JPS6333396B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to rechargeable electric equipment.

For electric equipment such as rechargeable circular saws and drills, it is desirable to be able to do as much work as possible (number of cuts, holes, etc., or cumulative distance) on a single charge.

To achieve this, we need to improve the motor's rotation speed-torque characteristics, battery discharge performance characteristics, and
The conditions for tools (circular saw blades, drills, etc.) are determined.
However, no matter how fixed the conditions of these tools are, the power consumption varies greatly depending on the conditions of use and the type of workpiece material. Therefore, in order to get the maximum effect from a single charge, it is necessary to use the device under conditions that always minimize power consumption, but without an appropriate sensor, the user may It was difficult to maintain these conditions at all times.

By the way, as an overload detection control system for DC type electric equipment, a system having a circuit configuration as shown in FIG. 1 (see Japanese Patent Laid-Open No. 52-55100) has already been provided. This conventional example is characterized in that an inertial force buffering member such as a coil spring is interposed between the drive source of the electric screwdriver with a built-in DC motor M and the driver shaft, and the electric screwdriver is driven by a current control method. The purpose is to absorb the inertial force generated in the rotor and other rotating parts when the screw is stopped after tightening, and to prevent damage to the threads and breakage of the object to be tightened. Figure 2 shows the torque current characteristics of the conventional motor mentioned above.
It shows that the motor current increases as the load torque increases. In this conventional example, when this current exceeds a predetermined value, an impedance control element such as a transistor _T1 is provided between the DC power supply device DC that step-down rectifies the commercial AC power supply AC and the motor M, and when the motor current reaches a predetermined value, When the motor current is about to exceed a certain value, the impedance is increased to control the motor current so that it does not exceed a certain predetermined value. On the other hand, in terms of ease of use, electric appliances are desirable because they require a cord to be pulled when using a commercial AC power source, so it is desirable to have a portable, portable type with a built-in secondary battery so that it can be used freely even in places where there is no power source. ing. After conducting various studies using the above-mentioned conventional circuit, it was found that electric equipment using such a secondary battery as a power source has the following drawbacks. One of them is that in electric equipment with large load torque such as electric drills and electric circular saws, the motor current becomes _large . For example, in Figure 1, the power loss in the resistors Ra, Rb, and Rc (corresponding to resistors Ra, Rb, and Rc) is large, and the power of the storage battery cannot be used effectively.

The second drawback is that when cutting a wide board from one end, especially when using an electric circular saw, if it bends or meanders even a little, the edge of the circular saw blade will cut on both sides. As the frictional force increases, the load torque increases, and the motor current also tries to increase by that amount, but the current control value is set very large to prevent the motor M from stopping easily. If bending or meandering occurs, if a buffer member such as an elastic spring is interposed between the motor M and the blade mounting shaft, the motor will not stop but the blade will stop, and the buffer member will prevent the sliding clutch from working. When the switch is pressed, the motor current is held down to a certain value, but as long as the switch is pressed, the current continues to flow and only the reactive power increases, which greatly consumes battery power and significantly reduces the number of sheets that can be cut on one charge. .

When using it as an electric drill, we made a prototype and confirmed it, but when drilling metal materials in particular, a large load torque is required when the tip of the drill penetrates the plate material, and the shock absorbing member part may slip and cause the drill to fail. It was found that there were times when the hole could only be drilled partway because it stopped rotating, and the reactive power was not reduced. FIG. 3 shows a sectional view of the tip of the electric drill used on a trial basis. A buffer member 3 such as an elastic spring is interposed between the motor M and the mounting shaft 2 of the drill bit 1, and the above-mentioned sliding clutch function is shown in FIG. It is designed to obtain.

The present invention has been made in view of the above-mentioned problems, and its purpose is to provide a switching device between the secondary battery and the motor in order to extend the usable time per charge. It is an object of the present invention to provide a rechargeable electric device that can minimize the power consumption generated in the device and can control the current so that it does not exceed a predetermined value when the motor is locked.

The present invention will be explained below with reference to Examples. FIG. 4 is a block diagram illustrating the functions of the present invention, and includes a switching means composed of a secondary battery 4 such as a Ni-Cd battery or a lead-acid battery, an operation switch 5, and a semiconductor switch element such as a power transistor. Electric power is supplied to the motor M via 6. The control circuit block of A is the operation switch 5.
When the motor M is turned on, a current pulse or a voltage pulse sufficient to turn on the switching means 6 is sent from the pulse oscillation circuit 7 to the switching means 6, and power from the secondary battery 4 is supplied to the motor M via the switching means 6. In addition to rotating the motor M, the voltage divider is used to detect that if the rotating motor M is overloaded due to improper usage, a large current will flow through the motor M and the voltage across the battery will drop. 8
The voltage comparator 10 compares the divided voltage output V _i from the reference voltage generating circuit 9 with the reference setting voltage V ₁ generated by the reference voltage generation circuit 9, and the display is displayed when the divided voltage output _Vi falls below the reference setting voltage V ₁ . By activating the means 11 and displaying the information, and by performing a control operation to limit the time period during which the switching means 6 is turned on, the user is notified of the abnormal use, and an excessive current is caused to flow to the motor M. This is to prevent burnout of the motor M or wasteful consumption of battery power. 12 is a constant voltage power supply, and this constant voltage power supply 12 is connected to a reference voltage generation circuit 9,
It is used to supply power to the voltage comparator 10 and the amplifier circuit 13.

Figure 5 shows a specific circuit example based on Figure 4 used in a rechargeable circular saw electric device, and the secondary battery 4 has a voltage
It has a capacity of 12V, 2.5AHr, and when no load current is flowing, it is 13.1V (hereinafter referred to as open circuit voltage E ₀ ).
A lead-acid battery or a Ni-Cd battery is used, which has a starting power of .

Next, the operation of this circuit will be explained. When the operation switch 5 is turned on now, the constant voltage power supply 12 operates first,
A stabilized constant voltage V _b of 5-7 V is generated at the output terminal b of the power supply, and is supplied to the voltage comparator 10 , reference voltage generation circuit 9 , and amplifier circuit 13 as power supplies. On the other hand, via the operation switch 5,
A voltage divider 8 consisting of a series circuit of resistors R ₁ and R ₄ is connected to the battery 4, and this voltage divider 8 divides the battery voltage and takes out the divided voltage output from the distribution point c. It is applied to one input terminal of the voltage comparator 10. The voltage at this time is defined as _Vi . On the other hand, a reference setting voltage from a constant reference voltage generation circuit 9 is applied to the other end of the voltage comparator 10. The reference voltage generation circuit 9 divides the output voltage of the constant voltage power supply 12 with resistors R ₄ and R ₅ to generate a reference set voltage V ₁ . For example, when the motor torque increases during abnormal use, the battery voltage The ratio of resistors R ₄ and R ₅ is set so as to be equivalent to a predetermined voltage when the voltage decreases. Immediately after the operating switch 5 is closed as described above, however, the switching means 6 consisting of the power MOS transistor _Q22 is not yet turned on, and the battery voltage is close to the open circuit voltage _E0 . Transistor of comparator 10
The input voltage Vi to _Q7 is given by the following equation.

V _i ≒R ₂ /R ₁ +R ₂ ×E ₀ ... On the other hand, the reference setting voltage V ₁ is expressed by the following equation, where the output voltage of the constant voltage power supply 12 is V _b .

V ₁ ≒ R ₅ / R ₅ + R ₄ × V _b ... Here, when V _i > V ₁ , transistor Q ₇ is turned on and transistor Q ₈ is turned off. Voltage comparison is made using a known differential amplification type comparator circuit. Therefore, the output terminal e is “L” when V _i >V ₁ .
Transistor Q ₁₄ of the amplifier circuit 13 becomes the level
Turn on. This results in resistances R ₁₇ and R ₁₈
Current flows through and turns on transistor _Q16 ,
Transistor provided in pulse oscillation circuit 7 via diode-connected transistor _Q17
Turn off Q ₁₈ . When transistor Q ₁₈ turns off, transistor Q ₁₉ turns off and resistors R ₁₉ , R ₂₀
When no current flows through Q20, transistor _Q20 is turned off. At this time, the gate voltage of the power MOS transistor Q22, which is a variable impedance element constituting the switching means 6, is increased through a series circuit of the resistor _R9 and the light emitting diode _D1 , which are provided as the display means ₁₁ , and the switching means 6 is switched on. power
The MOS transistor _Q22 is instantly turned on, and DC power from the secondary battery 4 is supplied to the motor M, causing the motor M to rotate. On the other hand, when the voltage at point f in Fig. 5 rises, capacitor _C4 carries a charge,
Resistor R ₈ , Capacitor C ₃ , Resistor R ₇ , Capacitor C ₁
The potential at point g temporarily drops, turning transistor _Q19 on. When transistor Q ₁₉ is turned on, current flows through the series circuit of resistors R ₁₉ and R ₂₀ , and transistor Q ₂₀ is also turned on. Therefore, the voltage at point f decreases again, and the power
The gate voltage of the MOS transistor _Q22 is instantaneously turned off. In this way power
MOS type transistor Q ₂₂ is f of pulse oscillation circuit 7
The on and off operations are repeated in response to the rise and fall of the voltage at the point. FIG. 6 shows the state of voltage change at point f, and the on/off period can be freely selected. In this embodiment, the ratio of on and off times is set in the range of 10:1 to 5:1. In other words, if this ratio is made too small, the average value of the current supplied to the motor M will also drop in proportion to it, which is quite effective in terms of power saving.However, in the case of a circular saw, etc., the necessary cutting capacity is used in advance. This is determined based on the conditions, and therefore the stall torque and output horsepower required for motor M are also determined, so it is necessary to set a value that can secure enough current to satisfy this target, and it is not just a matter of saving. This is because the on/off time ratio cannot be determined solely from the viewpoint of power. On the other hand, while this on and off operation is repeated, the light emitting diode _D1 of the display means 11 blinks, but to the human eye it appears that it is hardly lit. It is better to set the value of resistor R ₉ and the on/off time ratio so that the condition is satisfied.

Now, in this embodiment, it takes about 1 to 2 seconds for the motor M to start rotating and reach steady rotation.In the conventional case, the inrush current at startup is very large, but the power MOS type switching means 6 The on/off operation of the transistor _Q22 can be significantly suppressed, making it possible to reduce power consumption during startup. FIG. 7 shows the effect of reducing the rush current to the motor M at the time of starting, where the curve aa represents the current when the switching means 6 consisting of the power MOS transistor _Q22 is not provided, and the curve bb represents the current when the switching means 6 consisting of the power MOS transistor Q22 is not provided. The case is shown below.

Next, a means for notifying the user of an abnormality such as the occurrence of abnormal torque during use, and an operating principle for preventing motor burnout will be explained.

In general, it is already known that secondary batteries 4 such as Ni-Cd batteries and lead batteries have some internal resistance (usually 10 mΩ to 100 mΩ), and abnormal torque may occur in the motor M. It is also known that the current increases proportionally when the load torque increases due to the torque-current characteristics of a DC motor. Therefore, the voltage across the secondary battery 4 is not constant during cutting, but responds to current changes. Then, it changes as shown in Fig. 8. Figure a shows the current change during actual use of the rechargeable electric device of the present invention, and Figure b shows the voltage change at that time.

Now, the no-load current of the embodiment shown in Figure 5 during normal use is 2A, and the motor current when it starts to be used, that is, when it starts cutting 12mm thick plywood in a straight line, is approximately
At about 10A, the current increases slightly due to the frictional force caused by the side of the saw blade being pressed strongly by the plywood at the end of cutting, but it was found to be within 30A at most. In addition, the battery voltage drop at that time is only about 10.5V, and the cutting time at that time is 20cm wide.
It was possible to cut plywood in about 0.8 to 1 second. Furthermore, the pressing force at that time was 1.5 to 2 kg.

As mentioned above, when using the example device to cut more quickly, we tried pressing it with 3 to 5 kg or intentionally making the cut in a meandering manner. It was found that there was a tendency for the rotation to decrease and the current to increase.

Therefore, in the circuit of the embodiment shown in FIG. 5, the switching means 6 was short-circuited and the above-mentioned abnormal usage experiment was conducted, and the current and voltage changes at that time were investigated.
b, the current is 40 to 60A, and the voltage is
It was found that the voltage decreased to about 9.5V to 8.8V, and it became clear that it could be clearly distinguished from the current and voltage fluctuation range during normal use.

I also tried using the circuit shown in Figure 5 for an electric drill, and found that although the current and voltage ranges that distinguish between normal and abnormal ranges differ depending on the purpose of use, motor, battery voltage, capacity, etc., there are clearly distinguishable regions for each. It was found that there exists

Next, the abnormality detection operation of the present invention will be explained. For convenience of explanation, an embodiment of a rechargeable electric circular saw, ie, the circuit shown in FIG. 5, will be described.

Now, as already clarified in Fig. 8b, the battery voltage decreases during abnormal use, but in this embodiment, the lower limit of the optimal usage condition is 9.3V, which is the point where the predetermined plate is not cut and the motor M is on the verge of being locked. value, and this voltage is used as the voltage for abnormality determination.

Therefore, the above-mentioned reference setting voltage V ₁ can be determined from the equations by adjusting the resistance R so as to satisfy the relationship V ₁ = _Vi = R ₂ / R ₁ + R ₂ ×9.8V = R ₅ / R ₅ + R ₄ × V _b . ₁ to _R5 and the output voltage _Vb of the constant voltage power supply 12 were determined.

However, when an overload occurs and the motor speed decreases to the point where it no longer functions normally, the node voltage V _i of the voltage divider 8 becomes smaller than the reference setting voltage V ₁ , so the transistor Q of the voltage comparator 10 ₇ is turned off and transistor Q ₈ is turned on. When transistor Q ₇ is turned off, transistor Q ₁₄ is turned off, transistor Q ₁₆ is also turned off, transistor Q ₁₅ is turned on, transistor Q ₁₉ is turned on, and transistor Q ₂₀ is also turned on, and the pulse generation circuit is turned on. The voltage at point f in FIG. 7 decreases, the power MOS transistor _Q22 of the switching means 6 is turned off, and the current to the motor M is cut off. As a result, the battery voltage increases and V _i >V ₁ becomes true, so that the power type transistor Q ₂₂ of the switching means 6 is turned on again. The on/off cycle at this time is relatively short when the secondary battery 4 has just been charged and has sufficient power, but the capacitor C ₄ and the resistor are By determining the values of R ₉ and R ₂₂ , the current flowing through the motor M when an overload occurs can be reduced to about 1/2 of the maximum current when the motor is locked.

Also, when the secondary battery 4 becomes exhausted, the secondary battery 4
As the internal resistance of the motor M increases, the voltage drop across the battery when an overload occurs on the motor M becomes larger than that immediately after charging. Turning on the pulse oscillation circuit 7,
Since the circuit is configured so that the off period of the off period is long, the light emitting diode of the display means 11
Lighting up of D ₁ means that transistor Q ₂₀ is on, i.e. power is on.
Since this is performed when the MOS transistor _Q22 is off, the lighting time becomes longer and the blinking becomes clearer.

Therefore, when an overload occurs immediately after charging the secondary battery 4, the light emitting diode _D1 lights up at a medium brightness, and when the secondary battery 4 is exhausted and needs to be recharged, the brightness becomes more clear. A lighting display will be performed. The user can use the device while determining both abnormal use and recharging time based on the brightness of the light emitting diode _D1 .

The reason why a power MOS type transistor _Q22 was used as the switching means 6 is because it requires almost no current just by applying a gate voltage, so the pulse oscillation circuit 7
It is easy to make the transistor Q ₂₀ small, which is convenient for portable electric appliances, and for circular saws that require large currents to flow through the motor M, the on/off switching time is shorter than that of a normal bipolar power transistor. This is because the heat loss that occurs in the transistor each time it is turned on or off can be reduced because the transistor is short. In addition, in all the cases described above, the control operation of the power MOS transistor _Q22 is such that the current is sent in pulse form to the motor M by intermittent ON/OFF operation, so that a current proportional to the base current flows. For example, when using a series regulator type transistor, the current
Even when used at 10 A and a voltage of about 5 V between the collector and emitter, a power loss of 50 W would occur, but in this embodiment, the power loss can be reduced to 10 W or less, allowing effective use of battery power.

Further, although the charging circuit is omitted from the circuit of the embodiment, it goes without saying that charging of the secondary battery 4 is performed by an appropriately provided charging circuit.

Further, as the display means 11, a stimulation means made of an electromagnetic solenoid or a sound display means such as a buzzer may be used.

The present invention sets the lower limit of the voltage across the secondary battery under optimal usage conditions before the motor is locked due to overload as the reference setting voltage, and compares the voltage across the secondary battery during actual use with the reference voltage. It has a voltage comparator that converts the comparative output of the voltage comparator into a pulse signal that is intermittent when an overload occurs, and in addition to display means and switching means provided between the secondary battery and the motor. Since the display means is configured to display information intermittently and the switching means is configured to switch intermittently, the user can tell whether the operating condition is outside the optimum operating condition range by the display on the display means. It is possible to set the operating condition to the optimum operating condition while checking the display status of the display means, and in the event that the operating condition becomes overloaded outside the optimum operating condition, the switching means repeats on and off at high speed, and the secondary By controlling the average current from the battery to the motor so that the off time becomes longer when the degree of overload is large, it is possible to suppress the excessive current within a certain range when a motor overload occurs. A variable impedance element such as a transistor is used as the switching means because the intermittent pulse signal is applied to the gate of the variable impedance element and the on/off time ratio is changed in accordance with the amount of overload. It is possible to obtain the effect of minimizing the switching loss power when

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of the conventional example, Fig. 2 is an explanatory diagram of the same operation as above, Fig. 3 is a sectional view of the tip of the electric drill, Fig. 4 is a circuit block diagram showing the functions of the present invention, Fig. 5
The figure is a circuit diagram of an embodiment of the present invention, FIG. 6 is a waveform diagram of the output voltage of the pulse oscillation circuit same as above, FIGS. 7 and 8 a and b are operation explanatory diagrams, and FIGS. b is an explanatory diagram of the same operation as above, M is a motor, V ₁ is a reference setting voltage, 4 is a secondary battery, 10 is a voltage comparator,
11 is a display means.

Claims (1)

[Claims] 1. In rechargeable electric equipment that operates a drive motor using a secondary battery as a power source, the lower limit of the voltage across the secondary battery under optimal usage conditions before the motor is locked due to overload is set as the reference setting voltage. A voltage comparator that compares the voltage across the secondary battery and a reference voltage during actual use, converts the comparison output of the voltage comparator into a pulse-like signal that is intermittent when an overload occurs, and converts the pulse-like voltage into the above-mentioned pulse-like signal. In addition to the switching means and display means provided between the secondary battery and the motor, the pulse generation means causes the display means to display intermittently and the switching means to switch intermittently, and the switching means includes a variable impedance element. A rechargeable electric device characterized in that the on/off time ratio is changed in accordance with the amount of overload by applying the intermittent pulsed signal to the gate of the variable impedance element.