1. Field of the Invention
The invention relates generally to exercise equipment. Specifically, this invention relates to weight-lifting equipment, such as Olympic bars.
2. Background Art
When one lifts a barbell from the ground to a position above one's head, the bar rotates 180 degrees. If weight plates do not rotate freely, they would generate a substantial torque that would be transmitted to the lifter's wrist/skeletal systems. Because the weights lifted by athletes may range from 100-500 lbs or more, such torque transfer not only can be painful, but also can cause an “overuse injury” to the athletes. For safety and comfort, barbells may be equipped with rotating sleeves to allow weight plates to rotate and to make strength training more productive and safer.
Olympic barbells (Olympic bars) are specially designed for professional use at Olympic games and other competitive events. Common features of Olympic bar designs include sleeves that can rotate freely and smoothly, while supporting the weight of the plates. This makes it easier for user to practice more “explosive” weight lifting.
An Olympic bar for men is about 2.2 m (7.22 ft) long and weighs about 20 kg (44.1 lbs). The outer ends (rotating sleeves) are about 50 mm (1.9685 in) in diameter for accommodating the weight plates, while the grip section is about 28 mm (1.1024 in) in diameter, and 1,310 mm (51.57 in) in length. A women's Olympic bar is similar to the men's bar, but is shorter—2.05 m (6.73 ft)—and lighter—15 kg (33.07 lbs)—with a smaller grip section diameter (25 mm).
To allow sleeves to rotate freely, Olympic bars typically incorporate bushings, ball bearings, or needle bearings in their rotation mechanisms. Because needle bearings have long, thin bearing elements that have more surface areas than ball bearings, needle bearings can take the weight loads better and are preferred over ball bearings. In addition, bushings are commonly used because of their durability and low maintenance.
In addition to the rotation mechanism, the Olympic bars also need to have a retention mechanism that allows the rotating sleeves to stay on a shaft (i.e., without longitudinal sliding), while allowing the rotating sleeves to have free rotation. Common retention mechanisms may include bolts, pins, or snap rings. An example that uses a bolt to secure a rotating sleeve to a handle bar is shown in FIG. 1, while an example that uses a roller pin is shown in FIG. 2.
FIG. 1 shows a cross-sectional view of a bar assembly 10 that uses a bolt to join the rotating sleeves and the shaft, as disclosed in U.S. Pat. No. 6,770,016 issued to Anderson et al. As shown, the bar assembly 10 includes a shaft 14 (a handle bar). A sleeve 12 is slide over the shaft 14. The sleeve 12 together with an end element 11 are retained on the shaft 14 by a bolt 16. The bolt 16 is threaded into a female threaded end portion 18 on the shaft 14. Once the bolt 16 is fixed at the end portion 18 of the shaft 14, it helps to retain the end element 11 and the sleeve 12 on the shaft 14 and prevent them from sliding off the end of the shaft 14.
To allow rotational freedom of the sleeve 12 around the shaft 14, the bolt 16 passes through a hole in the end element 11 and is then threaded into the end portion 18 of the shaft 14. The bolt 16 is inserted inline with the longitudinal axis of the shaft 14 (or the rotational axis of the sleeves 12) to allow the sleeve 12 to freely rotate around the shaft 14. However, sleeve rotation might from time to time exerts rotational force on the bolt 16. As a result, the bolt 16 may gradually come loose.
An alternative to a bolt is to use a roll pin or a snap ring to retain a rotating sleeve on a shaft. With this mechanism, a roll pin or a snap ring is lodged in matched grooves on the shaft and the rotating sleeve to prevent them from sliding in the longitudinal direction, while allowing rotational motions. FIG. 2 shows an example of a bar assembly 20 that uses a roll pin to retain a rotating sleeve on a handle bar.
As shown in FIG. 2, a bar assembly 20 includes a roll pin 26 to retain a sleeve 22 on a shaft 24. The roll pin 26 may be made by rolling a piece of metal in a way that it would exhibit elasticity such that it can be forced into a groove 28. Once lodged in the groove 28, the roll pin 26 can expand to lock the sleeve 22 on the shaft 24 to prevent the sleeve 22 from sliding off the end of the shaft 24. In a similar manner, a snap ring (in a form of an incomplete circle) can also be used (instead of a roller pin) to retain sleeve 22 on the shaft 24. In order to allow a roller pin 26 (or a snap ring) to fit into the groove 28, the thickness of the roll pin 26 must be smaller than the width of the groove 28. As a result, there is small gap (clearance) in the groove/roller pin setup. The gap allows the sleeve 22 to slide longitudinally on the shaft 24, albeit very slightly. In addition, while the grooves may be only millimeters deep, such grooves would weaken the bars and the sleeves.
While these prior art approaches to sleeve retentions on the shafts (e.g., using bolts, pins, and/or snap rings) are satisfactory in most situations, there is still a need for improved mechanisms to secure rotating sleeves on shafts.