Frequently Asked Questions
A nanopositioner is a mechanical stage that consists of a movable component inside a rigid frame. The movable and static portions are electrodischarge machined (EDM) from a monolithic block and connected by flexure "hinges." The movable component can move in any or all of three translational axes, as well as in angular axes such as rotation or tilt. The flexure mounting used by nPoint insures that motion in one dimension does not cause motion in any other dimension. A closed-loop control system allows the user to provide inputs to the positioner and to monitor the positioner parameters.
An nPoint motion control or positioning system is comprised of four elements:
- Piezo actuators providing motion
- Mechanical translation mechanism (stage)
- Position sensor
- Control electronics to maintain the desired position
To realize positioning at nanometer levels of precision, these four elements need to be carefully designed and optimized. The desired attributes of a nanopositioner are extremely high resolution, accuracy, stability, and fast response. Conventional motion control technologies are unable to meet these requirements and provide nanometer positioning.
The key factors are accurate position sensing, careful mechanical design, and closed-loop control of the motion. nPoint nanopositioning devices have capacitance position sensors, piezo actuators, and flexure motion control integrated into a single system. Stages that control motion in one, two or three axes are available, with virtually zero cross-talk between motion directions.
nPoint technology provides a wide range of motion, combined with precise location and high scan speed. nPoint features a patented use of materials for a unique combination of high-load capacity and high-speed response. nPoint employs Finite Element Analysis in the development of these ultra precise positioning systems which are based on flexure-guiding mechanisms. Flexure-guiding mechanisms achieve a pure, independent, single-axis (x-, y- or z-) motion with minimal parasitic errors.
The use of kinematic mounting virtually eliminates the effect of distortions that the piezo movement causes to the frame of the stage. It is assumed that the frame is rigid with respect to the part of the stage that moves; this is not true and can be detrimental to achieving true nanometer precision in positioning. The use of kinematic mounting also diminishes the effect that temperature variations can have on the drift of the stage.
Flexure stages employ a non-conventional 'flexure bearing' mechanism in the system, in which the moving platform is linked to a static base by flexure hinges. The platform's movement, driven by piezo actuators, is guided by the flexure mechanism. The guiding motion is generated by elastic deformation of the flexure material. Therefore, the linkage is friction and stiction free, resulting in smooth motion. Optimization of the flexure design mechanism results in high stiffness and load capacity while simultaneously neutralizing the parasitics errors, such as out-of-plan motion, titling errors and crosstalk.
nPoint flexure designs employ a multiple amplification factor to the piezo actuator's travel range enabling shorter piezos to be used for greater travel ranges. Stages can be built smaller and more economically than without the advantage of flexure amplification. Flexures do not experience frictional wear and operate within the elastic range of the material eliminating the need for routine maintenance while performance remains consistent over the operational lifetime of the stage.
nPoint's stages are available in Aluminum, Super Invar and Stainless Steel.
Assuming the same mechanical design, an aluminum stage will have the highest resonant frequency, which will translate to higher scanning speeds and faster settling times. Aluminum exhibits a high strength to weight ratio making it an excellent choice for weight critical applications (e.g. aerospace). However, an aluminum stage is more susceptible to thermal drift.
The primary advantage of the Super Invar stages is the superb thermal stability. The thermal expansion co-efficient of Super Invar is approximately 50 times smaller than that of aluminum. When a stage is to be integrated into a larger instrument, the materials of the rest of the system's components need to be taken into consideration.
nPoint has even employed multiple materials into a single stage design, thus utilizing the benefits of each material for optimum performance. Understanding the requirements and operating environment the stage will operate in will enable us to recommend the right material for your project.
Our nanopositioners use piezo actuators to generate motion. The expansion of a piezo actuator is normally proportional to the driving voltage. In an open-loop system a linear voltage is applied for motion control. However, piezo actuators exhibit nonlinearity, hysteresis and creeping, which will be translated as positioning errors in the positioning system. The term "closed-loop" in nanopositioning indicates that a position sensor is used to monitor the position of the stage in real time and feed back the readings to the controller for error correction. It guarantees that the nanopositioner reaches its precise commanded position. The position sensor is most commonly a capacitor, a LVDT or a strain gage. The control electronics are either analog or digital. nPoint nanopositioners use capacitor sensors coupled with digital control electronics to achieve closed-loop control.
90 days from completion of the product design. The timeline for a product design is determined by the individual customer. The intricacy of performance specifications, the uniqueness of the footprint requirements, and the level of integration into the customer's system all factor into the product design time. nPoint's design team has worked with a wide range of OEM and custom research end users to achieve their specific product needs. nPoint's experience will help prioritize your systems operational parameters and achieve a system that will best fit your product specifications.
45 days ARO.
nPoint nanopositioners are available as stand alone units. Some researchers prefer to develop their own electronic controls for use with our stages. Other researchers want to drive the stage in open loop. To achieve maximum benefit with nPoint nanopositioners, we recommend purchasing an nPoint system which includes the positioner, electronic controller, and operating software. nPoint systems are mated at our factory where the positioner is calibrated and optimized to operate with the nPoint controller.
Yes, all nPoint stages are compatible at 10 -6 Torr, we also offer certain stages compatible at UHV, 10 -12 Torr.
Yes, our nanopositioners use high quality multi-layer piezoelectric actuators for movement. nPoint purchases its piezos from the industry leader in multi-layer piezoelectric solutions. Our relationship ensures that the piezos used in our nanopositioners are optimized for our specific product needs.
The scanning speed of a stage depends on the resonant frequency of the stage and the control scheme that is employed in the controller. As a general rule, the maximum full-range scanning speed of a stage is approximately equal to one tenth of the resonant frequency. This will prevent destruction of the stage but it will not guarantee excellent response. The response of the stage is characterized by the delay (phase-lag) between the actual position and the commanded position. For most of our nanopositioning stages an excellent response is present for scanning speeds of up to 10Hz. The phase lag increases noticeably for higher scanning speeds. Advanced control schemes can be implemented in order to optimize the response for high scanning speeds. Note: the resonant frequency of the stage can be lowered significantly when a heavy sample is mounted on it.
Bandwidth is the frequency at which the actual oscillation amplitude is attenuated by -3dB from the commanded oscillation amplitude. This is approximately equal to the frequency at which the actual oscillation amplitude attenuates by 30% from the commanded oscillation amplitude. The bandwidth has to be tested with small driving signal, which guarantees that the attenuation of the actual oscillation amplitude is caused by bandwidth limitation, not by driving current limitation.
As an example: when a stage is driven to oscillate with a 1µm amplitude at 1Hz it will respond by oscillating at 1Hz with a 1µm amplitude. If its bandwidth is 80Hz, when it is driven with an 80Hz signal it will respond by oscillating with an amplitude of 0.7µm.
nPoint offers scanning ranges of up to 400µm in the X and Y axes, 600µm in the X axis, and 400µm in the Z axis. Please visit our Nanopositioning Stages page for a complete listing of scan range options.
A nanopositioner with a high resonant frequency will have a fast step response specification. A nanopositioner with a fast step response specification allows the user to increase the bandwidth of the control loop. A high bandwidth control loop reduces phase delay, which in turn allows the user to scan at an increased rate. Phase delay induces tracking errors that are especially noticeable at the corners of common scanning waveforms.