VN0010 - Mirror Vibration Evaluation Procedure (GMW14201)

Technical Notes

Author Ryan Quellet

Abstract

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GMW14201 specifies a rearview mirror performance test approved by General Motors Worldwide. It is a rotational vibration measurement test for inside and outside automotive rearview mirrors and measures the mirror’s rotational response when subjected to vertical input vibration.

QUESTION

How do I perform a test that meets GMW14201?

ANSWER

Required Tools

The following are the tools Vibration Research recommends for conducting the test:

  • GMW14201 specification from General Motors Corporation
  • VR9500 or VR10500 vibration controller
  • RandomVIEW software test module
  • RecorderVIEW waveform recording option
  • MATLAB 7(r14) or newer and GMW14201 MATLAB script
  • Three (3) lightweight single-axis matched 100 mV/g accelerometers with low transverse sensitivity
  • One (1) shaker control accelerometer
  • One (1) shaker with fixturing capable of running the specification

Running the Test

The standard instructs the test technician to mount three accelerometers on the mirror’s reflective surface in a triangular pattern. The technician should measure and document the distance (m) between each of the accelerometers. In the VibrationVIEW software, they can enter the values into a form for later calculations.

Figure 1 lays out the shaker setup and location of the lens accelerometers.

car mirror mounted on shaker

Figure 1. Test setup. Copyright of GMC.

Next, the standard instructs the technician to mount the mirror assembly to a rigid fixture on a shaker head. The specified random test profile shakes the mirror vertically. As the test runs, VibrationVIEW can use the RecorderVIEW module to record the values of the input and response accelerometers at a high sample rate.

Post-process

After the test ends, the technician must compute the total angular acceleration spectrum of the mirror rotation setup. They can do so using a custom MATLAB script. The accelerometers are arranged so that the difference in acceleration between two accelerometers divided by the distance between them determines their angular acceleration (rad/s2).

Figure 2 is a 2D representation of the triangular array in Figure 1. X1, X2, and X3 represent the readings of the three physical accelerometers in Figure 1. X4 is a virtual, estimated accelerometer. A13 and A24 in Figure 2 denote the angular acceleration calculated between points 1 and 3 and 2 and 4, respectively. A13 represents the yaw of the mirror, and A24 represents its pitch.

2-D representation of the triangular array

Figure 2. Mirror rotation setup schematic. Copyright of GMC.

Test Results

The MATLAB script outputs a series of graphs. One is Transmissibility vs. Frequency, and the other is Rotation vs. Frequency.

Transmissibility vs. Frequency graph

Transmissibility vs. Frequency

Rotation vs. Frequency graph

Rotation vs. Frequency

If you are interested in running the GMW14201 specification with the recommended tools above, please contact Vibration Research Corporation’s sales department at vrsales@vibrationresearch.com.

Last updated: August 2, 2022.

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