Method and Apparatus for Modulating Haptic Feedback

Abstract

The present invention concerns a method and apparatus for the modulation of an acoustic field for providing tactile sensations. A method of creating haptic feedback using ultrasound is provided. The method comprises the steps of generating a plurality of ultrasound waves with a common focal point using a phased array of ultrasound transducers, the common focal point being a haptic feedback point, and modulating the generation of the ultrasound waves using a waveform selected to produce little or no audible sound at the haptic feedback point.

Claims

1-24. (canceled)

25. A method of creating haptic feedback using ultrasound comprising the steps of: using a plurality of ultrasonic transducers, generating a plurality of ultrasound waves, wherein at least two of the plurality of ultrasound waves form a focal point, wherein the focal point is a haptic feedback point; first modulating the generating of the plurality of ultrasound waves using a waveform to produce a haptic sensation at the haptic feedback point, which produces less audible sound pressure level than would be produced at the haptic feedback point when second modulating the generating of the plurality of ultrasound waves using a square wave modulation pattern.

26. The method as in claim 25, wherein the waveform is varied according to a linear interpolation.

27. The method as in claim 25, wherein the waveform is varied according to a cosine interpolation.

28. The method as in claim 25, wherein the waveform is varied according to a polynomial interpolation.

29. The method as in claim 25, wherein the waveform is varied according to trigonometric interpolation.

30. The method as in claim 25, wherein the waveform is varied according to a parametric speaker interpolation.

31. The method as in claim 25, wherein the square wave modulation pattern matches the modulation frequency of the waveform.

32. The method as in claim 31, wherein, at the focal point, a first peak amplitude of the first modulating is equal to a second peak amplitude of the second modulating.

33. The method as in claim 25, wherein the waveform comprises an interpolation of phase of at least one of the plurality of the ultrasonic transducers.

34. The method as in claim 25, wherein the waveform comprises an interpolation of amplitude of at least one of the plurality of the ultrasonic transducers.

35. The method of claim 25, wherein the generating a plurality of ultrasound waves use ultrasound with a frequency at or above 40 kHz.

36. The method of claim 25, wherein the first modulating the generating of the plurality of ultrasound waves uses a frequency from 1 Hz to 500 Hz.

37. The method of claim 25, further comprising: varying a position of the focal point.

38. The method of claim 37, wherein the position of the focal point is constantly varied.

39. The method of claim 37, wherein the position of the focal point oscillates about a central point.

40. A system comprising: a plurality of ultrasonic transducers for generation of a plurality of ultrasound waves, wherein at least two of the plurality of ultrasound waves form a focal point, wherein the focal point is a haptic feedback point; a first modulation of the generation of the plurality of ultrasound waves using a waveform to produce a haptic sensation at the haptic feedback point, which produces less audible sound pressure level than would be produced at the haptic feedback point during a second modulation of the generation of the plurality of ultrasound waves using a square wave modulation pattern.

41. The system as in claim 40, wherein the waveform is varied according to a linear interpolation.

42. The system as in claim 40, wherein the waveform is varied according to a cosine interpolation.

43. The system as in claim 40, wherein the waveform is varied according to a polynomial interpolation.

44. The system as in claim 40, wherein the waveform is varied according to trigonometric interpolation.

45. The system as in claim 40, wherein the waveform is varied according to a parametric speaker interpolation.

46. The system as in claim 40, wherein the square wave modulation pattern matches the modulation frequency of the waveform.

47. The system as in claim 46, wherein, at the focal point, a peak amplitude of the first modulation is equal to a peak amplitude of the second modulation.

48. The system as in claim 40, wherein the waveform comprises an interpolation of phase of at least one of the plurality of the ultrasonic transducers.

49. The system as in claim 40, wherein the waveform comprises an interpolation of amplitude of at least one of the plurality of the ultrasonic transducers.

50. The system of claim 40, wherein the generation of the plurality of ultrasound waves use ultrasound with a frequency at or above 40 kHz.

51. The system of claim 40, wherein the first modulation of the generation of the plurality of ultrasound waves uses a frequency from 1 Hz to 500 Hz.

52. The system of claim 40, further comprising: variance of a position of the focal point.

53. The system of claim 52, wherein the position of the focal point is constantly varied.

54. The system of claim 52, wherein the position of the focal point oscillates about a central point.

Description

DESCRIPTION OF THE DRAWINGS

[0024] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

[0025] FIG. 1 shows a schematic view of a haptic feedback system according to a first embodiment of the invention;

[0026] FIG. 2 shows a prior art square wave modulation pattern and the resultant waveform produced at the focal point;

[0027] FIG. 3 shows a linear interpolation modulation pattern and the resultant waveform produced at the focal point according to a second aspect of the invention;

[0028] FIG. 4 shows a cosine interpolation modulation pattern and the resultant waveform produced at the focal point according to a third aspect of the invention;

[0029] FIG. 5 shows a parametric speaker interpolation modulation pattern and the resultant waveform produced at the focal point according to a fourth aspect of the invention;

[0030] FIG. 6 shows an acoustic field generated at a focal point by a cosine interpolation modulation;

[0031] FIG. 7 shows an acoustic field generated at a focal point by a parametric speaker interpolation modulation; and

[0032] FIG. 8 shows an acoustic field generated at a focal point by a square wave modulation.

DETAILED DESCRIPTION

[0033] In an example embodiment of the method, firstly the 3D position of a focal point is decided. A phased array is arranged to create an acoustic field, with the phases and amplitudes of each transducer calculated to achieve a high pressure at the focal point and a low pressure in surrounding areas. Two states then exist, firstly the focal point state, with the computed phases and amplitudes, and secondly the off state, with all of the transducers of a phased array set at zero amplitude. A frequency at which to modulate the feedback is then chosen in dependence on the desired feel of the feedback. Then a modulation waveform is chosen at the desired frequency, the modulation frequency chosen to minimise or reduce the audible sound produced at the focal point. An example modulation waveform is a cosine waveform. The modulation waveform is then applied to the operation of the transducers to interpolate between the two states identified above.

[0034] A more specific example, as applied to a particular haptic feedback system, is now described with reference to FIG. 1.

[0035] FIG. 1 shows an example haptic feedback system 10 comprising a transducer array 12, a screen 14, a projector 16, a hand tracker 20, a PC 22, a driving unit 24, and a user's hand 26. The system 10 is shown to illustrate the invention, which is in no way limited to a particular system for producing haptic feedback using ultrasound. The transducer array 12 is located underneath the screen 14 and arranged such that pressure patterns may be transmitted through the screen 14 to a region above the screen 14. In this particular embodiment, the transducer array comprises 320 muRata MA40S4S transducers arranged in a 16×20 grid formation. Each transducer unit is 10 mm in diameter and the transducers are positioned with no gap between them in order to minimise the transducer array 12 footprint. The transducers produce a large amount of sound pressure (20 Pascals of pressure at a distance of 30 cm) and have a wide angle of directivity (60 degrees). The transducers are arranged to transmit ultrasound waves at a frequency of 40 kHz. The projector 16 is arranged to project visual information onto the screen 14 from above the screen 14 as shown. In an alternative embodiment, the projector may be placed between the transducer array and the screen, with the projection coming from below the screen.

[0036] A user interacts with this visual information and the movement and position of the user's hand 26 is tracked by the hand tracker 20. In this particular embodiment, the hand tracker 20 is a Leap Motion controller arranged to provide the 3D coordinates of the user's fingertips and palm at up to 200 frames per second. The system 10 is controlled by a PC 22, which sends control data to the projector 16, receives user data from the hand tracker 20, and controls the drive unit 24 for driving the transducer array 12. The PC 22 controls the driving unit 24 such that a pressure pattern is created in the region above the transducer array 12. In response to the hand movements of a user, the PC 22 may drive the driving unit 24 to cause the transducer array 12 to change the pressure pattern formed above the transducer array 12.

[0037] In order to compute the amplitude and phase of the acoustic wave each acoustic transducer must transmit for the desired pressure pattern to be created, an algorithm adapted from that proposed by Gavrilov (“The possibility of generating focal regions of complex configurations in application to the problems of stimulation of human receptor structures by focused ultrasound”, L. R. Gavrilov, 2008, Acoustical Physics Volume 54, Issue 2, pp 269-278, Print ISSN 1063-7710) may be used. A volumetric box is defined above the transducer array 12. Within the box, a plurality of control points are defined. The control points may represent points where a maximum pressure value is desired, or points where minimum pressure values are desired. The pressure values are maximised or minimised by maximising or minimising the intensity of the ultrasound emitted by the transducer array 12 which is incident at the control points.

[0038] An algorithm is used to model the outputs of each of the transducers in the transducer array 12 required to obtain each of the desired pressure patterns which may be created within the volume defined above the transducer array 12. The algorithm may be split into three steps.

[0039] Firstly, the acoustic field generated by a single transducer is calculated to create a large modelled volume. Thereby, the phase and amplitude at any point within the modelled volume may be determined by offsetting the sample transducer for the position, phase, and amplitude, of each of the transducers in the real transducer array, and combining these values.

[0040] Secondly, the control points are defined in the 3D volume above the transducer array such that the control points take on the required distribution. The control points may be points of maximum intensity or minimum intensity (also known as null points). In addition to a 3D location, the desired modulation frequency of the maximum control points may be specified. Thirdly, the optimal phases are calculated using a minimum norm solver so that the resulting acoustic field is as close as possible to that specified by the control points. There may be more than one solution that will create an optimal focusing to the control points, but some solutions create a higher intensity than others. Solutions are therefore iteratively generated to find the one that creates the highest intensity.

[0041] The method according to an aspect of the invention comprises obtaining a modulation frequency that produces the required tactile sensation. For example, a relatively slow modulation frequency of 16 Hz would provide a slow, pulsing, sensation. A higher modulation frequency of 200 Hz would produce a near-continuous feeling. A modulation waveform is then selected at that frequency, which produces little or no audible sound at the feedback point. The modulation waveform may comprise an interpolation based on the required phase and amplitude of the waveform calculated as described above.

[0042] FIGS. 2 to 6 show a graph on the left hand side which represents the modulation waveform applied to the ultrasound emitted by an ultrasound transducer. The graph on the right hand side of the figures represents the audible waveform created at the focal point of the ultrasound transducer. Generally, the greater the amplitude and the more jagged the feedback waves created at the focal point, the louder the sound being produced will be.

[0043] In prior art systems, the modulation of the ultrasound corresponds to a simple square wave pattern, as shown in the graph on the left hand side of FIG. 2, where the array of transducers is simply turned on and off at the modulation frequency. The graph on the right hand side of FIG. 2 shows the waveform produced at the focal point of the ultrasound transducer when using a square wave modulation pattern. As is clear, the waveform is far from smooth and also the amplitude of the waveform is relatively high. This will result in a potentially loud and irritating sound being produced at the focal point of the haptic feedback system.

[0044] FIG. 3 shows an alternative modulation waveform, where the ultrasound is varied according to a linear interpolation. As can be seen in the graph on the right hand side of FIG. 3, the waveform produced at the focal point is smoother than that shown in FIG. 2, with an amplitude which is significantly smaller. Therefore, the sound produced at the focal point will be reduced compared to a square wave modulation.

[0045] FIG. 4 shows an alternative modulation waveform, where the ultrasound is varied according to a cosine interpolation. As can be seen in the graph on the right hand side of FIG. 4, the waveform produced at the focal point is smoother than that shown in FIG. 2, with an amplitude which is significantly smaller. Therefore, the sound produced at the focal point will be reduced compared to a square wave modulation.

[0046] FIG. 5 shows an alternative modulation waveform, where the ultrasound is varied according to a parametric speaker interpolation. As can be seen in the graph on the right hand side of FIG. 5, the waveform produced at the focal point is smoother than that shown in FIG. 2, with an amplitude which is significantly smaller. Therefore, the sound produced at the focal point will be reduced compared to the square wave modulation.

[0047] FIGS. 6, 7, and 8, show the acoustic field of audible waveforms that is produced from different modulation waveforms when a focal point is created from five point sources. The waveform at various points throughout the field are highlighted for comparison. FIG. 6 represents a cosine interpolation, FIG. 7 represents a parametric speaker interpolation, and FIG. 8 represents a square wave modulation method. As can be seen, FIG. 6 shows the smoothest, most uniform field. FIG. 7 shows a field which is not as smooth and uniform as FIG. 6, though still considerably smoother and more uniform than that shown in FIG. 8. Therefore it is evident that the cosine interpolation provides the optimum modulation compared to the others discussed. On investigation, the skilled person may discover alternative modulation waveforms which perform as well as or better than a cosine interpolation, whilst still falling within the scope of the present invention.

[0048] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein.

[0049] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.