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PI is a leading manufacturer of precision motion control and automation systems, hexapod 6-axis parallel robotic stages, air bearing motion systems, Gantry Systems, 3D printing, laser machining, and piezoelectric nano-positioning solutions. Applications include photonics, semiconductor technology, medical engineering, assembly, inspection,

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Advantages of Novel Low Profile XY Stages for High Resolution Microscopy

POSTED 03/01/2023

High resolution positioning of microscope samples has traditionally relied on motorized stages with a lead screw system, but this method has limitations. Lead screw mechanisms are typically designed with high gear ratios for relatively slow, yet high resolution movements, or low gear ratios for faster movements with reduced accuracy. To avoid these compromises, microscopy stages can be operated with ultrasonic piezo drives. Piezo-driven stages offer several advantages, such as eliminating gear ratio issues, backlash & play, while providing self-locking in position stability leading to an extremely stable image in long term exosures.

Ultraonic-Motor

Functional principle of of the ultrasonic linear motor.

When it comes to positioning samples in microscopes, XY stages should be as low-profile as possible to allow for easy integration and access. Linear direct-drive mechanisms, powered by compact piezomotors, eliminate the need for bulky attachments required by conventional stages, such as lead screw ducts and flanged-on stepper motors. This provides unparalleled dynamics, and a wide range of velocity and high resolution, which are essential elements for a high- resolution microscope. Due to the jitter-free position locking capabilities, piezo-motor-driven stages offer superb image stability and low-noise operation.

Utilizing their extensive expertise in piezo actuators, piezo motors and nanopositioning mechanisms, PI (Physik Instrumente) has developed a highly versatile microscopy stage with a low profile of just 30mm and without disruptive lead screw ducts or motor projections (see figure 1). This stage can achieve displacements up to 85×135 mm and features a large aperture capable of accommodating holders for Petri dishes, standard object slides, or microtiter plates.

The use of ultrasonic piezo drives results in excellent velocity stability across a broad range, from 10 µm/s to 100 mm/s. Consequently, the stage is suitable for direct visual observation at high magnification (100x objective at approximately 10 µm/s) without the occurrence of visual artifacts such as jerking that can interfere with and tire the user. Moreover, the same microscope stage is equally well-suited for automated scanning applications that require high velocities of up to 100mm/s and short settling times.

 

Motorized Microscope XY Stage, w/Controller & Joystick

PI U-780 XY low-profile microscope stage. Due to the compact direct-drive piezo motor principle there are no interfering lead screw ducts or motor protrusions. The long-travel motorized stage can be combined with the piezo Z nanopositioning stages for Z-stack image acquisition.

Velocity Stability / Constant Velocity:

The broad dynamic range of 10 µm/s to 100 mm/s allows for excellent velocity stability thanks to the ultrasonic piezo drives used. Imaging results allow high magnification.  For example with an 100X objective an extremely low velocity at approximately 10µm/s can be recorded, without visual artifacts caused by "jerking" that will degrade imaging quality. Additionally, this microscopy stage is equally adept at automated scanning applications that necessitate high velocities of up to 100mm/s and short settling times

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Video: Basic function of the ultrasonic motor-driven microscope stage

Dynamic Range:

The high dynamic range of the XY stage results from the use of piezo ultrasonic linear drives (see figure 2), where the high-frequency oscillation of a piezoelectric transducer generates the propulsion force. The patented ultrasonic motors work directly without intermediate elements, unlike rotary motors that require lead screws or gears.  The direct-drive mechanism is backlash-free. When combined with a linear encoder, the stage can achieve a positioning resolution of 0.1 µm and a bidirectional repeatability of 0.4µm, making it possible to reliably locate and precisely approach "points of interest." This feature is particularly beneficial in "high content screening" analysis technology when scanning numerous tissue samples. In addition to short settling times, this level of repeatability is critical for "tiling" images in this type of application.

Low Thermal Drift:

In contrast to directly driven electromagnetic linear motors, stepper motors, and DC servo motors, the piezo-based motor does not consume any energy to maintain a stable stage position, resulting in no heat generation when the stage is at rest. Consequently, there is hardly any thermal drift, in contrast to conventional electromagnetic drives, and the position is maintained with a high degree of stability. This characteristic is particularly beneficial for super-resolution microscopy applications that require extended recording times, lasting several minutes.

Components of the Piezo Drive:

The piezo drive comprises a stator that houses the piezoceramic oscillator and a runner called a friction bar that is directly attached to the movable part of a carriage. The oscillation profile of the piezoceramic generates the forward and backward motion of the drive, allowing for a theoretically unlimited travel range. The ceramic is preloaded against the friction bar, which keeps it in its 'at rest' position when powered down.

XY Motion Controller:

The controller, adapted to the motorized microscope stage and equipped with a comprehensive software package, has "trace memory," which enables the display of the trajectory as a position/time diagram on a connected host PC. This feature enables the control parameters to be optimally adjusted for the specific application.

Piezo Flexure Z-Nanopositioning Stages:

The flexure guided piezo-Z nanopositioning stages from the same manufacturer, which also have a designed with a very low profile, are suitable for high-resolution positioning tasks in the direction of the optical axis, such as Z-stack recordings for 3D imaging applications. They have a clear aperture of 160x110 mm and a vertical range of 200µm, with 1 nanometer resolution and can be mounted on the XY stage without an adapter and controlled using the same controller.