35 www.drivesncontrols.com October 2026 PRECISION MOTION n However, proper material matching is equally important. For instance, bolting an Invar stage onto an aluminium structure can be counterproductive, because the thermal expansion of aluminium may cause the Invar stage to bend. Direct-measuring encoders and frictionless direct-drive motors, positioned as close as possible to the centre of a linear stage, reduce measurement errors caused by torque applied to the moving platform. A centrally mounted linear motor also reduces geometric errors in the moving platform. Precision in XY and XY-Rot-Z positioning systems can be enhanced with a planar design in which all axes reference the same base plate – a parallel-kinematic approach. This architecture is particularly effective in coplanar air-bearing motion system’s magnetic levitation stages, and piezo flexure stages, where inherent stiffness, lack of friction, and high geometric stability contribute to improved accuracy. For six DOF (degree-of-freedom) positioning systems, parallel-kinematic hexapods offer significant advantages over traditional stacked designs. These include a smaller footprint, greater structural stiffness, a programmable pivot point, and the elimination of cumulative guiding errors from individual axes. Additionally, hexapods avoid friction and torque caused by cable drag, further enhancing precision and dynamic performance. External metrology systems – such as laser interferometers – can enhance accuracy significantly by providing direct position feedback, independent of the drive mechanism, providing an even higher level of accuracy. Advanced control algorithms and drives with minimal current ripple, such as the ACS NanoPWM drives, improve stability and resolution. Error mapping using external metrology is a technique where an error profile is created in the controller and applied in real-time to correct for deviations from the ideal position. If the controller has a high bandwidth and sufficient processing power, the correction can even be used during high-speed motion, not just at the end of a move. Recent innovations Optical encoder technology has been improving continuously. The latest devices provide picometre resolution. Positioning accuracy in a motion system relies strongly on the quality of the position sensor. Other improvements include hybrid approaches that combine traditional servomotor actuators with piezoelectric mechanisms. These use a common subnanometre resolution linear encoder for feedback and a specialised servo controller that splits the control signal – sending highfrequency components to the piezo drive for fine correction, and low-frequency components to the servodrive for coarse motion. For example, the Extreme Large Telescope (ELT) – the world’s largest optical telescope – uses this hybrid concept in more than 2,000 nanopositioning actuators. Three actuators per mirror segment achieve single-digit nanometre path accuracy. Motion control algorithms based on AI and machine learning can provide additional benefits. In traditional feedback and feedforward servo schemes, the ability to reject disturbances is limited by the system’s servobandwidth. However, with the latest control technologies – such as learning-based motion control – disturbances beyond this conventional bandwidth limit can now be compensated effectively, resulting in significantly reduced steady-state jitter and improved disturbance rejection, leading to superior motion performance. Advances in control algorithms now enable improved step-and-settle behaviour, reduced following errors, and more efficient use of motor dynamics. These innovations can increase a motor’s force constant virtually, allowing it to run cooler or deliver higher performance from a smaller form factor – enhancing both precision and system efficiency. Recent developments in PWM servodrives – specifically, NanoPWM technology – now achieve the low noise levels typically associated with linear amplifiers, while offering substantial savings in cost, size and weight. This reduced noise enables position resolutions below 1nm, making them ideal for ultra-precision applications. Multi-axis error compensation represents a key innovation in precision motion control. In this approach, a complex factory metrology system measures positioning errors across multiple degrees of freedom. These error profiles are stored in a compensation table in the controller, which adjusts every motion command automatically to correct for the known deviations in each axis. This process is entirely transparent to the user, enhancing system accuracy without requiring additional effort during operation. Future trends The trend toward higher-precision sensors is expected to continue, while AI is poised to further enhance the performance of motion controllers. Integrating complementary technologies – such as piezo actuation with air bearings – will allow long-travel motion with sub-nanometre precision, meeting the requirements of next-generation semiconductor test and manufacturing systems, for example, and pushing the limits of what’s possible in precision motion control. Magnetic levitation technology allows bearing-free motion with six degrees of freedom, eliminating mechanical contact and friction, resulting in ultra-smooth, precise positioning that is ideal for applications requiring clean-room compatible, maintenance-free operation and high dynamic performance. Active surface topology nano-manipulation and shaping technologies using piezoactuators allows nanometre-level control of surface flatness, enhancing accuracy in critical optical and semiconductor wafer applications. Additionally, smart actuator technologies can cancel internal vibrations actively in motion systems, supporting higher control bandwidths and increased throughput, without compromising precision. The key takeaway is that the precision of any motion control system depends on a complex interplay of static and dynamic parameters, including mechanical design, control-loop bandwidth, feedback resolution, thermal stability and environmental influences. To achieve specified performance targets, users will progress most efficiently by engaging with an experienced motion-system vendor capable of identifying critical performance drivers and asking the right diagnostic questions early in the design phase. n Positioning errors and repeatability of an air bearing rotary stage before and after error mapping.
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