Ball mill frequency conversion control device controlled by PLC (Programmable Logic Controller)

Abstract

The invention relates to a PLC-controlled frequency conversion control device for a ball mill, which realizes the automatic operation of the ball mill through the cooperative work of a programmable controller, a frequency converter and a peripheral circuit. The core of the method is that a PLC executes a preset program, and a motor is controlled to complete a complete cycle of power-on, time delay, forward soft start and operation, stop, time delay, reverse soft start and operation, stop and power-off in sequence. In a key circuit, output points Y02 and Y03 of the PLC are connected with a forward rotation control terminal and a reverse rotation control terminal of the frequency converter respectively, smooth starting and stopping of the motor are achieved by setting acceleration time (300 seconds) and deceleration time (10 seconds) of the frequency converter, and mechanical and current impact is effectively reduced. The forward and reverse rotation time is flexibly set through a PLC parameter interface, grinding medium segregation is eliminated through automatic alternate operation, and the grinding uniformity and the product quality are improved. Double safety protection of program normal stop and hard wire sudden stop is integrated, and safety, high efficiency and automation of ball mill control are achieved.

Description

Technical Field

[0001] This invention relates to the field of industrial grinding equipment control technology, and in particular to a PLC-controlled ball mill frequency conversion control device. Background Technology

[0002] Ball mills are key equipment used for crushing and grinding materials in industries such as metallurgy, mining, building materials, and chemicals. They are driven by a motor to rotate a cylinder loaded with grinding media, utilizing the impact and grinding action of the media to achieve the desired particle size.

[0003] Traditional ball mill drive and control methods have the following limitations:

[0004] Significant Start-up and Shutdown Impacts: Most traditional ball mills use direct start-up or simple star-delta start-up methods. The instantaneous starting current is very large, reaching 5-7 times the rated current, causing a significant impact on the power grid. At the same time, the large starting torque generates mechanical shocks to the mechanical transmission system (such as couplings, gears, and bearings), easily leading to component fatigue damage and generating a lot of noise. When stopping, if the power is directly cut off, due to the great inertia of the cylinder and the internal grinding media, the sudden stop will generate a large inertial impact force. Long-term operation can easily lead to serious failures such as liner cracking, drive shaft deformation, or even breakage.

[0005] Limited Operation Modes and Grinding Efficiency: Under traditional control methods, ball mills typically operate continuously in one direction. This causes the grinding media (such as steel balls) inside the mill to tend to accumulate on one side under the influence of centrifugal force and gravity, resulting in a "segregation" phenomenon. This leads to uneven material distribution across the cross-section of the mill, with some areas being over-ground and others under-ground, resulting in uneven particle size, difficulty in controlling product quality, and low overall grinding efficiency.

[0006] Low level of automation and inconvenient process adjustment: The control of running time mostly relies on manual operation by operators or simple time-delay relays, making it difficult to achieve precise timing and forward / reverse switching. When the material type, filling amount, or target particle size changes, process parameters such as the running time of forward and reverse rotation need to be readjusted. Traditional systems lack flexible and convenient parameter modification interfaces, making the adjustment process cumbersome and difficult to ensure product process consistency.

[0007] Inadequate protection functions: Although equipped with basic circuit breakers and thermal relays, the system lacks integrated safety logic control for the entire system's procedural emergency shutdown and automatic recovery after soft faults, and the system's reliability and safety need to be improved.

[0008] Therefore, developing a ball mill control device that can achieve smooth start-up and shutdown, automatic forward and reverse operation, flexible adjustment of process parameters, and comprehensive protection functions is of great significance for improving equipment life, ensuring product quality, and reducing energy consumption and maintenance costs. Summary of the Invention

[0009] To solve the above technical problems, the present invention provides a PLC-controlled ball mill frequency conversion control device, including a main circuit and a control circuit. The main circuit includes a main circuit breaker QF1, the main contacts of a contactor KM1 and the power input terminal of a frequency converter connected in sequence. The output terminal of the frequency converter is connected to a motor M1 that drives the ball mill.

[0010] The control circuit includes a programmable logic controller (PLC), a start button SB1, a stop button SB2, an emergency stop button SB3, a power indicator light HL1, and a motor running indicator light HL2.

[0011] The input terminals X00 and X01 of the programmable logic controller (PLC) are connected to the start button SB1 and the stop button SB2, respectively; its output terminal Y00 is connected to the coil of the contactor KM1 to control its on / off state; the output terminal Y01 is connected to the motor running indicator light HL2; and the output terminals Y02 and Y03 are connected to the forward control terminal S1 and the reverse control terminal S2 of the frequency converter, respectively.

[0012] The programmable logic controller (PLC) is configured to execute the following automatic control process:

[0013] In response to the start signal of X00, output Y00 closes, controlling the contactor KM1 to engage and energizing the main circuit;

[0014] After a first preset time delay, outputs Y01 and Y02 close, the motor operation indicator HL2 lights up, the frequency converter drives the motor M1 to start in the forward soft start and begins forward rotation timing;

[0015] When the forward rotation timer reaches the set forward rotation time, disconnect Y01 and Y02, motor M1 stops rotating forward, and indicator light HL2 goes out;

[0016] After a second preset time delay, outputs Y01 and Y03 close, the motor operation indicator HL2 lights up, the frequency converter drives the motor M1 to run in reverse soft start and starts the reverse timing;

[0017] When the reverse timing reaches the set reverse time, disconnect Y01 and Y03, motor M1 stops reversing, and indicator light HL2 goes out;

[0018] After a third preset time delay, Y00 is disconnected, causing contactor KM1 to release and cutting off the main power supply to the frequency converter.

[0019] In one embodiment of the present invention, the control circuit further includes an isolated DC regulated power supply for powering the programmable controller (PLC). The circuit includes circuit breakers QF2 and QF3 to convert the external AC power supply into the 24V DC voltage required by the PLC.

[0020] In one embodiment of the present invention, the emergency stop button SB3 is connected in series on the +24V terminal of the power supply circuit of the programmable controller PLC. When it is triggered and self-locked, it directly cuts off the working power supply of the PLC, thereby causing the PLC to lose power and the contactor KM1 to release power, thus realizing emergency stop.

[0021] In one embodiment of the present invention, the power indicator HL1 is connected in parallel to the output terminal of the DC regulated power supply to indicate the power-on status of the device.

[0022] In one embodiment of the present invention, the acceleration time parameter C1-01 of the frequency converter is set to 300.0 seconds and the deceleration time parameter C1-02 is set to 10.0 seconds to achieve smooth start and stop of motor M1 and reduce mechanical and current shocks.

[0023] In one embodiment of the present invention, the forward rotation time and reverse rotation time of the motor are variables stored in the user parameters of the programmable controller (PLC) and can be modified and set via an LCD display and buttons.

[0024] In one embodiment of the present invention, the programmable controller (PLC) is further configured to: in response to the X01 signal triggered by the stop button SB2 at any stage of the operation, immediately disconnect the output terminals Y01, Y02, and Y03, causing the motor to stop and the indicator light HL2 to turn off, and disconnect the output terminal Y00 after a fourth preset time delay, causing the contactor KM1 to release.

[0025] Compared with the prior art, the above-mentioned technical solution of the present invention has the following advantages: The ball mill frequency conversion control device of the present invention, through the long acceleration time (300 seconds) of the frequency converter for soft start, greatly reduces the starting current and the impact on the mechanical transmission components. Through the deceleration time (10 seconds) for soft stop, a large amount of inertial kinetic energy of the ball mill is smoothly released, protecting the mechanical transmission mechanism. Moreover, the automatic timed forward and reverse operation breaks the segregation phenomenon of the grinding media, making the material grinding more uniform and significantly improving the consistency of product particle size; it also has dual protection of normal programmed stop and high-voltage emergency stop. Attached Figure Description

[0026] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0027] Figure 1This is a circuit diagram of the PLC-controlled ball mill frequency conversion control device of the present invention. Detailed Implementation

[0028] This embodiment provides a PLC-controlled ball mill frequency converter control device, which combines the program logic of the programmable logic controller (PLC) with the precise drive of the frequency converter to achieve automatic, stable, and efficient operation of the ball mill. The system mainly consists of the following parts:

[0029] Main circuit: The high-voltage circuit that provides power to the motor mainly includes circuit breaker QF1, the main contacts of contactor KM1 and frequency converter, which ultimately drives the ball mill motor M1.

[0030] Control loop: The low-voltage circuit that realizes the system logic control and operation. The core is the UBODA series PLC, and it includes start, stop, emergency stop buttons and status indicator lights.

[0031] Human-machine interaction and parameter setting: Key process parameters such as motor forward and reverse rotation time can be set through the PLC's user parameter interface.

[0032] like Figure 1 As shown, the specific connection relationship of the ball mill frequency converter control device system is as follows:

[0033] Main circuit connection: The three-phase 380V AC power supply is connected to the main contacts of contactor KM1 after passing through the main circuit breaker QF1. The output terminals of the KM1 main contacts are connected to the power input terminals (L1, L2, L3) of the frequency converter. The output terminals (U, V, W) of the frequency converter are directly connected to the ball mill motor M1.

[0034] Control circuit power supply: The control power is provided by independent circuit breakers QF2 and QF3, which convert the 220V AC power to the 24V DC power required by the PLC.

[0035] PLC input circuit:

[0036] The start button SB1 is connected to the PLC's 24V+ power supply at one end and to input point X00 at the other end. The stop button SB2 is connected to the PLC's 24V+ power supply at one end and to input point X01 at the other end. The emergency stop button SB3 (normally closed contact) is connected in series in the PLC's +24V power supply circuit to achieve high-voltage safety protection.

[0037] PLC output circuit:

[0038] Output point Y00 connects to the coil of contactor KM1 to control the on / off state of the main circuit. Output point Y01 connects to the motor running indicator light HL2. Output point Y02 connects to the forward control terminal S1 of the frequency converter. Output point Y03 connects to the reverse control terminal S2 of the frequency converter.

[0039] Indicator circuit: The power indicator light HL1 is connected in parallel across the DC regulated power supply. When the equipment is powered, it indicates that the main circuit is powered.

[0040] Specifically, the ball mill frequency converter control device described in this embodiment has its control core implemented by a PLC program, and its workflow is as follows: Power-on standby: Close circuit breakers QF1, QF2, and QF3. Power indicator HL1 lights up, the PLC is powered on and initialized, and the system enters standby mode.

[0041] Start-up and soft start: Press the start button SB1, and the PLC inputs the X00 signal. The PLC program responds, immediately sets the output Y00, the contactor KM1 engages, and the inverter's main circuit is energized.

[0042] 5-second delay: PLC internal timing, this short delay ensures that the frequency converter initialization is complete.

[0043] Forward rotation: After 5 seconds, the PLC sets outputs Y01 and Y02. Y01 illuminates the motor operation indicator HL2; Y02 sends a forward rotation command to the inverter's S1 terminal. The inverter begins a soft start according to the preset acceleration time C1-01 (300.0 seconds), and motor M1 smoothly accelerates to its rated speed. Simultaneously, the PLC's internal forward rotation timer U00 begins timing.

[0044] Forward rotation stop and interval: When the value of timer U00 reaches the user-set forward rotation time U_Dat00, the PLC resets and outputs Y01 and Y02. The motor running indicator HL2 goes out, the frequency converter stops outputting, and the motor M1 starts to smoothly stop according to the preset deceleration time C1-02 (10.0 seconds).

[0045] 10-second delay: After stopping, the PLC delays for 10 seconds to allow the movement of materials and grinding media inside the cylinder to come to a complete stop.

[0046] Reverse Operation and Stop: After a 10-second interval, the PLC sets output Y01 again and simultaneously sets Y03 (reverse). HL2 lights up again, and the inverter receives the reverse command via the S2 terminal, soft-starting to rated speed with a 300-second acceleration time. The internal reverse timer U01 starts counting. After reaching the user-set reverse time U_Dat01, the PLC resets Y01 and Y03, and the motor smoothly stops again with a 10-second delay.

[0047] Cycle completion and system power failure: After completing one forward and reverse cycle, the PLC delays for 10 seconds, then resets Y00, contactor KM1 releases, and the main power supply to the frequency converter is completely cut off. If the process requires multiple consecutive cycles, a cycle counting logic can be set in the program.

[0048] Normal Stop: At any stage of operation, pressing the stop button SB2 (X01) will immediately reset all motor control outputs (Y01, Y02, Y03) of the PLC, causing the motor to stop smoothly. After a 3-second delay, Y00 will be reset, and KM1 will be disconnected.

[0049] Emergency Stop: In case of emergency, pressing the emergency stop button SB3 directly cuts off the power supply to the PLC, causing the PLC to lose power instantly. All PLC outputs immediately become disabled, Y00 disconnects, releasing KM1, and the frequency converter immediately stops outputting due to the power failure in the main circuit, achieving the highest level of emergency stop safety.

[0050] In order to achieve the best process results, the following key parameters need to be set:

[0051] PLC user parameters (modified via LCD display or programming software):

[0052] Motor forward rotation time U_Dat00: can be set according to material characteristics, for example, 1800 seconds (30 minutes).

[0053] Motor reverse rotation time U_Dat01: can be set to be the same as or different from the forward rotation time, for example, 1800 seconds (30 minutes).

[0054] Inverter parameters (set via inverter panel):

[0055] b1-02 (Run Command Selection) = 1 (Control Circuit Terminal)

[0056] C1-01 (Acceleration Time 1) = 300.0s (Achieves slow start-up, avoiding mechanical shock and high current surge)

[0057] C1-02 (Deceleration Time 2) = 10.0s (Achieves smooth deceleration, releases significant inertia, and protects mechanical components)

[0058] H1-01 (Terminal S1 function) = 40 (Forward rotation)

[0059] H1-02 (Terminal S2 function) = 41 (Reverse operation)

[0060] This embodiment, through the specific implementation method combining the above-described hardware and software, achieves the following beneficial effects:

[0061] Effectively reduces impact: The long acceleration time (300 seconds) of the frequency converter for soft start greatly reduces the starting current and the impact on mechanical transmission components, as well as the problem of uneven distribution of materials and grinding balls. The deceleration time (10 seconds) for soft stop smoothly releases a large amount of inertial kinetic energy of the ball mill, protecting the mechanical transmission mechanism.

[0062] Improved grinding quality: Automatic timed forward and reverse operation breaks the segregation phenomenon of grinding media, making the material grinding more uniform and significantly improving the consistency of product particle size.

[0063] High degree of automation and flexibility: The entire work cycle is completed automatically without manual intervention. Key process parameters such as forward and reverse rotation time can be flexibly modified through the PLC interface to adapt to different materials and production requirements.

[0064] Safe and reliable: Equipped with dual protection of normal programmed shutdown and emergency power stop, ensuring the safety of equipment and personnel.

[0065] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A PLC-controlled ball mill frequency converter control device, comprising a main circuit and a control circuit, characterized in that: The main circuit includes a main circuit breaker QF1, the main contacts of a contactor KM1 and the power input terminal of a frequency converter connected in sequence, and the output terminal of the frequency converter is connected to a motor M1 that drives the ball mill. The control circuit includes a programmable logic controller (PLC), a start button SB1, a stop button SB2, an emergency stop button SB3, a power indicator light HL1, and a motor running indicator light HL2. The input terminals X00 and X01 of the programmable logic controller (PLC) are connected to the start button SB1 and the stop button SB2, respectively; its output terminal Y00 is connected to the coil of the contactor KM1 to control its on / off state; the output terminal Y01 is connected to the motor running indicator light HL2; and the output terminals Y02 and Y03 are connected to the forward control terminal S1 and the reverse control terminal S2 of the frequency converter, respectively. The programmable logic controller (PLC) is configured to execute the following automatic control process: In response to the start signal of X00, output Y00 closes, controlling the contactor KM1 to engage and energizing the main circuit; After a first preset time delay, outputs Y01 and Y02 close, the motor operation indicator HL2 lights up, the frequency converter drives the motor M1 to start in the forward soft start and begins forward rotation timing; When the forward rotation timer reaches the set forward rotation time, disconnect Y01 and Y02, motor M1 stops rotating forward, and indicator light HL2 goes out; After a second preset time delay, outputs Y01 and Y03 close, the motor operation indicator HL2 lights up, the frequency converter drives the motor M1 to run in reverse soft start and starts the reverse timing; When the reverse timing reaches the set reverse time, disconnect Y01 and Y03, motor M1 stops reversing, and indicator light HL2 goes out; After a third preset time delay, Y00 is disconnected, causing contactor KM1 to release and cutting off the main power supply to the frequency converter.

2. The ball mill frequency conversion control device according to claim 1, characterized in that: The control circuit also includes an isolated DC regulated power supply for powering the programmable controller (PLC), and the circuit includes circuit breakers QF2 and QF3.

3. The ball mill frequency conversion control device according to claim 1, characterized in that: The emergency stop button SB3 is connected in series with the +24V terminal in the power supply circuit of the programmable controller (PLC). When it is triggered and self-locked, it directly cuts off the PLC's operating power, thereby causing the PLC to lose power and the contactor KM1 to de-energize and release.

4. The ball mill frequency conversion control device according to claim 1, characterized in that: The power indicator light HL1 is connected in parallel to the output terminal of the DC regulated power supply. After the device is powered on and all circuit breakers are closed, the power indicator light HL1 will light up.

5. The ball mill frequency conversion control device according to claim 1, characterized in that: The acceleration time parameter C1-01 of the frequency converter is set to 300.0 seconds, and the deceleration time parameter C1-02 is set to 10.0 seconds.

6. The ball mill frequency conversion control device according to claim 1, characterized in that: The forward and reverse rotation times of the motor are variables stored in the user parameters of the programmable logic controller (PLC).

7. The ball mill frequency conversion control device according to claim 1, characterized in that: The programmable controller (PLC) is also configured to: respond to the X01 signal triggered by the stop button SB2 at any stage of the operation, immediately disconnect the output terminals Y01, Y02, and Y03, stop the motor and turn off the operation indicator HL2, and disconnect the output terminal Y00 after a fourth preset time delay, so that the contactor KM1 is released and the inverter input power is cut off.

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