The recent trend in has been to reduce cost, size and complexity of servo systems while increasing performance. High-end machining has always used the best the industry had to offer, but increasingly we are seeing a demand for higher speeds and accuracy in the small/economy machine market. Using a proprietary servo interface and high-speed components offers a higher level of performance for less cost than ever before. Servo control and amplifier advances The ever-increasing speeds of DSPs and extremely high-resolution feedback devices have increased performance without increasing the price. Today's servo systems close all three servo loops within the CNC control, which use a high speed DSP per 2 axes (4 w/series 3xi) of control and a million count/rev encoder (an optional 16 million count is available) for servo control. This not only allows for a very fast update rate, it also tightly integrates the servo with the CNC control. This level of integration and speed is possible by using a proprietary high-speed serial communication system over fiber optic cables like the Fanuc Serial Servo Bus. It provides serial communication between up to 16 servo amplifiers and the CNC control.

Fiber optics can handle large amounts of data and are completely immune to electrical noise, thus allowing devices to be separated by large distances without risk. A bidirectional communication cable between the high-resolution serial encoders on the Alpha is and Beta is servomotors, and the drive amplifier is used for secure data transfer. The use of a full serial communication system eliminates the risk of false feedback and command data, which is a common cause of error, or worse, servo runaway.

With a serial communication system an error can only result in a system alarm and a safe shutdown. Servo architectures that are common across the entire product line allow for high speed machining functions and servo tuning flexibility that are impossible with analog command and feedback systems. In an analog command drive, the drive uses a +/- 10VDC signal to produce a velocity command to the motor. These systems may be full analog or use digital amplifier circuitry but must have the current and velocity loops tuned at the amplifier. While the position loop and any motor matching must be tuned at the CNC.

The flexibility and tuning options of this system are severely limited because the CNC functions and amplifier functions are separated. Only an analog output command and position feedback is exchanged. Any additional information requires hardwired I/O, adding wiring complexity to the system. In addition, digital servo systems utilizing analog command voltage have inherent error produced by the use of a digital to analog converter on both ends.

The process of converting digital to analog then back to digital creates scaling error, limited resolution, axis drift and also limits the update s