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Power wrench for tightening screw joints

  • US 5,155,421 A
  • Filed: 11/05/1991
  • Issued: 10/13/1992
  • Est. Priority Date: 06/12/1989
  • Status: Expired due to Fees
First Claim
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1. A power wrench for two-step tightening of a screw joint, the first step of said two steps comprising an initial tightening to a predetermined torque snug level and the second step of said two steps comprising a final tightening from said predetermined torque snug level to a desired final torque level,said power wrench comprising:

  • a housing (13);

    an electric motor (10) having a rotor (25), and an output shaft (24) drivingly coupled to said rotor (25); and

    a power supply means (11) including a variable voltage and frequency output power converter for supplying power to said motor;

    said power supply means comprising;

    a current responsive power shut-off means for interrupting the power supply to said motor (10) at attainment of said final torque level; and

    a torque overshoot protective retardation responsive switch means (12,

         28) associated with said rotor (25) for delivering an electrical shut-off signal to said power converter to stop the supply of power to said motor at attainment of a predetermined retardation magnitude during said first tightening step, said torque overshoot protective retardation responsive switch means being located completely out of contact with the screw joint, a screw joint engaging protruding spindle or a base surface surrounding the screw joint.

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