Visual speed compensation of pitch-constrained blue-bottle flies under retinal-image velocity perturbation in a flight mill

ABSTRACTIn the presence of wind or background image motion, flies are able to maintain a constant retinal-image velocity via regulating flight speed to the extent permitted by their locomotor capacity. Here we investigated the speed regulation of semi-tethered blue-bottle flies (Calliphora vomitoria) flying along an annular corridor in a magnetically levitated flight mill enclosed by two motorized cylindrical walls. We perturbed the flies’ retinal-image motion via spinning the cylindrical walls, generating bilaterally-averaged velocity perturbations from -0.3 to 0.3 m·s-1. Flies compensated retinal-image velocity perturbations by adjusting airspeed up to 20%, thereby maintaining a relatively constant retinal-image velocity. When the retinal-image velocity perturbation became greater than ∼0.1 m·s-1, the compensation weakened as airspeed plateaued, suggesting that flies were unable to further change airspeed. The compensation gain, i.e., the ratio of airspeed compensation and retinal-image velocity perturbation, depended on the spatial frequency of the grating patterns, being the largest at 12 m-1.

Adaptive Tracking Control without Image Velocity Measurement

This paper presents a adaptive controller for visual servoing systems to allow the tracking of a 2D reference trajectory without using image velocity measurements when the kinematics and dynamics parameters are uncertain. To avoid performance decaying caused by measurement errors of the image velocity, we proposed the adaptive controller, with which image velocity need not be directly measured. The first derivative of designed sliding mode vector is not affected by actual image speed. The parameter estimation of image position is used to replace the parameter estimation of image speed. We removed the filter structure in controller, which is used to predict the image velocity. The method makes the controller structure is simpler and more reliable, and reduces the difficulty of project implementation and tuning parameters. The asymptotic stability of the system is proved by using the Lyapunov’s method. Simulation results show that the SCARA robot end effector is able to converge to a desired trajectory.