U Yong Nam, a section head at the Robotics Institute, has developed a tower clock.
The tower clock is composed of a driving ball-worm gearing box (1:84) and a clock gearing box (reduction ratio of the hour hand and the minute hand 1:12). The accuracy of the clock is ensured by the side clearance and the motion smoothness of the driving ball-worm gearing box.
When the worm shaft rotates in the driving ball-worm gearing box, the rolling balls in the circular workspace between the worm and the worm wheel transfer torque to the ball-worm wheel. Then, the balls circulate along the ball recirculation passage through 2~3 teeth. At the input and output of the passage is a piece to guide the balls back smoothly. And there is a ball-bush to stop the balls from dispersing.
The control system is composed of a main clock and terminal clocks calibrated by the national standard time. The control device consists of a digit I/O part, a serial communication part, a display, control buttons, and a power circuit.
The terminal clocks receive time pulses through RS-485 communication every 30s from the main clock and send them to the drive module to drive the motor.
The large-size tower clock with a ball-worm gearing box has several advantages.
First, it is much easier to achieve the dimensional accuracy and the assembling accuracy of the gearing box than a clock with a planetary gearing box.
Second, its service life is semipermanent or permanent.
Third, it ensures a high degree of accuracy and it is easy to operate.
It will find use at the front gates of factories and enterprises, in the waiting rooms of stations, and at public places.
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