CN112497126A - Electric impact wrench controlled by current PID - Google Patents

Abstract

The invention discloses an electric impact wrench controlled by current PID, which comprises a power supply, a driving motor, a planetary gear reducer, an impact mechanism and a control system. The wrench is connected with the planetary gear reducer through the driving motor to drive the impact mechanism to carry out bolt fastening; the control system comprises a single chip microcomputer, a motor driving module, a sensor detection module and a key control module; the method comprises the steps that a relation model of motor current and output torque is driven by a wrench in a single chip microcomputer, corresponding current values of different torque values are prestored in a database by using the relation model and a relation curve, after a preset torque value is given, an actual measurement value of the motor current is detected by a control current sensor and is enabled to reach the prestored value, and bolt fastening operation is stopped after the preset torque value is reached. The invention realizes the constant torque output of the electric impact wrench by monitoring the current of the motor in real time and combining the double closed loop PID control of the rotating speed and the current, thereby obtaining higher assembly precision.

Description

An electric impact wrench controlled by current PID

technical field

The invention belongs to the technical field of electric torque wrenches, in particular to an electric impact wrench controlled by a current PID.

Background technique

Impact type electric torque wrench refers to a type of wrench with a rotating belt tangential impact mechanism. Due to its advantages of high work efficiency, small reaction torque and low energy consumption, it plays an important role in thread assembly. However, its assembling torque is usually judged by the operator's feeling of holding the wrench and the observation of the rotation of the sleeve to determine whether the required torque is reached. In this case, there is a large precision error in the assembling torque. Due to the complex working principle of the electric impact wrench, there are many parts involved in the work, which makes it difficult to analyze the principle and accurately model it. How to realize constant torque control of electric impact wrench is a key problem to be solved at present. When the electric impact wrench is tightening different types of bolts, it is necessary to avoid the bolts being deformed and damaged due to "over-tightening" due to excessive torque, or loosening and falling off due to "under-tightening" due to too small torque. In order to prevent the occurrence of the above situation, it is required that the electric impact wrench can realize constant torque control.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art, and to provide a current PID-controlled electric impact wrench, which uses the relationship model of the wrench drive motor current and output torque built in the single-motor control system, and uses the relationship model to convert different The torque value and its corresponding current value are pre-stored in the database. When the preset torque value is given, the measured value of the motor current is detected by controlling the current sensor to make it reach the pre-stored value. After reaching the preset torque value, combined with the speed And the double closed-loop PID control of the current can achieve higher assembly requirements and achieve better control accuracy.

In order to achieve the above purpose, the present invention adopts the following technical solutions: an electric impact wrench controlled by current PID, comprising a brushless DC motor 1, a planetary gear reducer 2, a main shaft 3, a main pressure spring 4, a driving block 5, a driven block 6, casing 7, power supply 8, display device 9 and control system 10;

The kinetic energy generated by the brushless DC motor 1 built into the wrench is partially converted into the kinetic energy driving the rotation of the active block 5 through the planetary gear reducer 2, and a part is converted into the potential energy compressed and stored by the main pressure spring 4, and another part of the energy is converted into thermal energy and mechanical energy. The form of loss disappears. The potential energy compressed and stored by the main pressure spring 4 acts on the active block 5, a part of which is converted into translational kinetic energy of the active block 5, and a part is converted into the kinetic energy of the rotation of the active block 5, and part of the energy is lost in this process. The shoulder of the active block 5 drives the driven block 6, thereby generating impact torque;

The output torque of the wrench is transmitted to the bolt or nut through the sleeve, so that the bolt or nut rotates at a certain angle, and the cycle of impact will continue until the bolt loading and unloading work is completed;

The power source 8 of the wrench is a rechargeable battery, which provides electrical energy for the drive motor and the display device, and can be detachably installed;

The circuit board of the control system 10 includes the following modules:

Microprocessor module of single-chip microcomputer, the single-chip microcomputer has a built-in relationship model for controlling the current of the driving motor and the output torque. According to the relationship model, the corresponding current values of different torque values are stored in the single-chip microcomputer database. After inputting the set torque value, it is detected by the control current sensor. The measured value of the outgoing motor current makes it reach the pre-stored value, and stops the bolt tightening operation after reaching the preset torque value;

The communication module stores the working data of the wrench in the EEPROM. When connected to the upper computer, the upper computer can read the stored data and record and monitor the use of the electric impact wrench in real time;

The motor drive module uses a drive chip and an inverter circuit to drive the motor. The single-chip microprocessor outputs 6-channel PWM signals and transmits them to the input pins of the drive chip, and then the output pins of the drive chip are output to the MOSFET to control the conduction of the MOSFET. and turn off;

Detection module, the detection module is divided into a current detection module and a position detection module, wherein the current detection module collects the current of the driving motor through a current sensor, and the collected signal is input into the single-chip microprocessor module, and the data is processed to obtain real-time data. Torque value, so as to carry out precise control of torque. The position detection module detects the rotor position through 3 Hall sensors. The microprocessor of the single-chip microcomputer sends a corresponding trigger signal according to the position signal collected by the Hall sensor to control the on-off of the MOSFET, and finally passes the high and low levels of the 3 Hall sensors. The signal calculates the speed of the motor.

Further, the relational model is obtained by fitting the experimental data samples according to polynomials, and the output torque signal of the electric impact wrench and the current signal of the drive motor are collected in real time by building a signal acquisition system. The data is used as a data sample for polynomial fitting, so as to obtain the relationship model and relationship curve between the output torque of the electric impact wrench and the current of the drive motor.

Further, the relationship curve between the output torque of the electric impact wrench and the current of the driving motor can realize the prediction and control of the output torque of the electric impact wrench, so as to achieve the purpose of constant torque control of the wrench.

Further, the sensors of the detection module include a current sensor and a Hall sensor. The current sensor is used to collect the current signal when the wrench motor is working, and the Hall sensor is used to detect the rotor position, and the motor speed is calculated by the obtained position signal.

Further, the control system controls the output torque by monitoring the motor current. After the system is powered on, the port register of the microcontroller of the single-chip microcomputer is initialized, the sensor starts to collect data, the display device starts to display, and the expected value of the output torque is set. The motor current pre-stored value is obtained, the PWM signal output in the control system is output, the motor is driven to rotate, the current detection module starts to detect the actual value of the motor current, and the actual current value reaches the current pre-stored value, the drive motor stops, and the system enters the standby state.

Further, the double closed-loop PID control of the control system is used to improve the response speed and stability of the control system, the drive motor current feedback is used as the inner loop, the rotor position provides speed feedback as the outer loop, and the inner loop is used to improve the system stability, The outer loop is used to reduce external interference, and combined with PID algorithm to improve the control accuracy of the system.

The technical effect of the present application is: when the electric impact wrench is tightening the bolts, the relationship model between the motor current and the output torque is driven by the built-in single chip wrench, and the current values corresponding to different torque values are pre-stored in the database by using the relationship model and the relationship curve. , when the preset torque value is given, the measured value of the motor current is detected by the control current sensor to make it reach the pre-stored value, and after reaching the preset torque value, combined with the double closed-loop PID control of speed and current, to achieve electric shock The constant torque output of the wrench can achieve higher assembly accuracy.

Description of drawings

Figure 1 is a sectional view of an electric impact wrench, wherein 1- brushless DC motor, 2- planetary gear reducer, 3- main shaft, 4- main pressure spring, 5- driving block, 6- driven block, 7- casing , 8-power, 9-display device, 10-control system;

Figure 2 is a front view and a side view of an electric impact wrench impact block, wherein Figure 2(a) is a front view and a side view of the impact block, and Figure 2(b) is a simplified front view and side view of the impact block;

Figure 3 is a graph showing the relationship between output torque and motor current in the process of tightening bolts by an electric impact wrench;

4 is a structural block diagram of an electric impact wrench according to an embodiment of the present invention;

Fig. 5 is a control flow chart of the present invention.

Detailed ways

In order to better illustrate the technical solutions and innovative features of the present invention, the present invention will be further described below according to the accompanying drawings and in conjunction with the embodiments.

As shown in Figure 1, an electric impact wrench controlled by current PID includes a brushless DC motor 1, a planetary gear reducer 2, a main shaft 3, a main pressure spring 4, a driving block 5, a driven block 6, a casing 7, Power supply 8 , display device 9 and control system 10 . The kinetic energy generated by the brushless DC motor 1 built into the wrench is partially converted into the kinetic energy driving the rotation of the active block 5 through the planetary gear reducer 2, and a part is converted into the potential energy compressed and stored by the main pressure spring 4, and the other part of the energy is converted into thermal energy and mechanical loss. form disappears. The potential energy compressed and stored by the main pressure spring 4 acts on the active block 5, a part of which is converted into translational kinetic energy of the active block 5, and a part is converted into the kinetic energy of the rotation of the active block 5, and part of the energy is lost in this process. The shoulder of the active block 5 drives the driven block 6 to generate impact torque; the output torque of the wrench is transmitted to the bolt or nut through the sleeve, so that the bolt or nut rotates at a certain angle, and the impact cycle will continue until the bolt loading and unloading work is completed. ;

The planetary gear reducer 2 of the electric impact wrench consists of a sun gear, a ring and three planetary gears. The sun gear is the driving gear, the three planetary gears are the driven gears, and the ring is fixed on the casing by the driven gears. After the required planetary gear transmission ratio is determined, the appropriate number of sun gear, ring and planetary gear teeth can be selected for the electric impact wrench according to the expression of the transmission ratio.

Planetary gear reduction ratio calculation:

Among them, i is the reduction ratio of the planetary gear, n ₁ is the rotational speed of the sun gear, n _H is the rotational speed of the ring, z ₁ is the number of teeth of the sun gear, and z ₃ is the number of teeth of the ring gear.

Calculation of the average load of the main pressure spring:

Among them, F _a is the average load of the main pressure spring, F ₁ is the minimum load of the spring, F ₂ is the maximum load of the spring, k is the spring constant, s ₁ is the minimum elastic deformation amount, and s ₂ is the minimum elastic deformation amount.

As shown in Figure 2, the impact block of the wrench presents an irregular shape. In order to facilitate the calculation of the mass m of the impact block, a simplified impact block is used for dynamic calculation.

Impact block quality:

Among them, ρ is the material density of the impact block, α, D ₀ , d ₁ , d ₂ , l ₁ , l ₂ , l ₃ , and _ls are the corresponding impact blocks in Fig. 2(b), respectively

department

The size parameter of the points, l ₃ = _ls -l ₁ -l ₂ .

Absolute angular velocity of the impact block before impact: ω ₀ =ω _a +ω _t

Among them, w ₀ is the absolute angular velocity of the impact block before the impact, w _a is the additional angular velocity of the impact block, and w _t is the average angular velocity of the main shaft.

The principle of the electric impact wrench is to periodically store and release the rotational kinetic energy generated by the motor, thereby continuously generating high-torque impact. Since the output torque is large at the moment of impact, but will decay quickly, the residual torque obtained by the final fastener is a cumulative torque.

When tightening different types of bolts, the wrench should avoid deformation and damage to the bolts caused by "over-tightening" due to excessive torque, or loosening of the bolts due to "under-tightening" due to too small torque. In order to prevent the occurrence of the above situation, it is required that the electric impact wrench can realize constant torque control.

Due to the complex working principle of the electric impact wrench, there are many parts involved in the work, which makes it difficult to analyze the principle and accurately model it. How to realize constant torque control of electric impact wrench is a key problem to be solved at present.

For the current electric impact wrench, adding a sensor inside the wrench will increase the cost and manufacturing difficulty of the wrench, and will generate large impact vibration and noise during the use of the wrench, so it is difficult to directly establish the output torque of the wrench and the motor. Current relationship model.

However, it is not accurate enough to obtain the relationship model between the driving motor current and the electromagnetic torque only by analyzing the driving motor of the electric impact wrench, because the transmission mechanism of the electric impact wrench is complex, and the working process contains uncertain factors such as vibration and noise. , which will directly affect the precision of the final wrench output torque. Therefore, in the implementation process of the present invention, the current signal of the driving motor and the wrench output torque signal are directly collected in real time through the signal collection system.

Due to the interference factors such as vibration and noise during the signal acquisition process of the wrench, the collected torque signal appears spur-like. accuracy of the model. In order to obtain accurate modeling data samples, it is necessary to perform noise reduction processing on the noise signal in the output torque signal through the SG filter.

After obtaining valid data samples, the relationship between the output torque T of the electric impact wrench and the motor current I was modeled by polynomial fitting. Make a one-to-one correspondence between the output torque data after noise reduction and the original data of the motor current in the time domain, and select the output torque value at a certain moment and the motor current value at the corresponding moment as a valid data point, in MATLAB Curve-fit the selected data points.

Fitted curve expression:

为拟合处理后的输出扭矩预测值，n为多项式拟合的阶数，a_k为多项式待定系数，其中k＝0，1，…，n。in,

is the predicted value of the output torque after fitting, n is the order of polynomial fitting, a _k is the polynomial undetermined coefficient, where k=0, 1, . . . , n.

According to the effect and accuracy of different order polynomial fitting, the third order polynomial fitting expression is selected as the polynomial mathematical model reflecting the relationship between the wrench output torque and the motor current.

Mathematical model of the relationship between wrench output torque and motor current:

As shown in Figure 3, the application also provides a relationship curve between the output torque of the electric impact wrench and the motor current when tightening the bolt, which can be divided into three stages. During operation, the output torque value of about 0.5N m is generated. At this stage, the wrench has not yet tightened the bolts; in the stage of 263mA to 794mA, the motor current continues to increase, while the output torque of the wrench increases slowly, and the wrench pre-tightens the bolts. . After the motor current is 794mA, the curve continues to incline, the wrench performs the action of tightening the bolt, and the output torque continues to increase until the bolt tightening is completed.

Through the established mathematical model and relationship curve of the relationship between the output torque of the wrench and the motor current, the data under different specifications of bolt tightening are organized and stored in the single-chip control system, and the current detection module in the control system is used to realize the output torque of the electric impact wrench. Predict and control to achieve the purpose of constant torque control of the wrench.

As shown in FIG. 4 , this embodiment discloses an electric impact wrench controlled by a current PID. The single-chip microprocessor of the control system generates 6 PWM signals, and the signals are transmitted to the driving circuit. The driving chip controls the on-off of the 6 MOSFETs according to the PWM, and realizes the conversion and energization of the three-phase windings of the driving motor. The current sensor sampling circuit detects the motor current signal and feeds it back to the microcontroller to adjust the current in real time. The Hall position sensor detects the rotor position, and the single-chip microprocessor obtains the feedback pulse signal, determines the correct position of the rotor, outputs the corresponding PWM signal for commutation control, and calculates the speed as a speed feedback to adjust the speed. The keyboard circuit controls the set speed and torque through the keys. The display circuit can display the given speed, torque and actual speed and torque through the LCD display.

The power supply module of the electric impact wrench supplies power to the wrench drive motor and the single-chip microcomputer, and the wrench motor drives the wrench impact mechanism to rotate the tightening bolt through the planetary gear reducer. The mechanical switch of the wrench is connected with the wrench driving motor, which is used to control the power on and off of the wrench motor, and can also be controlled by the control system.

During use,

In step S1, the speed and torque values are set through the key control of the keyboard circuit, and a corresponding calculated value of the motor current can be converted through the relationship model between the wrench output torque and the motor current built in the single-chip microcomputer.

Step S2, manually turn on the switch, or use the single chip microcomputer to control the switch on through the built-in control program, so that the power supply powers the drive motor of the wrench, thereby driving the impact mechanism of the wrench to rotate and output torque to tighten the bolt.

In step S3, the current sensor detects the current signal of the wrench-driven motor and transmits it to the microprocessor of the single-chip microcomputer, and calculates the real-time current value through the built-in control program of the single-chip microcomputer to adjust the current in real time. The Hall position sensor detects the rotor position and is used to calculate the speed as a speed feedback to adjust the speed.

In step S4, when the current of the driving motor reaches the calculated current value, the preset torque value is reached at this time, and the tightening action is stopped; and the control program built in the single-chip microcomputer controls the switch to disconnect, or manually turns off the switch to stop the power supply.

As shown in FIG. 5 , when the electric impact wrench of this embodiment is in use, after the control system is powered on, the port register of the single-chip microcontroller performs initialization operation, the sensor data acquisition circuit works, the liquid crystal display is powered on, and the real-time collected wrench outputs The torque signal and drive motor current signal are displayed on the LCD screen. After setting the torque value, through the obtained polynomial mathematical model between the output torque of the wrench and the current of the driving motor, the microcontroller starts to calculate the corresponding pre-stored value of the current of the driving motor. After getting the pre-stored value of the drive motor current, the PWM output module inside the microcontroller starts to output the PWM signal, and the drive motor drives the spindle to rotate. During the rotation of the drive motor, the current sensor detects the actual value of the motor current, and compares the actual value of the drive motor current with the drive motor current pre-stored value corresponding to the wrench output torque setting value. If the current actual value is less than the current pre-stored value, the PWM output cycle will continue to be executed; if the current actual value reaches the current pre-stored value, the drive motor will stop, the wrench will stop tightening and the action will be locked. The wrench outputs the real-time torque value, and the system enters the standby state.

Through the technical solution of this embodiment, the current monitoring method has better stability and higher anti-interference than the single speed control method, and the torque output accuracy can be controlled within ≤±10%. The control method improves the control precision and robustness of the control system.

The above descriptions are only preferred embodiments of the present invention, but not all embodiments. Any simple modifications or changes made to the above embodiments according to the technical essence of the present invention fall within the protection scope of the technical solutions of the present invention.

Claims (6)

1. An electric impact wrench controlled by a current PID, characterized in that: comprising a brushless DC motor (1), a planetary gear reducer (2), a main shaft (3), a main pressure spring (4), an active block (5) , a driven block (6), a casing (7), a power supply (8), a display device (9) and a control system (10); The kinetic energy generated by the brushless DC motor (1) built into the wrench is partially converted into the kinetic energy driving the rotation of the active block (5) through the planetary gear reducer (2), and a part is converted into the potential energy compressed and stored by the main pressure spring (4), A part of the energy disappears in the form of thermal energy and mechanical loss; the potential energy compressed and stored by the main compression spring (4) acts on the active block (5), part of which is converted into translational kinetic energy of the active block (5), and part is converted into the active block ( 5) The kinetic energy of rotation, and this process also has a part of the energy that disappears; the shoulder of the active block (5) drives the driven block (6), thereby generating impact torque; The output torque of the wrench is transmitted to the bolt or nut through the sleeve, so that the bolt or nut rotates at a certain angle, and the cycle of impact will continue until the bolt loading and unloading work is completed; The power source (8) of the wrench is a rechargeable battery, which provides electrical energy for the drive motor and the display device (9), and is detachably installed; The circuit board of the control system (10) includes the following modules: Microprocessor module of single-chip microcomputer, the single-chip microcomputer has a built-in relationship model for controlling the current of the driving motor and the output torque. According to the relationship model, the corresponding current values of different torque values are stored in the single-chip microcomputer database. After inputting the set torque value, it is detected by the control current sensor. The measured value of the outgoing motor current makes it reach the pre-stored value, and stops the bolt tightening operation after reaching the preset torque value; The communication module stores the working data of the wrench in the EEPROM. When connected to the upper computer, the upper computer can read the stored data and record and monitor the use of the electric impact wrench in real time; The motor drive module uses a drive chip and an inverter circuit to drive the motor. The single-chip microprocessor outputs 6-channel PWM signals and transmits them to the input pins of the drive chip, and then the output pins of the drive chip are output to the MOSFET to control the conduction of the MOSFET. and turn off; Detection module, the detection module is divided into a current detection module and a position detection module, wherein the current detection module collects the current of the driving motor through a current sensor, and the collected signal is input into the single-chip microprocessor module, and the data is processed to obtain real-time data. Torque value, so as to carry out precise control of torque. The position detection module detects the rotor position through 3 Hall sensors. The microprocessor of the single-chip microcomputer sends a corresponding trigger signal according to the position signal collected by the Hall sensor to control the on-off of the MOSFET, and finally passes the high and low levels of the 3 Hall sensors. The signal calculates the speed of the motor. The double closed-loop PID control of the speed and current is used to drive the feedback of the motor current signal and the rotor position signal, so as to improve the control accuracy of the system and reduce the motor rotation overshoot. 2. the electric impact wrench of a kind of current PID control according to claim 1, is characterized in that, described relational model is obtained according to polynomial fitting experimental data sample, by building signal acquisition system real-time acquisition electric impact wrench output torque signal And the current signal of the drive motor, the signal is subjected to noise reduction processing by SG (Savitzky-Golay) filter, and the data obtained after processing is used as the data sample of polynomial fitting, so as to obtain the relationship between the output torque of the electric impact wrench and the current of the drive motor. Relationship lines. 3. The electric impact wrench of a kind of current PID control according to claim 2, it is characterized in that, the relationship curve between the output torque of the electric impact wrench and the current of the driving motor can realize the prediction and control of the output torque of the electric impact wrench , to achieve the purpose of constant torque control of the wrench. 4. the electric impact wrench of a kind of current PID control according to claim 1, is characterized in that, the sensor of detection module comprises current sensor and Hall sensor, current sensor is used for collecting the current signal when the wrench motor works, Hall The sensor is used to detect the rotor position, and the motor speed is calculated by the obtained position signal. 5. The electric impact wrench of a current PID control according to claim 1, wherein the control system controls the output torque by monitoring the motor current, and after the system is powered on, the port register of the single-chip microcontroller is initialized, The sensor starts to collect data, the display device displays the collected torque value and current value, sets the expected output torque value, and the microcontroller internally calculates the pre-stored value of the motor current, controls the PWM signal output in the system, drives the motor to rotate, and the current detection module starts to detect the motor. The actual value of the current. After the actual value of the current reaches the current pre-stored value, the drive motor stops and the system enters the standby state. 6. The electric impact wrench of a current PID control according to claim 1, wherein the double closed-loop PID control of the control system is used to improve the response speed and stability of the control system, and the drive motor current feedback is used as an internal The outer loop is the outer loop, the rotor position provides speed feedback, the inner loop is used to improve the system stability, and the outer loop is used to reduce the external interference, and the PID algorithm is used to improve the control accuracy of the system.

Images