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Z-axis positioning plays a key role in a wide variety of applications, including DNA sequencing, chip-level inspection, cell counting, photonics, and more. In autofocusing for scientific instrumentation, for example, the positioning stage needs to rapidly step the objective through a sequence of high-resolution incremental moves, while maintaining a high level of in-position stability as imaging occurs. The Motion Solutions Engineered Solutions group frequently designs these types of systems for our customers. The challenges of these applications led us to develop the Lassen MSL linear motor positioning stage (now available as part of our Vertex product line).

 

We designed the Lassen MSL to provide excellent accuracy and resolution with fast settling times. The stage’s performance in the XY orientation is well known. We wanted to also characterize its performance and suitability for Z-focus applications. For this effort, we set up a vertical axis testbed (see figure 1). The results showed that Lassen MSL stages can settle to within a 10.0-nm position window and remain stable to within 8.0 nm.

Building the testbed
To evaluate the performance of the Lassen MSL, we configured a testbed using an off-the-shelf Lassen stage. The stages can be specified with either magnetic or pneumatic counterbalances, each available in a range of forces and lengths of travel (see table 1). For this project, we added a 0.5 kg load to the stage, offsetting it with a 10 N magnetic counterbalance that offers 20 mm of travel.

Table 1: Counterbalance options for the Lassen MSL linear motor positioning stage

table

Figure 1: Lassen MSL linear motor stage in vertical orientation incorporates a magnetic or pneumatic counterbalance to deliver high accuracy, high resolution positioning with fast settling times.

Lassen stages are equipped with Renishaw encoders. Gold and stainless-steel scales are available to optimize scale accuracy and sub-divisional errors. In the case of this project, the gold scale was sufficient to meet performance targets.

We monitored stage motion and stability with a Renishaw laser interferometer.

The test data demonstrated that the Lassen MSL stage in this setup was capable of settling within a 10-nm position window and maintaining an in-position stability of 8 nm (see figure 3).

Figure 3: Display of the Renishaw interferometer (units of millimeters) shows system stability of 8 nm.
Figure 4. Plot of error (µm) as a function of axial position (mm) shows very consistent performance.

These results should be considered representative; in addition to the Lassen MSL stage, the overall system performance depends upon other system elements such as the drive and controller. The Motion Solutions team can help customers identify the appropriate solution for their specific application requirements.

Lassen MSL solutions are high accuracy, high performance stages available at competitive prices with short lead times. They are offered with a variety of motor, encoder, and counterbalance options to support optimization of a solution around a customer’s application requirements.

It’s important to remember that Z-axis positioning is just one factor in the overall performance of a high precision instrument or microscope. Successfully meeting topline performance targets is highly dependent on many variables introduced by other motion axes and design aspects of the instrument. Our Motion Solutions team has great expertise in building sophisticated electromechanical systems for applications requiring high resolution and high stability positioning. We partner with our customers, leveraging our experience and resources to take a systems-level approach to motion-system design. Our process results in assemblies that meet system performance goals and provide stable and repeatable solutions for OEM production.

byline - Shawn HakimAbout the Author
Shawn Hakim is engineering manager at Motion Solutions.

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