JP2004066413A - Impact tightening power tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an impact tightening power tool capable of tightening a screw etc. with optimal tightening torque. <P>SOLUTION: When the difference between the number of rotations of a motor 15 and the number of rotations of an anvil 40 reaches the difference of the number of rotations based on the torque control switch 36, the motor 15 is stopped to rotate. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an impact tightening power tool such as an impact driver and an impact wrench.
[0002]
[Prior art]
The impact tightening power tool has a hammer that is rotated by a motor and an anvil that is rotated by engaging with a screw or the like. Then, the hammer and the anvil collide with each other, and the hammer rotates the anvil.
[0003]
In this case, when a force equal to or more than a predetermined value is applied between the hammer and the anvil, the hammer is connected to the anvil so that it rotates freely.
[0004]
With such a configuration, when the screw is screwed with a light load, the hammer continuously rotates the anvil and continuously tightens the screw. On the other hand, when the screw is tightened and a force equal to or more than a predetermined value is applied between the anvil and the hammer, the hammer starts to rotate as described above, and after hitting the predetermined angle, collides with the anvil. By repeating the operation of the idle rotation and the collision, the anvil rotates due to the collision of the hammer, and the screw is tightened each time.
[0005]
In the case of such an impact tightening power tool, the final tightening torque of the screw depends on the number of collisions. For this reason, conventionally, as a technique for adjusting the tightening torque, setting means for setting the number of collisions between the hammer and the anvil is provided, and the motor is stopped when the hammer and the anvil collide for the number of times set by the setting means, so that an appropriate An invention in which a screw is tightened with a tightening torque has been proposed (for example, see Patent Documents 1 and 2).
[0006]
(Patent Document 1)
JP-A-5-200677 (Patent Document 2)
JP 2001-269874 A
[0007]
[Problems to be solved by the invention]
As a method for detecting the number of collisions between the hammer and the anvil in Patent Documents 1 and 2, a microphone is attached near the hammer, the collision sound is picked up by the microphone, and the number of collisions is counted in accordance with the collision sound. It has a structure.
[0008]
For this reason, a microphone is provided inside the impact tightening power tool, and a circuit for counting the number of collisions based on the sound picked up from the microphone is required, resulting in a very complicated structure.
[0009]
In view of the above problems, the present invention provides an impact tightening power tool capable of tightening a screw or the like with an optimum tightening torque.
[0010]
[Means for Solving the Problems]
The invention according to claim 1 is an impact tightening power tool for tightening a tightening target such as a screw, a bolt, a nut, or the like, by rotating the anvil when a hammer rotated by a motor collides with the anvil; An impact fastening power tool, comprising: a torque control circuit for stopping rotation of the motor when a difference between the rotation speed of the anvil and the rotation speed reaches a predetermined difference.
[0011]
The invention according to claim 2 is an impact tightening electric tool for rotating a hammer rotated by a brushless DC motor against an anvil to rotate the anvil and tighten a tightening target such as a screw, a bolt or a nut. A rotor position detecting means for detecting a rotational position of the rotor, and a rotor position detecting circuit for outputting a motor rotational speed signal related to the rotational speed of the motor based on a signal from the rotor position detecting means, An inverter circuit that outputs a drive signal to a brushless DC motor, a gate drive circuit that controls the inverter circuit, and an arithmetic circuit that performs PWM control of the gate drive circuit based on the motor speed signal, and Anvil position detecting means for detecting a rotational position, and an anvil position detecting means A torque control switch for setting a torque set value for tightening the object to be tightened, the circuit having an anvil position detection circuit for outputting an anvil speed signal relating to the speed of the anvil based on the signals. When the difference between the rotation speed of the motor based on the number signal and the rotation speed of the anvil based on the anvil rotation speed signal reaches a predetermined rotation speed difference based on the torque set value, the brushless DC An impact tightening power tool having a torque control circuit for instructing the arithmetic circuit to stop the rotation of the motor.
[0012]
The invention according to claim 3 is an impact tightening power tool for tightening an object to be tightened such as a screw, a bolt or a nut by rotating the anvil when a hammer rotated by the brushless DC motor collides with the anvil. A rotor position detection circuit that detects a rotation position of the rotor from a drive signal flowing through a coil of the stator and outputs a motor rotation speed signal related to a rotation speed of the motor; and outputs a drive signal to the brushless DC motor. An inverter circuit, a gate drive circuit for controlling the inverter circuit, and an arithmetic circuit for performing PWM control of the gate drive circuit based on the motor speed signal, and an anvil position detection for detecting a rotation position of the anvil Means based on the signal from the anvil position detecting means. An anvil position detection circuit that outputs an anvil rotation speed signal related to the rotation speed of the anvil, a torque control switch that sets a torque set value for tightening the tightening target, and a motor control based on the motor rotation speed signal. When the difference between the rotation speed and the rotation speed of the anvil based on the anvil rotation speed signal reaches a predetermined rotation speed difference based on the torque set value, the rotation of the brushless DC motor is stopped. And a torque control circuit for instructing the arithmetic circuit.
[0013]
[Operation]
According to the first aspect of the present invention, when a rotation speed difference between the rotation speed of the rotor and the rotation speed of the anvil reaches a predetermined rotation speed, the rotation of the motor is determined to have reached a set tightening torque. It stops and stops the tightening work.
[0014]
According to the second and third aspects of the present invention, when the rotation speed difference between the rotation speed of the rotor and the rotation speed of the anvil reaches the rotation speed based on the torque set value, the rotation speed reaches the set tightening torque. , The rotation of the brushless DC motor is stopped, and the tightening operation is stopped.
[0015]
That is, when the rotation speeds of the anvil and the hammer are the same, they are tightened with the minimum torque, and when the rotation speed of the anvil is 0, and when the rotation speed of the motor is maximum, they are tightened with the maximum torque. It is in a state. Therefore, the present invention focuses on the rotation speed of the anvil, and when the difference between the rotation speed of the anvil and the rotation speed of the motor is maximized, the maximum tightening torque is generated, and the difference in rotation speed is zero. In the case of, it is assumed that the minimum tightening torque is obtained.
[0016]
Then, since the difference between the rotation speeds corresponds to the tightening torque, the difference between the rotation speeds is defined based on the torque setting value, and the difference between the defined rotation speed and the rotation speed between the anvil and the rotor is defined. If the difference becomes the same, the rotation of the brushless DC motor is stopped, assuming that the set tightening torque has been reached.
[0017]
When a gearbox for changing the rotation speed is provided between the hammer and the rotating shaft of the brushless DC motor, the difference in the changed rotation speed is also taken into consideration.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to FIGS.
[0019]
The present embodiment relates to an impact driver 10 which is one of impact tightening power tools.
[0020]
(1) Configuration of Impact Driver 10 FIG. 1 is a side view of the impact driver 10 according to the present embodiment.
[0021]
The configuration of the impact driver 10 will be described with reference to FIG.
[0022]
The impact driver 10 includes a main body 12 having a substantially cylindrical outer shape, which is a body, a chuck portion 13 in which a driver tool is mounted on a tip end of the main body 12, and a grip portion 14 formed to be a pistol type. Have.
[0023]
A brushless DC motor (hereinafter, simply referred to as a motor) 15, a gearbox 16 as a speed change mechanism, and a tightening unit 11 as a tightening mechanism are built in a rear portion of the main body 12.
[0024]
The grip portion 14 is formed so that an operator can grip it with a hand, and a trigger-like trigger switch 17 is arranged at a position where a finger is located in the grip state.
[0025]
A circuit board of a control device 18 that controls the motor 15 with a predetermined rotation speed and torque by operating the trigger switch 17 is disposed below the motor 15.
[0026]
A battery 19 and a large-capacity power supply voltage smoothing capacitor 20 that is electrically connected in parallel with the battery 19 are housed inside the holding unit 14.
[0027]
On the side surface of the main body 12, a rotation direction switch 26 for switching the rotation direction and a variable torque control switch 36 are provided.
[0028]
(2) Impact unit 11
(2-1) Structure of the Impact Unit 11 The structure of the fastening unit 11 will be described with reference to FIG.
[0029]
The tightening portion 11 includes a hammer 38 and an anvil 40.
[0030]
A plurality of grooves 48 are formed in an output shaft 46 of the gearbox 16 in a V-shape, and a hammer 38 is arranged on the output shaft 46 so as to be freely rotatable. A ball 50 is interposed between the hammer 38 and the groove 48. A cam mechanism is formed by the groove 48 and the ball 50, and the hammer 38 can move relative to the output shaft 46 along the groove 48. A coiled spring 44 is accommodated between the hammer 38 and the output shaft 46 via a ball 52 and a washer 54 in a compressed state, and the hammer 38 is constantly urged toward the anvil 40. .
[0031]
An anvil 40 is rotatably attached to the main body 12 via a bearing 42 on the distal end side of the hammer 38. The chuck 13 is attached to the tip of the anvil 40.
[0032]
A pair of wing portions 56 extending in the diameter direction are formed on the rear side surface of the anvil 40, that is, the surface corresponding to the hammer 38. A claw 58 extending in the diameter direction is also formed on the front side of the hammer 38, that is, on the side of the anvil 40, so that the blade 56 and the side surface of the claw 58 are configured to abut.
[0033]
The tip of the rotation shaft 60 of the anvil 40 is connected to the chuck portion 13 as described above, and a disk-shaped position detection plate 62 is coaxially attached to the rotation shaft 60. The position detection plate 62 is provided with fan-shaped permanent magnets having N poles and S poles in order to detect its rotation (see FIG. 3). The number of the N-pole and S-pole permanent magnets is the same as that of the N-pole and S-pole permanent magnets provided inside the rotor of the motor 15, that is, two poles are arranged.
[0034]
Hall elements H4, H5, H6 for detecting the rotation state are arranged at positions corresponding to the position detecting permanent magnets 64. These three Hall elements H4, H5, H6 are fixed to a fixed plate 70 protruding from the inside of the main body 12, and output anvil rotation signals S4, S5, S6.
[0035]
The roles of the permanent magnet 64 for detecting the position of the anvil 40 and the three Hall elements H4, H5, H6 will be described later.
[0036]
(2-2) Operation of the Tightening Part 11 In this tightening part 11, when the screw is tightened with a light load, the hammer 38 is pressed against the anvil 40 by the force of the spring 44. Therefore, the rotation of the gearbox 16 is continuously transmitted to the hammer 38 and the anvil 40, and the screws are continuously tightened.
[0037]
However, when the tightening force on the screw increases, the motor 15 continues to rotate, and the spring 44 contracts while pulling the hammer 38, so that a repulsive force is accumulated. Further, when the hammer 38 is pulled and the claw portion 58 gets over the blade portion 56 of the anvil 40, the force stored in the spring 44 is released at a stretch, and the hammer 38 rotates strongly while pressing. Then, the claw portion 58 of the hammer 38 strongly strikes the blade portion 56 of the anvil 40, and tightens the screw with a strong tightening torque that does not occur only by rotation.
[0038]
In this case, if the tightening torque is too large, a problem occurs that the head of the screw is broken. Therefore, it is necessary to set the maximum value of the tightening torque. For this purpose, the maximum value of the tightening torque is set by the torque control switch 36. This setting will be described later in detail.
[0039]
(3) Structure of Motor 15 The motor 15 is an IPM (Interior Permanent Magnet) type brushless DC motor having three slots and two poles.
[0040]
The stator has three teeth projecting inward, and a coil 34 is wound around each tooth. The coil 34 wound around each tooth portion is Y-connected to form three phases of a U phase, a V phase, and a W phase.
[0041]
Since the motor 15 is a two-pole IPM type, N-pole and S-pole permanent magnets are respectively built in the rotor.
[0042]
(4) Configuration of Control Device 18 Next, the control device 18 for controlling the motor 15 will be described with reference to FIG.
[0043]
FIG. 3 is a block diagram showing the control device 18 of the motor 15.
[0044]
A drive signal is supplied from the inverter circuit 21 to the U-phase, V-phase, and W-phase coils 34 of the motor 15. Bipolar driving is performed by using the six switching transistors constituting the inverter circuit 21 to drive the motor 15 by passing a bidirectional driving current to the three-phase coils 34 connected in a Y-connection. As a bipolar driving method, a 120 ° energized rectangular wave driving method may be used. The inverter circuit 21 is supplied with DC power as a battery 19, and the power supply voltage smoothing capacitor 20 is connected between the inverter circuit 21 and the battery 19 in parallel with the battery 19.
[0045]
The rotation signals S1, S2, S3 from the Hall elements H1, H2, H3 for detecting the rotation position of the rotor 88 of the motor 15 are output to the rotor position detection circuit 23, and the motor position signal is output from the rotor position detection circuit 23. A is output.
[0046]
A gate drive circuit 28 for sending a gate signal to the gate terminals of the switching transistors Tr1 to Tr6 of the inverter circuit 21 is provided, and an arithmetic circuit 22 for supplying a PWM (pulse width modulation) signal to the gate drive circuit 28 is provided. I have. The arithmetic circuit 22 performs PWM based on a motor speed signal A from the rotor position detection circuit 23, a speed command signal B from the speed command circuit 24, and a rotation direction command signal C from the rotation direction command circuit 25. The signal is output to the gate drive circuit 28.
[0047]
The above-described trigger switch 17 is connected to the speed command circuit 24 that outputs the speed command signal B. The speed command circuit 24 sends the speed command signal B to the arithmetic circuit 22 according to the pressing state of the trigger switch 17 by the operator. Output. That is, the speed command signal B is output so as to rotate faster by pulling the trigger switch 17 many times.
[0048]
By switching the rotation direction changeover switch 26 of the main body 12 to forward rotation or reverse rotation, the rotation direction instruction signal C corresponding to the rotation direction is output from the rotation direction instruction circuit 25 to the arithmetic circuit 22.
[0049]
A lock protection circuit 27 is provided between the gate drive circuit 28 and the arithmetic circuit 22. The lock protection circuit 27 detects that the rotation of the motor 15 is not detected by the rotation signals from the Hall elements H1, H2, and H3 even though the drive current is output to the motor 15, Is a circuit that forcibly cuts off a signal from the arithmetic circuit 22 to the gate drive circuit 28 when is detected.
[0050]
A resistor 32 for detecting a drive current output from the battery 19 is connected, and an overcurrent protection circuit 29 for detecting a drive current flowing through the resistor 32 is provided. When the drive current flowing through the resistor 32 exceeds a set value, the overcurrent protection circuit 29 determines that the current is an overcurrent and outputs a control signal to the arithmetic circuit 22 to instruct the arithmetic circuit 22 to reduce the rotation speed or the torque. . When this control signal is output, the arithmetic circuit 22 forcibly narrows the pulse width of the PWM waveform and lowers the output of the motor 15. As a result, further generation of heat of the motor 15 is suppressed, and the control device 18 can be prevented from being damaged by heat without causing a temperature rise.
[0051]
The control unit 18 is also provided with an anvil position detection circuit 66 and a torque control circuit 68.
[0052]
The anvil position detection circuit 66 receives the anvil rotation signals S4, S5, and S6 from the three Hall elements H4, H5, and H6 corresponding to the permanent magnets 64 for detecting the position of the anvil 40, and detects the rotation speed of the anvil 40. Then, an anvil rotation speed signal D is output.
[0053]
The torque control circuit 68 receives an anvil rotation speed signal D from the anvil position detection circuit 66 and a rotor rotation speed signal A from the rotor position detection circuit 23, and a torque control switch provided on the main body 12. 36 is also connected. Further, in the memory of the torque control circuit 68, data of a graph of FIG. 5 showing a correspondence relationship between the rotation speed difference, which is a difference between the rotor rotation speed and the anvil rotation speed, and the torque control switch 36 is stored. ing.
[0054]
(5) Operation of the Torque Control Circuit 68 The torque control circuit 68 controls the tightening torque for the screw. According to the tightening torque set by the torque control switch 36, the torque of the currently tightened anvil 40 is controlled. When the force reaches the set torque value, the torque control circuit 68 outputs a stop signal E for stopping the motor 15 to the arithmetic circuit 22.
[0055]
The operation will be described below.
[0056]
When the impact driver 10 is operated to start screw tightening and the tightening torque is weak, the anvil 40 and the hammer 38 are rotating at the same rotational speed as described above. Therefore, the rotation speed difference between the anvil 40 and the hammer 38 is zero. Then, even when the rotational speed of the motor 15 and the rotational speed of the anvil 40 are compared in consideration of the gear ratio of the gear box 16, the difference between the rotational speeds of the two is zero. In this case, the tightening torque is minimal.
[0057]
Thereafter, the screw is tightened, the tightening torque gradually increases, the rotation speed of the anvil 40 becomes zero, the rotation speed of the motor 15 becomes maximum, and when the hammer 38 idles with respect to the anvil 40, The tightening torque is maximized. That is, when the rotation speed of the anvil 40 becomes 0 and the rotation speed of the motor 15 increases and becomes the maximum, the maximum tightening torque is obtained.
[0058]
From this viewpoint, the current tightening torque of the impact driver 10 can be measured. Specifically, the difference between the rotation speed of the anvil 40 and the rotation speed of the motor 15 is calculated. If there is no difference in the rotation speed, the tightening torque is the minimum, and if the difference in the rotation speed is the maximum, the maximum tightening torque is obtained. Torque. Therefore, the tightening torque corresponding to the difference in the number of rotations is set by the torque control switch 36, and when the difference in the number of rotations between the anvil 40 and the motor 15 becomes the difference in the number of rotations set by the torque control switch 36, Is determined to be in the state of being tightened with the target tightening torque, and the torque control circuit 68 outputs the stop signal E. Note that the correspondence between the value of the torque control switch 36 and the difference between the rotational speeds is determined in advance by an experiment and stored in the memory of the torque control circuit 68 as the data of the graph shown in FIG.
[0059]
The above relationship will be described based on the flowchart of FIG.
[0060]
In step 1, the operator sets the tightening torque in the work by using the torque control switch 36.
[0061]
In step 2, the work of tightening the screws is started.
[0062]
In step 3, the torque control circuit 68 detects the rotation speed of the motor 15. In step 4, the torque control circuit 68 detects the rotation speed of the anvil 40.
[0063]
In step 5, a difference M1 between the rotation speed of the motor 15 and the rotation speed of the anvil 40 is calculated.
[0064]
In step 6, the torque control circuit 68 reads the difference M2 in the number of revolutions corresponding to the set tightening torque from the memory.
[0065]
In step 7, if M1 becomes larger than M2, that is, if the set tightening torque is reached, the process proceeds to step 8, otherwise returns to step 3.
[0066]
In step 8, since the set tightening torque has been reached, the torque control circuit 68 outputs the stop signal E to the arithmetic circuit 22 so as to stop the motor 15, and ends.
[0067]
According to the above configuration, when the tightening torque set by the operator is reached, the motor 15 is stopped, so that the screw is not tightened with an excessive tightening torque and the head of the screw is not broken.
[0068]
(Modification 1)
In the above embodiment, the impact driver 10 has been described. However, the present invention is not limited to this and may be applied to another impact tightening power tool such as an impact wrench.
[0069]
(Modification 2)
In the above embodiment, the number of rotations of the motor 15 is detected by providing the three Hall elements H1, H2, H3, but a sensorless control device 18 may be used instead.
[0070]
Specifically, a drive current flowing from the inverter circuit 21 to the coil 34 of the stator may be detected, and the rotational position of the rotor may be detected based on the detected drive current to determine the rotational speed of the motor 15.
[0071]
【The invention's effect】
As described above, according to the impact tightening power tool of the present invention, the motor stops at the set tightening torque, so that the object to be tightened such as a screw is not broken.
[Brief description of the drawings]
FIG. 1 is a side view of an impact driver showing one embodiment of the present invention.
FIG. 2 is a side view showing a structure of a fastening portion.
FIG. 3 is a block diagram of a motor control device.
FIG. 4 is a flowchart showing the processing content of a torque control circuit.
FIG. 5 is a graph showing a relationship between a value of a torque control switch and a difference between rotation speeds.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Impact driver 11 Tightening part 15 Motor 17 Trigger switch 18 Controller 21 Inverter circuit 22 Arithmetic circuit 23 Rotor position detection circuit 24 Speed command circuit 25 Rotation direction command circuit 26 Rotation direction switch 28 Gate drive circuit 29 Overcurrent protection circuit 36 Torque control switch 38 Hammer 40 Anvil 44 Spring 62 Position detection plate 64 Permanent magnet 66 Anvil position detection circuit 68 Torque control circuit

Claims (3)

In an impact tightening power tool for tightening a tightening target such as a screw, a bolt, a nut, or the like, the anvil rotates when a hammer rotated by a motor collides with the anvil.
When the difference between the rotation speed of the motor and the rotation speed of the anvil reaches a predetermined difference between the rotation speeds, a torque control circuit that stops the rotation of the motor is provided. . An impact tightening power tool for tightening a tightening target such as a screw, a bolt or a nut by rotating the anvil when a hammer rotated by a brushless DC motor collides with the anvil,
Rotor position detection means for detecting the rotation position of the rotor of the brushless DC motor; and a rotor position detection circuit for outputting a motor rotation number signal relating to the rotation number of the motor based on a signal from the rotor position detection means. Has,
An inverter circuit that outputs a drive signal to the brushless DC motor, a gate drive circuit that controls the inverter circuit, and an arithmetic circuit that performs PWM control on the gate drive circuit based on the motor speed signal,
Anvil position detection means for detecting a rotation position of the anvil, and an anvil position detection circuit for outputting an anvil rotation number signal relating to the rotation number of the anvil based on a signal from the anvil position detection means,
A torque control switch for setting a torque set value for tightening the tightening target,
When the difference between the rotation speed of the motor based on the motor rotation speed signal and the rotation speed of the anvil based on the anvil rotation speed signal reaches a predetermined rotation speed difference based on the torque setting value, An impact tightening power tool comprising a torque control circuit for instructing the arithmetic circuit to stop the rotation of the brushless DC motor. An impact tightening power tool for tightening a tightening target such as a screw, a bolt or a nut by rotating the anvil when a hammer rotated by a brushless DC motor collides with the anvil,
A rotor position detection circuit that detects a rotation position of a rotor of the brushless DC motor from a drive signal flowing through a coil of a stator and outputs a motor rotation speed signal related to a rotation speed of the motor,
An inverter circuit that outputs a drive signal to the brushless DC motor, a gate drive circuit that controls the inverter circuit, and an arithmetic circuit that performs PWM control on the gate drive circuit based on the motor speed signal,
Anvil position detection means for detecting a rotation position of the anvil, and an anvil position detection circuit for outputting an anvil rotation number signal relating to the rotation number of the anvil based on a signal from the anvil position detection means,
A torque control switch for setting a torque set value for tightening the tightening target,
When the difference between the rotation speed of the motor based on the motor rotation speed signal and the rotation speed of the anvil based on the anvil rotation speed signal reaches a predetermined rotation speed difference based on the torque setting value, An impact tightening power tool comprising a torque control circuit for instructing the arithmetic circuit to stop the rotation of the brushless DC motor.

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