In about 1990, DSP based motion control products started allowing sophisticated motion profiling and digital communication via serial networks. Such rapid changes in technology created a breakdown in standardizing motion control products. Network protocols such as Profibus (1989), DeviceNet (1994, and Smart Distributed Systems (1994) attempted to take over the Control Area Network (CAN0 market. One of the first networks, CAN, had been around since the mid-1980's for automotive communication; it proved so versatile that it moved into the automation world in the 90's. Sercos came out in the early 90's using it's own hardware layer with fiber optic transmission lines while other proprietary networks arrived using an RS-485 hardware layer.
There's an evolution happening in the world of industrial automation. A battle between two systems, the old versus the new distributed versus centralized.
Centralized systems are the grand daddy's of motion control systems. In the days of large computers, a central motion controller would be connected to multiple amplifiers and motors located elsewhere on the machine and the signals would be sent back and forth to the controller. On small systems, this works just fine, but when you have larger systems of axis, there is a problem with the amount of wiring. The large amount of wiring not only takes up spaces but makes it more difficult to trouble shooting any problems in the system.
As computers have become smaller and faster, distributed systems have began to emerge. These systems have moved the controller next to the axes, while being more costly, it does reduce the amount of cabling required but it may be more difficult to synchronize motion across axes. These issues have led to the next evolution in distributed systems that of flexible distributed motion control Now, instead of one controller looking after one axis, we now have one controller looking after a small number of axes, essentially creating islands. The controllers of these islands are then connected to each other. With a smaller number of axis per controller, this approach further reduces cabling and speeds up maintenance.
There's no right or wrong to these systems, it depends on the project you're building, but as controllers get smaller and it becomes easier to remotely manage the from afar, the trend is moving towards flexible distributed motion control.