A PLC-based method for position accuracy control of an electric screw press

Abstract

This invention relates to a PLC-based method for controlling the position accuracy of an electric screw press. By providing real-time feedback on the return position of the slider, the PLC programmable controller calculates the current required speed value. As the slider gets closer to the target stop position, the speed value calculated by the PLC programmable controller decreases, ensuring that the motor stops rotating when the slider reaches the target position. This achieves a slider stop position accuracy of ±1mm, fundamentally solving the problem of inaccurate slider return position control in electric screw presses. This significantly improves the control accuracy of the slider position, thereby ensuring the accuracy of the press's impact energy and guaranteeing product quality.

Description

Technical Field

[0001] This invention relates to the field of electric screw press technology, and more specifically to a PLC-based method for controlling the position accuracy of an electric screw press. Background Technology

[0002] The working principle of an electric screw press is as follows: The forward and reverse rotation of the motor drives the flywheel and screw to rotate synchronously in both directions, thus enabling the slide block to strike the workpiece as it descends along the screw and return to the starting position. The return displacement of the slide block is the stroke that strikes the workpiece and is a crucial factor affecting the striking energy of the press. Therefore, the precision control of the return displacement has always been a primary concern for press manufacturers and users, affecting workpiece quality. This is especially true when manufacturing high-precision parts for aerospace and other applications, where the striking accuracy requirements of the press are extremely high.

[0003] Existing electric screw presses use a set motor speed to drive a slide block upwards and backwards at a predetermined speed. Simultaneously, real-time position detection ensures the motor stops when the slide block reaches its starting position, as commanded by the controller. However, this system suffers from several problems: the slide block often fails to stop precisely, resulting in a discrepancy between the actual return stop point and the target return position. This inaccurate positional control of the slide block significantly impacts the accuracy of the press's impact energy. Summary of the Invention

[0004] The purpose of this invention is to provide a PLC-based method for controlling the position accuracy of an electric screw press, which fundamentally solves the problem of inaccurate control of the slide return position of the electric screw press, greatly improves the control accuracy of the slide position, thereby ensuring the accuracy of the press's impact energy and guaranteeing product quality.

[0005] The technical solution of this invention is:

[0006] A PLC-based method for controlling the position accuracy of an electric screw press, the key technical points of which include the following steps:

[0007] Step 1: Pre-set the target values ​​for the forward rotation speed of the press motor, the initial reverse rotation speed, the slide return position, and the motor reverse rotation speed proportional coefficient.

[0008] Step 2: The motor starts and rotates forward at the target speed. After the slider moves down until it contacts and strikes the workpiece, the PLC programmable controller assigns the initial reverse speed target value to the motor.

[0009] Step 3: The motor reverses to drive the slider upwards. The displacement sensor collects the real-time position value of the slider, and the PLC programmable controller calculates the motor's reverse speed. The calculation formula is as follows:

[0010]

[0011] Step 4: The PLC programmable controller determines whether the calculated motor reverse speed is less than the target value of the initial reverse speed. If so, the PLC programmable controller assigns the calculated motor reverse speed to the motor. If the calculated motor reverse speed is greater than or equal to the target value of the initial reverse speed, the PLC programmable controller assigns the target value of the initial reverse speed to the motor.

[0012] Step 5: The PLC programmable controller determines whether the real-time position value of the slider is equal to the target value of the slider's return position. If so, the motor stops rotating and the slider stops moving. Otherwise, continue to execute steps 3 and 4.

[0013] The above-mentioned PLC-based electric screw press position accuracy control method sets the motor reverse speed proportional coefficient as follows: To ensure that the slider return stop position accuracy is between -1mm and 1mm, the motor reverse speed value at the last 20mm of the slider stroke is less than or equal to 50 rpm. Therefore, the motor reverse speed proportional coefficient is less than or equal to 150. Within this range, the larger the coefficient, the shorter the return time.

[0014] The beneficial effects of this invention are:

[0015] By employing a PLC programmable controller, a speed value is assigned to the motor's set reverse speed (driving speed of the slider's upward movement) based on conditions. This speed value includes the initial target speed of the motor's reverse movement and the calculated speed. Through real-time feedback on the slider's return position, the PLC programmable controller calculates the current speed value to be assigned. As the slider approaches the target stop position, the speed value calculated by the PLC programmable controller decreases, ensuring that the motor stops rotating when the slider reaches the target position. The stop position accuracy can reach ±1mm, fundamentally solving the problem of inaccurate control of the slider's return position in electric screw presses. This significantly improves the control accuracy of the slider position, thereby ensuring the accuracy of the press's impact energy and guaranteeing product quality. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the present invention. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the accompanying drawings.

[0018] like Figure 1As shown, the PLC-based electric screw press position accuracy control method includes a PLC programmable controller, a control component and a position feedback component connected to the signal input terminal of the PLC programmable controller, and an execution component connected to the signal output terminal of the PLC programmable controller. In this embodiment, the control component is an HMI touch screen, the position feedback component is a displacement sensor mounted on the slider, and the execution component is a motor. The motor drives the screw to rotate through a flywheel assembly, and the screw drives the slider to move up and down along it through a helical pair.

[0019] The working steps of this control method are as follows:

[0020] Step 1: Power on the PLC programmable controller. The operator uses the HMI touch screen to set the target values ​​for the forward speed of the motor, the initial reverse speed of the motor, the return position of the slider, and the proportional coefficient of the reverse speed of the motor.

[0021] In this embodiment, the target value for the forward rotation speed of the motor is 300 rpm, the target value for the initial reverse rotation speed of the motor is 200 rpm, the target value for the return position of the slider is 400 mm, and the motor reverse rotation speed is set to be less than or equal to 50 rpm at the last 20 mm position. The motor reverse rotation speed proportional coefficient is less than or equal to 150. Within this range, the larger the coefficient, the shorter the return time.

[0022] Step 2: The motor starts and rotates forward at the target speed. After the slider moves down until it contacts and strikes the workpiece, the PLC programmable controller assigns the initial reverse speed target value to the motor.

[0023] Step 3: The motor reverses to drive the slider upwards. The displacement sensor collects the real-time position value of the slider, and the PLC programmable controller calculates the motor's reverse speed. The calculation formula is as follows:

[0024]

[0025] Step 4: The PLC programmable controller determines whether the calculated value of the motor's reverse speed is less than the target value of the initial reverse speed. If so, the PLC programmable controller assigns the calculated value of the motor's reverse speed to the motor. If the calculated value of the motor's reverse speed is greater than or equal to the target value of the initial reverse speed, the PLC programmable controller assigns the target value of the initial reverse speed to the motor.

[0026] Step 5: The PLC programmable controller determines whether the real-time position value of the slider is equal to the target value of the slider's return position. If so, the motor stops rotating and the slider stops moving. Otherwise, continue to execute steps 3 and 4.

[0027] In this method, during steps 1 to 5, as the slider moves upward, the PLC programmable controller continuously updates and compares the collected data according to the pre-set calculation formula and judgment conditions. It then sends control commands to the motor in real time. As the slider approaches its return position, the speed value calculated by the PLC programmable controller decreases. When the displacement sensor indicates that the slider has reached the target return position, the PLC programmable controller sends a stop command to the motor, stopping the motor and halting the slider's movement. Because the motor speed is very low before approaching the target position, it can stop immediately upon receiving the stop command, ensuring a slider position accuracy of ±1mm and achieving precise positional control.

[0028] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of this patent.

Claims

1. A PLC-based method for controlling the position accuracy of an electric screw press, characterized in that, Includes the following steps: Step 1: Pre-set the target values ​​for the forward rotation speed of the press motor, the initial reverse rotation speed, the slide return position, and the motor reverse rotation speed proportional coefficient. Step 2: The motor starts and rotates forward at the target speed. After the slider moves down until it contacts and strikes the workpiece, the PLC programmable controller assigns the initial reverse speed target value to the motor. Step 3: The motor reverses to drive the slider upwards. The displacement sensor collects the real-time position value of the slider, and the PLC programmable controller calculates the motor's reverse speed. The calculation formula is as follows: ， Step 4: The PLC programmable controller determines whether the calculated motor reverse speed is less than the target value of the initial reverse speed. If so, the PLC programmable controller assigns the calculated motor reverse speed to the motor. If the calculated motor reverse speed is greater than or equal to the target value of the initial reverse speed, the PLC programmable controller assigns the target value of the initial reverse speed to the motor. Step 5: The PLC programmable controller determines whether the real-time position value of the slider is equal to the target value of the slider's return position. If so, the motor stops rotating and the slider stops moving. Otherwise, continue to execute steps 3 and 4. The motor reverse speed proportional coefficient is set according to the following: In order to ensure that the accuracy of the slider return stop position is between -1mm and 1mm, it is necessary to ensure that the motor reverse speed value is less than or equal to 50 rpm at the last 20mm of the slider stroke. Therefore, the motor reverse speed proportional coefficient is less than or equal to 150. Within this range, the larger the coefficient, the shorter the return time. During the execution of steps 1 to 5 above, as the slider moves upward, the PLC programmable controller continuously refreshes the collected data for calculation and comparison based on the pre-set calculation formula and judgment conditions. Then, it sends control commands to the motor in real time. As the slider gets closer to the return position, the speed value calculated by the PLC programmable controller will become smaller and smaller. When the displacement sensor reports that the slider has reached the target return position, the PLC programmable controller sends a stop command to the motor, the motor stops, and the slider stops moving. Since the motor speed is very small before approaching the target position, the motor can stop immediately after receiving the stop command, ensuring that the slider position accuracy can reach ±1mm, thus achieving precise control of position accuracy.

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