Leading nanometer-level motion control technology innovator — ALIO Industries — is continuing to advocate the examination of the impact of 6D repeatability testing and performance on single and multi-axis motion control systems. Advancements in manufacturing processes and metrology sensors along with the continuing demand from industry to create innovative technologies and products is driving a greater need for motion systems that are both highly accurate and repeatable at the nanometer level.

All motion systems operate in 3-dimensional space and have errors in 6 degrees of freedom (6-DOF). However, motion systems are often only characterized by performance data of a single or subset of these 6-DOF. This practice leaves several error sources unaccounted for in performance data and specifications. ALIO suggests that repeatability performance for metrology inspection and manufacturing systems must now be analyzed and specified using a “point repeatability” method that accounts for 6D spatial errors in order to provide true representation of nanometer-precision performance.

Traditional systems and test methods — plane repeatability. Many traditional stage and motion systems specify repeatability as a single number representing the variation in linear displacement along an axis of travel, i.e. plane repeatability. Historically, this practice was valid as the repeatability specifications were large enough that other error factors were only a small percentage of the total error and could be ignored.

The repeatability of the plane position along the axis is effectively measured over many cycles at a target position. The intersections of this plane with the axis is a point on the axis line and the collection of these points results in 1D repeatability performance.

This test method makes a critical assumption, namely that the plane only moves in one dimension and the axis is perfectly straight. At the nanometer-level, this assumption is not realistic.

6D nano precision — point repeatability. In nanometer-level precision systems, “other” errors that were previously ignored in less accurate systems often become equal to or greater contributors to the 6D repeatability performance. At the nanometer-level, the axis of travel should actually be shown as bending and twisting through three-dimensional space and thus plane visualization becomes meaningless as it will tip, tilt, and twist as the stage moves along the axis. The stage moves in 6D space, therefore neglecting these additional error sources can result in a misrepresentation of actual stage repeatability performance.

Each linear (or angular) direction the stage moves (or rotates) in results in a positional error in that direction. That motion, which must not be neglected when nanometer-precision is desired, will have an associated repeatability of that error motion. Each point on a stage mounting surface will move in 3D space as of a result of this error motion in 6 degrees of freedom. It is the point repeatability of an infinite number of points attached to a stage, that must be characterized by testing and specification data. Thus, each point repeatability will result in a spherical repeatability range.

Measuring 6D point repeatability. To accurately characterize repeatability, X, Y, and Z components must be measured in a systematic process to characterize the point repeatabilities of a stage along the entire axis. Additionally, a process must be implemented to test the influence of pitch, yaw, and roll errors of the axis and their influence on repeatability. In order to have a high confidence in integrated system performance the motion subsystems must be correctly characterized for 6D performance accounting for all error components of stage motion. Without this, claims of accuracy and repeabality are at best pointless, and at worst knowingly misleading.

ALIO Industries has just announced the availability of its new Angulares^TM Hybrid Hexapod®. The 60-degree tip/tilt travel of the Angulares^TM Hybrid Hexapod® is by far the most angular travel range available from any 6-Degree-Of-Freedom (6-DOF) positioner on the market and offers the same unmatched positioning performance found in any of ALIO’s full-line of Hybrid Hexapod systems.

The Angulares^TM features precision crossed roller bearing guides, optical incremental or absolute encoder feedback on all axes, linear motor and/or servo ball screw drives, unlimited programmable tool center point locations and coordinate offsets, and zero backlash on all axes. The design makes the Angulares^TM capable of unlimited XY travel, Z travel for 62 mm which can be increased to 208 mm using other tripod models, tip/tilt travel of 60 degrees (+/- 30 degrees) with continuous 360 degree Theta-Z, XYZ bidirectional repeatability of less than +/- 0.6 arc-seconds, velocity up to 100 mm/second XY and Z, and less than 10 nanometers linear and 0.1 arc-seconds angular minimum incremental motion.

The Hybrid Hexapod® was developed by ALIO Industries to address the inherent performance limitations of conventional hexapods. ALIO’s Patented 6-DOF design seamlessly blends and takes advantage of the strengths of serial and parallel kinematic structures while avoiding their weaknesses. The Hybrid Hexapod offers far greater functional versatility, nanometer-level accuracy, repeatability, and superior 6-DOF trajectories than is possible with any traditional hexapod or stacked stage configuration.

Standard hexapods satisfactorily service applications where micron motion tolerances are required, but as the demand for nanometer requirements expands, standard hexapods struggle. This is because there are performance limitations inherent in all “conventional” hexapod designs.  They operate within 3-dimensional space, and have errors in all 6 DOF.  However, hexapod motion systems have typically only been characterized by performance data of a single degree of freedom.  This practice leaves error sources unaccounted for in several degrees of freedom, especially in the areas of flatness and straightness, which are critical precision needs at the nanometer-level.  The hexapod’s best flatness and straightness of travel is still no more precise than more than 2 orders of magnitude (2 decimal point less) for basic XY motion.

Because hexapods have six independently controlled links joined together moving a common platform, the motion error of the platform will be a function of the errors of ALL links and joints.  Hexapods are known to have optimum precision when performing Z-axis moves, because all links perform the same motion at the same relative link angle.  However, when any other X, Y, pitch, yaw or roll motion is commanded, precision and geometric path performance of the hexapod degrades substantially because all links are performing different motions.  In the case of conventional hexapods built with non-precision joints, bearings, and motion controllers that are not capable of forward and inverse kinematics equations, the source of error is even more pronounced.

The unique design of the Hybrid Hexapod® is comprised of a parallel kinematic tripod to deliver Z plane and tip/tilt motion. This tripod is integrated with a monolithic serial kinematic stage for XY planar motion. A rotary stage integrated into the top of the tripod (or beneath depending on application needs) provides 360- degree continuous  (Theta-Z) rotation.

In this hybrid design, individual axes can be customized to provide XY travel ranges from millimeters to virtually unlimited ranges while maintaining nanometer-levels of precision. Novel forward and inverse controller kinematics provide an unlimited number of programmable tool center point locations plus unmatched path precision and performance.

The 60 degree tip/tilt travel of the Angulares^TM Hybrid Hexapod®, by far the most angular travel range available from any 6-DOF positioner on the market, is perfectly suited for applications including aspheric and freeform optical metrology, silicon photonics packaging and probing, laser micro processing (non-planar substrates and taper control), wafer metrology, camera module alignment and assembly, sensor/image stabilization testing, and optical element and fiber alignment.

To find out more about ALIO’s Angulares^TM or its full range of Hybrid Hexapod systems, contact a member of the team today.

The patented Hybrid Hexapod® was developed by ALIO to address the critical weaknesses of conventional legacy hexapod designs, as well as the weaknesses of stacked serial stages, and to achieve nanometer-level accuracy, repeatability, and high-integrity flatness and straightness during motion.  It utilizes a tripod parallel kinematics structure to deliver Z plane and tip/tilt motion, integrated with a monolithic serial kinematic structure for XY motion.  A rotary stage integrated into the top of the tripod (or underneath it, depending on application needs) provides 360-degree continuous Theta Z rotation.  In this hybrid design, individual axes can be customized to provide travel ranges from millimeters to over one meter, while maintaining nanometer-levels of precision.

However, Bill Hennessey, CEO of ALIO Industries doesn’t look pleased. “I think that maybe the use of the words precision and accuracy by companies working in the motion control sector should be banned. They are meaningless words unless qualified, and even when qualified, can still mean nothing. I see companies claiming, ‘high precision’, ‘best accuracy possible’, ‘ultra precision’. What do these phrases mean to an end-user? How useful are they? Are they just marketing speak, or do they have a currency in industry? Nothing, not at all, and no I’d say!! At ALIO we talk of nanometer-level repeatability, accuracy and precision which actually means something, and as such the use of our motion control solutions in industry grows exponentially.”

The source of Hennessey’s disquiet is that he has positioned ALIO Industries as the world’s only provider of true nanometer-level motion control solutions, and with the Hybrid Hexapod, for example, has developed a technology that exhibits such True Nano Precision® that existing industry validation standards are useless, and a set of new standards based on ALIO’s Point Precision® methodology is being developed by NIST.

“You see, when discussing precision and accuracy, when it comes to motion control there are too many variables that are not fully understood by customers, and which technology suppliers are fully aware of and swerve in their marketing and communications, using data that flatters to deceive, or deceives completely”, Hennessey continues.

“In many ways, the most accurate end of the motion control market is quite a confusing place to be, as the handful of extremely accurate motion systems suppliers tend to use non-consistent and often illusory ways of describing the levels of precision that they can attain. ALIO has always worked in the area of nanometer-level motion control, and as such has a unique perspective on what really works when looking for this level of precision. Because of this, and with the Hybrid Hexapod® very much front and center, we have focussed on educating the customer base to navigate alternative solutions, and give them the tools to interrogate solutions providers in such a way that they can secure a motion control technology suited to their specific applications.

The Hybrid Hexapod had been a game changer for enabling new and novel processes.”

ALIO Industries believes that any claim of precision or accuracy must be first meaningful, and second provable. When looking at motion control solutions such as the Hybrid Hexapod, this is vital, as in common with all hexapods it is a motion control technology that operates with 6 degrees of freedom (DOF), and operates in 3-dimensional space. Because of this the conversation needs to move toward volumetric accuracy.

Despite this, all 6-DOF motion control solutions suppliers are characterised by performance data of a single degree of freedom. This practice leaves error sources unaccounted for in several degrees of freedom, especially in the areas of flatness and straightness, which are critical precision needs at the nanometer-level.  The traditional hexapod’s best flatness and straightness of travel is still no more precise than in the order of magnitude of tens of microns per axis. 

Because hexapods have six independently controlled links joined together moving a common platform, the motion error of the platform will be a function of the errors of ALL links and joints.  Hexapods are known to have optimum accuracy and repeatability when performing Z-axis moves, because all links perform the same motion at the same relative link angle.  However, when any other X, Y, pitch, yaw or roll motion is commanded, accuracy and geometric path performance of the hexapod degrades substantially because all links are performing different motions. 

It is generally accepted that hexapods have relatively good stiffness compared to serial stacked multi-axis systems.  However, it is often only the hexapod’s “Z” (vertical) stiffness that is considered.  Geometric design stiffness has a critical impact on and hexapod’s platform repeatability and rigidity.  A lack of design stiffness relates directly to a weak XY plane stiffness with the conventional hexapod working platform.  Moreover, this inherent design flaw of the conventional hexapod negatively affects XY axis performance, especially with thermal bonding or machining applications that require more force to be performed accurately within the XY plane.

Hennessey continues, “Traditional hexapod providers are aware of these issues, but instead of confronting them, mask the inefficiencies inherent in the system by throwing meaningless precision claims at the situation or not drawing attention to them at all. One for example makes accuracy claims that seem really good, but are in fact impossible to achieve on any 6-link architecture, and above all would be totally out of reach of any customer. The reason for this is that the precision specs that they quote only apply to single axis moves from the center / mid-stroke default position. Who would ever buy a 6 DOF hexapod to only use it one axis at a time at its center of travel?  The accuracy as you move to different positions and angles has to degrade probably by multiples of 5x to 10x.”

The Hybrid Hexapod^® represents a quantum step forward in motion control, and for the first time provides the ability to achieve repeatable nano-level precision, stimulating innovation and promoting manufacturing efficiency previously considered impossible. It is redefining the area of precision motion control, and the rule book is having to be rewritten to accommodate it and to position it correctly against industry alternatives.

The level of precision achievable with the Hybrid Hexapod renders the vague and illusory industry standard claims of micron and sub-micron precision redundant, and has forced industry to move towards the concept of Point Precision^®.

Point Precision^® includes all 6 DOF of errors of each axis in motion, guaranteeing the precision point in the full work envelop, and allows for a “precision number” to be quoted based on an exact point on the wall (as if you used a laser pointer) whereas today’s standard only gives the measurement to the wall as if using a flood light. As a signifier of accuracy and precision today, Point Precision^® truly is a must for many applications from laser processing to metrology.

ALIO Industries has spent 2019 working with numerous customers from across industry that are exploiting the ability to innovate through the use of true nanometer-level motion control solutions.

2019 has been a pivotal year for established nanometer-level motion control solution provider ALIO Industries. Throughout the year, news and coverage of ALIO’s Hybrid Hexapod® has reached every corner of industry globally, and the momentum that has been gained has been exciting as ALIO has helped existing and new customers reach new levels of precision in motion control.

Bill Hennessey says, “In many ways, the ultra-precise end of the motion control market is quite a confusing place to be, as the handful of extremely precise motion control suppliers tend to use non-consistent and often illusory ways of describing the levels of precision that they can attain. ALIO has always worked in the area of nanometer-level motion control, and as such has a unique perspective on what really works when looking for this level of precision. Because of this, during 2019, and with the Hybrid Hexapod® very much front and center, we have focussed on educating the customer base to navigate alternative solutions, and give them the tools to interrogate solutions providers in such a way that they can secure a motion control technology suited to their specific applications.”

In the area of hexapods, this has required ALIO Industries to identify where the usefulness of conventional hexapods expires, as it is here that the Hybrid Hexapod® finds its unique niche.

Hexapods are motion control technologies that operate with 6 degrees of freedom (DOF), and the standard hexapods that abound on the market today satisfactorily service applications where micron motion tolerances are required, but as the demand for nanometer requirements expands, standard hexapods struggle somewhat.

This is because there are performance limitations inherent in all “conventional” hexapod designs.  They operate within 3-dimensional space, and have errors in all 6 DOF.  However, hexapod motion systems have typically only been characterized by performance data of a single degree of freedom.  This practice leaves error sources unaccounted for in several degrees of freedom, especially in the areas of flatness and straightness, which are critical precision needs at the nanometer-level.  The hexapod’s best flatness and straightness of travel is still no more precise than in the order of magnitude of tens of microns per axis. 

Because hexapods have six independently controlled links joined together moving a common platform, the motion error of the platform will be a function of the errors of ALL links and joints.  Hexapods are known to have optimum accuracy and repeatability when performing Z-axis moves, because all links perform the same motion at the same relative link angle.  However, when any other X, Y, pitch, yaw or roll motion is commanded, accuracy and geometric path performance of the hexapod degrades substantially because all links are performing different motions.  In the case of legacy hexapods built with non-precision joints and motion controllers that are not capable of forward and inverse kinematics equations, the source of error is even more pronounced.

Furthermore, it is generally accepted that hexapods have relatively good stiffness compared to serial stacked multi-axis systems.  However, it is often only the hexapod’s “Z” (vertical) stiffness that is considered.  Geometric design stiffness has a critical impact on and hexapod’s platform repeatability and rigidity.  A lack of design stiffness relates directly to a weak XY plane stiffness with the conventional hexapod working platform.  Moreover, this inherent design flaw of the conventional hexapod negatively affects XY axis performance, especially with thermal bonding or machining applications that require more force to be performed accurately within the XY plane.

The Hybrid Hexapod® was developed by ALIO to address the critical weaknesses of conventional legacy hexapod designs, as well as the weaknesses of stacked serial stages, and to achieve nanometer -level accuracy, repeatability, and high-integrity flatness and straightness during motion.  It utilizes a tripod parallel kinematics structure to deliver Z plane and tip/tilt motion, integrated with a monolithic serial kinematic structure for XY motion.  A rotary stage integrated into the top of the tripod (or underneath it depending on application needs) provides 360-degree continuous yaw rotation.  In this hybrid design, individual axes can be customized to provide travel ranges from millimeters to over one meter, while maintaining nanometer-levels of precision. 

Hennessey continues, “Engineers working at the cutting edge of what is possible must be stimulated to ask more as they see that this technology reaches places others cannot, has the potential to promote innovations, and can optimise efficiency and cost-effectiveness in manufacture. The Hybrid Hexapod® is orders of magnitude more precise than traditional hexapods, being 100 x stiffer, 30 x faster, and with 10x the usable work envelope of industry standard options.”

ALIO is always eager to discuss how the Hybrid Hexapod® can be used to benefit customer applications, and the company will work to customize specific solutions for particular customer applications.