| 摘要 |
A shutoff mechanism for a pneumatic tool such as a nut runner senses both the instantaneous speed and the instantaneous rate of change of speed of the drive components of the tool. The mechanism controls the flow of air to the motor and terminates such flow as the drive speed decreases while approaching a stall condition. The mechanism comprises a main air valve operated by a centrifugal governor having a plurality of pivoted weights with their pivot axes oriented at acute angles to radial lines intersecting the centers of the weights rather than oriented at right angles to such radial lines as in conventional governor assemblies. So oriented, the weights sense both instantaneous speed and instantaneous rate of change of speed of the drive components. By sensing these two operating parameters, the shutoff mechanism, in effect, anticipates the stall condition of the drive, terminates air flow thereto more rapidly and accurately than conventional shutoff devices and provides improved consistency of torque application.
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