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Piezo Tip/Tilt Mirrors & Scanners: Fundamentals

Single-Axis Systems / Scanners
Two designs of single-axis (qX) tilt platforms are available:

I. Single-Flexure, Single-Actuator Tilt Platform
Examples: S-224 and S-226, p. see link.
The platform is supported by one flexure and pushed by one linear piezo actuator (see Fig. 1). The flexure determines the pivot point and doubles as a preload for the piezo actuator. The advantages of the single-flexure, single-actuator design are the straightforward construction, low cost and small size. If angular stability over a wide temperature range is a critical issue, the differential piezo drive is recommended.

II. Differential-Piezo-Drive Tilt Platform
This design features two pie-zo actuators operating in push/pull mode supporting the platform (see Fig. 2). The actuators are wired in a bridge which is supplied with a constant and a variable drive volt-age. The case features integrated zero-friction, zero-stiction flexures which assure excellent guiding accuracy.

The differential design exhibits excellent angular stability over a wide temperature range. With this arrangement, temperature changes only affect the vertical position of the platform (piston motion) and have no influence on the angular position. In the closed-loop models, availability of two sensor signals permits better linearity and resolution.

A variety of single- and multi-axis implementations is possible.



Multi-Axis Tip/Tilt Systems / Scanners


PI offers two standard designs, both using parallel kinematics. Parallel kinematics systems have the following advantages over serial systems: only one moving platform, fixed pivot point, better dynamics, smaller form-factor. In addition, the design offers better linearity than attainable with two single-axis systems (e.g. two galvoscanners) in a stacked configuration.

I. Piezo Tripod Z/Tip/Tilt Platform
Examples: S-315 and S-316, p. see link, S-325 p. see link.

The platform is supported by three piezo actuators spaced at 120° intervals. Because expansion of an individual actuator affects both qX and qY, more complex control algorithms are required.

With coordinate transformation, platform position commands can be resolved into targets for individual actuators (see the equations and Fig. 3 for details). The piezo tripod has one advantage over the differential drive: in addition to tilt motion, it allows active vertical control (piston motion) of the platform—an important feature for applications involving optical path-length adjustment (phase-shifting).

Also, the design allows for a central clear aperture, ideal for transmitted-light applications. As with the differential drives, temperature changes have no effect on the angular stability.

II. Differential-Piezo-Drive Tip/Tilt Platform
Examples: S-334, S-330, S-340, p. see link, see link and see link.

The platform is driven by two pairs of piezo actuators arranged at 90° angles. Each pair is controlled as a unit in push-pull mode. The four actuators are connected in a bridge circuit and supplied with one fixed and two variable volt-ages. Because each actuator pair is parallel to one of the orthogonal tip/tilt axes qX and qY, no coordinate transformation is required.

Like the piezo tripod design, the differential drive exhibits excellent angular stability over a wide temperature range. In the closed-loop models, availability of two sensor signals permits better linearity and resolution.


Application Articles, Background Information, External Links

Drawings & Images:
 
Fig. 1. Single-flexure, single-piezo actuator tilt platform design.
Fig. 1. Single-flexure, single-piezo actuator tilt platform design.

Fig. 2. Design of a differential-piezo-drive tilt platform.
Fig. 2. Design of a differential-piezo-drive tilt platform.

Fig. 3. Piezo tripod drive: A, B, C are the linear displacements of the respective actuators.<br><br>a =  [2A - (B+C)] / 2 a                  <br>b = (B-C) / b<br>z = (A+B+C) / 3<br><br>Example:<br>S-315 tip/tilt platform (see page <a class=Bildunterschrift href=http://www.physikinstrumente.com/en/products/prdetail.php?sortnr=300600>see link</a>). <br>Ř = 13.9 mm<br>a = 10.4 mm<br>b = 12.0 mm<br>A, B, C   0 to 12 µm
Fig. 3. Piezo tripod drive: A, B, C are the linear displacements of the respective actuators.

a = [2A - (B+C)] / 2 a
b = (B-C) / b
z = (A+B+C) / 3

Example:
S-315 tip/tilt platform (see page see link).
Ř = 13.9 mm
a = 10.4 mm
b = 12.0 mm
A, B, C 0 to 12 µm


Papers & Articles
 
Related Information:
 
S-224 · S-226
High-Speed Miniature Piezo Tilt Mirror
 
S-325 Piezo Z/Tip/Tilt Platform
High-Speed Tripod System for Mirrors and Optics
 
S-334 Piezo Tip/Tilt-Mirror
High Dynamics, Large Tilt Angle, Factory-Installed Mirror
 




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