Electro-hydraulic Servomechanisms

• Published in: Journal of electronics and control 1958-12, Vol.5 (6), p.569-592
• Main Author: PEARSON, E. B.
• Format: Article
• Language: English
• ISSN: 0368-1947
• DOI: 10.1080/00207215808953954

The additional complications of hydraulic elements have not prevented servomechanism engineers from resorting frequently in recent years to the use of high-pressure hydraulic motors in place of electric motors. The reasons for this trend are examined in relation to the performance demanded in many modern servomechanisms, particularly these in which a high natural frequency must be associated with small overall size and weight, and the methods adopted for driving hydraulic motors are described. The combination of the well-established electronic servo ' shaping ' techniques and servo amplifiers with a hydraulic motor is achieved by means of an electromechanical transducer and examples of this element are described. Some special features of hydraulic components are dealt with, such as the effects of stiction and hydrodynamic forces in piston valves, and in addition the serious destabilizing effects of the integrating action of certain hydraulic elements on a servo loop, and its reduction with subsidiary feedback devices, is referred to. Finally the pros and cons of all-electric and electro-hydraulic servomechanisms are discussed briefly, with a view to showing that the latter typo, in spite of its added complexity, is essential in many modern control systems.