Tool driving or impacting – Automatic control of power operated means – Drive means responsive to torque or speed condition
Reexamination Certificate
1998-12-03
2001-03-06
Vo, Peter (Department: 3721)
Tool driving or impacting
Automatic control of power operated means
Drive means responsive to torque or speed condition
C173S093000, C173S093500, C173S181000, C173S217000
Reexamination Certificate
active
06196332
ABSTRACT:
The invention relates generally to rotational energy storage devices including springs and more particularly to rotational energy storage devices that may be used in inertia based torquing tools.
Springs are components or devices that, with high efficiency, store energy as they deflect under an applied force, e.g., torque, force, bending moment, or any combination thereof, and release the stored energy as they return to their original position when the applied force is removed. Their primary characteristic is that they deflect either linearly or non-linearly in proportion to the amplitude and direction of the applied force. Various types of springs are used in machines and tools to store energy as they deflect and react applied forces. Some examples of real springs include helical-wound torsion springs, helical-wound compression springs, torsion bars, multiple-leaf springs, and gas-filled bladders.
Springs are used in various applications, e.g., in low reaction tools for tightening threaded fasteners. These tools are typically devices that accelerate a rotary inertia mass through a relatively large travel angle. This acceleration is developed using a motor with a torque output that is relatively low compared to the output torque capability of the tool. As the inertia mass accelerates, it develops kinetic energy. After the inertia mass has traveled through a significant angle (for example,
180
degrees or more), a clutching means engages the rotary inertia mass to a workpiece, via some type of torsion spring. The subsequent negative acceleration of the inertia mass results in a torque output that is relatively high compared to that supplied by the accelerating motor. This high torque output is not reacted on the user, as the reaction is provided by the torque associated with the negative acceleration of the flywheel or inertia mass.
In order to tighten a threaded fastener, one must rotate a bolt via applying a torque to clamp a joint. All bolts have some lead or helix angle that permits the clockwise rotation, for right-hand fasteners, to translate a nut or member to cause tension in the bolt. This angle makes the bolt more difficult to turn (i.e., higher torque) when clamping a joint versus the reverse direction, which is loosening a joint. When considering a low reaction tool with an oscillatory drive system, having an energy storage device which applies an equal forward and reverse torque to the fastener will cause the joint to loosen for the reason discussed above.
In commonly assigned U.S. patent application Ser. No. 08/865,037 (now U.S. Pat. No. 5,845,715) titled “Resonant Oscillating MassBased Torquing Tool,” which application is incorporated herein by reference, a resonant torquing tool is disclosed which overcomes this obstacle by applying a bias torque on the drive motor so that the developed tightening torque is greater that the loosening torque. This bias torque, however, creates a bias torque on the tool housing which must be reacted by the operator. For low torque range tools, where the bias torque would be small, this may be appropriate.
In a second commonly assigned U.S. patent application Ser. No. 08/865,043 (now U.S. Pat. No. 5,848,655) titled “Oscillating Mass-Based Tool With Dual Stiffness Spring,” which application is incorporated herein by reference, a resonant torquing tool is disclosed which uses a dual stiffness spring. As taught therein, the dual stiffness spring has a greater resistance to torsion (i.e., greater stiffness) in the tightening direction and a smaller resistance to torsion (i.e., softer stiffness) in the loosening direction. The energy used for torquing a workpiece is developed by oscillating a mass spring system at or near its resonant frequency, with the means for biasing the output torque being provided by the dual stiffness spring. This system provides for a reactionless tightening system by significantly reducing or eliminating the resultant net torque on the tool housing. As a result, this system is particularly well suited for higher torque range tools.
In designing springs for these low reaction torquing tools, as well as for a variety of other applications, one important characteristic is how the torque applied varies with the angular displacement of the spring. Dual stiffness springs such as those described in allowed U.S. patent application Ser. No. 08/865,043 (now U.S. Pat. No. 5,848,655) provide for torque-angle relationships (i.e., spring stiffnesses) that differ depending on the direction of applied torque. While these stiffnesses differ in the forward and reverse torsioning directions, they are only slightly nonlinear in each direction, and, while not impossible, it is not easy to tailor the torque-angle relationship of these springs to provide various linear or non-linear stiffness profiles in either or both directions. It would be desirable to provide a spring in which the torque-angle relationship could be easily tailored to provide a substantially different linear or nonlinear spring stiffness when being deflected in either or both directions. This would provide designers and engineers greater flexibility than that provided by typical torsion springs and bars.
When torque is applied to a rotational spring such that it displaces angularly, work is done on the spring and the spring stores energy. If the spring is purely elastic, all the energy stored is recoverable by allowing the spring to rotate back through its displaced angle, and the spring is said to be 100% efficient.
FIG. 1
shows an example of a torque-angle relationship for a rotational spring exhibiting such an elastic relationship. If the spring is not purely elastic, as is the case with all real springs, some amount of energy is lost as the spring rotates back through its displaced angle and only a portion of the stored energy is recoverable.
FIGS. 2 and 3
show examples of torque-angle relationships for rotational springs exhibiting inelastic, “lossy” behavior in which the amount of energy lost is represented by the area between the curves shown. In many applications a highly elastic spring is desirable, while in other applications a less elastic spring may be desirable. Thus, it would be desirable to provide a spring design in which the degree of elasticity can easily be varied, from almost 100% efficiency to some desired lower efficiency.
Another design criteria known as the load capacity, that is, the maximum torque that can be applied to the energy storage device without damaging it is also important. In many applications, the volume required to house the energy storage device is also important. Thus, an energy storage device having a high load capacity and small package size would also be desirable.
The foregoing illustrates limitations known to exist in present springs. Thus it is apparent that it would be advantageous to provide an alternative spring design directed to overcoming one or more of the limitations set forth above. Accordingly, a novel spring is provided including the features more fully disclosed hereinafter.
SUMMARY OF THE INVENTION
According to the present invention, a rotational energy storage device or spring is provided which includes a roller-cam assembly having a shaft, a ring rotatably disposed about the shaft, and at least one roller disposed between shaft and ring. The roller is configured such that, upon rotating the ring relative to the shaft, the roller interferes with the ring and the shaft to convert and effect storage of mechanical energy created by the relative rotation of the ring and the shaft. Preferably a plurality of spaced rollers are positioned between ring and shaft. A cam geometry which is symmetrical or asymmetrical is provided on the shaft, the ring, the roller, and combinations thereof. A rotational energy storage device having a back-up ring with alternating thin and thick cross-sectional areas is further provided which is indexed to provide low and high stiffness regions against each roller.
The foregoing and other aspects will become apparent from the following detailed description of the invention whe
Albert Gregory P.
Cooper Timothy R.
Ryan James P.
Stahlman David B.
Calve Jim
Ingersoll-Rand Company
Nigohosian, Jr. Leon
Vo Peter
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