Torque control device for electrical tools

1. Field of the Invention

The present invention relates to a torque control device, and more particularly to a torque control device for electrical tools, where the control device can automatically interrupt a power supply of the electrical tools if a detected actual torque is greater than a default torque value.

2. Description of Related Art

Electrical tools commonly have an electrical motor to drive a tool head thus assisting an operator to easily accomplish operations such as screwing or drilling. Each kind of tool head can sustain a particular torque corresponding to a target object to be driven. Therefore, the torque generated by the electrical tools is required to be adjustable for accommodating different target objects. If the torque exceeds a tolerable range that the tool head can sustain, this tool head will be temporarily disengaged from the motor so as to avoid possible damage to the tool head and the motor.

The default torque setting can be accomplished by mechanically varying the compressing extent of a spring installed in the electrical tools. The tool head is driven by the motor as long as the torque is within the default value. However, using the spring to mechanically set the torque and obtaining a precise default value are both very difficult. Further, even when the tool head has been temporarily disengaged under the motor, the motor in the idling status continuously consumes power.

Therefore, the invention provides a torque control device for electrical tools to mitigate or obviate the aforementioned problem.

An objective of the present invention is to provide a torque control device for electrical tools, wherein a default torque can be precisely set. If the actual torque value of a motor of the electrical tools is greater than the default value, the power supply to the motor can be interrupted to protect the motor.

To accomplish the objective, the torque control device provides:

a switching circuit connected between the motor and the DC voltage source;

a processor with an output terminal connected to the switching circuit to turn on/off the switching circuit;

a voltage detecting circuit having an input terminal connected between the motor and the DC voltage source for detecting voltage variation data of the motor;

a torque detecting circuit connected between the voltage detecting circuit and the processor, wherein the torque detecting circuit produces a motor torque value based on the voltage variation data, wherein the motor torque value is output to the processor; and

a torque setting unit connected to the processor, wherein a default torque is set in the processor by the torque setting unit.

Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

FIG. 1 is a block diagram of a torque control device in accordance with the present invention;

FIG. 2 is a circuit diagram of the torque control device according to a first embodiment of the present invention; and

FIG. 3 is a circuit diagram of the torque control device according to a second embodiment of the present invention.

With reference to FIG. 1 , a torque control device for electrical tools comprises a switching circuit ( 10 ), a processor ( 20 ), a voltage detecting circuit ( 30 ), a torque detecting circuit ( 40 ), a high voltage protecting circuit ( 50 ), a low voltage protecting circuit ( 60 ), a torque setting unit ( 70 ) and a display ( 80 ).

The switching circuit ( 10 ) is connected between a motor and a DC voltage source, wherein the DC voltage source can be a battery.

The processor ( 20 ) has a first output terminal connected to the switching circuit ( 10 ) so as to control its on/off statuses.

The voltage detecting circuit ( 30 ) has an input terminal connected between the DC voltage source and the motor, whereby voltage or current variations of the motor can be detected.

The torque detecting circuit ( 40 ) is connected between the voltage detecting circuit ( 30 ) and the processor ( 20 ). Based on voltage and/or current variation data of the motor or their varying frequency within a time unit, the torque detecting circuit ( 40 ) can based on the detected data to generate a torque value of the motor and supplies the torque value to the processor ( 20 ).

The high voltage protecting circuit ( 50 ) connects between the voltage detecting circuit ( 30 ) and the processor ( 20 ). The high voltage protecting circuit ( 50 ) compares the detected voltage value from the voltage detecting circuit ( 30 ) with a high reference voltage. If the detected voltage is greater than the high reference voltage, the high voltage protecting circuit ( 50 ) outputs a signal to the processor ( 20 ) so that the switching circuit ( 10 ) can be turned off upon reception of the command of the processor.

The low voltage protecting circuit ( 60 ) is connected between the voltage detecting circuit ( 30 ) and the processor ( 20 ). The low voltage protecting circuit ( 60 ) compares the detected voltage value from the voltage detecting circuit ( 30 ) with a low reference voltage. If the detected voltage is smaller than the low reference voltage, the low voltage protecting circuit ( 50 ) outputs a signal to the processor ( 20 ) so that the switching circuit ( 10 ) can be turned off upon reception of the command output from the processor ( 20 ).

The torque setting unit ( 70 ) is connected to the processor ( 20 ). An operator can set a default torque in the processor ( 20 ) through the torque setting unit ( 70 ).

The display ( 80 ) is connected to an output terminal of the processor ( 20 ) for displaying the default torque level set by the operator.

With reference to FIG. 2 , the switching circuit ( 10 ) comprises a driving transistor ( 11 ) and a switching transistor ( 12 ). The driving transistor ( 11 ) comprises a bipolar junction transistor (BJT) with a base, a collector and an emitter. The switching transistor ( 12 ) is a MOSFET with a gate, a source and a drain. The driving transistor ( 11 ) provides its base connecting to the processor ( 20 ) through a resistor, and its collector is connected to the gate of the switching transistor ( 12 ). The drain and source of the switching transistor ( 12 ) are respectively connected to the DC voltage source and the motor. When the processor ( 20 ) output a signal with a high voltage level to activate the driving transistor ( 11 ), the switching transistor ( 12 ) is subsequently turned on which allows the DC voltage source provides power to the motor. Otherwise, when the driving transistor ( 11 ) is deactivated, the switching transistor ( 12 ) is accordingly turned off, whereby the power supply to the motor can be terminated.

The voltage detecting circuit ( 30 ) is composed of a voltage dividing circuit with two resistors R 1 , R 2 connected in series. One terminal of the resistor R 1 is connected to the DC voltage source and the switching circuit ( 10 ). The other terminal of the resistor R 1 to which the resistor R 2 is connected is coupled to the high voltage protecting circuit ( 50 ).

The torque detecting circuit ( 40 ) comprises an operation amplifier U 2 B and an RC circuit formed by a resistor R 3 and a capacitor C 1 . The operation amplifier is configured as a buffer, wherein the negative terminal and the output terminal of the operation amplifier are connected together to form a negative feedback loop.

The high voltage protecting circuit ( 50 ) is formed by an operation amplifier U 1 B that serves as a comparator. The comparator has a positive input terminal and a negative input terminal which are respectively coupled to the high reference voltage and the voltage detecting circuit ( 30 ). If the output voltage of the voltage detecting circuit ( 30 ) is greater than the high reference voltage, the comparator outputs a signal with a low level to notify the processor ( 20 ). The processor ( 20 ) can subsequently turn off the switching circuit ( 10 ) to avoid possible damage.

The low voltage protecting circuit ( 60 ) is also formed by an operation amplifier U 3 B serving as a comparator. The comparator has a positive input terminal and a negative input terminal which are respectively coupled to the voltage detecting circuit ( 30 ) and a low reference voltage. If the output voltage of the voltage detecting circuit ( 30 ) is smaller than the low reference voltage, the comparator outputs a signal with a low level to notify the processor ( 20 ). The processor ( 20 ) can subsequently turn off the switching circuit ( 10 ).

The torque setting unit ( 70 ) comprises a switch ( 71 ) having multiple nodes and a torque setting circuit ( 72 ). The torque setting circuit ( 72 ) is formed by multiple resistors. When one node in the switch ( 71 ) is selected, a respective input terminal of the processor ( 20 ) corresponding to the node represents a voltage. The processor ( 20 ) according to the represented voltage determines the torque value.

The display ( 80 ) is preferably a seven-segment display element with multiple input terminals connected to the processor ( 20 ).

With reference to FIG. 3 , the second embodiment is substantially similar to the first one of FIG. 2 . The modification in this embodiment aims at the torque setting unit ( 70 ′). The torque setting unit ( 70 ′) includes a rheostat ( 73 ) and a torque setting circuit ( 72 ′), wherein the torque setting circuit ( 72 ′) consists of a resistor R 6 , a capacitor C 2 and an operation amplifier U 4 B. The operation amplifier U 4 B is configured to form a buffer.

The voltage detecting circuit accompanying the torque detecting circuit can acquire the instant torque value of a motor according to the voltage and/or current variation data between the motor and the DC voltage source, or the varying frequency of the voltage and/or current in a time unit. The processor further compares the torque value with a default torque to determine whether the motor should be turned off. If the torque value of the motor is greater than the default value, the power supply to the motor is interrupted. Thus, the default value can be precisely set by a torque setting unit.

It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.