High Performance Motion Control – Systems Approach Provides Nanometer Precision for Industrial Applications

Back to PI Website, www.pi-usa.usHigh performance motion control plays a key part in positioning and handling applications, such as those in semiconductor manufacturing, laser and materials processing, optical inspection systems, additive manufacturing or industrial digital printing. In addition to providing reliability and robustness, deterministic behavior with minimized latency, high-speed synchronization with external devices, such as lasers and cameras, is required to achieve sub-micrometer path accuracy, exact positioning repeatability, high dynamics, and throughput. Safety, ease of operation, and state-of-the-art connectivity for integration into industrial network environments are further requirements.

EtherCat-based modular motion controllers provide the brain power to run multi-axis systems with focus on maximum throughput in industrial nanopositioning applications. (Image: PI / ACS)
EtherCat-based modular motion controllers provide the brain power to run multi-axis systems with focus on maximum throughput in industrial nanopositioning applications. (Image: PI / ACS)

The higher the dynamics and throughput targets of a multi-axis precision motion system, the more holistic the design approach that has to be taken to achieve success. The best positioning mechanics cannot follow multi-dimensional motion profiles without an industry grade motion controller that will synchronize the individual axes on a sub-millisecond time scale, while at the same time communicating with a higher-level automation environment. A systems approach where mechanics, control electronics, and software are designed by the same team, provides obvious advantages for the user.

Customized Complete Systems from One Single Source

When ACS Motion Control joined the PI Group, this was one of the goals. Based on 30+ years of design experience with industrial precision automation, the latest generation of modular controllers from ACS now provides the motion control brain power for PI’s engineered motion systems for industrial applications with the highest demands on precision and dynamics. Over the last 4 decades, PI’s precision positioning systems have enabled countless high-end applications in industries from semiconductor manufacturing to biotechnology.

EtherCat-based controllers make it possible to easily combine different motion subsystems, such as parallel kinematic hexapods and traditional serial kinematics consisting of individual linear and rotary stages. (Image: PI) Watch Video: Hexapod with XY Range Extender https://www.youtube.com/embed/4e44R-6nlJc?rel=0
EtherCat-based controllers make it possible to easily combine different motion subsystems, such as parallel kinematic hexapods and traditional serial kinematics consisting of individual linear and rotary stages. (Image: PI)
Watch Video: Hexapod with XY Range Extender

100,000:1 Dynamic Range, EtherCAT, Extensive Trigger Functionality

ACS motion controllers are modular by design, interchangeable, scalable, and communicate with various Ethernet protocols. They are also EtherCAT masters, responsible for managing all the network nodes (drives, I/Os, sensors) of the EtherCAT network. The servo loop is handled inside each universal drive module for each axis. All current, velocity, and position loops run at 20kHz, regardless of the numbers of axes, a prerequisite for achieving high dynamics with excellent axis synchronization. Extensive, modular trigger functionality aids integration of external devices, such as lasers and cameras.

Performance of V-551 linear motor positioning stage, controlled by with ACS motion controller. The combination of low noise drive technology and proprietary high resolution linear encoders allows for high signal to noise ratio even for step sizes as small as 1nm as shown in the graph above (Image: PI/ACS)
Performance of V-551 linear motor positioning stage, controlled by with ACS motion controller. The combination of low noise drive technology and proprietary high resolution linear encoders allows for high signal to noise ratio even for step sizes as small as 1nm as shown in the graph above (Image: PI/ACS)

In conjunction with the linear and rotational axes, planar scanners or parallel kinematic hexapods, the controllers are part of a customer-selectable complete system designed by PI.

Advanced algorithms in the motion controller minimize jitter, reduce settle times, and prevent vibration. Patented technology allows for the design of extremely quiet, compact PWM drives with dynamic ranges of 100,000:1 – which results in sub-nanometer level standstill jitter and pushes the envelope for metrology applications.

Measurements have also shown these drives to achieve nanometer level of tracking errors while scanning a wafer. Further features are the integrated 3-DOF compensation of positioning errors and yaw compensation for gantry solutions.

Dynamic error correction improves XY positioning accuracy (Image: ACS)
Dynamic error correction improves XY positioning accuracy (Image: ACS)

Tuning and optimization are simplified by a so-called Servo-Boost™ algorithm that identifies the root cause of disturbances in real time and minimizes its effect, making the system more robust and less sensitive to changing loads and interactions between different axes mounted on the same frame.

The result is improved stability and robust control with high positioning accuracy and reduced settling times.

Air-Bearing Planar Stage for Scanning and Wafer Inspection

An example for the application of high-end motion controllers is shown in the 3-motor planar XY-Yaw air-bearing stage that was developed for wafer inspection. Over the entire travel range of 500 x 1000mm, it operates with a straightness/flatness of ±10nm per 10mm travel. To achieve optimal orthogonality alignment between the X and Y axes, the system is mapped on a laser interferometer and the data is uploaded onto the controller, which varies the yaw precisely and dynamically during motion to provide the highest XY accuracy. The controller also dampens oscillation actively using the profile-shaping algorithm.

PIglide HS, standard planar air-bearing XY-Yaw linear motor stage for high-precision scanning and inspection applications. (Image: PI) Watch Video: How Air Bearings Work https://www.youtube.com/embed/l2B12U6NtQw?rel=0
PIglide HS, standard planar air-bearing XY-Yaw linear motor stage for high-precision scanning and inspection applications. (Image: PI)
Watch Video: How Air Bearings Work

The air-bearing planar stage is powered by electromagnetic linear motor direct drives. Its modular design allows for different travel ranges and encoder types, depending on the required positioning accuracy. The friction and wear-free air bearings ensure extremely level motion, constant velocity, and virtually unlimited lifetime.

Custom XYZ-Theta-Z air bearing multi-axis system for wafer inspection. The gantry-mounted Z-stage is equipped with a pneumatic counterbalance. (Image: PI)
Custom XYZ-Theta-Z air bearing multi-axis system for wafer inspection. The gantry-mounted Z-stage is equipped with a pneumatic counterbalance. (Image: PI)

Highly Accurate Positioning System for Laser Processing

Precision motion control is also required for imaging and laser processing applications. In the case of laser cutting for example, a highly dynamic XY positioning system, based on ironless linear motors and crossed–roller bearings is employed. Mechanical bearings cannot provide quite the precision of air bearings, but high-end crossed roller bearings are good enough for many sub-micron-positioning applications and they are more compact than air bearings, allowing easy integration into tighter spaces. The compact XY-stage in this example provides a straightness/flatness of ±3µm over the entire travel range of 200mm, with position repeatability of 0.2µm and load capacity of up to 20kg. The controller used in this motion system supports both position- and velocity-dependent laser triggering to optimize synchronization of motion and laser pulses when cutting corners or arcs.

Integrated low-profile XY linear motor stage system with cross-roller bearings for laser cutting applications. (Image: PI)
Integrated low-profile XY linear motor stage system with cross-roller bearings for laser cutting applications. (Image: PI)

The roundness of the points and the gap spacing determine the quality of the cutting line. A special algorithm in the controller synchronizes the motion with the laser pulses so that the size of the points and the gaps remain constant even in corners. The laser performance remains constant, and velocity of the motion is adjusted correspondingly. The same applies to cutting arcs and circles. This also avoids inaccuracies that are caused by a possible discontinuation behavior when moving along an arc. Roundness and arc cutting are no longer dependent on motion parameters.

Precision Laser Machining Demo

The excellent synchronization between motion and the laser pulse results in a consistent center line distance between adjacent dots (Image: ACS)
The excellent synchronization between motion and the laser pulse results in a consistent center line distance between adjacent dots (Image: ACS)

Similar increases in accuracy can also be achieved in other application fields. Advanced motion algorithms allow for significant throughput increases in industrial multi-axis motion applications by looking ahead and setting motion parameters properly according to the upcoming segments. The software allows the user to decide whether a corner should be passed with reduced velocity for maximum accuracy, or without velocity change in order to improve throughput.

The large bandwidth of motion controllers and nano and micro-positioning mechanisms together with the systems design experience gathered over decades between engineering teams at PI and ACS provides an excellent basis for cutting-edge motion projects in industries from semiconductor manufacturing to nanotechnology and medical engineering.

Watch Video: A 10-axis precision automation system https://www.youtube.com/embed/RcBa2VJDQPk?rel=0 (Image: PI)
Watch Video: A 10-axis precision automation system (Image: PI)

 

WATCH video: Air Bearing Capabilities at PI USA>
WATCH video: Air Bearing Capabilities at PI USA

 

Further Reading:

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About PI

PI (Physik Instrumente) is a leading manufacturer of precision motion control equipment, piezo motors, air bearing stages and hexapod parallel-kinematics for semiconductor applications, photonics, bio-nano-technology and medical engineering. PI has been developing and manufacturing standard & custom precision products with piezoceramic and electromagnetic drives for 4 decades. The company has been ISO 9001 certified since 1994 and provides innovative, high-quality solutions for OEM and research. PI is present worldwide with fifteen subsidiaries, R&D / engineering on 3 continents and total staff of more than 1,000.

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