Articulated robots win points for flexibility and dexterity.

Position:Robotics - Cover story


Te need for automation and robotics grows stronger every day as labor costs rise and competition from low-wage overseas locations intensifies. At the same time, today's product lifecycles are becoming shorter and the demand for customization and subsequent part complexity grows greater. Many products (not to mention their components) are becoming smaller and tolerances tighter. Flexible, controlled automation often is the only way to guarantee production efficiency and high quality.

As a result of the advancements of automation in general and robotics in particular, the assembly process is faster, more efficient, and more precise than ever before. Fortunately, as each new generation of robot technology is introduced, speed and performance improve and costs decrease. Automation and robotics, therefore, become more affordable and valuable to the manufacturer.

Conventional wisdom of the past steered some assemblers to the Cartesian coordinate robot, which consists of an orthogonal-axis structure.

"Two- and three-axis non-servo Cartesian devices have a lot of components like cylinders, solenoids, tubing, and switches," explains James C. Cooper, distribution network account manager for FANUC Robotics America Inc. "This complexity leads to several points of potential failure, but that can all be replaced by one of our robots, at a significantly higher mean time between failure, which is now 78,000 hours for our robots."

The current most popular robotics solution for assembly is the four-axis SCARA robot arm, which can move to any X-Y-Z coordinate within its work envelope. There is a fourth axis of motion, which is the wrist rotation. The X, Y, and roll movements are obtained with three parallel-axis rotary joints. The vertical Z motion is usually an independent linear axis at the wrist or in the base. SCARA robots are typically used in 2-D assembly operations where the final move to insert the part is a single vertical motion. Component insertion into printed circuit boards is an example. SCARAs are very common in pick-and-place, assembly, and packaging applications.

"You could do a specific pick and place with a pneumatic mechanism, but if you get into an application where you needed to possibly shift the part or rotate the part, then you're adding two or more mechanisms together," says Mike English, president of the Warwick, RI-based integrator Interplex Automation. "With how robot prices have come down so much over the years, I could design and build a pick-and-place unit and by the time I put all the slides together and make or buy adaptor plates, put sensors on the mechanism, assemble it, wire it, plumb it, and add up my raw material cost and my labor cost, it's about the same as what a robot's going to cost. With a robot, you just bolt it to a table, program it, and it's ready to go."

The advantages of a vertically articulated robot compared to a...

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