Protective drive-level limiter for an electro-hydraulic vibrator

Claim 2

An automatic protective drive-level limiting network for use with a seismic vibrator of the type having a ground contacting base plate coupled to a hydraulically-driven linear actuator that is controlled by an electrohydraulic servo mechanism consisting of at least a main servo valve having a valve spool, coupled in series with a pilot valve controlled by an electrical current-driven torque motor that is responsive to an input reference driver signal, said actuator and said valve spool having mechanical displacement limits, comprising: means for generating first and second error signals when said valve spool and said actuator approach their respective mechanical displacement limits within a predetermined clearance; means for monitoring the current flow through said torque motor; means coupled to said monitoring means for generating a third error signal when said current flow in said torque motor exceeds a preselected upper limit; and means coupled to said error signal generating means for attenuating said input reference driver signal as a function of the larger of said first, second, and third error signals.

Claim 3

An automatic protective drive-level limiting circuit for use with a seismic vibrator having a ground-contacting base plate that is reciprocatingly driven by a hydraulic linear actuator that is controlled by an electro-hydraulic servo device consisting of at least a main servo valve, having a valve spool, coupled in series with a pilot valve that is controlled by a current-actuated torque motor in response to a driver signal, having a preselected level, provided by a driver signal generator, said linear actuator and said valve spool having mechanical displacement limits, comprising: first means for generating a first signal having a level proportional to the displacement of said linear actuator; second means for generating a second signal having a level proportional to the displacement of said valve spool; third means for generating a third signal having a level proportional to the current flow through said torque motor; means for comparing said first, second and third signal levels with a threshold signal level to define first, second and third error signals; means for selecting the largest one of said first, second and third error signals; and means for scaling said driver signal by an amount sufficient to reduce said largest error signal level to zero.

Claim 4

An automatic protective drive-level limiting circuit for use with a seismic vibrator having a ground-contacting base plate that is reciprocatingly driven by a hydraulic linear actuator that is controlled by an electro-hydraulic servo device consisting of at least a main servo valve, having a valve spool, coupled in series with a pilot valve that is controlled by a current-actuated torque motor in response to a driver signal, having a preselected level, provided by a driver signal generator, said linear actuator and said valve spool having mechanical displacement limits, comprising: first means for generating a first signal having a level proportional to the displacement of said linear actuator; second means for generating a second signal having a level proportional to the displacement of said valve spool; third means for generating a third signal having a level proportional to the current flow through said torque motor; means for comparing said first, second and third signal levels with a threshold signal level to define first, second and third error signals; means for selecting the largest one of said first, second and third error signals; and means for scaling said driver signal by an amount sufficient to reduce said largest error signal level to zero.

Claim 5

The automatic protective drive-level limiting circuit as defined by claim 2, wherein said first, second and third signal generating means each comprises: gain-conditioning means for normalizing the levels of said first, second and third signals respectively to a common reference level.

Claim 6

The automatic protective drive-level limiting circuit as defined by claim 3, wherein said comparing means comprises: threshold-detecting means, coupled to said gain-conditioning means, for determining, as an error signal, the excess of any one of said first second and third signal levels over a limiting safe value for any one of the parameters of spool displacement, actuator displacement and torque-motor current flow; and integrating means, coupled to said threshold-detecting means, for filtering each said error signal with respect to time, said integrating means having a short attack time constant and a longer release time constant.

Claim 7

The automatic protective drive-level limiting circuit as defined in claim 4, wherein the scaling means comprises: attenuating means, interconnected between said driver-signal generator and said torque motor, and further coupled to said error-signal selecting means, which in turn is coupled to said integrating means, for reducing the driver signal level as an inverse function of said largest error signal.