Six Degrees-of-Freedom Control Technology
The MAST System's 6-DOFs (vertical, lateral, longitudinal, yaw, pitch, and roll) are driven by a sophisticated MTS controller. The controller seamlessly converts controls in six degrees-of-freedom space into drive commands for each of the eight actuators, accounting for geometric nonlinearity. A key feature of the controller is the ability to rotate the X-Y axes about the Z axis to simplify specimen tested on a diagonal.
The controller provides mixed-mode control, which allows each DOF to be controlled either in displacement or force control. Moreover, the controller can slave any DOF to any combination of other DOFs. This technology opens up a wide range of testing possibilities. For example, the mixed-mode control features can be used to specify a lateral displacement history in the horizontal plane while maintaining a constant gravity load or varying axial load on the subassemblage to simulate overturning load effects.
In addition, moments can be controlled about orthogonal axes to simulate specified moment-to-shear ratios that would correspond to assumed lateral load distributions on the structural subassemblage. Rotation or moment about the vertical axis can be controlled to eliminate or simulate limited torsional effects on the test structure. Furthermore, the MAST System can test planar assemblies in a straightforward manner, which in traditional laboratory setups often requires cumbersome ancillary lateral framing schemes to constrain out-of-plane effects. At the MAST Lab, the 6-DOF control can be used to eliminate out-of-plane deformations.
Hydraulic Control Computer (HCC)
Hydraulic control software (HCC) was developed in-house as the principal means of controlling the MAST System actuators. The HCC interfaces with the control software provided by MTS Systems to present a heads-up display of the system status and to enable control of the system using a ramp and hold protocol.
The target endlevels describing the new position or force level of the crosshead and ancillary actuators are input along with the time period to reach those levels. The MAST System operator then sets the move command and ramp function in order to achieve the desired endlevels.
Features of HCC include:
Heads-up status display that puts key system information into an easily understood format:
- Feedbacks (crosshead DOFs, ancillary and individual actuators)
- Errors (crosshead DOFs, ancillary actuators)
- Crosshead shear and warp
- Limit detector settings
- Modes (interface also supports mode switching)
- Slaving matrices
Target endlevels may be input from several sources:
- Operator console input
- Read pre-determined endlevels from a file
- A single, consistent user-defined coordinate system is provided throughout the test.