Black Boxes

Another older approach, but still very-much used today, is the standalone drive. In this architecture the controller is a box, either rack-mounted, or standalone on the floor. It is often, but not always, a single axis device.

Figure 2 shows the configuration of this architectural approach. In this scheme programming tends to be PLC-oriented, with lots of digital inputs and outputs. Alternatively many boxes allow you to download a complete motion program, generally using some sort of vendor-specific language.

Stand-alone drives work well when the behavior of each axis is fairly simple, and more or less autonomous. For example it is easy to perform functions such as electronic gearing, or motion sequences such as “when PLC input 3 goes high, start profile number 7.” It is difficult though, to synchronize multiple axis to perform coordinated actions.

Relative to motion cards, standalone drives have an advantage of simplified wiring, since the connections between the “motion computing” function and the amplifier function of the controller are internal to the drive. Another advantage is that drives can be located close to the motor or actuator. This reduces cable lengths and improves reliability.

A disadvantage of these devices, at least historically, is that their programming tends to be a bit clunky. They are designed to be externally controlled by PLC, or alternatively, using vendorspecific downloadable languages. It is rare to find a stand-alone drive that can be programmed in standard languages such as C, Java, or even Visual Basic.