- OEM / SystemsOEM Systems | Precision Components | Automation Sub-SystemsPI offers 1000’s of proven, off-the-shelf precision motion products that can be quickly modified for the OEM or into a custom automation sub-system.
- Meeting the Demands of OEMsOEM Systems | Precision Components | Automation Sub-SystemsPI has a long track record of working with OEMs in the most demanding industries from Semiconductor Technology to Medical Design – industries where product performance, quality, and the ability to ramp up quickly are not the only parameters required to satisfy the customer's demands. Working with technology leaders all around the world forces you to continuously improve your yield, process, and product performance. And unless your quality is outstanding, you cannot become a key supplier to major US, European, and Japanese companies in the Optics, Photonics, Semiconductor, and Automotive industry.
- Engineered Motion / Automation Sub-SystemsPrecision Automation Solutions | Engineered SystemsPI is a supplier of high-end precision motion systems and makes use of own drive components and high-precision positioners to build customized positioning and automation sub-systems —“motion engines”—for our customers. With the largest portfolio of precision motion technologies in the industry, PI engineers have the best foundation to find a solution that matches your requirements in terms of precision, quality and budget – in a timeframe that works for you.
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- ProductsPrecision Motion Technologies | Positioning SystemsOverview of the Broadest & Deepest Portfolio of Precision Motion and Automation Technologies from Piezo to Air Bearings and Linear Motors
- Products: Overview, New, Finder, ShopFind Precision Positioning Solutions Quickly - Product Finder | PI USAWith thousands of standard products and customization available, PI has the motion control positioning product solution for your application.
- Products OverviewProducts OverviewOverview of the Broadest & Deepest Portfolio of Precision Motion and Automation Technologies from Piezo to Air Bearings and Linear Motors
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- Product FinderUse the PI Product Finder - it's fast and easy!Select the product type specified by the axes of motion required. Selection of more criteria expands or shortens the list of results. Select more than one filter at at time, for example, to find positioning stages designed for higher load capacity, too.
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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.
- Overview - Motorized Linear/Rotary StagesOverview - Motorized Linear/Rotary Stages
- Linear StagesLinear Stages - Precision Positioning Solutions | PI USASeveral types of motorized precision linear translation stages | PI USA
- Fast Linear Motor Stages and ActuatorsOverview: Linear Stage, Linear Motor Driven, Fast Brushless Motor Positioning Stages | PI USABrushless linear motor-driven stages provide high speed, precision and long life.
- Z-Stages (Vertical Motion)Vertical Linear Stages – Precision Motorized Z-Positioners | PI USA
- XY StagesXY Stages – 2-Axis Motorized Precision Positioning Stages | PI USASeveral types of planar XY stages: Direct-driven stages, ball-screw stages and air bearing planar XY stages
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- Rotary Stages / GoniometersPrecision Rotation Stage, High Resolution Rotary Positioners, Rotation Tables, Goniometers, by PI USASeveral types of motorized rotation stages: Direct-driven stages, ball-bearing stages and air bearing stages
- Heavy Duty Stages / Industrial AutomationHigh Speed / Performance Positioning Stages for Automation - Linear Stages | Rotary Stages | PI USAHigh performance motorized stages, designed for heavy duty applications in industrial precison automation.
- Sub-Systems for AutomationSYS > Engineered Motion/Automation Sub-SystemsThe PI group employs over 1,200 people in 15 countries and runs engineering and manufacturing centers on 3 continents. Select from the broadest portfolio of precision motion technologies, including piezoelectric and air bearing systems, with 1,000’s of standard products or have our engineers provide you with a custom solution.
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- Linear ActuatorsActuators | Precision | Linear | Actuator SystemA precision linear actuator is a positioning device that provides motion in 1 degree of freedom. PI designs and manufactures a variety of precision linear actuators (pushers) including economical stepper-motor driven actuators, high-speed linear motor types for automation and nanometer precise piezo-motor actuators.
- Gantries / Cartesian RobotsGantry Stages | Gantries | Cartesian RobotA gantry precision positioning stage is sometimes called a linear robot or Cartesian robot. Gantries typically provide motion in 2 or 3 linear degrees of freedom (X-Y and X-Y-Z) and are often used for pick and place applications, 3D printing or laser machining, and welding applications.
- 6-Axis Hexapods / Parallel PositionersHexapod Positioner | Six DOF | Stewart PlatformsHexapod positioners are often referred to as Stewart Platforms. A hexapod is based on a 6-axis (XYZ, Pitch, Roll, Yaw) actuator system arranged in parallel between a top and bottom platform. PI parallel kinematics (PKM) precision positioning systems have many advantages over serial kinematics stages, such as lower inertia, improved dynamics, smaller package size and higher stiffness. In addition hexapods are more flexible than conventional 6 axis positioners.
- 6-Axis Hexapods / Parallel Positioners6-Axis Hexapods / Parallel Positioners
- 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.
- Overview - Piezo Flexure StagesOverview - Piezo Flexure Stages
- Linear Piezo Flexure StagesLinear Piezo Stages for Nanopositioning – Flexure-Guided Precision NanoPositioners | PI USALargest selection of frictionless, high performance piezo-stack-driven flexure linear nanopositioning stages | PI USA
- Vertical & Tip/Tilt Piezo StagesPiezo Z-Stage, Piezo Z-Tip-Tilt Platform. Flexure Guided Nanopositioning Stages| PI USALarge selection of Piezo Z-Stages and Tip/Tilt scanners with nanometer precision | PI USA
- Fast Steering Mirrors & Tip/Tilt PlatformsPiezo Steering Mirrors | Active Optics
- Nanofocus Lens ScannersFast Piezo Focus Lens Positioners and Scanners – Piezo Flexure Guided Precision Positioners | PI USALargest Selection of Nano-Focus drives for microscope lenses – flexure-guided precision positioners
- XY Piezo Flexure StagesPiezo Stages | XY | Nanopositioning StagesLargest selection of integrated XY piezo flexure stages with nanometer precision.
- XYZ Piezo Flexure StagesXYZ Piezo Nanopositioning Stages – Flexure Guided 3-Axis Precision Positioners | PI USALargest selection of integrated XYZ piezo flexure stages with nanometer precision.
- 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.
- Overview - Piezo Flexure Stages
- 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.
- Overview - Piezo Motors (Stages/Actuators)Overview - Piezo Motors (Stages/Actuators)
- Actuators with Piezo MotorsCompact precision linear actuators stages with several types of piezo motor drives – ultrasonic, stick-slip, piezo-walk, piezo-ratchet. | PI USA
- Linear Stages with Piezo MotorsPrecision linear stages with several types of piezo motor drives – ultrasonic, stick-slip, piezo-walk, piezo-ratchet. | PI USA
- XY Stages with Piezo MotorsXY piezo motor linear stages with several types of precision piezo motor drives – ultrasonic, stick-slip, piezo-walk | PI USA
- 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.
- Rotary Stages with Piezo MotorsRotary piezo motor stages with several types of precision piezo motors– ultrasonic, stick-slip (inertia), | PI USA
- 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.
- Overview - Piezo Motors (Stages/Actuators)
- 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.
- Piezo Ceramic ComponentsPiezo Ceramic Components
- Piezo Actuators & Transducers: Stacks, Chips, Benders, Tubes, Spheres, Shear…
- 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.
- Stages for Microscopy & Bio-ImagingStages for Microscopy & Bio-Imaging
- Applications: Life Sciences / MedicalPrecision motion control for medical engineering and life sciences applications | PI USA
- Stages for Microscopy & Bio-Imaging
- 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.
- VacuumProduct Series with Vacuum-Ready ItemsPI offers specific catalogue items for selected product series that are already suitable for high vacuum (HV) or ultra-high vacuum (UHV).
- Vacuum
- Controllers, Drivers, Motion SoftwareMotion Controllers, Piezo Drivers-High Voltage Amplifiers, and Motion Software Overview | PI USA
- Overview - Controllers & Motion SoftwareOverview - Controllers & Motion Software
- 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!
- Software - Motion Control SoftwareMotion Control Software | Software Tools | Positioning SolutionsFor LabView, C++, VB, Matlab, Image Acquisitiong Packages, NI DAC Cards, ..... PI provides high-level, robust, easy-to-use software tools for fast, seamless integration of motion systems into application control software.
- Overview - Controllers & Motion Software
- Capacitive SensorsNanometer Resolution: Capacitance Sensors for Nano-Measuring, Nano-Metrology | PIA capacitive sensor is a proximity sensor that detects nearby objects by their effect on the electrical field created by the sensor.
- Accessories: Plates, Brackets, CablesAdapters and Cables for PI Precision Motion ComponentsStandardization is common with adapter plates and brackets, but we can create a custom accessory to fit your application system. PI products ship with the required cables. Customization is always an option.
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- Tech BlogPI Blog / Tech Articles on Advancements in Precision Motion Control, Automation and Piezo Technology | PI USAPI’s tech blog offers 50 years of insight into innovative applications of precision motion control, nanopositioning, and micropositioning in industry, science, and research. We hope the PI blog is an enjoyable and informative resource, and a starting-point for innovation across disciplines.
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Why Use Piezo Motion?
Piezo motion is used when a combination of any of these parameters is required:
- Fast response
- High precision
- High force
- Long life
- Maintenance and lubricants free
- Compact dimensions
- Non-magnetic, UHV compatible
Different Piezo Actuator and Piezo Motor Technologies to Solve Different Problems
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.
There is not one single type of piezo drive that works for every application. PI provides a large variety of piezo actuator and piezo motor drive technologies, each one optimized for different parameters such as cost, precision, force, speed and size. To use the advantages of piezoelectric positioning technology to its full extent, it is important to carefully analyze the application in which a piezo drive or nano-positioning system is to be used. Close contact between user and manufacturer is the best recipe for success.
This tutorial includes an introduction to the piezoelectric effect, a discussion of the difference bewtween a piezo actuator and a piezo motors, an explanation of hybrid mechanisms, and a quick start guide to PI piezo motion products. Email our engineers if you have additional questions about using PI piezo motion products to solve your application problem.Table of Contents
- Introduction
- Piezo Actuator and Piezo Motor: What is the Difference?
- Types of Piezo Actuators / Flexure Nano-Mechanisms
- Control Interface: Digital or Analog or Both?
- Advanced Servo Algorithms: APC and Digital Dynamic Linearization (DDL)
- Hybrid Mechanisms: Coarse / Fine Positioning
- Types of Piezo Motors
- Quick Start Guide
Piezo drives are vital in today's ultra-precision motion control systems. They provide the best combination of stability, accuracy, responsiveness and resolution.
The piezoelectric effect – the conversion of electrical energy to mechanical energy and vice versa - is exhibited by natural materials, such as quartz, etc. However, man-made polycrystalline ferroelectric ceramic materials, such as Lead Zirconate Titanate (PZT), have far advanced material properties and achieve more gain. Ferroelectric ceramics need to be poled to become piezoelectric. Charge separation between the positive and negative ions is the reason for electric dipole behavior of the piezoelectric effect. Piezoelectric ceramics come in many variations optimized for actuator or sensor applications.PZT unit cell: 1. Perovskite-type lead zirconate titanate (PZT) unit cell in the symmetric cubic state above the Curie temperature. 2. Tetragonally distorted unit cell below the Curie temperature. Origin of Piezo
The term “piezo” is derived from the Greek word for pressure. In 1880, Jacques and Pierre Curie discovered that an electric potential could be generated by applying pressure to quartz crystals; they named this phenomenon the “piezo effect”. Later, they ascertained that when exposed to an electric potential, piezoelectric materials change shape. This they named the “inverse piezo effect”.
More on the fundamentals of the piezo effect, equations and background information
Piezoelectric materials are used to convert electrical energy to mechanical energy, and vice-versa. The precise motion that results when an electric potential is applied to a piezoelectric material is of primordial importance for nanopositioning. Actuators using the piezo effect have been commercially available for 35 years and in that time have transformed the world of precision positioning and motion control.
Piezo ceramics needs to be polarized to show the piezo effect.Basic principle of a traditional piezo stack actuator and the displacement graph in open and closed-loop (linearized) operation. Open and Closed Loop Operation
In most applications, piezo positioners are used with a position feedback sensor and closed-loop control.
In contrast to many other types of drive systems, some piezo actuators can be operated without servo-control for a variety of applications. With suitable controllers, closed-loop operation enables reproducibilities in the sub-nanometer range as well as elimination of the piezo hysteresis. Learn more on digital vs. analog piezo controllers for closed-loop operationPiezo tape casting equipment at the PI Ceramic factory, essential for multilayer piezo actuator production PZT Ceramics Manufacturing Process
PI develops and manufactures its own piezo ceramic materials at its PI Ceramic factory. Multilayer and bulk piezo actuators use different manufacturing processes. Both require a number of highly specialized machines. More information on piezo manufacturing technologies at PI Ceramic.
For a quick overview, click here
Piezo motion devices are often divided into two groups: actuators and motors.
Traditional piezo actuators expand analogous to the applied drive voltage. They provide short travel ranges typically under 1mm.
Piezoelectric motors require more complex drive electronics and can provide long travel ranges (up to 100’s of mm). They typically consist of one or more of piezo elements driving a runner.Piezo Motors are based on different drive principles optimized for high force, high speed, minimized dimensions and cost. All piezo motors are intrinsically non-magnetic, vacuum compatible and self-locking at rest.
Piezo Inertia motors (stick-slip) are most compact and simple with relatively low forces of 1N to 10N and speed to 10 mm/sec.
Ultrasonic resonant motors provide a wide dynamic range from microns/second and below to 100’s of mm/sec.
PiezoWalk® linear motors can achieve the highest forces along with picometer resolution, however velocity is limited from 1mm/sec for high force devices and up to 15mm/second for the new V-8 PicmaWalk drives.
Piezo Actuators and Flexure Nano-Mechanisms
Actuators are the most basic form of piezo drive elements and provide travel ranges from a few microns to a few 100 microns (1-2 mm in the case of bimorph or lever amplified actuators).
Actuators are divided into these basic groups:
- Piezo Stacks
- Highest stiffness & resonant frequency, travel typically 10 to 300 microns. Preloaded for push/pull.
- Programmable Piezo Shims
- Programmable shims are similar to piezo stack actuators but do not require a continuous voltage source to hold a position once programmed.
- Piezo Benders & Bimorphs
- Low profile, long travel to 2 mm, relatively low stiffness, and resonant frequency.
- Piezo Tubes
- Short travel (10 micron range) multi-axis motion feasible, often used as scanners in AFM.
- Piezo Shear Plates / Actuators
- Lateral motion, travel 10-20 microns, high stiffness, fast response.
The latest generation multilayer piezo actuators are based on polymer-free, all-ceramic cofired designs. They can handle high humidity environments unlike their conventionally polymer insulated siblings. PICMA® actuators feature a monolithic design with improved properties compared to descrete stacked piezo wafers or piezo chip designs where many small segments are glued together to form one actuator. Lifetime / Ceramic Encapsulation of Cofired Piezo Stacks
PI's piezo flexure nanopositioning systems employ the patented, award-winning PICMA® piezo actuators, the only polymer-free actuators with co-fired ceramic encapsulation. The monolithic PICMA® actuators are space qualified and were submitted to 100 billion cycles of life testing at NASA's JPL. Read about the testing
The PICMA piezo technology was specifically developed by PI’s piezoceramic division to provide higher performance and lifetime in nanopositioning applications. Cofired multilayer piezo actuators are similar to ceramic capacitors and are not affected by wear and tear. PI nanopositioning systems are designed to be driven at lower voltages than most other piezo systems (100 V vs. 150 V). The research literature, PI’s own test data, and 30+ years of experience all confirm that lower average electric fields lead to longer lifetime.In addition, PI’s monolithic ceramic-encapsulated design provides better humidity protection than conventional polymer-film insulation. Diffusion of water molecules into the insulation layer is greatly reduced by the use of co-fired, outer ceramic encapsulation. Humidity is the main influence on the longterm reliability in low-dynamics or quasi-static operation modes, where the piezo actuator is supplied with a DC voltage to maintain a position for a long time.
The diagram shows the dependence of force and displacement in piezo actuators. The piezo actuator stiffness should be higher than the preload springs. NOTE: Force and displacement in piezo motors are usually not interdependent. Force Generation: High Speed Valves, Dispensers, Pumps
One of the advantages of piezo ceramics is their high force generation and extremely fast response capabilities. This is why piezo actuators (mostly stacks and flexure amplified stacks) are often used to replace solenoids or other classical actuators in fast valve applications, micro-dispensers or pumps. It is helpful to understand how displacement and force correlate to get the most work out of an actuator. Internal and external spring constants should be similar. FEA simulations help optimize dynamics.
This flexure guided and motion amplified actuator can be used in high-speed and precision dispensing applications. It is available in different versions optimized for response, force, and travel. Actuators like these can move full travel in less than one millisecond if used with advanced control techniques. Flexure Guided Actuators and Positioners, Mechanical Amplification
Guided piezo actuators (1 to 6 axes) are complex nanopositioners with integrated piezo drives and solid-state, friction-free linkages (flexures). They are used when requirements like the following need be met:
- Extremely straight and flat motion, or multi-axis motion with accuracy requirements in the sub-nanometer or sub-microradian range
- Isolation of the actuator from external forces and torques, protection from humidity and foreign particles
With the use of flexure guides and mechanical levers, the motion of a piezo stack can be multiplied (up to 100’s of microns or even a few mm) and guided at the same time. Flexure motion is based on the elastic deformation (flexing) of a solid material. Friction and stiction are entirely eliminated, and flexures exhibit high stiffness, load capacity, and resistance to shock and vibration. Flexures are maintenance free and not subject to wear. They are vacuum compatible, operate over a wide temperature range, and require neither lubricants nor compressed air for operation.Piezo Stages: Positioners with Nanometer Class Guiding Precision and High Dynamics
PI piezo flexure nanopositioning and scanning stages provide frictionless flexure guidance with smoother and significantly straighter motion compared to conventional guiding systems (crossed roller bearings, etc.). The achievable resolution, reproducibility, straightness and flatness can only be matched by air bearing systems. PI piezo-driven flexure nanopositioners can easily achieve repeatability and minimum incremental motion in the subnanometer realm, which is measured and documented in our nano-metrology labs.
Left: Wire EDM-cut flexures in a piezo nanopositioning stages provide friction-free motion and extreme guiding precision.
Center: Motion performance of a P-752.11C piezo flexure stage driven with a square wave control signalshows crisp response and true sub-nm positional stability, incremental motion and bidirectional repeatability.
Right: Sub-µrad bidirectional trajectory repeatability means processes may be performed bidirectionally for twice the productivity.Parallel and Serial Kinematic Piezo Stage Designs
There are two ways to achieve multi-axis motion: parallel and serial kinematics. Serial kinematics (nested or stacked systems) are simpler and less costly to implement, but they have some limitations compared to parallel kinematics systems.
Serial Kinematics for Lower Cost / Standard Applications
In a multi-axis serial kinematics system, each actuator (and usually each sensor) is assigned to exactly one degree of freedom. Serial kinematic designs have advantages when it comes to cost and simplicity, and work very well for most standard applications.
Crosstalk
However, the manufacturing precision of even the best machines (and technicians) does not allow for crosstalk-free mechanics at the nanometer level, even in quasistatic operation. For many applications this is not an issue. In a parallel kinematics multi-axis system, all actuators drive only one moving platform, enabling reduced size and inertia, and the elimination of microfriction caused by moving cables. This way, the same resonant frequency and symmetrical dynamic behavior can be obtained for both the X and Y axes. The advantages are higher dynamics and scanning rates, better trajectory guidance, as well as better reproducibility and stability. Still, without the proper test metrology / instrumentation these advantages can easily be overlooked, and a serial kinematics system may appear to the best solution and the conclusion that there is no cross talk could be drawn (see also Coupled and Uncoupled Motion... below).
Parallel Metrology with Parallel Kinematics Provides Higher Multi-Axis Precision and Dynamics
For the ultimate in dynamics straightness/flatness/orthogonality and for coordinate transformation situations (such as rotating about an arbitrary point in space), parallel kinematics are required. Parallel kinematics systems, if designed well, are superior to serial kinematics systems. To reap the benefits of parallel kinematics, you must have high-bandwidth, direct drivetrain-output metrology, so the workpiece can be simultaneously observed and controlled in multiple degrees of freedom.
Since it takes more experience and more advanced controllers to produce a good parallel kinematics precision positioning system, some designers try to avoid that challenge dismissing the technology as unpredictable, uncontrollable. Everyone who has seen a modern hexapod 6-axis motion system compared to a classical stack of translation and rotation stages will immediately understand the benefits of parallel kinematics.Coupled and Uncoupled Motion, Static and Dynamic
Serial kinematics are sometimes referred to as uncoupled motion systems vs. coupled motion systems for parallel kinematics. When it comes the nanometer realm, uncoupled motion does not exist. By nesting or stacking a second and/or third axis onto a translation stage, there will be an influence on the first axis. Any load attached will have a further influence on all axes, even when at rest. And in positioning, things are not always at rest; actually most nanopositioning / scanning applications require very high dynamics. The seemingly uncoupled multiaxis-system then provides coupled (unwanted) motion in many degrees of freedom that cannot be detected by its internal serial metrology sensors, and hence goes partially uncontrolled. These errors may not be critical in many applications, but can be detrimental in some others.
Working principle of a monolithic XY rot-Z parallel kinematics piezo stage. All actuators directly drive the central platform. Integrated parallel metrology keeps all motion in all controlled degrees of freedom inside the servo-loop. The position of the central, moving platform is measured directly with capacitive sensors, permitting all deviations from the prescribed trajectory to be corrected in real-time. This feature, called active trajectory control, is not feasible with serial metrology. Direct Parallel Metrology: All Motion Inside the Servo Loop
Multi-Axis Measurements Relative to a Fixed Reference
Parallel kinematics facilitates implementation of Direct Parallel Metrology — measurement of all controlled degrees of freedom relative to ground. This is a more difficult design to build but it leads to clear performance advantages.
The parallel-kinematics / parallel metrology system “sees" motion in all controlled degrees of freedom and will respond to it. This means that all motion is inside the servo-loop, no matter which actuator (or unwanted external force / crosstalk) may have caused it, resulting in superior multi-axis precision, repeatability, and flatness. Direct parallel metrology also allows stiffer servo settings for faster response. Off-axis disturbances—external or internal, such as induced vibration caused by a fast step of one axis—can be damped by the servo.Position Feedback Sensors for Closed-Loop Control
High accuracy position feedback is essential in a good nanopositioning system, and direct motion metrology is the preferred choice. Direct metrology measures motion where it matters most to the application. Examples of high-resolution, direct metrology sensors are capacitive sensors, laser interferometers, and non-contact optical, incremental encoders. PI employs these and other sensors depending on the application requirements.
Capacitive Sensors
For travel ranges of less than 1mm, capacitive sensors have emerged as the default choice. They are compact, high-bandwidth and absolute measuring devices providing sub-nanometer resolution. For less demanding applications, strain gauge sensors (piezoresistive sensors) are a good alternative.
Capacitive sensors are high-value sensors composed of diamond-machined plates which directly measure the absolute position of the stage platform. Two-plate capacitive sensors consist of two RF-excited plates that are part of a capacitive bridge. One plate is fixed, the other plate is connected to the object to be positioned (e.g., the platform of a stage). The distance between the plates is inversely proportional to the capacitance, from which the displacement is calculated. Short-range, two-plate sensors can achieve resolution on the order of picometers. Residual tip/tilt errors are greatly reduced by PI’s ILS linearization system.
Traditionally deployed in high-end semiconductor manufacturing tools and advanced microscopy applications, such as single-molecule studies, capacitive sensors provide especially precise, accurate, and fast position metrology. Since the stage platform is measured directly, cross-talk and orthogonality can be eliminated. Since no glue is used to attach the sensors to the platform, they are exceptionally stable and reproducible and are usually calibrated to 4th order or higher. Their tightly-controlled RF signal is consequently robust against noise. Their inherent stability makes them an ideal fine-positioning addition to the self-clamping piezomotor long-travel positioning stages.Serial-kinematics (nested) XY piezo flexure stage. Piezoresistive strain gauges derive position information from warp of the flexures or a structural element in the stage. Piezoresistive (Semiconductor) Strain Gauge Sensors
Piezoresistive strain gauge sensors (PRS) are low-cost, high-resolution, but temperature-sensitive devices that are easily integrated in positioning devices. Like most strain gauge sensors, they are glued to the flexure structure or piezo stack, but the extra layer of epoxy between the sensor and structure makes it a challenge to get sufficient long-term stability. PRS do not measure distance directly, but infer position of the moving platform from the nanoscale warping of the structure. Due to the indirect measure of position, inaccuracies can occur and orthogonality errors are unobservable. Calibration to an interferometer allows them to achieve adequate accuracies for classical microscopy applications. Since their output signal is a low voltage DC current, the derived position can be more susceptible to noise pickup and drift.
Classical Film Strain Gauge Sensors
Film strain gauge sensors are another implementation of inferred metrology and are typically chosen for cost-sensitive applications. An SGS sensor consists of a resistive film bonded to the piezo stack or a guidance element; the film resistance changes when strain occurs. Up to four strain gauges (the actual configuration varies with the actuator construction) form a Wheatstone bridge driven by a DC voltage (5 to 10 V). When the bridge resistance changes, the sensor electronics converts the resulting voltage change into a signal proportional to the displacement.
Laser Interferometers
Laser interferometers are capable of accurately measuring long distances and some provide sub-nanometer resolution, although bulky optics must be mounted onto the moving elements of the motion system. PI uses interferometers in testing, calibrating, and qualifying nanopositioning systems.
Optical Encoders
Optical encoders are more compact and rely on diffraction between a moving reticle and a scale composed of finely pitched lines. Position is determined by counting fringes and interpolating between individual peaks, similar to interferometry. The latest linear encoders can provide resolution in the 100 picometer range and below.
Interferometers and incremental optical encoders are relative position sensors that must be initialized at a reference position. The stability of this reference position also influences the overall precision. While not yet common, high resolution absolute encoders break the nanometer barrier, but are still held back by high cost and more complex interfacing.Choice of Control Interface: Digital or Analog or Both?
Analog interfacing provides high bandwidth and remains a popular way of commanding piezoelectric motion systems. It is usually the choice when the control signal in the application is provided in analog form. A key advantage of analog interfacing is its intrinsic deterministic (real-time) behavior, contrasted to the difficulty of accurately timing high-bandwidth communications on present-day multitasking PCs.
However, when analog control signals are not available, or when a significant distance between the control signal source and the nanopositioning controller would affect signal quality, digital interfacing (which must not be confused with digital control) is the preferred choice.
Digital signals can be transferred through copper wires, or for complete EMI immunity, through optical fibers.
Several types of digital interfaces are typically used in piezo-nanopositioning applications: TCP/IP, parallel-port, USB, SPI, RS-232, Fiber Link, GPIB, and, with some digital controllers, direct DSP links. For dynamic, high-precision applications, the exact timing of an interface can be significantly more important than the data transfer rate.Interface Speed: Bandwidth vs. Timing and Determinacy. When does it matter?
Piezo-driven stages can respond to a motion command on a millisecond or microsecond time scale.
That is why synchronization of motion commands and data acquisition have a high impact on the quality of many applications, like imaging or micromachining. Often it is not about interfacing speed, but determinacy; USB and TCP/IP are indeterminate, even though they are good at transmitting huge amounts of data. USB was designed to transfer large blocks of data at high speeds, but exact timing was not a big concern. While insignificant in less responsive positioning systems, this kind of nondeterministic behavior may not be tolerable in high-speed tracking or scanning applications. Each motion command—comprising just a few bytes—must be transferred instantaneously and without latency. A lowerbandwidth bus with higher timing accuracy may perform better in many applications. There are several factors that affect the response of a digital interface:
- the timing accuracy of the operating system on the controlling computer
- the bus timing protocol
- the bandwidth of the bus
- the time it takes the digital interface (in the piezo controller) to process each command
Parallel-port interfaces do not require command parsing and offer the best combination of throughput and timing accuracy.
In addition to the interface properties, the bandwidth of the nanopositioning system (mechanics and servo) matters. A slow system (e.g., 100 Hz resonant frequency) will not benefit from a responsive interface as much as a high-speed mechanism.Servo Control: Digital or Analog and the Difference between Interface and Servo?
Modern closed-loop piezo motors are always operated with digital servo controllers. For piezo actuators and flexure positioners (where the displacement is proportional to the drive voltage) digital and analog servos are available.
The difference between a digital and analog piezo controller has nothing to do with the control interface. Analog controllers with digital interfaces are available as well as digital controllers with analog control interfaces. The answer lies in the servo part of the controller. Traditionally, piezo controllers were based on analog servos, due to the analog output nature of the position sensors employed. Digital servos permit the use of advanced control algorithms, error correction, and linearization schemes not feasible with analog servos. Learn more on digital and analog servo controllers
In addition, parameters can be changed on the fly, and optimization or adaptation to different load and operating conditions can be performed remotely without touching the controller hardware. There are other advantages, such as stage / controller interchangeability, etc.
However, all digital controllers are not the same. Poor implementations can add noise and lack certain capabilities of a well-designed analog implementation, such as fast settling time, compatibility with advanced feed-forward techniques, stability, and robust operation.
PI offers both analog and digital servo controllers. Overview here
All PI nanopositioning controllers (analog and digital) are equipped with one or more user-tunable notch filters. A controller with notch filter can be tuned to provide higher bandwidth because side-effects of system resonances can be suppressed before they affect system stability.Rapid scanning motion of a P-621.1CD (commanded rise time 5 ms) with one of PI's high end digial servo piezo controllers and DDL option. Digital Dynamic Linearization virtually eliminates the tracking error (<20 nm) during the scan. The improvement over a classical PID controller is up to 3 orders of magnitude, and increases with the scanning frequency. Advanced Servo Algorithms: APC and Digital Dynamic Linearization (DDL)
Conventional piezo controllers cannot completely eliminate phaseshift and tracking errors in applications with rapid, periodic motion. This is due in part to the non-linear nature of the piezoelectric material, the finite control bandwidth, and the inherent limitations of P-I-D (proportional integral derivative) servo-control, which cannot react before a position error is detected.
The DDL firmware upgrade option, available with most digital piezo controllers, solves this problem. This technology, developed by PI, reduces the error between the current and desired position to imperceptible values. The dynamic linearity and effectively usable bandwidth are thus improved by up to three orders of magnitude (1000-fold). DDL is of benefit to single- and multi-axis applications where motion follows a given trajectory repeatedly.APC vs. PID Servo Control Algorithm
An alternative control concept to PID is available for the modular E-712 controller for nanopositioning systems: Advanced Piezo Control. It is based on a state controller which, in turn, is based on a model of the positioning system. Advanced Piezo Control actively damps the resonance frequency, in contrast to conventional PID controllers with notch filter where the mechanical resonance is cut out of the excitation spectrum.
Advanced Piezo Control provides faster settling times and lower sensitivity with respect to interferences from the outside. The phase trueness is significantly improved compared to the damping with one or even two notch filters. This has immediate effects on the trajectory trueness and the settling response.
Limitations: If the mechanical system has too many resonances close together, or if the resonance frequency to be damped is about 1 kHz or more, the state controller in this form no longer has any advantage over conventional PID controllers. Learn more on advanced control algorithms
Power Requirements for Linear Amplifiers / Piezo Actuator Operation
The operating limits of a linear piezo amplifier depend on the amplifier power, the amplifier design, and last but not least, the electrical capacitance of the piezo mechanism. For dynamic applications, piezo mechanisms require high charge and discharge currents. Those requirements are best met by power amplifiers that can source and sink high peak currents. The average current is usually of secondary importance. For exact information on maximum operating frequency with a given piezo load refer to the individual operating limits graphs in the PI product spec sheets.
Open-loop operating limits data for PI piezo power amplifiers are tested 15 minutes of continuous operation at room temperature. At power up, (cold conditions) the maximum operating frequency can be higher.
The indicated capacitance values for piezo actuators and mechanisms in PI datasheets are small-signal values (measured at 1 V, 1000 Hz, 20 °C, no load). The capacitance of piezo ceramics changes significantly with amplitude, temperature, and load, up to approximately 200% of the unloaded small-signal capacitance at room temperature. Therefore, the operating limits graphs actually reflect a significantly higher load to the amplifier compared to what a standard capacitor of the same value would represent.
More information is available in the tutorial on the PI Ceramic websitePiezo actuation can also be used to enhance the performance of classical motors and drive systems, forming a coarse/fine positioning system. Traditional coarse/fine mechanisms were run with independent control loops, hindering overall system repeatability and accuracy. The advent of higher-performance motion-control chips and linear encoders with nanometer-scale resolution has allowed construction of hybrid mechanisms in which one feedback sensor provides information to both the coarse- and fine-control loops.
The construction of such a hybrid servo is significantly more complex (analogous to controlling an internal combustion engine and electric motor in a hybrid vehicle at the same time) and the result is the combination of piezo-class dynamics, repeatability, and high stiffness with many centimeters of travel. Requirements for motion devices like these come from the astronomy community, where the next generation of multimirror optical telescopes need long travel, extremely high forces, and motion uniformity with tracking accuracy of less than 2 nm and short-term interpolation errors of less than 0.5 nm.Piezo Motors
Piezo motors are used where long travel ranges in the millimeter to 100’s of mm range are required. Piezo motors can be divided into three main categories:
- Resonant Motors (Ultrasonic Motors)
- High speed, compact, quiet
- Piezo-Walk Motors (Stepping Motors)
- High force, more complex, very high resolution and stability, low speed
- Inertia Motors (Stick-Slip Motors)
- Most compact, lowest cost
A great advantage of piezo motors is their intrinsic steady-state auto-locking capability. It does away with servo dither and the accompanying heat generation, an undesirable feature of electromagnetic linear motors. Stepping and resonant (continuous) piezo motors are in principle nonmagnetic and vacuum-compatible, a requirement for many applications in the semiconductor optics and medical industry.
The motion of resonant piezo motors is based on high frequency oscillation with microscopic amplitudes. The oscillatory motion of the piezo ceramic block is transmitted to a ceramic runner (linear or circular) coupled to a moving stage. Ultrasonic motors are very compact and can attain high speeds combined with resolutions down to a few nanometers or better. Rotary motors feature high torques, especially at low rpm.
By eliminating lead-screws and their inertia and associated linkages and structures, such mechanisms can be significantly smaller and more responsive than classical motor drives. For example, off-the-shelf linear stages can provide 20mm of travel at up to 100’s of mm/s speed, 10g acceleration with a 0.1 mm resolution linear encoder, all in a package 35mm square.
In-position stability is superior to conventional stages since the actuator acts as a brake when quiescent. Fieldlessness, vacuum-compatibility, long life, and other signature advantages of piezo actuation also apply.
The drawback to these piezomotors has traditionally been their difficulty of control. These problems were solved with the latest generation of ultrasonic motor controllers developed by PI. An autotuning circuit constantly keeps the oscillator frequency in the optimum range; and a fast processor now automatically switches between gainsets, enabling the user to take full advantage of excellent velocity constancy, wide dynamic range, and the exceptional stability these friction motors provide at rest.
Learn more on Ultrasonic MotorsBy combining piezo elements acting in longitudinal and transverse directions, the foundation for a walking actuator is composed. These elements can be compressed against a longitudinal rod to confer motion. One familiar progenitor of this family of mechanisms was the Burleigh Inchworm. More recently-developed mechanisms offer extraordinary stiffness and holding force and are optimized for reliability in applications requiring long-term position hold while providing centimeters of travel with picometer-class resolution.
An even newer solution uses cost-effective bender-type piezo elements. Size and cost are substantially reduced; speed is increased by a factor of 10 while power-off stiffness is still remarkable, with 10N holding force. This design also provides centimeters of travel range and picometer-class resolution, ideal for applications like optic positioning in microlithography and sample positioning in electron microscopy.These compact motors are based on the stick-slip effect (analogous to the tablecloth trick), a cyclical alternation of static and sliding friction between a moving runner and the drive element. PI provides linear and rotary stick-slip motors. Like the other types of piezo motors described above, they provide high resolution and excellent long term stability with self-locking capabilities.
Energy-saving, Low Cost Drive Electronics
These motors are used when cost and compact dimensions are a major concern. PI offers several low-cost positioners based on piezo inertia drives with relatively high holding forces of up to 10 N, velocities of more than 5 mm/s and a travel range that is only limited by the length of the moving carriage or runner. The driving element is a miniature multilayer low-voltage piezo stack.Several drive-modes are available, some operating at a frequency beyond what the human ear can pick up. At a standstill, the drive produces its maximum clamping force, with zero holding current and no heat generation. Because of the relatively simple drive concept, drive electronics can be designed compact and cost efficient, many piezo motor types can run on 48 V or less.
Conclusion
The field of piezo motion control has expanded rapidly in recent years, with many new concepts introduced, all aimed at eliminating previous limitations while preserving their unmatched resolution, force, and responsiveness capabilities. Consequently, not only is piezo actuation increasingly suitable for applications formerly addressable only by magnetic linear and rotary motors, but significant benefits accrue in terms of size, speed, fieldlessness, reliability, vacuum compatibility, resolution, dynamics, and reliability. These in turn are enablers for significant advances in existing and new applications.
Basic Piezo Actuators (PZT Stacks, Tubes, Shear-Actuator, Benders)
These actuators expand /contract proportionally to the applied drive voltage. Displacement is typically 10 to 100s of microns, up to a few mm for benders. Usually, there is a tradeoff between force and displacement.
Features- High to very high forces up to 50,000 N
- Very fast response – microsecond to millisecond range
- No wear and tear, no friction, sub-nanometer resolution feasible
- 100 billion cycles life tested for the MARS mission
- Travel range typically 10 to 200 µm (stacks); few mm for bimorph and benders
- Closed-loop operation with feedback sensor for higher linearity
Sub-Groups- Stacked Actuators
- Cofired multilayer construction (low voltage) and classical design (stack of discrete PZT disks/electrodes). High force, motion typically up to 200 µm. Also available with aperture.
- Shear Actuators
- Lateral motion allows design of small, very fast XY and XYZ positioners, also used in piezo stepping motor designs. High force, travel typically limited to 20 µm.
- Tube Actuators
- Often used as scanner tubes for AFM microscopy and for microdispensing (pump) applications. Very fast response (low inertia), low force (fragile), travel range typically <20 µm. XY scanner tubes available.
- Bender Actuators
- Available in multilayer construction (60 V); and classical (bimorph) design (200 to 1,000 V). Low force (< 10 N), very long deflection (to several millimeters), medium response (approximately 10 msec).
Flexure Guided Actuators / Positioning Stages (1-6 Axes)
Flexure-guided, piezo stack-driven nanopositioning and scanning stages or actuators are available. These devices use frictionless flexures and motion amplifiers to provide extremely straight and flat motion, along with longer displacement than can be accomplished with simple piezo actuators. For the highest accuracy, integrated capacitive position sensors provide sub-nanometer precision in multiple degrees of freedom.
Features- Frictionless, fast response (0.1 to 10 ms), nanometer to sub-nanometer resolution, high scanning frequencies to kilohertz range
- Integrated multiaxis-positioning stages available
- Internal motion amplifiers provide motion range up to 2,000 µm
- Essential for nanoalignment, imaging, scanning and nanomanipulation
- Position feedback sensor can be integrated (typically strain gauges for entry level, or capacitive for high-end systems and independent multi-axis measurements)
For both basic and flexure guided actuators, displacement is proportional to the DC output voltage of the piezo driver/servo controller. A position feedback sensor is required for linearization, due to the nonlinear behavior of piezo material. If linearity is not critical, open loop application is also possible.Piezo motors use different types of controllers, and typically, incremental feedback sensors. Force and displacement are not interdependent.
Ultrasonic Motors (Resonant Motors)
Features- Based on high frequency oscillation of a piezo plate (stator) at the nanoscale
- Oscillation is transferred to a slide or rotor via micro-friction
- Unlimited motion range, high speed (to 1000 mm/s in some of the latest designs), fast response (10 to 10s of ms)
- Resolution typically 10 to 50 nanometers, forces, typically 2 to 10 N
- Power-off, position-hold capability (self clamping)
- Small amount of particle generation due to friction
Piezo Stepping Motors (PiezoWalk), such as PI NEXLINE® and NEXACT® Drive
Features- Virtually unlimited motion range
- Based on accumulation of small highly controllable steps
- Picometer resolution by means of direct piezo actuation (linear mode, dither mode)
- High forces to 800 N
- Speed 1 to 10 mm/s
- Fast response (< 1 m/sec feasible)
- Very high stiffness
- Drift-free position-hold when powered down
- Resources