Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

Chapter 2 Indirect Power Transfer Devices 95
Figure 2-20 A variable-speed
transmission consists of two sets
of worm gears feeding a differential
mechanism. The output shaft
speed depends on the difference
in rpm between the two input
worms. When the worm speeds
are equal, output is zero. Each
worm shaft carries a cone-shaped
pulley. These pulley are mounted
so that their tapers are in opposite
directions. Shifting the position
of the drive belt on these
pulleys has a compound effect on
their output speed.
Speed range increase differential (Figure 2-19). This arrangement
achieves a wide range of speed with the low limit at zero or in the reverse
direction.
TWIN-MOTOR PLANETARY GEARS PROVIDE
SAFETY PLUS DUAL-SPEED
Many operators and owners of hoists and cranes fear the possible catastrophic
damage that can occur if the driving motor of a unit should fail
for any reason. One solution to this problem is to feed the power of two
motors of equal rating into a planetary gear drive.
Power supply. Each of the motors is selected to supply half the
required output power to the hoisting gear (see Figure 2-21). One motor
drives the ring gear, which has both external and internal teeth. The second
motor drives the sun gear directly.
Both the ring gear and sun gear rotate in the same direction. If both
gears rotate at the same speed, the planetary cage, which is coupled to