JPH0424711A - Motor-driven tool - Google Patents

Abstract

PURPOSE:To control a torque lower than a prescribed value by detecting a current flowing to a motor coil, and limiting this current not to be higher than a prescribed current value for obtaining the desired torque. CONSTITUTION:A detecting means 7 is provided to detect the current flowing to the motor coil, and current limiting means 41 - 43 are provided to limit this current not to be higher than the prescribed current value for obtaining the desired torque. In a DC motor having a linear revolving number/torque characteristic, the current flowing to the motor coil is proportional to the torque (maximum torque) and by limiting the current flowing to the motor coil not to be higher than the prescribed current value, the torque can be limited as well. Therefore, the current flowing to the motor coil is limited not to be higher than the prescribed current value for obtaining the desired torque. Thus, the torque can be controlled lower than the prescribed value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power tool equipped with a DC motor having a linear rotation speed-torque characteristic.

[Conventional Technique 1) Frl Some power tools such as electric screwdrivers are equipped with a DC motor having a linear rotation speed-torque characteristic. As a torque control method for this type of power tool, a current value corresponding to the desired torque is calculated in advance, and when the set current value is exceeded, for example, the three-phase fill is short-circuited and sudden braking is applied. There are two methods: stopping the motor abruptly, and detecting the rotational speed of the motor, stopping the motor once at about 80% of the set speed, and then gradually bringing the motor closer to the set speed.

[Problem to be Solved by the Invention 1] However, when the former torque control method is used in an electric screwdriver to suddenly stop the motor, sometimes a large impact torque is applied to the screw thread depending on the length of the tightening stroke and the number of rotations. As a result, problems arise such as the threads of the plastic screw being destroyed and the tightening force of the screw being unable to be constant.

In addition, in the latter torque control method, the circuit configuration is I! There were problems in that it became sloppy and had poor operability.

The present invention has been made in view of the above points, and its purpose is to provide a power tool that can control torque to a predetermined value or less, has a simple configuration, and has good operability. .

[! Means for Solving Problem 1] In order to achieve the above object, the present invention detects the current flowing through the motor coil and limits the current so that it does not exceed a predetermined current value at which a desired torque can be obtained. have the means.

The current limiting means may, for example, control the current supplied to the motor coil so that the current flowing through the motor coil does not exceed a predetermined current value at which a desired torque can be obtained.

Further, the current limiting means may gradually increase the current limiting amount as the current flowing through the motor coil increases.

[Effect 1 time (default) In a DC motor with a linear torque characteristic, the current flowing through the motor coil is proportional to the torque (maximum torque), and if the current flowing through the motor coil is limited so that it does not exceed a predetermined current value, , torque can also be limited.

Therefore, in the present invention, by providing the above-mentioned configuration, the current flowing through the motor coil is limited so as not to exceed a predetermined current value at which a desired torque can be obtained, and the torque is controlled to be below a predetermined value. be.

[Example 1] 1 to 4 show a further embodiment of the present invention.

In this embodiment, the present invention is applied to a power tool equipped with a three-phase DC brushless motor, and in this DC brushless motor, the position of the permanent magnet rotor 1 is changed to
According to the output of the Hall element) (u+Hv, Hv), the motor drive circuit shown in Fig. It rotates the rotor 1. Here,
The Hall elements H, lHv, H, are arranged at a mechanical angle of 60 degrees as shown in FIG. Outputs a signal according to the density. This Hall element H
,,The voltage waveform of the output of HVt Hl is the third [(a)~
(As shown in el, each phase becomes a sine wave with a shift of 2/3. The above motor drive circuit is a buff-MO5FE
It is composed of a trunk inverter 2 using TQ to Q6 as switching elements, and this inverter 2 has two
FETs (Ql and Q, ,Q, and Q9. Lv,
The other end of the inverter 2 is connected to the FET QQ of the inverter 2 according to the output of the distribution circuit 3 which creates a drive signal from the output of the Hall element Hg r Hv t Hv.
6 is turned on and off. The distribution circuit 3 includes a Hall element Hu.
, Hv, and Hv in Fig. 3(d)-(i)
Outputs the rectangular wave timing signal shown in . The upper FETQ in Figure 1, ~Q is the transistor Q 13tQ
,,, A drive circuit (for example, in the case of FETQ, a totem-pole connected NPN type and two PNP type transistors Q 1 + r Q + :) 51 to 5 are controlled to turn on and off. In addition, in the drive circuit 55 of the upper FETQ, ~Q, there is a backflow blocking guide D1 ~ between the drive power supply +V and the ground.
A 70-ring power supply 61-6. consisting of capacitors C1-C1 and resistors R, -R connected in series via D3.
The driving power is supplied from the
The upper FETs Q to Q3 are connected to the drains of the lower FETs Q and Q6, and the potential seen from the ground is the same as that of the lower FETs.
This is because it fluctuates depending on the on/off state of Qi to Q6.

By the way, this motor drive circuit includes a stator winding L u
+f−V
, ~Q6's commonly connected sources and the ground are connected to the ground, and the current detection circuit 7 is composed of a humparator CP that compares the voltage across the resistor Rs with the reference voltage vR set by the variable resistor VR; The current limiting means is constituted by four NOR games 141 to 141 which take the NOR between the output of the detection circuit 7 and the output of the distribution circuit 3.

First, the basic operation of the circuit shown in FIG. 1 will be explained. This operation explanation is based on the state in which the motor is driven steadily, and at this time, the Hall elements Hut Hv, HV are shown in Figure 3 (a) to (
The output shown in c) is obtained, and the distribution circuit 3 outputs the output shown in Fig. 3 (,1
) to (i) are provided to the drive circuit 556. In addition, fixed 1,000 volume IIALU, L
A case will be described in which the current flowing through V and Lv does not exceed a predetermined current value at which the desired torque is obtained and the output of the current detection circuit 7 is at a low level. First, at time t1, l@3 (e).

As shown in (h), the outputs of terminals 2 and 5 of the distribution circuit 3 become low level, so FETQ, Q are turned on, driving power supply element V, FETQ3, fixed winding Lv, fixed 8
Fixed 1,000 turns #il l-tl in the path of wire, FETQ
Current flows through r L w. And the time. At this time, the 4th and 5th terminals of the distribution circuit 3 become low level, so at this time, FETQ3. Q turns on, drive power supply element ■, FETQ, fixed winding Lv, fixed winding Lv, FE
Stator winding Lv along the path of TQ.

A current flows through Lv. In addition, at this time, the fixed 1,000 volume IR
A current continues to flow in the same direction from time t1 to L w, and the supply of current to the fixed 1,000 turns @L u is cut off, and instead, current is supplied to the fixed 1,000 turns 1) L v. At the clock time, the 1st and 4th terminals of the distribution circuit 3 become low level, FETQ, Q5 turn on, and the drive 'la' is turned on.
+V, FETQ, Fixed winding IIAL u, Fixed winding @LV
, a current flows through the stator winding LLIILv through the path of FETQ5, and at this time, a current in the same direction continues to flow through the fixed winding II Lv from time t2, and at the same time, current is supplied to the fixed winding II Lv. is cut off, and current is supplied to the stator winding Lu instead. In addition, fixed 1,000 volumes 1) 1
The direction of the current flowing through L u is now reversed from before. Furthermore, at time t4, terminals 1 and 6 of the distribution circuit 3 become low level, FETQ, Q6 are turned on, current continues to flow through the fixed 1,000 turns @L u from time E3, and the fixed 1,000 turns ill. The supply of current to L v is cut off, and the current flows in the opposite direction to the previous one. In other words, in the motor drive circuit of this embodiment, which of the fixed 1,000 windings #il Lu, Lv, Lw always flows current to the two phases, and the current direction of the stator winding to which the new current flows is determined. is now the opposite of what it was before.

The operation of the current limiting means as a vf characteristic of this embodiment will be explained below. In addition, fixed 1,000 volumes #iL L t5. L
The current flowing to V+LW is small! As shown in Figure PJ4 (, ), if the voltage across the resistor Rs has not reached the reference voltage vR of the comparator CP, the output of the comparator CP is at a low level, and the current limiting means has no effect on the operation of the inverter 2. The inverter 2 operates in the same manner as described above.

Now, suppose that the current flowing through the fixed 1,000-volume 1iLu, Lv-Lw increases and the voltage across the resistor Rs reaches the reference voltage ■6 of the humpator CP. In this case, as shown in Figure 4 (h). 2.4.6 of the distribution circuit 3 as shown in the figure (d).
Noah 'y'-) 4 +~4. All outputs of drive circuit 5. are fixed at low level, as shown in FIG. 5(e). ~5, the outputs are also fixed at low level. Therefore, the lower FETQ of the transistor inverter 2.

Q6 will all be turned off, and the current supply to all stator windings L u , L v , L w will be disconnected, so the current flowing to the stator windings L u = L v , L v is limited so that it does not exceed a predetermined value.

However, in FIG. 4, as shown in FIG. 4(b), terminals 2, 4, and 6 of the distribution circuit 3 are at a low level to turn on FETs Q, .about.Q.

By the way, this type of DC has a linear rotation speed-torque characteristic.
For DC motors such as brushless motors, fixed 1,000-volume A1L
The maximum torque (kg-cm
) is proportional to the stator winding LυHL as shown in Figure 7.
Limiting the current flowing to V + L W limits the maximum torque. Therefore, as described above, when the current limiting means limits the current flowing through the stator windings L u = L v and L w so that it does not exceed a predetermined value, the torque can be controlled to a desired value or less.

For example, when this embodiment is applied to an electric screwdriver, the state in which the current flowing through the fixed 1,000-turn MLυt L V t L V reaches a predetermined value is the state in which the tightening torque of the screw has increased to a desired value. Therefore, the motor rotation stops. Therefore, when the set current value is exceeded, for example, the stator winding Lυy L V y L V is short-circuited and a sudden brake is applied to abruptly stop the motor, as in the conventional method.
This eliminates problems such as large impact torque sometimes being applied to the screw threads depending on the length of the screw tightening stroke and the number of times the screw is tightened, resulting in damage to the threads of the plastic screw or the inability to maintain a constant screw tightening force.

However, the supply of current to the stator windings L u , L v −L w is cut off, and the voltage across the resistor Rs becomes the reference voltage VR.
If the voltage is below, the supply of current to the fixed 1,000-volume #Lu, Lv-Lw will be restarted, but for example, with an electric screwdriver, the motor will remain in a stopped state unless the tightening torque becomes small. It will be done.

[Example 2] Another embodiment of the invention is shown in FIGS. 5 and 6.

In the case of the first embodiment described above, the stator winding LlltL
When the current flowing through v and Lv reaches a predetermined value, at that point the stator winding Lυt L V? The current to the stator winding Lυ + L v + L V was limited by continuously cutting off the current supply to the L V, but in this embodiment, the current to the stator winding L
As the current in u, LV+LV increases, the limit amount of the current flowing through the fixed 1,000-turn #jlLt, LV, Lv is gradually increased. Therefore, in this embodiment, instead of the current detection circuit 7, the fixed 1,000-volume #iLu, Lv,
An oscillator 9 and an integrator 1 are provided with a control signal generation circuit 8 that generates an output according to the current flowing through L1, and output a rectangular wave signal.
0, and a triangular wave generation circuit 1) that generates a triangular wave.
A humperator C that compares the triangular wave voltage that is the output of the resistor Rs and the triangular generating circuit 1) with the voltage across the resistor Rs.
P constitutes the control signal generating circuit 8. In addition,
In this triangular wave generating circuit 1), the output voltage can be variably set by a variable resistor VR so that the limiting current value can be variably set.

In the case of this embodiment, when the current flowing through the fixed 1,000-volume #1 Lu-Lv and Lv increases as shown in FIG. 6(b), the pulse width of the rectangular wave output of the control signal generation circuit 8 gradually increases. However, for this reason, the ON period of FETQ, ~Q6 becomes gradually shorter, and when this embodiment is applied to an electric drive, for example, when the tightening torque reaches a predetermined value, the rotation of the motor should be stopped immediately. be. 6(a) shows the output waveform of the oscillator 9, FIG. 6(b) shows the output waveform of the triangular wave generating circuit 1) and the voltage across the resistor Rs, and FIG. 6(d) shows the output of the distribution circuit 3. (e) is the output waveform of Noah Day F, the same figure (
f) is the drive circuit 5. ~56 output waveforms are shown.

[Effect of the Invention 1] As described above, the present invention is equipped with a current limiting means that detects the current flowing through the motor coil and limits this current so that it does not exceed a predetermined current value at which a desired torque can be obtained. It is possible to limit the current flowing through the motor coil so that it does not exceed a predetermined current value that provides the desired torque, and to control the torque to a predetermined value or less. , the problem of variations in tightening torque does not occur. Moreover, since it is sufficient to detect the current flowing through the motor coil and convert this current to Ilf i, the configuration can be simplified. Furthermore, unlike the method of detecting the rotational speed of the motor, stopping the motor once at about 80% of the set speed, and then gradually approaching the set speed, the operation does not become vJ#.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the arrangement of Hall elements, Fig. 3 is an explanatory diagram showing the basic operation of the same, and Fig. 4 is an explanation of the main part operation. 5 is a circuit diagram of another embodiment, FIG. 6 is an explanatory diagram of the operation of the main parts same as the above, and FIG. 7 is an explanatory diagram of the rotation speed-torque characteristic. 4, -4. Ha/Adate, L III L V? L
I is a stator winding, 7 is a current detection circuit, and 8 is a control signal generation circuit. Agent Patent Attorney Ishi 1) Ai Figure 7, Figure 2, Figure 3 ↑ t2 ↑3 t4 Figure 7, Figure 7, 7 (ki o, rI) Voluntary proposal to write procedural amendments July 21, 1990

Claims (3)

[Claims] (1) In a power tool equipped with a DC motor with a linear rotation speed-torque characteristic, the current flowing through the motor coil is detected and the current is limited so that the current does not exceed a predetermined current value that provides the desired torque. A power tool characterized by comprising a limiting means. (2) A claim characterized in that the current limiting means controls the current supplied to the motor coil so that the current flowing through the motor coil does not exceed a predetermined current value at which a desired torque can be obtained. The power tool described in item 1. (3) The power tool according to claim 1, wherein the current limiting means gradually increases the current limiting amount as the current flowing through the motor coil increases.