JPH11215871A - Motor controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To immediately stop the rotation of a DC motor when abnormality is detected, and besides, lighten the voltage stress or current stress of a MOSFET. SOLUTION: A switch circuit 1 is equipped with a MOSFET Q1 connected in series to a DC motor M, and a MOSFET Q2 connected in parallel with the DC motor M. The series circuit of the DC motor M and the MOSFET Q1 is connected to a battery B at low voltage. When the MOSFET Q1 is turned on by a control signal generating circuit 22, the DC motor M is driven. Moreover, when the load of the DC motor M becomes large, and an overload signal is generated, the control signal generating circuit 22 turns off the MOSFET Q1 and turns on the MOSFET Q2, and lets the regenerated current of the DC motor M flow to the MOSFET Q2. In short, the DC motor M is stopped in a short time by letting the regenerated current flow to the DC motor M.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor control device for controlling a DC motor for a power tool.

[0002]

2. Description of the Related Art Conventionally, as a power tool, a tool such as an electric screwdriver or an electric drill for rotating a bit in a normal or reverse direction using a DC motor has been provided. In this type of power tool, the direction of rotation of the DC motor is switched between forward and reverse by switching the polarity of the voltage applied to the DC motor with a changeover switch also serving as a power switch. The changeover switch inserts a mechanical contact between the DC power supply and the DC motor, and a relatively large current flows through the DC motor in order to secure a relatively large torque with a power tool. There is a problem that the contact is easily consumed by the arc. Generally, the life of this type of changeover switch is said to be two to three years, and is extremely short as compared with the life of other members constituting a power tool such as a DC motor. Therefore, it has been considered to extend the service life by using a semiconductor switch element instead of using a mechanical contact between the DC power supply and the DC motor.

[0003] By the way, electric power tools using a commercial power supply as a power supply have been conventionally provided. However, there is a problem that the power supply becomes a hindrance when the commercial power supply is used as a power supply. As the current capacity per volume has increased as a result, power tools with a built-in secondary battery have become widespread. On the other hand, MOSFETs whose power can be easily controlled are often used as semiconductor switch elements. On the other hand, MOSFETs have a large on-resistance when the gate-source voltage is low, so that the on-resistance is sufficiently small (for example, 5 mΩ). It is necessary to secure a relatively high (for example, 15 V) gate-source voltage. That is, if a secondary battery is used, a series connection is required to secure a high voltage as a gate-source voltage, and eventually, a disadvantage arises in that the weight ratio of the secondary battery closed to the power tool increases.

Therefore, it has been considered to provide a booster circuit for boosting the output voltage of the secondary battery to secure the gate-source voltage and reduce the on-resistance of the MOSFET used for the semiconductor switch element (Japanese Patent Application Laid-Open No. HEI 9-1994). 2-2
No. 49995).

[0005]

As described above, the MO
When the DC motor is turned on and off and the direction of rotation is switched using a semiconductor switch element made of an SFET, the life is prolonged and the occurrence of noise to the outside is reduced due to the non-contact. By the way, when an overload is applied to the DC motor, if the rotation is continued beyond that, there is a possibility that the load of the DC motor may be damaged. Therefore, it is necessary to stop the DC motor. In addition, since the MOSFET is easily damaged by voltage stress or current stress, when the load of the DC motor is further increased and locked, the back electromotive voltage generated by the DC motor coil is applied to the MOSFET, Overcurrent caused by DC current flowing through the coil of DC motor is MOSFET
Need to be protected from flowing into

In order to satisfy such a demand, it is conceivable to stop supplying power to the DC motor when an overload is detected.
The rotation of the DC motor may continue for a while due to inertia, and the load may be damaged. Further, merely stopping the power supply to the DC motor does not solve the voltage stress or the current stress that occurs when the DC motor is locked.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to stop the rotation of a DC motor immediately when an abnormality such as overload is detected,
An object of the present invention is to provide a motor control device in which voltage stress and current stress of an FET are reduced.

[0008]

According to a first aspect of the present invention, there is provided a first semiconductor switch comprising a DC motor driven by a low-voltage DC power supply, and a MOSFET inserted between the DC power supply and the DC motor. An element, a second semiconductor switch element comprising a MOSFET connected in parallel to the DC motor, and a booster circuit for increasing an output voltage of the DC power supply.
A control signal generation circuit that turns on and off each semiconductor switch element using the output of the booster circuit as a power supply; and an overload detection circuit that outputs an overload signal when the load of the DC motor exceeds a specified value. When an overload signal is generated, a brake signal for turning off the first semiconductor switch element and turning on the second semiconductor switch element is generated. According to this configuration, since the brake signal is generated at the time of overload to turn on the second semiconductor switch element connected in parallel to the DC motor, the regenerative current generated when the DC motor is stopped is supplied to the second semiconductor switch. It can flow through the element and consequently function as an electric brake to stop the rotation of the DC motor in a short time. In other words, excessive rotation due to the inertia of the DC motor can be prevented, and if the bit of the driver is rotated by the DC motor, it is possible to prevent excessive tightening of the screw, and if the bit of the drill is rotated. If it is, breakage of the bit due to overload can be prevented. In addition, since the regenerative current flows through the second semiconductor switch element connected in parallel to the DC motor, it is possible to prevent an excessive current from flowing and an excessive voltage from being applied to the second semiconductor switch element. Current stress and voltage stress on the first and second semiconductor switch elements can be reduced. Further, since the first semiconductor switch element turns the power supply path from the battery to the DC motor on and off, the radiation on and off at a location where a relatively large current flows is compared with the case where the mechanical switch is used to turn on and off the current. The generation of noise is small, and the influence of noise on various devices can be prevented.

According to a second aspect of the present invention, in the first aspect of the present invention, the first semiconductor switch element is provided between the first terminal of the DC motor and the positive electrode of the DC power supply.
The DC motor has a second terminal connected to a negative electrode of the DC power supply. According to this configuration, since only one MOSFET is inserted between the DC motor and the power supply, power loss due to the ON resistance of the MOSFET is small.

According to a third aspect of the present invention, in the second aspect of the present invention, the first semiconductor switching element is provided between the first terminal of the DC motor and the negative terminal of the DC power supply.
The DC motor has a second terminal connected to a positive electrode of the DC power supply. According to this configuration, since only one MOSFET is inserted between the DC motor and the power supply, power loss due to the ON resistance of the MOSFET is small.

According to a fourth aspect of the present invention, in the first aspect, the first semiconductor switch element is inserted between the first terminal of the DC motor and one output terminal of the DC power supply. And a second MO inserted between a second terminal of the DC motor and the other output terminal of the DC power supply.
A third MOSFET inserted between the SFET and a second terminal of the DC motor and one output terminal of the DC power supply;
And a fourth MOSFET inserted between a first terminal of the DC motor and the other output terminal of the DC power supply, wherein the second semiconductor switch element includes second and fourth M
It is made of OSFET. According to this configuration, 4
Since the bridge circuit is formed by the MOSFETs, not only a path through which the regenerative current flows can be formed by controlling the MOSFETs, but also the rotation direction of the DC motor can be switched between forward and reverse.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the control signal includes a non-inverting signal for turning on the first and fourth MOSFETs simultaneously and turning off both the second and third MOSFETs; A reverse signal for turning off the first and fourth MOSFETs and turning on the second and third MOSFETs at the same time, and a brake for turning on both the second and fourth MOSFETs and turning off both the first and third MOSFETs It is a signal. According to this configuration, the rotation direction of the DC motor can be switched between forward and reverse by the forward rotation signal and the reverse point signal, and a path through which the regenerative current flows by the brake signal can be formed.

According to a sixth aspect of the present invention, in the first aspect of the invention, when the brake signal is generated while the DC motor is rotating, the second semiconductor switch is turned off after the first semiconductor switch element is turned off. A control circuit is provided with a delay circuit for delaying the time until the element is turned on. According to this configuration, the first and second semiconductor switch elements connected in series are prevented from being simultaneously turned on, and both ends of the battery are short-circuited via the first and second semiconductor switch elements. Can be prevented.

According to a seventh aspect of the present invention, in the first aspect of the present invention, a start circuit is provided for starting power supply to the booster circuit when a pressing force acts on a bit rotated by the DC motor. Is provided with a mechanical contact that is turned on with the movement of the bit when a pressing force acts on the bit, and supplies power from a battery to the booster circuit via the contact. According to this configuration, it is possible to automatically rotate the DC motor simply by pressing the bit of the electric screwdriver or the electric drill against the object and applying a pressing force to the bit. Since it is used, power is not consumed when not in use.

According to an eighth aspect of the present invention, in the first aspect of the present invention, there is provided a start circuit for starting power supply to the booster circuit when a pressing force acts on a bit rotated by the DC motor. Is a photoelectric sensor that detects the movement of the bit when a pressing force acts on the bit, and supplies power from a battery to a booster circuit via the photoelectric sensor. According to this configuration, the DC motor can be automatically rotated simply by pressing the bit of the electric screwdriver or the electric drill against the object and applying a pressing force to the bit. Since it is possible to detect that the pressing force has acted on the bit in this state, the rotation of the bit is not affected.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) In this embodiment, an example in which a bit of a driver or a drill is rotated by a DC motor will be described assuming that the present invention is used for an electric driver or an electric drill. The idea is also applicable to other devices using DC motors.

FIG. 2 shows the overall configuration of the circuit. In the present embodiment, a battery B of a relatively low voltage (1 to 3.6 V) is used as a power supply. The battery B may be either a primary battery or a secondary battery, but a secondary battery is generally used in a power tool. Battery B is connected to DC motor M via switch circuit 1. The switch circuit 1 is a MOSFE as described later.
A semiconductor switch element made of T is provided. The connection relation between the DC motor M and the battery B is switched by turning on and off the semiconductor switch element, and a path for flowing a regenerative current generated when the DC motor M is stopped is formed.

The semiconductor switch elements of the switch circuit 1 are turned on and off by the control circuit 2. The control circuit 2 is supplied with power from the battery B via the start circuit 3. The start circuit 3 supplies power to the control circuit 2 while the pressing force by pressing the bit against the member on the other side acts on the bit. Specifically, as shown in FIG.
And a reed switch 32, and a series circuit of the reed switch 32 and the resistor R1 is connected between both ends of the battery B.
A connection point between the reed switch 32 and the resistor R1 is connected to the base of the pnp transistor Tr1 via the resistor R2. The transistor Tr1 is inserted in a power supply path from the battery B to the control circuit 2, and when the transistor Tr1 is turned on, power supply to the control circuit 2 is started.

The bit is mounted so as to move by receiving a pressing force, and the permanent magnet 31 is arranged so as to move with the movement of the bit and approach the reed switch 32.
Therefore, when the bit is pressed against the drilled object or screw, the bit moves and the reed switch 32 is turned on. At this time, the transistor Tr1 is turned on, so that the power is supplied to the control circuit 2 and the control circuit 2 operates. Start.

The control circuit 2 includes a battery B as shown in FIG.
And a control signal generation circuit 22 that generates a control signal for controlling the switch circuit 1 using the output of the booster circuit 21 as a power supply. A voltage monitoring circuit 23 for monitoring the voltage of the battery B and a DC motor M
Overload detection circuit 24 for detecting that an overload is applied to
Is also provided in the control circuit 2. The reason why the booster circuit 21 is provided is that if the output voltage of the battery B is applied between the gate and the source of the MOSFET constituting the switch circuit 1, the on-resistance is large and the loss is large. By increasing the voltage and applying a required voltage (for example, 15 V) between the gate and the source of the MOSFET, the on-resistance of the MOSFET is reduced (for example, 8 m).
Ω or less). Here, the booster circuit 21 uses a chopper circuit to boost the voltage using magnetic energy stored in the inductor, but may use a charge pump type booster circuit to boost the voltage using electric charges stored in a capacitor. The booster circuit 21 is controlled so as to keep the output voltage constant (in the chopper circuit, the output voltage can be kept constant by performing PWM control on the switching element according to the output voltage).

The voltage monitoring circuit 23 generates a reference voltage based on the output voltage of the booster circuit 21 and compares the output voltage of the battery B with the reference voltage. Voltage drop signal (L level)
Occurs. That is, the output voltage of the booster 21 is
Is kept constant until the output voltage of the battery B decreases until the output voltage of the battery B decreases while the output voltage of the booster circuit 21 is kept substantially constant. It reports the voltage drop.

The overload detection circuit 24 outputs an overload signal (H level) when the load acting on the bit exceeds a predetermined value. If the load is an electric screwdriver, the overload detection circuit 24 detects that the screw is tightened. In the case of an electric drill, it is detected that the rotation is locked. A specific configuration for detecting overload is described in Japanese Patent Application Laid-Open No. 7-205050. That is, a clutch is provided between the DC motor M and the bit, and the relative movement between the driving side (DC motor M side) and the driven side (bit side) of the clutch when the load is increased is detected. An overload is detected.

As shown in FIG. 1, the switch circuit 1 has two MOSFETs as semiconductor switch elements.
TQ1 and Q2 are connected in series. In the illustrated example, the MOSFET Q1 on the positive electrode side of the battery B is connected in series to the DC motor M, and the MOSFET Q2 on the negative electrode side of the battery B is connected in parallel to the DC motor M. Here, contact points r1 and r2 of a mechanical changeover switch for switching the rotation direction between forward and reverse are inserted at both ends of the DC motor M (contact points r1 and r2 are schematically illustrated in FIG. 1). Can switch the connection polarity of the DC motor M). Therefore, the rotation direction of the DC motor M can be switched by operating the changeover switch.

The control circuit 2 (control signal generation circuit 22)
A state in which the MOSFET Q1 connected in series to the DC motor M is turned on, a state in which the MOSFET Q2 connected in parallel to the DC motor M is turned on,
A state in which Q1 and Q2 are turned off is selected. Where M
When OSFET Q1 is ON, battery B is DC motor M
And the DC motor M rotates (this state is called a rotation mode). When both MOSFETs Q1 and Q2 are turned off, power is not supplied to DC motor M, and DC motor M stops (this state is called a stop mode). This state is the same as the state where power is not supplied to the control circuit 2.

When only the MOSFET Q2 is ON, the DC motor M is stopped because power is not supplied to the DC motor M. At this time, the MOSFET Q2 is also conducting in the reverse direction by a parasitic diode.
That is, the MOSFET Q2 conducts in both directions, and current can flow in the loop circuit formed by the MOSFET Q2 and the DC motor M. As a result, the regenerative current generated by the motor coil when the DC motor M is stopped can flow through the loop circuit, and the regenerative current can be converted into heat energy to shorten the stop time of the DC motor M (a type of electric brake). Works as). This state is called a brake mode.

The control signal generating circuit 22 is configured using a logic circuit as shown in FIG. 1 to enable the control of the rotation mode, the stop mode, and the brake mode as described above. Here, since the power supply of the control signal generation circuit 22 is the output voltage of the booster circuit 21, it is desirable to use a CMOS logic circuit to obtain a withstand voltage of about 15V. The control signal generation circuit 22 includes a mechanical main switch SW for selecting a rotation mode and a stop mode, and the main switch SW inputs (turns on) an H-level signal to one input terminal of the AND circuit AN1. Or input (off) of an L level signal. Here, the state in which the H-level signal is input to the AND circuit AN1 corresponds to the ON state. The other input terminal of the AND circuit AN1 receives the voltage drop signal from the voltage monitoring circuit 23 described above. Therefore, if the output voltage of battery B is normal, AND circuit A
N1 functions as a buffer and passes a signal from the main switch SW.

The output of the AND circuit AN1 is
2 is input to one input terminal. A signal obtained by inverting an overload signal from the overload detection circuit 24 by the knot circuit NT1 is input to the other input terminal of the AND circuit AN2. That is, in a state where the main switch SW is on and neither the voltage drop signal nor the overload signal is generated, the output of the AND circuit AN2 becomes H level, and the MOSFET Q1 is turned on.

When the main switch SW is on and a voltage drop signal is generated in a state where no overload signal is generated, the output of the AND circuit AN2 goes low and the MOSFET Q1 is turned off. Even when the voltage drop signal and the overload signal are not generated, the main switch S
If W is off, MOSFET Q1 is off. By the way, the overload signal has four knot circuits NT2 to NT5.
, A capacitor C3, a resistor R3, and a diode D3 to a gate of the MOSFET Q2 through a delay circuit. That is, when the overload signal is generated, the MOSF is delayed by the time required for discharging the capacitor C3 via the resistor R3 (here, set to 75 μsec), and
ETQ2 turns on. When an overload signal is generated, the output of the AND circuit AN2 becomes L level and the MOSFET Q1
Is turned off, the MOSFET Q2
Turns on later than 1 off. That is, it is possible to prevent the two MOSFETs Q1 and Q2 connected in series from being turned on at the same time and short-circuiting between both ends of the battery B.
When the overload signal is released, the MOSFET
Q1 is turned on. At this time, the capacitor C3 is instantaneously charged through the diode D3.
TQ2 is also turned off without delay, and both MOSFETs Q
Even if there is a period during which both Q1 and Q2 are turned on at the same time, it is very short and no problem occurs. In addition, each MO
Pull-down resistors R4 and R5 are connected to the gates of the SFETs Q1 and Q2, respectively, so that the MOSFETs Q1 and Q2 are normally off.

FIG. 4 summarizes the above operations. That is, at the time of use, the rotation direction of the DC motor M is selected by the changeover switches (contact points r1 and r2) (S1), and the main switch SW is turned on. In this state, when the pressing force acts on the bit (hereinafter referred to as bit push) is detected by the reed switch 32 (S
2) The power is supplied to the control circuit 2 and the boosting circuit 21 starts boosting the output voltage of the battery B (S3). That is, power is supplied to the control signal generation circuit 22, the voltage monitoring circuit 23, and the overload detection circuit 24, and the control signal generation circuit 22 turns on the MOSFET Q1 of the switch circuit 1 (S4). However, when a voltage drop signal is generated from the voltage monitoring circuit 23 (that is, when the output voltage of the battery B is lowered) (S5), the mode shifts to the stop mode (S6) in which both MOSFETs Q1 and Q2 are turned off. Then, the rotation of the DC motor M is stopped (S7). When the rotation of the DC motor M stops, the bid push is released (that is, the bit is separated from the object) (S8), the reed switch SW32 of the start circuit 3 is turned off, and the power supply to the booster circuit 21 is stopped. Then, the entire circuit is stopped (S9).

By the way, if the voltage drop signal has not been generated at the time of the bit push, it is determined whether or not there is an overload signal (S10). If the overload signal has not been generated, the DC motor M continues to rotate. When the work is completed in this way (S11), the bit push is released (S8), and the entire circuit is stopped (S9). On the other hand, if an overload signal is generated (S10), as described above, after the MOSFET Q1 is turned off, the MOSFET Q2 is turned on to enter the brake mode in which the regenerative current of the DC motor M flows (S1).
2) The DC motor M is stopped quickly (S13). This brake mode prevents inconveniences such as excessive tightening of screws. Then, if the bit push is released (S
8), the power supply to the booster circuit 21 stops, and the entire circuit stops (S9).

As described above, in the present embodiment, the battery B
Since the DC motor M is rotated and stopped by inserting the MOSFET Q1 into the power supply path from the power supply to the DC motor M and turning the MOSFET Q1 on and off, a relatively large current flowing through the DC motor M is turned on and off by a mechanical switch. In comparison with the case, the generation of radiation noise is small and the life can be extended. Here, in the present embodiment, the battery B is used for switching between the forward and reverse rotation directions of the DC motor M.
Switch (contact r) inserted between the motor and the DC motor M
Although the switching of the rotation direction is generally selected before the rotation of the DC motor M is started,
Radiation noise is not generated by switching the rotation direction, and the life of the device is hardly affected.

In addition, a brake mode in which the MOSFET Q2 is turned on at the time of overload is selected, and the regenerative current of the DC motor M is supplied to the MOSFET Q2 to quickly stop the DC motor M, thereby preventing inconveniences such as excessive tightening of screws. can do. Moreover, since both ends of the DC motor M are short-circuited by the MOSFET Q2, it is possible to prevent the MOSFET Q1 from being damaged due to voltage stress or current stress.

(Embodiment 2) In the embodiment 1, in the series circuit of the DC motor M and the MOSFET Q1,
Although the FET Q1 is connected to the positive electrode side of the battery B, in the present embodiment, as shown in FIG.
Is connected to the negative electrode side. In this configuration, the same operation is performed by performing control in the same manner as in the first embodiment. Other configurations are the same as in the first embodiment.

(Embodiment 3) In this embodiment, as shown in FIG. 6, four MOSFETs as semiconductor switch elements are used.
TQ11 to Q14 are bridge-connected to form a switch circuit 1, and each pair of M
A DC motor M is connected between the connection points of the OSFETs Q11, Q12, Q13, and Q14. The control circuit 2 (control signal generation circuit 22) includes two MOSFETs Q11,
Q14 is turned on, and two MOSFETs Q connected in series between both ends of the battery B with the DC motor M interposed therebetween.
12 and Q13, and two MOSFETs Q12, Q12 forming a loop circuit with DC motor M.
14 is turned on. Now, MOSFE
If DC motor M rotates forward when TQ11 and Q14 are on (this state is referred to as a forward rotation mode), MOSF
When the ETQ12 and Q13 are on, the DC motor M reversely rotates (this state is called a reverse rotation mode). That is, the forward rotation and the reverse rotation of the DC motor M can be switched by the switch circuit 1. In addition, MOSFETQ
11 and Q13 are turned off (MOSFET Q12,
Since no power is supplied to the DC motor M (when the power supply 14 is turned on), the DC motor M stops (this state is called a stop mode).

When the MOSFETs Q12 and Q14 are on, the DC motor M is stopped because power is not supplied to the DC motor M.
2, Q14 is also conducting in the reverse direction by the parasitic diode. That is, both MOSFETs Q12, Q
14 conducts in both directions, and the MOSFET Q1
2, a current can flow through a loop circuit formed by Q14 and DC motor M. As a result, the DC motor M
The regenerative current generated by the motor coil when the motor is stopped can flow through the loop circuit, and the regenerative current can be converted into heat energy to shorten the stop time of the DC motor M (function as a kind of electric brake). This state is called a brake mode. Here, in the present embodiment, the MOSFETs Q11 to Q1 in the stop mode and the brake mode are used.
The on / off state of No. 4 is the same.

To enable control of the normal rotation mode, the reverse rotation mode, the stop mode, and the brake mode as described above,
The control signal generation circuit 22 has the configuration shown in FIG. That is,
The control signal generation circuit 22 includes a mechanical main switch SW capable of selecting a stop mode, a forward rotation mode, and a reverse rotation mode.
0, V1 and three combinations of (H level, H level), (H level, L level) and (L level, L level) can be selected as the state of both outputs V0, V1. Note that even if a combination of (L level, H level) occurs, the resistors R11 and R12 and the diode D11
Thus, the combination of (H level, H level) is made equivalent. That is, if the output V1 of the main switch SW is at the L level even if the output V0 of the main switch SW is at the H level, the output V0 of the main switch SW is substantially treated as the H level by being pulled up by the resistor R11. I have.

Both outputs V0 and V1 (actually, the voltage values at both ends of the resistor R11) are input to AND circuits AN11 and AN12, and the output of one AND circuit AN11 is inverted by the NOT circuit NT11. The output of the knot circuit NT11 and the output of the AND circuit AN12 are variously combined, and when the MOSFETs Q11 and Q14 are on,
Q12 and Q13 are in the normal rotation mode in which the MOSFET Q1 is off.
2, Q13 is on and MOSFETs Q11 and Q14 are off, reverse mode, MOSFETs Q12 and Q14 are on and M
Each control signal (normal rotation signal, reverse rotation signal,
Brake signal).

The control signal to the MOSFET Q11 is generated by an OR circuit OR11 for calculating the logical sum of the outputs of the NOT circuit NT11 and the AND circuit AN12, and a NOT circuit NT12 for inverting the output of the OR circuit OR11. That is, if the output of the AND circuit AN11 is at the L level or the output of the AND circuit AN12 is at the H level, the output goes to the H level.

The control signal to the MOSFET Q12 is a knot circuit NT13 for inverting the output of the AND circuit AN12.
AND circuit AN13 for obtaining the logical product of the outputs of both knot circuits NT11 and NT13, knot circuit NT14 for inverting the output of knot circuit NT11, and AND circuit AN
AND circuit AN14 for obtaining the logical product of the outputs of the AND circuit 12 and the knot circuit NT14, and both AND circuits AN13 and AN14
And an OR circuit OR12 for calculating the logical sum of the outputs of That is, when both the output values of the AND circuits AN11 and AN12 are at the H level or the L level, the output level becomes the H level.

The control signal to the MOSFET Q13 is generated by the AND circuit AN15 as the logical product of the output values of the above-described knot circuit NT14 and AND circuit AN12. That is, the output of the AND circuit AN15 becomes H level when both the output values of the AND circuits AN11 and AN12 become H level. The control signal to the MOSFET Q14 is the output of the NOT circuit NT13 that inverts the output of the AND circuit AN12, and goes high when the output of the AND circuit AN12 is low.

Each of the control signals described above is connected to a resistor R3
1 through R34, capacitors C31 through C34, and diodes D31 through D34. Each MOSFET Q is passed through a gate that is opened and closed by an overload signal.
11 to Q14. The gate is provided with a signal obtained by delaying the overload signal by a delay circuit including a resistor R3, a capacitor C3, and a diode D3, and MOSFETs Q12 and Q1.
OR circuit OR21 for calculating the logical sum with the control signal to the OR 4
The circuit is composed of an OR22 and AND circuits AN21 and AN22 for calculating a logical product of a signal obtained by inverting an overload signal by a knot circuit NT21 and a control signal to the MOSFETs Q11 and Q13. That is, when an H level overload signal is generated, the MOSFETs Q11 and Q13 are forcibly turned off and the MOSFETs Q12 and Q14 are forcibly turned on. This is the state of the brake mode.

Each of the MOSFETs Q11 to Q11
14 and the outputs V0 and V of the main switch SW.
As is clear from the combination with No. 1, the output V of the main switch SW when no overload signal is generated.
According to 0 and V1, three states are selected in which the MOSFETs Q11 and Q14 are on (forward rotation mode), the MOSFETs Q12 and Q13 are on (reverse rotation mode), and the MOSFETs Q12 and Q13 are on (stop mode and brake mode). Here, by providing the delay circuit, each pair of MOs forming each arm of the bridge circuit is provided.
The SFETs Q11, Q12 or Q13, Q14 are prevented from turning on at the same time when each mode is switched. In this embodiment, the time constant of the delay circuit is set to 50 μsec.

The other configuration and operation of the present embodiment are the same as those of the first embodiment, and the description is omitted. Fourth Embodiment In the first embodiment, the bit push is detected by the permanent magnet 31 and the reed switch 32, but can be detected by using the photo interrupter 33 as shown in FIG. Photo interrupter 33
The light emitting diode LED and the phototransistor PT are opposed to each other. A series circuit of the light emitting diode LED and the resistor R6 and a series circuit of the phototransistor PT and the resistor R1 are connected between both ends of the battery B. , The base of the transistor Tr1 is connected to the connection point between the resistor R1 and the phototransistor PT via the resistor R2.

In this circuit, the space between the light emitting diode LED and the phototransistor PT is always shielded from light,
When the bit is pressed against the object and the bit moves, the light from the light emitting diode LED is transmitted to the phototransistor PT.
To receive the light. When the phototransistor PT is turned on in this way, the transistor Tr
1 conducts and power is supplied to the control circuit 2. In this configuration, since the light emitting diode LED is always turned on, it can be adopted only when the discharge life of the battery B is not considered. Other configurations and operations are the same as those of the first embodiment.

(Embodiment 5) In this embodiment, as shown in FIG. 8, a mechanical detection switch 34 such as a microswitch is used as a configuration for detecting a bit push. In short, a detection switch 34 may be connected instead of the reed switch 32 shown in FIG.
The circuit configuration is the same as that of the first embodiment (the resistor R1 is not illustrated, but is included in the detection switch 34 in the illustrated example). The detection switch 34 may be arranged at a position where it is turned on when the bit moves. Other configurations and operations are the same as those of the first embodiment.

[0046]

According to the first aspect of the present invention, there is provided a DC motor driven by a low-voltage DC power supply, a first semiconductor switch element comprising a MOSFET inserted between the DC power supply and the DC motor, MOS connected in parallel to the motor
A second semiconductor switch element composed of an FET, a booster circuit for boosting the output voltage of the DC power supply, a control signal generating circuit for turning on and off each semiconductor switch element using the output of the booster circuit as a power supply, and a load of the DC motor. An overload detection circuit that outputs an overload signal when the value exceeds a prescribed value, wherein the control signal generation circuit turns off the first semiconductor switch element and turns on the second semiconductor switch element when an overload signal is generated. Since the second semiconductor switch element connected in parallel to the DC motor is turned on by generating a brake signal at the time of overload, a regenerative current generated when the DC motor is stopped is generated by the second semiconductor switch element. It can flow through the semiconductor switch element, and consequently functions as an electric brake to stop the rotation of the DC motor in a short time. There is an advantage of that. In other words, it is possible to prevent excessive rotation due to the inertia of the DC motor,
When the bit of the driver is rotated by the DC motor, the screw can be prevented from being overtightened, and when the bit of the drill is rotated, the bit can be prevented from being broken due to overload. In addition, since the regenerative current flows through the second semiconductor switch element connected in parallel to the DC motor, it is possible to prevent an excessive current from flowing and an excessive voltage from being applied to the second semiconductor switch element. There is an advantage that current stress and voltage stress on the first and second semiconductor switch elements can be reduced. Further, since the first semiconductor switch element turns the power supply path from the battery to the DC motor on and off, the radiation on and off at a location where a relatively large current flows is compared with the case where the mechanical switch is used to turn on and off the current. There is an advantage that generation of noise is small and the influence of noise on various devices can be prevented.

According to a second aspect of the present invention, the first semiconductor switch element comprises a first MOSFET inserted between a first terminal of the DC motor and a positive electrode of the DC power supply,
In the case where the second terminal of the DC motor is connected to the negative electrode of the DC power supply, one MOS transistor is provided between the DC motor and the power supply.
Since only FET is inserted, MOSFET
There is an advantage that the power loss due to the on-resistance is small.

According to a third aspect of the present invention, the first semiconductor switch element comprises a first MOSFET inserted between a first terminal of the DC motor and a negative electrode of the DC power supply,
In the case where the second terminal of the DC motor is connected to the positive electrode of the DC power supply, one MOS transistor is provided between the DC motor and the power supply.
Since only FET is inserted, MOSFET
There is an advantage that the power loss due to the on-resistance is small.

A first MOSFET in which the first semiconductor switch element is inserted between a first terminal of the DC motor and one output terminal of the DC power supply.
And a second MOSFET inserted between a second terminal of the DC motor and the other output terminal of the DC power supply, and a second MOSFET between the second terminal of the DC motor and one output terminal of the DC power supply. And the first MOSFET of the DC motor
And a fourth MOSFET inserted between the terminal of the DC power supply and the other output terminal of the DC power supply, and when the second semiconductor switch element is composed of the second and fourth MOSFETs, four MOSFETs Has the advantage that not only a path through which a regenerative current flows can be formed by controlling the MOSFET, but also the direction of rotation of the DC motor can be switched between forward and reverse. According to the fifth aspect of the present invention, the control signal is supplied by simultaneously turning on the first and fourth MOSFETs and setting the second and third MOSFETs on.
A non-inverting signal for turning off both MOSFETs, a reverse signal for turning off both the first and fourth MOSFETs and turning on the second and third MOSFETs at the same time,
With the brake signal that turns on both the fourth and fourth MOSFETs and turns off the first and third MOSFETs, the rotation direction of the DC motor can be switched between forward and reverse by the forward rotation signal and the reverse point signal. Also, there is an advantage that a path through which a regenerative current flows can be formed by a brake signal.

When a brake signal is generated while the DC motor is rotating, the first semiconductor switch element is turned off and then the second semiconductor switch element is turned on. Is provided in the control signal generation circuit, the first and second semiconductor switch elements connected in series are prevented from being simultaneously turned on, and the first and second semiconductor switch elements are connected between both ends of the battery. Also, there is an advantage that a short circuit through the second semiconductor switch element can be prevented.

According to a seventh aspect of the present invention, there is provided a start circuit for starting power supply to the booster circuit when a pressing force acts on a bit rotationally driven by the DC motor. It is provided with a mechanical contact that is turned on with the movement of the bit when pressure is applied, and in the case where power is supplied from the battery to the booster circuit via the contact, the bit of an electric screwdriver or electric drill is pressed against the object. Not only can the DC motor be automatically rotated just by applying a pressing force to the bit, but it also has the advantage that power is not consumed when not in use because it uses mechanical contacts. is there.

According to an eighth aspect of the present invention, there is provided a start circuit for starting power supply to the step-up circuit when a pressing force is applied to a bit rotationally driven by the DC motor. In the case of a photoelectric sensor that detects the movement of a bit when pressure is applied and that supplies power to a booster circuit from a battery via the photoelectric sensor, a bit of an electric screwdriver or an electric drill is pressed against an object and pressed against the bit. Of course, it is possible to automatically rotate the DC motor just by applying pressure,
Since it is possible to detect that the pressing force acts on the bit in a state where the bit is not in contact with the bit, there is an advantage that the rotation of the bit is not affected.

[Brief description of the drawings]

FIG. 1 is a main part circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing an overall configuration of the above.

FIG. 3 is a main part circuit diagram of the same.

FIG. 4 is an operation explanatory view of the above.

FIG. 5 is a main part circuit diagram showing Embodiment 2 of the present invention.

FIG. 6 is a main part circuit diagram showing a third embodiment of the present invention.

FIG. 7 is a main part circuit diagram showing a fourth embodiment of the present invention.

FIG. 8 is a main part circuit diagram showing a fifth embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 21 switch circuit 22 control signal generation circuit B battery M DC motor Q1, Q2 MOSFET r1, r2 Contact point of changeover switch SW main switch

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Atsushi Kubota 1048 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Works, Ltd.

Claims (8)

[Claims] 1. A DC motor driven by a low-voltage DC power supply; a first semiconductor switch element including a MOSFET inserted between the DC power supply and the DC motor;
The second consisting of a MOSFET connected in parallel to the DC motor
A semiconductor switch element, a booster circuit that boosts the output voltage of the DC power supply, a control signal generation circuit that turns on and off each semiconductor switch element using the output of the booster circuit as a power supply, and when the load of the DC motor becomes a specified value or more. An overload detection circuit that outputs an overload signal, wherein the control signal generation circuit generates a brake signal that turns off the first semiconductor switch element and turns on the second semiconductor switch element when the overload signal is generated A motor control device characterized by the above-mentioned. 2. The first semiconductor switch element comprises a first MOSFET inserted between a first terminal of a DC motor and a positive electrode of the DC power supply, and a second terminal of the DC motor is connected to the DC power supply. The motor control device according to claim 1, wherein the motor control device is connected to a negative electrode of the motor. 3. The first semiconductor switch element comprises a first MOSFET inserted between a first terminal of a DC motor and a negative electrode of the DC power supply, and a second terminal of the DC motor is connected to the DC power supply. The motor control device according to claim 1, wherein the motor control device is connected to a positive electrode of the motor. 4. A first semiconductor switching element includes a first MOSFET inserted between a first terminal of the DC motor and one output terminal of the DC power supply, and a second terminal of the DC motor. A second MOSFET inserted between the other output terminal of the DC power supply, and a third MOSFET inserted between a second terminal of the DC motor and one output terminal of the DC power supply.
An SFET, and a fourth MOSFET inserted between a first terminal of the DC motor and the other output terminal of the DC power supply, wherein the second semiconductor switch element is a second MOSFET connected to the second and fourth MOSFETs. The motor control device according to claim 1, wherein: 5. The control signal includes first and fourth MOSFs.
A non-inverting signal for simultaneously turning on ET and turning off both the second and third MOSFETs, and a first and fourth MOS
2nd and 3rd MOSFETs with both FETs off
And the second and fourth MOs
Turn on both the SFET and the first and third MOSFETs
5. The motor control device according to claim 4, wherein a brake signal for turning off both T is provided. 6. A delay for delaying a time from when a first semiconductor switch element is turned off to when a second semiconductor switch element is turned on when a brake signal is generated while the DC motor is rotating. 2. The motor control device according to claim 1, wherein the circuit is provided in the control signal generation circuit. 7. A start circuit for starting power supply to said step-up circuit when a pressing force is applied to a bit rotationally driven by said DC motor, said start circuit comprising a bit for applying a pressing force to said bit. The motor control device according to claim 1, further comprising a mechanical contact that is turned on in accordance with the movement of the motor, and supplying power from a battery to the booster circuit via the contact. 8. A start circuit for starting power supply to said step-up circuit when a pressing force is applied to a bit rotationally driven by said DC motor. The motor control device according to claim 1, wherein the photoelectric conversion sensor detects movement of the motor, and supplies power to a booster circuit from a battery via the photoelectric sensor.