With the assortment of robots available on the injection molding market, sifting through the choices can be daunting. Unlike other equipment, robots are not easily classified and evaluated: different axes, stroke lengths and inconsistent specifications, as well as limited industry standards make comparisons difficult.

      The prospective buyer can make an informed decision with the aid of a few guidelines. To effectively compare the different offerings, begin with the basics; and by understanding the fundamentals, you are well on your way to intelligently selecting a robot.

How much stroke

      The distance a robot travels, known as its stroke, depends upon the size of the part, its drop location and the dimensions of the machine. For simplicity, this distance is generally defined in terms of three axes: for this discussion we will use X, Y and Z.

      X-Axis. This distance, typically called the kick stroke, depends upon part depth. To handle a pail, for instance, a robot requires sufficient stroke to reach out and pull the pail from the mold.

      Y-Axis. Defined as vertical stroke, this distance is determined by machine height and desired drop height; i.e., the robot must be high enough to have the part clear the machine gates, yet low enough to drop the parts at a reasonable height from the floor.

      Z-Axis. Traverse stroke depends on whether the robot drops the parts at the side of the machine or behind it. Part of this stroke is used just to clear the machine.

      The easiest way to determine the required stroke is by a layout drawing. Layouts not only define each stroke but also describe other items of interest on the floor plan, such as auxiliary equipment, support pillars and clearance areas.

      Payload is the weight handled by the robot and is defined as the weight of the parts plus the weight of the end-of-arm-tool. Part weights are often known for a given application; however, the end-of-arm-tools are not. End-of-arm-tool weights are estimated and can be obtained from...         

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