Abstract: A seismic shaker for exercising an excitation force on the ground has a base plate and a reaction mass connected to the base plate via a resilient structure and an actuator parallel thereto. A first comparison unit sends a difference signal which is the difference between a displacement measured by a displacement sensor and a set value of the displacement. A control unit calculates a correction value as a function of this difference signal, and sends it to a second comparison unit, which adds the correction value to a value of the excitation force to be exerted set in the second comparison unit. This second comparison unit is connected to a controller unit which controls the actuator. At Low frequency this position control will track the ground force through the position set-point. The position feedback loop will be able to suppress the interfering force of the spring and any hysteresis.

Abstract: A seismic shaker for exercising an excitation force on the ground has a base plate and a reaction mass connected to the base plate via a resilient structure and an actuator parallel thereto. A first comparison unit sends a difference signal which is the difference between a displacement measured by a displacement sensor and a set value of the displacement. A control unit calculates a correction value as a function of this difference signal, and sends it to a second comparison unit, which adds the correction value to a value of the excitation force to be exerted set in the second comparison unit. This second comparison unit is connected to a controller unit which controls the actuator. At Low frequency this position control will track the ground force through the position set-point.