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.
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. U.S. Pat. Nos. 5,018,314, 5,317,838, 5,384,984, 5,392,568, 5,807,169, 6,503,133, 6,527,631, 7,104,873, 7,270,598, 7,371,150, 10,046,433, 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 U.S. Pat. No. 6,110,028 also disclose other forms of braking for the sanding pad, but the previously mentioned problems still exist in implementation.
A main object of the invention is to solve various problems existing in the braking means used in conventional random orbital sanders.
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.
In one 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.
In one 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.
In one embodiment, the at least one flexible contact part is a tubular structure.
In one embodiment, an extension line of an inner space of the tubular structure intersects the sanding pad.
In one embodiment, an extension line of an inner space of the tubular structure is parallel to the sanding pad.
In one 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.
In one embodiment, the base forms an assembling opening assembling the eccentric block, and the assembling part is disposed close to the assembling opening.
In one embodiment, the base includes a plurality of blades arranged at intervals on a side opposite to the sanding pad.
In one 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.
In one embodiment, a level height of the base is higher than a bottom edge of the second part of the eccentric block.
In one embodiment, the friction member is disposed on an air flow generating member attached to the eccentric block.
In one 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.
In one 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.
The detailed description and technical content of the invention are described below with reference to the accompanying drawings.
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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.
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