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L298N Based Control Design of Pressure in Ion Nitriding

  • Contents

I. Introduction

As we all know, the ion nitriding process requires relatively high control of the pressure inside the furnace, so this paper designs a gas flow controller based on the L298N chip driven DC motor control, which can be used to control the gas flow of the reactor. So let's first understand the ion nitriding theory.

 

Catalog

I.Introduction

II.Ion Nitriding Theory

III.System Flow and Pressure Measurement and Control Block Diagram

IV. L298N Chip Introduction

V. Controller Principle

VI. Conclusion

FAQ

Ordering & Quantity

 

II. Ion Nitriding Theory

 

Nitriding is a chemical heat treatment method to strengthen the metal surface. It is to place metal parts in an active nitrogen medium, and at a certain temperature and holding time, the nitrogen element can penetrate into the metal surface, thereby changing the chemical composition of the metal layer to make it have high wear resistance, fatigue strength, corrosion resistance and burn resistance, etc., so it is widely used in industry.

 

Ion nitriding is carried out in a low-temperature plasma. The low-pressure gas is ionized under the action of an electric field to produce high-energy ions and high-energy neutral atoms. These high-energy particles can improve the structure of the infiltration layer, promote the chemical reaction process, and accelerate the nitriding layer formation. Ion nitriding is carried out in glow discharge. In the process of ion nitriding, the pressure control accuracy of the furnace is relatively high, and the control deviation reaches several tens of Pa. According to Paschen’s Law:

formula 1

Among them:

       P is the gas pressure;

 

  D is the distance between parallel plate electrodes;

 

  V is the cathode secondary electron emission coefficient;

 

  B is Stolev's constant;

 

  A is a constant.

 

Taking the derivative of formula (1), the breakdown voltage expression (2) can be obtained:

formula 2

 

It can be seen from formula (2) that the breakdown voltage V is related to the gas pressure and d, and in general experiments, d is fixed, so ion nitriding is extremely important for pressure control.

 

III. System Flow and Pressure Measurement and Control Block Diagram

 

The flowmeter controls the gas flow at the inlet. When the inlet and exhaust flows are balanced, the furnace pressure remains stable. Due to the internal influence of furnace gas leakage and other interference factors, the internal pressure of the furnace  fluctuates up and down, and the system deviates from the equilibrium state, which affects the plasma process in severe cases. We use an ordinary DC motor to drive the DC motor through the L298N, and the motor drives the cone to rotate through the reduction lever. When the cone is screwed in, the gas pumped out per unit time is reduced; when it is screwed out, the gas pumped out increases, so that the pressure inside the furnace is stabilized at the required value. The change of furnace pressure is measured by the pressure sensor and passed through the transmitter, which sends the gas flow controller to the feedback voltage. The electric vacuum butterfly valve used for the suction port is expensive, as shown in Figure 1.

Block diagram of system flow and pressure measurement and control

Figure 1 Block diagram of system flow and pressure measurement and control

 

IV. L298N Chip Introduction

 

L298N can accept standard TTL logic level signal VSS, and VSS can be connected to 4.5~7V voltage. 4 pin VS is connected to the power supply voltage, and the VS voltage range VIH is +2.5~46V. The output current can reach 2.5A, which can drive inductive loads. The emitters of pin 1 and pin 15 are separately led out to connect the current sampling resistor to form a current sensing signal. L298 can drive two motors, OUT1, OUT2 and OUT3, OUT4 can be connected to each motor, this experimental device we choose to drive one motor. Pins 5, 7, 10 and 12 are connected to the input control level to control the forward and reverse rotation of the motor. EnA and EnB are connected to the control potential energy end to control the stalling of the motor. Figure 2 is the L298N functional logic diagram, Table 1 is the L298N internal funtional module.

L298N internal functional module

Figure 2 L298N functional logic diagram

 

EnA

In1

In2

Operative Condition

0

×

×

Stop

1

1

0

Rotating forward

1

0

1

Inversion

1

1

1

Brake

1

0

0

Stop

Table1 L298N internal functional module

 

The functional module of In3 and In4 is the same as Table 1. It can be seen from Table 1 that when EnA is low level, the input level has an effect on motor control. When EnA is high level, when EnA is high, the input level is one high and one low, and the motor rotates forward or reverse. If they are both low level, the motor will stop, and if they are both high level, the motor will brake.

 

V. Controller Principle

 

Figure 3 is the schematic diagram of the controller, composed of 3 dashed block diagrams:

controller schematic diagram

Figure 3 The schematic diagram of the controller

The following are the functions of the 3 dashed block diagrams:

 

(1) The dashed block diagram 1 controls the forward and reverse rotation of the motor, U1A and U2A are comparators, and VI comes from the voltage of the furnace pressure sensor. When VI>VRBF1, U1A outputs high level, U2A output high level turns into low level through inverter, and the motor rotates forward. Similarly, when VI<VRBF1, the motor reverses. The forward and reverse rotation of the motor can control the flow of gas extracted by the air extractor, thereby changing the pressure inside the furnace.

 

(2) In the dashed block diagram 2, two comparators U3A and U4A form a dual-limit comparator. When VB<VI<VA, it outputs low level, and when VI>VA, VI<VB, it outputs high level. VA, VB are the upper and lower limits of the voltage converted by the furnace pressure transducer, that is, the control range of the reaction furnace pressure. According to process requirements, we can specify the values of VA and VB by ourselves, as long as the furnace pressure is within the range determined by VA and VB, the motor stops (note that VB<VRBF1<VA, if it is not in this range, the system is unstable).

 

(3) The dashed block diagram 3 is a long delay circuit. U5A is a comparator, Rs1 is the sampling resistor, VRBF2 is the motor overcurrent voltage. The voltage on Rs1 is greater than VREF2, the motor is overcurrent, and U5A outputs low level. It can be seen from the above that block 1 controls the forward and reverse rotation of the motor, and block 2 controls the size of the ripple of the furnace pressure. When the furnace pressure is too small or too large, the motor turns to a fixed position at both ends to stop, according to the steady-state operating equation of the DC motor:

formula 3

Among them:

       Ф is the magnetic flux of each pole of the motor;

 

  Ce is the electromotive force constant;

 

  N is the number of motor revolutions;

 

  Ia is the armature current;

 

       Ra is the armature loop resistance.

 

When the number of revolutions of the motor N is 0, the current of the motor increases sharply, and the motor will burn out if the time is too long. But when the motor starts, the current in the coil in the motor also increases sharply, so we must separate these two states. The long delay circuit can distinguish these two states. The working principle of the long-delay circuit: When the Rs1 overcurrent U5A generates a negative pulse and is differentiated, the pulse triggers pin 2 of 555, the circuit is set, and pin 3 outputs high level. Because the discharge terminal 7 pin is open, C1, R5 and U6A formed as an integration, then start working, the charging voltage on the capacitor C1 rises linearly, and the integration constant of the delay operational amplifier is 100R5C1.

 

When the charging voltage on C1, that is, the voltage on pin 6 exceeds 2/3VCC, the 555 circuit resets and outputs a low level. The motor generally start-up in less than 0.8s, and the C1 charging time is generally 0.8~1s.

 

The output level of U5A is ORed with the output level of pin 3 of 555 via U7. If the output low level of U5A is longer than the charging time of C1, U7 outputs low level after C1 is charged. The AND gate U8 inputs to the 6 pin ENA terminal of L298N. The motor stops. If the output level of U5A is less than the charging time of C1, pin 6 will not act and the motor will start normally. The long delay circuit absorbs the motor start-up overcurrent voltage waveform, so that the motor starts normally.

 

VI. Conclusion

 

This article summarizes the design scheme for the pressure control of ion nitriding based on the L298N chip. It has been proved that the use of this controller to control the gas flow can reduce production costs, increase the system cost performance, and improve the control dynamic performance and stability of the entire system control.


FAQ

  • What is l298n?

This L298N Motor Driver Module is a high power motor driver module for driving DC and Stepper Motors. This module consists of an L298 motor driver IC and a 78M05 5V regulator. L298N Module can control up to 4 DC motors, or 2 DC motors with directional and speed control.

  • What is the use of l298n?

The L298N is a dual H-Bridge motor driver which allows speed and direction control of two DC motors at the same time. The module can drive DC motors that have voltages between 5 and 35V, with a peak current up to 2A.

  • How does l298n control DC motor speed?

1.If you send a HIGH signal to the enable 1 pin, motor A is ready to be controlled and at the maximum speed;

2.If you send a LOW signal to the enable 1 pin, motor A turns off;

3.If you send a PWM signal, you can control the speed of the motor. The motor speed is proportional to the duty cycle.

  • What is l298n motor driver module?

This L298N Motor Driver Module is a high power motor driver module for driving DC and Stepper Motors. This module consists of an L298 motor driver IC and a 78M05 5V regulator. L298N Module can control up to 4 DC motors, or 2 DC motors with directional and speed control.

  • How does l298n motor driver work?

The L298N is a dual H-Bridge motor driver which allows speed and direction control of two DC motors at the same time. The module can drive DC motors that have voltages between 5 and 35V, with a peak current up to 2A.

  • How do i use a l298 motor driver with Arduino?

Start by connecting power supply to the motors. In our experiment we are using DC Gearbox Motors(also known as 'TT' motors) that are usually found in two-wheel-drive robots. They are rated for 3 to 12V. So, we will connect external 12V power supply to the VCC terminal.

  • What is the function of H bridge?

An H-bridge is an electronic circuit that switches the polarity of a voltage applied to a load. These circuits are often used in robotics and other applications to allow DC motors to run forwards or backwards.

  • What is the difference between l293d and l298n?

L293 is quadruple half-H driver while L298 is dual full-H driver, i.e, in L293 all four input- output lines are independent while in L298, a half H driver cannot be used independently, only full H driver has to be used. ... Hence, heat sink is provided in L298.

 

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