BH8-Series – User’s Manual
www.barrett.com
© 2007 Barrett Technology®, Inc.
Document: D3000, Version: AF.00
Page 61 of 82
The following description follows the progression of Figure 23. When the clutch is engaged, both
worm gear drives and their corresponding finger links are coupled to the geared servo-motor
pinion. In this state, the ratios of motor position to joint position for the 3
st
and 2
nd
finger joints
are 93.75:1 and 125:1, respectively.
When a finger opens against its motion stop, the threaded spur gear is tightened against the
Belleville spring washers with a known motor torque; thereby setting the threshold torque for
disengaging the spur gear. If the inner finger link, while closing, contacts a target object of
sufficient stiffness to increase the torque in the gear train above the threshold torque, the clutch
will disengage from the Belleville spring washers.
When the clutch is disengaged, the threaded spur gear “free-wheels” on the threaded shaft,
allowing the motor pinion to turn without inducing motion in the inner link. Instead, only the
smaller spur gear, solidly fixed to its shaft, is driven. This fixed spur gear actuates the worm gear
drive for the fingertip. Thus, when the clutch is disengaged, the inner finger link remains
motionless while the fingertip continues to move allowing the fingers to form-fit around any
shape.
