Frequency Response of our Motion Base Servo
The Engineering Team at Servos & Simulation, Inc., has analyzed the performance of one of our motion base designs. The plots for the performance show the maximum position as a function of frequency, the maximum velocities as a function of frequency, and the maximum accelerations as a function of frequency. The servo has an inner rate loop using the encoder on the motor for feedback allowing the servo to have a bandwidth of more than 40 Hz. The outer loop is a position loop with a bandwidth of 4 Hz. The position loop gain is limited by the gain available in the drive amplifier (power amplifier that drives the motor). Servos’ engineers add electronics to the servos and increase the gain by at least a factor of 4 which increases the position loop bandwidth to 16 Hz.
The structure of the motion base is stiff enough that it does not limit the bandwidth of the position loop. This includes the motor/gearbox. Since the structure is stiff, the bandwidth does not need to be limited to less than 16 Hz. The backlash in the gearboxes has been reduced to almost zero. This is necessary since at high frequency the motor movement is quite small. If the gearboxes had any significant backlash, the gearbox output shaft would not move. Servos’ engineers reworked the stock gearmotors to successfully remove the backlash from the gearmotors.
Another set of plots shows the motion base performance with a 16 Hz position loop bandwidth. As can be seen from the plots, the high frequency response is much better with a 16 Hz bandwidth than with a 4 Hz bandwidth.
In these cases, the roll velocity is limited to 16.47 deg/sec, and the roll acceleration is limited to 230 deg/sec^2. Pitch and yaw are similarly limited. The Longitudinal velocity is limited to 15 inches/second and the acceleration is limited to 188 inches/second^2. Lateral and vertical are similarly limited. The velocity and acceleration limits can be increased within limits by changing the motors and gear ratios in the gear boxes.If you would like more information on our entire product line, please contact us at [email protected] or check out our web site at www.servos.com.
