| 摘要 |
A vertically oriented support frame engages a vertically oriented traveling frame for movement between a retracted position, wherein the traveling frame is positioned in front of the support frame, and an extended position wherein the traveling frame is positioned primarily above the support frame. An electric motor is fixed to the support frame and rotates a drive screw engaged with the support frame while the traveling frame is engaged with the drive screw so as to be moved vertically as the drive screw rotates. Upper and lower limit switches sense when the traveling frame is in the extended position and in the retracted position and send signals to a motor control to stop the motor.
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