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NTS Series Linear NanopositionersNanometer positioning with 10 mm (NTS-10), 25 mm (NTS-25) and 100 mm (NTS-100) travel!
Features
The NTS SolutionThe NTS Series combines both superior 0.4 nm high-resolution incremental stepping and extended travel range to 10 mm (NTS-10), 25 mm (NTS-25) or 100 mm (NTS-100). By comparison, competing technologies are limited in that they provide either high resolution or extended travel range, but not both. Commercially available piezoelectric translators (PZTs) used for nanopositioning have very limited travel range, typically 5-200 µm. Alternative motorized stages, such as DC or stepper motors, offer extended travel ranges up to 100 mm but provide low resolution (>0.1 µm), making them inadequate for accurate nanopositioning applications. Piezoelectric Motor PropertiesThe NTS Series stage converts the rotary motion of its advanced piezoelectric motor into linear motion of the stage. The motor's features include a high initial torque (0.2 Newton meter), variable speeds and high angular resolution. Additionally, the motor uses a shaft-mounted 4000 counts/revolution optical encoder. Combined, these features enable both continuous or step operation modes to provide accurate angular positioning. When the system's piezoelectric motor is de-energized, the motor operates as a position holder (brake) with virtually undetectable backlash and drift. The piezomotor design helps to eliminate heat dissipation in the steady-state mode, making the NTS Series ideal for ultra-high vacuum applications. Angular ResolutionThe angular resolution of the system's piezoelectric rotary motor is critical in determining the linear resolution of the NTS Series. The minimum angular increment/step of 1 arc sec. is measured using a laser autocollimator and a mirror attached to the stage's platform. As the motor is rotated at its minimum angular increment, the change in angular reflection of a collimated light beam, originated from the autocollimator and reflected back from the mirror, is measured. This method ensures that the angular movement can be resolved to better than 0.5 arc/sec. TorqueThe system's piezoelectric motor has an extremely high initial torque (0.2 Nm), compared to the 0.01-0.05 Nm torque of a comparable stepper motor. The high torque allows the use of a high-tension spring load to ensure continuous contact between the lead screw and the moving stage platform. Combined, these features minimize backlash and guarantee the high 0.4 nm resolution of the system. Translation StageThe mechanical characteristics of the translation stage were designed to provide the highest resolution (0.4 nm) achievable. Lead Screw AssemblyThe lead screw assembly is precision engineered to provide the accuracy required for precise stage movement. Each lead screw is manufactured from Class 12 polished chrome steel. The screw is fitted into the assembly with the same level of tolerance assured for all stages. Unevenness of the screw's surface is kept below 0.1 mm. Strict control of the lead screw's shaft material and design ensures that mechanical hysteresis of the stage is minimized. Translation Stage GuideSurface irregularities on a translation stage guide can affect the accuracy of movement. Tight tolerances are placed on the fabrication of the guide's surface and the quality of its polishing to minimize surface imperfections. Straightness of MovementThe straightness of the stage's linear movements are tested to be better than 1 µm per 1 mm displacement. Each guiding groove is individually adjusted on an optical bench during assembly and calibration. BearingsAny surface irregularities in the ball bearings or bearing guides can affect the accuracy of the stage's linear movement. To ensure optimal performance, eight balls made of Class 12 polished chrome steel are used in the NTS-10/NTS-100 bearings; each ball has a spherical tolerance of better than 0.1 mm. A bearing composed of multiple balls results in the tolerances being averaged; the final inaccuracy resulting from ball geometry uncertainties is less than the worst-case tolerance of a single ball. The NTS Series uses eight balls in its bearings to ensure the effect on accuracy arising from ball imperfections is nearly imperceptible. HysteresisHysteresis is the difference in achieved positions which may occur when the stage is moved to the same fixed point from two opposite directions. Two factors that can contribute to hysteresis are:
If the lateral tension applied to the ball bearings is too weak, a sideways wobbling affects the stage. If the tension is too great, an increase in friction of the ball bearings may result in nonsymmetrical drag. A spring tension is used in the NTS Series to minimize these effects. To correct a deviation from colinearity between the shaft and the lead screw, a proprietary elastic transmission is used to provide orthogonal elasticity of ~1 mm/N. BacklashThe NTS Series has two proprietary anti-backlash springs, each with 10 N force. The springs are used to preload the lead screw to significantly reduce backlash in the system by ensuring constant contact between the moving components in the system's stage, regardless of the direction of movement. To avoid significant wear from the high torques used, the NTS Series is designed with all elements subjected to friction having a hardness of not less than 60 harness units (HRS) on the Rockwell scale. Overcoming the "Stick/Slip" Effect"Stick/Slip" is detrimental to system resolution. The effect manifests when the coefficient of static friction is greater than the coefficient of dynamic friction. When a driving force is applied to a nanopositioner, movement from rest is slightly delayed on the applied force; there is no movement until the force exceeds static friction. At this point there is a jump in position. Frictionless devices such as solid-state actuators exhibit zero measurable friction to provide resolution that is superior to traditional mechanical positioners. The NTS Series overcomes the "Stick/Slip" effect because of a unique start-stop characteristic of the rotary piezoelectric motor. Any angular position of the rotor is locked by the self-decelerating torque of the motor. The same force locks the whole friction system of the translation stage. To limit the effect of any jump when initiating motion the unlocking process must occur almost instantaneously with a time constant from 10-100 µsec. The system's piezoelectric motor was designed to implement a step formation within 50-60 µm per 1/arc sec. This timing results in an angular step of the motor that translates immediately into an equivalent linear step and eliminates any static friction effects. NTS ControllerThe NTS Controller is available in either 1-, 2- or 3-channel configurations. An NTS controller is a recommended component for the NTS system. The NTS Controller connects to a PC or notebook computer and provides the communication band control link between the NTS-10/NTS-100 and Windows 2000/XP operating software. The PC's monitor displays easy-to-use menus from the NTS-10/NTS-25/NTS-100 software and prompts the operator to select or enter parameters for the chosen mode of operation. The software processes the digitized input signal and applies the operator-selected information to real-time display and control of the stage. The internal architecture of the NTS controller is based on digital signal processing (DSP) to enable a wide dynamic range and high measurement accuracy. The controller is portable and operates from a 12 VDC power supply. A full range of accessories are available, including brackets for the XY and XYZ configurations. Optional Joystick
Pricing
* Note: NTS-series LabVIEW software also available. Contact an Applications Scientist for details.Specifications
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