Slide
9
The
sketch is a schematic of the machine with a sample gripped between
the top grip and the bottom grip. The portion above the top grip
shows the fixed crosshead. The RVDT and the hydraulic servo valve
are connected to the rotary actuator. The first step is to apply
a command signal, in our case a desired rotation. The command signal
goes to a comparator where the actual rotation of the machine is
compared with the command signal. This generates the error signal.
The error signal is the desired rotation subtracted from the actual
rotation. The error signal is fed to the controller. The controller
then generates a current and sends it to the servo valve. Depending
on sign and intensity of the current, the servo valve adjusts the
flow of hydraulic fluid to the actuator in order to move the actuator
closer to the desired rotation, i.e. to minimize the error signal.
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