Application cases of frequency converters on circular knitting machines

I. Introduction to circular knitting machine technology

1. Introduction to circular knitting machines

Circular knitting machines (as shown in Figure 1) are machines that weave cotton yarn into tubular cloth. They are mainly used to weave various types of fleece knitted fabrics, T-shirt fabrics, and various types of patterned fabrics with holes.

2. Process requirements

(1) The frequency converter is required to have strong environmental resistance, because the working environment temperature on site is high, and cotton wool can easily cause the cooling fan to block and damage, and the cooling holes to be blocked.

(2) It is required to have a flexible inching operation function. The equipment is equipped with inching buttons in many places, and the frequency converter is required to have a fast response speed.

(3) Three speeds are required in speed control: the first is the inching operation speed, which is usually around 6Hz; the second is the normal weaving speed, with a maximum frequency of 70Hz; and the third is the low-speed cloth collection operation, which requires a frequency of around 20Hz.

(4) During the operation of the circular knitting machine, the motor reversal and rotation are absolutely prohibited, otherwise the needles of the needle bed will be bent or broken. If the circular knitting machine uses a single-phase bearing, this can be ignored. On the other hand, DC braking needs to be set to eliminate rotation.

3. Site requirements and debugging plan

1）Site requirements

The circular knitting machine industry has relatively simple requirements for the control function of the inverter. Generally, the terminal is connected to control the start and stop, the analog frequency is given, or the multi-speed frequency is used. The requirement for jog or low-speed operation is fast, so the inverter is required to be able to control the motor to generate a large low-frequency torque at low frequency. Generally, in the application of circular knitting machines, the inverter can meet the requirements in V/F mode.

2） Debugging plan

The solution we adopted is: SOWAKAM200 series sensorless current vector inverter power: 3.7 and 5.5KW.