| As an essential component of mobile terminals,touchscreens not only provide visual information but also support multi-touch functionality.With the increasing integration and intelligence of mobile terminals,traditional physical keyboards and mechanical buttons are gradually disappearing.The multi-touch functionality of touchscreens allows users to operate with multiple fingers simultaneously,enabling functions such as text input,image zooming,and volume adjustment.However,the absence of physical buttons on the screen makes it difficult for users to distinguish different boundaries with their fingers,increasing the probability of errors and reliance on visual cues.Users often need to frequently check virtual button responses or track target movements,leading to decreased interaction efficiency and visual fatigue issues.Utilizing surface haptic devices to provide tactile feedback during the interaction process of mobile terminals is an effective method to solve these problems.Surface haptic interaction includes typical implementation methods such as changing shape,electrotactile,mechanical vibration,squeeze film,and electroadhesion.Electroadhesion device presents tactile sensations by altering the electroadhesion forces between the finger and the tactile panel without requiring additional actuators.It features miniaturization,low power consumption,and rapid response,making it suitable for integration into mobile terminals.Existing research indicates that electroadhesion tactile interaction conforms to Fitts’ Law.It enhances the interactive performance of gesture operations such as panning and zooming.The application of electroadhesion tactile technology on mobile terminals must ensure that it does not disrupt the regular functions of mobile terminals while improving the performance of complex interaction tasks.Simultaneously,it needs to meet requirements such as miniaturization,low power consumption,high stability,and low cost.Advancing the application of electroadhesion tactile technology on mobile terminals urgently requires addressing three main issues:sharing positioning functions between electroadhesion devices and touchscreens on mobile terminals,the significant effect of contact conditions on electroadhesion force,and methods for applying electroadhesion tactile feedback in steering tasks.Addressing the aforementioned issues,this thesis primarily investigates an antimony doped tin oxide(ATO)solution for integrating electroadhesion tactile devices with mobile terminals.This thesis develops an integrated prototype and obtains metrics such as the minimum perceived linewidth,absolute threshold,discrimination threshold,and electroadhesion force.This thesis reveals the general principle of how contact conditions affect the stability of electroadhesion and analyzes the effects of ATO coating and insulation on the stability of electroadhesion.Furthermore,this thesis proposes a method of closed-loop control of electroadhesion using current regulation to enhance the stability of electroadhesion.This thesis also investigates the effect of electroadhesion tactile feedback on the interactive performance of steering tasks and the application method of electroadhesion tactile feedback in steering tasks.This thesis provides insights into the application of electroadhesion tactile technology on mobile terminals.The main contributions are as follows:(1)Addressing the issue of sharing positioning functions between electroadhesion devices and touchscreens on mobile terminals,this thesis proposes an ATO coating solution.It establishes an electroadhesion effective voltage model based on ATO coating and develops an integrated electroadhesion device.By utilizing an ATO semiconductor layer that does not affect the positioning function as the conductive layer of the tactile panel,this solution enables electroadhesion devices to share the positioning function of the touchscreen.This thesis establishes an effective voltage model incorporating four types of impedance and optimizes ATO impedance.A prototype integrated with a Microsoft Surface tablet is developed,achieving micrometer-level measurement of the minimum perceived linewidth through optimized cursor control methods and precise hardware design.This thesis also clarifies the dual effect of perceived intensity and finger sliding speed on the minimum perceived linewidth.Experimental results are obtained for absolute threshold,discrimination threshold,electroadhesion force,and minimum perceived linewidth,compared with conventional electroadhesion devices based on 3M tactile panels,demonstrating that the ATO coating solution is a method for integrating electroadhesion tactile feedback with touchscreen at the cost of sacrificing drive voltage.(2)Addressing the effect of finger contact conditions on the stability of electroadhesion,this thesis derives electroadhesion force calculation formulas based on current and contact area,achieving precise calculation under constant contact area.General principle regarding the effect of finger contact conditions on electroadhesion stability are obtained.Based on formulas proposed by Shultz et al.,this thesis treats the air layer as a capacitor and deduces that electroadhesion force is solely affected by current and contact area.Validation is conducted using electroadhesion force measured under four contact conditions.Experimental results show that under controlled contact area,electroadhesion force can be accurately calculated by measuring current amplitude,with average relative errors of 8.5%and 6.6%when using 3M tactile panels and ATO tactile panels,respectively.(3)Addressing the problem of suppressing the effect of finger contact conditions on the stability of electroadhesion,this thesis proposes an electroadhesion closed-loop control method based on current detection,reducing the relative error in electroadhesion force caused by changing contact conditions.This method relies on the approximation that the overall impedance is nearly equal to the insulation impedance when the finger is stationary,while it is nearly equal to the air layer impedance when the finger is sliding.By using a current sensor to measure the current when the finger is stationary and sliding,a 30 N normal force is applied to compress the air when the finger is stationary,thereby making the overall impedance approximate to the insulation impedance.By measuring impedance amplitude,phase,insulation thickness,and relative permittivity,the contact area is calculated.The calculated contact area and the current during sliding are used as two parameters for proportional control,jointly adjusting the drive voltage after changes in contact conditions.This method achieves an enhancement in electroadhesion stability with only the addition of a current sensor.Experimental results demonstrate that compared to scenarios without closed-loop control,the average relative error in closed-loop control is reduced by over 34%.(4)Addressing methods for applying electroadhesion tactile feedback in steering tasks,this thesis investigates the effect of typical loading methods on the interaction performance of steering tasks and determines the optimal loading method for applying electroadhesion tactile feedback within tunnels.Evaluation of the optimal loading method is based on objective assessments of standard deviation of tunnel centerline distance and completion time,as well as subjective evaluations using the NASA-TLX scale.The thesis analyzes the effect of applied location and perceived intensity on the three indices.Experimental results demonstrate that applying electroadhesion tactile feedback in steering tasks conforms to Steering Law,improving interaction efficiency and experience while maintaining interaction accuracy.Compared to applying tactile warning signals outside the tunnel,applying tactile prompts inside the tunnel results in shorter task completion times and better interaction experiences.Applying tactile feedback inside the tunnel reduces completion time by 7.6%and enhances interaction experience without sacrificing interaction accuracy compared to the scenario without electroadhesion tactile feedback. |
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