Bearings – Linear bearing – Recirculating
Reexamination Certificate
2002-08-06
2004-05-11
Footland, Leonard A. (Department: 3682)
Bearings
Linear bearing
Recirculating
C384S045000
Reexamination Certificate
active
06733179
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rolling element interference preventer for a guide device, such as a linear guide device having an continuous circulation path for rolling elements, a swing bearing, a ball screw, and a spline. The rolling element interference preventer prevents the rolling elements rolling at regular intervals within the continuous circulation path formed between a pair of bearing races from interfering with each other.
2. Description of the Related Art
In various rolling guide devices having a bearing, a linear motion or rotation of a pair of bearing races is enabled by use of the rolling motion of rolling elements consisting of balls or rollers carried between the bearing races. To reduce the frictional resistance by avoiding the contact between each rolling element and to produce the smooth motion by arranging each rolling element at predetermined position, it is common practice that a number of rolling elements are incorporated between bearing races, using a metallic retainer.
In the conventional guide device using the metallic retainer, since a cage has a number of pockets and rolling elements are put rotatably into these pockets, there is an advantage that the operation of incorporating a number of rolling elements into the guide device is facilitated. However, it is required to hold a number of rolling elements incorporated into the pockets of the cage not to fall off, resulting in a problem that it takes a lot of time to fabricate the cage itself.
Thus, to solve this problem, a ball interference preventer (rolling element interference preventer) for use in a guide device to prevent interference between each ball has been proposed. The endless guide device includes a track rail having a rolling path, a sliding board having a rolling groove mutually opposed to the rolling path and moving along the track rail, and a number of balls (rolling elements). With a load applied, the balls roll in a continuous circulation path formed between the rolling path of the track rail and the rolling groove of the sliding board. The ball interference preventer is composed of a flexible resin connector having an interposing portion interposed between each ball and a connecting portion for connecting between the interposing portions, and holding each ball in an arranged state and rollably. Thereby, many appreciable results were achieved including 1) attaining low noise and good sound quality by removing the metallic sound due to collision between the balls (low noise), 2) reducing the wear of ball and increasing the retention of grease (maintenance free for long term), 3) attaining excellent high speed by decreasing the relative friction velocity (high speed), and 4) smoothing the motion by greatly reducing the rolling fluctuation (sliding property) (JP-B-6-56181, JP-A-5-52217, JP-A-5-126149, JP-A-5-196036, JP-A-5-196037, and JP-A-9-14264).
By the way, thus structured ball interference preventer composed of the resin connector is immersed in, or subjected to grease, lubricating oil, or coolant in the environment where the preventer is incorporated in the circulation path for the rolling guide device. Also, the ball interference preventer undergoes actions such as bending, tension, compression, twisting, or contact friction with the ball at any time. When reciprocated in the circulation path at high speed, this ball interference preventer undergoes an operation of bending, tension and compression severely and repeatedly. Further, when the ball interference preventer composed of the resin connector is immersed in, or subjected to grease, lubricating oil, or coolant, it absorbs water and oil to swell, causing a circulation failure in the circulation path and ablation of the preventer, and degrading the durability, sliding property and wear resistance.
Therefore, the rolling element interference preventer composed of the resin connector is required to have the excellent chemical strength of oil resistance, water resistance, and chemical resistance to the grease, lubricating oil and coolant, in addition to the mechanical strength of durability, sliding property and wear resistance. In view of the life of the guide device, it is required to be so durable and resistant to wear as to run about 30,000 km or more, with small sliding resistance variation, as well as resistant to oil, water and chemicals.
Moreover, the rolling element interference preventer composed of the resin connector was not too problematical in that an unnatural load was applied only on a part of the resin connector during the use, because the minimum radius of curvature for the continuous circulation path formed in the guide device was relatively large, the ball was employed as the rolling element, and the shape of the resin connector was devised. In recent years, however, the guide device is demanded for smaller size and higher speed, and the roller is employed as the rolling element, resulting in a problem that the durability, wear resistance and sliding property may be impaired.
SUMMARY OF THE INVENTION
The present inventors made researches to attain more excellent durability and wear resistance without impairing various features (low noise, maintenance free for long term, high speed, and sliding property) of the rolling element interference preventer, especially when subjected to severe and repetitive actions of bending, tension and compression, and found that the rolling element interference preventer should be produced using a thermoplastic resin elastomer having specific balance (relation) for a 10% elongation stress, a tensile stress and a bending modulus of elasticity to achieve the aim, thus completing this invention.
Accordingly, it is an object of the invention to provide a rolling element interference preventer for a guide device, which prevents a number of rolling elements rolling at regular intervals in a continuous circulation path of the guide device from interfering with each other. The rolling element interference preventer is not only excellent in low noise, maintenance free for long term, high speed and sliding property, but also excellent in durability and wear resistance, and can be used stably over the long term.
The present invention provides a rolling element interference preventer for a guide device to prevent a number of rolling elements rolling at regular intervals in a continuous circulation path of the guide device from interfering with each other, wherein the rolling element interference preventer is formed of a thermoplastic resin elastomer having a physical property in accordance with an expression, (A×B)÷C≧18, where A is a 10% elongation stress, B is a tensile strength, and C is a bending modulus of elasticity.
As the thermoplastic resin elastomer, polyamide resin elastomer, polyester resin elastomer, polyurethane resin elastomer, styrene resin elastomer, and olefine resin elastomer are exemplified. They should be highly resistant to oil, water and chemicals in the service environment of the rolling guide device, especially in the service environment where the guide device is immersed in, or subjected to grease, lubricating oil, or coolant. The coefficient of water absorption measured in the environment of equilibrium moisture percentage 23° C., 65% RH is 1.5 wt % (% by weight) or less, and preferably 0.5 wt % or less. The swelling factor measured in an immersion test of chemical at a temperature of 85° C. for 672 hours is 3% or less. Furthermore, the tensile strength retention in an immersion test of boiling water at 100° C. is 70% or more after ten days, and preferably 80% or more.
In this invention, the thermoplastic resin elastomers satisfying a physical property in accordance with the expression, (A×B)÷C≧18 (A: 10% elongation stress, B: tensile strength, and C: bending modulus of elasticity) are employed. Though slightly different depending on the type of the rolling guide device and whether the rolling element is a ball or a roller, the 10% elongation stress A is from 60 to 200 kgf/cm
Honjyo Yoshiyuki
Iida Katsuya
Michioka Hidekazu
Murata Tomozumi
Footland Leonard A.
THK Co. Ltd.
Westerman Hattori Daniels & Adrian LLP
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