9 Key Questions & Answers for Precision Motion & Positioning System Users

For example, an application may require coupling an optical fiber to a laser diode with 0.02 dB reproducibility, verified through statistically valid measurements. While classical positioning repeatability is important, it is not sufficient to achieve this level of precision. More critical is the performance of the motion controller’s alignment algorithms. The speed at which these algorithms complete the task is also a key consideration. Addressing such challenges requires a supplier with deep expertise — not only in motion control but also in the broader application context.

So, we would “define precision in the framework of motion control” as just part of a deep-dive conversation about the application and its goals. More information can be found in our article » “Defining Micropositioning and Nanopositioning Terminology”.

Semiconductor Manufacturing: High-precision motion control is essential in lithography, wafer test and assembly, where even single digit nanometer inaccuracies can affect product quality.

Aerospace: Precision is critical for beam steering systems used for free space optical communication between satellites as well as for alignment of cameras and optical components.

Optics: Manufacturing of high precision optics requires active optical alignment of multi-lens systems, from cell phone cameras to the highly complex lenses and mirrors used in modern lithography systems often requires nanometer to sub-nanometer precision.

Semiconductor Technology: Modern society depends heavily on semiconductors — particularly integrated circuits such as CPUs, microcontrollers, and memory modules. The familiar downward physical scaling of Moore’s Law drives both an upward trend in capability and processing power and a downward trend in cost due to the ability to generate more chips per wafer. These are only possible with ever-improving capabilities to control motion with sub- micron or even nanoscale repeatabilities. Structures in the first microprocessors from the 1960’s were on the order of 10 microns and have been reduced to single digit nanometers for the latest generation of chips. Without the continuous advancements in motion control, precision mechanics, and optics, no such progress would be possible and AI and autonomous vehicles would still be science fiction.

Sensor Bandwidth, Resolution and Accuracy: The resolution and linearity of encoders are main error sources.  Here, encoders with a high pitch, plus linearization in the controller firmware – accomplished during calibration with external highly accurate laser interferometers – can make significant impacts on the precision.

Control SystemBandwidth: Here, limitations can lead to sloppy behavior, following errors and slow settling. Choosing a system with high servo update rates and an EtherCat based architecture is a good base for success.

Another challenge is that motion control vendors often generate specifications with poor relationship to actual application usage. For example, you will often see “repeatability” demonstrated with beehive charts composed of N motions in one direction followed by N motions in the opposite direction. In such a test, the repeatability is alleged to be demonstrated by the correspondence of each forward step with its reverse-step partner. The limitation, however, is that there is only one reversal in the entire test. In that sense, it does not yield N data points. A more stringent standard for these measurements is ISO 230-1.

Another even more statistically valid approach would be to start at each of M random offset positions, with each followed by a random motion, followed by a return. The difference in measured position between each random offset and the return to that position, compiled over a large number M of trials, builds a typically Gaussian statistical picture of the positioner’s repeatability. Note that each data point involves a reversal! That is how most applications typically work.  But this testing methodology is time-consuming and very illuminating of any flaws in a motion device.  

Many real-world applications for precision motion control require motion in multiple directions and therefore its combined performance can’t be simply derived from the specifications of a data sheet for a single component actuator or stage. Error mapping in more than one axis  is complicated but provides significant precision gains for multi-axis motion applications. 

Another challenge is that precision data is often presented as static where the name suggests motion is a dynamic property. How a system performs with a contour velocity of 30mm/sec can be quite different to when it is moving at 500mm/sec. 

Vibration, as mentioned above, must be controlled to a level commensurate with the application’s goals.  For example, if a task requires scanning to discern 0.5 micron features — a requirement common in applications ranging from the life-sciences to photonics to semiconductors — then the vibrational amplitude of the supporting structure and all contributing elements must be smaller than that. Similarly, thermal variations that could cause micron-scale dimensional changes must be controlled. Environmental electrical noise is also an additional route for corrupting data and hence, precision. 

System complexity could be something as ordinary as managing multiple cables, and each cable is a potential path for vibration and unwanted forces to travel to the sensitive parts of an application. Complexity can mean more mechanisms bolted together, reducing structural rigidities, a source for vibration and other errors. Complexity may necessitate longer elements, imparting torque moments and lowering stiffness and resonant frequencies – increasing settling time. Clearly, simple, elegant and compact designs with good attention to kinematics will have an edge in precision and overall application performance. An example is the parallel-kinematic approach of a 6-axis hexapod compared to a stack of six individual stages. 

Addressing precision limitations in motion systems involves advanced technologies and strategies that target the root causes of the errors. Consider a case where high precision is required across a wide temperature range: here, materials with a low coefficient of thermal expansion (CTE) — such as granite, Invar, ceramics, or Zerodur (a lithium-aluminosilicate glass-ceramic) — are commonly used. However, proper material matching is equally important. For instance, bolting an Invar stage onto an aluminum structure can be counterproductive, as the thermal expansion of aluminum may cause the Invar stage to bend. Direct measuring encoders and frictionless direct drive motors, positioned as close as possible to the center of a linear stage, reduce measurement errors caused by torque applied to the moving platform. A centrally mounted linear motor also minimizes 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 planar air-bearing motion systems magnetic levitation stages, and piezo flexure stages, where inherent stiffness, lack of friction, and high geometric stability contribute to improved accuracy.

The most important strategy is to talk to an experienced motion system provider willing to share their knowledge and be a partner for an application or project. Beyond the benefits of having such a partner involved at the earliest stages of application development, a desirable motion supplier will have a deep toolkit of technologies to draw from, and a business model that can support the process from earliest explorations to rapid scaling and deployment. 

In the rapidly growing field of silicon photonics, aligning optical fibers to components, such as lasers, microlenses, waveguides, and fiber arrays, requires nanometer-level precision. For high-volume industrial production, both alignment speed and accuracy are critical. New AI-supported alignment algorithms and mechanisms have reduced alignment times by orders of magnitude.

Optical encoder technology has been improved continuously. The latest encoders provide picometer range resolution. Positioning accuracy in a motion system very strongly relies on the quality of the position sensor.

Other improvements include hybrid approaches that combine traditional servo-motor actuators with piezoelectric mechanisms. These systems use a common sub-nanometer resolution linear encoder for feedback and a specialized servo controller that splits the control signal — sending high-frequency components to the piezo drive for fine correction and low-frequency components to the servo drive for coarse motion.

Recent developments in PWM servo drives — 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 1 nanometer, 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 within the controller, which automatically adjusts every motion command 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.

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 enable long-travel motion with sub-nanometer precision, meeting the demanding requirements of next-generation semiconductor test and manufacturing systems and pushing the limits of what’s possible in precision motion control.

Magnetic Levitation technology enables completely bearing-free motion with six degrees of freedom, eliminating mechanical contact and friction. This allows for ultra-smooth, precise positioning, ideal for applications requiring clean-room compatible, maintenance-free operation and high dynamic performance.

Active surface shaping technologies using piezo actuators enable precise control of surface flatness, enhancing accuracy in critical optical and semiconductor wafer applications. Additionally, smart actuator technologies can actively cancel internal vibrations within motion systems, supporting higher control bandwidths and increased throughput without compromising precision.