Control of resonant vibration in a spring-fatigue-testing instrument

The paper describes the design and implementation of control systems in an instrument for the fatigue testing of springs. A manual control system is used to establish a spring in a condition of mechanical resonance at a chosen amplitude of vibration, and an automatic control system is used to maintain this condition throughout the duration of a fatigue test. The problem of measuring the vibration amplitude is described, and the nature of the problem of controlling a resonant spring is discussed. For automatic control, an algorithm for the simultaneous extremal control of forcing signal frequency and regulatory control of forcing signal amplitude is developed, and implemented by means of a microprocessor. The methods used may be of more general application, particularly in vibration testing, and possible design improvements for such applications are discussed.