EP4450224A1

EP4450224A1 - Random orbital sanding tool

Info

Publication number: EP4450224A1
Application number: EP23168268.3A
Authority: EP
Inventors: Bach Pangho Chen
Original assignee: Xpole Precision Tools Inc
Current assignee: Xpole Precision Tools Inc
Priority date: 2023-04-17
Filing date: 2023-04-17
Publication date: 2024-10-23

Abstract

A random orbital sanding tool (20) includes a power motor (21), a driving spindle (22) connected to the power motor (21), an eccentric block (23) connected to the driving spindle (22), a tool holder (24) disposed on the eccentric block (23), and a sanding pad (25) connected to the tool holder (24) and indirectly driven by the power motor (21). The random orbital sanding tool (20) includes a friction member (26) disposed on the eccentric block (23), the friction member (26) contacts the sanding pad (25). The friction member (26) has a first state of providing a pre-pressure to the sanding pad (25) when the power motor (21) is not activated, a second state of displacing with the eccentric block (23) and deforming with revolving of the sanding pad (25) when the power motor (21) is activated, and a third state of providing a braking force to the sanding pad (25) when the power motor (21) stops running.

Description

FIELD OF THE INVENTION

The invention relates to a random orbital sanding tool, and more particularly to a random orbital sanding tool equipped with a friction member providing a braking force to a sanding pad.

BACKGROUND OF THE INVENTION

Random orbital sander is composed of a balancer (commonly known as eccentric block) connected with a spindle of a power motor. The balancer is provided with a bearing housing, the bearing housing is provided for a tool holder (also called bearing) to dispose therein, a centerline of the bearing housing is parallel to but not coaxial with a centerline of the spindle of the power motor, that is, there is an eccentric distance between the two centerlines. In addition, a rotating spindle is disposed at a center of the bearing, and a sanding pad of the random orbital sander is connected to the rotating spindle through locking screws, so that an axis of the sanding pad and an axis of the power motor are also parallel to but not coaxial with each other. The eccentric distance between the two axes indicates that the sanding pad and the power motor are eccentrically linked with each other. Since the sanding pad is connected with the balancer via the bearing, the sanding pad is capable of rotating freely instead of being hard-linked with the power spindle.
When the power motor revolves, the motor spindle drives the balancer to revolve synchronously, and drives the sanding pad to revolve through the balancer. At this point, the sanding pad will produce two different motions: the first one is that the sanding pad maintains the eccentric distance from the spindle of the motor and revolves around the motor spindle, the orbital motion that revolves around the motor spindle is called "orbital revolution", and the revolving speed is synchronized with the revolving speed of the motor spindle and the revolving speed of the balancer.
The second is that the sanding pad revolutes on its own axis, which is called "rotation". The reason for rotation of the sanding pad is that the sanding pad is eccentrically linked to the motor spindle, and the sanding pad is capable of revolving freely on the bearing. When the sanding pad revolutes orbitally around the motor spindle, the inner and outer sides of the sanding pad receive different inertial forces. The outer part is farther away from the axis than the inner part, so the inertial force received is larger, and the sanding pad generates rotational motion along the orbital revolution direction. The rotational speed is mainly affected by the eccentric distance between the sanding pad axis and the motor axis. The larger the eccentric distance, the higher the rotational speed, and the smaller the eccentric distance, the lower the rotational speed.
Take a 5 mm random orbital sander (with an eccentricity of 2.5 mm) equipped with a 6 inches (6") sanding pad as an example. When the motor spindle revolves at 10,000 revolutions per minute (rpm), the sanding pad performs a motion of orbital revolution with a diameter of 5 mm around the motor spindle at a position 2.5 mm away from the motor spindle. Under no-load conditions, the sanding pad also performs an eccentric rotational motion at about 5500 rpm at the same time. When the random orbital sander performs sanding, the friction force produced by a sanded object contacting the sanding pad will cause the rotational motion speed of the sanding pad to decrease. The heavier the load on the power tool, the greater the drop in the rotational speed of the sanding pad. For example, the rotational speed of the sanding pad is about 300 rpm to 400 rpm under light load, and the rotational speed of the sanding pad is about 150 rpm to 300 rpm under heavy load.
When the power motor stops revolving, the kinetic energy stored in the balancer during the previous revolving will drive the balancer to continue revolving for several seconds until the stored kinetic energy is consumed. At this point, the rotational motion of the sanding pad stops. Take a 6" sanding pad mounted on a random orbit sander with an eccentric distance of 2.5 mm (diameter of revolutional orbit being 5 mm) as an example. When the motor stops revolving, the sanding pad will continue to revolve for 9 to 12 seconds before stopping completely. Under specific use conditions, when the random orbital sander is required to stop the power motor from operating, the sanding pad must stop revolving in a short time (1-3 seconds), and therefore it is required to install a brake mechanism on the tool.
The conventional main braking means is to dispose an elastic rubber ring on a windshield (or a shell) of the random orbital sander, one side of the elastic rubber ring is fixed on the windshield, and another side of the elastic rubber ring is pressed against the surface of the sanding pad by its own elasticity. Because the windshield is fixed and does not revolve, when the power motor is not revolving, the sanding pad is pressed by the elastic rubber ring and is prevented from moving. When the power motor is activated to revolve, force of the power motor exceeds the frictional force of the elastic rubber ring pressing on the sanding pad, the power motor will be able to drag the sanding pad to revolve. When the power motor stops running, the sanding pad loses the dragging power of the power motor, and is affected by the frictional force generated by the elastic rubber ring to stop revolving in a short time. Related patents are: Taiwan utility model patent Nos. TWM279440 , TWM574093 , Chinese patent publication Nos. CN2858182Y , CN108290265A , CN213136241U , CN103813884B , CN1088001C , CN206393407U , CN110594316A , U.S. patent publication Nos. US5018314 , US5317838 , US5384984 , US5392568 , US5807169 , US6503133 , US6527631 , US7104873 , US7270598 , US7371150 , US10046433 , US2010062695 , US2022/0126417 , Japanese Patent No. JP4061053B2 , Patent Cooperation Treaty publication No. WO2004030864 , United Kingdom patent publication No. GB2359266 .
However, if the elastic rubber ring drags and rubs on the surface of the sanding pad over a long duration, the elastic rubber ring will wear out soon and lose its function. Furthermore, when the power motor is running, the elastic rubber ring keeps pressing on the sanding pad, which will not only increase the load of the power motor, reduce the revolving speed of the power motor and the revolutional speed of the sanding pad, but also reduce the rotational speed of the sanding pad, thus affecting the sanding efficiency and sanding quality.
In addition to the above patents, TWM279441 and US6110028 also disclose other forms of braking for the sanding pad, but the previously mentioned problems still exist in implementation.

SUMMARY OF THE INVENTION

A main object of the invention is to solve various problems existing in the braking means used in conventional random orbital sanders. In particular, it is an object of the present invention to provide an enhanced random orbital sander tool enabling a good sanding efficiency and sanding quality with an efficient and low-cost set-up.
According to the present invention, this problem is solved by a random orbital sander tool as claimed in claim 1. Further advantageous embodiments are the subject-matter of the dependent claims.
In order to achieve the above object, the invention provides a random orbital sanding tool including a power motor, a driving spindle connected to the power motor, an eccentric block connected to the driving spindle, a tool holder disposed on the eccentric block, and a sanding pad connected to the tool holder and indirectly driven by the power motor. The random orbital sanding tool includes a friction member disposed on the eccentric block, the friction member contacts the sanding pad, the friction member has a first state of providing a pre-pressure to the sanding pad when the power motor is not activated, a second state of displacing with the eccentric block and being deformed by revolving of the sanding pad when the power motor is activated, and a third state of providing a braking force to the sanding pad when the power motor stops running.
According to a further embodiment, an eccentric distance is between the sanding pad and the driving spindle, and an end of the friction member contacting the sanding pad has an offset range greater than or equal to twice the eccentric distance.
According to a further embodiment, the friction member has a base, an assembling part disposed on the base and attached on the eccentric block, and at least one flexible contact part disposed on a side of the base facing the sanding pad.
According to a further embodiment, the at least one flexible contact part is a tubular structure.
According to a further embodiment, an extension line of an inner space of the tubular structure intersects the sanding pad.
According to a further embodiment, an extension line of an inner space of the tubular structure is parallel to the sanding pad.
According to a further embodiment, the at least one flexible contact part is a foot structure, the foot structure has a bending direction, and the bending direction bends toward a revolving direction of the driving spindle.
According to a further embodiment, the base forms an assembling opening assembling the eccentric block, and the assembling part is disposed close to the assembling opening.
According to a further embodiment, the base includes a plurality of blades arranged at intervals on a side opposite to the sanding pad.
According to a further embodiment, the eccentric block includes a first part connected with the driving spindle, and a second part being offset relative to the first part, and the assembling part is connected with the second part.
According to a further embodiment, a level height of the base is higher than a bottom edge of the second part of the eccentric block.
According to a further embodiment, the friction member is disposed on an air flow generating member attached to the eccentric block.
According to a further embodiment, the eccentric block includes a first part connected with the driving spindle, and a second part being offset relative to the first part, and the air flow generating member is connected with the second part.
According to a further embodiment, the eccentric block includes a first part connected with the driving spindle, and a second part being offset relative to the first part, and the friction member is connected with the second part.
Through the aforementioned implementation of the invention, compared with the conventional technique, the invention has the following characteristics: the random orbital sanding tool of the invention is provided with the friction member disposed on the eccentric block, the friction member not only deforms in the second state in response to motion of the sanding pad, also a rotational speed of the sanding pad will not be excessively reduced as the eccentric block revolves, thereby avoiding a significant decline in sanding efficiency and sanding quality. In the third state, the friction member provides a braking force to the sanding pad, so that the sanding pad is capable of stopping from revolving in a short time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of the invention.
FIG. 2 is a sanding track of a sanding pad of the invention.
FIG. 3 is an assembly diagram of an eccentric block and a friction member of the embodiment of the invention.
FIG. 4 is a schematic diagram of swinging of the friction member of the embodiment of the invention in a first state.
FIG. 5 is a perspective structural view of another embodiment of the friction member of the invention.
FIG. 6 is a cross-sectional view of a partial structure of the another embodiment of the friction member of the invention.
FIG. 7 is a schematic diagram of swinging of the another embodiment of the friction member of the invention in the first state.
FIG. 8 is a perspective view of yet another embodiment of the friction member of the invention.
FIG. 9 is a side view of a partial structure of the yet another embodiment of the friction member of the invention.
FIG. 10 is a schematic diagram of swinging of the yet another embodiment of the friction member of the invention in the first state.
FIG. 11 is a schematic diagram of an additional another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The detailed description and technical content of the invention are described below with reference to the accompanying drawings.
Please refer to FIG. 1, the invention provides a random orbital sanding tool 20, the random orbital sanding tool 20 includes a power motor 21, a driving spindle 22 connected to the power motor 21, an eccentric block 23 connected to the driving spindle 22, a tool holder 24 disposed on the eccentric block 23, and a sanding pad 25 connected to the tool holder 24. The power motor 21 is implemented pneumatically or electrically, and the invention is not limited thereto. Although the tool holder 24 is assembled with the sanding pad 25, the tool holder 24 does not restrict revolving of the sanding pad 25. Further, the sanding pad 25 is still capable of revolving relative to the eccentric block 23 when the power motor 21 is not revolving. The sanding pad 25 is indirectly driven by the power motor 21. During revolving of the power motor 21, the sanding pad 25 revolutes orbitally relative to the driving spindle 22and also rotates on its own axis. If only a single point on the sanding pad 25 is tracked, a sanding track of the sanding pad 25 is not a simple circle, but is as shown by numeral 50 in FIG. 2. Also, for basic implementation of the random orbital sanding tool 20, reference can be made to European Patent Publication No. EP0860235A2 and U.S. Patent No. US5,040,340 . Furthermore, there is an eccentric distance 40 between a center of the sanding pad 25 and an axis of the driving spindle 22.
Please refer to FIG. 1 and FIG. 3, the random orbital sanding tool 20 of the invention includes a friction member 26 disposed on the eccentric block 23, and an end of the friction member 26 contacts a surface of the sanding pad 25 over a long duration. The friction member 26 is mainly provided for eliminating rotation of the sanding pad 25 on its own axis when the power motor 21 stops running. That is to say, the invention makes the sanding pad 25 stop rotating in a short time through the friction member 26 when the power motor 21 stops running. The friction member 26 has a first state of providing a pre-pressure to the sanding pad 25 when the power motor 21 is not activated, a second state of being deformed by revolving of the sanding pad 25 when the power motor 21 is activated, and a third state of providing a braking force to the sanding pad 25 when the power motor 21 stops running. Specifically, when the power motor 21 of the invention is not activated, the end of the friction member 26 facing the sanding pad 25 presses against the surface of the sanding pad 25 to provide a pre-pressure to the sanding pad 25. When the power motor 21 is activated, the friction member 26 enters the second state. At this point, the eccentric block 23 revolves with the driving spindle 22 of the power motor 21, and the eccentric block 23 simultaneously causes the friction member 26 to revolve and to displace. At this point, a motional speed of the friction member 26 corresponds with an orbital revolution speed of the sanding pad 25, and the friction member 26 does not affect a rotational speed of the sanding pad 25 on its own axis, thereby sanding efficiency and sanding quality of the sanding pad 25 is maintained. Since the sanding pad 25 revolves on a non-circular track, the end of the friction member 26 contacting the surface of the sanding pad 25 moves with part of the sanding pad 25. The friction member 26 is deformed to response to motion of the end of the friction member 26 contacting the surface of the sanding pad 25, and the friction member 26 keeps contact with the sanding pad 25. In terms of action as shown in FIG. 4, the friction member 26 swings in the second state. Observing from the end (indicated by 261 in the figure) of the friction member 26 contacting the sanding pad 25, when the end 261 revolves on the sanding pad 25, the end 261 deviates relative to an original position of the end 261, and an offset range 41 of the end 261 is greater than or equal to twice the eccentric distance 40. It should be understood that the offset range 41 of the end 261 does not refer to a sliding range of the end 261 on the surface of the sanding pad 25.
When the power motor 21 stops running, the driving spindle 22 stops revolving thereupon, and the eccentric block 23 stops together. At this point, the friction member 26 no longer revolves with the eccentric block 23 and enters the second state. Immobility of the friction member 26 is a resistance to the sanding pad 25 as the sanding pad 25 is still in rotational motion on its own axis, and a frictional force generated by the friction member 26 contacting the surface of the sanding pad 25 is used as a braking force for stopping revolving of the sanding pad 25. A design of the invention makes the friction member 26 in the third state only need to resist against a speed difference between a rotational speed of the sanding pad 25 and a revolving speed of the eccentric block 23. A position of the friction member 26 contacting the sanding pad 25 being relatively closer to a center of the sanding pad 25 makes the friction member 26 bear less torsion force, which is capable of effectively prolonging service life. The invention avoids a problem that the sanding pad 25 does not stop with the power motor 21, causing the sanding pad 25 to rotate on its own axis at a low speed and damaging a surface of a sanded object.
Please refer to FIG. 3. In one embodiment, the friction member 26 includes a base 262, an assembling part 263 disposed on the base 262 and attached on the eccentric block 23, and at least one flexible contact part 264 disposed on a side of the base 262 facing the sanding pad 25. Wherein the assembling part 263 is implemented by a hook or other structures that hangs the friction member 26 onto the eccentric block 23. Furthermore, a free length of the at least one flexible contact part 264 is not limited to being equal to a distance from a bottom edge of the base 262 to the surface of the sanding pad 25. The free length of the at least one flexible contact part 264 is slightly greater than the distance from the bottom edge of the base 262 to the surface of the sanding pad 25, thereby producing a pre-pressure. When the friction member 26 is in the second state, the at least one flexible contact part 264 is a main part with which the friction member 26 deforms. In this embodiment, the at least one flexible contact part 264 is implemented as a foot structure (indicated by 265 in the figures), the foot structure 265 is solid and is not hollow or containing spaces or gaps, the foot structure 265 has a bending direction, the bending direction bends toward a revolving direction of the driving spindle 22, a bent part of the foot structure 265 is close to an end of the foot structure 265 contacting the surface of the sanding pad 25. Further, the friction member 26 includes the at least one flexible contact parts 264, the at least one flexible contact parts 264 is arranged at intervals on a side of the base 262 facing the sanding pad 25, the at least one flexible contact parts 264 are not limited to disposing in equidistant interval, and the at least one flexible contact parts 264 are disposed in groups, as shown in FIG. 1.
Please refer to FIG. 5, FIG. 6, FIG. 7, and FIG. 8, besides the aforementioned of the at least one flexible contact part 264 of the invention, in one embodiment, the at least one flexible contact part 264 is a tubular structure (indicated by 266 in the figures), an extension line 267 of an inner space of the tubular structure 266 intersects the sanding pad 25 (as shown in FIG. 8 and FIG. 9), or is parallel to the sanding pad 25 (as shown in FIG. 5 and FIG. 6).
Please refer to FIG. 1 and FIG. 3, the base 262 of the friction member 26 forms an assembling opening 268 assembling the eccentric block 23, a shape of the assembling opening 268 can correspond to a shape of the eccentric block 23, so that there is no obvious lateral displacement relative to the eccentric block 23 when the friction member 26 is assembled. The assembling part 263 is disposed near the assembling opening 268. In one embodiment, the assembling part 263 is composed of two hooks located on two opposite sides of the assembling opening 268. In one embodiment, the friction member 26 includes a positioning wall 269 disposed around the assembling opening 268.
Please refer to FIG. 11, in one embodiment, the base 262 includes a plurality of blades 260 arranged at intervals on a side opposite to the sanding pad 25. When the friction member 26 is in the first state, the blades 260 generate an air flow in a shield 27 of the random orbital sanding tool 20, and the air flow dissipates heat of structures. In addition, based on concepts of this embodiment, the friction member 26 of the invention is disposed on an air flow generating member 28 attached to the eccentric block 23, the air flow generating member 28 is disassembled or assembled relative to the eccentric block 23, and the base 262 of the friction member 26 is implemented as a base plate of the air flow generating member 28.
Please refer to FIG. 3, the eccentric block 23 includes a first part 231 connected to the driving spindle 22, and a second part 232 being offset relative to the first part 231. In one embodiment, the friction member 26 is connected with the second part 232. Further, a level height of the base 262 is higher than a bottom edge of the second part 232 of the eccentric block 23. Please refer to FIG. 11, in the embodiment in which the friction member 26 is disposed on the air flow generating member 28, that shows that the air flow generating member 28 is connected to the second part 232.

Claims

A random orbital sanding tool (20) comprising a power motor (21), a driving spindle (22) connected to the power motor (21), an eccentric block (23) connected to the driving spindle (22), a tool holder (24) disposed on the eccentric block (23), and a sanding pad (25) connected to the tool holder (24) and indirectly driven by the power motor (21), characterized in that:
the random orbital sanding tool (20) comprises a friction member (26) disposed on the eccentric block (23), the friction member (26) contacts the sanding pad (25), the friction member (26) has a first state of providing a pre-pressure to the sanding pad (25) when the power motor (21) is not activated, a second state of displacing with the eccentric block (23) and being deformed by revolving of the sanding pad (25) when the power motor (21) is activated, and a third state of providing a braking force to the sanding pad (25) when the power motor (21) stops running.
The random orbital sanding tool (20) as claimed in claim 1, wherein an eccentric distance (40) is between the sanding pad (25) and the driving spindle (22), and an end of the friction member (26) contacting the sanding pad (25) has an offset range (41) greater than or equal to twice the eccentric distance (40).
The random orbital sanding tool (20) as claimed in claim 2, wherein the friction member (26) has a base (262), an assembling part (263) disposed on the base (262) and attached on the eccentric block (23), and at least one flexible contact part (264) disposed on a side of the base (262) facing the sanding pad (25).
The random orbital sanding tool (20) as claimed in claim 3, wherein the at least one flexible contact part (264) is a tubular structure (266).
The random orbital sanding tool (20) as claimed in claim 4, wherein an extension line (267) of an inner space of the tubular structure (266) intersects the sanding pad (25).
The random orbital sanding tool (20) as claimed in claim 4, wherein an extension line (267) of an inner space of the tubular structure (266) is parallel to the sanding pad (25).
The random orbital sanding tool (20) as claimed in claim 3, wherein the at least one flexible contact part (264) is a foot structure (265), the foot structure (265) has a bending direction, and the bending direction bends toward a revolving direction of the driving spindle (22).
The random orbital sanding tool (20) as claimed in claim 3, wherein the base (262) forms an assembling opening (268) assembling the eccentric block (23), and the assembling part (263) is disposed close to the assembling opening (268).
The random orbital sanding tool (20) as claimed in claims 3 to 8, wherein the base (262) comprises a plurality of blades (260) arranged at intervals on a side opposite to the sanding pad (25).
The random orbital sanding tool (20) as claimed in claims 3 to 8, wherein the eccentric block (23) comprises a first part (231) connected with the driving spindle (22), and a second part (232) being offset relative to the first part (231), and the assembling part (263) is connected with the second part (232).
The random orbital sanding tool (20) as claimed in claim 10, wherein a level height of the base (262) is higher than a bottom edge of the second part (232) of the eccentric block (23).
The random orbital sanding tool (20) as claimed in any of the preceding claims, wherein the friction member (26) is disposed on an air flow generating member (28) attached to the eccentric block (23).
The random orbital sanding tool (20) as claimed in claim 12, wherein the eccentric block (23) comprises a first part (231) connected with the driving spindle (22), and a second part (232) being offset relative to the first part (231), and the air flow generating member (28) is connected with the second part (232).
The random orbital sanding tool (20) as claimed in any of the preceding claims, wherein the eccentric block (23) comprises a first part (231) connected with the driving spindle (22), and a second part (232) being offset relative to the first part (231), and the friction member (26) is connected with the second part (232).