Servo - September 2016

the individual pieces.

Dave Freeman — the owner of Advanced Computer Products in Santa Ana, CA — gave me a Novag chess robot. A customer had broken the robot arm, and I tried to fix the broken casting to no avail. I still have it. The arm’s two segments covered the board and the forearm segment swiveled up and down to raise and lower the gripper, much as a human arm moving objects about a board.

The gripper had three pieces arranged 120° apart to close in on or release a chess piece. It was amazing to watch a robot playing a game back in 1982 when robots were becoming popular.

Our Amazing Human Hand

I would like to present a few scenarios and discuss just how uniquely functional the human hand really is as compared to the very best robot hands and grippers. Before delving into a robot’s gripper, just sit back in your chair right now and look at your own hand. Wiggle all of your fingers and thumb. Hold it up in the Vulcan sign shown in Figure 3 that Spock always used to, and then would say, “Live long and prosper.” Notice the two fingers separated, as well as the thumb. You can begin to see just how versatile our hands are. The fingers just don’t curl inward to hold something and neither does our opposing thumb that can move in several directions. We can wrap the thumb around a baseball bat and then place it in another position to press a button atop a gaming joystick. We can curl just the tops of each finger or curl them all the way. We can separate individual fingers like the Vulcan hand sign. Feel the tendons below your wrist stiffen when you make a fist. We are talking about some amazing mechanics here.

I won’t delve into the physiology of the human hand and its phalanges and metacarpals as I did a bit over a year ago. I want to discuss ‘end effectors’ in a more robotic way.

Typical Robot Grippers and End Ef fec tors

The earliest industrial robots were designed for specific duties and had their end effectors optimized for the task at hand. (Pun intended.) The site, WhatIs.com described an end effector thusly: “In robotics, an end effector is a device or tool that’s connected to the end of a robot arm where the hand would be. The end effector is the part of the robot that interacts with the environment. The structure of an end effector and the nature of the programming and hardware that drives it depend on the task the robot will be performing. In manufacturing, a robot arm can accommodate only certain tasks without changes to its end effector’s ancillary hardware and/or programming. If a robot needs to pick something up, a type of robot hand called a gripper is the most functional end effector. If a robot needs to be able to tighten screws, however, then the robot must be fitted with an end effector that can spin.” As you can realize from above, the end effector can be a special tool such as a wrench or screwdriver, or it can be a type of gripper to pick up or maneuver an object. If you remember, little R2D2 in Star Wars had a series of tools or probes (one of which is shown in Figure 4) that he could insert into a computer data interface on the Death Star to download all sorts of things. It looked more mechanical than digital to me, but our heroes were able to determine the Death Star’s weaknesses with the retrieved data, and also avoid being squashed in a garbage compactor. However, it is the basic gripper that is most used in industrial applications as well as personal robotics.