Proposal of dynamic response sampling method for 6DoF control of irregularly shaped micro-scale objects with optical tweezers

3D position and orientation control (6DoF control) of micro-scale objects is needed among diverse applications such as cell manipulation, micro-assembly, and analysis of environmental microparticles. While optical tweezers technique is a promising tool for micro-manipulation including rotational control, the majority of previous studies depend on a priori knowledge on object shapes, which limits their applicability to real tasks where object shapes are usually irregular and not predetermined. To overcome this, we have proposed a concept of real-time adaptive optical tweezers, which generates illumination patterns of optical tweezers in real time based on acquired real-time information about objective particles. In this paper, as a new method which realizes real-time adaptive optical tweezers, we propose what we call Dynamic Response Sampling Method (DRSM). This method consists of two steps. Firstly, in the sampling step, illumination with randomly generated patterns and recording of instant 6DoF motion (i.e. velocity and angular velocity) are conducted. Secondly, a set of non-negative coefficients of superposition of the illumination patterns which realize desired 6DoF motion are calculated using algorithms such as the non-negative least squares method, then 6DoF control is realized using this superposed illumination pattern. We demonstrated this method in simulation and experiments. First, we confirmed that desired velocity and angular velocity are applied to Gaussian random ellipsoids (a model of irregularly shaped particles) with ray-optics based simulation. In addition, we successfully applied desired velocity to rounded L-shape resin microparticles (~20 μm) and irregularly shaped polystyrene microparticles (~50μm) in experiments.