Power wrench for tightening screw joints
First Claim
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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Accused Products
Abstract
A power wrench for two-step tightening of screw joints, has a housing (13), an electric motor (10) including a rotor (25), an output shaft (24) coupled to the rotor (25), and a power supply. The power supply includes a power converter (11) with a variable frequency and voltage output and a current responsive power shut-off device. A retardation responsive inertia device (28) is coupled to the motor rotor (25) via a spring (32) and a cam (29, 30) for corotation with the motor rotor (25) and for activation of a switch (12) as a certain predetermined retardation magnitude in the motor rotor (25) is exceeded. The latter is used for obtaining a fast torque interruption of the initial tightening step of the two-step tightening process, whereas the final tightening step is discontinued automatically as a predetermined current magnitude in the power supply is reached.
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Citations
2 Claims
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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. - View Dependent Claims (2)
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Specification