Position Hexapods With Maximum Freedom

2023 Author : Hannah Pearcy | [email protected] . Last modified: 2023-05-24 11:12

Quite on the move: More and more positioning and movement tasks in industrial automation, whether in assembly, in semiconductor production, in laser material processing, in inspection systems or in additive manufacturing, require multi-axis positioning systems.

The demands placed on these systems are high: They range from exact reproducibility of the positions, to accuracies down to the micro or even nanometer range and high dynamics. At the same time, these systems should be as compact and robust as possible, work reliably and ultimately also be networkable.

Master high requirements with ease

What sounds like a machine builder's wish for the egg-laying Wollmilchsau is part of everyday life for the Karlsruhe company Physik Instrumente (PI): With their hexapod robots, the Baden-Württembergers, who are celebrating their 50th anniversary this year, have a wide range multi-axis systems for positioning tasks that more than meet these high requirements.

Additional information on the topic of enablers in construction: hexapods

Simulation, lightweight construction, smart components - which developments will prevail? Konstruktionsspraxis has awarded the “Enablers of Construction” to companies whose solutions can change design and development in the long term.

Challenge: Industrial automation applications increasingly require multi-axis positioning systems . Exact reproducibility of the positions, accuracies with very high resolutions and high dynamics are required. The systems should also be robust, reliable and networkable.

Solution: The hexapods from Physik Instrumente (PI) meet these high requirements. The multi-axis positioning systems are characterized, among other things, by high path fidelity, repeat accuracy and resolution, high dynamics for all axes of motion, and a compact design. In addition, the devices offer repeatability in the nanometer range.

What good does it do: If positioning tasks place high demands on accuracy, dynamics and repeatability, the designer has access to versatile complete solutions with the hexapods from Physik Instrumente (PI), with which even complex motion profiles can be implemented.

The most important features of the hexapods from PI: They are characterized, among other things, by high path accuracy, repeatability and resolution, as well as high dynamics and a compact design for all axes of movement. They also offer the frequently required repetition accuracy in the submicron range.

Position in six axes in space

What exactly is a hexapod? It is a system for moving and positioning, adjusting and moving loads in six axes in space, three linear and three rotary. The devices have a parallel kinematic structure, and the six drives work together on a single platform that they move.

Construction Practice Podcast

Episode 1: Hexapods

The Konstruktionsspraxis podcast, the specialist magazine for listening, provides quick and entertaining information about exciting technology topics. In this episode we talk to Markus Spanner, Managing Director of Physik Instrumente (PI), about hexapods.

PI systems are based on piezoelectric or electromechanical drives and are therefore much more precise than hydraulic hexapods, as they are known from flight or driving simulators. Since the length of the individual drives can be varied, the platform can be moved in all six spatial degrees of freedom. This design of the hexapods ensures a high overall rigidity. It also allows a large central aperture.

Parallel kinematic hexapods are the purest pack donkeys: Depending on the version, the flexible six-legged tools move and position tools, workpieces or complex components with weights from 2 kg to 2000 kg with high precision - regardless of the respective assembly orientation.

Enabler of construction

These technologies have game-changing potential

Diverse application scenarios

The automotive industry has long known the advantages of this parallel kinematics. The tire manufacturer Dunlop, for example, was already using hexapod technology in the early 20th century to test car tires. A lot has happened since these early days: The experts at Physik Instrumente (PI) continuously developed their hexapods further technologically and expanded the product range by numerous models.

Today the systems of industry and research are used in numerous different applications :

• in prototype construction , high-precision machining of complex components or in contactless processes such as laser welding
• as a flexible “hand” for classic industrial robots to compensate for inaccuracies in the robot arm
• for exact alignment and attachment of camera lenses in the production of smartphones
• in test facilities for acceleration or gyroscopic sensors, such as those used in smartphones and cameras, to detect changes in position, such as the trembling movements of the photographer
• for the handling of filigree optical fibers in an automatic assembly and adjustment system for the manufacturing process in silicon electronics
• in interferometers for positioning lenses and calibration balls to measure aspherical shape accuracies in the nanometer range.

Design ensures high precision

This variety of applications already indicates the many advantages that make parallel kinematic hexapods so interesting for use in industrial automation. They offer:

• precise positioning
• a compact structure
• a very high dynamic for all motion axes
• high web fidelity and repeatability
• easy integration
• Communication via standard protocols .

One factor stands out clearly: the six-legged devices often position more precisely than serial, i.e. stacked, systems of classic robotics. Serial-kinematic systems consist of individual axes or actuators that are mechanically connected in series. This structure means that guide errors from the individual drives can add up, which impairs accuracy and repeatability. This problem is irrelevant for the design of hexapods, since all six actuators act directly on the platform.

All set for movement

At the same time, this construction enables a significantly more compact structure . This feature simplifies setting up safety circuits, for example, because the Hexapod only moves within a comparatively manageable work area. The working space is the entirety of all combinations of translations and rotations that a hexapod robot can approach from its current position.

In addition to the significantly more precise movement compared to stacked systems, there are other advantages such as the lower moving mass, since the drives only move the platform including the payload, but not the mass of the subsequent drives including cables. This results in higher dynamics , significantly better path accuracy and repeatability for all axes of motion. Because there are no towed cables, the resulting friction or moments have no influence on the precision. The parallel structure also increases the rigidity and thus also the natural frequencies of the overall system.

Integration made easy

And what about the integration ability of the hexapods? Thanks to the direct connection to the controller via fieldbus interfaces, the positioning systems can be integrated into practically any automation network with little effort . Clock synchronization with other components is no longer a headache, because a digital controller takes over the calculations and controls the individual motors in real time. Movements and rotations of the platform are commanded in Cartesian coordinates.

Additional information on the topic of physics instruments - specialist for high-precision positioning technology and piezo applications

Physik Instrumente (PI), headquartered in Karlsruhe, is a leader in high-precision positioning technology and piezo applications for the semiconductor industry, life sciences, photonics and industrial automation. In cooperation with customers worldwide, the approximately 1,300 PI specialists have been setting technical standards and developing tailor-made solutions for 50 years. More than 350 patents granted and pending confirm the company's claim to leadership with six manufacturing locations and 15 sales and service branches in Europe, North America and Asia. PI's core technologies are:

• Piezoceramic area transducers and actuators
• Electromagnetic drives
• Nanometric sensors
• Motion control systems for maximum precision and dynamics

An important property of the hexapods is the possibility to conveniently adjust the position and orientation of the reference coordinate system as well as the pivot point (pivot point) to the respective application using software. In order to adapt the trajectory of an application, various coordinate systems can be defined, such as work and tool coordinate systems, which relate to the position of a workpiece or tool.

Communication via standard protocol

The controller communicates with the hexapod using a standard protocol. In addition to RS232 and TCP / IP , established fieldbus protocols such as Ethercat and Profinet are also available. The hexapod system then behaves like an intelligent multi-axis drive on the bus.

PI supplies the digital motion controllers with an extensive software package that covers all aspects of an application, starting with the easy to carry out commissioning, the comfortable control of the systems via graphic interfaces up to the quick and clear integration into external programs.

Develop applications virtually

With the help of a virtual controller , users can develop complex application programs without having all the components already on site. Using simulation tools, for example, the work space can be calculated or objects can be integrated to avoid collisions. Development libraries and sample applications make implementation easier for the user.

So much for the theory. How does this translate into hard facts? One example is the filigree Hexapod H-811. I2 from the product portfolio of Physik Instrumente (PI). The typical representative of its genus works at a speed of up to 20 mm / s. His legs move with a resolution of 5 nm, which achieves a high repetition accuracy of ± 0.15 (X and Y axes) and ± 0.06 µm (in the Z axis). The smallest increment is 0.2 µm (X and Y axes) and 0.08 µm (in the Z axis).

Loads up to 5 kg

The Hexapod covers travel ranges up to ± 17 mm in the X and ± 16 mm in the Y axis and ± 6.5 mm in the Z axis. The H-811. I2 can position loads up to 5 kg with high precision, quickly and over long operating times. The system is also available in vacuum compatible versions.

The driving force behind the miniature hexapods are brushless DC motors . They are particularly well suited for high speeds, can be regulated very precisely and thus enable high precision. In this case, too, PI controllers are used to control the positioning system and command the motion profiles. If there is a higher-level controller, the controllers also communicate via the standard Ethercat protocol.

Typical areas of application of the small power pack are industry and research in the application areas:

• Microfabrication ,
• Medical technology or
• Tool control .

It can also work in vacuum environments.

Exactly and quickly

Hexapods from Physik Instrumente (PI) are the ideal solution for industrial automation applications with special requirements for positioning tasks , in which objects have to be moved dynamically and with high precision in several axes. The payload can be a few milligrams or up to a few tons, depending on the version. The user gains additional flexibility from the freely selectable pivot point.

Standardized fieldbus interfaces such as Ethercat enable connection to higher-level PLCs or CNC controls, which simplifies the integration of the hexapods and enables isochronous work with other automation components in the network. (jv)