The Find Contact function moves a stage until a predefined load variation (stop criteria) is measured by the load cell, then it analyses the load-displacement curve and repositions the stage based on the selected stage repositioning option. This function can be used, for example, to detect the exact location of a sample surface or the bottom of a testing chamber (in this case the stage must be moved very slowly to avoid overloading the load cell), or to place an indenter in contact with a sample using a predefined load.
STAGE AXIS - On multi-axis systems, the user must specify which axis will perform the “Find Contact”.
LOAD CELL AXIS - When using a multiple-axis load cell, the force component on which the stop criteria (load or torque) will be applied has to be selected.
Note: The selected “Load Cell Axis” must be consistent with the “Stage Axis”. For example, if the “Vertical (z)” stage axis is selected, the “Load Cell Axis” must have a component along the vertical axis, such as the load or force along the z axis, or the torque along the x or y axis for the multiple-axis load cell, in order to fulfill the “Stop Criteria” at some point. FAILURE TO MATCH THE “LOAD CELL AXIS” TO THE “STAGE AXIS” CAN RESULT IN DAMAGE TO THE LOAD CELL.
DIRECTION - Specify if the stage has to start moving in the positive or negative direction. With a positive displacement, a vertical stage will move down (compression), a horizontal stage will move right, and a rotation stage will move clockwise. Enter a negative value for stage displacements in opposite directions.
STAGE VELOCITY, MM/S - Specify the speed at which the stage will move. Refer to the specifications of your Mach-1 model to learn of the velocity range allowed. In Mach-1 Motion, the speed is always specified in absolute value terms.
CONTACT CRITERIA, GF - The user specifies the “Contact Criteria” which corresponds to the variation of the load (relative to the load measured when this function is executed) and not the absolute load. For instance, if the load cell indicates 10.0 g when the function “Find Contact” is executed with a 2.0 g “Contact Criteria”, the stage will move in the positive direction until the load cell reads 12.0 g, or in the negative direction until the load reads 8.0 g.
STAGE LIMIT, MM - The user specifies the “Stage Limit” which corresponds to the maximum relative displacement of the executed function. This serve as a safety precaution for the load cell. For example, in the case of indenting very soft materials, this parameter can serve as an emergency stop if the contact criteria is never met. The stage can stop before hitting the sample holder and possibly damaging the load cell.
STAGE REPOSITIONING - Depending on the predefined stage velocity, the stage will continue to move (position will overshoot), more or less, following the reaching of the stop criteria (hardware delay). In order to compensate for this overshoot, this function automatically analyses the load-displacement curve generated and repositions the stage based on the selected stage repositioning option. There are three stage repositioning options:
- “None”; the stage remains at the position where it has stopped (overshoot)
- “Stop Criteria”; the stage is repositioned where the load variation first corresponded to the stop criteria (overshoot compensation)
- “2X Load Resolution”; the stage is repositioned where the load variation first corresponded to twice the load cell resolution (surface detection)
