US20130260653A1

US20130260653A1 - Power tool

Info

Publication number: US20130260653A1
Application number: US13/769,162
Authority: US
Inventors: Naoki Tadokoro
Original assignee: Hitachi Koki Co Ltd
Current assignee: Koki Holdings Co Ltd
Priority date: 2012-03-28
Filing date: 2013-02-15
Publication date: 2013-10-03
Also published as: DE102013101307A1; CN103358211A; JP2013202734A

Abstract

A first recess and protrusion engagement portion and a second recess and protrusion engagement portion making a fan guide and one end portion of a leg swingably abut on each other and making a base plate and the other end portion of the leg swingably abut on each other, respectively, and restricting a deviation of the leg relative to the fan guide and the base plate in a horizontal direction while allowing swinging of the leg relative to the fan guide and the base are provided between the fan guide and the one end portion and between the base plate and the other end portion, respectively. The leg can swing with almost no resistance without involving any elastic deformation during the orbital motion of the base, and stress to cause elastic deformation is not applied to the leg unlike the conventional art.

Description

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. 2012-074260 filed on Mar. 28, 2012, the content of which is hereby incorporated by reference into this application.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a power tool which is provided with a main body part having a driving source, a rotation shaft provided in the driving source, and a base moving in an approximately circular motion in a horizontal direction with respect to the main body part along with rotation of the rotation shaft, and performs grinding work using a polishing sheet held by the base.

BACKGROUND OF THE INVENTION

Conventionally, power tools are used to efficiently grind and smoothen a surface of a wood or the like, and the power tools include a so-called orbital sander provided with a main body part having a driving source, a rotation shaft provided in the driving source, and a base moving in an approximately circular motion in a horizontal direction with respect to the main body part along with rotation of the rotation shaft (making an orbital motion). Also, the base is designed to hold a polishing paper (polishing sheet). Therefore, when a user grasps a grip of the main body part to rotationally drive the driving source and presses the polishing paper onto a surface of a wood or the like, the base makes an orbital motion with respect to the main body part to efficiently grind and smoothen the surface of the wood or the like.
As such an orbital sander (power tool), for example, an electric power tool described in Japanese Patent Application Laid-Open Publication No. 2008-100302 (Patent Document 1) has been known. In the electric power tool (power tool) described in Patent Document 1, a motor (driving source) is housed in a housing (main body part) and a ball bearing is provided at a distal end portion of a motor shaft (rotation shaft) of the motor so as to be eccentric to an axial center of the motor shaft. Further, a base provided with a pad which holds a polishing paper is fixed to the ball bearing, and a plurality of flexible legs (posts) are provided between the housing and the base and around the ball bearing. These legs restrict relative rotation of the base with respect to the housing and also allow swinging action of the base relative to the housing centered around the ball bearing, so that the base (polishing paper) makes an orbital motion along with rotation of the motor shaft.

SUMMARY OF THE INVENTION

According to the power tool described in Patent Document 1 mentioned above, however, since one ends of the respective posts are fixed to the main body part and the other ends thereof are fixed to the base, each time when the base makes an orbital motion with respect to the main body part, namely, each time when the power tool is used, the respective posts repeat elastic deformation such as extension and contraction. Therefore, when the respective posts deteriorate due to a long-term use of the power tool, cracks occur in the respective posts in some cases, which results in the necessity of maintenance such as replacement. In particular, in the case where the power tool is frequently used in a site where an ambient temperature is low, not only the deterioration of the respective posts is accelerated to shorten a maintenance cycle but also the respective posts are hardened to make the elastic deformation difficult. As a result, an operation resistance of the base is increased, which may result in such a problem that the grinding performance lowers.
An object of the present invention is to provide a power tool capable of preventing the increase in the operation resistance of the base and extending the maintenance cycle of the posts.
According to one embodiment, a power tool includes: a main body part having a driving source; a rotation shaft provided in the driving source; a base moving in an approximately circular motion with respect to the main body part in a horizontal direction along with rotation of the rotation shaft; a polishing sheet held by the base; a post provided between the main body part and the base; and recess and protrusion engagement portions provided between the main body part and one end portion of the post and between the base and the other end portion of the post, respectively, making the main body part and the one end portion swingably abut on each other and making the base and the other end portion swingably abut on each other, respectively, and restricting a deviation of the post relative to the main body part and the base in a horizontal direction while allowing swinging of the post relative to the main body part and the base.
According to the present invention, the post is swung with almost no resistance without involving any elastic deformation during the orbital motion of the base. Therefore, stress (load) to elastically deform the post like the conventional art is not applied to the post, and the increase in the operation resistance of the base can be prevented and the life of the posts can be prolonged to extend the maintenance cycle.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a perspective view showing an orbital sander according to a first embodiment of the present invention;

FIG. 2 is a partial sectional view of the orbital sander taken along a longitudinal direction of the orbital sander as viewed from the side of arrow A in FIG. 1;

FIG. 3 is a partial sectional view showing a portion B circled by a broken line in FIG. 2 in an enlarged fashion;

FIG. 4A is an operation explanatory diagram for describing an operation state of a leg;

FIG. 4B is an operation explanatory diagram for describing the operation state of the leg;

FIG. 5 is a partial sectional view showing a leg and a surrounding structure thereof according to a second embodiment and corresponding to FIG. 3;

FIG. 6 is a partial sectional view showing a leg and a surrounding structure thereof according to a third embodiment and corresponding to FIG. 3; and

FIG. 7 is a partial sectional view showing a leg and a surrounding structure thereof according to a fourth embodiment and corresponding to FIG. 3.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention will be described below in detail with reference to the drawings.
FIG. 1 is a perspective view showing an orbital sander according to the first embodiment of the present invention, FIG. 2 is a partial sectional view of the orbital sander taken along a longitudinal direction of the orbital sander as viewed from the side of arrow A in FIG. 1, FIG. 3 is a partial sectional view showing a portion B circled by a broken line in FIG. 2 in an enlarged fashion, and FIGS. 4A and 4B are operation explanatory diagrams for describing an operation state of a leg.
As shown in FIG. 1 and FIG. 2, an orbital sander 10 as a power tool is provided with a sander main body 20 and a base 30. The sander main body 20 is provided with a housing 21 which can be divided into a left side portion and a right side portion (a far side portion and a near side portion in FIG. 1) along a longitudinal direction of the orbital sander 10, and the housing 21 is formed from a resin material such as plastic so as to have a hollow shape.
The housing 21 is provided with a motor housing portion 21 a and a grip portion 21 b. A motor 22 serving as a driving source in an upright position is housed inside the motor housing portion 21 a and an operation switch 11 for turning ON and OFF the orbital sander 10 is provided on the grip portion 21 b. A stopper button 12 (see FIG. 1) is provided in the vicinity of the operation switch 11 on the grip portion 21 b. Then, by pressing the stopper button 12 in a state where the operation switch 11 has been operated to ON, the continuous operation state where the operation switch 11 is not operated to OFF is achieved.
Here, for easy understanding of an internal structure of the housing 21, illustrations of electric wires for electrically connecting the operation switch 11 and the motor 22, a power source cord 13, a polishing paper 14, clips 15 (see FIG. 1), and the like are omitted in FIG. 2.
A fan guide 23 formed in a predetermined shape from a resin material such as plastic is provided in the housing 21 near the base 30. The fan guide 23 is fixed inside the housing 21, and a rotation shaft 22 a extending in a downward direction below the motor 22 penetrates through an approximately central portion of the fan guide 23. The rotation shaft 22 a of the motor 22 is rotatably supported by a first radial bearing B1 attached to the fan guide 23, and a cooling fan 24 is fixed to a distal end side of the rotation shaft 22 a below the first radial bearing B1 in an axial direction so as to be rotated integrally with the rotation shaft 22 a. Here, the sander main body 20 is composed of the housing 21 and the fan guide 23, and the housing 21 and the fan guide 23 constitute a main body part in the present invention.
The cooling fan 24 is rotatably housed inside the fan guide 23 via a dust guide 25, and is provided with a dust collecting function to collect grinding dusts (not shown) generated during the grinding work in addition to a cooling function to cool the motor 22. A plurality of cooling fins 24 a are provided on the motor 22 side of the cooling fan 24, and a plurality of dust collecting fins 24 b are provided on the base 30 side of the cooling fan 24 so as to face an exhaust port 25 a of the dust guide 25. Therefore, external air can be fed to the motor 22 along with the rotation of the cooling fan 24, and grinding dusts can be fed to the inside of a dust collecting bag 26 (see FIG. 1) via the exhaust port 25 a. Here, the dust collecting bag 26 is formed of, for example, a cloth with a mesh size allowing the air to pass but not allowing the dusts to pass.
An eccentric piece 27 is fixed to a distal end side of the rotation shaft 22 a below the cooling fan 24 in the axial direction of the rotation shaft 22 a via a fastening screw S. The eccentric piece 27 is designed to make an orbital motion (eccentric circular motion) around an axial center C2 at a position decentered (offset) from an axial center C1 of the rotation shaft 22 a by about 1.0 mm, and an inner side of a second radial bearing B2 is attached to a piece main body 27 a forming the eccentric piece 27. Further, a cylindrical portion 31d provided integrally on a base plate 31 forming the base 30 is fixed to an outer side of the second radial bearing B2, so that the base 30 also makes an orbital motion via the second radial bearing B2 by the orbital motion of the eccentric piece 27 along with the rotation of the rotation shaft 22 a. More specifically, the base 30 is designed to move in an approximately circular motion in a horizontal direction with respect to the housing 21 and the fan guide 23 along with the movement of the eccentric piece 27.
A weight 27 b is provided partially around the piece main body 27 a so as to cancel (balance out) vibrations in a horizontal direction caused by the orbital motion of the base 30. Specifically, as shown in FIG. 2, when the base 30 moves to the right side in FIG. 2, the weight 27 b moves to the left side in FIG. 2. Thus, by cancelling the vibrations in the horizontal direction during the operation of the orbital sander 10 in this manner, the movement of the grip portion 21 b grasped by a worker in the horizontal direction can be prevented.
The base 30 is composed of the base plate 31 made of an aluminum material and a sponge-like pad 32 made of a rubber material, and a polishing paper 14 (see FIG. 1) serving as a polishing sheet is attached to the pad 32. When the polishing paper 14 is to be attached to the pad 32, both end portions of the polishing paper 14 in a longitudinal direction of the orbital sander 10 are folded back to the side of the base plate 31 and they are secured by clips 15 attached to the base plate 31. Here, a hole is also formed in the polishing paper 14 so as to coincide with dust collecting hole (not shown) formed in the base plate 31 and the pad 32. Therefore, grinding dusts generated during the grinding work are collected in the dust collecting bag 26 via the hole formed in the polishing paper 14, the dust collecting hole, and the dust guide 25 (exhaust port 25 a).
A total of four legs (posts) 40 are provided between the fan guide 23 forming the sander main body 20 and the base plate 31 forming the base 30. Though only two legs are shown in FIG. 2, the respective legs 40 are each formed in an approximately columnar shape from an elastic material such as rubber, and they are arranged at predetermined intervals at front, back, left and right positions along the horizontal direction of the fan guide 23 and the base plate 31 so as to interpose the rotation shaft 22 a of the motor 22. Here, since the respective legs 40 and surrounding structures thereof are all identical to one another, one leg 40 and a surrounding structure thereof will be described in detail with reference to FIG. 3.
As shown in FIG. 3, a first recess and protrusion engagement portion (recess and protrusion engagement portion) 50 is provided between a base-side surface 23 a of the fan guide 23 and one end portion 40 a (upper side in FIG. 3) of the leg 40. The first recess and protrusion engagement portion 50 is composed of a columnar member 51 integrally provided so as to extend in the axial direction of the rotation shaft 22 a from the base-side surface 23 a toward the base plate 31 and a spherical recess portion 52 formed so as to be recessed from the one end portion 40 a of the leg 40 toward the other end portion 40 b thereof. A spherical protrusion portion 51 a is integrally provided at a distal end of the columnar member 51, and the spherical protrusion portion 51 a abuts on the spherical recess portion 52. Therefore, swinging of the leg 40 relative to the fan guide 23 is allowed and axial deviation of the leg 40 relative to the fan guide 23, namely, relative movement (deviation) of the leg 40 with respect to the fan guide 23 in the horizontal direction is restricted.
A radius R1 of the spherical protrusion portion 51 a is set to be slightly smaller than a radius R2 of the spherical recess portion 52 (R1<R2). Therefore, a distal end of the spherical protrusion portion 51 a is brought in point contact with a bottom of the spherical recess portion 52. By brining the spherical protrusion portion 51 a and the spherical recess portion 52 into point contact with each other in this manner, the leg 40 can swing smoothly with almost no resistance during the orbital motion of the base 30. Here, a height of the columnar member 51 including the spherical protrusion portion 51 a is set to be larger than a depth of the spherical recess portion 52. In this manner, in the swinging action of the leg 40 relative to the fan guide 23, the contact between the one end portion 40 a of the leg 40 and the base-side surface 23 a is prevented, so that the base 30 can make an orbital motion smoothly.
An annular first surrounding wall 23 b is integrally provided around the columnar member 51 of the fan guide 23 so as to surround the columnar member 51. The one end portion 40 a of the leg 40 in its longitudinal direction is housed in the first surrounding wall 23 b in a non-contact state, and a height of the first surrounding wall 23 b from the base-side surface 23 a is set to h1. By setting the height of the first surrounding wall 23 a to h1 in this manner, about ⅓ of the leg 40 in the longitudinal direction is covered with the first surrounding wall 23 b. As a result, even if the leg 40 is elastically deformed largely by any cause, the leg 40 is prevented from flying out of the first surrounding wall 23 b.
A taper surface 23 c gradually thinned toward a distal end (lower side in FIG. 3) of the first surrounding wall 23 b is formed on a radially inner side of the first surrounding wall 23 b. An inclination angle of the taper surface 23 c is set to α°, and the inclination angle α° is set to be equal to the maximum inclination angle of the leg 40 when the leg 40 swings. In this manner, _the one end portion 40 a of the leg 40 is easily housed in the first surrounding wall 23 b when assembling the orbital sander 10. Further, the contact between the leg 40 and the first surrounding wall 23 b during the swinging action of the leg 40 can be prevented, so that the base 30 can make an orbital motion smoothly (see FIG. 4).
A second recess and protrusion engagement portion (recess and protrusion engagement portion) 60 is provided between a fan-guide-side surface 31 a of the base plate 31 and the other end portion 40 b (lower side in FIG. 3) of the leg 40. The second recess and protrusion engagement portion 60 is composed of a columnar member 61 integrally provided so as to extend in an axial direction of the rotation shaft 22 a from the fan-guide-side surface 31 a toward the fan guide 23 and a spherical recess portion 62 formed so as to be recessed from the other end portion 40 b of the leg 40 toward the one end portion 40 a thereof. A spherical protrusion portion 61 a is integrally provided at a distal end of the columnar member 61, and the spherical protrusion portion 61 a abuts on the spherical recess portion 62. Therefore, swinging of the leg 40 relative to the base plate 31 is allowed and axial deviation of the leg 40 relative to the base plate 31, namely, relative movement (deviation) of the leg 40 with respect to the base plate 31 in the horizontal direction is restricted.
A radius R1 of the spherical protrusion portion 61 a is set to be slightly smaller than a radius R2 of the spherical recess portion 62 (R1<R2). Therefore, a distal end of the spherical protrusion portion 61 a and a bottom of the spherical recess portion 62 are brought into point contact with each other. By bringing the spherical protrusion portion 61 a and the spherical recess portion 62 into point contact with each other in this manner, the leg 40 can swing smoothly with almost no resistance during the orbital motion of the base 30. Here, a height of the columnar member 61 including the spherical protrusion portion 61 a is set to be larger than a depth of the spherical recess portion 62. In this manner, in the swinging action of the leg 40 relative to the base plate 31, the contact between the other end portion 40 b of the leg 40 and the fan-guide-side surface 31 a can be prevented, so that the base 30 can make an orbital motion smoothly.
An annular second surrounding wall 31 b is integrally provided around the columnar member 61 of the base plate 31 so as to surround the columnar member 61. The other end portion 40 b of the leg 40 in its longitudinal direction is housed in the second surrounding wall 31 b in a non-contact state, and a height of the second surrounding wall 31 b from the fan-guide-side surface 31 a is set to h2 (h2<h1). By setting the height of the second surrounding wall 31 b to h2 in this manner, about ¼ of the leg 40 in the longitudinal direction is covered with the second surrounding wall 31 b. As a result, even if the leg 40 is elastically deformed largely by any cause, the leg 40 is prevented from flying out of the second surrounding wall 31 b.
Here, the height hi of the first surrounding wall 23 b and the height h2 of the second surrounding wall 31 b can be arbitrarily set, respectively. For example, they may be set so as to have a magnitude relationship opposite to that described above. However, in setting the heights h1 and h2, it is desirable that a predetermined clearance (with the size of about ¼ of the leg 40 in the longitudinal direction) is formed between the first surrounding wall 23 b and the second surrounding wall 31 b so as to absorb slight displacement of the base 30 relative to the fan guide 23 in the operation of the orbital sander 10.
A taper surface 31 c gradually thinned toward a distal end (upper side in FIG. 3) of the second surrounding wall 31 b is formed on a radially inner side of the second surrounding wall 31 b. An inclination angle of the taper surface 31 c is set to α°, and the inclination angle α° is set to be equal to the maximum inclination angle of the leg 40 when the leg 40 swings. In this manner, the other end portion 40 b of the leg 40 is easily housed in the second surrounding wall 31 b when assembling the orbital sander 10. Further, the contact between the leg 40 and the second surrounding wall 31 b during the swinging action of the leg 40 can be prevented, so that the base 30 can make an orbital motion smoothly (see FIG. 4).
Next, the action of the orbital sander 10 formed in the above-described manner, particularly, the swinging action of the leg 40 during the orbital motion of the base 30 will be described in detail with reference to the drawings.
As shown in FIG. 2, first, when a worker grasps the grip portion 21 b of the orbital sander 10 and operates the operation switch 11 to turn ON in this state, driving current is supplied to the motor 22. Then, the rotation shaft 22 a is rotated about the axial center C1 and the eccentric piece 27 makes an orbital motion about the axial center C2 along with the rotation. As a result, the base 30 (base plate 31) also makes an orbital motion via the second radial bearing B2, so that the polishing paper 14 (see FIG. 1) attached to the pad 32 also makes an orbital motion. Thereafter, by pressing the polishing paper 14 onto a surface of a wood or the like, the pressed portion of the surface can be efficiently ground to be smoothened.
At this time, as shown by arrows SW1 and SW2 in FIGS. 4A and 4B, the base 30 makes an orbital motion with respect to the fan guide 23, and the leg 40 makes a swinging action so as to pivot on the columnar members 51 and 61 within the range of the maximum inclination angle α° (see FIG. 3) along with the orbital motion of the base 30. Here, since FIGS. 4A and 4B are planar views, they represent swinging actions only in the left and right directions (arrows SW1 and SW2) of the leg 40, but the leg 40 actually swings also in a depth direction in FIGS. 4A and 4B.
In the swinging action of the leg 40, since the leg 40 is made of rubber, is in point contact with the columnar member 51 made of plastic and the columnar member 61 made of aluminum, and is not elastically deformed, the leg 40 is less likely to be worn or deteriorated early, and the increase in an operation resistance of the orbital sander 10 does not occur. Therefore, the life of the leg 40 is prolonged as compared with the conventional art, and only periodical greasing (lubrication) to the first recess and protrusion engagement portion 50 and the second recess and protrusion engagement portion 60 is required for maintenance of the orbital sander 10. Further, since the leg 40 is made of rubber, operating noise of the orbital sander 10 can be reduced while absorbing size errors of parts forming the orbital sander 10. However, when it is possible to form the parts with the precision with which almost no size error occurs, the leg 40 may be made of, for example, hard plastic or aluminum (high hardness member) instead of rubber.
As described in detail above, according to the orbital sander 10 of the first embodiment, the first recess and protrusion engagement portion 50 and the second recess and protrusion engagement portion 60, which make the fan guide 23 and the one end portion 40 a of the leg 40 swingably abut on each other and make the base plate 31 and the other end portion 40 b of the leg 40 swingably abut on each other, and restrict the deviation of the leg 40 relative to the fan guide 23 and the base plate 31 in the horizontal direction while allowing the swinging of the leg 40 relative to the fan guide 23 and the base plate 31, are provided between the fan guide 23 and the one end portion 40 a and between the base plate 31 and the other end portion 40b, respectively. As a result, the leg 40 can swing with almost no resistance without involving any elastic deformation during the orbital motion of the base 30. Accordingly, since the stress (load) to cause the elastic deformation is not applied to the leg 40 unlike the conventional art, the increase in operation resistance of the base 30 can be prevented and the life of the leg 40 can be prolonged to extend the maintenance cycle.
Also, according to the orbital sander 10 of the first embodiment, the first recess and protrusion engagement portion 50 and the second recess and protrusion engagement portion 60 are composed of the spherical protrusion portions 51 a and 61 a provided on the fan guide 23 and the base plate 31, respectively, and the spherical recess portions 52 and 62 provided on the one end portion 40 a and the other end portion 40b, respectively. Further, the radii R1 of the spherical protrusion portions 51 a and 61 a are set to be smaller than the radii R2 of the spherical recess portions 52 and 62 (R1<R2). Therefore, the fan guide 23 and the leg 40 can be brought into point contact with each other and the base plate 31 and the leg 40 can be brought into point contact with each other, so that the leg can be swung smoothly.
Next, a second embodiment of the present invention will be described in detail with reference to the drawings. Incidentally, portions having the same functions as those of the above-described first embodiment are denoted by the same reference numerals and detail descriptions thereof are omitted. FIG. 5 is a partial sectional view showing a leg and a surrounding structure thereof according to the second embodiment and corresponding to FIG. 3.
As shown in FIG. 5, an orbital sander (power tool) 70 according to the second embodiment is different from the orbital sander 10 according to the first embodiment in a leg and a surrounding structure thereof. Specifically, a first recess and protrusion engagement portion (recess and protrusion engagement portion) 80 of the orbital sander 70 is composed of a steel ball 81 having a radius R3 and a spherical recess portion 82 having a radius R3 and provided at one end portion 100 a of a leg (post) 100. Also, a second recess and protrusion engagement portion (recess and protrusion engagement portion) 90 of the orbital sander 70 is composed of a steel ball 91 having a radius R3 and a spherical recess portion 92 having a radius R3 and provided at the other end portion 100 b of the leg 100.
Here, the respective steel balls 81 and 91 constitute spherical protrusion portions in the present invention, and the respective steel balls 81 and 91 are attached to an engagement recess portion 71 b formed in a base-side surface 71 a of a fan guide (main body part) 71 and an engagement recess portion 72 b formed in a fan-guide-side surface 72 a of a base plate 72, respectively. Approximately halves of the respective steel balls 81 and 91 protrude toward the leg 100, respectively, and they enter the respective spherical recess portions 82 and 92 of the leg 100 to come in sliding contact with them. Incidentally, depths of the respective spherical recess portions 82 and 92 are set to be smaller than the radii R3 of the respective steel balls 81 and 91. In this manner, in the swinging action of the leg 100, the contact between the one end portion 100 a and the base-side surface 71 a and the contact between the other end portion 100 b and the fan-guide-side surface 72 a are prevented.
In the first recess and protrusion engagement portion 80 and the second recess and protrusion engagement portion 90, unlike the first embodiment, the leg 100 and the respective steel balls 81 and 91 are made to swingably abut on (come in sliding contact with) each other through spherical surfaces having the same radius R3. Therefore, rattling of the leg 100 can be further suppressed as compared with the first embodiment. However, it is desired that sufficient grease is applied to the sliding contact portions in order to prevent the abrasion of the leg 100 and realize the smooth orbital motion of the base 30.
The orbital sander 70 according to the second embodiment is provided with an annular first surrounding wall 71 c with a height h3 protruding from the base-side surface 71 a of the fan guide 71, and further an annular second surrounding wall 72 c with a height h4 protruding from the fan-guide-side surface 72 a of the base plate 72 (h4<h3). However, the heights h3 and h4 of the first surrounding wall 71 c and the second surrounding wall 72 c can be arbitrarily set like the first embodiment (see FIG. 3).
Annular gaps G1 which are larger than those in the first embodiment are formed between the first and second surrounding walls 71 c and 72 c and the leg 100. As a result, even if the inclination angle of the leg 100 reaches the maximum inclination angle α° in the swinging action of the leg 100, the contact between the first and second surrounding walls 71 c and 72 c and the leg 100 can be prevented. Therefore, the taper surfaces on the radially inner sides of the first surrounding wall and the second surrounding wall provided in the first embodiment are not provided.
As described in detail above, also in the orbital sander 70 according to the second embodiment, the function effects similar to those in the first embodiment can be achieved except for the function effect obtained by “point contact” in the above-described first embodiment. In addition, since the respective steel balls 81 and 91 are used in the first recess and protrusion engagement portion 80 and the second recess and protrusion engagement portion 90 in the second embodiment, cost reduction of the orbital sander 70 can be realized by adopting general-purpose steel balls defined in JIS or the like as the respective steel balls 81 and 91.
Next, a third embodiment of the present invention will be described in detail with reference to the drawings. Incidentally, portions having the same functions as those of the above-described first embodiment are denoted by the same reference numerals and detail descriptions thereof are omitted. FIG. 6 is a partial sectional view showing a leg and a surrounding structure thereof according to the third embodiment and corresponding to FIG. 3.
As shown in FIG. 6, an orbital sander (power tool) 110 according to the third embodiment is different from that according to the first embodiment in a leg and a surrounding structure thereof. Specifically, the relationship of recess and protrusion in a first recess and protrusion engagement portion (recess and protrusion engagement portion) 120 and a second recess and protrusion engagement portion (recess and protrusion engagement portion) 130 is inverted to that in the first embodiment. In other words, spherical protrusion portions 121 and 131 having a radius R4 are integrally provided to one end portion 140 a and the other end portion 140 b of a leg (post) 140 so as to protrude toward a fan guide (main body part) 111 and a base plate 112. Here, in the third embodiment, the leg 140 is made of aluminum.
A spherical recess portion 122 with a radius R4 which the spherical protrusion portion 121 enters and comes in sliding contact with is provided on a base-side surface 111 a of the fan guide 111. Here, the spherical protrusion portion 121 and the spherical recess portion 122 form the first recess and protrusion engagement portion 120. On the other hand, a flexible rubber seat 113 is placed on a fan-guide-side surface 112 a of the base plate 112, and a spherical recess portion 132 with a radius R4 which the spherical protrusion portion 131 enters and comes in sliding contact with is provided on a fan-guide-side surface 113 a of the rubber seat 113. Here, the spherical protrusion portion 131 and the spherical recess portion 132 form the second recess and protrusion engagement portion 130. Incidentally, when it is possible to form the parts with the precision with which almost no size error occurs, it is possible to adopt the configuration in which the rubber seat 113 is eliminated and a spherical recess portion is formed in the base plate 112 so that the spherical protrusion portion 131 enters the spherical recess portion to be brought into sliding contact with the same.
Here, the contact between the one end portion 140 a of the leg 140 and the base-side surface 111 a and the contact between the other end portion 140 b of the leg 140 and the fan-guide-side surface 113 a of the rubber seat 113 are prevented in the swinging action of the leg 140. In the first recess and protrusion engagement portion 120 and the second recess and protrusion engagement portion 130, since the leg 140 and the spherical recess portions 122 and 132 are made to swingably abut on (brought into sliding contact with) each other through spherical surfaces having the same radius R4, rattling of the leg 140 can be further suppressed like the second embodiment. However, it is desired that sufficient grease is applied to the sliding contact portions in order to prevent the abrasion of the rubber seat 113 and the fan guide 111 and realize the smooth orbital motion of the base 30.
The orbital sander 110 according to the third embodiment is provided with an annular first surrounding wall 111 b with a height h5 protruding from the base-side surface 111 a of the fan guide 111. Further, an annular second surrounding wall 112 b with a height h6 is provided on the base plate 112 of the orbital sander 110 so as to protrude from the fan-guide-side surface 113 a of the rubber seat 113 (h6<h5). However, the heights h5 and h6 of the first surrounding wall 111 b and the second surrounding wall 112 b can be arbitrarily set like the first embodiment (see FIG. 3).
Annular gaps G2 larger than those in the first embodiment are formed between the first and second surrounding walls 111 b and 112 b and the leg 140 like the second embodiment. Therefore, even if the inclination angle of the leg 140 reaches the maximum inclination angle α° along with the swinging action of the leg 140, the contact between the first and second surrounding walls 111 b and 112 b and the leg 140 can be prevented. Accordingly, also in the third embodiment, taper surfaces on the radially inner sides of the first surrounding wall and the second surrounding wall are not provided like the second embodiment.
As described in detail above, also in the orbital sander 110 according to the third embodiment, the function effects similar to those in the first embodiment can be achieved except for the function effect obtained by “point contact” in the above-described first embodiment.
Next, a fourth embodiment of the present invention will be described in detail with reference to the drawings. Incidentally, portions having the same functions as those of the above-described first embodiment are denoted by the same reference numerals and detail descriptions thereof are omitted. FIG. 7 is a partial sectional view showing a leg and a surrounding structure thereof according to the fourth embodiment and corresponding to FIG. 3.
As shown in FIG. 7, an orbital sander (power tool) 150 according to the fourth embodiment is different from that according to the first embodiment in a leg and a surrounding structure thereof. Specifically, a first recess and protrusion engagement portion (recess and protrusion engagement portion) 160 of the orbital sander 150 is composed of a conical protrusion portion 161 with an angle of β° provided on a fan guide (main body part) 151 and a conical recess portion 162 with an angle of γ° provided at one end portion 170 a of a leg (post) 170 (γ°>β°) Further, a second recess and protrusion engagement portion (recess and protrusion engagement portion) 180 of the orbital sander 150 is composed of a conical protrusion portion 181 with an angle of β° provided on a base plate 152 and a conical recess portion 182 with an angle of γ° provided at the other end portion 170 b of the leg 170.
A height of the conical protrusion portion 161 from a base-side surface 151 a of the fan guide 151 is set to be larger than a depth of the conical recess portion 162 from one end portion 170 a of the leg 170. Further, a height of the conical protrusion portion 181 from a fan-guide-side surface 152 a of the base plate 152 is set to be larger than a depth of the conical recess portion 182 from the other end portion 170 b of the leg 170. In this manner, in the swinging action of the leg 170, the contact between the one end portion 170 a and the base-side surface 151 a and the contact between the other end portion 170 b and the fan-guide-side surface 152 a are prevented.
However, the leg 170 is not limited to that made of rubber and it maybe made of hard plastic or aluminum with hardness higher than that of rubber. In this case, in order to reduce operating noise due to the swinging action of the leg 170, a rubber seat may be disposed on the base plate 152 like the orbital sander 110 (see FIG. 6) of the third embodiment. In this case, the conical protrusion portion may be provided integrally on the rubber seat or a conical protrusion portion made of aluminum may be placed on the rubber seat.
As described in detail above, also in the orbital sander 150 according to the fourth embodiment, since distal end portions of the conical protrusion portions 161 and 181 are brought into almost point contact with bottom portions of the conical recess portions 162 and 182, function effects similar to those of the above-described first embodiment can be achieved.
It goes without saying that the present invention is not limited to the respective embodiments described above and various modifications and alterations can be made within the gist of the present invention. In the respective embodiments described above, structures where the first surrounding walls 23 b, 71 c and 111 b are provided on the fan guides 23, 71, 111, and 151 and the second surrounding walls 31 b, 72 c and 112 b are provided on the base plates 31, 72, 112, and 152 have been shown, but the present invention is not limited to these. For example, if it is possible to increase the hardness of the legs, the legs do not elastically deform and do not fly out of the respective surrounding walls, and the respective surrounding walls can be eliminated. In this case, the structures of the fan guide and the base plate can be simplified and the manufacturing cost of the orbital sander can be reduced.

Claims

What is claimed is:

1. A power tool comprising:

a main body part having a driving source;

a rotation shaft provided in the driving source;

abase moving in an approximately circular motion with respect to the main body part in a horizontal direction along with rotation of the rotation shaft;

a polishing sheet held by the base;

a post provided between the main body part and the base; and

recess and protrusion engagement portions provided between the main body part and one end portion of the post and between the base and the other end portion of the post, respectively, making the main body part and the one end portion swingably abut on each other and making the base and the other end portion swingably abut on each other, respectively, and restricting a deviation of the post relative to the main body part and the base in a horizontal direction while allowing swinging of the post relative to the main body part and the base.

2. The power tool according to claim 1,

wherein the recess and protrusion engagement portions are composed of spherical protrusion portions or spherical recess portions provided on the main body part and the base, respectively, and spherical recess portions or spherical protrusion portions provided on the one end portion and the other end portion, respectively.

3. The power tool according to claim 2,

wherein radii of the spherical protrusion portions are set to be smaller than radii of the spherical recess portions.