Besides manual tension control, there are two ways to control tension automatically. Control the output torque of motor or control the speed of motor.
① Open-loop torque control.
A. tension open-loop control. The control scheme that the inverter only controls the tension according to the output frequency or torque is the tension open-loop control system. Because there is no tension measuring signal, it is called tension open-loop control. The torque control mode is adopted, that is, the inverter controls the torque of the motor, not the speed, so the output frequency changes with the speed of the conveyed object.
Because the tension of conveying materials only comes from the torque of the winding shaft, the tension of materials can be controlled by the torque of the winding shaft, that is, T=FR. The motor torque is calculated according to the tension, which is used to control the current loop of the frequency converter to control the motor output torque. This tension open-loop control system is often used in situations where the tension control accuracy is not high.
B. the realization of tension open-loop control. The tension open-loop control system consists of the following functional modules.
First, the tension setting. The set value of tension is related to the material to be transported and the requirements of crimping. The tension cone is used to control the tension to decrease with the increase of winding diameter and improve the winding forming effect.
Two. Calculation of winding diameter. Used to calculate and obtain the roll diameter information. When the winding diameter is calculated by the linear velocity of the conveyed material, the linear velocity is input into the functional module; When calculating the coil diameter through thickness accumulation, the related functional module for calculating the coil diameter through thickness accumulation is used.
Roman numeral 3. Torque compensation. Part of the output torque of the motor is used to overcome the inertia moment of the winding (unwinding) roller during acceleration and deceleration. Inertia compensation in frequency converter can automatically compensate torque according to the acceleration and deceleration rate by setting appropriate parameters. It enables the system to obtain stable tension during acceleration and deceleration. Friction compensation is used to overcome the influence of system resistance on tension.
C. tension open-loop control mode. Figure 6-29 is the basic structure of the tension open-loop control system. This control mode is also called coil diameter detection mode. That is, when winding and unfolding, the outer diameter of the drum is automatically detected to control the torque of winding and unfolding. There are two common methods to detect the outer diameter of drum.
Figure 6-29? Tension open-loop control
1. Use the proximity switch installed on the drum to detect the rotating speed of the drum, and calculate the thickness of the drum diameter according to the rotating speed, the shaft diameter of the drum and the material thickness, so as to obtain the outer diameter of the drum. According to the proximity switch, each pulse output indicates that the drum rotates once, so the drum diameter is calculated by multiplying the original drum diameter by the material thickness.
Two. Use the proximity switch and rotary encoder on the reel to detect the speed of the feed roller for calculation. That is, the rotation period of the drum increases with the increase of the drum diameter, while the pulse output of the rotary encoder installed on the feed roller with a fixed diameter does not change at a constant speed. When the drum rotates once, the current drum diameter is calculated according to the number of pulses output by the feed roller. As long as there is no slip between the feed roller and the material, the calculation accuracy of this method is better than the cumulative calculation based on thickness.
② Closed-loop speed control.
A. tension closed-loop control. Tension as a feedback signal constitutes a tension closed-loop control system. Its speed control means that the frequency converter adjusts the output frequency of the frequency converter according to the tension feedback signal. Here, the speed control mode can work in any of three modes: vector control without speed sensor, vector control with speed sensor and U/f control.
It calculates the matching frequency setting value f 1 through the linear speed of the conveyed material and the actual winding diameter, and generates the frequency value f2 through the PID operation of the tension (position) feedback signal, so the final output frequency is f= f 1+f2. Here, the output of PID control is used as a feedback control signal, and the frequency signal obtained by calculating the linear speed and the actual winding diameter is a feedforward control signal. When the linear speed of the drum roller does not match the linear speed of the material with the increase of the winding diameter, a correction signal will be output to reduce the output frequency of the frequency converter in time.
The tension closed-loop control system can stabilize the tension at the set value of PID controller. When tension (position) feedback signals such as tension pendulum and floating roller are used as feedback detection elements, changing the setting of PID controller may not necessarily change the actual tension. Changing tension requires changing the configuration of tension machinery, such as the counterweight of tension pendulum or floating roller.
Whether tension open-loop control or closed-loop control is adopted, the system needs to provide extra torque to overcome the moment of inertia of the whole system when accelerating and decelerating. Without compensation, the tension is too small during winding acceleration, too large during deceleration, too large during unwinding acceleration and too small during deceleration.
Tension closed-loop control system is often used in applications that require high tension control accuracy. Such as papermaking and textile.
B. the realization of tension closed-loop control. The tension closed-loop control system consists of the following functional modules.
First, PID controller. Used to detect tension feedback signal and output frequency signal f2 through PID operation.
Two. Linear speed input. It has two functions:
Calculate the matched frequency setting value f1according to the linear speed;
Calculate the winding diameter according to the linear speed.
Roman numeral 3. Calculation of coil diameter. Used to calculate the actual winding diameter. The frequency converter obtains the matching frequency of the frequency converter according to the linear speed and the actual winding diameter. When calculating the coil diameter with linear velocity, if the calculated coil diameter is different from the actual coil diameter, it means that the linear velocity is different, and the linear velocity input can be corrected by the calculation result of the coil diameter. It should be noted that the matching frequency of the inverter obtained according to the linear speed and the actual winding diameter is not the actual output frequency of the inverter. The actual output frequency of the inverter is the working frequency used to calculate the winding diameter according to the linear speed and working frequency.
Four. The second group of PID controllers. In order to improve the precision of tension control, two groups of different PID controller parameters can be set. When the first set of PID controller parameters can not meet the control accuracy, the second set of PID controller parameters is used for control. For example, when the winding diameter is small, the first set of PID controller parameters is adopted, and with the increase of winding diameter, the second set of PID controller parameters is adopted to realize high-precision control in the whole process.
Figure 6-30 is the basic structure of the tension closed-loop control system. It detects tension through a tension detector and uses feedback control to keep the actual value of tension consistent with the set value. Therefore, the control accuracy is improved.
Figure 6-30? Tension closed-loop control
③ Basic structure of unwinding. The unwinding structure can be divided into single-axis unwinding mechanism, multi-axis simultaneous unwinding mechanism, forward unwinding mechanism and reverse driving unwinding mechanism. Fig. 6-3 1 is their mechanism diagram.
The single-shaft unwinding mechanism is equipped with a brake on the reel. With the decrease of drum diameter, only by reducing the corresponding braking torque can a certain tension be obtained. This mechanism can also add gears, pulleys and other acceleration and deceleration mechanisms between the drum and the brake.
Figure 6-3 1? Deployment mechanism
At the same time, the multi-axis unwinding mechanism is used to unwind materials on multiple reels simultaneously. Such as laminators and sizing machines. In order to control the tension of all unwinding equipment, it is necessary to control the torque of each brake and keep it consistent.
The forward unwinding mechanism and the reverse driving unwinding mechanism are unwinding mechanisms with motors. The active unwinding mechanism is used when the drum is heavy or the automatic feeding device is used, and it is desired to control the rotation speed of the standby drum to be consistent with the unwinding speed of the drum in use. They need to unwind actively to correct the mechanical loss and realize inertia compensation.
The reverse drive unwinding mechanism is used in situations where materials need to be wound and unwound reversibly, and situations where low-speed reverse drive is needed to prevent the materials from loosening when the drum stops.
④ Basic structure of winding. The winding structure is divided into small capacity winding mechanism, medium capacity winding mechanism, direct motor winding mechanism, direct roller winding mechanism, multi-axis simultaneous winding mechanism, multi-axis selective winding mechanism and so on. Table 6-9 shows the structure and characteristics of the winding mechanism.
Table 6-9? Structure and characteristics of winding mechanism
What are the structural characteristics of type mechanism?
Small capacity winding mechanism
① The clutch and brake are large. Product of heat with its sliding speed and transmitted torque
worthy
② For pay-off braking, the larger the winding diameter, the greater the torque and the smaller the sliding speed.
So the heat production is basically unchanged.
③ For the clutch, the larger the winding diameter, the greater the torque and the greater the sliding speed. Therefore,
The worse the fever. For this reason, a larger model of motor is needed.
④ Unwinding power =0. 0 167 fv。 Where f is tension, n; V is the linear velocity,
Meter/minute
Motor direct winding mechanism
(1) Use the rotating shaft of DC motor and servo motor for direct winding.
② According to the drum ratio (maximum diameter/minimum diameter), the motor model is larger.
change
(3) Because the output torque of the motor is less than that of the clutch, in order to ensure
When winding torque is needed, a reducer is usually set.
④ When the speed ratio of the reducer is large, the reduction of the efficiency of the reducer will lead to tension.
Large fluctuations are not conducive to controlling tension through torque control.
⑤ This winding control method is suitable for winding with low relative tension and high speed.
Process?
Medium-capacity collection
Winding mechanism
① Tension control device with sliding speed control function should be adopted to control winding.
The motor speed keeps the sliding speed of the winding clutch approximately the same.
② The slip power of the clutch can be reduced.
③ With the change of drum ratio, the motor model changes greatly.
Press roller direct winding mechanism?
(1) Press the circumference of the winding reel on the bottom roller with a press roller.
② The clutch is used to control the drive shaft on the lower roller to obtain constant tension.
③ The model of driving motor does not change with the change of drum ratio.
④ The sliding speed does not change with the winding diameter, so the sliding loss of the clutch is small?
Multi-axis synchronous winding mechanism
① Use winding motor to drive winding.
② Clutch should be installed on each drum.
③ Suitable for slitter (film cutting and tape making) and slitter (multilayer film).
Winding after separation)?
Multi-axis selective winding mechanism
Figure 6-32 shows a multi-axis selective winding mechanism.
① It can be divided into two types: clutch and brake are installed on swing arm mechanism and fixed frame.
(2) In order to ensure the same circumferential speed, pre-drive the winding.
⑤ Other controls. According to the different conveyed materials, when multiple driven rollers need to be driven, the tension at the front end is large due to the mechanical loss of driven rollers. Therefore, each driven roller should be controlled according to the expansion and contraction of the material. For example, the rear roller drive is gradually higher than the front roller for fine-tuning transmission; The driven roller is driven by servo motor, and various transmission ratios are set, so that the driving of the rear motor is gradually improved compared with that of the front motor. The elongation of different transmission materials is different, generally 0. 1% ~ 5%. This control of increasing the driving force of the back roller in turn is called stretching control.
Figure 6-32? Multi-axis selective winding mechanism
When the actual tension of the material is required to be less than the tension caused by the acceleration and deceleration of the drum and the tension caused by the mechanical loss between the drum and the driven roller, the elastic adjusting roller mechanism should be used for control. It controls the speed of each motor according to the constant position of the elastic roller. The tension of the material is half of the mass of the elastic adjusting roller.
⑥ Actuator of tension controller.
A. magnetic powder clutch and brake. The commonly used actuators of tension controller are magnetic powder clutch and brake. The working principle of magnetic powder clutch and brake is similar to that of magnetic powder dynamometer. Magnetic powder is filled between the driving body and the driven body, the magnetic powder is magnetized after the excitation coil is energized, and the torque of the driving body is transmitted to the driven body to be used as a clutch. If the driven body is fixed, the torque of the transmission body is consumed and can be used as a brake. Magnetic powder clutch and brake have the following characteristics.
A, excitation current is roughly proportional to the transmitted torque, as shown in figure 6-33.
Two. The transmission torque can be controlled within 3% ~ 100% of the rated torque. The torque at idle speed is lower than 1%.
Roman numeral 3 .. Small magnetic powder clutches and brakes can transmit very large torque.
Four. Compared with motor armature control mode, the excitation current of magnetic powder clutch and brake is small, which can make the device miniaturized and reduce the cost. Running under the specified sliding power, the service life of magnetic powder is about 5000 ~ 8000 h, and it can slide continuously.
The rated torque of V magnetic powder clutch and brake can be selected in the range of 0.5 ~ 4000 N m..
According to its structure, intransitive verbs can be divided into two types: overhanging axis and hollow axis. According to its cooling methods, it can be divided into fan cooling type, forced air cooling type, water cooling type and heat dissipation block type.
Roman numeral 7 .. Its transmission torque does not change with the output speed and taxi speed, but can remain unchanged.
Figure 6-33? Magnetic particle clutch and brake characteristics
Figure 6-34? Hysteresis clutch and brake characteristics
B. hysteresis clutch and brake. For small applications, hysteresis clutches and brakes can also be selected, and their characteristics are as follows.
A, excitation current is roughly proportional to the transmitted torque, as shown in figure 6-34.
Two. The rated torque range is small, from 0.003 to10n m. ..
Roman numeral 3 .. Its structure is similar to magnetic powder clutch and brake. But there are no parts to be replaced.
Four. Hysteresis clutch consists of a first rotor integrated inside and outside, and generates torque transmission with a cylindrical second rotor (unmagnetized permanent magnet). When the first rotor and the excitation coil are fixed together, a hysteresis brake is formed.
V its transmission torque does not change with the output speed and sliding speed, and can basically remain unchanged.
The intransitive verb can run continuously under the specified sliding power without mechanical wear.
Roman numeral 7 .. Compared with the motor, the control power is small and the control device can be miniaturized.
⑦ Servo motor, vector frequency converter/motor. Matters needing attention in the selection and setting of servo motor and vector inverter/motor are as follows.
A. Set the servo motor and vector inverter/motor to torque control mode so that the output torque is proportional to the input signal. When the input signal is proportional to the winding diameter, constant tension control can be obtained.
B the rated output power of the motor is related to the rated speed and the output power of continuous operation. During winding and unwinding, the torque will increase with the increase of winding diameter. At the maximum winding diameter, the output torque should also be maximum. Therefore, when the winding diameter ratio becomes larger, a large-capacity motor is needed. But if the output power is constant, sometimes it is necessary to reduce the motor capacity.
C in tension control, the torque of the motor should be selected according to the torque during continuous operation. The maximum torque should not be selected in a short time.
D. Compared with AC servo motor, the torque control range of vector inverter/motor is smaller, which is not suitable for the application of large torque ratio (winding diameter ratio * maximum tension/minimum tension).
E for high-speed applications, AC servo motors should not be selected. Compared with magnetic powder clutch and brake, the output torque of AC servo motor is very small. When it is used to drive a reel, a reducer is needed. The reduction rate should not be too large, otherwise the tension control cannot be carried out correctly.
Figure 6-35 shows the relationship between output torque and speed of AC servo motor and vector inverter/motor.
The above motor is the same as hysteresis clutch and brake, without mechanical wear and maintenance.
The unwinding mechanism with motor can be used for braking and driving, so the structure can be simplified. However, it is difficult to use on the reducer with large speed change, and it is only suitable for low torque unwinding. It can cooperate with magnetic powder clutch and fixed slip control for large torque winding.
Figure 6-35? Relationship between output torque and speed of different motors
Figure 6-36? Output torque characteristics of torque motor
F. Torque motor is a specially designed AC box motor, which has the drooping characteristic that the output torque decreases with the increase of torque, as shown in Figure 6-36. For applications with relatively small winding diameter, constant speed winding operation can be realized. The winding can also be realized by using a sliding simple voltage tuner.