Tools – Wrench – screwdriver – or driver therefor – Responsive to torque on work
Patent
1991-12-18
1993-04-20
Meislin, D. S.
Tools
Wrench, screwdriver, or driver therefor
Responsive to torque on work
81474, 81 5714, B25B 25151
Patent
active
052032426
ABSTRACT:
A power tool for two-step tightening of screw joints by a first high speed step for tightening the screw joint to a predetermined torque snug level (T.sub.1) and a second low speed step for tightening the screw joint to a desired final torque level (T.sub.2). The power tool (10) includes an electric motor, an output shaft (17), a mechanical power transmission coupling the motor to an output shaft (17), a power supply (11) connected to the motor, signal producing device (16) delivering a signal reflective of the output torque of the tool (10), and a comparator device (19, 23) for comparing the torque reflective signal with predetermined limit values corresponding to the torque snug level and to the desired final torque level and for delivering power shut-off initiating signals as the torque reflective signal attains these limit values. The power tool (10) comprises a torque and speed responsive override clutch (30) for limiting the output torque to a safety torque level (T.sub.s) well below the desired final torque level (T.sub.2) but exceeding the snug level (T.sub.1) in case of an inertia related torque overshoot during the first high speed tightening step. A centrifugal weight (48, 49) operated lock element (45) unlocks the clutch (30) for overriding at speed levels exceeding a predetermined level only. During the second low speed tightening step, the clutch (30) is locked against overriding and transfers torque without limitation.
REFERENCES:
patent: 3319494 (1967-05-01), Ulbing
patent: 3965778 (1976-06-01), Aspers et al.
patent: 4881435 (1989-11-01), Hansson
patent: 4883130 (1989-11-01), Dixon
patent: 5076120 (1991-12-01), Lin
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