US patent granted for hybrid hexapod technology

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New nanometre-accurate hexapod opens up applications in laser processing and metrology

Earlier this year Alio Industries received a US patent for its hybrid hexapod, a device that the firm claims overcomes the performance limitations of traditional hexapod designs to offer nanometre, rather than micrometre, tolerances. The hexapod has uses in photonics, laser processing, optical inspection, semiconductor, micromachining, metrology, and medical applications.

Traditional hexapods, also known as Gough-Stewart platforms, were first used in flight simulators and amusement rides. They feature six extendable links or actuators that join a stationary bottom plate with a top plate that performs coordinated motion in six degrees of freedom. A sample, fixture, sensor, or any device can be mounted on the top plate and be manipulated to any location and orientation in the available range of travel.

According to Alio, however, in recent years the miniaturisation of components, better sensors, and improved laser beam delivery have challenged the precision capabilities associated with the kinematics and path performance of traditional hexapods. There is a demand for higher accuracy, improved repeatability, and better geometric performance.

There are performance limitations inherent in the design of traditional hexapods, which require movement coordinated in all six axes to accomplish a motion profile, even if the top plate only moves in one axis. In addition, Alio explained, despite hexapods exhibiting good stiffness compared to serial stacked multi-axis systems, this is really only in the vertical z axis, with weaknesses in the xy plane.

‘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,’ explained Nathan Brown, vice president of engineering at Alio Industries. ‘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.’

Semiconductor fabrication is one area where nanometre positioning is needed

The newly patented hybrid hexapod is made from a hybrid serial and parallel kinematic structure, rather than a six-link pure parallel kinematic design structure seen in traditional hexapods. It uses 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° continuous yaw rotation.

In this hybrid design, individual axes can be customised to provide travel ranges from millimetres to over one metre, while maintaining nanometre levels of precision – it can achieve less than 100nm 3D six-axis point precision repeatability, according to Alio.

‘If you are happy with micron accuracy a traditional hexapod may serve you well,’ commented Brown. ‘But the hybrid hexapod provides orders of magnitude improvements in precision, path performance, speed, stiffness, and larger work envelope with virtually unlimited xy travel.’

According to Alio, the hybrid hexapod technology’s ability to deliver nanometre-level precision over all six degrees of freedom of a body in motion is unique, and that with it the firm is now seeing interest from OEMs working on nanometre applications in the optical, semiconductor, manufacturing, metrology, laser processing, and micromachining sectors.


Commercial products

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The M3 family of piezoelectric motion controllers from New Scale Technologies offer unrivalled compactness, ready for easy integration into your system. The success of the M3 range relies partly on the fully embedded driver electronics which allow the devices to be truly miniaturised. Adding further to this superior compactness is the patented SQUIGGLE piezoelectric ultrasonic motors. From a systems engineering viewpoint, this is key to streamlining the product design process, where every space counts. There is no need to concentrate engineering resources on integrating both the driver electronics and mechanical system, as they are part of an all-in-one package. These systems are ideal for compact and portable photonics systems requiring precision motion control.

Every aspect of motion control for photonics systems is covered by one of the M3 products: lens rotation using the M3-RS-U rotary stage module; linear positioning with the M3-LS range of linear smart stages; M3-L linear actuators; and lens focus control with the M3-F and M3-FS focus modules. Get your products to market faster with easy integration of these fully embedded, compact, precision motion controllers from New Scale Technologies.


Other commercial products

A range of new positioning stages have become available for photonic applications. Physik Instrumente’s (PI’s) A-341 hybrid gantry xy/xyz positioning stage provides the framework for controlled precise overhead motion in 3D printing, assembly, pick-and-place, alignment, inspection, and industrial automation applications.

The A-341 HGS from PI has a hybrid design and combines maximum throughput with smooth and highly accurate motion in a compact envelope. Its cross axis uses a frictionless air bearing guiding system, which enables excellent velocity control, repeatability, straightness, and cleanliness, while its lower dual-motor axis uses precision mechanical linear bearings for rigidity and reduced size. This combination of bearing technologies offers an overhead gantry motion platform optimised for step-and-scan applications in a small form factor.

Optimal Engineering Systems’ AY110-100-SC rotary stage has a pattern of threaded mounting holes in the rotary table and holes in the base for easy integration into new and existing applications. The travel of the rotary stage is 360°, and it is capable of continuous rotation.

The table is driven by a 180:1 worm gear at up to 14° per second, and has a resolution of 0.0001° with a 10 micro-step per step stepper motor driver. The low cost, low profile rotary stage, with a load capacity of 45kg, features a parallelism of 80µm, a backlash of 0.0005°, surface roundness of 15µm, positional accuracy of 0.001°, and a transmission deviation of 5µm. The rotary stage is suitable for microscopy, laser positioning and machining, inspection, assembly, testing, and other critical applications.

Applied Scientific Instrumentation’s (ASI) compact 3D/4D stage incorporates three ASI linear stages and an optional motorised rotating stage employed for a theta axis. The linear stages, comprising the xyz elements, offer travel options of 25mm, 50mm, 100mm, or 200mm, and each axis can be chosen separately.

These stages derive smooth and accurate motion from closed-loop DC servomotors, crossed-roller bearings, high-precision lead screws, and high-resolution encoders for positioning feedback. They can move uniformly at extremely slow speeds for in-motion acquisition. All stages offer various speed and accuracy options and have been designed to move samples around fixed optics.

Finally, MKS Instruments has upgraded its HXP50 hexapod, which has had its spring-loaded joints replaced with encapsulated joints in order to improve the overall robustness and reliability of the device. Standard hexapod joints are dynamic load-bearing points that suffer from typical mechanical failure modes, such as material wear, deformation, corrosion or thermal stress. The spherical shape of the encapsulated joints has been designed to enhance rigidity, while reducing material stress and deformation. The coated ceramic spherical ball joints are harder, stiffer, corrosion free and feature better geometrical tolerances than conventional steel ball joints.