Page 200 - Anatomy of a Robot

07_200256_CH07/Bergren 4/10/03 3:30 PM Page 185
ENERGY CONTROL AND SOFTWARE 185
Safety
If the robot gets in a difficult situation, it may have to stop quickly. This can occur if an
obstacle appears, a malfunction occurs, or operators press the panic button. Note that in
the case of a panic, brakes might actually hurt instead of helping. Consider the case where
someone has become accidentally caught in moving mechanisms. Once motion is halted
because of a panic, the brakes should be released as long as no more motion ensues. With
the brakes released, the mechanisms may be moved to extricate a trapped operator. In
designing the robot, don’t forget that the brakes can be as dangerous as the motors.
The control system software to deal with braking is a lot more sophisticated than it
might seem at first glance. Consider for the moment antilock braking systems (ABS) in
cars. When the computer that runs ABS senses a skid, it pumps the brakes to help keep
the car skidding in a straight line and to maximize brake’s gripping action. Here’s an
article on ABS using fuzzy logic, if a fuzzy braking system appeals to you:
www.intel.com/design/mcs96/designex/2351.htm. Some more good articles on ABS
can be found at www.howstuffworks.com/anti-lock-brake.htm and www-s.ti.com/sc/
psheets/slit114a/slit114a.pdf. Some engineers spend their entire careers in this field.

Power Failure
If power fails, the robot may go out of control. What happens next depends on the brake
design. Cars have two kinds: temporary brakes (the operator can press the brake pedal)
or flip-flop brakes (the operator can pull the emergency brake and release it later). A
third option would be automatic braking on power failure, where the brakes are kept off
until the power fails. The astute robot designer must choose between these options.
Control system software will only be of use until the power completely fails. If the
robot’s power supply has PFD built in, some warning will be given in advance. Although
the primary braking system can become complex, keep the emergency braking systems
dirt simple.

Speed

The fastest way to go from point A to point B is to accelerate at the maximum rate for
half the journey, and then decelerate at the maximum rate for the other half of the jour-
ney. Those well versed in calculus will recognize the several flaws in this last statement,
but it gives us the basic concept. If speed of operation is the goal (instead of energy con-
servation), then techniques such as this braking maneuver can be used to decrease travel
time. We leave it up to the reader to work out the math model involved to truly mini-
mize the overall trip time.