Servo - January 2007

ROBOT SAFETY

by Bryan Bergeron

My first robotic arm kit — a six DOF,

all-metal model with high-speed, heavy-

duty servos, and ample power supply —

taught me not to be lulled into the

apparent plug-and-play world of hobby

robots.

When I applied power to the servos, the joints abruptly hyper-extended, flinging a hot soldering iron against a wall. Then, when I applied power to the servo controller, the uncalibrated servo chain contracted, digging the gripper into the workbench. The unsecured arm flipped onto its side, knocking over a hot glue gun in the process. Fortunately, the gun and iron landed harmlessly on the shop floor and the arm was undamaged.

Robotics presents a real-word test of AI, computer vision, and sensor technologies. Moreover, because robotics involves physical, as well as

computational challenges,

the dangers associated with building and operating robots extend beyond keyboard-induced carpal tunnel syndrome. This is especially true with the current trend toward heavier, faster, and more complex robots. Following is a discussion of robot design, construction, and operating practices that can improve the survivability of your robots and minimize the safety risks to you and bystanders.

Design

Safety should be explicitly designed into a robot, as opposed to an add-on made in response to a injury or robot failure. Appropriate platform layout, the use of safety subroutines,

as well as physical sensors, intuitive state indicators, energy management hardware and software, and kill switches all contribute to a comprehensive safety design.

Platform Layout

In designing a robot platform layout, the primary goal is to provide a stable support for sensors and associated electronics within a structure capable of withstanding the mechanical stress of motion. In addition, the platform should be configured in a way that

protects onboard electronics and minimizes damage to anything or anyone unfortunate enough to be hit by the robot body or effectors.

For example, in designing a crawler, consider using rubber cushions to provide hard limits on the range of leg motion so that the legs don’t clash into the body while you experiment with various gaits. This safety precaution can limit damage to the robot body and servos, and minimize pinch points that can entangle your fingers.

Similarly, avoid sharp edges and protruding corners on fast-moving wheeled robots over a few pounds, which have a way of colliding with furniture legs and shins. I have several robots based on the Traxxas e-Maxx truck chassis — a popular platform for robot development. Because the e-Maxx drive system is capable of speeds in excess of 30 mph, the potential for damage to both person and robot is significant.

If you’re working with a high-speed platform, consider a roll bar and sturdy frame to protect electronics and a bumper system that will minimize damage to human and furniture legs. I’ve found a pair of calf-high boots handy when debugging high-speed robots capable of sudden and unexpected acceleration.