Innovative High-Bandwidth Hexapod Concept for Nanopositioning Applications

Parallel kinematic machines (hexapods) with sub-micrometer precision and six degrees of freedom (6-DoF) are gaining traction in photonics, micro-optics, and wafer-level alignment. To meet industrial demands for reliability, precision, and high dynamics, PI developed a compact, direct-drive 6-DoF hexapod using lever-based actuators to reduce complexity, improve performance, and minimize wear. This article outlines the system design and evaluates its precision and dynamic capabilities for industrial-scale use.

However, traditional compact, screw-driven 6-DoF PKMs are limited in performing high-frequency, high-amplitude motion. As shown by Rudolf et al.^[2], these systems can also be subject to accelerated wear during small-amplitude, high-frequency operation, requiring special design solutions, such as implemented in the H-815 ruggedized hexapod to run them in 24/7 demanding industrial applications. In contrast, direct-drive PKMs offer higher accelerations and velocities with reduced mechanical wear, thanks to their simplified design.

While flexure-based systems like PI’s H-860^[2] or the T-Flex hexapod^[3] offer excellent precision, their size and workspace limitations make them less suitable for industrial production lines. To address this, PI has developed a compact, direct-drive 6-DoF PKM comparable in size to existing screw-driven hexapods, combining high dynamics with precision to support increased throughput and reduced downtime in industrial environments.

The newly developed lever-actuated 6‑DoF positioning system (see Figure 3) employs a parallel-kinematic design^[4]. It comprises six identical actuators arranged between a fixed base platform and a movable top platform. This configuration enables the top platform to perform precise lateral and rotational motions along all six axes: X, Y, Z, pitch, roll, and yaw.

The system’s actuators are integrated into the base platform and consist of brushless DC (BLDC) motors with ceramic bearings, each fitted with a lever attached to the motor shaft. This design eliminates moving sensor- or power cables, preventing parasitic forces from degrading system performance. Each lever connects to the top platform via passive struts offering five degrees of freedom — enabled by two universal joints and one rotational joint. Rotating a lever moves the strut’s lower endpoint along a circular path, thereby driving the motion of the top platform. Lever position is measured using a scale mounted opposite the lever (Figures 4a & 4b).

The passive strut and lever lengths were carefully selected to match the workspace of PI’s screw-driven H‑811 hexapod. As shown in Table 1, the functional model delivers slightly reduced X/Y travel, increased Z travel, identical rotations around X/Y, but approximately half the Z-axis rotation. Despite a lower payload due to the absence of drive-screws, it supports many photonics alignment tasks, achieving peak speeds of ~65 mm/s with counterweights — more than 3 times faster than the H‑811’s 20 mm/s. A summary of system specifications is provided in Table 1.

The hexapod’s theoretical resolution depends on the lever position (with pure Z-motion extremes detailed in Table 1); however, along the sensor scale it consistently achieves about 20 nm precision.