Application of frequency converter in cement bag double-head sewing machine

I. Process introduction

The cement bag double-head sewing machine is a kind of fully automatic bag sewing machine. It controls the industrial sewing machine and conveyor belt through computer, automatically sews the two ends of the woven bag, automatically cuts the seam between the bags, and stacks the bags. It is an application of efficient fully automatic industrial sewing machine.

II. Working principle

            Figure 1 Schematic diagram of sewing machine

As shown in Figure 1, the cement bag double-head sewing machine mainly includes feeding conveyor belt, tooth block, main conveyor belt, unloading conveyor belt, industrial sewing machine, paper feeder, air shear and other parts. Among them, the feeding conveyor belt, main conveyor belt and industrial sewing machine are driven by frequency converter, and their linear speed is required to be the same when working. The feeding conveyor belt keeps running after starting, and the woven bags are manually put on the feeding conveyor belt by workers. The pneumatic stopper separates the bags according to the spacing set on the touch screen. When the spacing between the bags is greater than the set spacing, the main conveyor belt and the sewing machine stop, waiting for the woven bags on the feeding conveyor belt to reach the stopper position, the main conveyor belt and the sewing machine stop and continue to run; when the spacing between the bags is less than the set spacing, the main conveyor belt and the sewing machine do not stop. This is the only way to ensure efficient production operation.

III. Control scheme of the hemming machine

This electronic control system consists of a touch screen, PLC, 4 1.5KW SOWAKAM SW200 series inverters, stopper solenoid valves, etc. The width of the bag, the spacing of the bag, the speed of the production line and other parameters can be set through the touch screen. As we mentioned in the previous working principle, the linear speed of each transmission mechanism is the same during operation, so it can be calculated according to the formula: Linear speed =π* diameter * motor speed / transmission ratio

 Feeding conveyor belt     Main conveyor belt      Left sewing machine     Right sewing machine

Figure 2 Electrical diagram of the hemming machine

PLC calculates the target frequency of each process of the feeding conveyor belt inverter, the main conveyor belt inverter, the left sewing machine inverter, and the right sewing machine inverter in real time, and controls the inverter speed regulation through MODBUS communication.

The control difficulty of the system mainly lies in the control of the tooth block and the main conveyor belt inverter. The PLC timer should be used to accurately calculate the retraction and blocking time of the tooth block, and the running time of the main conveyor belt inverter should also be controlled. When the left tooth block photoelectric signal and the right tooth block electro-optical signal are blocked by the bag at the same time, the tooth block is immediately retracted, and the main conveyor belt inverter blocks the tooth in advance or delays the tooth block for a certain time. Therefore, the response speed of the inverter is relatively high. In addition, the main conveyor belt is heavily loaded, and a large torque is required when starting. The maximum operating line speed of this system is 30m/min. At the highest operating speed, the host inverter reaches 58Hz and the maximum current reaches 110% of the rated value. The excellent vector control performance of the SW200 series inverter meets the special process requirements of the system.

IV. Advantages of the system solution

(1) The inverter is operated in the way of external terminal setting, which can accurately control the operating time of the main conveyor belt inverter. If the inverter is operated in the communication mode, MODBUS communication may be interfered, which will affect the spacing of the bags.

(2) The host inverter has a large starting torque and strong overload capacity. It can run for a long time under 110% overload. At the same time, it improves production speed and efficiency.

(3) The host inverter has a short acceleration and deceleration time, fast response speed, and accurate spacing of the bags.

(4) The inverter has high steady speed accuracy. The same speed of the entire line is required during operation. If the steady speed accuracy is low, it is easy to cause the sewing machine needle to be broken.