Machine Design

Slick moves for microscope slides

PZT motors make possible an innovative way of digitizing slides of medical specimens.

Visible in the ScanScope interior is the Nanomotion motor powering the microscope focus. Aperio considered conventional motors for the motion system but found their dynamic stiffness was not up to the task. The Nanomotion PZT motors were also much smaller and were better able to provide a uniform velocity, important for constructing digital images without artifacts.

Superimposed on this view of a Nanomotion motor is a representation of the device's PZT actuator as a contorts to generate motion at its friction tip. The PZT stack resides on a pole passing through its center. Stack contortions on the pole push the friction tip out and pull it away from the stage surface to generate linear motion.

Pathologists need no longer squint through a microscope eyepiece to scrutinize tissue samples thanks to a cleverly designed digital slide imaging system.

Aperio Technologies Inc. in San Diego deploys its ScanScope system using three direct-drive, PZT-based servomotors to position slides under microscope optics. Slides get digitized 20 times faster than with comparable devices through use of a CCD imaging chip that records 15 15-mm slides one line at a time. The system steps the slide under the microscope optics at a constant velocity to ensure image stripes align without introducing image artifacts.

One complicating factor is that the slide surface can be rough on a microscopic scale. The optics must follow tissue contours to keep focus as the sample moves under the objective.

Aperio worked with automation distributor Minarik Automation and Control, San Diego, to devise the motion system. Three PZT motors from Nanomotion Inc., Ronkonkoma, N.Y., focus the lens and position the slide. All three operate as servomotors. PZT motors powering the X and Y axes move the slide into position under the lens system once it has been plucked from a slide magazine. The Z-axis motor handles lens autofocus. It can move and settle fast with micrometer-scale resolution. It also can hold and brake the lens mechanism, a feat not possible with other kinds of servosystems.

Aperio says its line-scanning technique works better than methods used in other slide-canning systems. The usual approach image one small rectangle of slide area at a time step-and-repeat process. This makes it tough to tissue contours accurately because focus is limited one focal position per image tile. In contrast, of the PZT motors lets the ScanScope focus orders of magnitude faster than that possible with ordinary scanners.


Aperio Technologies Inc.
(760) 539-1100
Minarik Automation and Control
(888) 646-2745
Nanomotion Inc.
(800) 821-6266

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