JPS59232776A - Motor tool - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a motor-driven power tool in which the motor rotation speed is controlled by a switching element such as a thyristor or a triac.

In general, power tools in which the rotation speed of the drive motor is controlled by a switching element include a switching element, a control circuit connected to the gate of the switching element, a cooling fin to cool the switching element, and an element to improve noise resistance. Since it is stored inside the tool body, it is inevitably larger and heavier than a tool without a control, but for example, as shown in Fig. 1, the grinding wheel is attached to the tip of the housing 1 through a gear cover 2. In the disc grinder 7, the controller unit 6 is rotatably mounted and the main switch 5 and control components are housed in the handle 4 at the rear end of the housing 1. Since they are all built into the handle 4 only, the main body becomes longer by the length of the control unit 6, and the area near the air intake port provided in the handle 4 is narrow and the air passage resistance increases. there were. In particular, those in which the switching element 8 is attached to the stator 10 of the motor 9 have the following drawbacks. That is, the air for cooling the +11 switching element 8 passes through the commutator 12 of the armature 11, which is a heating element, and around the pole bearing 13 supporting the armature 11, so it is heated, and the switching element 8 is heated by passing through the vicinity of the commutator 12 of the armature 11, which is a heating element, and the pole bearing 13 supporting the armature 11. Since the switching element 8 is attached to the stator 10, which has the highest temperature rise in the interior, cooling of the switching element 8 is poor. Especially in the case of tools that tend to be used under overload, such as disc grinders, the switching element 8 is not cooled, but is affected by heat from the outside. It may even be destroyed. To prevent this, a large motor and a large cooling fan are required to reduce the temperature rise of the motor, and a large handle and large housing are necessary to widen the air path and improve the cooling effect. .

(2) Gate of switching element 8 and control unit 6
Since the gate signal line connecting the two crosses near the contact surface between the commutator 12 and the carbon brush 14, which is a source of noise in the power tool, noise is likely to be added to the gate signal line. Therefore, it is necessary to add parts to improve noise resistance, and a space is required to accommodate these parts.

(3) The abrasion powder of the carbon brush 14 causes poor insulation of the tool, but since the wind containing this abrasion powder is applied to the switching element 8, the connection terminal of the switching element 8, which is a live part, is Must be sufficiently insulated. In particular, in the case of a disc grinder where the housing 1 has a metal shaft and is used in an environment with a lot of conductive powder, it is necessary not only to cover the connection terminals of the switching element 8 with an insulating material, but also to cover the inner wall of the housing 1 with an insulating material. A sufficient distance must be maintained between the terminal and the connecting terminal, and a large housing is required.

Due to the shortcomings of the plate, the power tool was larger than necessary, increased tool weight, and was difficult to use, and at the same time, the production cost increased significantly. In addition, a safety device for a power tool that controls the rotational speed of the motor using a switching element detects abnormal rotation, such as rotation that could cause the grindstone of a disc grinder to break and fly off, and prevents the motor from rotating. A common method is to cut off the power supply.

Mechanical methods are the safest method for shutting off, as abnormal rotation is often caused by an electrical problem, such as a control unit failure or a switching element failure due to a short-circuit current between the stator and housing. It is considered suitable for the device.

For example, as shown in FIGS. 1 and 2, the blocking piece 16 is movable in the radial direction of the rotating member 15 connected to one end of the armature 1, and the blocking piece 16 is moved in the axial direction of the rotating member 15 by the pin F and the spring 18. It is installed in a pre-loaded state,
When the rotational speed of the motor 9, that is, the armature 11, exceeds the set rotational speed, the centrifugal force acting on the blocking piece 16 becomes greater than the biasing force of the spring 18, and the blocking piece 16 is suddenly displaced outward. A method often used is to cut off the power supply to the motor by turning off a safety switch 19 connected in series to the power supply and the motor 9.

If this safety device is to prevent the risk of the grinding wheel 3 being damaged and flying off if it is rotated at a speed exceeding the allowable rotation speed, such as in the case of the disc grinder 7, the rotation when the blocking piece 16 is displaced outward is The number of rotations, that is, the operating rotation speed of the safety device must be set so as to never exceed the allowable rotation speed of the grinding wheel 3, but at the same time, since high-speed rotation is a feature of this type of power tool, the operating rotation speed Nor can the number be set unnecessarily low. In other words, the challenge for this type of power tool was how to accurately set the operating rotation speed of the safety device, that is, to set it as high as possible without exceeding the allowable rotation speed.

In the structure described above, the operating rotation speed NA is expressed by the distance between Due to individual variations in the above-mentioned parts, the operating rotational speed NA also varies. As in the example in Figure 2, if no special consideration is given to this variation, it is out of the question and the bottle 1 in Figure 2 is out of the question.
7 is shaped like a cam, and this pin is rotated to adjust the amount of deflection of the spring 18, that is, the biasing force F, thereby eliminating variations in the operating rotation speed pA, or as shown in Fig. 3, there is an adjustment method. By displacing the screw 20 in the radial direction, the blocking piece 16 is similarly displaced, and the distance R″l between the center of gravity of the blocking piece 16 and the rotation axis center is bent, and at the same time, the blocking piece 16 is connected to the rotating member. A widely used method is to change the amount of deflection of the spring 18 to eliminate variations in the operating rotational speed NA.
7) After adjustment, if a part of the adjustment mechanism, i.e., the cam-shaped pin 17' in the former case and the adjustment screw 20 in the latter case, is not fixed with adhesive, etc., the operating rotation speed will be distorted due to vibrations etc. when using the tool. There was a problem. - The fixing work for this purpose was quite troublesome because the safety device including the adjustment mechanism is compactly constructed and the blocking piece 16 must not be attached with adhesive.

In addition, after the above safety devices are activated, the power supply and motor 9
For example, the safety switch 19 can be made usable again by resetting the electrical circuit connected in series with it, but the electrical circuit for the safety switch 19 etc. is in a state inside the control unit 6 that cannot be reset from the outside. The controller unit 6 was fixed to the housing 1 or the like. Also, the cause of the safety device activation is the switching element 8.
In addition to malfunctions of the main body such as continuity breakdown, there are also errors in use, such as loss of control due to the use of a DC power supply, and failure of the safety switch 1 without investigating the cause.
9 was reset and the safety device was activated again, which resulted in a relatively high number of cases. The resetting work, which occurs relatively frequently and can only be done after the control section unit 6 has been removed, is troublesome. In addition, as shown in FIGS. 1 and 2, in the case where a magnet 21 is disposed on the rotating member 15 and a magnetically sensitive element 22 is embedded in the control unit d in correspondence with this magnet 21, this magnet 21 Since the distance between the magnetically sensitive element 22 and the magnetically sensitive element 22 greatly affects the detection of the rotation speed, it is better not to change the position of the magnetically sensitive element 22, that is, the position of the control section unit 6. It was not convenient to remove unit 6.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, reduce the size of the power tool by 41%, and also make the safety device reliable and simple.

The present invention provides this type of device by storing a part of the control unit in the rear part of the housing, thereby forming an air path through which cooling air directly hits the switching elements, thereby increasing the cooling effect of the switching elements. This was an attempt to make power tools smaller and lighter. At the same time, we attempted to make the safety device reliable and simple by cutting off a part of the cutoff piece to adjust the operating rotation speed of the safety device, and by configuring the safety device's electrical circuit unit to be removable. This is what I did.

An embodiment in which the present invention is applied to a disc grinder will be described below with reference to FIGS. 4 to 9.

A grindstone 25 is rotatably mounted via a gear cover 24 connected to the front part of a plastic housing 23.
It is driven by a motor 26 housed within the housing 23. In order to reduce the outer diameter of the housing 23, the gap between the outer periphery of the stator 27 of the motor 26 and the inner wall of the housing 23 is small, so the armature f-nia 28 of the motor 26 is equipped with a centrifugal fan that can ensure air volume even if the air path resistance is large. 29 is fixed. No Ujinobu 23
Inside the plastic nozzle 30 connected to the rear part, a switching element 31 for controlling the rotation speed of the 7-j 26, and a control circuit 32 connected to the gate of this switching element 31 are integrally molded in resin. A section unit 33 and a main switch 34 are incorporated. A part of the control unit 33 is connected to the opposing carbobrush 3.
5 and protrudes into the rear of the housing 23 and close to the stator 27 of the motor 26.

Therefore, the rear portion of the housing 23 except for the carbon brush 35 is blocked by a portion of the control unit 33. The handle 30 is provided with a wind window 36 whose longitudinal direction is in the same direction as the facing surface of the carbon brush 35 and whose longitudinal direction is in the axial direction. Cooling fins 37 for cooling the element 31 are attached to the control unit 33.

In this state, the cooling air sucked in by the centrifugal fan 29 from the wind window 36 of the handle 30 passes through the air path formed by the cooling fins 37 and the inner wall of the handle 30, and passes through the control unit connected to this air path. 33 and the inner wall of the housing 23, that is, an air path along the carbon brush 35 and the commutator 38 of the armature 28, and further flows toward the vicinity of the coil of the stator 27 of the motor 26. Since a continuous air path is formed in this way, most of the cooling air directly cools the cooling fins 37, carbon brushes 35, armature 28, commutator 38, and stator 27, and the cooling effect is Significantly larger than conventional products.

Next, a magnet 41 for detecting the rotation speed of the motor 26 is disposed on a rotating member 39 connected to one end of the armature 28 of the motor 26 in correspondence with a pickup 40 in the control unit 33. In addition, a blocking piece 42 made of an aluminum plate is attached so as to be movable in the radial direction of the rotating member 39 and urged in the axial direction of the rotating member 39 by a spring 43. The blocking piece 42 and the rotating member 39 are formed so that a part of the blocking piece 42 is exposed outward from the rotating member 39 in the above state, and a scale 44 is formed on a part of the exposed part. It is attached.

Now, when the rotation speed of the motor 26 increases to the permissible rotation speed of the grindstone 25, for example 95 degrees, due to a failure of the control unit 33, centrifugal force acting on the blocking piece 42 is applied to the spring 43.
, the Mlar piece 42 suddenly displaces outward, and the electrical circuit member 47 made of a steel plate, which is connected in series to the main switch 45 and the motor 26 and housed in the electrical circuit unit 46, is The power supply to the motor 26 is cut off.

The number of rotations when this blocking piece 42 is displaced outward, that is, the operating rotational speed NA of this safety device, is determined by the biasing force of the spring 43 in the above state, the mass of the blocking piece m1, the center of gravity of the blocking piece 42, and the mass of the blocking piece 42. Assuming that the distance between the rotational axes of the rotating member 39 is R, if one of the scales 44 of the blocking piece 42 is cut in the above state, m will change and the center of gravity of the blocking piece will also change in position. , if the above m changes to m' and R changes to R', the spring 43 remains in the above state, so the operating rotation aNA' cuts off a part of the blocking piece as shown above. Then, the operating rotation can be determined. Therefore, if you decide in advance the ratio of NA and NA' corresponding to each of the scales attached to the cut-off piece, and cut the cut-off piece so that NA' does not exceed, for example, 95 inches, which is the allowable rotation speed of the grindstone. , the minimum value of NA' is N
Since it can be made larger than the minimum value of A, NA′
It is possible to make the paramutation and the bias of NA smaller than that of NA.

Now, the operating rotation speed NA before adjustment is HAmtn≦NA≦N
There is variation in AmaX, and the operating rotation speed when cutting at mth of n scales is NAm', NAm'/N
If A=(tmXNAm'≦NAmax, then i) m
=o (when the blocking piece is not cut) ii) When O<m<n tit) When m=n, NAm'min=NAminXd(m-1). m
In order to keep NAm'mln constant regardless of the value of, for example, if the operating speed NA before adjustment is 76≦NA≦100
If there is a variation in , and if a 4-division scale is attached to a part of the cutoff piece, (1) The first scale is NA'/ NA = 1.056
4 = cttf21 2 ty s
=1.1160=d2(3) 3 1
/1 =1.1790=('3(414N
# Set the scale so that = 1.2455 = σ4 (11" x When NAArnax<NA<NAmax, do not cut.

α1 (2)↓X NAmaX < NA (” x NAm
When ax, cut at the first d2 α1 scale.

f3)"XNAmaX<NA("When XNAmax, cut at the second α3 '2 scale.

■ (4) XNAmax (NA ("When XNAmax, cut at the third d4 α3 scale.

(51NAm1n(NA) Cut at the 4th scale (L4 when using XNAmax).

When adjusted as follows, NA' min = g47.
becomes.

That is, the operating rotation speed, which varied from 76 to 100 before adjustment, can be changed to between 94.7 and 100. In this way, the operating rotation speed can be adjusted by cutting the blocking piece 42. Therefore, the operating rotation speed will not go out of order after adjustment, and since no adhesive or the like is used, there is no need to worry about the blocking piece 42 being fixed with adhesive or the like, making it possible to provide a reliable and simple safety device. .

The blocking piece 42 is attached to the rotating member 39 via the spring 43 as described above, and the blocking piece 42 does not hit during normal rotation, but is shut off when the blocking piece 42 rotates abnormally, that is, when the blocking piece 42 is displaced outward. At the position where the piece 42 hits, a steel plate electrical circuit member 47 having a notch in a part thereof is placed in a state where the axial direction is the longitudinal direction and a tensile force is applied in the longitudinal direction.
The lead wires attached to both ends of the electric circuit member 47 are connected to the main switch 34 and the motor 26, respectively.

The electric circuit unit 46, in which the electric circuit member 47, the fixed plate 48, and the lead wire are integrally molded with resin, is integrated with the control unit 33 incorporated in the handle 30, and is attached to the rotating member 39 and the ball lowered to the armature 28. It is formed so that the bearing 49 can be prevented from being jinxed and can be attached to and removed from the control unit 33 in the state in which the control unit 33 is assembled into the handle 30.

Therefore, in order to replace the electrical circuit member 47 that has been cut by the cutoff piece 42, it is necessary to fix the electrical circuit unit 46 to the control unit 33 by 1. All you have to do is remove the screws 50 connected to the electrical circuit member 47 and remove the lead wires connected to the electric circuit member 47, and there is no need to remove the control unit 33. Therefore, the characteristics of the rotation speed detection will not change, and the connection from the control unit 33 will not change. The length of the protruding lead wires can be minimized, and the space for wiring can also be reduced.

Next, FIG. 9 is an electric circuit block diagram of this embodiment.

The rotation speed of the motor is detected by a rotation speed detector consisting of a magnet placed on a rotating member connected to the motor and a magnetic pickup built into the control unit, and converted into voltage by an F-V converter. The differential amplifier circuit outputs the difference between the output voltage of the reference voltage circuit 1 and the set rotation speed.

This output generates a trigger signal that brings the motor rotation speed closer to the set rotation speed, that is, a trigger signal that widens the conduction angle of the triac when the motor rotation decreases, and decreases the conduction angle when the rotation increases. It is occurring in the control circuit.

The output of the load current detection circuit is compared with the voltage of the reference voltage circuit 2 by a comparator, but if the load becomes large and this output becomes higher than the voltage of the reference voltage circuit 2, the conduction angle suppression circuit and phase control The circuit reduces the conduction angle of the triac to limit the power supplied to the motor.

Note that the startup waiting operation blocking circuit prevents the current during startup from being detected. At startup, the conduction angle of the triac is gradually increased by the soft start circuit and phase control circuit, and the rotation of the motor is gradually increased.

Due to the electric circuit described above, this disk glider allows the motor rotation to gradually increase when starting up, resulting in a small reaction force at startup, and during regular work, the motor rotation can be kept almost constant even when the load fluctuates. Because of this, grinding efficiency is good, and in the event of an overload, the power supplied to the motor is limited and the motor rotational speed is extremely reduced to notify the operator of the overload.

In this embodiment, the copper plate side is used as the electrical circuit of the safety device, and -C1 is disconnected to cut off the power supply to the motor, but it may be configured to turn off the switch. Further, a magnetically sensitive element may be used in place of the magnetic pickup for detecting the motor rotation speed, and overload may be detected using the load current based on the motor rotation speed.

As described above, according to the present invention, since a part of the control unit is housed in the housing, the tool body can be shortened, and the switching element can be connected to the air passage formed by the control unit, the handle, the housing, etc. Since the cooling air directly hits the contact surface of the motor, especially the armature's conomitator and carbide brushes, and the stator coil, the cooling effect is good, and the capacity of the motor and switching elements can be reduced, as well as the generation of radio noise. Since it is possible to eliminate elements for improving noise resistance, the power tool can be made smaller and lighter in proportion to its capacity.

Furthermore, since the operating rotation speed of the safety device is adjusted by cutting out a part of the cutoff piece, no fixing work is required after adjustment, and the electrical circuit of the safety device is configured independently.
Since this electric circuit can be replaced while the control unit is still installed in the tool body, the safety device can be made simple and reliable.

[Brief explanation of drawings]

Fig. 1 is a partially longitudinal side view of a conventional example, - Fig. 2 is a partially longitudinal front view of a conventional safety device, Fig. 3 is a longitudinal sectional front view of a conventional safety device with an adjustment mechanism, and Fig. 4 5 is a partial cross-sectional side view of the present invention applied to a disc grinder, FIG. 5 is a partial cross-sectional plan view of FIG. 4, FIG. 6 is a 1-1m longitudinal cross-sectional view of FIG. 4, and FIG. FIG. 8 is a partially vertical front view of the safety device of the present invention, and FIG. 9 is a block diagram of the electric circuit of this embodiment. 26...Motor 3.1...Switching element, 33...m control unit, 3o...
・Handle 23...Housing, 46...
Electrical circuit unit, 28...armature, 39
...Rotating member, 42...Blocking piece

Claims (1)

[Claims] (1) A control unit that houses a control circuit that is connected in series with a motor for driving a power tool and connected to the gate of a switching element that controls the rotation speed of the motor is assembled in the handle. What is claimed is: 1. A power tool that is compact in size, wherein a part of the control section unit protrudes into the housing, and an air passage is formed by the control section unit, the handle, and the housing. (21 Connect in series the motor for driving a power tool, the switching element that controls the rotation speed of the motor, and the electric circuit of the safety device that cuts off the power supply to the motor when the motor reaches an abnormal rotation speed. (3) An electric tool controlled by a switching element, characterized in that the electric circuit unit housing the electric circuit of the sulfur safety device is configured to be independent from other parts and can be removed. When the tool drive motor reaches an abnormal rotation speed, a shutoff piece is attached to a rotating member connected to one end of the armature of the motor so as to be movable in the radial direction and biased in the axial direction. In a safety device that displaces outward to interrupt an electric circuit connected in series to the motor and a power source, a part of the interrupting piece is cut to adjust the operating rotation speed of the safety device. A power tool specially designed to have a safety device configured to