Motion systems project file – August 2012

Micromech Systems provides a comprehensive motion service ranging from just simple modifications to motors, to bespoke multi axis control systems including full installation, commissioning and after sales service.

Year 2010 to 2011

Industry or research faculty: research facility

Location: Harwell Science and Innovation Campus

Application:
The requirement was to fit up to nine miniature positioning stages into a very confined volume with positioning resolution of only 0.1 microns. Some stages were required to have a practical move velocity of 10mm per second or faster.

Scope of overall contract
To propose and supply three sets comprising of nine stages with defined performance and control compatibility to meet the customer’s electrical standards.

Description of equipment and services supplied
The application solution was provided by specifying a combination of miniature ‘PiezoLegs’ walking-beam driven cross–roller RTP type stages from PM Bearings, Holland, together with three slightly larger miniature stepper/screw-driven  cross – roller stages supplied by Parker Daedal, USA. Some stages needed to be mounted in combinations of vertical and ‘edge-on’ horizontal. All stages were built with Renishaw 0.1 Micron Linear encoders.

Merits of solution provided
The four smallest stages RTP1510 have dimensions of only 17mm high x 50mm x 50mm. Cables are flat and exit from one end only. The linear drive-force is 0.7 kg (7.0 Newtons) reducing to around 0.3kg at 10mm per second. The vertical load capacity is in excess of 1.5kg.

The larger RTP2025 and RTP3100 stages have forces of 15N and 30N respectively so handling a much higher load capacity. The ‘Piezo-Legs’ stages are ‘non-tuned’ piezos, which are totally stable when de-energised due to the set pre-load of the motor stack on the stage cross-roller bearings. This characteristic is a most useful advantage for precision beam-line sample position and scanning applications in which power must be turned off during the experiment to minimise any electrical noise.

There is also zero ‘parasitic’ movement of the piezo motor when power is cycled as the piezo stack feet are flat in form, engaging with the ceramic transport bar over a significant surface rather than just a single tip as with other piezo drive technologies.

A further advantage of the ‘Piezo-Legs’ technology is the use of simple pulse and direction commanded drive cards from our supplier Trinamic, Germany. These drive cards have a ‘stepper-drive’ electronic format but use voltage in place of current with different phasing to suit the Piezo Element charge requirements. The 0.1micron encoders feed directly back to an 8-axis Delta Tau Motion Controller for precise closed loop control. As there are no rotational parts the position sensitivity of the system is extremely high and an accuracy of 0.1micron can be achieved readily without any dither.

On the three axes where faster positioning of targets was necessary, with higher forces, the Parker Daedal  MX80 screw driven stages were implemented. Linear drive forces of 40N were achieved at speeds of 20 to 30mm per second using a 2mm pitch backlash free Teflon coated lead-screw. Stepper drive technology used to control the algorithm from the Delta Tau controller was very similar to that employed for the piezo legs stages.

The MX80 Stages are only 35mm high with 80mm width. The length depended on travel required but is 80mm minimum. Vertical load capacity is 8Kg.

Partners in the contract collaboration

The suppliers and franchised partners who have assisted with the successful completion of this project are:

PM Bearings –  Holland                                                 http://www.pmbearings.nl
Parker Hannifin – Europe/ Parker Daedal – USA http://www.parker-eme.com
Piezo Motor –  Sweden                                                   http://www.piezomotor.se

Supplementary information on RTP Piezo Stages and Parker MX80 stages

Many positioning applications in Laser research and Beamline research are required to be performed in vacuum varying from Low Vac through Hi Vac to UHV Ultra High Vac.

The stages used in these applications can all be supplied in variants to suit these levels of vacuum.

RTP Stages from size RTP2025 and larger can be supplied with Renishaw ‘TONIC’ linear encoders. The benefit of this type of encoder is the extended resolution available by selection of the particular interpolation interface, which is mounted remote from the stage at up to 10metres distance (through the vacuum feed through if necessary). Renishaw offer Interpolator resolutions 1nanometre up to 5microns in various steps of nanometric resolution. It is evident from the physical construction of the cross-roller stages that ‘positioning accuracy’s’ down to these levels may not be achievable but the fine resolution will assist with positioning integrity within the stages machanical capability and extremely smooth low speed control of the stages.

Micromech Systems builds motion control systems to customer’s specifications, ranging from simple single-axis applications to complex multi-axis systems. We will design, build test, and produce application software, install and commission providing a cost-effective trouble-free solution to your Motion Control problems. Whether the application is a machine upgrade or a new project, Micromech Systems have the answer.         

Septembers project: Aerodynamic test equipment

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