JPH05220677A - Protecting device for power tool - Google Patents

Abstract

PURPOSE:To limit motor lock time to suppress the calorific value without reducing the output torque of a motor, and prevent the burning of the motor or a power source circuit. CONSTITUTION:In a power tool which receives a power supply from a discharge circuit to drive a motor by turning on a power source switch SW1, the protecting device of the power tool has rotating speed detecting means (3, 4, 5) of a motor 1, a judging means 3 for detecting the motor nearly stopped, a timer for starting the counting of a set time after detecting the nearly stopped state of the motor, and an opening means (3, SW2) for opening the discharge circuit after the lapse of the set time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a portable electric tool such as an electric drill, an electric screwdriver, a circular saw and a jigsaw, and more particularly to a protection device against tool burnout and the like during use.

[0002]

2. Description of the Related Art In many work sites, the portable power tools as motor application products have been widely used in consideration of convenience and work efficiency.

Further, in a small electric device such as an electric razor, there has been proposed a device in which power supply to the motor is cut off when the motor is overloaded to protect the motor from overload (Japanese Patent Laid-Open No. 61-4481). Publication).

[0004]

By the way, when using the electric power tool, from the standpoint of the operator, the electric power tool exerts a required torque even in various usages, especially in extreme usages. Designed to be possible is required. For example, just before the motor stops due to overload,
That is, it is desired that the worker operates as he / she desires up to the maximum stalling torque so that the protection power supply is not suddenly cut off during the work.

On the other hand, from the side of the electric power tool, when the motor lock is continued due to extreme use, the effect of the heat radiation fan cannot be expected, and there is a possibility that the motor burns, the circuit burns out or smokes, or fires occur. It may occur, which is not preferable.
Therefore, in order to maintain the required motor torque, it is conceivable to adopt a larger motor and increase the heat radiation area to increase the heat capacity, but it is too large for a portable tool and its usability is reduced. It will be.

Further, in order to prevent burnout, it is necessary to limit the heat generation amount J, but J (joule) = W (watt) .t
In (seconds), limiting W reduces the motor output and the tool performance.

The conventional protection circuit described in Japanese Patent Laid-Open No. 61-4881 is an overload protection that prevents thermal destruction of the motor and semiconductor switching element due to heat generation when the load becomes excessive. It is about.

The present invention has been made in view of the above,
An object of the present invention is to provide a protective device for an electric tool that limits motor lock time and prevents burnout of a motor or a power supply circuit without reducing output torque of the motor.

[0009]

SUMMARY OF THE INVENTION A power tool protection device according to the present invention detects a rotation speed of a motor in a power tool in which a motor is driven by receiving power supply from a discharge circuit when a power switch is turned on. Means, a determining means for detecting that the rotation of the motor is in a substantially stopped state, a timer for starting the measurement of a set time after the detection of the substantially stopped state of the motor, and a discharge circuit after the lapse of the set time. And a circuit opening means for opening the circuit (Claim 1).

Further, a motor temperature measuring means and a set time changing means for changing and setting the set time according to the measured temperature may be provided (claim 2).

The opening means may be reset by turning off the power switch (claim 3).

Further, it is preferable to provide an informing means for informing that the discharge circuit is opened after the rotation of the motor is substantially stopped until the power switch is turned off. 4).

Further, a contact opening member for opening a contact connected in series to the discharge circuit may be used as the opening means (claim 5).

[0014]

According to the first aspect of the present invention, when the power switch is turned on, the motor is rotated by receiving power supply from the discharge circuit. The rotation speed detection means detects the rotation speed of the motor, and further the discrimination means detects that the rotation speed of the motor is zero or less than a value near zero, that is, the motor is in a substantially stopped state. The timer measures the set time after the substantially stopped state of the motor rotation is detected, and after the set time has elapsed, the discharge circuit is opened by the opening means and the locked state of the motor is released.

According to the second aspect of the invention, the heat generation temperature of the motor is measured by the motor temperature measuring means, and the set time changing means changes the set time of the timer according to the measured temperature. For example, the setting time is shortened as the measured temperature rises.

According to the third aspect of the invention, when the power switch is turned off, the circuit opening means is reset,
By this reset operation, the open circuit state of the discharge circuit is returned to the initial state, so that re-driving becomes possible.

According to the fourth aspect of the invention, after the rotation of the motor is substantially stopped, the notifying means notifies that the discharge circuit is opened until the power switch is turned off.

According to the fifth aspect of the invention, when the contact opening member operates to open the contact connected in series to the discharge circuit, the discharge circuit is opened in response to the operation.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit block diagram showing an embodiment of an electric power tool to which the protection device according to the present invention is applied.

In the figure, reference numeral 1 is a power supply, which is a power supply terminal 1a,
It can be connected between 1b. This power supply 1 is directly connected to a commercial power supply with a power cord, or is housed in a storage battery, particularly a battery pack, and can be attached / detached to / from an electric tool as it is. The battery may be electrically charged to the electric power tool and electrically connected to the discharge circuit while being attached to the electric power tool. A discharge circuit is composed of the power switch SW1 and the open switch SW2 described later from the terminals 1a and 1b.
A motor 2 which is a drive source of the tool is connected in series to this discharge circuit.

The power switch SW1 is provided at an appropriate position on the grip of the electric tool so as to be turned on and off in the form of a trigger. The open-circuit switch SW2 is a normally-closed switch, which is opened upon receiving a switch-means drive signal from the microcomputer 3 described later to open the discharge circuit. The open circuit switch SW2 can also adopt the configuration shown in FIG. 3 as described later.

The motor 2 drives a working portion of a power tool, such as a driver or a drill attached to a chuck portion of the tool. As shown in FIG. 2, the motor 2 has a characteristic that the output torque and the rotation speed n are in inverse proportion to each other, and is designed to be usable until the time at which the stall torque occurs immediately before the rotation stops (motor lock). There is.

In addition to the above-mentioned open circuit switch SW2, this power tool protection device comprises a microcomputer 3, a pulse generator 4, a pulse detection circuit 5, a temperature sensor 6 and a microcomputer power supply 7. Reference numeral 8 is a notification means including a lighting display element such as an LED. The notification means 8 may be one that displays the notification content instead of the lighting display, or one that notifies by sound or voice using a buzzer or the like.

The pulse generator 4 is composed of a pulse disk and a reading element which are concentrically provided via a drive shaft or a gear of the motor 2, and a large number of holes are equally spaced on one circumference of the disk. Alternatively, a magnet piece is arranged, and an optical or magnetic reading element is arranged at a proper position facing the hole or the locus of the magnet, and a pulse is generated every time the hole or the magnet passes. .. That is, the pulse generator 4 generates a pulse train having a frequency proportional to the rotation speed of the motor. The pulse generator 4 may be a commercial product that sends out a pulse every predetermined rotation.
The pulse detection circuit 5 takes in the pulse train input from the pulse generator 4 and performs waveform shaping, and the next stage microcomputer 3
Will lead to.

The microcomputer 3 determines the pulse frequency from the pulse train input from the pulse detection circuit 5, that is, the motor 2
Is calculated, and a timer operation described later is started based on the result of comparison between the calculation result n and the set value No, a notification signal is output to the notification means 8, and further the open circuit switch SW2 is connected. It also outputs a switch means drive signal. By the switch means drive signal, the open circuit switch SW2 holds the open circuit state of the discharge circuit, for example, until the power supply switch SW1 is turned off and the microcomputer power supply circuit 7 is turned off.
Further, the microcomputer 3 is provided with an internal timer, and the internal timer measures the initial time immediately after the power is turned on and the elapse of the set time To after the motor is substantially stopped.

As the set value No, a value of zero or near zero can be adopted, and not only when the motor 2 is in the motor lock state, but also when it is almost in the motor lock state. Including these, these states are called a substantially stopped state. However, in the examples described below,
In this substantially stopped state, the case of motor lock (n = 0) will be described as an example.

The temperature sensor 6 is arranged near the motor 2 to measure the heat generation temperature of the motor 2, and the measurement signal is input to the microcomputer 3. The microcomputer 3 is based on an arithmetic expression programmed in advance or has a built-in conversion RO.
Based on the M table, from the measured temperature to the lock time T
I try to ask for o. This lock time To is
This is the set time from when the motor 2 locks the motor until the switch drive signal is output, and the set time is shortened as the motor heat generation temperature increases.

The microcomputer power supply 7 is connected to the power supply 1 via the power switch SW1. With this configuration, the microcomputer 3 performs a reset start operation every time the power switch SW1 is operated from OFF to ON. ing.

FIG. 3 is a circuit diagram showing a concrete example of the open switch SW2 portion. FIG. 3A shows a case where the FET 11 is connected in series to the discharge circuit, and the microcomputer 3 is connected to the gate thereof.
The drive signal from the switch means is input. FIG. 2B shows a relay circuit connected to a discharge circuit, which includes a relay contact 12, a relay coil 13, and a FET 1.
It is composed of 4 etc. When the switching means drive signal is input from the microcomputer 3 to the FET 14, the relay coil 1
Current flows from the power supply 1 into the relay 3, which causes the relay contact 1
2 is opened.

In a low voltage power tool, a current of about 80 to 100 A may flow when the motor is locked.
If a protection means such as an open circuit switch SW2 is connected to this type of tool, the load current during normal operation will be suppressed and the motor torque will be reduced, and the tool will not be able to exert its full potential. Therefore, without providing a separate switch,
For example, both contacts of the power switch SW1, contacts of a forward / reverse changeover switch (not shown) for switching the motor rotation direction, or a connection terminal 1a.
The discharge circuit may be opened by opening the contacts already provided as an electric tool such as 1b. In this case, after the set time To elapses from the motor lock, the contact is forcibly opened by using the operating piece operated by the solenoid, the shape memory alloy or the bimetal operated by heating, and the discharge circuit is opened. You can also do so.

FIG. 4 is a time chart for explaining the contents of microcomputer control when the rotation is started and the motor is locked. That is, when the motor 2 is overloaded from the required number of revolutions and shifts to the motor lock at time t1 when the number of revolutions n becomes zero, the microcomputer is reset after a preset time (To time, that is, t2 time). A switch drive signal is output from 3 to the open switch SW2.
Further, thereafter, the operator operates the power switch SW1 to be off (at time t3). The notification means 8 has the above t1 to t3.
During the period, the light is turned on, and the operator is informed that the motor lock to the protection function is in operation. By this notification, the worker
It is possible to easily and accurately grasp the current state of the motor, such as the fact that the lock operation is being avoided and the motor is locked or not.

Next, the operation of the protection device will be described with reference to the flowchart of FIG. 5 showing the procedure of the protection operation.

After the power source 1 is turned on to the power tool, the power source switch SW1 is turned on to start resetting (step S1), the motor 2 is rotationally driven. During the initial time required for the motor 2 to rise from the start of rotation to the required number of rotations, the lock detection operation is waited so that the lock detection function does not work (step S2). After the initial time has elapsed, the motor temperature is measured, and the set time To for limiting the motor lock is obtained based on the measured temperature result (steps S3, 4). Next, it is determined whether or not the rotation speed n of the motor 2 is zero, that is, whether or not the motor is locked (step S5). If the motor rotation speed n is not zero, it is determined to be within the normal operation range and the process returns to step S3 to repeat the measurement of the motor temperature. On the other hand, if the motor is locked, a notification signal such as an LED lighting signal is output to the notification unit 8 (step S6), and the timer starts counting the set time To (step S7). The timer for timer is reset and started only when "NO" is changed to "YES" in step S5, and when the above "YES" is continued, the timing operation is continued.

Then, it is judged whether or not the duration t of the motor lock state has reached the set time To obtained in step S4 (step S8). If the time is equal to or less than the set time To, the process returns to step S5 to repeat the determination as to whether or not the motor is in the locked state. On the other hand, if the time reaches the set time To, the switch means drive signal is sent to the open switch SW2 to open the discharge circuit ( Step S9), the switch SW
Open 2.

As described above, since the discharge circuit is opened at the set time To, as described above, the time t is limited by limiting the time t in the relationship with the heat generation amount J represented by J = W · t. The heat generation amount J can be suppressed within an allowable range without reducing the motor output W at all.

The lighting display on the LED and the output of the switch driving signal by the notifying means 8 are held until the power switch SW1 is turned off, that is, the microcomputer power supply circuit 7 is turned off (step S10, S1
1).

After that, the power switch SW1 is turned on again from the off state, whereby the reset start operation according to the present flowchart is started.

6 to 9 show an embodiment in which the power tool protection device according to the present invention is mechanically constructed, and FIG. 10 is a circuit block diagram thereof.

FIG. 6 shows the state of non-use, FIG. 7 shows the state of normal use, FIG. 8 shows the state immediately after the start of the protective operation for the motor lock, and FIG. 9 shows the state during the protective operation for the motor lock.

Reference numeral 20 denotes a position which is gripped by an operator when using the electric power tool, and is a trigger provided at a position where it can be easily operated by a finger or the like, and an unoperated position pulled out as shown in FIG. As shown in FIG. 7, it is configured so as to be slidable between the retracted operation positions, and in a non-operated state, it is urged by a spring 21 in a pullout direction (left in the figure). Trigger 20
A slide member 22 is attached to the slide member 22, and a push rod 22a, which is vertically movable as shown in a partial cross section, is urged downward by a spring 22b at the lower right end of the slide member 22 in the figure. It is provided in. On the other hand, the seesaw plate 2 also made of a conductive material is arranged below the push rod 22a in the moving direction of the slide member 22 and is rotatably arranged by a fulcrum member 23 made of a conductive material.
4 are provided. On the seesaw plate 24, a movable contact 25 is formed at an appropriate position on the side different from the fulcrum position, and a fixed contact 26 is disposed so that the movable contact 25 can rotate at an appropriate position. When the seesaw plate 24 is rotated clockwise by the push rod 22a biased downward by the spring 22b, the movable contact 25 and the fixed contact 26 come into contact with each other to connect the power source 1 and the motor 2 to each other. I am trying to do it. That is, the configuration from the trigger 20 to the fixed contact 26 corresponds to the power switch SW1 described above.

The contact opening mechanism has the following structure. That is, on the right end side of the slide member 22 in the drawing, the return cam 31 urged downward by the spring 30 is arranged so as to be movable in the vertical direction, and the side surface 31a on the trigger 20 side is formed with an inclination. , The upper right end 22c of the slide member 22 comes into contact therewith, and the trigger 20
By sliding according to the movement of the return cam 31
Are moved upward against the biasing force of the spring 30. Further, below the lower end portion 31b of the return cam 31, a release pin 41 biased upward by a spring 40 is disposed so as to be movable in the vertical direction. The upper end 41a of the release pin 41 is formed at a position where the lower end portion 31b of the return cam 31 comes into contact, and also comes into contact with the lower right portion of the seesaw plate 24 so that the seesaw plate 24 can be pushed by the push rod 22a. Spring 22b
It is for turning a predetermined amount in the counterclockwise direction against the urging force of. Immediately below the upper end 41a, a recess 41b for engagement is formed on one side surface thereof, and a lower side surface 41c thereof is formed with an inclination.

50 is a solenoid, and its plunger 51
Is urged by the spring 52 in the pull-out direction. The plunger 51 is in the pulled-out state when the solenoid 50 is off, and is in the retracted state when the solenoid 50 is on. The solenoid 50 has a power source 1 via a switch 53.
Are connected in series. This switch 53 is the microcomputer 3
When the switch drive signal is input from
The solenoid 50 is energized to change the plunger 51 from the state shown in FIG. 6 to the state shown in FIG.

In this structure, each operating state will be described next. In the state of FIG. 6, the trigger 20 is not operated and the power tool is in an unused state. That is, in this state, the push rod 22a is on the left side of the fulcrum member 23 in the figure, and the movable contact 25 and the fixed contact 26 are separated from each other, so that the motor 2 and the power source 1 are in the open state. Further, the plunger 51 is engaged with the concave portion 41b to regulate the release pin 41 to the lower position, and the return cam 31 is held at the lower position by the spring 30.

In this state, as shown in FIG. 7, when the trigger 20 is pulled in, the push rod 22a slides on the seesaw plate 24 in the right direction in the figure, and the seesaw plate 24 rotates clockwise. The movable contact 25 and the fixed contact 26 are brought into contact with each other. As a result, the power supply 1 and the motor 2 are connected and the rotational driving of the motor 2 is started. At this time, the return cam 31 is pushed upward by the upper right end 22c of the slide member 22.

When the motor lock occurs and the set time To elapses, the state shifts to the state shown in FIG. That is, the microcomputer 3 outputs a switch means drive signal, and the switch 53 is turned on. When the switch 53 is turned on, the solenoid 50 causes the plunger 51 to be retracted, and the engagement between the plunger 51 and the recess 41b is released. The release pin 41 is pushed upward by the urging force of the spring 40 by releasing the engagement between the plunger 51 and the recess 41b. And this upper end 41a
Comes into contact with the lower right end of the seesaw plate 22 and urges the seesaw plate 22 to rotate in the counterclockwise direction, thereby separating the movable contact 25 and the fixed contact 26 from each other, and the power source 1 and the motor 2
To disconnect from.

By adopting such a configuration, the power source 1
Even when the motor 2 is opened and the microcomputer 3 is turned off by stopping the power supply at the same time, the release pin 41 stably separates the movable contact 25 and the fixed contact 26 by the urging force of the spring 40. Since the circuit is self-held, the circuit system on the motor 2 side and the circuit system on the microcomputer 3 side can be turned on / off by one main contact. As a result, the self-holding control in the microcomputer 3 is unnecessary, and moreover, the current consumption in the microcomputer 3 is eliminated when the main contact is off, and the power loss can be reduced accordingly.

In the above, the movable contact 25 and the fixed contact 2
When 6 and 6 are separated from each other and the microcomputer 3 is turned off, the energization of the solenoid 50 from the microcomputer 3 is stopped, so that the plunger 51 is pulled out by the spring 52 as shown in FIG.

Then, after this, when the operator releases the trigger 20, the slide member 22 starts to move to the left in conjunction with the sliding of the trigger 20 to the left, and the downward regulation of the return cam 31 is released. Come to do. Therefore, the return cam 3
1 starts moving downward due to the urging force of the spring 30.

Next, since the urging force of the spring 30 is set to be equal to or more than the urging force of the spring 40, the lower end 31b of the return cam 31 is connected to the upper end 41a of the release pin 41.
Is pushed downward and the release pin 41 is pushed downward, so that the plunger 51 at the position pulled out by turning off the solenoid 50 relatively rises while slidably contacting the inclined lower side surface 41c, and the concave portion 41b. To fit. Then, due to this engagement, the initial state of FIG. 6 is reset.

The configuration will be described with reference to the circuit block diagram shown in FIG. The same reference numerals as in FIG. 1 have the same functions.

In FIG. 10, instead of the open circuit switch SW2 of FIG. 1, a series circuit including a switch 53 as a contact opening section and a solenoid 50 is connected in parallel with the motor 2.

The operation will be described. When the motor is locked during use of the electric power tool and the set time To further elapses, the microcomputer 3 outputs a switch driving signal to turn on the switch 53. When the switch 53 is turned on, the solenoid 50 is energized to operate the relay and open the contact of the power switch SW1. As a result, the power supply 1 is opened from the discharge circuit.

[0053]

As described above, according to the present invention,
Since the discharge circuit is opened after the set time elapses after detecting that the rotation of the motor is almost stopped, the duration of the substantially stopped state of the motor is limited.
The heat generation amount can be suppressed without reducing the output torque of the motor, and the motor and the power supply circuit can be prevented from burning.

Further, since the above-mentioned time limit is changed and set according to the heat generation temperature of the motor, an appropriate time limit is set according to the usage condition of the motor, and more effective protection can be achieved. Since the circuit opening means is reset by turning off the power switch, it is possible to simplify the structure without the need to provide a separate reset means. Also, from the time when the motor is almost stopped until the power switch is turned off. Since the notification means for notifying that the discharge circuit is opened is provided, the operator can accurately and easily grasp the current situation regarding whether or not the motor is substantially stopped while avoiding the substantially stopped state of the motor. Become.

Further, since the contact opening member for opening and closing the contacts connected in series to the discharge circuit is provided to open the discharge circuit, the contact resistance of the switch accompanying the provision of the additional switch means is included. It is possible to suppress an increase in the resistance component, reduce the torque of the motor, and efficiently exhibit the performance as an electric tool.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing an example of an electric power tool to which a protection device according to the present invention is applied.

FIG. 2 is a characteristic diagram showing a relationship between output torque of a motor and rotation speed.

FIG. 3 is a circuit diagram showing a specific example of an open circuit switch SW2 part. FIG. 3 (a) shows a case where an FET 11 is connected in series to a discharge circuit, and FIG. 3 (b) shows a case where a relay circuit is connected to a discharge circuit. Is.

FIG. 4 is a time chart for explaining the contents of microcomputer control in the case of shifting from rotation start to motor lock.

FIG. 5 is a flowchart showing a procedure of an operation of the protection device.

FIG. 6 is a configuration diagram showing an embodiment in which a protection circuit for an electric power tool according to the present invention is mechanically configured, showing a non-use state.

FIG. 7 is a configuration diagram showing an embodiment in which a protective circuit for an electric power tool according to the present invention is mechanically configured, showing a normal use time.

FIG. 8 is a configuration diagram showing an embodiment in which a protection circuit for an electric power tool according to the present invention is mechanically configured, and shows a state immediately after disclosure of a protection operation for a motor lock.

FIG. 9 is a configuration diagram showing an embodiment in the case of mechanically configuring a protection circuit for an electric power tool according to the present invention, showing a state during a protection operation for a motor lock.

FIG. 10 is a circuit block diagram in an embodiment in which the power tool protection device according to the present invention is mechanically configured.

[Explanation of symbols]

 1 Power Supply 2 Motor 3 Microcomputer 4 Pulse Generator 5 Pulse Detection Circuit 6 Temperature Sensor 7 Microcomputer Power Supply 8 Notification Means SW1 Power Switch SW2 Open Circuit Switch 11,14 FET 12 Relay Contact 13 Relay Coil 20 Trigger 21, 30, 40, 52 Spring 22 Slide member 23 Support point member 24 Seesaw plate 25 Moving contact 26 Fixed contact 31 Return cam 41 Release pin 50 Solenoid 51 Plunger 53 Switch

Claims (5)

[Claims] 1. A power tool in which a motor is driven by receiving power supply from a discharge circuit when a power switch is turned on, and the rotation speed detection means of the motor and the rotation of the motor are substantially stopped. Discriminating means for detecting
A protective device for an electric tool, comprising: a timer that starts timing of a set time after a substantially stopped state of the motor is detected; and an opening means that opens the discharge circuit after the set time has elapsed. 2. The electric tool protection device according to claim 1, further comprising motor temperature measuring means and set time changing means for changing and setting the set time according to the measured temperature. Tool protector. 3. The power tool protection device according to claim 1, wherein the circuit opening means is reset by turning off the power switch. 4. The power tool protection device according to claim 1, wherein the discharge circuit is opened until the power switch is turned off after the rotation of the motor is substantially stopped. An electric tool protection device comprising an informing means for informing. 5. The power tool protection device according to claim 1, wherein the circuit opening means is a contact opening member that operates to open a contact connected in series to the discharge circuit. Protective device.