Hollow shaft reduction gear with overload protecting device

A hollow shaft reduction gear with overload protecting device, comprising:

• a gear case having reduction gears therein;
• a hollow output shaft, open at both ends, extended through and supported for rotation in said gear case, coupled to one of said reduction gears in said case, and having at least one end portion projecting outside from the gear case;
• a driven shaft mounted against axial movement in the hollow output shaft so as to be only rotatable relative to the output shaft and having a first end portion projecting from said at least one end portion of the hollow output shaft and a second end portion projecting from said hollow shaft at the end opposite to said at least one projecting end portion of the hollow output shaft, whereby said hollow output shaft circumscribes said driven shaft between said first and second end portions;
• and
• an overload protecting device outside of said gear case coupled between the hollow output shaft and the driven shaft, said overload protecting device including
• a drive plate fixedly mounted on said at least one end portion of the hollow output shaft;
• a driven plate mounted on said first end portion of the driven shaft so as to be axially slidable and restrained from rotation relative to the driven shaft;
• said drive plate and said driven plate respectively having confronting axial surfaces, and an interlocking recess formed in one of said confronting surfaces and a holding recess formed in the other of said confronting surfaces;
• a ball held between the interlocking recess and the holding recess;
• a spring biasing the driven plate toward the drive plate;
• and
• a spring-pressure adjusting mechanism for adjusting the axial position of the driven plate on the driven shaft to adjust the spring pressure of the spring;
• said spring seating at one end against said spring-pressure adjusting mechanism and engaging said driven plate at the other end, and the spring-pressure adjusting mechanism including an externally threaded portion in said first end portion of the driven shaft and a spring pressure adjusting nut screwed on the externally threaded portion of the driven shaft to adjust the compression of the spring,
• said interlocking recess and the holding recess being formed in shapes that keep the ball in the holding recess and allow the ball to move axially out of the interlocking recess when the driven shaft is overloaded,
• said reduction gears comprising a first gear element having a rotary axis concentric with said hollow output shaft and mounted on the exterior of said hollow output shaft, and a second gear element having a rotary axis perpendicular to the axis of said hollow output shaft, whereby rotating said second gear element at a high speed drives said first gear and the second end portion of said driven shaft at a reduced speed with overload protection provided by said overload protecting device.