Command Languages

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Authored by: Mark F. Russo

Most automated instruments are complex assemblies of a variety of individual components including motors, actuators, sensors, pumps, structural parts, and other equipment. Coordinating the actions of an instrument rarely involves the direct control of its parts. Instead, instrument manufacturers provide some form of command language that ensures the instrument's components operates in a coordinated manner. A command language includes a set of functions that instructs the instrument to perform actions at a higher conceptual level.

A good example of this is the way that a typical articulated robot is programmed to move from place to place within its work envelope. Articulated robot arms come with many options, but all share a common configuration that involves a series of linkages connected end-to-end with rotational or linear motors connecting endpoints. Usually found on the last linkage is a tool designed to manipulate the robot's environment, referred to as its end effector. The most common form of end effector used with articulated laboratory robots is a gripper, which is designed to grasp a container or other object being manipulated by the robot. The gripper must be moved through the robot's work envelope in straight lines or smooth arcs to ensure that the object is handled with care, avoiding unwanted behavior such spillage, collisions, or other damage. Achieving smooth movements can require complex coordinated control of the motors and actuators connecting the robot's linkages. Fortunately, it is standard practice for articulated robot controllers to perform these kinematic computations automatically.

Articulated robot command languages almost always include a command that instructs the robot to move its end effector along a well-defined trajectory to a predetermined location in space. To achieve this motion it is likely that the individual motors that make up the robot will each execute a nonlinear kinematic profile over time that varies speed and direction. When all motors are carefully synchronized, the cumulative effect is the motion of the end effector along the desired trajectory.

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