G - Physics
05
D
341/108.1
G05D 17/02 (2006.01) B25B 23/145 (2006.01)
Patent
CA 1095611
TIGHTENING SYSTEM Jerry A. Sigmund ABSTRACT OF THE DISCLOSURE A tightening and control system is disclosed for auto- matically tightening a fastener to a predetermined tightened condition in a workpiece, where the fastener is of the type which exhibits more than one installation region on a graph of two tightening characteristics during a complete tightening cycle. Typical of such fasteners are thread tapping fasteners, such as thread-cutting or thread forming types, which first generate a mating thread in a workpiece material and there- after are tightened in the workpiece to a predetermined load condition. Such fasteners typically exhibit a curve of two related input tightening characteristics, such as torque and rotation, or torque and time, for example, having a thread forming region characterized by a generally linear portion of the curve followed by a marked drop off in the slope, an intermediate region and a tightening region having a somewhat similar shape to the thread forming region. The intermediate region may assume any one of several characteristic shapes. Apparatus describing several embodiments is generally disclos- ed for determining the gradient of the torque-rotation curve through which the assembly including the thread tapping fastener is tightened, determining when a first condition indicative of having formed the thread has occurred, and there- after determining when the tightening region has been reached and utilizing the gradient information of the curve to determine when tightening should be discontinued at the predetermined tightened condition. Typically, this predetermined tightened condition may be the yield point of the assembly. In another embodiment of the invention, the gradient is used to determine the occurrence of the first condition following the thread forming region of the curve. The instant- aneous torque value at this first condition is obtained and Stored, and tightening is discontinued when the instantaneous torque bears some predetermined relationship to the instant- aneous torque value at the first condition.
293929
Gowling Lafleur Henderson Llp
Sps Technologies Inc.
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