Rotary Encoders for Servo Drives with Improved Control Quality and Integrated Safety Technology

HEIDENHAIN has provided its new ExN 1300 series rotary encoders with EnDat 2.2 interface and new optoelectronic scanning and evaluation electronics. Unlike the components previously available on the market, these encoders are prepared for safety technology with purely digital data transmission. This change has no effect on the dimensions of the encoders, so that no mechanical modification is required.

Encoders built into servomotors can become contaminated by traces of oil from the bearing, dust from the breaks, and gases from the motor windings. However, the encoder's tolerance to contamination in the area of the optical scanning is essential for the signal quality of the encoder and therefore the control quality of the drives. The use of the new scanning and evaluation electronics significantly improves reliability under the influence of contaminants and increases the encoder's accuracy.

The unconditioned signals are processed directly and converted to digital information. The optimized scanning and internal compensation improve the quality of the internal signals by a factor of 4 to 5. This is why reliable 14-bit interpolation is now possible in the chip. The new scanning technique by itself without digital signal compensation reduces the interpolation error by half. This means that the elaborate and cost-intensive interpolation in the subsequent electronics can be dispensed with, and the transmission is hardly influenced by outer noise. This manner of combining scanning and evaluation electronics with integrated safety technology is unique among the solutions now offered on the market. An improved signal quality and the decrease of thermal influence over the entire temperature range make it possible to increase control loop performance and reduce velocity fluctuation.

Rotary encoders for electrical drives measure the rotary movement of synchronous servomotors. These data, usually absolute, are transferred to the subsequent electronics for use in control and positioning.

With the EnDat 2.2 serial interface, data is transmitted without carrying analog signals at the same time, which results in high noise immunity. There is no need for interpolation in the subsequent electronics. At the same time, cables with six lines and single shield reduce cost. The system costs are reduced by up to 50%, depending on the cable length.

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