 Hello, my name is Angelica Torres and I am here to present my paper on mechanisms of friction reduction in longitudinal ultrasonic surface haptic devices with non-colinear vibration and finger displacement. This is a work that I have completed with my team at the L2EP laboratory in Lille with GoTouch and the University of Birmingham. As we know, ultrasonic surface haptic device allows us to create the illusion of a textured surface by modulating its friction using ultrasonic vibration. This has many applications. Longitudinal vibrations can be used for this purpose. The vibration decreases friction. The friction decrease is a function of vibration amplitude, which can be modulated to create an illusion. Few studies have focused on this phenomenon for longitudinal vibration, so we propose two interaction models, one collinear with the motion and one non-colinear. The collinear model is called the ratchet mechanisms. It states that in one dimension the vibration shifts the direction of the force, thus reducing the total lateral forces on average. The problem with this theory is that it assumes columbic dynamic friction. An uncollinear finger motion would mean for this model that the finger is always in slip mode, so it does not explain friction reduction with non-colinear exploration. For this reason, we propose the alternative velocity-dependent friction model. It states that exploring at an angle, the middle velocity is increased and higher velocities we need arranged, the friction is decreased. We verify this hypothesis experimentally using a longitudinal surface haptic device mounted on a trivometer and measured a group of participants at different velocities. We found that friction does reduce with velocity. We believe this has two explanations. The first one is that assuming that the finger behaves like an elastomer, the adhesive molecular bonds between this finger and the optical smooth surface are decreased with velocity. The second one assumes that the shear strength of these bonds is increased with contact time. Based on these two assumptions, we created the model. And we were able to fit the model to the mean of the measurements. So why does vibration reduce friction? Imagine that the orange line is the trajectory of exploration of a finger. If vibrations are on, the trajectory will be modified into the blue one. As a whole, the travel distance has increased but the time remained constant, so the velocity is increased. We can calculate exactly by how much if we know the angle. We can calculate the friction as well using the fitted model and the calculated velocity. The model provides a theoretical friction value at every angle. We see that it is less accurate as the angle approaches zero. Another mechanism takes place. However, it gives rather correct results at high angles as we verify it experimentally. Thank you very much.