Material handling, in most cases, refers to operations where components are moved between processes with little or no value added during the transition. In other words, there are no changes to the form, shape, or content of the materials being moved. As a result, material-handling interval times should be kept to a minimum. Other important considerations for material-handling operations include product stability (how the products are maneuvered or gripped), accuracy (how accurately the are positioned), and environment (clean room, wash-down, high heat, etc.)

How does a typical material-handling operation work?

There are three main components in a material-handling (MH) system: a controller, a motor or engine that converts energy into motion, and a mechanical system that employs the energy to perform a useful function. The controller, power device, and mechanical system could be any of a number of combinations.

A MH system's CPU or controller monitors operator input and feedback signals, using the information to control the power devices that generate the motion. Feedback signals typically include the output from discrete sensors on the ends of the travel, as well as position (from proximity sensors and encoders), force, torque, and time measurements.

What are the primary types of motion encountered in materialhandling applications?

Material-handling systems involve all sorts of motion. Some applications require the motion axes to operate independently, achieving point-to-point motion. Typically, the motion profile (velocity vs. time) is trapezoidal or triangular.

The acceleration profile for the standard trapezoidal move (the derivative of velocity vs. time) is usually characterized by abrupt step changes. One way to smooth the reactions from acceleration is S-curving. S-curve acceleration can accomplish a move in the same amount of time as trapezoidal, but without the jerking associated with the step changes. This allows products to move more smoothly, which is easier on the mechanics of the machine and sometimes critical for successful material handling.

In other MH applications, the axes are coordinated with each other in either linear or circular movements. In coordinated motion, all of the axes start and stop at the same instant, typically on the same interrupt or within microseconds of one another. The resulting 'path' of motion traces out a straight line (for a linear move) or an arc (for a circular move).

In a circular coordinated move, the individual axes move in sinusoidal relationship. For example, the X-axis motion may be a sine wave, and the Yaxis a cosine wave. The resulting path is an arc. Sometimes velocity is S-curved or ramped to its final value for smoother operation.

Yet another type of motion encountered in material handling is master-slave profiling, including velocity ratioing, gearing, and camming. On a gantry, for example, the motion on one side would be "geared" to the motion on the other to prevent twisting or skewing.

Some material-handling applications involve a mix of independent, geared, and linear/circular axes all on the same machine.