SMARPOD - A Hexapod-like Positioning System

Working Principle

The SMARPOD is a parallel kinematics positioning system. The top plate is actuated by the simultaneous movement of multiple linear stages in contrast to a serial kinematic approach where each translation is the result of the movement of a specific linear or rotation stage. The parallel arrangement of the SMARPOD’s stages contributes to the overall stiffness of the system and allows to the top plate to be translated and rotated in six degrees of freedom.

Control in Cartesian Coordinates

Calculation of the kinematics model and device control is encapsulated in a software package. Programming interfaces and graphical user interfaces allow to move the SMARPOD in Cartesian coordinates (X, Y, Z, roll, pitch and yaw) and to adjust the systems pivot point and coordinate system.

User-Definable Pivot Point and Axis Alignment

The great advantage of the SMARPOD is the possibility to freely set the rotations’ pivot point. Thus, defining the center of rotation for all axis which allows you to precisely rotate around any point in space. This is a great advantage in many applications, e.g. for the alignment of optical components. For example, when mounting a fiber optic holder with a free standing fiber onto the SMARPOD you can easily define the end face of the fiber as the pivot point. Such a setup allows you to precisely change the orientation of the emitted beam while keeping the fiber end point pinned to a fixed point in space. The coordinate system can be adjusted as well. Shifting and rotating the base coordinate system allows the SMARPOD axes to be aligned with objects in its environment.

Apertures

All SMARPODs with circular base plates include an aperture in the base and in the top plate, respectively. These apertures allow to gain access from beneath the positioning system to electrically connect the payload or to gain optical access to mounted components.

Environmental Specific

For in-vacuo applications SmarAct SMARPODs are available in high and ultra-high vacuum compatible versions. Furthermore, they can also be made out of fully non-magnetic materials to be used in applications utilizing charged particle beams or high magnetic fields. A minor restriction applies to the P-SLL SMARPOD as its X stage is based on a SLL stage which is only HV compatible and is not available in a non-magnetic version.

High Resolution

A backlash-free mechanical design makes it possible to achieve a movement performance of the positioning system which is in the same order of magnitude as for our single stages. The smallest movement increment is 1 nm for linear and 1 μrad for rotary motions.

Linear Repeatability

When using the whole travel range the linear bidirectional repeatability in X, Y and Z is 200 nm. For smaller movements the repeatability is in the order of several nanometers which has been verified in a test bench setup utilizing SmarAct’s PICOSCALE Interferometer.
For this test, a plane mirror was mounted to the top plate of a SMARPOD facing a PICOSCALE sensor head. The SMARPOD was then commanded to move 10 steps back and forth with a step height of 10 nm and hold time between each step of 200 ms. The position data recorded with the PICOSCALE Interferometer verifies the excellent linear repeatability of the SMARPOD.
When repeating the test for longer travel ranges of 1 mm the linear bidirectional repeatability shows that the reference position can be repeatedly reached with an accuracy of 7 nm.