I .Overview

In the paper printing production, there are processes related to winding operations such as unwinding and rewinding, the paper tension changes dynamically. If the tension is too small, the paper will become loose and wrinkled, and it will also deviate horizontally, resulting in uneven edges of the paper roll. If the tension is too large, it will cause the paper to be over-stretched, and raised ribs will appear on the surface of the paper. In severe cases, the paper may even be deformed and broken. In order to ensure the production efficiency, the surface quality of the paper and the neatness of the edges of the paper roll, it is very necessary to maintain a constant tension. This system ensures a constant tension on the paper by controlling the speeds of the paper feeding roller and the rewinding roller, which belongs to the synchronous control of speeds.

II. Solution

1. System

The system is composed of one paper feeding frequency inverter (Yolico YD33P7 T4 BN), one rewinding frequency inverter (Yolico YD37P5 T4 BN), one 2.2kW paper feeding motor, one 3.7kW rewinding motor, one potentiometer for the position identification of the floating roller, two encoders, one Yolico PG-B card, an input-output filter (optional), one Emerson EC10 PLC, one 2-channel analog input module and one 2-channel analog output module.

The main mechanical parts include the paper feeding roller, the floating roller, the length measuring roller, the floating roller cylinder and the rewinding roller.

2. System Description and Block Diagram

The system ensures the tension on the paper remains constant by controlling the linear speeds to be the same of the paper feeding roller and the paper winding drum. The tension’s magnitude is determined by the pressure of the cylinder on the floating roller (since the swinging amplitude of the floating roller is not large, changing the pressure of the cylinder can change the tension on the paper). During the winding operation, as the diameter of the paper winding drum is constantly changing, in order to control the winding linear speed to be consistent with the paper feeding linear speed, the diameter of the paper winding drum must be calculated in real-time during the winding process.

Yolico YD53P7 frequency inverter is used to control the paper feeding motor to regulate the running speed of the paper. It operates in an open-loop vector control mode, and the frequency command is given by one of the analog output (AO) ports of the PLC. This signal is controlled by the speed-up/speed-down buttons connected to the digital input ports of the PLC (when the speed-up button is pressed, the speed rises slowly and steadily; when the speed-down button is pressed, the speed drops slowly and steadily). The speed of the winding motor is controlled by a Yolico YD37P5 T4 BN frequency inverter, which operates in a closed-loop vector control mode. The frequency command is also given by one of the AO ports of the PLC. This frequency command is related to the frequency command of the paper feeding frequency inverter, the diameter ratio between the paper feeding roller and the winding roller, the mechanical transmission ratio, and the position quantity detected by the potentiometer of the floating roller. The commands of the two AO ports are given simultaneously after calculation. The winding encoder is used to detect the number of revolutions of the winding roller within a unit time and for the vector control of the winding motor. The length measuring encoder is used to detect the length of the paper fed within a unit time. The analog quantity output by the potentiometer for detecting the floating roller is sent to the analog input (AI) port of the PLC, which is used to detect the stress condition of the paper and the position of the floating roller, and to make compensation for the speed of the winding roller.

3. Equipment Operation Process

Press the winding start button. The PLC controls the frequency inverter to start the winding motor at a very low speed, and slowly pulls the floating roller to the middle position. After reaching the position, use the zero servo function of the Yolico frequency inverter to lock the motor, so that the floating roller remains in the middle position. During this process, the length measuring roller also moves synchronously with the paper, and the diameter of the winding drum can be automatically obtained by combining the number of revolutions of the winding roller.

Press the paper feeding start button, press and hold the speed-up button. The paper starts to move. Release the speed-up button after reaching the required paper speed.

During the operation process, the paper speed can be freely changed by using the speed-up/speed-down button.

When the winding job is approaching completion, reduce the speed to 0 and press the total stop button to stop the equipment.

4. Calculation of the Frequency Command

1. Calculation formula for the roll diameter:

D = L / (π × N)

In the formula, D is the diameter of the winding drum, L is the length of the paper fed within a unit time, and N is the number of revolutions of the winding roller within a unit time.

L = n × c

In the formula, n is the number of revolutions of the length measuring roller within a unit time, which is obtained from the encoder of the length measuring roller, and c is the circumference of the length measuring roller.

Calculation of the Frequency Command:

The system controls to make the linear speed of the winding drum equal to the linear speed of the paper feeding, so V1 = V2. The relationship between the speed of the paper feeding roller and the speed of the winding roller is related to the diameters of the paper feeding roller and the winding drum.

Therefore:

F1 = f × (d / D) × i

In the formula, F1 is the basic speed of the winding roller motor, f is the speed of the paper feeding roller motor, which is determined by the speed-up/speed-down buttons. D is the diameter of the winding drum, d is the diameter of the paper feeding roller, and i is the reduction ratio.

Since there are other factors affecting the control accuracy, such as mechanical losses, the flexibility of the paper, the change in the inertia of the load during acceleration and deceleration, the characteristics of the actuators like the motor, etc., the detection of the floating roller is introduced. When the force on the paper changes, the floating roller swings correspondingly. The change amount is detected by the potentiometer, and the basic speed of the winding motor is corrected. The correction amount F2 is:

F2 = The deviation amount of the floating roller × F1 × X

The deviation amount of the floating roller is the difference between the middle position of the floating roller and the actual position amount. X is a coefficient, and the optimal value of this coefficient needs to be found during the debugging process.

In order to prevent the system from overshooting during adjustment, the correction amount F2 should be limited within 5% to 15% of F1.

The final given frequency F of the winding roller is:

F = F1 ± F2

5. PLC Control

PLC I/O:

X0 is the pulse input of the length measuring roller, X1 is the pulse input of the winding roller, X2 is the winding start, X3 is the paper feeding start, X4 is the total stop, X5 is the speed-up, and X6 is the speed-down.

Y3 is the start signal of the paper feeding roller, Y4 is the start signal of the winding roller, and Y5 is the zero servo signal of the winding roller motor.

CH1 of the 2AD module is the input for the floating roller detection.

CH1 of the 2DA module is the frequency for the paper feeding roller, and CH2 is the frequency for the winding roller.

Program Flow:

1. 1.Initialization; After powering on, constant information such as the diameters and circumferences of the rollers required for the operation, the mechanical reduction ratio of π, the number of lines of the encoder, and the middle position value of the floating roller are automatically written.
2. 2.Pulling up and hold the floating roller;
3. 3.Acceleration and deceleration; The vehicle speed is smoothly increased or decreased through two buttons.
4. 4.Pulse collection of the encoder; Use the high-speed counting instruction to collect the number of revolutions of each roller within a unit time.
5. 5.Real-time calculation of the roll diameter.
6. 6.Calculation of the frequency for the winding roller; Calculate the basic frequency of the winding roller and then superimpose it with the feedback compensation amount of the floating roller.
7. 7.Output the analog quantity frequency command.
8. 8.Parameters of the Frequency Inverter

1. Winding Frequency Inverter YD57P5:

A1-01=4
A1-02=PG Vector Control
B9-01=10; Zero servo gain, adjust as needed
C1-01=0; Acceleration/deceleration time controlled by PLC (set to 0 to synchronize motor responses)
C1-02=0
C2-01=0
C2-02=0
C2-03=0
C2-04=0
C6-01=2
E1-01=380
E1-04=80; Increased setting to synchronize with paper feed speed during small diameter (empty reel), related to reduction ratio and maximum system speed
E1-05=380
E1-06=50
E1-13=380
E2-01=8.8
E2-02=1.63
E2-03=3.56
E2-05=2.416
E2-07=0.36
E2-08=0.61
F1-01=612; Encoder line count (multiplied by reduction ratio due to encoder installation on winding drum)
F1-05=1
H1-01=72; Multi-function terminal zero servo function code
L3-04=0; Disable stall prevention during operation to avoid floating roller vibration

Note: These parameters optimize the frequency inverter for closed-loop vector control with zero servo locking, ensuring precise tension control and synchronization with the paper feed system. Adjustments account for mechanical characteristics and dynamic load changes during the winding process.

2. Frequency Inverter YD57P5:

A1-01=4

A1-02=Sensorless Vector Control

C1-01=0; Acceleration/deceleration time controlled by PLC (set to 0 to synchronize motor responses)

C1-02=0

C2-01=0

C2-02=0

C2-03=0

C2-04=0

C6-01=2

E1-01=380

E1-04=50

E1-05=380

E1-06=50

E1-08=25.1

E1-10=4.6

E2-01=5

E2-02=1.51

E2-03=2.25

E2-05=6.902

E2-07=0.36

E2-08=0.62

L3-04=0; Disable stall prevention during operation to avoid floating roller vibration

Note: These parameters configure the frequency inverter for sensor less vector control, allowing precise speed regulation without encoder feedback. The acceleration/deceleration times are set to 0 to enable PLC control, ensuring synchronous operation with the winding motor. The stall prevention function is disabled to maintain stability during tension adjustments, while motor-specific parameters (E1-E2 groups) are optimized for the connected load characteristics.

7. Conmissioning

1.Perform self-learning on the motor.

2.Let the motor run briefly to check if the read pulse count is correct.

3.After startup, gradually increase the frequency to pull up the floating roller. Adjust the zero servo position value and locking force (B9-01).

4.Adjust the acceleration/deceleration curve in the PLC. A too-steep curve may cause OC (Overcurrent) and OV (Overvoltage). If the load inertia is large and the curve is steep, install a braking resistor.

5.Adjust the angle of the floating roller potentiometer and the output 5V when the floating roller is in the middle position.

6. Run the system and observe the fluctuations of the floating roller during acceleration, deceleration, and constant-speed operation. Adjust the coefficient X and the upper/lower limits of the compensation amount in the formula.

7. Observe the entire winding start/stop process and adjust various parameters to optimize system performance.

III. Conclusion

The diameter of the winding roller can change by up to 8 times. During operation, the paper speed can be adjusted within the range of 180 m/min. During the start-up acceleration and stop deceleration in winding process, the swinging amplitude of the floating roller does not exceed ±5 cm. During the speed regulation and constant-speed operation processes, the swinging amplitude of the floating roller does not exceed ±1 cm.

The original system was controlled by a magnetic powder clutch. Its main disadvantages include the inability to achieve high paper speeds. During operation, the high-speed friction of the magnetic powder generate a high temperature, shortens the service life (affecting production efficiency, being vulnerable, and requiring frequent maintenance), as well as high energy consumption.

Therefore, it can be clearly seen that the existing equipment still maintains control characteristics no less than then pervious system (high-precision tension control requirements), and is more efficient, making the system have obvious production automation characteristics.