Electromagnet clamping jaw control circuit and method based on PWM

Abstract

The invention relates to the field of electromagnet clamping jaw control, and provides a PWM-based electromagnet clamping jaw control circuit and method.The PWM-based electromagnet clamping jaw control circuit comprises an industrial personal computer and a control panel, the control panel comprises an RS232 communication circuit, a control chip MCU, an MOS drive circuit and an output sampling circuit, the industrial personal computer is connected with the control chip MCU through the RS232 communication circuit, and the control chip MCU is connected with the MOS drive circuit through the output sampling circuit; the control chip MCU is connected with the control chip MCU and used for sending data to the control chip MCU and changing control parameters of the control chip MCU, the control chip MCU obtains clamping jaw magnetic force data in a corresponding time period according to the control parameters, calculates the duty ratio of a PWM signal according to the current clamping jaw magnetic force data and outputs the PWM signal with the corresponding duty ratio to a controlled end of the MOS driving circuit, and the controlled end of the MOS driving circuit is connected with the control chip MCU. The output end of the MOS drive circuit is connected with the electromagnet clamping jaw so as to generate magnetic force needed in the current time period. Through a pulse width modulation method, the clamping force of the clamping jaw can be changed according to different working conditions.

Description

Technical Field

[0001] The invention relates to the field of electromagnetic clamp control, and in particular to a PWM-based electromagnetic clamp control circuit and method. Background Art

[0002] Electromagnetic clamps are widely used in product conveying mechanisms of semiconductor die bonding equipment, where the control of clamping and releasing of the clamps is key. Existing technical solutions usually control the clamping and releasing of the electromagnet clamps by simply turning on and off a relay, but are unable to control the clamping force of the clamps according to different working conditions. Furthermore, the electromagnets generate severe heat when working for a long time. Summary of the invention

[0003] The problem solved by the present invention is how to provide an electromagnetic clamping jaw control circuit which can change the clamping force of the clamping jaw according to different working conditions through a pulse width modulation method.

[0004] To solve the above problems, the present invention provides a PWM-based electromagnetic clamp control circuit and method, including: an industrial computer and a control board, the control board including an RS232 communication circuit, a control chip MCU, a MOS drive circuit and an output sampling circuit, the industrial computer is connected to the control chip MCU through the RS232 communication circuit to send data to the control chip MCU and change the control parameters of the control chip MCU, the control chip MCU obtains the clamp magnetic force data in the corresponding time period according to the control parameters, the control chip MCU calculates the duty cycle of the PWM signal according to the current clamp magnetic force data, and outputs the PWM signal of the corresponding duty cycle to the controlled end of the MOS drive circuit, the output end of the MOS drive circuit is connected to the electromagnetic clamp, the MOS drive circuit outputs a corresponding voltage to the electromagnetic clamp according to the PWM signal to generate the magnetic force required for the current time period, and the output sampling circuit is connected to the control chip MCU to transmit the electromagnet current sampling information to the control chip MCU to protect it in case of overcurrent.

[0005] Furthermore, the MOS driving circuit includes a MOS driver, a first MOS tube and a voltage limiting circuit, the input end of the MOS driver is connected to the PWM signal output end of the control chip MCU, the output end is connected to the gate of the first MOS tube, the source of the first MOS tube is grounded, the drain of the first MOS tube is connected to a 24V power supply via the voltage limiting circuit, and a voltage is output to the electromagnet clamp.

[0006] Furthermore, the voltage limiting circuit includes a first diode and a second diode, the cathode of the first diode is connected to a 24V power supply, the anode is connected to the drain of the first MOS tube, the anode of the second diode is grounded, and the cathode is connected to the anode of the first diode.

[0007] Furthermore, the output sampling circuit includes a resistor sampling circuit, a second-order low-pass filter circuit and an operational amplifier circuit. The output end of the resistor sampling circuit is connected to the input end of the operational amplifier circuit via the second-order low-pass filter circuit. The resistor sampling circuit converts the electromagnet current into a voltage signal through resistor sampling and outputs it to the operational amplifier circuit. The output end of the operational amplifier circuit is connected to the input end of the control chip MCU.

[0008] Furthermore, the output sampling circuit also includes a first clamping diode, which is connected to the input end of the control chip MCU for voltage limiting protection.

[0009] Furthermore, the operational amplifier circuit includes a first operational amplifier and an amplification factor adjustment circuit, the same-direction input terminal of the first operational amplifier is connected to the output terminal of the resistance sampling circuit via the second-order low-pass filter circuit, the reverse input terminal is grounded, and the amplification factor adjustment circuit is arranged between the output terminal and the reverse input terminal of the first operational amplifier.

[0010] Furthermore, the control chip MCU calculates the duty cycle of the PWM signal based on the current gripper magnetic force data, including: calculating the relationship between the electromagnet magnetic force and voltage of the gripper, and then obtaining the required voltage across the electromagnet; and obtaining the duty cycle of the PWM signal for voltage regulation based on the required voltage across the electromagnet.

[0011] Furthermore, the calculation of the relationship between the electromagnetic force and voltage of the clamping jaw includes:

[0012] Obtain the required working air gap magnetic induction intensity B, the expression is:

[0013]

[0014] Combined with the electromagnetic force formula, the expression of the relationship between the electromagnetic force and voltage is obtained;

[0015] The magnetic force formula of electromagnet is:

[0016]

[0017] The relationship between the magnetic force and voltage of the electromagnet is expressed as:

[0018]

[0019] Among them, N is the number of coil turns; U is the required voltage across the electromagnet; R is the winding resistance; δ is the air gap length, μ0 is the vacuum permeability, which is a constant; S is the cross-sectional area of ​​the magnetic circuit.

[0020] Furthermore, the duty cycle of the PWM signal for voltage regulation is obtained according to the required voltage across the electromagnet, and its expression is:

[0021]

[0022] Among them, U0 is the rated voltage of the electromagnet, which is also the maximum voltage that the PWM control board can output; is the duty cycle of PWM, T0 is the cycle time of PWM, and T is the time that the control board maintains high-level output in one cycle.

[0023] The present invention also provides a PWM-based electromagnetic clamp control method, comprising:

[0024] When the clamping operation starts, the control chip MCU outputs a PWM signal with a duty cycle from small to large and a time interval of 10ms to the MOS drive circuit, so that the voltage at both ends of the electromagnet gradually increases, and the clamping force of the electromagnet claw gradually increases;

[0025] When the electromagnetic clamp reaches the maximum clamping force or the target clamping force, the PWM signal output is maintained, the current clamping force is maintained, the working material is clamped, and the electromagnetic clamp is moved to the working position;

[0026] When the machine reaches the working position, the control chip MCU calculates the control parameters and outputs a PWM signal with a corresponding duty cycle to reduce and maintain the clamping force on the working material.

[0027] After the operation is completed, the electromagnet reaches the maximum clamping force or the target clamping force again and maintains it, and the electromagnet clamping claw is moved to transport the operating material to the next station or the discharge port;

[0028] When the material is discharged, the control chip MCU continues to reduce the duty cycle of the PWM signal until the PWM signal output stops, causing the electromagnet clamp to release the material, and the material discharge is completed.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The pulse width modulation method is used to control the clamping force of the electromagnetic clamp. The control chip MCU calculates the magnetic force and its changes required to be output during the current operation period according to the control parameters received from the industrial computer, and then obtains the required duty cycle of the PWM signal output by the MOS drive circuit, and then outputs the corresponding PWM signal. The voltage is converted through the PWM control circuit to control the clamping force of the electric clamp by changing the size of the electromagnet current. It can achieve large current for clamping and small current for holding, and effectively reduce the heat generated by the electromagnet during the operation of the equipment. At the same time, the external output current is monitored to prevent damage to the electromagnet when the current is too large. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the overall principle structure of an embodiment of the present invention;

[0032] Figure 2 Schematic diagram of the principle structure of a MOS driving circuit according to an embodiment of the present invention;

[0033] Figure 3 A schematic diagram of the principle structure of an output sampling circuit according to an embodiment of the present invention;

[0034] Figure 4 Schematic diagram of waveforms showing changes in the electromagnet clamping force and PWM duty cycle according to an embodiment of the present invention.

[0035] Description of reference numerals:

[0036] 1-industrial computer; 2-RS232 communication circuit; 3-control chip MCU; 4-MOS drive circuit; 5-output sampling circuit; 6-electromagnetic clamp. DETAILED DESCRIPTION

[0037] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0038] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] In the description of this specification, the description with reference to the terms "embodiment", "one embodiment" and "one implementation" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or implementation are included in at least one embodiment or implementation of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or implementation. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or implementations in a suitable manner.

[0040] like Figure 1 As shown, the present invention provides a PWM-based electromagnetic clamp control circuit and method, including: an industrial computer 1 and a control board, the control board including an RS232 communication circuit 2, a control chip MCU3, a MOS drive circuit 4 and an output sampling circuit 5, the industrial computer 1 is connected to the control chip MCU3 through the RS232 communication circuit 2 to send data to the control chip MCU3 and change the control parameters of the control chip MCU3, the control chip MCU3 obtains the clamp magnetic force data in the corresponding time period according to the control parameters, and according to the current clamp magnetic force data, the control chip MCU3 calculates the duty cycle of the PWM signal, and outputs the PWM signal of the corresponding duty cycle to the controlled end of the MOS drive circuit 4, the output end of the MOS drive circuit 4 is connected to the electromagnetic clamp 6, the MOS drive circuit 4 outputs the corresponding voltage to the electromagnetic clamp 6 according to the PWM signal to generate the magnetic force required for the current time period, and the output sampling circuit 5 is connected to the control chip MCU3, and is used to transmit the electromagnet current sampling information to the control chip MCU3 to protect it when overcurrent occurs.

[0041] It should be noted that the existing technical solution of Dassault is to control the clamping and releasing of the electromagnet clamp 6 by simply turning on and off the relay, and it is impossible to change the clamping force of the clamp according to different working conditions. In addition, when working for a long time, the electromagnet will generate serious heat, and it is impossible to perform corresponding protection when the external circuit is damaged and short-circuited. In this embodiment, the pulse width modulation method is used to control the clamping force of the electromagnet clamp 6. The control chip MCU3 calculates the magnetic force and its change required to be output during the current operation period according to the control parameters received from the industrial computer 1, and then obtains the required duty cycle of the PWM signal output to the MOS drive circuit 4, and then outputs the corresponding PWM signal. The voltage conversion is realized through the PWM control circuit, so as to control the clamping force of the electric clamp by changing the size of the electromagnet current. It can realize large current for clamping and small current for clamping, and effectively reduce the heat generated by the electromagnet during the operation of the equipment. At the same time, the external output current is monitored to prevent damage to the electromagnet when the current is too large.

[0042] like Figure 2 As shown, in the MOS drive circuit 4, the control chip MCU3 is connected to the MOS driver U1, and outputs a PWM control signal to the MOS driver U1; the MOS driver U1 is connected to the gate of the first MOS tube Q1, the source of the first MOS tube Q1 is grounded, and the drain is connected to the power supply, and the control chip MCU3 controls the MOS driver U1 to work through the VAL-CTR signal. The model of the MOS driver U1 is EG27517, and the switch of the first MOS tube Q1 is controlled by resistors R18 and R40, and the model of the first MOS tube Q1 is IRF640N. The first diode D1 and the second diode D2 perform voltage limiting processing to protect the MOS tube Q1 from being damaged by high voltage.

[0043] The control chip MCU3 outputs a PWM signal to control the MOS driver U1, and then controls the switch of the first MOS tube Q1, which can control the on-off of the 24V power supply of the electromagnetic clamp 6, and then control the clamping and release of the electromagnetic clamp 6. The control chip MCU3 can further output PWM signals with different duty cycles to change the effective value of the voltage at both ends of the electromagnetic clamp 6 to control the clamping force of the electromagnetic clamp 6.

[0044] like Figure 3 As shown, in the output sampling circuit 5, the current sampling signal VAL-ADC is converted into a voltage signal through the resistor R1, and then connected to the same direction end U17B of the operational amplifier unit in the first operational amplifier U17 through a second-order low-pass filter circuit composed of a resistor R3 and C1, R4 and C2. The model of the first operational amplifier U17 is LMV358M. Resistors R8 and R6 constitute the amplification adjustment, and the sampling signal is output through the output end of the operational amplifier unit U17B, and is low-pass filtered through resistor R7 and capacitor C3. At the same time, the first clamping diode D2 performs voltage limiting to protect the IO port of the control chip MCU3. The model of the first clamping diode D2 is BAV99LT1; the current sampling signal is output to the ADC sampling port of the control chip MCU3, and is compared with the current threshold. If a short circuit abnormality occurs, the protection mode is entered. At the same time, the current sampling of the two electromagnet outputs is mainly used to detect whether the external connection has excessive current. If so, the output protection is turned off.

[0045] It should be noted that the duty cycle of the PWM signal output by the control chip MCU3 is based on the clamping force of the electromagnet clamp 6 required at each time stage of the control process, that is, the magnetic force of the electromagnet. Before the work starts, the control chip MCU3 will receive the control parameters from the industrial computer 1, calculate the magnetic force and its change required to be output during the set working period, calculate the voltage requirement at both ends of the electromagnet, and then obtain the duty cycle of the PWM signal output by the MOS drive circuit 4, as follows:

[0046] According to the magnetic force formula of electromagnet,

[0047]

[0048] Where B is the magnetic flux density of the working air gap; μ0 is the vacuum magnetic permeability, which is a constant; S is the cross-sectional area of ​​this circuit. Without considering the air gap between leakage flux and other connecting parts, the magnetic flux density B can be written as the following formula:

[0049]

[0050] In the formula, N is the number of coil turns; U is the voltage across the electromagnet; R is the winding resistance; δ is the air gap length, that is, the working stroke of the electromagnet. By integrating the above two formulas, we can get the relationship between the magnetic force and voltage of the electromagnet,

[0051]

[0052] From the formula, we can see that the magnetic force of the electromagnet is proportional to the square of the voltage across the electromagnet, that is,

[0053] F∝U 2

[0054] Therefore, the effective voltage across the electromagnet can be adjusted by adjusting the duty cycle of PWM to control the magnetic force of the electromagnet, thereby controlling the clamping force of the electromagnet clamp 6.

[0055]

[0056] In the formula, U0 is the rated voltage of the electromagnet, which is also the maximum voltage that the PWM control board can output; is the duty cycle of PWM, T0 is the cycle time of PWM, and T is the time that the control board maintains high-level output in one cycle.

[0057] During the operation, the clamping force of the electromagnet and the PWM duty cycle change as follows Figure 4 As shown in the waveform diagram,

[0058] T1: When the electromagnetic clamp 6 starts to clamp the working material, the control chip MCU3 will output a PWM signal with a duty cycle from small to large and a time interval of 10ms to the MOS drive circuit 4 after receiving the signal from the industrial computer 1 to control the electromagnetic clamp 6 to clamp. This avoids the situation that the electromagnetic clamp outputs the maximum clamping force at the beginning to clamp and damage the working material under simple on-off control. The target clamping force of the electromagnetic clamp 6 can also be controlled by changing the maximum duty cycle of PWM;

[0059] T2: When the electromagnet reaches the maximum clamping force or the target clamping force, it maintains for a period of time to ensure that the working material is completely clamped. When the electromagnet clamping jaw 6 clamps the working material and moves, this clamping force is also used;

[0060] T3: When the electromagnetic clamp 6 delivers the working material to the working position, the electromagnetic clamp 6 is stationary at this time, and only needs to maintain the force capable of clamping the material;

[0061] T4: When the workpiece is finished, the electromagnetic clamp 6 clamps the material again with the maximum clamping force and transports the material to the next workstation or discharges the material;

[0062] T5: After reaching the discharging position, the electromagnet clamp 6 releases the material and the material discharging is completed.

[0063] Although the disclosure is disclosed as above, the protection scope of the disclosure is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A PWM-based electromagnetic clamp control circuit, characterized in that: include: An industrial computer (1) and a control board, wherein the control board comprises an RS232 communication circuit (2), a control chip MCU (3), a MOS drive circuit (4) and an output sampling circuit (5); the industrial computer (1) is connected to the control chip MCU (3) via the RS232 communication circuit (2) to send data to the control chip MCU (3) and change the control parameters of the control chip MCU (3); the control chip MCU (3) obtains the magnetic force data of the gripper within a corresponding time period according to the control parameters; and according to the current magnetic force data of the gripper, the control chip The MCU (3) calculates the duty cycle of the PWM signal, and outputs the PWM signal of the corresponding duty cycle to the controlled end of the MOS drive circuit (4); the output end of the MOS drive circuit (4) is connected to the electromagnet clamp (6); the MOS drive circuit (4) outputs a corresponding voltage to the electromagnet clamp (6) according to the PWM signal, so as to generate the magnetic force required in the current period; the output sampling circuit (5) is connected to the control chip MCU (3), and is used to transmit the electromagnet current sampling information to the control chip MCU (3), so as to provide protection in case of overcurrent.

2. The PWM-based electromagnetic clamp control circuit according to claim 1, characterized in that: The MOS drive circuit (4) comprises a MOS driver, a first MOS transistor and a voltage limiting circuit, wherein the input end of the MOS driver is connected to the PWM signal output end of the control chip MCU (3), the output end is connected to the gate of the first MOS transistor, the source of the first MOS transistor is grounded, the drain of the first MOS transistor is connected to a 24V power supply via the voltage limiting circuit, and a voltage is output to the electromagnet clamp (6).

3. The PWM-based electromagnetic clamp control circuit according to claim 2, characterized in that: The voltage limiting circuit includes a first diode and a second diode. The cathode of the first diode is connected to a 24V power supply, and the anode is connected to the drain of the first MOS tube. The anode of the second diode is grounded, and the cathode is connected to the anode of the first diode.

4. The PWM-based electromagnetic clamp control circuit according to claim 1, characterized in that: The output sampling circuit (5) comprises a resistance sampling circuit, a second-order low-pass filter circuit and an operational amplifier circuit. The output end of the resistance sampling circuit is connected to the input end of the operational amplifier circuit via the second-order low-pass filter circuit. The resistance sampling circuit converts the electromagnet current into a voltage signal through resistance sampling and outputs the voltage signal to the operational amplifier circuit. The output end of the operational amplifier circuit is connected to the input end of the control chip MCU (3).

5. The PWM-based electromagnetic clamp control circuit according to claim 4, characterized in that: The output sampling circuit (5) further comprises a first clamping diode, which is connected to the input end of the control chip MCU (3) and is used for voltage limiting protection.

6. The PWM-based electromagnetic clamp control circuit according to claim 5, characterized in that: The operational amplifier circuit includes a first operational amplifier and an amplification factor adjustment circuit. The same-direction input terminal of the first operational amplifier is connected to the output terminal of the resistance sampling circuit via the second-order low-pass filter circuit, and the reverse input terminal is grounded. The amplification factor adjustment circuit is arranged between the output terminal and the reverse input terminal of the first operational amplifier.

7. The PWM-based electromagnetic clamp control circuit and method according to claim 1, characterized in that: The control chip MCU (3) calculates the duty cycle of the PWM signal according to the current clamping jaw magnetic force data, including: calculating the relationship between the electromagnetic force and voltage of the clamping jaw, thereby obtaining the required voltage across the electromagnet; and obtaining the duty cycle of the PWM signal for voltage regulation according to the required voltage across the electromagnet.

8. The PWM-based electromagnetic clamp control circuit and method according to claim 7, characterized in that: The calculation of the relationship between the electromagnetic force and voltage of the clamping jaws includes: Obtain the required working air gap magnetic induction intensity B, the expression is: Combined with the electromagnetic force formula, the expression of the relationship between the electromagnetic force and voltage is obtained; The magnetic force formula of the electromagnet is: The relationship between the electromagnet magnetic force and voltage is expressed as: Among them, N is the number of coil turns; U is the required voltage across the electromagnet; R is the winding resistance; δ is the air gap length, μ0 is the vacuum permeability, which is a constant; S is the cross-sectional area of ​​the magnetic circuit.

9. The PWM-based electromagnetic clamp control circuit and method according to claim 8, characterized in that: The duty cycle of the PWM signal for voltage regulation is obtained according to the required voltage across the electromagnet, and its expression is: Among them, U0 is the rated voltage of the electromagnet, which is also the maximum voltage that the control board can output; is the duty cycle of PWM, T0 is the cycle time of PWM, and T is the time that the control board maintains high-level output in one cycle.

10. A PWM-based electromagnetic clamp control method, based on the PWM-based electromagnetic clamp control circuit according to any one of claims 1 to 9, characterized in that: include: When the clamping operation starts, the control chip MCU (3) outputs a PWM signal with a duty cycle from small to large and a time interval of 10ms to the MOS drive circuit (4), so that the voltage at both ends of the electromagnet gradually increases, and the clamping force of the electromagnet clamp (6) gradually increases; When the electromagnetic clamp (6) reaches the maximum clamping force or the target clamping force, the PWM signal output is maintained, the current clamping force is maintained, the working material is clamped, and the electromagnetic clamp (6) is moved to the working position; When the machine reaches the working position, the control chip MCU (3) calculates according to the control parameters and outputs a PWM signal with a corresponding duty cycle to reduce and maintain the clamping force on the working material; After the operation is completed, the electromagnet reaches the maximum clamping force or the target clamping force again and maintains it, and the electromagnet clamping claw (6) is moved to transport the operating material to the next work station or the discharge port; When the material is discharged, the control chip MCU (3) continuously reduces the duty cycle of the PWM signal until the PWM signal output stops, causing the electromagnet clamp (6) to release the material, and the material discharge is completed.

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