The winding control of suspended high-vacuum roll-to-roll coating machines requires high-precision torque control. Previously, DC drives were generally used, but with the rapid development of AC drive technology, AC permanent magnet synchronous servo motors or AC asynchronous motors are now increasingly being adopted. The Danfoss FC302 series driver offers servo-level drive performance and achieves smooth torque control when driving AC asynchronous motors, providing an easy-to-use solution for the industry. Users only need to set a few simple parameters to meet actual production needs, and operation and debugging are also very simple.
I. Transmission Structure of a Suspended High Vacuum Roll-up Coating Machine:
Unwinding direction is positive.
Unwinding direction is negative.
A typical transmission structure for a 3-drive suspended high vacuum roll-up coating machine includes:
M1 is the cooling roller, with a constant diameter, driven by one FC302 motor. The speed of the cooling roller is the linear speed of the coating process.
M2 is the take-up roller, wound around the center with a gradually increasing diameter, driven by one FC302 motor, providing take-up tension.
M3 is the unwind roller, wound around the center with a gradually decreasing diameter, driven by one FC302 motor, providing unwind tension.
The directions of the cooling roller and take-up roller are fixed. However, the unwind roller, due to the different winding direction of the roll, has two directions of rotation during operation: positive and negative, corresponding to two different torques.
Features of the transmission system in a vacuum coating machine:
1. Due to the limited space within the vacuum chamber, tension detection devices cannot be installed. Therefore, the winding and unwinding tensions must be directly controlled by the motors driving the winding and unwinding. Consequently, both the winding and unwinding drives operate in torque mode. For lighter and thinner materials, the winding process must also include a tension taper function.
2. Due to process limitations, the cooling roller, which plays a primary driving role, lacks a pressure roller. Therefore, the cooling roller relies solely on friction to move the film. When the winding and unwinding tensions differ significantly, the film can easily slip on the cooling roller. Preventing slippage is a significant challenge in drive control.
II. Control System Structure:
The take-up system uses a Danfoss FC302+MCO305 encoder. The MCO305 has two encoder interfaces: a master encoder and a slave encoder. The master encoder signal comes from the cooling roller motor encoder and is responsible for acquiring the linear speed signal. The slave encoder signal comes from the machine motor encoder, acquiring the machine speed and serving as the feedback source for flux vector control.
The unwinding configuration and control method are basically the same as the take-up system.
The cooling roller control is relatively simple, mainly responsible for constant linear speed control and meter counting.
The PLC handles general digital logic control; all calculations are completed within the motion controller MCO305.
Roll Diameter Calculation:
Based on the principle of constant linear speed:
The take-up and unwinding roll diameters can be calculated.
Tension Taper Control for Take-up:
With the current roll diameter and the tension taper setpoint, the current tension can be calculated. The relationship between tension and roll diameter is as follows: when the tension taper is 0, the tension remains constant, which is equivalent to constant tension control; when the tension taper is 100%, the tension decreases by half for every doubling of the roll diameter, which is equivalent to constant torque control.
The calculation formula is as follows:
Where: D is the current roll diameter
Dmin is the minimum roll diameter
Tap is the tension taper
Tref is the reference value of the tension taper when reducing the roll diameter
When Tap=0, Ttap=Tref
When Tap=1, Ttap=
Acceleration/deceleration torque and friction torque:
To achieve high-precision tension control, friction torque and acceleration/deceleration torque compensation must also be added to the program.
Acceleration torque Tβ=β×J
Where, β is the angular acceleration;
Moment of inertia J=
III. Conclusion:
On-site operation has proven that the Danfoss FC302 driver + MCO305 motion controller solution fully meets the winding control requirements of the vacuum coating machine. The acceleration and deceleration speeds of the entire machine exceed those of the original control method, significantly reducing material waste. Control system debugging and parameter setting are relatively convenient. What satisfies the customer most is that a relatively economical AC asynchronous motor can be used; an upgrade to an AC permanent magnet synchronous motor is only necessary in applications requiring higher tension control precision. Since the FC302 can drive both asynchronous and synchronous motors, system upgrades only require a simple motor replacement.
