Dynamic friction indicator and tightening system usable therewith
First Claim
1. A system for determining a value representative of the coefficient of friction in a threaded joint assembly comprising:
- means for tigtening the joint assembly;
gradient calculating means for developing a gradient signal representative of the slope of a torque-rotation curve which could be plotted for the joint assembly being tightened;
first means for providing a signal representative of the product of the pitch diameter of a threaded fastener member of the joint assembly and the tension rate of the joint assembly; and
computing means responsive to said gradient signal and said first means signal for computing the value representative of the coefficient of friction in the joint assembly and providing an output signal indicative thereof.
2 Assignments
0 Petitions
Accused Products
Abstract
Apparatus and method for determining dynamic friction in a threaded joint and an associated tightening system for tightening such joints including threaded fasteners. A value representative of the coefficient of friction in the threaded joint is obtained by determining the gradient of a torque-rotation curve which could be plotted for the joint being tightened, and dividing this gradient by the product of the fastener pitch diameter and the tension rate of the joint. The desired tightened condition is achieved by computing the tightening torque required to induce a predetermined preload in the threaded fastener and comparing this computed torque with the instantaneous torque being imparted to the fastener. When the two torques are equal, tightening of the fastener is stopped. The desired tightening torque may be computed by obtaining the product of the value representative of the coefficient of friction, the predetermined preload and the pitch diameter of the fastener, or alternatively, by obtaining the product of the gradient of the torque-rotation curve and the quotient of the predetermined preload divided by the tension rate of the joint.
58 Citations
22 Claims
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1. A system for determining a value representative of the coefficient of friction in a threaded joint assembly comprising:
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means for tigtening the joint assembly; gradient calculating means for developing a gradient signal representative of the slope of a torque-rotation curve which could be plotted for the joint assembly being tightened; first means for providing a signal representative of the product of the pitch diameter of a threaded fastener member of the joint assembly and the tension rate of the joint assembly; and computing means responsive to said gradient signal and said first means signal for computing the value representative of the coefficient of friction in the joint assembly and providing an output signal indicative thereof. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. Apparatus for tightening a joint assembly including a threaded fastener to a desired preload comprising:
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means for tightening the joint assembly by imparting torque and rotation to the fastener, the torque-rotation curve and the preload-rotation curve for the assembly each having a substantially linear tightening portion; torque sensing means responsive to said means for tightening the joint assemby for developing a first torque signal representative of the torque imparted to the fastener; angle sensing means responsive to said means for tightening the joint assembly for developing an angle signal representative of the rotation imparted to the fastener; gradient calculating means for developing a gradient signal representative of the slope of the torque-rotation curve which could be plotted for the joint assembly being tightened; first means for providing signals representative of the desired preload, a selected load at the onset of the substantially linear portion of the preload-rotation curve, the tension rate of the joint assembly, and the pitch diameter of the threaded fastener gate means responsive to said gradient signal for developing a gate signal at the onset of said substantially linear tightening portion, said gate means being operative to receive said first torque signal and output a selected torque signal representative of the torque imparted to the fastener at said onset of said substantially linear tightening portion; computing means responsive to said gradient signal, said selected torque signal and said first means signals for computing an output signal representative of the desired torque necessary to produce the desired preload in the joint assembly. - View Dependent Claims (14, 15, 16, 17)
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18. A method of determining a value representative of the coefficient of friction in a threaded joint assembly comprising the steps of:
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determining the tension rate (TR) of the joint assembly; providing the pitch diameter (d) of a threaded fastener member of the joint assembly; tightening the joint assembly; calculating the gradient (M) of a torque-rotation curve for the joint assembly being tightened during the substantially linear portion thereof; and computing on the fly the value representative of the coefficient of friction (C1) as a function of said gradient, said pitch diameter and said tension rate. - View Dependent Claims (19, 20)
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21. A method of tightening a joint assembly including a threaded fastener to a desired preload comprising the steps of:
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establishing a desired predetermined preload (PD) which is to be induced in the joint assembly; determining a selected load (PL) at the onset of the substantially linear portion of the preload-rotation curve; determing the tension rate (TR) of the joint assembly; providing the pitch diameter (d) of the threaded fastener; tightening the joint assembly by imparting torque and rotation to the fastener; calculating the gradient (M) of the torque-rotation curve during the substantially linear portion thereof; identifying said onset of said substantially linear tightening portion of said torque-rotation curve; measuring a selected torque (TL) imparted to the fastener at said onset of said substantially linear tightening portion; computing a desired tightening torque (TF) necessary to induce the desired predetermined preload in the joint assembly, as a function of said predetermined preload, said selected load, said gradient, said tension rate, said pitch diameter and said selected torque; determining when said torque imparted to the fastener is equal to said desired tightening torque (TF); and discontinuing tightening the joint assembly when said torque imparted to the fastener is equal to said desired tightening torque (TF). - View Dependent Claims (22)
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Specification