WO2008018611A1

WO2008018611A1 - Power tool

Info

Publication number: WO2008018611A1
Application number: PCT/JP2007/065795
Authority: WO
Inventors: Nobuhito Hosokawa
Original assignee: Hitachi Koki Co., Ltd.
Priority date: 2006-08-11
Filing date: 2007-08-07
Publication date: 2008-02-14

Abstract

A power tool (1) comprises a housing (2) having intake ports (2a), and a ventilation duct (2c). A barrier wall section (21) is formed in the rear section of the ventilation duct near the intake ports. An accommodiation section (21a) shaped as a rectangular hole elongated in the front-to-rear direction is formed in the bottom of the barrier wall section (21). The accommodation section functions to accommodate a dust-collecting case (22) The dust-collecting case accommodates a plurality of magnets (24) and is detachably mounted in the housing.

Description

DESCRIPTION

POWER TOOL Technical Field The present invention relates to a power tool for use in environments high in magnetic particulate, such as iron powder. Background Art

When using a power tool, loss or damage can occur due to heat, vibrations, and noise produced by the motor. To prevent damage to the motor caused by heat, a cooling fan is commonly provided in the housing of the power tool, the cooling fan rotates together with the drive shaft of the motor to introduce air into the housing through an intake port. The air introduced into the housing serves as cooling air that flows along a ventilation duct in the housing toward an exhaust port, thus cooling the motor and suppressing the generation of heat. Accordingly, the motor can be operated continuously. Electric grinders or other power tools used for metalworking and having the construction described above are used in an environment with airborne particulate, including nonmagnetic particulate such as wood dust, and magnetic particulate such as iron powder produced in metalworking. This particulate is often sucked into the housing through the intake port of the power tool. If the particulate gets into the motor, the rotor, which rotates at a high speed, may incur damage. Therefore, dust-collecting structures have been proposed for collecting particulate that gets into the housing.

For example, the dust-collecting structure shown in Fig. 13 includes a power tool 800, and a separately provided collector 801 connected via a hose 802. With this construction, particulate that enters the housing of the power tool 800 is drawn up and collected in the collector 801 and subsequently discharged from the collector 801. The dust-collecting structure shown in Fig. 14 includes a cooling fan 901, and a separate dust-collecting fan 902 fixed to a rotational shaft 903. Airflow generated by the rotation of the dust-collecting fan 902 draws airborne particulate in the work area into a housing 904. The particulate is then collected in a dust bag 905 attached to a connector of the housing 904.

However, the conventional dust-collecting structures shown in Figs. 12 and 13 cannot completely collect all particulate, allowing some particulate to pass into the housing through the intake port and enter the motor. Particularly when a DC motor is used in the power tool, magnetic particulate such as iron powder is attracted to the permanent magnet in the stator and can interfere with the rotation of the rotor. Further, since magnetic particulate such as iron powder produced in metalworking operations often has sharp edges and has been hardened by heat, such particulate can greatly affect operations of the power tool if the particulate enters the motor.

Therefore, constructions employing magnetic poles to attract magnetic particulate have been proposed as methods of collecting magnetic particulate from a fluid. For example, Japanese unexamined patent application publication No. SHO-63-278570 discloses an iron powder attracting magnet for attracting particulate, while Japanese unexamined patent application publication No. HEI-4-027450 discloses a dust collector for attracting particulate with a magnet. Japanese unexamined patent application publication No. HEI- 5-329311 discloses an iron powder attracting filter having a turbulent flow generating plate and a magnet arranged in an oil channel through which flows oil containing iron powder. The turbulent flow generating plate generates turbulence in the oil, while the magnet attracts the iron powder. Japanese unexamined patent application publication No. HEI- 9-162028 discloses a magnet plate for attracting iron powder from a fluid, and a magnet filter having a channel in which the magnet plate is inserted. Japanese unexamined patent application publication No. HEI-11-178282 discloses an iron powder removing device for attracting iron powder in a ventilation duct. The ventilation duct is provided with curved walls for forcing cooling air containing particulate along a curved path. Magnets are provided on the wall surfaces for attracting the particulate.

While the methods described above can use magnetic poles to attract magnetic particulate from a fluid, it is predictable that the attracted particulate will accumulate on the magnetic poles, eventually reducing the attracting capacity of the poles. Disclosure of Invention

In view of the foregoing, it is an object of the present invention to provide a power tool capable of effectively preventing magnetic particulate from entering the motor and capable of facilitating removal of particulate from the power tool.

This and other object of the present invention will be attained by a power tool including a housing, a motor, a fan, a magnet unit. The housing has an intake port, an exhaust port, and a ventilation space fluidly connecting the intake port to the exhaust port. The motor is accommodated in the housing and has a rotational shaft. The fan is disposed in the housing and is fixed to the rotational shaft. The magnet unit is disposed in the ventilation space near the intake port of the housing and detachably mounted in the housing. With this arrangement, when a certain amount of particulate has accumulated on the magnet unit, the magnet unit can be detached from the housing, and the particulate accumulated on the magnet unit can be removed by blowing air on the magnet unit, for example. After removing the particulate from the magnet unit, the magnet unit is mounted into the housing, enabling the magnet unit to once again separate particulate from the air. Hence, this construction facilitates a maintenance operation for removing particulate that has been attracted to and accumulated on the magnet unit. Further, the magnet unit can be repeatedly reused without a decrease in attraction force caused by particulate accumulating on the magnet unit. Since particulate is removed from the air when attracted to the magnet unit, this particulate is not attracted to the permanent magnet used in the stator. The particulate does not hinder rotation of the rotor, enabling the motor to operate with stability and increasing the durability and life of the motor.

Preferably, a barrier section is disposed in the ventilation space and has a barrier walls for reducing the airflow speed of cooling air flowing through the ventilation space. The magnet units are disposed on the barrier walls.

With this arrangement, the barrier wall section functions to reduce the speed of air containing particulate that is introduced into the housing through the intake ports, facilitating separation of particulate from the air. Hence, this construction attracts and removes particulate more effectively. Preferably, the magnet unit comprises a plurality of magnets each having attraction surfaces. The plurality of magnets are juxtaposed with alternating magnetic polarity on the attraction surfaces of the plurality of magnets. With this arrangement, since the plurality of magnets are juxtaposed so that the magnetic polarity on the attraction surfaces, one of the magnet unit can reliably attract particulate contained in air flowing along the barrier section, thereby increasing the efficiency of dust collection.

Preferably, the magnet unit comprises an iron core, a coil wounding around the iron core, and a yoke covering the coil and the iron core. The housing has a power-supplying member supplying power to a power-receiving member. The power-receiving member connected to the coil. The power- supplying member is connected the power-receiving member when the magnet unit is mounted in the housing.

With this arrangement, it is possible to provide the magnet unit with a capacity to attract particulate while accommodated in the housing and to reduce the attraction force when removed from the housing. Accordingly, the particulate can be easily removed at this time.

Preferably, the power-receiving member is a flexible electrode receiving power through contact with the power- supplying member.

With this arrangement, since the power-receiving member has elasticity, the power-receiving member can compress and expand in the width direction of the magnet unit, when the magnet unit is detached from or mounted in the housing. Accordingly, the power-receiving member does not hinder sliding of the magnet unit.

Preferably, the power tool further comprises a detecting unit detecting a displacement of the magnet unit, a vibrating unit vibrating the magnet unit, and a controller unit. The control unit drives the vibrating unit when the detecting unit detects the displacement of the magnet unit. With this arrangement, the detecting unit detects the displacement of the magnet unit when the magnet unit is detached from the housing; the vibration unit vibrates the magnet unit. The power-receiving member is disconnected from the power-supplying member, as the magnet unit is detached from the housing. As a result, the magnet unit loses its polarity, reducing the force for attracting particulate. By vibrating the magnet unit, the particulate accumulated on the magnet unit is more likely to separate from the magnet unit, thereby further facilitating the particulate removing process. The magnet unit has a capacity to attract particulate when mounted in the housing.

Preferably, the power tool further comprises a removing unit removing a particulate accumulated on the magnet member. With this arrangement, by removing particulate that has been attracted to the magnet unit, the magnet unit can be repeatedly reused without a decrease in attraction force by particulate accumulating on the magnet unit. Brief Description of the Drawings In the drawings:

Fig. 1 is an explanatory diagram conceptually illustrating a power tool according to a first embodiment of the present invention;

Fig. 2 is a cross-sectional view showing the internal structure of the power tool according to the first embodiment;

Fig. 3 is a cross-sectional view of the power tool along the line III-III in Fig. 2;

Fig. 4 is a partial cross-sectional view of the power tool according to the first embodiment when a dust- collecting case has been pulled outward; Fig. 5 is a plan view of the dust-collecting case accommodating magnets of the power tool according to the first embodiment;

Fig. 6A is a plan view of the dust-collecting case accommodating magnets of a power tool according to a second embodiment;

Fig. 6B is a side view of the dust-collecting case accommodating magnets of a power tool according to a second ^• embodiment;

Fig. 7 is a partial cross-sectional view of the housing of the power tool according to the second embodiment;

Fig. 8 is a partial cross-sectional view of the power tool according to the second embodiment when a dust- collecting case has been pulled outward; Fig. 9 is a partial plan view of the power tool according to the second embodiment;

Fig. 10 is a circuit diagram for a power tool according to a third embodiment;

Fig. 11 is a partial cross-sectional view of the power tool according to the third embodiment;

Fig. 12 is a explanation drawing of a conventional dust-collecting structure; and

Fig. 13 is a partial cross-sectional view of another conventional dust-collecting structure. Best Mode for Carrying Out the Invention

A power tool according to a first embodiment of the present invention will be described with reference to Figs. 1 through 5. As shown in Figs. 1 and 2, a power tool 1 has a housing 2 in which are formed intake ports 2a and exhaust ports 2b. Within the housing 2 are provided a motor 3 having a rotational shaft (output shaft) 4, bearings 5 and 6 (see Fig. 2) supporting the rotational shaft 4, a mechanical unit 7 (see Fig. 1) for converting the rotational force of the motor 3 to a prescribed motion, a tip tool 8 (see Fig. 1) to which the rotational force of the motor 3 is transmitted via the mechanical unit 7 (see Fig. 1) , a cooling fan 9 fixed to the rotational shaft 4, and a power supply 10 for applying a driving force to the motor 3. As shown in Figs. 2 and 3, the intake ports 2a are formed as a plurality of slits in both sides of the rear end portion of the housing 2. As shown in Fig. 2, the exhaust ports 2b are formed as a plurality of circular holes in the housing 2 around the cooling fan 9. A ventilation duct 2c fluidly connects the intake ports 2a and the exhaust ports 2b is formed in the housing 2. As will be described later in greater detail, a dust collection path 2d is formed in the ventilation duct 2c near the intake ports 2a. In the following description, the tip tool 8 side of the power tool 1 will be referred to as the front side, the power supply 10 side as the rear side, the dust collection path 2d side as the upper side, and the power supply 10 side as the lower side.

As shown in Fig. 2, the motor 3 is configured of a stator 3a formed of a permanent magnet, and a rotor 3b fixed to the rotational shaft 4, which penetrates the rotor 3b. The stator 3a is fixed to the housing 2, and the rotor 3b is rotatably supported by the bearings 5 and 6 via the rotational shaft 4. The tip tool 8 is detachably mounted on a distal end of the rotational shaft 4 via the mechanical unit 7. The cooling fan 9 is fixed to the rotational shaft 4 on the rear side of the bearing 6, and the power supply 10 is disposed to the rear of the motor 3.

With the power tool 1 having the above construction, the user grips the housing 2 and presses a switch (not shown) provided on the housing 2 for electrically connecting the power supply 10 to the motor 3. At this time, the power supply 10 supplies power to the motor 3 for driving the same. The motor 3 has a structure well known in the art for transmitting the rotational force of the rotational shaft 4 to the tip tool 8 via the mechanical unit 7, driving the tip tool 8 to rotate for performing a desired operation.

As shown in Fig. 4, a barrier wall section 21 is formed in the housing 2 in the rear section of the ventilation duct 2c near the intake ports 2a (diagonally above and forward of the intake ports 2a) . The barrier wall section 21 has a plurality of ribs 21A arranged at suitable intervals in the front-to-rear direction. An accommodating section 21a shaped as a rectangular hole elongated in the front-to-rear direction is formed in the bottom of the barrier wall section 21. The accommodating section 21a functions to accommodate a dust-collecting case 22 that is detachably mounted in the housing 2. A fixture 23 for fixing the dust-collecting case 22 is provided in the rear section of the housing 2.

As shown in Fig. 5, three magnets 24 juxtaposed in the front-to-rear direction are accommodated in the dust- collecting case 22. The dust-collecting case 22 is molded in a rectangular box shape with an open top surface. The three magnets 24 are permanent magnets formed in the shape of rectangular plates and are arranged so that the magnetic polarity on the top surface (attracting surface) sides alternate in polarity in the order N-pole, S-pole, and N- pole. An engaging groove 22a formed in the top surface of the dust-collecting case 22 on the rear end thereof. The engaging groove 22a extends in the width direction (right- to-left direction) and is shaped to engage with the fixture 23. The dust-collecting case 22 is fixed in the housing by engaging the fixture 23 in the engaging groove 22a.

As shown in Fig. 2, when the dust-collecting case 22 is accommodated in the accommodating section 21a (see Fig. 4) of the barrier wall section 21 formed in the housing 2, the dust collection path 2d describes a labyrinthine path in a portion of the ventilation duct 2c. Specifically, the dust collection path 2d is defined by the ribs 21A in the barrier wall section 21, and the top surface of the dust- collecting case 22 (including the top surfaces of the magnets 24) accommodated in the barrier wall section 21.

With the power tool 1 described above, air containing particulate that is introduced into the housing 2 through the intake ports 2a is slowed while flowing through the labyrinthine dust collection path 2d formed by the ribs 21A of the barrier wall section 21. As a result, the particulate contained in the air is separated and attracted to the surfaces of the magnets 24 by magnetic attraction. After the particulate has been separated and removed in the dust collection path 2d, the remaining clean air continues to flow forward through the ventilation duct 2c toward the exhaust ports 2b as cooling air. When passing near the motor 3, the cooling air cools the motor 3, thereby preventing heat damage to the motor 3 and enabling continuous operation of the power tool 1. The cooling air, having increased in temperature by cooling the motor 3, is subsequently discharged from the housing through the plurality of exhaust ports 2b.

Further, the magnets 24 can be inserted into and removed from the accommodating section 21a of the barrier wall section 21 together with the dust-collecting case 22 accommodating the magnets 24. When a certain amount of particulate has accumulated on the magnets 24, the dust- collecting case 22 accommodating the magnets 24 can be pulled out through the rear side of the housing 2, as shown in Fig. 4, and the particulate accumulated on the magnets 24 can be removed by blowing air on the magnets 24, for example. After removing the particulate from the magnets 24, the dust-collecting case 22 accommodating the magnets 24 is inserted into the rear side of the housing 2 and mounted in the accommodating section 21a of the barrier wall section 21, as shown in Fig. 2, enabling the magnets 24 to once again separate particulate from the air. Hence, this construction facilitates a maintenance operation for removing particulate that has been attracted to and accumulated on the magnets 24. Further, the magnets 24 can be repeatedly reused without a decrease in attraction force caused by particulate accumulating on the attracting surface. Since particulate is removed from the air when attracted to the magnets 24, this particulate is not attracted to the permanent magnet used in the stator 3a. Accordingly, the particulate does not hinder rotation of the rotor 3b, enabling the motor 3 to operate with stability and increasing the durability and life of the motor 3.

The barrier wall section 21 functions to reduce the speed of air containing particulate that is introduced into the housing 2 through the intake ports 2a, facilitating separation of particulate from the air. Hence, this construction attracts and removes particulate more effectively.

As described above, the dust collection path 2d is partially defined by the top surface of the three magnets 24. Since the magnets 24 are juxtaposed so that the magnetic polarity on the top surfaces are arranged in the order N- pole, S-pole, and N-pole, one of the magnets 24 can reliably attract particulate contained in air flowing along the dust collection path 2d, whether the magnetic pole of the particulate is an N-pole or an S-pole, thereby increasing the efficiency of dust collection.

Next, a power tool according to a second embodiment of the present invention will be described with reference to Figs. 6A through 9. In the second embodiment, three electromagnets 124 are disposed in a dust-collecting case 122. Each of the electromagnets 124 includes iron cores 125, coils 126 wound around the iron cores 125, and a yoke 127 covering the coils 126 and iron cores 125. Power-receiving electrodes 131 corresponding to the electromagnets 124 are provided on both left and right side surfaces of the dust- collecting case 122 and are each electrically connected to the coils 126 of the corresponding electromagnet 124. The power-receiving electrodes 131 are formed in a plate shape and have elasticity. Each of the power-receiving electrodes 131 has a base end fixed to the dust-collecting case 122, and a free end 131A that can pivot about the base end when the dust-collecting case 122 is completely removed from the power tool. The power-receiving electrodes 131 protrude outwardly from the dust-collecting case 122 in the width direction. As shown Figs. 7 and 8, power-supplying electrodes 132 formed in plate shapes are disposed on surfaces of a housing 102 opposing the left and right side surfaces of the dust- collecting case 122 when the dust-collecting case 122 is mounted in the housing 102. The power-supplying electrodes 132 are electrically connected to the power supply 10 via a resistor 133 for regulating the power supply. When the dust-collecting case 122 is mounted in the housing 102, the power-supplying electrodes 132 contact the power-receiving electrodes 131, electrically connecting the power supply 10 to the coils 126 via the resistor 133, power-supplying electrodes 132, and power-receiving electrodes 131 so that each electromagnet 124 has a magnetic polarity. In the second embodiment, the electromagnets 124 are electrically connected so that the magnetic polarity of the attracting surface (top surface of the yoke 127) sides alternate in polarity in the order N-pole, S-pole, and N-pole. With the construction described above, the power- receiving electrodes 131 contact the power-supplying electrodes 132 when the dust-collecting case 122 is mounted in the housing 102, electrically connecting the electromagnets 124 to the power supply 10 and giving the electromagnets 124 polarity. Accordingly, the electromagnets 124 can attract magnetic particulate contained in air. However, the power-receiving electrodes 131 are disconnected from the power-supplying electrodes 132 when removing the dust-collecting case 122 from the housing 102 in order to remove particulate that has accumulated on the yokes 127 of the electromagnets 124. Hence, since the electromagnets 124 have no polarity when not supplied with power, the attraction between the accumulated particulate and the yokes 127 is reduced, facilitating removal of the particulate.

Further, by providing the power-receiving electrodes 131 corresponding to the electromagnets 124, it is possible to provide each of the electromagnets 124 with a capacity to attract particulate while accommodated in the housing 102 and to reduce the attraction force when removed from the housing 102. For example, when the dust-collecting case 122 is pulled out of the housing 102 so that only the rearmost electromagnet 124 is positioned outside the housing 102, while the two electromagnets 124 positioned on the front side remain inside the housing 102, the power-receiving electrodes 131 corresponding to the rearmost electromagnet 124 are separated and electrically disconnected from the power-supplying electrodes 132. Accordingly, the rearmost electromagnet 124 has lost its polarity at this time. On the other hand, the power-receiving electrodes 131 corresponding to the two electromagnets 124 positioned on the front side remain in contact with and electrically connected to the power-supplying electrodes 132, maintaining the polarity of the two electromagnets 124 positioned on the front side. Hence, the two front electromagnets 124 continue to attract the particulate until pulled out of the housing 102, preventing the accumulated particulate from scattering inside the housing 102. As the dust-collecting case 122 is pulled farther out of the housing 102, each electromagnet 124 becomes electrically disconnected upon leaving the housing 102, thereby reducing the force of attraction for the particulate. Accordingly, the particulate can be easily removed at this time.

Further, since the power-receiving electrodes 131 have elasticity, the power-receiving electrodes 131 can compress and expand in the width direction of the dust-collecting case 122 when the dust-collecting case 122 is inserted in or removed from the housing 102. Accordingly, the power- receiving electrodes 131 do not hinder sliding of the dust- collecting case 122.

Next, a power tool according to a third embodiment of the present invention will be described with reference to Figs. 10 and 11. In addition to the structure of the power tool described in the second embodiment, the power tool according to the third embodiment includes a sensor 141 for detecting sliding of the dust-collecting case 122 in the housing 102, a vibration motor 142 for vibrating the dust- collecting case 122, and a controller 143 for controlling the vibration motor 142. When the dust-collecting case 122 is removed from the housing 102 to remove particulate, the sensor 141 detects sliding of the dust-collecting case 122. At this time, the controller 143 drives the vibration motor

142 to transmit vibrations to the dust-collecting case 122. With this construction, the sensor 141 detects sliding of the dust-collecting case 122 when the dust-collecting case 122 is pulled from the housing 102, and the controller

143 begins driving the vibration motor 142 based on this detection. As described above, the power-receiving electrodes 131 are disconnected from the power-supplying electrodes 132 for each of the electromagnets 124 as the electromagnets 124 are pulled out of the housing 102. As a result, the electromagnet 124 (yoke 127) loses its polarity, reducing the force for attracting particulate. By vibrating the dust-collecting case 122 and the yokes 127, the particulate accumulated on the yokes 127 is more likely to separate from the yokes 127, thereby further facilitating the particulate removing process. As with the power tool according to the second embodiment, each of the electromagnets 124 has a capacity to attract particulate when accommodated in the housing 102. Hence, particulate attracted to electromagnets 124 accommodated in the housing 102 does not separate from the yokes 127 due to vibrations applied by the vibration motor 142, preventing particulate from scattering inside the housing 102.

While the invention has been described in detail with reference to specific embodiments thereof, it would be apparent to those skilled in the art that many modifications and variations may be made therein without departing from the spirit of the invention, the scope of which is defined by the attached claims. For example, while three magnets are used in the preferred embodiments described above, the present invention has no particular limitation on the number of magnets used.

Further, while the magnets 24 are described as permanent magnets in the first embodiment, electromagnets may be used in place of the permanent magnets. Conversely, while the electromagnets 124 are used as the magnets in the third embodiment, permanent magnets may be used in place of the electromagnets 124.

The power-receiving electrodes 131 and power-supplying electrodes 132 are described as plate-shaped in the second and third embodiments, but the present invention is not limited to this shape. The power-receiving electrodes 131 and power-supplying electrodes 132 may be arbitrarily shaped provided that an electrical connection can be established between the two.

In the preferred embodiments described above, particulate accumulated on the magnets is blown off with air or the like when the dust-collecting case is removed from the housing, but another method may be used for removing particulate from the magnets. Industrial Applicability

The power tool of the present invention is preferably used in a disk grinder or the like employed in metalworking.

Claims

1. A power tool comprising; a housing having an intake port, an exhaust port, and a ventilation space fluidly connecting the intake port to the exhaust port; a motor accommodated in the housing and having a rotational shaft; a fan disposed in the housing and fixed to the rotational shaft; and a magnet unit disposed in the ventilation space near the intake port of the housing and detachably mounted in the housing.

2. The power tool according to claim 1, further comprising a barrier section disposed in the ventilation space and having a barrier walls for reducing airflow speed of a air introduced into the ventilation space through the intake port by the fan, wherein the ventilation space is formed by the barrier walls and the magnet unit, and wherein the magnet unit is disposed in the barrier section.

3. The power tool according to claim 1, wherein the magnet unit comprises a plurality of magnets each having attraction surfaces, and wherein the plurality of magnets are juxtaposed with alternating magnetic polarity on the attraction surfaces of the plurality of magnets.

4. The power tool according to claim 1, wherein the magnet unit comprises an iron core, a coil wounding around the iron core, and^' a yoke covering the coil and the iron core, the power tool further comprising a power-receiving member connected to the coil, and wherein the housing has a power-supplying member supplying power to the power-receiving member and connected the power-receiving member when the magnet unit is mounted in the housing.

5. The power tool according to claim 4, wherein the power-receiving member comprises a flexible electrode receiving power through contact with the power-supplying member.

6. The power tool according to claim 1, further comprising a detecting unit detecting a displacement of the magnet unit, a vibrating unit vibrating the magnet unit, and a control unit driving the vibrating unit when the detecting unit detects the displacement of the magnet member.

7. The power tool according to claim 1, further comprising a removing unit removing a particulate accumulated on the magnet member.