Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

Chapter 11 Proprioceptive and Environmental Sensing Mechanisms and Devices 277
• A hard stop that is strong enough to withstand the stopping force
(and yet not damage the object) can be placed just after the trip point
of the switch.
• The layout can allow the object to pass by the switch, tripping it but
not being physically stopped by anything. The robot’s stopping
mechanism is then the main means of preventing harm.
• The travel of the sensor’s lever or button, after the sensor has been
tripped, can be made long enough to allow sufficient time for the
robot to stop.
Figure 11-8 Direct sensing with
separate hard stop
Let’s take a look at each layout.
Combination Trip (Sense) and Hard Stop
This is probably the simplest layout to implement. The switch directly
stops the sensed object (Figure 11-7), which means the switch must be
strong enough to withstand repeated impacts from the thing being
sensed. Alternatively, there is a separate hard stop that is in line with the
switch that absorbs the force of the impact after it has been tripped
(Figure 11-8). Using a switch with a long throw eases implementation,
and nearly any mechanical limit switch can be made to work with this
layout, though the button and lever designs are usually best.