Serial manipulator
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Serial manipulators are by far the most common industrial robots. Often they have an anthropomorphic mechanical arm structure, i.e. a serial chain of rigid links, connected by (mostly revolute) joints, forming a "shoulder", an "elbow", and a "wrist". Their main advantage is their large workspace with respect to their own volume and occupied floor space. Their main disadvantages are
- the low stiffness inherent to an open kinematic structure
- errors are accumulated and amplified from link to link
- the fact that they have to carry and move the large weight of most of the actuators
- the relatively low effective load that they can manipulate
From rigid body motion it is known that it requires at least six degrees of freedom to place a manipulated object in an arbitrary position and orientation in the workspace of the robot. Hence, many serial robots have six joints. However the most popular application for serial robots in today's industry is pick-and-place assembly. Since this only requires four degrees of freedom, special assembly robots of the so called SCARA type are built.
[edit] Kinematics
The position and orientation of a robot's end effector are derived from the joint positions by means of a geometric model of the robot arm. For serial robots, the mapping from joint positions to end-effector pose is easy, the inverse mapping is more difficult. Therefore, most industrial robots have special designs that reduce the complexity of the inverse mapping.
