The present invention relates generally to cloth spreading machines and in particular to a method and apparatus for spreading cloth in a uniform manner on a cutting surface.
Cloth spreading machines are widely used in the garment industry and are generally employed to deposit a layer or layers of cloth on a cutting surface. One type of prior art spreader is mounted above a stationary cutting table and is adapted to travel reciprocally above the table, dispensing a layer of cloth from a cloth supply spindle, as it traverses the length of the table. If multiple layers of cloth are to be laid, the spreader will either return to its starting position and dispense another layer of cloth on the table or alternately, a second layer will be deposited during the return travel of the spreader.
Many of the prior spreaders, include sensors for monitoring the tension in the cloth web. These sensors attempt to control the rate of cloth feed so that the cloth is spread onto the cutting surface uniformly at a predetermined tension, or "tension free".
In some prior art spreaders, a sensor in the form of a dancer roll is used to monitor cloth tension. The dancer roll is generally pivotally mounted and interposed in the web path so that changes in web tension will cause positional changes in the dancer roll. In one spreader, the dancer roll is operatively connected to a switch that controls the cloth drive; and in another spreader, the dancer roll is connected to a potentiometer which modifies the speed of the cloth drive.
Because most dancer rolls are spring biased, a predetermined tension in the web is necessary to overcome the dancer roll force and move it to an equilibrium position. In machines that use dancer rolls, it is difficult, if not impossible, to deposit a uniform layer of cloth on a cutting table, substantially "tension free", for the dancer roll itself will produce some tension in the web.
Other sensors have been suggested which do not contribute to the web tension. These include loop sensors which monitor the droop or sag in the web at a predetermined location. In one suggested spreader, the droop in the web is sensed optically whereas in another spreader, the droop is monitored by a radiant energy sensor. These sensing devices have not been totally satisfactory and in the case of the radiant energy sensor, have been rather expensive.
A variation in tension along the width of the cloth web is often encountered. Most prior art spreaders do not address this problem, but merely monitor the tension at one position on the web and adjust the cloth feed rate accordingly. Compensation for tension variation across the web is ignored. In the case of patterned fabric, specifically plaids, a variation in tension will skew the orientation of the cloth with respect to the cutting surface and a pattern mismatch will result when the garment is assembled.
With the advent of automatic cutting machines, new problems arise and the old problems are compounded. One type of automatic cutting machine is a laser cutter which includes a computer controlled laser head that directs a minute laser beam over a ply of cloth on a cutting surface and cuts out individual garment pieces while simultaneously fusing the edges. The cutting surface is a honey combed conveyor that extends to either side of the laser cutting station. A ply of cloth is laid upon the loading side of the conveyor surface and is then advanced into the cutting station. The cut pieces and the remnants are transported by the conveyor out of the cutting station to an unloading area.
Spreaders adapted for automatic cutting systems have been proposed. For the laser cutting system described above, a spreader has been proposed which is positioned at the input end of the conveyor and includes a cloth feed roll, an associated drive motor and an optical loop sensor for maintaining a predetermined tension in the web as it is deposited on the conveyor. In the suggested spreader, the cloth feed drive is controlled by the laser cutting machine and dispenses cloth onto the conveyor as it advances toward the cutting station. Because the conveyor speed is quite high, the cloth feed must accelerate quickly to match the speed of the conveyor. Any lag in the cloth feed mechanism will be manifested as an area of excessive tension or stretch in the cloth layer. Garment pieces cut from these stretched areas will not be dimensionally stable. The problem is further aggravated with pattern fabrics, especially plaids, for any nonuniformity is reflected in stripe or pattern skewing. In practice, it has been found that this spreader could not be made to spread cloth consistently on a high speed laser cutting system.
Another problem associated with this and other prior suggested spreaders is the inability of the operator adequately to inspect the cloth prior to advancing into the cutting station to insure that it has been spread uniformly. Moreover, even if the operator observes nonuniformity, no provision for rewinding the cloth onto the spreader is provided so that it can be re-spread.
Finally, it is quite common for remnants to remain on, and by adhered to, the cutting surface after leaving the unloading station. These remnants should be removed because the presence of one will cause distortions in subsequent spreading and cutting operations. Because the prior suggested spreaders are mounted at the input end of the conveyor, it is virtually impossible for the operator to inspect the conveyor prior to cloth spreading, and as a consequence, it is difficult to be certain that all remnants have been removed.