| 摘要 |
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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