Measurements

Table of Contents

Back to main page.

1 Experimental conditions

  • Measurement made in a metrology lab
  • The granite is not glued to the floor
  • The Y-Translation stage is powered and in closed-loop
  • The spindle is not powered
  • Mass is placed on top of the Hexapod (how much?) (figure 1).
  • Made by Marc Lesourd on the 17th of November 2017

accelerometers.png

Figure 1: Accelerometers position

instrumented_hammer.png

Figure 2: Instrumented Hammer used

2 Measurements procedure

3-axis Accelerometers (specifications table 1) are glued on (see figure 1):

  • Marble
  • Y-Translation stage
  • Tilt stage
  • top of Hexapod
Table 1: Pieozoelectric acc. 356b18 - 3 axis
Sensitivity 0.102 V/(m/s2)
Measurement Range 4.9 m/s2 pk
Frequency Range 0.5 to 3000 Hz
resonant frequency >20000 Hz
broadband resolution 0.0005 m/s2 rms

The structure is excited using an instrumented hammer with impacts on (see figure 2):

  • Marble
  • Hexapod

3 Measurement Files

Two measurements files are:

  • id31_microstation_2017_11_17_frf.mat that contains:
    • freq_frf the frequency vector in Hz
    • Computed frequency response functions (see table 2)
  • id31_microstation_2017_11_17_coh.mat
    • Computed coherence

For each of the measurement, the measured channels are shown on table 3.

Table 2: Description of the location of direction of the excitation for each measurement
Object name Location Direction
frfhexax Hexapod X
frfhexay Hexapod Y
frfhexaz Hexapod Z
frfmarblex Marble X
frfmarbley Marble Y
frfmarblez Marble Z
Table 3: Description of each measurement channel
Ch. nb Element Location Direction
1 Not wired na na
2 Accelerometer Marble X
3 Accelerometer Marble Y
4 Accelerometer Marble Z
5 Accelerometer Ty X
6 Accelerometer Ty Y
7 Accelerometer Ty Z
8 Accelerometer Tilt X
9 Accelerometer Tilt Y
10 Accelerometer Tilt Z
11 Accelerometer Hexapod X
12 Accelerometer Hexapod Y
13 Accelerometer Hexapod Z

4 Data Analysis

4.1 Loading of the data

load('./raw_data/id31_microstation_2017_11_17_coh.mat',...
     'coh_hexa_x',...
     'coh_hexa_y',...
     'coh_hexa_z',...
     'coh_marble_x',...
     'coh_marble_y',...
     'coh_marble_z');

load('./raw_data/id31_microstation_2017_11_17_frf.mat',...
     'freq_frf',...
     'frf_hexa_x',...
     'frf_hexa_y',...
     'frf_hexa_z',...
     'frf_marble_x',...
     'frf_marble_y',...
     'frf_marble_z');

4.2 Pre-processing of the data

The FRF data are scaled with the sensitivity of the accelerometer and integrated two times to have the displacement instead of the acceleration.

accel_sensitivity = 0.102; % [V/(m/s2)]
w = j*2*pi*freq_frf; % j.omega in [rad/s]

frf_hexa_x =  1/accel_sensitivity*frf_hexa_x./(w.^2);
frf_hexa_y = -1/accel_sensitivity*frf_hexa_y./(w.^2);
frf_hexa_z = -1/accel_sensitivity*frf_hexa_z./(w.^2);

frf_marble_x =  1/accel_sensitivity*frf_marble_x./(w.^2);
frf_marble_y =  1/accel_sensitivity*frf_marble_y./(w.^2);
frf_marble_z = -1/accel_sensitivity*frf_marble_z./(w.^2);

4.3 X-direction FRF

marble_x_frf.png

Figure 3: Response to a force applied on the marble in the X direction

hexa_x_frf.png

Figure 4: Response to a force applied on the hexa in the X direction

4.4 Y-direction FRF

marble_y_frf.png

Figure 5: Response to a force applied on the marble in the Y direction

hexa_y_frf.png

Figure 6: Response to a force applied on the hexa in the Y direction

4.5 Z-direction FRF

marble_z_frf.png

Figure 7: Response to a force applied on the marble in the Z direction

hexa_z_frf.png

Figure 8: Response to a force applied on the hexa in the Z direction

Author: Thomas Dehaeze

Created: 2019-03-15 ven. 11:41

Validate