact with said cam follower disengaging lever (39) for displacement axially with said shaft (30) during the first part of the rotation of said knob (24) for disengaging from said disk (27) and for locking said disk (27) when said knob (24) is released, said hollow shaft (26) being fixed to a toothed pulley (22), engaged by the free ends of said U-shaped element (33) for rotating during the second part of the rotation of said knob (24) and displacing said cam stack (20).

Inventors: BISSON, FLAVIO, DOTT. ING.
Applicants: NECCHI SOCIETA PER AZIONI
Application year: 1987
Main classification: D05B19
IPC codes: D05B19, D05B3