Precision in Motion Control: Overcoming Challenges to Achieve Accuracy and Reliability

When developing a precision motion control system, it’s critical to understand the application’s goals in terms of accuracy and repeatability.

Without precision motion control, artificial intelligence (AI) and autonomous vehicles would still be science fiction. After all, the world today runs on semiconductors — specifically integrated circuits. Modern CPUs, microcontrollers, and RAM are only possible with ever-improving capabilities to control motion with sub-micron or even nanoscale repeatability.

Structures in the first microprocessors from the 1960s were on the order of 10 microns; that measurement has been reduced to single-digit nanometers for the latest generation of chips. 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. Without the continuous advancements in motion control, precision mechanics, and optics, such progress would be impossible.

Precision enables motion control systems to automate manufacturing and inspection processes. Without precision specifications, process quality cannot be guaranteed. While precision is required to automate a task, the level of precision depends on the process’s sensitivity to positional errors, such as errors in accuracy and repeatability.

For example, a milk bottling factory may require precision on the order of 0.25 mm, while a semiconductor mask inspection system would require precision on the order of single-digit nanometers. With regard to motion control applications, the term “precision motion” implies accuracy and repeatability specifications at the micron and sub-micron levels. Such precision motion systems are capable of resolving sub-nanometer moves over travels of up to a few meters according to Brett Heintz, controls product management group leader at Aerotech Inc.

“To put that into perspective, such high resolution is analogous to looking at a photo of the continental United States and being able to see the top of a pencil eraser located somewhere between L.A. and New York,” Heintz explains. “Precision at this level is critical to medical device manufacturers, semiconductor device fabricators, electronics manufacturers, and defense contractors, as they all rely on precision motion systems to ensure their products meet strict quality standards.”

Precision motion control — generally a system’s ability to minimize deviations from the commanded position, velocity, and torque — ensures that machine movements are executed with high accuracy and consistency. It also involves the system’s ability to hold the commanded position while moving or settling into place. Encompassing both the accuracy of the final position and the repeatability of achieving that position over multiple attempts, precision is critical to enhancing manufacturing tolerances and leads to higher performance, reliability, and longevity.

“Ultimately, precision motion control ensures that components are produced to exact specifications, reducing errors and improving overall product quality,” says Ryan LaVoie, director of product management and marketing at Copley Controls. “Poor precision can result in poor quality of automated output, affecting the end product’s performance and reliability.”

Precision Motion Control Guarantees Dependable Performance

Precision is vital in motion control systems as it guarantees accurate, consistent, and dependable performance in applications where even minor deviations can cause failure or poor yield. Positioning precision directly impacts process variability, but it is not the only contributor according to Cliff Jolliffe, Scott Jordan, and Stefan Vorndran at PI (Physik Instrumente).

“It’s a combination of the mechanics, including any feedback devices or lack thereof, the quality of the electronics, and the capability of the motion controller that generates and corrects the trajectory required,” they explain. “Additional factors that will ultimately affect the overall precision and hence the process variability relate to sensor data accuracy or other information that the system calls upon to create or adapt motion.”

Precision Motion Control Enables Higher Speeds

Precision in motion control provides accurate, consistent, and repeatable processes and performance, even with increasing operating speeds. In motion control systems, precision is critical for many reasons. Accurate, consistent, and repeatable processes produce predictable outputs with consistent performance and quality.

“Precision also allows for the processes to be run at higher speeds — reducing cycle times and therefore production costs while maintaining high quality and consistency,” notes Brian Mishuk, vice president of sales and marketing at Zero-Max, Inc.

Defining Precision Motion Control

In motion control, precision is typically defined by a motion system’s accuracy and repeatability. When commanding a system’s motion, a user expects the system to go directly to the commanded location. However, errors within the system and disturbances from outside the system can cause positioning errors.

Accuracy is the difference between the actual position and the commanded position. Repeatability is the variation in error when the system returns to a single commanded position. To visualize accuracy, it is helpful to think of throwing darts at the bullseye on a dartboard. If the darts land all over the board, the process is neither repeatable nor accurate.

If the darts land in a grouping far from the center, the throw is repeatable but not accurate. If the darts land in a grouping around or close to the bullseye, the throw is both repeatable and accurate.

“Precision can also include specifications such as minimum incremental motion and in-position stability,” explains Heintz. “These are defined as the smallest resolvable step a motion system can make and a system’s motion over a specified time period while the position command is constant.”

According to Jolliffe, Jordan, and Vorndran, “precision” is a classical mechanical engineering term with a formal definition: the dispersion about the mean for a significant number of positioning trials as measured by a perfect ruler.

“While this is impacted by the classical precision specification for hardware, much more actually goes into it,” they explain. “Depending on system requirements, precision can also include how consistently velocity and a multidimensional path can be controlled with minimal deviation.”

In addition to repeatability, which is the ability to consistently return to the same position, precision includes factors such as minimum incremental motion (often confused with sensor resolution) and accuracy (how closely the actual position matches the intended one). In some applications, following a path based on predefined coordinates and velocity may not be the highest priority. Instead, tracking a target precisely based on some external feedback might be more important.

For example, an application may require that an optical fiber be coupled to a laser diode with 0.02 dB reproducibility as measured in a statistically valid manner. Classical positioning repeatability is important but is insufficient for achieving such a goal. More critical would be the performance of the controller’s inbuilt alignment algorithms. The speed with which these get the job done would also be a topic of concern.

“Discussion of all this requires that the supplier be expert not only about motion but about the general application challenges,” says the PI team. “So we would define precision in the context of motion control as just part of a deep-dive conversation about the application and its goals.”

Precision Motion Control in Manufacturing

Precision motion control is the foundation of automation in medical device manufacturing, semiconductor device fabrication, electronics manufacturing, and the defense industry. Practitioners in these fields rely on precision motion specifications to guarantee quality in their products and processes.

In the medical device industry, manufacturers must meet stringent quality requirements set by governing bodies. Manufacturers producing coronary stents, intraocular lenses, and cardiac pacemakers have relied on precision motion control for decades to meet quality requirements governing life-altering devices implanted within patients’ bodies.

In the defense industry, contractors rely on precision motion systems to position free space communication systems by controlling the rotation of a mirrored optic to sub–arc second resolution.

In the semiconductor industry, precision motion has been a key enabler in pushing Moore’s law forward for the past 50 years. High-precision motion control is essential in lithography and wafer testing and assembly, where even single-digit nanometer inaccuracies can affect product quality.

“Shrinking transistor features require high-precision motion for mask inspection, wafer positioning, and back-end processing,” says Heintz. “Current state-of-the-art semiconductor processes require complex motion control systems using magnetically levitated stages capable of controlling motion in six degrees of freedom at the sub-nanometer level while providing high-dynamic step and settle capabilities.”

Other real-world applications where precision in motion control has made a significant impact include wafer fabrication (enhancing transistor density and throughput), robotic-assisted surgery (enabling minimally invasive procedures with greater accuracy, reducing recovery times), microscopic metrology, chip wire bonding, 3D printing, ion implantation, and medical imaging.

High-Precision Motion Control in Manufacturing

In laser materials processing, positioner precision goes directly to the quality of the process, according to Jolliffe, Jordan, and Vorndran. Using a sloppy positioner — one with poor repeatability, path control, and velocity control — will result in parts of poor conformity and yield. Classic issues found in laser cutting and drilling include elliptical holes with undesirable bumps rather than clean round circles, or side walls with undesirable tapers where the controller or mechanics can’t compensate for the desired side wall profile. Such errors are amplified as throughput increases.

In microscopy, the ability to scan or section a specimen and then return to a specified point (for further analysis, for example) is determined by the positioner’s repeatability performance. In photonics, the demand for photonic integrated circuits (PICs) is predicted to soon grow by three orders of magnitude. The ability to localize and identify a position of best alignment depends on the positioner’s ability to scan a photonic coupling and return reliably to the point of observed or calculated maximum photonic throughput. Automatic alignment, test, and assembly equipment must be as precise as a few tens of nanometers to achieve performance targets.

In aerospace applications, precision is critical for beam steering systems used for free space optical communication between satellites as well as alignment of cameras and optical components. The manufacturing of high-precision optics, from the latest generation of cellphone cameras to the highly complex lenses and mirrors used in modern lithography systems, often requires nanometer to sub-nanometer precision.

Precision Motion Control for Measuring Precision

Precision is even needed to measure precision. Metrology and inspection systems need motion control that can provide a capability typically 10 times above the level of the device being measured, according to Jolliffe, Jordan, and Vorndran.

Precision metrology ensures that tolerances are met, reducing the likelihood of defects. Applications involving high-tolerance lenses need precision to measure curvature and surface smoothness, as minor imperfections will distort light and impact optical performance.

Super-resolution scanning microscopy relies on progress in nano-positioning scanning technology and precision motion control, which have enabled optical resolution for the imaging of biological processes in the low nanometer range. This is orders of magnitude better than what can be achieved by classic static microscopes, which are limited by the laws of diffraction.

Without recent advancements in the precision and speed of motion stages and controllers, DNA sequencing would not have been possible. Here, typically motion control in three axes is required. Samples are scanned in the XY plane, and a high-speed focusing stage in the Z-axis ensures that optimal optical resolution and maximum throughput are achieved.

Precision Motion Control Challenges

Many factors can impact the success of a high-precision motion control system. Dimensions, tolerances, inertia, environment, and wear are important factors to consider. One of the most important factors is component selection for all parts of the system.

“A system can utilize a very precise servomotor and gearbox or actuator for motion control but fail to realize its full potential if the proper mating components are not chosen,” says Mishuk. “For example, if a lower-performance shaft coupling is used to connect these precise drive components, consistency and speed of the output will be affected. Secure shaft connections of components are also critical to maximize performance, especially in systems with high cycle rates and/or short cycle times.”

Other common factors in achieving high-precision motion control involve the accuracy, repeatability, and resolution of feedback devices. Challenges involve electromagnetic interference, actuator machining errors, control system responsiveness (servo loop bandwidth), bearing tolerances, and permanent magnet motor cogging. Dynamically changing loads (such as during robotic arm extension), low-quality motors with high cog, poor-quality feedback systems, mechanical flatness and straightness, and signal noise can also impact precision in motion system design.

“Noise can be introduced into a system for various reasons, such as poor cabling, shielding, grounding, cable length, and network speed,” LaVoie explains. “When considering the precision of a motion control system, each component needs to be assessed independently and as part of the complete system.”

Consider a system that utilizes a high-performance servo drive with high bandwidth and fast current loop update. The motor is zero-cog for smooth performance. The controller/drive utilizes the EtherCAT field bus for fast and reliable data transmission. However, if the encoder selected is low-resolution/accuracy/repeatability, it will be difficult to realize the benefits of these components.

Likewise, if a motion system pairs a precision linear actuator with minimal backlash and a high-resolution encoder with a poorly designed mechanical coupling/linkage that introduces play into the final assembly, the benefits of the high-precision components will be negated.

Lost Motion Challenges in Precision Motion Control

Precision can be achieved by harnessing sources of lost motion. Whether dealing with rotary or linear systems, addressing sources of lost motion with reduced or zero backlash components is an important design consideration.

Rotational windup that occurs under torque can be another source of lost motion in rotating systems, according to Mishuk. Consequently, torsional stiffness can increase precision in many designs. Precision in terms of concentricity is also important.

“Any eccentricity can affect balance of mounted components, especially as higher speeds are achieved in motion control systems,” says Mishuk. “Imbalance can introduce vibration and mechanical noise, which can affect smooth operation and accuracy of processes performed on a machine.”

Precision in motion control systems is particularly important in high-volume production or in situations with multiple steps where delays and errors can be introduced. Assembly and packaging processes are prime examples. 

“X-Y-Z positioning for machine tools or machining centers with multiple operations can benefit greatly from precision by increasing output without sacrificing quality or creating waste,” Mishuk explains. “High-speed test equipment benefits from precision by achieving more accurate test results, whether it is for longer-term R&D testing or short-term production line quality testing.”

Vibration Challenges in Precision Motion Control

In general, challenges multiply as precision requirements go up. Mechanical issues include friction, backlash, vibration, and noise from bearings. These are best addressed with frictionless air bearings, magnetic bearings or flexures, and frictionless direct drive motors, such as linear or torque motors or piezoelectric actuation.

“The biggest challenge, of course, is that there is more to success in these applications than just precision,” Jolliffe, Jordan, and Vorndran explain. “There are many factors, including control of ambient and motion-generated vibrations. Ideally, a motion supplier would act as a consulting partner and draw from long experience in similar applications.”

Vibrations from external sources, those internal to a system (from motors or bearings), or those induced by rapid acceleration or poor velocity control can impact system performance. These can be addressed by stiff designs, intelligent control algorithms such as input shaping, servo boost, or NanoPWM drives. They can be dampened by additional onboard vibration cancellation units. External vibrat ions deriving from the ground can be kept away with passive air-based isolation systems or active, mostly piezo-based vibration cancellation systems, such as TMC’s Stacis III system.

Many high-performance servo drive manufacturers such as Copley include tools and algorithms to enable reduction of mechanical vibration or resonance at the system level. The nested current/velocity/position loops can be tuned in the frequency domain using frequency analysis to display the frequency response of a system while running a sine sweep.

“Resonances can be easily identified in the bode plot, and filters can be introduced to remove the mechanical resonance,” LaVoie explains. “Furthermore, frequency domain analysis allows for a better understanding of a systems stability margins. Engineers can examine the bode plot to ensure the phase and gain margins are adequate, which helps in preventing instability and oscillations.”

Sensor Bandwidth Challenges in Precision Motion Control

In terms of sensor bandwidth, resolution, and accuracy, the resolution and linearity of encoders are main error sources. Encoders with a high pitch, linearization in the controller firmware, and external interferometers can make significant impacts on precision. Control system bandwidth 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 step for success, according to Jolliffe, Jordan, and Vorndran.

Another challenge is that motion control vendors often generate specifications with poor relationships to actual application usage. For example, repeatability is often demonstrated with beehive charts composed of N motions in one direction followed by N motions in the opposite direction. In such a test, repeatability is alleged to be demonstrated by the correspondence of each forward step with its reverse-step partner.  

The problem is that there is only one reversal in the entire test. In that sense, it does not yield N data points. A much 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,” explains the PI team. “That is how applications typically work. But this testing methodology is time-consuming and very illuminating of any flaws in a motion device. Hence it is used only by the most credible suppliers.”

Many motion control systems require motion in multiple directions, so a system’s 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 huge precision gains for multi-axis motion applications.

Another challenge is that data is often presented as static, but motion is a dynamic property. The way a system performs with a contour speed of 100 mm/s can be quite different compared to when it’s moving at 300 mm/s.

Full Motion System Metrology Loop Challenges

Common challenges in achieving high precision in motion control systems include system stiffness, environmental effects, workpoint offsets, and system complexity. Motion control suppliers design high-precision components — everything from mounting surfaces and bearing rails to servos — with stiffness in mind. However, the full motion system’s metrology loop has to be considered when installing precision motion equipment.

Considerations include stiffness of the machine base material (granite, breadboard, etc.), process equipment, and payloads, according to Heinz. Environmental effects such as thermal expansion and ground/floor vibrations are constant challenges when specifications are in microns and nanometers.

“Left unchecked, these effects can easily render a system unsuccessful,” says Heintz. “For lab systems, mitigating environmental effects may mean shielding the system from the HVAC system’s drafts. For production systems, this may mean supplying adequate airflow through the bottom of a control cabinet.”

Precision motion systems rely on position feedback devices that close servo loops to reject noise. The distance from the workpoint, or point of interest, to the feedback device amplifies off-axis errors such as roll, pitch, and yaw.

“Greater workpoint offsets result in larger errors that are not measured by the feedback device,” says Heintz. “Keeping the workpoint as close as possible to the feedback device is important to reduce the effect of angular errors at the workpoint.”

Finally, system complexity can cause users to miss out on performance benefits inherent in their systems. Complex controller configurations, tuning tools that aren’t user-friendly, and complicated programming environments make it difficult to know if a system is performing to its full potential. Working with an intuitive control platform such as Automation1 gives users confidence that their system is running at its best, concludes Heintz.

Environmental Challenges in Precision Motion Control

Environmental conditions, such as thermal expansion and contraction, can compromise precision by causing physical changes in system components.

“Thermal effects are one of the biggest factors to the apparent non-repeatability of a motion system,” says Heintz. “A large motion system with 100 nm repeatability in a thermally stable environment may easily exceed many microns of non-repeatability over time if the environmental temperature changes by 1 degree Celsius. Thermal expansion of materials such as aluminum and granite as well as the offset between the measurement device (typically an optical encoder or laser interferometer in the case of a large system) and the workpoint contribute to thermal effects.”

There are several ways to minimize the effects of thermal expansion on a precision motion system. Environmental chambers achieve the highest performance. They control temperature, airflow, and humidity within the chamber to a tight tolerance over many hours.

However, due to their cost, environmental chambers are not always the most effective solutions. Simply adding shrouds around a system to protect it from an HVAC system’s direct airflow is a good start for lab and light manufacturing environments.

“For high-precision systems with laser interferometer feedback, temperature control is a must due to the change in the index refraction of air at different temperatures and humidities,” says Heintz. “Weather stations can be used to monitor the temperature and humidity of the environment and adjust the motion system feedback loop accordingly.”

Thermal Growth and Shrinkage Challenges

Temperature variations can cause components to expand or contract, affecting tolerances and alignment, especially when different materials are used in one system, such as steel bearings on an aluminum stage body. This can lead to misalignment in guides, impacting positioning accuracy.

“Low temperatures, especially when looking at space applications, can increase friction in bearings and screw drives, and high temperature can affect viscosity of lubricants, rendering them less effective,” say Jolliffe, Jordan, and Vorndran. “Vacuum applications require special materials, lubricants, and venting of all blind holes to eliminate virtual leaks.”

System Complexity Challenges

In addition to such environmental conditions and stack-up tolerances, system complexity can impact operating and/or mechanical performance, resulting in a negative effect on the overall precision of a motion control system. Complexity can mean more cables, for example, 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 of vibration and other errors. Complexity may necessitate longer elements, imparting torque moments and lowering resonant frequencies. Simple, elegant, and compact designs with good attention to kinematics will have an edge in precision and overall application performance.

Since stack-up tolerances in complex systems can lead to cumulative errors, further affecting precision, poor or marginal tuning for one condition may lead to instability or poor precision in another.

“Strategies to overcome these challenges include calibration via lookup table offsets, which can correct for known deviations,” LaVoie explains. “Advanced feedback devices that self-calibrate can also improve accuracy by continuously adjusting for errors. Products such as Copley Plus drives, which include high-resolution current loops, fast update rates, advanced 32-bit floating-point multiple filters, and FPGA high-speed timer counter circuits, can significantly enhance precision.”

Component Durability Challenges

Durability of components and even corrosion can affect performance and ultimately precision. Designers must look at the complete system for achieving the best results, which makes material and component selection critical. It is essential that all components of the machine are designed and built to handle challenging conditions.

For proper component selection, it is important to partner with a trusted supplier with a proven track record in motion control systems used in demanding environments, according to Mishuk. Components must be reliable and robust enough to handle difficult conditions as well as have the proper ratings and performance to provide the precise output the machine is capable of.

“In many cases, customization is an added strategy to overcome these unique challenges,” says Mishuk. “For example, Zero-Max’s application and engineering team works with customers to customize solutions for their exact needs when a particularly challenging application arises.”

Environmental Vibration Challenges

Other environmental factors include ground/floor vibration and acoustic vibration, which are the enemies of precision motion. Ground/floor vibrations — from other machines, forklifts, and foot traffic — travel through the floor into the machine base and through the motion system. Servo loops try to compensate for the disturbance.

“Depending on the magnitude and frequency of the disturbance versus the servo loop bandwidth, including the zero-magnitude crossover frequency (when viewing a bode plot of the system’s frequency response) and the phase margin, the system may be able to reject some or none of the ground/floor vibration,” says Heintz. “For an inspection tool using a precision motion system, this causes unwanted noise in the inspection result and could lead to failure to successfully inspect a part. Similarly, acoustic disturbances due to pressure variations in airflow across a system can cause disturbances that may impact its success.”

Several isolation methods can be used to minimize the effect of ground/floor vibrations. For large systems with a large moving mass, isolation pads made of elastomeric material can dampen ground/floor vibrations. For higher levels of isolation, passive air bladders can be used between the machine base and the frame. These bladders are designed with a low natural frequency for superior vibration isolation. They can lead to a 30x or greater reduction in magnitude of foot traffic disturbances compared to an elastomeric solution, according to Heintz.

Motion-Generated Vibration

Both ambient and motion-generated vibration must be controlled to a level commensurate with the application’s goals. If an application requires scanning to discern 0.5 micron features — a requirement common in applications ranging from the life sciences to photonics to semiconductors — the vibrational amplitude of the supporting structure and all contributing elements must be better than that, according to Jolliffe, Jordan, and Vorndran.  

Input shaping is another example of the kind of filter that can be deployed to address mechanical resonance or vibration. “Input shaping is a method by which the unwanted command induced vibrations (mechanical frequency) are kept to a minimum by damping them with superimposed impulses,” says LaVoie. “This produces a command that will drive the system with limited residual vibration.”

Similarly, thermal variations that could cause micron-scale dimensional changes must be controlled. Environmental electrical noise is an additional route for corrupting data and hence precision. Multi-axis motion systems are significantly more complex to manage in terms of precision because guiding errors of each degree of freedom accumulate and affect the precision of all involved axes.

For example, even if the Y-axis precision is perfect, if the X-axis produces an unwanted lateral runout of 1 micron, the position will be off by 1 micron. This can be fixed by multi-axis error mapping with a complex interferometer test setup during calibration.

Overcoming Precision Motion Control Limitations

Overcoming precision limitations in motion design requires advanced strategies and technologies that attack the root causes of errors. For example, when precision over a wide temperature range is required, materials with a low CTE, such as Invar, ceramics, and Zerodur, can be used. However, material match is also critical. Bolting an Invar stage onto an aluminum structure can have negative effects. As the aluminum expands, it will distort the Invar stage.

Direct measuring encoders and direct drive motors positioned as close as possible to the center of a linear stage reduce measuring errors otherwise induced by torque applied on the moving platform. A center-mounted linear motor also reduces geometric errors of the moving platform.

XY and XY Theta-Z positioning precision can be improved with a planar design where all axes use the same base plate as a reference (parallel kinematics). This works well with air-bearing-based motion systems, magnetic levitation stages, and piezo flexure stages.

For six-axis motion systems, parallel kinematic hexapods provide many advantages over conventional stacked six-axis motion systems: reduced size, high stiffness, programmable pivot points, no cumulation of guiding errors of individual axes, no friction and torque from dragged cables.

When the highest precision is required, external metrology, such as a laser interferometer, can further improve precision. Advanced control algorithms and drivers with minimal current ripple improve stability and resolution.

With error mapping using external metrology, an error profile created in the controller is 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 Advancements in Precision Motion Control

Recent advancements in precision motion control include the development of self-calibrating feedback devices and high-resolution incremental encoders like the Renishaw VIONiC. These devices enhance accuracy by automatically adjusting for deviations, reducing the need for manual calibration and improving overall system performance, according to LaVoie.

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

In the field of servo drives, advances in wide band gap devices like gallium nitride field effect transistors (GaN FETs) enable high efficiency at increasing current loop update rates. As for safety, there is a continued trend toward pushing more and more safety requirements into drives to minimize the amount of external components and cabling required for system-level safety.

Other advancements include hybrid drives — a combination of long-travel servo-motor-driven actuators and piezo actuators running off a common high-resolution encoder — and a hybrid servo controller directing high-frequency outputs to the piezo drive and lower-frequency components to the servo drive.

“This concept was employed in nano-positioning actuators for ELT, the largest optical telescope in the world,” explain Jolliffe, Jordan, and Vorndran. “More than 2,000 actuators position mirror segments with single-digit nanometer path accuracy.”

AI- and machine learning–based motion control algorithms are another advancement. In the classic feedback and feed forward servo schemes, the frequency range of disturbances that can be rejected is limited by the so-called servo bandwidth.

With the latest control technology, disturbances well above this limit can be compensated for. That means that steady state jitter can be improved and disturbances can be rejected much more effectively, providing superior overall motion performance.

Advances in control algorithms also allow for better step and settling, reduced following errors, and virtually improving the force constant of a motor, either by running the motor cooler or extracting more performance out of a smaller motor.

Advances in PMW servo drives, so-called NanoPWM drives, can now provide the low noise level of traditional linear drives with significant cost, size, and weight savings, according to Jolliffe, Jordan, and Vorndran. The reduced noise level allows for position resolution below 1 nanometer.

Multi-axis error compensation is another advancement in precision motion control. Here, a complex metrology system at the factory is used to measure errors in a motion system in multiple degrees of freedom. The multi-axis errors are uploaded to an error compensation table in the controller, which automatically modifies each motion command to account for the errors in each axis. This is completely transparent to the user.

Improvements in motion control communication bus technologies increase communication rates and decrease jitter between distributed clocks within motion systems. This results in improved motion synchronization between axes even when they are physically separated by long distances.

For highest performance,  Ethernet Fieldbuses such as EtherCAT can be replaced with fiber optic HyperWire networks and communication protocols that provide deterministic, high-bandwidth communication at network rates of 100 kHz and jitter between clocks below 1 nanosecond. This allows for transfer of encoder positions, axis signals, and sensor data between all drives on the fiber optic network within one servo loop cycle, which in turn enables decoupled control for multi-input systems such as magnetically levitated, multi-degree-of-freedom stages used in high-dynamic semiconductor applications.

“Recent advancements in optimization tools such as EasyTune automated servo tuning and optimized path planning allow users to squeeze the last drop of performance out of their systems without having to be motion control experts,” says Heintz. “This empowers users to focus on their process with confidence — knowing they are getting maximum precision from their motion system.”

Future Trends in Precision Motion Control

With the constant demand for more advanced products, there is a greater need for higher position accuracy and systems that run at higher speeds. To meet this demand, we see a growing trend toward customization of components for motion control systems. Each application is unique, and the motion control system being designed should be optimized for a specific application.

Whether making a small modification to a field-proven solution or creating a new design from scratch, system designers can’t afford to sacrifice precision at any level of the system. Innovative suppliers recognize this trend and are committed to customizing solutions to meet unique requirements. “Zero-Max, for example, attributes nearly half of its sales to customized solutions designed for specific customer motion control and precision requirements,” says Mishuk.

Future trends and innovations in the field of motion control may include higher update rates, floating point resolutions, dynamic tuning and compensation countermeasures, improved efficiency, and enhanced safety, according to LaVoie. Advanced system modeling and dynamic correction techniques will allow for real-time adjustments and improvements in precision, further enhancing the capabilities and applications of motion control systems.

AI continues to be a buzzword in the industry. It remains to be seen how AI can help innovate in the field of motion control, but it’s very likely that we’ll see it employed to improve predictive maintenance, error correction, and optimization of control algorithms.

The trend toward higher-precision sensors will continue, and AI will improve the performance of motion controllers, predict Jolliffe, Jordan, and Vorndran. The combination of sub-nanometer precision and the next generation of semiconductor test and production technology, such as piezo actuation and air bearings for long-travel motion, will continue to push boundaries. Magnetic levitation technology will allow for completely bearing-free motion with six degrees of freedom. 

As precision requirements increase and the need for precision motion control reaches more manufacturing floors, ease of use, connectivity, distributed systems, and multi-input control schemes will dominate, according to Heintz. Users of precision motion systems will expect systems to learn from user input, automatically optimizing trajectories and servo gains for optimal performance.

Motion controllers will be increasingly connected to third-party sensors, systems, and robots to interface with factory automation equipment. Motion controllers and drives will move out of control cabinets and into motor hardware to reduce wiring requirements, creating distributed systems that will rely on industrial motion bus technology for interconnectivity.

Finally, motion controllers will support the connection of a vast array of sensors throughout the distributed network. Sensor data will need to be shared across the motion bus at high speed to close multi-input, multi-output control loops using modern space-control techniques.