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What is a Parallel Robot?

Nick Oza
Nick Oza

A parallel robot, also called a parallel manipulator, is a mechanism presenting very good performance in terms of stability, rigidity and accuracy to manipulate large loads. Parallel robots consist of three or more rotary or prismatic axes that function parallel to each other. They have been used in a number of applications such as flight simulators and astronomy, and they are growing in popularity in the machine-tool industry. Some examples of these types of robots are delta, hexapod and tricept robots.

Theoretical works by English and French geometricians that are related to parallel mechanisms, and in particular hexapods, date back many centuries. Homer described walking tripods in his epic work The Illiad. Aristotle envisioned such mechanisms that obeyed the will of others. The first parallel robot came only 17 years after the term "robot" was coined in 1921. Designed for automated spray painting, it is generally considered to be the first industrial parallel robot designed.

Woman holding a disc
Woman holding a disc

When it comes to robotics, an end effector is a rigid body at the end of a robotic arm. For each link of a robot, the connection degree is the number of rigid bodies attached to the link by a joint. In closed-loop kinematic chains, one of the links, but not the base, possesses a connection degree greater than or equal to three. Parallel robots are mechanisms where the end effector is connected to the base through several kinematic chains forming a closed loop.

Since the end effector of a parallel robot is supported in several places, this results in high structural stiffness. A number of legs connect the end effector to a base platform. Construction of a parallel robot is light. These features allow parallel robots to be capable of a wide range of motion. Their major drawback, however, is that they have a limited workspace because the legs can collide.

Used more frequently for industrial purposes is a robot known as a serial manipulator. It is constructed in such a way as to form the shape of an elbow, wrist and a shoulder. One of the major advantages of serial manipulators over parallel robots is their large workspace. Serial manipulators are the most common type of industrial robots.

Advances in robot kinematics, the study of the motion of robots, have led to applications in various fields, including surgery, manufacturing, locomotion and biomechanics. Robot kinematics can be divided into mobile robot kinematics, humanoid kinematics, parallel robot kinematics and serial manipulator kinematics. Analyses of the velocity, acceleration and position of all of the links are calculated without taking into consideration the forces that cause the motion.

Another application of parallel robots is in high speed, high-accuracy positioning. An example of this is in the assembly of printed circuit boards. A parallel robot can also function as a micro manipulator for serial manipulators by being mounted on the end effector.

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