Tension control of fasteners

A method of tightening a joint including a threaded fastener through a region characterized by relatively free rotation and no fastener stress at least partially into a region characterized by increasing fastener stress, increasing torque, a substantially linear torque rate, and a substantially linear tension rate, comprising

• tightening the fastener;
• sensing torque applied to the fastener and the angle of threading advance;
• determining, during tightening, the torque rate of the fastener from the sensed values of torque and angle in the region where the torque rate is substantially linear;
• determining an angle origin of one of the linear rates from the determined torque rate;
• determining a shut off parameter based on the angle origin;
• and
• terminating tightening in response to the shut off parameter.

A method of fastener tensioning in a joint system comprising

• rotating the fastener;
• monitoring a tension-related function applied to the fastener and a function of rotation applied to the fastener;
• determining a constant rate of change of the tension-related function per unit of the function of rotation;
• determining a starting point for rotation based on a linear projection of the constant rate determined, said starting point corresponding to the zero value of the tension-related function intercept of the function of rotation;
• rotating the fastener a proportionally determined amount of rotation from said starting point;
• and
• stopping the rotation of the fastener in response to the fastener being rotated the proportionally determined amount.

A method of fastener tensioning comprising

• rotating the fastener by a power wrench;
• monitoring a tension-related function applied to the fastener and a function of rotation applied to the fastener;
• determining a constant rate of change of the tension-related function per unit of the function of rotation;
• determining a shut off parameter utilizing said constant rate and an amount of rotation;
• and
• stopping rotation of the fastener by shutting off said power wrench when said determined shut off parameter is reached.

A method for tightening a threaded fastener, comprising

• threadably advancing the fastener into a region of increasing stress where a torque-angle curve is substantially linear;
• determining an angle location lying on an imaginary line comprising an extension of the linear portion of the torque-angle curve;
• determining a shutoff parameter based on the angle location;
• and
• terminating tightening in response to the tightening parameter.

Apparatus for pretensioning a screw joint to a predetermined axial load F.sub.D where the axial load/rotational relationship FR of the joint is known, comprising:

• means for delivering torque to the screw joint,
• torque sensing and signal delivering means coupled to said torque delivering means,
• rotation sensing and signal delivering means coupled to said torque delivering means,
• a control unit connected to said torque sensing and rotation sensing means to receive signals therefrom in response to the instantaneous torque and rotation values of the screw joint, said control unit comprising
• first calculating means for determining the actual torque/rotation relationship TR,
• second calculating means for determining a theoretical tensionless angular position .alpha..sub.origin of the joint, and
• means for initiating shut off of said torque delivering means when the joint has been rotated from said theoretical tensionless angular position .alpha..sub.origin an angular interval which, according to said known axial load/rotation relationship FR corresponds to said predetermined axial load F.sub.D.

Apparatus for tightening a joint including a threaded fastener through a region characterized by relatively free rotation and no fastener stress at least partially into a region characterized by increasing fastener stress, increasing torque, a substantially linear torque rate and a substantially linear tension rate, comprising

• a powered tool for tightening the fastener;
• means for sensing the torque applied to the fastener and the angle of threading advance;
• means for determining, during tightening, the torque rate of the fastener from the sensed values of torque and angle in the region where the torque rate is substantially linear;
• means for determining the angle origin of one of linear rates from the determined torque rate;
• means for determining a shut off parameter based on the angle origin;
• and
• means for terminating operation of the powered tool in response to the shut off parameter.

An apparatus for threaded fastener tensioning in a joint system comprising

• wrench means for rotating the fastener;
• means for measuring a tension-related function applied to the fastener;
• means for measuring a function of rotation applied to the fastener;
• means for receiving the measurement of the tension-related function and the measurement of the function of rotation and for determining a constant rate of change of said tension-related function with respect to the function of rotation;
• means for determining a starting point for rotation based on a linear projection of the constant rate determined, said starting point corresponding to the zero value of the tension-related function intercept of the function of rotation;
• means for rotating the fastener a proportitonally determined amount of rotation from said starting point;
• and
• means for stopping the rotation of said fastener in response to the fastener being rotated the proportionally determined amount.

An apparatus for fastener tensioning comprising

• means for rotating the fastener;
• means for monitoring a tension-related function applied to the fastener and a function of rotation applied to the fastener;
• means for determining a constant rate of change of the tension-related function per unit of the function of rotation;
• means for determining a shut off parameter utitlizing said constant rate and an amount of rotation;
• and
• means for stopping the rotation of the fastener when said determining shut off parameter is reached.

An apparatus for tightening a threaded fastener at least into a region of increasing stress where a torque-angle curve is substantially linear, comprising

• means for threadably advancing the fastener into the region;
• means for determining an angle location lying on an imaginery line comprising an extension of the linear portion of the torque-angle curve;
• means for determining a shut off parameter based on the angle location;
• and
• means for terminating tightening in response to the shut off parameter.