AU2014201922B1

AU2014201922B1 - Torque control device for electrical hand tools

Info

Publication number: AU2014201922B1
Application number: AU2014201922A
Authority: AU
Inventors: Fu-Hsiang Chung
Original assignee: Techway Industrial Co Ltd
Current assignee: Techway Industrial Co Ltd
Priority date: 2014-04-03
Filing date: 2014-04-03
Publication date: 2015-01-22
Anticipated expiration: 2034-04-03

Abstract

A torque control device for electrical hand tools has a reverser (33), a control module (35), a current detector (381), a switch module (34), a voltage sensing module (37), a rotation direction sensing module (36), a torque sensing 5 module (38) and a torque setting module (39). The reverser (33) controls a motor (20) to rotate in a forward or a reverse direction. The rotation direction sensing module (36) detects rotation direction of the motor (20). When the motor (20) rotates forwardly in the forward direction, the control module (351) refers to a torque set value, a detected output torque of the motor (20) and a 10 detected driving voltage to compensate the output torque of the motor (20). When the motor rotates in the forward direction, the control module (35) refers to a single default reverse torque set value to drive the motor (20).

Description

TORQUE CONTROL DEVICE FOR ELECTRICAL HAND TOOLS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque control device for electrical 5 hand tools, and more particularly to a torque control device capable of compensating an output torque of a motor of the electrical hand tool. 2. Description of the Prior Art An electrical hand tool usually comprises a motor, a tool head and a speed adjusting mechanism. The motor drives the tool head such as a 10 screwdriver to rotate quickly via the speed adjusting mechanism. Because different tool heads should be driven by different torques to obtain the optimal operations, the speed adjusting mechanism may comprise a torque adjusting device for users to set appropriate torques. When the output torque of the DC motor exceeds a torque set value, the DC motor will automatically disconnect 15 from the head tool to avoid damages. The torque adjusting device may be a mechanical type device, such as a spring-based torque adjusting device as described in U.S. patent 4,249,435. Different forces applied to the spring may correspond to different torque set values. When the output torque exceeds the torque set value, the DC motor will 20 temporarily disconnect from the head tool. However, the mechanical type device is hard to set a precise torque set value. Even the head tool has disconnected from the motor, the motor does not immediately stop but still remains rotating for a time. Therefore, electrical torque adjusting devices have been developed for 2 setting the torque set value and sensing the output torque of the motor. The electrical torque adjusting device is electrically connected to a control circuit and the motor of the electrical hand tool. When the electrical torque adjusting device senses that the output torque of the motor exceeds the torque set value, 5 the control circuit will stop the power of the motor. However, the output torque of the motor connected to the electrical torque adjusting device will be interfered by variation of the power, and deviates from the torque set value. Furthermore, when the motor rotates in a reverse direction, for example detaching a screw from an object, the user is 10 required to manually set a reverse torque for the motor. Such a manually setting of the reverse torque is superfluous and inconvenient for the user. SUMMARY OF THE INVENTION An objective of the present invention is to provide a torque control device for electrical hand tools, wherein the motor operates according to a 15 torque set value selected by the user when it is rotating in a forward direction, otherwise the motor operates according to a single default reverse set torque when it is rotating in a reverse direction. The output torque of the motor is also compensated to approach the torque set value as close as possible. The torque control device for electrical hand tools has a reverser, a 20 control module, a current detector, a switch module, a voltage sensing module, a rotation direction sensing module, a torque sensing module and a torque setting module. The reverser controls a motor of an electrical hand tool to rotate in a forward direction or a reverse direction. The rotation direction sensing module detects the rotation direction of the motor. The current detector 3 senses a driving current of the motor. When the motor is controlled to rotate in the forward direction, the control module refers to a torque set value, a detected output torque of the motor, and a detected driving voltage to compensate the output torque and 5 rotation speed of the motor. When the motor is controlled to rotate in the forward direction, the control module refers to a single default reverse torque set value to drive the motor. Because the output torque and the rotation speed of the motor will be compensated when the motor rotates in the forward direction to reduce 10 influence resulted from the voltage variation, the output torque can meet the torque set value. Further, the user does not need to manually set a reverse torque for the motor when it is switched to rotate in the reverse direction. Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description when taken in 15 conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. I is a block diagram of a torque control device for electrical hand tools of the present invention; Fig. 2 is a circuit diagram of Fig. 1; 20 Fig. 3 shows a first embodiment of a torque setting module of the present invention; and Fig. 4 shows a second embodiment of a torque setting module of the present invention.

4 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to Figs. I and 2, a torque control device 30 of the present invention is connected between a DC power 10 and a DC motor 20. The torque control device has a power input port 31 and a power output port 32. 5 The power input port 31 has a positive terminal 311 and a negative terminal 312 respectively connected to a positive pole and a negative pole of the DC power 10, wherein the negative terminal 312 is also connected to a ground. The output power output port 32 has a first output end 321, a second output end 322 and a voltage sensing end 323. The first output end 321 and the second output 10 end 322 are respectively connected to two power terminals of the DC motor 20. The first output end 321 is also connected to the positive terminal 311. The tour control device further comprises a reverser 33, a switch module 34, a control module 35, a rotation direction sensing module 36, a voltage sensing module 37, a torque sensing module 38, a current detector 381, 15 and a torque setting module 39. The reverser 33 has a first power end, a second power end, a first load end and a second load end. The first and second power ends are respectively connected to the first and second output ends 321, 322. The first load end is connected to the voltage sensing end 323 and one of the power terminals of the 20 DC motor 20. The second load end is connected to the other of the power terminals of the DC motor 20. As shown in Fig 2, the reverser 33 in this embodiment is implemented by a double throw double pole switch having two normal-close contacts, two normal-open contacts, and two common contacts. The two normal-close 5 contacts are connected to the two power terminals of the DC motor 20. The two normal-open contacts are connected to two power terminals of the DC motor but in a reversed connection configuration different from that of the normal-close contacts. 5 When the two common contacts are switched to connect the two normal-close contacts, the reverser 33 is switched in a forward mode. Otherwise when the two common contacts are switched to connect the two normal-open contacts, the reverser 33 is operated in a reverse mode. Polarities of a driving voltage applied to the DC motor 20 may be changed as the reverser 10 33 changes to the forward mode or the reverse mode so that the rotation direction of the DC motor 20 can be reversed. The switch module 34 has an input end, an output end and a control end. The input end is connected to the second output end 322 of the power output port 32. The output end is connected to the current detector 381. The 15 control end is connected to the control module 35. The switch module 34 controls whether the driving voltage from the DC power 10 can be applied to the DC motor 20. The switch module 34 comprises a driving transistor 341 implemented by a BJT (bipolar junction transistor) and a switch transistor 342 implemented by a MOSFET (metal oxide 20 semiconductor field effect transistor). A base of the driving transistor 341 is connected to the control module 35 through a transistor R, a collector of the driving transistor 341 is connected to a gate of the switch transistor 342, and an emitter of the driving transistor 341 is connected to the ground. A drain and a source of the switch transistor 342 are respectively connected to the second 6 output terminal 322 and the current detector 381. The current detector 381 is implemented by a resistor R3 in this embodiment. When the control module 35 a signal to turn on the driving transistor 341, the switch transistor 342 will also be turned on. Therefore, the driving 5 voltage from the DC power 10 can pass through a power loop formed by the power input port 31, the power output port 32, the reverser 33, the switch module 34 and the current detector 10. The DC motor 20 can be driven by the driving voltage. When the driving transistor 341 is turned off, the switch transistor 342 and the DC motor 20 will also be turned off. 10 The control module 35 has multiple input ports and output ports, wherein the switch module is connected to one of the output ports. The input ports are connected to the rotation direction sensing module 36, the voltage sensing module 37, the torque sensing module 38, and the torque setting module 39. The control module 35 includes a torque compensation and speed 15 adjust unit 351. The torque compensation and speed adjust unit 351, based on a real time voltage signal generated by the voltage sensing module 37, a torque signal generated by the torque sensing module 38 and a torque set value of the torque setting module 39, compensates the decreased torque resulted from the voltage variation of the DC power 10, and adjusts the rotations speed of the DC 20 motor 20. The rotation direction sensing module 36 has a sensing end connected to the voltage sensing end of the power output port 32, and an output end connected to one of the input ports of the control module 36. The rotation direction sensing module 35 detects the polarity of the driving voltage at the 7 voltage sensing end 323 and transmits the detected polarity to the control module 35. The control module 35 can determine whether the DC motor 20 is rotating in a forward direction or in a reverse direction. As shown in Fig. 2, the rotation direction module 36 comprises a first 5 operational amplifier U5B having a non-inverting input as the sensing end, an inverting input receiving a reference voltage Vref, and an output as the output end of the rotation direction module 36. If the detected voltage at the non-inverting input is higher than the reference voltage Vref, the reverser 33 operates in the forward mode and the DC motor 20 rotates in the forward 10 direction. If the detected voltage at the non-inverting input is lower than the reference voltage Vref, the reverser 33 operates in the reverse mode and the DC motor 20 rotates in the reverse direction. Thus, the control module determines the rotation direction of the DC motor 20 based on an output signal of the operational amplifier U5B. 15 The voltage sensing module 37 has an input end connected to the positive terminal 311 of power input port 31, and an output end connected to one of the input ports of the control module 35. The voltage sensing module 37 senses the power status of the power input port 31, such as the voltage level, the voltage variation, to generate the real time voltage signal. As shown in Fig. 20 2, the voltage sensing module 37 is implemented by a voltage dividing circuit composed of a first resistor R1 and a second resistor R2 connected in series between the positive terminal and the ground. A connection node between the first resistor RI and the second resistor R2 forms as the output end of the voltage sensing module 37.

8 The torque sensing module 38 has two input ends connected across the current detector 381, and an output end connected to one of the input ports of the control module 35. The torque sensing module 38 senses a voltage across the current detector 381 to generate the torque signal, As shown in Fig. 2, the 5 torque sensing module is implemented by three resistors R4, R5, R6 and a second operational amplifier U2B as a signal amplifier. The resistor R4 is connected between one end of the current detector 381 and the non-inverting input of the second operational amplifier U2B. The resistor RS is connected between the other end of the current detector 381 and the inverting input of the 10 second operational amplifier U2B. The resistor R6 is connected between the inverting input and the output of the second operational amplifier U2B. The output of the second operation amplifier U2B is connected to the input port of the control module 35. The torque setting module 39 is connected to one of the input ports of 15 the control module 35 for setting the torque set value. As shown in Fig. 2, the torque setting module 39 is implemented by a variable resistor 391 and a setting unit 392. The variable resistor 391 has three pins, wherein the first and the third pins are connected to an operating voltage, and the second pin is connected to the setting unit 392, The setting unit 392 comprises a resistor R7, 20 a capacitor, C2 and a third operational amplifier U4B connected in a negative feedback configuration. The resistor R7 is connected between the variable resistor 391 and the non-inverting input of the third operational amplifier U4B. The capacitor C2 is connected between the non-inverting input of the third operational amplifier U41B and the ground. The output of the third operational 9 amplifier U4B is connected to one of the input ports of the control module 35. By adjusting the resistance of the variable resistor 391, users can change the torque value. With reference to Fig. 3, a second embodiment of the torque setting 5 unit 39A is implemented by a variable resistor 391 having three pins, wherein the first and the third pins are connected to an operating voltage, and the second pin is directly connected to the control module 35. The control module obtains the resistance value of the variable resistor 391A. With reference to Fig. 4, a third embodiment of the torque setting unit 10 39B is implemented by a variable resistor 391 and an operational amplifier U4B. The first and the third pins are connected to an operating voltage, and the second pin is connected to the non-inversing input of the operational amplifier U4B. The inversing input of the operational amplifier U4B receivers a reference voltage Vref. The output of the operational amplifier U4B is 15 connected to the control module 35. When the present invention is applied to electrical hand tools, the control module 35 obtains the polarity of the driving voltage through the rotation direction sensing module 36. When the DC motor 20 rotates in the forward rotation, the torque compensation and speed adjust unit 351, based on 20 the real time voltage signal, the torque signal and the torque set value selected by the user, compensates the output torque and adjusts the rotation of the DC motor 20.Therefore, the output torque of the DC motor 20 can much approximate the torque set value selected by the user. When the DC motor 20 rotates in the reverse direction, the control module 35 drives the DC motor 10 based on a default revere torque set value. In another embodiment of the torque control device 30 in accordance with the present invention, a high voltage sensing module 41, a low voltage sensing module 42 and a display module 43 are included. 5 The high voltage sensing module 41 has an input end and an output end, wherein the input end is connected to the output end of the voltage sensing module 37, and the output end is connected to one of the input ports of the control module 35. The high voltage sensing module 41 compares the output voltage of the voltage sensing module 37 with a high reference voltage Vhig, If 10 the output voltage of the voltage sensing module 37 is larger than the high reference voltage Vbig, the control module 35 turns off the switch module 34. The high voltage sensing module 41 is implemented by a fourth operational amplifier UlB with a non-inversing input receiving the high reference voltage V 1 g, and an inversing input receives the output voltage from 15 the voltage sensing circuit 37. If the output voltage received is lower than the high reference voltage V1%jgh, the driving voltage output from the DC power 10 is normal. On the contrary, if the output voltage received is higher than the high reference voltage Vhigh, such comparison result indicates that the driving voltage is abnormally high and the switch module 34 will be immediately 20 turned off to protect the DC motor 20 from burning up. The low voltage sensing module 42 has an input end and an output end, wherein the input end is connected to the output end of the voltage sensing module 37, and the output end is connected to one of the input ports of the control module 35. The low voltage sensing module 42 compares the output 11 voltage of the voltage sensing module 37 with a low reference voltage V1, If the output voltage of the voltage sensing module 37 is smaller than the low reference voltage Vl,, the control module 35 turns off the switch module 34. The low voltage sensing module 42 is implemented by a fifth 5 operational amplifier U3B with an inversing input receiving the low reference voltage Vjw and an non-inversing input receives the output voltage from the voltage sensing circuit 37. If the output voltage received is higher than the low reference voltage V 1 0 , the driving voltage output from the DC power 10 is normal, On the contrary, if the output voltage received is lower than the low 10 reference voltage V 1

,

0 , the comparison result indicates that the driving voltage is abnormally low and the switch module 34 will be immediately turned off. The display module 43 is used to show operating information of the control module 35, such as the torque set value selected by the user, the driving voltage, the driving current and etc. The display module 43 may be 15 implemented by a liquid crystal display (LCD). 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 features of the invention, the disclosure is illustrative only. Changes may be made in the details, especially in matters of shape, size, and 20 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.

Claims

1. A torque control device for electrical hand tools, the torque control device adapted to be connected between a DC power and a DC motor and comprising: 5 a power input port for connecting to the DC power and receiving a driving voltage from the DC power; a power output port for connecting to the DC motor; a reverser being switched to either a forward mode or a reverse mode, changing a rotation direction of the DC motor by reversing polarities of the 10 driving voltage applied to the DC motor, and comprising: a first power end and a second power end both connected to the power output port; and a first load end and a second load end both connected to the DC motor; 15 a switch module connected between the power input port and the power output port, turning on or off the DC motor based on a control signal; a current detector connected between the switch module and a ground for sensing a current flowing through the DC motor; a rotation direction sensing module connected to the reverser to sense 20 the polarities of the driving voltage applied to the DC motor; a voltage sensing module connected to the power input port for detecting a voltage level and voltage variation of the driving voltage, and accordingly generating a real time voltage signal; a torque sensing module connected to the current detector and 13 generating a torque signal based on the current detected by the current detector; a torque setting module for setting and adjusting a torque set value; a control module connected to the switch module, the rotation direction sensing module, the voltage sensing module, the torque sensing module and the 5 torque setting module and comprising a torque compensation and speed adjust unit, multiple output ports and multiple input ports; wherein the control module determines whether the reverser is switched to the forward mode or the reverse mode based on the polarities of the driving voltage sensed by the rotation direction sensing module; 10 when the reverser is switched to the forward mode, the torque compensation and speed adjust unit adjusts and compensates an output torque of the DC motor based on the torque set value, the torque signal, and the real time voltage signal so that the output torque is close to the torque set value; and when the reverser is switched to the forward mode, the control module 15 drives the DC motor based on a default reverse torque set value.

2. The torque control device as claimed in claim 1, wherein the power input port comprises a positive terminal and a negative terminal respectively connected to a positive pole and a negative pole of the DC power, wherein the negative terminal is used as a ground; 20 the power output port comprises a first output end and a second output end respectively connected to two power terminals of the DC motor, wherein the first output end is further connected to the positive terminal of the power input port; and a voltage sensing end connected to the first load end of the 14 reverser.

3. The torque control device as claimed in claim 2, wherein the first power end of the reverser is connected to the first output end of the power output port; 5 the second power end of the reverser is connected to the second output end of the power output port; the first load end is connected to one of the two power terminals of the DC motor; and the first load end is connected to the other of the two power terminals 10 of the DC motor,

4. The torque control device as claimed in claim 3, wherein the switch module comprises an input end connected to the second output end of the power output port; 15 an output end connected to the current detector; and a control end connected to one of the output ports of the control module.

5. The torque control device as claimed in claim 4. wherein the rotation direction sensing module comprises: 20 a sensing end connected to the voltage sensing end of the power output port; and an output end connected to one of the input ports of the control module; wherein rotation direction sensing module senses the polarities of the 15 driving voltage through the sensing end and transmits the sensed polarities to the control module,

6. The torque control device as claimed in claim 5, where the rotation direction sensing module comprises 5 a first operational amplifier having a non-inverting input as the sensing end of the rotation direction sensing module; an inverting receiving a reference voltage; and an output as the output end of the rotation direction sensing 10 module.

7. The torque control device as claimed in claim 6, wherein the voltage sensing module comprises a first resistor and a second resistor connected in series; wherein one end of the first resistor is connected to the positive 15 terminal of the power input port; and a connection between the first resistor and the second resistors forms an output end of the voltage sensing module and is connected to one of the input ports of the control module.

8. The torque control device as claimed in claim 1, wherein the torque sensing module comprises: 20 a second operational amplifier having a non-inversing input, an inversing input and an output, wherein the output of the second operational amplifier is connected to one of the input ports of the control module; a third resistor connected between the non-inversing input of the second operational amplifier and one end of the current detector; 16 a fourth resistor connected between the inversing input of the second operational amplifier and the other end of the current detector; and a fifth resistor connected between the inversing input and the non-inversing input of the second operational amplifier. 5

9. The torque control device as claimed in claim 8, wherein the torque setting module comprises: a variable resistor having a first, a second and a third pins, wherein the first and the third pins are connected to an operating voltage; a torque setting unit comprising 10 a sixth resistor connected to the third pin of the variable resistor a third operational amplifier having a non-inverting input connected to the sixth resistor, an inverting input connected to an output of the third operational amplifier; and a capacitor connected to the non-inverting input of the third 15 operational amplifier.

10. The torque control device as claimed in claim 9, further comprising: a high voltage sensing module having an input end connected to the voltage sensing module, and an output end connected to the control module, 20 wherein the high voltage sensing detects whether the driving voltage is higher than a high reference voltage; a low voltage sensing module having an input end connected to the voltage sensing module, and an output end connected to the control module, wherein the low voltage sensing detects whether the driving voltage is lower 17 than a low reference voltage; and a display connected to the control module for displaying operating information.