Phase Optimization For Multi-point Haptic Feedback Based On Ultrasound Transducer Array

Traditional haptic interaction methods are mostly contact tactile feedback,where devices are in direct contact with humans and feedback are generated through resistance,vibration,or electrical stimuli.Such devices tend to limit the user’s activity space due to the need for direct contact and the cost is also high due to complex structure design.Differently,haptic feedback method based on ultrasound transducer array not only can generate the sense of touch in the space,but also can control the position of tactile point flexibly.Compared to traditional tactile devices,its overall structure is relatively simple and therefore has great potential.Aiming at existing problems in traditional contact haptic feedback,this paper mainly focus on contactless haptic feedback method based on ultrasound transducer array.In order to explain the principle of realizing tactile feedback by ultrasound,this paper combines the mechanism of tactile sensation generated by human body and the characteristics of ultrasound wave during its propagation in the air.Based on the basic laws of ultrasound physics,the mathematical model that describe sound field and sound pressure of a single ultrasound transducer and of an ultrasound phased array are derived respectively.The distribution characteristics of sound pressure and directivity of the sound field are then simulated in Matlab based on the model.Distribution of the sound pressure of the phased array under different phase control are shown clearly.Beside the realization of single-point tactile feedback,this paper mainly focuses on the generation of multi-point feedback and complex forms.Various methods are proposed to solve the phase problem,including time multiplexing/array block method,genetic algorithm and pseudo-inverse algorithm.The mathematical relationship between the phase of each transducer and multiple focal points in the space is detailed derived and established.And for the problem that the amplitude of the solution is not uniform,phase solution are further optimized using weighted amplitude iteration to facilitate the actual experiment.In this paper,a complete ultrasound haptic feedback experimental platform composed of FPGA controller,driving circuit and ultrasound transducer array is built.Single-point haptic feedback experiment,dynamic trajectory haptic feedback experiment and multi-point haptic feedback experiment are performed based on this platform.Experimental results prove that the phase solving method proposed in this paper is reliable and effective.Under the control of solved phases,the sound pressure distribution of the phased array is also consistent with the theoretical simulation results.