Apparatus for and method of determining rotational and linear stiffness

A meter for determining the stiffness of an assembly including a member comprising:

• output means for imparting movement to the member;
• input means for receiving power;
• deflectable coupling means between said output means and said input means for transmitting power from said input means to said output means;
• first sensing means responsive to said input means for developing a first series of pulses representative of the displacement of said input means;
• second sensing means responsive to said output means for developing a second series of pulses representative of the displacement by said coupling means of said output means, and
• comparator means responsive to said first and said second series of pulses for determining the difference of the number of pulses in said first and said second series of pulses during a datum number of consecutive pulses in said second series of pulses as power is transmitted by said coupling means for said input means to said output means, said difference being a function of the stiffness of said assembly.

A meter for determining torque gradient of an assembly including a member comprising:

• output means for imparting rotary movement to the member;
• input means for receiving rotary power;
• torsionally deflectable coupling means between said output means and said input means for transmitting torque from said input means to said output means;
• first sensing means responsive to said input means for developing a first series of signals representative of the rotary displacement of said input means;
• second sensing means responsive to said output means for developing a second series of signals representative of the rotary displacement by said coupling means of said output means, and
• comparator means responsive to said first and second series of signals for determining the difference of the number of signals in said first and said second series of signals during a datum number of consecutive signals in said second series of signals as power is transmitted by said coupling means from said input means to said output means, said difference being a function of the gradient of the torque operatively transmitted by said coupling means to the member.

A meter for determining torque gradient of an assembly including a member comprising:

• output means for imparting rotary movement to the member;
• input means for receiving rotary power;
• torsionally deflectable coupling means between said output means and said input means for transmitting torque from said input means to said output means;
• first sensing means responsive to said input means for developing a first series of pulses representative of the rotary displacement of said input means;
• second sensing means responsive to said output means for developing a second series of pulses representative of the rotary displacement by said coupling means of said output means;
• comparator means responsive to said first and second series of pulses for determining the difference of the number of pulses in said first and said second series of pulses during a datum number of consecutive pulses in said second series of pulses as power is transmitted by said coupling means from said input means to said output means, said difference being a function of the gradient of the torque transmitted by the coupling means, and
• circuit means responsive to said comparator means for sequentially storing information representative of the maximum torque gradient developed up to any given point during the driving of said member.

Apparatus for tightening an assembly including a fastener comprising:

• fastener engaging means for imparting tightening movement to the fastener;
• power input means;
• deflectable coupling means between said fastener engaging means and said power input means for transmitting power to said fastener engaging means;
• first sensing means responsive to movement of said power input means for developing a first series of signals representative of the displacement of said power input means;
• second sensing means responsive to movement of said fastener engaging means for developing a second series of signals representative of the displacement by said coupling means of said fastener engaging means;
• comparator means responsive to signals of said first and second series for determining the difference of the number of signals in said first and second series of signals during a datum number of consecutive signals in said second series of signals as power is transmitted by said coupling means from said power input means to said fastener engaging means, said difference being a function of the instantaneous stiffness of the assembly;
• circuit means responsive to said comparator means for sequentially storing information representative of the maximum stiffness of the assembly developed during the tightening of the assembly and for producing a control signal when said instantaneous stiffness has dropped to a predetermined ratio of the maximum stiffness developed during the tightening of the assembly and control means responsive to said control signal for controlling power input by said power input means.

Apparatus for tightening an assembly including a fastener comprising:

• fastener engaging means for imparting tightening movement to the fastener;
• power input means;
• deflectable coupling means between said fastener engaging means and said power input means for transmitting power to said fastener engaging means;
• first sensing means responsive to movement of said power input means for developing a first series of pulses representative of the displacement of said power input means;
• second sensing means responsive to movement of said fastener engaging means for developing a second series of pulses representative of the displacement by said coupling means of said fastener engaging means;
• comparator means responsive to pulses by said first and second series for determining the difference of the number of pulses in said first and second series of pulses during a datum number of consecutive pulses in said second series of pulses as power is transmitted by said coupling means from said power input means to said fastener engaging means, said difference being a function of the instantaneous stiffness of the assembly;
• circuit means responsive to said comparator means for sequentially storing information representative of the maximum stiffness of the assembly developed during the tightening of the assembly and for producing a control signal when said instantaneous stiffness has dropped to a predetermined ratio of the maximum stiffness developed during the tightening of the assembly, and
• control means responsive to said control signal for controlling power input by said power input means.

Apparatus for tightening a screw-threaded fastener comprising:

• fastener engaging means for imparting rotary movement to a threaded fastener;
• rotary power input means;
• torsionally deflectable coupling means between said fastener engaging means and said rotary power input means for transmitting rotary power to said fastener engaging means;
• first sensing means responsive to movement of said rotary power input means for developing a first series of signals representative of the rotary displacement of said rotary power input means;
• second sensing means responsive to said fastener engaging means for developing a second series of signals representative of the displacement by said coupling means of said fastener engaging means;
• comparator means responsive to signals of said first and second series for determining the difference of the number of signals in said first and second series of signals as rotary power is transmitted by said coupling means from said rotary power input means to said fastener engaging means, said difference being a function of the instantaneous torque gradient of the fastener;
• circuit means responsive to said comparator means for sequentially storing information representative of the maximum torque gradient developed during the tightening of the fastener and for producing a control signal when said instantaneous torque gradient has dropped to a predetermined ratio of the maximum torque gradient developed during the tightening of the fastener, and
• control means responsive to said control signal for controlling power input by said rotary power input means.

The method of tightening an assembly including a fastener by power input means driving fastener engaging means through deflectable coupling means, the method consisting of the steps of developing

• a first series of signals representative of the displacement of said power input means;
• a second series of signals representative of the displacement by said coupling means of said fastener engaging means;
• comparing said first and second series of signals by counting the difference of the number of signals in said first and second series of signals during a datum number of consecutive signals in said second series of signals as power is transmitted by said coupling means from said power input means to said fastener engaging means, said difference being a function of the instantaneous stiffness of the assembly;
• sequentially storing information representative of the maximum stiffness of the assembly developed during the tightening of the assembly, and
• producing a control signal controlling said power input means when said instantaneous stiffness has dropped to a predetermined ratio of the maximum stiffness developed during the tightening of the assembly.

The method of tightening a screw-threaded fastener by rotary power input means driving fastener engaging means through torsionally deflectable coupling means, the method consisting of the steps of developing

• a first series of signals representative of the rotary displacement of said rotary power input means;
• a second series of signals representative of the displacement by said coupling means of said fastener engaging means;
• comparing said first and second series of signals by counting the difference of the number of signals in said first and second series of signals during a datum number of consecutive signals in said second series of signals as power is transmitted by said coupling means from said rotary power input means to said fastener engaging means, said difference being a function of the instantaneous torque gradient of the fastener;
• sequentially storing information representative of the maximum torque gradient developed during the tightening of the fastener, and
• producing a control signal controlling said rotary power input means when said instantaneous torque gradient has dropped to a predetermined ratio of the maximum torque gradient developed during the tightening of the fastener.

Apparatus for tightening an assembly including a threaded fastener comprising:

• first means for imparting torque and rotation to said fastener;
• second means connected to said first means for developing a signal representative of the instantaneous gradient of the torque-rotation curve through which the assembly is being tightened;
• and
• third means responsive to said gradient signal for determining a significant change in slope following a tightening region on the torque-rotation curve through which the assembly is being tightened, said third means including means for storing a signal representative of the gradient of the torque-rotation curve throughout the tightening region thereof and for developing a control signal when said instantaneous gradient signal is a predetermined percentage of said stored signal.

Apparatus for tightening an assembly including a fastener until the yield point or a similarly significant change in slope of a torque-rotation curve for the assembly has been reached, said apparatus comprising:

• wrenching means for imparting torque and rotation to said fastener assembly;
• means for developing a signal representative of the instantaneous torque imparted to said fastener assembly;
• means for developing a signal representative of the angular rotation of said fastener assembly;
• means responsive to said torque signal and said rotation signal for developing a signal representative of the instantaneous torque gradient of the torque-rotation curve through which said fastener assembly is being tightened;
• means responsive to one of said signals having a certain relationship relative to said torque gradient signal through the tightening region of said torque-rotation curve for developing a control signal.

A meter for determining the yield point or a similarly significant change in the slope of any torque-rotation curve comprising:

• means for developing a changing signal representative of the torque gradient of the torque imparted to an assembly;
• means responsive to said gradient signal for storing an information signal representative of the torque gradient developed through the generally linear portion of the torque-rotation curve;
• and,
• comparator means for comparing said gradient signal and said information signal and developing a control signal when said gradient signal has changed to a predetermined percentage of said information signal.

A method of tightening an assembly including a fastener by power input means driving a fastener engaging means, the method comprising:

• applying torque and rotation to the fastener;
• developing a changing signal representative of the torque gradient of the torque imparted to the fastener with respect to the rotation thereof;
• determining the largest torque gradient developed up to any point and storing an information signal representative thereof;
• and,
• comparing said stored information signal and said gradient signal and developing a control signal when said gradient signal has changed to a predetermined percentage of said information signal.

A method of determining the yield point or a similarly significant change in slope of any torque-rotation curve comprising:

• applying torque and rotation to a member;
• developing a changing signal representative of the torque gradient of the curve which could be plotted for the torque imparted to the member with respect to the rotation thereof;
• determining the torque-gradient in the generally linear portion of said curve and storing an information signal representative thereof;
• and,
• comparing said stored information signal and said gradient signal and developing a control signal when said gradient signal has changed to a predetermined percentage of said information signal.

Apparatus for sensing a significant change in slope beyond a generally linear portion on a curve representing the variation of first and second related variables, wherein said related variables are torque and rotation imparted to a threaded fastener and said curve is the torque-rotation curve through which the fastener is being tightened, said apparatus comprising:

• first means for continuously measuring the torque applied to the fastener;
• second means for comparing different measurements of torque at discrete intervals of rotation of the fastener to develop instantaneous difference signals representative of the instantaneous gradient of said curve;
• third means for comparing instantaneous difference signals with the largest difference signal previously developed and for storing the largest difference signal so far developed representative of the largest instantaneous gradient so far encountered on said curve;
• and
• fourth means responsive to said instantaneous difference signals and said stored difference signal for developing a control signal when said instantaneous difference signal has a predetermined relationship relative to said stored difference signal.

Apparatus for tightening an assembly including a threaded fastener, said apparatus comprising:

• first means for imparting torque and rotation to said fastener;
• second means connected to said first means for developing a signal representative of the instantaneous gradient of the torque-rotation curve through which the assembly is being tightened;
• and
• third means responsive to said gradient signal for determining a significant change in slope on the torque-rotation curve through which the assembly is being tightened, said third means including means for storing a signal representative of the maximum gradient of the torque-rotation curve throughout the tightening region thereof and for developing a control signal when said instantaneous gradient signal is a predetermined percentage of said stored signal.