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- Air Bearings & Ultra High Precision StagesAir Bearing Stages | Motorized | Linear | RotaryAir bearings provide advantages over mechanical bearings when vibration-free motion is required, highly constant velocity control is crucial, and when angular repeatability and geometric performance must be optimal. Air bearing stages (linear, rotary, and spherical) replace mechanical contact by a thin air film, avoiding wear, friction, vibration, and hysteresis effects.
- Miniature Positioning StagesMiniature Positioning Stages | Supplier | ManufacturerCompact positioning stages are crucial for the miniaturization process in cutting-edge research and industrial applications, for test & measurement, optical and opto-mechanical alignment, and component assembly. PI provides the largest portfolio of miniature stages, including high-speed linear motor stages, economical stepper motor units, and ultra-compact piezo motor positioners.
- Motorized Stages: Linear, Rotary, XYMotorized Stages | Positioning | ManufacturerPI offers the broadest and deepest range of precision motion technologies for micro and nano precision applications. Our engineers work with our customers to find the best drive and bearing technology for each individual application. Having access to multiple drive and positioning technologies allows an open discussion with a better outcome for the customer.
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- Control of Hexapod / Stewart Platforms: Hexapod Motion Controllers & Simulation Software6DOF Motion Platforms | Hexapod Controllers & Simulation Software | Stewart Platform | ManufacturerControllers, software and accessories for Hexapod Stewart platforms and parallel kinematic motion systems | PI USA
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- Piezo Flexure Nanopositioning StagesNanometer Precision: Piezo Stages for Nanopositioning, Piezo Nanopositioners, Piezo Flexure Scanning Stages | PI USAPI offers the broadest and deepest portfolio of nanometer precision motion technologies, from piezo-driven nanopositioning and scanning stages to motorized 6-axis hexapod positioning systems.
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- 6-Axis Piezo Flexure Stages6-Axis Piezo Nanopositioning Stages – Flexure Guided Precision Positioners | PI USAPiezo-driven fast steering mirrors (FSM) achieve nanoradian resolution and high bandwidth.
- Tutorial - Piezo NanopositioningNanometer Precision: Nanopositioning Basics Tutorial. Piezo Nanopositioners, Scanning Stages, Flexure Guided Positioners | PI USAThere are several ways to achieve nanometer precision motion. The best positioning systems avoid friction all together, in both the drive system (motor) and in the guiding system (bearings). Frictionless bearings also avoid the bearing rumble caused by balls and rollers and provide vibration-free motion with highly constant velocity.
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- Piezo Motors: Stages & ActuatorsPiezo Motors | Linear Motor Positioners | ManufacturerPiezo Motors are intrinsically vacuum compatible, non-magnetic and self locking at rest, providing long travel compared to traditional piezo mechanisms. The individual drive concepts are optimized for different applications, they differ in their design, size, cost, force & speed and other performance parameters.
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- XY Piezo Flexure StagesXY Piezo Flexure StagesHigh-precision 2-axis nanopositioning systems integrate PICMA® piezo actuators for maximum reliability. Repeatable, drift-free positioning with optimal stability is possible by the use of high-quality nanometrology sensors.
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- Tutorial - Piezo Motion ControlWhy All Piezo Motors are NOT Created Equal: The piezoelectric effect for precision motion control - PI Physik Instrumente.The demand for higher speed and/or precision in fields such as bio-nanotechnology, semiconductors, metrology, data comm, and photonics keep pushing manufacturers to come up with innovative drive technologies.
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- Piezo Transducers & ActuatorsPiezo Actuator | Piezo Transducer | ManufacturerPiezoelectric translators (transducers) are precision ceramic actuators which convert electrical energy directly into linear motion with high speed, force and virtually unlimited resolution. These actuators are used in every modern high tech field from semiconductor test & inspection to super-resolution microscopy, bio-nanotechnology and astronomy/aerospace technology.
- Piezo Actuators & Transducers: Stacks, Chips, Benders, Tubes, Spheres, Shear…Piezo Actuators & Transducers: Stacks, Chips, Benders, Tubes, Spheres, Shear…
- Value-Added Piezo Transducers & Piezo AssembliesValue Added Piezo Assemblies: Transducers, Actuators, Sensors, Manufactured by PI CeramicDeveloping and manufacturing piezo ceramic materials and components are complex processes. PI Ceramic - PI’s piezo material design and manufacturing facility - boasts several decades of experience as well as the right tools for rapid prototyping of custom engineered piezo components and assemblies. From the formulation of advanced piezo materials to the processing steps such as cutting, milling, grinding, and the precision assembly, every stage is controlled by our engineers and product specialists.
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- Microscopy, Bio-Imaging, Life SciencesHigh Precision Microscope Stages, Piezo Lens Scanners, Tools for Bio-Imaging | PI-USAPiezo nano-positioning stages are essential tools for high-resolution microscopy, such as Super Resolution Microscopy or AFM. Their sub-atomic resolution and extremely fast response allow researchers to create higher-quality images faster. PI provides a large variety of fast Z-Stages and collar piezo objective positioners for 3D imaging (Z-stack acquisition), deconvolution, and fast focusing applications.
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- Photonics Alignment SolutionsActive Photonics Alignment | Optics Alignment | SolutionsPI provides a variety of innovative fiber alignment systems from motorized fiber positioners to automated optic and photonic alignment such as used in telecommunication, data commumication and for packaging / automation. In addition to fiber-based applications, fast steering systems for free-space-optical communication are also available. Products range from motorized 6D micromotion alignment systems for industrial photonics automation, through ultra-fast piezoelectric scanning & alignment modules to modular devices with manual control for laboratory test setups. All motorized systems come with extensive software for easy setup and integration.
- Vacuum Positioning Stages & ActuatorsVacuum / UHV Compatible Stages - Linear & Rotary Positioners for Vacuum, Wide Temperature Ranges | PI USAPI miCos has extensive experience in the design and manufacturing of vacuum and high vacuum compatible precision optomechanical positioning equipment for low temperature and wide temperature ranges. We provide translation stages, vertical linear stages, rotation stages, XY stages and complex multi-axis positioning systems in vacuum spec.
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- Piezo Controller, Driver, Nanopositioning Controller, High-Voltage Amplifier, Piezo Power Supply by PI USAPiezo Drivers | Piezo Motion Controllers | ManufacturerA piezo controller or driver is used to control the motion of a piezo positioning device. There are open and closed loop controllers. Open-loop controllers are often referred to as piezo driver or even piezo power supply. Closed-loop controllers are divided in two basic types: analog-servo and digital servo controllers.
- Controllers/Drivers for Motorized StagesMotion Controller | Drivers | Positioning SystemsPI provides a large variety of hardware & software solutions for high precision motion control. Our portfolio spans from integrated compact single axis servo controllers / drivers, such as popular Mercury-class motion controllers, to complex multi-axis systems for parallel-kinematics positioners, such as hexapods.
- ACS Motion ControlACS Motion Control for Industrial AutomationWe recommend the controllers of our partner, ACS Motion Control especially for automation with industrial standards. Ask us about your integrated solution!
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Digital piezo nanopositioning controllers have a reputation for being expensive and only cost efficient in high-end applications. A recent new design approach has changed this situation, making advanced digital control features affordable for main stream piezo motion applications.
History of Digital Motion Controllers
Position control for magnetic motors has been almost exclusively digital for nearly three decades. In the mid-1980s, digital motion control chips began to be available, such as the pioneering HCTL-1000 chip from HP. These chips were easy for controls engineers to interface with the position feedback encoders of the era that provided simple, incremental quadrature signals suitable for digital processing. Also, for motors, the drive signal is a velocity or force command, so only low output resolution was necessary, regardless of axis travel. 10 bit analog or 8 bit PWM output resolutions were common, and these were very tractable for controller designers to employ in cost-effective designs. With the exception of analog tachometer feedback integrated as a supplementary loop for higher-performance systems of that era, magnetic motor control has been virtually all-digital ever since.
Why Piezo Nanopositioning Control is Different
In the world of piezo nanopositioning systems, the situation was and remains quite different. The purpose of these systems is to provide extremely high position resolution in the nanometer and sub-nanometer range with very fast response in the sub-millisecond range. Here, the position feedback is traditionally provided by analog, absolute measuring sensors (strain gauges, piezo resistive gauges, capacitive gauges or LVDTs). For piezo stack actuator-driven positioners, the drive signal from the controller operates in the position domain rather than representing a velocity or force command as is the case with magnetic motors. Consequently, any electrical noise or drift of the drive signal results in an unwanted position change.
Note: Piezo-stack driven nanopositioning systems are not to be confused with piezo motor positioners, which provide longer travel ranges and have more similarities with traditional motorized positioning systems. For more information on different types of piezo motors read the piezo motion tutorial.
This necessitates high-quality, low-noise, low-drift circuit design for the mission-critical servo circuit. In particular, the coarse DAC or PWM designs common in motor controllers were inappropriate for nanoscale piezo positioning. In addition, the high responsiveness of piezo mechanisms necessitates very fast processing that traditionally was too costly for all but the most elite nanopositioning applications.
This is why most affordable nanopositioning controllers have historically utilized analog servos. A microcontroller driving a digital-to-analog converter (DAC) was often added to provide a display and perhaps simple interfaces for computer commandability, but the critical servo-control and linearization functionality still relied on legacy, fixed-function analog circuits. Calibration and tuning for significant load changes required careful adjustment of tiny trim-pots using precision external metrology. Linearization could accommodate second-order sensor nonlinearities at best, but drift in the internal or external DAC would cause an unwanted positional change.
Effects of the interaction of the PZT ceramics, preload, flexures, and couplings show up in the graph and the result is different from a straight line.
Still, these controllers remained the affordable, robust workhorses of nanopositioning for both research and industrial applications.
The measured phase and amplitude response of a P-713 piezo flexure stage (Eigenfrequency 2.2kHz). Piezo flexure mechanisms can respond very rapidly to drive signal changes and resolve motion to atomic distances which is why they need very fast, ultra-low-noise servo controllers to take full advantage of these mechanical features. (Image: PI) PI’s implementation was unusual in that even its most affordable analog nanopositioning controllers implemented a notch filter. This desensitizes the servo to resonances in the nanopositioning mechanism, allowing the servo to run at high gain for unusually good positioning throughput.
All-Digital Started with High End Applications
All-digital piezo controllers have existed since the early 1990s, but they tended to be costly. These units replaced the analog servo-control circuit with a fast, real-time digital loop that integrated the DAC, providing automatic stabilization to a previously unachievable degree. These controllers quickly became the default for drift-intolerant applications in single-molecule biophysics, atomic force microscopy and semiconductor microlithography. These controllers quickly surpassed the 16 bits resolution common among prior-generation instrumentation-quality DACs. Suddenly, 18 to 21 bit positional resolution could be achieved, sometimes even more. This, in turn, facilitated the development of really long-travel piezo flexure guided stages that retained fast nanoscale positionability, even with travels exceeding 1mm.
PI’s E-710 was a pioneering all-digital nanopositioning controller in the early 1990s. Besides offering a then-astounding 20-bit resolution and software-adjustable calibration and tuning, it offered virtual coordinate systems, waveform generation, and Digital Dynamic Linearization (DDL) for high fidelity repetitive waveforms. (Image: PI) The functionality of digital nanopositioning servo controllers quickly thrived in novel, application-enabling ways. Data recorders and waveform generators were integrated; advanced high-order linearization broke new ground for nanoscale accuracy. Advanced new servo techniques were just a firmware update away, facilitating novel tracking applications and implementing advanced settling-time-reduction algorithms. More information on advanced piezo control algorithms is here. The addition of a second notch filter helped passify challenging loads. And the integration of calibration “ID chips” in the nanopositioning mechanisms eliminated the need to keep controllers and mechanics as a matched set.
Design Advances Make Digital Nanopositioning Control Affordable for Main Stream Applications
Four decades of piezo controller design leads to advances and new ideas of approaching a problem. The recent introduction of PI’s E-709 (single axis) and new E-727 (multi-axis) digital controllers bring the benefits of true-digital design to highly affordable price points. Like all true-digital controllers;
- The digital-to-analog converter (DAC) chip is internal to the servo loop rather than external, facilitating stability, high-order linearization and better resolution.
- The calibration and tuning is accomplished via software, with no trim-pots.
- Communications interfaces of extraordinary speed are standard.
- Broad and deep software libraries are provided, allowing rapid, multi-platform application deployment and ready access to advanced functionality.
- Waveform generators and data recorders are integrated.
- ID Chip functionality is supported, allowing positioners to be mixed and matched with automatic calibration.
- High-performance, high-efficiency amplifiers are built in, providing a compact, single-box solution.
The E-727 multi-channel digital nanopositioning controller (shown with a P-563 XYZ stage) provides cost-effective, true-digital nanopositioning functionality. Advanced servo options are offered, such as Dynamic Digital Linearization, for accurate high-dynamic waveforms. USB, SPI, and TCP/IP Ethernet interfaces of extraordinary throughput plus digital trigger and sync lines provide industry-leading computer controllability. (Image: PI) Learn more In Detail: Analog vs. Digital Piezo Control
Traditional (analog) nanopositioning controller designs utilize sensitive op-amp circuits to implement the familiar and robust Proportional-Integral feedback-driven servo. The job of the servo is to reduce the difference between the command signal (generally a voltage generated by a DAC elsewhere in the controller or on a card in the user’s PC) and the feedback signal from the position sensor embedded in the motion device.
The most sophisticated examples of this popular architecture integrate features, such as:
- Sensor linearization, which improves the absolute accuracy of the motion system.
- Piezo relaxation compensation, which helps ensure crisp pull-in and stable position-hold in point-to-point operation.
- A notch filter, especially valuable in high-dynamic applications since they desensitize the servo to the mechanism’s observable resonances and thereby allow higher-gain operation. These are standard features of all PI analog servo electronics.
However, in this time-tested architecture, any change in the DAC’s output will drive a position change. This is of course very desirable behavior, but if the DAC drifts or noise enters the system through its connection, the result will be position instability.
This advanced analog servo design of a nanopositioning controller integrates a notch filter for higher dynamic capabilities. The DAC that commands position is external to the servo loop. (Image: PI) By comparison, digital controllers implement their servo functionality in a DSP rather than in analog circuitry.
Digital servos place the DAC inside the servo loop and implement the feedback-driven error minimization functionality as an algorithm. Note: There is an analog input as well – life science applications often prefer analog control signals. (Image: PI) This true-digital architecture allows the DAC to be integrated inside the servo loop. The best implementations provide sensor linearization up to 4th or 5th order, versus 2nd order for the best available analog designs. And DAC drift can be virtually eliminated since the system intelligence can differentiate between desired and undesired motions, as detected by the feedback sensor. This in turn enables integration of high-bitness (but sometimes drifty) DACs for finest resolution.
Note: While many analog piezo controllers add a microprocessor and DAC on top of a conventional analog servo circuit in order to satisfy user demands for computer interfaceability using USB, RS-232 or similar industry-standard interfaces, some suppliers misleadingly call these “digital” controllers, but their servo functionality remains analog.
The compact single-axis E-709 controller (shown with a PIFOC nanofocus mechanism) is the first of a family of cost-optimized, compact, true-digital controllers priced at a fraction of their forebears. Its advanced functionality and high performance makes it an enabler for many challenging applications in fields as diverse as microscopy, active optics, photonic alignment, and nanoprobing. High-throughput USB and SPI interfaces are standard together with analog position command and I/O and an array of useful TTL trigger and sync lines. (Image: PI) Learn more Driving a Savings Cascade for High Volume Applications
For the first time, breakthroughs in digital design have allowed commercialization of a digital piezo nanopositioning controller at the same price as conventional analog controllers. PI’s E-709 also was the first digital piezo controller to accommodate cost-effective strain gauge sensors for positional feedback. These sensors are based on the strain of metal foils or semiconductor films (piezoresistive sensors) and are used when space or cost limitations prevent the use of more advanced capacitive sensors, or where the requirements in terms of resolution or thermal sensitivity are not as critical. (E-709 and E-727 are, of course, also available for use with capacitive sensors for applications requiring the utmost in resolution, accuracy, EMI resistance, bandwidth, and stability.)
This means the nonlinearity of strain sensors can now be affordably addressed by real-time digital compensation, providing up to a 10X improvement in absolute accuracy.
Parameter Changes On the Fly: Quicker Set-Up, Increased Flexibility
Changing the gain settings of an analog nanopositioning servo (and the center-frequency of its notch filter, if so equipped) required physical access to trim-pots internal to the controller. These settings should be optimized for the system’s load. If the configuration changes significantly, re-adjustment is good practice, but access hassles, time costs, and the availability of skilled technicians sometimes prevent this. For example, a sophisticated optical apparatus with a piezo-based focusing mechanism like a PI PIFOC might be used with several microscopy objectives of significantly differing mass. In such situations, a compromise setting was traditionally used to ensure stable operation. This can impose a trade-off in responsiveness.
10µm X-axis move of a 200µm XYZ piezo positioning stage, settled to within 100nm (1% error band). The graph shows gentle tuning of the digital E-727 controller vs. an analog controller; the advanced servo algorithm allows for faster rise time without overshoot. (Image: PI) 10µm X-axis move of a 200µm XYZ piezo positioning stage, settled to within 100nm (1% error band). The graph shows aggressive tuning of the digital E-727 controller vs. an analog controller; the advanced servo algorithm of the digital controller achieves stable settling inside the 1% error band significantly faster than the analog controller. (Image: PI) By comparison, true digital controllers — including E-709 and E-727 — offer dynamic settings that can be easily changed remotely via software and then safely stored to the unit’s flash RAM. In the microscopy example just mentioned, optimized dynamic parameters can be downloaded to the controller at any time without requiring physical access to the unit or even a power-cycle.
This capability allows easy optimization for momentary application requirements in addition to configuration changes, such as a new load. In OEM applications, the tool’s embedded PC can download preconfigured settings on-the-fly and without pause to customize the system’s dynamical behavior to the requirements at that moment. The figure below for example, shows two settings for the same load: a fast motion of less than 5msec, and a gentler motion of the same amplitude. The faster, crisper motion might be desirable for time-critical applications like optical sectioning and nano-patterning, whereas the gentler motion might be more suitable for biological samples or surface-following probing applications like AFMs and nanotribology scanners.
These units are also unique among affordable nanopositioning controllers in providing two notch filters, allowing high-dynamic operation in situations where motion-driven ringing in the motion device and supporting structure would otherwise be problematic and require lower, less responsive gain settings.
E-709 provides advantages for autofocus applications, such as used in microscopy, industrial inspection, scanning, and genomics applications. It can interface in real time laser focus sensors, providing stable positions on the order of tens of milliseconds. It provides responsive real-time tracking, and it supports PI’s Fast Focus & Freeze capability, where the unit can be bumplessly switched from an external (focus) sensor to a position sensor in the piezo mechanism, allowing precise, high-stability motion with respect to the focal plane.
Interfacing Speed
E-709 and E-727 provide a wealth of interfacing capabilities together with highly optimized software building-blocks. To begin, there are responsive USB, RS-232, and SPI interfaces on both. High-speed TCP/IP Ethernet connectivity for easy integration into automation and remote-access architectures from lab to fab is available on the E-727. Waveform generation and data recording capability are built-in and facilitate repetitive scanning and similar applications, offloading position generation from the host.
These controllers offer three real-time interfaces:
- Analog I/O interfaces, sampled/updated at the full servo cycle rate, provide easy integration with National Instruments’ multifunction cards, among other external command-signal possibilities. LabVIEW® users can even leverage this interface using PI’s Analog GCS (General Command Set) library — the industry’s first plug-and-play library for analog nanopositioning.
- A standard high-speed SPI interface offers the ability to communicate digitally using industry-standard physical protocols. You can command and interact with the systems servo update rate with no risk of loss or noise pickup in cabling.
- TTL I/O functionality allows triggering and synchronization with other host processes. These controllers utilize the same PI GCS command set as all PI controllers. This means programmers can write consistent code for coarse/fine applications, with the coarse positioner (like the ceramic motor-driven, self-clamping U-751/M-686 microscopy stage and its C-867 controller). Included with Nanopositioning controllers is a wealth of software tools ranging from an extensive LabVIEW® library, to an industrial-class Windows .dll and Linux .so libraries. A graphical setup and exploration software, called PIMikroMove, helps with system startup.
Special OEM Configurations
These digital nanopositioning controllers are also available without a case for embedded OEM applications. A version with only an analog position-command interface (E-609) offers special economy for backwards-compatibility applications, formerly served by analog controls.
A caseless digital controller for OEM applications (Image: PI) Reference Class Applications
Controllers such as the E-727 and E-709 can handle most tasks precision motion engineers encounter in industrial and scientific nanopositioning applications. For situations with the most demanding requirements, a controller with a different architecture is also available. With more processing power and an even faster servo loop (50kHz), the E-712 modular controller can perform complex tasks such as automated multi-channel, multi-axis photonics alignment, coordinated motion of multiple piezo elements such as found in PiezoWalk® nanopositioning actuators and ultra-fast servo applications such as required for track following servos in high-speed read/write head testing.
Conclusion
Digital nanopositioning controllers help advance the field of nanotechnology. By providing features and capabilities formerly reserved for controllers costing many times their price, the E-727 and E-709 family enables a host of new research and industrial/OEM applications. OEMs will value their quick setup and remote customization capabilities combined with their power, space-saving design, and high responsiveness. Even their cabling scheme is targeted to make the OEM’s job easier and more productive. Meanwhile, research users will prize their stability, performance, wealth of supporting software, interfacing flexibility, and ease of use.
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