1965-02-01

A Hybrid Digital Hydraulic Servo 650317

In many applications, control system equations are being processed in a digital computer. Digital-to-analog (D/A) converters are then used to make command signals compatible with analog final control elements. It is more desirable to design a highly integrated system which uses a digital servo and does not require D/A conversion. However, digital hydraulic servo valves have not yet been highly developed, and some types are quite complex.
It was the object of this program to design a hydraulic digital servo which uses the standard, proven two-stage electrohydraulic servo valve. This was done by having the servo valve itself perform the function of a D/A converter. It accepts digital signals in computer format and quantizes actuator velocity. Initial design studies were performed, followed by analog and digital computer studies. A breadboard unit was built and evaluated. Two main conclusions have thus far been reached:
  1. 1.
    Performance comparable to analog servo systems can be obtained with the hybrid.
  2. 2.
    The basic concept provides inherent redundancy, thus high reliability; the hybrid servo operates at reduced performance with most single failures.
Experimental as well as analytical data are presented in the paper.

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