Patent Description:
Some chairs are provided with a foot ring at an appropriate height position of a supporting post used to support a seat, so that people's feet can be placed on the foot ring while sitting on the seat and feel comfortable.

A conventional foot ring of a chair includes a ring body and a hub arranged concentrically, and a plurality of spokes radially arranged between an inner periphery of the ring body and an outer periphery of the hub. The hub has a central hole for a supporting post or a pneumatic cylinder, which is used to support the seat of the chair, to penetrate through.

Some early foot rings for a chair were made by a fixed manner (that is, the height position of the foot rings cannot be adjusted), so those with a larger size may feel uncomfortable due to their knees bending too much when sitting, and those with a smaller size may also feel uncomfortable due to their knees stretching too much.

<CIT> provides a fixing device for ascending/descending a foot ring of a chair, which includes a clamping ring with a slot provided in a central hole of a hub of the foot ring. A sliding groove is provided axially on an inner wall of the hub, and a pressing sheet is arranged therein. The hub is provided with a screw hole radially extending through the inner wall of the hub and corresponding to the sliding groove for being fitted with a screw coupled to a knob. After a supporting post is inserted into the clamping ring, the screw coupled to the knob can be used to press against the pressing sheet for controlling whether the clamping ring is fixed to the supporting post or not. That is, when the clamping ring is not clamped and fixed, the height position of the foot ring on the supporting post can be adjusted up and down; and when a desired height position of the foot ring is reached, the clamping ring is clamped and fixed.

However, since the pressing sheet is a straight shape, when the screw coupled to the knob acts on the pressing sheet, the straight-shape pressing sheet only acts on a point of an outer surface of the clamping ring, so that the wall of the clamping ring on one side of the groove has a larger deformation, while the wall of the clamping ring on the other side of the groove is almost not deformed, which causes the clamping ring to receive an uneven force and thus reduces a clamping force of the clamping ring on the supporting post.

<CIT> provides an improved foot ring for a chair, which has a hub with a sliding groove on an inner wall and in parallel to a central axis thereof, and an arc-shape pressing sheet arranged in the sliding groove. A clamping ring with a slot is disposed in a central hole of the hub, so as to provide two ends of the arc-shape pressing sheet against two sides of the slot of the clamping ring. A screw coupled to a knob is screwed into a screw hole on the wall of the hub. A user can control whether the clamping ring is fixed to a supporting post penetrated through the clamping ring or not by tightening or loosening the knob.

<CIT> discloses a structure for fixing a foot ring to the main shaft of a chair in which the foot ring has a plain cylindrical central hub with an inner hole for receiving the main shaft. A collar connecting seat and a tapered collar are inserted into opposing ends of the inner hole and are threaded together, whereby tightening the collar connecting seat and tapered collar can secure the central hub to the main shaft. <CIT> and <CIT> disclose a somewhat similar structure but with a tapered and threaded tightening collar located between two threaded positioning pieces inside the central hub. In <CIT> the central hub is threaded and receives a threaded sleeve. The lower part of the sleeve is tapered outwardly and tightening the sleeve can secure the central hub to the main shaft. Other example of a known structure is disclosed in <CIT>.

The objective of the present invention is to provide a structure for fixing a foot ring to a supporting post of a chair with a more simplified structure and an easier operation.

The technical means of the present invention is to provide a structure for fixing a foot ring to a supporting post of a a chair, comprising: a ring body, a hub arranged concentrically with the ring body, and a plurality of spokes radially arranged between an inner periphery of the ring body and an outer periphery of the hub, wherein the hub has a central hole formed with internal threads on an inner surface thereof; and a bush being a cylindrical body having a tapered outer surface with external threads formed thereon, wherein the bush has a shaft hole penetrating along a longitudinal axis of the bush, characterised in that two recesses are formed on the opposite sides of the inner surface of the shaft hole, the two recesses extend axially along the inner surface of the shaft hole from a first end of the shaft hole to a second end of the shaft hole, and two pads are respectively disposed on, fixed in and protrude from the recesses, the two pads are softer and have a higher coefficient of friction compared to coefficient of friction of the inner surface of the shaft hole, and a groove penetrating through a wall of the bush, wherein two opposite sidewalls of the groove have a width spaced apart from each other, and form an angle in a widthwise direction thereof, wherein the range of the angle is <NUM>° to <NUM>°, wherein the range of the width is <NUM> to <NUM>, and wherein the bush is assembled with the hub by screwing the external threads of the bush with the internal threads of the hub, the supporting post penetrates through the shaft hole of the bush, and when the bush rotates toward a first direction, the wall of the bush is restricted by the central hole and the inner diameter of the shaft hole is reduced to clamp and fix the supporting post, when the bush rotates toward a second direction, the wall of the bush restricted by the central hole is released to make the shaft hole enlarge to release the clamping and fixing of the supporting post, wherein the first direction and the second direction are opposite to each other.

Preferably, an outer edge of a large diameter end of the tapered bush is formed with a flange protruding radially outward, so that the bush can rotate into the central hole of the hub until the flange is obstructed by an edge of the hub.

When the bush rotates into the central hole of the hub to reduce the inner diameter of the shaft hole, the two sidewalls of the groove gradually close to each other, and finally may contact with each other.

In a suitable embodiment, the pads may be adhesively fixed on a bottom surface of the recess.

In a suitable embodiment, the pads may be made of silicone or rubber material.

In a suitable embodiment, the supporting post may be a pneumatic cylinder for allowing a seat of the chair to be raised or lowered.

Compared with the conventional fixing structure of a foot ring for a chair, the fixing structure of the present invention used to fix the foot ring to a supporting post or a pneumatic cylinder is simple, easy to be assembled, and easy to adjust the height position of the foot ring on the supporting post.

The following describes the implementation of the present invention in more detail with drawings and numerals, so that those skilled in the art can implement it after studying the present specification.

As shown in <FIG>, the foot ring <NUM> of the present invention is assembled at an appropriate height position upon a supporting post <NUM> of a chair, so that the feet of a user sitting on the chair can step thereon and feel comfortable. The fixing structure is to allow the foot ring <NUM> to be quickly, stably and firmly mounted on the supporting post <NUM>. The chair is suitable for a chair having a single supporting post, such as an office chair and a high chair.

The supporting post <NUM> may be a rod generally used to support a chair, or may be a pneumatic cylinder used to support a seat of a chair and capable of controlling the seat to be raised or lowered in a vertical direction.

As shown in <FIG>, the fixing structure of the foot ring for a chair provided in the present invention preferably comprises a foot ring <NUM> and a bush <NUM>. The foot ring <NUM> can be made of any suitable material, for example, which is made of aluminum alloy material by casting. The foot ring <NUM> has a ring body <NUM> and a hub <NUM> arranged concentrically each other, and a plurality of spokes <NUM> are radially arranged between an inner periphery of the ring body <NUM> and an outer periphery of the hub <NUM>. The spokes <NUM> connect the ring body <NUM> and the hub <NUM> together and maintain both at a concentric position. The hub <NUM> has a central hole <NUM>, which is formed with internal threads <NUM> on an inner surface thereof by turning.

As shown in <FIG>, the bush <NUM> can be integrally formed by a plastic material, a composite material or any suitable material to be a cylindrical body having a tapered outer surface with external threads <NUM> formed thereon, so as to form the bush <NUM> with a shaft hole <NUM> penetrating along a longitudinal axis of the bush. An outer edge of the large diameter end of the tapered-shape bush <NUM> is formed with a flange <NUM> protruding radially outward. A groove <NUM> is formed to penetrate through a wall of the bush <NUM>. Two opposite sidewalls of the groove have a width W spaced apart from each other, and form an angle θ in a widthwise direction thereof. The angle θ is preferably <NUM>° to <NUM>°, and the width W is preferably <NUM> to <NUM>. The groove <NUM> may allow the wall of the bush <NUM> to be elastically deformed in a radial direction, so as to elastically reduce or enlarge an inner diameter of the shaft hole <NUM>. The angle θ may allow the opposite sidewalls of the groove <NUM> to be close to each other when the shaft hole <NUM> is reduced to a certain degree.

The width W of the groove <NUM> should be suitably set, so as to provide a sufficient contact area for obtaining a sufficient clamping force between an outer surface of the supporting post <NUM> and the inner surface of the shaft hole <NUM> when the supporting post <NUM> penetrates through the shaft hole <NUM>. In other words, if the width W is too large, the inner surface area of the shaft hole <NUM> will decrease, and thus the contact area between the outer surface of the supporting post <NUM> and the inner surface of the shaft hole <NUM> will decrease, thereby reducing the frictional force of the contact surface of the inner surface of the shaft hole <NUM> with the outer surface of the supporting post <NUM>. In contrast, if the width W is too small, although the inner surface area of the shaft hole <NUM> is relatively increased, the deformation amount of the bush <NUM> in the radial direction will be decreased due to the contact of the opposite sidewalls of the groove <NUM> with each other, and thereby decreasing the clamping force of the bush <NUM> on the supporting post <NUM>. Therefore, the optimal width W of the groove <NUM> at an outer edge of the bush <NUM> is <NUM> to <NUM>.

According to the present invention, two pads <NUM> are further provided on the inner surface of the shaft hole <NUM>, and the pads <NUM> protrude from the inner surface of the shaft hole <NUM>. The pads <NUM> are softer relative to the inner surface of the shaft hole <NUM> and have a high coefficient of friction. For example, the pads <NUM> may be made of silicone or rubber material. The recesses <NUM> are formed on opposite sides of the inner surface of the shaft hole <NUM>, and two pads <NUM> are respectively disposed in the recesses <NUM>. For example, the pad <NUM> may be fixed on a bottom surface of the recess <NUM> with an adhesive; or the pad <NUM> may be pressed into the recess <NUM> in a tight fit manner.

The operation method of fixing the foot ring <NUM> to the supporting post <NUM> using the fixing structure is described below: The bush <NUM> is assembled with the hub <NUM> by spirally fitting the internal thread <NUM> with the external thread <NUM>, so as to make the bush <NUM> penetrate into the central hole <NUM> along the longitudinal axis thereof. Since the bush <NUM> has a tapered outer surface and the central hole <NUM> has a uniform inner diameter, the wall of the bush <NUM> will be gradually restricted by the central hole <NUM> and radially deformed to shrink during a process of rotating the bush <NUM> toward a first direction (for example, clockwise) into the central hole, and thus to reduce the inner diameter of the shaft hole <NUM> until the flange <NUM> abuts against a lower edge of the hub <NUM>. In contrast, when rotating the bush <NUM> toward a second direction (for example, counterclockwise), the wall of the bush <NUM> restricted by the central hole <NUM> will be gradually released and radially expanded while the bush <NUM> gradually rotates out of the central hole <NUM>, and thus enlarges the inner diameter of the shaft hole <NUM>.

Therefore, when assembling the foot ring <NUM> on the supporting post <NUM>, the bush <NUM> should be rotated firstly and moved outward from the central hole <NUM> for enlarging the inner diameter of the shaft hole <NUM> to allow the supporting post <NUM> to penetrate through, and then insert the supporting post <NUM> into the shaft hole <NUM>, and then rotate and move the bush <NUM> into the central hole <NUM>. As described above, the shaft hole <NUM> will be shrunk during the movement of the bush <NUM> into the shaft hole <NUM>, and thus the inner diameter of the shaft hole <NUM> is decreased to clamp and fix the supporting post <NUM>, as shown in <FIG>. In particular, since the soft pads <NUM> provided on the shaft hole <NUM> protrude from the inner surface of the shaft hole <NUM>, the pads <NUM> will be compressed to deform during the process of clamping the supporting post <NUM> with the shaft hole <NUM> of the bush, so that the supporting post <NUM> can be supported and clamped by the pads <NUM> with a higher friction coefficient. Similarly, when needing the adjustment of the foot ring <NUM> to other height positions, the bush <NUM> is rotated to release the clamping on the supporting post <NUM>, as shown in <FIG>, the foot ring <NUM> can be moved upward and downward along the supporting post <NUM>, and then the bush <NUM> is rotated toward a reverse direction to fix it on the supporting post <NUM> after a desired height position is reached.

Claim 1:
A structure for fixing a foot ring (<NUM>) to a supporting post (<NUM>) of a chair, the structure comprising:
a ring body (<NUM>), a hub (<NUM>) arranged concentrically with the ring body (<NUM>), and a plurality of spokes (<NUM>) radially arranged between an inner periphery of the ring body (<NUM>) and an outer periphery of the hub (<NUM>),
wherein the hub (<NUM>) has a central hole (<NUM>) formed with internal threads (<NUM>) on an inner surface thereof; and
a bush (<NUM>) being a cylindrical body having a tapered outer surface with external threads (<NUM>) formed thereon, wherein the bush (<NUM>) has a shaft hole (<NUM>) penetrating along a longitudinal axis of the bush (<NUM>),
characterised in that two recesses (<NUM>) are formed on the opposite sides of the inner surface of the shaft hole (<NUM>), the two recesses (<NUM>) extend axially along the inner surface of the shaft hole (<NUM>) from a first end of the shaft hole (<NUM>) to a second end of the shaft hole (<NUM>), and two pads (<NUM>) are respectively disposed on, fixed in and protrude from the recesses (<NUM>), the two pads (<NUM>) are softer and have a higher coefficient of friction compared to a coefficient of friction of the inner surface of the shaft hole (<NUM>), and a groove (<NUM>) penetrating through a wall of the bush (<NUM>),
wherein two opposite sidewalls of the groove (<NUM>) have a width (W) spaced apart from each other, and form an angle (θ) in a widthwise direction thereof,
wherein the range of the angle (θ) is <NUM>° to <NUM>°,
wherein the range of the width (W) is <NUM> to <NUM>, and
wherein the bush (<NUM>) is assembled with the hub (<NUM>) by screwing the external threads (<NUM>) of the bush (<NUM>) with the internal threads (<NUM>) of the hub (<NUM>), the supporting post (<NUM>) is configured to penetrate through the shaft hole (<NUM>) of the bush (<NUM>), and when the bush (<NUM>) rotates toward a first direction, the wall of the bush (<NUM>) is restricted by the central hole (<NUM>) and the inner diameter of the shaft hole (<NUM>) is reduced, configured
to clamp and fix the supporting post (<NUM>), when the bush (<NUM>) rotates toward a second direction, the wall of the bush (<NUM>) restricted by the central hole (<NUM>) is released to make the shaft hole (<NUM>) enlarge to release the clamping and configured for fixing of the supporting post (<NUM>), wherein the first direction and the second direction are opposite to each other.