DOF Automated Objective Focuser

DOF-5 Microscope Nanopositioning Stage

The low-cost alternative to Piezo stages. Starting at $3,900; volume discounts available.

Objective Focusing Stage – DOF-5

The new Dover Objective Focusing (DOF) stage is a low cost, high-performance nanopositioning stage optimized for optical imaging applications. When compared to piezo flexure stages typically used for focusing, the DOF-5 offers greater travel (5 mm) and higher bandwidth (> 150 Hz), providing fast step and settle while maintaining image stability.

Advantages for Nanopositioning Microscopy

The use of a dedicated Z axis focusing stage based on piezo actuators is currently the most commonly applied technique for high-performance imaging; however, piezo-driven actuators have a number of very distinct limitations—despite their current dominance of the microscope focusing market.

The table below highlights some of these limitations and compares them with the features of our new DOF-5 objective focusing stage.

Piezo Flexure Stages DOF Objective Focusing Stages
Typically costs ~$8,000 – $12,000 with controls. Single unit price starting at $3,900 with controls.
Flexure bearing results in off-axis motion and position dependent parasitic force. Crossed roller bearing provides higher stiffness for faster moves. This results in increased throughput and longer nanopositioner life.
Stack or oscillating actuation have a non-linear response and bandwidth decreases as payload mass increases. Brushless linear servo motor actuation provides higher servo bandwidth and a linear response for optical microscopy.
< 300 μm travel requires precise alignment and an additional coarse axis when more travel is required. > 5 mm travel makes alignment easier. It also helps avoid microscope objective crashes and provides enough travel to clear interferences.
Oscillating piezos make a loud screeching noise. A quiet servo is valued by lab workers.
Off-axis, complex controls are typically proprietary which leads to higher costs. Onboard controls result in a lower cost of ownership due to less complexity and fewer cables.

DOF Applications in Optical Microscopy

The DOF-5 has been optimized for microscope objective focusing applications such as:

  • Next-generation sequencing (NGS)
  • Digital cell morphology
  • Automated digital pathology
  • Optical metrology instruments
  • Semiconductor and nanotechnology imaging
  • Digital microscopes
  • High content imaging
  • Automated cell counting
DOF-5 Applications

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The DOF-5 delivers significant performance advantages over piezo stages for a much lower cost. Complete the form below to get pricing information and inquire about volume discounts.

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Design Features

The DOF-5 offers the following features:

  • An innovative internal servo drive controller and optical encoder for precision position feedback.
  • A single connector provides power, communications (RS-232, RS-485, SPI, and CAN2.0B), and autofocus step and direction I/O.
  • A built-in constant force counterbalance prevents objective crashes using upwards bias for regular microscopes or downward bias for inverted microscopes.
  • For repeatable homing, a half travel homing vane is included.
  • Threaded holes allow for stage mounting bolts to be placed at either the front or back of the DOF-5.
  • To prevent objective crashes into the sample, finely adjustable positive and negative end of travel hard stops are located on the side of the stage. Upon power off, a constant force counterbalance will bias the microscope objective away from the sample.
  • Mounting brackets for common microscope objectives are also available.
  • 5 mm travel makes alignment easier and removes the need for additional coarse positioning axes often used with piezo stages.
  • Fully integrated motion control electronics to reduce cabling complexity and system cost.
  • Stiff crossed roller bearings for high bandwidth and linear response.
  • Integrated 1.25 nm or 5 nm resolution position feedback using optical linear encoder and glass scale.
  • High throughput design for fast move and settle performance with very low position jitter.
DOF-5 Overview
A Better Way to Focus
WHITE PAPER

A Better Way to Focus

Read more about high-performance Z axis focusing and recent innovations in this space.

Written by Dover Motion’s CTO, Kevin McCarthy

Download DOF White Paper

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DOF-5 Specifications

Description Specification
Travel (mm) > 5
Objective Payload (g) 100 – 1,000
Resolution (nm) 1.25 or 5
Servo Bandwidth (Hz) ≥ 150 Hz
Stability (nm RMS) +/- 35
Step & Settle 100 nm within
+/- 35 nm in < 10 ms
Bi-Directional Repeatability (nm) 15
Homing Repeatability (µm) 1
Overall Size, excluding objective mount (mm) 77 x 82 x 30
Max Acceleration (G) 300g 1.5
Max Velocity (mm/s) 125 (with 5 nm resolution)
Communications RS232, RS485 full or half Duplex, SPI, CAN2.0B
Inputs Step and direction

Options

The DOF-5 is configurable with the following available options:

  • Encoder feedback resolution of 5 nm or 1.25 nm
  • Communication protocols: RS232, RS485 multi-drop, SPI, CAN 2.0B
  • Objective threaded adapters: M25 x 0.75; M26 x 0.706; M27 x 0.75; M32 x 0.75; SM1, RMS
  • Objective orientation in the top, middle, or bottom of the table in either regular or inverted configuration
  • Counterbalance specified at time of order from 100 – 600 grams
  • Flying lead cables to connect to the stage with standard DOF connector

Performance Plots

 

Fast, Accurate, and Repeatable 100 nm Moves

The above staircase plot displays position vs. time for ten consecutive 100 nm upward moves, followed by ten consecutive 100 nm downward moves. The data for the plot was taken at a 10-kHz sample rate, using a laser interferometer, and a plane mirror mounted at the base of a 300-gram objective. This staircase plot demonstrates the DOF-5’s ability to execute the very fast, accurate, and repeatable small moves typical in focusing applications.

 

High Throughput Steps with Very Low Jitter

The above zoom-in on a single 100 nm step from the staircase plot demonstrates the high-throughput focusing capabilities of the DOF-5. In the above move, with an initial position stability of < +/- 3 nm, the objective performs a 100 nm step, settling into and remaining within a ± 7 nm window, in under 3 msec.

 

Nanometer Level Bi-directional Repeatability

The above plot shows a zoom box being shown over a pair of positions within the 100 nm staircase move sequence. The two selected positions are nominally the same, but are being approached from opposing directions. The position on the left was made during upward moves, while the position on the right was made while moving downward. As such, any lack of bidirectional repeatability will show up when comparing these two positions.

In this extreme zoom, with a vertical scale of 5 nm per division, the two positions (nominally at 400 nm) are each visible at high resolution. Despite being 2.8 seconds apart, and approached from opposing directions, the difference between the mean of the two positions during their 250 msec position hold is under 2 nm.

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