Measurements

Experimental conditions
Measurements procedure
Measurement Files
Data Analysis
Results

Experimental conditions

Date	2017-11-17
Sensors	Accelerometers
Excitation	Instrumented Hammer
Location	Laboratory

Dynamics of the station is evaluated using instrumented hammer and accelerometers fixed on each stage.

Goal:

Obtain a first estimation of resonance frequencies

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 fig:accelerometers).
Made by Marc Lesourd on the 17th of November 2017

/tdehaeze/nass-micro-station-measurements/media/commit/4020b2bef46942107b434e16683b6628827db3ed/2017-11-17%20-%20Marc/figs/accelerometers.png — Accelerometers position

/tdehaeze/nass-micro-station-measurements/media/commit/4020b2bef46942107b434e16683b6628827db3ed/2017-11-17%20-%20Marc/figs/instrumented_hammer.png — Instrumented Hammer used

Measurements procedure

3-axis Accelerometers (specifications table tab:accelerometer) are glued on (see figure fig:accelerometers):

Marble
Y-Translation stage
Tilt stage
top of Hexapod

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

Pieozoelectric acc. 356b18 - 3 axis

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

Marble
Hexapod

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 tab:data_name)
id31_microstation_2017_11_17_coh.mat
- Computed coherence

For each of the measurement, the measured channels are shown on table tab:meas_channels.

Object name	Location	Direction
frf_hexa_x	Hexapod	X
frf_hexa_y	Hexapod	Y
frf_hexa_z	Hexapod	Z
frf_marble_x	Marble	X
frf_marble_y	Marble	Y
frf_marble_z	Marble	Z

Description of the location of direction of the excitation for each measurement

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

Description of each measurement channel

Data Analysis

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');

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);