Caution: Input 15 A peak, 3.75 A continuous.
2.2.4 Lead Screw
The lead screw, shown by ID #4 in Figure 2.1, circulates through a ball nut, component #5 in Figure 2.1, that is
attached to the bottom of the shake table stage and is rotated by the motor. The lead screw has a pitch of 0.50
inches. Thus the shake table stage moves 0.50 inches, or 1.24 cm, per single ball-screw revolution.
Caution: Exposed moving parts.
2.2.5 Encoder
The encoder is embedded inside the DC motor and is used to measure the linear position of the stage. It cannot be
identified externally. The motor encoder has a resolution of 2048 lines per revolution. In quadrature mode this gives
8192 counts per full rotation motor shaft rotation. The effective resolution, i.e., minimum linear position that can be
detected, of the stage displacement is 3.10 µm.
2.2.6 Linear Bearing Block
For smooth motion, the stage is fitted with low friction linear ball bearing blocks, shown by ID #8 in Figure 2.1, that
glide on two ground hardened shafts, identified by component #7 in Figure 2.1.
2.2.7 Limit Switches
These Right, Home, and Left, proximity sensors are shown in Figure 2.1 with ID #10, 11, and 12, respectively.
The Left or Right limit switches get triggered when the top stage moves close to the left or right mechanical range.
Similarly, the Home sensor is set to high when the top stage is at the mid-stroke or center position. These sensors
are used to deactivate the power amplifier for safety as well as for calibrating the stage to its center position.
2.2.8 Accelerometer
A dual-axis ADXL325 accelerometer is mounted underneath the stage of the Shake Table II to measure the acceler-
ation of the stage in both the x and y directions. It is shown with ID #15 label in Figure 2.1. The sensor has a range
of ±10 g and its noise, in the operating range of the shake table, is approximately ±5.0 mV, i.e., ±5.0 mg. The
analog sensor is calibrated such that 1 V equals 1 g, or 9.81 m/s
2
. See the ADXL325 accelerometer specification
sheet [1] for more details.
Caution: The accelerometer readings can be misleading and lead to unexpected results. Please use caution
when using them as they are generally used as indicators.
STII User Manual
v 3.1
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