TRIPOD - A Hexapod-like Positioning System
The TRIPOD Product Series is the newest addition to SmarAct’s portfolio of compact and modular multidimensional positioning systems, combining serial and parallel kinematics in a hybrid design. Compared to classical hexapods, which are in some way limited in regard to the rotation around their Z-axis, TRIPODs offer continuous rotation capability and high stiffness over the whole working range.
Classic hexapods that should be able to rotate continuously around its Z-axis would have to be equipped with a rotation stage on its top plate which would influence system complexity and the overall cost of such a system. The TRIPOD on the other hand includes such rotation capabilities without mechanical and economical drawbacks.
The central component of a TRIPOD positioning system is the 3D TRIPOD Core, a tip-tilt stage offering two rotational and one translational degree of freedom in a very compact design. Because the TRIPOD is fully compatible to the SmarAct Modular System it can be mounted on top of a high precision XY platform made of SLS linear piezo stages.
The top plate offers a mounting space for an additional rotation stage, thus creating a modular positioning system with six degrees of freedom whereas the rotation around the Z-axis is continuous by design.
The central component of a TRIPOD positioning system is the 3D TRIPOD, a tip-tilt stage offering two rotational and one translational degree of freedom in a very compact design. Because the TRIPOD is fully compatible to the SmarAct Modular System, it can be mounted on top of a high precision XY platform made of SLS linear piezo stages. The resulting 5D system allows the positioning of the pivot point, as the common center of rotation, in all three dimensions. The top plate offers a mounting space for an additional rotation stage yielding to a modular positioning system with six degrees of freedom whereas the rotation around the Z-axis is continuous by design.
The TRIPOD, like all other SmarAct products, is highly customizable and can be integrated into completely customized setups. Regardless if your application requires only a modified base or top plate or a completely different configuration do not hesitate to contact us to discuss your requirements and to work together on the best solution. Let us assist you in bringing your idea to life.
The TRIPOD in its maximum configuration as a 6D stage is a hybrid of a parallel and a serial kinematic positioning system. The top plate is actuated by the simultaneous movement of multiple linear stages in contrast to pure serial kinematic approaches where each translation is the result of the movement of a specific linear or rotation stage.
The arrangement of all the TRIPOD’s linear stages contributes to the overall stiffness of the system and allows the top plate to be translated and rotated with five degrees of freedom, when the additional rotation stage is mounted on the top plate the number of degrees of freedom increases to six.
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 TRIPOD in Cartesian coordinates (X, Y, Z, roll, pitch and yaw) and to adjust the systems pivot point and coordinate system.
User-Definable Pivot Point
The great advantage of the TRIPOD, as well as the SMARPOD, is the possibility to freely set the rotations pivot point. Thereby defining the center of rotation for all axis which allows you to precisely rotate around any addressable point in space.
For applications that require vacuum conditions the SmarAct TRIPODs 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 higher magnetic fields.
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 positioners. The smallest movement increment is 1 nm for linear and 1 μrad for rotary motions.
The linear bidirectional repeatability when using the whole travel range 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 mirror was mounted to the top plate of a mid-size TRIPOD facing a PICOSCALE sensor head. The TRIPOD was then commanded to move 10 steps back and forth in the Z direction with a step height of 10 nm and hold time between each step of 600 ms. The position data recorded with the PICOSCALE Interferometer verifies the excellent linear repeatability of the TRIPOD. 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 12 nm.
The bidirectional angular repeatability when tilting the top plate back and forth was also measured with a test setup utilizing three PICOSCALE Interferometers. A mirror was mounted to the top plate of a mid-size TRIPOD facing the three sensor heads. When performing a rotation, the three sensor heads measure a change in the optical path length from which the rotation angle can be calculated. In this test the top plate was tilted in 10 steps of 1 μrad each back and forth. The hold time between each step was 300 ms. The angular data recorded with the PICOSCALE Interferometers verifies the excellent angular repeatability of the TRIPOD.