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09/11/2009
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Tom Shelley reports on a pick and place robot that can achieve high speed and accuracy by using arc shaped linear motors
 A novel very high speed mechanical handling robot derives its power, speed and positional accuracy from the use of two linear and two large curved linear motors. This remarkable machine was demonstrated on B&R Industrial Automation's stand at the recent Processing and Packaging Machinery Association show at the NEC in Birmingham.
Garry Siddon of B&R said the robot, called Galileo Sphere, was made by the Italian company Motor Power. Using curved linear motors, as opposed to conventional motors and gearboxes, allows very fast movements without backlash and the total elimination of energy normally lost as heat produced by meshing gears. Curved linear motors are not in themselves a new idea – they have been used in hard disk drives for years. They are also used to produce slow, smooth movement in medical scanners.
While they do not deliver as great a force as conventional motors driving through a speed reduction gearbox, their inherent lack of backlash and accuracy, fast acceleration and lower maintenance requirements offer many attractions. The curved track motors developed and made by Motor Power use iron core direct drive technology, with either three coils mounted on the outside of a magnet track, or three coils mounted on the inside. Another option is three coils on the outside and three coils mounted opposite them, making six coils in all. The modular design of the coils allows more units to be added on a single magnetic track, giving a final torque proportional to the number of coil modules. Conversely, the company also offers motors in which the coils are fixed, and the magnetic track moves.
These are generally recommended for systems with rotations of more than 360º. Siddon says that B&R wrote the control software and supplied the servo drives for the four main axes. The most prominent are the two curved motors on the outside. One, with three coils spaced at 120º, provides 360° rotation about a vertical axis. Dynamic torque is from 338Nm to 1320Nm. Rotation about the horizontal axis of the gripper assembly is achieved by a second curved linear motor, which delivers either 220Nm or 440Nm torque through 106º. In the Galileo Sphere, there are two more conventional ironless linear motors. These move two carbon fibre reinforced composite shanks that act on a linkage supporting a single rotary axis that carries the gripper.
These two linear motors deliver 150N or 300N. Depending on the robot model and the forces delivered by the various linear motors, it is possible to handle a payload of up to 8.8kg, in which case the pick and place cycle rate can be 20 per minute. If the load is very low – 700g or less, it can be as much as two per second. The unusual geometry allows work within a space that has a diameter of 1.9m, with a vertical reach of 0.4m. Precision and repeatability with a 1kg payload is 75 to 100µm, made possible through a relatively light construction. There is no need for cantilevered arms, supporting other cantilevered arms with weights and the inertias associated with heavy motors and gearboxes at each joint. Main applications are seen in assembly, material handling, packaging, picking, sorting and dispensing. The curved linear motors made by Motor Power are used in pharmaceutical handling machines, labelling carousels and capping machines.
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Author
Tom Shelley
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