Sewing Machine Having Automatic Feed Control System

This invention relates to sewing machines and more particularly to a sewing machine having differential feed systems and to an automatic system for controlling the actuation thereof.

Sewing machines with differential feed systems are well-known as are automatic control means for such feed systems, as examples by German Pat. No. 2,161,295. There are disadvantages, however, with such prior art devices. For example, in the area of changeover from one size of fabric plies to another.

In joining the two fabric plies, for example a pair of pants, undesirable shifting between the plies can occur. This shifting may occur either initially after the fabric plies have been aligned but before the start of sewing or during the sewing operation itself. As a result, the ends of the two fabric plies do not match, that is one is longer than the other.

The invention hereunder consideration involves a system which attaches to an appropriate sewing machine having a differential feed system as a part thereof and controls the actuation thereof. Fabric measuring means are employed to measure the fabric as it is being sewn, compare the values or lengths of the top and bottom plies and then cause the necessary actuation or deactuation of the proper differential feed to achieve the necessary alignment. By arranging one measuring means adjacent each fabric ply and measuring the amount of feed thereof it is possible to control the relations of the rate of feed of the two plies.

A second feature involves a measuring cycle which occurs generally prior to the sewing step. As is apparent it is desirable to join the two fabric plies such that the ends thereof match. If however, one ply is longer than the other it becomes necessary to feed and sew the long ply faster than the short to compensate for this excess of material. Thus, initially the two lengths or the lengths of the two fabric plies are measured and compared against a predetermined value. A logic system is then employed in conjunction with, for example, a stepper motor to cause the necessary and proper feed control such that in the finished product the ends of the two plies will match.

It is therefore, an object of this invention to provide a fabric length monitoring and logic system capable of controlling the feeding of two fabric plies. It is yet another object of this invention to provide a fabric length monitoring and logic system which measures two fabric plies prior to the joining thereof and controls the feed of each ply such that the ends thereof match. Another object of this invention is to provide a logic system for controlling the feed rates of two different plies of material which can be programmed to distribute errors in length over the entire length of the shorter piece or distribute such lengths error along given stretches of the shorter ply.

With the above and other objects in view, the nature of the invention will be more clearly understood by reference to the following detailed description and the accompanying drawings.

In the drawings:

FIG. 1 is a schematic representation of a sewing machine with the fabric length monitoring and logic systems attached thereto as viewed from the front;

FIG. 2 is a partial schematic view showing the device for monitoring the length of the fabric plies prior to the beginning of the sewing operation.

FIG. 3 shows a schematic view of the logic system, and

FIGS. 4 and 5 represent functions whereby the length differences can be either distributed uniformly across the shorter ply or just along sections thereof.

Turning now to the drawings and more particularly to FIG. 1 wherein is shown a sewing machine 1 which is provided with a drive pulley 2 and a differential feed system means 3, as is well-known in the art the differential feed adjustment means 3 can be employed whereby the rates of feed of the differential system can be varied. Adjacent the sewing head of the sewing machine 1 are polar or cog wheel means 4. These wheel means 4 are located such that one and only one wheel contacts each ply of fabric in a manner whereby the wheel measures the amount of material which passes. In the first embodiment of the invention herein described as the fabric plies A and B pass into the sewing machine their effective feed length, or amount which has passed into the machine is measured by the polar wheels. These lengths are effectively translated into pulses such as a and b which the wheels generate as they pass through a particular arc. The pulses are transmitted via trigger means, to counter means c1 and c2 as shown in FIG. 3. In a calculator or logic system means 22 the values of a and b are compared to determine a given value, such as Y. If the amount of material which has been fed is of the same length with regard to both plies, then Y equals zero and no adjustment is necessary. If however, different lengths of material have been fed then Y assumes a variable value which in turn causes the actuation of a stepper motor 24 to cause a change in the feed stroke of the proper differential feed to correct for the value differences between a and b. Such control or logic systems are well-known to those skilled in the art and can be constructed with a minimum amount of difficulty. Also stepper motors as well as linkage for controlling differential feeds are known in the art. Therefore, no further discussion of these assemblages will be made.

If it is initially realized that the two plies which are being joined are of different lengths, an assemblage as shown mainly in FIGS. 2 and 3 can be employed. This assemblage involves a light source means 11 and first and second photoelectric cell means 7 and 8 mounted on a support means 26 which is in turn carried on a track or other means (not shown) whereby the entire assembly can be moved in a vertical plane with regard to the cloth plate of the sewing machine. The two fabric plies are inserted under the presser foot of the sewing machine or otherwise held and the support system 26 is moved down along the plies toward their ends. The support system has secured thereto in a following relationship a third polar or cog wheel means 28 such as by a wire means 30. Prior to the start of the sewing operation the length of the two fabric plies can be accurately determined by the pulses being generated by the cog wheel 28 due to the downward movement of the system 26. These generated pulses indicated by 17 in FIG. 3 are passed through a similar system as with the embodiment previously discussed. That is, the impulses via triggers pass through a series of gate means to counter means c3 and c4. The pulses are counted in counter means c3 and c4, they being in turn controlled by the two gate means g1 and g2. These gate means g1 and g2 are in turn controlled by the photoelectric cell means 8 and 7 via appropriate wiring extending therebetween.

In operation the pulses generated by the cog wheel 28 are counted by the counters c3 and c4 which in turn give rise to values L-1 and L-2 until one of the plies, because it is shorter, uncovers the light source which is immediately sensed by the photoelectric cell. This in turn causes the blocking of the associated gate thus causing the counting associated with the shorter fabric length to step. The pulse counting, however, continues on the longer ply and as a result determines the amount of extra length of the remaining ply. Thus, the two values L-1 and L-2 are created. In the logic system 23, L-2 is subtracted from L-1 and the resultant difference is divided by L-1 and multiplied by a factor a. The factor Z obtained by this calculation is now compared with the value Y as previously determined. This function is shown in FIG. 4.

According to FIG. 4 the length difference between the two plies is uniformly distributed over the total length of the lower ply (pulses a) so that the ends of the plies will match. For example, if the upper ply A is longer than the lower ply B, Z will differ from 0. Assuming that there is no slippage between fabric and feed dogs and provided the measured difference Y is 0, the stepper motor will set the upper feed stroke to the calculated feed increasing value. Now, when the upper feed stroke has thus been corrected, the next calculated difference Y will be equal to Z and no further control of the stepper motor is necessary. In other words, when the stepper motor is set once according to the corrective value no further adjustment is required.

In case there is a length difference e.g. a miscut as described in the foregoing paragraph, and if there is in addition shifting of the two plies due to improper feeding as is also referred i.e. a- b = Y .noteq.0, then both control versions will work simultaneously resulting in compensation of the improper feeding as well as the difference in length.

However, if the length difference shall be compensated for at different rates over the total length, as shown in FIG. 5, a preprogrammed unit is used for generating Y. The preprogrammed unit can be controlled by a punched tape coupled to the feed drive mechanism of the sewing machine.

Scanning means 6 resets all counter means C and the logic system means to O as soon as the ends of the plies A and B pass. Such scanning systems are well-known and a man skilled in the art can construct it.

Control system 14 is used when a number of plies to be joined differs in the same and known amount of length. In other words, ##EQU1## is a known figure.

Then the control system 14 is adjusted to this figure and the corrective value y is generated by the control device in place of the unit shown in FIG. 2.

Adjustment system 15 is used in connection with the control system 14 to adjust the feed ratio to concentrate the length correction to certain portions of the length e.g. as shown in FIG. 5.

Thus it is apparent that there has been provided, in accordance with the invention, an Automatic Feed Control Device that fully satisfies the objects, aims, and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.