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Many people have seen serial robots in action either on assembly lines or in the movies. An example is a robotic arm that helps assemble a product. It is a serial robot because the arm has joints connected in a series, and each joint has one or more motors or actuators connected to rods that enable the arm to move in what seems to be a human way.
A human arm is attached by a shoulder joint first, then an elbow and finally a wrist. This is also a serial configuration, but it is a far more complex one than found in most serial robots. A person's shoulder joint allows for a wide range of movement, as does the wrist joint. To do this in robotics, several motors need to be employed with connecting rods that allow for a similar kind of movement. The "motors" in a person's arm are the muscles running throughout the arm and into the torso.
When one compares the grace of a professional dancer with the actions of the typical serial robot, the difference become obvious. The serial robot cannot be as graceful because it does not have as many possible variations of motion and force within the robotic motors. Even with sophisticated dancing robots, the motor forces are controlled by digital software, which brings in delays that restrict graceful movement.
Serial robots need only to be graceful enough to perform their task. Usually a part needs to be picked up, placed just so and treated in some manner, such as soldering to a circuit board or tightened with a tool. Performing this task does not necessarily require smooth or graceful movement.
In the early designs of serial robots, the human body was emulated for the purpose of replacing employees on assembly lines. Later designs went away from this model and considered only what was needed from the practical viewpoint. As the requirements for better accuracy increased, the designs were refined to the point that serial robots can — with the addition of laser cutting technology — emulate skilled artisans. Serial robots can sculpture accurate dental crowns as well.
Universal problems in serial robotics that require constant evaluation include error amplification from joint to joint, motor or actuator weight and the overall strength and stiffness. The serial robot must be strong enough to do its tasks hundreds of thousands of times but not so heavy as to slow down operations. This is especially important in a long assembly line. A minor delay can become a major problem down the line.
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