EP0032485A1

EP0032485A1 - Zigzag mechanism

Info

Publication number: EP0032485A1
Application number: EP81850007A
Authority: EP
Inventors: Lars-Erik Gustafsson
Original assignee: Husqvarna AB
Current assignee: Husqvarna AB
Priority date: 1980-01-15
Filing date: 1981-01-14
Publication date: 1981-07-22
Also published as: EP0032485B1; SE8000309L; DE3164626D1; SE423912B

Abstract

A frame (10) of a needle bar mechanism is mounted in a sewing machine arm and supports the swingable needle bar holder (13) by which the zigzag motion of the needle is enabled. A stepping motor (24) is mounted in the frame and connected by means of a link (26) from the shaft of the motor to the needle bar holder. The motor is controlled by stich codes supplied by amplification circuits and automatic control devices. Owing to the design of the link, the driving arrangement can be provided with calibration and an elastic engagement between the motor shaft and the needle bar holder. The transfer distance through only one link is short so the friction loss is small which in combination with a small keeping torque of the needle bar will restrict the dimension of the stepping motor.

Description

The present invention relates to a zigzag mechanism of a sewing machine. A frame of the mechanism is provided in the arm of the sewing machine and supports the pivoted needle bar holder by which the zigzag motions of the needle can be carried out.
A presser foot and needle bar unit with a body in the form of an elongated frame with points of attachment at both ends is priorly known from the Swedish patent specification no 370 732. The zigzag motion of the swingable needle bar holder of the unit is carried out in the usual way of mechanical sewing machines by means of a rotating curve disc and a follower transferring reciprocating movements to the needle bar holder.
In modern, electronic sewing machines a data memory and a code converter have replaced the curve disc and the follower in order to produce the zigzag motions to a seam pattern predetermined by the memory unit. A stepping motor is used as a code converter and controlled by a stitch code supplied by amplification circuits and automatic control devices of the said memory unit. Such a stepping motor and driving arrangements can according to the invention be joined to the needle bar unit into a complete, driving zigzag mechanism out of which the zigzag motions are directly obtained on output of drive signals from the amplification circuits. A composed unit of this kind can be assembled outside the machine and then placed directly in position at the assembly of the machine. It also represents an advantage from a service point, since a fault located in such a unit can easily be remedied by substituting the whole unit. A zigzag mechanism having these properties is closely defined in the charaterizing part of Claim 1.
An embodiment of a zigzag mechanism according to the invention is described in the following with references to the attached drawing which shows in Fig. 1 the zigzag mechanism in a side projection, Fig. 2 the same mechanism in a vertical projection mounted in a sewing machine, Fig. 3 the same mechanism in a perspective view.
The body of the mechanism is constituted of a frame 10 which has a fixing lug 11 and holes for a through passing bar 12 by which the mechanism is secured - to the machine. The needle bar guide is constituted of a holder 13 and bearings 14, 15 and keeps a movable needle bar 16, provided with a pivot 17 in a vertical position. The holder has a ball bearing 18 in the top of the frame 10 in which a through screw 19 is screwed and provided with a ball on which the holder is supported. It is then swingable sideways and controlled in its lower end by a guide rib 20 co-operating with a cam 21 on the frame.
The frame is also, on one side, provided with fixing lugs 22, 23, where a stepping motor 24 is mounted. The shaft of the stepping motor is provided with a pinion 25 meshing with a rack 26 extended across the frame. The rack has approximately at the middle of it an aperture 27 forming a pair of sloping side edges 28, 29 making an obtuse angle, and a fixing point of a screw spring 30 at the remote end of the rack shown in the perspective view of Fig. 3. The screw spring is fixed to a lug 31 on the frame and acts upwards on the said remote end of the rack. That one is by a pin 32 on the holder 13 connected to the holder, which thereby will follow the motion of the rack. The pin is normally kept in the vertex of the obtuse angle as a consequence of the spring force acting on the remote end and the sloping of the edges 28, 29, but it may also slide onto someone of the edges. This may, e.g., occur when the needle 33 is subjected to an external, lateral force, but when this force ceases the pin will return to the vertex of the angle as the side edges slope that way. The pin is also a fulcrum of the rack which thus can rotate a little angle around the pin. This is possible by raising the forward end (the toothed end) of the rack above the pinion 25 so that this one is disengaged from the rack. However, the pinion is usually in mesh with the rack owing to the spring force at its remote end, since the relative position between the rack and the pinion was adjusted at the assembly.
A well-defined initial position of the stepping motor is very important in its function as a setting device for the lateral position of the needle, which is determined by the drive pulses supplied by the motor drive circuits. In the present embodiment of the rack and pinion it is possible to use a mechanical stop in the form of a dog 34 on the rack, whereby a stationary well-defined position is created. The setting of the motor to this position, which constitues the initial position, takes place so that the automatic control device in the machine emits a number of pulses to the input of the motor which cause the motor to step forwards to the stop. After such a series of pulses the motor is calibrated, that is to say it is set in the initial position. When the drive circuits subsequently emit a series of pulses in the other direction, the motor responds in that it performs a corresponding number of steps from the initial position. A calibration can take place at suitable points of time in the working of the machine e.g. at the start of any fancy seam.
The design of a rack has two purposes, first to bring about an elastic engagement between the motor and the needle bar holder which engagement is self-adjusting to the vertex of the obtuse angle in the aperture 27, and then to provide a calibration position at the stationary dog 34 from which the working range of the motor is counted. The transfer distance of the motion is short and the friction loss small which in combination with a small keeping torque of the needle bar holder in adjusted positions contributes to the possibility of using a relatively small stepping motor for the zigzag cntrol.
The described embodiment may be altered within the scope of the invention, e.g. the aperture 27 may be positioned in the needle bar holder and the pin 32 on the rack. Variations of this kind are considered to be within the inventive idea.

Claims

1. A zigzag mechanism of a sewing machine provided with a laterally swingable needle bar holder and a stepping motor generating a zigzag motion, connecting means and a gear between said motor and holder, characterized in that the connecting means includes a pin (32) and a therewith associated aperture (27), one of which positioned on the holder (13) and the other on a portion included in the gear (26) and that both of them are kept to each other by means of an elastic member (30).

2. A zigzag mechanism according to Claim 1, characterized in that a portion of the gear is constituted of a rack (26) provided with one of said connecting means.

3. A zigzag mechanism according to Claim 2, characterized in that said rack has a fulcrum at the said pin and is kept in engagement with one pinion (₂5) provided on the motor (24) by means of the force of said elastic member.

4. A zigzag mechanism according to Claim 2, characterized in that the rack is provided with a dog (34) constituting a calibration position of the stepping motor.

₅. A zigzag mechanism according to Claim 1, characterized in that the aperture (27) has a greater width than the cross section of the pin and a position of equilibrium into which the pin is forced by means of of the said elastic member.