Optical Characterization of Parasitic Motion in a Long-Stroke Shaker

Area of Science:

• Metrology and Instrumentation
• Mechanical Engineering
• Vibration Analysis

Background:

• Long-stroke shakers are crucial for testing, but parasitic motions introduce significant errors.
• Accurate characterization of these motions is essential for reliable calibration and performance evaluation.
• Existing methods often lack the precision or scope to fully capture complex parasitic movements.

Purpose of the Study:

• To present a novel optical scheme for simultaneous characterization of cross-axis and rotational parasitic motions in long-stroke shakers.
• To enable independent sampling of pitch, yaw, and linear displacements at high frequencies.
• To provide a method for improving accelerometer calibration accuracy and understanding shaker dynamics.

Main Methods:

• Utilized a corner cube retroreflector mounted on the shaker load table.
• Employed an optical setup to independently sample pitch, yaw, and horizontal/vertical displacements.
• Achieved sampling rates exceeding 10 kHz for dynamic motion analysis.
• Applied the scheme to a 400-mm-stroke shaker across a frequency range of 0.1 Hz to 100 Hz.

Main Results:

• Successfully measured four parasitic degrees of freedom (pitch, yaw, horizontal, and vertical displacement) simultaneously.
• Identified shaker table trajectories, revealing bowed linear guides below 0.5 Hz.
• Detected higher harmonics and hysteresis in shaker motion above 10 Hz.
• Quantified the "gravity error" in accelerometer calibration at 0.1 Hz as (1.3 ± 0.1)% of acceleration amplitude.

Conclusions:

• The optical measurement scheme is an effective tool for characterizing parasitic motion in long-stroke shakers.
• The findings provide critical data for reducing accelerometer calibration uncertainties by up to an order of magnitude.
• This method enhances the understanding of shaker dynamics, leading to improved testing accuracy and reliability.