1. Introduction Roving frames are suitable for carded and combed cotton fibers, chemical fibers under 60mm, and other blended fibers. They process the drawn sliver into rovings of different numbers and twists for spinning on ring spinning frames. According to the requirements of the spinning process, the roving frame drafts the cotton sliver through the rollers, then exits through the front roller, twists it, and then winds it onto bobbins according to the requirements of package formation. Since the yarn exit speed of the front roller is constant, while the winding speed decreases as the winding diameter increases, traditional roving frames use a mechanical conical gear speed change mechanism. The belt moves parallel to the upper and lower conical gears to change the winding and lifting speeds, thus completing the roving winding and forming process. Traditional roving frames are driven by a single AC asynchronous motor. To address quality issues such as yarn breakage or uneven yarn distribution caused by rapid motor acceleration during startup, a reactor is connected in series in the AC motor's main circuit to achieve soft starting. Furthermore, when different yarn types require different speeds, manual replacement of pulleys is used for speed changes. In the mid-1990s, newer suspended-spindle roving frames gradually replaced traditional roving frames, and frequency conversion speed control was widely adopted on these frames. However, due to the poor stability of conical gear transmission speeds and the difficulty of operation, unstable roving quality was easily caused. Therefore, many manufacturers introduced new roving frames with multiple motor drives, including roving frames with 2, 3, 4, and 7 motors, with roving frames using 4 motors being the most common. 2. Key Technical Features: Spindle speed: Maximum speed 1500 r/min～1800 r/min; Number of spindles: 132, 120, 108, etc.; Control parameters: Start-up and stop time control (start-up time 6 s～16 s, stop time 8 s～3 s); Roving tension control, i.e., constant tension winding. 3. Drive System: The high-speed suspended spindle roving frame eliminates the conical wheel (commonly known as the "iron cannon"), forming mechanism, differential mechanism, oscillating mechanism, and reversing mechanism found in traditional roving frames. It also eliminates the gears for twist, lifting, winding, tension, and forming angle adjustments. Instead, it uses four motors to drive the drafting roller (generating the draft ratio), the spindle (winding the roving onto the bobbin), the bobbin (generating twist in the roving), and the roving lifting mechanism (completing the winding shape). The rollers, spindle, bobbin, and roving lifting mechanism are driven by 4kW, 4kW, 5.5kW, and 0.55kW AC asynchronous motors respectively, with frequency conversion speed regulation. By using four electric motors for transmission, in addition to simplifying the mechanical structure and eliminating the gears in the aforementioned mechanism, noise is reduced, machine speed is increased, roving breakage is reduced, and single-machine output is increased (the main machine speed is increased by more than 30%), ensuring stable roving quality. At the same time, the process is simplified and made faster. 4. Control System Currently, there are two control schemes for roving frames with four electric motors. The first scheme uses a PLC or PCC with a touch screen, controlling the operation of the four frequency converters and motors via RS-485 communication or CAN BUS fieldbus. The second scheme uses a self-made dedicated controller with a microcontroller, controlling the operation of the four frequency converters and motors via RS-485 communication. This scheme is cheaper, but its reliability and versatility are not as good as the first scheme. This will not be discussed in detail here. Using a PLC programmable controller or PCC programmable computer controller with a touch screen and CAN BUS fieldbus to control the operating speed of the four frequency converters and corresponding motors, such as the EJK211 roving frame, the entire machine control uses a PCC with a touch screen and CAN BUS bus control system. The system principle block diagram is shown in Figure 1. [align=center]Figure 1 Block Diagram of the Roving Frame Control System[/align] In this system, the PCC or PLC acts as the host computer, connected to the CAN bus via a CAN communication adapter card. All components on the CAN bus (inverters, etc.) must have a standard CAN communication interface. The four inverters use a common DC bus power supply. This can be achieved by connecting the DC power supplies of the four general-purpose inverters in parallel or by supplying the DC power of one inverter to the other three. All four motors are equipped with encoders to achieve closed-loop speed control, ensuring high-precision speed regulation. The PCC programmable computer controller controls the four inverters and motors via the CAN BUS fieldbus, using multiple mathematical models or based on measured roving tension. The four inverters and motors operate according to the required process parameters. For example, the spindle winding speed decreases as the winding diameter increases, ensuring constant tension winding. The operating speeds of the four motors driving the drafting rollers, spindles, bobbins, and roving ties should maintain a certain proportional relationship according to process requirements. If the draft ratio or roving twist needs to be changed, the roving speed and bobbin speed should also be changed accordingly. The frequencies and speeds of the four frequency converters and motors are set on the touch screen according to process requirements, input to the PCC via RS-485 communication, and then controlled by the frequency converters and motors via the CAN BUS bus. The touch screen is used for setting, modifying, recalling, storing, and displaying process parameters. The process parameters that can be set, modified, recalled, and stored include the maximum speed, roving count, twist, draft ratio, radial winding density, axial winding density, winding coefficient, spinning coefficient, etc. In addition to displaying the above process parameters, it also displays the hourly output per spindle, the cumulative length of yarn spun in one doff, the cumulative output per shift, the output frequency, current, voltage of each frequency converter, and fault alarms. 4.1 Variable frequency speed control multi-motor roving frames with common DC bus power supply adopt a common DC bus power supply method, which mainly has two types. (1) The DC circuits of the four frequency converters are connected in parallel. This common DC bus power supply method is shown in Figure 2. The DC side circuits of the four frequency converters are connected in parallel. During the start-up, speed-up, speed-down, and stop processes, if M1 and M4 are in motor operation and M2 and M3 are in generator operation, their regenerative energy is sufficient to be consumed in the motor operation of M1 and M4. Therefore, the voltage of the DC bus will not rise, and the speed ratio of each motor can remain stable. (2) The DC power supply of one frequency converter supplies power to the other three inverters. This common DC bus power supply method is shown in Figure 3. The rectifier bridge capacity of the main frequency converter needs to be appropriately increased to meet the DC power requirements of the other three inverters. The working principle of these two common DC bus power supply methods is not fundamentally different. The only difference is that the rectifier power supply is built into the main frequency converter in the second method, and the other three frequency converters are replaced with inverters. This simplifies the circuit and reduces the cost. The variable frequency speed regulation of the roving frame using common DC bus power supply has achieved good results. For example, it improves the synchronous and coordinated operation of the drafting roller, spindle, bobbin and duct lifting drive motor during speed increase, speed decrease, start and stop. For example, when the whole machine loses power, it can keep the roving from breaking. 4.2 CAN bus The CAN bus is designed specifically for transmitting short, real-time control information and is suitable for small-scale distributed real-time systems. For example, the automobile industry was the first to adopt the CAN bus. Now it is widely used in various mechanical equipment (including textile machinery) and building automation. CAN is a controller area network, a bus-type serial communication network. Its main features are: (1) It works in multiple ways. Any node on the network can actively send information to other nodes on the network at any time without occupying node information such as address. Therefore, it can be convenient to form a multi-machine backup system and can also receive information on the bus. (2) The direct communication distance of CAN can reach up to 10km (corresponding to a rate of less than 5kbps) and the communication rate can reach up to 1Mbps (corresponding to a transmission distance of 40m). (3) Node information on the CAN network is divided into different priorities to meet different real-time requirements. When two or more nodes send information to the bus at the same time, the node with lower priority actively withdraws from sending, while the node with the highest priority can continue to transmit data without being affected. (4) The communication medium of CAN can be twisted pair, coaxial cable or optical fiber, which is more flexible. (5) CAN uses short frame transmission, with 8 effective bytes per frame. The transmission time is short and the probability of interference is low. When a node fails, it can automatically shut down. It has strong anti-interference ability and high reliability. 5 Conclusion The roving frame is one of the main machines in cotton spinning equipment. In the past two years, the annual output of roving frames has reached more than 4,000 units, and more than 5,000 units are equipped with frequency converters. At present, single motor drive roving frames still account for a large proportion of sales, mainly because the price is lower. However, multi-motor drive roving frames have been increasing year by year, which is believed to be the development trend of roving frames.