FLEX: a new grid-based fibre positioner concept with large patrol area, small pitch, and very good clustering capabilities

Concepts for the next generation of spectroscopic survey facilities (e.g., WST, MSE, MegaMapper) require a fibre-fed multi-object multiplex of ~20,000 in a focal surface area with a diameter of order 1.0–1.5 metres. This puts extreme requirements on e.g., pitch between positioners, collision avoidance, and mass producibility that are hard to meet with current concepts. We present the new FLEX1 fibre positioner concept inspired by mechanisms used for minimally invasive surgery. The concept consists of a parallel mechanism that can be mass produced with laser cutting techniques and a tripod actuator mechanism for accomplishing both positioning and maintaining focus. Advantages of the new design compared to existing positioner designs include very large patrol diameter per fibre (>30 mm) while allowing for very small pitch (~7 mm), very small minimal approaches between fibres, good clustering capabilities (20 fibres can reach a given sky location), easy control path and collision avoidance, robustness, mass producibility, the ability to accommodate nontelecentric and low-order polynomial focal surfaces, and the minimal bending and twisting of the fibre. The mechanism is expected to be very robust and mass producible. While conceived for small pitch, high density applications, the principle can easily be scaled up for larger plate scale for more sparse pick-ups in ELT instruments. A few concept designs of possible implementations are presented together with further development plans.