One Controller for One MotionSystem Absolute Accuracy The servo-control loops forboth the motorized and thepiezo drive use the same posi- tion sensor. The result is a motion system with hundreds of millimeters travel but with the precision of a piezo-basednanopositioner. The resolutionand the positioning accuracy depend on the choice of the feedback sensor. PI hybrid sys- tems currently use optical lin- ear encoders with a resolutionof 2 nm. Depending on thestage, a minimum incremental motion or a repeatability of 4 nm can be achieved over theentire travel range. Integrated Servo-ControlSpans Both Drives The basic idea of combiningclassical motorized microposi- tioners with high-resolutionpiezo industrial actuators is not new. Forexample, PI offers a fiber-scan- ning and coupling system com- prising a 6-DoF microposition-er (F-206) mounted beside amulti-axis piezo system (P-611 Nanocube

Hybrid Nanopositioning Technology by PI

Long Travel Ranges with Nanometer Precision

In PI hybrid systems, the motor- leadscrew and piezo actuator are fully integrated to form one motion system. The motor and piezo act together at all times. The result is far more than a coarse-adjust/fine-adjust sys- tem: effects like startupstick/slip and backlash can becompletely compensated and a motion profile with high con- stancy of velocity can be fol- lowed. Because of the high piezo stiffness, setting to a few nanometers only takes a fewmilliseconds, significantly fas-ter than with conventional, higher-inertia, linear motor- driven stages. Furthermore minimal increments in the range of the sensor resolutioncan be reliably executed.To allow high velocities beyond 100 mm/sec and nanometer- range incremental resolution, position information must be transmitted and processed very rapidly and a complex controlalgorithm is required. PI’s C-702is a controller providing PWM signal generators, piezo ampli- fiers and control algorithms specially tailored for hybrid systems.
Working principle of the M-511.HD. The platform is decoupled from the motor drive train by the piezo actuator and the flexure industrial guides.This also reduces the inertia of the piezo-drivenplatform and allows for rapid response. Active Compensation of Stick/Slip During Startup and Settling Active Backlash Compensation Excellent Velocity Control Millisecond Settling to Nanometer Accuracy Reliable Execution of Minimal Increments High Drive and Holding Forces with Minimal Power The direct integration of piezoactuators in micropositioning stages allows combining travelranges of hundreds of millime-ters with resolutions in the nanometer range. Servo-con- trol of the system employs a single high-resolution position feedback sensor (parallel metrology) which means thatthe high resolution can be usedover the entire travel range. This makes hybrid systems ideal for applications where the position of an incident needs to be read and refound precisely,or where an externally speci-fied target position needs to be hit within few a nanometers, such as in surface inspection or metrology. The challenge of implementing hybrid technolo- gy is not only the mechanicaldesign of the positioning stage,but also the use of high-resolu- tion sensors over large travel ranges, the processing of the resulting high-frequency sig- nals and the design of specialcontrol algorithms to take fulladvantage of the hybrid design.
® ) with high positionresolution. The servo-control algorithms with stacked systems like these generally operate independ-ently, with the piezo systemonly becoming activated after the motorized positioner has come to a complete stop. Be-cause separate position sen-sors are used the absolute accuracy (not the resolution) is limited by the precision of themotorized long-range position-er. The new PI hybrid systems use a single high-resolution en-coder and a controller that canactuate both drives at the same time. Thus every move benefitsfrom the specific advantages of both the motorized actuatorand the piezo actuator from startup to settling.On the mechanical side, this isaccomplished by decoupling the motion platform of the hybrid positioning stage from the micropositioner’s motor- ballscrew-drive by frictionless flexures and stiff, fast response piezo actuators. The controller continuouslycompares the actual platform position (by reading the inte- grated linear encoder) with a calculated, smooth trajectory.The piezo actuators actively compensate out the irregulari-ties in the motion of the plat-form caused by the motorized drive train.
PI hybrid servo-controller output during a positioning command. The controller reads the system position off a high-resolution encoder and actuates both the motor and piezoelectric actuator at the same time giving a system with theadvantages of both drives. © PI 1998-2006.Subject to change without notice. This data sheet is superseded by any newrelease. The newest release is available for download at www.pi.ws. R1 06/05/29.0 7 a - 2 7 - 1 to 7-106 see the Hardbound Catalog