China's knitting industry is known as the world's factory. It is conservatively estimated that there are more than 40,000 computerized flat knitting machines and more than 120,000 electric flat knitting machines in this huge Beijing synchronous belt factory. over a million units. In the past three years, China's annual import of computerized flat knitting machines has remained at 4,000 to 5,000 units. From these figures, it can be clearly seen that the market potential of fully automatic computerized flat knitting machines is very huge.
There are more than 50,000 processing factories engaged in wool sweater production in China. Judging from this number, each factory has less than one computerized flat knitting machine on average. The processing factory with the most computerized flat knitting machines has nearly 1,500 computerized flat knitting machines. From these figures, we can see that the popularity of computerized flat knitting machines is not high now. Many sweater processing factories have not yet used computerized flat knitting machines, and now they are developing from hand-operated flat knitting machines to computerized flat knitting machines. The tide has come, and under this trend, the market space of computerized flat knitting machines has been greatly expanded. Driven by market demand, more factories will begin to use fully automatic computerized flat knitting machines.
From the perspective of the demand in the international market, in the environment of the continuous appreciation of the RMB and the increasing trade barriers, it is difficult to obtain profits by using cheap labor for low-value-added processing. Improving the competitiveness of products in terms of quality is the real channel for profit. Computerized flat knitting machines can achieve a level of craftsmanship that is more difficult to achieve than hand-operated flat knitting machines. Therefore, through the computerized flat knitting machine, sweaters with higher added value can be produced, so that manufacturers can obtain greater profits.
In summary, we can clearly judge that the market space for computerized flat knitting machines is huge, and the demand for computerized flat knitting machines in the domestic market will increase. At present, the single (double) system in the domestic computerized flat knitting industry is equipped with two sets of AC servos, the main servo is used for the head drive system, and the shaker servo is used for the needle bed shift system. With the increasing market demand for computerized flat knitting machines, servo as a main precision transmission supporting component will usher in a vast and huge market space.
From the flow chart of computerized flat knitting machine control data in Figure 1, we can clearly see the flow of data in the computerized flat knitting process. The following is a description of the data flow diagram:
1. The pattern preparation system generates the weaving control of the garment piece according to the required organization or pattern of the garment piece sample, and according to the garment piece parameters, such as weaving density, garment width, garment length, weaving speed, weaving system, etc. code.
2. The pattern file compiler compiles the pattern file input by the operator. If the input is incorrect or does not conform to the pattern file definition syntax, the compilation result will be displayed and returned.
3. The pattern file interpreter interprets the compiled file, converts it into data that can be directly used for control, and stores and manages the data according to a certain data structure.
4. The controller takes out the data control motion control card and the digital I/O card obtained through the processing in the third step.
5. Interrupt detection is to detect the interrupt source for a certain period. If a signal is detected, an interrupt signal will be generated immediately to notify the main program to process the interrupt.
6. The digital I/O card uses the obtained weak current signal to control the strong current signal, and directly controls the computerized flat knitting machine body.
7. The motion control card controls the strong electric signal with the weak electric signal obtained through the motion channel, and directly controls the computerized flat knitting machine body.
8. Data Feedback and Display Feedback the garment piece information and processing information to the operator through the operation interface.
9. The body of the flat knitting machine is knitted under a controlled state.
The hardware structure diagram of the computerized flat knitting machine control system is given. Taking the industrial computer as the center, peripheral devices such as keyboard, mouse and peripheral memory, etc., the function of the keyboard is to manually input the pattern knitting file code. Since the control software provides a user-friendly operation interface, the function of the mouse is to operate the interface buttons or menus. Peripheral storage includes a floppy drive or a USB stick.The motion control card is an ISA slot-based control card, which is inserted into the expansion board of the industrial computer. The motion control card has sixteen digital I/O ports, and all input and output signals have photoelectric isolation protection switches. The card has three motion channels, which can realize three-axis linkage, and the pulse frequency range is 1-16KPPS (pulses per second). The motion control card is connected to an optocoupler isolation circuit board, and most of the external signals communicate through the circuit board, the motion control card and the industrial control PC.
Computer flat knitting machines still have a lot of digital signals to process. The hardware system uses a digital I/O card based on a PCI slot. The digital I/O card has 192-bit input and output channels, and is divided into two sub-cards and a mother-card. This card is used to control the following moving parts of the computerized flat knitting machine: needle selector, tuck pressure plate, transfer pressure plate, triangle, input of interrupt signal, etc.
ESTUN servo selection model and specific signal wiring diagram and parameter settings:
Head drive system:
1. When the computerized flat knitting machine is working, the main servo motor drives the flat knitting machine head to do reciprocating motion to implement knitting. The head drive of the computerized flat knitting machine used in our servo drive adopts servo and synchronous toothed belt drive, and the head can automatically adjust the stroke. Generally, there are two-stage deceleration transmissions (65:45:25) from the servo to the machine head. When running at high and low speeds, the head of the servo motor is required to be stable, without jitter and vibration noise. Smooth and no obvious stuttering and strong jitter. Currently choose ESTUN10NM, 1500RPM1.57KW AC servo.
2. Generally, the machine head runs at high speed to 1.2M/S servo speed of about 725RPM. The load is maintained at about 45%, and the load changes to between 60-80% when the two ends are reversed. The normal head running speed is between 0.75M/S and 1M/S. The load variation is between 28%-50%. Servo speed between 425RPM-550RPM.
Synchronous belt drive design:
a. The number of meshing teeth The number of meshing teeth between the synchronous belt and the small pulley should be ≥6. If the mechanism allows, the center distance can be increased, or the diameter of the pulley can be kept at a small pitch, but it should be where permitted.
b. Timing belt width, pitch and pitch length are complicated to calculate due to the determination of timing belt width, so in actual design, the circular force is often calculated, and then refer to the allowable circular force in the relevant mechanical design manual Find out the corresponding bandwidth and pitch, generally take 5.08. After determining the pitch and bandwidth, calculate the length of the belt pitch line according to the initial center distance, and then select it according to the standard. If it does not meet the requirements, the center distance can be adjusted.
c. The tooth shape of the synchronous belt of the head drive mechanism of the computerized flat knitting machine is generally arc-shaped, and some are trapezoidal, but no matter what kind of tooth shape, a circle on the pulley must be tangent to the pitch line of the belt , and implement pure rolling, the second is that the distance between the corresponding points of the two adjacent teeth on the pulley on this arc is equal to the pitch of the synchronous belt. In order to ensure the good performance when the belt meshes with the pulley, the tooth profile angle of the pulley should be correctly selected during the design. From ° to 25°, the amount of interference between the gear teeth and the belt teeth is small, and the tooth profile angle deviation is about ±1°.
Needle bed shift system:
Needle bed traverse mechanism The flat knitting knitting machine is the main equipment for producing sweaters, and the change of the sweater's pattern and fabric structure depends not only on the change of the cam mechanism and the needle arrangement, but also on the traverse of the needle bed. effect. Fabrics with complex structures such as twill, twist, hollow, and transfer can be woven by using needle bed lateral movement. On the traditional hand-held flat knitting machine, the mechanism of the needle bed traversing usually adopts a helical cam, which is realized by a pin positioning after rotating a certain angle. But in the computerized flat knitting machine, manual operation obviously cannot be applied, and due to the structural characteristics of the machine itself and the automatic realization of the transfer function, it puts forward more requirements on the accuracy, stability, reliability and mechatronics of the needle bed traverse. Therefore, in the new type of computerized flat knitting machine, the traverse movement of the needle bed is generally realized by servo or stepper motor-ball screw nut pair transmission. The shaker motor and the ball screw are connected with a synchronous toothed belt, and the reduction ratio of the synchronous pulley is generally 24:15. When the needle bed needs to be traversed in knitting, a fast response of the servo motor is required. Generally, a servo motor with a speed of 3000RPM and 750W is selected.
Selection of Shaker Motor:
In the traverse mechanism, the motor should be selected first, and the torque to the screw can be calculated through the force analysis of the space force. The calculation formula is as follows:
M=KFRWsinαcosβ×918η1η2×1000(N1m)
Where: K——safety factor, generally 112～114;
F——Friction coefficient;
R——screw normal surface radius;
W——Needle plate quality
α——half angle of the base;
β——helix angle;
η1——Synchronous belt transmission efficiency;
η2——Transmission efficiency of screw nut pair;
M——torque.
According to the size of the torque, the power of the motor is determined, and the required motor specifications are selected accordingly. The stepping angle needs to be initially determined. At present, the stepping angle of the stepping motor produced by most domestic manufacturers is 019°P118°.
Ball screw nut pair transmission
Because of the high transmission precision and transmission efficiency of the ball screw nut pair transmission, this transmission method is generally used in modern new computerized flat knitting machines. The working principle is as follows: the control system sends out an electrical pulse signal according to the displacement, the signal feedback is carried out by the photoelectric encoder at the rear end of the motor, and the synchronous pulley and the screw nut pair are driven to pull the needle bed to move left and right.
According to its working principle, the calculation formula of needle bed traverse amount is listed:
A（traverse amount）=α360×i×T
α——motor rotation angle,α=number of pulses×step angle;
i——transmission ratio, i.e. i=number of teeth of driving gear/number of teeth of passive gear;
T——screw pitch.
The lateral movement of the needle bed is generally set at 1/4, 1/2, 3/4, between 1/4, 1/2, 3/4, a section and 0-2 inches, and any position can be controlled by one-time movement, as well as individual needles. Bit minor correction and other functions. When the above parameters are selected, the error value should be corrected to make the error as small as possible, otherwise the traverse accuracy will be affected, and the above parameters should be re-corrected.
