Scott Jordan, head of photonics, senior director NanoAutomation technologies, PI fellow, Physik Instrumente (PI)
The pace of innovation in the motion control industry has accelerated in the past decade, bringing to market fresh technologies ranging from new drive principles to new concepts in advanced controls. To the user, this has meant a steady progression of finer resolutions, higher speeds, better prices and performances, and smaller sizes. It has also meant more maturity and ubiquity of precision automated motion solutions. Additive manufacturing, for example, has commoditized to the point that appliance-class implementations with micron-scale precisions are plentiful and cheap. Even custom integrations of complicated engineered systems have been facilitated, with new open, extensible control architectures benefiting construction of arbitrarily complex applications.
However, some advancements represent fundamental inflection-points, both for the motion control industry and, more importantly, for the applications they animate. New drive technology is one example, while other innovations fall into the general category of newly intelligent positioning. In both cases, the motion system itself becomes the enabler of an application or its economic viability.
Drive technologies empower new applications
Familiar stepper-motor and direct current (DC) servomotor mechanisms are still the foundation of the motion control industry, but even these venerable drive principles have enjoyed significant advancements that have pushed applications forward. Dramatic cost reductions driven by chip-level implementations of electronic commutation (the sequencing of energising windings as the motor rotates) has democratised brushless motor designs, improving lifetime in intensive usage by eliminating commutation brushes and their inevitable wear. The same technology has allowed linear motor stages, with their high speeds and dynamical benefits, to see increasing deployment and popularity.
Where vendor-specific solutions were once the rule, now modular, open and standards-based control architectures, such as EtherCAT, allow integrators to build tightly synchronised and safe systems that can mix different motion technologies, with each element implemented in optimised fashion without compromise. In this way, specialised subsystems can perform targeted tasks in focused fashion in coordination with broader and often parallel actions and metrology elsewhere in the system.
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A miniaturised integrated X, Y stage, which is driven by closed-loop ultrasonic ceramic linear motors and provides high-speed motion with 20 nm resolution over a travel range of 22 x 22 mm. Image courtesy of PI
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A vacuum compatible nanopositioning motor, based on a piezo inertia ratchet mechanism. Image courtesy of PI
Clever new drive technologies have also emerged to address tough application challenges. Piezo-ceramic technology, for example, is still essential for its exceptional nanoscale positioning capability, leveraging the subatomic-scale potential resolution and supersonic responsiveness of this fascinating class of solid-state material. These actuators remain the vital technology underlying semiconductor microlithography, with its relentlessly tightening design rules and advancing nodes.
But new configurations of piezo-ceramic materials and mechanisms have surfaced in recent years, in addition to the layered stacks familiar from nanopositioning. Ultrasonic piezomotors are an example: tiny slabs of piezo-ceramic that are driven in resonance at ultrasonic frequencies, causing a pusher tip to oscillate in a micron-scale elliptical path to convey tangential force to a driven linear or rotary element. By replacing the bulky spindle assembly, these drives allow especially compact stage configurations with no overhanging motor assemblies. Speeds up to 500 mm/sec are routinely seen in stages built with these new motors, even in form factors barely 30 mm square, and elimination of a conventional spindle assembly also means that any slow, nanoscale drift caused by gradual lubricant displacement in the drivetrain is eliminated. This has enabled a wave of groundbreaking applications such as advanced microscopies in the life sciences and optical trapping in single-molecule biophysics, where the combination of speed, responsiveness and proven nanoscale in-position stability have given rise to new possibilities. As a bonus, stages based on these motors can offer reduced footprints of 30 percent or more versus legacy spindle-driven designs.
Other varieties of novel piezo-based mechanisms abound. In one example, clever stick-slip drive designs combined with new, compact linear encoder technologies allow closed-loop stages the size of a lozenge to be offered, with travels of many millimetres and resolutions down to the nanoscale. Other commercial examples include a piezomotor that drives a rotary screw for automated actuation of formerly micrometre-actuated mechanisms such as mirror mounts, and long-travel walking piezo-ceramic actuators that can provide previous unattainable combinations of travel, resolution and force. Novel piezo-ceramic shims are even available now, allowing fine adjustability of leveling and spacing of sensitive assemblies with permanent stability with power removed.
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The NanoCube 6-axis nanopositioning and scanning stage based on piezo flexure drives. Piezo flexure stages are available with up to six degrees of freedom (DOFs), allowing fast and highly precise scanning, positioning and alignment with virtually unlimited lifetime due to the non-wear and zero-friction design. Image courtesy of PI
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Application of compact X, Y, Z piezo flexure scanning stage in the TERA-print E series, mask-free, high-resolution desktop nanofabrication tool, a 2020 Prism Award winner. Image courtesy of TERA-print
Add to these some clever new implementations of voice coil actuation. This straightforward type of linear motor is known for its dynamical capabilities and has recently been deployed in new ways and with new control principles to build on this foundation to provide longer useful travels and new operating modalities. Examples include a force-controlled actuator for high-throughput industrial testing of touch-driven devices, and a six degrees of freedom (DOFs) hexapod offering extraordinary dynamics for simulation and testing in camera, drone and satellite development.
It is clear that recent advancements in drive technologies have significantly enabled a broad wave of applications. And perhaps the best news is that there is no sign this trend of innovation will abate anytime soon.
Controls gain intelligence and a new applications focus
Traditional motion controllers are general-purpose devices that simply perform positioning in response to commands. The most advanced examples also implement data recorders, waveform generation, utility interfaces and macro functionalities, but the fundamental position-per-command functionality is consistent across the whole industry. Motion systems vary in architectural approach but are often differentiated by speed, resolution and similar attributes. These can be regarded as metrics of obedience: a motion system capable of positioning with nanometre resolution is basically that much more obedient than a motion system with micron-scale positionability.
An automated system for optical device testing based on EtherCAT control architecture, gantry X, Y, Z Cartesian robot, hexapod 6-axis motion platforms and high-speed piezo nanoprecision mechanisms. Image courtesy of PI
Recently, however, advances in computing-power have enabled a new class of task-focused, internalised controller algorithms that speed and facilitate specific application needs. A globally significant example is seen in the revolutionary technology that addresses the need for rapid alignment of elements in testing and packaging of photonic networking products. Immense investments in data centres and networking infrastructure are ongoing worldwide, driven by the world’s appetite for data, which in turn is driven by phenomena ranging from personalised medicine to Industry 4.0, to genomics, social networks, streaming media, 5G and even selfies. Between capacity and throughput requirements, as well as scalability and energy consumption, photonic solutions are essential for meeting these demands. Similarly, trends in video frame-rates and pixel density as well as new computer bus architectures have birthed a new market of high-throughput optical HDMI, USB and Thunderbolt cables for consumer and business applications.
Multiple studies have shown that the costs of manufacturing photonic devices are dominated by the repeated alignments needed to optimise photonic couplings for testing and packaging. Since the dawn of fibre optics in the 1980s, these alignments have been performed by slow approaches, including meandering hill-climbs, raster scans and pointwise gradient searches. With photonic devices exponentiating in complexity and production volume, these approaches posed an intractable, escalating economic roadblock to the industry. To meet this challenge, a new class of alignment automation functionalities was developed in 2016 and implemented as built-in firmware commands in powerful industrial nanopositioning and hexapod controllers. These new commands included non-stop, vibration-eliminating sinusoidal and spiral area scans, which were much faster than legacy raster and serpentine scans, and a new category of parallel gradient search that could simultaneously align multiple elements, channels and inputs/outputs in multiple DOFs, in one fast step. The reduction in overall alignment time is not small; improvements of two orders of magnitude are common. This can have a profound impact on production economics. Prime examples of implementations include FormFactor’s photonic wafer probers and Tegema’s integrated photonics assembly tools.
An 18-axis double alignment system integrating parallel, multi-DOFs alignment functionality to provide fast multichannel alignment of silicon photonics (SiP) array devices in wafer probers. FormFactor’s CM300xi photonics-enabled engineering wafer probe station integrates PI’s fast multichannel photonics alignment systems for high-throughput, wafer-safe, nanoprecision optical probing of on-wafer silicon photonics devices. Image courtesy of Cascade Microtech, a FormFactor company
Moreover, the alignment technique is now seen to be broadly applicable, offering benefits to many other application fields well outside of photonics. After all, many manufacturing challenges boil down to adjusting or controlling positions of elements in multiple DOFs to peak up a signal or figure of merit. And so, the technology that has revolutionised the economics of photonic-device test and packaging can now do the same for applications as diverse as laser manufacturing and imaging-lens assembly.
The trends add up to opportunity
The many possible combinations of new motion drive technologies and new controls featuring autonomous, application-focused functionalities present opportunities for game-changing approaches to mission-critical applications. From the possibilities afforded by a matchbox-sized positioner with 500 mm/sec speeds, 18 mm travel and 100 nm resolution to the potential hundredfold reduction of alignment costs in photonic, optical and laser/electro-optic manufacturing, the new wave of motion innovations enables rapid and profitable progress in many fields.
Physik Instrumente (PI)