Arrangement in a sewing machine

The present invention relates to an arrangement in a sewing machine in which several function units are driven by means of an endless synchronous belt from a driving motor.

In prior art in this field it is known how to produce a sewing machine with a body comprising a post, an upper arm and a lower arm in which shafts, driving members and control means are secured and/or journalled, and a driving belt connects a motor to these members. A machine designed according to this principle is described in the Patent Specification US - A-2,793,600. However, the con­struction known thereby has a drawback in that the driving belt and the driving device of a thread take-up lever etc. are disposed on the opposite side of the machine body in relation to the other function units.

By the invention it is presented a solution of the problem to replace units which are difficult to mount, such as shafts etc. in the machine by a synchronous belt having a plane of rotation perpendicular to the feeding direction of the machine. The solution includes the favourable fact that all function units and the belt itself are mounted on one side of the machine body which is a very great advantage in view of assembling. Another advantage is that the driving motor is connected directly to the belt via a toothed wheel without an intervening primary transmission. The properties hereby allotted to a sewing machine according to the invention are stated in detail in the characterizing part of Claim 1.

An embodiment of a sewing machine according to the invention will now be described in the following with reference to the accompanying drawing which shows in a perspective view the machine body with function units and a driving belt.

A sewing machine needs a rigid body in order that relative movements between the function units within the machine shall not be possible. The body shown in the Figure is a design including a lower arm 10, a post 11 and an upper arm 12, the post being fixed on a bottom plate 13. The function units, such as the sewing head 14, the loop-taker and feeding device 15, the zig-zag mechanism 16, the hand wheel unit etc. are disposed on the front side of the body. Previous designs of a sewing head and a loop-taker and feeding unit have been described in the Swedish Patent Specifications No. 8206645-7 and 8106701-9, respectively, and both these function units can advantageously be used in the sewing machine described herein. However, a requirement herefore is that the driving wheel is positioned in the respective units so that driving by a belt on one long side of the body, as shown, is possible. The position of the wheels on driving shafts outside the bearings is here a modification of the previously shown embodiments of the respective unit. Both the said units use a stepper motor for carrying out zig-zag movements and feeding movements, respectively, which requires a control of the seam data of the machine by means of an electronic unit which in the present case is assumed to be positioned in a cover including i.a. a panel with guiding and indication means.

A code disc 17 or the like with a sensor, e.g. in the hand wheel unit of the machine, supplies signals to the electronic unit, thus indicating in which phase of the stitch forming cycle the machine is for the moment. Such signal givers are generally known and need no particular description.

The driving system of the machine is constituted of an electric motor 18 and an endless toothed belt 19 (alternatively a chain) which is tensioned between toothed wheels and backing rollers 20, 21, 22. The motor has a pinion 23 driving the system directly. The hand wheel 24 of the machine is journalled on a fixed or journalled shaft in the body and somewhat unconventionally positioned on the front side of the machine. By using toothed wheels 25, 26 with different diameters for driving the sewing head and the loop-taker, respectively, it is possible to guide the time relation between the functions of these units in the stitch forming. The r.p.m. of the loop-taker shall usually be double the r.p.m. of the sewing head, so the wheel 26 has half the diameter of the diameter of the wheel 25. Thanks to the assembling of the loop-taker and the cloth feeder in one unit, it is only necessary to adjust the time relation for the unit to the sewing head once, e.g. for the loop-taker, whereby the function of the feeder will also be right.

According to the Figure it is possible to assemble all components in the driving system on the front side of the machine. The backing rollers are entered on fixed or journalled shafts in the body, and the motor 18 is inserted into an aperture in the body and secured by means of lugs 27 on the front side of the body. In a similar way the details of the sewing head are supported on shafts 28, 29 which are disposed on the belt side of the machine.

Thanks to the belt transmission great possibilities are given in changing the appearance of the machine without changing the associated function units. The only necessary thing to do when the size of the machine is to be changed, is to use a shorter or longer belt on a bigger or smaller body. The conventional design of a sewing machine having long shafts as transmission members does usually not give such possibilities of model variations as thus the hereinbefore described design with belt transmission does.