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Glossary open and closed loop postitioning attoMOTION
Open Loop Positioning
In this mode , the positioner is simply driven forward or backward , without an encoder to read back the actual position or a feedback loop to control the desired target position . Many applications don ‘ t require either of the latter or provide inherent external means of controlling the position . Still , at least a rough estimate of the actual position can be deduced by counting the number of steps ( if the step size can be determined from an external measurement ). The step size itself is relatively uniform under fixed conditions ( temperature , humidity , pressure , load , etc ) and typically within 5 % over the full range but depends strongly on the applied force along the axis . The forward / backward asymmetry is also typically 5 % ( no external force assumed ).
Closed Loop Positioning
Positioners with an integrated or external encoder (/ RES , / NUM (+), / FPS ) can be used for closed loop position control . A feedback loop integrated into the control electronics minimizes the difference between target position and actual position . Setpoints can either be defined in a software interface ( ANC350 , ECC100 ) or on the front panel of the closed loop electronics ( ANC350 ). Settling time depends on the resonance frequency of the setup , speed of the feedback loop and measurement bandwidth .
Suitable Controllers
ANC300 ( open loop )
• modular , up to 7 axes
• suited for scanners and positioners
• USB and Ethernet
• controllable via : LabVIEW | text-based LUA-console | touchscreen
ANC350 ( closed loop )
• three axes (/ RES , / NUM , / FPS )
• USB and ( optionally ) Ethernet
• controllable via : LabVIEW | DLL | EPICS Windows Software | touchscreen
ECC100 ( open & closed loop )
• three axes
• USB and ( optionally ) Ethernet
• controllable via : LabVIEW | DLL | Windows software attoMOTION
Piezo-based Nano Drives