1. Introduction


A plastic bag making machine is made up of thermal sealing cutter, servo unit, frequency inverter, traction roller, bearing roller and controller. Its main technical feature is as follows: The thermal sealing cutter is mounted on the transmission shaft, which is driven by frequency inverter to move reciprocally upwards and downwards. The servo unit drives the traction roller at a certain speed and ensures the thermal sealing cutter to send the plastic bag of set length over the cutter before it leaves bearing roller and arrives at the bearing roller again. After that, the thermal sealing cutter arrives at bearing roller, seals the plastic bag and cuts it off.

This kind of equipment is mainly used for processing plastic bags and living plastic bags of various specifications. Earlier equipment adopted control mechanism such as brake clutch, and later it was replaced by step control system, and it has been developed into control mechanism composed of PLC, servo motor and frequency inverter. With upgraded and improved technology, higher positioning precision and better stability, quality and efficiency for plastic bags to be made will be improved constantly.

2. Working process

After the equipment is powered on, temperature controller controls heater at the position of sealing cutter to heat;

After temperature reaches the set value, variable frequency drive unit drives the main motor to control continuous upward and downward movement of the cutter and the sealing cutter through mechanical transmission unit.

Each time the cutter moves upward, the cam is connected, servo motor drives discharge roller to rotate for once together with plastic film, the cutter and the sealing cutter cut down to form a plastic bag.

When set number is reached or stop button is pressed, the machine will halt after the plastic bag is formed, and the cutter and sealing cutter stops at high halt position.

3. Control method

A bag making machine has two working ways:
One is sealing and cutting way of empty bag. Servo system control motor moves as per number of pulses preset by PLC, till the number of pulses is over. As a bag making cycle, this is a non-color mark operating way, and it is also called a fixed-length operating way.

The other is color-tracking sealing and cutting way. When color mark sealing and cutting is selected, its process is as follows: After the servo motor is started and signal is connected, the servo motor performs acceleration movement, constant-speed movement, speed-reduction movement and low-speed color-tracking as per the movement curve preset by PLC program. After PLC receives color mark signals, it stops the servo motor by means of cutting off.

In general, color-tracking length is 10mm, and color-tracking signal can only function within the color-tracking range, and interference signals shall be shielded if it is within other ranges. PLC program counts color mark signals in the process of color-tracking sealing and cutting. If the signal cannot be detected for three times, PLC stops running of various motors and drives alarm system to alarm. And PLC program count number in lots. When the lot reaches pre-alarm value, PLC drives the alarm system to prompt alarm.

4. Advantage

1.The configuration of pulse output frequency and double communication ports of IVC1 PLC 100K meet the equipment’s requirement for PLC performance satisfactorily.
2.High precision and intelligence of ITC temperature controllers can ensure accurate control of temperature.
3.Communication control of variable frequency inverter simplifies electrical control equipment.
4.The equipment features high positioning precision, good bag making effect and high efficiency.