This application claims priority on Japanese Patent Application No. 11-347847 filed on Dec. 7, 1999, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to sanders. More particularly, the present invention relates to a sander having a main body containing a motor and a base provided below the main body such that the rotation of the motor imparts an orbital motion to the base for sanding work pieces.
2. Description of the Related Art
A typical orbital sander includes a main body containing a motor with an output shaft protruding therefrom in the downward direction. Such a sander additionally includes a base eccentrically coupled to the output shaft such that the rotation of the motor and thus the output shaft imparts an orbital motion (i.e., an eccentric circular motion) to the base, thereby sanding workpiece surfaces when sanding paper is attached to the bottom surface of the base. Typically, such a sander also includes a plurality of feet disposed between the main body and the base for regulating the rotation of the base and for insulating vibration of the base, in particular vertical vibration that is cased by the orbital motion of the base. The majority of such vibration-insulating feet are made of one-piece or integral elastic bodies. Japanese Published Unexamined Utility Model Application No. 62-17857, however, discloses an orbital sander employing composite elastic feet. Each of these feet includes a main central cylinder or column made of a relatively hard elastic material and two other end cylinders made of an elastic material having lesser hardness, each affixed on each end of the main cylinder in order to provide an enhanced vibration insulating effect.
While this foot achieves its intended objective, it is not free from certain problems and inconveniences, thus leaving room for further improvement. As the above-described foot is made of elastic materials, its physical properties are subject to degradation due to heat buildup that occurs during the operation of the sander regardless of whether the foot is made of a combination of hard and less hard elastic materials. Such deterioration often results in a decrease in the vibration insulating effect and/or durability. In addition, the orbital motion of the base causes precession of the feet. The precession not only exerts a shear force and a bending stress on both ends of each foot (which are fixedly supported in the foot seats in the main body and the base), but it also causes wearing down of the foot, thus shortening the service life of the elastic feet.
SUMMARY OF THE INVENTION
In view of the above-identified problems, it is an important object of the present invention to provide a sander having effective vibration insulators of high durability to withstand heat and wear.
It is another object of the present invention to provide a sander with effective and low-cost vibration insulators.
Yet another object of the present invention is to provide a sander with vibration insulators that facilitate dissipation of heat generated during operation thereof.
The above objects and other related objects are realized by the invention, which provides a sander comprising a main body containing a motor and a base provided below the main body. The based is driven by the motor to perform an orbital motion. The sander further comprises a plurality of foot seats provided in the main body and the base and at least one foot assembly disposed between the main body and the base. Each of the at least one foot assembly includes a metal foot having upper and lower end portions and an axis. Additionally, each of the at least one foot assembly further includes elastic bodies adapted to support the end portions in the foot seats in the axial direction of the foot. According to the sander, the at least one foot assembly can effectively counteract vibration occurring in the axial directions of the feet and reduce vertical vibration of the base while facilitating a smooth orbital motion of the base. The arrangement also reduces the effects of heat generated by the operation of the sander as well as wear of the elastic bodies, thus enhancing the durability of the at least one foot assembly.
According to one aspect of the present invention, the sander has four foot assemblies, with each foot including reduced diameter sections provided at the upper and lower end portions thereof. In addition, the elastic bodies include O-rings fitted around the reduced diameter sections in the foot seats. Advantageously, the O-rings provide desired elasticity at a relatively low cost, thus reducing the overall manufacturing cost of the sander.
According to another aspect of the present invention, each O-ring has a circular cross-section, whereas each foot has a cylindrical shape and each reduced diameter section also has a cylindrical shape which has a smaller diameter than the diameter of the remainder of the foot and which is coaxially formed on one of the upper and lower end portions of the foot.
According to still another aspect of the present invention, each O-ring has a greater axial dimension than that of each reduced diameter section, such that a free end of each reduced diameter section does not exceed or project from an outermost end of the O-ring.
According to yet another aspect of the present invention, each foot is made of aluminum. A foot or feet made of aluminum are advantageous due its lightness, hardness, and heat radiation.
According to one feature of the present invention, each foot seat includes a recess sized and dimensioned so as to snugly accommodate an O-ring and a reduced diameter section.
According to another feature of the present invention, each O-ring is coaxially fitted around the reduced diameter portion in the foot seat, such that, when the sander is in use, the O-rings are subjected to compression but not to either shearing or bending.
Other general and more specific objects of the invention will in part be obvious and will in part be evident from the drawings and descriptions which follow.
Due to the orbital motion of the base 12, each foot assembly 22 undergoes precession, with the lower end of each foot assembly 22 secured in the lower seat 26 performing a circular motion that follows the movement of the base 12 with respect to the upper end secured in the upper seat 26. This precession regulates the movement of the base 12 while lessening the vertical vibration of the base 12. Each foot 23 of the foot assembly 22 is made of aluminum, and thus has a sufficient degree of hardness to effectively dampen the vertical vibration of the base 12 that occurs during the operation of the sander 1. Moreover, the feet 23 advantageously and effectively dissipate heat generated by the operation of the finishing sander 1. Additionally, as the upper and lower ends of each foot 23 are elastically supported by the O-rings 25 in such a manner as to allow relatively free movement of the foot ends, the foot 23 is able to undergo precession smoothly. As an added advantage, the O-rings 25 are subjected to compression only, but not to a shearing force or bending, and so the O-rings are less susceptible to wearing.
It should be noted that the manner or structure of supporting each foot's reduced diameter section 24 in the recessed seat 26 is not limited to that described in the foregoing. For example, a ring having a square or rectangular cross-section or a plurality of balls may replace the O-ring 25. Alternatively, the reduced diameter sections 24 may be omitted so that both ends of each foot are supported by rubber elements having a general shape of a cup with no handle. As a still another example, rubber balls or a flat plate may be interposed between each bottom surface of one of the foot seats and the foot end without the reduced portions. As long as each foot can be elastically supported in the axial direction, any other suitable structure may be employed. Moreover, different supporting structures may be used for the upper and lower ends of each foot. For example, while the lower end of the foot, which has a greater momentum than the upper end of the foot, may be supported by the structure of the embodiment (i.e., a reduced diameter section in an O-ring), balls or a flat plate may be employed for the upper end of the foot.