Throughout the world various types of metrology applications share a common need for increased precision. Metrology is the scientific study of measurement. Metrology applications take some type of measurement to collect certain data. Markets such as life science, semiconductor and electronics manufacturing rely on metrology instrumentation to ensure their process is completed correctly. The need for precision is further underscored when you realize the samples/products can be extremely small (i.e. human cell) as well as highly sensitive (i.e. touch-screen electronics). Having high precision motion technology is key to ensure the application will be completed successfully.
This blog post will cover the basics of metrology applications, but if you are interested in learning more, Parker has published a detailed white paper on the topic, which we encourage you to download here.Metrology applications
Listed below are some examples of metrology applications by market. Many applications can be used in more than one market as well. For example, all the markets will use some type of microscopy in their process.
- DNA sequencing
- Wafer inspection
- Optical profilometry
- Laser profilometry
- Non-contact metrology
There are different types of metrology applications, and each have their own key considerations. This blog post will focus on dynamic metrology.
- Dynamic metrology – applications where measurement data is collected while either the measurement sensor or the unit under measurement are in motion
- Static metrology – applications where measurement data is collected while both the measurement sensor and the unit under measurement are at a stable location
- Focusing – a special type of static metrology where an axis, typically vertical, is used to focus on a sample for measurement
Errors in positioning are normally specified in terms of the accuracy of positioning and the repeatability of positioning. The actual sources of these errors can occur in three sub categories – linear, Abbe (roll, pitch, yaw) and planar errors. The source for these errors varies and could have occurred during production or while the application is in process. Examples include deflection, friction, bearing and machining inconsistencies and feedback device.
Velocity control relates to the speed of the stage’s motion and the ability to control it. When there is a variation of velocity as compared to the commanded velocity, this is known as a velocity ripple. Velocity control is critical for dynamic metrology applications because if the speed varies throughout the application process, accurate and consistent results will not be obtained throughout.
The best actuator option for dynamic metrology applications requiring high precision and speed is a linear motor driven stage, specifically one with an ironless linear motor. Since the linear motor couples directly to the linear load, backlash, efficiency losses and other positional inaccuracies are greatly reduced compared to screw or belt driven actuators. Also, linear motors typically have a smaller form factor which overall will improve the stiffness and positional errors. Finally, linear motor actuators have the best control of its speed throughout the application.
While maintaining a reasonable commercial cost, linear motor actuators are the only ones that can meet the critical specifications for dynamic metrology applications previously discussed. To confirm this, Parker uses a laser interferometer to measure any potential positional errors. After testing, reports on the actuator’s performance are generated which consistently show that linear motor actuators outperform those with other drive train mechanisms.
Further details on dynamic metrology download the whitepaper, "Understanding Critical Specifications for Dynamic Metrology Applications."
Parker metrology application solutions
Stage stability and velocity control on a linear motor actuator are crucial in order to have a successful dynamic metrology application. With over 20 years of experience in the high technology precision markets, Parker offers the expertise and consulting services to help instrumentation developers optimize the precision of their equipment and their process. These process optimizations will contribute to continued reductions in the customer’s overall spend, while throughput increases. You can learn more about Parker’s linear motor stage capabilities by visiting our website.
Article contributed by Patrick Lehr, product manager for precision mechanics, Electromechanical and Drives Division North America, Parker Hannifin Corporation.