Torque wrench overcurrent protection method and circuit based on sampling resistor

Abstract

The invention relates to a torque wrench overcurrent protection method and circuit based on a sampling resistor, and the method employs a comparator to detect the working current of a motor, when the working current of the motor is larger, the voltage drop of the sampling resistor is larger, and the voltage at the normal-phase input end of the comparator is larger, and when the voltage at the normal-phase input end of the comparator is larger than the reference voltage, the voltage drop of the sampling resistor is smaller. The comparator outputs high level to conduct the third triode and further conduct the second triode, and after the second triode is conducted, the base voltage of the first triode is pulled down, so that the first triode is disconnected, a driving circuit of the motor is disconnected, and the motor stops rotating, and therefore overcurrent protection is achieved, a switch is not disconnected, and the protection state is not relieved. The protection state is automatically released after the switch is disconnected. No control chip is needed in the whole control process, the overcurrent protection response speed can be effectively improved, and the manufacturing cost of the control circuit is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of current detection, and in particular relates to a torque wrench overcurrent protection method and circuit based on a sampling resistor. Background Art

[0002] The torque detection of the torque wrench is achieved by detecting the working current of the motor. When the working current of the motor reaches the set value, it can be determined that the torque of the motor reaches the target value, and the motor is controlled to stop. The main components for control are data processing chips such as MCU. Since it needs to be processed by the data processing chip, the control feedback speed is slow, and the problem of excessive torque is prone to occur. At the same time, the use of chip control makes the cost of the torque wrench higher, and the parameter setting during torque adjustment is also more troublesome, which is not very friendly to older users. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a torque wrench overcurrent protection circuit based on a sampling resistor, so as to solve the technical problems of slow feedback speed and high manufacturing cost caused by using an MCU to process the sampling current and then feed back the output control signal.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a torque wrench overcurrent protection circuit based on a sampling resistor, comprising a switch and a motor connected in series on a power supply circuit, the switch is connected between the positive pole of the power supply and the motor, a sampling resistor is connected in series to the negative pole of the motor, the other end of the sampling resistor is grounded, a first triode is connected in series between the sampling resistor and the motor, a driving voltage and a second triode are connected in parallel to the base of the first triode, the collector of the second triode is connected to the first triode, the emitter is grounded, and the base is connected to the emitter of the third triode, the collector of the third triode is connected between the motor and the switch, a comparator is connected in parallel between the sampling resistor and the first triode, the output end of the comparator is connected to the base of the third triode, the non-inverting input end of the comparator is connected between the sampling resistor and the first triode, and the inverting input end of the comparator is connected to a reference voltage.

[0005] As a preferred solution, the sampling resistor is a resistor with adjustable resistance.

[0006] As a preferred solution, a voltage regulator is connected in series between the collector of the third transistor and the switch, and the voltage regulator is a voltage regulator chip or a resistor.

[0007] The technical problem to be further solved by the present invention is: to provide a torque wrench overcurrent protection method based on a sampling resistor, to solve the technical problems of slow feedback speed and high manufacturing cost caused by using an MCU to process the sampled current and then feed back the output control signal.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a torque wrench overcurrent protection method based on sampling resistor, a mechanical switch and an electronically controlled switch are connected in series on the motor power supply circuit of the torque wrench, and a sampling resistor is set at the ground terminal of the motor, a comparator is used to detect the positive electrode voltage of the sampling resistor and a control voltage is output through the output terminal of the comparator to control the on and off of the electronically controlled switch, a reference voltage of the comparator is set, when the positive electrode voltage of the sampling resistor is greater than the reference voltage, the comparator outputs the control voltage to control the electronically controlled switch to be disconnected, and when the positive electrode voltage of the sampling resistor is less than or equal to the reference voltage, the comparator has no voltage output.

[0009] As a preferred solution, the disconnected state of the electronically controlled switch is self-locked by utilizing the voltage of the negative electrode of the switch.

[0010] As a preferred solution, a sampling resistor with adjustable resistance is used to adjust the magnitude of the protection current.

[0011] The beneficial effects of the present invention are as follows: the present invention uses a comparator to detect the working current of the motor. When the working current of the motor is larger, the voltage drop of the sampling resistor is larger, and the voltage of the positive input terminal of the comparator is larger. When the voltage of the positive input terminal of the comparator is larger than the reference voltage, the comparator will output a high level to turn on the third transistor, and then turn on the second transistor. After the second transistor is turned on, the base voltage of the first transistor is pulled down to disconnect the first transistor, the driving circuit of the motor is disconnected, and the motor stops, thereby realizing overcurrent protection. The switch is not disconnected, the protection state is not released, and the protection state is automatically released after the switch is disconnected. The entire control process does not require the participation of the control chip, which can effectively improve the overcurrent protection reaction speed and reduce the manufacturing cost of the control circuit.

[0012] The present invention further sets the sampling resistor as an adjustable resistance resistor, so that the overcurrent protection circuit described in the present invention can adjust the current of the overcurrent protection by adjusting the resistance of the sampling resistor, thereby realizing the adjustment of the maximum torque value of the torque wrench, without the need for interface settings, greatly reducing the difficulty of torque value adjustment and improving user convenience. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings, wherein: Figure 1 It is a circuit diagram of the overcurrent protection circuit of the present invention. DETAILED DESCRIPTION

[0014] The specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0015] like Figure 1A torque wrench overcurrent protection circuit based on a sampling resistor is shown, comprising a switch S and a motor M connected in series on a power supply circuit, the switch S is connected between a positive electrode B+ of a power supply and the motor M, a sampling resistor R is connected in series to a negative electrode of the motor M, the other end of the sampling resistor R is grounded, a first transistor Q1 is connected in series between the sampling resistor R and the motor M, a driving voltage V+ and a second transistor Q2 are connected in parallel to the base of the first transistor Q1, the collector of the second transistor Q2 is connected to the first transistor Q1, the emitter is grounded, and the base is connected to the emitter of the third transistor Q3, the collector of the third transistor Q3 is connected between the motor M and the switch S, a comparator U1 is connected in parallel between the sampling resistor R and the first transistor Q1, the output end Vo of the comparator U1 is connected to the base of the third transistor Q3, the non-phase input end vi of the comparator U1 is connected between the sampling resistor R and the first transistor Q1, and the inverting input end er of the comparator U1 is connected to a reference voltage Vb.

[0016] The user first calculates the designed maximum operating current of the motor according to the torque extreme value of the torque wrench, and then calculates the positive terminal voltage of the sampling resistor R when the motor is at the designed maximum operating current according to the resistance value of the sampling resistor R, and sets the voltage as the reference voltage Vb. When the actual operating voltage of the motor is greater than the designed maximum operating voltage, the positive terminal voltage of the sampling resistor R will exceed the reference voltage Vb, so that the output terminal Vo of the comparator U1 outputs a high level to turn on the third transistor Q3, and then turns on the second transistor Q2. After the second transistor Q2 is turned on, it pulls down the base voltage of the first transistor Q1 to disconnect the first transistor Q1, disconnect the drive circuit of the motor M, and stop the motor M, thereby realizing overcurrent protection. The switch S is not disconnected, and the protection state is not released. When the switch S is disconnected, the protection state is automatically released.

[0017] The sampling resistor R in this embodiment is preferably an adjustable resistance resistor. The user can adjust the torque limit of the torque wrench by adjusting the resistance of the sampling resistor R. For example, when the resistance of the sampling resistor R is reduced, a larger motor working voltage is required to make the voltage value of the positive terminal of the sampling resistor R greater than the reference voltage Vb, so the torque limit of the torque wrench can be increased. Otherwise, the torque limit of the torque wrench can be reduced.

[0018] A voltage regulator W is connected in series between the collector of the third transistor Q3 and the switch S. The voltage regulator W is a voltage regulator chip or a resistor.

[0019] According to the above-mentioned torque wrench overcurrent protection circuit based on sampling resistor, the overcurrent protection method of the present invention is specifically as follows: the user first calculates the designed maximum working current of the motor according to the torque extreme value of the torque wrench, and then calculates the positive terminal voltage of the sampling resistor R when the motor is at the designed maximum working current according to the resistance value of the sampling resistor R, and sets the voltage as the reference voltage Vb. When the actual working voltage of the motor is greater than the designed maximum working voltage, the positive electrode voltage of the sampling resistor R will exceed the reference voltage Vb, so that the output terminal Vo of the comparator U1 outputs a high level to turn on the third transistor Q3, and then turns on the second transistor Q2. After the second transistor Q2 is turned on, it pulls down the base voltage of the first transistor Q1 to cause the first transistor Q1 to be disconnected, the drive circuit of the motor M is disconnected, and the motor M stops, thereby realizing overcurrent protection. The switch S is not disconnected, and the protection state is not released. When the switch S is disconnected, the protection state is automatically released.

[0020] When the user needs to increase the torque limit of the torque wrench, the user can reduce the resistance value of the sampling resistor R, and increasing the resistance value of the sampling resistor R can reduce the torque limit of the torque wrench.

[0021] The present invention actually realizes the limitation and adjustment of the torque extreme value of the torque wrench through the current limiting protection function.

[0022] The above embodiments are only illustrative of the principles and effects of the invention, as well as some embodiments of its application, and are not intended to limit the invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept of the invention, and all of these belong to the protection scope of the invention.

Claims

1. A torque wrench overcurrent protection circuit based on a sampling resistor, comprising a switch and a motor connected in series to a power supply circuit, characterized in that: The switch is connected between the positive pole of the power supply and the motor, a sampling resistor is connected in series to the negative pole of the motor, the other end of the sampling resistor is grounded, a first triode is connected in series between the sampling resistor and the motor, a driving voltage and a second triode are connected in parallel to the base of the first triode, the collector of the second triode is connected to the first triode, the emitter is grounded, and the base is connected to the emitter of the third triode, the collector of the third triode is connected between the motor and the switch, a comparator is connected in parallel between the sampling resistor and the first triode, the output end of the comparator is connected to the base of the third triode, the non-inverting input end of the comparator is connected between the sampling resistor and the first triode, and the inverting input end of the comparator is connected to a reference voltage.

2. The torque wrench overcurrent protection circuit based on sampling resistor according to claim 1, characterized in that: The sampling resistor is an adjustable resistance resistor.

3. The torque wrench overcurrent protection circuit based on sampling resistor according to claim 1, characterized in that: A voltage regulator is connected in series between the collector of the third triode and the switch, and the voltage regulator is a voltage regulator chip or a resistor.

4. A torque wrench overcurrent protection method based on sampling resistor, characterized in that: A mechanical switch and an electric control switch are connected in series in the motor power supply circuit of the torque wrench, and a sampling resistor is set at the ground terminal of the motor. A comparator is used to detect the positive voltage of the sampling resistor and a control voltage is output through the output terminal of the comparator to control the on and off of the electric control switch. A reference voltage of the comparator is set. When the positive voltage of the sampling resistor is greater than the reference voltage, the comparator outputs the control voltage to control the electric control switch to be disconnected. When the positive voltage of the sampling resistor is less than or equal to the reference voltage, the comparator has no voltage output.

5. The overcurrent protection method according to claim 4, characterized in that: The voltage at the negative pole of the switch is used to self-lock the disconnected state of the electronically controlled switch.

6. The overcurrent protection method according to claim 4, characterized in that: The protection current is adjusted by using a sampling resistor with adjustable resistance.

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