Steinmeyer Mechatronik

Experiment on electron storage ring Bessy II

Experiment on electron storage ring BESSY II

Piezoelectric micro motors on ropes

Special contract at the service of researchers: For an experiment on the electron storage ring BESSY II in Berlin, the positioner specialist Steinmeyer Mechatronik was commissioned to develop a sample manipulator. In addition to flexibility and high precision, the requirements also included a design that could withstand vacuum and magnetic forces. The company used PiezoMotor actuators for this challenging task.

Three-dimensional visualization of magnetism in live circuits was the goal of the researchers who approached the Dresden-based company Steinmeyer Mechatronik. For their experiment, the scientists needed extremely brilliant X-ray light, such as that generated by the synchrotron radiation source BESSY II. Researchers around the world can use this light source for their experiments, such as examining solar cells, materials for hydrogen generation, or quantum materials. The beam tubes at the side of the storage ring are equipped with state-of-the-art spectroscopy and microscopy methods.

The 5-axis manipulator was the main component of the RICXS experiment at the electron storage ring Bessy II in Berlin
Photo: Steinmeyer Mechatronik GmbH

“The so-called RICXS experiment consisted of a large set-up with several elements, including a sample manipulator, a camera with a guide system, and a sample mounting device”, explains Elger Matthes of Steinmeyer Mechatronik. The company, which specializes in high-precision positioning applications, offers innovative products and custom-tailored solutions for specific requirements. Steinmeyer Mechatronik’s focus is on development and production of OEM series, as well as complex multi-axis systems and one-off systems for experimental applications such as those of the researchers in Berlin.

The RICXS experiment required the creation of a 5-axis manipulator that raised a mounted electronic circuit into the magnetic field of a superconductor vector magnet, where it was exposed to a high-intensity light source. Matthes explains the principle: “The diffuse radiation was photographed by an orbiting camera to generate three-dimensional images.” Since this required a specific short-wavelength X-ray spectrum, the experiment would work only in an ultra-high vacuum environment at 10E-8 mbar.

The entire structure was built on a granite plate at one of the radiation lines of BESSY II
Photo: Helmholtz Zentrum Berlin

A suitable actuator for a challenging environment

Steinmeyer Mechatronik quickly realized who would be the ideal partner for this application: The company have been working in successful cooperation with PiezoMotor for more than 15 years. “We always use piezo motors in applications requiring very high resolutions and precision in combination with very small steps and long travel”, explains Matthes. Piezo motors use piezoelectricity to produce motions. When voltage is applied to a piezoelectric material, it expands. PiezoMotor has developed Piezo-LEGS®, which are made of ceramic and can both lengthen and bend laterally. This causes motion in the submicron to nanometre range. The actuators are self-locking, which means they hold their position with mechanical stability, and consume no energy in power-off state.

The advantage of piezo motors is that they require no lubricants and cause no abrasion or thermal evaporation. This makes them ideal for use in a vacuum environment. Since they are designed without the windings of an electric motor, they are not a source of magnetic flux and are not sensitive to magnetic interference, which also makes them suitable for applications where conventional motors would cause undesirable interactions. PiezoMotor offers completely non-magnetic motors. “Extreme magnetism in combination with ultra-high vacuum are challenging conditions for conventional motors”, confirms Elger Matthes of Steinmeyer Mechatronik. “In combination with the special requirements for precision in this project, the piezo motors provided an outstanding solution.”

The basic idea of the sample manipulator was the use of piezo motors in combination with ropes – here in the foreground you can clearly see how the rope made of aramid fibers attached to the drive rod is guided to a spring
Photo: Steinmeyer Mechatronik GmbH

Flexibility of motion with five axes

The result, after a one-year development period, was a 5-axis manipulator for small actuating distances that uses six linear motors from PiezoMotor. The platform, on which the sample is later exposed to magnetic forces, is clamped to six rope pairs with tension springs. The ropes were used because the installation space was limited to the size of a shoebox. Thanks to the ropes, the designers could now direct the force around corners. The six rope pairs define the position of the platform in space: Pulling on the ropes causes the platform to move accordingly. The ropes transfer the actuating force, while the springs generate the counterforce and compensate the gravitational force. “It works like a puppet theatre”, says Matthes. “The ropes were a brilliant idea provided by our customer: They make it possible to build complex mechanisms that operate with nanometre resolution and stability in very tight spaces.”

Motors like this LT20 were used. They are particularly suitable for use in vacuum
Photo: PiezoMotor

Piezo motors have a mechanical resolution of a few nanometres, combined with unlimited travel and tremendous rigidity. Whereas electro motors have to be regulated constantly for backlash-free operation, piezo motors solve this problem inherently. While the actuator rod in the motor is always in direct contact with the piezo elements, the friction coupling between the legs and the actuator rod produces zero backlash together with extremely short reaction time and high resolution. Since clamping and movement are performed by the same actuators, this ensures strong interlocking with no power consumption when stopped. The position of the sample in the award-winning RICXS experiment was controlled by six capacitive sensors. “The motors take steps”, explains Elger Matthes, “but the length of the steps varies. The sensors measure the step intervals and control the motor. This requires closed-loop operation.”

A total of six motors controlled the platform on the column, which then protruded into the 1.8 tesla magnet and was illuminated by extreme X-ray light
Photo: Steinmeyer Mechatronik GmbH

The set-up of the complex system took another year until it was ready for operation. PiezoMotor actuators were also used for X-ray camera adjustment and sample mounting in the RICXS experiment. The unique sample manipulator has made it possible to conduct numerous scientific experiments on magnetic forces.