34 n PRECISION MOTION October 2026 www.drivesncontrols.com motors, or piezoelectric actuators. Vibrations These can originate externally, or internally from system components such as motors and bearings, or they can induced by rapid acceleration or poor velocity control. Vibrations can impact system performance and are mitigated through stiff designs, intelligent control algorithms such as input shaping, servo boost or nano-PWM drives, or by incorporating on-board vibration cancellation. External vibrations can be isolated using passive systems or countered actively using piezo-based active vibration floor cancellation systems. Sensor bandwidth, resolution and accuracy Encoder resolution and linearity are a major source of errors. Encoders with a high pitch, plus linearisation in the controller firmware – accomplished during calibration using accurate external laser interferometers – can impact precision significantly. Control system bandwidth Limitations can lead to sloppy behaviour, following errors and slow settling. Choosing a system with high servo update rates and an EtherCatbased architecture is a good base for success. Another challenge is that motion control vendors often generate specifications with poor relationship to the application. 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. An alternative, 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 work. But this testing methodology is time-consuming and reveals any flaws in a motion device. Many real-world precision applications require motion in multiple directions and therefore the combined performance can’t be derived simply from datasheet specifications 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. An additional difficulty lies in the fact that precision data is often presented as static, whereas the name suggests motion is a dynamic property. How a system performs with a contour velocity of 30mm/s can be quite different to when it is moving at 500mm/s. Environmental conditions A variety of environmental conditions can affect precision in motion control systems, including: n Vibration As mentioned before, vibration must be controlled to a level commensurate with the application. For example, if a task requires scanning to discern 0.5 micron features – a requirement common in applications in life sciences and semiconductors – the vibrational amplitude of the supporting structure and all contributing elements must be smaller than that. Similarly, thermal variations that could cause micronscale dimensional changes must be controlled. Environmental electrical noise is also an additional route for corrupting data and hence, precision. n Temperature variations These can cause components to expand or contract, affecting tolerances and alignment, especially when different materials are used in a system – for example, steel bearings on an aluminium stage body. This can lead to misalignment in guides, impacting positioning accuracy. Low temperatures can increase friction in bearings and screw drives, and high temperature can affect viscosity of lubricants rendering them less effective. n Vacuum applications These require special materials, lubricants, and the venting of all blind holes to eliminate leaks. n Dust, moisture and particles These contaminants can severely impact the precision and reliability of motion and positioning systems. They introduce friction, contaminate bearings and encoders, and can cause electrical interference or mechanical wear. They degrade performance, reduce repeatability, and increase maintenance, especially in high-resolution or cleanroomsensitive applications. Motion systems must be designed to reduce their effects. When managing multiple cables, each cable is a potential path for vibration and unwanted forces to travel to the sensitive parts of an application. Another example of system complexity is bolting mechanisms together, reducing structural rigidities, and introducing 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. One example is the parallel-kinematic approach of six-axis hexapods compared to stacking six individual stages. In general, 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, if motion of an X-axis linear stage produces an unwanted lateral runout of 1 micron, the Y-axis linear accuracy itself could be perfect, yet the Y-position would still be off by 1 micron compared to the controlled and indicated position. This can be fixed by multiaxis error mapping with a sophisticated interferometer set-up. Overcoming challenges Addressing precision limitations in motion systems involves advanced technologies and strategies that target the root causes of the errors. Where high precision is required across a wide temperature range, materials with a low coefficient of thermal expansion – such as granite, Invar, ceramics or Zerodur – are commonly used. Two approaches to multi-axis positioning: (left) a multi-axis stack of individual single-axis stages (serial kinematics); and (right) a six-axis stage, based on a hexapod Stewart platform (parallel kinematics)
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